Abstract
Deep penetration is an important advantage in laser welding. This study was undertaken in order to investigate effect of reduced-pressure atmosphere from 0.1 kPa to ambient pressure (101 kPa) on partial penetration welding. A 16 kW disk laser of 1030 nm in wavelength was employed and Type 304 stainless steel and A5052 aluminum alloy was met-run welded in 17-mm/s welding speed. The penetration depths of the stainless steel and the aluminum alloy achieved 26 and 23 mm, respectively, at vacuum pressure of 10 kPa. The depths were over 1.6 times as deep as those obtained at 101 kPa. Decrease of boiling temperature calculated on the basis of the reduced-pressure atmosphere coincided with an increase of the penetration depth. At less than 1 kPa, however, the penetration depth in steel was kept 26 mm steady and it in aluminum decreased to 19 mm. Refraction angle caused by a laser-induced plume measured with a 532 nm-wavelength probe laser beam was drastically reduced corresponding to surrounding pressure of 101 to 0.1 kPa. According to observation of the keyhole inlet with high-speed video camera, its size in steel decreased and stabilized with the pressure reduction, which indicate that reduced-pressure atmosphere made an incident laser beam focused stably with little influence of the plume and led to the stable keyhole inlet. On the other hand, the keyhole inlet in aluminum expanded more than quadruple of the ambient-pressure inlet size at 1 and 0.1 kPa, which seems to make such an unstable process that the weld penetration was reduced.
