Weld pool oscillation during GTA welding of mild steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiao, Y.H.; Ouden, G. den

1993-08-01

In this paper the results are reported of a study dealing with the oscillation behavior of weld pools in the case of GTA bead-on-plate welding of mild steel, Fe 360. During welding, the weld pool was brought into oscillation by applying short current pulses, and the oscillation frequency and amplitude were measured by monitoring the arc voltage. It was found that the oscillation of the partially penetrated weld pool is dominated by one of two different oscillation modes (Mode 1 and Mode 2) depending on the welding conditions, whereas the oscillation of the fully penetrated weld pool is characterized bymore » a third oscillation mode (Mode 3). It is possible to maintain partially penetrated weld pool oscillation in Mode 1 by choosing appropriate welding conditions. Under these conditions, an abrupt decrease in oscillation frequency occurs when the weld pool transfers from partial penetration to full penetration. Thus, weld penetration can be in-process controlled by monitoring the oscillation frequency during welding.« less

Influence of the arc plasma parameters on the weld pool profile in TIG welding

NASA Astrophysics Data System (ADS)

Toropchin, A.; Frolov, V.; Pipa, A. V.; Kozakov, R.; Uhrlandt, D.

2014-11-01

Magneto-hydrodynamic simulations of the arc and fluid simulations of the weld pool can be beneficial in the analysis and further development of arc welding processes and welding machines. However, the appropriate coupling of arc and weld pool simulations needs further improvement. The tungsten inert gas (TIG) welding process is investigated by simulations including the weld pool. Experiments with optical diagnostics are used for the validation. A coupled computational model of the arc and the weld pool is developed using the software ANSYS CFX. The weld pool model considers the forces acting on the motion of the melt inside and on the surface of the pool, such as Marangoni, drag, electromagnetic forces and buoyancy. The experimental work includes analysis of cross-sections of the workpieces, highspeed video images and spectroscopic measurements. Experiments and calculations have been performed for various currents, distances between electrode and workpiece and nozzle diameters. The studies show the significant impact of material properties like surface tension dependence on temperature as well as of the arc structure on the weld pool behaviour and finally the weld seam depth. The experimental weld pool profiles and plasma temperatures are in good agreement with computational results.

Gravitational effects on weld pool shape and microstructural evolution during gas tungsten arc and laser beam welding on 304 stainless steel, nickel, and aluminum-4 wt.% copper alloy

NASA Astrophysics Data System (ADS)

Kang, Namhyun

The objective of the present work was to investigate effects of gravitational (acceleration) level and orientation on Ni 200 alloy (99.5% Ni purity), 304 stainless steel, and Al-4 wt.% Cu alloy during gas tungsten arc welding (GTAW) and laser beam welding (LBW). Main characterization was focused on the weld pool shape, microstructure, and solute distribution as a function of gravitational level and orientation. The welds were divided into two classes, i.e., 'stable' and 'unstable' welds, in view of the variation of weld pool shape as a function of gravitational level and orientation. In general, higher arc current and translational GTAW produced more significant effects of gravitational orientation on the weld pool shape than the case of lower arc current and spot welding. Cross-sectional area (CSA) was a secondary factor in determining the stability of weld pool shape. For the 'stable' weld of 304 stainless steel GTAW, the II-U weld showed less convexity in the pool bottom and more depression of the free surface, therefore producing deeper penetration (10--20%) than the case of II-D weld. The II-D weld of 304 stainless steel showed 31% deeper penetration, 28% narrower width, and more hemispherical shape of the weld pool than the case of II-U weld. For GTAW on 304 stainless steel, gravitational level variation from low gravity (LG ≈ 1.2 go) to high gravity (HG ≈ 1.8 go) caused 10% increase in width and 10% decrease in depth while maintaining the overall weld pool volume. Furthermore, LBW on 304 stainless steels showed mostly constant shape of weld pool as a function of gravitational orientation. GTAW on Ni showed similar trends of weld pool shape compared with GTAW on 304 stainless steel, i.e., the weld pool became unstable by showing more penetration in the II-D weld for slower arc translational velocity (V a) and larger weld pool size. However, the Ni weld pool shape had greater stability of the weld pool shape with respect to the gravitational orientation than the case of 304 stainless steel, i.e., higher current boundary and no humping. Regardless of the gravitational level, the ferrite content and the distribution of the solutes (Cr and Ni) remained constant for GTAW on 304 stainless steel. However, for GTAW on Al-4 wt.% Cu alloys, the gravitational orientation changed the weld pool shape associated with convection flows. In summary, gravity influenced the weld pool shape that was associated with convection flows and weld surface deformation for specific welding conditions. The variation of convection flows and weld pool shape played a role in modifying VS and GL. Solidification orientation and morphology were affected because VS and GL were changed as a function of gravity. Studies of gravity on the welding process are expected to play a significant role in the space-station construction and circumferential pipe welding on the earth. (Abstract shortened by UMI.)

Experimental investigation on the weld pool formation process in plasma keyhole arc welding

NASA Astrophysics Data System (ADS)

Van Anh, Nguyen; Tashiro, Shinichi; Van Hanh, Bui; Tanaka, Manabu

2018-01-01

This paper seeks to clarify the weld pool formation process in plasma keyhole arc welding (PKAW). We adopted, for the first time, the measurement of the 3D convection inside the weld pool in PKAW by stereo synchronous imaging of tungsten tracer particles using two sets of x-ray transmission systems. The 2D convection on the weld pool surface was also measured using zirconia tracer particles. Through these measurements, the convection in a wide range of weld pools from the vicinity of the keyhole to the rear region was successfully visualized. In order to discuss the heat transport process in a weld pool, the 2D temperature distribution on the weld pool surface was also measured by two-color pyrometry. The results of the comprehensive experimental measurement indicate that the shear force due to plasma flow is found to be the dominant driving force in the weld pool formation process in PKAW. Thus, heat transport in a weld pool is considered to be governed by two large convective patterns near the keyhole: (1) eddy pairs on the surface (perpendicular to the torch axis), and (2) eddy pairs on the bulk of the weld pool (on the plane of the torch). They are formed with an equal velocity of approximately 0.35 m s-1 and are mainly driven by shear force. Furthermore, the flow velocity of the weld pool convection becomes considerably higher than that of other welding processes, such as TIG welding and GMA welding, due to larger plasma flow velocity.

The use of electromagnetic body forces to enhance the quality of laser welds

NASA Astrophysics Data System (ADS)

Ambrosy, Guenter; Berger, P.; Huegel, H.; Lindenau, D.

2003-11-01

The use of electromagnetic body forces in laser beam welding of aluminum alloys is a new method to shape the geometry and to enhance the quality of the weld seams. In this new approach, electromagnetic volume forces are utilized by applying magnetic fields and electric currents of various origins. Acting in the liquid metal, they directly affect the flow field and can lead to favourable conditions for the melt dynamics and energy coupling. Numerous welds with full and partial penetration using both CO2 and Nd:YAG lasers demonstrate that this method directly influences the seam geometry and top-bead topography as well as the penetration depth and the evolution of pores and cracks. In the case of full penetration, it is also possible to lift or to lower the weld pool. The method, therefore, can be used to shape the geometry and to enhance the quality of the weld seam. Depending on the orientation of an external magnetic field, significant impacts are achieved in CO2 welding, even without an external current: the shape of the cross-sectional area can be increased of up to 50% and also the seam width is changed. Whereas for such conditions with Nd:YAG lasers no significant effect could be observed, it turned out that, when an external electric current is applied, similar effects are present with both wavelengths. In further investigations, the effect of electromagnetic body forces resulting from the interaction of an external current and its self-induced magnetic field was studied. Hereby, the current was fed into the workpiece via a tungsten electrode or a filler wire. The resulting phenomena are the same independent from wavelength and means of current feed.

3D finite element simulation of TIG weld pool

NASA Astrophysics Data System (ADS)

Kong, X.; Asserin, O.; Gounand, S.; Gilles, P.; Bergheau, J. M.; Medale, M.

2012-07-01

The aim of this paper is to propose a three-dimensional weld pool model for the moving gas tungsten arc welding (GTAW) process, in order to understand the main factors that limit the weld quality and improve the productivity, especially with respect to the welding speed. Simulation is a very powerful tool to help in understanding the physical phenomena in the weld process. A 3D finite element model of heat and fluid flow in weld pool considering free surface of the pool and traveling speed has been developed for the GTAW process. Cast3M software is used to compute all the governing equations. The free surface of the weld pool is calculated by minimizing the total surface energy. The combined effects of surface tension gradient, buoyancy force, arc pressure, arc drag force to drive the fluid flow is included in our model. The deformation of the weld pool surface and the welding speed affect fluid flow, heat flow and thus temperature gradients and molten pool dimensions. Welding trials study is presented to compare our numerical results with macrograph of the molten pool.

Modeling macro-and microstructures of Gas-Metal-Arc Welded HSLA-100 steel

NASA Astrophysics Data System (ADS)

Yang, Z.; Debroy, T.

1999-06-01

Fluid flow and heat transfer during gas-metal-arc welding (GMAW) of HSLA-100 steel were studied using a transient, three-dimensional, turbulent heat transfer and fluid flow model. The temperature and velocity fields, cooling rates, and shape and size of the fusion and heat-affected zones (HAZs) were calculated. A continuous-cooling-transformation (CCT) diagram was computed to aid in the understanding of the observed weld metal microstructure. The computed results demonstrate that the dissipation of heat and momentum in the weld pool is significantly aided by turbulence, thus suggesting that previous modeling results based on laminar flow need to be re-examined. A comparison of the calculated fusion and HAZ geometries with their corresponding measured values showed good agreement. Furthermore, “finger” penetration, a unique geometric characteristic of gas-metal-arc weld pools, could be satisfactorily predicted from the model. The ability to predict these geometric variables and the agreement between the calculated and the measured cooling rates indicate the appropriateness of using a turbulence model for accurate calculations. The microstructure of the weld metal consisted mainly of acicular ferrite with small amounts of bainite. At high heat inputs, small amounts of allotriomorphic and Widmanstätten ferrite were also observed. The observed microstructures are consistent with those expected from the computed CCT diagram and the cooling rates. The results presented here demonstrate significant promise for understanding both macro-and microstructures of steel welds from the combination of the fundamental principles from both transport phenomena and phase transformation theory.

Hot Forging of a Cladded Component by Automated GMAW Process

NASA Astrophysics Data System (ADS)

Rafiq, Muhammad; Langlois, Laurent; Bigot, Régis

2011-01-01

Weld cladding is employed to improve the service life of engineering components by increasing corrosion and wear resistance and reducing the cost. The acceptable multi-bead cladding layer depends on single bead geometry. Hence, in first step, the relationship between input process parameters and the single bead geometry is studied and in second step a comprehensive study on multi bead clad layer deposition is carried out. This paper highlights an experimental study carried out to get single layer cladding deposited by automated Gas Metal Arc Welding (GMAW) process and to find the possibility of hot forming of the cladded work piece to get the final hot formed improved structure. GMAW is an arc welding process that uses an arc between a consumable electrode and the welding pool with an external shielding gas and the cladding is done by alongside deposition of weld beads. The experiments for single bead were conducted by varying the three main process parameters wire feed rate, arc voltage and welding speed while keeping other parameters like nozzle to work distance, shielding gas and its flow rate and torch angle constant. The effect of bead spacing and torch orientation on the cladding quality of single layer from the results of single bead deposition was studied. Effect of the dilution rate and nominal energy on the cladded layer hot bending quality was also performed at different temperatures.

A Monte Carlo model for 3D grain evolution during welding

NASA Astrophysics Data System (ADS)

Rodgers, Theron M.; Mitchell, John A.; Tikare, Veena

2017-09-01

Welding is one of the most wide-spread processes used in metal joining. However, there are currently no open-source software implementations for the simulation of microstructural evolution during a weld pass. Here we describe a Potts Monte Carlo based model implemented in the SPPARKS kinetic Monte Carlo computational framework. The model simulates melting, solidification and solid-state microstructural evolution of material in the fusion and heat-affected zones of a weld. The model does not simulate thermal behavior, but rather utilizes user input parameters to specify weld pool and heat-affect zone properties. Weld pool shapes are specified by Bézier curves, which allow for the specification of a wide range of pool shapes. Pool shapes can range from narrow and deep to wide and shallow representing different fluid flow conditions within the pool. Surrounding temperature gradients are calculated with the aide of a closest point projection algorithm. The model also allows simulation of pulsed power welding through time-dependent variation of the weld pool size. Example simulation results and comparisons with laboratory weld observations demonstrate microstructural variation with weld speed, pool shape, and pulsed-power.

Nd:YAG laser welding of coated sheet steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Graham, M.P.; Kerr, H.W.; Weckman, D.C.

1994-12-31

Coated sheet steels are used extensively in the automotive industry for the fabrication of automobile body components; however, their reduced weldability by the traditional welding processes has led to numerous studies into the use of alternate process such as laser welding. In this paper, we present a modified joint geometry which allows high quality lap welds of coated sheet steels to be made by laser welding processes. Hot-dipped galvanized sheet (16 gauge), with a 60 g/m zinc coating was used in this study. A groove was created in the top sheet of a specimen pair by pressing piano wires ofmore » various diameters into the sheet. The specimens were clamped together in a lag-joint configuration such that they were in contacted only along the grove projection. A parametric study was conducted using the variables of welding speed, laser mean power (685 W, 1000 W and 1350 W), and grove size. Weld quality and weld pool dimensions were assessed using metallurgical cross-sections and image analysis techniques. Acceptable quality seam welds were produced in the galvanized sheet steel with both grove sizes when using 1000 W and 1350 W laser mean powers and a range of welding speeds. Results of the shear-tensile tests showed that high loads to failure, with failure occurring in the parent material, were predominately found in welds produced at speeds over 1.2 m/min and when using the high mean laser powers: 1000 W and 1350 W. A modified lap joint geometry, in which a groove is pre-placed in the top sheet of the lap-joint configuration, has been developed which permits laser welding of coated sheet steels. Good quality seam welds have been produced in 16 gauge galvanized sheet steels at speeds up to 2.7 m/min using a 2 kW CW Nd:YAG laser operating at 1350 W laser mean power. Weld quality was not affected by changes in groove size.« less

Real weld geometry determining mechanical properties of high power laser welded medium plates

NASA Astrophysics Data System (ADS)

Liu, Sang; Mi, Gaoyang; Yan, Fei; Wang, Chunming; Li, Peigen

2018-06-01

Weld width is commonly used as one of main factors to assess joint performances in laser welding. However, it changes significantly through the thickness direction in conditions of medium or thick plates. In this study, high-power autogenous laser welding was conducted on 7 mm thickness 201 stainless steel to elucidate the factor of whole weld transverse shape critically affecting the mechanical properties with the aim of predicting the performance visually through the weld appearance. The results show that single variation of welding parameters could result in great changes of weld pool figures and subsequently weld transverse shapes. All the obtained welds are composed of austenite containing small amount of cellular dendritic δ-Ferrite. The 0.2% proof stresses of Nail- and Peanut-shaped joint reach 458 MPa and 454 MPa, 88.2% and 87.5% of the base material respectively, while that of Wedge-shaped joint only comes to 371 MPa, 71.5% of the base material. The deterioration effect is believed to be caused by the axial grain zone in the weld center. The fatigue strength of joint P is a bit lower than N, but much better than W. Significant deformation incompatibility through the whole thickness and microstructure resistance to crack initiation should be responsible for the poor performance of W-shaped joints.

Penetration in GTA welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heiple, C.R.; Burgardt, P.

1990-01-01

The size and shape of the weld bead produced in GTA welding depends on the magnitude and distribution of the energy incident on the workpiece surfaces as well as the dissipation of that energy in the workpiece. The input energy is largely controllable through the welding parameters selected, however the dissipation of that energy in the workpiece is less subject to control. Changes in energy dissipation can produce large changes in weld shape or penetration. Heat transport away from the weld pool is almost entirely by conduction, but heat transport in the weld pool is more complicated. Heat conduction throughmore » the liquid is an important component, but heat transport by convection (mass transport) is often the dominant mechanism. Convective heat transport is directional and changes the weld pool shape from that produced by conduction alone. Surface tension gradients are often the dominant forces driving fluid flow in GTA weld pools. These gradients are sensitive functions of weld pool chemistry and the energy input distribution to the weld. Experimental and theoretical work conducted primarily in the past decade has greatly enhanced our understanding of weld pool fluid flow, the forces which drive it, and its effects on weld pool shape. This work is reviewed here. While less common, changes in energy dissipation through the unmelted portion of the workpiece can also affect fusion zone shape or penetration. These effects are also described. 41 refs., 9 figs.« less

Control of Gas Tungsten Arc welding pool shape by trace element addition to the weld pool

DOEpatents

Heiple, C.R.; Burgardt, P.

1984-03-13

An improved process for Gas Tungsten Arc welding maximizes the depth/width ratio of the weld pool by adding a sufficient amount of a surface active element to insure inward fluid flow, resulting in deep, narrow welds. The process is especially useful to eliminate variable weld penetration and shape in GTA welding of steels and stainless steels, particularly by using a sulfur-doped weld wire in a cold wire feed technique.

Computational modeling of GTA (gas tungsten arc) welding with emphasis on surface tension effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zacharia, T.; David, S.A.

1990-01-01

A computational study of the convective heat transfer in the weld pool during gas tungsten arch (GTA) welding of Type 304 stainless steel is presented. The solution of the transport equations is based on a control volume approach which utilized directly, the integral form of the governing equations. The computational model considers buoyancy and electromagnetic and surface tension forces in the solution of convective heat transfer in the weld pool. In addition, the model treats the weld pool surface as a deformable free surface. The computational model includes weld metal vaporization and temperature dependent thermophysical properties. The results indicate thatmore » consideration of weld pool vaporization effects and temperature dependent thermophysical properties significantly influence the weld model predictions. Theoretical predictions of the weld pool surface temperature distributions and the cross-sectional weld pool size and shape wee compared with corresponding experimental measurements. Comparison of the theoretically predicted and the experimentally obtained surface temperature profiles indicated agreement with {plus minus} 8%. The predicted weld cross-section profiles were found to agree very well with actual weld cross-sections for the best theoretical models. 26 refs., 8 figs.« less

A Monte Carlo model for 3D grain evolution during welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodgers, Theron M.; Mitchell, John A.; Tikare, Veena

Welding is one of the most wide-spread processes used in metal joining. However, there are currently no open-source software implementations for the simulation of microstructural evolution during a weld pass. Here we describe a Potts Monte Carlo based model implemented in the SPPARKS kinetic Monte Carlo computational framework. The model simulates melting, solidification and solid-state microstructural evolution of material in the fusion and heat-affected zones of a weld. The model does not simulate thermal behavior, but rather utilizes user input parameters to specify weld pool and heat-affect zone properties. Weld pool shapes are specified by Bezier curves, which allow formore » the specification of a wide range of pool shapes. Pool shapes can range from narrow and deep to wide and shallow representing different fluid flow conditions within the pool. Surrounding temperature gradients are calculated with the aide of a closest point projection algorithm. Furthermore, the model also allows simulation of pulsed power welding through time-dependent variation of the weld pool size. Example simulation results and comparisons with laboratory weld observations demonstrate microstructural variation with weld speed, pool shape, and pulsed-power.« less

A Monte Carlo model for 3D grain evolution during welding

DOE PAGES

Rodgers, Theron M.; Mitchell, John A.; Tikare, Veena

2017-08-04

Welding is one of the most wide-spread processes used in metal joining. However, there are currently no open-source software implementations for the simulation of microstructural evolution during a weld pass. Here we describe a Potts Monte Carlo based model implemented in the SPPARKS kinetic Monte Carlo computational framework. The model simulates melting, solidification and solid-state microstructural evolution of material in the fusion and heat-affected zones of a weld. The model does not simulate thermal behavior, but rather utilizes user input parameters to specify weld pool and heat-affect zone properties. Weld pool shapes are specified by Bezier curves, which allow formore » the specification of a wide range of pool shapes. Pool shapes can range from narrow and deep to wide and shallow representing different fluid flow conditions within the pool. Surrounding temperature gradients are calculated with the aide of a closest point projection algorithm. Furthermore, the model also allows simulation of pulsed power welding through time-dependent variation of the weld pool size. Example simulation results and comparisons with laboratory weld observations demonstrate microstructural variation with weld speed, pool shape, and pulsed-power.« less

Modeling macro-and microstructures of gas-metal-arc welded HSLA-100 steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Z.; Debroy, T.

1999-06-01

Fluid flow and heat transfer during gas-metal-arc welding (GMAW) of HSLA-100 steel were studied using a transient, three-dimensional, turbulent heat transfer and fluid flow model. The temperature and velocity fields, cooling rates, and shape and size of the fusion and heat-affected zones (HAZs) were calculated. A continuous-cooling-transformation (CCT) diagram was computed to aid in the understanding of the observed weld metal microstructure. The computed results demonstrate that the dissipation of heat and momentum in the weld pool is significantly aided by turbulence,m thus suggesting that previous modeling results based on laminar flow need to be re-examined. A comparison of themore » calculated fusion and HAZ geometries with their corresponding measured values showed good agreement. Furthermore, finger penetration, a unique geometric characteristic of gas-metal-arc weld pools, could be satisfactorily predicted from the model. The ability to predict these geometric variables and the agreement between the calculated and the measured cooling rates indicate the appropriateness of using a turbulence model for accurate calculations. The microstructure of the weld metal consisted mainly of acicular ferrite with small amounts of bainite. At high heat inputs, small amounts of allotriomorphic and Widmanstaetten ferrite were also observed. The observed microstructures are consistent with those expected from the computed CCT diagram and the cooling rates. The results presented here demonstrate significant promise for understanding both macro-and microstructures of steel welds from the combination of the fundamental principles from both transport phenomena and phase transformation theory.« less

An Assessment of Molten Metal Detachment Hazards During Electron Beam Welding in Space

NASA Technical Reports Server (NTRS)

Fragomeni, James M.; Nunes, Arthur C., Jr.

1998-01-01

The safety issue has been raised with regards to potential molten metal detachments from the weld pool and cold filler wire during electron beam welding in space. This investigation was undertaken to evaluate if molten metal could detach and come in contact with astronauts and burn through the fabric of the astronauts' Extravehicular Mobility Unit (EMU) during electron beam welding in space. Molten metal detachments from either the weld/cut substrate or weld wire could present harm to a astronaut if the detachment was to burn through the fabric of the EMU. Theoretical models were developed to predict the possibility and size of the molten metal detachment hazards during the electron beam welding exercises at Low Earth Orbit (LEO). The primary molten metal detachment concerns were those cases of molten metal separation from the metal surface due to metal cutting, weld pool splashing, entrainment and release of molten metal due to filler wire snap-out from the weld puddle, and molten metal accumulation and release from the end of the weld wire. Some possible ways of obtaining molten metal drop detachments would include an impulse force, or bump, to the weld sample, cut surface, or filler wire. Theoretical models were developed for these detachment concerns from principles of impact and kinetic energies, surface tension, drop geometry, surface energies, and particle dynamics. The surface tension represents the force opposing the liquid metal drop from detaching whereas the weight of the liquid metal droplet represents a force that is tending to detach the molten metal drop. Theoretical calculations have indicated that only a small amount of energy is required to detach a liquid metal drop; however, much of the energy of an impact is absorbed in the sample or weld plate before it reaches the metal drop on the cut edge or surface. The tendency for detachment is directly proportional to the weld pool radius and metal density and inversely proportional to the surface tension of the liquid metal. For a detachment the initial kinetic energy of the weld pool with respect to the plate has to exceed the energy to form the extra surface required for the detachment of the pool. The difficulty is in transferring the energy from the point of impact through the plate and sample to the cut edge. It is likely that not all of the kinetic energy is available for detaching the pool; some may be sequestered in weld pool oscillations. The coefficient of restitution for the collision will be lower than one if irreversible deformation, for example plastic flow deformation, takes place during the collision. Thus determining the amount of energy from an impact that actually reaches the molten metal droplet is critical. Various molten metal detachment scenarios were tested experimentally in an enclosed vacuum chamber using the Ukrainian Universal Hand Tool, an electron beam welder designed for space welding. The experimental testing was performed in a 4 ft. X 4 ft. vacuum chamber at Marshall Space Flight Center, evacuated to vacuum levels of at least 50 microTorr, and also some welding garment material was utilized to observe the effect of the molten metal detachments on the material. A "carillon" apparatus consisting of four pendulum hammer strikers, each weighing approximately 3.65 lbs, raised to predetermined specific heights was used to apply an impact force to the weld sample/plate during electron beam welding and cutting exercises. The strikers were released by switching on an electric motor to rotate a pin holding wires retaining the strikers at desired heights. The specimens were suspended so as to be free to respond to the blows with a sudden velocity increment. The specimens were mounted on a hinged plate for minimizing effective mass with the option to fasten it down so as to raise its effective mass closer to that anticipated for an actual space welding scenario. Measurements were made of the impact energy and the horizontal fling distances of the detached metal drops. It was not particularly easy to generate the detachments fo

An Assessment of Molten Metal Detachment Hazards During Electron Beam Welding in Space

NASA Technical Reports Server (NTRS)

Fragomeni, James M.; Nunes, Arthur C., Jr.

1998-01-01

The safety issue has been raised with regards to potential molten metal detachments from the weld pool and cold filler wire during electron beam welding in space. This investigation was undertaken to evaluate if molten metal could detach and come in contact with astronauts and burn through the fabric of the astronauts' Extravehicular Mobility Unit (EMU) during electron beam welding in space. Molten metal detachments from either the weld/cut substrate or weld wire could present harm to a astronaut if the detachment was to burn through the fabric of the EMU. Theoretical models were developed to predict the possibility and size of the molten metal detachment hazards during the electron beam welding exercises at Low Earth Orbit (LEO). The primary molten metal detachment concerns were those cases of molten metal separation from the metal surface due to metal cutting, weld pool splashing, entrainment and release of molten metal due to filler wire snap-out from the weld puddle, and molten metal accumulation and release from the end of the weld wire. Some possible ways of obtaining molten metal drop detachments would include an impulse force, or bump, to the weld sample, cut surface, or filler wire. Theoretical models were developed for these detachment concerns from principles of impact and kinetic energies, surface tension, drop geometry, surface energies, and particle dynamics. The surface tension represents the force opposing the liquid metal drop from detaching whereas the weight of the liquid metal droplet represents a force that is tending to detach the molten metal drop. Theoretical calculations have indicated that only a small amount of energy is required to detach a liquid metal drop; however, much of the energy of an impact is absorbed in the sample or weld plate before it reaches the metal drop on the cut edge or surface. The tendency for detachment is directly proportional to the weld pool radius and metal density and inversely proportional to the surface tension of the liquid metal. For a detachment the initial kinetic energy of the weld pool with respect to the plate has to exceed the energy to form the extra surface required for the detachment of the pool. The difficulty is in transferring the energy from the point of impact through the plate and sample to the cut edge. It is likely that not all of the kinetic energy is available for detaching the pool; some may be sequestered in weld pool oscillations. The coefficient of restitution for the collision will be lower than one if irreversible deformation, for example plastic flow deformation, takes place during the collision. Thus determining the amount of energy from an impact that actually reaches the molten metal droplet is critical. Various molten metal detachment scenarios were tested experimentally in an enclosed vacuum chamber using the Ukrainian Universal Hand Tool, an electron beam welder designed for space welding. The experimental testing was performed in a 4 ft. X 4 ft. vacuum chamber at Marshall Space Flight Center, evacuated to vacuum levels of at least 50 microTorr, and also some welding garment material was utilized to observe the effect of the molten metal detachments on the material. A "carillon" apparatus consisting of four pendulum hammer strikers, each weighing approximately 3.65 lbs, raised to predetermined specific heights was used to apply an impact force to the weld sample/plate during electron beam welding and cutting exercises. The strikers were released by switching on an electric motor to rotate a pin holding wires retaining the strikers at desired heights. The specimens were suspended so as to be free to respond to the blows with a sudden velocity increment. The specimens were mounted on a hinged plate for minimizing effective mass with the option to fasten it down so as to raise its effective mass closer to that anticipated for an actual space welding scenario. Measurements were made of the impact energy and the horizontal fling distances of the detached metal drops. It was not particularly easy to generate the detachments for this experiment. This document presents the details of the theoretical modeling effort and a summary of the experimental effort to measure molten metal drop detachments from terrestrial electron beam welding in the enclosed vacuum chamber. The results of the experimental effort have shown that molten metal detachments can occur from the sample/weld plate only if a sufficiently large impact force is applied to the weld plate. A "weld pool detachment parameter" was determined to indicate whether detachment would occur. Detachment can be either full or partial (dripping), Partial detachment means that the weld pool detached from one side of the liquid-solid boundary so as to leave a hole at the puddle site but remained attached over part of the liquid-solid boundary and dripped down the plate with no fully detached material detected. Full detachment, however, does not necessarily mean that the whole pool fully detached; in some cases only a smaller portion of the pool detached, the remainder dripping down the plate. The weld pool detachment parameter according to theory and according to the empirical data allows a determination of whether full detachments might occur. Theoretical calculations indicated titanium alloy would be the most difficult from which to detach molten metal droplets followed by stainless steel and then by aluminum. The experimental results were for the most part consistent with the theoretical analysis and predictions. The above theory is applicable to other situations as desired for assessing the potential for molten metal detachments.

Visualization of hump formation in high-speed gas metal arc welding

NASA Astrophysics Data System (ADS)

Wu, C. S.; Zhong, L. M.; Gao, J. Q.

2009-11-01

The hump bead is a typical weld defect observed in high-speed welding. Its occurrence limits the improvement of welding productivity. Visualization of hump formation during high-speed gas metal arc welding (GMAW) is helpful in the better understanding of the humping phenomena so that effective measures can be taken to suppress or decrease the tendency of hump formation and achieve higher productivity welding. In this study, an experimental system was developed to implement vision-based observation of the weld pool behavior during high-speed GMAW. Considering the weld pool characteristics in high-speed welding, a narrow band-pass and neutral density filter was equipped for the CCD camera, the suitable exposure time was selected and side view orientation of the CCD camera was employed. The events that took place at the rear portion of the weld pools were imaged during the welding processes with and without hump bead formation, respectively. It was found that the variation of the weld pool surface height and the solid-liquid interface at the pool trailing with time shows some useful information to judge whether the humping phenomenon occurs or not.

Gravitational effects on the weld pool shape and microstructural evolution during gas tungsten arc and laser beam welding of 304 stainless steel and Al-4 wt% Cu alloy.

PubMed

Kang, Namhyun; Singh, Jogender; Kulkarni, Anil K

2004-11-01

Effects of gravitational acceleration were investigated on the weld pool shape and microstructural evolution for 304 stainless steel and Al-4wt% Cu alloy. Effects of welding heat source were investigated by using laser beam welding (LBW) and gas tungsten arc welding (GTAW). As the gravitational level was increased from low gravity (LG approximately 1.2 g) to high gravity (HG approximately 1.8 g) using a NASA KC-135 aircraft, the weld pool shape for 304 stainless steel was influenced considerably during GTAW. However, insignificant change in the microstructure and solute distribution was observed at gravitational levels between LG and HG. The GTAW on Al-4 wt% Cu alloy was used to investigate the effect of gravitational orientation on the weld solidification behavior. Gravitational orientation was manipulated by varying the welding direction with respect to gravity vector; that is, by welding upward opposing gravity ( ||-U) and downward with gravity ( ||-D) on a vertical weld piece and welding perpendicular to gravity (perpendicular) on a horizontal weld piece. Under the same welding conditions, a larger primary dendrite spacing in the ||-U weld was observed near the weld pool surface and the fusion boundary than in the case of perpendicular or ||-D welds. The ||-D weld exhibited different solidification morphology and abnormal S shape of solidification rate curve during its growth. For 304 stainless steel GTAW, significant effects of gravitational orientation were observed on the weld pool shape that was associated with weld surface morphology and convection flow. However, the weld pool shape for LBW was mostly constant with respect to the gravitational orientation.

An investigation on capability of hybrid Nd:YAG laser-TIG welding technology for AA2198 Al-Li alloy

NASA Astrophysics Data System (ADS)

Faraji, Amir Hosein; Moradi, Mahmoud; Goodarzi, Massoud; Colucci, Pietro; Maletta, Carmine

2017-09-01

This paper surveys the capability of the hybrid laser-arc welding in comparison with lone laser welding for AA2198 aluminum alloy experimentally. In the present research, a continuous Nd:YAG laser with a maximum power of 2000 W and a 350 A electric arc were used as two combined welding heat sources. In addition to the lone laser welding experiments, two strategies were examined for hybrid welding; the first one was low laser power (100 W) accompanied by high arc energy, and the second one was high laser power (2000 W) with low arc energy. Welding speed and arc current varied in the experiments. The influence of heat input on weld pool geometry was surveyed. The macrosection, microhardness profile and microstructure of the welded joints were studied and compared. The results indicated that in lone laser welding, conduction mode occurred and keyhole was not formed even in low welding speeds and thus the penetration depth was so low. It was also found that the second approach (high laser power accompanied with low arc energy) is superior to the first one (low laser power accompanied with high arc energy) in hybrid laser-arc welding of Al2198, since lower heat input was needed for full penetration weld and as a result a smaller HAZ was created.

Automatic Welding System of Aluminum Pipe by Monitoring Backside Image of Molten Pool Using Vision Sensor

NASA Astrophysics Data System (ADS)

Baskoro, Ario Sunar; Kabutomori, Masashi; Suga, Yasuo

An automatic welding system using Tungsten Inert Gas (TIG) welding with vision sensor for welding of aluminum pipe was constructed. This research studies the intelligent welding process of aluminum alloy pipe 6063S-T5 in fixed position and moving welding torch with the AC welding machine. The monitoring system consists of a vision sensor using a charge-coupled device (CCD) camera to monitor backside image of molten pool. The captured image was processed to recognize the edge of molten pool by image processing algorithm. Neural network model for welding speed control were constructed to perform the process automatically. From the experimental results it shows the effectiveness of the control system confirmed by good detection of molten pool and sound weld of experimental result.

A unified 3D model for an interaction mechanism of the plasma arc, weld pool and keyhole in plasma arc welding

NASA Astrophysics Data System (ADS)

Jian, Xiaoxia; Wu, ChuanSong; Zhang, Guokai; Chen, Ji

2015-11-01

A 3D model is developed to perform numerical investigation on the coupled interaction mechanism of the plasma arc, weld pool and keyhole in plasma arc welding. By considering the traveling of the plasma arc along the welding direction, unified governing equations are solved in the whole domain including the torch, plasma arc, keyhole, weld pool and workpiece, which involves different physical mechanisms in different zones. The local thermodynamic equilibrium-diffusion approximation is used to treat the interface between the plasma arc and weld pool, and the volume-of-fluid method is used to track the evolution of the keyhole wall. The interaction effects between the plasma arc, keyhole and weld pool as well as the heat, mass and pressure transport phenomena in the whole welding domain are quantitatively simulated. It is found that when the torch is moving along the joint line, the axis of the keyhole channel tilts backward, and the envelope of molten metal surrounding the keyhole wall inside the weld pool is unsymmetrical relative to the keyhole channel. The plasma arc welding tests are conducted, and the predicted keyhole dimensions and the fusion zone shape are in agreement with the experimentally measured results.

Influence of the Gap Width on the Geometry of the Welded Joint in Hybrid Laser-Arc Welding

NASA Astrophysics Data System (ADS)

Turichin, G.; Tsibulskiy, I.; Kuznetsov, M.; Akhmetov, A.; Mildebrath, M.; Hassel, T.

The aim of this research was the experimental investigation of the influence of the gap width and speed of the welding wire on the changes of the geometry in the welded joint in the hybrid laser-arc welding of shipbuilding steel RS E36. The research was divided into three parts. First, in order to understand the influence of the gap width on the welded joint geometry, experimental research was done using continuous wave fiber laser IPG YLS-15000 with arc rectifier VDU-1500DC. The second part involved study of the geometry of the welded joint and hardness test results. Three macrosections from each welded joint were obtained. Influence of the gap width and welding wire speed on the welded joint geometry was researched in the three lines: in the right side of the plates, middle welded joint and in the root welded joint.

Method for enhanced control of welding processes

DOEpatents

Sheaffer, Donald A.; Renzi, Ronald F.; Tung, David M.; Schroder, Kevin

2000-01-01

Method and system for producing high quality welds in welding processes, in general, and gas tungsten arc (GTA) welding, in particular by controlling weld penetration. Light emitted from a weld pool is collected from the backside of a workpiece by optical means during welding and transmitted to a digital video camera for further processing, after the emitted light is first passed through a short wavelength pass filter to remove infrared radiation. By filtering out the infrared component of the light emitted from the backside weld pool image, the present invention provides for the accurate determination of the weld pool boundary. Data from the digital camera is fed to an imaging board which focuses on a 100.times.100 pixel portion of the image. The board performs a thresholding operation and provides this information to a digital signal processor to compute the backside weld pool dimensions and area. This information is used by a control system, in a dynamic feedback mode, to automatically adjust appropriate parameters of a welding system, such as the welding current, to control weld penetration and thus, create a uniform weld bead and high quality weld.

Examination of the physical processes associated with the keyhole region of variable polarity plasma arc welds in aluminum alloy 2219

NASA Technical Reports Server (NTRS)

Walsh, Daniel W.

1987-01-01

The morphology and properties of the Variable Polarity Plasma Arc (VPPA) weld composite zone are intimately related to the physical processes associated with the keyhole. This study examined the effects of oxide, halide, and sulfate additions to the weld plate on the keyhole and the weld pool. Changes in both the arc plasma character and the bead morphology were correlated to the chemical environment of the weld. Pool behavior was observed by adding flow markers to actual VPPA welds. A low temperature analog to the welding process was developed. The results of the study indicate that oxygen, even at low partial pressures, can disrupt the stable keyhole and weld pool. The results also indicate that the Marangoni surface tension driven flows dominate the weld pool over the range of welding currents studied.

Experimental and numerical studies on three dimensional GTA weld pool convection: Non-axisymmetric effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joshi, Y.; Dutta, P.; Schupp, P.E.

1995-12-31

Observations of surface flow patterns of steel and aluminum GTAW pools have been made using a pulsed laser visualization system. The weld pool convection is found to be three dimensional, with the azimuthal circulation depending on the location of the clamp with respect to the torch. Oscillation of steel pools and undulating motion in aluminum weld pools are also observed even with steady process parameters. Current axisymmetric numerical models are unable to explain such phenomena. A three dimensional computational study is carried out in this study to explain the rotational flow in aluminum weld pools.

Modeling of the Weld Shape Development During the Autogenous Welding Process by Coupling Welding Arc with Weld Pool

NASA Astrophysics Data System (ADS)

Dong, Wenchao; Lu, Shanping; Li, Dianzhong; Li, Yiyi

2010-10-01

A numerical model of the welding arc is coupled to a model for the heat transfer and fluid flow in the weld pool of a SUS304 stainless steel during a moving GTA welding process. The described model avoids the use of the assumption of the empirical Gaussian boundary conditions, and at the same time, provides reliable boundary conditions to analyze the weld pool. Based on the two-dimensional axisymmetric numerical modeling of the argon arc, the heat flux to workpiece, the input current density, and the plasma drag stress are obtained. The arc temperature contours, the distributions of heat flux, and current density at the anode are in fair agreement with the reported experimental results. Numerical simulation and experimental studies to the weld pool development are carried out for a moving GTA welding on SUS304 stainless steel with different oxygen content from 30 to 220 ppm. The calculated result show that the oxygen can change the Marangoni convection from outward to inward direction on the liquid pool surface and make the wide shallow weld shape become narrow deep one. The calculated result for the weld shape and weld D/W ratio agrees well with the experimental one.

Optimization of Laser Keyhole Welding Strategies of Dissimilar Metals by FEM Simulation

NASA Astrophysics Data System (ADS)

Garcia Navas, Virginia; Leunda, Josu; Lambarri, Jon; Sanz, Carmen

2015-07-01

Laser keyhole welding of dissimilar metals has been simulated to study the effect of welding strategies (laser beam displacements and tilts) and combination of metals to be welded on final quality of the joints. Molten pool geometry and welding penetration have been studied but special attention has been paid to final joint material properties, such as microstructure/phases and hardness, and especially to the residual stress state because it greatly conditions the service life of laser-welded components. For a fixed strategy (laser beam perpendicular to the joint) austenitic to carbon steel laser welding leads to residual stresses at the joint area very similar to those obtained in austenitic to martensitic steel welding, but welding of steel to Inconel 718 results in steeper residual stress gradients and higher area at the joint with detrimental tensile stresses. Therefore, when the difference in thermo-mechanical properties of the metals to be welded is higher, the stress state generated is more detrimental for the service life of the component, and consequently more relevant is the optimization of welding strategy. In laser keyhole welding of austenitic to martensitic stainless steel and austenitic to carbon steel, the optimum welding strategy is displacing the laser beam 1 mm toward the austenitic steel. In the case of austenitic steel to Inconel welding, the optimum welding strategy consists in setting the heat source tilted 45 deg and moved 2 mm toward the austenitic steel.

Application of welding science to welding engineering: A lumped parameter gas metal arc welding dynamic process model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murray, P.E.; Smartt, H.B.; Johnson, J.A.

1997-12-31

We develop a model of the depth of penetration of the weld pool in gas metal arc welding (GMAW) which demonstrates interaction between the arc, filler wire and weld pool. This model is motivated by the observations of Essers and Walter which suggest a relationship between droplet momentum and penetration depth. A model of gas metal arc welding was augmented to include an improved model of mass transfer and a simple model of accelerating droplets in a plasma jet to obtain the mass and momentum of impinging droplets. The force of the droplets and depth of penetration is correlated bymore » a dimensionless linear relation used to predict weld pool depth for a range of values of arc power and contact tip to workpiece distance. Model accuracy is examined by comparing theoretical predictions and experimental measurements of the pool depth obtained from bead on plate welds of carbon steel in an argon rich shielding gas. Moreover, theoretical predictions of pool depth are compared to the results obtained from the heat conduction model due to Christensen et al. which suggest that in some cases the momentum of impinging droplets is a better indicator of the depth of the weld pool and the presence of a deep, narrow penetration.« less

Weld pool oscillation during pulsed GTA welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aendenroomer, A.J.R.; Ouden, G. den

1996-12-31

This paper deals with weld pool oscillation during pulsed GTA welding and with the possibility to use this oscillation for in-process control of weld penetration. Welding experiments were carried out under different welding conditions. During welding the weld pool was triggered into oscillation by the normal welding pulses or by extra current pulses. The oscillation frequency was measured both during the pulse time and during the base time by analyzing the arc voltage variation using a Fast Fourier Transformation program. Optimal results are obtained when full penetration occurs during the pulse time and partial penetration during the base time. Undermore » these conditions elliptical overlapping spot welds are formed. In the case of full penetration the weld pool oscillates in a low frequency mode (membrane oscillation), whereas in the case of partial penetration the weld pool oscillates in a high frequency mode (surface oscillation). Deviation from the optimal welding conditions occurs when high frequency oscillation is observed during both pulse time and base time (underpenetration) or when low frequency oscillation is observed during both pulse time and base time (overpenetration). In line with these results a penetration sensing system with feedback control was designed, based on the criterion that optimal weld penetration is achieved when two peaks are observed in the frequency distribution. The feasibility of this sensing system for orbital tube welding was confirmed by the results of experiments carried out under various welding conditions.« less

Experimental measurement of stationary SS 304, SS 316L and 8630 GTA weld pool surface temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kraus, H.G.

1989-07-01

The optical spectral radiometric/laser reflectance experimental method, previously developed by the author, was extended to obtain high-resolution surface temperature maps of stationary GTA molten weld pools using thick-plate SS 304, SS316L, and 8630 steel. Increasing the welding current from 50 to 200 A resulted in peak pool surface temperatures from 1050{sup 0} to 2400{sup 0}C for the SS 304. At a constant welding current of 150 A, the SS 304 and various heats of SS 316L and 8630 resulted in peak weld pool temperatures from 2300{sup 0} to 2700{sup 0}C. Temperature contour plots of all the welds made are given.more » Surface temperature maps are classified into types that are believed to be indicative of the convective circulation patterns present in the weld pools.« less

Determination of a temperature sensor location for monitoring weld pool size in GMAW

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boo, K.S.; Cho, H.S.

1994-11-01

This paper describes a method of determining the optimal sensor location to measure weldment surface temperature, which has a close correlation with weld pool size in the gas metal arc (GMA) welding process. Due to the inherent complexity and nonlinearity in the GMA welding process, the relationship between the weldment surface temperature and the weld pool size varies with the point of measurement. This necessitates an optimal selection of the measurement point to minimize the process nonlinearity effect in estimating the weld pool size from the measured temperature. To determine the optimal sensor location on the top surface of themore » weldment, the correlation between the measured temperature and the weld pool size is analyzed. The analysis is done by calculating the correlation function, which is based upon an analytical temperature distribution model. To validate the optimal sensor location, a series of GMA bead-on-plate welds are performed on a medium-carbon steel under various welding conditions. A comparison study is given in detail based upon the simulation and experimental results.« less

A mathematical model of the chevron-like wave pattern on a weld piece

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dowden, J.; Kapadia, P.

1996-12-31

In welding processes in general the surface of a metallic weld displays a chevron-like pattern. Such a pattern is also clearly seen to be present if welding is carried out using a laser beam. In the welding process a laser beam is directed normally on the metal undergoing translation and usually penetrates it to form a keyhole. The keyhole is surrounded by a molten region, the weld pool. Even if a CO{sub 2} laser is used, there are numerous fluctuations and instabilities that occur, so that the keyhole imposes forcing frequencies on the molten weld pool, additional to vibrations attendantmore » on the process of translation. The weld pool in turn responds by supporting a spectrum of waves of different frequencies involving the natural frequency of the weld pool as well as various forcing frequencies. These waves are surface tension-type capillary waves and previous publications have attempted to model their behavior mathematically, although not all aspects of the problem have always been included. The wave pattern that is manifested in the chevron-like pattern seen on the weld piece is, however, not necessarily identical to the wave pattern present in the weld pool. This is because the chevron-like wave pattern forms as a result of several complicating effects that arise as the weld specimen cools on its surface immediately after the weld has been formed. This process involves the waves on the surface of the weld pool freezing to form the chevron-like wave pattern. A feature that is often ignored is the fact that the waves on the weld pool can only be regarded as irrotational if the translation speed is sufficiently low. This paper describes mathematically the formation of the chevron-like wave pattern based on suitable simplifying assumptions to model the process. The mathematical description of the way in which this chevron-like pattern forms is a step toward a more comprehensive understanding of this process.« less

Dynamic behavior of the weld pool in stationary GMAW

NASA Astrophysics Data System (ADS)

Chapuis, J.; Romero, E.; Bordreuil, C.; Soulié, F.; Fras, G.

2010-06-01

Because hump formation limits welding productivity, better understanding of the humping phenomena during the welding process is needed to access to process modifications that decrease the tendency for hump formation and then allow higher productivity welding. From a physical point of view, the mechanism identified is the Rayleigh instability initiated by strong surface tension gradient which induces a variation of kinetic flow. But the causes of the appearance of this instability are not yet well explained. Because of the phenomena complex and multi-physics, we chose in first step to conduct an analysis of the characteristic times involved in weld pool in pulsed stationary GMAW. The goal is to study the dynamic behavior of the weld pool, using our experimental multi physics approach. The experimental tool and methodology developed to understand these fast phenomena are presented first: frames acquisition with high speed digital camera and specific optical devices, numerical library. The analysis of geometric parameters of the weld pool during welding operation are presented in the last part: we observe the variations of wetting angles (or contact lines angles), the base and the height of the weld pool (macro-drop) versus weld time.

Fluid Flow Phenomena during Welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Wei

2011-01-01

MOLTEN WELD POOLS are dynamic. Liquid in the weld pool in acted on by several strong forces, which can result in high-velocity fluid motion. Fluid flow velocities exceeding 1 m/s (3.3 ft/s) have been observed in gas tungsten arc (GTA) welds under ordinary welding conditions, and higher velocities have been measured in submerged arc welds. Fluid flow is important because it affects weld shape and is related to the formation of a variety of weld defects. Moving liquid transports heat and often dominates heat transport in the weld pool. Because heat transport by mass flow depends on the direction andmore » speed of fluid motion, weld pool shape can differ dramatically from that predicted by conductive heat flow. Temperature gradients are also altered by fluid flow, which can affect weld microstructure. A number of defects in GTA welds have been attributed to fluid flow or changes in fluid flow, including lack of penetration, top bead roughness, humped beads, finger penetration, and undercutting. Instabilities in the liquid film around the keyhole in electron beam and laser welds are responsible for the uneven penetration (spiking) characteristic of these types of welds.« less

Numerical simulation of humping phenomenon in high speed gas metal arc welding

NASA Astrophysics Data System (ADS)

Chen, Ji; Wu, Chuan-Song

2011-06-01

It is of great significance to obtain a thorough understanding of the physical mechanisms responsible for humping bead phenomenon in high speed gas metal arc welding (GMAW) in order to raise welding efficiency. Experiments were conducted to observe the weld pool behaviors in high speed GMAW, and it was found that both the severely deformed weld pool surface and strong backward flowing play a dominant role in humping bead formation. In this study, a mathematical model is developed to quantitatively analyze the forming mechanism of humping beads for high speed GMAW through considering both the momentum and heat content distribution of the backward flowing molten metal inside the weld pool. The transient development of temperature profiles in the weld pool with severe deformation demonstrates the humping bead forming process under some welding conditions. The predicted and measured humping bead dimensions are in agreement.

Experimental characterization of the weld pool flow in a TIG configuration

NASA Astrophysics Data System (ADS)

Stadler, M.; Masquère, M.; Freton, P.; Franceries, X.; Gonzalez, J. J.

2014-11-01

Tungsten Inert Gas (TIG) welding process relies on heat transfer between plasma and work piece leading to a metallic weld pool. Combination of different forces produces movements on the molten pool surface. One of our aims is to determine the velocity on the weld pool surface. This provides a set of data that leads to a deeper comprehension of the flow behavior and allows us to validate numerical models used to study TIG parameters. In this paper, two diagnostic methods developed with high speed imaging for the determination of velocity of an AISI 304L stainless steel molten pool are presented. Application of the two methods to a metallic weld pool under helium with a current intensity of 100 A provides velocity values around 0.70 m/s which are in good agreement with literature works.

Optically controlled welding system

NASA Technical Reports Server (NTRS)

Gordon, Stephen S. (Inventor)

1988-01-01

An optically controlled welding system wherein a welding torch having through-the-torch viewing capabilities is provided with an optical beam splitter to create a transmitted view and a reflective view of a welding operation. These views are converted to digital signals which are then processed and utilized by a computerized robotic welder to make the welding torch responsive thereto. Other features include an actively cooled electrode holder which minimizes a blocked portion of the view by virtue of being constructed of a single spoke or arm, and a weld pool contour detector comprising a laser beam directed onto the weld pool with the position of specular radiation reflected therefrom, being characteristic of a penetrated or unpenetrated condition of the weld pool.

Determination and Dependencies of Melt Pool Dimensions in Laser Micro Welding

NASA Astrophysics Data System (ADS)

Patschger, Andreas; Bliedtner, Jens

Melt pool dimensions such as width and length influence the properties of the resulting weld joint and should be considered when designing the laser welding process. The melt pool width and as a consequence the weld seam width determine the strength of the joint. The melt pool length is directly linked to the solidification time which affects the resulting metallurgical micro structure. The melt pool dimensions can be estimated by given analytical solutions based on the capillary diameter. In order to test the given estimations, melt pool dimensions of bead-on-plate welds in stainless steel foils were measured by means of high speed imaging and microscopy. The welds were obtained by applying different focal diameters between 25 μm and 204 μm to foil thicknesses of 50 μm and 100 μm. As a result, simplified correlations based on the focal diameter are derived which is less complex to determine in practice. Regression analyses ensure a statistical comparability.

Integrated optical sensor

DOEpatents

Watkins, Arthur D.; Smartt, Herschel B.; Taylor, Paul L.

1994-01-01

An integrated optical sensor for arc welding having multifunction feedback control. The sensor, comprising generally a CCD camera and diode laser, is positioned behind the arc torch for measuring weld pool position and width, standoff distance, and post-weld centerline cooling rate. Computer process information from this sensor is passed to a controlling computer for use in feedback control loops to aid in the control of the welding process. Weld pool position and width are used in a feedback loop, by the weld controller, to track the weld pool relative to the weld joint. Sensor standoff distance is used in a feedback loop to control the contact tip to base metal distance during the welding process. Cooling rate information is used to determine the final metallurgical state of the weld bead and heat affected zone, thereby controlling post-weld mechanical properties.

Integrated optical sensor

DOEpatents

Watkins, A.D.; Smartt, H.B.; Taylor, P.L.

1994-01-04

An integrated optical sensor for arc welding having multifunction feedback control is described. The sensor, comprising generally a CCD camera and diode laser, is positioned behind the arc torch for measuring weld pool position and width, standoff distance, and post-weld centerline cooling rate. Computer process information from this sensor is passed to a controlling computer for use in feedback control loops to aid in the control of the welding process. Weld pool position and width are used in a feedback loop, by the weld controller, to track the weld pool relative to the weld joint. Sensor standoff distance is used in a feedback loop to control the contact tip to base metal distance during the welding process. Cooling rate information is used to determine the final metallurgical state of the weld bead and heat affected zone, thereby controlling post-weld mechanical properties. 6 figures.

Relationship between spatter formation and dynamic molten pool during high-power deep-penetration laser welding

NASA Astrophysics Data System (ADS)

Li, Shichun; Chen, Genyu; Katayama, Seiji; Zhang, Yi

2014-06-01

The spatter and the molten pool behavior, which were the important phenomena concerned with the welding quality, were observed and studied by using the high-speed camera and the X-ray transmission imaging system during laser welding under different welding parameters. The formation mechanism of spatter and the corresponding relationships between the spatter and molten pool behavior were investigated. The increase of laser power could cause more intense evaporation and lead to more spatter. When the focal position of laser beam was changed, different forms of spatter were generated, as well as the flow trends of molten metal on the front keyhole wall and at the rear molten pool were changed. The results revealed that the behavior of molten pool, which could be affected by the absorbed energy distribution in the keyhole, was the key factor to determine the spatter formation during laser welding. The relatively sound weld seam could be obtained during laser welding with the focal position located inside the metal.

Numerical Modeling of Fluid Flow, Heat Transfer and Arc-Melt Interaction in Tungsten Inert Gas Welding

NASA Astrophysics Data System (ADS)

Li, Linmin; Li, Baokuan; Liu, Lichao; Motoyama, Yuichi

2017-04-01

The present work develops a multi-region dynamic coupling model for fluid flow, heat transfer and arc-melt interaction in tungsten inert gas (TIG) welding using the dynamic mesh technique. The arc-weld pool unified model is developed on basis of magnetohydrodynamic (MHD) equations and the interface is tracked using the dynamic mesh method. The numerical model for arc is firstly validated by comparing the calculated temperature profiles and essential results with the former experimental data. For weld pool convection solution, the drag, Marangoni, buoyancy and electromagnetic forces are separately validated, and then taken into account. Moreover, the model considering interface deformation is adopted in a stationary TIG welding process with SUS304 stainless steel and the effect of interface deformation is investigated. The depression of weld pool center and the lifting of pool periphery are both predicted. The results show that the weld pool shape calculated with considering the interface deformation is more accurate.

Optically controlled welding system

NASA Technical Reports Server (NTRS)

Gordon, Stephen S. (Inventor)

1989-01-01

An optically controlled welding system (10) wherein a welding torch (12) having through-the-torch viewing capabilities is provided with an optical beam splitter (56) to create a transmitted view and a reflective view of a welding operation. These views are converted to digital signals which are then processed and utilized by a computerized robotic welder (15) to make the welding torch responsive thereto. Other features includes an actively cooled electrode holder (26) which minimizes a blocked portion of the view by virtue of being constructed of a single spoke or arm (28) and a weld pool contour detector (14) comprising a laser beam directed onto the weld pool with the position of specular radiation reflected therefrom being characteristic of a penetrated or unpenetrated condition of the weld pool.

Keyhole behavior and liquid flow in molten pool during laser-arc hybrid welding

NASA Astrophysics Data System (ADS)

Naito, Yasuaki; Katayama, Seiji; Matsunawa, Akira

2003-03-01

Hybrid welding was carried out on Type 304 stainless steel plate under various conditions using YAG laser combined with TIG arc. During arc and laser-arc hybrid welding, arc voltage variation was measured, and arc plasma, laser-induced plume and evaporation spots as well as keyhole behavior and liquid flow in the molten pool were observed through CCD camera and X-ray real-time transmission apparatus. It was consequently found that hybrid welding possessed many features in comparison with YAG laser welding. The deepest weld bead could be produced when the YAG laser beam of high power density was shot on the molten pool made beforehand stably with TIG arc. A keyhole was long and narrow, and its behavior was rather stable inside the molten pool. It was also confirmed that porosity was reduced by the suppression of bubble formation in hybrid welding utilizing a laser of a moderate power density.

Pearson's Functions to Describe FSW Weld Geometry

NASA Astrophysics Data System (ADS)

Lacombe, D.; Gutierrez-Orrantia, M. E.; Coupard, D.; Tcherniaeff, S.; Girot, F.

2011-01-01

Friction stir welding (FSW) is a relatively new joining technique particularly for aluminium alloys that are difficult to fusion weld. In this study, the geometry of the weld has been investigated and modelled using Pearson's functions. It has been demonstrated that the Pearson's parameters (mean, standard deviation, skewness, kurtosis and geometric constant) can be used to characterize the weld geometry and the tensile strength of the weld assembly. Pearson's parameters and process parameters are strongly correlated allowing to define a control process procedure for FSW assemblies which make radiographic or ultrasonic controls unnecessary. Finally, an optimisation using a Generalized Gradient Method allows to determine the geometry of the weld which maximises the assembly tensile strength.

Melting Efficiency During Plasma Arc Welding

NASA Technical Reports Server (NTRS)

McClure, J.C.; Evans, D. M.; Tang, W.; Nunes, A. C.

1999-01-01

A series of partial penetration Variable Polarity Plasma Arc welds were made at equal power but various combinations of current and voltage on 2219 aluminum. Arc Efficiency was measured calorimetrically and ranged between 48% and 66%. Melting efficiency depends on the weld pool shape. Increased current increases the melting efficiency as it increases the depth to width ratio of the weld pool. Higher currents are thought to raise arc pressure and depress the liquid at the bottom of the weld pool causing a more nearly two dimensional heat flow condition.

Grain fragmentation in ultrasonic-assisted TIG weld of pure aluminum.

PubMed

Chen, Qihao; Lin, Sanbao; Yang, Chunli; Fan, Chenglei; Ge, Hongliang

2017-11-01

Under the action of acoustic waves during an ultrasonic-assisted tungsten inert gas (TIG) welding process, a grain of a TIG weld of aluminum alloy is refined by nucleation and grain fragmentation. Herein, effects of ultrasound on grain fragmentation in the TIG weld of aluminum alloy are investigated via systematic welding experiments of pure aluminum. First, experiments involving continuous and fixed-position welding are performed, which demonstrate that ultrasound can break the grain of the TIG weld of pure aluminum. The microstructural characteristics of an ultrasonic-assisted TIG weld fabricated by fixed-position welding are analyzed. The microstructure is found to transform from plane crystal, columnar crystal, and uniform equiaxed crystal into plane crystal, deformed columnar crystal, and nonuniform equiaxed crystal after application of ultrasound. Second, factors influencing ultrasonic grain fragmentation are investigated. The ultrasonic amplitude and welding current are found to have a considerable effect on grain fragmentation. The degree of fragmentation first increases and then decreases with an increase in ultrasonic amplitude, and it increases with an increase in welding current. Measurement results of the vibration of the weld pool show that the degree of grain fragmentation is related to the intensity of acoustic nonlinearity in the weld pool. The greater the intensity of acoustic nonlinearity, the greater is the degree of grain fragmentation. Finally, the mechanism of ultrasonic grain fragmentation in the TIG weld of pure aluminum is discussed. A finite element simulation is used to simulate the acoustic pressure and flow in the weld pool. The acoustic pressure in the weld pool exceeds the cavitation threshold, and cavitation bubbles are generated. The flow velocity in the weld pool does not change noticeably after application of ultrasound. It is concluded that the high-pressure conditions induced during the occurrence of cavitation, lead to grain fragmentation in a pure aluminum TIG weld during an ultrasonic-assisted TIG welding process. Copyright © 2017 Elsevier B.V. All rights reserved.

Automated Welding System

NASA Technical Reports Server (NTRS)

Bayless, E. O.; Lawless, K. G.; Kurgan, C.; Nunes, A. C.; Graham, B. F.; Hoffman, D.; Jones, C. S.; Shepard, R.

1993-01-01

Fully automated variable-polarity plasma arc VPPA welding system developed at Marshall Space Flight Center. System eliminates defects caused by human error. Integrates many sensors with mathematical model of the weld and computer-controlled welding equipment. Sensors provide real-time information on geometry of weld bead, location of weld joint, and wire-feed entry. Mathematical model relates geometry of weld to critical parameters of welding process.

An Assessment of Molten Metal Detachment Hazards for Electron Beam Welding in the Space Environment: Analysis and Test Results

NASA Technical Reports Server (NTRS)

Nunes, A. C., Jr.; Russell, C.; Bhat, B.; Fragomeni, J. M.

1998-01-01

Conditions under which molten metal detachments might occur in a space welding environment are analyzed. A weld pool detachment parameter specifying conditions for pool detachment by impact is derived and corroborated by experimental evidence. Impact detachment for the pool is unlikely. Impact detachment for a drop of metal on the end of the weld wire may be possible under extreme conditions. Other potential causes of molten metal detachment considered, vaporization pressure forces and wire flickout from the pool, did not appear to present significant detachment threats.

Weld pool development during GTA and laser beam welding of Type 304 stainless steel; Part I - theoretical analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zacharia, T.; David, S.A.; Vitek, J.M.

1989-12-01

A computational and experimental study was carried out to quantitatively understand the influence of the heat flow and the fluid flow in the transient development of the weld pool during gas tungsten arc (GTA) and laser beam welding of Type 304 stainless steel. Stationary gas tungsten arc and laser beam welds were made on two heats of Type 304 austenitic stainless steels containing 90 ppm sulfur and 240 ppm sulfur. A transient heat transfer model was utilized to simulate the heat flow and fluid flow in the weld pool. In this paper, the results of the heat flow and fluidmore » flow analysis are presented.« less

Simulation and Technology of Hybrid Welding of Thick Steel Parts with High Power Fiber Laser

NASA Astrophysics Data System (ADS)

Turichin, Gleb; Valdaytseva, Ekaterina; Tzibulsky, Igor; Lopota, Alexander; Velichko, Olga

The article devoted to steady state and dynamic simulation of melt pool behavior during hybrid laser-arc welding of pipes and shipbuilding sections. The quasi-stationary process-model was used to determine an appropriate welding mode. The dynamical model of laser welding was used for investigation of keyhole depth and width oscillations. The experiments of pipe steel and stainless steel hybrid laser-MAG welding have been made with 15-kW fiber laser in wide range of welding mode parameters. Comparison of experimentally measured and simulated behavior of penetration depth as well as their oscillation spectra approved the self-oscillation nature of melt pool behavior. The welding mode influence of melt pool stability has also been observed. The technological peculiarities, which allow provide high quality weld seam, has been discussed also.

Active weld control

NASA Technical Reports Server (NTRS)

Powell, Bradley W.; Burroughs, Ivan A.

1994-01-01

Through the two phases of this contract, sensors for welding applications and parameter extraction algorithms have been developed. These sensors form the foundation of a weld control system which can provide action weld control through the monitoring of the weld pool and keyhole in a VPPA welding process. Systems of this type offer the potential of quality enhancement and cost reduction (minimization of rework on faulty welds) for high-integrity welding applications. Sensors for preweld and postweld inspection, weld pool monitoring, keyhole/weld wire entry monitoring, and seam tracking were developed. Algorithms for signal extraction were also developed and analyzed to determine their application to an adaptive weld control system. The following sections discuss findings for each of the three sensors developed under this contract: (1) weld profiling sensor; (2) weld pool sensor; and (3) stereo seam tracker/keyhole imaging sensor. Hardened versions of these sensors were designed and built under this contract. A control system, described later, was developed on a multiprocessing/multitasking operating system for maximum power and flexibility. Documentation for sensor mechanical and electrical design is also included as appendices in this report.

High Power Laser Beam Welding of Thick-walled Ferromagnetic Steels with Electromagnetic Weld Pool Support

NASA Astrophysics Data System (ADS)

Fritzsche, André; Avilov, Vjaceslav; Gumenyuk, Andrey; Hilgenberg, Kai; Rethmeier, Michael

The development of modern high power laser systems allows single pass welding of thick-walled components with minimal distortion. Besides the high demands on the joint preparation, the hydrostatic pressure in the melt pool increases with higher plate thicknesses. Reaching or exceeding the Laplace pressure, drop-out or melt sagging are caused. A contactless electromagnetic weld support system was used for laser beam welding of thick ferromagnetic steel plates compensating these effects. An oscillating magnetic field induces eddy currents in the weld pool which generate Lorentz forces counteracting the gravity forces. Hysteresis effects of ferromagnetic steels are considered as well as the loss of magnetization in zones exceeding the Curie temperature. These phenomena reduce the effective Lorentz forces within the weld pool. The successful compensation of the hydrostatic pressure was demonstrated on up to 20 mm thick plates of duplex and mild steel by a variation of the electromagnetic power level and the oscillation frequency.

Onset of Curved Dendrite Growth in an Al-Cu Welding Pool: A Phase Field Study

NASA Astrophysics Data System (ADS)

Wang, Lei; Wei, Yanhong

2018-02-01

A phase field model is developed to predict curved dendrite growth in the gas tungsten arc (GTA) welding pool of an Al-Cu alloy. The equations of temperature gradient, pulling velocity and dendrite growth orientation are proposed to consider the transient solidification process during welding. Solidification microstructures and solute diffusion along the fusion boundary in the welding pool are predicted by using the phase field model coupled with transient solidification conditions. Predicted primary dendrites are curved and point toward the welding direction. Welding experiments are carried out to observe solidification microstructures of the weld. Comparisons of simulation results with experimental measurements are conducted. Predicted dendritic morphology, dendrite growth orientation, primary dendrite arm spacing and initial cell spacing give a good agreement with experimental measurements.

Effects of electrode bevel angle on argon arc properties and weld shape

NASA Astrophysics Data System (ADS)

Dong, W. C.; Lu, S. P.; Li, D. Z.; Y Li, Y.

2012-07-01

A numerical modeling of coupled welding arc with weld pool is established using FLUENT software for moving shielded GTA welding to systematically investigate the effects of electrode bevel angle on the argon arc properties as well as the weld shape on SUS304 stainless steel. The calculated results show that the argon arc is constricted and the peak values of heat flux and shear stress on the weld pool decrease with increasing electrode bevel angle, while the radial distribution of heat flux and shear stress varying slightly. The weld shape is controlled by the pool flow patterns driving by the surface tension, gas shear stress, electromagnetic force and buoyancy. The Marangoni convection induced by surface tension plays an important role on weld shapes. All the weld shapes are wide and shallow with low weld metal oxygen content, while the narrow and deep weld shapes form under high weld metal oxygen content, which is related with the oxygen concentration in the shielding gas. The weld depth/width (D/W) ratio increases with increasing electrode bevel angle for high weld metal oxygen content and is not sensitive to the electrode bevel angle under low weld metal oxygen content. The calculated results for the weld shape, weld size and weld D/W ratio agree well with the experimental ones.

Wire Arc Additive Manufacturing of AZ31 Magnesium Alloy: Grain Refinement by Adjusting Pulse Frequency.

PubMed

Guo, Jing; Zhou, Yong; Liu, Changmeng; Wu, Qianru; Chen, Xianping; Lu, Jiping

2016-10-09

Wire arc additive manufacturing (WAAM) offers a potential approach to fabricate large-scale magnesium alloy components with low cost and high efficiency, although this topic is yet to be reported in literature. In this study, WAAM is preliminarily applied to fabricate AZ31 magnesium. Fully dense AZ31 magnesium alloy components are successfully obtained. Meanwhile, to refine grains and obtain good mechanical properties, the effects of pulse frequency (1, 2, 5, 10, 100, and 500 Hz) on the macrostructure, microstructure and tensile properties are investigated. The results indicate that pulse frequency can result in the change of weld pool oscillations and cooling rate. This further leads to the change of the grain size, grain shape, as well as the tensile properties. Meanwhile, due to the resonance of the weld pool at 5 Hz and 10 Hz, the samples have poor geometry accuracy but contain finer equiaxed grains (21 μm) and exhibit higher ultimate tensile strength (260 MPa) and yield strength (102 MPa), which are similar to those of the forged AZ31 alloy. Moreover, the elongation of all samples is above 23%.

Optical penetration sensor for pulsed laser welding

DOEpatents

Essien, Marcelino; Keicher, David M.; Schlienger, M. Eric; Jellison, James L.

2000-01-01

An apparatus and method for determining the penetration of the weld pool created from pulsed laser welding and more particularly to an apparatus and method of utilizing an optical technique to monitor the weld vaporization plume velocity to determine the depth of penetration. A light source directs a beam through a vaporization plume above a weld pool, wherein the plume changes the intensity of the beam, allowing determination of the velocity of the plume. From the velocity of the plume, the depth of the weld is determined.

Welding deviation detection algorithm based on extremum of molten pool image contour

NASA Astrophysics Data System (ADS)

Zou, Yong; Jiang, Lipei; Li, Yunhua; Xue, Long; Huang, Junfen; Huang, Jiqiang

2016-01-01

The welding deviation detection is the basis of robotic tracking welding, but the on-line real-time measurement of welding deviation is still not well solved by the existing methods. There is plenty of information in the gas metal arc welding(GMAW) molten pool images that is very important for the control of welding seam tracking. The physical meaning for the curvature extremum of molten pool contour is revealed by researching the molten pool images, that is, the deviation information points of welding wire center and the molten tip center are the maxima and the local maxima of the contour curvature, and the horizontal welding deviation is the position difference of these two extremum points. A new method of weld deviation detection is presented, including the process of preprocessing molten pool images, extracting and segmenting the contours, obtaining the contour extremum points, and calculating the welding deviation, etc. Extracting the contours is the premise, segmenting the contour lines is the foundation, and obtaining the contour extremum points is the key. The contour images can be extracted with the method of discrete dyadic wavelet transform, which is divided into two sub contours including welding wire and molten tip separately. The curvature value of each point of the two sub contour lines is calculated based on the approximate curvature formula of multi-points for plane curve, and the two points of the curvature extremum are the characteristics needed for the welding deviation calculation. The results of the tests and analyses show that the maximum error of the obtained on-line welding deviation is 2 pixels(0.16 mm), and the algorithm is stable enough to meet the requirements of the pipeline in real-time control at a speed of less than 500 mm/min. The method can be applied to the on-line automatic welding deviation detection.

