Laser absorption in high-power fiber laser welding of stainless steel and aluminum alloy

Abstract

High power and high brightness fiber lasers have been developed, and it is revealed that a deeper and narrower weld bead can be produced with the increase in the power density. Thus high absorptivity of laser energy is expected, but there are few systematic experimental researches of laser absorption in conjunction with a beam diameter and a keyhole diameter. Therefore, this study was undertaken by utilizing the calorimeter method and the observation technique of welding phenomena to obtain a fundamental knowledge of fiber laser absorption for stainless steel and aluminum alloy. The laser absorptivity of stainless steel and aluminum alloy was measured under various welding conditions. It was found that the absorptivity of 10 kW fiber laser in stainless steel increased with the decrease in the welding speed, and 90 % was obtained at 1 m/min. In order to investigate the relationship between the absorptivity and the keyhole inlet, the keyhole behavior in the molten pool, which was illuminated with a diode laser, was observed by a high-speed video camera at the framing rate of 10,000 frames/s. It was found that the laser beam didn’t fully enter into the keyhole and the laser absorptivity decreased because the keyhole position shifted backward from the laser irradiation point. The laser absorptivity of aluminum alloys was lower than that of stainless steel at low laser power, but was about 90 % during 10 kW laser welding, which was higher than that of stainless steel.High power and high brightness fiber lasers have been developed, and it is revealed that a deeper and narrower weld bead can be produced with the increase in the power density. Thus high absorptivity of laser energy is expected, but there are few systematic experimental researches of laser absorption in conjunction with a beam diameter and a keyhole diameter. Therefore, this study was undertaken by utilizing the calorimeter method and the observation technique of welding phenomena to obtain a fundamental knowledge of fiber laser absorption for stainless steel and aluminum alloy. The laser absorptivity of stainless steel and aluminum alloy was measured under various welding conditions. It was found that the absorptivity of 10 kW fiber laser in stainless steel increased with the decrease in the welding speed, and 90 % was obtained at 1 m/min. In order to investigate the relationship between the absorptivity and the keyhole inlet, the keyhole behavior in the molten pool, which was illuminated with a diode la...