<title>Method to evaluate Nd:YAG laser microscopic spot welding process using reflected laser power</title>

A system consisting of 11 photodiode sensors from 0 to 90 degrees with respect to the workpiece surface has been developed to detect the angular distribution of the reflected laser intensity. Spot welding process in thin copper sheet using pulsed Nd:YAG laser was experimentally analyzed by detecting angular distribution of reflected laser beam with time resolution. Spot welding was performed with pulse duration of 1 ms on a phosphorus copper thin sheet with thickness 250 (mu) m in atmospheric condition. The change in the contour of the molten pool was investigated by time-resolved angular distribution of the reflected laser beam and penetrating time at a sampling frequency of 40 kHz. The laser beam passing through the thin sheet was also detected; the penetration time through the thin sheet was approximately 0.6 ms at an incident power density of 2.7x106W/cm2. The reflectance determined by integrating angular distribution of the reflected laser intensity was approximately 85% at the beginning of the pulse and then decreased with time. It is also shown that this system can be used for monitoring the quality of the lap welding of thin sheet metals.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.