Influencing of Molten Pool Dynamic Behavior on the Weld Formation during the Laser-Arc Hybrid Welding of 12 mm Thick Steel

A numerical simulation model is put forward to study the molten pool dynamic behavior and clarify its influencing mechanism on the undercut defects in laser-arc hybrid welding (LAHW). The undercut defect is a common and challenging problem to address. However, a controversy exists on whether the dynamic process of molten pool can affect undercut defects, and the potential mechanism has been still unclear. The results suggest that profile variation of molten pool surface is driven by surface tension gradient, and the existence of eddy can alter the morphology and surface tension distribution of molten pool, which is the main factor to homogenize the flow field. Compared with the short-circuit transfer mode, the molten metal flows toward the welds edge at a constant velocity (2.5-3.75 m min-1) in the spray transfer mode, which improves the stability of molten pool flow. It can be observed that the irregular fluctuation of molten metal during the solidification process can directly cause the undercut defects.