Influence of the laser-induced plume on welding behavior in keyhole welding for stainless steel using a 16 kW disk laser

The spatter is one of the defect factors for laser welding. For high-quality laser welding, the elucidation of the spatter reduction mechanism is required. In our previous study, it was elucidated that the molten pool and keyhole fluctuation contribute to spatter generation from the observation of the keyhole and molten pool under different ambient pressure conditions. However, the main cause of the instability of the molten pool and keyhole has not been clarified. It is considered that the interaction between the laser and plume might cause these instabilities. Therefore, in this study, we focused on the plume generated by laser irradiation. The dynamics of the plume during laser welding and the attenuation of the laser were observed under different ambient pressures. According to these observations, the effect of the plume on instability in laser welding was elucidated. The SS304 was fixed in the vacuum chamber, and the disk laser with an output power of 6 kW swept on the sample to form the weld bead. At the same time, the plume behavior was observed by the Schlieren method, and the attenuation of the laser was measured using a probe laser. As a result, the metal vapor jet, which is a periodical plume ejection, was observed. The attenuation of the probe laser increased with increasing atmospheric pressure. These results suggest that the frequent generation of the metal vapor jet under atmospheric pressure caused instability in the heat input of the laser, which caused instability in the keyhole and molten pool.