Effect of Weld Tool Geometry on Friction Stir Welded AA2219-T87 Properties

NASA Technical Reports Server (NTRS)

Querin, Joseph A.; Schneider, Judy A.

2008-01-01

In this study, flat panels of AA2219-T87 were friction stir welded (FSWed) using weld tools with tapered pins The three pin geometries of the weld tools included: 0 (straight cylinder), 30 , and 60 angles on the frustum. For each weld tool geometry, the FSW process parameters were optimized to eliminate defects. A constant heat input was maintained while varying the process parameters of spindle rpm and travel speed. This provided a constant heat input for each FSW weld panel while altering the hot working conditions imparted to the workpiece. The resulting mechanical properties were evaluated from tensile test results of the FSW joint.

Geometry and Material Constraint Effects on Creep Crack Growth Behavior in Welded Joints

NASA Astrophysics Data System (ADS)

Li, Y.; Wang, G. Z.; Xuan, F. Z.; Tu, S. T.

2017-02-01

In this work, the geometry and material constraint effects on creep crack growth (CCG) and behavior in welded joints were investigated. The CCG paths and rates of two kinds of specimen geometry (C(T) and M(T)) with initial cracks located at soft HAZ (heat-affected zone with lower creep strength) and different material mismatches were simulated. The effect of constraint on creep crack initiation (CCI) time was discussed. The results show that there exists interaction between geometry and material constraints in terms of their effects on CCG rate and CCI time of welded joints. Under the condition of low geometry constraint, the effect of material constraint on CCG rate and CCI time becomes more obvious. Higher material constraint can promote CCG due to the formation of higher stress triaxiality around crack tip. Higher geometry constraint can increase CCG rate and reduce CCI time of welded joints. Both geometry and material constraints should be considered in creep life assessment and design for high-temperature welded components.

An integrated optical sensor for GMAW feedback control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taylor, P.L.; Watkins, A.D.; Larsen, E.D.

1992-08-01

The integrated optical sensor (IOS) is a multifunction feedback control sensor for arc welding, that is computer automated and independent of significant operator interaction. It is based on three major ``off-the-shelf`` components: a charged coupled device (CCD) camera, a diode laser, and a processing computer. The sensor head is compact and lightweight to avoid interference with weld head mobility, hardened to survive the harsh operating environment, and free of specialized cooling and power requirements. The sensor is positioned behind the GMAW torch and measures weld pool position and width, standoff distance, and postweld centerline cooling rate. Weld pool position andmore » width are used in a feedback loop, by the weld controller, to track the weld pool relative to the weld joint, thus allowing compensation for such phenomena as arc blow. Sensor stand off distance is used in a feedback loop to control the contact tip to base metal distance during the welding process. Cooling rate information is used to infer the final metallurgical state of the weld bead and heat affected zone, thereby providing a means of controlling post weld mechanical properties.« less

An integrated optical sensor for GMAW feedback control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taylor, P.L.; Watkins, A.D.; Larsen, E.D.

1992-01-01

The integrated optical sensor (IOS) is a multifunction feedback control sensor for arc welding, that is computer automated and independent of significant operator interaction. It is based on three major off-the-shelf'' components: a charged coupled device (CCD) camera, a diode laser, and a processing computer. The sensor head is compact and lightweight to avoid interference with weld head mobility, hardened to survive the harsh operating environment, and free of specialized cooling and power requirements. The sensor is positioned behind the GMAW torch and measures weld pool position and width, standoff distance, and postweld centerline cooling rate. Weld pool position andmore » width are used in a feedback loop, by the weld controller, to track the weld pool relative to the weld joint, thus allowing compensation for such phenomena as arc blow. Sensor stand off distance is used in a feedback loop to control the contact tip to base metal distance during the welding process. Cooling rate information is used to infer the final metallurgical state of the weld bead and heat affected zone, thereby providing a means of controlling post weld mechanical properties.« less

Contribution to study of heat transfer and fluid flow during GTA welding

NASA Astrophysics Data System (ADS)

Koudadje, Koffi; Delalondre, Clarisse; Médale, Marc; Carpreau, Jean-Michel

2014-06-01

In this paper, the effect of surface-active elements especially sulfur on weld pool shape has been reported. In our contribution, we analyze the influence of the weld pool chemical composition (Mn, Si, …), welding energy, sulphur gradient and electromagnetic effect. The computed results are in good agreement with the corresponding experimental results, indicating the validity of the modeling approach.

Status analysis of keyhole bottom in laser-MAG hybrid welding process.

PubMed

Wang, Lin; Gao, Xiangdong; Chen, Ziqin

2018-01-08

The keyhole status is a determining factor of weld quality in laser-metal active gas arc (MAG) hybrid welding process. For a better evaluation of the hybrid welding process, three different penetration welding experiments: partial penetration, normal penetration (or full penetration), and excessive penetration were conducted in this work. The instantaneous visual phenomena including metallic vapor, spatters and keyhole of bottom surface were used to evaluate the keyhole status by a double high-speed camera system. The Fourier transform was applied on the bottom weld pool image for removing the image noise around the keyhole, and then the bottom weld pool image was reconstructed through the inverse Fourier transform. Lastly, the keyhole bottom was extracted from the de-noised bottom weld pool image. By analyzing the visual features of the laser-MAG hybrid welding process, mechanism of the closed and opened keyhole bottom were revealed. The results show that the stable opened or closed status of keyhole bottom is directly affected by the MAG droplet transition in the normal penetration welding process, and the unstable opened or closed status of keyhole bottom would appear in excessive penetration welding and partial penetration welding. The analysis method proposed in this paper could be used to monitor the keyhole stability in laser-MAG hybrid welding process.

Effects of SO/sub 2/ torch gas additions on GTA weld shape

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heiple, C.R.; Burgardt, P.

1984-01-01

Small additions of sulfur or oxygen to the GTA weld pool in steels with low weld d/w (depth/width) ratios substantially increases the weld d/w ratio and furthermore the improved weld d/w ratio is largely independent of reasonable variations in base metal sulfur and oxygen content. The addition of small concentrations of SO/sub 2/ to the normal argon shielding gas is a simple and effective way to add sulfur to the weld pool and increase weld d/w ratio. Autogenous bead-on-plate welds under otherwise identical welding conditions were made on stainless steel plate with SO/sub 2/ concentrations in the torch gas rangingmore » between 0 and 2000 ppM.« less

Molten Pool Behavior and Mechanical Properties of Pulsed Current Double-Sided Synchronization GTA Welded Fe-18Cr-17Mn-Ni-N

NASA Astrophysics Data System (ADS)

Qiang, Wei; Wang, Kehong; Feng, Yuehai; Chen, Jiahe

2017-02-01

Double-sided synchronization vertical gas tungsten arc welding (DSSVW) procedure was used to weld high-nitrogen low-nickel stainless steel Fe-18Cr-17Mn-Ni-N without groove and filler wire. First, the molten pool behaviors and appearances of pulsed current DSSVW (PC-DSSVW) and constant current DSSVW (CC-DSSVW) were comparatively analyzed. The periodic variation occurs in the width of both the anode region of the arc and the molten pool tail during PC-DSSVW, while the contact angle first increases and then decreases, and both the width of the anode region and the length of arc plume increase progressively in CC-DSSVW. It is found that the weld appearance of PC-DSSVW is superior to that of CC-DSSVW. Second, the forces of the DSSVW molten pool were analyzed. The result indicates that the molten pool of the DSSVW procedure is in a state of unstable equilibrium, and it will easily lose balance after being disturbed, resulting in the asymmetrical weld or hump bead. Third, the PC-DSSVW experiments at various welding speeds were conducted to study the influence of welding speed on the weld profile, microstructure, tensile strength and impact toughness. Furthermore, the solidification mode of Fe-18Cr-17Mn-Ni-N was predicted to help determine the microstructure of the welded joint. Results indicate that the weld width, weld reinforcement and melting area all increase with decreasing welding speed, and Fe-18Cr-17Mn-Ni-N solidifies as A mode. The microstructure of the base metal (BM) and heat-affected zone (HAZ) is equiaxed austenite and that of the fusion zone (FZ) is austenite dendrite with some chromium carbides dispersed in the grain boundary; with decreasing welding speed, grains become coarse. The maximum tensile strength (UTS) and elongation of PC-DSSVW joint are 860 MPa and 8.1%, and the elongation decreases dramatically with decreasing welding speed. The impact toughness decreases substantially compared to the BM, achieving 48.2% of the BM.

Influence of modes of metal transfer on grain structure and direction of grain growth in low nickel austenitic stainless steel weld metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mukherjee, Manidipto; Saha, Saptarshi; Pal, Tapan Kumar, E-mail: tkpal.ju@gmail.com

2015-04-15

The present study elaborately discussed the effect of different modes of metal transfer (i.e., short circuit mode, spray mode and pulse mode) on grain structure and direction of grain growth in low nickel austenitic stainless steel weld metals. Electron backscattered diffraction (EBSD) analysis was used to study the grain growth direction and grain structure in weld metals. The changes in grain structure and grain growth direction were found to be essentially varied with the weld pool shape and acting forces induced by modes of metal transfer at a constant welding speed. Short circuit mode of metal transfer owing to highermore » Marangoni force (M{sub a}) and low electromagnetic force (R{sub m}) promotes the lower weld pool volume (Γ) and higher weld pool maximum radius (r{sub m}). Short circuit mode also shows curved and tapered columnar grain structures and the grain growth preferentially occurred in <001> direction. In contrast, spray mode of metal transfer increases the Γ and reduces the r{sub m} values due to very high R{sub m} and typically reveals straight and broad columnar grain structures with preferential growth direction in <111>. In the pulse mode of metal transfer relatively high M{sub a} and R{sub m} simultaneously increase the weld pool width and the primary penetration which might encourage relatively complex grain growth directions in the weld pool and cause a shift of major intensity from <001> to <111> direction. It can also be concluded that the fusion zone grain structure and direction of grain growth are solely dependent on modes of metal transfer and remain constant for a particular mode of metal transfer irrespective of filler wire used. - Highlights: • Welded joints of LNiASS were prepared by varying modes of metal transfer. • Weld pool shape, grain structure and grain growth direction were studied. • Short circuit mode shows curved and tapered grain growth in <001> direction. • Spray mode shows straight and broad columnar grain growth in <111> direction. • Pulse mode shows complex grain growth with a shift in growth direction.« less

ARC and Melting Efficiency of Plasma ARC Welds

NASA Technical Reports Server (NTRS)

McClure, J. C.; Nunes, A. C.; Evans, D. M.

1999-01-01

A series of partial penetration Variable Polarity Plasma Arc welds were made at equal power but various combinations of current and voltage on 2219 Aluminum. Arc efficiency was measured calorimetrically and ranged between 48% and 66% for the conditions of the welds. Arc efficiency depends in different ways on voltage and current. The voltage effect dominates. Raising voltage while reducing current increases arc efficiency. Longer, higher voltage arcs are thought to transfer a greater portion of arc power to the workpiece through shield gas convection. Melting efficiency depends upon weld pool shape as well as arc efficiency. Increased current increases the melting efficiency as it increases the depth to width ratio of the weld pool. Increased plasma gas flow does the same thing. Higher currents are thought to raise arc pressure and depress liquid at the bottom of the weld pool. More arc power then transfers to the workpiece through increasing plasma gas convection. If the power is held constant, the reduced voltage lowers the arc efficiency, while the pool shape change increases the melting efficiency,

The Influence of Friction Stir Weld Tool Form and Welding Parameters on Weld Structure and Properties: Nugget Bulge in Self-Reacting Friction Stir Welds

NASA Technical Reports Server (NTRS)

Schneider, Judy; Nunes, Arthur C., Jr.; Brendel, Michael S.

2010-01-01

Although friction stir welding (FSW) was patented in 1991, process development has been based upon trial and error and the literature still exhibits little understanding of the mechanisms determining weld structure and properties. New concepts emerging from a better understanding of these mechanisms enhance the ability of FSW engineers to think about the FSW process in new ways, inevitably leading to advances in the technology. A kinematic approach in which the FSW flow process is decomposed into several simple flow components has been found to explain the basic structural features of FSW welds and to relate them to tool geometry and process parameters. Using this modelling approach, this study reports on a correlation between the features of the weld nugget, process parameters, weld tool geometry, and weld strength. This correlation presents a way to select process parameters for a given tool geometry so as to optimize weld strength. It also provides clues that may ultimately explain why the weld strength varies within the sample population.

Three-dimensional modeling of the plasma arc in arc welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, G.; Tsai, H. L.; Hu, J.

2008-11-15

Most previous three-dimensional modeling on gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) focuses on the weld pool dynamics and assumes the two-dimensional axisymmetric Gaussian distributions for plasma arc pressure and heat flux. In this article, a three-dimensional plasma arc model is developed, and the distributions of velocity, pressure, temperature, current density, and magnetic field of the plasma arc are calculated by solving the conservation equations of mass, momentum, and energy, as well as part of the Maxwell's equations. This three-dimensional model can be used to study the nonaxisymmetric plasma arc caused by external perturbations such asmore » an external magnetic field. It also provides more accurate boundary conditions when modeling the weld pool dynamics. The present work lays a foundation for true three-dimensional comprehensive modeling of GTAW and GMAW including the plasma arc, weld pool, and/or electrode.« less

Laser Beam Oscillation Strategies for Fillet Welds in Lap Joints

NASA Astrophysics Data System (ADS)

Müller, Alexander; Goecke, Sven-F.; Sievi, Pravin; Albert, Florian; Rethmeier, Michael

Laser beam oscillation opens up new possibilities of influencing the welding process in terms of compensation of tolerances and reduction of process emissions that occur in industrial applications, such as in body-in-white manufacturing. The approaches are to adapt the melt pool width in order to generate sufficient melt volume or to influence melt pool dynamics, e.g. for a better degassing. Welding results are highly dependent on the natural frequency of the melt pool, the used spot diameter and the oscillation speed of the laser beam. The conducted investigations with an oscillated 300 μm laser spot show that oscillation strategies, which are adjusted to the joining situation improve welding result for zero-gap welding as well as for bridging gaps to approximately 0.8 mm. However, a complex set of parameters has to be considered in order to generate proper welding results. This work puts emphasize on introducing them.

Exploring infrared sensoring for real time welding defects monitoring in GTAW.

PubMed

Alfaro, Sadek C A; Franco, Fernand Díaz

2010-01-01

This paper presents an evaluation of an infrared sensor for monitoring the welding pool temperature in a Gas Tungsten Arc Welding (GTAW) process. The purpose of the study is to develop a real time system control. It is known that the arc welding pool temperature is related to the weld penetration depth; therefore, by monitoring the temperature, the arc pool temperature and penetration depth are also monitored. Various experiments were performed; in some of them the current was varied and the temperature changes were registered, in others, defects were induced throughout the path of the weld bead for a fixed current. These simulated defects resulted in abrupt changes in the average temperature values, thus providing an indication of the presence of a defect. The data has been registered with an acquisition card. To identify defects in the samples under infrared emissions, the timing series were analyzed through graphics and statistic methods. The selection of this technique demonstrates the potential for infrared emission as a welding monitoring parameter sensor.

Exploring Infrared Sensoring for Real Time Welding Defects Monitoring in GTAW

PubMed Central

Alfaro, Sadek C. A.; Franco, Fernand Díaz

2010-01-01

This paper presents an evaluation of an infrared sensor for monitoring the welding pool temperature in a Gas Tungsten Arc Welding (GTAW) process. The purpose of the study is to develop a real time system control. It is known that the arc welding pool temperature is related to the weld penetration depth; therefore, by monitoring the temperature, the arc pool temperature and penetration depth are also monitored. Various experiments were performed; in some of them the current was varied and the temperature changes were registered, in others, defects were induced throughout the path of the weld bead for a fixed current. These simulated defects resulted in abrupt changes in the average temperature values, thus providing an indication of the presence of a defect. The data has been registered with an acquisition card. To identify defects in the samples under infrared emissions, the timing series were analyzed through graphics and statistic methods. The selection of this technique demonstrates the potential for infrared emission as a welding monitoring parameter sensor. PMID:22219697

[Impact of introduction of O2 on the welding arc of gas pool coupled activating TIG].

PubMed

Huang, Yong; Wang, Yan-Lei; Zhang, Zhi-Guo

2014-05-01

In the present paper, Boltzmann plot method was applied to analyze the temperature distributions of the are plasma when the gas pool coupled activating TIG welding was at different coupling degrees with the outer gas being O2. Based on this study of temperature distributions, the changing regularities of are voltage and are appearance were studied. The result shows that compared with traditional TIG welding, the introduction of O2 makes the welding arc constricted slightly, the temperature of the are center build up, and the are voltage increase. When argon being the inner gas, oxygen serving as the outer gas instead of argon makes the are constricted more obviously. When the coupling degree increases from 0 to 2, the temperature of the are center and the are voltage both increase slightly. In the gas pool coupled activating TIG welding the are is constricted not obviously, and the reason why the weld penetration is improved dramatically in the welding of stainless steel is not are constriction.

Effect of Inverter Power Source Characteristics on Welding Stability and Heat Affected Zone Dimensions

NASA Astrophysics Data System (ADS)

Il'yaschenko, D. P.; Chinakhov, D. A.; Mamadaliev, R. A.

2018-01-01

The paper presents results the research in the effect of power sources dynamic characteristics on stability of melting and electrode metal transfer to the weld pool shielded metal arc welding. It is proved that when applying inverter-type welding power sources, heat and mass transfer characteristics change, arc gap short-circuit time and drop generation time are reduced. This leads to reduction of weld pool heat content and contraction of the heat-affected zone by 36% in comparison the same parameters obtained using a diode rectifier.

In situ laser-induced breakdown spectroscopy measurements of chemical compositions in stainless steels during tungsten inert gas welding

NASA Astrophysics Data System (ADS)

Taparli, Ugur Alp; Jacobsen, Lars; Griesche, Axel; Michalik, Katarzyna; Mory, David; Kannengiesser, Thomas

2018-01-01

A laser-induced breakdown spectroscopy (LIBS) system was combined with a bead-on-plate Tungsten Inert Gas (TIG) welding process for the in situ measurement of chemical compositions in austenitic stainless steels during welding. Monitoring the weld pool's chemical composition allows governing the weld pool solidification behavior, and thus enables the reduction of susceptibility to weld defects. Conventional inspection methods for weld seams (e.g. ultrasonic inspection) cannot be performed during the welding process. The analysis system also allows in situ study of the correlation between the occurrence of weld defects and changes in the chemical composition in the weld pool or in the two-phase region where solid and liquid phase coexist. First experiments showed that both the shielding Ar gas and the welding arc plasma have a significant effect on the selected Cr II, Ni II and Mn II characteristic emissions, namely an artificial increase of intensity values via unspecific emission in the spectra. In situ investigations showed that this artificial intensity increase reached a maximum in presence of weld plume. Moreover, an explicit decay has been observed with the termination of the welding plume due to infrared radiation during sample cooling. Furthermore, LIBS can be used after welding to map element distribution. For austenitic stainless steels, Mn accumulations on both sides of the weld could be detected between the heat affected zone (HAZ) and the base material.

Wire Arc Additive Manufacturing of AZ31 Magnesium Alloy: Grain Refinement by Adjusting Pulse Frequency

PubMed Central

Guo, Jing; Zhou, Yong; Liu, Changmeng; Wu, Qianru; Chen, Xianping; Lu, Jiping

2016-01-01

Wire arc additive manufacturing (WAAM) offers a potential approach to fabricate large-scale magnesium alloy components with low cost and high efficiency, although this topic is yet to be reported in literature. In this study, WAAM is preliminarily applied to fabricate AZ31 magnesium. Fully dense AZ31 magnesium alloy components are successfully obtained. Meanwhile, to refine grains and obtain good mechanical properties, the effects of pulse frequency (1, 2, 5, 10, 100, and 500 Hz) on the macrostructure, microstructure and tensile properties are investigated. The results indicate that pulse frequency can result in the change of weld pool oscillations and cooling rate. This further leads to the change of the grain size, grain shape, as well as the tensile properties. Meanwhile, due to the resonance of the weld pool at 5 Hz and 10 Hz, the samples have poor geometry accuracy but contain finer equiaxed grains (21 μm) and exhibit higher ultimate tensile strength (260 MPa) and yield strength (102 MPa), which are similar to those of the forged AZ31 alloy. Moreover, the elongation of all samples is above 23%. PMID:28773944

Analysis of droplet transfer mode and forming process of weld bead in CO 2 laser-MAG hybrid welding process

NASA Astrophysics Data System (ADS)

Liu, Shuangyu; Liu, Fengde; Zhang, Hong; Shi, Yan

2012-06-01

In this paper, CO 2 laser-metal active gas (MAG) hybrid welding technique is used to weld high strength steel and the optimized process parameters are obtained. Using LD Pumped laser with an emission wavelength of 532 nm to overcome the strong interference from the welding arc, a computer-based system is developed to collect and visualize the waveforms of the electrical welding parameters and metal transfer processes in laser-MAG. The welding electric signals of hybrid welding processes are quantitatively described and analyzed using the ANALYSATOR HANNOVER. The effect of distance between laser and arc ( DLA) on weld bead geometry, forming process of weld shape, electric signals, arc characteristic and droplet transfer behavior is investigated. It is found that arc characteristic, droplet transfer mode and final weld bead geometry are strongly affected by the distance between laser and arc. The weld bead geometry is changed from "cocktail cup" to "cone-shaped" with the increasing DLA. The droplet transfer mode is changed from globular transfer to projected transfer with the increasing DLA. Projected transfer mode is an advantage for the stability of hybrid welding processes.

Improving Processes of Mechanized Pulsed Arc Welding of Low-Frequency Range Variation of Mode Parameters

NASA Astrophysics Data System (ADS)

Saraev, Yu N.; Solodskiy, S. A.; Ulyanova, O. V.

2016-04-01

A new technology of low-frequency modulation of the arc current in MAG and MIG welding is presented. The technology provides control of thermal and crystallization processes, stabilizes the time of formation and crystallization of the weld pool. Conducting theoretical studies allowed formulating the basic criteria for obtaining strong permanent joints for high-duty structures, providing conditions for more equilibrium structure of the deposited metal and the smaller width of the HAZ. The stabilization of time of the formation and crystallization of the weld pool improves the formation of the weld and increases productivity in welding thin sheet metal.

Stability of Full Penetration, Flat Position Weld Pools

NASA Technical Reports Server (NTRS)

Nunes, Arthur C., Jr.; Coan, Al. B.

1999-01-01

The dynamics of the dropthrough distance of a full penetration, flat position weld pool is described. Close to incipient root side penetration the dropthrough is metastable, so that a small drop in power can cause a loss of penetration if not followed soon enough by a compensating rise in power. The SPA (Soft Plasma Arc) process with higher pressure on top of the weld pool loses penetration more quickly than the GTA (Gas Tungsten Arc) process. 2195 aluminum-lithium alloy with a lower surface tension loses penetration more quickly than 2219 aluminum alloy. An instance of loss of penetration of a SPA weld in 2195 aluminum-lithium alloy is discussed in the light of the model.

Effect of Heat Input on Geometry of Austenitic Stainless Steel Weld Bead on Low Carbon Steel

NASA Astrophysics Data System (ADS)

Saha, Manas Kumar; Hazra, Ritesh; Mondal, Ajit; Das, Santanu

2018-05-01

Among different weld cladding processes, gas metal arc welding (GMAW) cladding becomes a cost effective, user friendly, versatile method for protecting the surface of relatively lower grade structural steels from corrosion and/or erosion wear by depositing high grade stainless steels onto them. The quality of cladding largely depends upon the bead geometry of the weldment deposited. Weld bead geometry parameters, like bead width, reinforcement height, depth of penetration, and ratios like reinforcement form factor (RFF) and penetration shape factor (PSF) determine the quality of the weld bead geometry. Various process parameters of gas metal arc welding like heat input, current, voltage, arc travel speed, mode of metal transfer, etc. influence formation of bead geometry. In the current experimental investigation, austenite stainless steel (316) weld beads are formed on low alloy structural steel (E350) by GMAW using 100% CO2 as the shielding gas. Different combinations of current, voltage and arc travel speed are chosen so that heat input increases from 0.35 to 0.75 kJ/mm. Nine number of weld beads are deposited and replicated twice. The observations show that weld bead width increases linearly with increase in heat input, whereas reinforcement height and depth of penetration do not increase with increase in heat input. Regression analysis is done to establish the relationship between heat input and different geometrical parameters of weld bead. The regression models developed agrees well with the experimental data. Within the domain of the present experiment, it is observed that at higher heat input, the weld bead gets wider having little change in penetration and reinforcement; therefore, higher heat input may be recommended for austenitic stainless steel cladding on low alloy steel.

Experimental characterization of fatigue strength in butt welded joint considering the geometry and the effect of cooling rate of the weld

NASA Astrophysics Data System (ADS)

Arzola, Nelson; Hernández, Edgar

2017-05-01

In this work the experimental characterization of fatigue strength in butt welded joints considering the geometry and the post-weld cooling cycle was performed. ASTM A-36 structural steel was used as the base metal for the shielded metal arc welding process, with welding electrode E6013. Two experimental factors were established: weld bead geometry and the post-weld cooling rate. Two levels for each factor, the welding reinforcement (1 and 3 mm), and the rate of cooling, slow (quiet air) and fast (immersion in water) are evaluated respectively. For the uniaxial fatigue tests, 8 samples were selected for each treatment for a total of 32 specimens. The mechanical and fractomechanical properties of fusion zone, heat affected zone and base metal in relation to the analysis of failure mechanisms were analysed. The fatigue crack growth rates were estimated based on the counting of microstrations. Furthermore, experimental tests, such as uniaxial tension, microindentation hardness, Charpy impact and metallographic analysis, were made to know the influence of the experimental factors in the fatigue strength. On this research, about the 78.13% of the samples obtained a resistance higher than the recommended one by class FAT 100. The results showed that the geometry of the joint is the factor of greatest influence on fatigue strength for butt welded joints; the greater the weld reinforcement the lower the fatigue strength of the joint. Although it is also important to consider other geometric factors of less impact as it is the weld toe radius and the welding chord width.

Modeling of weld bead geometry for rapid manufacturing by robotic GMAW

NASA Astrophysics Data System (ADS)

Yang, Tao; Xiong, Jun; Chen, Hui; Chen, Yong

2015-03-01

Weld-based rapid prototyping (RP) has shown great promises for fabricating 3D complex parts. During the layered deposition of forming metallic parts with robotic gas metal arc welding, the geometry of a single weld bead has an important influence on surface finish quality, layer thickness and dimensional accuracy of the deposited layer. In order to obtain accurate, predictable and controllable bead geometry, it is essential to understand the relationships between the process variables with the bead geometry (bead width, bead height and ratio of bead width to bead height). This paper highlights an experimental study carried out to develop mathematical models to predict deposited bead geometry through the quadratic general rotary unitized design. The adequacy and significance of the models were verified via the analysis of variance. Complicated cause-effect relationships between the process parameters and the bead geometry were revealed. Results show that the developed models can be applied to predict the desired bead geometry with great accuracy in layered deposition with accordance to the slicing process of RP.

Welding wire pressure sensor assembly

NASA Technical Reports Server (NTRS)

Morris, Timothy B. (Inventor); Milly, Peter F., Sr. (Inventor); White, J. Kevin (Inventor)

1994-01-01

The present invention relates to a device which is used to monitor the position of a filler wire relative to a base material being welded as the filler wire is added to a welding pool. The device is applicable to automated welding systems wherein nonconsumable electrode arc welding processes are utilized in conjunction with a filler wire which is added to a weld pool created by the electrode arc. The invention senses pressure deviations from a predetermined pressure between the filler wire and the base material, and provides electrical signals responsive to the deviations for actuating control mechanisms in an automatic welding apparatus so as to minimize the pressure deviation and to prevent disengagement of the contact between the filler wire and the base material.

Weld bead profile of laser welding dissimilar joints stainless steel

NASA Astrophysics Data System (ADS)

Mohammed, Ghusoon R.; Ishak, M.; Aqida, S. N.; Abdulhadi, Hassan A.

2017-10-01

During the process of laser welding, the material consecutively melts and solidifies by a laser beam with a peak high power. Several parameters such as the laser energy, pulse frequency, pulse duration, welding power and welding speed govern the mode of the welding process. The aim of this paper is to investigate the effect of peak power, incident angle, and welding speed on the weld bead geometry. The first investigation in this context was conducted using 2205-316L stainless steel plates through the varying of the welding speed from 1.3 mm/s to 2.1 mm/s. The second investigation was conducted by varying the peak power from 1100 W to 1500 W. From the results of the experiments, the welding speed and laser power had a significant effect on the geometry of the weld bead, and the variation in the diameter of the bead pulse-size. Due to the decrease in the heat input, welding speed affected penetration depth more than bead width, and a narrow width of heat affected zone was achieved ranging from 0.2 to 0.5 mm. Conclusively, weld bead geometry dimensions increase as a function of peak power; at over 1350 W peak power, the dimensions lie within 30 μm.

Investigation on the Mechanism and Failure Mode of Laser Transmission Spot Welding Using PMMA Material for the Automotive Industry

PubMed Central

Wang, Xiao; Liu, Baoguang; Liu, Wei; Zhong, Xuejiao; Jiang, Yingjie; Liu, Huixia

2017-01-01

To satisfy the need of polymer connection in lightweight automobiles, a study on laser transmission spot welding using polymethyl methacrylate (PMMA) is conducted by using an Nd:YAG pulse laser. The influence of three variables, namely peak voltages, defocusing distances and the welding type (type I (pulse frequency and the duration is 25 Hz, 0.6 s) and type II (pulse frequency and the duration is 5 Hz, 3 s)) to the welding quality was investigated. The result showed that, in the case of the same peak voltages and defocusing distances, the number of bubbles for type I was obviously more than type II. The failure mode of type I was the base plate fracture along the solder joint, and the connection strength of type I was greater than type II. The weld pool diameter:depth ratio for type I was significantly greater than type II. It could be seen that there was a certain relationship between the weld pool diameter:depth ratio and the welding strength. By the finite element simulation, the weld pool for type I was more slender than type II, which was approximately the same as the experimental results. PMID:28772383

Shielding gas selection for increased weld penetration and productivity in GTA welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leinonen, J.I.

1996-12-31

The effects of hydrogen and helium additions to the argon shielding gas on GTA weld pool profiles in the case of two austenitic stainless steel sheets 3 mm thick are investigated here in detail. One of the test steels shows good weldability, with a relatively deep, narrow weld pool profile, but the other is poorly weldable, with a shallow, wide weld pool when argon shielding gas is used. Bead-on-plate test welds were produced with arc shields of argon, argon with hydrogen additions of 2 to 18.2% and argon with helium additions of 20 to 80%. The hydrogen additions increases themore » depth of weld penetration in both test steels, but productivity with respect to maximum welding speed can be improved to an accepted level only with steel sheets of good weldability in terms of a relatively high depth/width (D/W) ratio. The depth of penetration in the test steel of good weldability increased somewhat with helium additions and the D/W ratio remained unchanged, while these parameters increased markedly in the poorly weldable steel when a He-20% Ar shielding gas was used and resembled those of the more weldable steel.« less

Investigation on the Mechanism and Failure Mode of Laser Transmission Spot Welding Using PMMA Material for the Automotive Industry.

PubMed

Wang, Xiao; Liu, Baoguang; Liu, Wei; Zhong, Xuejiao; Jiang, Yingjie; Liu, Huixia

2017-01-01

To satisfy the need of polymer connection in lightweight automobiles, a study on laser transmission spot welding using polymethyl methacrylate (PMMA) is conducted by using an Nd:YAG pulse laser. The influence of three variables, namely peak voltages, defocusing distances and the welding type (type I (pulse frequency and the duration is 25 Hz, 0.6 s) and type II (pulse frequency and the duration is 5 Hz, 3 s)) to the welding quality was investigated. The result showed that, in the case of the same peak voltages and defocusing distances, the number of bubbles for type I was obviously more than type II. The failure mode of type I was the base plate fracture along the solder joint, and the connection strength of type I was greater than type II. The weld pool diameter:depth ratio for type I was significantly greater than type II. It could be seen that there was a certain relationship between the weld pool diameter:depth ratio and the welding strength. By the finite element simulation, the weld pool for type I was more slender than type II, which was approximately the same as the experimental results.

The influence of arc plasma parameters on the form of a welding pool

NASA Astrophysics Data System (ADS)

Frolov, V. Ya.; Toropchin, A. I.

2015-07-01

The influence of the Marangoni force on the form of a welding pool has been considered. Results of computer simulation of the processes of welding arc generation with a non-consumable tungsten electrode in inert gas are shown. The experimental results are reported and comparatively analyzed. The calculations were carried out in a package of applied programs at various currents.

Surface-active element effects on the shape of GTA, laser, and electron-beam welds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heiple, C.R.; Roper, J.R.; Stagner, R.T.

1983-03-01

Laser and electron-beam welds were passed across selenium-doped zones in 21-6-9 stainless steel. The depth/width (d/w) ratio of a defocused laser weld with a weld pool shape similar to a GTA weld increased by over 200% in a zone where 66 ppm selenium had been added. Smaller increases were observed in selenium-doped zones for a moderately defocused electron beam weld with a higher d/w ratio in undoped base metal. When laser or electron beam weld penetration was by a keyhole mechanism, no change in d/w ratio occurred in selenium-doped zones. The results confirm the surface-tension-driven fluid-flow model for the effectmore » of minor elements on GTA weld pool shape. Other experimental evidence bearing on the effect of minor elements on GTA weld penetration is summarized.« less

Computational simulation of weld microstructure and distortion by considering process mechanics

NASA Astrophysics Data System (ADS)

Mochizuki, M.; Mikami, Y.; Okano, S.; Itoh, S.

2009-05-01

Highly precise fabrication of welded materials is in great demand, and so microstructure and distortion controls are essential. Furthermore, consideration of process mechanics is important for intelligent fabrication. In this study, the microstructure and hardness distribution in multi-pass weld metal are evaluated by computational simulations under the conditions of multiple heat cycles and phase transformation. Because conventional CCT diagrams of weld metal are not available even for single-pass weld metal, new diagrams for multi-pass weld metals are created. The weld microstructure and hardness distribution are precisely predicted when using the created CCT diagram for multi-pass weld metal and calculating the weld thermal cycle. Weld distortion is also investigated by using numerical simulation with a thermal elastic-plastic analysis. In conventional evaluations of weld distortion, the average heat input has been used as the dominant parameter; however, it is difficult to consider the effect of molten pool configurations on weld distortion based only on the heat input. Thus, the effect of welding process conditions on weld distortion is studied by considering molten pool configurations, determined by temperature distribution and history.

Probing Reliability of Transport Phenomena Based Heat Transfer and Fluid Flow Analysis in Autogeneous Fusion Welding Process

NASA Astrophysics Data System (ADS)

Bag, S.; de, A.

2010-09-01

The transport phenomena based heat transfer and fluid flow calculations in weld pool require a number of input parameters. Arc efficiency, effective thermal conductivity, and viscosity in weld pool are some of these parameters, values of which are rarely known and difficult to assign a priori based on the scientific principles alone. The present work reports a bi-directional three-dimensional (3-D) heat transfer and fluid flow model, which is integrated with a real number based genetic algorithm. The bi-directional feature of the integrated model allows the identification of the values of a required set of uncertain model input parameters and, next, the design of process parameters to achieve a target weld pool dimension. The computed values are validated with measured results in linear gas-tungsten-arc (GTA) weld samples. Furthermore, a novel methodology to estimate the overall reliability of the computed solutions is also presented.

Modeling growth and dissolution of inclusions during fusion welding of steels

NASA Astrophysics Data System (ADS)

Hong, Tao

The characteristics of inclusions in the weld metals are critical factors to determine the structure, properties and performance of weldments. The research in the present thesis applied computational modeling to study inclusion behavior considering thermodynamics and kinetics of nucleation, growth and dissolution of inclusion along its trajectory calculated from the heat transfer and fluid flow model in the weld pool. The objective of this research is to predict the characteristics of inclusions, such as composition, size distribution, and number density in the weld metal from different welding parameters and steel compositions. To synthesize the knowledge of thermodynamics and kinetics of nucleation, growth and dissolution of inclusion in the liquid metal, a set of time-temperature-transformation (TTT) diagrams are constructed to represent the effects of time and temperature on the isothermal growth and dissolution behavior of fourteen types of individual inclusions. The non-isothermal behavior of growth and dissolution of inclusions is predicted from their isothermal behavior by constructing continuous-cooling-transformation (CCT) diagrams using Scheil additive rule. A well verified fluid flow and heat transfer model developed at Penn State is used to calculate the temperature and velocity fields in the weld pool for different welding processes. A turbulent model considering enhanced viscosity and thermal conductivity (k-ε model) is applied. The calculations show that there is vigorous circulation of metal in the weld pool. The heat transfer and fluid flow model helps to understand not only the fundamentals of the physical phenomena (luring welding, but also the basis to study the growth and dissolution of inclusions. The calculations of particle tracking of thousands of inclusions show that most inclusions undergo complex gyrations and thermal cycles in the weld pool. The inclusions experience both growth and dissolution during their lifetime. Thermal cycles of thousand of inclusions nucleated in the liquid region are tracked and their growth and dissolution are calculated to estimate the final size distribution and number density of inclusions statistically. The calculations show that welding conditions and weld metal compositions affect the inclusion characteristics significantly. Good agreement between the computed and the experimentally observed inclusion size distribution indicates that the inclusion behavior in the weld pool can be understood from the fundamentals of transport phenomena and transformation kinetics.

Effects of shielding gas composition on arc profile and molten pool dynamics in gas metal arc welding of steels

NASA Astrophysics Data System (ADS)

Wang, L. L.; Lu, F. G.; Wang, H. P.; Murphy, A. B.; Tang, X. H.

2014-11-01

In gas metal arc welding, gases of different compositions are used to produce an arc plasma, which heats and melts the workpiece. They also protect the workpiece from the influence of the air during the welding process. This paper models gas metal arc welding (GMAW) processes using an in-house simulation code. It investigates the effects of the gas composition on the temperature distribution in the arc and on the molten pool dynamics in gas metal arc welding of steels. Pure argon, pure CO2 and different mixtures of argon and CO2 are considered in the study. The model is validated by comparing the calculated weld profiles with physical weld measurements. The numerical calculations reveal that gas composition greatly affects the arc temperature profile, heat transfer to the workpiece, and consequently the weld dimension. As the CO2 content in the shielding gas increases, a more constricted arc plasma with higher energy density is generated as a result of the increased current density in the arc centre and increased Lorentz force. The calculation also shows that the heat transferred from the arc to the workpiece increases with increasing CO2 content, resulting in a wider and deeper weld pool and decreased reinforcement height.

Pin Tool Geometry Effects in Friction Stir Welding

NASA Technical Reports Server (NTRS)

Querin, J. A.; Rubisoff, H. A.; Schneider, J. A.

2009-01-01

In friction stir welding (FSW) there is significant evidence that material can take one of two different flow paths when being displaced from its original position in front of the pin tool to its final position in the wake of the weld. The geometry of the pin tool, along with the process parameters, plays an important role in dictating the path that the material takes. Each flow path will impart a different thermomechanical history on the material, consequently altering the material microstructure and subsequent weld properties. The intention of this research is to isolate the effect that different pin tool attributes have on the flow paths imparted on the FSWed material. Based on published weld tool geometries, a variety of weld tools were fabricated and used to join AA2219. Results from the tensile properties and microstructural characterization will be presented.

In Process Measurement of Hydrogen in Welding

DTIC Science & Technology

1986-09-01

Specimen Geometry.........40 Figure 4.8 GTAW Diffusible Hydrogen Specimen Geometry .......... 40 Figure 4.9 Schematic of Specimen Outgassing Container for... GTAW ) and gas metal arc welding (GMAW) have the lowest potentials for hydrogen pickup, while -. the flux-cored arc welding (FCAW) and submerged arc...wire during welding which is the major source of hydrogen in GMAW and GTAW . Although the FCAW process was originally considered an intrinsi- cally low

Interaction of trace elements and welding parameters on GTA weld shape. [Variation with penetration and tip angle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burgardt, P.; Heiple, C.R.

1985-01-01

Good penetration and poor penetration steels have different responses to changes in temperature distribution on the weld pool surface. Penetration of 304 SS was varied using S and Se dopants. The weld parameter investigated was the electrode tip angle. Results of bead-on-plate GTA welds show that there is a difference in response of weld pool shape to tip angle depending on penetration: Low penetration base metal showed no dependence, intermediate penetration steel showed a small linear decrease of weld depth-to-width ratio (d/w) with tip angle, while high penetration steel showed an increase of d/w up to a maximum at aboutmore » 50/sup 0/, followed by a decrease in d/w. (DLC)« less

Predicting laser weld reliability with stochastic reduced-order models. Predicting laser weld reliability

DOE PAGES

Emery, John M.; Field, Richard V.; Foulk, James W.; ...

2015-05-26

Laser welds are prevalent in complex engineering systems and they frequently govern failure. The weld process often results in partial penetration of the base metals, leaving sharp crack-like features with a high degree of variability in the geometry and material properties of the welded structure. Furthermore, accurate finite element predictions of the structural reliability of components containing laser welds requires the analysis of a large number of finite element meshes with very fine spatial resolution, where each mesh has different geometry and/or material properties in the welded region to address variability. We found that traditional modeling approaches could not bemore » efficiently employed. Consequently, a method is presented for constructing a surrogate model, based on stochastic reduced-order models, and is proposed to represent the laser welds within the component. Here, the uncertainty in weld microstructure and geometry is captured by calibrating plasticity parameters to experimental observations of necking as, because of the ductility of the welds, necking – and thus peak load – plays the pivotal role in structural failure. The proposed method is exercised for a simplified verification problem and compared with the traditional Monte Carlo simulation with rather remarkable results.« less

Influence of Oxides on Microstructures and Mechanical Properties of High-Strength Steel Weld Joint

NASA Astrophysics Data System (ADS)

Cai, Yangchuan; Luo, Zhen; Huang, Zunyue; Zeng, Yida

2016-11-01

A comprehensive investigation was conducted into the effect of oxides on penetrations, microstructures and mechanical properties of BS700MC super steel weld bead. Boron oxide changed the penetration of weld bead by changing the Marangoni convection in the weld pool and contracting the welding arc. Chromium oxide only changed the Marangoni convection in the weld pool to increase the penetration of super steel. Thus, the super steel weld bead has higher penetration coated with flux boron oxide than that coated with chromium oxide. In other words, the activating flux TIG (A-TIG) welding with flux boron oxide has less welding heat input than the A-TIG welding with flux chromium oxide. As a result, on the one hand, there existed more fine and homogeneous acicular ferrites in the microstructure of welding heat-affected zone when the super steel was welded by A-TIG with flux boron oxide. Thus, the weld beads have higher value of low-temperature impact toughness. On the other hand, the softening degree of welding heat-affected zone, welded by A-TIG with flux boron oxide, will be decreased for the minimum value of welding heat input.

Effect of welding position on porosity formation in aluminum alloy welds

NASA Technical Reports Server (NTRS)

Haryung, J.; Wroth, R. S.

1967-01-01

Program investigates the effects of varied welding positions on weld qualities. Progressive changes in bead geometry occur as the weld plane angle is varied from upslope to downslope. The gravitational effect on the weld puddle varies greatly with welding position.

Weld geometry strength effect in 2219-T87 aluminum

NASA Technical Reports Server (NTRS)

Nunes, A. C., Jr.; Novak, H. L.; Mcilwain, M. C.

1981-01-01

A theory of the effect of geometry on the mechanical properties of a butt weld joint is worked out based upon the soft interlayer weld model. Tensile tests of 45 TIG butt welds and 6 EB beads-on-plate in 1/4-in. 2219-T87 aluminum plate made under a wide range of heat sink and power input conditions are analyzed using this theory. The analysis indicates that purely geometrical effects dominate in determining variations in weld joint strength with heat sink and power input. Variations in weld dimensions with cooling rate are significant as well as with power input. Weld size is suggested as a better indicator of the condition of a weld joint than energy input.

Performance Improvement of Friction Stir Welds by Better Surface Finish

NASA Technical Reports Server (NTRS)

Russell, Sam; Nettles, Mindy

2015-01-01

The as-welded friction stir weld has a cross section that may act as a stress concentrator. The geometry associated with the stress concentration may reduce the weld strength and it makes the weld challenging to inspect with ultrasound. In some cases, the geometry leads to false positive nondestructive evaluation (NDE) indications and, in many cases, it requires manual blending to facilitate the inspection. This study will measure the stress concentration effect and develop an improved phased array ultrasound testing (PAUT) technique for friction stir welding. Post-welding, the friction stir weld (FSW) tool would be fitted with an end mill that would machine the weld smooth, trimmed shaved. This would eliminate the need for manual weld preparation for ultrasonic inspections. Manual surface preparation is a hand operation that varies widely depending on the person preparing the welds. Shaving is a process that can be automated and tightly controlled.

Analysis of Welding Zinc Coated Steel Sheets in Zero Gap Configuration by 3D Simulations and High Speed Imaging

NASA Astrophysics Data System (ADS)

Koch, Holger; Kägeler, Christian; Otto, Andreas; Schmidt, Michael

Welding of zinc coated sheets in zero gap configuration is of eminent interest for the automotive industry. This Laser welding process would enable the automotive industry to build auto bodies with a high durability in a plain manufacturing process. Today good welding results can only be achieved by expensive constructive procedures such as clamping devices to ensure a defined gad. The welding in zero gap configuration is a big challenge because of the vaporised zinc expelled from the interface between the two sheets. To find appropriate welding parameters for influencing the keyhole and melt pool dynamics, a three dimensional simulation and a high speed imaging system for laser keyhole welding have been developed. The obtained results help to understand the process of the melt pool perturbation caused by vaporised zinc.

Adaptive Neuro-Fuzzy Inference System (ANFIS)-Based Models for Predicting the Weld Bead Width and Depth of Penetration from the Infrared Thermal Image of the Weld Pool

NASA Astrophysics Data System (ADS)

Subashini, L.; Vasudevan, M.

2012-02-01

Type 316 LN stainless steel is the major structural material used in the construction of nuclear reactors. Activated flux tungsten inert gas (A-TIG) welding has been developed to increase the depth of penetration because the depth of penetration achievable in single-pass TIG welding is limited. Real-time monitoring and control of weld processes is gaining importance because of the requirement of remoter welding process technologies. Hence, it is essential to develop computational methodologies based on an adaptive neuro fuzzy inference system (ANFIS) or artificial neural network (ANN) for predicting and controlling the depth of penetration and weld bead width during A-TIG welding of type 316 LN stainless steel. In the current work, A-TIG welding experiments have been carried out on 6-mm-thick plates of 316 LN stainless steel by varying the welding current. During welding, infrared (IR) thermal images of the weld pool have been acquired in real time, and the features have been extracted from the IR thermal images of the weld pool. The welding current values, along with the extracted features such as length, width of the hot spot, thermal area determined from the Gaussian fit, and thermal bead width computed from the first derivative curve were used as inputs, whereas the measured depth of penetration and weld bead width were used as output of the respective models. Accurate ANFIS models have been developed for predicting the depth of penetration and the weld bead width during TIG welding of 6-mm-thick 316 LN stainless steel plates. A good correlation between the measured and predicted values of weld bead width and depth of penetration were observed in the developed models. The performance of the ANFIS models are compared with that of the ANN models.

Effect of Weld Tool Geometry on Friction Stir Welded Ti-6Al-4V

NASA Technical Reports Server (NTRS)

Querin, Joseph A.; Schneider, Judy A.

2008-01-01

In this study, flat 0.250" thick Ti-6Al-4V panels were friction stir welded (FSWed) using weld tools with tapered pins. The five different pin geometries of the weld tools included: 0 degree (straight cylinder), 15 degree, 30 degree, 45 degree, and 60 degree angles on the frustum. All weld tools had a smooth 7 degree concave shoulder and were made from microwave sintered tungsten carbide. For each weld tool geometry, the FSW process parameters were optimized to eliminate internal defects. All the welds were produced in position control with a 2.5 degree lead angle using a butt joint configuration for the panels. The process parameters of spindle rpm and travel speed were varied, altering the hot working conditions imparted to the workpiece. Load cells on the FSWing machine allowed for the torque, the plunge force, and the plow force to be recorded during welding. Resulting mechanical properties were evaluated from tensile tests results of the FSWjoints. Variations in the material flow were investigated by use of microstructural analysis including optical microscopy (OM), scanning electron microscopy (SEM), and orientation image mapping (aIM).

Self-Aligning Sensor-Mounting Fixture

NASA Technical Reports Server (NTRS)

Gilbert, Jeffrey L.; Mills, Rhonda J.

1991-01-01

Optical welding sensors replaced without realignment. Mounting fixture for optical weld-penetration sensor enables accurate and repeatable alignment. Simple and easy to use. Assembled on welding torch, it holds sensor securely and keeps it pointed toward weld pool. Designed for use on gas/tungsten arc-welding torch, fixture replaces multipiece bracket.

Research on the welding process of aluminum alloy based on high power fiber laser

NASA Astrophysics Data System (ADS)

Zhang, Jian; Zhang, Wei; Pan, Xiaoming; Huang, Shanshi; Liu, Wenwen

2017-08-01

To research the formation and variation principle of the weld seam and molten pool for aluminum alloy high power fiber laser welding, the welding experiments for 5052 aluminum alloy were carried out. The influences of laser power, scanning velocity and protection gas on the welding process were systematically researched. The results show that with the increase of power and scanning velocity, the depth to width ratio first increases and then decreases. The ratio reaches the maximum value at 2.6 KW and 30 mm/s, respectively. When the power located at 2.6 KW to 2.8 KW or the velocity located at 25 mm/s to 30 mm/s, stable deep penetration welding can be obtained. The weld seam shows relative flat appearance and the molten pool presents typical "T shape" topography. Moreover, the protection gas also influences the appearance of the weld seam. Using the independently designed fixture, the quality of the weld seam can be well improved.

Microstructure and Porosity of Laser-welded Dissimilar Material Joints of HR-2 and J75

NASA Astrophysics Data System (ADS)

Shen, Xianfeng; Teng, Wenhua; Zhao, Shuming; He, Wenpei

Dissimilar laser welding of HR-2 and J75 has a wide range of applications in high-and low-temperature hydrogen storage. The porosity distributions of the welded joints were investigated at different line energies, penetration status, and welding positions (1G, 2G, and 3G). The effect of the welding position on the welding appearance was evident only at high line energies because of the essential effect of gravity of the larger and longer dwelling molten pool. The porosity of the welded joints between the solutionised and aged J75 and HR-2 at the 3G position and partial penetration was located at the weld centre line, while the porosity at the 2G position with full penetration was distributed at the weld edges, which is consistent with the distribution of floating slag. Full keyhole penetration resulted in minimum porosity, partial penetration resulted in moderate porosity, and periodic molten pool penetration resulted in maximum porosity.

Acoustic-Emission Weld-Penetration Monitor

NASA Technical Reports Server (NTRS)

Maram, J.; Collins, J.

1986-01-01

Weld penetration monitored by detection of high-frequency acoustic emissions produced by advancing weld pool as it melts and solidifies in workpiece. Acoustic emission from TIG butt weld measured with 300-kHz resonant transducer. Rise in emission level coincides with cessation of weld penetration due to sudden reduction in welding current. Such monitoring applied to control of automated and robotic welders.

Experimental research on the dynamic behaviors of the keyhole and molten pool in laser deep-penetration welding

NASA Astrophysics Data System (ADS)

Zhang, Yi; Lin, Qida; Yin, Xuni; Li, Simeng; Deng, Jiquan

2018-04-01

Both the morphology and temperature are two important characteristics of the keyhole and the molten pool in laser deep-penetration welding. The modified ‘sandwich’ method was adopted to overcome the difficulty in obtaining inner information about the keyhole and the molten pool. Based on this method, experimental platforms were built for observing the variations in the surface morphology, the longitudinal keyhole profile and the internal temperature. The experimental results of three dynamic behaviors exbibit as follows. The key factor, which makes the pool width go into a quasi-steady state, lies in the balance between the vortex and the sideways flows around the keyhole. Experimental observation shows that the keyhole goes through three stages in laser welding: the rapid drilling stage, the slow drilling stage and the quasi-steady state. The time for achieving a relative fixed keyhole depth is close to the formation time of the maximum pool width. The internal temperatures inside the keyhole and the molten pool first experience a rapid increase, then a decrease and finally go into a quasi-steady state. Compared to that in the unstable stage, the liquid–metal uphill formed in the stable stage of laser welding has less influence on the internal temperature.

Detection of defects in laser welding of AZ31B magnesium alloy in zero-gap lap joint configuration by a real-time spectroscopic analysis

NASA Astrophysics Data System (ADS)

Harooni, Masoud; Carlson, Blair; Kovacevic, Radovan

2014-05-01

The effect of surface oxide layer existing at the lap-joint faying surface of magnesium sheets is investigated on the keyhole dynamics of the weld pool and weld bead qualities. It is observed that by removing the oxide layer from the faying surface of the lap joint, a high quality weld can be achieved in the laser welding process. However, the presence of an oxide layer deteriorates the quality of the weld by forming pores at the interface of the two overlapped sheets. The purpose of this paper is to identify the correlation between the integrity of the weld and the interaction between the laser and material. A spectroscopy sensor was applied to detect the spectra emitted from a plasma plume during the laser welding of AZ31B magnesium alloy in a zero-gap lap joint configuration. The electron temperature was calculated by applying a Boltzmann plot method based on the detected spectra, and the correlation between the pore formation and the spectral signals was studied. The laser molten pool and the keyhole condition were monitored in real-time by a high speed charge-coupled device (CCD) camera. A green laser was used as an illumination source in order to detect the influence of the oxide layer on the dynamic behavior of the molten pool. Results revealed that the detected spectrum and weld defects had a meaningful correlation for real-time monitoring of the weld quality during laser welding of magnesium alloys.

Fluid Flow Characteristics and Porosity Behavior in Full Penetration Laser Welding of a Titanium Alloy

NASA Astrophysics Data System (ADS)

Chang, Baohua; Allen, Chris; Blackburn, Jon; Hilton, Paul; Du, Dong

2015-04-01

In this paper, a computational fluid mechanics model is developed for full penetration laser welding of titanium alloy Ti6Al4V. This has been used to analyze possible porosity formation mechanisms, based on predictions of keyhole behavior and fluid flow characteristics in the weld pool. Numerical results show that when laser welding 3 mm thickness titanium alloy sheets with given laser beam focusing optics, keyhole depth oscillates before a full penetration keyhole is formed, but thereafter keyhole collapses are not predicted numerically. For lower power, lower speed welding, the fluid flow behind the keyhole is turbulent and unstable, and vortices are formed. Molten metal is predicted to flow away from the center plane of the weld pool, and leave a gap or void within the weld pool behind the keyhole. For higher power, higher speed welding, fluid flow is less turbulent, and such vortices are not formed. Corresponding experimental results show that porosity was absent in the melt runs made at higher power and higher welding speed. In contrast, large pores were present in melt runs made at lower power and lower welding speed. Based on the combination of experimental results and numerical predictions, it is proposed that porosity formation when keyhole laser welding may result from turbulent fluid flow behind the keyhole, with the larger the value of associated Reynolds number, the higher the possibility of porosity formation. For such fluid flow controlled porosities, measures to decrease Reynolds number of the fluid flow close to the keyhole could prove effective in reducing or avoiding porosity.

Welding polarity effects on weld spatters and bead geometry of hyperbaric dry GMAW

NASA Astrophysics Data System (ADS)

Xue, Long; Wu, Jinming; Huang, Junfen; Huang, Jiqiang; Zou, Yong; Liu, Jian

2016-03-01

Welding polarity has influence on welding stability to some extent, but the specific relationship between welding polarity and weld quality has not been found, especially under the hyperbaric environment. Based on a hyperbaric dry welding experiment system, gas metal arc welding(GMAW) experiments with direct current electrode positive(DCEP) and direct current electrode negative(DCEN) operations are carried out under the ambient pressures of 0.1 MPa, 0.4 MPa, 0.7 MPa and 1.0 MPa to find the influence rule of different welding polarities on welding spatters and weld bead geometry. The effects of welding polarities on the weld bead geometry such as the reinforcement, the weld width and the penetration are discussed. The experimental results show that the welding spatters gradually grow in quantity and size for GMAW with DCEP, while GMAW with DCEN can produce fewer spatters comparatively with the increase of the ambient pressure. Compared with DCEP, the welding current and arc voltage waveforms for DCEN is more stable and the distribution of welding current probability density for DCEN is more concentrated under the hyperbaric environment. When the ambient pressure is increased from 0.1 MPa to 1.0 MPa, the effects of welding polarities on the reinforcement, the weld width and the penetration are as follows: an increase of 0.8 mm for the weld reinforcement is produced by GMAW with DCEN and 1.3 mm by GMAW with DCEP, a decrease of 7.2 mm for the weld width is produced by DCEN and 6.1 mm by DCEP; and an increase of 3.9 mm for the penetration is produced by DCEN and 1.9 mm by DCEP. The proposed research indicates that the desirable stability in the welding procedure can be achieved by GMAW with DCEN operation under the hyperbaric environment.

The Effect of Process Parameters and Tool Geometry on Thermal Field Development and Weld Formation in Friction Stir Welding of the Alloys AZ31 and AZ61

NASA Astrophysics Data System (ADS)

Zettler, R.; Blanco, A. C.; dos Santos, J. F.; Marya, S.

An increase in the use of magnesium (Mg) in the car manufacturing industry has raised questions concerning its weldability. Friction Stir Welding (FSW) has the advantage of achieving metallic bonding below that of the melting point of the base material thus avoiding many of the metallurgical problems associated with the solidification process. The present study presents the results of a development program carried out to investigate the response of Mg alloys AZ31 and AZ61 to different FSW tool geometries and process parameters. Temperature development across the weld zone was monitored and the produced welds have been subjected to microstructural analysis and mechanical testing. Defect free welds have been produced with optimised FSW-tool and parameters. The micro structure of the welded joint resulted in similar ductility and hardness levels as compared to that of the base material. The results also demonstrated that tool geometry plays a fundamental role in the response of the investigated alloys to the FSW process.

Study of the stability of electrode metal melting and transfer in the process of consumable electrode welding powered by supplies with differing dynamic characteristics

NASA Astrophysics Data System (ADS)

Saraev, Y. N.; Chinakhov, D. A.; Il'yashchenko, D. P.; Kiselev, A. S.; Gardiner, A. S.; Raev, I. V.

2016-11-01

In the paper we present the results of the study of the power supply characteristics effect upon the stability of electrode metal melting and transfer into the weld pool in the process of consumable electrode welding. It was shown that application of inverter type welding power supplies of the new generation results in changing the characteristics of the heat and mass transfer which has a decisive impact upon the heat content of the weld pool, reduction of residual stresses in the heat-affected zone (HAZ). The authors also substantiate the tendency to the reduction of the structural constituents in the area of the permanent joint.

Experimental study of hot cracking at circular welding joints of 42CrMo steel

NASA Astrophysics Data System (ADS)

Zhang, Yan; Chen, Genyu; Chen, Binghua; Wang, Jinhai; Zhou, Cong

2017-12-01

The hot cracking at circular welding joints of quenched and tempered 42CrMo steel were studied. The flow of the molten pool and the solidification process of weld were observed with a high-speed video camera. The information on the variations in the weld temperature was collected using an infrared (IR) thermal imaging system. The metallurgical factors of hot cracking were analyzed via metallographic microscope and scanning electron microscope (SEM). The result shows that leading laser laser-metal active gas (MAG) hybrid welding process has a smaller solid-liquid boundary movement rate (VSL) and a smaller solid-liquid boundary temperature gradient (GSL) compared with leading arc laser-MAG hybrid welding process and laser welding process. Additionally, the metal in the molten pool has superior permeability while flowing toward the dendritic roots and can compensate for the inner-dendritic pressure balance. Therefore, leading laser laser-MAG hybrid welding process has the lowest hot cracking susceptibility.

Numerical modeling of keyhole dynamics in laser welding

NASA Astrophysics Data System (ADS)

Zhang, Wen-Hai; Zhou, Jun; Tsai, Hai-Lung

2003-03-01

Mathematical models and the associated numerical techniques have been developed to study the following cases: (1) the formation and collapse of a keyhole, (2) the formation of porosity and its control strategies, (3) laser welding with filler metals, and (4) the escape of zinc vapor in laser welding of galvanized steel. The simulation results show that the formation of porosity in the weld is caused by two competing mechanisms: one is the solidification rate of the molten metal and the other is the speed that molten metal backfills the keyhole after laser energy is terminated. The models have demonstrated that porosity can be reduced or eliminated by adding filler metals, controlling laser tailing power, or applying an electromagnetic force during keyhole collapse process. It is found that a uniform composition of weld pool is difficult to achieve by filler metals due to very rapid solidification of the weld pool in laser welding, as compared to that in gas metal arc welding.

Variable-Polarity Plasma Arc Welding Of Alloy 2219

NASA Technical Reports Server (NTRS)

Walsh, Daniel W.; Nunes, Arthur C., Jr.

1989-01-01

Report presents results of study of variable-polarity plasma arc (VPPA) welding of aluminum alloy 2219. Consists of two parts: Examination of effects of microsegregation and transient weld stress on macrosegregation in weld pool and, electrical characterization of straight- and reverse-polarity portions of arc cycle.

In-field Welding and Coating Protocols

DOT National Transportation Integrated Search

2009-05-12

Gas Technology Institute (GTI) and Edison Welding Institute (EWI) created both laboratory and infield girth weld samples to evaluate the effects of weld geometry and hydrogen off-gassing on the performance of protective coatings. Laboratory made plat...

Investigation on the hot melting temperature field simulation of HDPE water supply pipeline in gymnasium pool

NASA Astrophysics Data System (ADS)

Cai, Zhiqiang; Dai, Hongbin; Fu, Xibin

2018-06-01

In view of the special needs of the water supply and drainage system of swimming pool in gymnasium, the correlation of high density polyethylene (HDPE) pipe and the temperature field distribution during welding was investigated. It showed that the temperature field distribution has significant influence on the quality of welding. Moreover, the mechanical properties of the welded joint were analyzed by the bending test of the weld joint, and the micro-structure of the welded joint was evaluated by scanning electron microscope (SEM). The one-dimensional unsteady heat transfer model of polyethylene pipe welding joints was established by MARC. The temperature field distribution during welding process was simulated, and the temperature field changes during welding were also detected and compared by the thermo-couple temperature automatic acquisition system. Results indicated that the temperature of the end surface of the pipe does not reach the maximum value, when it is at the end of welding heating. Instead, it reaches the maximum value at 300 sand latent heat occurs during the welding process. It concludes that the weld quality is the highest when the welding pressure is 0.2 MPa, and the heating temperature of HDPE heat fusion welding is in the range of 210 °C-230 °C.

Heat flow in variable polarity plasma arc welds

NASA Technical Reports Server (NTRS)

Abdelmessih, Amanie N.

1992-01-01

The space shuttle external tank and the space station Freedom are fabricated by the variable polarity plasma arc (VPPA) welding. Heat sink effects (taper) are observed when there are irregularities in the work-piece configuration especially if these irregularities are close to the weld bead. These heat sinks affect the geometry of the weld bead, and in extreme cases they could cause defects such as incomplete fusion. Also, different fixtures seem to have varying heat sink effects. The objective of the previous, present, and consecutive research studies is to investigate the effect of irregularities in the work-piece configuration and fixture differences on the weld bead geometry with the ultimate objective to compensate automatically for the heat sink effects and achieve a perfect weld.

Narrow gap laser welding

DOEpatents

Milewski, John O.; Sklar, Edward

1998-01-01

A laser welding process including: (a) using optical ray tracing to make a model of a laser beam and the geometry of a joint to be welded; (b) adjusting variables in the model to choose variables for use in making a laser weld; and (c) laser welding the joint to be welded using the chosen variables.

Narrow gap laser welding

DOEpatents

Milewski, J.O.; Sklar, E.

1998-06-02

A laser welding process including: (a) using optical ray tracing to make a model of a laser beam and the geometry of a joint to be welded; (b) adjusting variables in the model to choose variables for use in making a laser weld; and (c) laser welding the joint to be welded using the chosen variables. 34 figs.

Effect of Pin Geometry on the Mechanical Strength of Friction-Stir-Welded Polypropylene Composite Plates

NASA Astrophysics Data System (ADS)

Kordestani, F.; Ashenai Ghasemi, F.; Arab, N. B. M.

2017-09-01

Friction stir welding (FSW) is a solid-state welding process, which has successfully been applied in aerospace and automotive industries for joining materials. The friction stir tool is the key element in the FSW process. In this study, the effect of four different tool pin geometries on the mechanical properties of two types of polypropylene composite plates, with 30% glass and carbon fiber, respectively, were investigated. For this purpose, four pins of different geometry, namely, a threaded-tapered pin, square pin, four-flute threaded pin, and threaded-tapered pin with a chamfer were made and used to carry out the butt welding of 5-mm-thick plates. The standard tensile and Izod impact tests were performed to evaluate the tensile strength and impact toughness of welded specimens. The results indicated that the threaded-tapered pin with a chamfer produced welds with a better surface appearance and higher tensile and impact strengths. The tests also showed that, with the threaded-tapered pin with a chamfer, the impact strength of the glass- and carbon-fiber composite welds were about 40 and 50%, respectively, of that of the base materials.

Modelling of fluid flow phenomenon in laser+GMAW hybrid welding of aluminum alloy considering three phase coupling and arc plasma shear stress

NASA Astrophysics Data System (ADS)

Xu, Guoxiang; Li, Pengfei; Cao, Qingnan; Hu, Qingxian; Gu, Xiaoyan; Du, Baoshuai

2018-03-01

The present study aims to develop a unified three dimensional numerical model for fiber laser+GMAW hybrid welding, which is used to study the fluid flow phenomena in hybrid welding of aluminum alloy and the influence of laser power on weld pool dynamic behavior. This model takes into account the coupling of gas, liquid and metal phases. Laser heat input is described using a cone heat source model with changing peak power density, its height being determined based on the keyhole size. Arc heat input is modeled as a double ellipsoid heat source. The arc plasma flow and droplet transfer are simulated through the two simplified models. The temperature and velocity fields for different laser powers are calculated. The computed results are in general agreement with the experimental data. Both the peak and average values of fluid flow velocity during hybrid welding are much higher than those of GMAW. At a low level of laser power, both the arc force and droplet impingement force play a relatively large role on fluid flow in the hybrid welding. Keyhole depth always oscillates within a range. With an increase in laser power, the weld pool behavior becomes more complex. An anti-clockwise vortex is generated and the stability of keyhole depth is improved. Besides, the effects of laser power on different driving forces of fluid flow in weld pool are also discussed.

Through-Thickness Residual Stress Profiles in Austenitic Stainless Steel Welds: A Combined Experimental and Prediction Study

NASA Astrophysics Data System (ADS)

Mathew, J.; Moat, R. J.; Paddea, S.; Francis, J. A.; Fitzpatrick, M. E.; Bouchard, P. J.

2017-12-01

Economic and safe management of nuclear plant components relies on accurate prediction of welding-induced residual stresses. In this study, the distribution of residual stress through the thickness of austenitic stainless steel welds has been measured using neutron diffraction and the contour method. The measured data are used to validate residual stress profiles predicted by an artificial neural network approach (ANN) as a function of welding heat input and geometry. Maximum tensile stresses with magnitude close to the yield strength of the material were observed near the weld cap in both axial and hoop direction of the welds. Significant scatter of more than 200 MPa was found within the residual stress measurements at the weld center line and are associated with the geometry and welding conditions of individual weld passes. The ANN prediction is developed in an attempt to effectively quantify this phenomenon of `innate scatter' and to learn the non-linear patterns in the weld residual stress profiles. Furthermore, the efficacy of the ANN method for defining through-thickness residual stress profiles in welds for application in structural integrity assessments is evaluated.

Laser Beam Welding of Nitride Steel Components

NASA Astrophysics Data System (ADS)

Gu, Hongping; Yin, Guobin; Shulkin, Boris

Laser beam welding is a joining technique that has many advantages over conventional GMAW welding, such as low heat input, short cycle time as well as good cosmetic welds. Laser beam welding has been widely used for welding powertrain components in automotive industry. When welding nitride steel components, however, laser beam welding faces a great challenge. The difficulty lies in the fact that the nitride layer in the joint releases the nitrogen into the weld pool, resulting in a porous weld. This research presents an industrial ready solution to prevent the nitrogen from forming gas bubbles in the weld.

Surface preparation effects on GTA (gas tungsten arc) weld penetration in JBK-75 stainless steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campbell, R.D.; Heiple, C.R.; Sturgill, P.L.

1989-01-01

The results of a study are reported here on the effects of surface preparation on the shape of GTA welds on JBK-75, an austenitic precipitation hardenable stainless steel similar to A286. Minor changes in surface (weld groove) preparation produced substantial changes in the penetration characteristics and welding behavior of this alloy. Increased and more consistent weld penetration (higher d/w ratios) along with improved arc stability and less arc wander result from wire brushing and other abrasive surface preparations, although chemical and machining methods did not produce any improvement in penetration. Abrasive treatments roughen the surface, increase the surface area, andmore » increase the surface oxide thickness. The increased weld d/w ratio is attributed to oxygen added to the weld pool from the surface oxide on the base metal. The added oxygen alters the surface-tension driven fluid flow pattern in the weld pool. Similar results were observed with changes in filler wire surface oxide thickness, caused by changes in wire production conditions. 15 refs., 14 figs., 4 tabs.« less

Influence of Filler Wire Feed Rate in Laser-Arc Hybrid Welding of T-butt Joint in Shipbuilding Steel with Different Optical Setups

NASA Astrophysics Data System (ADS)

Unt, Anna; Poutiainen, Ilkka; Salminen, Antti

In this paper, a study of laser-arc hybrid welding featuring three different process fibres was conducted to build knowledge about process behaviour and discuss potential benefits for improving the weld properties. The welding parameters affect the weld geometry considerably, as an example the increase in welding speed usually decreases the penetration and a larger beam diameter usually widens the weld. The laser hybrid welding system equipped with process fibres with 200, 300 and 600 μm core diameter were used to produce fillet welds. Shipbuilding steel AH36 plates with 8 mm thickness were welded with Hybrid-Laser-Arc-Welding (HLAW) in inversed T configuration, the effects of the filler wire feed rate and the beam positioning distance from the joint plane were investigated. Based on the metallographic cross-sections, the effect of process parameters on the joint geometry was studied. Joints with optimized properties (full penetration, soundness, smooth transition from bead to base material) were produced with 200 μm and 600 μm process fibres, while fiber with 300 μm core diameter produced welds with unacceptable levels of porosity.

