Fine micro-welding of thin stainless steel sheet by high speed laser scanning

Fraunhofer Institute for Laser Technology had developed the SHADOW welding technique, in which high speed joining with minimal distortion is possible using a pulsed Nd:YAG laser. The possibility of high speed, high quality welding had been also reported by use of a single-mode fiber laser. The combination of micro-beam and high speed laser scanning offers potential advantages for thin metal sheet welding. Therefore, the characteristics of micro-welding for thin stainless sheet were investigated here by high speed laser scanning with both single-mode fiber laser and pulsed Nd:YAG laser. The results were a narrow welding region obtained using a laser beam with a large focus diameter of 160 μm without pulse control, while a small focus diameter of 22 μm was found in general to provide good control of the welding state. A small focus diameter can result in an excellent welding seam from the start, even without pulse control. The penetration depth could be controlled by the energy density with a small focus diameter. For the smaller beam foucus diameter, an unique periodic structure appeared at high beam scanning velocities. Moreover, by using a laser beam with a small focus diameter, the overlap welding of 25 μm thickness sheet could be successfully performed, regardless of the presence of a small gap distance between two sheets.