Showing papers by "Hai-Lung Tsai published in 2003"

Method of improving weld quality

Abstract: A method of improving weld quality between aluminum members by slowing the rate of solidification of a molten weld trough into solidified material. Upper and lower aluminum members are positioned together in contact between facing surfaces thereof to expose a first outer surface of the upper aluminum member to laser irradiation. A welding laser beam is moved in a path over the first outer surface, wherein the welding laser beam has an energy and width to progressively melt a trough of molten metal to a depth through the upper aluminum member and into the lower aluminum member. The molten metal in the trough has a void filled with gas, and the molten metal re-solidifies into re-solidified metal after the passage of the welding laser beam. An area in and around the trough is heated to slow the rate of solidification of the molten metal into the re-solidified metal, thereby preventing entrainment of the gas within the re-solidified metal.

Modeling the Transport Phenomena During Hybrid Laser-MIG Welding Process

Abstract: Hybrid laser-MIG welding technology has several advantages over laser welding alone or MIG welding alone. These include the possibility of modifying weld bead shape including the elimination of undercut, the change of weld compositions, and the reduction of porosity formation in the weld. Although the hybrid laser-MIG welding method is becoming popular in industry, its development has been based on the trial-and-error procedure. In this paper, mathematical models and the associated numerical techniques were developed to calculate the heat and mass transfer and fluid flow during the laser-MIG welding process. The continuum formulation was used to handle solid phase, liquid phase, and mushy zone during the melting and solidification processes. The volume-of-fluid (VOF) method was employed to handle free surfaces, and the enthalpy method was used for latent heat. The absorption (Inverse Bremsstrahlung and Fresnel absorption) and the thermal radiation by the plasma in the keyhole, and multiple reflections at the keyhole wall were all considered in the models. The transient keyhole dynamics, interactions between droplets and weld pool, and the shape and composition of the solidified weld bead were all predicted for both the pulsed laser-MIG welding and three-dimensional moving laser-MIG welding. Computer animations showing the fluid flow, weld pool dynamics, and the interaction between droplets and weld pool will be shown in the presentation.Copyright © 2003 by ASME

Fluid Flow and Weld Pool Dynamics in Dual-Beam Laser Keyhole Welding

Abstract: The use of dual or multiple laser beams is necessary for welding thick-section metals, especially for Nd:Yag lasers which are limited to relatively low power as compared to CO2 lasers. It was also reported that the use of dual laser beams for welding can increase keyhole stability leading to a better weld quality. So far, the development of dual-beam laser welding technologies has been in the experimental stage. The objective of this paper is to develop mathematical models and the associated numerical techniques to calculate the transient heat transfer and fluid flow in the weld pool and to study weld pool dynamics during the dual-beam laser welding process. The simulation was conducted for a three-dimensional stationary dual-beam laser welding. A very interesting change of the top-surface view of the weld pool was predicted. During the welding process, the top-view shape of the weld pool changes, starting from an oval-shape with the long-axis connecting the centers of the two laser beams, to a circle, and finally to an oval-shape with the short-axis connecting the centers of the two laser beams. Although a direct comparison with published experimental observation is impossible (due to the lack of detailed experimental data), the predicted weld pool shape is similar to that observed from experiments. The dynamical change of the weld pool shape can be well explained by the predicted fluid flow field.Copyright © 2003 by ASME

Modeling of hybrid laser-MIG keyhole welding process

Abstract: Recently, hybrid laser-MIG welding technology has increasingly attracted interest in both industry and academia. By combining the two welding processes, it can modify the weld bead shape including the elimination of undercut, change the weld compositions, reduce the porosity, improve welding bridgeability, decrease the susceptibility of hot cracking, and increase welding speed. So far, the development of laser-MIG welding technology has been based on the trial-and-error procedure.In this paper, mathematical models and the associated numerical techniques have been developed to simulate the laser-MIG welding process. The transient keyhole dynamics, interaction between droplets and weld pool, and the shape and composition of the solidified weld were predicted for a three-dimensional moving laser-MIG welding. The heat and mass transfer and fluid flow in molten metal and temperature distribution inside the keyhole were studied. In the model, the volume-of-fluid (VOF) method was employed to track free surfaces. The Inverse Bremsstrahlung absorption of laser energy inside plasma, Fresnel absorption and the multiple reflections at the keyhole wall, and the thermal radiation by the plasma in the keyhole were all considered. Computer animations showing the fluid flow, weld pool dynamics, and the interaction between droplets and weld pool will be shown in the presentation.Recently, hybrid laser-MIG welding technology has increasingly attracted interest in both industry and academia. By combining the two welding processes, it can modify the weld bead shape including the elimination of undercut, change the weld compositions, reduce the porosity, improve welding bridgeability, decrease the susceptibility of hot cracking, and increase welding speed. So far, the development of laser-MIG welding technology has been based on the trial-and-error procedure.In this paper, mathematical models and the associated numerical techniques have been developed to simulate the laser-MIG welding process. The transient keyhole dynamics, interaction between droplets and weld pool, and the shape and composition of the solidified weld were predicted for a three-dimensional moving laser-MIG welding. The heat and mass transfer and fluid flow in molten metal and temperature distribution inside the keyhole were studied. In the model, the volume-of-fluid (VOF) method was employed to track free surfaces....

Modeling of weld pool dynamics during dual-beam laser welding process

Abstract: Dual-beam laser welding has been used to weld thick-section metals and for increasing keyhole stability leading to a better weld quality. So far, the development of dual-beam laser welding technologies has been in the experimental stage.The objective of this paper is to develop mathematical models and the associated numerical techniques to calculate the transient heat transfer and fluid flow in the weld pool and to study weld pool dynamics during the dual-beam laser welding process. The simulation was conducted for a three-dimensional stationary dual-beam laser welding. The predicted changes of weld pool shape from an oval-like shape with a long-axis connecting the two lasers to another oval-like shape with a short-axis connecting the two lasers are similar to those observed from experiments. This interesting dynamical shape of the weld pool can be well explained by the predicted fluid flow field. Parametric studies were also conducted to investigate the effect of beam distance between the two lasers on the dynamical shape of the weld pool. Computer animations showing the transient fluid flow and weld pool dynamics will be presented.Dual-beam laser welding has been used to weld thick-section metals and for increasing keyhole stability leading to a better weld quality. So far, the development of dual-beam laser welding technologies has been in the experimental stage.The objective of this paper is to develop mathematical models and the associated numerical techniques to calculate the transient heat transfer and fluid flow in the weld pool and to study weld pool dynamics during the dual-beam laser welding process. The simulation was conducted for a three-dimensional stationary dual-beam laser welding. The predicted changes of weld pool shape from an oval-like shape with a long-axis connecting the two lasers to another oval-like shape with a short-axis connecting the two lasers are similar to those observed from experiments. This interesting dynamical shape of the weld pool can be well explained by the predicted fluid flow field. Parametric studies were also conducted to investigate the effect of beam distance between the two lasers on t...

Modeling the transport phenomena during dual beam laser welding process

Abstract: The objective of this paper is to establish mathematical models and the associated numerical techniques to calculate the transient heat transfer and fluid flow in the melt pool, and to understand the mechanisms leading to the oval shape of the melt pool during dual beam laser welding. By combining several Nd:Yag lasers one can increase the total output power to achieve deep penetration.