In-process monitoring and feedback control during laser microspot lap welding of copper sheets

摘要

The establishment of laser welding of copper sheets, as an electronics manufacturing process is anticipated. This study was performed with an objective of stably and consistently producing fully penetrated lap welds in two copper sheets of 0.1 mm thickness. A new procedure for in-process monitoring and feedback control was developed for microspot lap welding with combined beams of a pulsed fundamental yttrium-aluminum-garnet (YAG) laser and an AO Q -switched second harmonic YAG laser. It was found that reflected laser power and heat radiated from the weld area were effective as process monitoring signals. A database of these values corresponding to the sizes of the bottom fusion xones of laser spot welds was prepared in terms of joint strength for feedback control utilizing a neural network model. A pulse width during the irradiation of a fundamental YAG laser was controlled at 0.15 ms intervals according to the neural network prediction based upon the monitoring signals. Upon investigation of 200 samples, incomplete melting was detected in seven samples under the laser irradiation conditions used conventionally. On the other hand, fully penetrated spot welds were repeatedly produced in 200 samples subjected to laser lap welding under the proposed in-process monitoring and feedback control.