Weld penetration and phenomena in 10 kW fiber laser welding

Abstract

A high-power fiber laser can produce an ultra-high peak power density of MW/mm2 level corresponding to a focused electron beam, and is promising as one of the desirable heat sources for high-speed and deep-penetration welding. This research was undertaken with the objective of obtaining a fundamental knowledge of 10 kW high-power fiber laser welding on Type 304 stainless steel plates in Ar shielding gas. The fiber laser-induced plume behavior was firstly observed and spectroscopic analyses of plumes were made. It was found that the plume was in a weakly ionized state and grew up periodically in about kHz cycles by 10 kW fiber laser. However, the weakly ionized plume had a slight interaction with the fiber laser beam of 1.09 µm wavelength. Subsequently, laser absorption was measured under various power densities. It was confirmed that the absorption increased to a great extent according to the variation from heat-conduction type welding to keyhole-type welding due to the increase in the laser power density. The effects of laser power and its density on weld penetration were clarified, and the formation mechanisms of welding defects were invetigated by high-speed video cameras. 10 kW laser power could produce deep weld penetration of more than 20 mm. The laser power and its density exerted a remarkable effect on the increase in weld penetration at lower and higher welding speeds, respectively. As for welding defects, it was found that underfilling with spatters was induced by strong shear force accompanying by the laser-induced plume, and humming was caused by not only the surface tension due to narrow bead width but also the backward melt flow.A high-power fiber laser can produce an ultra-high peak power density of MW/mm2 level corresponding to a focused electron beam, and is promising as one of the desirable heat sources for high-speed and deep-penetration welding. This research was undertaken with the objective of obtaining a fundamental knowledge of 10 kW high-power fiber laser welding on Type 304 stainless steel plates in Ar shielding gas. The fiber laser-induced plume behavior was firstly observed and spectroscopic analyses of plumes were made. It was found that the plume was in a weakly ionized state and grew up periodically in about kHz cycles by 10 kW fiber laser. However, the weakly ionized plume had a slight interaction with the fiber laser beam of 1.09 µm wavelength. Subsequently, laser absorption was measured under various power densities. It was confirmed that the absorption increased to a great extent according to the variation from heat-conduction type welding to keyhole-type welding due to the increase in the laser power density...