Optical properties of laser-induced plume during high power laser welding

Abstract

Remote/scanning welding has many advantages; however, it is often difficult to use shielding gases due to its long focal length. The previous researches revealed that the weld bead changed from full to partial penetration during remote welding without shielding gas [1, 2]. It was attributed to the phenomena that a laser-induced plume ascended high and an incident laser beam was refracted and defocused by its interaction to the plume. It was also considered that the interaction zone between a plume and a laser beam was heated spatially above a specimen and consequently its refractive index distribution affected beam shape and focusing.In this study, therefore, the laser-induced plume and refractive index distributions above a specimen during laser welding in air and with fan were simultaneously observed with normal high speed video method and a Michelson interferometer, respectively. As a result of experiments, it was confirmed that the zones with small refractive indices ascended high and exerted a great effect on welding results in air. Furthermore, it was found that the refractive index distributions within the plume had the inclination and the refractive indices decreased toward the beam central axis.Remote/scanning welding has many advantages; however, it is often difficult to use shielding gases due to its long focal length. The previous researches revealed that the weld bead changed from full to partial penetration during remote welding without shielding gas [1, 2]. It was attributed to the phenomena that a laser-induced plume ascended high and an incident laser beam was refracted and defocused by its interaction to the plume. It was also considered that the interaction zone between a plume and a laser beam was heated spatially above a specimen and consequently its refractive index distribution affected beam shape and focusing.In this study, therefore, the laser-induced plume and refractive index distributions above a specimen during laser welding in air and with fan were simultaneously observed with normal high speed video method and a Michelson interferometer, respectively. As a result of experiments, it was confirmed that the zones with small refractive indices ascended high and exerted a great ...