Heat sink effects in variable polarity plasma arc welding

NASA Technical Reports Server (NTRS)

Abdelmessih, Amanie N.

1991-01-01

The Space Shuttle External Tank is fabricated by the variable polarity plasma arc (VPPA) welding process. In VPPA welding, a noble gas, usually argon, is directed through an arc to emerge from the torch as a hot plasma jet. This jet is surrounded by a shielding gas, usually helium, to protect the weld from contamination with air. The high velocity, hot plasma jet completely penetrates the workpiece (resembling a line heat source) when operated in the 'keyhole' mode. The metal melts on touching the side of the jet, as the torch travels in the perpendicular direction to the direction of the jet, and melted metal moves around the plasma jet in the keyhole forming a puddle which solidifies behind the jet. Heat sink effects are observed when there are irregularities in the workpiece configuration, especially, if these irregularities are close to the weld bead. These heat sinks affect the geometry of the weld bead, i.e., in extreme cases they could cause defects such as incomplete fusion. Also, different fixtures seem to have varying heat sink effects. The objective of this research is to study the effect of irregularities in workpiece configuration and fixture differences (heat sink effects) on the weld bead geometry with the ultimate objective to compensate for the heat sink effects and achieve a perfect weld. Experiments were performed on different workpiece geometries and compared to approximate models.

The effect of the welding direction on the plasma and metal transfer behavior of CO2 laser+GMAW-P hybrid welding processes

NASA Astrophysics Data System (ADS)

Zhang, Wang; Hua, Xueming; Liao, Wei; Li, Fang; Wang, Min

2014-07-01

During laser-arc hybrid welding, the welding direction exerts direct effects on the plasma properties, the transient behavior of the droplet, the weld pool behavior, and the temperature field. Ultimately, it will affect the welding process and the weld quality. However, the behavior of the CO2 laser+GMAW-P hybrid welding process has not been systematically studied. In this paper, the current-voltage characteristics of different welding processes were analyzed and compared. The dynamics of the droplet transfer, the plasma behavior, and the weld pool behavior were observed by using two high-speed camera systems. Moreover, an optical emission spectroscopy was applied to analyze the plasma temperature and the electron number density. The results indicated that the electrical resistance of the arc plasma reduced in the laser leading mode. For the same pulse duration, the metal transfer mode was the spray type with the laser leading arrangement. The temperature and electron density distribution showed bimodal behavior in the case of arc leading mode, while this phenomenon does not exist in the caser of laser leading mode. The double elliptic-planar distribution which conventional simulation process used was not applicable in the laser leading mode.

Surface preparation effects on GTA weld shape in JBK-75 stainless steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campbell, R.D.; Robertson, A.M.; Heiple, C.R.

1993-02-01

The results of a study are reported here on the effects of surface preparation on the shape of autogenous gas tungsten arc (GTA) welds in JBK-75, an austenitic precipitation hardenable stainless steel similar to A286. Minor changes in surface preparation produced substantial changes in the fusion zone shape and welding behavior of this alloy. Increased and more consistent depth of fusion (higher d/w ratios) along with improved arc stability and less arc wander resulted from wire brushing and other abrasive surface preparations, although chemical and machining methods did not produce any increase in depth of fusion. Abrasive treatments roughen themore » surface, increase the surface area, increase the surface oxide thickness, and entrap oxide. The increased weld d/w ratio is attributed to oxygen added to the weld pool from the surface oxide on the base metal. The added oxygen alters the surface-tension-driven fluid flow pattern in the weld pool. Increased depth of fusion in wire-fed U-groove weld joints also resulted when welding wire with a greater surface oxide thickness was used. Increasing the amount of wire brushing produced even deeper welds. However, a maximum in depth of fusion was observed with further wire brushing, beyond which weld fusion depth decreased.« less

Prediction Analysis of Weld-Bead and Heat Affected Zone in TIG welding using Artificial Neural Networks

NASA Astrophysics Data System (ADS)

Saldanha, Shamith L.; Kalaichelvi, V.; Karthikeyan, R.

2018-04-01

TIG Welding is a high quality form of welding which is very popular in industries. It is one of the few types of welding that can be used to join dissimilar metals. Here a weld joint is formed between stainless steel and monel alloy. It is desired to have control over the weld geometry of such a joint through the adjustment of experimental parameters which are welding current, wire feed speed, arc length and the shielding gas flow rate. To facilitate the automation of the same, a model of the welding system is needed. However the underlying welding process is complex and non-linear, and analytical methods are impractical for industrial use. Therefore artificial neural networks (ANN) are explored for developing the model, as they are well-suited for modelling non-linear multi-variate data. Feed-forward neural networks with backpropagation training algorithm are used, and the data for training the ANN taken from experimental work. There are four outputs corresponding to the weld geometry. Different training and testing phases were carried out using MATLAB software and ANN approximates the given data with minimum amount of error.

Process modeling and parameter optimization using radial basis function neural network and genetic algorithm for laser welding of dissimilar materials

NASA Astrophysics Data System (ADS)

Ai, Yuewei; Shao, Xinyu; Jiang, Ping; Li, Peigen; Liu, Yang; Yue, Chen

2015-11-01

The welded joints of dissimilar materials have been widely used in automotive, ship and space industries. The joint quality is often evaluated by weld seam geometry, microstructures and mechanical properties. To obtain the desired weld seam geometry and improve the quality of welded joints, this paper proposes a process modeling and parameter optimization method to obtain the weld seam with minimum width and desired depth of penetration for laser butt welding of dissimilar materials. During the process, Taguchi experiments are conducted on the laser welding of the low carbon steel (Q235) and stainless steel (SUS301L-HT). The experimental results are used to develop the radial basis function neural network model, and the process parameters are optimized by genetic algorithm. The proposed method is validated by a confirmation experiment. Simultaneously, the microstructures and mechanical properties of the weld seam generated from optimal process parameters are further studied by optical microscopy and tensile strength test. Compared with the unoptimized weld seam, the welding defects are eliminated in the optimized weld seam and the mechanical properties are improved. The results show that the proposed method is effective and reliable for improving the quality of welded joints in practical production.

Weld pool development during GTA and laser beam welding of Type 304 stainless steel; Part II-experimental correlation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zacharia, T.; David, S.A.; Vitek, J.M.

1989-12-01

In part I of the paper, the results of the heat flow and the fluid flow analysis were presented. Here, in Part II of the paper, predictions of the computational model are verified by comparing the numerically predicted and experimentally observed fusion zone size and shape. Stationary gas tungsten arc and laser beam welds were made on Type 304 stainless steel for different times to provide a variety of solidification conditions such as cooling rate and temperature gradient. Calculated temperatures and cooling rates are correlated with the experimentally observed fusion zone structure. In addition, the effect of sulfur on GTAmore » weld penetration was quantitatively evaluated by considering two heats of 304 stainless steel containing 90 and 240 ppm sulfur. Sulfur, as expected, increased the depth/width ratio by altering the surface tension gradient driven flow in the weld pool.« less

Surface temperature distribution of GTA weld pools on thin-plate 304 stainless steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zacharia, T.; David, S.A.; Vitek, J.M.

1995-11-01

A transient multidimensional computational model was utilized to study gas tungsten arc (GTA) welding of thin-plate 304 stainless steel (SS). The model eliminates several of the earlier restrictive assumptions including temperature-independent thermal-physical properties. Consequently, all important thermal-physical properties were considered as temperature dependent throughout the range of temperatures experienced by the weld metal. The computational model was used to predict surface temperature distribution of the GTA weld pools in 1.5-mm-thick AISI 304 SS. The welding parameters were chosen so as to correspond with an earlier experimental study that produced high-resolution surface temperature maps. One of the motivations of the presentmore » study was to verify the predictive capability of the computational model. Comparison of the numerical predictions and experimental observations indicate excellent agreement, thereby verifying the model.« less

Numerical Simulation of Stationary AC Tungsten Inert Gas Welding of Aluminum Plate in Consideration of Oxide Layer Cleaning

NASA Astrophysics Data System (ADS)

Tashiro, Shinichi; Tanaka, Manabu

An unified numerical simulation model of AC TIG welding of the aluminum plate considering energy balance among the electrode, the arc and the base metal and employing an analytical model for calculating cleaning rate of the oxide layer has been developed for investigating heat transport properties and weld pool formation process in AC TIG welding of aluminum plate. As a result of this simulation, it was shown that although the heat flux from the arc onto the base metal increases in EN (Electrode Negative) phase due to the electron condensation, that in EP (Electrode Positive) phase conversely decreases because mainly of cooling caused by the electron emission. Furthermore, the validity of the simulation model was confirmed by comparing to experimental results such as the arc voltage, the area of cleaning zone and the shape of weld pool.

Laser Spot Welding of Copper-aluminum Joints Using a Pulsed Dual Wavelength Laser at 532 and 1064 nm

NASA Astrophysics Data System (ADS)

Stritt, Peter; Hagenlocher, Christian; Kizler, Christine; Weber, Rudolf; Rüttimann, Christoph; Graf, Thomas

A modulated pulsed laser source emitting green and infrared laser light is used to join the dissimilar metals copper and aluminum. The resultant dynamic welding process is analyzed using the back reflected laser light and high speed video observations of the interaction zone. Different pulse shapes are applied to influence the melt pool dynamics and thereby the forming grain structure and intermetallic phases. The results of high-speed images and back-reflections prove that a modulation of the pulse shape is transferred to oscillations of the melt pool at the applied frequency. The outcome of the melt pool oscillation is shown by the metallurgically prepared cross-section, which indicates different solidification lines and grain shapes. An energy-dispersivex-ray analysis shows the mixture and the resultant distribution of the two metals, copper and aluminum, within the spot weld. It can be seen that the mixture is homogenized the observed melt pool oscillations.

A hot-cracking mitigation technique for welding high-strength aluminum alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Y.P.; Dong, P.; Zhang, J.

2000-01-01

A hot-cracking mitigation technique for gas tungsten arc welding (GTAW) of high-strength aluminum alloy 2024 is presented. The proposed welding technique incorporates a trailing heat sink (an intense cooling source) with respect to the welding torch. The development of the mitigation technique was based on both detailed welding process simulation using advanced finite element techniques and systematic laboratory experiments. The finite element methods were used to investigate the detailed thermomechanical behavior of the weld metal that undergoes the brittle temperature range (BTR) during welding. As expected, a tensile deformation zone within the material BTR region was identified behind the weldmore » pool under conventional GTA welding process conventional GTA welding process conditions for the aluminum alloy studied. To mitigate hot cracking, the tensile zone behind the weld pool must be eliminated or reduce to a satisfactory level if the weld metal hot ductility cannot be further improved. With detailed computational modeling, it was found that by the introduction of a trailing heat sink at some distance behind the welding arc, the tensile strain rate with respect to temperature in the zone encompassing the BTR region can be significantly reduced. A series of parametric studies were also conducted to derive optimal process parameters for the trailing heat sink. The experimental results confirmed the effectiveness of the trailing heat sink technique. With a proper implementation of the trailing heat sink method, hot cracking can be completely eliminated in welding aluminum alloy 2024 (AA 2024).« less

Real-time monitoring of the laser hot-wire welding process

NASA Astrophysics Data System (ADS)

Liu, Wei; Liu, Shuang; Ma, Junjie; Kovacevic, Radovan

2014-04-01

The laser hot-wire welding process was investigated in this work. The dynamics of the molten pool during welding was visualized by using a high-speed charge-coupled device (CCD) camera assisted by a green laser as an illumination source. It was found that the molten pool is formed by the irradiation of the laser beam on the filler wire. The effect of the hot-wire voltage on the stability of the welding process was monitored by using a spectrometer that captured the emission spectrum of the laser-induced plasma plume. The spectroscopic study showed that when the hot-wire voltage is above 9 V a great deal of spatters occur, resulting in the instability of the plasma plume and the welding process. The effect of spatters on the plasma plume was shown by the identified spectral lines of the element Mn I. The correlation between the Fe I electron temperature and the weld-bead shape was studied. It was noted that the electron temperature of the plasma plume can be used to real-time monitor the variation of the weld-bead features and the formation of the weld defects.

Structural and mechanical properties of welded joints of reduced activation martensitic steels

NASA Astrophysics Data System (ADS)

Filacchioni, G.; Montanari, R.; Tata, M. E.; Pilloni, L.

2002-12-01

Gas tungsten arc welding and electron beam welding methods were used to realise welding pools on plates of reduced activation martensitic steels. Structural and mechanical features of these simulated joints have been investigated in as-welded and post-welding heat-treated conditions. The research allowed to assess how each welding technique affects the original mechanical properties of materials and to find suitable post-welding heat treatments. This paper reports results from experimental activities on BATMAN II and F82H mod. steels carried out in the frame of the European Blanket Project - Structural Materials Program.

Laser welding in space

NASA Technical Reports Server (NTRS)

Kaukler, W. F.; Workman, G. L.

1991-01-01

Autogenous welds in 304 stainless steel were performed by Nd-YAG laser heating in a simulated space environment. Simulation consists of welding on the NASA KC-135 aircraft to produce the microgravity and by containing the specimen in a vacuum chamber. Experimental results show that the microgravity welds are stronger, harder in the fusion zone, have deeper penetration and have a rougher surface rippling of the weld pool than one-g welds. To perform laser welding in space, a solar-pumped laser concept that significantly increases the laser conversion efficiency and makes welding viable despite the limited power availability of spacecraft is proposed.

Research on the Effect of Welding Speed on the Quality of Welding Seam Based on the Local Dry Underwater Welding

NASA Astrophysics Data System (ADS)

Liu, Lei; Chen, Wu; Wang, Huagang; Ba, Jinyu; Li, Bing

2017-12-01

The repair of nuclear spent fuel pool has a high requirement for the quality of welding, the welding speed directly affects the quality of the weld when local dry automatic underwater welding is used to repair the damaged surface. Under the condition of the same condition, the local dry automatic underwater welding test was carried out under the condition of the same welding condition. Taking the 20cm as the experimental condition, after massive experiments show that when the welding speed is approximately 48cm/min the weld quality is high, meeting the design requirements, based on the double layer shrinkage nozzle chamber of local dry underwater automatic welding.

Annual report, FY 1979 Spent fuel and fuel pool component integrity.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, A.B. Jr.; Bailey, W.J.; Schreiber, R.E.

International meetings under the BEFAST program and under INFCE Working Group No. 6 during 1978 and 1979 continue to indicate that no cases of fuel cladding degradation have developed on pool-stored fuel from water reactors. A section from a spent fuel rack stand, exposed for 1.5 y in the Yankee Rowe (PWR) pool had 0.001- to 0.003-in.-deep (25- to 75-..mu..m) intergranular corrosion in weld heat-affected zones but no evidence of stress corrosion cracking. A section of a 304 stainless steel spent fuel storage rack exposed 6.67 y in the Point Beach reactor (PWR) spent fuel pool showed no significant corrosion.more » A section of 304 stainless steel 8-in.-dia pipe from the Three Mile Island No. 1 (PWR) spent fuel pool heat exchanger plumbing developed a through-wall crack. The crack was intergranular, initiating from the inside surface in a weld heat-affected zone. The zone where the crack occurred was severely sensitized during field welding. The Kraftwerk Union (Erlangen, GFR) disassembled a stainless-steel fuel-handling machine that operated for 12 y in a PWR (boric acid) spent fuel pool. There was no evidence of deterioration, and the fuel-handling machine was reassembled for further use. A spent fuel pool at a Swedish PWR was decontaminated. The procedure is outlined in this report.« less

Influence of tool geometry and processing parameters on welding defects and mechanical properties for friction stir welding of 6061 Aluminium alloy

NASA Astrophysics Data System (ADS)

Daneji, A.; Ali, M.; Pervaiz, S.

2018-04-01

Friction stir welding (FSW) is a form of solid state welding process for joining metals, alloys, and selective composites. Over the years, FSW development has provided an improved way of producing welding joints, and consequently got accepted in numerous industries such as aerospace, automotive, rail and marine etc. In FSW, the base metal properties control the material’s plastic flow under the influence of a rotating tool whereas, the process and tool parameters play a vital role in the quality of weld. In the current investigation, an array of square butt joints of 6061 Aluminum alloy was to be welded under varying FSW process and tool geometry related parameters, after which the resulting weld was evaluated for the corresponding mechanical properties and welding defects. The study incorporates FSW process and tool parameters such as welding speed, pin height and pin thread pitch as input parameters. However, the weld quality related defects and mechanical properties were treated as output parameters. The experimentation paves way to investigate the correlation between the inputs and the outputs. The correlation between inputs and outputs were used as tool to predict the optimized FSW process and tool parameters for a desired weld output of the base metals under investigation. The study also provides reflection on the effect of said parameters on a welding defect such as wormhole.

Friction stir welding tool and process for welding dissimilar materials

DOEpatents

Hovanski, Yuri; Grant, Glenn J; Jana, Saumyadeep; Mattlin, Karl F

2013-05-07

A friction stir welding tool and process for lap welding dissimilar materials are detailed. The invention includes a cutter scribe that penetrates and extrudes a first material of a lap weld stack to a preselected depth and further cuts a second material to provide a beneficial geometry defined by a plurality of mechanically interlocking features. The tool backfills the interlocking features generating a lap weld across the length of the interface between the dissimilar materials that enhances the shear strength of the lap weld.

Welding pool measurement using thermal array sensor

NASA Astrophysics Data System (ADS)

Cho, Chia-Hung; Hsieh, Yi-Chen; Chen, Hsin-Yi

2015-08-01

Selective laser melting (SLM) is an additive manufacturing (AM) technology that uses a high-power laser beam to melt metal powder in chamber of inert gas. The process starts by slicing the 3D CAD data as a digital information source into layers to create a 2D image of each layer. Melting pool was formed by using laser irradiation on metal powders which then solidified to consolidated structure. In a selective laser melting process, the variation of melt pool affects the yield of a printed three-dimensional product. For three dimensional parts, the border conditions of the conductive heat transport have a very large influence on the melt pool dimensions. Therefore, melting pool is an important behavior that affects the final quality of the 3D object. To meet the temperature and geometry of the melting pool for monitoring in additive manufacturing technology. In this paper, we proposed the temperature sensing system which is composed of infrared photodiode, high speed camera, band-pass filter, dichroic beam splitter and focus lens. Since the infrared photodiode and high speed camera look at the process through the 2D galvanometer scanner and f-theta lens, the temperature sensing system can be used to observe the melting pool at any time, regardless of the movement of the laser spot. In order to obtain a wide temperature detecting range, 500 °C to 2500 °C, the radiation from the melting pool to be measured is filtered into a plurality of radiation portions, and since the intensity ratio distribution of the radiation portions is calculated by using black-body radiation. The experimental result shows that the system is suitable for melting pool to measure temperature.

Effect of Electromagnetic Stirring on Weld Pools.

DTIC Science & Technology

1983-10-01

R136 71S EFFECT OF ELECTROMAGNET1C STIRRING ON WELD POOL5(U) i/lD DAVID W TAYLOR NAVAL SH-IP RE5ERRCH AND DEVELOPMENT CENTER ANN. R DENRLE ET RL...COMMANDER TECHNICAL DIRECTOR 01 OFFICER-IN-CHARGE OFFICER-IN-CHARGE CARDEROCK ANNAPOLIS 06 04 SYSTEMS DEVELOPMENT DEPARTMENT 11 SHIP PERFORMANCE AVIATION AND...SHIP ACOUSTICS PROPULSION AND DEPARTMENT AUXILIARY SYSTEMS DEPARTMENT 19 27 SHIP MATERIALS CENTRAL ENGINEERING INSTRUMENTATION DEPARTMENT DEPARTMENT28

Real-time monitoring of laser welding of galvanized high strength steel in lap joint configuration

NASA Astrophysics Data System (ADS)

Kong, Fanrong; Ma, Junjie; Carlson, Blair; Kovacevic, Radovan

2012-10-01

Two different cases regarding the zinc coating at the lap joint faying surface are selected for studying the influence of zinc vapor on the keyhole dynamics of the weld pool and the final welding quality. One case has the zinc coating fully removed at the faying surface; while the other case retains the zinc coating on the faying surface. It is found that removal of the zinc coating at the faying surface produces a significantly better weld quality as exemplified by a lack of spatters whereas intense spatters are present when the zinc coating is present at the faying surface. Spectroscopy is used to detect the optical spectra emitted from a laser generated plasma plume during the laser welding of galvanized high strength DP980 steel in a lap-joint configuration. A correlation between the electron temperature and defects within the weld bead is identified by using the Boltzmann plot method. The laser weld pool keyhole dynamic behavior affected by a high-pressure zinc vapor generated at the faying surface of galvanized steel lap-joint is monitored in real-time by a high speed charge-coupled device (CCD) camera assisted with a green laser as an illumination source.

Effects of Cr2O3 Activating Flux on the Plasma Plume in Pulsed Laser Welding

NASA Astrophysics Data System (ADS)

Yi, Luo; Yunfei, Du; Xiaojian, Xie; Rui, Wan; Liang, Zhu; Jingtao, Han

2016-11-01

The effects of Cr2O3 activating flux on pulsed YAG laser welding of stainless steel and, particularly, on the behavior of the plasma plume in the welding process were investigated. According to the acoustic emission (AE) signals detected in the welding process, the possible mechanism for the improvement in penetration depth was discussed. The results indicated that the AE signals detected in the welding process reflected the behavior of the plasma plume as pulsed laser energy affecting the molten pool. The root-mean-square (RMS) waveform, AE count, and power spectrum of AE signals were three effective means to characterize the behavior of the plasma plume, which indicated the characteristics of energy released by the plasma plume. The activating flux affected by the laser beam helped to increase the duration and intensity of energy released by the plasma plume, which improved the recoil force and thermal effect transferred from the plasma plume to the molten pool. These results were the main mechanism for Cr2O3 activating flux addition improving the penetration depth in pulsed YAG laser welding.

Effects of current on droplet generation and arc plasma in gas metal arc welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, J.; Tsai, H. L.

2006-09-01

In gas metal arc welding (GMAW), a technology using pulsed currents has been employed to achieve the one-droplet-per-pulse (ODPP) metal transfer mode with the advantages of low average currents, a stable and controllable droplet generation, and reduced spatter. In this paper, a comprehensive model was developed to study the effects of different current profiles on the droplet formation, plasma generation, metal transfer, and weld pool dynamics in GMAW. Five types of welding currents were studied, including two constant currents and three wave form currents. In each type, the transient temperature and velocity distributions of the arc plasma and the moltenmore » metal, and the shapes of the droplet and the weld pool were calculated. The results showed that a higher current generates smaller droplets, higher droplet frequency, and higher electromagnetic force that becomes the dominant factor detaching the droplet from the electrode tip. The model has demonstrated that a stable ODPP metal transfer mode can be achieved by choosing a current with proper wave form for given welding conditions.« less

Hydrogen Transport and Rationalization of Porosity Formation during Welding of Titanium Alloys

NASA Astrophysics Data System (ADS)

Huang, Jianglin; Warnken, Nils; Gebelin, Jean-Christophe; Strangwood, Martin; Reed, Roger C.

2012-02-01

The transport of hydrogen during fusion welding of the titanium alloy Ti-6Al4V is analyzed. A coupled thermodynamic/kinetic treatment is proposed for the mass transport within and around the weld pool. The modeling indicates that hydrogen accumulates in the weld pool as a consequence of the thermodynamic driving forces that arise; a region of hydrogen depletion exists in cooler, surrounding regions in the heat-affected zone and beyond. Coupling with a hydrogen diffusion-controlled bubble growth model is used to simulate bubble growth in the melt and, thus, to make predictions of the hydrogen concentration barrier needed for pore formation. The effects of surface tension of liquid metal and the radius of preexisting microbubble size on the barrier are discussed. The work provides insights into the mechanism of porosity formation in titanium alloys.

Sensor Fusion to Estimate the Depth and Width of the Weld Bead in Real Time in GMAW Processes

PubMed Central

Sampaio, Renato Coral; Vargas, José A. R.

2018-01-01

The arc welding process is widely used in industry but its automatic control is limited by the difficulty in measuring the weld bead geometry and closing the control loop on the arc, which has adverse environmental conditions. To address this problem, this work proposes a system to capture the welding variables and send stimuli to the Gas Metal Arc Welding (GMAW) conventional process with a constant voltage power source, which allows weld bead geometry estimation with an open-loop control. Dynamic models of depth and width estimators of the weld bead are implemented based on the fusion of thermographic data, welding current and welding voltage in a multilayer perceptron neural network. The estimators were trained and validated off-line with data from a novel algorithm developed to extract the features of the infrared image, a laser profilometer was implemented to measure the bead dimensions and an image processing algorithm that measures depth by making a longitudinal cut in the weld bead. These estimators are optimized for embedded devices and real-time processing and were implemented on a Field-Programmable Gate Array (FPGA) device. Experiments to collect data, train and validate the estimators are presented and discussed. The results show that the proposed method is useful in industrial and research environments. PMID:29570698

Sensor Fusion to Estimate the Depth and Width of the Weld Bead in Real Time in GMAW Processes.

PubMed

Bestard, Guillermo Alvarez; Sampaio, Renato Coral; Vargas, José A R; Alfaro, Sadek C Absi

2018-03-23

The arc welding process is widely used in industry but its automatic control is limited by the difficulty in measuring the weld bead geometry and closing the control loop on the arc, which has adverse environmental conditions. To address this problem, this work proposes a system to capture the welding variables and send stimuli to the Gas Metal Arc Welding (GMAW) conventional process with a constant voltage power source, which allows weld bead geometry estimation with an open-loop control. Dynamic models of depth and width estimators of the weld bead are implemented based on the fusion of thermographic data, welding current and welding voltage in a multilayer perceptron neural network. The estimators were trained and validated off-line with data from a novel algorithm developed to extract the features of the infrared image, a laser profilometer was implemented to measure the bead dimensions and an image processing algorithm that measures depth by making a longitudinal cut in the weld bead. These estimators are optimized for embedded devices and real-time processing and were implemented on a Field-Programmable Gate Array (FPGA) device. Experiments to collect data, train and validate the estimators are presented and discussed. The results show that the proposed method is useful in industrial and research environments.

A novel ultrasonic NDE for shrink fit welded structures using interface waves.

PubMed

Lee, Jaesun; Park, Junpil; Cho, Younho

2016-05-01

Reactor vessel inspection is a critical part of safety maintenance in a nuclear power plant. The inspection of shrink fit welded structures in a reactor nozzle can be a challenging task due to the complicated geometry. Nozzle inspection using pseudo interface waves allows us to inspect the nozzle from outside of the nuclear reactor. In this study, layered concentric pipes were manufactured with perfect shrink fit conditions using stainless steel 316. The displacement distributions were calculated with boundary conditions for a shrink fit welded structure. A multi-transducer guided wave phased array system was employed to monitor the welding quality of the nozzle end at a distance from a fixed position. The complicated geometry of a shrink fit welded structure can be overcome by using the pseudo interface waves in identifying the location and size of defects. The experimental results demonstrate the feasibility of detecting weld delamination and defects. Copyright © 2016 Elsevier B.V. All rights reserved.

Effect of Forced Convection Heat Transfer on Weld Pools.

DTIC Science & Technology

1986-01-01

Cooling Curves for GTAW Welds Superimposed on CCT Diagram ............. 26 11 - Photomacrographs Showing Weld Macrostructure (TS Plane...decomposition kinetics. Superposition of the weld metal cooling rates measured in this study on the CCT diagram shows that the time for nucleation and growth...m - TABLE 2 - TRANSFORMATION AND COOLING TIMES FROM CCT DIAGRAM *II I I. I I I Cooling Rate I Transformation I Time to Cool tL-I- I Heat Input I

Associations of welding and manganese exposure with Parkinson disease

PubMed Central

Borenstein, Amy R.; Nelson, Lorene M.

2012-01-01

Objective: To examine associations of welding and manganese exposure with Parkinson disease (PD) using meta-analyses of data from cohort, case-control, and mortality studies. Methods: Epidemiologic studies related to welding or manganese exposure and PD were identified in a PubMed search, article references, published reviews, and abstracts. Inclusion criteria were 1) cohort, case-control, or mortality study with relative risk (RR), odds ratio (OR), or mortality OR (MOR) and 95 confidence intervals (95% CI); 2) RR, OR, and MOR matched or adjusted for age and sex; 3) valid study design and analysis. When participants of a study were a subgroup of those in a larger study, only results of the larger study were included to assure independence of datasets. Pooled RR/OR estimates and 95% CIs were obtained using random effects models; heterogeneity of study effects were evaluated using the Q statistic and I2 index in fixed effect models. Results: Thirteen studies met inclusion criteria for the welding meta-analysis and 3 studies for the manganese exposure meta-analysis. The pooled RR for the association between welding and PD for all study designs was 0.86 (95% CI 0.80–0.92), with absence of between-study heterogeneity (I2 = 0.0). Effect measures for cohort, case-control, and mortality studies were similar (0.91, 0.82, 0.87). For the association between manganese exposure and PD, the pooled OR was 0.76 (95% CI 0.41–1.42). Conclusions: Welding and manganese exposure are not associated with increased PD risk. Possible explanations for the inverse association between welding and PD include confounding by smoking, healthy worker effect, and hormesis. PMID:22965675

The Measurement and Monitoring of Resistance Spot Welds Using Infrared Thermography

NASA Astrophysics Data System (ADS)

Brown, Bruce; Bangs, Edmund

1986-03-01

The ability to monitor the spot welding process and provide a real time inspection is of interest to the automotive, aircraft, and aircraft turbine industries. A series of experiments was performed using the infrared radiometer during the welding operation when welding coated and uncoated automotive gage steels. It has been determined that the isotherm radiated at the electrode/base material surface contains apometric information that can be used in the detection of the weld nugget and its quality. Weld nugget measurement and tensile shear tests results show good correlation between isotherm geometry, weld joint strength, and weld nugget size.

Microstructural Evolution in Friction Stir Welding of Ti-6Al-4V

NASA Technical Reports Server (NTRS)

Rubisoff, H.; Querin, J.; Magee, D.; Schneider, J.

2008-01-01

Friction stir welding (FSW) is a thermo-mechanical process that utilizes a nonconsumable rotating pin tool to consolidate a weld joint. In the conventional FSW process, the pin tool is responsible for generating both the heat required to soften the material and the forces necessary to deform and combine the weld seam. As such, the geometry of the pin tool is important to the quality of the weld and the process parameters required to produce the weld. Because the geometry of the pin tool is limitless, a reduced set of pin tools was formed to systematically study their effect on the weldment with respect to mechanical properties and resultant microstructure. In this study 0deg, 15deg, 30deg, 45deg, and 60deg tapered, microwave sintered, tungsten carbide (WC) pin tools were used to FSW Ti-6Al-4V. Transverse sections of the weld were used to test for mechanical properties and to document the microstructure using optical microscopy. X-ray diffraction (XRD) was also used to characterize the microstructure in the welds. FSW results for the 45deg and 60deg pin tools are reported in this paper.

Laser-TIG Welding of Titanium Alloys

NASA Astrophysics Data System (ADS)

Turichin, G.; Tsibulsky, I.; Somonov, V.; Kuznetsov, M.; Akhmetov, A.

2016-08-01

The article presents the results of investigation the technological opportunity of laser-TIG welding of titanium alloys. The experimental stand for implementation of process with the capability to feed a filler wire was made. The research of the nature of transfer the filler wire into the welding pool has been demonstrated. The influence of distance between the electrode and the surface of the welded plates on the stability of the arc was shown. The relationship between welding velocity, the position of focal plane of the laser beam and the stability of penetration of plates was determined.

Problems of Pore Formation in Welded Joints of Titanium Alloys

NASA Astrophysics Data System (ADS)

Murav'ev, V. I.

2005-07-01

Special features of formation of the connection zone in front of the front of molten pool and changes in the macro- and microstructure of the weld metal are considered for conditions of fusion welding of titanium alloys on an example of pseudo-α-titanium alloy VT20.Ways for forming macrotexture on the surface of joined preforms are determined with the aim of obtaining weld metal with structure and properties close to those of the base metal.

Study on the special vision sensor for detecting position error in robot precise TIG welding of some key part of rocket engine

NASA Astrophysics Data System (ADS)

Zhang, Wenzeng; Chen, Nian; Wang, Bin; Cao, Yipeng

2005-01-01

Rocket engine is a hard-core part of aerospace transportation and thrusting system, whose research and development is very important in national defense, aviation and aerospace. A novel vision sensor is developed, which can be used for error detecting in arc length control and seam tracking in precise pulse TIG welding of the extending part of the rocket engine jet tube. The vision sensor has many advantages, such as imaging with high quality, compactness and multiple functions. The optics design, mechanism design and circuit design of the vision sensor have been described in detail. Utilizing the mirror imaging of Tungsten electrode in the weld pool, a novel method is proposed to detect the arc length and seam tracking error of Tungsten electrode to the center line of joint seam from a single weld image. A calculating model of the method is proposed according to the relation of the Tungsten electrode, weld pool, the mirror of Tungsten electrode in weld pool and joint seam. The new methodologies are given to detect the arc length and seam tracking error. Through analyzing the results of the experiments, a system error modifying method based on a linear function is developed to improve the detecting precise of arc length and seam tracking error. Experimental results show that the final precision of the system reaches 0.1 mm in detecting the arc length and the seam tracking error of Tungsten electrode to the center line of joint seam.

Longitudinal Weld Land Buckling in Compression-Loaded Orthogrid Cylinders

NASA Technical Reports Server (NTRS)

Thornburgh, Robert P.; Hilburger, Mark W.

2010-01-01

Large stiffened cylinders used in launch vehicles (LV), such as the Space Shuttle External Tank, are manufactured by welding multiple curved panel sections into complete cylinders. The effects of the axial weld lands between the panel sections on the buckling load were studied, along with the interaction between the acreage stiffener arrangement and the weld land geometry. This document contains the results of the studies.

Effect of adding powder on joint properties of laser penetration welding for dual phase steel and aluminum alloy

NASA Astrophysics Data System (ADS)

Zhou, D. W.; Liu, J. S.; Lu, Y. Z.; Xu, S. H.

2017-09-01

The experiments of laser penetration welding for dual phase steel and aluminum alloy were carried out, and the effect of adding Mn or Si powder on mechanical properties and microstructure of the weld was investigated. Some defects, such as spatter, inclusion, cracks and softening in heat affected zone (HAZ), can be avoided in welding joints, and the increased penetration depth is obtained by adding Mn or Si powder. The average tensile-shear strength of Si-added joint is 3.84% higher than that of Mn-added joint, and the strength of both joints exceeds that of no-added joint. In the case of adding Mn powder, small amount of liquid Al is mixed into steel molten pool, and the Al content increases in both sides of the weld, which leads to the increased weld width in aluminum molten pool. Thus, transverse area increases in jointing steel to aluminum, which is significant for the improved tensile-shear strength of joints. As far as adding Si powder is concerned, it is not the case, the enhancement of the joint properties benefits from improvement of metallurgical reaction.

Contribution For Arc Temperature Affected By Current Increment Ratio At Peak Current In Pulsed Arc

NASA Astrophysics Data System (ADS)

Kano, Ryota; Mitubori, Hironori; Iwao, Toru

2015-11-01

Tungsten Inert Gas (TIG) Welding is one of the high quality welding. However, parameters of the pulsed arc welding are many and complicated. if the welding parameters are not appropriate, the welding pool shape becomes wide and shallow.the convection of driving force contributes to the welding pool shape. However, in the case of changing current waveform as the pulse high frequency TIG welding, the arc temperature does not follow the change of the current. Other result of the calculation, in particular, the arc temperature at the reaching time of peak current is based on these considerations. Thus, the accurate measurement of the temperature at the time is required. Therefore, the objective of this research is the elucidation of contribution for arc temperature affected by current increment ratio at peak current in pulsed arc. It should obtain a detail knowledge of the welding model in pulsed arc. The temperature in the case of increment of the peak current from the base current is measured by using spectroscopy. As a result, when the arc current increases from 100 A to 150 A at 120 ms, the transient response of the temperature didn't occur during increasing current. Thus, during the current rise, it has been verified by measuring. Therefore, the contribution for arc temperature affected by current increment ratio at peak current in pulsed arc was elucidated in order to obtain more knowledge of welding model of pulsed arc.

Plasma effect on weld pool surface reconstruction by shape-from-polarization analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coniglio, N.; Mathieu, A., E-mail: alexandre.mathieu@u-bourgogne.fr; Aubreton, O.

2014-03-31

The polarimetric state of the thermal radiations emitted by the weld metal contains geometric information about the emitting surface. Even though the analysed thermal radiation has a wavelength corresponding to a blind spectral window of the arc plasma, the physical presence of the arc plasma itself interferes with the rays radiated by the weld pool surface before attaining the polarimeter, thus modifying the geometric information transported by the ray. In the present work, the effect of the arc plasma-surrounding zone on the polarimetric state and propagation direction of the radiated ray is analyzed. The interaction with the arc plasma zonemore » induces a drop in ray intensity and a refraction of ray optical path.« less

Initial Parameter Estimation for Inverse Thermal Analysis of Ti-6Al-4V Deep Penetration Welds

DTIC Science & Technology

2014-05-16

theory, for the case of deep-penetration welding, is simulation of the coupling of keyhole formation, melting, fluid flow in the weld melt pool and...isothermal boundaires, e.g., TTB and TM. A specific procedure for interpolation, however, has not been considered. For the present study, the close ...Clarendon Press, Oxford, 2nd ed, 374, 1959. 19. R. Rai, J.W. Elmer, T.A. Palmer, T. DebRoy, Heat Transfer and Fluid Flow During Keyhole Mode Laser Welding

Self-Reacting Friction Stir Welding for Aluminum Complex Curvature Applications

NASA Technical Reports Server (NTRS)

Brown, Randy J.; Martin, W.; Schneider, J.; Hartley, P. J.; Russell, Carolyn; Lawless, Kirby; Jones, Chip

2003-01-01

This viewgraph representation provides an overview of sucessful research conducted by Lockheed Martin and NASA to develop an advanced self-reacting friction stir technology for complex curvature aluminum alloys. The research included weld process development for 0.320 inch Al 2219, sucessful transfer from the 'lab' scale to the production scale tool and weld quality exceeding strenght goals. This process will enable development and implementation of large scale complex geometry hardware fabrication. Topics covered include: weld process development, weld process transfer, and intermediate hardware fabrication.

A Study on Tooling and Its Effect on Heat Generation and Mechanical Properties of Welded Joints in Friction Stir Welding

NASA Astrophysics Data System (ADS)

Tikader, Sujoy; Biswas, Pankaj; Puri, Asit Baran

2018-04-01

Friction stir welding (FSW) has been the most attracting solid state welding process as it serves numerous advantages like good mechanical, metallurgical properties etc. Non weldable aluminium alloys like 5XXX, 7XXX series can be simply joined by this process. In this present study a mathematical model has been developed and experiments were successfully performed to evaluate mechanical properties of FSW on similar aluminium alloys i.e. AA1100 for different process parameters and mainly two kind of tool geometry (straight cylindrical and conical or cylindrical tapered shaped pin with flat shoulder). Tensile strength and micro hardness for different process parameters are reported of the welded plate sample. It was noticed that in FSW of similar alloy with tool made of SS-310 tool steel, friction is the major contributor for the heat generation. It was seen that tool geometry, tool rotational speed, plunging force by the tool and traverse speed have significant effect on tensile strength and hardness of friction stir welded joints.

Fine-tuned Remote Laser Welding of Aluminum to Copper with Local Beam Oscillation

NASA Astrophysics Data System (ADS)

Fetzer, Florian; Jarwitz, Michael; Stritt, Peter; Weber, Rudolf; Graf, Thomas

Local beam oscillation in remote laser welding of aluminum to copper was investigated. Sheets of 1 mm thickness were welded in overlap configuration with aluminum as top material. The laser beam was scanned in a sinusoidal mode perpendicular to the direction of feed and the influence of the oscillation parameters frequency and amplitude on the weld geometry was investigated. Scanning frequencies up to 1 kHz and oscillation amplitudes in the range from 0.25 mm to 1 mm were examined. Throughout the experiments the laser power and the feed rate were kept constant. A decrease of welding depth with amplitude and frequency is found. The scanning amplitude had a strong influence and allowed coarse setting of the welding depth into the lower material, while the frequency allowed fine tuning in the order of 10% of the obtained depth. The oscillation parameters were found to act differently on the aluminum sheet compared to copper sheet regarding the amount of fused material. It is possible to influence the geometry of the fused zones separately for both sheets. Therefore the average composition in the weld can be set with high precision via the oscillation parameters. A setting of the generated intermetallics in the weld zone is possible without adjustment of laser power and feed rate.

Friction Stir Welding of Magnesium Alloy Type AZ 31

NASA Astrophysics Data System (ADS)

Kupec, Tomáš; Behúlová, Mária; Turňa, Milan; Sahul, Miroslav

The paper deals with welding of Mg alloy of the type AZ 31 by Friction Stir Welding technology (FSW). The FSW technology is at present predominantly used for welding light metals and alloys, as aluminium, magnesium and their alloys. Experimental part consists of performing the simulation and fabrication of welded joints on a new-installed welding equipment available at the Welding Research Institute — Industrial Institute of SR Bratislava. Welding tools made of tool steel type H 13 were used for welding experiments. Geometry of welding tools was designed on the base of literature knowledge. Suitable welding parameters and conditions were determined using numerical simulation. Main emphasis was laid upon the tool revolutions, welding speed and tool bevel angle. The effect of welding parameters on the quality of welded joints was assessed. Assessment of welded joints was carried out by radiography, light microscopy, hardness measurement and EDX microanalysis. Static tensile test was employed for mechanical testing.

Interactions between pool geometry and hydraulics

USGS Publications Warehouse

Thompson, Douglas M.; Nelson, Jonathan M.; Wohl, Ellen E.

1998-01-01

An experimental and computational research approach was used to determine interactions between pool geometry and hydraulics. A 20-m-long, 1.8-m-wide flume was used to investigate the effect of four different geometric aspects of pool shape on flow velocity. Plywood sections were used to systematically alter constriction width, pool depth, pool length, and pool exit-slope gradient, each at two separate levels. Using the resulting 16 unique geometries with measured pool velocities in four-way factorial analyses produced an empirical assessment of the role of the four geometric aspects on the pool flow patterns and hence the stability of the pool. To complement the conclusions of these analyses, a two-dimensional computational flow model was used to investigate the relationships between pool geometry and flow patterns over a wider range of conditions. Both experimental and computational results show that constriction and depth effects dominate in the jet section of the pool and that pool length exhibits an increasing effect within the recirculating-eddy system. The pool exit slope appears to force flow reattachment. Pool length controls recirculating-eddy length and vena contracta strength. In turn, the vena contracta and recirculating eddy control velocities throughout the pool.

Welding of Thin Steel Plates by Hybrid Welding Process Combined TIG Arc with YAG Laser

NASA Astrophysics Data System (ADS)

Kim, Taewon; Suga, Yasuo; Koike, Takashi

TIG arc welding and laser welding are used widely in the world. However, these welding processes have some advantages and problems respectively. In order to improve problems and make use of advantages of the arc welding and the laser welding processes, hybrid welding process combined the TIG arc with the YAG laser was studied. Especially, the suitable welding conditions for thin steel plate welding were investigated to obtain sound weld with beautiful surface and back beads but without weld defects. As a result, it was confirmed that the shot position of the laser beam is very important to obtain sound welds in hybrid welding. Therefore, a new intelligent system to monitor the welding area using vision sensor is constructed. Furthermore, control system to shot the laser beam to a selected position in molten pool, which is formed by TIG arc, is constructed. As a result of welding experiments using these systems, it is confirmed that the hybrid welding process and the control system are effective on the stable welding of thin stainless steel plates.

A fundamental study on the structural integrity of magnesium alloys joined by friction stir welding

NASA Astrophysics Data System (ADS)

Rao, Harish Mangebettu

The goal of this research is to study the factors that influence the physical and mechanical properties of lap-shear joints produced using friction stir welding. This study focuses on understanding the effect of tool geometry and weld process parameters including the tool rotation rate, tool plunge depth and dwell time on the mechanical performance of similar magnesium alloy and dissimilar magnesium to aluminum alloy weld joints. A variety of experimental activities were conducted including tensile and fatigue testing, fracture surface and failure analysis, microstructure characterization, hardness measurements and chemical composition analysis. An investigation on the effect of weld process conditions in friction stir spot welding of magnesium to magnesium produced in a manner that had a large effective sheet thickness and smaller interfacial hook height exhibited superior weld strength. Furthermore, in fatigue testing of friction stir spot welded of magnesium to magnesium alloy, lap-shear welds produced using a triangular tool pin profile exhibited better fatigue life properties compared to lap-shear welds produced using a cylindrical tool pin profile. In friction stir spot welding of dissimilar magnesium to aluminum, formation of intermetallic compounds in the stir zone of the weld had a dominant effect on the weld strength. Lap-shear dissimilar welds with good material mixture and discontinues intermetallic compounds in the stir zone exhibited superior weld strength compared to lap-shear dissimilar welds with continuous formation of intermetallic compounds in the stir zone. The weld structural geometry like the interfacial hook, hook orientation and bond width also played a major role in influencing the weld strength of the dissimilar lap-shear friction stir spot welds. A wide scatter in fatigue test results was observed in friction stir linear welds of aluminum to magnesium alloys. Different modes of failure were observed under fatigue loading including crack propagation into the top sheet, into the bottom sheet, and interfacial separation. Investigation of the tested welds revealed that the voids in the weld nugget reduced the weld strength, resulting in lower fatigue life. A thin layer of IMCs formed along the faying surface which accelerated the fatigue failure.

Final Report: A Transport Phenomena Based Approach to Probe Evolution of Weld Macro and Microstructures and A Smart Bi-directional Model of Fusion Welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dr. Tarasankar DebRoy

In recent years, applications of numerical heat transfer and fluid flow models of fusion welding have resulted in improved understanding of both the welding processes and welded materials. They have been used to accurately calculate thermal cycles and fusion zone geometry in many cases. Here we report the following three major advancements from this project. First, we show how microstructures, grain size distribution and topology of welds of several important engineering alloys can be computed starting from better understanding of the fusion welding process through numerical heat transfer and fluid flow calculations. Second, we provide a conclusive proof that themore » reliability of numerical heat transfer and fluid flow calculations can be significantly improved by optimizing several uncertain model parameters. Third, we demonstrate how the numerical heat transfer and fluid flow models can be combined with a suitable global optimization program such as a genetic algorithm for the tailoring of weld attributes such as attaining a specified weld geometry or a weld thermal cycle. The results of the project have been published in many papers and a listing of these are included together with a list of the graduate thesis that resulted from this project. The work supported by the DOE award has resulted in several important national and international awards. A listing of these awards and the status of the graduate students are also presented in this report.« less

Effects of conventional welding and laser welding on the tensile strength, ultimate tensile strength and surface characteristics of two cobalt-chromium alloys: a comparative study.

PubMed

Madhan Kumar, Seenivasan; Sethumadhava, Jayesh Raghavendra; Anand Kumar, Vaidyanathan; Manita, Grover

2012-06-01

The purpose of this study was to evaluate the efficacy of laser welding and conventional welding on the tensile strength and ultimate tensile strength of the cobalt-chromium alloy. Samples were prepared with two commercially available cobalt-chromium alloys (Wironium plus and Diadur alloy). The samples were sectioned and the broken fragments were joined using Conventional and Laser welding techniques. The welded joints were subjected to tensile and ultimate tensile strength testing; and scanning electron microscope to evaluate the surface characteristics at the welded site. Both on laser welding as well as on conventional welding technique, Diadur alloy samples showed lesser values when tested for tensile and ultimate tensile strength when compared to Wironium alloy samples. Under the scanning electron microscope, the laser welded joints show uniform welding and continuous molt pool all over the surface with less porosity than the conventionally welded joints. Laser welding is an advantageous method of connecting or repairing cast metal prosthetic frameworks.

Sensors control gas metal arc welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siewert, T.A.; Madigan, R.B.; Quinn, T.P.

1997-04-01

The response time of a trained welder from the time a weld problem is identified to the time action is taken is about one second--especially after a long, uneventful period of welding. This is acceptable for manual welding because it is close to the time it takes for the weld pool to solidify. If human response time were any slower, manual welding would not be possible. However, human response time is too slow to respond to some weld events, such as melting of the contact tube in gas metal arc welding (GMAW), and only automated intelligent control systems can reactmore » fast enough to correct or avoid these problems. Control systems incorporate welding knowledge that enables intelligent decisions to be made about weld quality and, ultimately, to keep welding parameters in the range where only high-quality welds are produced. This article discusses the correlation of electrical signals with contact-tube wear, changes in shielding gas, changes in arc length, and other weld process data.« less

Automatic control system of high precision welding of workpieces in mechanical engineering

NASA Astrophysics Data System (ADS)

Kuznetsov, I. N.; Zvezdin, V. V.; Israfilov, I. H.; Portnov, S. M.

2014-12-01

In this paper, based on the conducted patent research, the system of laser welding control with different geometry of weld and shapes of parts is developed. The method of monitoring the position of the spot of laser radiation in relation to the curved weld is worked out; it is based on the tracking the edges of the welded parts by low-power laser radiation reflected from the surface of the parts. It allows to make the positioning of the focus of laser radiation in relation to the juncture of the welded parts automatically.

Numerical and Experimental Investigations of Humping Phenomena in Laser Micro Welding

NASA Astrophysics Data System (ADS)

Otto, Andreas; Patschger, Andreas; Seiler, Michael

The Humping effect is a phenomenon which is observed approximately since 50 years in various welding procedures and is characterized by droplets due to a pile-up of the melt pool. It occurs within a broad range of process parameters. Particularly during micro welding, humping effect is critical due to typically high feed rates. In the past, essentially two approaches (fluid-dynamic approach of streaming melt within the molten pool and the Plateau-Rayleigh instability of a liquid jet) were discussed in order to explain the occurrence of the humping effect. But none of both can fully explain all observed effects. For this reason, experimental studies in micro welding of thin metal foils were performed in order to determine the influence of process parameters on the occurrence of humping effects. The experimental observations were compared with results from numerical multi-physical simulations (incorporating beam propagation, incoupling, heat transfer, fluid dynamics etc.) to provide a deeper understanding of the causes for hump formation.

Solidification microstructures in single-crystal stainless steel melt pools

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sipf, J.B.; Boatner, L.A.; David, S.A.

1994-03-01

Development of microstructure of stationary melt pools of oriented stainless steel single crystals (70%Fe-15%Ni-15%Cr was analyzed. Stationary melt pools were formed by electron-beam and gas-tungsten-arc heating on (001), (011), and (111) oriented planes of the austenitic, fcc-alloy crystals. Characterization and analysis of resulting microstructure was carried out for each crystallographic plane and welding method. Results showed that crystallography which favors ``easy growth`` along the <100> family of directions is a controlling factor in the microstructural formation along with the melt-pool shape. The microstructure was found to depend on the melting method, since each method forms a unique melt-pool shape. Thesemore » results are used in making a three-dimensional reconstruction of the microstructure for each plane and melting method employed. This investigation also suggests avenues for future research into the microstructural properties of electron-beam welds as well as providing an experimental basis for mathematical models for the prediction of solidification microstructures.« less

Preliminary study on detection technology of the cladding weld of spent fuel storage pool

NASA Astrophysics Data System (ADS)

Qi, Pan; Cui, Hongyan; Feng, Meiming; Shao, Wenbin; Liao, Shusheng; Li, Wei

2018-04-01

As the first barrier of the Spent fuel storage pool, the steel cladding using different sizes (length×width) of 304L stainless steel with 3˜6mm thickness plate argon arc welded together which is direct contacted with boric acid water. Environmental humidity between the back of steel cladding and concrete, makes phosphate, chloride ion overflowed from the concrete that corroded on the weld zone with different mechanism. Part of the corrosion defects can penetrate leaded to leakage of boric acid water in penetration position accelerated crack propagation. In view of the above situation and combined with the actual needs of the power plant, the development of effective underwater nondestructive testing means of the weld area for periodic inspection and monitoring is necessary. A single method may lead to the missing of defects detection due to weld reinforcement unpolished. In this paper, eddy current array (ARRAY) and Alternating Current Field Measurement (ACFM) are adapted to test the limit sensitivity and resolution through by the specimens with artificial defects which make their detection abilities close to satisfy engineering requirements. The preliminary study found that Φ0.5mm through-wall hole and with 2mm length and 0.3mm width through-wall crack in the weld can be good inspected.

Effect of laser welding process on the microstructure, mechanical properties and residual stresses in Ti-5Al-2.5Sn alloy

NASA Astrophysics Data System (ADS)

Junaid, Massab; Khan, Fahd Nawaz; Rahman, Khalid; Baig, Mirza Nadeem

2017-12-01

Pulsed Nd-YAG laser was employed in bead on plate configuration for welding of 1.6 mm thick Ti-5Al-2.5Sn alloy sheet. The effect of laser processing parameters on the weld pool shape, pulse overlap, oxide formation, and microstructure were studied using scanning electron and optical microscope. It was found out that laser peak power had a significant influence on the FZ oxygen contents and grain size whereas, both peak power and heat input per unit length were important in defining the weld pool shape. Processing parameters for full penetration welds with acceptable joint properties and low oxygen contents were selected for further study in terms of residual stresses and mechanical properties. Formation of acicular α and α‧ martensite in fusion and heat affected zone, led to an increase in microhardness by about 55 HV0.2 as compared to base metal. Induced residual stresses were found to be significantly less than the yield strength resulting in plate deformation less than 1 mm. Transverse residual stresses present at different depths below the surface tend to counter effect each other resulting in tensile strength of welded specimen becoming nearly equal to that of the base metal.

The keyhole region in VPPA welds

NASA Technical Reports Server (NTRS)

Walsh, Daniel W.

1988-01-01

The morphology and properties of the Variable Polarity Plasma Arc (VPPA) weld composite zone are intimately related to the physical processes associated with the keyhole. The effects of microsegregation and transient weld stress on macrosegregation in the weld tool are examined. In addition the electrical character of straight and reverse polarity portions of the arc cycle were characterized. The results of the former study indicate that alloy 2219 is weldable because large liquid volumes are available during latter stages of weld solidification. Strains in the pool region, acting in conjunction with weld microsegregation can produce macrosegregation great enough to produce radiographic contrast effects in welds. Mechanisms of surface copper enrichment were identified. The latter study has demonstrated that increased heat is delivered to workpieces if the reverse polarity proportion of the weld cycle is increased. Current in the straight polarity portion of the welding cycle increased as the reverse cycle proportion increased. Voltage during reverse polarity segments is large.

Friction Stir Welding of Dissimilar Al/Al and Al/Non-Al Alloys: A Review

NASA Astrophysics Data System (ADS)

Wang, Xiangbin; Pan, Yi; Lados, Diana A.

2018-05-01

Friction stir welding is a solid-state welding technique that has many advantages over traditional fusion welding, and has been widely adopted in the aerospace and automotive industries. This article reviews research developments in friction stir welding of dissimilar alloys systems, including combinations of aluminum alloys with Mg alloys, Cu, and steel. Microstructural evolution, hardness, tensile and fatigue properties, residual stresses, and corrosion behavior of dissimilar welds will be reported. The effects of processing parameters such as tool rotation and traverse speeds, tool position, material position, and tool geometry on the weld quality are also presented. Discussions on future research directions in friction stir welding will also be provided in the context of existing literature and future high-integrity applications.

Deconvoluting the Friction Stir Weld Process for Optimizing Welds

NASA Technical Reports Server (NTRS)

Schneider, Judy; Nunes, Arthur C.

2008-01-01

In the friction stir welding process, the rotating surfaces of the pin and shoulder contact the weld metal and force a rotational flow within the weld metal. Heat, generated by the metal deformation as well as frictional slippage with the contact surface, softens the metal and makes it easier to deform. As in any thermo-mechanical processing of metal, the flow conditions are critical to the quality of the weld. For example, extrusion of metal from under the shoulder of an excessively hot weld may relax local pressure and result in wormhole defects. The trace of the weld joint in the wake of the weld may vary geometrically depending upon the flow streamlines around the tool with some geometry more vulnerable to loss of strength from joint contamination than others. The material flow path around the tool cannot be seen in real time during the weld. By using analytical "tools" based upon the principles of mathematics and physics, a weld model can be created to compute features that can be observed. By comparing the computed observations with actual data, the weld model can be validated or adjusted to get better agreement. Inputs to the model to predict weld structures and properties include: hot working properties ofthe metal, pin tool geometry, travel rate, rotation and plunge force. Since metals record their prior hot working history, the hot working conditions imparted during FSW can be quantified by interpreting the final microstructure. Variations in texture and grain size result from variations in the strain accommodated at a given strain rate and temperature. Microstructural data from a variety of FSWs has been correlated with prior marker studies to contribute to our understanding of the FSW process. Once this stage is reached, the weld modeling process can save significant development costs by reducing costly trial-and-error approaches to obtaining quality welds.

Effect of Shielding Gas on the Properties of AW 5083 Aluminum Alloy Laser Weld Joints

NASA Astrophysics Data System (ADS)

Vyskoč, Maroš; Sahul, Miroslav; Sahul, Martin

2018-04-01

The paper deals with the evaluation of the shielding gas influence on the properties of AW 5083 aluminum alloy weld joints produced with disk laser. Butt weld joints were produced under different shielding gas types, namely Ar, He, Ar + 5 vol.% He, Ar + 30 vol.% He and without shielding weld pool. Light and electron microscopy, computed tomography, microhardness measurements and tensile testing were used for evaluation of weld joint properties. He-shielded weld joints were the narrowest ones. On the other hand, Ar-shielded weld joints exhibited largest weld width. The choice of shielding gas had significant influence on the porosity level of welds. The lowest porosity was observed in weld joint produced in Ar with the addition of 5 vol.% He shielding atmosphere (only 0.03%), while the highest level of porosity was detected in weld joint produced in pure He (0.24%). Except unshielded aluminum alloy weld joint, the lowest tensile strength was recorded in He-shielded weld joints. On the contrary, the highest average microhardness was measured in He-shielded weld joints.

Optimization of hybrid laser - TIG welding of 316LN steel using response surface methodology (RSM)

NASA Astrophysics Data System (ADS)

Ragavendran, M.; Chandrasekhar, N.; Ravikumar, R.; Saxena, Rajesh; Vasudevan, M.; Bhaduri, A. K.

2017-07-01

In the present study, the hybrid laser - TIG welding parameters for welding of 316LN austenitic stainless steel have been investigated by combining a pulsed laser beam with a TIG welding heat source at the weld pool. Laser power, pulse frequency, pulse duration, TIG current were presumed as the welding process parameters whereas weld bead width, weld cross-sectional area and depth of penetration (DOP) were considered as the process responses. Central composite design was used to complete the design matrix and welding experiments were conducted based on the design matrix. Weld bead measurements were then carried out to generate the dataset. Multiple regression models correlating the process parameters with the responses have been developed. The accuracy of the models were found to be good. Then, the desirability approach optimization technique was employed for determining the optimum process parameters to obtain the desired weld bead profile. Validation experiments were then carried out from the determined optimum process parameters. There was good agreement between the predicted and measured values.

Effect of Pulse Parameters on Weld Quality in Pulsed Gas Metal Arc Welding: A Review

NASA Astrophysics Data System (ADS)

Pal, Kamal; Pal, Surjya K.

2011-08-01

The weld quality comprises bead geometry and its microstructure, which influence the mechanical properties of the weld. The coarse-grained weld microstructure, higher heat-affected zone, and lower penetration together with higher reinforcement reduce the weld service life in continuous mode gas metal arc welding (GMAW). Pulsed GMAW (P-GMAW) is an alternative method providing a better way for overcoming these afore mentioned problems. It uses a higher peak current to allow one molten droplet per pulse, and a lower background current to maintain the arc stability. Current pulsing refines the grains in weld fusion zone with increasing depth of penetration due to arc oscillations. Optimum weld joint characteristics can be achieved by controlling the pulse parameters. The process is versatile and easily automated. This brief review illustrates the effect of pulse parameters on weld quality.

Novel Process Revolutionizes Welding Industry

NASA Technical Reports Server (NTRS)

2008-01-01

Glenn Research Center, Delphi Corporation, and the Michigan Research Institute entered into a research project to study the use of Deformation Resistance Welding (DRW) in the construction and repair of stationary structures with multiple geometries and dissimilar materials, such as those NASA might use on the Moon or Mars. Traditional welding technologies are burdened by significant business and engineering challenges, including high costs of equipment and labor, heat-affected zones, limited automation, and inconsistent quality. DRW addresses each of those issues, while drastically reducing welding, manufacturing, and maintenance costs.

Effects of Pulse Parameters on Weld Microstructure and Mechanical Properties of Extra Pulse Current Aided Laser Welded 2219 Aluminum Alloy Joints.

PubMed

Zhang, Xinge; Li, Liqun; Chen, Yanbin; Yang, Zhaojun; Chen, Yanli; Guo, Xinjian

2017-09-15

In order to expand the application range of laser welding and improve weld quality, an extra pulse current was used to aid laser-welded 2219 aluminum alloy, and the effects of pulse current parameters on the weld microstructure and mechanical properties were investigated. The effect mechanisms of the pulse current interactions with the weld pool were evaluated. The results indicated that the coarse dendritic structure in the weld zone changed to a fine equiaxed structure using an extra pulse current, and the pulse parameters, including medium peak current, relatively high pulse frequency, and low pulse duty ratio benefited to improving the weld structure. The effect mechanisms of the pulse current were mainly ascribed to the magnetic pinch effect, thermal effect, and electromigration effect caused by the pulse current. The effect of the pulse parameters on the mechanical properties of welded joints were consistent with that of the weld microstructure. The tensile strength and elongation of the optimal pulse current-aided laser-welded joint increased by 16.4% and 105%, respectively, compared with autogenous laser welding.

Effects of Pulse Parameters on Weld Microstructure and Mechanical Properties of Extra Pulse Current Aided Laser Welded 2219 Aluminum Alloy Joints

PubMed Central

Zhang, Xinge; Li, Liqun; Chen, Yanbin; Yang, Zhaojun; Chen, Yanli; Guo, Xinjian

2017-01-01

In order to expand the application range of laser welding and improve weld quality, an extra pulse current was used to aid laser-welded 2219 aluminum alloy, and the effects of pulse current parameters on the weld microstructure and mechanical properties were investigated. The effect mechanisms of the pulse current interactions with the weld pool were evaluated. The results indicated that the coarse dendritic structure in the weld zone changed to a fine equiaxed structure using an extra pulse current, and the pulse parameters, including medium peak current, relatively high pulse frequency, and low pulse duty ratio benefited to improving the weld structure. The effect mechanisms of the pulse current were mainly ascribed to the magnetic pinch effect, thermal effect, and electromigration effect caused by the pulse current. The effect of the pulse parameters on the mechanical properties of welded joints were consistent with that of the weld microstructure. The tensile strength and elongation of the optimal pulse current-aided laser-welded joint increased by 16.4% and 105%, respectively, compared with autogenous laser welding. PMID:28914825

Effect of Multipass TIG and Activated TIG Welding Process on the Thermo-Mechanical Behavior of 316LN Stainless Steel Weld Joints

NASA Astrophysics Data System (ADS)

Ganesh, K. C.; Balasubramanian, K. R.; Vasudevan, M.; Vasantharaja, P.; Chandrasekhar, N.

2016-04-01

The primary objective of this work was to develop a finite element model to predict the thermo-mechanical behavior of an activated tungsten inert gas (ATIG)-welded joint. The ATIG-welded joint was fabricated using 10 mm thickness of 316LN stainless steel plates in a single pass. To distinguish the merits of ATIG welding process, it was compared with manual multipass tungsten inert gas (MPTIG)-welded joint. The ATIG-welded joint was fabricated with square butt edge configuration using an activating flux developed in-house. The MPTIG-welded joint was fabricated in thirteen passes with V-groove edge configuration. The finite element model was developed to predict the transient temperature, residual stress, and distortion of the welded joints. Also, microhardness, impact toughness, tensile strength, ferrite measurement, and microstructure were characterized. Since most of the recent publications of ATIG-welded joint was focused on the molten weld pool dynamics, this research work gives an insight on the thermo-mechanical behavior of ATIG-welded joint over MPTIG-welded joint.

Sensing the gas metal arc welding process

NASA Technical Reports Server (NTRS)

Carlson, N. M.; Johnson, J. A.; Smartt, H. B.; Watkins, A. D.; Larsen, E. D.; Taylor, P. L.; Waddoups, M. A.

1994-01-01

Control of gas metal arc welding (GMAW) requires real-time sensing of the process. Three sensing techniques for GMAW are being developed at the Idaho National Engineering Laboratory (INEL). These are (1) noncontacting ultrasonic sensing using a laser/EMAT (electromagnetic acoustic transducer) to detect defects in the solidified weld on a pass-by-pass basis, (2) integrated optical sensing using a CCD camera and a laser stripe to obtain cooling rate and weld bead geometry information, and (3) monitoring fluctuations in digitized welding voltage data to detect the mode of metal droplet transfer and assure that the desired mass input is achieved.

Sensing the gas metal arc welding process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carlson, N.M.; Johnson, J.A.; Smartt, H.B.

1992-01-01

Control of gas metal arc welding (GMAW) requires real-time sensing of the process. Three sensing techniques for GMAW are being developed at the Idaho National Engineering Laboratory (INEL). These are (1) noncontacting ultrasonic sensing using a laser/EMAT (electromagnetic acoustic transducer) to detect defects in the solidified weld on a pass-bypass basis, (2) integrated optical sensing using a CCD camera and a laser stripe to obtain cooling rate and weld bead geometry information, and (3) monitoring fluctuations in digitized welding voltage data to detect the mode of metal droplet transfer and assure that the desired mass input is achieved.

Sensing the gas metal arc welding process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carlson, N.M.; Johnson, J.A.; Smartt, H.B.

1992-10-01

Control of gas metal arc welding (GMAW) requires real-time sensing of the process. Three sensing techniques for GMAW are being developed at the Idaho National Engineering Laboratory (INEL). These are (1) noncontacting ultrasonic sensing using a laser/EMAT (electromagnetic acoustic transducer) to detect defects in the solidified weld on a pass-bypass basis, (2) integrated optical sensing using a CCD camera and a laser stripe to obtain cooling rate and weld bead geometry information, and (3) monitoring fluctuations in digitized welding voltage data to detect the mode of metal droplet transfer and assure that the desired mass input is achieved.

Novel low-cost vision-sensing technology with controllable of exposal time for welding

NASA Astrophysics Data System (ADS)

Zhang, Wenzeng; Wang, Bin; Chen, Nian; Cao, Yipeng

2005-02-01

In the process of robot Welding, position of welding seam and welding pool shape is detected by CCD camera for quality control and seam tracking in real-time. It is difficult to always get a clear welding image in some welding methods, such as TIG welding. A novel idea that the exposal time of CCD camera is automatically controlled by arc voltage or arc luminance is proposed to get clear welding image. A set of special device and circuits are added to a common industrial CCD camera in order to flexibly control the CCD to start or close exposal by control of the internal clearing signal of the accumulated charge. Two special vision sensors according to the idea are developed. Their exposal grabbing can be triggered respectively by the arc voltage and the variety of the arc luminance. Two prototypes have been designed and manufactured. Experiments show that they can stably grab clear welding images at appointed moment, which is a basic for the feedback control of automatic welding.

Friction Stir Weld Tools

NASA Technical Reports Server (NTRS)

Carter, Robert W. (Inventor); Payton, Lewis N. (Inventor)

2007-01-01

A friction stir weld tool sleeve is supported by an underlying support pin. The pin material is preferably selected for toughness and fracture characteristics. The pin sleeve preferably has a geometry which employs the use of an interrupted thread, a plurality of flutes and/or eccentric path to provide greater flow through. Paddles have been found to assist in imparting friction and directing plastic metal during the welding process.

Friction stir weld tools

NASA Technical Reports Server (NTRS)

Carter, Robert W. (Inventor); Payton, Lewis N. (Inventor)

2007-01-01

A friction stir weld tool sleeve is supported by an underlying support pin. The pin material is preferably selected for toughness and fracture characteristics. The pin sleeve preferably has a geometry which employs the use of an interrupted thread, a plurality of flutes and/or eccentric path to provide greater flow through. Paddles have been found to assist in imparting friction and directing plastic metal during the welding process.

The technology and welding joint properties of hybrid laser-tig welding on thick plate

NASA Astrophysics Data System (ADS)

Shenghai, Zhang; Yifu, Shen; Huijuan, Qiu

2013-06-01

The technologies of autogenous laser welding and hybrid laser-TIG welding are used on thick plate of high strength lower alloy structural steel 10CrNiMnMoV in this article. The unique advantages of hybrid laser-TIG welding is summarized by comparing and analyzing the process parameters and welding joints of autogenous laser welding laser welding and hybrid laser-TIG welding. With the optimal process parameters of hybrid welding, the good welding joint without visible flaws can be obtained and its mechanical properties are tested according to industry standards. The results show that the hybrid welding technology has certain advantages and possibility in welding thick plates. It can reduce the demands of laser power, and it is significant for lowering the aspect ratio of weld during hybrid welding, so the gas in the molten pool can rise and escape easily while welding thick plates. Therefore, the pores forming tendency decreases. At the same time, hybrid welding enhances welding speed, and optimizes the energy input. The transition and grain size of the microstructure of hybrid welding joint is better and its hardness is higher than base material. Furthermore, its tensile strength and impact toughness is as good as base material. Consequently, the hybrid welding joint can meet the industry needs completely.

Investigation of Weld Pool Structure and Property Control in Pulsed Arc Welding.

