Effects of beam shape formed by beam-splitting diffractive optical element on keyhole and molten pool behavior in high-power laser welding of stainless steel

In this study, for a ring beam shape formed by a beam-splitting diffractive optical element, the relationship among the penetration depth, the penetration efficiency, the size and shape of the keyhole and molten pool, and the number of spatters generated during bead-on-plate welding was investigated on stainless steel (AISI304). Regarding penetration depth, deeper melting was obtained with a higher energy ratio of the central beam. With a single spot, several hundred spatters were generated within a 10 mm-long bead. With energy distributed to the ring portion, the number of spatters decreased to less than 100. Measurements of the keyhole diameter showed that the maximum values were approximately 0.48 mm for a single spot. In contrast, they were up to 0.96 with beam shaping. It was suggested that the number of spatters can be reduced by using a longer distance between the center of the keyhole and the liquid-solid interface using beam shaping. The behavior of the keyhole formed on the stainless steel edge face was observed through quartz glass. When a single spot was used, the keyhole diameter varied in the range of 0.59–1.65 mm and spatter was generated. On the other hand, spatter generation was suppressed when the keyhole diameter was kept relatively stable (0.72–0.88 mm) with beam shaping. It was also found that even when the change in the keyhole diameter was suppressed, spatter was generated when the internal shape of the keyhole collapsed.