In-process monitoring and adaptive control for prevention of through-holes in full-penetration lap welds of aluminum alloy sheets

The availability of adaptive control for microspot lap welding of A3003 aluminum alloy sheets of 0.1 mm in thickness with a pulsed fundamental yttrium-aluminum-garnet laser beam was investigated with the objective of the stable production of sound full-penetration spot welds without through-holes. Two full-penetration welds with through-holes were produced among 20 samples subjected to a normal pulse laser beam. The in-process monitoring results of the reflected light and heat radiation signals showed that the minimum value of the reflected light intensity was lower and the maximum variations in rate of change of the heat radiation were higher due to the generation of a through-hole. Therefore, the laser power was controlled at 0.15 ms intervals in order to maintain both the reflected light intensity and the variation of heat radiation within the levels for the formation of normal full-penetration welds. Consequently, sound fully penetrated welds were consistently produced in all the 20 samples, owing to the stable growth of a molten area under the adaptive control of a pulsed laser power.