Collaboration of physical and metallurgical viewpoints for understanding and process development of laser welding

Abstract

In Matsunawa laboratory at JWRI of Osaka University, laser welding phenomena were interpreted and laser weldability was evaluated from collaboration of welding physical and metallurgical viewpoints. It was observed by TEM that ultrafine particles were formed during laser welding, and then Prof. Matsunawa particularly suggested that Inverse Bremstrahlung and Rayleigh Scattering should exert an important role in the interaction between laser beam and laser-induced plasma or plume during CO2 laser welding and YAG laser welding, respectively. He was also expecting the effect of pulse-shaping on YAG laser spot weldability, which was confirmed by experiment. A microfocused X-ray tranmission real-time imaging system was newly constructed, by which keyhole behavior, melt flows, and bubbles and pores formation mechanisms were elucidated, and some remedies for prevension of porosity were proposed. Thereafter, in succeeded Katayama laboratory, the welding phenomena were more clearly observed by improved high speed video camera and illumination system, and the plumes induced with high power YAG or fiber laser were mainly in the vapor or weakly ionized state depending upon the power, and their interaction to a fiber laser beam was better understood by visualization of probe laser beam behavior. The importance of melt flows was also demonstrated and confirmed to understand YAG laser-TIG hybrid welding mechanism, which Prof. Matsunawa would like to know. The fact is that these research results were obtained not by one professor but by collaboration of many students and researchers.In Matsunawa laboratory at JWRI of Osaka University, laser welding phenomena were interpreted and laser weldability was evaluated from collaboration of welding physical and metallurgical viewpoints. It was observed by TEM that ultrafine particles were formed during laser welding, and then Prof. Matsunawa particularly suggested that Inverse Bremstrahlung and Rayleigh Scattering should exert an important role in the interaction between laser beam and laser-induced plasma or plume during CO2 laser welding and YAG laser welding, respectively. He was also expecting the effect of pulse-shaping on YAG laser spot weldability, which was confirmed by experiment. A microfocused X-ray tranmission real-time imaging system was newly constructed, by which keyhole behavior, melt flows, and bubbles and pores formation mechanisms were elucidated, and some remedies for prevension of porosity were proposed. Thereafter, in succeeded Katayama laboratory, the welding phenomena were more clearly observed by improved high speed v...