DTIC Science & Technology

1981-03-04

noted, elsewhere, freezing rate in the trailing and transverse directions show similarly contrasting behavior (6 𔄁 ). The movement of the solidus and...rise to low freezing eutectics and, hence, should be kept to the lowest possible level.1 3 󈧒 Solidification Cracking in Stainless Steel Welds It has...been observed 1 5 that hot cracking in austenitic stainless steel weldments is reduced or prevented when a small amount of delta ferrite is present

Understanding heat and fluid flow in linear GTA welds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zacharia, T.; David, S.A.; Vitek, J.M.

1992-01-01

A transient heat flow and fluid flow model was used to predict the development of gas tungsten arc (GTA) weld pools in 1.5 mm thick AISI 304 SS. The welding parameters were chosen so as to correspond to an earlier experimental study which produced high-resolution surface temperature maps. The motivation of the present study was to verify the predictive capability of the computational model. Comparison of the numerical predictions and experimental observations indicate good agreement.

Understanding heat and fluid flow in linear GTA welds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zacharia, T.; David, S.A.; Vitek, J.M.

1992-12-31

A transient heat flow and fluid flow model was used to predict the development of gas tungsten arc (GTA) weld pools in 1.5 mm thick AISI 304 SS. The welding parameters were chosen so as to correspond to an earlier experimental study which produced high-resolution surface temperature maps. The motivation of the present study was to verify the predictive capability of the computational model. Comparison of the numerical predictions and experimental observations indicate good agreement.

Laser Overlap Welding of Zinc-coated Steel on Aluminum Alloy

NASA Astrophysics Data System (ADS)

Kashani, Hamed Tasalloti; Kah, Paul; Martikainen, Jukka

Local reinforcement of aluminum with laser welded patches of zinc-coated steel can effectively contribute to crashworthiness, durability and weight reduction of car body. However, the weld between Zn-coated steel and aluminum is commonly susceptible to defects such as spatter, cavity and crack. The vaporization of Zn is commonly known as the main source of instability in the weld pool and cavity formation, especially in a lap joint configuration. Cracks are mainly due to the brittle intermetallic compounds growing at the weld interface of aluminum and steel. This study provides a review on the main metallurgical and mechanical concerns regarding laser overlap welding of Zn-coated steel on Al-alloy and the methods used by researchers to avoid the weld defects related to the vaporization of Zn and the poor metallurgical compatibility between steel and aluminum.

Weld analysis and control system

NASA Technical Reports Server (NTRS)

Kennedy, Larry Z. (Inventor); Rodgers, Michael H. (Inventor); Powell, Bradley W. (Inventor); Burroughs, Ivan A. (Inventor); Goode, K. Wayne (Inventor)

1994-01-01

The invention is a Weld Analysis and Control System developed for active weld system control through real time weld data acquisition. Closed-loop control is based on analysis of weld system parameters and weld geometry. The system is adapted for use with automated welding apparatus having a weld controller which is capable of active electronic control of all aspects of a welding operation. Enhanced graphics and data displays are provided for post-weld analysis. The system provides parameter acquisition, including seam location which is acquired for active torch cross-seam positioning. Torch stand-off is also monitored for control. Weld bead and parent surface geometrical parameters are acquired as an indication of weld quality. These parameters include mismatch, peaking, undercut, underfill, crown height, weld width, puddle diameter, and other measurable information about the weld puddle regions, such as puddle symmetry, etc. These parameters provide a basis for active control as well as post-weld quality analysis and verification. Weld system parameters, such as voltage, current and wire feed rate, are also monitored and archived for correlation with quality parameters.

Parameters optimization of laser brazing in crimping butt using Taguchi and BPNN-GA

NASA Astrophysics Data System (ADS)

Rong, Youmin; Zhang, Zhen; Zhang, Guojun; Yue, Chen; Gu, Yafei; Huang, Yu; Wang, Chunming; Shao, Xinyu

2015-04-01

The laser brazing (LB) is widely used in the automotive industry due to the advantages of high speed, small heat affected zone, high quality of welding seam, and low heat input. Welding parameters play a significant role in determining the bead geometry and hence quality of the weld joint. This paper addresses the optimization of the seam shape in LB process with welding crimping butt of 0.8 mm thickness using back propagation neural network (BPNN) and genetic algorithm (GA). A 3-factor, 5-level welding experiment is conducted by Taguchi L25 orthogonal array through the statistical design method. Then, the input parameters are considered here including welding speed, wire speed rate, and gap with 5 levels. The output results are efficient connection length of left side and right side, top width (WT) and bottom width (WB) of the weld bead. The experiment results are embed into the BPNN network to establish relationship between the input and output variables. The predicted results of the BPNN are fed to GA algorithm that optimizes the process parameters subjected to the objectives. Then, the effects of welding speed (WS), wire feed rate (WF), and gap (GAP) on the sum values of bead geometry is discussed. Eventually, the confirmation experiments are carried out to demonstrate the optimal values were effective and reliable. On the whole, the proposed hybrid method, BPNN-GA, can be used to guide the actual work and improve the efficiency and stability of LB process.

Analysis of ripple formation in single crystal spot welds

NASA Technical Reports Server (NTRS)

Rappaz, M.; Corrigan, D.; Boatner, L. A.

1997-01-01

Stationary spot welds have been made at the (001) surface of Fe-l5%Ni-15%Cr single crystals using a Gas Tungsten Arc (GTA). On the top surface of the spot welds, very regular and concentric ripples were observed after solidification by differential interference color microscopy. Their height (typically 1--5 micrometers and spacing, typically approximately 60 micrometers) decreased with the radius of the pool. These ripples were successfully accounted for in terms of capillary-wave theory using the fundamental mode frequency f(sub 0) given by the first zero of the zero-order Bessel function. The spacing d between the ripples was then equated to v(sub s)/f(sub 0), where v(sub s) is the solidification rate. From the measured ripple spacing, the velocity of the pool was deduced as a function of the radius, and this velocity was in good agreement with the results of a heat-flow simulation.

Experimental and theoretical characterization of deep penetration welding threshold induced by 1-μm laser

NASA Astrophysics Data System (ADS)

Zou, J. L.; He, Y.; Wu, S. K.; Huang, T.; Xiao, R. S.

2015-12-01

The deep penetration-welding threshold (DPWT) is the critical value that describes the welding mode transition from the thermal conduction to the deep penetration. The objective of this research is to clarify the DPWT induced by the lasers with wavelength of 1 μm (1-μm laser), based on experimental observation and theoretical analysis. The experimental results indicated that the DPWT was the ratio between laser power and laser spot diameter (P/d) rather than laser power density (P/S). The evaporation threshold was smaller than the DPWT, while the jump threshold of the evaporated mass flux in the molten pool surface was consistent with the DPWT. Based on the force balance between the evaporation recoil pressure and the surface tension pressure at the gas-liquid interface of the molten pool as well as the temperature field, we developed a self-focusing model, which further confirmed the experimental results.

Investigation of molten pool oscillation during GMAW-P process based on a 3D model

NASA Astrophysics Data System (ADS)

Wang, L. L.; Lu, F. G.; Cui, H. C.; Tang, X. H.

2014-11-01

In order to better reveal the oscillation mechanism of the pulsed gas metal arc welding (GMAW-P) process due to an alternately varied welding current, arc plasma and molten pool oscillation were simulated through a self-consistent three-dimensional model. Based on an experimental analysis of the dynamic variation of the arc plasma and molten pool captured by a high-speed camera, the model was validated by comparison of the measured and predicted results. The calculated results showed that arc pressure was the key factor causing the molten pool to oscillate. The variation in arc size and temperature from peak time to base time resulted in a great difference in the heat input and arc pressure acting on the molten pool. The surface deformation of the molten pool due to the varying degrees of arc pressure induced alternate displacement and backflow in the molten metal. The periodic iteration of deeper and shallower surface deformation, drain and backflow of molten metal caused the molten pool to oscillate at a certain frequency. In this condition, the arc pressure at the peak time is more than six times higher than that at the base time, and the maximum surface depression is 1.4 mm and 0.6 mm, respectively, for peak time and base time.

The Mechanism of Ultrasonic Vibration on Grain Refining and Degassing in GTA Spot Welding of Copper Joints.

PubMed

Al-Ezzi, Salih; Quan, Gaofeng; Elrayah, Adil

2018-05-07

This paper examines the effect of ultrasonic vibration (USV) on grain size and interrupted porosity in Gas Tungsten Arc (GTA) spot-welded copper. Grain size was refined by perpendicularly attaching a transducer to the welded sheet and applying USV to the weld pool for a short time (0, 2, 4, and 6 s) in addition improvements to the degassing process. Results illustrate a significant reduction of grain size (57%). Notably, USV provided interaction between reformations (fragmentation) and provided nucleation points (detaching particles from the fusion line) for grains in the nugget zone and the elimination of porosity in the nugget zone. The GTA spot welding process, in conjunction with USV, demonstrated an improvement in the corrosion potential for a copper spot-welded joint in comparison to the joint welded without assistance of USV. Finally, welding of copper by GTA spot welding in conjunction with ultrasound for 2 s presented significant mechanical properties.

The Mechanism of Ultrasonic Vibration on Grain Refining and Degassing in GTA Spot Welding of Copper Joints

PubMed Central

Quan, Gaofeng

2018-01-01

This paper examines the effect of ultrasonic vibration (USV) on grain size and interrupted porosity in Gas Tungsten Arc (GTA) spot-welded copper. Grain size was refined by perpendicularly attaching a transducer to the welded sheet and applying USV to the weld pool for a short time (0, 2, 4, and 6 s) in addition improvements to the degassing process. Results illustrate a significant reduction of grain size (57%). Notably, USV provided interaction between reformations (fragmentation) and provided nucleation points (detaching particles from the fusion line) for grains in the nugget zone and the elimination of porosity in the nugget zone. The GTA spot welding process, in conjunction with USV, demonstrated an improvement in the corrosion potential for a copper spot-welded joint in comparison to the joint welded without assistance of USV. Finally, welding of copper by GTA spot welding in conjunction with ultrasound for 2 s presented significant mechanical properties. PMID:29735894

Influence of FSW pin tool geometry on plastic flow of AA7075 T651

NASA Astrophysics Data System (ADS)

Lertora, Enrico; Mandolfino, Chiara; Gambaro, Carla

2016-10-01

In this paper the behaviour of the plastic flow during Friction Stir Welding of AA7075 T651 plates, realized with different shaped tools, has been investigated. In particular, the influence of the shape of three tools was studied using copper strips placed along the welds. After welding, radiography and metallurgical analysis were used in order to investigate the marker movement and its fragmentation.

Gravitational effects on the development of weld-pool and solidification microstructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boatner, L.A.; David, S.A.; Workman, G.

1994-09-01

This research effort has as its objective the development of a quantitative understanding of the effects of both low- and high-g environments on the solidification microstructures and morphologies that are produced in alloy single crystals during a variety of melting and solidification processes. The overall goal of the effort is to delineate the nature of the roles played by natural convection, surface-tension-driven convection, and mass transport effects due to interactions associated with various heating methods that are used to form melt pools in practical, commercially important alloy systems. The experimental and theoretical investigations comprising this effort encompass the study ofmore » configurations in which stationary heat sources are employed as well as melt pools formed by moving heat sources like those frequently used in fusion-welding processes.« less

Non Destructive Analysis of Fsw Welds using Ultrasonic Signal Analysis

NASA Astrophysics Data System (ADS)

Pavan Kumar, T.; Prabhakar Reddy, P.

2017-08-01

Friction Stir Welding is an evolving metal joining technique and is mostly used in joining materials which cannot be easily joined by other available welding techniques. It is a technique which can be used for welding dissimilar materials also. The strength of the weld joint is determined by the way in which these material are mixing with each other, since we are not using any filler material for the welding process the intermixing has a significant importance. The complication with the friction stir welding process is that there are many process parameters which effect this intermixing process such as tool geometry, rotating speed of the tool, transverse speed etc., In this study an attempt is made to compare the material flow and weld quality of various weldments by changing the parameters. Ultrasonic signal Analysis is used to characterize the microstructure of the weldments. use of ultrasonic waves is a non destructive, accurate and fast way of characterization of microstructure. In this method the relationship between the ultrasonic measured parameters and microstructures are evaluated using background echo and backscattered signal process techniques. The ultrasonic velocity and attenuation measurements are dependent on the elastic modulus and any change in the microstructure is reflected in the ultrasonic velocity. An insight into material flow is essential to determine the quality of the weld. Hence an attempt is made in this study to know the relationship between tool geometry and the pattern of material flow and resulting weld quality the experiments are conducted to weld dissimilar aluminum alloys and the weldments are characterized using and ultra Sonic signal processing. Characterization is also done using Scanning Electron Microscopy. It is observed that there is a good correlation between the ultrasonic signal processing results and Scanning Electron Microscopy on the observed precipitates. Tensile tests and hardness tests are conducted on the weldments and compared for determining the weld quality.

T-joints of Ti alloys with hybrid laser-MIG welding: macro-graphic and micro-hardness analyses

NASA Astrophysics Data System (ADS)

Spina, R.; Sorgente, D.; Palumbo, G.; Scintilla, L. D.; Brandizzi, M.; Satriano, A. A.; Tricarico, L.

2012-03-01

Titanium alloys are characterized by high mechanical properties and elevated corrosion resistance. The combination of laser welding with MIG/GMAW has proven to improve beneficial effects of both processes (keyhole, gap-bridging ability) while limiting their drawbacks (high thermal gradient, low mechanical resistance) In this paper, the hybrid Laser-GMAW welding of Ti-6Al-4V 3-mm thick sheets is investigated using a specific designed trailing shield. The joint geometry was the double fillet welded T-joint. Bead morphologies, microstructures and mechanical properties (micro-hardness) of welds were evaluated and compared to those achieved for the base metals.

Friction pull plug welding: dual chamfered plate hole

NASA Technical Reports Server (NTRS)

Coletta, Edmond R. (Inventor); Cantrell, Mark A. (Inventor)

2001-01-01

Friction Pull Plug Welding (FPPW) is a solid state repair process for defects up to one inch in length, only requiring single sided tooling (OSL) for usage on flight hardware. Early attempts with FPPW followed the matching plug/plate geometry precedence of the successful Friction Push Plug Welding program, however no defect free welds were achieved due to substantial plug necking and plug rotational stalling. The dual chamfered hole has eliminated plug rotational stalling, both upon initial plug/plate contact and during welding. Also, the necking of the heated plug metal under a tensile heating/forging load has been eliminated through the usage of the dual chamfered plate hole.

Hot-crack test for aluminium alloys welds using TIG process

NASA Astrophysics Data System (ADS)

Niel, A.; Deschaux-Beaume, F.; Bordreuil, C.; Fras, G.

2010-06-01

Hot cracking is a critical defect frequently observed during welding of aluminium alloys. In order to better understand the interaction between cracking phenomenon, process parameters, mechanical factors and microstructures resulting from solidification after welding, an original hot-cracking test during welding is developed. According to in-situ observations and post mortem analyses, hot cracking mechanisms are investigated, taking into account the interaction between microstructural parameters, depending on the thermal cycles, and mechanical parameters, depending on geometry and clamping conditions of the samples and on the thermal field on the sample. Finally, a process map indicating the limit between cracking and non-cracking zones according to welding parameters is presented.

Heavy-section welding with very high power laser beams: the challenge

NASA Astrophysics Data System (ADS)

Goussain, Jean-Claude; Becker, Ahim; Chehaibou, A.; Leca, P.

1997-08-01

The 45 kW CO2 laser system of Institut de Soudure was used to evaluate and explore the possibilities offered by the high power laser beams for welding different materials in various thickness and in different welding positions. Stainless steels, low carbon steels, aluminum and titanium alloys were studied. Butt joints in 10 to 35 mm thick plates were achieved and evaluated by radiographic, metallurgical and mechanical tests. Gaps and alignment tolerances were determined with and without filler wire in order to obtain acceptable welds concerning the weld geometry, the aspect on front and end root sides. The main problem raised by heavy section welding concerns weld porosity in the weld which increases drastically with the thickness of the weld. Indications are given on their origin and the way to proceed in order to better control them. Lastly some large parts, recently welded on the system, are presented and discussed before drawing some conclusions on the prospects of very high power laser welding.

Mechanical properties of friction stir welded butt joint of steel/aluminium alloys: effect of tool geometry

NASA Astrophysics Data System (ADS)

Syafiq, W. M.; Afendi, M.; Daud, R.; Mazlee, M. N.; Majid, M. S. Abdul; Lee, Y. S.

2017-10-01

This paper described the mechanical properties from hardness testing and tensile testing of Friction Stir Welded (FSW) materials. In this project, two materials of aluminium and steel are welded using conventional milling machine and tool designed with different profile and shoulder size. During welding the temperature along the weld line is collected using thermocouples. Threaded pins was found to produce stronger joints than cylindrical pins. 20 mm diameter shoulder tool welded a slightly stronger joint than 18 mm diameter one, as well as softer nugget zone due to higher heat input. Threaded pins also contributed to higher weld temperature than cylindrical pins due to increase in pin contact surface. Generally, higher temperatures were recorded in aluminium side due to pin offset away from steel.

Initial Study of Friction Pull Plug Welding

NASA Technical Reports Server (NTRS)

Rich, Brian S.

1999-01-01

Pull plug friction welding is a new process being developed to conveniently eliminate defects from welded plate tank structures. The general idea is to drill a hole of precise, optimized dimensions and weld a plug into it, filling the hole perfectly. A conically-shaped plug is rotated at high angular velocity as it is brought into contact with the plate material in the hole. As the plug is pulled into the hole, friction rapidly raises the temperature to the point at which the plate material flows plastically. After a brief heating phase, the plug rotation is terminated. The plug is then pulled upon with a forging force, solidly welding the plug into the hole in the plate. Three aspects of this process were addressed in this study. The transient temperature distribution was analyzed based on slightly idealized boundary conditions for different plug geometries. Variations in hole geometry and ram speed were considered, and a program was created to calculate volumes of displaced material and empty space, as well as many other relevant dimensions. The relation between the axially applied forging force and the actual forging pressure between the plate and plug surfaces was determined for various configurations.

Optimization of laser welding thin-gage galvanized steel via response surface methodology

NASA Astrophysics Data System (ADS)

Zhao, Yangyang; Zhang, Yansong; Hu, Wei; Lai, Xinmin

2012-09-01

The increasing demand of light weight and durability makes thin-gage galvanized steels (<0.6 mm) attractive for future automotive applications. Laser welding, well known for its deep penetration, high speed and small heat affected zone, provides a potential solution for welding thin-gage galvanized steels in automotive industry. In this study, the effect of the laser welding parameters (i.e. laser power, welding speed, gap and focal position) on the weld bead geometry (i.e. weld depth, weld width and surface concave) of 0.4 mm-thick galvanized SAE1004 steel in a lap joint configuration has been investigated by experiments. The process windows of the concerned process parameters were therefore determined. Then, response surface methodology (RSM) was used to develop models to predict the relationship between the processing parameters and the laser weld bead profile and identify the correct and optimal combination of the laser welding input variables to obtain superior weld joint. Under the optimal welding parameters, defect-free weld were produced, and the average aspect ratio increased about 30%, from 0.62 to 0.83.

Hybrid laser arc welding: State-of-art review

NASA Astrophysics Data System (ADS)

Acherjee, Bappa

2018-02-01

Hybrid laser arc welding simultaneously utilizes the arc welding and the laser welding, in a common interaction zone. The synergic effects of laser beam and eclectic arc in the same weld pool results in an increase of welding speed and penetration depth along with the enhancement of gap bridging capability and process stability. This paper presents the current status of this hybrid technique in terms of research, developments and applications. Effort is made to present a comprehensive technical know-how about this process through a systematic review of research articles, industrial catalogues, technical notes, etc. In the introductory part of the review, an overview of the hybrid laser arc welding is presented, including operation principle, process requirements, historical developments, benefits and drawbacks of the process. This is followed by a detailed discussion on control parameters those govern the performance of hybrid laser arc welding process. Thereafter, a report of improvements of performance and weld qualities achieved by using hybrid welding process is presented based on review of several research papers. The succeeding sections furnish the examples of industrial applications and the concluding remarks.

Welding of 316L Austenitic Stainless Steel with Activated Tungsten Inert Gas Process

NASA Astrophysics Data System (ADS)

Ahmadi, E.; Ebrahimi, A. R.

2015-02-01

The use of activating flux in TIG welding process is one of the most notable techniques which are developed recently. This technique, known as A-TIG welding, increases the penetration depth and improves the productivity of the TIG welding. In the present study, four oxide fluxes (SiO2, TiO2, Cr2O3, and CaO) were used to investigate the effect of activating flux on the depth/width ratio and mechanical property of 316L austenitic stainless steel. The effect of coating density of activating flux on the weld pool shape and oxygen content in the weld after the welding process was studied systematically. Experimental results indicated that the maximum depth/width ratio of stainless steel activated TIG weld was obtained when the coating density was 2.6, 1.3, 2, and 7.8 mg/cm2 for SiO2, TiO2, Cr2O3, and CaO, respectively. The certain range of oxygen content dissolved in the weld, led to a significant increase in the penetration capability of TIG welds. TIG welding with active fluxes can increase the delta-ferrite content and improves the mechanical strength of the welded joint.

Influence of Joint Configuration on the Strength of Laser Welded Presshardened Steel

NASA Astrophysics Data System (ADS)

Kügler, H.; Mittelstädt, C.; Vollertsen, F.

Presshardened steel is used in nowadays automotive production. Due to its high strength, sheet thicknesses can be reduced which results in decreasing weight of car body components. However, because of microstructure softening and coating agglomerations in the seam, welding is still a challenge. In this paper laser beam welding of 22MnB5 with varying energy input per irradiated area is presented. It is found that increasing energy input per seam length reduces tensile strength. Using a small spot size of 200 μm, tensile strength of 1434 N/mm2 can be reached in bead on plate welds. In lap welds tensile strength is limited because of coating particles agglomerating at the melt pool border line. However, the resulting strength is higher when using several small weld seams than using one seam with the same total seam width. With three weld seams, each 0.5mm in width, tensile strength of 911N/mm2 is reached in lap welding.

Coupling of Laser with Plasma Arc to Facilitate Hybrid Welding of Metallic Materials: A Review

NASA Astrophysics Data System (ADS)

Zhiyong, Li; Srivatsan, T. S.; Yan, LI; Wenzhao, Zhang

2013-02-01

Hybrid laser arc welding combines the advantages of laser welding and arc welding. Ever since its origination in the late 1970s, this technique has gained gradual attention and progressive use due to a combination of high welding speed, better formation of weld bead, gap tolerance, and increased penetration coupled with less distortion. In hybrid laser arc welding, one of the reasons for the observed improvement is an interaction or coupling effect between the plasma arc, laser beam, droplet transfer, and the weld pool. Few researchers have made an attempt to study different aspects of the process to facilitate a better understanding. It is difficult to get a thorough understanding of the process if only certain information in a certain field is provided. In this article, an attempt to analyze the coupling effect of the process was carried out based on a careful review of the research work that has been done which provides useful information from a different prospective.

Study of Mechanical Properties and Characterization of Pipe Steel welded by Hybrid (Friction Stir Weld + Root Arc Weld) Approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lim, Yong Chae; Sanderson, Samuel; Mahoney, Murray

Friction stir welding (FSW) has recently attracted attention as an alternative construction process for gas/oil transportation applications due to advantages compared to fusion welding techniques. A significant advantage is the ability of FSW to weld the entire or nearly the entire wall thickness in a single pass, while fusion welding requires multiple passes. However, when FSW is applied to a pipe or tube geometry, an internal back support anvil is required to resist the plunging forces exerted during FSW. Unfortunately, it may not be convenient or economical to use internal backing support due to limited access for some applications. Tomore » overcome this issue, ExxonMobil recently developed a new concept, combining root arc welding and FSW. That is, a root arc weld is made prior to FSW that supports the normal loads associated with FSW. In the present work, mechanical properties of a FSW + root arc welded pipe steel are reported including microstructure and microhardness.« less

Analysis of the correlation between plasma plume and keyhole behavior in laser metal welding for the modeling of the keyhole geometry

NASA Astrophysics Data System (ADS)

Tenner, F.; Brock, C.; Klämpfl, F.; Schmidt, M.

2015-01-01

The process of laser metal welding is widely used in industry. Nevertheless, there is still a lack of complete process understanding and control. For analyzing the process we used two high-speed cameras. Therefore, we could image the plasma plume (which is directly accessible by a camera) and the keyhole (where most of the process instabilities occur) during laser welding isochronously. Applying different image processing steps we were able to find a correlation between those two process characteristics. Additionally we imaged the plasma plume from two directions and were able to calculate a volume with respect to the vaporized material the plasma plume carries. Due to these correlations we are able to conclude the keyhole stability from imaging the plasma plume and vice versa. We used the found correlation between the keyhole behavior and the plasma plume to explain the effect of changing laser power and feed rate on the keyhole geometry. Furthermore, we tried to outline the phenomena which have the biggest effect on the keyhole geometry during changes of feed rate and laser power.

Multiscale characterization and mechanical modeling of an Al-Zn-Mg electron beam weld

NASA Astrophysics Data System (ADS)

Puydt, Quentin; Flouriot, Sylvain; Ringeval, Sylvain; Parry, Guillaume; De Geuser, Frédéric; Deschamps, Alexis

Welding of precipitation hardening alloys results in multi-scale microstructural heterogeneities, from the hardening nano-scale precipitates to the micron-scale solidification structures and to the component geometry. This heterogeneity results in a complex mechanical response, with gradients in strength, stress triaxiality and damage initiation sites.

Intelligent Modeling Combining Adaptive Neuro Fuzzy Inference System and Genetic Algorithm for Optimizing Welding Process Parameters

NASA Astrophysics Data System (ADS)

Gowtham, K. N.; Vasudevan, M.; Maduraimuthu, V.; Jayakumar, T.

2011-04-01

Modified 9Cr-1Mo ferritic steel is used as a structural material for steam generator components of power plants. Generally, tungsten inert gas (TIG) welding is preferred for welding of these steels in which the depth of penetration achievable during autogenous welding is limited. Therefore, activated flux TIG (A-TIG) welding, a novel welding technique, has been developed in-house to increase the depth of penetration. In modified 9Cr-1Mo steel joints produced by the A-TIG welding process, weld bead width, depth of penetration, and heat-affected zone (HAZ) width play an important role in determining the mechanical properties as well as the performance of the weld joints during service. To obtain the desired weld bead geometry and HAZ width, it becomes important to set the welding process parameters. In this work, adaptative neuro fuzzy inference system is used to develop independent models correlating the welding process parameters like current, voltage, and torch speed with weld bead shape parameters like depth of penetration, bead width, and HAZ width. Then a genetic algorithm is employed to determine the optimum A-TIG welding process parameters to obtain the desired weld bead shape parameters and HAZ width.

Experimental and numerical studies on the issues in laser welding of light-weight alloys in a zero-gap lap joint configuration

NASA Astrophysics Data System (ADS)

Harooni, Masoud

It is advantageous for the transportation industry to use lightweight components in the structure in order to save mass and reduce CO2 emissions. One of the lightest structural metals, magnesium, fulfills the need for mass reduction within the automotive industry. Many of the body structure components in the automotive industry are assembled using joining processes such as fusion welding. Furthermore, laser welding offers a low heat impact, high process rate, joining method which is becoming increasingly popular as the cost for laser systems continues to decrease. However, there is a limited body of work investigating the laser welding of magnesium and therefore, in the current study, different techniques and methods for laser welding of magnesium alloys are numerically and experimentally studied in order to optimize process parameters to achieve high quality welds. A feasibility study was designed in order to study the effect of various laser welding process parameters (such as laser power levels and welding speeds) on weld quality. Three regression models were developed to find the best fit model that relates process parameters to the shear load of the weld. Furthermore, to understand the effect of laser welding parameters on temperature distribution in laser welding of AZ31B magnesium alloy, a numerical model was developed. A rotary Gaussian volumetric body heat source was applied in this study to obtain the temperature history during the laser welding process. Cross-sectional views of the weld beads, temperature history recorded by thermocouples, and temperature history recorded by infrared camera were used to validate the numerical model. In order to study the real-time dynamic behavior of the molten pool and the keyhole during the welding process, a high speed charge-coupled device (CCD) assisted with a green laser as an illumination source was used. In order to observe the presence of pores, prior studies destructively evaluated the weld bead however; in the current study a non-destructive evaluation method based on spectroscopy is proposed to detect the presence of pores in the lap joint of laser welded AZ31B magnesium alloy. The electron temperature that is calculated by the Boltzmann plot method is correlated to the presence of pores in the weld bead. A separate series of experiments was performed to evaluate the effect of an oxide coating layer on the dynamic behavior of the molten pool in the laser welding of an AZ31B magnesium alloy in a zero-gap lap joint configuration. A high speed CCD camera assisted with a green laser as an illumination source was selected to record the weld pool dynamics. Another technique used in this study was two-pass laser welding process to join AZ31B magnesium sheet in a zero-gap, lap-shear configuration. Two groups of samples including one pass laser welding (OPLW) and two pass laser welding (TPLW) were studied. In the two pass laser welding procedure, the first pass is performed by a defocused laser beam on the top of the two overlapped sheets in order to preheat the faying surface prior to laser welding, while the second pass is applied to melt and eventually weld the samples. Tensile and microhardness tests were used to measure the mechanical properties of the laser welded samples. A spectrometer was also used in real-time to correlate pore formation with calculated electron temperature using the Boltzmann plot method. The results of calculated electron temperature confirmed the previous results in earlier chapter. Magnesium and aluminum are two alloys which are used in different industries mainly due to their light weight. The main use of these two alloys is in automotive industry. Since different parts of the automobiles can be manufactured with each of these two alloys, it is essential to evaluate the joining feasibility of dissimilar metals such as aluminum to magnesium. A 4 kW fiber laser is used to join AZ31B magnesium alloy to AA 6014 using an overlap joint configuration. Two different methods including focused beam laser welding (FBLW) and defocused beam laser welding (DBLW) are performed. The cross-sections of the welds were studied using an optical microscope, scanning electron microscope (SEM) as well as energy-dispersive X-ray spectroscopy (EDS) to reveal the quality of the obtained dissimilar welds. The mechanical properties of the welds were studied using a tensile test and microhardness testing machines. The results show that the defocused laser welding process could help to achieve a better quality of weld. (Abstract shortened by UMI.)

SLAM examination of solar cells and solar cell welds. [Scanning Laser Acoustic Microscope

NASA Technical Reports Server (NTRS)

Stella, P. M.; Vorres, C. L.; Yuhas, D. E.

1981-01-01

The scanning laser acoustic microscope (SLAM) has been evaluated for non-destructive examination of solar cells and interconnector bonds. Using this technique, it is possible to view through materials in order to reveal regions of discontinuity such as microcracks and voids. Of particular interest is the ability to evaluate, in a unique manner, the bonds produced by parallel gap welding. It is possible to not only determine the area and geometry of the bond between the tab and cell, but also to reveal any microcracks incurred during the welding. By correlating the SLAM results with conventional techniques of weld evaluation a more confident weld parameter optimization can be obtained.

Microstructural Characterization of Friction Stir Welded Aluminum-Steel Joints

NASA Astrophysics Data System (ADS)

Patterson, Erin E.; Hovanski, Yuri; Field, David P.

2016-06-01

This work focuses on the microstructural characterization of aluminum to steel friction stir welded joints. Lap weld configuration coupled with scribe technology used for the weld tool have produced joints of adequate quality, despite the significant differences in hardness and melting temperatures of the alloys. Common to friction stir processes, especially those of dissimilar alloys, are microstructural gradients including grain size, crystallographic texture, and precipitation of intermetallic compounds. Because of the significant influence that intermetallic compound formation has on mechanical and ballistic behavior, the characterization of the specific intermetallic phases and the degree to which they are formed in the weld microstructure is critical to predicting weld performance. This study used electron backscatter diffraction, energy dispersive spectroscopy, scanning electron microscopy, and Vickers micro-hardness indentation to explore and characterize the microstructures of lap friction stir welds between an applique 6061-T6 aluminum armor plate alloy and a RHA homogeneous armor plate steel alloy. Macroscopic defects such as micro-cracks were observed in the cross-sectional samples, and binary intermetallic compound layers were found to exist at the aluminum-steel interfaces of the steel particles stirred into the aluminum weld matrix and across the interfaces of the weld joints. Energy dispersive spectroscopy chemical analysis identified the intermetallic layer as monoclinic Al3Fe. Dramatic decreases in grain size in the thermo-mechanically affected zones and weld zones that evidenced grain refinement through plastic deformation and recrystallization. Crystallographic grain orientation and texture were examined using electron backscatter diffraction. Striated regions in the orientations of the aluminum alloy were determined to be the result of the severe deformation induced by the complex weld tool geometry. Many of the textures observed in the weld zone and thermo-mechanically affected zones exhibited shear texture components; however, there were many textures that deviated from ideal simple shear. Factors affecting the microstructure which are characteristic of the friction stir welding process, such as post-recrystallization deformation and complex deformation induced by tool geometry were discussed as causes for deviation from simple shear textures.

Optimization of hybrid laser arc welding of 42CrMo steel to suppress pore formation

NASA Astrophysics Data System (ADS)

Zhang, Yan; Chen, Genyu; Mao, Shuai; Zhou, Cong; Chen, Fei

2017-06-01

The hybrid laser arc welding (HLAW) of 42CrMo quenched and tempered steel was conducted. The effect of the processing parameters, such as the relative positions of the laser and the arc, the shielding gas flow rate, the defocusing distance, the laser power, the wire feed rate and the welding speed, on the pore formation was analyzed, the morphological characteristics of the pores were analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that the majority of the pores were invasive. The pores formed at the leading a laser (LA) welding process were fewer than those at the leading a arc (AL) welding process. Increasing the shielding gas flow rate could also facilitate the reduction of pores. The laser power and the welding speed were two key process parameters to reduce the pores. The flow of the molten pool, the weld cooling rate and the pore escaping rate as a result of different parameters could all affect pore formation. An ideal pore-free weld was obtained for the optimal welding process parameters.

The porosity formation mechanism in the laser-MIG hybrid welded joint of Invar alloy

NASA Astrophysics Data System (ADS)

Zhan, Xiaohong; Gao, Qiyu; Gu, Cheng; Sun, Weihua; Chen, Jicheng; Wei, Yanhong

2017-10-01

The porosity formation mechanism in the laser-metal inter gas (MIG) multi-layer hybrid welded (HW) joint of 19.05 mm thick Invar alloy is investigated. The microstructure characteristics and energy dispersive spectroscopy (EDS) are analyzed. The phase identification was conducted by the X-ray diffractometer (XRD). Experimental results show that the generation of porosity is caused by the relatively low laser power in the root pass and low current in the cover pass. It is also indicated that the microstructures of the welded joints are mainly observed to be columnar crystal and equiaxial crystal, which are closely related to the porosity formation. The EDS results show that oxygen content is significantly high in the inner wall of the porosity. The XRD results indicate that the BM and the WB of laser-MIG HW all are composed of Fe0.64Ni0.36 and γ-(Fe,Ni). When the weld pool is cooled quickly, [NiO] [FeO] and [MnO] are formed that react on C to generate CO/CO2 gases. The porosity of laser-MIG HW for Invar alloy is oxygen pore. The root source of metallurgy porosity formation is that the dissolved gases are hard to escape sufficiently and thus exist in the weld pool. Furthermore, 99.99% pure Argon is recommended as protective gas in the laser-MIG HW of Invar alloy.

Experimental and Simulative Investigation of Laser Transmission Welding under Consideration of Scattering

NASA Astrophysics Data System (ADS)

Devrient, M.; Da, X.; Frick, T.; Schmidt, M.

Laser transmission welding is a well known joining technology for thermoplastics. Because of the needs of lightweight, cost effective and green production thermoplastics are usually filled with glass fibers. These lead to higher absorption and more scattering within the upper joining partner with a negative influence on the welding process. Here an experimental method for the characterization of the scattering behavior of semi crystalline thermoplastics filled with short glass fibers and a finite element model of the welding process capable to consider scattering as well as an analytical model are introduced. The experimental data is used for the numerical and analytical investigation of laser transmission welding under consideration of scattering. The scattering effects of several thermoplastics onto the calculated temperature fields as well as weld seam geometries are quantified.

Investigation of Laser Welding of Ti Alloys for Cognitive Process Parameters Selection.

PubMed

Caiazzo, Fabrizia; Caggiano, Alessandra

2018-04-20

Laser welding of titanium alloys is attracting increasing interest as an alternative to traditional joining techniques for industrial applications, with particular reference to the aerospace sector, where welded assemblies allow for the reduction of the buy-to-fly ratio, compared to other traditional mechanical joining techniques. In this research work, an investigation on laser welding of Ti⁻6Al⁻4V alloy plates is carried out through an experimental testing campaign, under different process conditions, in order to perform a characterization of the produced weld bead geometry, with the final aim of developing a cognitive methodology able to support decision-making about the selection of the suitable laser welding process parameters. The methodology is based on the employment of artificial neural networks able to identify correlations between the laser welding process parameters, with particular reference to the laser power, welding speed and defocusing distance, and the weld bead geometric features, on the basis of the collected experimental data.

Investigation of Laser Welding of Ti Alloys for Cognitive Process Parameters Selection

PubMed Central

2018-01-01

Laser welding of titanium alloys is attracting increasing interest as an alternative to traditional joining techniques for industrial applications, with particular reference to the aerospace sector, where welded assemblies allow for the reduction of the buy-to-fly ratio, compared to other traditional mechanical joining techniques. In this research work, an investigation on laser welding of Ti–6Al–4V alloy plates is carried out through an experimental testing campaign, under different process conditions, in order to perform a characterization of the produced weld bead geometry, with the final aim of developing a cognitive methodology able to support decision-making about the selection of the suitable laser welding process parameters. The methodology is based on the employment of artificial neural networks able to identify correlations between the laser welding process parameters, with particular reference to the laser power, welding speed and defocusing distance, and the weld bead geometric features, on the basis of the collected experimental data. PMID:29677114

Studying heat-affected zone deformations of electric arc welding

NASA Astrophysics Data System (ADS)

Suleimanov, R. I.; Zainagalina, L. Z.; Khabibullin, M. Ya; Zaripova, L. M.; Kovalev, N. O.

2018-03-01

The paper studies the influence of the most common defects in permanent electric arc welds made during the welding butt joints in infield oil pipelines, onto the strength characteristics of the welded pipe material around the heat-affected zone. A specimen of a butt weld with an obvious defect was used as a subject of the study. The changes in the geometric parameters of the weld were measured with the standard means; Rockwell hardness in the heat-affected zone was determined in certain areas with justification for the weld process modes. The cause of softening was found to be an increased width of the hot spot on the one side of the weld, where an enlarged crystalline structure appears as a result of the pipe material recrystallization under the influence of heat. Changes in the geometry of the thermal action area are determined by accumulation of molten filler on the one side of the weld when the welding rate is decreased. Some recommendations are given to prevent destruction of the welded structures and appearance of emergencies in infield oil pipelines.

Grain Refinement of AZ31 Magnesium Alloy Weldments by AC Pulsing Technique

NASA Astrophysics Data System (ADS)

Kishore Babu, N.; Cross, C. E.

2012-11-01

The current study has investigated the influence of alternating current pulsing on the structure and mechanical properties of AZ31 magnesium alloy gas tungsten arc (GTA) weldments. Autogenous full penetration bead-on-plate GTA welds were made under a variety of conditions including variable polarity (VP), variable polarity mixed (VPM), alternating current (AC), and alternating current pulsing (ACPC). AC pulsing resulted in significant refinement of weld metal when compared with the unpulsed conditions. AC pulsing leads to relatively finer and more equiaxed grain structure in GTA welds. In contrast, VP, VPM, and AC welding resulted in predominantly columnar grain structures. The reason for this grain refinement may be attributed to the periodic variations in temperature gradient and solidification rate associated with pulsing as well as weld pool oscillation observed in the ACPC welds. The observed grain refinement was shown to result in an appreciable increase in fusion zone hardness, tensile strength, and ductility.

Analysis of ripple formation in single crystal spot welds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rappaz, M.; Corrigan, D.; Boatner, L.A.

1997-10-01

Stationary spot welds have been made at the (001) surface of Fe-l5%Ni-15%Cr single crystals using a Gas Tungsten Arc (GTA). On the top surface of the spot welds, very regular and concentric ripples were observed after solidification by differential interference color microscopy. Their height (typically 1--5 {micro}m) and spacing (typically {approximately} 60 {micro}m) decreased with the radius of the pool. These ripples were successfully accounted for in terms of capillary-wave theory using the fundamental mode frequency f{sub 0} given by the first zero of the zero-order Bessel function. The spacing d between the ripples was then equated to v{sub s}/f{submore » 0}, where v{sub s} is the solidification rate. From the measured ripple spacing, the velocity of the pool was deduced as a function of the radius, and this velocity was in good agreement with the results of a heat-flow simulation.« less

Hot-wire Laser Welding of Deep and Wide Gaps

NASA Astrophysics Data System (ADS)

Näsström, J.; Frostevarg, J.; Silver, T.

Heavy section Gas Metal Arc Welding (GMAW) usually requires special edge preparation and several passes. One alternative for increased performance is Laser Arc Hybrid Welding (LAHW). For very thick sheets however, imperfections like root drops or solidification cracks can occur. In this study, other techniques are also studied, including multi-pass filling of deep gaps with wire deposition. A laser is then used to melt the filler and base material. The hot- and cold wire laser welding processes are highly sensitive to wire-laser positioning, where controlled melting of the wire is essential. Apart from a comprehensive literature survey, preliminary experiments were also performed in order to find a novel method variant that can successfully fill deep and wide gaps. The method applied uses a defocused laser that generates the melt pool. A resistance heated wire is fed into the melt pool front in a leading position. This is similar to additive manufacturing techniques such as laser direct metal deposition with wire. A layer height of several millimeters can be achieved and rather low laser power can be chosen. The preliminary experiments were observed using high speed imaging and briefly evaluated by visual examination of the resulting beads. Using a defocused laser beam turned out to have two major advantages; 1. It adds heat to the melt pool in a manner that properly fuses the bottom and walls of the base material. 2. It counteracts difficulties due to an irregularly oscillating filler wire. These early results show that this can be a promising technique for joining thick steels with wide gaps.

Process control of laser conduction welding by thermal imaging measurement with a color camera.

PubMed

Bardin, Fabrice; Morgan, Stephen; Williams, Stewart; McBride, Roy; Moore, Andrew J; Jones, Julian D C; Hand, Duncan P

2005-11-10

Conduction welding offers an alternative to keyhole welding. Compared with keyhole welding, it is an intrinsically stable process because vaporization phenomena are minimal. However, as with keyhole welding, an on-line process-monitoring system is advantageous for quality assurance to maintain the required penetration depth, which in conduction welding is more sensitive to changes in heat sinking. The maximum penetration is obtained when the surface temperature is just below the boiling point, and so we normally wish to maintain the temperature at this level. We describe a two-color optical system that we have developed for real-time temperature profile measurement of the conduction weld pool. The key feature of the system is the use of a complementary metal-oxide semiconductor standard color camera leading to a simplified low-cost optical setup. We present and discuss the real-time temperature measurement and control performance of the system when a defocused beam from a high power Nd:YAG laser is used on 5 mm thick stainless steel workpieces.

Investigation of the Microstructure of Laser-Arc Hybrid Welded Boron Steel

NASA Astrophysics Data System (ADS)

Son, Seungwoo; Lee, Young Ho; Choi, Dong-Won; Cho, Kuk-Rae; Shin, Seung Man; Lee, Youngseog; Kang, Seong-Hoon; Lee, Zonghoon

2018-05-01

The microstructure of boron steel for automotive driving shaft manufacturing after laser-arc hybrid welding was investigated. Laser-arc hybrid welding technology was applied to 3-mm-thick plates of boron steel, ST35MnB. The temperature distribution of the welding pool was analyzed using the finite element method, and the microstructure of the welded boron steel was characterized using optical microscopy and scanning and transmission electron microscopies. The microstructure of the weld joint was classified into the fusion zone, the heat-affected zone (HAZ), and the base material. At the fusion zone, the bainite grains exist in the martensite matrix and show directionality because of heat input from the welding. The HAZ is composed of smaller grains, and the hardness of the HAZ is greater than that of the fusion zone. We discuss that the measured grain size and the hardness of the HAZ originate from undissolved precipitates that retard the grain growth of austenite.

The Effect of Ultrasonic Peening on Service Life of the Butt-Welded High-Temperature Steel Pipes

NASA Astrophysics Data System (ADS)

Daavari, Morteza; Vanini, Seyed Ali Sadough

2015-09-01

Residual stresses introduced by manufacturing processes such as casting, forming, machining, and welding have harmful effects on the mechanical behavior of the structures. In addition to the residual stresses, weld toe stress concentration can play a determining effect. There are several methods to improve the mechanical properties such as fatigue behavior of the welded structures. In this paper, the effects of ultrasonic peening on the fatigue life of the high-temperature seamless steel pipes, used in the petrochemical environment, have been investigated. These welded pipes are fatigued due to thermal and mechanical loads caused by the cycle of cooling, heating, and internal pressure fluctuations. Residual stress measurements, weld geometry estimation, electrochemical evaluations, and metallography investigations were done as supplementary examinations. Results showed that application of ultrasonic impact treatment has led to increased fatigue life, fatigue strength, and corrosion resistance of A106-B welded steel pipes in petrochemical corrosive environment.

Microstructural characterization and hardness properties of electric resistance welding titanium joints for dental applications.

PubMed

Ceschini, Lorella; Boromei, Iuri; Morri, Alessandro; Nardi, Diego; Sighinolfi, Gianluca; Degidi, Marco

2015-06-01

The electric resistance welding procedure is used to join a titanium bar with specific implant abutments in order to produce a framework directly in the oral cavity of the patient. This investigation studied the effects of the welding process on microstructure and hardness properties of commercially pure (CP2 and CP4) Ti components. Different welding powers and cooling procedures were applied to bars and abutments, normally used to produce the framework, in order to simulate the clinical intraoral welding procedure. The analyses highlighted that the joining process did not induce appreciable changes in the geometry of the abutments. However, because of unavoidable microstructural modifications in the welded zones, the hardness decreased to values lower than those of the unwelded CP2 and CP4 Ti grades, irrespective of the welding environments and parameters. © IMechE 2015.

Vision-sensing image analysis for GTAW process control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Long, D.D.

1994-11-01

Image analysis of a gas tungsten arc welding (GTAW) process was completed using video images from a charge coupled device (CCD) camera inside a specially designed coaxial (GTAW) electrode holder. Video data was obtained from filtered and unfiltered images, with and without the GTAW arc present, showing weld joint features and locations. Data Translation image processing boards, installed in an IBM PC AT 386 compatible computer, and Media Cybernetics image processing software were used to investigate edge flange weld joint geometry for image analysis.

High-precision and high-speed laser microjoining for electronics and microsystems

NASA Astrophysics Data System (ADS)

Gillner, Arnold; Olowinsky, Alexander; Klages, Kilian; Gedicke, Jens; Sari, Fahri

2006-02-01

The joining processes in electronic device manufacturing are today still dominated by conventional joining techniques like press fitting, crimping and resistance welding. Laser beam joining techniques have been under intensive investigations and subsequently new processes for mass manufacturing and high accuracy assembling were established. With the newly developed SHADOW (R) welding technology technical aspects such as tensile strength, geometry and precision of the weld could be improved. This technology provides highest flexibility in weld geometry with a minimum welding time as well as new possibilities in using application adapted materials. Different parts and even different metals can be joined by a non-contact process. The application of a relative movement between the laser beam and the part to be joined at feed rates of up to 60 m/min produces weld seams with a length from 0.6 mm to 15.7 mm using a pulsed Nd:YAG laser with a pulse duration of up to 50 ms. Due to the low energy input, typically 1 J to 6 J, a weld width as small as 50 μm and a weld depth as small as 20 pm have been attained. This results in low distortion of the joined watch components. Within this paper this new welding process will be explained and several examples of joined components will be presented with respect to fundamentals and the sustainable implementation of the SHADOW (R) welding technique into watch manufacturing and electronic industry. For microsystem applications the laser joining technology is modified to join even silicon and glass parts without any melting based on the formation of a thermally induced oxygen bond. New fields of applications for joining different materials such as steel to brass or steel to copper for electrical interconnects will be discussed. Here the SHADOW (R) welding technique offers new possibilities for the combination of good electrical properties of copper with high mechanical stiffness of steel. The paper will give a closer look to microjoining applications especially using the SHADOW (R) welding technique. Basics of the process as well as its application on dedicated examples will be shown for small parts such as axis-wheel combinations and electrical connectors.

Development of a gas pressure bonded four-pole alternator rotor

NASA Technical Reports Server (NTRS)

Lessmann, G. G.; Bryant, W. A.

1972-01-01

Methods were developed for fabrication of a solid four pole alternator rotor by hot isostatic pressure welding. The rotor blanks welded in this program had complex geometrical mating interfaces and were of considerable bulk, being approximately 3-1/2 inches (0.089 meters) in diameter and 14 inches (0.356 meters) long. Magnetic end pieces were machined from AlSl 4340 steel, while the non-magnetic central section was of Inconel 718. Excellent welds were produced which were shown to be responsive to post weld heat treatments which substantially improved joint strength. Prior to welding the rotors, test specimens of complex geometry were welded to demonstrate that complex surfaces with intentional mechanical misfit could be readily joined using HIP welding. This preliminary work demonstrated not only that interface compliance is achieved during welding but that welding pressure is developed in these thick sections sufficient to produce sound joints. Integral weld-heat treatment cycles were developed that permitted the attainment of magnetic properties while minimizing residual stress associated with the allotropic transformation of 4340 steel.

Process Stability of Ultrasonic-Wave-Assisted Gas Metal Arc Welding

NASA Astrophysics Data System (ADS)

Fan, Chenglei; Xie, Weifeng; Yang, Chunli; Lin, Sanbao; Fan, Yangyang

2017-10-01

As a newly developed arc welding method, ultrasonic-wave-assisted arc welding successfully introduced power ultrasound into the arc and weld pool, during which the ultrasonic acts on the top of the arc in the coaxial alignment direction. The advanced process for molten metals can be realized by using an additional ultrasonic field. Compared with the conventional gas metal arc welding (GMAW), the welding arc is compressed, the droplet size is decreased, and the droplet transfer frequency is increased significantly in ultrasonic-wave-assisted GMAW (U-GMAW). However, the stability of the metal transfer has deep influence on the welding quality equally, and the ultrasonic wave effect on the stability of the metal transfer is a phenomenon that is not completely understood. In this article, the stabilities of the short-circuiting transfer process and globular transfer process are studied systematically, and the effect of ultrasonic wave on the metal transfer is analyzed further. The transfer frequency and process stability of the U-GMAW process are much higher than those of the conventional GMAW. Analytical results show that the additional ultrasonic wave is helpful for improving welding stability.

Method for welding an article and terminating the weldment within the perimeter of the article

NASA Technical Reports Server (NTRS)

Snyder, John H. (Inventor); Smashey, Russell W. (Inventor); Boerger, Eric J. (Inventor); Borne, Bruce L. (Inventor)

2000-01-01

An article is welded, as in weld repair of a defect, by positioning a weld lift-off block at a location on the surface of the article adjacent to the intended location of the end of the weldment on the surface of the article. The weld lift-off block has a wedge shape including a base contacting the surface of the article, and an upper face angled upwardly from the base from a base leading edge. A weld pool is formed on the surface of the article by directly heating the surface of the article using a heat source. The heat source is moved relative to the surface of the article and onto the upper surface of the weld lift-off block by crossing the leading edge of the wedge, without discontinuing the direct heating of the article by the heat source. The heating of the article with the heat source is discontinued only after the heat source is directly heating the upper face of the weld lift-off block, and not the article.

Evaluation Of Four Welding Arc Processes Applied To 6061 Aluminium Alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benoit, A.; Laboratoire de Genie des Materiaux et Procedes Associes; Paillard, P.

At a time when greenhouse gas emissions must be reduced, the use of the aluminium alloys is expanding, in particular in the transportation industry. In order to extend the possibilities of aluminium assembly design, new Metal Inert Gas (MIG) welding processes have been conceived. They work at lower temperatures than usual arc processes (classic MIG or Tungsten Inert Gas). This study compares four arc welding processes, applied to the 6061 aluminium alloy. These four weld processes have been studied through the metallurgical analysis of the weld beads. Metallography, micro-hardness testings, X Ray radiography have been carried out on the producedmore » weld beads. The processes are classified according to the quality of the beads like geometry of beads, size of the heat affected zone and presence of defects.« less

Study the Effect of SiO2 Based Flux on Dilution in Submerged Arc Welding

NASA Astrophysics Data System (ADS)

kumar, Aditya; Maheshwari, Sachin

2017-08-01

This paper highlights the method for prediction of dilution in submerged arc welding (SAW). The most important factors of weld bead geometry are governed by the weld dilution which controls the chemical and mechanical properties. Submerged arc welding process is used generally due to its very easy control of process variables, good penetration, high weld quality, and smooth finish. Machining parameters, with suitable weld quality can be achieved with the different composition of the flux in the weld. In the present study Si02-Al2O3-CaO flux system was used. In SiO2 based flux NiO, MnO, MgO were mixed in various proportions. The paper investigates the relationship between the process parameters like voltage, % of flux constituents and dilution with the help of Taguchi’s method. The experiments were designed according to Taguchi L9 orthogonal array, while varying the voltage at two different levels in addition to alloying elements. Then the optimal results conditions were verified by confirmatory experiments.

Towards Fast Tracking of the Keyhole Geometry

NASA Astrophysics Data System (ADS)

Brock, C.; Hohenstein, R.; Schmidt, M.

We describe a sensor principle permitting the fast online measurement of the position of the optical process emissions in deep penetration laser welding. Experiments show a strong correlation between the position of the vapour plume and the keyhole geometry, demonstrated here by varying the penetration depth of the weld. In order to achieve an absolute position measurement, the sensor was calibrated using a light source with well defined characteristics. The setup for the calibration measurements and the corresponding data evaluation methods are discussed. The precision of the calibration with a green LED is 6 μm in lateral and 55 μm in axial direction, for a working distance of 200 mm.

Implicit Geometry Meshing for the simulation of Rotary Friction Welding

NASA Astrophysics Data System (ADS)

Schmicker, D.; Persson, P.-O.; Strackeljan, J.

2014-08-01

The simulation of Rotary Friction Welding (RFW) is a challenging task, since it states a coupled problem of phenomena like large plastic deformations, heat flux, contact and friction. In particular the mesh generation and its restoration when using a Lagrangian description of motion is of significant severity. In this regard Implicit Geometry Meshing (IGM) algorithms are promising alternatives to the more conventional explicit methods. Because of the implicit description of the geometry during remeshing, the IGM procedure turns out to be highly robust and generates spatial discretizations of high quality regardless of the complexity of the flash shape and its inclusions. A model for efficient RFW simulation is presented, which is based on a Carreau fluid law, an Augmented Lagrange approach in mapping the incompressible deformations, a penalty contact approach, a fully regularized Coulomb-/fluid friction law and a hybrid time integration strategy. The implementation of the IGM algorithm using 6-node triangular finite elements is described in detail. The techniques are demonstrated on a fairly complex friction welding problem, demonstrating the performance and the potentials of the proposed method. The techniques are general and straight-forward to implement, and offer the potential of successful adoption to a wide range of other engineering problems.

Temperature and emissivity determination of liquid steel S235

NASA Astrophysics Data System (ADS)

Schöpp, H.; Sperl, A.; Kozakov, R.; Gött, G.; Uhrlandt, D.; Wilhelm, G.

2012-06-01

Temperature determination of liquid metals is difficult but a necessary tool for improving materials and processes such as arc welding in the metal-working industry. A method to determine the surface temperature of the weld pool is described. A TIG welding process and absolute calibrated optical emission spectroscopy are used. This method is combined with high-speed photography. 2D temperature profiles are obtained. The emissivity of the radiating surface has an important influence on the temperature determination. A temperature dependent emissivity for liquid steel is given for the spectral region between 650 and 850 nm.

On the hot cracking susceptibility of a semisolid aluminium 6061 weld: Application of a coupled solidification- thermomechanical model

NASA Astrophysics Data System (ADS)

Zareie Rajani, H. R.; Phillion, A. B.

2015-06-01

A coupled solidification-thermomechanical model is presented that investigates the hot tearing susceptibility of an aluminium 6061 semisolid weld. Two key phenomena are considered: excessive deformation of the semisolid weld, initiating a hot tear, and the ability of the semisolid weld to heal the hot tear by circulation of the molten metal. The model consists of two major modules: weld solidification and thermomechanical analysis. 1) By means of a multi-scale model of solidification, the microstructural evolution of the semisolid weld is simulated in 3D. The semisolid structure, which varies as a function of welding parameters, is composed of solidifying grains and a network of micro liquid channels. The weld solidification module is utilized to obtain the solidification shrinkage. The size of the micro liquid channels is used as an indicator to assess the healing ability of the semisolid weld. 2) Using the finite element method, the mechanical interaction between the weld pool and the base metal is simulated to capture the transient force field deforming the semisolid weld. Thermomechanical stresses and shrinkage stresses are both considered in the analysis; the solidification contractions are extracted from the weld solidification module and applied to the deformation simulation as boundary conditions. Such an analysis enables characterization of the potential for excessive deformation of the weld. The outputs of the model are used to study the effect of welding parameters including welding current and speed, and also welding constraint on the hot cracking susceptibility of an aluminium alloy 6061 semisolid weld.

Metal Flow in Friction Stir Welding

NASA Technical Reports Server (NTRS)

Nunes, Arthur C., Jr.

2006-01-01

The plastic deformation field in Friction Stir Welding (FSW) is compared to that in metal cutting. A shear surface around the FSW tool analogous to the metal cutting shear plane is identified and comprises the basis of the "rotating plug" flow field model and the "wiping" model of tool interaction with weld metal. Within the context of these models: The FSW shear rate is estimated to be comparable to metal cutting shear rates. The effect of tool geometry on the FSW shear surface is discussed and related to published torque measurements. Various FS W structural features are explained, including a difference in structure of bimetallic welds when alloys on the advancing and retreating sides of the weld seam are exchanged. The joining mechanism and critical parameters of the FSW process are made clear.

Detection and Sizing of Fatigue Cracks in Steel Welds with Advanced Eddy Current Techniques

NASA Astrophysics Data System (ADS)

Todorov, E. I.; Mohr, W. C.; Lozev, M. G.

2008-02-01

Butt-welded specimens were fatigued to produce cracks in the weld heat-affected zone. Advanced eddy current (AEC) techniques were used to detect and size the cracks through a coating. AEC results were compared with magnetic particle and phased-array ultrasonic techniques. Validation through destructive crack measurements was also conducted. Factors such as geometry, surface treatment, and crack tightness interfered with depth sizing. AEC inspection techniques have the potential of providing more accurate and complete sizing flaw data for manufacturing and in-service inspections.

Thermomechanically coupled conduction mode laser welding simulations using smoothed particle hydrodynamics

NASA Astrophysics Data System (ADS)

Hu, Haoyue; Eberhard, Peter

2017-10-01

Process simulations of conduction mode laser welding are performed using the meshless Lagrangian smoothed particle hydrodynamics (SPH) method. The solid phase is modeled based on the governing equations in thermoelasticity. For the liquid phase, surface tension effects are taken into account to simulate the melt flow in the weld pool, including the Marangoni force caused by a temperature-dependent surface tension gradient. A non-isothermal solid-liquid phase transition with the release or absorption of additional energy known as the latent heat of fusion is considered. The major heat transfer through conduction is modeled, whereas heat convection and radiation are neglected. The energy input from the laser beam is modeled as a Gaussian heat source acting on the initial material surface. The developed model is implemented in Pasimodo. Numerical results obtained with the model are presented for laser spot welding and seam welding of aluminum and iron. The change of process parameters like welding speed and laser power, and their effects on weld dimensions are investigated. Furthermore, simulations may be useful to obtain the threshold for deep penetration welding and to assess the overall welding quality. A scalability and performance analysis of the implemented SPH algorithm in Pasimodo is run in a shared memory environment. The analysis reveals the potential of large welding simulations on multi-core machines.

Limit load solution for electron beam welded joints with single edge weld center crack in tension

NASA Astrophysics Data System (ADS)

Lu, Wei; Shi, Yaowu; Li, Xiaoyan; Lei, Yongping

2012-05-01

Limit loads are widely studied and several limit load solutions are proposed to some typical geometry of weldments. However, there are no limit load solutions exist for the single edge crack weldments in tension (SEC(T)), which is also a typical geometry in fracture analysis. The mis-matching limit load for thick plate with SEC(T) are investigated and the special limit load solutions are proposed based on the available mis-matching limit load solutions and systematic finite element analyses. The real weld configurations are simplified as a strip, and different weld strength mis-matching ratio M, crack depth/width ratio a/ W and weld width 2H are in consideration. As a result, it is found that there exists excellent agreement between the limit load solutions and the FE results for almost all the mis-matching ration M, a/ W and ligament-to-weld width ratio ( W-a)/ H. Moreover, useful recommendations are given for evaluating the limit loads of the EBW structure with SEC(T). For the EBW joints with SEC(T), the mis-matching limit loads can be obtained assuming that the components are wholly made of base metal, when M changing from 1.6 to 0.6. When M decreasing to 0.4, the mis-matching limit loads can be obtained assuming that the components are wholly made of base metal only for large value of ( W-a)/ H. The recommendations may be useful for evaluating the limit loads of the EBW structures with SEC(T). The engineering simplifications are given for assessing the limit loads of electron beam welded structure with SEC(T).

Effects of SO/sub 2/ shielding gas additions on GTA weld shape

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heiple, C.R.; Burgardt, P.

1985-06-01

Substantial increases in GTA weld depth/width ratio resulted from small additions of sulfur dioxide (SO/sub 2/) to the torch shielding gas when welding two stainless steels. The improvement was demonstrated on both Types 304 and 21-6-9 austenitic stainless steels, but would be expected for iron-base alloys generally. The weld pool shape achieved was essentially independent of variations in both SO/sub 2/ content of the torch gas and base metal composition when SO/sub 2/ in the shielding gas was in the range of 500 to 1400 ppm. With 700 ppm SO/sub 2/ in the torch gas, less than 30 ppm sulfurmore » was added to an autogenous weld bead. For alloys where this additional sulfur can be tolerated and appropriate measures can be taken to handle the toxic SO/sub 2/, this technique offers a promising way to improve GTA weld joint penetration while suppressing variable penetration.« less

Improving Keyhole Stability by External Magnetic Field in Full Penetration Laser Welding

NASA Astrophysics Data System (ADS)

Li, Min; Xu, Jiajun; Huang, Yu; Rong, Youmin

2018-05-01

An external magnetic field was used to improve the keyhole stability in full penetration laser welding 316L steel. The increase of magnetic field strength gave rise to a shorter flying time of the spatter, a weaker size and brightness of the spatter, and a larger spreading area of vapor plume. This suggested that the dynamic behavior of the keyhole was stabilized by the external magnetic field. In addition, a stronger magnetic field could result in a more homogeneous distribution of laser energy, which increased the width of the weld zone, and the height of the bottom weld zone from 381 μm (0 mT) to 605 μm (50 mT). Dendrite and cellular crystal near the weld center disappeared, and grain size was refined. The external magnetic field was beneficial to the keyhole stability and improved the joint quality, because the weld pool was stirred by a Lorentz force resulting from the coupling effect of the magnetic field and inner thermocurrent.

A Preliminary Report on the Strength and Metallography of a Bimetallic Friction Stir Weld Joint Between AA6061 and MIL-DTL-46100E High Hardness Steel Armor

DTIC Science & Technology

2012-11-26

alloy and High Hardness steel armor (MIL- STD-46100) were successfully joined by the friction stir welding (FSW) process using a tungsten- rhenium ...tungsten- rhenium stir tool. Process parameter variation experiments, which included inductive pre-heating, tool design geometry, plunge and traverse

Numerical simulation and experimental investigation of laser dissimilar welding of carbon steel and austenitic stainless steel

NASA Astrophysics Data System (ADS)

Nekouie Esfahani, M. R.; Coupland, J.; Marimuthu, S.

2015-07-01

This study reports an experimental and numerical investigation on controlling the microstructure and brittle phase formation during laser dissimilar welding of carbon steel to austenitic stainless steel. The significance of alloying composition and cooling rate were experimentally investigated. The investigation revealed that above a certain specific point energy the material within the melt pool is well mixed and the laser beam position can be used to control the mechanical properties of the joint. The heat-affected zone within the high-carbon steel has significantly higher hardness than the weld area, which severely undermines the weld quality. A sequentially coupled thermo-metallurgical model was developed to investigate various heat-treatment methodology and subsequently control the microstructure of the HAZ. Strategies to control the composition leading to dramatic changes in hardness, microstructure and service performance of the dissimilar laser welded fusion zone are discussed.

Characterization and Optimization of Ni-WC Composite Weld Matrix Deposited by Plasma-Transferred Arc Process

NASA Astrophysics Data System (ADS)

Tahaei, Ali; Horley, Paul; Merlin, Mattia; Torres-Torres, David; Garagnani, Gian Luca; Praga, Rolando; Vázquez, Felipe J. García; Arizmendi-Morquecho, Ana

2017-03-01

This work is dedicated to optimization of carbide particle system in a weld bead deposited by PTAW technique over D2 tool steel with high chromium content. The paper reports partial melting of the original carbide grains of the Ni-based filling powder, and growing of the secondary carbide phase (Cr, Ni)_3W_3C in the form of dendrites with wide branches that enhanced mechanical properties of the weld. The optimization of bead parameters was made with design of experiment methodology complemented by a complex sample characterization including SEM, EDXS, XRD, and nanoindentation measurements. It was shown that the preheat of the substrate to a moderate temperature 523 K (250° C) establishes linear pattern of metal flow in the weld pool, resulting in the most homogeneous distribution of the primary carbides in the microstructure of weld bead.

Development of an intelligent system for cooling rate and fill control in GMAW. [Gas Metal Arc Welding (GMAW)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Einerson, C.J.; Smartt, H.B.; Johnson, J.A.

1992-01-01

A control strategy for gas metal arc welding (GMAW) is developed in which the welding system detects certain existing conditions and adjusts the process in accordance to pre-specified rules. This strategy is used to control the reinforcement and weld bead centerline cooling rate during welding. Relationships between heat and mass transfer rates to the base metal and the required electrode speed and welding speed for specific open circuit voltages are taught to a artificial neural network. Control rules are programmed into a fuzzy logic system. TRADITOINAL CONTROL OF THE GMAW PROCESS is based on the use of explicit welding proceduresmore » detailing allowable parameter ranges on a pass by pass basis for a given weld. The present work is an exploration of a completely different approach to welding control. In this work the objectives are to produce welds having desired weld bead reinforcements while maintaining the weld bead centerline cooling rate at preselected values. The need for this specific control is related to fabrication requirements for specific types of pressure vessels. The control strategy involves measuring weld joint transverse cross-sectional area ahead of the welding torch and the weld bead centerline cooling rate behind the weld pool, both by means of video (2), calculating the required process parameters necessary to obtain the needed heat and mass transfer rates (in appropriate dimensions) by means of an artificial neural network, and controlling the heat transfer rate by means of a fuzzy logic controller (3). The result is a welding machine that senses the welding conditions and responds to those conditions on the basis of logical rules, as opposed to producing a weld based on a specific procedure.« less

Optimization of laser butt welding parameters with multiple performance characteristics

NASA Astrophysics Data System (ADS)

Sathiya, P.; Abdul Jaleel, M. Y.; Katherasan, D.; Shanmugarajan, B.

2011-04-01

This paper presents a study carried out on 3.5 kW cooled slab laser welding of 904 L super austenitic stainless steel. The joints have butts welded with different shielding gases, namely argon, helium and nitrogen, at a constant flow rate. Super austenitic stainless steel (SASS) normally contains high amount of Mo, Cr, Ni, N and Mn. The mechanical properties are controlled to obtain good welded joints. The quality of the joint is evaluated by studying the features of weld bead geometry, such as bead width (BW) and depth of penetration (DOP). In this paper, the tensile strength and bead profiles (BW and DOP) of laser welded butt joints made of AISI 904 L SASS are investigated. The Taguchi approach is used as a statistical design of experiment (DOE) technique for optimizing the selected welding parameters. Grey relational analysis and the desirability approach are applied to optimize the input parameters by considering multiple output variables simultaneously. Confirmation experiments have also been conducted for both of the analyses to validate the optimized parameters.

Development of an intelligent system for cooling rate and fill control in GMAW

DOE Office of Scientific and Technical Information (OSTI.GOV)

Einerson, C.J.; Smartt, H.B.; Johnson, J.A.

1992-09-01

A control strategy for gas metal arc welding (GMAW) is developed in which the welding system detects certain existing conditions and adjusts the process in accordance to pre-specified rules. This strategy is used to control the reinforcement and weld bead centerline cooling rate during welding. Relationships between heat and mass transfer rates to the base metal and the required electrode speed and welding speed for specific open circuit voltages are taught to a artificial neural network. Control rules are programmed into a fuzzy logic system. TRADITOINAL CONTROL OF THE GMAW PROCESS is based on the use of explicit welding proceduresmore » detailing allowable parameter ranges on a pass by pass basis for a given weld. The present work is an exploration of a completely different approach to welding control. In this work the objectives are to produce welds having desired weld bead reinforcements while maintaining the weld bead centerline cooling rate at preselected values. The need for this specific control is related to fabrication requirements for specific types of pressure vessels. The control strategy involves measuring weld joint transverse cross-sectional area ahead of the welding torch and the weld bead centerline cooling rate behind the weld pool, both by means of video (2), calculating the required process parameters necessary to obtain the needed heat and mass transfer rates (in appropriate dimensions) by means of an artificial neural network, and controlling the heat transfer rate by means of a fuzzy logic controller (3). The result is a welding machine that senses the welding conditions and responds to those conditions on the basis of logical rules, as opposed to producing a weld based on a specific procedure.« less

Welding Residual Stress Analysis and Fatigue Strength Assessment at Elevated Temperature for Multi-pass Dissimilar Material Weld Between Alloy 617 and P92 Steel

NASA Astrophysics Data System (ADS)

Lee, Juhwa; Hwang, Jeongho; Bae, Dongho

2018-03-01

In this paper, welding residual stress analysis and fatigue strength assessment were performed at elevated temperature for multi-pass dissimilar material weld between Alloy 617 and P92 steel, which are used in thermal power plant. Multi-pass welding between Alloy 617 and P92 steel was performed under optimized welding condition determined from repeated pre-test welding. In particular, for improving dissimilar material weld-ability, the buttering welding technique was applied on the P92 steel side before multi-pass welding. Welding residual stress distribution at the dissimilar material weld joint was numerically analyzed by using the finite element method, and compared with experimental results which were obtained by the hole-drilling method. Additionally, fatigue strength of dissimilar material weld joint was assessed at the room temperature (R.T), 300, 500, and 700 °C. In finite element analysis results, numerical peak values; longitudinal (410 MPa), transverse (345 MPa) were higher than those of experiments; longitudinal (298 MPa), transverse (245 MPa). There are quantitatively big differences between numerical and experimental results, due to some assumption about the thermal conductivity, specific heat, effects of enforced convection of the molten pool, dilution, and volume change during phase transformation caused by actual shield gas. The low fatigue limit at R.T, 300 °C, 500 °C and 700 °C was assessed to be 368, 276, 173 and 137 MPa respectively.

