2019 年 37 巻 4 号 p. 187-192
We investigated the effect of laser-irradiating conditions—specifically laser spot size, laser power density and laser weaving. Three laser spot widths of 10, 4 and 2mm were applied by changing the optical-lens and fiber-cable combination to investigate the effects of the laser power density and laser spot width. The weaving-irradiating method was applied with narrow laser widths of 4 and 2mm. The effects of the laser-irradiating condition were obtained based on high-speed imaging during welding and cross-sectional observation. Stable laser irradiation by a 10-mm laser spot width provided a lower power density than the critical value of 35W/mm2 and a lack of fusion. Weaving laser irradiation by a 4- or 2-mm laser spot width provided a higher power density, reduced the large lack of fusion and achieved a large penetration of base metal. The ratio between the laser beam-spot width and gap width (WL/WG ratio) affect the base-metal fusion significantly. A sound WL/WG ratio promoted base-metal fusion by providing a uniform and stable molten-pool temperature, whereas a small WL/WG ratio maintained a smaller fusion area because of the sudden temperature drop and temperature fluctuation of the molten pool.