Influence mechanism of laser power on hybrid laser-MAG welding undercut defect

The undercut is an undesired defect in high-speed hybrid laser-arc welding, which will deteriorate the mechanical properties of the weld. Laser power has a significant impact on undercut formation, while research on the corresponding mechanism is insufficient. Exploring the mechanism of laser power influence on undercut has an important theoretical guiding significance for industrial production. In this study, the variation law of undercut is investigated by analyzing the arc characteristic, droplet transfer, and the flow state of the molten pool surface assisted by a visual sensing system. We analyze the change of arc pressure and droplet impact in detail momentum to explain the behavior of molten metal in the arc gouge region. Furthermore, combined with the arc drag force, fluctuating state, and the solidification direction of the weld pool, we discuss the flow state of liquid metal at the weld toe. The results show that the increase of laser power keeps more molten metal in the arc gouge region and slows down the backward flow of liquid metal. High laser power is beneficial for molten metal to fill the weld toe and suppressed undercut effectively. By increasing the laser power to 10 kW, the forming quality of the upper and lower surfaces of welds can reach the B-level in welding standard: ISO13919-2:2021.