The numerical simulation of arc welding process provides insight and information not available from experiments for process development, but has not been used in practical welding applications. In order to demonstrate its usefulness in welding applications, a three-dimensional numerical simulation of the pulsed gas metal arc welding (P-GMAW) process using Volume of Fluid technique was developed based on mathematical models. It was validated by the comparison of weld deposit geometry, transient radius, and temperature history. The physical mechanism of weld bead hump formation, which has not been clearly understood, and a suppression technique were explored based on heat and fluid flow profiles and solid/liquid interface contours obtained from the numerical simulation of P-GMAW and hybrid (P-GMAW + laser) processes.;The mechanism of hump formation was investigated by using the numerical simulation. According to simulation results of P-GMAW, traveling at a high travel speed, the events leading to the formation of a humped bead were identified. In the initial stage of hump formation, a thin, elongated, molten bead was formed and then pinched due to capillary instability, resulting in a dramatically reduced cross section of the molten weld bead. Solidification then divided the weld pool into front and back sections, guaranteeing hump formation.;The numerical simulation was also used to demonstrate the suppression of hump formation by hybrid process. Simulation results of hybrid process showed that a defocused laser beam located in front of the P-GMA weld pool could suppress hump formation. A shallow "skin" melt produced by the defocused laser beam, with sufficient beam intensity and beam radius, promoted a wider weld bead with a smaller internal contact angle, which was less susceptible to capillary instability of weld metal deposit.
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