Welding Residual Stress Analysis and Fatigue Strength Assessment at Elevated Temperature for Multi-pass Dissimilar Material Weld Between Alloy 617 and P92 Steel

NASA Astrophysics Data System (ADS)

Lee, Juhwa; Hwang, Jeongho; Bae, Dongho

2018-07-01

In this paper, welding residual stress analysis and fatigue strength assessment were performed at elevated temperature for multi-pass dissimilar material weld between Alloy 617 and P92 steel, which are used in thermal power plant. Multi-pass welding between Alloy 617 and P92 steel was performed under optimized welding condition determined from repeated pre-test welding. In particular, for improving dissimilar material weld-ability, the buttering welding technique was applied on the P92 steel side before multi-pass welding. Welding residual stress distribution at the dissimilar material weld joint was numerically analyzed by using the finite element method, and compared with experimental results which were obtained by the hole-drilling method. Additionally, fatigue strength of dissimilar material weld joint was assessed at the room temperature (R.T), 300, 500, and 700 °C. In finite element analysis results, numerical peak values; longitudinal (410 MPa), transverse (345 MPa) were higher than those of experiments; longitudinal (298 MPa), transverse (245 MPa). There are quantitatively big differences between numerical and experimental results, due to some assumption about the thermal conductivity, specific heat, effects of enforced convection of the molten pool, dilution, and volume change during phase transformation caused by actual shield gas. The low fatigue limit at R.T, 300 °C, 500 °C and 700 °C was assessed to be 368, 276, 173 and 137 MPa respectively.

Distribution of Argon Arc Contaminated with Nitrogen as Function of Frequency in Pulsed TIG Welding

NASA Astrophysics Data System (ADS)

Takahashi, Hiroki; Tanaka, Tatsuro; Yamamoto, Shinji; Iwao, Toru

2016-09-01

TIG arc welding is the high-quality and much applicable material joining technology. However, the current has to be small because the cathode melting should be prevented. In this case, the heat input to the welding pool becomes low, then, the welding defect sometimes occurs. The pulsed TIG arc welding is used to improve this disadvantage This welding can be controlled by some current parameters such as frequency However, few report has reported the distribution of argon arc contaminated with nitrogen It is important to prevent the contamination of nitrogen because the melting depth increases in order to prevent the welding defects. In this paper, the distribution of argon arc contaminated as function of frequency with nitrogen in pulsed TIG welding is elucidated. The nitrogen concentration, the radial flow velocity, the arc temperature were calculated using the EMTF simulation when the time reached at the base current. As a result, the nitrogen concentration into the arc became low with increasing the frequency The diffusion coefficient decreased because of the decrement of temperature over 4000 K. In this case, the nitrogen concentration became low near the anode. Therefore, the nitrogen concentration became low because the frequency is high.

Mechanical properties and microstructures of a magnesium alloy gas tungsten arc welded with a cadmium chloride flux

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Z.D.; Liu, L.M.; Shen, Y.

2008-01-15

Gas tungsten arc (GTA) welds were prepared on 5-mm thick plates of wrought magnesium AZ31B alloy, using an activated flux. The microstructural characteristics of the weld joint were investigated using optical and scanning microscopy, and the fusion zone microstructure was compared with that of the base metal. The elemental distribution was also investigated by electron probe microanalysis (EPMA). Mechanical properties were determined by standard tensile tests on small-scale specimens. The as-welded fusion zone prepared using a CdCl{sub 2} flux exhibited a larger grain size than that prepared without flux; the microstructure consisted of matrix {alpha}-Mg, eutectic {alpha}-Mg and {beta}-Al{sub 12}Mg{submore » 17}. The HAZ was observed to be slightly wider for the weld prepared with a CdCl{sub 2} flux compared to that prepared without flux; thus the tensile strength was lower for the flux-prepared weld. The fact that neither Cd nor Cl was detected in the weld seam by EPMA indicates that the CdCl{sub 2} flux has a small effect on convection in the weld pool.« less

Laser vision seam tracking system based on image processing and continuous convolution operator tracker

NASA Astrophysics Data System (ADS)

Zou, Yanbiao; Chen, Tao

2018-06-01

To address the problem of low welding precision caused by the poor real-time tracking performance of common welding robots, a novel seam tracking system with excellent real-time tracking performance and high accuracy is designed based on the morphological image processing method and continuous convolution operator tracker (CCOT) object tracking algorithm. The system consists of a six-axis welding robot, a line laser sensor, and an industrial computer. This work also studies the measurement principle involved in the designed system. Through the CCOT algorithm, the weld feature points are determined in real time from the noise image during the welding process, and the 3D coordinate values of these points are obtained according to the measurement principle to control the movement of the robot and the torch in real time. Experimental results show that the sensor has a frequency of 50 Hz. The welding torch runs smoothly with a strong arc light and splash interference. Tracking error can reach ±0.2 mm, and the minimal distance between the laser stripe and the welding molten pool can reach 15 mm, which can significantly fulfill actual welding requirements.

Dynamic modeling of GMA fillet welding using cross-correlation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hellinga, M.; Huissoon, J.; Kerr, H.

1996-12-31

The feasibility of employing the cross-correlation system identification technique as a dynamic modeling method for the GMAW process was examined. This approach has the advantages of modeling speed, the ability to operate in low signal to noise environments, the ease of digital implementation, and the lack of model order assumption, making it ideal in a welding application. The width of the weld pool was the parameter investigated as a function of torch travel speed. Both on-line and off-line width measurements were used to identify the impulse response. Experimental results are presented and comparisons made with both step and ramp response.

Manufacture of thin-walled clad tubes by pressure welding of roll bonded sheets

NASA Astrophysics Data System (ADS)

Schmidt, Hans Christian; Grydin, Olexandr; Stolbchenko, Mykhailo; Homberg, Werner; Schaper, Mirko

2017-10-01

Clad tubes are commonly manufactured by fusion welding of roll bonded metal sheets or, mechanically, by hydroforming. In this work, a new approach towards the manufacture of thin-walled tubes with an outer diameter to wall thickness ratio of about 12 is investigated, involving the pressure welding of hot roll bonded aluminium-steel strips. By preparing non-welded edges during the roll bonding process, the strips can be zip-folded and (cold) pressure welded together. This process routine could be used to manufacture clad tubes in a continuous process. In order to investigate the process, sample tube sections with a wall thickness of 2.1 mm were manufactured by U-and O-bending from hot roll bonded aluminium-stainless steel strips. The forming and welding were carried out in a temperature range between RT and 400°C. It was found that, with the given geometry, a pressure weld is established at temperatures starting above 100°C. The tensile tests yield a maximum bond strength at 340°C. Micrograph images show a consistent weld of the aluminium layer over the whole tube section.

Effect of Nd:YAG laser beam welding on weld morphology and mechanical properties of Ti-6Al-4V butt joints and T-joints

NASA Astrophysics Data System (ADS)

Kashaev, Nikolai; Ventzke, Volker; Fomichev, Vadim; Fomin, Fedor; Riekehr, Stefan

2016-11-01

A Nd:YAG single-sided laser beam welding process study for Ti-6Al-4V butt joints and T-joints was performed to investigate joining techniques with regard to the process-weld morphology relationship. An alloy compatible filler wire was used to avoid underfills and undercuts. The quality of the butt joints and T-joints was characterized in terms of weld morphology, microstructure and mechanical properties. Joints with regular shapes, without visible cracks, pores, and geometrical defects were achieved. Tensile tests revealed high joint integrity in terms of strength and ductility for both the butt joint and T-joint geometries. Both the butt joints and T-joints showed base material levels of strength. The mechanical performance of T-joints was also investigated using pull-out tests. The performance of the T-joints in such tests was sensitive to the shape and morphology of the welds. Fracture always occurred in the weld without any plastic deformation in the base material outside the weld.

Effect of heat input on microstructure and properties of hybrid fiber laser-arc weld joints of the 800 MPa hot-rolled Nb-Ti-Mo microalloyed steels

NASA Astrophysics Data System (ADS)

Wang, X.-N.; Zhang, S.-H.; Zhou, J.; Zhang, M.; Chen, C.-J.; Misra, R. D. K.

2017-04-01

Hybrid fiber laser-arc welding (HLAW) process was applied to a novel hot-rolled Nb-Ti-Mo microalloyed steels of 8 mm thickness. The steel is primarily used to manufacture automotive and construction machinery components, etc. To elucidate the effect of heat input on geometry, microstructure and mechanical properties, different heat inputs (3.90, 5.20 and 7.75 kJ/cm) were used by changing the welding speeds. With increased heat input, the depth/width of penetration was decreased, and the geometry of fusion zone (FZ) changed to "wine cup-like" shape. In regard to the microstructural constituents, the martensite content was decreased, but granular bainite (GB) content was increased. The main microstructural difference was in the FZ cross-section at 7.75 kJ/cm because of the effect of thermal source on the top and bottom. The microstructure of the top part consisted of GB, grain boundary ferrite, and acicular ferrite, while the bottom part was primarily lath martensite. The hardness distribution was similar for different heat inputs. Hardness in FZ, coarse-grained HAZ and mixed-grained HAZ was higher than the base metal (BM), but for the fine-grained HAZ was similar or marginally less than the base metal (BM). Tensile strain was concentrated in the BM such that the fracture occurred in this region. In summary, the geometry, microstructure, and mechanical properties of weld joints were superior at heat input of 5.20 kJ/cm.

Characterization of Friction Welded Titanium Alloy and Stainless Steel with a Novel Interlayer Geometry

NASA Astrophysics Data System (ADS)

Kumar, R.; Balasubramanian, M.

The main purpose of the current research work is to identify and investigate a novel method of holding an intermediate metal and to evaluate its metallurgical and mechanical properties. Copper was used as an interlayer material for the welding of this dissimilar Ti-6Al-4V (Ti alloy) and 304L stainless steel (SS). The study shows that the input parameters and surface geometry played a very significant role in producing a good quality joints with minimum heat affected zone and metal loss. A sound weld was achieved between Ti-6Al-4V and SS304L, on the basis of the earlier experiments conducted by the authors in their laboratory, by using copper rod as intermediate metal. Box-Behnken method was used for performing a minimum number of experiments for the study. In the present study, Ti-6Al-4V alloy and SS304L were joined by a novel method of holding the interlayer and new surface geometry for the interlayer. Initially, the drop test was used for determining the quality of the fabricated joint and, subsequently, non-destructive techniques like radiography and C-scan were used. Further optical micrograph, SEM-EDS, hardness and tensile test were done for understanding the performance of the joint.

Study of gas tungsten arc welding procedures for tantalum alloy T-111 (Ta-8 W-2Hf) plate

NASA Technical Reports Server (NTRS)

Gold, R. E.; Kesterson, R. L.

1973-01-01

Methods of eliminating or reducing underbread cracking in multipass GTA welds in thick T-111 plate were studied. Single V butt welds prepared using experimental filler metal compositions and standard weld procedures resulted in only moderate success in reducing underbread cracking. Subsequent procedural changes incorporating manual welding, slower weld speeds, and three or fewer fill passes resulted in crack-free single V welds only when the filler metal was free of hafnium. The double V joint design with successive fill passes on opposite sides of the joint produced excellent welds. The quality of each weld was determined metallographically since the cracking, when present, was very slight and undetectable using standard NDT techniques. Tensile and bend tests were performed on selected weldments. The inherent filler metal strength and the joint geometry determined the strength of the weldment. Hardness and electron beam microprobe traverses were made on selected specimens with the result that significant filler metal-base metal dilution as well as hafnium segregation was detected. A tentative explanation of T-111 plate underbread cracking is presented based on the intrinsic effects of hafnium in the weldment.

LPT. EBOR (TAN646) interior, installing reactor in STF pool ("vault"). ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

LPT. EBOR (TAN-646) interior, installing reactor in STF pool ("vault"). Pressure vessel shows core barrel and outlet nozzle (next to man below) to inner duct weld, which is prepared and in position for stress relieving. Camera facing southeast. Photographer: Comiskey. Date: January 20, 1965. INEEL negative no. 65-239 - Idaho National Engineering Laboratory, Test Area North, Scoville, Butte County, ID

Effect of A-TIG Welding Process on the Weld Attributes of Type 304LN and 316LN Stainless Steels

NASA Astrophysics Data System (ADS)

Vasudevan, M.

2017-03-01

The specific activated flux has been developed for enhancing the penetration performance of TIG welding process for autogenous welding of type 304LN and 316LN stainless steels through systematic study. Initially single-component fluxes were used to study their effect on depth of penetration and tensile properties. Then multi-component activated flux was developed which was found to produce a significant increase in penetration of 10-12 mm in single-pass TIG welding of type 304LN and 316LN stainless steels. The significant improvement in penetration achieved using the activated flux developed in the present work has been attributed to the constriction of the arc and as well as reversal of Marangoni flow in the molten weld pool. The use of activated flux has been found to overcome the variable weld penetration observed in 316LN stainless steel with <50 ppm of sulfur. There was no degradation in the microstructure and mechanical properties of the A-TIG welds compared to that of the welds produced by conventional TIG welding on the contrary the transverse strength properties of the 304LN and 316LN stainless steel welds produced by A-TIG welding exceeded the minimum specified strength values of the base metals. Improvement in toughness values were observed in 316LN stainless steel produced by A-TIG welding due to refinement in the weld microstructure in the region close to the weld center. Thus, activated flux developed in the present work has greater potential for use during the TIG welding of structural components made of type 304LN and 316LN stainless steels.

Estimation and control of droplet size and frequency in projected spray mode of a gas metal arc welding (GMAW) process.

PubMed

Anzehaee, Mohammad Mousavi; Haeri, Mohammad

2011-07-01

New estimators are designed based on the modified force balance model to estimate the detaching droplet size, detached droplet size, and mean value of droplet detachment frequency in a gas metal arc welding process. The proper droplet size for the process to be in the projected spray transfer mode is determined based on the modified force balance model and the designed estimators. Finally, the droplet size and the melting rate are controlled using two proportional-integral (PI) controllers to achieve high weld quality by retaining the transfer mode and generating appropriate signals as inputs of the weld geometry control loop. Copyright © 2011 ISA. Published by Elsevier Ltd. All rights reserved.

Hybrid Laser-Arc Welding of 10-mm-Thick Cast Martensitic Stainless Steel CA6NM: As-Welded Microstructure and Mechanical Properties

NASA Astrophysics Data System (ADS)

Mirakhorli, Fatemeh; Cao, Xinjin; Pham, Xuan-Tan; Wanjara, Priti; Fihey, Jean-Luc

2016-07-01

Cast CA6NM martensitic stainless steel plates, 10 mm in thickness, were welded using hybrid laser-arc welding. The effect of different welding speeds on the as-welded joint integrity was characterized in terms of the weld bead geometry, defects, microstructure, hardness, ultimate tensile strength, and impact energy. Significant defects such as porosity, root humping, underfill, and excessive penetration were observed at a low welding speed (0.5 m/min). However, the underfill depth and excessive penetration in the joints manufactured at welding speeds above 0.75 m/min met the specifications of ISO 12932. Characterization of the as-welded microstructure revealed untempered martensite and residual delta ferrite dispersed at prior-austenite grain boundaries in the fusion zone. In addition, four different heat-affected zones in the weldments were differentiated through hardness mapping and inference from the Fe-Cr-Ni ternary phase diagram. The tensile fracture occurred in the base metal for all the samples and fractographic analysis showed that the crack path is within the martensite matrix, along primary delta ferrite-martensite interfaces and within the primary delta ferrite. Additionally, Charpy impact testing demonstrated slightly higher fracture energy values and deeper dimples on the fracture surface of the welds manufactured at higher welding speeds due to grain refinement and/or lower porosity.

Real-Time Measurement of Width and Height of Weld Beads in GMAW Processes.

PubMed

Pinto-Lopera, Jesús Emilio; S T Motta, José Mauricio; Absi Alfaro, Sadek Crisostomo

2016-09-15

Associated to the weld quality, the weld bead geometry is one of the most important parameters in welding processes. It is a significant requirement in a welding project, especially in automatic welding systems where a specific width, height, or penetration of weld bead is needed. This paper presents a novel technique for real-time measuring of the width and height of weld beads in gas metal arc welding (GMAW) using a single high-speed camera and a long-pass optical filter in a passive vision system. The measuring method is based on digital image processing techniques and the image calibration process is based on projective transformations. The measurement process takes less than 3 milliseconds per image, which allows a transfer rate of more than 300 frames per second. The proposed methodology can be used in any metal transfer mode of a gas metal arc welding process and does not have occlusion problems. The responses of the measurement system, presented here, are in a good agreement with off-line data collected by a common laser-based 3D scanner. Each measurement is compare using a statistical Welch's t-test of the null hypothesis, which, in any case, does not exceed the threshold of significance level α = 0.01, validating the results and the performance of the proposed vision system.

Real-time GMAW quality classification using an artificial neural network with airborne acoustic signals as inputs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matteson, A.; Morris, R.; Tate, R.

1993-12-31

The acoustic signal produced by the gas metal arc welding (GMAW) arc contains information about the behavior of the arc column, the molten pool and droplet transfer. It is possible to detect some defect producing conditions from the acoustic signal from the GMAW arc. An intelligent sensor, called the Weld Acoustic Monitor (WAM) has been developed to take advantage of this acoustic information in order to provide real-time quality assessment information for process control. The WAM makes use of an Artificial Neural Network (ANN) to classify the characteristic arc acoustic signals of acceptable and unacceptable welds. The ANN used inmore » the Weld Acoustic Monitor developed its own set of rules for this classification problem by learning a data base of known GMAW acoustic signals.« less

Effect of temporal pulse shaping on the reduction of laser weld defects in a Pd-Ag-Sn dental alloy.

PubMed

Bertrand, C; Poulon-Quintin, A

2011-03-01

To describe the influence of pulse shaping on the behavior of a palladium-based dental alloy during laser welding and to show how its choice is effective to promote good weld quality. Single spots, weld beads and welds with 80% overlapping were performed on Pd-Ag-Sn cast plates. A pulsed Nd:Yag laser was used with a specific welding procedure using all the possibilities for pulse-shaping: (1) the square pulse shape as the default setting, (2) a rising edge slope for gradual heating, (3) a falling edge slope to slow the cooling and (4) a combination of a rising and falling edges called bridge shape. The optimization of the pulse shape is supposed to enhance weldability and produce defect-free welds (cracks, pores…) Vickers microhardness measurements were made on cross sections of the welds. A correlation between laser welding parameters and microstructure evolution was found. Hot cracking and internal porosities were systematically detected when using rapid cooling. The presence of these types of defects was significantly reduced with the slow cooling of the molten pool. The best weld quality was obtained with the use of the bridge shape. The use of a slow cooling ramp is the only way to significantly reduce the presence of typical defects within the welds for this Pd-based alloy studied. Copyright © 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Development of Real Time Ultrasonic Imaging

DTIC Science & Technology

1999-01-01

piezoelectric material known as poly vinyl difluoride ( PVDF ) which enables the conversion of mechanical energy to charge the CCD chip. The system...geometries such as curved (wing) surfaces. Other future applications might include heavy gauge welds in plate, corrosion in piping, welds in piping...Harrison, G. "A Novel High Speed, High Resolution Ultrasound Imaging System", QNDE Review of Progress In Quantitative NDE, Plenum Press, Volume 17B, pp

Investigation the Amplitude Uniformity on the Surface of the Wide-Blade Ultrasonic Plastic Welding Horn

NASA Astrophysics Data System (ADS)

Hai Nguyen, Thanh; Thanh Quang, Quang; Luat Tran, Cong; Loc Nguyen, Huu

2017-10-01

Ultrasonic welding has been applied for joining thermoplastic components due to their advantages such as clean, fast and reliable. The basic principle is to use the mechanical energy of ultrasonic frequency vibration to produce the molten pool at the interface of the joined components under high pressure to create solid-state welding joints. Depending on the specific application, the ultrasonic horn is designed to generate suitable amplitudes on the surface of the welding zone. Uniformity of the amplitudes can be a challenge as the welding area increases. Therefore, design a welding horn in order to obtain the uniform amplitudes at the large area is significant difficult. This work presents a method for obtaining the uniform amplitudes at the working surface of the stepped wide-blade horn. Finite element method is used to analyze the amplitude distribution at the horn surface of 250 × 34 mm2 with working frequency of 15 kHz and aluminum alloy 7075. The uniformity of amplitude is obtained by changing the shape of the horn.

Thermal regulation in multiple-source arc welding involving material transformations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doumanidis, C.C.

1995-06-01

This article addresses regulation of the thermal field generated during arc welding, as the cause of solidification, heat-affected zone and cooling rate related metallurgical transformations affecting the final microstructure and mechanical properties of various welded materials. This temperature field is described by a dynamic real-time process model, consisting of an analytical composite conduction expression for the solid region, and a lumped-state, double-stream circulation model in the weld pool, integrated with a Gaussian heat input and calibrated experimentally through butt joint GMAW tests on plain steel plates. This model serves as the basis of an in-process thermal control system employing feedbackmore » of part surface temperatures measured by infrared pyrometry; and real-time identification of the model parameters with a multivariable adaptive control strategy. Multiple heat inputs and continuous power distributions are implemented by a single time-multiplexed torch, scanning the weld surface to ensure independent, decoupled control of several thermal characteristics. Their regulation is experimentally obtained in longitudinal GTAW of stainless steel pipes, despite the presence of several geometrical, thermal and process condition disturbances of arc welding.« less

Numerical analysis on temperature field in single-wire flux-aided backing-submerged arc welding

NASA Astrophysics Data System (ADS)

Pu, Juan; Wu, Ming Fang; Pan, Haichao

2017-07-01

Single-wire flux-aided backing-submerged arc welding (FAB-SAW) technology has been widely used to weld thick steel plate due to its easy assembly and high heat input. The microstructure and property of welded joint are closely related to the thermal field of FAB-SAW process. In this research, the feature of thermal field for single-wire FAB-SAW was investigated. Based on the heat transfer mechanism, a three-dimensional transient model for thermal field was developed based on the influence of steel thickness, groove angle and ceramic backing. The temperature profile in single-wire FAB-SAW of D36 steel under different welding conditions was simulated by ANSYS. The characteristic of thermal field was analyzed and the influences of groove angle on temperature field for different plate thicknesses were discussed. The calculated geometries and dimensions of weld cross-section under different conditions show a good agreement with the experimental results. This newly built model can describe the thermal field accurately, which would be helpful to understanding the thermophysical mechanism of FAB-SAW and optimizing the welding process.

Correlations of Melt Pool Geometry and Process Parameters During Laser Metal Deposition by Coaxial Process Monitoring

NASA Astrophysics Data System (ADS)

Ocylok, Sörn; Alexeev, Eugen; Mann, Stefan; Weisheit, Andreas; Wissenbach, Konrad; Kelbassa, Ingomar

One major demand of today's laser metal deposition (LMD) processes is to achieve a fail-save build-up regarding changing conditions like heat accumulations. Especially for the repair of thin parts like turbine blades is the knowledge about the correlations between melt pool behavior and process parameters like laser power, feed rate and powder mass stream indispensable. The paper will show the process layout with the camera based coaxial monitoring system and the quantitative influence of the process parameters on the melt pool geometry. Therefore the diameter, length and area of the melt pool are measured by a video analytic system at various parameters and compared with the track wide in cross-sections and the laser spot diameter. The influence of changing process conditions on the melt pool is also investigated. On the base of these results an enhanced process of the build-up of a multilayer one track fillet geometry will be presented.

Microstructures and Mechanical Properties of Friction Stir Spot Welded Aluminum Alloy AA2014

NASA Astrophysics Data System (ADS)

Babu, S.; Sankar, V. S.; Janaki Ram, G. D.; Venkitakrishnan, P. V.; Madhusudhan Reddy, G.; Prasad Rao, K.

2013-01-01

Friction stir spot welding (FSSW) is a relatively recent development, which can provide a superior alternative to resistance spot welding and riveting for fabrication of aluminum sheet metal structures. In the current work, FSSW experiments were conducted in 3-mm thick sheets of aluminum alloy 2014 in T4 and T6 conditions, with and without Alclad layers. The effects of tool geometry and welding process parameters on joint formation were investigated. A good correlation between process parameters, bond width, hook height, joint strength, and fracture mode was observed. The presence of Alclad layers and the base metal temper condition were found to have no major effect on joint formation and joint strength. Friction stir spot welds produced under optimum conditions were found to be superior to riveted joints in lap-shear and cross-tension tests. The prospects of FSSW in aluminum sheet metal fabrication are discussed.

Investigation on the Interface Morphologies of Explosive Welding of Inconel 625 to Steel A516 Plates

NASA Astrophysics Data System (ADS)

Mousavi, S. A. A. Akbari; Zareie, H. R.

2011-01-01

The purpose of this study is to produce composite plates by explosive cladding process. This is a process in which the controlled energy of explosives is used to create a metallic bond between two similar or dissimilar materials. The welding conditions were tailored through parallel geometry route with different operational parameters. In this investigation, a two-pronged study was adopted to establish the conditions required for producing successful solid state welding: (a) Analytical calculations to determine the weldability domain or welding window; (b) Metallurgical investigations of explosive welding experiments carried out under different explosive ratios to produce both wavy and straight interfaces. The analytical calculations confirm the experimental results. Optical microscopy studies show that a transition from a smooth to wavy interface occurs with an increase in explosive ratio. SEM studies show that the interface was outlined by characteristic sharp transition between two materials.

Weldability of a high entropy CrMnFeCoNi alloy

DOE PAGES

Wu, Zhenggang; David, Stan A.; Feng, Zhili; ...

2016-07-19

We present the high-entropy alloys are unique alloys in which five or more elements are all in high concentrations. In order to determine its potential as a structural alloy, a model face-centered-cubic CrMnFeCoNi alloy was selected to investigate its weldability. Welds produced by electron beam welding show no cracking. The grain structures within the fusion zone (FZ) are controlled by the solidification behavior of the weld pool. The weldment possesses mechanical properties comparable to those of the base metal (BM) at both room and cryogenic temperatures. Finally, compared with the BM, deformation twinning was more pronounced in the FZ ofmore » the tested alloy.« less

A model for heat and mass input control in GMAW

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smartt, H.B.; Einerson, C.J.

1993-05-01

This work describes derivation of a control model for electrode melting and heat and mass transfer from the electrode to the work piece in gas metal arc welding (GMAW). Specifically, a model is developed which allows electrode speed and welding speed to be calculated for given values of voltage and torch-to-base metal distance, as a function of the desired heat and mass input to the weldment. Heat input is given on a per unit weld length basis, and mass input is given in terms of transverse cross-sectional area added to the weld bead (termed reinforcement). The relationship to prior workmore » is discussed. The model was demonstrated using a computer-controlled welding machine and a proportional-integral (PI) controller receiving input from a digital filter. The difference between model-calculated welding current and measured current is used as controller feedback. The model is calibrated for use with carbon steel welding wire and base plate with Ar-CO[sub 2] shielding gas. Although the system is intended for application during spray transfer of molten metal from the electrode to the weld pool, satisfactory performance is also achieved during globular and streaming transfer. Data are presented showing steady-state and transient performance, as well as resistance to external disturbances.« less

Energetic additive manufacturing process with feed wire

DOEpatents

Harwell, Lane D.; Griffith, Michelle L.; Greene, Donald L.; Pressly, Gary A.

2000-11-07

A process for additive manufacture by energetic wire deposition is described. A source wire is fed into a energy beam generated melt-pool on a growth surface as the melt-pool moves over the growth surface. This process enables the rapid prototyping and manufacture of fully dense, near-net shape components, as well as cladding and welding processes. Alloys, graded materials, and other inhomogeneous materials can be grown using this process.

Cooling Rate Determination in Additively Manufactured Aluminum Alloy 2219

NASA Astrophysics Data System (ADS)

Brice, Craig A.; Dennis, Noah

2015-05-01

Metallic additive manufacturing processes generally utilize a conduction mode, welding-type approach to create beads of deposited material that can be arranged into a three-dimensional structure. As with welding, the cooling rates in the molten pool are relatively rapid compared to traditional casting techniques. Determination of the cooling rate in the molten pool is critical for predicting the solidified microstructure and resultant properties. In this experiment, wire-fed electron beam additive manufacturing was used to melt aluminum alloy 2219 under different thermal boundary conditions. The dendrite arm spacing was measured in the remelted material, and this information was used to estimate cooling rates in the molten pool based on established empirical relationships. The results showed that the thermal boundary conditions have a significant effect on the resulting cooling rate in the molten pool. When thermal conduction is limited due to a small thermal sink, the dendrite arm spacing varies between 15 and 35 µm. When thermal conduction is active, the dendrite arm spacing varies between 6 and 12 µm. This range of dendrite arm spacing implies cooling rates ranging from 5 to 350 K/s. Cooling rates can vary greatly as thermal conditions change during deposition. A cooling rate at the higher end of the range could lead to significant deviation from microstructural equilibrium during solidification.

Effect of process parameters on microstructure and mechanical properties of friction stir welded joints: A review

NASA Astrophysics Data System (ADS)

Wanare, S. P.; Kalyankar, V. D.

2018-04-01

Friction stir welding is emerging as a promising technique for joining of lighter metal alloys due to its several advantages over conventional fusion welding processes such as low thermal distortion, good mechanical properties, fine weld joint microstructure, etc. This review article mainly focuses on analysis of microstructure and mechanical properties of friction stir welded joints. Various microstructure characterization techniques used by previous researchers such as optical microscopes, x-ray diffraction, electron probe microscope, transmission electron microscope, scanning electron microscopes with electron back scattered diffraction, electron dispersive microscopy, etc. are thoroughly overviewed and their results are discussed. The effects of friction stir welding process parameters such as tool rotational speed, welding speed, tool plunge depth, axial force, tool shoulder diameter to tool pin diameter ratio, tool geometry etc. on microstructure and mechanical properties of welded joints are studied and critical observations are noted down. The microstructure examination carried out by previous researchers on various zones of welded joints such as weld zone, heat affected zone and base metal are studied and critical remarks have been presented. Mechanical performances of friction stir welded joints based on tensile test, micro-hardness test, etc. are discussed. This article includes exhaustive literature review of standard research articles which may become ready information for subsequent researchers to establish their line of action.

Control of the electrode metal transfer by means of the welding current pulse generator

NASA Astrophysics Data System (ADS)

Knyaz'kov, A.; Pustovykh, O.; Verevkin, A.; Terekhin, V.; Shachek, A.; Knyaz'kov, S.; Tyasto, A.

2016-04-01

The paper presents a generator of welding current pulses to transfer an electrode metal into the molten pool. A homogeneous artificial line is used to produce near rectangular pulses. The homogeneous artificial line provides the minimum heat input with in the pulse to transfer the electrode metal, and it significantly decreases the impact of disturbances affecting this transfer. The pulse frequency does not exceed 300 Hz, and the duration is 0.6 ÷ 0.9 ms.

A Fundamental Study of Laser Beam Welding Aluminum-Lithium Alloy 2195 for Cryogenic Tank Applications

NASA Technical Reports Server (NTRS)

Martukanitz, R. P.; Jan. R.

1996-01-01

Based on the potential for decreasing costs of joining stiffeners to skin by laser beam welding, a fundamental research program was conducted to address the impediments identified during an initial study involving laser beam welding of aluminum-lithium alloys. Initial objectives of the program were the identification of governing mechanism responsible for process related porosity while establishing a multivariant relationship between process parameters and fusion zone geometry for laser beam welds of alloy 2195. A three-level fractional factorial experiment was conducted to establish quantitative relationships between primary laser beam processing parameters and critical weld attributes. Although process consistency appeared high for welds produced during partial completion of this study, numerous cracks on the top-surface of the welds were discovered during visual inspection and necessitated additional investigations concerning weld cracking. Two experiments were conducted to assess the effect of filler alloy additions on crack sensitivity: the first experiment was used to ascertain the effects of various filler alloys on cracking and the second experiment involved modification to process parameters for increasing filler metal dilution. Results indicated that filler alloys 4047 and 4145 showed promise for eliminating cracking.

Study of fatigue behavior of longitudinal welded pipes

NASA Astrophysics Data System (ADS)

Simion, P.; Dia, V.; Istrate, B.; Hrituleac, G.; Hrituleac, I.; Munteanu, C.

2016-08-01

During transport and storage of the various fluids, welded pipes are subjected to cyclic loading due to pressure fluctuations that often exceed the prescribed values for normal operation. These cyclic loading can significantly reduce the life of the pipes; as a result the design should be based on the fatigue strength not only on static resistance. In general the fatigue strength of pipes is dependent by strength, pipe geometry and surface quality. In case of the electric longitudinal welded pipes, the fatigue strength is significantly limited by concentration of residual stress and the size of existing defects in the weld seam. This paper presents the fatigue behaviour of the electric welded pipes by high frequency, under conditions that simulate real operating conditions pipes. Fatigue testing was performed on welded pipes made of micro alloyed carbon steels. Some of these pipes were previously subjected to a heat treatment of normalization, in order to also determine the influence of heat treatment on the fatigue strength of welded pipes. To determine and correlate the different factors affecting the fatigue strength, welded pipes were also subjected to various tests: tensile tests, impact tests, measurement of micro hardness, microstructural analysis by optical microscopy and scanning electron microscopy.

Cellular Automaton Study of Hydrogen Porosity Evolution Coupled with Dendrite Growth During Solidification in the Molten Pool of Al-Cu Alloys

NASA Astrophysics Data System (ADS)

Gu, Cheng; Wei, Yanhong; Yu, Fengyi; Liu, Xiangbo; She, Lvbo

2017-09-01

Welding porosity defects significantly reduce the mechanical properties of welded joints. In this paper, the hydrogen porosity evolution coupled with dendrite growth during solidification in the molten pool of Al-4.0 wt pct Cu alloy was modeled and simulated. Three phases, including a liquid phase, a solid phase, and a gas phase, were considered in this model. The growth of dendrites and hydrogen gas pores was reproduced using a cellular automaton (CA) approach. The diffusion of solute and hydrogen was calculated using the finite difference method (FDM). Columnar and equiaxed dendrite growth with porosity evolution were simulated. Competitive growth between different dendrites and porosities was observed. Dendrite morphology was influenced by porosity formation near dendrites. After solidification, when the porosities were surrounded by dendrites, they could not escape from the liquid, and they made pores that existed in the welded joints. With the increase in the cooling rate, the average diameter of porosities decreased, and the average number of porosities increased. The average diameter of porosities and the number of porosities in the simulation results had the same trend as the experimental results.

Weldability of extruded aluminum-alumina composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gedeon, S.A.; Lane, C.; Altshuller, B.

1994-12-31

Acceptable procedure were developed for welding the following types of aluminum particle-reinforced aluminum: 6061/Al{sub 2}O{sub 3}/10p-T6, 6061/Al{sub x}/O{sub 3}20p-T6, and 7005Al{sub 2}O{sub 3}/10p-T6,. Automated and manual procedures were developed and using both gas tungsten arc welding (GTAW), with a cold wire feed, and gas metal arc welding (GMAW). The effect of welding procedures on porosity, reinforcing particulate distribution, and mechanical properties was determined. Postweld heat treatment and microhardness testing were used to understand the effect of the welded microstructure on the strength and ductility of the joint. Fracture surfaces and transverse microsections of mechanical test specimens were examined to determinemore » the origins and mechanisms of failure. Cleanliness of the joint and weld wire were found to be essential to eliminate porosity. Based on these experimentally determined data, general guidelines for welding aluminum oxide particle-reinforced aluminum composites are proposed. Discussion includes proper selection of weld joint geometry, filler metals, travel speed, voltage, and current ranges. These parameters are compared to those used in an actual production environment for composite products. Distinctions between welding these composites and others produced via powder metallurgy or with silicon carbide reinforcements are also discussed.« less

Microstructure and fatigue resistance of high strength dual phase steel welded with gas metal arc welding and plasma arc welding processes

NASA Astrophysics Data System (ADS)

Ahiale, Godwin Kwame; Oh, Yong-Jun; Choi, Won-Doo; Lee, Kwang-Bok; Jung, Jae-Gyu; Nam, Soo Woo

2013-09-01

This study presents the microstructure and high cycle fatigue performance of lap shear joints of dual phase steel (DP590) welded using gas metal arc welding (GMAW) and plasma arc welding (PAW) processes. High cycle fatigue tests were conducted on single and double lap joints under a load ratio of 0.1 and a frequency of 20 Hz. In order to establish a basis for comparison, both weldments were fabricated to have the same weld depth in the plate thickness. The PAW specimens exhibited a higher fatigue life, a gentle S-N slope, and a higher fatigue limit than the GMAW specimens. The improvement in the fatigue life of the PAW specimens was primarily attributed to the geometry effect that exhibited lower and wider beads resulting in a lower stress concentration at the weld toe where cracks initiate and propagate. Furthermore, the microstructural constituents in the heat-affected zone (HAZ) of the PAW specimens contributed to the improvement. The higher volume fraction of acicular ferrite in the HAZ beneath the weld toe enhanced the PAW specimen's resistance to fatigue crack growth. The double lap joints displayed a higher fatigue life than the single lap joints without changing the S-N slope.

The effect of weld metal matching on girth weld performance: Volume III - an ECA analysis. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Denys, R.M.; Martin, J.T.

1995-02-01

Modern pipeline standards contain alternative methodologies for determining the acceptable defect size in pipeline welds. Through the use of fracture mechanics and plastic collapse assessments, the mechanical and toughness properties of the defective region relate to the applied stress at the defect and defect geometry. The assumptions made in these methodologies are not always representative of the situation accurring in pipeline girth welds. To determine the effect of the various input parameters on acceptable defect size, The Welding Supervisory Committee of the American Gas Association commenced in 1990, in collaboration with the Laboratorium Soete of the University Gent, Belgium, amore » series of small scale (Charpy V impact and CTOD) and large scale (fatigue pre-cracked wide plate) tests. All the experimental investigations were intended to evaluate the effects of weld metal mis-match, temperature, defect size, defect type, defect interaction, pipe wall thickness and yield to tensile ratio on girth weld fracture behaviour. The aim of this report was to determine how weld metal yield strength overmatching or undermatching influences girth weld defect size prediction. A further analysis was conducted using the newly revised PD6493:1991 to provide a critical analysis with the objective of explaining the behaviour of the wide plate tests.« less

On the non-proportionality between wheel/rail contact forces and speed during wheelset passage over specific welds

NASA Astrophysics Data System (ADS)

Correa, Nekane; Vadillo, Ernesto G.; Santamaria, Javier; Blanco-Lorenzo, Julio

2018-01-01

This study investigates the influence on the wheel-rail contact forces of the running speed and the shape and position of weld defects along the track. For this purpose, a vertical dynamic model in the space domain is used. The model is obtained from the transformation between the domains of frequency and space using a Rational Fraction Polynomials (RFP) method, which is modified with multiobjective genetic algorithms in order to improve the fitting of track receptance and to assist integration during simulations. This produces a precise model with short calculation times, which is essential to this study. The wheel-rail contact is modelled using a non-linear Hertz spring. The contact forces are studied for several types of characteristic welds. The way in which forces vary as a function of weld position and running speed is studied for each type of weld. This paper studies some of the factors that affect the maximum forces when the vehicle moves over a rail weld, such as weld geometry, parametric excitation and contact stiffness. It is found that the maximum force in the wheel-rail contact when the vehicle moves over a weld is not always proportional to the running speed. The paper explains why it is not proportional in specific welds.

The Effect of Weld Reinforcement and Post-Welding Cooling Cycles on Fatigue Strength of Butt-Welded Joints under Cyclic Tensile Loading.

PubMed

Araque, Oscar; Arzola, Nelson; Hernández, Edgar

2018-04-12

This research deals with the fatigue behavior of butt-welded joints, by considering the geometry and post-welding cooling cycles, as a result of cooling in quiet air and immersed in water. ASTM A-36 HR structural steel was used as the base metal for the shielded metal arc welding (SMAW) process with welding electrode E6013. The welding reinforcement was 1 mm and 3 mm, respectively; axial fatigue tests were carried out to determine the life and behavior in cracks propagation of the tested welded joints, mechanical characterization tests of properties in welded joints such as microhardness, Charpy impact test and metallographic analysis were carried out. The latter were used as input for the analysis by finite elements which influence the initiation and propagation of cracks and the evaluation of stress intensity factors (SIF). The latter led to obtaining the crack propagation rate and the geometric factor. The tested specimens were analyzed, by taking photographs of the cracks at its beginning in order to make a count of the marks at the origin of the crack. From the results obtained and the marks count, the fatigue crack growth rate and the influence of the cooling media on the life of the welded joint are validated, according to the experimental results. It can be concluded that the welded joints with a higher weld reinforcement have a shorter fatigue life. This is due to the stress concentration that occurs in the vicinity of the weld toe.

The Effect of Weld Reinforcement and Post-Welding Cooling Cycles on Fatigue Strength of Butt-Welded Joints under Cyclic Tensile Loading

PubMed Central

Arzola, Nelson; Hernández, Edgar

2018-01-01

This research deals with the fatigue behavior of butt-welded joints, by considering the geometry and post-welding cooling cycles, as a result of cooling in quiet air and immersed in water. ASTM A-36 HR structural steel was used as the base metal for the shielded metal arc welding (SMAW) process with welding electrode E6013. The welding reinforcement was 1 mm and 3 mm, respectively; axial fatigue tests were carried out to determine the life and behavior in cracks propagation of the tested welded joints, mechanical characterization tests of properties in welded joints such as microhardness, Charpy impact test and metallographic analysis were carried out. The latter were used as input for the analysis by finite elements which influence the initiation and propagation of cracks and the evaluation of stress intensity factors (SIF). The latter led to obtaining the crack propagation rate and the geometric factor. The tested specimens were analyzed, by taking photographs of the cracks at its beginning in order to make a count of the marks at the origin of the crack. From the results obtained and the marks count, the fatigue crack growth rate and the influence of the cooling media on the life of the welded joint are validated, according to the experimental results. It can be concluded that the welded joints with a higher weld reinforcement have a shorter fatigue life. This is due to the stress concentration that occurs in the vicinity of the weld toe. PMID:29649117

Microstructure and Porosity of Laser Welds in Cast Ti-6Al-4V with Addition of Boron

NASA Astrophysics Data System (ADS)

Tolvanen, Sakari; Pederson, Robert; Klement, Uta

2018-03-01

Addition of small amounts of boron to cast Ti-6Al-4V alloy has shown to render a finer microstructure and improved mechanical properties. For such an improved alloy to be widely applicable for large aerospace structural components, successful welding of such castings is essential. In the present work, the microstructure and porosity of laser welds in a standard grade cast Ti-6Al-4V alloy as well as two modified alloy versions with different boron concentrations have been investigated. Prior-β grain reconstruction revealed the prior-β grain structure in the weld zones. In fusion zones of the welds, boron was found to refine the grain size significantly and rendered narrow elongated grains. TiB particles in the prior-β grain boundaries in the cast base material restricted grain growth in the heat-affected zone. The TiB particles that existed in the as cast alloys decreased in size in the fusion zones of welds. The hardness in the weld zones was higher than in the base material and boron did not have a significant effect on hardness of the weld zones. The fusion zones were smaller in the boron-modified alloys as compared with Ti-6Al-4V without boron. Computed tomography X-ray investigations of the laser welds showed that pores in the FZ of the boron modified alloys were confined to the lower part of the welds, suggesting that boron addition influences melt pool flow.

Vaccum Gas Tungsten Arc Welding, phase 1

NASA Astrophysics Data System (ADS)

Weeks, J. L.; Krotz, P. D.; Todd, D. T.; Liaw, Y. K.

1995-03-01

This two year program will investigate Vacuum Gas Tungsten Arc Welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. VGTAW appears to offer a significant improvement in weldability because of the clean environment and lower heat input needed. The overall objective of the program is to develop the VGTAW technology and implement it into a manufacturing environment that will result in lower cost, better quality and higher reliability aerospace components for the space shuttle and other NASA space systems. Phase 1 of this program was aimed at demonstrating the process's ability to weld normally difficult-to-weld materials. Phase 2 will focus on further evaluation, a hardware demonstration and a plan to implement VGTAW technology into a manufacturing environment. During Phase 1, the following tasks were performed: (1) Task 11000 Facility Modification - an existing vacuum chamber was modified and adapted to a GTAW power supply; (2) Task 12000 Materials Selection - four difficult-to-weld materials typically used in the construction of aerospace hardware were chosen for study; (3) Task 13000 VGTAW Experiments - welding experiments were conducted under vacuum using the hollow tungsten electrode and evaluation. As a result of this effort, two materials, NARloy Z and Incoloy 903, were downselected for further characterization in Phase 2; and (4) Task 13100 Aluminum-Lithium Weld Studies - this task was added to the original work statement to investigate the effects of vacuum welding and weld pool vibration on aluminum-lithium alloys.

Vaccum Gas Tungsten Arc Welding, phase 1

NASA Technical Reports Server (NTRS)

Weeks, J. L.; Krotz, P. D.; Todd, D. T.; Liaw, Y. K.

1995-01-01

This two year program will investigate Vacuum Gas Tungsten Arc Welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. VGTAW appears to offer a significant improvement in weldability because of the clean environment and lower heat input needed. The overall objective of the program is to develop the VGTAW technology and implement it into a manufacturing environment that will result in lower cost, better quality and higher reliability aerospace components for the space shuttle and other NASA space systems. Phase 1 of this program was aimed at demonstrating the process's ability to weld normally difficult-to-weld materials. Phase 2 will focus on further evaluation, a hardware demonstration and a plan to implement VGTAW technology into a manufacturing environment. During Phase 1, the following tasks were performed: (1) Task 11000 Facility Modification - an existing vacuum chamber was modified and adapted to a GTAW power supply; (2) Task 12000 Materials Selection - four difficult-to-weld materials typically used in the construction of aerospace hardware were chosen for study; (3) Task 13000 VGTAW Experiments - welding experiments were conducted under vacuum using the hollow tungsten electrode and evaluation. As a result of this effort, two materials, NARloy Z and Incoloy 903, were downselected for further characterization in Phase 2; and (4) Task 13100 Aluminum-Lithium Weld Studies - this task was added to the original work statement to investigate the effects of vacuum welding and weld pool vibration on aluminum-lithium alloys.

Dual-beam laser welding of AZ31B magnesium alloy in zero-gap lap joint configuration

NASA Astrophysics Data System (ADS)

Harooni, Masoud; Carlson, Blair; Kovacevic, Radovan

2014-03-01

Porosity within laser welds of magnesium alloys is one of the main roadblocks to achieving high quality joints. One of the causes of pore formation is the presence of pre-existing coatings on the surface of magnesium alloy such as oxide or chromate layers. In this study, single-beam and dual-beam laser heat sources are investigated in relation to mitigation of pores resulting from the presence of the as-received oxide layer on the surface of AZ31B-H24 magnesium alloy during the laser welding process. A fiber laser with a power of up to 4 kW is used to weld samples in a zero-gap lap joint configuration. The effect of dual-beam laser welding with different beam energy ratios is studied on the quality of the weld bead. The purpose of this paper is to identify the beam ratio that best mitigates pore formation in the weld bead. The laser molten pool and the keyhole condition, as well as laser-induced plasma plume are monitored in real-time by use of a high speed charge-coupled device (CCD) camera assisted with a green laser as an illumination source. Tensile and microhardness tests were used to measure the mechanical properties of the laser welded samples. Results showed that a dual-beam laser configuration can effectively mitigate pore formation in the weld bead by a preheating-welding mechanism.

Verifying and Validating Proposed Models for FSW Process Optimization

NASA Technical Reports Server (NTRS)

Schneider, Judith

2008-01-01

This slide presentation reviews Friction Stir Welding (FSW) and the attempts to model the process in order to optimize and improve the process. The studies are ongoing to validate and refine the model of metal flow in the FSW process. There are slides showing the conventional FSW process, a couple of weld tool designs and how the design interacts with the metal flow path. The two basic components of the weld tool are shown, along with geometries of the shoulder design. Modeling of the FSW process is reviewed. Other topics include (1) Microstructure features, (2) Flow Streamlines, (3) Steady-state Nature, and (4) Grain Refinement Mechanisms

Fatigue properties of dissimilar metal laser welded lap joints

NASA Astrophysics Data System (ADS)

Dinsley, Christopher Paul

This work involves laser welding austenitic and duplex stainless steel to zinc-coated mild steel, more specifically 1.2mm V1437, which is a Volvo Truck Coiporation rephosphorised mild steel. The work investigates both tensile and lap shear properties of similar and dissimilar metal laser welded butt and lap joints, with the majority of the investigation concentrating on the fatigue properties of dissimilar metal laser welded lap joints. The problems encountered when laser welding zinc-coated steel are addressed and overcome with regard to dissimilar metal lap joints with stainless steel. The result being the production of a set of guidelines for laser welding stainless steel to zinc-coated mild steel. The stages of laser welded lap joint fatigue life are defined and the factors affecting dissimilar metal laser welded lap joint fatigue properties are analysed and determined; the findings suggesting that dissimilar metal lap joint fatigue properties are primarily controlled by the local stress at the internal lap face and the early crack growth rate of the material at the internal lap face. The lap joint rotation, in turn, is controlled by sheet thickness, weld width and interfacial gap. Laser welded lap joint fatigue properties are found to be independent of base material properties, allowing dissimilar metal lap joints to be produced without fatigue failure occurring preferentially in the weaker parent material, irrespective of large base material property differences. The effects of Marangoni flow on the compositions of the laser weld beads are experimentally characterised. The results providing definite proof of the stirring mechanism within the weld pool through the use of speeds maps for chromium and nickel. Keywords: Laser welding, dissimilar metal, Zinc-coated mild steel, Austenitic stainless steel, Duplex stainless steel, Fatigue, Lap joint rotation, Automotive.

Real-Time Measurement of Width and Height of Weld Beads in GMAW Processes

PubMed Central

Pinto-Lopera, Jesús Emilio; S. T. Motta, José Mauricio; Absi Alfaro, Sadek Crisostomo

2016-01-01

Associated to the weld quality, the weld bead geometry is one of the most important parameters in welding processes. It is a significant requirement in a welding project, especially in automatic welding systems where a specific width, height, or penetration of weld bead is needed. This paper presents a novel technique for real-time measuring of the width and height of weld beads in gas metal arc welding (GMAW) using a single high-speed camera and a long-pass optical filter in a passive vision system. The measuring method is based on digital image processing techniques and the image calibration process is based on projective transformations. The measurement process takes less than 3 milliseconds per image, which allows a transfer rate of more than 300 frames per second. The proposed methodology can be used in any metal transfer mode of a gas metal arc welding process and does not have occlusion problems. The responses of the measurement system, presented here, are in a good agreement with off-line data collected by a common laser-based 3D scanner. Each measurement is compare using a statistical Welch’s t-test of the null hypothesis, which, in any case, does not exceed the threshold of significance level α = 0.01, validating the results and the performance of the proposed vision system. PMID:27649198

Detection of a Pool in Semi-Continuous Castings Made of Heat-Treatable Aluminum Alloys

NASA Astrophysics Data System (ADS)

Krushenko, G. G.; Nazarov, V. P.

2017-12-01

Various products (sheets, sections, etc.) manufactured by metal forming (rolled products, forged pieces, etc.) from semi-continuous castings are widely used in the aerospace industry. The so-called pool, which is the conical volume of a liquid metal, exists at the top of the liquid metal. Experience demonstrates that the geometry, the depth, and the shape of the pool substantially affect the structure formation in a casting and its quality. The application of a titanium nitride nanopowder, which is introduced in a melt in the volume of a rod, as a modifier allowed us to find the exact geometry of the pool.

Friction stir welding of T joints of dissimilar aluminum alloy: A review

NASA Astrophysics Data System (ADS)

Thakare, Shrikant B.; Kalyankar, Vivek D.

2018-04-01

Aluminum alloys are preferred in the mechanical design due to their advantages like high strength, good corrosion resistance, low density and good weldability. In various industrial applications T joints configuration of aluminum alloys are used. In different fields, T joints having skin (horizontal sheet) strengthen by stringers (vertical sheets) were used to increase the strength of structure without increasing the weight. T joints are usually carried out by fusion welding which has limitations in joining of aluminum alloy due to significant distortion and metallurgical defects. Some aluminum alloys are even non weldable by fusion welding. The friction stir welding (FSW) has an excellent replacement of conventional fusion welding for T joints. In this article, FSW of T joints is reviewed by considering aluminum alloy and various joint geometries for defect analysis. The previous experiments carried out on T joints shows the factors such as tool geometry, fixturing device and joint configurations plays significant role in defect free joints. It is essential to investigate the material flow during FSW to know joining mechanism and the formation of joint. In this study the defect occurred in the FSW are studied for various joint configurations and parameters. Also the effect of the parameters and defects occurs on the tensile strength are studied. It is concluded that the T-joints of different joint configurations can be pretended successfully. Comparing to base metal some loss in tensile strength was observed in the weldments as well as overall reduction of the hardness in the thermos mechanically affected zone also observed.

The ultrasonic characteristics of high frequency modulated arc and its application in material processing.

PubMed

He, Longbiao; Yang, Ping; Li, Luming; Wu, Minsheng

2014-12-01

To solve the difficulty of introducing traditional ultrasonic transducers to welding molten pool, high frequency current is used to modulate plasma arc and ultrasonic wave is excited successfully. The characteristics of the excited ultrasonic field are studied. The results show that the amplitude-frequency response of the ultrasonic emission is flat. The modulating current is the main factor influencing the ultrasonic power and the sound pressure depends on the variation of arc plasma stream force. Experimental study of the welding structure indicates grain refinement by the ultrasonic emission of the modulated arc and the test results showed there should be an energy region for the arc ultrasonic to get best welding joints. Copyright © 2014 Elsevier B.V. All rights reserved.

Pulsed infrared thermography for assessment of ultrasonic welds

NASA Astrophysics Data System (ADS)

McGovern, Megan E.; Rinker, Teresa J.; Sekol, Ryan C.

2018-03-01

Battery packs are a critical component in electric vehicles. During pack assembly, the battery cell tab and busbar are ultrasonically welded. The properties of the welds ultimately affect battery pack durability. Quality inspection of these welds is important to ensure durable battery packs. Pack failure is detrimental economically and could also pose a safety hazard, such as thermal runaway. Ultrasonic welds are commonly checked by measuring electrical resistance or auditing using destructive mechanical testing. Resistance measurements are quick, but sensitive to set-up changes. Destructive testing cannot represent the entire weld set. It is possible for a weak weld to satisfy the electrical requirement check, because only sufficient contact between the tabs and busbar is required to yield a low resistance measurement. Laboratory techniques are often not suitable for inline inspection, as they may be time-consuming, use couplant, or are only suitable for coupons. The complex surface geometry also poses difficulties for conventional nondestructive techniques. A method for inspection of ultrasonic welds is proposed using pulsed infrared thermography to identify discrepant welds in a manufacturing environment. Thermal measurements of welds were compared to electrical and mechanical measurements. The heat source distribution was calculated to obtain thermal images with high temporal and spatial resolution. All discrepant welds were readily identifiable using two thermographic techniques: pixel counting and the gradient image. A positive relationship between pixel count and mechanical strength was observed. The results demonstrate the potential of pulsed thermography for inline inspection, which can complement, or even replace, conventional electrical resistance measurements.

Virtual welding equipment for simulation of GMAW processes with integration of power source regulation

NASA Astrophysics Data System (ADS)

Reisgen, Uwe; Schleser, Markus; Mokrov, Oleg; Zabirov, Alexander

2011-06-01

A two dimensional transient numerical analysis and computational module for simulation of electrical and thermal characteristics during electrode melting and metal transfer involved in Gas-Metal-Arc-Welding (GMAW) processes is presented. Solution of non-linear transient heat transfer equation is carried out using a control volume finite difference technique. The computational module also includes controlling and regulation algorithms of industrial welding power sources. The simulation results are the current and voltage waveforms, mean voltage drops at different parts of circuit, total electric power, cathode, anode and arc powers and arc length. We describe application of the model for normal process (constant voltage) and for pulsed processes with U/I and I/I-modulation modes. The comparisons with experimental waveforms of current and voltage show that the model predicts current, voltage and electric power with a high accuracy. The model is used in simulation package SimWeld for calculation of heat flux into the work-piece and the weld seam formation. From the calculated heat flux and weld pool sizes, an equivalent volumetric heat source according to Goldak model, can be generated. The method was implemented and investigated with the simulation software SimWeld developed by the ISF at RWTH Aachen University.

An elastic-plastic fracture mechanics analysis of weld-toe surface cracks in fillet welded T-butt joint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fu, B.

1994-12-31

This paper describes an elastic-plastic fracture mechanics (EPFM) study of shallow weld-toe cracks. Two limiting crack configurations, plane strain edge crack and semi-circular surface crack in fillet welded T-butt plate joint, were analyzed using the finite element method. Crack depth ranging from 2 to 40% of plate thickness were considered. The elastic-plastic analysis, assuming power-law hardening relationship and Mises yield criterion, was based on incremental plasticity theory. Tension and bending loads applied were monotonically increased to a level causing relatively large scale yielding at the crack tip. Effects of weld-notch geometry and ductile material modeling on prediction of fracture mechanicsmore » characterizing parameter were assessed. It was found that the weld-notch effect reduces and the effect of material modeling increases as crack depth increases. Material modeling is less important than geometric modeling in analysis of very shallow cracks but is more important for relatively deeper cracks, e.g. crack depth more than 20% of thickness. The effect of material modeling can be assessed using a simplified structural model. Weld magnification factors derived assuming linear elastic conditions can be applied to EPFM characterization.« less

Study on Mg/Al Weld Seam Based on Zn–Mg–Al Ternary Alloy

PubMed Central

Liu, Liming; Liu, Fei; Zhu, Meili

2014-01-01

Based on the idea of alloying welding seams, a series of Zn–xAl filler metals was calculated and designed for joining Mg/Al dissimilar metals by gas tungsten arc (GTA) welding. An infrared thermography system was used to measure the temperature of the welding pool during the welding process to investigate the solidification process. It was found that the mechanical properties of the welded joints were improved with the increasing of the Al content in the Zn–xAl filler metals, and when Zn–30Al was used as the filler metal, the ultimate tensile strength could reach a maximum of 120 MPa. The reason for the average tensile strength of the joint increasing was that the weak zone of the joint using Zn–30Al filler metal was generated primarily by α-Al instead of MgZn2. When Zn–40Al was used as the filler metal, a new transition zone, about 20 μm-wide, appeared in the edge of the fusion zone near the Mg base metal. Due to the transition zones consisting of MgZn2- and Al-based solid solution, the mechanical property of the joints was deteriorated. PMID:28788508

Modeling the Formation of Transverse Weld during Billet-on-Billet Extrusion

PubMed Central

Mahmoodkhani, Yahya; Wells, Mary; Parson, Nick; Jowett, Chris; Poole, Warren

2014-01-01

A comprehensive mathematical model of the hot extrusion process for aluminum alloys has been developed and validated. The plasticity module was developed using a commercial finite element package, DEFORM-2D, a transient Lagrangian model which couples the thermal and deformation phenomena. Validation of the model against industrial data indicated that it gave excellent predictions of the pressure during extrusion. The finite element predictions of the velocity fields were post-processed to calculate the thickness of the surface cladding as one billet is fed in after another through the die (i.e., the transverse weld). The mathematical model was then used to assess the effect a change in feeder dimensions would have on the shape, thickness and extent of the transverse weld during extrusion. Experimental measurements for different combinations of billet materials show that the model is able to accurately predict the transverse weld shape as well as the clad surface layer to thicknesses of 50 μm. The transverse weld is significantly affected by the feeder geometry shape, but the effects of ram speed, billet material and temperature on the transverse weld dimensions are negligible. PMID:28788629

Investigating the Effects of Pin Tool Design on Friction Stir Welded Ti-6Al-4V

NASA Technical Reports Server (NTRS)

Rubisoff, H. A.; Querin, J. A.; Schneider, Judy A.; Magee, D.

2009-01-01

Friction stir welding (FSWing), a solid state joining technique, uses a non-consumable rotating pin tool to thermomechanically join materials. Heating of the weldment caused by friction and deformation is a function of the interaction between the pin tool and the work piece. Therefore, the geometry of the pin tool is in part responsible for the resulting microstructure and mechanical properties. In this study microwave sintered tungsten carbide (WC) pin tools with tapers and flats were used to FSW Ti-6Al-4V. Transverse sections of welds were mechanically tested, and the microstructure was characterized using optical microscopy (OM) and scanning election microscopy (SEM). X-ray diffraction (XRD) and electron back-scatter diffraction (EBSD) were used to characterize the texture within the welds produced from the different pin tool designs.

Examinations on Laser Remote Welding of Ultra-thin Metal Foils Under Vacuum Conditions

NASA Astrophysics Data System (ADS)

Petrich, Martin; Stambke, Martin; Bergmann, Jean Pierre

Metal foils are commonly used for catalytic converters, vacuum insulations, in medical and electrical industry as well as for sensor applications and packaging. The investigations in this paper determine the influence of reduced atmospheric pressure during the welding process with a highly brilliant 400 W single-mode fiber laser combined with a 2D-scanning system. The laser beam is transmitted through a highly transparent glass into a vacuum chamber, where AISI 304 stainless steel foils with a thickness of 25 μm, 50 μm and 100 μm are positioned. The effects of reduced atmospheric pressure on the plasma formation are investigated by means of high-speed videography. Furthermore, the geometry of the weld seam is compared to atmospheric conditions as well as means of the process stability and the process efficiency. The welds were also evaluated by means of metallography. The research is a contribution for extending the range of micro welding applications and shows new aspects for future developments.

Building A Simulation Model For The Prediction Of Temperature Distribution In Pulsed Laser Spot Welding Of Dissimilar Low Carbon Steel 1020 To Aluminum Alloy 6061

NASA Astrophysics Data System (ADS)

Yousef, Adel K. M.; Taha, Ziad. A.; Shehab, Abeer A.

2011-01-01

This paper describes the development of a computer model used to analyze the heat flow during pulsed Nd: YAG laser spot welding of dissimilar metal; low carbon steel (1020) to aluminum alloy (6061). The model is built using ANSYS FLUENT 3.6 software where almost all the environments simulated to be similar to the experimental environments. A simulation analysis was implemented based on conduction heat transfer out of the key hole where no melting occurs. The effect of laser power and pulse duration was studied. Three peak powers 1, 1.66 and 2.5 kW were varied during pulsed laser spot welding (keeping the energy constant), also the effect of two pulse durations 4 and 8 ms (with constant peak power), on the transient temperature distribution and weld pool dimension were predicated using the present simulation. It was found that the present simulation model can give an indication for choosing the suitable laser parameters (i.e. pulse durations, peak power and interaction time required) during pulsed laser spot welding of dissimilar metals.

In situ strain and temperature measurement and modelling during arc welding

DOE PAGES

Chen, Jian; Yu, Xinghua; Miller, Roger G.; ...

2014-12-26

In this study, experiments and numerical models were applied to investigate the thermal and mechanical behaviours of materials adjacent to the weld pool during arc welding. In the experiment, a new high temperature strain measurement technique based on digital image correlation (DIC) was developed and applied to measure the in situ strain evolution. In contrast to the conventional DIC method that is vulnerable to the high temperature and intense arc light involved in fusion welding processes, the new technique utilised a special surface preparation method to produce high temperature sustaining speckle patterns required by the DIC algorithm as well asmore » a unique optical illumination and filtering system to suppress the influence of the intense arc light. These efforts made it possible for the first time to measure in situ the strain field 1 mm away from the fusion line. The temperature evolution in the weld and the adjacent regions was simultaneously monitored by an infrared camera. Finally and additionally, a thermal–mechanical finite element model was applied to substantiate the experimental measurement.« less

A New Perspective on Fatigue Performance of Advanced High- Strength Steels (AHSS) GMAW Joints

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Zhili; Chiang, Dr. John; Kuo, Dr. Min

2008-01-01

Weld fatigue performance is a critical aspect for application of advanced high-strength steels (AHSS) in automotive body structures. A comparative study has been conducted to evaluate the fatigue life of AHSS welds. The material studied included seven AHSS of various strength levels - DP 600, DP 780, DP 980, M130, M220, solution annealed boron and fully hardened boron steels. Two conventional steels, HSLA 590 and DR 210, were also included for baseline comparison. Lap fillet welds were made on 2-mm nominal thick sheets by the gas metal arc welding process (GMAW). Fatigue test was conducted under a number of stressmore » levels to obtain the S/N curves of the weld joints. It was found that, unlike in the static and impact loading conditions, the fatigue performance of AHSS is not influenced by the HAZ softening in AHSS. There are appreciable differences in the fatigue lives among different AHSS. Changes in weld parameters can influence the fatigue life of the weld joints, particularly of these of higher strength AHSS. A model is developed to predict the fatigue performance of AHSS welds. The validity of the model is benchmarked with the experimental results. This model is capable to capture the effects of weld geometry and weld microstructure and strength on the fatigue performance experimentally observed. The theoretical basis and application of the newly developed fatigue modeling methodology will be discussed.« less

Cancer incidence among welders: possible effects of exposure to extremely low frequency electromagnetic radiation (ELF) and to welding fumes.

PubMed Central

Stern, R M

1987-01-01

Epidemiological studies of cancer incidence among welders disclose a pooled total of 146 cases of leukemia observed versus 159.46 expected, a risk ratio of 0.92, and 40 cases of acute leukemia observed versus 43.39 expected, a risk ratio of 0.92. For respiratory tract cancer, the pooled total is 1789 cases observed versus 1290.7 expected, a risk ratio of 1.39. Most electric welders are exposed to extremely low frequency electromagnetic radiation (ELF) (magnetic flux densities of up to 100,000 microT), a suspected leukemogen, and to concentrated metallic aerosols (up to 200 mg/m3), which can contain the putative respiratory tract carcinogens Cr(VI) and Ni. The two exposures are usually coincident, since welding with an electric current produces welding fumes. The observation of an excess risk for respiratory tract cancer strongly suggests significant exposure both to fumes and to ELF. The absence of increased risk for all leukemia or for acute leukemia among ELF-exposed welders does not support the hypothesis that the observed excess risk for leukemia or acute leukemia among workers in the electrical trades is due to their ELF exposure, which on the average is lower than that of welders. PMID:3447902

Studying the Issues in Laser Joining of Lightweight Materials in a Coach-Peel Joint Configuration

NASA Astrophysics Data System (ADS)

Yang, Guang

In the automotive industry, aluminum alloys have been widely used and partially replaced the conventional steel structures in order to decrease the weight of a car and improve its fuel efficiency. This Thesis focuses on the development of laser joining of light-weight materials, such as aluminum alloys and high-strength galvanized steels. Among different joint types, the coach-peel configuration is of a specific design that requires a heat source capable of heating up a large surface area of the joint. Coach-peel joints applied on the visible exterior of a car require a smooth transition from the weld surface to the panel surface and low surface roughness without any need for post-processing. Although these joints are used as non-load-bearing components, a desirable strength of the weld is also needed. A fusion-brazing process using a dual-beam laser allows the automotive components such as the roof and side member panels to be joined in a coach-peel configuration with a high surface quality as well as an acceptable strength of the weld. To improve the weld surface quality, processing parameters such as laser beam configuration, laser-wire position, and shielding gas parameters were optimized for joining of aluminum alloy to aluminum alloy. Laser power was optimized for dual-beam laser joining of aluminum alloy to galvanized steel at high speed. The feasibility of joining as-received panels with lubricant was also explored. The identification of strain hardening models of aluminum alloys was conducted for the mechanical finite element analysis of the joint. Control of the molten pool solidification through the selection of laser beam configuration is one approach to improve joint quality. Laser joining of aluminum alloy AA 6111-T4 coach peel panels with the addition of AA 4047 filler wire was investigated using three configurations of laser beam: a single beam, dual beams in-line with the weld bead, and dual beams aligned perpendicular to the weld bead (herein referred to as cross-beam). To compare the three joining processes, the transient heat distribution, cooling rates, and solidification rates were analyzed by three-dimensional finite element models using ANSYS. Microstructure evolution, tensile strength, fracture mechanisms, and surface roughness of joints were investigated accordingly. To improve the weld surface quality of aluminum joints, the laser-wire position and the gas parameters were optimized. Visualization of the gas flow by a CCD camera revealed the effects of nozzle shape, flow rate, inclination angle of the gas tube, nozzle position, and gas compositions (argon and helium) on the weld surface quality. The suppression of plasma plume and the effects of oxidation on the molten pool were illustrated in detail. With an optimized set of processing parameters, the weld surface roughness (Ra) of approximately 1 microm can be achieved. The feasibility of fabricating the aluminum alloy panel joint in the as-received condition, i.e., with stamping lubricant, by using the cross-beam laser was investigated. Two commercial mineral oils, Bonderite L-FM MP-404 and Ferrocote 61 MAL HCL, were applied onto clean panels prior to joining in order to simulate the conditions of the production environment. The formation and growth of hydrogen bubbles inside the molten pool, the stability of welding process, and the possible energy absorption capability of the porous weld were explained. Besides joining of similar materials, cross-beam laser was applied to join aluminum alloy 6111 to hot-dip galvanized steel in the coach-peel configuration. The filler material was not only brazed onto the galvanized steel but also partially fusion-welded with the aluminum panel. Through adjusting the laser power to 3.4 kW, a desirable wetting and spreading of filler wire on both panel surfaces could be achieved, and the thickness of intermetallic layer in the middle section of the interface between the weld bead and steel was less than 2 microm. To better understand the solid/liquid interfacial reaction at the brazing interface, two rotary Gaussian heat source models were introduced to simulate the temperature distribution in the molten pool by using the finite element method. Joint properties were examined in terms of microstructure and mechanical properties. Simulation of the mechanical response of a coach-peel joint is instructive for improvement of the joining process. The effective true stress-strain curve of fusion-brazed AA 4047 was difficult to obtain experimentally. Therefore, the von Mises isotropic flow function of the weld bead was inversely derived by image-based finite element analysis. Through iterative correction, the predicted tensile response of the coach-peel joint matched well with the experiment. The von Mises fracture stresses at the fusion zone boundary and the brazing interface were identified, respectively.

