Weld outline comparison between various pulsed Nd:YAG laser welding and pulsed Nd:YAG laser–TIG arc welding

In this study, four welding methods, pulsed laser welding, defocused pulsed laser welding, laser–arc tandem welding, and laser–arc hybrid welding, were tested on 304 stainless steel sheets, and the differences between the weld cross-section outlines, especially the weld depth, were compared under different welding conditions. The author suggests that during the hybrid welding process, the upper part of the keyhole was surrounded by a large amount of melt such that the evaporation recoil pressure caused the gas–liquid interface to move towards the solid–liquid interface near weld pool surface. This flow behavior promoted both heat transfer from the central region of the weld pool to the solid–liquid interface near the weld pool surface, which resulted in an increased weld width, and increased the diameter of the upper part of the keyhole, which reduced the number of times the laser beam is reflected inside the keyhole and the coupling efficiency of laser energy. During pulse Nd:YAG laser–TIG arc tandem welding, there was a smaller amount of melt around the keyhole, which made it easier to form a U-shaped keyhole, which benefited the multiple reflection of laser beam in the keyhole and promoted the coupling of laser energy. The weld depths obtained from tandem welding and laser–arc hybrid welding were similar, which may be related to the difference in the keyhole shapes produced from the two welding processes.