Comparison of keyhole and molten pool behavior in pure copper welding using IR laser with ring shape formed by diffractive optical element and Blue-IR hybrid laser

Pure copper is a difficult material to weld due to its high reflectivity to infrared (IR) lasers. Various approaches have been taken in laser welding copper to improve welding quality. In recent years, beam shaping technologies that create a ring-shaped intensity distribution for IR laser and Blue-IR hybrid laser have been developed and are being adopted in mass production lines. However, few phenomenological studies have directly compared these two technologies. In this study, we performed bead-on-plate welding of pure copper plates using an IR single spot beam, an IR ring core beam formed by a diffractive optical element, and a Blue-IR hybrid beam and compared the bead quality, the number of melt ejections and spatters, and the keyhole behavior. As a result, it was found that there was a clear difference when the welding speed was low. At a welding speed of 2.5 m/min, melt ejections occurred in the IR single spot and the IR ring core, resulting in bead defects. On the other hand, the Blue-IR hybrid did not cause melt ejections and formed a stable molten pool and bead. When observing the internal behavior of the keyhole at a glass-assisted side-view observation method, unstable fluctuations in the keyhole shape, spatter, and melt ejection were observed when the IR ring core was applied. In the Blue-IR hybrid, the keyhole and the liquid phase in front of the keyhole were formed stably, and no spatter or melt ejection was observed.