Prediction of guided wave scattering by defects in rails using numerical modelling

NASA Astrophysics Data System (ADS)

Long, Craig S.; Loveday, Philip W.

2014-02-01

A guided wave based monitoring system for welded freight rail, has previously been developed. The current arrangement consists of alternating transmit and receive stations positioned roughly 1 km apart, and is designed to reliably detect complete breaks in a rail. Current research efforts are focused on extending this system to include a pulse-echo mode of operation in order to detect, locate, monitor and possibly characterize damage, before a complete break occurs. For monitoring and inspection applications, it is beneficial to be able to distinguish between scattering defects which do not represent damage (such as welds) and cracks which could result in rail breaks. In this paper we investigate the complex interaction between selected propagating modes and various weld and crack geometries in an attempt to relate scattering behaviour to defect geometry. An efficient hybrid method is employed which models the volume containing the defect with conventional solid finite elements, while the semi-infinite incoming and outgoing waveguides are accounted for using the SAFE method. Four candidate modes, suitable for long range propagation, are identified and evaluated. A weighted average reflection coefficient is used as a measure to quantify mode conversion between these four modes, and results are represented graphically in the form of reflection maps. The results show that it should be possible to distinguish between a large crack in the crown of the rail and a weld. We also show that there may be difficulties associated with reliably identifying cracks in the web as well as cracks in the crown which occur at a thermite weld. We suspect that it will be difficult to detect damage in the foot of the rail.

FRICTION STIR LAP WELDING OF ALUMINUM - POLYMER USING SCRIBE TECHNOLOGY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Upadhyay, Piyush; Hovanski, Yuri; Fifield, Leonard S.

2015-02-16

Friction Stir Scribe (FSS) technology is a relatively new variant of Friction Stir Welding (FSW) which enables lap joining of dissimilar material with very different melting points and different high temperature flow behaviors. The cutter scribe attached at the tip of FSW tool pin effectively cuts the high melting point material such that a mechanically interlocking feature is created between the dissimilar materials. The geometric shape of this interlocking feature determines the shear strength attained by the lap joint. This work presents first use of scribe technology in joining polymers to aluminum alloy. Details of the several runs of scribemore » welding performed in lap joining of ~3.175mm thick polymers including HDPE, filled and unfilled Nylon 66 to 2mm thick AA5182 are presented. The effect of scribe geometry and length on weld interlocking features is presented along with lap shear strength evaluations.« less

Heat Transfer Analysis of Localized Heat-Treatment for Grade 91 Steel

NASA Astrophysics Data System (ADS)

Walker, Jacob D.

Many of the projects utilizing Grade 91 steel are large in scale, therefore it is necessary to assemble on site. The assembly of the major pieces requires welding in the assembly; this drastically changes the superior mechanical properties of Grade 91 steel that it was specifically developed for. Therefore, because of the adverse effects of welding on the mechanical properties of Grade 91, it is necessary to do a localized post weld heat treatment. As with most metallic materials grade 91 steel requires a very specific heat treatment process. This process includes a specific temperature and duration at that temperature to achieve the heat treatment desired. Extensive research has been done to determine the proper temperatures and duration to provide the proper microstructure for the superior mechanical properties that are inherent to Grade 91 steel. The welded sections are typically large structures that require local heat treatments and cannot be placed in an oven. The locations of these structures vary from indoors in a controlled environment to outdoors with unpredictable environments. These environments can be controlled somewhat, however in large part the surrounding conditions are unchangeable. Therefore, there is a need to develop methods to accurately apply the surrounding conditions and geometries to a theoretical model in order to provide the proper requirements for the local heat treatment procedure. Within this requirement is the requirement to define unknowns used in the heat transfer equations so that accurate models can be produced and accurate results predicted. This study investigates experimentally and numerically the heat transfer and temperature fields of Grade 91 piping in a local heat treatment. The objective of this thesis research is to determine all of the needed heat transfer coefficients. The appropriate heat transfer coefficients are determined through the inverse heat conduction method utilizing a ceramic heat blanket. This will be done through an inverse method by collecting actual data from different conditions and temperatures. Then the heat transfer coefficients are used to set up a model to determine the appropriate post-weld heat treatment conditions for Grade 91 steel. This will enable one to use the derived coefficients to run a forward analysis with the specific geometry and conditions they will encounter in the heat treatment process for their application. The analysis will provide a theoretical determination of time and temperatures needed to maintain the temperature for the proper time needed to properly heat treat the welded section in the desired areas that have been joined together through a welding process. Finally time and temperature combinations are compared with experimentally measured data. The forward model code applied to the parameters of the heat-treatment can then appropriately assist to determine the proper post-weld heat treatment conditions for the desired toughness and creep properties. This research is very beneficial to the joining of metals industry because it provides a way to ensure the method used to heat treat the welded section is being properly done, and the required heat treatment is achieved. It is applicable to many different geometries so that it can be modified to specific situations.

A comparison of LBW and GTAW processes in miniature closure welds

NASA Astrophysics Data System (ADS)

Knorovsky, G. A.; Fuerschbach, P. W.; Gianoulakis, S. E.; Burchett, S. N.

When small electronic components with glass-to-metal seals are closure welded, the residual stresses that develop in the glass are of concern. If these stresses exceed allowable tensile levels' the resulting weld-induced seal failure may cause the entire component to be scrapped or reworked at a substantial cost. Conventional wisdom says the best welding process for these applications is that which provides the least heat input, and so in that respect, Laser Beam Welding (LBW) provides less heat input than Gas Tungsten Arc Welding (GTAW), however, other concerns, such as weld fit-up, part variability, and material weldability, can modify the final choice of a welding process. In this paper, we compare the characteristic levels of heat input and the residual stresses generated in glass seals for two processes (as calculated by a 3D Finite Element Analysis) as a function of heat input and travel speed, and contrast some of the other manufacturing decisions that must be made in choosing a production process. The geometry chosen is that of a standing edge corner weld in a cylindrical container about 20 mm diameter by 35 mm tall. Four metal pins are glassed into the part lid. The stresses calculated from the resulting from continuous wave CO2 LBW are compared with those resulting from GTAW. The total energy required by the laser weld is significantly less than that needed for the equivalent size GTA weld. The energy input requirements for a given size weld is inversely proportional to the travel speed, but approaches a saturation level as the travel speed increases. LBW travel speeds ranging from 10 mm/s to 50 mm/s were examined.

Effects of beam configurations on wire melting and transfer behaviors in dual beam laser welding with filler wire

NASA Astrophysics Data System (ADS)

Ma, Guolong; Li, Liqun; Chen, Yanbin

2017-06-01

Butt joints of 2 mm thick stainless steel with 0.5 mm gap were fabricated by dual beam laser welding with filler wire technique. The wire melting and transfer behaviors with different beam configurations were investigated detailedly in a stable liquid bridge mode and an unstable droplet mode. A high speed video system assisted by a high pulse diode laser as an illumination source was utilized to record the process in real time. The difference of welding stability between single and dual beam laser welding with filler wire was also compartively studied. In liquid bridge transfer mode, the results indicated that the transfer process and welding stability were disturbed in the form of "broken-reformed" liquid bridge in tandem configuration, while improved by stabilizing the molten pool dynamics with a proper fluid pattern in side-by-side configuration, compared to sigle beam laser welding with filler wire. The droplet transfer period and critical radius were studied in droplet transfer mode. The transfer stability of side-by-side configuration with the minium transfer period and critical droplet size was better than the other two configurations. This was attributed to that the action direction and good stability of the resultant force which were beneficial to transfer process in this case. The side-by-side configuration showed obvious superiority on improving welding stability in both transfer modes. An acceptable weld bead was successfully generated even in undesirable droplet transfer mode under the present conditions.

Role of Oxygen as Surface-Active Element in Linear GTA Welding Process

NASA Astrophysics Data System (ADS)

Yadaiah, Nirsanametla; Bag, Swarup

2013-11-01

Although the surface-active elements such as oxygen and sulfur have an adverse effect on momentum transport in liquid metals during fusion welding, such elements can be used beneficially up to a certain limit to increase the weld penetration in the gas tungsten arc (GTA) welding process. The fluid flow pattern and consequently the weld penetration and width change due to a change in coefficient of surface tension from a negative value to a positive value. The present work is focused on the analysis of possible effects of surface-active elements to change the weld pool dimensions in linear GTA welding. A 3D finite element-based heat transfer and fluid flow model is developed to study the effect of surface-active elements on stainless steel plates. A velocity in the order of 180 mm/s due to surface tension force is estimated at an optimum concentration of surface-active elements. Further, the differential evolution-based global optimization algorithm is integrated with the numerical model to estimate uncertain model parameters such as arc efficiency, effective arc radius, and effective values of material properties at high temperatures. The effective values of thermal conductivity and viscosity are estimated to be enhanced nine and seven times, respectively, over corresponding room temperature values. An error analysis is also performed to find out the overall reliability of the computed results, and a maximum reliability of 0.94 is achieved.

Numerical simulation of spatter formation during fiber laser welding of 5083 aluminum alloy at full penetration condition

NASA Astrophysics Data System (ADS)

Wu, Dongsheng; Hua, Xueming; Huang, Lijin; Zhao, Jiang

2018-03-01

The droplet escape condition in laser welding is established in this paper. A three-dimensional numerical model is developed to study the weld pool convection and spatter formation at full penetration during the fiber laser welding of 5083 aluminum alloy. It is found that when laser power is 9 kW, the bottom of the keyhole is dynamically opened and closed. When the bottom of the keyhole is closed, the molten metal at the bottom of the back keyhole wall flows upwards along the fusion line. When the bottom of the keyhole is opened, few spatters can be seen around the keyhole at the top surface, two flow patterns exists in the rear part of the keyhole: a portion of molten metal flows upwards along the fusion line, other portion of molten metal flows to the bottom of the keyhole, which promote the spatter formation at the bottom of the keyhole rear wall.

Investigation of Microstructural Features Determining the Toughness of 980 MPa Bainitic Weld Metal

NASA Astrophysics Data System (ADS)

Cao, R.; Zhang, X. B.; Wang, Z.; Peng, Y.; Du, W. S.; Tian, Z. L.; Chen, J. H.

2014-02-01

The microstructural features that control the impact toughness of weld metals of a 980 MPa 8 pct Ni high-strength steel are investigated using instrumented Charpy V tester, optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), electron back-scattered diffraction (EBSD), and finite-element method (FEM) calculation. The results show that the critical event for cleavage fracture in this high-strength steel and weld metals is the propagation of a bainite packet-sized crack across the packet boundary into contiguous packets, and the bainitic packet sizes control the impact toughness. The high-angle misorientation boundaries detected in a bainite packet by EBSD form fine tear ridges on fracture surfaces. However, they are not the decisive factors controlling the cleavage fracture. The effects of Ni content are essential factors for improving the toughness. The extra large cleavage facets seriously deteriorate the toughness, which are formed on the interfaces of large columnar crystals growing in welding pools with high heat input.

Friction Stir Spot Welding (FSSW) of Advanced High Strength Steel (AHSS)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Santella, M. L.; Hovanski, Yuri; Pan, Tsung-Yu

Friction stir spot welding (FSSW) is applied to join advanced high strength steels (AHSS): galvannealed dual phase 780 MPa steel (DP780GA), transformation induced plasticity 780 MPa steel (TRIP780), and hot-stamped boron steel (HSBS). A low-cost Si3N4 ceramic tool was developed and used for making welds in this study instead of polycrystalline cubic boron nitride (PCBN) material used in earlier studies. FSSW has the advantages of solid-state, low-temperature process, and the ability of joining dissimilar grade of steels and thicknesses. Two different tool shoulder geometries, concave with smooth surface and convex with spiral pattern, were used in the study. Welds weremore » made by a 2-step displacement control process with weld time of 4, 6, and 10 seconds. Static tensile lap-shear strength achieved 16.4 kN for DP780GA-HSBS and 13.2kN for TRIP780-HSBS, above the spot weld strength requirements by AWS. Nugget pull-out was the failure mode of the joint. The joining mechanism was illustrated from the cross-section micrographs. Microhardness measurement showed hardening in the upper sheet steel (DP780GA or TRIP780) in the weld, but softening of HSBS in the heat-affect zone (HAZ). The study demonstrated the feasibility of making high-strength AHSS spot welds with low-cost tools.« less

Hybrid FSWeld-bonded joint fatigue behaviour

NASA Astrophysics Data System (ADS)

Lertora, Enrico; Mandolfino, Chiara; Gambaro, Carla; Pizzorni, Marco

2018-05-01

Aluminium alloys, widely used in aeronautics, are increasingly involved in the automotive industry due to the good relationship between mechanical strength and specific weight. The lightening of the structures is the first objective, which allows the decreasing in the weight in motion. The use of aluminium alloys has also seen the introduction of the Friction Stir Welding (FSW) technique for the production of structural overlapping joints. FSW allows us to weld overlap joints free from defects, but with the presence of a structural notch further aggravated by the presence of a "hook" defect near the edge of the weld. Furthermore, FSW presents a weld penetration area connected to the tool geometry and penetration. The experimental activity will be focused on the combination of two different joining techniques, which can synergistically improve the final joint resistance. In particular, the welding and bonding process most commonly known as weld-bonding is defined as a hybrid process, as it combines two different junction processes. In this paper we analyse FSWelded AA6082 aluminium alloy overlapped joint with the aim of quantitatively evaluating the improvement provided by the presence of an epoxy adhesive between the plates. After optimising the weld-bonding process, the mechanical behaviour of welded joints will be analysed by static and dynamic tests. The presence of the adhesive should limit the negative effect of the structural notch inevitable in a FSW overlapped joint.

Numerical simulation of metallic wire arc additive manufacturing (WAAM)

NASA Astrophysics Data System (ADS)

Graf, M.; Pradjadhiana, K. P.; Hälsig, A.; Manurung, Y. H. P.; Awiszus, B.

2018-05-01

Additive-manufacturing technologies have been gaining tremendously in popularity for some years in the production of single-part series with complex, close-to-final-contour geometries and the processing of special or hybrid materials. In principle, the processes can be subdivided into wire-based and powder-based processes in accordance with the Association of German Engineers (VDI) Guideline 3405. A further subdivision is made with respect to the smelting technology. In all of the processes, the base material is applied in layers at the points where it is needed in accordance with the final contour. The process that was investigated was wire-based, multi-pass welding by means of gas-metal arc welding. This was accomplished in the present study by determining the material parameters (thermo-mechanical and thermo-physical characteristics) of the welding filler G3Si1 (material number: 1.5125) that were necessary for the numerical simulation and implementing them in a commercial FE program (MSC Marc Mentat). The focus of this paper was on simulation and validation with respect to geometry and microstructural development in the welding passes. The resulting minimal deviation between reality and simulation was a result of the measurement inertia of the thermocouples. In general, however, the FE model can be used to make a very good predetermination of the cooling behaviour, which affects the microstructural development and thus the mechanical properties of the joining zone, as well as the geometric design of the component (distortion, etc.).

Advanced Process Possibilities in Friction Crush Welding of Aluminum, Steel, and Copper by Using an Additional Wire

NASA Astrophysics Data System (ADS)

Besler, Florian A.; Grant, Richard J.; Schindele, Paul; Stegmüller, Michael J. R.

2017-12-01

Joining sheet metal can be problematic using traditional friction welding techniques. Friction crush welding (FCW) offers a high speed process which requires a simple edge preparation and can be applied to out-of-plane geometries. In this work, an implementation of FCW was employed using an additional wire to weld sheets of EN AW5754 H22, DC01, and Cu-DHP. The joint is formed by bringing together two sheet metal parts, introducing a wire into the weld zone and employing a rotating disk which is subject to an external force. The requirements of the welding preparation and the fundamental process variables are shown. Thermal measurements were taken which give evidence about the maximum temperature in the welding center and the temperature in the periphery of the sheet metals being joined. The high welding speed along with a relatively low heat input results in a minimal distortion of the sheet metal and marginal metallurgical changes in the parent material. In the steel specimens, this FCW implementation produces a fine grain microstructure, enhancing mechanical properties in the region of the weld. Aluminum and copper produced mean bond strengths of 77 and 69 pct to that of the parent material, respectively, whilst the steel demonstrated a strength of 98 pct. Using a wire offers the opportunity to use a higher-alloyed additional material and to precisely adjust the additional material volume appropriate for a given material alignment and thickness.

Experimental and numerical study of spatter formation and composition change in fiber laser welding of aluminum alloy

NASA Astrophysics Data System (ADS)

Wu, Dongsheng; Hua, Xueming; Ye, Youxiong; Huang, Lijin; Li, Fang; Huang, Ye

2018-05-01

A laser welding experiment with glass is conducted to directly observe the keyhole behavior and spatter formation in fiber laser welding of aluminum alloy. A 3D model is developed to investigate the spatter formation and composition change. An additional conservation equation is introduced to describe the Mg element distribution, and the Mg element loss due to evaporation is also considered. Based on numerical and experimental results, it is found that the keyhole geometry in laser welding of aluminum alloy is different from that in laser welding of steel. There are three required steps for spatter formation around the keyhole. The high momentum of the molten metal, the high recoil pressure and vapor shear stress, and the low surface tension around the keyhole contribute to the easy formation of spatter. The in-homogeneous distribution of Mg element in the weld can be attributable to the continuous evaporation of Mg element at the top surface of keyhole rear, the upward flow of low Mg element region from the bottom of the keyhole to the top surface of keyhole rear along the fusion line, the collapse of the keyhole, and the ejection of spatters.

The numerical simulation of heat transfer during a hybrid laser-MIG welding using equivalent heat source approach

NASA Astrophysics Data System (ADS)

Bendaoud, Issam; Matteï, Simone; Cicala, Eugen; Tomashchuk, Iryna; Andrzejewski, Henri; Sallamand, Pierre; Mathieu, Alexandre; Bouchaud, Fréderic

2014-03-01

The present study is dedicated to the numerical simulation of an industrial case of hybrid laser-MIG welding of high thickness duplex steel UR2507Cu with Y-shaped chamfer geometry. It consists in simulation of heat transfer phenomena using heat equivalent source approach and implementing in finite element software COMSOL Multiphysics. A numerical exploratory designs method is used to identify the heat sources parameters in order to obtain a minimal required difference between the numerical results and the experiment which are the shape of the welded zone and the temperature evolution in different locations. The obtained results were found in good correspondence with experiment, both for melted zone shape and thermal history.

Motion Simulation Analysis of Rail Weld CNC Fine Milling Machine

NASA Astrophysics Data System (ADS)

Mao, Huajie; Shu, Min; Li, Chao; Zhang, Baojun

CNC fine milling machine is a new advanced equipment of rail weld precision machining with high precision, high efficiency, low environmental pollution and other technical advantages. The motion performance of this machine directly affects its machining accuracy and stability, which makes it an important consideration for its design. Based on the design drawings, this article completed 3D modeling of 60mm/kg rail weld CNC fine milling machine by using Solidworks. After that, the geometry was imported into Adams to finish the motion simulation analysis. The displacement, velocity, angular velocity and some other kinematical parameters curves of the main components were obtained in the post-processing and these are the scientific basis for the design and development for this machine.

Crack-free conditions in welding of glass by ultrashort laser pulse.

PubMed

Miyamoto, Isamu; Cvecek, Kristian; Schmidt, Michael

2013-06-17

The spatial distribution of the laser energy absorbed by nonlinear absorption process in bulk glass w(z) is determined and thermal cycles due to the successive ultrashort laser pulse (USLP) is simulated using w(z) based on the transient thermal conduction model. The thermal stress produced in internal melting of bulk glass by USLP is qualitatively analyzed based on a simple thermal stress model, and crack-free conditions are studied in glass having large coefficient of thermal expansion. In heating process, cracks are prevented when the laser pulse impinges into glass with temperatures higher than the softening temperature of glass. In cooling process, shrinkage stress is suppressed to prevent cracks, because the embedded molten pool produced by nonlinear absorption process behaves like an elastic body under the compressive stress field unlike the case of CW-laser welding where the molten pool having a free surface produced by linear absorption process is plastically deformed under the compressive stress field.

Artificial neural networks application for modeling of friction stir welding effects on mechanical properties of 7075-T6 aluminum alloy

NASA Astrophysics Data System (ADS)

Maleki, E.

2015-12-01

Friction stir welding (FSW) is a relatively new solid-state joining technique that is widely adopted in manufacturing and industry fields to join different metallic alloys that are hard to weld by conventional fusion welding. Friction stir welding is a very complex process comprising several highly coupled physical phenomena. The complex geometry of some kinds of joints makes it difficult to develop an overall governing equations system for theoretical behavior analyse of the friction stir welded joints. Weld quality is predominantly affected by welding effective parameters, and the experiments are often time consuming and costly. On the other hand, employing artificial intelligence (AI) systems such as artificial neural networks (ANNs) as an efficient approach to solve the science and engineering problems is considerable. In present study modeling of FSW effective parameters by ANNs is investigated. To train the networks, experimental test results on thirty AA-7075-T6 specimens are considered, and the networks are developed based on back propagation (BP) algorithm. ANNs testing are carried out using different experimental data that they are not used during networks training. In this paper, rotational speed of tool, welding speed, axial force, shoulder diameter, pin diameter and tool hardness are regarded as inputs of the ANNs. Yield strength, tensile strength, notch-tensile strength and hardness of welding zone are gathered as outputs of neural networks. According to the obtained results, predicted values for the hardness of welding zone, yield strength, tensile strength and notch-tensile strength have the least mean relative error (MRE), respectively. Comparison of the predicted and the experimental results confirms that the networks are adjusted carefully, and the ANN can be used for modeling of FSW effective parameters.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stine, Andrew Martin; Pierce, Stanley W.; Moniz, Paul F.

The welding equipment used for welding iridium containers (clads) at Los Alamos National Laboratory is twenty five years old and is undergoing an upgrade. With the upgrade, there is a requirement for requalification of the welding process, and the opportunity for process improvement. Testing of the new system and requalification will require several welds on iridium test parts and clads, and any efforts to improve the process will add to the need for iridium parts. The extreme high cost of iridium imposes a severe limitation on the extent of test welding that can be done. The 2 inch diameter, 0.027more » inch thick, iridium blank disc that the clad cup is formed from, is useful for initial weld trials, but it costs $5000. The development clad sets needed for final tests and requalification cost $15,000 per set. A solution to iridium cost issue would be to do the majority of the weld development on a less expensive surrogate metal with similar weld characteristics. One such metal is molybdenum. Since its melting index (melting temperature x thermal conductivity) is closest to iridium, welds on molybdenum should be similar in size for a given weld power level. Molybdenum is inexpensive; a single 2 inch molybdenum disc costs only $9. In order to evaluate molybdenum as a surrogate for iridium, GTA welds were first developed to provide full penetration on 0.030 inch thick molybdenum discs at speeds of 20, 25, and 30 inches per minute (ipm). These weld parameters were then repeated on the standard 0.027 inch thick iridium blanks. The top surface and bottom surface (root) width and grain structure of the molybdenum and iridium welds were compared, and similarities were evident between the two metals. Due to material and thickness differences, the iridium welds were approximately 35% wider than the molybdenum welds. A reduction in iridium weld current of 35% produce welds slightly smaller than the molybdenum welds yet showed that current could be scaled according to molybdenum/iridium weld width ratio to achieve similar welds. Further weld trials using various thicknesses of molybdenum determined that 0.024 inch thick molybdenum material would best match the 0.027 inch thick iridium in achieving comparable welds when using the same welding parameters. Across the range of welding speeds, the characteristic weld pool shape and solidification grain structure in the two materials was also similar. With the similarity of welding characteristics confirmed, and the appropriate thickness of molybdenum determined, it has been concluded that the use of molybdenum discs and tube sections will greatly expand the weld testing opportunities prior to iridium weld qualification« less

Experimental Study and Fractal Analysis on the Anisotropic Performance of Explosively Welded Interfaces of 304 Stainless Steel/245 Carbon Steel

NASA Astrophysics Data System (ADS)

Fu, Yanshu; Qiu, Yaohui; Li, Yulong

2018-03-01

The mechanical anisotropy of an explosive welding composite plate made of 304 stainless steel/245 steel was studied through shear experiments performed on explosively welded wavy interfaces along several orientation angles. The results indicated that the strength and the fracture energy of samples significantly varied with the orientation angles. The fracture surfaces of all samples were observed using a scanning electron microscope and through three-dimensional structure microscopy. The periodic features of all the fracture surfaces were clearly shown in different fracture modes. The fractal dimension of the fracture surfaces was calculated based on the fractal geometry by the box-counting method in MATLAB. The cohesive element model was used to analyze the fracture energy according to the physical dependence of the fractal dimension on thermodynamic entropy and interface separation energy. The fracture energy was an exponential function of the fractal dimension value, which was in good agreement with the experimental results. All results were validated for effective use in the application of anisotropy analysis to the welded interface and structural optimization of explosively welded composite plates.

Comparison of the Effects of Tool Geometry for Friction Stir Welding Thin Sheet Aluminum Alloys for Aerospace Applications

NASA Technical Reports Server (NTRS)

Merry, Josh; Takeshita, Jennifer; Tweedy, Bryan; Burford, Dwight

2006-01-01

In this presentation, the results of a recent study on the effect of pin tool design for friction stir welding thin sheets (0.040") of aluminum alloys 2024 and 7075 are provided. The objective of this study was to investigate and document the effect of tool shoulder and pin diameter, as well as the presence of pin flutes, on the resultant microstructure and mechanical properties at both room temperature and cryogenic temperature. Specifically, the comparison between three tools will include: FSW process load analysis (tool forces required to fabricate the welds), Static Mechanical Properties (ultimate tensile strength, yield strength, and elongation), and Process window documenting the range of parameters that can be used with the three pin tools investigated. All samples were naturally aged for a period greater than 10 days. Prior research has shown 7075 may require post weld heat treatment. Therefore, an additional pair of room temperature and cryogenic temperature samples was post-weld aged to the 7075-T7 condition prior to mechanical testing.

Experimental Study and Fractal Analysis on the Anisotropic Performance of Explosively Welded Interfaces of 304 Stainless Steel/245 Carbon Steel

NASA Astrophysics Data System (ADS)

Fu, Yanshu; Qiu, Yaohui; Li, Yulong

2018-05-01

The mechanical anisotropy of an explosive welding composite plate made of 304 stainless steel/245 steel was studied through shear experiments performed on explosively welded wavy interfaces along several orientation angles. The results indicated that the strength and the fracture energy of samples significantly varied with the orientation angles. The fracture surfaces of all samples were observed using a scanning electron microscope and through three-dimensional structure microscopy. The periodic features of all the fracture surfaces were clearly shown in different fracture modes. The fractal dimension of the fracture surfaces was calculated based on the fractal geometry by the box-counting method in MATLAB. The cohesive element model was used to analyze the fracture energy according to the physical dependence of the fractal dimension on thermodynamic entropy and interface separation energy. The fracture energy was an exponential function of the fractal dimension value, which was in good agreement with the experimental results. All results were validated for effective use in the application of anisotropy analysis to the welded interface and structural optimization of explosively welded composite plates.

A model for prediction of fume formation rate in gas metal arc welding (GMAW), globular and spray modes, DC electrode positive.

PubMed

Dennis, J H; Hewitt, P J; Redding, C A; Workman, A D

2001-03-01

Prediction of fume formation rate during metal arc welding and the composition of the fume are of interest to occupational hygienists concerned with risk assessment and to manufacturers of welding consumables. A model for GMAW (DC electrode positive) is described based on the welder determined process parameters (current, wire feed rate and wire composition), on the surface area of molten metal in the arc and on the partial vapour pressures of the component metals of the alloy wire. The model is applicable to globular and spray welding transfer modes but not to dip mode. Metal evaporation from a droplet is evaluated for short time increments and total evaporation obtained by summation over the life of the droplet. The contribution of fume derived from the weld pool and spatter (particles of metal ejected from the arc) is discussed, as are limitations of the model. Calculated droplet temperatures are similar to values determined by other workers. A degree of relationship between predicted and measured fume formation rates is demonstrated but the model does not at this stage provide a reliable predictive tool.

Structural analysis of a reflux pool-boiler solar receiver

NASA Astrophysics Data System (ADS)

Hoffman, E. L.; Stone, C. M.

1991-06-01

Coupled thermal-structural finite element calculations of a reflux pool-boiler solar receiver were performed to characterize the operating stresses and to address issues affecting the service life of the receiver. Analyses performed using shell elements provided information for receiver material selection and design optimization. Calculations based on linear elastic fracture mechanics principles were performed using continuum elements to assess the vulnerability of a seam-weld to fatigue crack growth. All calculations were performed using ABAQUS, a general purpose finite element code, and elements specifically formulated for coupled thermal-structural analysis. Two materials were evaluated: 316L SS and Haynes 230 alloys. The receiver response was simulated for a combination of structural and thermal loads that represent the startup and operating conditions of the receiver. For both materials, maximum stresses in the receiver developed shortly after startup due to uneven temperature distribution across the receiver surface. The largest effective stress was near yield in the 316L SS receiver and below 39 percent of yield in the Haynes 230 receiver. The calculations demonstrated that stress reductions of over 25 percent could be obtained by reducing the aft dome thickness to one closer to the absorber. The fatigue calculations demonstrated that the stress distribution near the seam-weld notch depends primarily on the structural load created by internal pressurization of the receiver rather than the thermal, indicating that the thermal loads can be neglected when assessing the stress intensity near the seam-weld notch. The stress intensity factor, computed using the J-integral method and crack opening-displacement field equations, was significantly below the fatigue threshold for most steels. The calculations indicated that the weld notch was always loaded in compression, a condition which is not conducive to fatigue crack growth.

Controls on the size and occurrence of pools in coarse-grained forest rivers

Treesearch

John M. Buffington; Thomas E. Lisle; Richard D. Woodsmith; Sue Hilton

2002-01-01

Controls on pool formation are examined in gravel- and cobble-bed rivers in forest mountain drainage basins of northern California, southern Oregon, and southeastern Alaska. We demonstrate that the majority of pools at our study sites are formed by flow obstructions and that pool geometry and frequency largely depend on obstruction characteristics (size, type, and...

Exposure to welding fumes increases lung cancer risk among light smokers but not among heavy smokers: evidence from two case-control studies in Montreal.

PubMed

Vallières, Eric; Pintos, Javier; Lavoué, Jérôme; Parent, Marie-Élise; Rachet, Bernard; Siemiatycki, Jack

2012-08-01

We investigated relationships between occupational exposure to gas and arc welding fumes and the risk of lung cancer among workers exposed to these agents throughout the spectrum of industries. Two population-based case-control studies were conducted in Montreal. Study I (1979-1986) included 857 cases and 1066 controls, and Study II (1996-2001) comprised 736 cases and 894 controls. Detailed job histories were obtained by interview and evaluated by an expert team of chemist-hygienists to estimate degree of exposure to approximately 300 substances for each job. Gas and arc welding fumes were among the agents evaluated. We estimated odds ratios (ORs) and 95% confidence intervals (CIs) of lung cancer using logistic regression, adjusting for smoking history and other covariates. The two studies provided similar results, so a pooled analysis was conducted. Among all subjects, no significant association was found between lung cancer and gas welding fumes (OR = 1.1; 95% CI = 0.9-1.4) or arc welding fumes (OR = 1.0; 95% CI = 0.8-1.2). However, when restricting attention to light smokers, there was an increased risk of lung cancer in relation to gas welding fumes (OR = 2.9; 95% CI = 1.7-4.8) and arc welding fumes (OR = 2.3; 95% CI = 1.3-3.8), with even higher OR estimates among workers with the highest cumulative exposures. In conclusion, there was no detectable excess risk of lung cancer due to welding fumes among moderate to heavy smokers; but among light smokers we found an excess risk related to both types of welding fumes.

Exposure to welding fumes increases lung cancer risk among light smokers but not among heavy smokers: evidence from two case–control studies in Montreal

PubMed Central

Vallières, Eric; Pintos, Javier; Lavoué, Jérôme; Parent, Marie-Élise; Rachet, Bernard; Siemiatycki, Jack

2012-01-01

We investigated relationships between occupational exposure to gas and arc welding fumes and the risk of lung cancer among workers exposed to these agents throughout the spectrum of industries. Two population-based case–control studies were conducted in Montreal. Study I (1979–1986) included 857 cases and 1066 controls, and Study II (1996–2001) comprised 736 cases and 894 controls. Detailed job histories were obtained by interview and evaluated by an expert team of chemist–hygienists to estimate degree of exposure to approximately 300 substances for each job. Gas and arc welding fumes were among the agents evaluated. We estimated odds ratios (ORs) and 95% confidence intervals (CIs) of lung cancer using logistic regression, adjusting for smoking history and other covariates. The two studies provided similar results, so a pooled analysis was conducted. Among all subjects, no significant association was found between lung cancer and gas welding fumes (OR = 1.1; 95% CI = 0.9–1.4) or arc welding fumes (OR = 1.0; 95% CI = 0.8–1.2). However, when restricting attention to light smokers, there was an increased risk of lung cancer in relation to gas welding fumes (OR = 2.9; 95% CI = 1.7–4.8) and arc welding fumes (OR = 2.3; 95% CI = 1.3–3.8), with even higher OR estimates among workers with the highest cumulative exposures. In conclusion, there was no detectable excess risk of lung cancer due to welding fumes among moderate to heavy smokers; but among light smokers we found an excess risk related to both types of welding fumes. PMID:23342253

Risk of ischemic heart disease following occupational exposure to welding fumes: a systematic review with meta-analysis.

PubMed

Mocevic, Emina; Kristiansen, Pernille; Bonde, Jens Peter

2015-04-01

Air pollution has been linked to an increased risk of ischemic heart disease (IHD), but less is known about occupational exposure to welding fumes and the risk of IHD. The objective of this paper was to review the epidemiological evidence on causal links between welding fume exposure and risk of IHD and to investigate whether the risk of IHD depends on specific welding characteristics. A systematic search in Medline 1979-2013 and EMBASE 1974-2013 identified 18 epidemiological studies with at least one risk estimate of IHD morbidity or mortality among workers exposed to welding fumes. Following an assessment of completeness of reporting, confounding, and bias, each risk estimate was characterized as more or less reliable. Pooled risk estimates were computed across studies by random effect meta-analyses. The weighted relative risk (RR) for IHD following exposure to welding fumes was 1.09 [95 % confidence interval (CI) 1.00, 1.19]. We calculated a RR of 1.39 (95 % CI 0.96, 2.02) among studies using an internal reference group and 1.08 (95 % CI 0.99, 1.18) for studies using an external reference group. An increased risk was observed for acute myocardial infarction RR = 1.69 (95 % CI 1.18, 2.42) and other IHDs RR = 1.06 (95 % CI 0.98, 1.14). There was too limited evidence to evaluate the risk of IHD related to specific welding characteristics. Several studies indicate that welding is associated with a moderately increased risk of IHD; however, bias and confounding cannot be ruled out with reasonable confidence.

The effects of short pulse laser surface cleaning on porosity formation and reduction in laser welding of aluminium alloy for automotive component manufacture

NASA Astrophysics Data System (ADS)

AlShaer, A. W.; Li, L.; Mistry, A.

2014-12-01

Laser welding of aluminium alloys typically results in porosity in the fusion zones, leading to poor mechanical and corrosion performances. Mechanical and chemical cleaning of surfaces has been used previously to remove contaminants for weld joint preparations. However, these methods are slow, ineffective (e.g. due to hydrogen trapping) or lead to environmental hazards. This paper reports the effects of short pulsed laser surface cleaning on porosity formation and reduction in laser welding of AC-170PX (AA6014) aluminium sheets (coated with Ti/Zr and lubricated using a dry lubricant AlO70) with two types of joints: fillet edge and flange couch, using an AA4043 filler wire for automotive component assembly. The effect of laser cleaning on porosity reduction during laser welding using a filler wire has not been reported before. In this work, porosity and weld fusion zone geometry were examined prior to and after laser cleaning. The nanosecond pulsed Nd:YAG laser cleaning was found to reduce porosity significantly in the weld fusion zones. For the fillet edge welds, porosity was reduced to less than 0.5% compared with 10-80% without laser cleaning. For flange couch welds, porosity was reduced to 0.23-0.8% with laser cleaning from 0.7% to 4.3% without laser cleaning. This has been found to be due to the elimination of contaminations and oxide layers that contribute to the porosity formation. The laser cleaning is based on thermal ablation. This research focuses on porosity reduction in laser welding of aluminium alloy. Weld quality was investigated for two joints, fillet edge and flange couch joints. The effect of laser cleaning on porosity reduction after welding was investigated. It was found that laser cleaning reduced porosity less than 1% in both joints. Weld dimensions and strength were evaluated and discussed for both types of joints.

Characterization of nitrogen effects in high energy density weldments of Nitronic 40 stainless steel

NASA Astrophysics Data System (ADS)

Pfeif, Erik Andrew

Variation in the welding environment for laser beam welding and electron beam welding can alter the resulting weld chemical composition, microstructure and therefore the mechanical properties. The room temperature mechanical properties of Nitronic 40 stainless steel weld metal from three different heats containing 0.24, 0.28, and 0.31 wt. pct. nitrogen were evaluated for continuous mode Ytterbium doped Fiber laser welds conducted with argon and nitrogen shielding gases, and for electron beam welds. The bulk nitrogen contents were monitored and the resulting properties were then related to microstructural features measured using Electron BackScatter Diffraction (EBSD). Traditional tensile testing of weld metal is conducted on composite tensile bars consisting of base metal and weld metal often leading to failure in the region adjacent to the weld due to strength mismatch at the weld interface. These tests provide composite strength but do not specifically determine the mechanical properties of the heterogeneous weld metal. In this research, microtensile testing was conducted to characterize the properties of the different regions of the weld. The microtensile testing procedures were developed using two geometries of tensile bars measuring the properties through the thickness of 3 mm full penetration welds. In all cases an increase in the strength of the weld metal was found to occur, though the electron beam welds exhibited a higher strength than the laser welds. Standard predictive equations were found to under-predict the strength of the laser welds, even when average grain size or intercept distances were measured. The contribution of nitrogen solid solution strengthening was consistent at approximately 513 MPa per wt. pct. nitrogen. Similar cooling rates and heat inputs allow for a comparison across high energy density welding techniques. Though microstructural differences through the depth of the weld metal were observed as nitrogen vaporization decreased and cooling rates increased. Vermicular ferrite, lacy ferrite and intercellular ferrite were identified as predicted in prior research done on high nitrogen austenitic stainless steels. The resulting laser weld metal microstructures were analyzed with EBSD for grain size and ferrite content measurements, while grain boundary character was determined for a Hansen model used for multi-scale mechanical property measurements. It was found that the low angle grain boundaries were the predominant microstructural feature responsible for strengthening within the weld metal and that this contribution must be accounted for when predicting yield strength of the weld metal.

Method for laser spot welding monitoring

NASA Astrophysics Data System (ADS)

Manassero, Giorgio

1994-09-01

As more powerful solid state laser sources appear on the market, new applications become technically possible and important from the economical point of view. For every process a preliminary optimization phase is necessary. The main parameters, used for a welding application by a high power Nd-YAG laser, are: pulse energy, pulse width, repetition rate and process duration or speed. In this paper an experimental methodology, for the development of an electrooptical laser spot welding monitoring system, is presented. The electromagnetic emission from the molten pool was observed and measured with appropriate sensors. The statistical method `Parameter Design' was used to obtain an accurate analysis of the process parameter that influence process results. A laser station with a solid state laser coupled to an optical fiber (1 mm in diameter) was utilized for the welding tests. The main material used for the experimental plan was zinc coated steel sheet 0.8 mm thick. This material and the related spot welding technique are extensively used in the automotive industry, therefore, the introduction of laser technology in production line will improve the quality of the final product. A correlation, between sensor signals and `through or not through' welds, was assessed. The investigation has furthermore shown the necessity, for the modern laser production systems, to use multisensor heads for process monitoring or control with more advanced signal elaboration procedures.

Welding and Lung Cancer in a Pooled Analysis of Case-Control Studies

PubMed Central

Kendzia, Benjamin; Behrens, Thomas; Jöckel, Karl-Heinz; Siemiatycki, Jack; Kromhout, Hans; Vermeulen, Roel; Peters, Susan; Van Gelder, Rainer; Olsson, Ann; Brüske, Irene; Wichmann, H.-Erich; Stücker, Isabelle; Guida, Florence; Tardón, Adonina; Merletti, Franco; Mirabelli, Dario; Richiardi, Lorenzo; Pohlabeln, Hermann; Ahrens, Wolfgang; Landi, Maria Teresa; Caporaso, Neil; Consonni, Dario; Zaridze, David; Szeszenia-Dabrowska, Neonila; Lissowska, Jolanta; Gustavsson, Per; Marcus, Michael; Fabianova, Eleonora; ‘t Mannetje, Andrea; Pearce, Neil; Tse, Lap Ah; Yu, Ignatius Tak-sun; Rudnai, Peter; Bencko, Vladimir; Janout, Vladimir; Mates, Dana; Foretova, Lenka; Forastiere, Francesco; McLaughlin, John; Demers, Paul; Bueno-de-Mesquita, Bas; Boffetta, Paolo; Schüz, Joachim; Straif, Kurt; Pesch, Beate; Brüning, Thomas

2013-01-01

Several epidemiologic studies have indicated an increased risk of lung cancer among welders. We used the SYNERGY project database to assess welding as a risk factor for developing lung cancer. The database includes data on 15,483 male lung cancer cases and 18,388 male controls from 16 studies in Europe, Canada, China, and New Zealand conducted between 1985 and 2010. Odds ratios and 95% confidence intervals between regular or occasional welding and lung cancer were estimated, with adjustment for smoking, age, study center, and employment in other occupations associated with lung cancer risk. Overall, 568 cases and 427 controls had ever worked as welders and had an odds ratio of developing lung cancer of 1.44 (95% confidence interval: 1.25, 1.67) with the odds ratio increasing for longer duration of welding. In never and light smokers, the odds ratio was 1.96 (95% confidence interval: 1.37, 2.79). The odds ratios were somewhat higher for squamous and small cell lung cancers than for adenocarcinoma. Another 1,994 cases and 1,930 controls had ever worked in occupations with occasional welding. Work in any of these occupations was associated with some elevation of risk, though not as much as observed in regular welders. Our findings lend further support to the hypothesis that welding is associated with an increased risk of lung cancer. PMID:24052544

Welding and lung cancer in a pooled analysis of case-control studies.

PubMed

Kendzia, Benjamin; Behrens, Thomas; Jöckel, Karl-Heinz; Siemiatycki, Jack; Kromhout, Hans; Vermeulen, Roel; Peters, Susan; Van Gelder, Rainer; Olsson, Ann; Brüske, Irene; Wichmann, H-Erich; Stücker, Isabelle; Guida, Florence; Tardón, Adonina; Merletti, Franco; Mirabelli, Dario; Richiardi, Lorenzo; Pohlabeln, Hermann; Ahrens, Wolfgang; Landi, Maria Teresa; Caporaso, Neil; Consonni, Dario; Zaridze, David; Szeszenia-Dabrowska, Neonila; Lissowska, Jolanta; Gustavsson, Per; Marcus, Michael; Fabianova, Eleonora; 't Mannetje, Andrea; Pearce, Neil; Tse, Lap Ah; Yu, Ignatius Tak-Sun; Rudnai, Peter; Bencko, Vladimir; Janout, Vladimir; Mates, Dana; Foretova, Lenka; Forastiere, Francesco; McLaughlin, John; Demers, Paul; Bueno-de-Mesquita, Bas; Boffetta, Paolo; Schüz, Joachim; Straif, Kurt; Pesch, Beate; Brüning, Thomas

2013-11-15

Several epidemiologic studies have indicated an increased risk of lung cancer among welders. We used the SYNERGY project database to assess welding as a risk factor for developing lung cancer. The database includes data on 15,483 male lung cancer cases and 18,388 male controls from 16 studies in Europe, Canada, China, and New Zealand conducted between 1985 and 2010. Odds ratios and 95% confidence intervals between regular or occasional welding and lung cancer were estimated, with adjustment for smoking, age, study center, and employment in other occupations associated with lung cancer risk. Overall, 568 cases and 427 controls had ever worked as welders and had an odds ratio of developing lung cancer of 1.44 (95% confidence interval: 1.25, 1.67) with the odds ratio increasing for longer duration of welding. In never and light smokers, the odds ratio was 1.96 (95% confidence interval: 1.37, 2.79). The odds ratios were somewhat higher for squamous and small cell lung cancers than for adenocarcinoma. Another 1,994 cases and 1,930 controls had ever worked in occupations with occasional welding. Work in any of these occupations was associated with some elevation of risk, though not as much as observed in regular welders. Our findings lend further support to the hypothesis that welding is associated with an increased risk of lung cancer.

Static behavior of the weld in the joint of the steel support element using experiment and numerical modeling

NASA Astrophysics Data System (ADS)

Krejsa, M.; Brozovsky, J.; Mikolasek, D.; Parenica, P.; Koubova, L.

2018-04-01

The paper is focused on the numerical modeling of welded steel bearing elements using commercial software system ANSYS, which is based on the finite element method - FEM. It is important to check and compare the results of FEM analysis with the results of physical verification test, in which the real behavior of the bearing element can be observed. The results of the comparison can be used for calibration of the computational model. The article deals with the physical test of steel supporting elements, whose main purpose is obtaining of material, geometry and strength characteristics of the fillet and butt welds including heat affected zone in the basic material of welded steel bearing element. The pressure test was performed during the experiment, wherein the total load value and the corresponding deformation of the specimens under the load was monitored. Obtained data were used for the calibration of numerical models of test samples and they are necessary for further stress and strain analysis of steel supporting elements.

Residual Stress Analysis in Girth-welded Ferritic and Austenitic Steel Pipes Using Neutron and X-Ray Diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hempel, Nico; Bunn, Jeffrey R; Nitschke-Pagel, Thomas

This paper is dedicated to the thorough experimental analysis of the residual stresses in the vicinity of tubular welds and the mechanisms involved in their formation. Pipes made of a ferritic-pearlitic structural steel and an austenitic stainless steel are investigated in this study. The pipes feature a similar geometry and are MAG welded with two passes and comparable parameters. Residual strain mappings are carried out using X-ray and neutron diffraction. The combined use of both techniques permits both near-surface and through-wall analyses of the residual stresses. The findings allow for a consistent interpretation of the mechanisms accounting for the formationmore » of the residual stress fields due to the welding process. Since the results are similar for both materials, it can be concluded that residual stresses induced by phase transformations, which can occur in the structural steel, play a minor role in this regard.« less

Out of the SHADOW: watch parts in the spotlight -- laser beam microwelding of delicate watch components

NASA Astrophysics Data System (ADS)

Kramer, Thorsten; Olowinsky, Alexander M.

2003-07-01

Conventional joining techniques like press fitting or crimping require the application of mechanical forces to the parts which, in combination with the tolerances of both parts to be joined, lead to imprecision and poor tensile strength. In contrast, laser beam micro welding provides consistent joining and high flexibility and it acts as an alternative as long as press fitting, crimping, screwing or gluing are not capable of batch production. Different parts and even different metals can be joined in a non-contact process at feed rates of up to 60 m/min and with weld seam lengths from 0.6 mm to 15.7 mm. Due to the low energy input, typically 1 J to 6 J, a weld width as small as 50 μm and a weld depth as small as 20 μm have been attained. This results in low distortion of the joined watch components. Since the first applications of laser beam micro welding of watch components showed promising results, the process has further been enhanced using the SHADOW technique. Aspects of the technique such as tensile strength, geometry and precision of the weld seam as well as the acceptance amongst the -mostly conservative- watch manufacturers have been improved.

Global and Local Mechanical Properties of Autogenously Laser Welded Ti-6Al-4V

NASA Astrophysics Data System (ADS)

Cao, Xinjin; Kabir, Abu Syed H.; Wanjara, Priti; Gholipour, Javad; Birur, Anand; Cuddy, Jonathan; Medraj, Mamoun

2014-03-01

Ti-6Al-4V sheets, 3.2-mm in thickness, were butt welded using a continuous wave 4 kW Nd:YAG laser welding system. The effect of two main process parameters, laser power and welding speed, on the joint integrity was characterized in terms of the joint geometry, defects, microstructure, hardness, and tensile properties. In particular, a digital image correlation technique was used to determine the local tensile properties of the welds. It was determined that a wide range of heat inputs can be used to fully penetrate the Ti-6Al-4V butt joints during laser welding. At high laser power levels, however, significant defects such as underfill and porosity, can occur and cause marked degradation in the joint integrity and performance. At low welding speeds, however, significant porosity occurs due to its growth and the potential collapse of instable keyholes. Intermediate to relatively high levels of heat input allow maximization of the joint integrity and performance by limiting the underfill and porosity defects. In considering the effect of the two main defects on the joint integrity, the underfill defect was found to be more damaging to the mechanical performance of the weldment than the porosity. Specifically, it was determined that the maximum tolerable underfill depth for Ti-6Al-4V is approximately 6 pct of the workpiece thickness, which is slightly stricter than the value of 7 pct specified in AWS D17.1 for fusion welding in aerospace applications. Hence, employing optimized laser process parameters allows the underfill depth to be maintained within the tolerable limit (6 pct), which in turn prevents degradation in both the weld strength and ductility. To this end, the ability to maintain weld ductility in Ti-6Al-4V by means of applying a high energy density laser welding process presents a significant advantage over conventional arc welding for the assembly of aerospace components.

A Quantitative Model of Keyhole Instability Induced Porosity in Laser Welding of Titanium Alloy

NASA Astrophysics Data System (ADS)

Pang, Shengyong; Chen, Weidong; Wang, Wen

2014-06-01

Quantitative prediction of the porosity defects in deep penetration laser welding has generally been considered as a very challenging task. In this study, a quantitative model of porosity defects induced by keyhole instability in partial penetration CO2 laser welding of a titanium alloy is proposed. The three-dimensional keyhole instability, weld pool dynamics, and pore formation are determined by direct numerical simulation, and the results are compared to prior experimental results. It is shown that the simulated keyhole depth fluctuations could represent the variation trends in the number and average size of pores for the studied process conditions. Moreover, it is found that it is possible to use the predicted keyhole depth fluctuations as a quantitative measure of the average size of porosity. The results also suggest that due to the shadowing effect of keyhole wall humps, the rapid cooling of the surface of the keyhole tip before keyhole collapse could lead to a substantial decrease in vapor pressure inside the keyhole tip, which is suggested to be the mechanism by which shielding gas enters into the porosity.

Joining of thin glass with semiconductors by ultra-fast high-repetition laser welding

NASA Astrophysics Data System (ADS)

Horn, Alexander; Mingaeev, Ilja; Werth, Alexander; Kachel, Martin

2008-02-01

Lighting applications like OLED or on silicon for electro-optical applications need a reproducible sealing process. The joining has to be strong, the permeability for gasses and humidity very low and the process itself has to be very localized not affecting any organic or electronic parts inside the sealed region. The actual sealing process using glue does not fulfil these industrial needs. A new joining process using ultra-fast laser radiation offers a very precise joining with geometry dimensions smaller than 50 μm. Ultra-fast laser radiation is absorbed by multi-photon absorption in the glass. Due to the very definite threshold for melting and ablation the process of localized heating can be controlled without cracking. Repeating the irradiation at times smaller than the heat diffusion time the temperature in the focus is increased by heat accumulation reaching melting of the glass. Mowing the substrate relatively to the laser beam generates a seal of re-solidified glass. Joining of glass is achieved by positioning the laser focus at the interface. A similar approach is used for glass-silicon joining. The investigations presented will demonstrate the joining geometry by microscopy of cross-sections achieved by welding two glass plates (Schott D263 and AF45) with focused IR femtosecond laser radiation (wavelength λ = 1045nm, repetition rate f = 1 MHz, pulse duration t p = 500 fs, focus diameter w 0 = 4 μm, feeding velocity v= 1-10 mm/s). The strength of the welding seam is measured by tensile stress measurements and the gas and humidity is detected. A new diagnostic method for the on-line detection of the welding seam properties will be presented. Using a non-interferometric technique by quantitative phase microscopy the refractive index is measured during welding of glass in the time regime 0-2 μs. By calibration of the measured refractive index with a relation between refractive index and temperature a online-temperature detection can be achieved.

Thermal Skin fabrication technology

NASA Technical Reports Server (NTRS)

Milam, T. B.

1972-01-01

Advanced fabrication techniques applicable to Thermal Skin structures were investigated, including: (1) chemical machining; (2) braze bonding; (3) diffusion bonding; and (4) electron beam welding. Materials investigated were nickel and nickel alloys. Sample Thermal Skin panels were manufactured using the advanced fabrication techniques studied and were structurally tested. Results of the program included: (1) development of improved chemical machining processes for nickel and several nickel alloys; (2) identification of design geometry limits; (3) identification of diffusion bonding requirements; (4) development of a unique diffusion bonding tool; (5) identification of electron beam welding limits; and (6) identification of structural properties of Thermal Skin material.

Optimization of cladding parameters for resisting corrosion on low carbon steels using simulated annealing algorithm

NASA Astrophysics Data System (ADS)

Balan, A. V.; Shivasankaran, N.; Magibalan, S.

2018-04-01

Low carbon steels used in chemical industries are frequently affected by corrosion. Cladding is a surfacing process used for depositing a thick layer of filler metal in a highly corrosive materials to achieve corrosion resistance. Flux cored arc welding (FCAW) is preferred in cladding process due to its augmented efficiency and higher deposition rate. In this cladding process, the effect of corrosion can be minimized by controlling the output responses such as minimizing dilution, penetration and maximizing bead width, reinforcement and ferrite number. This paper deals with the multi-objective optimization of flux cored arc welding responses by controlling the process parameters such as wire feed rate, welding speed, Nozzle to plate distance, welding gun angle for super duplex stainless steel material using simulated annealing technique. Regression equation has been developed and validated using ANOVA technique. The multi-objective optimization of weld bead parameters was carried out using simulated annealing to obtain optimum bead geometry for reducing corrosion. The potentiodynamic polarization test reveals the balanced formation of fine particles of ferrite and autenite content with desensitized nature of the microstructure in the optimized clad bead.

Behaviour of several fatigue prone bridge details

NASA Astrophysics Data System (ADS)

Kubiš, Petr; Ryjáček, Pavel

2017-09-01

Three fatigue welded bridge joints analysed in this work are the alternative details of the bottom flange connection. This construction detail is mainly used for the erection connection for steel and composite bridges. If applied in the place, where live load is significant, the fatigue becomes the main design criterion. The detail category is thus very important factor. The aim of this paper is to analyse the possibilities of the improving the behaviour of this detail, by various methods. First solution is to modify the shape of the cope hole to the elliptic shape. Second option is to use the “Olemutz” fully welded detail. This detail is often used in bridge designing despite there is no exact information about the fatigue category, and doubts of the performance exists. “Olemutz” is a long web plate slit that is filled by the double bevel weld after the execution of the bottom flange weld. The last detail is the elliptic cope hole filled by the plate-cap welded into an empty hole. The geometry is the same, as in the first case. The conclusion of the numerical analysis and the pilot fatigue experiments is discussed with several practical recommendations for designing.

Rheology, thermography, and interlayer welding in polymer extrusion 3D printing

NASA Astrophysics Data System (ADS)

Seppala, Jonathan; Davis, Chelsea; Migler, Kalman

In polymer extrusion 3D printing, thermoplastic filament is extruded though a rastering nozzle onto previously deposited layers. The resulting strength of the 3D produced part is limited by the strength of the weld between each layer. During this thermal processing, the temperature of the interface between layers dictates the chain mobility, interdiffusion, entanglement, and thus weld strength. In quiescent welding experiments, it has been found that the weld strength in symmetric linear polymer systems scales with t 0.25, where t is the isothermal annealing time, before plateauing to the bulk strength. However, 3D printing is highly non isothermal and we calculated an equivalent isothermal annealing time using a combination of in situ infrared thermography and horizontal shift factors from offline rheological measurements of the neat polymer. Interlayer adhesion energy was measured directly by mode III fracture using a simplified geometry limiting the measurement to a single interlayer. Since the processing conditions are known a prioi this approach provides the data needed to estimate the final build strength at time of design. The resulting agreement between annealing time and adhesion energy for a range of printing conditions and thermoplastics are discussed.

Electron temperature and density measurement of tungsten inert gas arcs with Ar-He shielding gas mixture

NASA Astrophysics Data System (ADS)

Kühn-Kauffeldt, M.; Marques, J.-L.; Forster, G.; Schein, J.

2013-10-01

The diagnostics of atmospheric welding plasma is a well-established technology. In most cases the measurements are limited to processes using pure shielding gas. However in many applications shielding gas is a mixture of various components including metal vapor in gas metal arc welding (GMAW). Shielding gas mixtures are intentionally used for tungsten inert gas (TIG) welding in order to improve the welding performance. For example adding Helium to Argon shielding gas allows the weld geometry and porosity to be influenced. Yet thermal plasmas produced with gas mixtures or metal vapor still require further experimental investigation. In this work coherent Thomson scattering is used to measure electron temperature and density in these plasmas, since this technique allows independent measurements of electron and ion temperature. Here thermal plasmas generated by a TIG process with 50% Argon and 50% Helium shielding gas mixture have been investigated. Electron temperature and density measured by coherent Thomson scattering have been compared to the results of spectroscopic measurements of the plasma density using Stark broadening of the 696.5 nm Argon spectral line. Further investigations of MIG processes using Thomson scattering technique are planned.

Laser based spot weld characterization

NASA Astrophysics Data System (ADS)

Jonietz, Florian; Myrach, Philipp; Rethmeier, Michael; Suwala, Hubert; Ziegler, Mathias

2016-02-01

Spot welding is one of the most important joining technologies, especially in the automotive industry. Hitherto, the quality of spot welded joints is tested mainly by random destructive tests. A nondestructive testing technique offers the benefit of cost reduction of the testing procedure and optimization of the fabrication process, because every joint could be examined. This would lead to a reduced number of spot welded joints, as redundancies could be avoided. In the procedure described here, the spot welded joint between two zinc-coated steel sheets (HX340LAD+Z100MB or HC340LA+ZE 50/50) is heated optically on one side. Laser radiation and flash light are used as heat sources. The melted zone, the so called "weld nugget" provides the mechanical stability of the connection, but also constitutes a thermal bridge between the sheets. Due to the better thermal contact, the spot welded joint reveals a thermal behavior different from the surrounding material, where the heat transfer between the two sheets is much lower. The difference in the transient thermal behavior is measured with time resolved thermography. Hence, the size of the thermal contact between the two sheets is determined, which is directly correlated to the size of the weld nugget, indicating the quality of the spot weld. The method performs well in transmission with laser radiation and flash light. With laser radiation, it works even in reflection geometry, thus offering the possibility of testing with just one-sided accessibility. By using heating with collimated laser radiation, not only contact-free, but also remote testing is feasible. A further convenience compared to similar thermographic approaches is the applicability on bare steel sheets without any optical coating for emissivity correction. For this purpose, a proper way of emissivity correction was established.

Experimental and numerical evaluation of the fatigue behaviour in a welded joint

NASA Astrophysics Data System (ADS)

Almaguer, P.; Estrada, R.

2014-07-01

Welded joints are an important part in structures. For this reason, it is always necessary to know the behaviour of them under cyclic loads. In this paper a S - N curve of a butt welded joint of the AISI 1015 steel and Cuban manufacturing E6013 electrode is showed. Fatigue tests were made in an universal testing machine MTS810. The stress ratio used in the test was 0,1. Flaws in the fatigue specimens were characterized by means of optical and scanning electron microscopy. SolidWorks 2013 software was used to modeling the specimens geometry, while to simulate the fatigue behaviour Simulation was used. The joint fatigue limit is 178 MPa, and a cut point at 2 039 093 cycles. Some points of the simulations are inside of the 95% confidence band.

Friction Stir Welding of Al-B4C Composite Fabricated by Accumulative Roll Bonding: Evaluation of Microstructure and Mechanical Behavior

NASA Astrophysics Data System (ADS)

Moradi Faradonbeh, Alireza; Shamanian, Morteza; Edris, Hossein; Paidar, Moslem; Bozkurt, Yahya

2018-02-01

In this investigation, friction stir welding (FSW) of Al-B4C composite fabricated by 10 cycles accumulative roll bonding was conducted. In order to investigate the influences of pin geometry on microstructure and mechanical properties, four different pin geometries (cylindrical, square, triangular and hexagonal) were selected. It was found that FSW parameters had a major effect on the fragmentation and distribution of reinforcement particles in stir zone. When the tool travel speed was increased, the distribution of B4C particles was become gradually uniform in the aluminum matrix. The effect of tool rotational speed on the peak temperature was determined to be greater than the tool travel speed. The attained data of tensile properties and microhardness tests showed that the tool travel speed had bilateral effect on the tensile strength. The maximum tensile joint efficiency was obtained as 238% for FSWed of Al-2%B4C composite to annealed base Al sheet.

Transient Response of Arc Temperature and Iron Vapor Concentration Affected by Current Frequency with Iron Vapor in Pulsed Arc

NASA Astrophysics Data System (ADS)

Tanaka, Tatsuro; Maeda, Yoshifumi; Yamamoto, Shinji; Iwao, Toru

2016-10-01

TIG arc welding is chemically a joining technology with melting the metallic material and it can be high quality. However, this welding should not be used in high current to prevent cathode melting. Thus, the heat transfer is poor. Therefore, the deep penetration cannot be obtained and the weld defect sometimes occurs. The pulsed arc welding has been used for the improvement of this defect. The pulsed arc welding can control the heat flux to anode. The convention and driving force in the weld pool are caused by the arc. Therefore, it is important to grasp the distribution of arc temperature. The metal vapor generate from the anode in welding. In addition, the pulsed current increased or decreased periodically. Therefore, the arc is affected by such as a current value and current frequency, the current rate of increment and the metal vapor. In this paper, the transient response of arc temperature and the iron vapor concentration affected by the current frequency with iron vapor in pulsed arc was elucidated by the EMTF (ElectroMagnetic Thermal Fluid) simulation. As a result, the arc temperature and the iron vapor were transient response as the current frequency increase. Thus, the temperature and the electrical conductivity decreased. Therefore, the electrical field increased in order to maintain the current continuity. The current density and electromagnetic force increased at the axial center. In addition, the electronic flow component of the heat flux increased at the axial center because the current density increased. However, the heat conduction component of the heat flux decreased.

Numerical analysis of fume formation mechanism in arc welding

NASA Astrophysics Data System (ADS)

Tashiro, Shinichi; Zeniya, Tasuku; Yamamoto, Kentaro; Tanaka, Manabu; Nakata, Kazuhiro; Murphy, Anthony B.; Yamamoto, Eri; Yamazaki, Kei; Suzuki, Keiichi

2010-11-01

In order to clarify the fume formation mechanism in arc welding, a quantitative investigation based on the knowledge of interaction among the electrode, arc and weld pool is indispensable. A fume formation model consisting of a heterogeneous condensation model, a homogeneous nucleation model and a coagulation model has been developed and coupled with the GTA or GMA welding model. A series of processes from evaporation of metal vapour to fume formation from the metal vapour was totally investigated by employing this simulation model. The aim of this paper is to visualize the fume formation process and clarify the fume formation mechanism theoretically through a numerical analysis. Furthermore, the reliability of the simulation model was also evaluated through a comparison of the simulation result with the experimental result. As a result, it was found that the size of the secondary particles consisting of small particles with a size of several tens of nanometres reached 300 nm at maximum and the secondary particle was in a U-shaped chain form in helium GTA welding. Furthermore, it was also clarified that most part of the fume was produced in the downstream region of the arc originating from the metal vapour evaporated mainly from the droplet in argon GMA welding. The fume was constituted by particles with a size of several tens of nanometres and had similar characteristics to that of GTA welding. On the other hand, if the metal transfer becomes unstable and the metal vapour near the droplet diffuses directly towards the surroundings of the arc not getting into the plasma flow, the size of the particles reaches several hundred nanometres.

Effect of acoustic field parameters on arc acoustic binding during ultrasonic wave-assisted arc welding.

PubMed

Xie, Weifeng; Fan, Chenglei; Yang, Chunli; Lin, Sanbao

2016-03-01

As a newly developed arc welding method, power ultrasound has been successfully introduced into arc and weld pool during ultrasonic wave-assisted arc welding process. The advanced process for molten metals can be realized by utilizing additional ultrasonic field. Under the action of the acoustic wave, the plasma arc as weld heat source is regulated and its characteristics make an obvious change. Compared with the conventional arc, the ultrasonic wave-assisted arc plasma is bound significantly and becomes brighter. To reveal the dependence of the acoustic binding force on acoustic field parameters, a two-dimensional acoustic field model for ultrasonic wave-assisted arc welding device is established. The influences of the radiator height, the central pore radius, the radiator radius, and curvature radius or depth of concave radiator surface are discussed using the boundary element method. Then the authors analyze the resonant mode by this relationship curve between acoustic radiation power and radiator height. Furthermore, the best acoustic binding ability is obtained by optimizing the geometric parameters of acoustic radiator. In addition, three concave radiator surfaces including spherical cap surface, paraboloid of revolution, and rotating single curved surface are investigated systematically. Finally, both the calculation and experiment suggest that, to obtain the best acoustic binding ability, the ultrasonic wave-assisted arc welding setup should be operated under the first resonant mode using a radiator with a spherical cap surface, a small central pore, a large section radius and an appropriate curvature radius. Copyright © 2015 Elsevier B.V. All rights reserved.

Development of an innovative method to predict and to characterize the performances of Ti-6Al-4V LBW joints

NASA Astrophysics Data System (ADS)

Liberini, Mariacira; Esposito, Sara; Reshad, Kambitz; Previtali, Barbara; Viola, Marco; Squillace, Antonino

2016-10-01

Every manufacturing process leaves on the surface of the piece a typical "technology signature". In particular, the laser welding leaves a feature at the edge of the weld bead called "undercut". In this work an experimental campaign has been conducted on Ti6Al4V butt joints. In particular a Central Composite Design (CCD) with the central point repeated three times has been investigated. In the CCD there are two factors (power and speed of the fiber laser) and five levels for each factor. This paper deals with the investigation about the correlation between the severity of the undercut and the process parameters of the laser welding. In particular, through the confocal microscopy, the original geometry of the joint was accurately acquired and rebuilt in order to make a FEM model and simulate the mechanical behavior using Ansys14.5. Moreover, response surfaces and level curves were carried out to understand and predict the depth and the width of the undercut starting from the power and the speed of the laser. At last a mathematic and geometry regression was performed in order to find a unique conical curve that interpolates all the different undercuts and that varies its parameters according to the process parameters. It is established that the process with higher speed minimizes and optimizes the undercut in the joints.

A study on the control of melting ratio to increase mechanical properties of laser welded joints between AISI 440C and AISI 430F

NASA Astrophysics Data System (ADS)

Romoli, L.; Rashed, C. A. A.; Lovicu, G.; Ishak, R.

2015-05-01

Laser beam welding of dissimilar AISI 440C and AISI 430F stainless steels was investigated in a circular constrained configuration. The beam incidence angle and the offset of the focusing position respect to the contact point between the two materials were used as main control parameters to vary the melting ratio inside the seam. The objective of the study is twofold: to avoid surface microcracks related to the high percentage of carbon of the martensitic steel and to enhance the shear strength of the weld by making it less brittle. To reach this scope the effects of incidence angle and offset on weld bead geometry and melting ratio were studied by means of metallographic analyses, microstructure and microhardness characterization. As last step, the weld mechanical strength was tested by tensile-shear stress test on the whole seam. Experiments demonstrated that varying incidence angle and offsetting the focal position is a reliable method to modify the melting ratio and maintaining the expected resistance length at the material interface, as well. It was found that increasing the percentage of ferritic steel into the joint has beneficial effects on the weld quality and on the shear resistance. The critical carbon content determining the mechanical properties in the fusion zone can be calculated by taking into account the melting ratio.

Repulsive Interaction of Sulfide Layers on Compressor Impeller Blades Remanufactured Through Plasma Spray Welding

NASA Astrophysics Data System (ADS)

Chang, Y.; Zhou, D.; Wang, Y. L.; Huang, H. H.

2016-12-01

This study investigated the repulsive interaction of sulfide layers on compressor impeller blades remanufactured through plasma spray welding (PSW). Sulfide layers on the blades made of FV(520)B steel were prepared through multifarious corrosion experiments, and PSW was utilized to remanufacture blade specimens. The specimens were evaluated through optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy, 3D surface topography, x-ray diffraction, ImageJ software analysis, Vicker's micro-hardness test and tensile tests. Results showed a large number of sulfide inclusions in the fusion zone generated by sulfide layers embodied into the molten pool during PSW. These sulfide inclusions seriously degraded the mechanical performance of the blades remanufactured through PSW.

Three-dimensional transient thermoelectric currents in deep penetration laser welding of austenite stainless steel

NASA Astrophysics Data System (ADS)

Chen, Xin; Pang, Shengyong; Shao, Xinyu; Wang, Chunming; Xiao, Jianzhong; Jiang, Ping

2017-04-01

The existence of thermoelectric currents (TECs) in workpieces during the laser welding of metals has been common knowledge for more than 15 years. However, the time-dependent evolutions of TECs in laser welding remain unclear. The present study developed a novel three-dimensional theoretical model of thermoelectric phenomena in the fiber laser welding of austenite stainless steel and used it to observe the time-dependent evolutions of TECs for the first time. Our model includes the complex physical effects of thermal, electromagnetic, fluid and phase transformation dynamics occurring at the millimeter laser ablated zone, which allowed us to simulate the TEC, self-induced magnetic field, Lorentz force, keyhole and weld pool behaviors varying with the welding time for different parameters. We found that TECs are truly three-dimensional, time-dependent, and uneven with a maximum current density of around 107 A/m2 located at the liquid-solid (L/S) interface near the front or bottom part of the keyhole at a laser power of 1.5 kW and a welding speed of 3 m/min. The TEC formed three-dimensional circulations moving from the melting front to solidification front in the solid part of workpiece, after which the contrary direction was followed in the liquid part. High frequency oscillation characteristics (2.2-8.5 kHz) were demonstrated in the TEC, which coincides with that of the keyhole instability (2.0-5.0 kHz). The magnitude of the self-induced magnetic field and Lorentz force can reach 0.1 mT and 1 kN/m3, respectively, which are both consistent with literature data. The predicted results of the weld dimensions by the proposed model agree well with the experimental results. Our findings could enhance the fundamental understanding of thermoelectric phenomena in laser welding.

