Asymmetric molten zone and hybrid heat source modeling in laser welding carbon steel and cast iron with nickel alloy wires

Molten pool morphology in dissimilar metals welding is different from that in same metal and influenced by the position of the welding wire, which concerns the welding crack occurrence. In this study, a newly designed ring gear and differential case of electric vehicle whose materials are carbon steel and cast iron, respectively, was welded by laser beam. The nickel-based alloy was used as welding wire. The location of welding wire in transverse direction can result in an asymmetric shape of the molten zone defined by the wire offset position “e” and form a “golf club-like” molten pool, which was clearly observed in experiments. A novel hybrid heat source model consists of a cylinder heat source model and a Goldak heat source model was developed in numerical calculation. The value “es” defined the offset distance between the center of heat source and seam of base metal as eccentricity to simulate heat flux that changed with the welding wire position. The results predicted a well asymmetric molten pool shape which was consistent with the experiment when “e” changed from −0.4 mm to 0.2 mm. And the predicted cooling rate in the metal surface was about 1200 °C/s, which consistent with the experimentally measured value. This study can be guidance for understanding the morphology of molten zone and temperature field at different welding wire positions.