In-Process Monitoring and Adaptive Control during Pulsed YAG Laser Spot Welding of Aluminum Alloy Thin Sheets

Recently aluminum alloys have been often used as weight saving materials in automobile and electronics industries. It is difficult to stably produce high quality welds in aluminum alloys because of high heat conductivity/diffusivity and low laser absorptance. Moreover, the deformation is easily induced around the welded spot due to high linear expansion coefficient. Therefore, in-process monitoring and adaptive control are important as one of the ways to solve the problems in laser welding of aluminum alloys. In this study, a new procedure of in-process monitoring and adaptive control has been developed for laser micro-spot lap welding of A3003 aluminum alloy sheets of 0.1 mm and 1mm in thickness. It was revealed that the reflected laser light and the radiated heat from the welding area were effective as in-process monitoring signals in detecting melting, keyhole generation and though-hole formation in the upper sheet during laser irradiation. Laser pulse duration and peak power and were controlled at every 0.15 ms interval during the laser spot welding on the basis of the heat radiation signal detecting the though-hole. Upon investigation of 20 samples, 4 non-bonded welds with holes were formed under conventionally used conditions. However, good laser lap spot welds could be always produced by utilizing newly developed in-process monitoring and adaptive control system.