Precision Micro-Welding Using Single-Mode Fiber Laser

—Effect of Laser-Induced Plume and Assist Gas on Welding Process—

Abstract

Welding process of thin stainless foil was studied using a single mode Yb-fiber laser with a CW output of 40W at maximum. The spot size of approximately 10 μm in diameter at 1/e² power density of the value at beam center was obtained by a focusing lens, the focal length of which was 55mm. Laser-plume interaction in welding process was discussed based on the effect of assist gas on the bead width, the back-reflected laser power W_R and the laser power passing through the metal foil W_P. It was found that defocusing by the refraction in the plume couldn't be neglected in laser welding with such a fine beam spot at especially low welding speeds. The use of assist gas effectively improved both the bead width and the shape of bead cross section.