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.