Abstract
Laser light reflection in pulsed YAG laser welding and a monitoring method of laser welding are investigated. Pulsed YAG laser welding involves several processes such as surface melting, beamhole forming, beam-hole vanishing, and solidification. During a pulse, the reflectivity changes with each process. The reflectivity of a cold rolled plate is about 40% of the polished surface. The molten surface reflectivity is about 80% of the polished 'one. In the cold rolled plate, reflection of laserlight increases with the surface melting. Laser light comes to be absorbed efficiently when the beam-hole is formed. By observing the change of the reflected light intensity, it is possible to detect a timing when the beam-hole is formed. By using the time from laser irradiation to the beam-hole forming, power density of irradiated laser beam can be estimated. In the lap joint, when the beamhole has penetrated an upper plate, transient increase of the reflected light is observed. A gap malfunction in the lap joint can be detected by the excessive increase.
