Abstract
A novel in-process monitoring system employing two detectors set above the work at different aiming angles of 5 and 75 degree was developed to detect whether or not the CO2 laser welding is of full penetration through the back surface of the steel sheets. The acquired signal involved AC components with frequencies up to approximately 10kHz of the light emission of the laserinduced plasma in both the plume and in the keyhole. The mean square value of the AC signal obtained by using 75-degree sensor in the full-penetration welding was found to be much larger than that of the partial penetration welding. Whether or not full penetration has occurred can be determined by simply comparing the mean square value of the 75-degree sensor with a predetermined threshold value.
