Numerical Analysis of Welding Defects in the Horizontal Position Laser-Metal Inert Gas Hybrid Fillet Welding

Undercut and hump bead defects are formed when the welding power or welding speed exceeds a certain critical value in horizontal position laser-arc hybrid fillet weld and their physical mechanisms are unclear. The influence mechanism of laser power on the formation of undercut and hump bead defects in laser-MIG hybrid fillet welding of Q235 mild steel plate was investigated by developing a three-dimensional transient model, which considered the coupling with keyhole, droplet transfer and molten pool. With the increase in laser power, undercut defects disappear first and then reappear, and the hump defects gradually disappear. A suitable laser power can effectively suppress welding defects. At a lower laser power, insufficient molten metal in the melt pool and premature solidification of thin metal region are the main factors for the formation of undercut and hump bead defects. At the higher laser power, the larger melt pool volume and flow velocity are more likely to sag to the horizontal plate under gravity, resulting in the formation of undercut defects at the vertical plate.