The dynamic behavior and geometry of GTA as well as laser weld pools have significant effects on the weld quality. Most of the previous studies are limited due to simplified geometry and assumptions. In this study, effects of surface depression on convection and geometry of stationary GTA and laser weld pools are simulated numerically by adopting the Volume of Fluid (VOF) method. The effects of arc pressure, electromagnetic force and surface tension gradients on surface depression, convection and temperature distribution are calculated for the GTA weld pool. Formation and collapse of the laser keyhole are also predicted using the VOF method.
The pool surface is depressed mainly by arc pressure and the top surfaces of fully penetrated weld pools are easily depressed since they are only supported by surface tension. As the current increases, surface depression affects the pool geometry. Deep penetration by the pulsed current is generated mainly by surface depression produced by arc pressure at the peak current period. The burn-through phenomena and weld pool oscillation are also predicted numerically.
In the area of laser welding, the preliminary studies are performed to predict the mechanism of keyhole formation and collapse considering multiple reflection of laser beam and resultant recoil pressure. The aspect ratio of the keyhole is increased by Marangoni flow. Keyhole is calculated to collapse at middle region of almost vertical wall where absorption energy is low. It is found that other mechanisms should be considered to maintain stationary keyhole in addition to the recoil pressure by multiple reflection.