Landmark vs. Geometry Learning: Explaining Female Rats' Selective Preference for a Landmark

ERIC Educational Resources Information Center

Torres, Marta N.; Rodríguez, Clara A.; Chamizo, V. D.; Mackintosh, N. J.

2014-01-01

Rats were trained in a triangular-shaped pool to find a hidden platform, whose location was defined in terms of two sources of information, a landmark outside the pool and a particular corner of the pool. Subsequent test trials without the platform pitted these two sources of information against one another. In Experiment 1 this test revealed a…

The structural significance of HAZ sigma phase formation in welded 25%Cr super duplex pipework

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wiesner, C.S.; Garwood, S.J.; Bowden, P.L.

1993-12-31

The welding of 25%Cr duplex stainless steel can lead to the formation of sigma phase in both weld metal and heat affected zone (HAZ) regions. It has generally been accepted that this can be avoided by the adoption of appropriate welding procedure controls, generally aimed at reducing heat input and promoting rapid cooling rates. However, experience during pipe spool fabrication for the Marathon East Brae Project has shown that it is extremely difficult to satisfy a welding specification requiring sigma free HAZs. This has proved a particular problem with thin wall pipe welds made in the 2G/5G or 6G fixedmore » positions, where the joint geometry reduces heat flow away from the weld and welding conditions tend to result in the use of higher heat inputs. This paper examines the effect of sigma phase on the fracture toughness of 25%Cr super duplex steel (UNS S32760). It is shown that the CTOD toughness at {minus}20 C decreases as soon as any sigma phase is present and continues to decrease with increasing sigma levels. The toughness of the sigmatized specimens produced by heat treatment was shown to be conservative compared to the toughness measured in the HAZ of 14.2mm and 7.1mm thick pipe weldments, made with welding parameters chosen to enhance HAZ sigma phase formation. Based on the CTOD versus percent sigma level relationship derived from the laboratory specimens, fracture assessment calculations of tolerable flaw sizes were performed. These demonstrated that under the severest design conditions, assuming the maximum flaw sizes which could remain undetected in the pipework, sigma levels up to 2.5% can be tolerated safely. The conservatism of the fracture assessments for predicting the performance of weldments was demonstrated by full scale tensile testing of 2 inch nominal bore x 2.77 mm wall thickness pipe butt welds containing through-thickness circumferential fatigue cracks located in the sigmatized HAZ.« less

Towards and FVE-FAC Method for Determining Thermocapillary Effects on Weld Pool Shape

NASA Technical Reports Server (NTRS)

Canright, David; Henson, Van Emden

1996-01-01

Several practical materials processes, e.g., welding, float-zone purification, and Czochralski crystal growth, involve a pool of molten metal with a free surface, with strong temperature gradients along the surface. In some cases, the resulting thermocapillary flow is vigorous enough to convect heat toward the edges of the pool, increasing the driving force in a sort of positive feedback. In this work we examine this mechanism and its effect on the solid-liquid interface through a model problem: a half space of pure substance with concentrated axisymmetric surface heating, where surface tension is strong enough to keep the liquid free surface flat. The numerical method proposed for this problem utilizes a finite volume element (FVE) discretization in cylindrical coordinates. Because of the axisymmetric nature of the model problem, the control volumes used are torroidal prisms, formed by taking a polygonal cross-section in the (r, z) plane and sweeping it completely around the z-axis. Conservation of energy (in the solid), and conservation of energy, momentum, and mass (in the liquid) are enforced globally by integrating these quantities and enforcing conservation over each control volume. Judicious application of the Divergence Theorem and Stokes' Theorem, combined with a Crank-Nicolson time-stepping scheme leads to an implicit algebraic system to be solved at each time step. It is known that near the boundary of the pool, that is, near the solid-liquid interface, the full conduction-convection solution will require extremely fine length scales to resolve the physical behavior of the system. Furthermore, this boundary moves as a function of time. Accordingly, we develop the foundation of an adaptive refinement scheme based on the principles of Fast Adaptive Composite Grid methods (FAC). Implementation of the method and numerical results will appear in a later report.

In-line process control for laser welding of titanium by high dynamic range ratio pyrometry and plasma spectroscopy

NASA Astrophysics Data System (ADS)

Lempe, B.; Taudt, C.; Baselt, T.; Rudek, F.; Maschke, R.; Basan, F.; Hartmann, P.

2014-02-01

The production of complex titanium components for various industries using laser welding processes has received growing attention in recent years. It is important to know whether the result of the cohesive joint meets the quality requirements of standardization and ultimately the customer requirements. Erroneous weld seams can have fatal consequences especially in the field of car manufacturing and medicine technology. To meet these requirements, a real-time process control system has been developed which determines the welding quality through a locally resolved temperature profile. By analyzing the resulting weld plasma received data is used to verify the stability of the laser welding process. The determination of the temperature profile is done by the detection of the emitted electromagnetic radiation from the material in a range of 500 nm to 1100 nm. As detectors, special high dynamic range CMOS cameras are used. As the emissivity of titanium depends on the wavelength, the surface and the angle of radiation, measuring the temperature is a problem. To solve these a special pyrometer setting with two cameras is used. That enables the compensation of these effects by calculating the difference between the respective pixels on simultaneously recorded images. Two spectral regions with the same emissivity are detected. Therefore the degree of emission and surface effects are compensated and canceled out of the calculation. Using the spatially resolved temperature distribution the weld geometry can be determined and the laser process can be controlled. The active readjustment of parameters such as laser power, feed rate and inert gas injection increases the quality of the welding process and decreases the number of defective goods.

Mössbauer characterization of joints of steel pieces in transient liquid phase bonding experiences

NASA Astrophysics Data System (ADS)

di Luozzo, N.; Martínez Stenger, P. F.; Canal, J. P.; Fontana, M. R.; Arcondo, B.

2011-11-01

Joining of seamless, low carbon, steel tubes were performed by means of Transient Liquid Phase Bonding process employing a foil of Fe-Si-B metallic glass as filler material. The influence of the main parameters of the process was evaluated: temperature, holding time, pressure and post weld heat treatment. Powder samples were obtained from the joint of tubes and characterized employing Mössbauer Spectroscopy in transmission geometry. The sampling was performed both in tubes successfully welded and in those which show joint defects. The results obtained are correlated with the obtained microstructure and the diffusion of Si and B during the process.

Field comparison of three inhalable samplers (IOM, PGP-GSP 3.5 and Button) for welding fumes.

PubMed

Zugasti, Agurtzane; Montes, Natividad; Rojo, José M; Quintana, M José

2012-02-01

Inhalable sampler efficiency depends on the aerodynamic size of the airborne particles to be sampled and the wind speed. The aim of this study was to compare the behaviour of three personal inhalable samplers for welding fumes generated by Manual Metal Arc (MMA) and Metal Active Gas (MAG) processes. The selected samplers were the ones available in Spain when the study began: IOM, PGP-GSP 3.5 (GSP) and Button. Sampling was carried out in a welding training center that provided a homogeneous workplace environment. The static sampling assembly used allowed the placement of 12 samplers and 2 cascade impactors simultaneously. 183 samples were collected throughout 2009 and 2010. The range of welding fumes' mass concentrations was from 2 mg m(-3) to 5 mg m(-3). The pooled variation coefficients for the three inhalable samplers were less than or equal to 3.0%. Welding particle size distribution was characterized by a bimodal log-normal distribution, with MMADs of 0.7 μm and 8.2 μm. For these welding aerosols, the Button and the GSP samplers showed a similar performance (P = 0.598). The mean mass concentration ratio was 1.00 ± 0.01. The IOM sampler showed a different performance (P < 0.001). The mean mass concentration ratios were 0.90 ± 0.01 for Button/IOM and 0.92 ± 0.02 for GSP/IOM. This information is useful to consider the measurements accomplished by the IOM, GSP or Button samplers together, in order to assess the exposure at workplaces over time or to study exposure levels in a specific industrial activity, as welding operations.

Weld Bead Geometry of Ni-Based Alloy Deposited by PTA Process for Pipe Conduction of Shale Gas

NASA Astrophysics Data System (ADS)

Echavarria-Figueroa, C.; García-Vázquez, F.; Ruiz-Mondragón, J.; Hernández-García, H. M.; González-González, D.; Vargas, A.

The transportation of shale gas has the problem that the piping used for the extraction does not resist the erosion generated by the amount of solids causing cracks over the surface and it is necessary to extend the life of the pipelines. Plasma transferred arc (PTA) welded coatings are used to improve the surface properties of mechanical parts. Therefore, in this paper is studied the use of Ni-based filler metal as weld bead deposits on A36 steel substrates by PTA. In order to determine the suitable conditions to ensure coating quality on the substrate a design of experiments (DOE) was determined. Welding current, feed rate, and travel speed were used as input parameters and the dilution percentage as the response variable. The composition and properties of hardfacing or overlay deposited are strongly influenced by the dilution obtained. Control of dilution is important, where typically low dilution is desirable. When the dilution is low, the final deposit composition will be closer to that of the filler metal, and the wear and corrosion resistance of the hardfacing will also be maintained. To evaluate the features on the weld beads/substrate interface a microstructural characterization was performed by using scanning electron microscopy and to evaluate the mechanical properties was carried out hardness test.

Remote Laser Welding of Zinc Coated Steel Sheets in an Edge Lap Configuration with Zero Gap

NASA Astrophysics Data System (ADS)

Roos, Christian; Schmidt, Michael

Remote Laser Welding (RLW) of zinc-coated steel sheets is a great challenge for the automotive industry but offers high potentials with respect to flexibility and costs. In state of the art applications, sheets are joined in overlap configuration with a preset gap for a stable zinc degassing. This paper investigates RLW of fillets without a preset gap and conditions for a stable process. The influence of process parameters on weld quality and process stability is shown. Experimental data give evidence, that the degassing of zinc through the capillary and the rear melt pool are the major degassing mechanisms. Furthermore the paper gives experimental validation of the zinc degassing in advance of the process zone to the open side of the fillet. Chemical analysis of the hot-dip galvanized zinc coating proof the iron-zinc-alloys to be the reason for a limited effectiveness of this mechanism in comparison to pure zinc as intermediate.

Thermal Imaging for Assessment of Electron-Beam Free Form Fabrication (EBF(sup 3)) Additive Manufacturing Welds

NASA Technical Reports Server (NTRS)

Zalameda, Joseph N.; Burke, Eric R.; Hafley, Robert A.; Taminger, Karen M.; Domack, Christopher S.; Brewer, Amy R.; Martin, Richard E.

2013-01-01

Additive manufacturing is a rapidly growing field where 3-dimensional parts can be produced layer by layer. NASA s electron beam free-form fabrication (EBF(sup 3)) technology is being evaluated to manufacture metallic parts in a space environment. The benefits of EBF(sup 3) technology are weight savings to support space missions, rapid prototyping in a zero gravity environment, and improved vehicle readiness. The EBF(sup 3) system is composed of 3 main components: electron beam gun, multi-axis position system, and metallic wire feeder. The electron beam is used to melt the wire and the multi-axis positioning system is used to build the part layer by layer. To insure a quality weld, a near infrared (NIR) camera is used to image the melt pool and solidification areas. This paper describes the calibration and application of a NIR camera for temperature measurement. In addition, image processing techniques are presented for weld assessment metrics.

Carbon pools along headwater streams with differing valley geometry in Rocky Mountain National Park, Colorado (Abstract)

Treesearch

Kathleen A. Dwire; Ellen E. Wohl; Nicholas A. Sutfin; Roberto A. Bazan; Lina Polvi-Pilgrim

2012-01-01

Headwaters are known to be important in the global carbon cycle, yet few studies have investigated carbon (C) pools along stream-riparian corridors. To better understand the spatial distribution of C storage in headwater fluvial networks, we estimated above- and below-ground C pools in 100-m-long reaches in six different valley types in Rocky Mountain National Park,...

Effect of Laser Power and Scan Speed on Melt Pool Characteristics of Commercially Pure Titanium (CP-Ti)

NASA Astrophysics Data System (ADS)

Kusuma, Chandrakanth; Ahmed, Sazzad H.; Mian, Ahsan; Srinivasan, Raghavan

2017-07-01

Selective laser melting (SLM) is an additive manufacturing technique that creates complex parts by selectively melting metal powder layer-by-layer using a laser. In SLM, the process parameters decide the quality of the fabricated component. In this study, single beads of commercially pure titanium (CP-Ti) were melted on a substrate of the same material using an in-house built SLM machine. Multiple combinations of laser power and scan speed were used for single bead fabrication, while the laser beam diameter and powder layer thickness were kept constant. This experimental study investigated the influence of laser power, scan speed, and laser energy density on the melt pool formation, surface morphology, geometry (width and height), and hardness of solidified beads. In addition, the observed unfavorable effect such as inconsistency in melt pool width formation is discussed. The results show that the quality, geometry, and hardness of solidified melt pool are significantly affected by laser power, scanning speed, and laser energy density.

Characterization of disk-laser dissimilar welding of titanium alloy Ti-6Al-4V to aluminum alloy 2024

NASA Astrophysics Data System (ADS)

Caiazzo, Fabrizia; Alfieri, Vittorio; Cardaropoli, Francesco; Corrado, Gaetano; Sergi, Vincenzo

2013-02-01

Both technical and economic reasons suggest to join dissimilar metals, benefiting from the specific properties of each material in order to perform flexible design. Adhesive bonding and mechanical joining have been traditionally used although adhesives fail to be effective in high-temperature environments and mechanical joining are not adequate for leak-tight joints. Friction stir welding is a valid alternative, even being difficult to perform for specific joint geometries and thin plates. The attention has therefore been shifted to laser welding. Interest has been shown in welding titanium to aluminum, especially in the aviation industry, in order to benefit from both corrosive resistance and strength properties of the former, and low weight and cost of the latter. Titanium alloy Ti-6Al-4V and aluminum alloy 2024 are considered in this work, being them among the most common ones in aerospace and automotive industries. Laser welding is thought to be particularly useful in reducing the heat affected zones and providing deep penetrative beads. Nevertheless, many challenges arise in welding dissimilar metals and the aim is further complicated considering the specific features of the alloys in exam, being them susceptible to oxidation on the upper surface and porosity formation in the fused zone. As many variables are involved, a systematic approach is used to perform the process and to characterize the beads referring to their shape and mechanical features, since a mixture of phases and structures is formed in the fused zone after recrystallization.

A Lossless hybrid wavelet-fractal compression for welding radiographic images.

PubMed

Mekhalfa, Faiza; Avanaki, Mohammad R N; Berkani, Daoud

2016-01-01

In this work a lossless wavelet-fractal image coder is proposed. The process starts by compressing and decompressing the original image using wavelet transformation and fractal coding algorithm. The decompressed image is removed from the original one to obtain a residual image which is coded by using Huffman algorithm. Simulation results show that with the proposed scheme, we achieve an infinite peak signal to noise ratio (PSNR) with higher compression ratio compared to typical lossless method. Moreover, the use of wavelet transform speeds up the fractal compression algorithm by reducing the size of the domain pool. The compression results of several welding radiographic images using the proposed scheme are evaluated quantitatively and compared with the results of Huffman coding algorithm.

Advanced ultrasonic techniques for nondestructive testing of austenitic and dissimilar welds in nuclear facilities

NASA Astrophysics Data System (ADS)

Juengert, Anne; Dugan, Sandra; Homann, Tobias; Mitzscherling, Steffen; Prager, Jens; Pudovikov, Sergey; Schwender, Thomas

2018-04-01

Austenitic stainless steel welds as well as dissimilar metal welds with nickel alloy filler material, used in safety relevant parts of nuclear power plants, still challenge the ultrasonic inspection. The weld material forms large oriented grains that lead, on the one hand, to high sound scattering and, on the other hand, to inhomogeneity and to the acoustic anisotropy of the weld structure. The ultrasonic wave fronts do not propagate linearly, as in ferritic weld joints, but along the curves, which depend on the specific grain structure of the weld. Due to the influence of these phenomena, it is difficult to analyze the inspection results and to classify the ultrasonic indications, which could be both from the weld geometry and from the material defects. A correct flaw sizing is not possible. In an ongoing research project, different techniques to improve the reliability of ultrasonic testing at these kinds of welds are investigated. In a first step (in the previous research project) two ultrasonic inspection techniques were developed and validated on plane test specimens with artificial and realistic flaws. In the ongoing project, these techniques are applied to circumferential pipe welds with longitudinal and transverse flaws. The technique developed at the Federal Institute for Materials Research and Testing (BAM) in Germany uses a combination of ray tracing and synthetic aperture focusing technique (SAFT). To investigate the unknown grain structure, the velocity distribution of weld-transmitting ultrasound waves is measured and used to model the weld by ray tracing. The second technique, developed at the Fraunhofer Institute for Nondestructive Testing (IZFP) in Germany, uses Sampling Phased Array (Full Matrix Capture) combined with the reverse phase matching (RPM) and the gradient elastic constant descent algorithm (GECDM). This inspection method is able to estimate the elastic constants of the columnar grains in the weld and offers an improvement of the reliability of ultrasonic testing through the correction of the sound field distortion. The unknown inhomogeneity and anisotropy are investigated using a reference indication and the special optimization algorithm. Both reconstruction techniques give quantitative inspection results and allow the defect sizing. They have been compared to conventional ultrasonic testing with techniques that are state of the art for components in nuclear power plants. The improvement will be quantified by the comparison of the probability of detection (POD) of each technique.

On the microstructure analysis of FSW joints of aluminium components made via direct metal laser sintering

NASA Astrophysics Data System (ADS)

Scherillo, Fabio; Astarita, Antonello; di Martino, Daniela; Contaldi, Vincenzo; di Matteo, Luca; di Petta, Paolo; Casarin, Renzo; Squillace, Antonino; Langella, Antonio

2017-10-01

Additive Manufacturing (AM), applied to metal industry, is a family of processes that allow complex shape components to be realized from raw materials in the form of powders. The compaction of the powders can be achieved by local melting of the powder bed or by solid state sintering. Direct Metal Laser Sintering (DMLS) is an additive manufacturing process in which a focalized laser beam is the heat source that allows the powders to be compacted. By DMLS it is possible to realize complex shape components. One of the limits of DMLS, as for every additive layer manufacturing techniques, is the unfeasibility to realize large dimension parts. Due to this limit the study of joining process of parts made via ALM is of great interest. One of the most promising options is the Friction Stir Welding (FSW), a solid state welding technique that has been proven to be very effective in the welding of metals difficult to weld, above all aluminium alloys. Since FSW is a solid-state technique, the microstructure of the various zone of the weld bead depends not only by the process itself but also by the parent microstruct ure of the parts to be welded. Furthermore, parts made of aluminium alloy via DMLS have a particular microstructure that is the result of repeated severe thermal cycles. In the present work the authors, starting from the description of the parent microstructure of parts made of AlSi10Mg aluminium alloy, study the microstructure evolution occurred within the joint made by Friction Stir Welding, analysing in details the microstructure of the main well recognized zone of the weld bead. The structure of the parent material is characterized by the presence of melting pools with a very fine microstructure. In the joint the recrystallization, the grain refinement and, above all, the redistribution of intermetallic phases occurs, resulting in an homogenization of the microstructure and in an increase of micro hardness.

Sex differences after environmental enrichment and physical exercise in rats when solving a navigation task.

PubMed

Chamizo, V D; Rodríguez, C A; Sánchez, J; Mármol, F

2016-09-01

The effects of early environmental enrichment (EE) and voluntary wheel running on the preference for using a landmark or pool geometry when solving a simple spatial task in adult male and female rats were assessed. After weaning, rats were housed in same-sex pairs in enriched or standard cages (EE and control groups) for two and a half months. Then the rats were trained in a triangular-shaped pool to find a hidden platform whose location was defined in terms of these two sources of information, a landmark outside the pool and a particular corner of the pool. As expected, enriched rats reached the platform faster than control animals, and males and females did not differ. Enriched rats also performed better on subsequent test trials without the platform with the cues individually presented (either pool geometry or landmark). However, on a preference test without the platform, a clear sex difference was found: Females spent more time in an area of the pool that corresponded to the landmark, whereas males spent more time in the distinctive corner of the pool. The present EE protocol did not alter females' preference for the landmark cue. The results agree with the claim that environmental enrichment is a consequence of a reduced anxiety response (measured by thigmotaxis) during cognitive testing. A possible implication of ancestral selection pressures is discussed.

Afterlife of a Drop Impacting a Liquid Pool

NASA Astrophysics Data System (ADS)

Saha, Abhishek; Wei, Yanju; Tang, Xiaoyu; Law, Chung K.

2017-11-01

Drop impact on liquid pool is ubiquitous in industrial processes, such as inkjet printing and spray coating. While merging of drop with the impacted liquid surface is essential to facilitate the printing and coating processes, it is the afterlife of this merged drop and associated mixing which control the quality of the printed or coated surface. In this talk we will report an experimental study on the structural evolution of the merged droplet inside the liquid pool. First, we will analyze the depth of the crater created on the pool surface by the impacted drop for a range of impact inertia, and we will derive a scaling relation and the associated characteristic time-scale. Next, we will focus on the toroidal vortex formed by the moving drop inside the liquid pool and assess the characteristic time and length scales of the penetration process. The geometry of the vortex structure which qualitatively indicates the degree of mixedness will also be discussed. Finally, we will present the results from experiments with various viscosities to demonstrate the role of viscous dissipation on the geometry and structure formed by the drop. This work is supported by the Army Research Office and the Xerox Corporation.

Welding of Al6061and Al6082-Cu composite by friction stir processing

NASA Astrophysics Data System (ADS)

Iyer, R. B.; Dhabale, R. B.; Jatti, V. S.

2016-09-01

Present study aims at investigating the influence of process parameters on the microstructure and mechanical properties such as tensile strength and hardness of the dissimilar metal without and with copper powder. Before conducting the copper powder experiments, optimum process parameters were obtained by conducting experiments without copper powder. Taguchi's experimental L9 orthogonal design layout was used to carry out the experiments without copper powder. Threaded pin tool geometry was used for conducting the experiments. Based on the experimental results and Taguchi's analysis it was found that maximum tensile strength of 66.06 MPa was obtained at 1400 rpm spindle speed and weld speed of 20 mm/min. Maximum micro hardness (92 HV) was obtained at 1400 rpm spindle speed and weld speed of 16 mm/min. At these optimal setting of process parameters aluminium alloys were welded with the copper powder. Experimental results demonstrated that the tensile strength (96.54 MPa) and micro hardness (105 HV) of FSW was notably affected by the addition of copper powder when compared with FSW joint without copper powder. Tensile failure specimen was analysed using Scanning Electron Microscopy in order to study the failure mechanism.

Effect of pin tool design on the material flow of dissimilar AA7075-AA6061 friction stir welds

NASA Astrophysics Data System (ADS)

Hasan, Mohammed M.; Ishak, M.; Rejab, M. R. M.

2017-10-01

Tool design is the most influential aspect in the friction stir welding (FSW) technology. Influence of pin tool geometry on material flow pattern are studied in this work during the FSW of dissimilar AA7075 and AA6061 aluminium alloys. Three truncated pin tool profiles (threaded, threaded with single flat, and unthreaded with single flat) were used to prepare the weldments. The workpieces were joined using a custom-made clamping system under 1100 rpm of spindle speed, 300 mm/min of traverse rate and 3° of tilt angle. The metallographic analysis showed that defect-free welds can be produced using the three pin tools with significant changes in the mixing stir zone structure. The results declared that the introducing of the flat on the cone of the probe deviates the pattern of the onion rings without changing the chemical composition of the created layers. This in turn improves the hardness distribution and tensile strength of the welded joint. It was also noted that both heat affected zone (HAZ) and thermal-mechanical affected zone (TMAZ) are similar in composition to their corresponding base materials (BM).

Friction Stir Weld Application and Tooling Design for the Multi-purpose Crew Vehicle Stage Adapter

NASA Technical Reports Server (NTRS)

Alcorn, John

2013-01-01

The Multi-Purpose Crew Vehicle (MPCV), commonly known as the Orion capsule, is planned to be the United States' next manned spacecraft for missions beyond low earth orbit. Following the cancellation of the Constellation program and creation of SLS (Space Launch System), the need arose for the MPCV to utilize the Delta IV Heavy rocket for a test launch scheduled for 2014 instead of the previously planned Ares I rocket. As a result, an adapter (MSA) must be used in conjunction with the MPCV to account for the variation in diameter of the launch vehicles; 5.5 meters down to 5.0 meters. Prior to ight article fabrication, a path nder (test article) will be fabricated to ne tune the associated manufacturing processes. The adapter will be comprised of an aluminum frustum (partial cone) that employs isogrid technology and circumferential rings on each end. The frustum will be fabricated by friction stir welding (FSW) three individual panels together on a Vertical Weld Tool (VWT) at NASA Marshall Space Flight Center. Subsequently, each circumferential ring will be friction stir welded to the frustum using a Robotic Weld Tool (RWT). The irregular geometry and large mass of the MSA require that extensive tooling preparation be put into support structures for the friction stir weld. The tooling on the VWT will be comprised of a set of conveyors mounted on pre-existing stanchions so that the MSA will have the ability to be rotated after each of the three friction stir welds. The tooling requirements to friction stir weld the rings with the RWT are somewhat more demanding. To support the mass of the MSA and resist the load of the weld tool, a system of mandrels will be mounted to stanchions and assembled in a circle. The goal of the paper will be to explain the design, fabrication, and assembly of the tooling, to explain the use of friction stir welding on the MSA path nder, and also to discuss the lessons learned and modi cations made in preparation for ight article fabrication in support of the 2014 launch of the Orion MPCV.

Optical sensing in laser machining

NASA Astrophysics Data System (ADS)

Smurov, Igor; Doubenskaia, Maria

2009-05-01

Optical monitoring of temperature evolution and temperature distribution in laser machining provides important information to optimise and to control technological process under study. The multi-wavelength pyrometer is used to measure brightness temperature under the pulsed action of Nd:YAG laser on stainless steel substrates. Specially developed "notch" filters (10-6 transparency at 1.06 μm wavelength) are applied to avoid the influence of laser radiation on temperature measurements. The true temperature is restored based on the method of multi-colour pyrometry. Temperature monitoring of the thin-walled gilded kovar boxes is applied to detect deviation of the welding seam from its optimum position. The pyrometers are used to control CO2-laser welding of steel and Ti plates: misalignment of the welded plates, variation of the welding geometry, internal defects, deviation of the laser beam trajectory from the junction, etc. The temperature profiles along and across the welding axis are measured by the 2D pyrometer. When using multi-component powder blends in laser cladding, for example metal matrix composite with ceramic reinforcement, one needs to control temperature of the melt to avoid thermal decomposition of certain compounds (as WC) and to assure melting of the base metal (as Co). Infra-red camera FLIR Phoenix RDAS provides detailed information on distribution of brightness temperature in laser cladding zone. CCD-camera based diagnostic system is used to measure particles-in-flight velocity and size distribution.

Design of Friction Stir Welding Tool for Avoiding Root Flaws

PubMed Central

Ji, Shude; Xing, Jingwei; Yue, Yumei; Ma, Yinan; Zhang, Liguo; Gao, Shuangsheng

2013-01-01

In order to improve material flow behavior during friction stir welding and avoid root flaws of weld, a tool with a half-screw pin and a tool with a tapered-flute pin are suggested. The effect of flute geometry in tool pins on material flow velocity is investigated by the software ANSYS FLUENT. Numerical simulation results show that high material flow velocity appears near the rotational tool and material flow velocity rapidly decreases with the increase of distance away from the axis of the tool. Maximum material flow velocity by the tool with the tapered-flute pin appears at the beginning position of flute and the velocity decreases with the increase of flow length in flute. From the view of increasing the flow velocity of material near the bottom of the workpiece or in the middle of workpiece, the tool with the half-screw pin and the tool with the tapered-flute pin are both better than the conventional tool. PMID:28788426

Design of Friction Stir Welding Tool for Avoiding Root Flaws.

PubMed

Ji, Shude; Xing, Jingwei; Yue, Yumei; Ma, Yinan; Zhang, Liguo; Gao, Shuangsheng

2013-12-12

In order to improve material flow behavior during friction stir welding and avoid root flaws of weld, a tool with a half-screw pin and a tool with a tapered-flute pin are suggested. The effect of flute geometry in tool pins on material flow velocity is investigated by the software ANSYS FLUENT. Numerical simulation results show that high material flow velocity appears near the rotational tool and material flow velocity rapidly decreases with the increase of distance away from the axis of the tool. Maximum material flow velocity by the tool with the tapered-flute pin appears at the beginning position of flute and the velocity decreases with the increase of flow length in flute. From the view of increasing the flow velocity of material near the bottom of the workpiece or in the middle of workpiece, the tool with the half-screw pin and the tool with the tapered-flute pin are both better than the conventional tool.

Detailed Microstructural Characterization and Restoration Mechanisms of Duplex and Superduplex Stainless Steel Friction-Stir-Welded Joints

NASA Astrophysics Data System (ADS)

Santos, T. F. A.; Torres, E. A.; Lippold, J. C.; Ramirez, A. J.

2016-12-01

Duplex stainless steels are successfully used in a wide variety of applications in areas such as the food industry, petrochemical installations, and sea water desalination plants, where high corrosion resistance and high mechanical strength are required. However, during fusion welding operations, there can be changes to the favorable microstructure of these materials that compromise their performance. Friction stir welding with a non-consumable pin enables welded joints to be obtained in the solid state, which avoids typical problems associated with solidification of the molten pool, such as segregation of alloying elements and the formation of solidification and liquefaction cracks. In the case of superduplex stainless steels, use of the technique can avoid unbalanced proportions of ferrite and austenite, formation of deleterious second phases, or growth of ferritic grains in the heat-affected zone. Consolidated joints with full penetration were obtained for 6-mm-thick plates of UNS S32101 and S32205 duplex stainless steels, and S32750 and S32760 superduplex steels. The welding heat cycles employed avoided the conditions required for formation of deleterious phases, except in the case of the welded joint of the S32760 steel, where SEM images indicated the formation of secondary phases, as corroborated by decreased mechanical performance. Analysis using EBSD and transmission electron microscopy revealed continuous dynamic recrystallization by the formation of cellular arrays of dislocations in the ferrite and discontinuous dynamic recrystallization in the austenite. Microtexture evaluation indicated the presence of fibers typical of shear in the thermomechanically affected zone. These fibers were not obviously present in the stir zone, probably due to the intensity of microstructural reformulation to which this region was subjected.

Metallurgical Effects of Shunting Current on Resistance Spot-Welded Joints of AA2219 Sheets

NASA Astrophysics Data System (ADS)

Jafari Vardanjani, M.; Araee, A.; Senkara, J.; Jakubowski, J.; Godek, J.

2016-08-01

Shunting effect is the loss of electrical current via the secondary circuit provided due to the existence of previous nugget in a series of welding spots. This phenomenon influences on metallurgical aspects of resistance spot-welded (RSW) joints in terms of quality and performance. In this paper RSW joints of AA2219 sheets with 1 mm thickness are investigated metallurgically for shunted and single spots. An electro-thermal finite element analysis is performed on the RSW process of shunted spot and temperature distribution and variation are obtained. These predictions are then compared with experimental micrographs. Three values of 5 mm, 20 mm, and infinite (i.e., single spot) are assumed for welding distance. Numerical and experimental results are matching each other in terms of nugget and HAZ geometry as increasing distance raised nugget size and symmetry of HAZ. In addition, important effect of shunting current on nugget thickness, microstructure, and Copper segregation on HAZ grain boundaries were discovered. A quantitative analysis is also performed about the influence of welding distance on important properties including ratio of nugget thickness and diameter ( r t), ratio of HAZ area on shunted and free side of nugget ( r HA), and ratio of equivalent segregated and total amount of Copper, measured in sample ( r Cu) on HAZ. Increasing distance from 5 mm to infinite, indicated a gain of 111.04, -45.55, and -75.15% in r t, r HA, and r Cu, respectively, while obtained ratios for 20 mm welding distance was suitable compared to single spot.

Characterization of Microstructure and Texture of 13Cr4Ni Martensitic Stainless Steel Weld Before and After Tempering =

NASA Astrophysics Data System (ADS)

Mokhtabad Amrei, Mohsen

13Cr4Ni martensitic stainless steels are known for their outstanding performances in the hydroelectric industry, where they are mainly used in the construction of turbine components. Considering the size and geometry of turbine runners and blades, multi-pass welding procedures are commonly used in the fabrication and repair of such turbines. The final microstructure and mechanical properties of the weld are sensitive to the welding process parameters and thermal history. In the case of 13Cr4Ni steel, the thermal cycles imposed by the multi-pass welding operation have significant effects on the complex weld microstructure. Additionally, post-weld heat treatments are commonly used to reduce weld heterogeneity and improve the material's mechanical properties by tempering the microstructure and by forming a "room-temperature-stable austenite." In the first phase of this research, the microstructures and crystallographic textures of aswelded single-pass and double-pass welds were studied as a basis to studying the more complex multi-pass weld microstructure. This study found that the maximum hardness is obtained in high temperature heat affected zone inside the base metal. In particular, the results showed that the heat cycle exposed by the second pass increases the hardness of the previous pass because it produces a finer martensite microstructure. In areas of heat affected zone, a tempering effect is reported from 3 up to 6 millimeters far from the fusion line. Finding austenite phase in these areas are matter of interest and it can be indicative of the microstructure complexity of multi-pass welds. In the second phase of research, the microstructure of multi-pass welds was found to be more heterogeneous than that of single- and double-pass welds. Any individual pass in a multi-pass weld consists of several regions formed by adjacent weld passes heat cycle. Results showed that former austenite grains modification occurred in areas close to the subsequent weld passes. Furthermore, low angle interface laths were observed inside martensite sub-blocks over different regions. The hardness profile of a multi-pass weld was explained by the overlaying heat effects of surrounding passes. In some regions, a tempered matrix was observed, while in other regions a double-quenched microstructure was found. The final aspect of this study focused on the effects of post-weld heat treatments on reformed austenite and carbide formations, and evolution of hardness. The effects of tempering duration and temperature on microstructure were investigated. The study found that nanometer-sized carbides form at martensite lath interfaces and sub-block boundaries. Additionally, it was determined that for any holding duration, the maximum austenite percentage is achievable by tempering at 610 °C. Similarly, the maximum softening was reported for tempering at 610 °C, for any given holding period.

Detection and evaluation of weld defects in stainless steel using alternating current field measurement

NASA Astrophysics Data System (ADS)

Wei-Li, Ma, Weiping; Pan-Qi, Wen-jiao, Dou; Yuan, Xin'an; Yin, Xiaokang

2018-04-01

Stainless steel is widely used in nuclear power plants, such as various high-radioactive pool, tools storage and fuel transportation channel, and serves as an important barrier to stop the leakage of high-radioactive material. NonDestructive Evaluation (NDE) methods, eddy current testing (ET), ultrasonic examination (UT), penetration testing (PT) and hybrid detection method, etc., have been introduced into the inspection of a nuclear plant. In this paper, the Alternating Current Field Measurement (ACFM) was fully applied to detect and evaluate the defects in the welds of the stainless steel. Simulations were carried out on different defect types, crack lengths, and orientation to reveal the relationship between the signals and dimensions to determine whether methods could be validated by the experiment. A 3-axis ACFM probe was developed and three plates including 16 defects, which served in nuclear plant before, were examined by automatic detection equipment. The result shows that the minimum detectable crack length on the surface is 2mm and ACFM shows excellent inspection results for a weld in stainless steel and gives an encouraging prospect of broader application.

Analysis of plasma characteristics and conductive mechanism of laser assisted pulsed arc welding

NASA Astrophysics Data System (ADS)

Liu, Shuangyu; Chen, Shixian; Wang, Qinghua; Li, Yanqing; Zhang, Hong; Ding, Hongtao

2017-05-01

This study aims to investigate the arc plasma shape and the spectral characteristics during the laser assisted pulsed arc welding process. The arc plasma shape was synchronously observed using a high speed camera, and the emission spectrum of plasma was obtained by spectrometer. The well-known Boltzmann plot method and Stark broadening were used to calculate the electron temperature and density respectively. The conductive mechanism of arc ignition in laser assisted arc hybrid welding was investigated, and it was found that the plasma current moved to the arc anode under the action of electric field. Thus, a significant parabolic channel was formed between the keyhole and the wire tip. This channel became the main method of energy transformation between the arc and the molten pool. The calculation results of plasma resistivity show that the laser plasma has low resistivity as the starting point of conductive channel formation. When the laser pulse duration increases, the intensity of the plasma radiation spectrum and the plasma electron density will increase, and the electron temperature will decrease.

The Effect of Oscillating Traverse Welding on Performance of Cr-Fe-C Hardfacing Alloys

NASA Astrophysics Data System (ADS)

Lai, Hsuan-Han; Hsieh, Chih-Chun; Wang, Jia-Siang; Lin, Chi-Ming; Wu, Weite

2015-11-01

In this study, a series of experiments involving Cr-Fe-C hardfacing alloys is conducted to evaluate the effect of oscillating traverse welding on microstructure and performance of clad alloys. The alloys are designed to exhibit hypoeutectic, eutectic, and hypereutectic morphology. The morphology of the heat-affected zone (HAZ) of the unmelted metal, the solidified remelted metal, and the fusion boundary exhibited distinct characteristics. In the hypoeutectic and the eutectic alloys, the same lamellar eutectic structure can be observed as the solidified structure, and they also showed the same evolution in the HAZ. In the hypereutectic alloy, the incomplete weld pool blending results in a eutectic morphology instead of a fully hypereutectic morphology. The hardness result reveals that, for the hypereutectic alloy, the eutectic region, instead of the HAZ, is the weak point. The wear test shows that the hypoeutectic alloy exhibits the same wear behaviors in both the remelted metal and the HAZ, and so is the hypereutectic alloy; the eutectic alloy remelted metal and the HAZ have different wear morphologies.

Study of issues in difficult-to-weld thick materials by hybrid laser arc welding

NASA Astrophysics Data System (ADS)

Mazar Atabaki, Mehdi

There is a high interest for the high strength-to-weight ratio with good ductility for the welds of advanced alloys. The concern about the welding of thick materials (Advanced high strength steels (AHSS) and 5xxx and 6xxx series of aluminum alloys) has stimulated the development of manufacturing processes to overcome the associated issues. The need to weld the dissimilar materials (AHSS and aluminum alloys) is also required for some specific applications in different industries. Hence, the requirement in the development of a state-of-the-art welding procedure can be helpful to fulfill the constraints. Among the welding methods hybrid laser/arc welding (HLAW) has shown to be an effective method to join thick and difficult-to-weld materials. This process benefits from both advantages of the gas metal arc welding (GMAW) and laser welding processes. The interaction of the arc and laser can help to have enough penetration of weld in thick plates. However, as the welding of dissimilar aluminum alloys and steels is very difficult because of the formation of brittle intermetallics the present work proposed a procedure to effectively join the alloys. The reports showed that the explosively welded aluminum alloys to steels have the highest toughness, and that could be used as an "insert" (TRICLAD) for welding the thick plates of AHSS to aluminum alloys. Therefore, the HLAW of the TRICLAD-Flange side (Aluminum alloy (AA 5456)) to the Web side (Aluminum alloys (AA 6061 and AA 5456)) and the TRICLAD-Flange side (ASTM A516) to the Web side (AHSS) was studied in the present work. However, there are many issues related to HLAW of the dissimilar steels as well as dissimilar aluminum alloys that have to be resolved in order to obtain sound welds. To address the challenges, the most recent welding methods for joining aluminum alloys to steels were studied and the microstructural development, mechanical properties, and on-line monitoring of the welding processes were discussed as well. The heat and mass transfer and the issues in joining of dissimilar alloys by the hybrid laser/arc welding process (HLAW) were explicitly explained in details. A finite element model was developed to simulate the heat transfer in HLAW of the aluminum alloys. Two double-ellipsoidal heat source models were considered to describe the heat input of the gas metal arc welding and laser welding processes. An experimental procedure was also developed for joining thick advanced high strength steel plates by using the HLAW, by taking into consideration different butt joint configurations. The geometry of the weld groove was optimized according to the requirements of ballistic test, where the length of the softened heat affected zone should be less than 15.9 mm measured from the weld centerline. Since the main issue in HLAW of the AHSS was the formation of the pores, the possible mechanisms of the pores formation and their mitigation methods during the welding process were investigated. Mitigation methods were proposed to reduce the pores inside in the weld area and the influence of each method on the process stability was investigated by an on-line monitoring system of the HLAW process. The groove angle was optimized for the welding process based on the allowed amount of heat input along the TRICLADRTM interface generated by an explosive welding. The weld was fractured in the heat affected zone of the aluminum side in the tensile test. The microharness was shown that the temperature variation caused minor softening in the heat affected zone satisfying the requirement that the width of the softened heat affected zone in the steel side falls within 15.9 mm far away from the weld centerline. The microstructure analysis showed the presence of tempered martensite at the vicinity of the weld area, which it was a cause of softening in the heat affected zone.

High-Powered, Ultrasonically Assisted Thermal Stir Welding

NASA Technical Reports Server (NTRS)

Ding, Robert

2013-01-01

This method is a solid-state weld process capable of joining metallic alloys without melting. The weld workpieces to be joined by thermal stir welding (TSW) are drawn, by heavy forces, between containment plates past the TSW stir tool that then causes joining of the weld workpiece. TSW is similar to friction stir welding (FSW) in that material is heated into a plastic state (not melted) and stirred using a stir rod. The FSW pin tool is an integrated geometrical structure consisting of a large-diameter shoulder, and a smaller-diameter stir pin protruding from the shoulder. When the pin is plunged into a weld workpiece, the shoulder spins on the surface of the weld workpiece, thus inducing frictional heat into the part. The pin stirs the fraying surfaces of the weld joint, thus joining the weld workpiece into one structure. The shoulder and stir pin of the FSW pin tool must rotate together at a desired rotational speed. The induced frictional energy control and stir pin control of the pin tool cannot be de-coupled. The two work as one integrated unit. TSW, on the other hand, de-couples the heating and stirring of FSW, and allows for independent control of each process element. A uniquely designed induction coil heats the weld workpiece to a desired temperature, and once heated, the part moves into a stir rod whose RPM is also independently controlled. As the weld workpiece moves into the stir rod, the piece is positioned, or sandwiched, between upper and lower containment plates. The plate squeezes together, thus compressing the upper and lower surfaces of the weld workpiece. This compressive force, also called consolidation force, consolidates the plastic material within the weld nugget material as it is being stirred by the stir rod. The stir rod is positioned through the center of the top containment plate and protrudes midway through the opposite lower containment plate where it is mechanically captured. The upper and lower containment plates are separated by a distance equal to the thickness of the material being welded. The TSW process can be significantly improved by reducing the draw forces. This can be achieved by reducing the friction forces between the weld workpieces and the containment plates. High-power ultrasonic (HPU) vibrations of the containment plates achieve friction reduction in the TSW process. Furthermore, integration of the HPU energy into the TSW stir rod can increase tool life of the stir rod, and can reduce shear forces to which the stir rod is subjected during the welding process. TSW has been used to successfully join 0.500-in (˜13-mm) thick commercially pure (CP) titanium, titanium 6AL- 4V, and titanium 6AL-4V ELI in weld joint lengths up to 9 ft (˜2.75-m) long. In addition, the TSW process was used to fabricate a sub-scale hexagonally shaped gun turret component for the U.S. Navy. The turret is comprised of six 0.5000-in (˜13-mm) thick angled welds. Each angled weld joint was prepared by machining the mating surfaces to 120deg. The angled weld joint was then fixtured using an upper and lower containment plate of the same geometry of the angled weld joint. The weld joint was then stirred by the stir rod as it and the upper and lower containment plates traverse through the angled joint prep.

Study of the structure and properties of laser-welded joints of the Al-Mg-Li alloy

NASA Astrophysics Data System (ADS)

Pugacheva, N. B.; Antenorova, N. P.; Senaeva, E. I.

2015-12-01

The macro- and microstructures, the distribution of chemical elements and of the values of the microhardness over the width of the zones of remelting and heat-affected zone have been studied after the laser welding of sheets of an Al-Mg-Li alloy. It has been shown that the material of the zone of remelting (1.2 mm thick) represents in itself finely dispersed misoriented dendrites, in the primary branches of which particles of the strengthening δ' phase (Al3Li) with dimensions of no more than 10 nm and in the interdendrite spaces, dispersed particles of the S phase (Al2MgLi and FeAl2) have been revealed. The hardness of the material of the zone of remelting was 108-123 HV 0.05; the hardness of the basic alloy, 150-162 HV 0.05. In the heat-affected zones of thickness 2 mm, the primary recrystallization occurred only in a narrow zone directly at the boundary with the weld. The strength of the welded junction was 470-490 MPa, which corresponds to the regulated degree of strength of the aluminum alloys of this class. The relative elongation of the material of the weld proved to be considerably less than that in the alloy matrix because of the microporosity of the weld material. It is shown that the convective stirring of the melt in the welding pool upon the laser welding made it possible to avoid the appearance of macroscopic defects, but on the microlevel there are observed micropores in the form of spheres with dimensions of 5-50 μm. The solidification of the alloy occurred in such a way that the dendrites had time to grow around the gas bubbles prior to their collapse, forming a sufficiently strong carcass. Inside the dendritic carcass, there have been revealed coarse inclusions (to 200 μm) that consist of oxides (Al2O3, Fe2O3, MgO, SiO2, CaO), of an iron-based alloy, and of the host aluminum alloy.

Influence of thickness of zinc coating on CMT welding-brazing with AlSi5 alloy wire

NASA Astrophysics Data System (ADS)

Jin, Pengli; Wang, Zhiping; Yang, Sinan; Jia, Peng

2018-03-01

Effect of thickness of zinc coating on Cold Mattel Transfer (CMT) brazing of aluminum and galvanized steel is investigated. The thickness of zinc coating is 10 μm, 30 μm, and 60 μm, respectively. A high-speed camera was used to capture images of welding process of different specimens; the microstructure and composition analyses of the welding seam were examined by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS); the mechanical properties were measured in the form of Nano-indentation experiments. The results showed that arc characteristics and metal transfer behavior were unsteady at the beginning of welding process and that became stable after two cycles of CMT. With the thickness of zinc coating thickening, arc characteristics and metal transfer behaviors were more deteriorated. Compared with 10 μm and 30 μm, clad appearance of 60 μm was straight seam edges and a smooth surface which wetting angle was 60°. Zinc-rich zone at the seam edges was formed by zinc dissolution and motel pool oscillating, and zinc content of 10 μm and 30 μm were 5.8% and 7.75%. Zinc content of 60 μm was 14.61%, and it was a belt between galvanized steel and welding seam. The thickness of intermetallic compounds layer was in the range of 1-8 μm, and it changed with the thickness of zinc coating. The average hardness of the reaction layer of 60 μm is 9.197 GPa.

Use of schlieren methods to study gas flow in laser technology

NASA Astrophysics Data System (ADS)

Mrňa, Libor; Pavelka, Jan; Horník, Petr; Hrabovský, Jozef

2016-11-01

Laser technologies such as welding and cutting rely on process gases. We suggest to use schlieren imaging to visualize the gas flow during these processes. During the process of laser welding, the shielding gas flows to the welded area to prevent oxidation of the weld pool by surrounding air. The gas also interacts with hot plasma spurting from the key hole induced by the laser beam incident on the molten material. This interaction is quite complicated because hot plasma mixes with the cold shielding gas while the system is moving along the weld. Three shielding gases were used in the presented experiment: Ar, He and N2. Differences in dynamics of the flow are clearly visible on schlieren images. Moreover, high speed recording reveals a structure consisting of hot gas bubbles. We were also able to determine the velocity of the bubbles from the recording. During laser cutting, the process gas flows coaxially with the laser beam from the nozzle to remove the molten material out of the kerf. The gas flow is critical for the quality of the resulting edge of the cut. Schlieren method was used to study gas flow under the nozzle and then under the material being cut. This actually creates another slot nozzle. Due to the very low speed of flow below the material the schleiren method is already at the limit of its sensitivity. Therefore, it is necessary to apply a differential technique to increase the contrast. Distinctive widening of the flow shaped by the kerf was observed.

Non-Equilibrium Phenomena in High Power Beam Materials Processing

NASA Astrophysics Data System (ADS)

Tosto, Sebastiano

2004-03-01

The paper concerns some aspects of non-equilibrium materials processing with high power beams. Three examples show that the formation of metastable phases plays a crucial role to understand the effects of beam-matter interaction: (i) modeling of pulsed laser induced thermal sputtering; (ii) formation of metastable phases during solidification of the melt pool; (i) possibility of carrying out heat treatments by low power irradiation ``in situ''. The case (i) deals with surface evaporation and boiling processes in presence of superheating. A computer simulation model of thermal sputtering by vapor bubble nucleation in molten phase shows that non-equilibrium processing enables the rise of large surface temperature gradients in the boiling layer and the possibility of sub-surface temperature maximum. The case (ii) concerns the heterogeneous welding of Cu and AISI 304L stainless steel plates by electron beam irradiation. Microstructural investigation of the molten zone has shown that dwell times of the order of 10-1-10-3 s, consistent with moderate cooling rates in the range 10^3-10^5 K/s, entail the formation of metastable Cu-Fe phases. The case (iii) concerns electron beam welding and post-welding treatments of 2219 Al base alloy. Electron microscopy and positron annihilation have explained why post-weld heat transients induced by low power irradiation of specimens in the as welded condition enable ageing effects usually expected after some hours of treatment in furnace. The problem of microstructural instability is particularly significant for a correct design of components manufactured with high power beam technologies and subjected to severe acceptance standards to ensure advanced performances during service life.

Fatigue assessment for selected connections of structural steel bridge components using the finite elements method

NASA Astrophysics Data System (ADS)

Śledziewski, Krzysztof

2018-01-01

Material fatigue it is one of the most frequent causes of steel bridge failures, particularly the bridges already existing. Thus, the procedure of fatigue life assessment is one of the most relevant procedures in a comprehensive assessment of load-carrying capacity and service life of the structure. A reliable assessment of the fatigue life is predominantly decisive for estimation of the remaining service life. Hitherto, calculation methods of welded joints took into account only stresses occurring in cross sections of whole elements and did not take into account stress concentration occurring in the vicinity of the weld, caused by geometrical aspects of the detail. At present, use of the Finite Element Analysis, makes possible looking for more accurate approach to the fatigue design of steel structures. The method of geometrical stresses is just such approach which is based on definition of stresses which take into account geometry of the detail. The study presents fatigue assessment of a representative type of welded joint in welded bridge structures. The testing covered longitudinal attachments. The main analyses were carried out on the basis of FEM and the method of local stresses, so-called "hot-spot" stresses. The obtained values of stresses were compared with the values obtained in accordance with the method of nominal stress.

Modeling of electric and heat processes in spot resistance welding of cross-wire steel bars

NASA Astrophysics Data System (ADS)

Iatcheva, Ilona; Darzhanova, Denitsa; Manilova, Marina

2018-03-01

The aim of this work is the modeling of coupled electric and heat processes in a system for spot resistance welding of cross-wire reinforced steel bars. The real system geometry, dependences of material properties on the temperature, and changes of contact resistance and released power during the welding process have been taken into account in the study. The 3D analysis of the coupled AC electric and transient thermal field distributions is carried out using the finite element method. The novel feature is that the processes are modeled for several successive time stages, corresponding to the change of contact area, related contact resistance, and reduction of the released power, occurring simultaneously with the creation of contact between the workpieces. The values of contact resistance and power changes have been determined on the basis of preliminary experimental and theoretical investigations. The obtained results present the electric and temperature field distributions in the system. Special attention has been paid to the temperature evolution at specified observation points and lines in the contact area. The obtained information could be useful for clarification of the complicated nature of interrelated electric, thermal, mechanical, and physicochemical welding processes. Adequate modeling is also an opportunity for proper control and improvement of the system.

Melt-Pool Temperature and Size Measurement During Direct Laser Sintering

DOE Office of Scientific and Technical Information (OSTI.GOV)

List, III, Frederick Alyious; Dinwiddie, Ralph Barton; Carver, Keith

2017-08-01

Additive manufacturing has demonstrated the ability to fabricate complex geometries and components not possible with conventional casting and machining. In many cases, industry has demonstrated the ability to fabricate complex geometries with improved efficiency and performance. However, qualification and certification of processes is challenging, leaving companies to focus on certification of material though design allowable based approaches. This significantly reduces the business case for additive manufacturing. Therefore, real time monitoring of the melt pool can be used to detect the development of flaws, such as porosity or un-sintered powder and aid in the certification process. Characteristics of the melt poolmore » in the Direct Laser Sintering (DLS) process is also of great interest to modelers who are developing simulation models needed to improve and perfect the DLS process. Such models could provide a means to rapidly develop the optimum processing parameters for new alloy powders and optimize processing parameters for specific part geometries. Stratonics’ ThermaViz system will be integrated with the Renishaw DLS system in order to demonstrate its ability to measure melt pool size, shape and temperature. These results will be compared with data from an existing IR camera to determine the best approach for the determination of these critical parameters.« less

Effect of Convection on Weld Pool Shape and Microstructure.

DTIC Science & Technology

1986-07-01

latent heat of fusion 11 u dynamic viscosity Iwo V kinematic viscosity P density a Stefan -Boltzman constant stress tensor 0, functions defined the...and temperature. The convections for velocities and temperature are based on a mixed Gauss- -* Seidel and Jacobi schemes, proceeding from line-to...line according to the Gauss- Seidel scheme, updating values as each line is completed. With each line, however, the point-by-point iteration is based on

Computational modeling of heat transfer and visco-plastic flow in friction stir welding

NASA Astrophysics Data System (ADS)

Nandan, Rituraj

With a focus to develop a quantitative understanding of the FSW process, a comprehensive three dimensional heat transfer and plastic flow model is developed. The model can predict variables such as temperature and velocity fields and torque based on the given welding parameters like weld velocity, tool rotational speed and axial pressure. It considers tool design dependent spatially variable heat generation rates, deformational work, non-Newtonian viscosity as a function of local strain rate, temperature and the nature of the material and temperature dependent thermal conductivity, specific heat capacity and yield stress. It is shown that the temperature fields, cooling rates, the plastic flow fields and the geometry of the thermo-mechanically affected zone (TMAZ) can be adequately described by solving the equations of conservation of mass, momentum and energy in three dimensions with appropriate boundary conditions and constitutive equations for viscosity. The model is tested for four different alloys: (1) AA 6061-T6, (2) 1018 Mn steel, (3) 304L stainless steel and (4) Ti-6Al-4V which have widely different thermophysical and rheological properties. Numerically computed temperature fields, variations of peak temperatures with FSW variables and TMAZ geometry were compared with the experimental results. Currently, due to unknown parameters in existing transport phenomena based models, the computed temperature and velocity fields and torque may not always agree with the corresponding experimentally determined values and may not show the same trend as experimental results for a range of welding variables. Here, it is shown that this problem can be solved by combining the rigorous phenomenological process sub-model with a multivariable optimization scheme called Differential Evolution. The values of the uncertain model input parameters from a limited volume of independent experimental data which includes temperature measurements obtained using thermocouples and torque measured using dynamometers. This approach resulted in agreement between the phenomenological model and the experimental results with a greater degree of certainty. It is tested for FSW of: (1) dissimilar AA 6061-T6 to AA 1200, (2) 1018 Mn steel and (3) Ti-6Al-4V. Independent thermocouple and dynamometer measurements are also used for validation and verification of results. Improvement in the reliability of the numerical model is an important first step towards increasing its practical usefulness. Also, one of the reasons why current models do not find extensive applications is because they cannot be used to tailor weld attributes. The aim of the present research is to develop a reliable bi-directional model which can find wide use in manufacturing and process control. It is shown that by coupling a reliable model with an evolutionary search algorithm, we can find multiple sets of welding parameters to achieve a target peak temperature and cooling rate in welds. The model is tested for dissimilar welds of AA 6351 and AA 1200. FSW is being increasingly used for dissimilar metal joining. Models are needed to calculate the redistribution of alloying elements when two alloys with dissimilar alloying element contents are joined. The transport and mixing of magnesium from Mg-rich AA 6061 alloy into a commercially pure aluminum AA 1200 was examined experimentally and numerically at various locations in the welded workpiece. The concentration of the solute is measured in transverse cross-sections across the weld-center line at various depths from the top surface of the workpiece. The measurement was done using electron probe micro-analysis (EPMA) of polished transverse-cut friction-stir welded samples. The comparison of the experimental and computed concentration profiles of magnesium shows imperfect mixing of the plasticized alloys during FSW. The plasticized material seem to move in layers without significant diffusive interlayer mixing. A comprehensive model for FSW is developed with capability of calculating temperature fields, material flow patterns and concentration fields in both similar and dissimilar welds in three dimensions. The model is tested for the FSW of alloys with widely different thermophysical properties. A mechanism for improving reliability and ability to provide guidance to tailor weld attributes is incorporated into the model to increase its practical usefulness. This is done by by combining the transport phenomena based model with Differential Evolution algorithm to minimize the objective function based on limited volume of experimental thermal cycles and torque measurements. (Abstract shortened by UMI.)

Propulsion and Energetics Panel Working Group 20 on Test Cases for Engine Life Assessment Technology (Cas d’Essai pour la Gestion de la Duree de Vie des Moteurs)

DTIC Science & Technology

1992-09-01

the 10 Figure 2.1 LARZAC ENGINE - welded disk-shaft 1 - shaft-spacer 2 -cone 3 - aft seal 4 - blades 5 Figure 2.2 COMPONENT GEOMETRY OEZ 0 9LL 0 It- C4...57 ൒--m-- 5.735 29.475 95 12.525 0.08 F60,45 chom at 456 -- - 6 1 Holes equall WIN 2,24! sae 80 T RIo.2 R838*20’ •-R2o4..6 0537,6 4 0640.226 R4...steel attempt was made Lo predict wire. Control thermocouples were initiation at the oil feed holes, welded to the compressor and since the stated goal of

Stochastic Model of Fracture Frequency Heterogeneity in a Welded Tuff EGS reservoir, Snake River Plain, Idaho, USA

NASA Astrophysics Data System (ADS)

Moody, A.; Fairley, J. P., Jr.

2014-12-01

In light of recent advancements in reservoir enhancement and injection tests at active geothermal fields, there is interest in investigating the geothermal potential of widespread subsurface welded tuffs related to caldera collapse on the Snake River Plain (SRP). Before considering stimulation strategies, simulating heat extraction from the reservoir under in-situ fracture geometries will give a first-order estimation of extractable heat. With only limited deep boreholes drilled on the SRP, few analyses of the bulk hydrologic properties of the tuffs exist. Acknowledging the importance of the spatial heterogeneity of fractures to the permeability and injectivity of reservoirs hosted in impermeable volcanic units, we present fracture distributions from ICDP hole 5036-2A drilled as a part of Project HOTSPOT. The core documents more than 1200 m of largely homogeneous densely welded tuff hosting an isothermal warm-water reservoir at ~60˚ C. Multiple realizations of a hypothetical reservoir are created using sequential indicator algorithms that honor the observed vertical fracture frequency statistics. Results help form criteria for producing geothermal energy from the SRP.

Characterization of Electron Beam Free-Form Fabricated 2219 Aluminum and 316 Stainless Steel

NASA Technical Reports Server (NTRS)

Ekrami, Yasamin; Forth, Scott C.; Waid, Michael C.

2011-01-01

Researchers at NASA Langley Research Center have developed an additive manufacturing technology for ground and future space based applications. The electron beam free form fabrication (EBF3) is a rapid metal fabrication process that utilizes an electron beam gun in a vacuum environment to replicate a CAD drawing of a part. The electron beam gun creates a molten pool on a metal substrate, and translates with respect to the substrate to deposit metal in designated regions through a layer additive process. Prior to demonstration and certification of a final EBF3 part for space flight, it is imperative to conduct a series of materials validation and verification tests on the ground in order to evaluate mechanical and microstructural properties of the EBF3 manufactured parts. Part geometries of EBF3 2219 aluminum and 316 stainless steel specimens were metallographically inspected, and tested for strength, fatigue crack growth, and fracture toughness. Upon comparing the results to conventionally welded material, 2219 aluminum in the as fabricated condition demonstrated a 30% and 16% decrease in fracture toughness and ductility, respectively. The strength properties of the 316 stainless steel material in the as deposited condition were comparable to annealed stainless steel alloys. Future fatigue crack growth tests will integrate various stress ranges and maximum to minimum stress ratios needed to fully characterize EBF3 manufactured specimens.

Preliminary development of the LBL/USGS three-dimensional site-scale model of Yucca Mountain, Nevada

USGS Publications Warehouse

1995-01-01

A three-dimensional model of moisture flow within the unsaturated zone at Yucca Mountain is being developed at Lawrence Berkeley Laboratory (LBL) in cooperation with the U.S. Geological Survey (USGS). This site-scale model covers and area of about 34 km2 and is bounded by major faults to the north, east and west. The model geometry is defined (1) to represent the variations of hydrogeological units between the ground surface and the water table; (2) to be able to reproduce the effect of abrupt changes in hydrogeological parameters at the boundaries between hyrdogeological units; and (3) to include the influence of major faults. A detailed numerical grid has been developed based on the locations of boreholes, different infiltration zones, hydrogeological units and their outcrops, major faults, and water level data. Contour maps and isopatch maps are presented defining different types of infiltration zones, and the spatial distribution of Tiva Canyon, Paintbrush, and Topopah Spring hydrogeological units. The grid geometry consists of seventeen non-uniform layers which represent the lithological variations within the four main welded and non-welded hydrogeological units. Matrix flow is approximated using the van Genuchten model, and the equivalent continuum approximation is used to account for fracture flow in the welded units. The fault zones are explicitly modeled as porous medium using various assumptions regarding their permeabilities and characteristic curves. One-, two-, and three-dimensional simulations are conducted using the TOUGH2 computer program. Steady-state simulations are performed with various uniform and non-uniform infiltration rates. The results are interpreted in terms of the effect of fault characteristics on the moisture flow distribution, and on location and formation of preferential pathways.

Modeling of sheet metal fracture via cohesive zone model and application to spot welds

NASA Astrophysics Data System (ADS)

Wu, Joseph Z.

Even though the cohesive zone model (CZM) has been widely used to analyze ductile fracture, it is not yet clearly understood how to calibrate the cohesive parameters including the specific work of separation (the work of separation per unit crack area) and the peak stress. A systematic approach is presented to first determine the cohesive values for sheet metal and then apply the calibrated model to various structure problems including the failure of spot welds. Al5754-0 was chosen for this study since it is not sensitive to heat treatment so the effect of heat-affected-zone (HAZ) can be ignored. The CZM has been applied to successfully model both mode-I and mode-III fracture for various geometries including Kahn specimens, single-notch specimens, and deep double-notch specimens for mode-I and trouser specimens for mode-III. The mode-I fracture of coach-peel spot-weld nugget and the mixed-mode fracture of nugget pull-out have also been well simulated by the CZM. Using the mode-I average specific work of separation of 13 kJ/m2 identified in a previous work and the mode-III specific work of separation of 38 kJ/m 2 found in this thesis, the cohesive peak stress has been determined to range from 285 MPa to 600 MPa for mode-I and from 165 MPa to 280 MPa for mode-III, depending on the degree of plastic deformation. The uncertainty of these cohesive values has also been examined. It is concluded that, if the specific work of separation is a material constant, the peak stress changes with the degree of plastic deformation and is therefore geometry-dependent.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Korinko, P.; Howard, S.; Maxwell, D.

During final preparations for start of the PDCF Inner Can (IC) qualification effort, welding was performed on an automated weld system known as the PICN. During the initial weld, using a pedigree canister and plug, a weld defect was observed. The defect resulted in a hole in the sidewall of the canister, and it was observed that the plug sidewall had not been consumed. This was a new type of failure not seen during development and production of legacy Bagless Transfer Cans (FB-Line/Hanford). Therefore, a team was assembled to determine the root cause and to determine if the process couldmore » be improved. After several brain storming sessions (MS and T, R and D Engineering, PDC Project), an evaluation matrix was established to direct this effort. The matrix identified numerous activities that could be taken and then prioritized those activities. This effort was limited by both time and resources (the number of canisters and plugs available for testing was limited). A discovery process was initiated to evaluate the Vendor's IC fabrication process relative to legacy processes. There were no significant findings, however, some information regarding forging/anneal processes could not be obtained. Evaluations were conducted to compare mechanical properties of the PDC canisters relative to the legacy canisters. Some differences were identified, but mechanical properties were determined to be consistent with legacy materials. A number of process changes were also evaluated. A heat treatment procedure was established that could reduce the magnetic characteristics to levels similar to the legacy materials. An in-situ arc annealing process was developed that resulted in improved weld characteristics for test articles. Also several tack welds configurations were addressed, it was found that increasing the number of tack welds (and changing the sequence) resulted in decreased can to plug gaps and a more stable weld for test articles. Incorporating all of the process improvements for the actual can welding process, however, did not result in an improved weld geometry. Several possibilities for the lack of positive response exist, some of which are that (1) an insufficient number of test articles were welded under prototypic conditions, (2) the process was not optimized so that significant improvements were observable over the 'noise', and (3) the in-situ arc anneal closed the gap down too much so the can was unable to exhaust pressure ahead of the weld. Several operational and mechanical improvements were identified. The weld clamps were changed to a design consistent with those used in the legacy operations. A helium puff operation was eliminated; it is believed that this operation was the cause of the original weld defect. Also, timing of plug mast movement was found to correspond with weld irregularities. The timing of the movement was changed to occur during weld head travel between tacks. In the end a three sequential tack weld process followed by a pulse weld at the same current and travel speed as was used for the legacy processes was suggested for use during the IC qualification effort. Relative to legacy welds, the PDC IC weld demonstrates greater fluctuation in the region of the weld located between tack welds. However, canister weld response (canister to canister) is consistent and with the aid of the optical mapping system (for targeting the cut position) is considered adequate. DR measurements and METs show the PDC IC welds to have sufficient ligament length to ensure adequate canister pressure/impact capacity and to ensure adequate stub function. The PDC welding process has not been optimized as a result of this effort. Differences remain between the legacy BTC welds and the PDC IC weld, but these differences are not sufficient to prevent resumption of the current PDC IC qualification effort. During the PDC IC qualification effort, a total of 17 cans will be welded and a variety of tests/inspections will be performed. The extensive data collected during that qualification effort should be of a sufficient population to determine if additional weld process optimization is necessary prior to production release.« less

Scanning and transmission electron microscopy study of the microstructural changes occurring in aluminium matrix composites reinforced with SiC particles during casting and welding: interface reactions

PubMed

Urena; Gomez De Salazar JM; Gil; Escalera; Baldonedo

1999-11-01

Processing of aluminium matrix composites (AMCs), especially those constituted by a reactive system such as Al-SiC, presents great difficulties which limit their potential applications. The interface reactivity between SiC and molten Al generates an aluminium carbide which degrades the composite properties. Scanning and transmission electron microscopes equipped with energy-dispersive X-ray spectroscopes are essential tools for determining the structure and chemistry of the Al-SiC interfaces in AMCs and changes occurring during casting and arc welding. In the present work, an aluminium-copper alloy (AA2014) reinforced with three different percentages of SiC particles was subjected to controlled remelting tests, at temperatures in the range 750-900 degrees C for 10 and 30 min. Arc welding tests using a tungsten intert gas with power inputs in the range 850-2000 W were also carried out. The results of these studies showed that during remelting there is preferential SiC particle consumption with formation of Al4C3 by interface reaction between the solid SiC particle and the molten aluminium matrix. The formation of Al4C3 by the same mechanism has also been detected in molten pools of arc welded composites. However, in this case there was formation of an almost continuous layer of Al4C3, which protects the particle against further consumption, and formation of aciculate aluminium carbide on the top weld. Both are formed by fusion and dissolution of the SiC in molten aluminium followed by reaction and precipitation of the Al4C3 during cooling.

Development of Mini-Compact Tension Test Method for Determining Fracture Toughness Master Curves for Reactor Pressure Vessel Steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sokolov, Mikhail A.

Small specimens are playing the key role in evaluating properties of irradiated materials. The use of small specimens provides several advantages. Typically, only a small volume of material can be irradiated in a reactor at desirable conditions in terms of temperature, neutron flux, and neutron dose. A small volume of irradiated material may also allow for easier handling of specimens. Smaller specimens reduce the amount of radioactive material, minimizing personnel exposures and waste disposal. However, use of small specimens imposes a variety of challenges as well. These challenges are associated with proper accounting for size effects and transferability of smallmore » specimen data to the real structures of interest. Any fracture toughness specimen that can be made out of the broken halves of standard Charpy specimens may have exceptional utility for evaluation of reactor pressure vessels (RPVs) since it would allow one to determine and monitor directly actual fracture toughness instead of requiring indirect predictions using correlations established with impact data. The Charpy V-notch specimen is the most commonly used specimen geometry in surveillance programs. Validation of the mini compact tension specimen (mini-CT) geometry has been performed on previously well characterized Midland beltline Linde 80 (WF-70) weld in the unirradiated condition. It was shown that the fracture toughness transition temperature, To, measured by these Mini-CT specimens is almost the same as To value that was derived from various larger fracture toughness specimens. Moreover, an International collaborative program has been established to extend the assessment and validation efforts to irradiated Linde 80 weld metal. The program is underway and involves the Oak Ridge National Laboratory (ORNL), Central Research Institute for Electrical Power Industry (CRIEPI), and Electric Power Research Institute (EPRI). The irradiated Mini-CT specimens from broken halves of previously tested Charpy specimens of Midland beltline weld have been machined and just arrived to ORNL as part of this international collaboration. The ORNL will initiate tests of the irradiated Linde 80 weld in FY2017 and results of this international program will be reported in FY2018.« less

The influence of oxygen additions on argon-shielded gas metal arc welding processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joensson, P.G.; Murphy, A.B.; Szekely, J.

