The influences of dynamic behavior characteristics of molten pool and keyhole on pore formation in oscillating laser beam welding of hidden T-joint with gap

The pore formation process is significantly influenced by the dynamic behaviors of molten pool and keyhole. To analyze the conventional laser beam welding (CLBW) and oscillating laser beam welding (OLBW) of hidden T-joint with a gap, a 3D dynamic model of molten pool and keyhole is proposed by considering an improved ray tracing model based on virtual grid refinement and a weighted average method for recoil pressure of dissimilar materials. The established model is validated by comparing the experimental result with simulated result. The dynamic behaviors of molten pool and keyhole in CLBW and OLBW are calculated through solving the model. The evolution processes of gas cavities during CLBW and OLBW are analyzed and discussed in details. The results demonstrate that the formation of gas cavity connected to the joint gap is due to the keyhole collapse. Additionally, the flow of molten metal (MM) from the face plate toward the joint gap causes the depression of upper surface of molten pool. During the collapse of the gas cavity, the narrow gas cavity channel is separated into two parts by the MM and the rear of gas cavity is evolving into the pore defect at the joint gap gradually. Compared to CLBW, the probability of pore defect occurring at the joint gap during OLBW is decreased, which indicates that OLBW is beneficial for reducing the pore defect in weld. The developed model is helpful for understanding the influences of dynamic behaviors on pore formation during CLBW and OLBW of hidden T-joint with a gap.