1995-02-01

It has been observed experimentally that small additions of oxygen to the argon shielding gas affect the general operation of GMAW processes. By theoretically modeling the arc column, it is shown that the addition of 2 to 5% oxygen to argon has an insignificant effect on the arc characteristics. This corresponds to the minor changes in the thermophysical transport and thermodynamic properties caused by the oxygen addition. Therefore, it is concluded that the addition of oxygen to the argon shielding gas mainly affects the anode and the cathode regions. From the literature, it was found that the formation of oxidesmore » initiates arcing at the cathode and decreases the movement of the cathode spots. These oxides can also improve the wetting conditions at the workpiece and the electrode. Finally, oxygen is found to affect the surface tension gradient and thereby the convective flow of liquid metal in the weld pool.« less

Contribution a l'etude du comportement en fatigue des aciers inoxydables 13%Cr-4%Ni: Contraintes residuelles de soudage et transformation sous contrainte de l'austenite de reversion

NASA Astrophysics Data System (ADS)

Thibault, Denis

The objectives of the present study are to characterize some of the main parameters affecting fatigue behaviour of 13%Cr-4%Ni martensitic stainless steels used for hydraulic turbines manufacturing. Two aspects are studied: the residual stresses left after autogenous welding of these steels and the stress-assisted transformation of the reformed austenite contained in this alloy. The residual stresses induced by welding were characterized by four different methods: the hole-drilling method, X-ray diffraction, neutron diffraction and the contour method. The state of stress was characterized in two different joints geometries, both using 41ONiMo weld filler metal. The characterization was made before and after post-weld heat treatment. A stress distribution completely different of the stress distribution commonly found in structural steels was measured. Triaxial compression was found in the last bead with a maximum value of approximately 400 MPa. Tensile stress was measured around the heat-affected zone and just below the last weld layer. The low temperature martensitic transformation occuring during weld cooling (˜300°C) explains this unusual stress distribution. The results also showed that the post-weld heat treatment commonly used in the industry is efficient in lowering residual stresses. A maximum stress of about 150 MPa was found after heat treament. The austenite formed during this post-weld heat treatment is mechanically unstable. The results presented in this thesis show that after fatigue crack propagation testing, all the reformed austenite found near the fracture surface has transformed to martensite under cyclic stress loading. These measurements made by X-ray diffraction are confirmed by low-cycle fatigue tests showing that the reformed austenite found in this alloy transforms gradually to martensite during strain cycling. The transformation is completed after 100 cycles. The fatigue crack growth behaviour of the tested alloys does not seem to be influenced by this phenomenon occuring at all values of stress intensity factor. The practical implications of this work on fabrication and repair of hydraulic turbines made of 13%Cr-4%Ni are also discussed in this thesis. Keywords: martensitic stainless steel, fatigue, residual stress, welding

Advances in Solid State Joining of Haynes 230 High Temperature Alloy

NASA Technical Reports Server (NTRS)

Ding, R. Jeffrey; Schneider, Judy; Walker, Bryant

2010-01-01

The J-2X engine is being designed for NASA s new class of crew and launch vehicles, the Ares I and Ares V. The J-2X is a LOX/Hydrogen upper stage engine with 294,000 lbs of thrust and a minimum Isp of 448 seconds. As part of the design criteria to meet the performance requirements a large film-cooled nozzle extension is being designed to further expand the hot gases and increases the specific impulse. The nozzle extension is designed using Haynes 230, a nickel-chromium-tungsten-molybdenum superalloy. The alloy was selected for its high strength at elevated temperatures and resistance to hydrogen embrittlement. The nozzle extension is manufactured from Haynes 230 plate spun-forged to form the contour and chemically-milled pockets for weight reduction. Currently fusion welding is being evaluated for joining the panels which are then mechanically etched and thinned to required dimensions for the nozzle extension blank. This blank is then spun formed into the parabolic geometry required for the nozzle. After forming the nozzle extension, weight reduction pockets are chemically milled into the nozzle. Fusion welding of Haynes results in columnar grains which are prone to hot cracking during forming processes. This restricts the ability to use spin forging to produce the nozzle contour. Solid state joining processes are being pursued as an alternative process to produce a structure more amenable to spin forming. Solid state processes have been shown to produce a refined grain structure within the joint regions as illustrated in Figure 1. Solid state joining processes include friction stir welding (FSW) and a patented modification termed thermal stir welding (TSW). The configuration of TSWing utilizes an induction coil to preheat the material minimizing the burden on the weld tool extending its life. This provides the ability to precisely select and control the temperature. The work presented in this presentation investigates the feasibility of joining the Haynes 230 alloy using the solid state welding processes of FSW and TSW. Process descriptions and attributes of each weld process will be presented. Weld process set-up and welding techniques will be discussed leading to the challenges experienced in joining the superalloy. Mechanical property data will also be presented.

Online measurement of bead geometry in GMAW-based additive manufacturing using passive vision

NASA Astrophysics Data System (ADS)

Xiong, Jun; Zhang, Guangjun

2013-11-01

Additive manufacturing based on gas metal arc welding is an advanced technique for depositing fully dense components with low cost. Despite this fact, techniques to achieve accurate control and automation of the process have not yet been perfectly developed. The online measurement of the deposited bead geometry is a key problem for reliable control. In this work a passive vision-sensing system, comprising two cameras and composite filtering techniques, was proposed for real-time detection of the bead height and width through deposition of thin walls. The nozzle to the top surface distance was monitored for eliminating accumulated height errors during the multi-layer deposition process. Various image processing algorithms were applied and discussed for extracting feature parameters. A calibration procedure was presented for the monitoring system. Validation experiments confirmed the effectiveness of the online measurement system for bead geometry in layered additive manufacturing.

Combining of different data pools for calculating a reliable POD for real defects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kanzler, Daniel, E-mail: daniel.kanzler@bam.de, E-mail: christina.mueller@bam.de; Müller, Christina, E-mail: daniel.kanzler@bam.de, E-mail: christina.mueller@bam.de; Pitkänen, Jorma, E-mail: jorma.pitkanen@posiva.fi

2015-03-31

Real defects are essential for the evaluation of the reliability of non destructive testing (NDT) methods, especially in relation to the integrity of components. But in most of the cases the amount of available real defects is not sufficient to evaluate the system. Model-assisted and transfer functions are one way to handle that challenge. This study is focused on a combination of different data pools to create a sufficient amount of data for the reliability estimation. A widespread approach for calculating the Probability of Detection (POD) was used on a radiographic testing (RT) method. The highest contrast to noise ratiomore » (CNR) of each indication is usually selected as the signal in the 'â vs. a' (signal-response) approach for RT. By combining real and artificial defects (flat bottom holes, side drill holes, flat bottom squares, notches, etc) in RT the highest signals are close to each other, but the process of creating and evaluating real defects is much more complex. The solution is seen in the combination of real and artificial data using a weighted least square approach. The weights for real or artificial data were based on the importance, the value and the different detection behavior of the different data. For comparison, the alternative combination through the Bayesian Updating was also applied. As verification, a data pool with a large amount of real data was available. In an advanced approach for evaluating the digital RT data, the size of the indication (perpendicular to the X-ray beam) was introduced as additional information. The signal now consists of the CNR and the area of the indication. The detectability is changing depending on the area of the indication, a fact that was ignored in the previous POD calculations for RT. This points out that a weighted least square approach to pool the data might no longer be adequate. The Bayesian Updating of the estimated parameters of the relationship between the signal field (the area of the indication) and the geometry of the defects is seen as the appropriate model to combine the different defect types in a useful and meaningful way. This work was carried out together with the Finnish company for spent nuclear fuel and waste management - Posiva Oy. The digital RT is one of the NDT methods that might be used for the inspection of the weld of the copper canister to be used for the spent nuclear fuel in the Scandinavian concept of final disposal.« less

Fiberprint: A subject fingerprint based on sparse code pooling for white matter fiber analysis.

PubMed

Kumar, Kuldeep; Desrosiers, Christian; Siddiqi, Kaleem; Colliot, Olivier; Toews, Matthew

2017-09-01

White matter characterization studies use the information provided by diffusion magnetic resonance imaging (dMRI) to draw cross-population inferences. However, the structure, function, and white matter geometry vary across individuals. Here, we propose a subject fingerprint, called Fiberprint, to quantify the individual uniqueness in white matter geometry using fiber trajectories. We learn a sparse coding representation for fiber trajectories by mapping them to a common space defined by a dictionary. A subject fingerprint is then generated by applying a pooling function for each bundle, thus providing a vector of bundle-wise features describing a particular subject's white matter geometry. These features encode unique properties of fiber trajectories, such as their density along prominent bundles. An analysis of data from 861 Human Connectome Project subjects reveals that a fingerprint based on approximately 3000 fiber trajectories can uniquely identify exemplars from the same individual. We also use fingerprints for twin/sibling identification, our observations consistent with the twin data studies of white matter integrity. Our results demonstrate that the proposed Fiberprint can effectively capture the variability in white matter fiber geometry across individuals, using a compact feature vector (dimension of 50), making this framework particularly attractive for handling large datasets. Copyright © 2017 Elsevier Inc. All rights reserved.

An Assessment of Molten Metal Detachment Hazards During Electron Beam Welding in the Space Shuttle Bay at LEO for the International Space Welding Experiment

NASA Technical Reports Server (NTRS)

Fragomeni, James M.

1996-01-01

In 1997, the United States [NASA] and the Paton Electric Welding Institute are scheduled to cooperate in a flight demonstration on the U.S. Space Shuttle to demonstrate the feasibility of welding in space for a possible repair option for the International Space Station Alpha. This endeavor, known as the International Space Welding Experiment (ISWE), will involve astronauts performing various welding exercises such as brazing, cutting, welding, and coating using an electron beam space welding system that was developed by the E.O. Paton Electric Welding Institute (PWI), Kiev Ukraine. This electron beam welding system known as the "Universal Weld System" consists of hand tools capable of brazing, cutting, autogeneous welding, and coating using an 8 kV (8000 volts) electron beam. The electron beam hand tools have also been developed by the Paton Welding Institute with greater capabilities than the original hand tool, including filler wire feeding, to be used with the Universal Weld System on the U.S. Space Shuttle Bay as part of ISWE. The hand tool(s) known as the Ukrainian Universal Hand [Electron Beam Welding] Tool (UHT) will be utilized for the ISWE Space Shuttle flight welding exercises to perform welding on various metal alloy samples. A total of 61 metal alloy samples, which include 304 stainless steel, Ti-6AI-4V, 2219 aluminum, and 5456 aluminum alloys, have been provided by NASA for the ISWE electron beam welding exercises using the UHT. These samples were chosen to replicate both the U.S. and Russian module materials. The ISWE requires extravehicular activity (EVA) of two astronauts to perform the space shuttle electron beam welding operations of the 61 alloy samples. This study was undertaken to determine if a hazard could exist with ISWE during the electron beam welding exercises in the Space Shuttle Bay using the Ukrainian Universal Weld System with the UHT. The safety issue has been raised with regard to molten metal detachments as a result of several possible causes such as welder procedural error, externally applied impulsive forces(s), filler wire entrainment and snap-out, cutting expulsion, and puddle expulsion. Molten metal detachment from either the weld/cut substrate or weld wire could present harm to a astronaut in the space environment it the detachment was ti burn through the fabric of the astronaut Extravehicular Mobility Unit (EMC). In this paper an experimental test was performed in a 4 ft. x 4 ft. vacuum chamber at MSFC enabling protective garment to be exposed to the molten metal drop detachments to over 12 inches. The chamber was evacuated to vacuum levels of at least 1 x 10(exp -5) torr (50 micro-torr) during operation of the 1.0 kW Universal Hand Tool (UHT). The UHT was manually operated at the power mode appropriate for each material and thickness. The space suit protective welding garment, made of Teflon fabric (10 oz. per yard) with a plain weave, was placed on the floor of the vacuum chamber to catch the molten metal drop detachments. A pendulum release mechanism consisting of four hammers, each weighing approximately 3.65 lbs, was used to apply an impact forces to the weld sample/plate during both the electron beam welding and cutting exercises. Measurements were made of the horizontal fling distances of the detached molten metal drops. The volume of a molten metal drop can also be estimated from the size of the cut. Utilizing equations, calculations were made to determine chande in surafec area (Delat a(surface)) for 304 stainless steel for cutting based on measurements of metal drop sizes at the cut edges. For the cut sample of 304 stainless steel based on measurement of the drop size at the edge, Delta-a(surface) was determined to be 0.0054 2 in . Calculations have indicated only a small amount of energy is required to detach a liquid metal drop. For example, approximately only 0.000005 ft-lb of energy is necessary to detach a liquid metal steel drop based on the above theoretical analysis. However, some of the energy will be absorbed by the plate before it reaches the metal drop. Based on the theoretical calculations, it was determined that during a weld cutting exercise, the titanium alloy would be the most difficult to detach molten metal droplets followed by stainless steel and then by aluminum. The results of the experimental effort have shown that molten metal will detach if large enough of a hammer blow is applied to the weld sample plate during the full penetration welding and cutting exercises. However, no molten metal detachments occurred as a result of the filler wire snap-out tests from the weld puddle since it was too difficult to cause the metal to flick-out from the pool. Molten metal detachments, though not large in size, did result from the direct application of the electron beam on the end of the filler weld wire.

Defect features, texture and mechanical properties of friction stir welded lap joints of 2A97 Al-Li alloy thin sheets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Haiyan

1.4 mm 2A97 Al-Li alloy thin sheets were welded by friction stir lap welding using the stirring tools with different pin length at different rotational speeds. The influence of pin length and rotational speed on the defect features and mechanical properties of lap joints were investigated in detail. Microstructure observation shows that the hook defect geometry and size mainly varies with the pin length instead of the rotational speed. The size of hook defects on both the advancing side (AS) and the retreating side (RS) increased with increasing the pin length, leading to the effective sheet thickness decreased accordingly. Electronmore » backscatter diffraction analysis reveals that the weld zones, especially the nugget zone (NZ), have the much lower texture intensity than the base metal. Some new texture components are formed in the thermo-mechanical affected zone (TMAZ) and the NZ of joint. Lap shear test results show that the failure load of joints generally decreases with increasing the pin length and the rotational speed. The joints failed during the lap shear tests at three locations: the lap interface, the RS of the top sheet and the AS of the bottom sheet. The fracture locations are mainly determined by the hook defects. - Highlights: • Hook defect size mainly varies with the pin length of stirring tool. • The proportion of LAGBs and substructured grains increases from NZ to TMAZ. • Weld zones, especially the NZ, have the much lower texture intensity than the BM. • Lap shear failure load and fracture location of joints is relative to the hook defects.« less

ME8373 Spring 2015 ICME Proposal ICME Analysis of Fatigue Crack Growth Through a Weld in SA-516 Grade 70 Plate

NASA Technical Reports Server (NTRS)

Woods, Jody L.

2015-01-01

This paper describes work accomplished to predict the service life of a flexure joint design which is a component of a diffuser duct in the A3 Test Stand, an altitude simulation rocket engine test facility at NASA's Stennis Space Center. The duct has two pressure shells separated by cooling water passages and connected by stiffening ribs and flexure joints. Rocket exhaust flows within the duct and heats the inner pressure shell while the outer pressure shell remains at ambient temperature. The flexure joints allow for differential thermal expansion of the inner and outer pressure shells and are subject to in-service loading by this thermal expansion along with water pressure in the cooling water passage, atmospheric pressure outside the duct, near vacuum conditions within the duct, and vibrational loads from operation of the facility and rocket engine. Figure 1 shows a schematic axisymmetric cross section of the diffuser pressure shells and flexure joints with a zoomed in view of the flexure joint. The flexure joints are expected to eventually fail by fatigue cracking leading to leaks from the cooling water passages to the outside. The zoomed in view in Figure 1 indicates where cracking is expected to occur, namely through a weld bead between two plates of SA-516 Grade 70 steel. This weld bead acts as the fulcrum of the flexure joint and it is clear from inspection of the geometry and loading represented in the zoomed in portion of Figure 1 that inherent in the design there is a severe notch formed between the flexure plate, weld bead, and stiffening ring that will be the site of crack initiation and location from which the crack grows to the outer surface of the weld bead.

The effect of heat sinks in GTA microwelding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Knorovsky, G.A.; Burchett, S.N.

1989-01-01

When miniature devices containing glass-to-metal seals are closure welded it is accepted practice to incorporate thermal heat sinks into the fixturing. This is intended to assure that the heat from gas tungsten arc (GTA) welding will not cause thermal stress-induced cracking of the seals and loss of hermeticity. The design of these heat sinks has never been systematically studied; instead only ''engineering horse sense'' has been applied. This practice has been successful in the past; however, the component being GTA welded have become smaller and more complex (i.e., more pins) and glass cracking problems are being encountered. The technology ofmore » producing glass seal-containing lids (called ''headers'') has benefited from finite element analyses in deciding how to optimally dimension pin-to-glass seal diameter ratios and glass-to-metal thickness ratios in order to minimize thermal stresses locked in during manufacture. It appeared likely that an analysts of the stresses generated by welding would also be beneficial. Recently, computer speed and code capabilities have increased to the point where finite element analysis of a close simulation of real hardware can be made, including the effect of external heat sinks. The work reported here involves an analysis (with some supporting experimental data) of a miniature thermal battery which encountered glass cracking problems. In the course of the analysis various heat sink practices were examined. Among other findings, through-thickness thermal gradients in a header with a heat sink were found to equal in-plane thermal gradients in a header without any heat sinking at the glass seal positions. Also noted were significant variations due to relatively minor changes in the weld preparation geometry. A summary of good practice for heat sinking will be presented. 4 refs., 6 figs., 2 tabs.« less

Method and apparatus for optimizing the efficiency and quality of laser material processing

DOEpatents

Susemihl, Ingo

1990-01-01

The efficiency of laser welding and other laser material processing is optimized according to this invention by rotating the plane of polarization of a linearly polarized laser beam in relation to a work piece of the material being processed simultaneously and in synchronization with steering the laser beam over the work piece so as to keep the plane of polarization parallel to either the plane of incidence or the direction of travel of the beam in relation to the work piece. Also, depending to some extent on the particular processing being accomplished, such as welding or fusing, the angle of incidence of the laser beam on the work piece is kept at or near the polarizing or Brewster's angle. The combination of maintaining the plane of polarization parallel to plane of incidence while also maintaining the angle of incidence at or near the polarizing or Brewster's angle results in only minimal, if any, reflection losses during laser welding. Also, coordinating rotation of the plane of polarization with the translation or steering of a work piece under a laser cutting beam maximizes efficiency and kerf geometry, regardless of the direction of cut.

Method and apparatus for optimizing the efficiency and quality of laser material processing

DOEpatents

Susemihl, I.

1990-03-13

The efficiency of laser welding and other laser material processing is optimized according to this invention by rotating the plane of polarization of a linearly polarized laser beam in relation to a work piece of the material being processed simultaneously and in synchronization with steering the laser beam over the work piece so as to keep the plane of polarization parallel to either the plane of incidence or the direction of travel of the beam in relation to the work piece. Also, depending to some extent on the particular processing being accomplished, such as welding or fusing, the angle of incidence of the laser beam on the work piece is kept at or near the polarizing or Brewster's angle. The combination of maintaining the plane of polarization parallel to plane of incidence while also maintaining the angle of incidence at or near the polarizing or Brewster's angle results in only minimal, if any, reflection losses during laser welding. Also, coordinating rotation of the plane of polarization with the translation or steering of a work piece under a laser cutting beam maximizes efficiency and kerf geometry, regardless of the direction of cut. 7 figs.

Fundamental Study of Material Flow in Friction Stir Welds

NASA Technical Reports Server (NTRS)

Reynolds, Anthony P.

1999-01-01

The presented research project consists of two major parts. First, the material flow in solid-state, friction stir, butt-welds as been investigated using a marker insert technique. Changes in material flow due to welding parameter as well as tool geometry variations have been examined for different materials. The method provides a semi-quantitative, three-dimensional view of the material transport in the welded zone. Second, a FSW process model has been developed. The fully coupled model is based on fluid mechanics; the solid-state material transport during welding is treated as a laminar, viscous flow of a non-Newtonian fluid past a rotating circular cylinder. The heat necessary for the material softening is generated by deformation of the material. As a first step, a two-dimensional model, which contains only the pin of the FSW tool, has been created to test the suitability of the modeling approach and to perform parametric studies of the boundary conditions. The material flow visualization experiments agree very well with the predicted flow field. Accordingly, material within the pin diameter is transported only in the rotation direction around the pin. Due to the simplifying assumptions inherent in the 2-D model, other experimental data such as forces on the pin, torque, and weld energy cannot be directly used for validation. However, the 2-D model predicts the same trends as shown in the experiments. The model also predicts a deviation from the "normal" material flow at certain combinations of welding parameters, suggesting a possible mechanism for the occurrence of some typical FSW defects. The next step has been the development of a three-dimensional process model. The simplified FSW tool has been designed as a flat shoulder rotating on the top of the workpiece and a rotating, cylindrical pin, which extends throughout the total height of the flow domain. The thermal boundary conditions at the tool and at the contact area to the backing plate have been varied to fit experimental data such as temperature profiles, torque and tool forces. General aspects of the experimentally visualized material flow pattern are confirmed by the 3-D model.

Making Superconducting Welds between Superconducting Wires

NASA Technical Reports Server (NTRS)

Penanen, Konstantin I.; Eom, Byeong Ho

2008-01-01

A technique for making superconducting joints between wires made of dissimilar superconducting metals has been devised. The technique is especially suitable for fabrication of superconducting circuits needed to support persistent electric currents in electromagnets in diverse cryogenic applications. Examples of such electromagnets include those in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) systems and in superconducting quantum interference devices (SQUIDs). Sometimes, it is desirable to fabricate different parts of a persistent-current-supporting superconducting loop from different metals. For example, a sensory coil in a SQUID might be made of Pb, a Pb/Sn alloy, or a Cu wire plated with Pb/Sn, while the connections to the sensory coil might be made via Nb or Nb/Ti wires. Conventional wire-bonding techniques, including resistance spot welding and pressed contact, are not workable because of large differences between the hardnesses and melting temperatures of the different metals. The present technique is not subject to this limitation. The present technique involves the use (1) of a cheap, miniature, easy-to-operate, capacitor-discharging welding apparatus that has an Nb or Nb/Ti tip and operates with a continuous local flow of gaseous helium and (2) preparation of a joint in a special spark-discharge welding geometry. In a typical application, a piece of Nb foil about 25 m thick is rolled to form a tube, into which is inserted a wire that one seeks to weld to the tube (see figure). The tube can be slightly crimped for mechanical stability. Then a spark weld is made by use of the aforementioned apparatus with energy and time settings chosen to melt a small section of the niobium foil. The energy setting corresponds to the setting of a voltage to which the capacitor is charged. In an experiment, the technique was used to weld an Nb foil to a copper wire coated with a Pb/Sn soft solder, which is superconducting. The joint was evaluated as part of a persistent-current circuit having an inductance of 1 mH. A current was induced in a loop, and no attenuation of the current after a time interval 1,000 s was discernible in a measurement having a fractional accuracy of 10(exp -4): This observation supports the conclusion that the weld had an electrical resistance <10(exp -10) omega.

Microstructural Characterization of a Polycrystalline Nickel-Based Superalloy Processed via Tungsten-Intert-Gas-Shaped Metal Deposition

NASA Astrophysics Data System (ADS)

Clark, Daniel; Bache, Martin R.; Whittaker, Mark T.

2010-12-01

Recent trials have produced tungsten-inert-gas (TIG)-welded structures of a suitable scale to allow an evaluation of the technique as an economic and commercial process for the manufacture of complex aeroengine components. The employment of TIG welding is shown to have specific advantages over alternative techniques based on metal inert gas (MIG) systems. Investigations using the nickel-based superalloy 718 have shown that TIG induces a smaller weld pool with less compositional segregation. In addition, because the TIG process involves a pulsed power source, a faster cooling rate is achieved, although this rate, in turn, compromises the deposition rate. The microstructures produced by the two techniques differ significantly, with TIG showing an absence of the detrimental delta and Laves phases typically produced by extended periods at a high temperature using MIG. Instead, an anisotropic dendritic microstructure was evident with a preferred orientation relative to the axis of epitaxy. Niobium was segregated to the interdendritic regions. A fine-scale porosity was evident within the microstructure with a maximum diameter of approximately 5 μm. This porosity often was found in clusters and usually was associated with the interdendritic regions. Subsequent postdeposition heat treatment was shown to have no effect on preexisting porosity and to have a minimal effect on the microstructure.

Empirical modeling for intelligent, real-time manufacture control

NASA Technical Reports Server (NTRS)

Xu, Xiaoshu

1994-01-01

Artificial neural systems (ANS), also known as neural networks, are an attempt to develop computer systems that emulate the neural reasoning behavior of biological neural systems (e.g. the human brain). As such, they are loosely based on biological neural networks. The ANS consists of a series of nodes (neurons) and weighted connections (axons) that, when presented with a specific input pattern, can associate specific output patterns. It is essentially a highly complex, nonlinear, mathematical relationship or transform. These constructs have two significant properties that have proven useful to the authors in signal processing and process modeling: noise tolerance and complex pattern recognition. Specifically, the authors have developed a new network learning algorithm that has resulted in the successful application of ANS's to high speed signal processing and to developing models of highly complex processes. Two of the applications, the Weld Bead Geometry Control System and the Welding Penetration Monitoring System, are discussed in the body of this paper.

Multiphysics Simulation of Welding-Arc and Nozzle-Arc System: Mathematical-Model, Solution-Methodology and Validation

NASA Astrophysics Data System (ADS)

Pawar, Sumedh; Sharma, Atul

2018-01-01

This work presents mathematical model and solution methodology for a multiphysics engineering problem on arc formation during welding and inside a nozzle. A general-purpose commercial CFD solver ANSYS FLUENT 13.0.0 is used in this work. Arc formation involves strongly coupled gas dynamics and electro-dynamics, simulated by solution of coupled Navier-Stoke equations, Maxwell's equations and radiation heat-transfer equation. Validation of the present numerical methodology is demonstrated with an excellent agreement with the published results. The developed mathematical model and the user defined functions (UDFs) are independent of the geometry and are applicable to any system that involves arc-formation, in 2D axisymmetric coordinates system. The high-pressure flow of SF6 gas in the nozzle-arc system resembles arc chamber of SF6 gas circuit breaker; thus, this methodology can be extended to simulate arcing phenomenon during current interruption.

A FRAMEWORK TO DEVELOP FLAW ACCEPTANCE CRITERIA FOR STRUCTURAL INTEGRITY ASSESSMENT OF MULTIPURPOSE CANISTERS FOR EXTENDED STORAGE OF USED NUCLEAR FUEL

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lam, P.; Sindelar, R.; Duncan, A.

2014-04-07

A multipurpose canister (MPC) made of austenitic stainless steel is loaded with used nuclear fuel assemblies and is part of the transfer cask system to move the fuel from the spent fuel pool to prepare for storage, and is part of the storage cask system for on-site dry storage. This weld-sealed canister is also expected to be part of the transportation package following storage. The canister may be subject to service-induced degradation especially if exposed to aggressive environments during possible very long-term storage period if the permanent repository is yet to be identified and readied. Stress corrosion cracking may bemore » initiated on the canister surface in the welds or in the heat affected zone because the construction of MPC does not require heat treatment for stress relief. An acceptance criteria methodology is being developed for flaw disposition should the crack-like defects be detected by periodic Inservice Inspection. The external loading cases include thermal accident scenarios and cask drop conditions with the contribution from the welding residual stresses. The determination of acceptable flaw size is based on the procedure to evaluate flaw stability provided by American Petroleum Institute (API) 579 Fitness-for-Service (Second Edition). The material mechanical and fracture properties for base and weld metals and the stress analysis results are obtained from the open literature such as NUREG-1864. Subcritical crack growth from stress corrosion cracking (SCC), and its impact on inspection intervals and acceptance criteria, is not addressed.« less

U.S. pipeline industry enters new era

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnsen, M.R.

1999-11-01

The largest construction project in North America this year and next--the Alliance Pipeline--marks some advances for the US pipeline industry. With the Alliance Pipeline system (Alliance), mechanized welding and ultrasonic testing are making their debuts in the US as primary mainline construction techniques. Particularly in Canada and Europe, mechanized welding technology has been used for both onshore and offshore pipeline construction for at least 15 years. However, it has never before been used to build a cross-country pipeline in the US, although it has been tested on short segments. This time, however, an accelerated construction schedule, among other reasons, necessitatedmore » the use of mechanized gas metal arc welding (GMAW). The $3-billion pipeline will delivery natural gas from northwestern British Columbia and northeastern Alberta in Canada to a hub near Chicago, Ill., where it will connect to the North American pipeline grid. Once the pipeline is completed and buried, crews will return the topsoil. Corn and other crops will reclaim the land. While the casual passerby probably won't know the Alliance pipeline is there, it may have a far-reaching effect on the way mainline pipelines are built in the US. For even though mechanized welding and ultrasonic testing are being used for the first time in the United States on this project, some US workers had already gained experience with the technology on projects elsewhere. And work on this pipeline has certainly developed a much larger pool of experienced workers for industry to draw from. The Alliance project could well signal the start of a new era in US pipeline construction.« less

Towards a better understanding of the interaction between bed roughness and flow hydraulics in small eroded channels

NASA Astrophysics Data System (ADS)

Giménez, Rafael; Zubieta, Elena; Campo-Bescós, Miguel A.; Casalí, Javier

2016-04-01

Rills eroding cohesive materials are hydraulically different from rivers or large channels. Unlike rivers, rills are small, shallow flow stream with frequently a relatively steep slope gradient. Besides, rills evolve morphologically over much shorter timescales due to active bed erosion. This leads to a strong interaction between the channel flow and bed roughness. This interaction gives rise to a reconfiguration of the bed geometry generated by the important erosive action of the flow. This new shape is characterized by a typical alternance between concavities (pools) and more or less flat reaches (steps). The new rill geometry affects, in turn, the behaviour of the flow that is why we talk about interaction or feedback. In addition, the greatest energy dissipation occurs in the pools -mainly due to the action of hydraulic jumps- which, in turn, lead to an increase in the pool size. We hypothesize there is a regular spacing of step-pools units and that, both the frequency and the depth of the pools will be strongly conditioned by the discharge and the general rill slope. The determination of that periodicity (if any) would be an important contribution for concentrated flow erosion modelling of small channels. That is because the majority of erosion models are based on formulations which assume that a rill has a flat bed, only affected by micro-roughness. For instance, equations like Manning's - widely used in river and large channel hydraulics -, if a constant value of roughness is assumed, would be inappropriate in erosion rills since, as explained above, the roughness is not constant. The objectives of this work are then: (i) to investigate the geometry of erosion rills aiming at determining if there is a spatial arrangement of the macro roughness of their beds; and (ii) to establish (semi)-empirical models of prediction of this periodicity, mainly based on topographic parameters. Rills were generated in an agricultural field in a homogeneous hillslope (with no abrupt slope changes) by the action of different discharges and slopes. The protocol of experimentation in each rill is briefly as follows. The presence of pools along the channel was identified using markers of the position of the pools following and ad hoc procedure. Then, pictures of the rill were taken and a detailed DEM of it was obtained by photogrammetry. Moreover, a morphological characterization of the channel -e.g., longitudinal height profile- was made from the DEM. Preliminary results from 3 contrasting discharges and a similar slope suggest that in well defined -i.e. no incipient- rills there is a systematic and regular spacing of pools along the channel. More experiments are needed to confirm these findings.

Sediment transport through self-adjusting, bedrock-walled waterfall plunge pools

NASA Astrophysics Data System (ADS)

Scheingross, Joel S.; Lamb, Michael P.

2016-05-01

Many waterfalls have deep plunge pools that are often partially or fully filled with sediment. Sediment fill may control plunge-pool bedrock erosion rates, partially determine habitat availability for aquatic organisms, and affect sediment routing and debris flow initiation. Currently, there exists no mechanistic model to describe sediment transport through waterfall plunge pools. Here we develop an analytical model to predict steady-state plunge-pool depth and sediment-transport capacity by combining existing jet theory with sediment transport mechanics. Our model predicts plunge-pool sediment-transport capacity increases with increasing river discharge, flow velocity, and waterfall drop height and decreases with increasing plunge-pool depth, radius, and grain size. We tested the model using flume experiments under varying waterfall and plunge-pool geometries, flow hydraulics, and sediment size. The model and experiments show that through morphodynamic feedbacks, plunge pools aggrade to reach shallower equilibrium pool depths in response to increases in imposed sediment supply. Our theory for steady-state pool depth matches the experiments with an R2 value of 0.8, with discrepancies likely due to model simplifications of the hydraulics and sediment transport. Analysis of 75 waterfalls suggests that the water depths in natural plunge pools are strongly influenced by upstream sediment supply, and our model provides a mass-conserving framework to predict sediment and water storage in waterfall plunge pools for sediment routing, habitat assessment, and bedrock erosion modeling.

Mathematical modelling of convective processes in a weld pool under electric arc surfacing

NASA Astrophysics Data System (ADS)

Sarychev, V. D.; Granovskii, A. Yu; Nevskii, S. A.; Konovalov, S. V.

2017-01-01

The authors develop the mathematical model of convective processes in a molten pool under electric arc surfacing with flux-cored wire. The model is based on the ideas of how convective flows appear due to temperature gradient and action of electromagnetic forces. Influence of alloying elements in the molten metal was modeled as a non-linear dependence of surface tension upon temperature. Surface tension and its temperature coefficient were calculated according to the electron density functional method with consideration to asymmetric electron distribution at the interface “molten metal / shielding gas”. Simultaneous solution of Navier-Stokes and Maxwell equations according to finite elements method with consideration to the moving heat source at the interface showed that there is a multi-vortex structure in the molten metal. This structure gives rise to a downward heat flux which, at the stage of heating, moves from the centre of the pool and stirs it full width. At the cooling stage this flux moves towards the centre of the pool and a single vortex is formed near the symmetry centre. This flux penetration is ∼ 10 mm. Formation of the downward heat flux is determined by sign reversal of the temperature coefficient of surface tension due to the presence of alloying elements.

Preliminary Empirical Models for Predicting Shrinkage, Part Geometry and Metallurgical Aspects of Ti-6Al-4V Shaped Metal Deposition Builds

NASA Astrophysics Data System (ADS)

Escobar-Palafox, Gustavo; Gault, Rosemary; Ridgway, Keith

2011-12-01

Shaped Metal Deposition (SMD) is an additive manufacturing process which creates parts layer by layer by weld depositions. In this work, empirical models that predict part geometry (wall thickness and outer diameter) and some metallurgical aspects (i.e. surface texture, portion of finer Widmanstätten microstructure) for the SMD process were developed. The models are based on an orthogonal fractional factorial design of experiments with four factors at two levels. The factors considered were energy level (a relationship between heat source power and the rate of raw material input.), step size, programmed diameter and travel speed. The models were validated using previous builds; the prediction error for part geometry was under 11%. Several relationships between the factors and responses were identified. Current had a significant effect on wall thickness; thickness increases with increasing current. Programmed diameter had a significant effect on percentage of shrinkage; this decreased with increasing component size. Surface finish decreased with decreasing step size and current.

Optimal Control of Thermo--Fluid Phenomena in Variable Domains

NASA Astrophysics Data System (ADS)

Volkov, Oleg; Protas, Bartosz

2008-11-01

This presentation concerns our continued research on adjoint--based optimization of viscous incompressible flows (the Navier--Stokes problem) coupled with heat conduction involving change of phase (the Stefan problem), and occurring in domains with variable boundaries. This problem is motivated by optimization of advanced welding techniques used in automotive manufacturing, where the goal is to determine an optimal heat input, so as to obtain a desired shape of the weld pool surface upon solidification. We argue that computation of sensitivities (gradients) in such free--boundary problems requires the use of the shape--differential calculus as a key ingredient. We also show that, with such tools available, the computational solution of the direct and inverse (optimization) problems can in fact be achieved in a similar manner and in a comparable computational time. Our presentation will address certain mathematical and computational aspects of the method. As an illustration we will consider the two--phase Stefan problem with contact point singularities where our approach allows us to obtain a thermodynamically consistent solution.

Compaction and gas loss in welded pyroclastic deposits as revealed by porosity, permeability, and electrical conductivity measurements of the Shevlin Park Tuff

USGS Publications Warehouse

Wright, Heather M.; Cashman, Katharine V.

2014-01-01

Pyroclastic flows produced by large volcanic eruptions commonly densify after emplacement. Processes of gas escape, compaction, and welding in pyroclastic-flow deposits are controlled by the physical and thermal properties of constituent material. Through measurements of matrix porosity, permeability, and electrical conductivity, we provide a framework for understanding the evolution of pore structure during these processes. Using data from the Shevlin Park Tuff in central Oregon, United States, and from the literature, we find that over a porosity range of 0%–70%, matrix permeability varies by almost 10 orders of magnitude (from 10–20 to 10–11 m2), with over three orders of magnitude variation at any given porosity. Part of the variation at a given porosity is due to permeability anisotropy, where oriented core samples indicate higher permeabilities parallel to foliation (horizontally) than perpendicular to foliation (vertically). This suggests that pore space is flattened during compaction, creating anisotropic crack-like networks, a geometry that is supported by electrical conductivity measurements. We find that the power law equation: k1 = 1.3 × 10–21 × ϕ5.2 provides the best approximation of dominant horizontal gas loss, where k1 = permeability, and ϕ = porosity. Application of Kozeny-Carman fluid-flow approximations suggests that permeability in the Shevlin Park Tuff is controlled by crack- or disk-like pore apertures with minimum widths of 0.3 and 7.5 μm. We find that matrix permeability limits compaction over short times, but deformation is then controlled by competition among cooling, compaction, water resorption, and permeable gas escape. These competing processes control the potential for development of overpressure (and secondary explosions) and the degree of welding in the deposit, processes that are applicable to viscous densification of volcanic deposits in general. Further, the general relationships among porosity, permeability, and pore geometry are relevant for flow of any fluid through an ignimbritic host.

Laser dimpling process parameters selection and optimization using surrogate-driven process capability space

NASA Astrophysics Data System (ADS)

Ozkat, Erkan Caner; Franciosa, Pasquale; Ceglarek, Dariusz

2017-08-01

Remote laser welding technology offers opportunities for high production throughput at a competitive cost. However, the remote laser welding process of zinc-coated sheet metal parts in lap joint configuration poses a challenge due to the difference between the melting temperature of the steel (∼1500 °C) and the vapourizing temperature of the zinc (∼907 °C). In fact, the zinc layer at the faying surface is vapourized and the vapour might be trapped within the melting pool leading to weld defects. Various solutions have been proposed to overcome this problem over the years. Among them, laser dimpling has been adopted by manufacturers because of its flexibility and effectiveness along with its cost advantages. In essence, the dimple works as a spacer between the two sheets in lap joint and allows the zinc vapour escape during welding process, thereby preventing weld defects. However, there is a lack of comprehensive characterization of dimpling process for effective implementation in real manufacturing system taking into consideration inherent changes in variability of process parameters. This paper introduces a methodology to develop (i) surrogate model for dimpling process characterization considering multiple-inputs (i.e. key control characteristics) and multiple-outputs (i.e. key performance indicators) system by conducting physical experimentation and using multivariate adaptive regression splines; (ii) process capability space (Cp-Space) based on the developed surrogate model that allows the estimation of a desired process fallout rate in the case of violation of process requirements in the presence of stochastic variation; and, (iii) selection and optimization of the process parameters based on the process capability space. The proposed methodology provides a unique capability to: (i) simulate the effect of process variation as generated by manufacturing process; (ii) model quality requirements with multiple and coupled quality requirements; and (iii) optimize process parameters under competing quality requirements such as maximizing the dimple height while minimizing the dimple lower surface area.

Numerical simulation of heat transfer and fluid flow in laser drilling of metals

NASA Astrophysics Data System (ADS)

Zhang, Tingzhong; Ni, Chenyin; Zhou, Jie; Zhang, Hongchao; Shen, Zhonghua; Ni, Xiaowu; Lu, Jian

2015-05-01

Laser processing as laser drilling, laser welding and laser cutting, etc. is rather important in modern manufacture, and the interaction of laser and matter is a complex phenomenon which should be detailed studied in order to increase the manufacture efficiency and quality. In this paper, a two-dimensional transient numerical model was developed to study the temperature field and molten pool size during pulsed laser keyhole drilling. The volume-of-fluid method was employed to track free surfaces, and melting and evaporation enthalpy, recoil pressure, surface tension, and energy loss due to evaporating materials were considered in this model. Besides, the enthalpy-porosity technique was also applied to account for the latent heat during melting and solidification. Temperature fields and melt pool size were numerically simulated via finite element method. Moreover, the effectiveness of the developed computational procedure had been confirmed by experiments.

An International Round-Robin Test of NDE Reliability for PWSCC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schuster, George J.; Cumblidge, Stephen E.; Doctor, Steven R.

2007-12-01

In this paper we describe the round robin tests that have been designed and are being conducted in the international program. Participants in the PINC have offered more than 30 test blocks for use in round-robin tests of NDE effectiveness. The test blocks have more than 130 flaws in nickel-base weld metal that are intended to simulate PWSCC in a variety of component geometries. NDE techniques representative of current in-service inspections are being applied, along with emerging NDE approaches.

The dynamics of hurricane balls

NASA Astrophysics Data System (ADS)

Andersen, W. L.; Werner, Steven

2015-09-01

We examine the theory of the hurricane balls toy. This toy consists of two steel balls, welded together that are sent spinning on a horizontal surface somewhat like a top. Unlike a top, at high frequency the symmetry axis approaches a limiting inclination that is not perpendicular to the surface. We calculate (and experimentally verify) the limiting inclinations for three toy geometries. We find that at high frequencies, hurricane balls provide an easily realized and testable example of the Poinsot theory of freely rotating symmetrical bodies.

Controls on Filling and Evacuation of Sediment in Waterfall Plunge Pools

NASA Astrophysics Data System (ADS)

Scheingross, J. S.; Lamb, M. P.

2014-12-01

Many waterfalls are characterized by the presence of deep plunge pools that experience periods of sediment fill and evacuation. These cycles of sediment fill are a first order control on the relative magnitude of lateral versus vertical erosion at the base of waterfalls, as vertical incision requires cover-free plunge pools to expose the bedrock floor, while lateral erosion can occur when pools are partially filled and plunge-pool walls are exposed. Currently, there exists no mechanistic model describing sediment transport through waterfall plunge pools, limiting our ability to predict waterfall retreat. To address this knowledge gap, we performed detailed laboratory experiments measuring plunge-pool sediment transport capacity (Qsc_pool) under varying waterfall and plunge-pool geometries, flow hydraulics, and sediment size. Our experimental plunge-pool sediment transport capacity measurements match well with a mechanistic model we developed which combines existing waterfall jet theory with a modified Rouse profile to predict sediment transport capacity as a function of water discharge and suspended sediment concentration at the plunge-pool lip. Comparing the transport capacity of plunge pools to lower gradient portions of rivers (Qsc_river) shows that, for transport limited conditions, plunge pools fill with sediment under modest water discharges when Qsc_river > Qsc_pool, and empty to bedrock under high discharges when Qsc_pool > Qsc_river. These results are consistent with field observations of sand-filled plunge pools with downstream boulder rims, implying filling and excavation of plunge pools over single-storm timescales. Thus, partial filling of waterfall plunge pools may provide a mechanism to promote lateral undercutting and retreat of waterfalls in homogeneous rock in which plunge-pool vertical incision occurs during brief large floods that expose bedrock, whereas lateral erosion may prevail during smaller events.

From antidunes to step-pools

NASA Astrophysics Data System (ADS)

Recking, Alain; Leduc, Pauline

2014-05-01

Step-pools are bed morphologies that are typical in high-gradient streams , recognizable by a staircase-like longitudinal profile resulting from accumulation of cobbles and boulders that are transverse to the channel and alternating with pools containing finer sediments. Within the last two decades step-pools have been the subject of increased efforts to characterize their nature; however their origin is still in debate. Researchers have very soon suspected step-pools to be the residual form of antidunes produced during flooding, but this hypothesis was continuously contested. Other theories has been proposed, considering, that step-pool profile develops a maximum flow resistance, or that pools geometry is controlled by the energy of a falling jet, or that steps form by boulders accumulation in a channel-spanning manner. All these theories gave very satisfying results when compared with experimental data, but does it mean that the antidune theory should we abandoned? We performed new flume experiments on steep slopes to investigate the antidune origin for step-pools. Our experiments showed that step-pools can have several origins, depending on the flow conditions and sediment mixture used. In some circumstances antidunes were well observed but did not produce stable step-pools morphology. In many occasions, step-pools obtained in the flume were isolated step-pools, with no real apparent periodicity. Only a few flow and sediment conditions allowed us to reproduce trains of antidunes which stabilized at the flow recession to produce stable periodical step-pools. These conditions are presented and discussed.

An Experimental Investigation On The Antidune Origin of Step-pools

NASA Astrophysics Data System (ADS)

Recking, A.; Leduc, P.

2013-12-01

Step-pools are bed morphologies that are typical in high-gradient streams , recognizable by a staircase-like longitudinal profile resulting from accumulation of cobbles and boulders that are transverse to the channel and alternating with pools containing finer sediments. Within the last two decades step-pools have been the subject of increased efforts to characterize their nature; however their origin is still in debate. Researchers have very soon suspected step-pools to be the residual form of antidunes produced during flooding, but this hypothesis was continuously contested. Other theories has been proposed, considering, that step-pool profile develops a maximum flow resistance, or that pools geometry is controlled by the energy of a falling jet, or that steps form by boulders accumulation in a channel-spanning manner. All these theories gave very satisfying results when compared with experimental data, but does it mean that the antidune theory should we abandoned? We performed new flume experiments on steep slopes to investigate the antidune origin for step-pools. Our experiments showed that step-pools can have several origins, depending on the flow conditions and sediment mixture used. In some circumstances antidunes were well observed but did not produce stable step-pools morphology. In many occasions, step-pools obtained in the flume were isolated step-pools, with no real apparent periodicity. Only a few flow and sediment conditions allowed us to reproduce trains of antidunes which stabilized at the flow recession to produce stable periodical step-pools. These conditions are presented and discussed.

Microstructure and hydrogen induced failure mechanisms in iron-nickel weldments

NASA Astrophysics Data System (ADS)

Fenske, Jamey Alan

A recent series of inexplicable catastrophic failures of specific subsea dissimilar metal Fe-Ni butter welds has illuminated a fundamental lack of understanding of both the microstructure created along the fusion line as well as its impact on the hydrogen susceptibility of these interfaces. In order to remedy this, the present work compares and contrasts the microstructure and hydrogen-induced fracture morphology of AISI 8630-IN 625 and F22-IN 625 dissimilar metal weld interfaces as a function of post-weld heat treatment duration. A variety of techniques were used to study details of both the microstructure and fracture morphology including optical microscopy, scanning electron microscopy, secondary ion mass spectrometry, transmission electron microscopy, electron backscatter diffraction, and energy dispersive x-ray spectroscopy. For both systems, the microstructure along the weld interface consisted of a coarse grain heat-affected zone in the Fe-base metal followed by discontinuous martensitic partially-mixed zones and a continuous partially-mixed zone on the Ni-side of the fusion line. Within the partially mixed zone on the Ni-side there exists a 200 nm-wide transition zone within a 20 mum-wide planar solidification region followed by a cellular dendritic region with Nb-Mo rich carbides decorating the dendrite boundaries. The size, area fraction and composition of the discontinuous PMZ were determined to be controlled by uneven mixing in the liquid weld pool influenced by convection currents produced from the welding procedure. The virgin martensitic microstructure produced in these regions is formed as consequence of a both the local composition and the post-weld heat treatment. The local higher Ni content results in these regions being retransformed into austenite during the post-weld heat treatment and then virgin martensite while cooling to room temperature. Although there were differences in the volume of the discontinuous partially mixed-zones, the major difference in the weld metal interfaces was the presence of M 7C3 precipitates in the planar solidification region. The formation of these precipitates, which were found in what was previously referred to as the "featureless-zone," were determined to be dependent on the carbon content of the Fe-base metal and the duration of the post-weld heat treatment. A high density of these ordered 100 nm-long by 10 nm-wide needle-like precipitates were found in the AISI 8630-IN 625 weldment in the 10 hour post-weld heat treatment condition while only the initial stages of their nucleation were evident in the F22-IN 625 15 hour post-weld heat treatment specimen. The study of the fractured specimens revealed that the M7C 3 carbides play a key role in the susceptibility to hydrogen embrittlement of the Fe-Ni butter weldments. The fractures initially nucleate along the isolated Fe-base metal -- discontinuous partially mixed zone interfaces. The M7C3 carbides accumulate hydrogen and then provide a low energy fracture path between the discontinuous partially mixed zones leading to catastrophic failure. The result is a fracture morphology that alternates between flat regions produced by fracture along the discontinuous partially mixed zones and cleavage-like fracture regions produced by fracture along the ordered carbide matrix interfaces.

Optimization of Experimental Conditions of the Pulsed Current GTAW Parameters for Mechanical Properties of SDSS UNS S32760 Welds Based on the Taguchi Design Method

NASA Astrophysics Data System (ADS)

Yousefieh, M.; Shamanian, M.; Saatchi, A.

2012-09-01

Taguchi design method with L9 orthogonal array was implemented to optimize the pulsed current gas tungsten arc welding parameters for the hardness and the toughness of super duplex stainless steel (SDSS, UNS S32760) welds. In this regard, the hardness and the toughness were considered as performance characteristics. Pulse current, background current, % on time, and pulse frequency were chosen as main parameters. Each parameter was varied at three different levels. As a result of pooled analysis of variance, the pulse current is found to be the most significant factor for both the hardness and the toughness of SDSS welds by percentage contribution of 71.81 for hardness and 78.18 for toughness. The % on time (21.99%) and the background current (17.81%) had also the next most significant effect on the hardness and the toughness, respectively. The optimum conditions within the selected parameter values for hardness were found as the first level of pulse current (100 A), third level of background current (70 A), first level of % on time (40%), and first level of pulse frequency (1 Hz), while they were found as the second level of pulse current (120 A), second level of background current (60 A), second level of % on time (60%), and third level of pulse frequency (5 Hz) for toughness. The Taguchi method was found to be a promising tool to obtain the optimum conditions for such studies. Finally, in order to verify experimental results, confirmation tests were carried out at optimum working conditions. Under these conditions, there were good agreements between the predicted and the experimental results for the both hardness and toughness.

Laser beam joining of optical fibers in silicon V-grooves

NASA Astrophysics Data System (ADS)

Kaufmann, Stefan; Otto, Andreas; Luz, Gerhard

2000-06-01

The increasing use of optical data transmission systems and the development of new optical components require adjustment-insensitive and reliable joining and assembling techniques. The state of the art includes the utilization of silicon submounts with anisotropically etched V-grooves. Several glass fibers are fixed in these V-grooves with adhesive. Adhesive bonds tend towards degradation under the influence of temperature and moisture. For this reason, the alternative joining processes laser beam welding and laser beam soldering are relevant. The goal is a reliable joining of optical fibers in V-grooves without damage to the fibers or the silicon submount. Because of the anomaly of silicon during phase transformation, a positive joining can be realized by laser beam welding. A melt pool is created through the energy of a Nd:YAG-laser pulse. During solidification, the volume of silicon increases and a bump is formed in the center. Experiments have shown that this phenomenon can be used for joining optical fibers in silicon-V-grooves. With suitable parameters the silicon flows half around the fiber during solidification. For each fiber, several welding points are necessary. Another promising joining method is laser bema soldering. In this case, a second silicon sheet with a solder deposit is placed on the fibers which lie in the V-grooves of the metallized silicon submount. The laser heats the upper silicon until the solder metals by heat conduction.

Automated Agricultural Field Extraction from Multi-temporal Web Enabled Landsat Data

NASA Astrophysics Data System (ADS)

Yan, L.; Roy, D. P.

2012-12-01

Agriculture has caused significant anthropogenic surface change. In many regions agricultural field sizes may be increasing to maximize yields and reduce costs resulting in decreased landscape spatial complexity and increased homogenization of land uses with potential for significant biogeochemical and ecological effects. To date, studies of the incidence, drivers and impacts of changing field sizes have not been undertaken over large areas because of computational constraints and because consistently processed appropriate resolution data have not been available or affordable. The Landsat series of satellites provides near-global coverage, long term, and appropriate spatial resolution (30m) satellite data to document changing field sizes. The recent free availability of all the Landsat data in the U.S. Landsat archive now provides the opportunity to study field size changes in a global and consistent way. Commercial software can be used to extract fields from Landsat data but are inappropriate for large area application because they require considerable human interaction. This paper presents research to develop and validate an automated computational Geographic Object Based Image Analysis methodology to extract agricultural fields and derive field sizes from Web Enabled Landsat Data (WELD) (http://weld.cr.usgs.gov/). WELD weekly products (30m reflectance and brightness temperature) are classified into Satellite Image Automatic Mapper™ (SIAM™) spectral categories and an edge intensity map and a map of the probability of each pixel being agricultural are derived from five years of 52 weeks of WELD and corresponding SIAM™ data. These data are fused to derive candidate agriculture field segments using a variational region-based geometric active contour model. Geometry-based algorithms are used to decompose connected segments belonging to multiple fields into coherent isolated field objects with a divide and conquer strategy to detect and merge partial circle segments. Results are presented for several 5000 x 5000 30m pixel WELD tiles encompassing rectangular and circular (pivot irrigation) fields in Texas and California and the results are validated qualitatively by comparison with high spatial resolution images obtained from the National Geospatial-Intelligence Agency (NGA) Commercial Archive. Implications and recommendations for algorithm refinement and application to decadal conterminous United States WELD data are discussed.

Welding, longitudinal lung function decline and chronic respiratory symptoms: a systematic review of cohort studies.

PubMed

Szram, Joanna; Schofield, Susie J; Cosgrove, Martin P; Cullinan, Paul

2013-11-01

While the acute respiratory risks of welding are well characterised, more chronic effects, including those on lung function, are less clear. We carried out a systematic review of published longitudinal studies of lung function decline in welders. Original cohort studies documenting two or more sequential measurements of lung function were reviewed. Meta-analysis was carried out on studies with suitable data on forced expiratory volume in 1 s (FEV1). Seven studies were included; their quality (measured on the Newcastle-Ottawa scale) was good, although exposure assessment was limited and the studies showed significant heterogeneity. Five had data suitable for meta-analysis; the pooled estimate of the difference in FEV1 decline between welders and nonwelders was -9.0 mL · year(-1) (95% CI -22.5-4.5; p=0.193). The pooled estimates of difference in annual FEV1 decline between welders and referents who smoked was -13.7 mL · year(-1) (95% CI -33.6-6.3; p=0.179). For welders and referents who did not smoke the estimated difference was -3.8 mL · year(-1) (95% CI -20.2-12.6; p=0.650). Symptom prevalence data were mainly narrative; smoking appeared to have the greatest effect on symptom evolution. Collectively, available longitudinal data on decline of lung function in welders and respiratory symptoms suggest a greater effect in those who smoke, supporting a focus on smoking cessation as well as control of fume exposure in this trade. Further prospective studies are required to confirm these findings.

Vapor plume oscillation mechanisms in transient keyhole during tandem dual beam fiber laser welding

NASA Astrophysics Data System (ADS)

Chen, Xin; Zhang, Xiaosi; Pang, Shengyong; Hu, Renzhi; Xiao, Jianzhong

2018-01-01

Vapor plume oscillations are common physical phenomena that have an important influence on the welding process in dual beam laser welding. However, until now, the oscillation mechanisms of vapor plumes remain unclear. This is primarily because mesoscale vapor plume dynamics inside a millimeter-scale, invisible, and time-dependent keyhole are difficult to quantitatively observe. In this paper, based on a developed three-dimensional (3D) comprehensive model, the vapor plume evolutions in a dynamical keyhole are directly simulated in tandem dual beam, short-wavelength laser welding. Combined with the vapor plume behaviors outside the keyhole observed by high-speed imaging, the vapor plume oscillations in dynamical keyholes at different inter-beam distances are the first, to our knowledge, to be quantitatively analyzed. It is found that vapor plume oscillations outside the keyhole mainly result from vapor plume instabilities inside the keyhole. The ejection velocity at the keyhole opening and dynamical behaviors outside the keyhole of a vapor plume both violently oscillate with the same order of magnitude of high frequency (several kHz). Furthermore, the ejection speed at the keyhole opening and ejection area outside the keyhole both decrease as the beam distance increases, while the degree of vapor plume instability first decreases and then increases with increasing beam distance from 0.6 to 1.0 mm. Moreover, the oscillation mechanisms of a vapor plume inside the dynamical keyhole irradiated by dual laser beams are investigated by thoroughly analyzing the vapor plume occurrence and flow process. The vapor plume oscillations in the dynamical keyhole are found to mainly result from violent local evaporations and severe keyhole geometry variations. In short, the quantitative method and these findings can serve as a reference for further understanding of the physical mechanisms in dual beam laser welding and of processing optimizations in industrial applications.

Microstructure and Mechanical Properties of Cr-SiC Particles-Reinforced Fe-Based Alloy Coating

NASA Astrophysics Data System (ADS)

Wang, Fu-cheng; Du, Xiao-dong; Zhan, Ma-ji; Lang, Jing-wei; Zhou, Dan; Liu, Guang-fu; Shen, Jian

2015-12-01

In this study, SiC particles were first coated with Cr to form a layer that can protect the SiC particles from dissolution in the molten pool. Then, the Cr-SiC powder was injected into the tail of molten pool during plasma-transferred arc welding process (PTAW), where the temperature was relatively low, to prepare Cr-SiC particles reinforced Fe-based alloy coating. The microstructure and phase composition of the powder and surface coatings were analyzed, and the element distribution and hardness at the interfacial region were also evaluated. The protective layer consists of Cr3Si, Cr7C3, and Cr23C6, which play an important role in the microstructure and mechanical properties. The protective layer is dissolved in the molten pool forming a flocculent region and a transition region between the SiC particles and the matrix. The tribological performance of the coating was also assessed using a ring-block sliding wear tester with GGr15 grinding ring under 490 and 980 N load. Cr-SiC particles-reinforced coating has a lower wear rate than the unreinforced coating.

Laboratory investigation and simulation of breakthrough curves in karst conduits with pools

NASA Astrophysics Data System (ADS)

Zhao, Xiaoer; Chang, Yong; Wu, Jichun; Peng, Fu

2017-12-01

A series of laboratory experiments are performed under various hydrological conditions to analyze the effect of pools in pipes on breakthrough curves (BTCs). The BTCs are generated after instantaneous injections of NaCl tracer solution. In order to test the feasibility of reproducing the BTCs and obtain transport parameters, three modeling approaches have been applied: the equilibrium model, the linear graphical method and the two-region nonequilibrium model. The investigation results show that pools induce tailing of the BTCs, and the shapes of BTCs depend on pool geometries and hydrological conditions. The simulations reveal that the two-region nonequilibrium model yields the best fits to experimental BTCs because the model can describe the transient storage in pools by the partition coefficient and the mass transfer coefficient. The model parameters indicate that pools produce high dispersion. The increased tailing occurs mainly because the partition coefficient decreases, as the number of pools increases. When comparing the tracer BTCs obtained using the two types of pools with the same size, the more appreciable BTC tails that occur for symmetrical pools likely result mainly from the less intense exchange between the water in the pools and the water in the pipe, because the partition coefficients for the two types of pools are virtually identical. Dispersivity values decrease as flow rates increase; however, the trend in dispersion is not clear. The reduced tailing is attributed to a decrease in immobile water with increasing flow rate. It provides evidence for hydrodynamically controlled tailing effects.

Effect of Thread and Rotating Speed on Material Flow Behavior and Mechanical Properties of Friction Stir Lap Welding Joints

NASA Astrophysics Data System (ADS)

Ji, Shude; Li, Zhengwei; Zhou, Zhenlu; Wu, Baosheng

2017-10-01

This study focused on the effects of thread on hook and cold lap formation, lap shear property and impact toughness of alclad 2024-T4 friction stir lap welding (FSLW) joints. Except the traditional threaded pin tool (TR-tool), three new tools with different thread locations and orientations were designed. Results showed that thread significantly affected hook, cold lap morphologies and lap shear properties. The tool with tip-threaded pin (T-tool) fabricated joint with flat hook and cold lap, which resulted in shear fracture mode. The tools with bottom-threaded pin (B-tool) eliminated the hook. The tool with reverse-threaded pin (R-tool) widened the stir zone width. When using configuration A, the joints fabricated by the three new tools showed higher failure loads than the joint fabricated by the TR-tool. The joint using the T-tool owned the optimum impact toughness. This study demonstrated the significance of thread during FSLW and provided a reference to optimize tool geometry.

Evaluation of the Pool Critical Assembly Benchmark with Explicitly-Modeled Geometry using MCNP6

DOE PAGES

Kulesza, Joel A.; Martz, Roger Lee

2017-03-01

Despite being one of the most widely used benchmarks for qualifying light water reactor (LWR) radiation transport methods and data, no benchmark calculation of the Oak Ridge National Laboratory (ORNL) Pool Critical Assembly (PCA) pressure vessel wall benchmark facility (PVWBF) using MCNP6 with explicitly modeled core geometry exists. As such, this paper provides results for such an analysis. First, a criticality calculation is used to construct the fixed source term. Next, ADVANTG-generated variance reduction parameters are used within the final MCNP6 fixed source calculations. These calculations provide unadjusted dosimetry results using three sets of dosimetry reaction cross sections of varyingmore » ages (those packaged with MCNP6, from the IRDF-2002 multi-group library, and from the ACE-formatted IRDFF v1.05 library). These results are then compared to two different sets of measured reaction rates. The comparison agrees in an overall sense within 2% and on a specific reaction- and dosimetry location-basis within 5%. Except for the neptunium dosimetry, the individual foil raw calculation-to-experiment comparisons usually agree within 10% but is typically greater than unity. Finally, in the course of developing these calculations, geometry that has previously not been completely specified is provided herein for the convenience of future analysts.« less

Estudio numerico y experimental del proceso de soldeo MIG sobre la aleacion 6063--T5 utilizando el metodo de Taguchi

NASA Astrophysics Data System (ADS)

Meseguer Valdenebro, Jose Luis

Electric arc welding processes represent one of the most used techniques on manufacturing processes of mechanical components in modern industry. The electric arc welding processes have been adapted to current needs, becoming a flexible and versatile way to manufacture. Numerical results in the welding process are validated experimentally. The main numerical methods most commonly used today are three: finite difference method, finite element method and finite volume method. The most widely used numerical method for the modeling of welded joints is the finite element method because it is well adapted to the geometric and boundary conditions in addition to the fact that there is a variety of commercial programs which use the finite element method as a calculation basis. The content of this thesis shows an experimental study of a welded joint conducted by means of the MIG welding process of aluminum alloy 6063-T5. The numerical process is validated experimentally by applying the method of finite element through the calculation program ANSYS. The experimental results in this paper are the cooling curves, the critical cooling time t4/3, the weld bead geometry, the microhardness obtained in the welded joint, and the metal heat affected zone base, process dilution, critical areas intersected between the cooling curves and the curve TTP. The numerical results obtained in this thesis are: the thermal cycle curves, which represent both the heating to maximum temperature and subsequent cooling. The critical cooling time t4/3 and thermal efficiency of the process are calculated and the bead geometry obtained experimentally is represented. The heat affected zone is obtained by differentiating the zones that are found at different temperatures, the critical areas intersected between the cooling curves and the TTP curve. In order to conclude this doctoral thesis, an optimization has been conducted by means of the Taguchi method for welding parameters in order to obtain an improvement on mechanical properties in aluminum metal joint. Los procesos de soldadura por arco electrico representan unas de las tecnicas mas utilizadas en los procesos de fabricacion de componentes mecanicos en la industria moderna. Los procesos de soldeo por arco se han adaptado a las necesidades actuales, haciendose un modo de fabricacion flexible y versatil. Los resultados obtenidos numericamente en el proceso de soldadura son validados experimentalmente. Los principales metodos numericos mas empleados en la actualidad son tres, metodo por diferencias finitas, metodos por elementos finitos y metodo por volumenes finitos. El metodo numerico mas empleado para el modelado de uniones soldadas, es el metodo por elementos finitos, debido a que presenta una buena adaptacion a las condiciones geometricas y de contorno ademas de que existe una diversidad de programas comerciales que utilizan el metodo por elementos finitos como base de calculo. Este trabajo de investigacion presenta un estudio experimental de una union soldada mediante el proceso MIG de la aleacion de aluminio 6063-T5. El metodo numerico se valida experimentalmente aplicando el metodo de los elementos finitos con el programa de calculo ANSYS. Los resultados experimentales obtenidos son: las curvas de enfriamiento, el tiempo critico de enfriamiento t4/3, geometria del cordon, microdurezas obtenidas en la union soldada, zona afectada termicamente y metal base, dilucion del proceso, areas criticas intersecadas entre las curvas de enfriamiento y la curva TTP. Los resultados numericos son: las curvas del ciclo termico, que representan tanto el calentamiento hasta alcanzar la temperatura maxima y un posterior enfriamiento. Se calculan el tiempo critico de enfriamiento t4/3, el rendimiento termico y se representa la geometria del cordon obtenida experimentalmente. La zona afectada termicamente se obtiene diferenciando las zonas que se encuentran a diferentes temperaturas, las areas criticas intersecadas entre las curvas de enfriamiento y la curva TTP. Para finalizar el trabajo de investigacion se ha realizado una optimizacion, con la aplicacion del metodo de Taguchi, de los parametros de soldeo con el objetivo de obtener una mejora sustancial en las propiedades mecanicas de las uniones metalicas de aluminio.

Cross-Beam Laser Joining of AA 6111 to Galvanized Steel in a Coach Peel Configuration

NASA Astrophysics Data System (ADS)

Yang, Guang; Mohammadpour, Masoud; Yazdian, Nima; Ma, Junjie; Carlson, Blair; Wang, Hui-Ping; Kovacevic, Radovan

2017-06-01

Cross-beam laser joining of aluminum alloy 6111 to hot-dip galvanized steel in the coach-peel configuration was investigated with the addition of AA 4047 filler wire. The filler material was not only brazed onto the galvanized steel but also partially fusion-welded with the aluminum panel. Through adjusting the laser power to 3.4 kW, a desirable wetting and spreading of filler wire on both panel surfaces could be achieved, and the thickness of intermetallic layer in the middle section of the interface between the weld bead and steel was less than 2 μm. To better understand the solid/liquid interfacial reaction at the brazing interface, two rotary Gaussian heat source models were introduced to simulate the temperature distribution in the molten pool by using the finite element method. Joint properties were examined in terms of microstructure and mechanical properties. During the tensile test, the fracture of coupons took place at the aluminum side rather than along the interface between the intermetallic layer and steel panel. No failure occurred during the three-point bending test.

Optimization of porthole die geometrical variables by Taguchi method

NASA Astrophysics Data System (ADS)

Gagliardi, F.; Ciancio, C.; Ambrogio, G.; Filice, L.

2017-10-01

Porthole die extrusion is commonly used to manufacture hollow profiles made of lightweight alloys for numerous industrial applications. The reliability of extruded parts is affected strongly by the quality of the longitudinal and transversal seam welds. According to that, the die geometry must be designed correctly and the process parameters must be selected properly to achieve the desired product quality. In this study, numerical 3D simulations have been created and run to investigate the role of various geometrical variables on punch load and maximum pressure inside the welding chamber. These are important outputs to take into account affecting, respectively, the necessary capacity of the extrusion press and the quality of the welding lines. The Taguchi technique has been used to reduce the number of the required numerical simulations necessary for considering the influence of twelve different geometric variables. Moreover, the Analysis of variance (ANOVA) has been implemented to individually analyze the effect of each input parameter on the two responses. Then, the methodology has been utilized to determine the optimal process configuration individually optimizing the two investigated process outputs. Finally, the responses of the optimized parameters have been verified through finite element simulations approximating the predicted value closely. This study shows the feasibility of the Taguchi technique for predicting performance, optimization and therefore for improving the design of a porthole extrusion process.

Effect of dual laser beam on dissimilar welding-brazing of aluminum to galvanized steel

NASA Astrophysics Data System (ADS)

Mohammadpour, Masoud; Yazdian, Nima; Yang, Guang; Wang, Hui-Ping; Carlson, Blair; Kovacevic, Radovan

2018-01-01

In this investigation, the joining of two types of galvanized steel and Al6022 aluminum alloy in a coach peel configuration was carried out using a laser welding-brazing process in dual-beam mode. The feasibility of this method to obtain a sound and uniform brazed bead with high surface quality at a high welding speed was investigated by employing AlSi12 as a consumable material. The effects of alloying elements on the thickness of intermetallic compound (IMC) produced at the interface of steel and aluminum, surface roughness, edge straightness and the tensile strength of the resultant joint were studied. The comprehensive study was conducted on the microstructure of joints by means of a scanning electron microscopy and EDS. Results showed that a dual-beam laser shape and high scanning speed could control the thickness of IMC as thin as 3 μm and alter the failure location from the steel-brazed interface toward the Al-brazed interface. The numerical simulation of thermal regime was conducted by the Finite Element Method (FEM), and simulation results were validated through comparative experimental data. FEM thermal modeling evidenced that the peak temperatures at the Al-steel interface were around the critical temperature range of 700-900 °C that is required for the highest growth rate of IMC. However, the time duration that the molten pool was placed inside this temperature range was less than 1 s, and this duration was too short for diffusion-control based IMC growth.

HYDROSTATIC PRESSURIZATION AND DEPLETION OF TRAPPED LUBRICANT POOL DURING CREEP CONTACT OF A RIPPLED INDENTER AGAINST A BIPHASIC ARTICULAR CARTILAGE LAYER

PubMed Central

Soltz, Michael A.; Basalo, Ines M.; Ateshian, Gerard A.

2010-01-01

This study presents an analysis of the contact of a rippled rigid impermeable indenter against a cartilage layer, which represents a first simulation of the contact of rough cartilage surfaces with lubricant entrapment. Cartilage was modeled with the biphasic theory for hydrated soft tissues, to account for fluid flow into or out of the lubricant pool. The findings of this study demonstrate that under contact creep, the trapped lubricant pool gets depleted within a time period on the order of seconds or minutes as a result of lubricant flow into the articular cartilage. Prior to depletion, hydrostatic fluid load across the contact interface may be enhanced by the presence of the trapped lubricant pool, depending on the initial geometry of the lubricant pool. According to friction models based on the biphasic nature of the tissue, this enhancement in fluid load support produces a smaller minimum friction coefficient than would otherwise be predicted without a lubricant pool. The results of this study support the hypothesis that trapped lubricant decreases the initial friction coefficient following load application, independently of squeeze-film lubrication effects. PMID:14618917