In-process Monitoring and Adaptive Control for Laser Spot and Seam Welding of Pure Titanium

Abstract

In-process monitoring and adaptive control is increasingly expected for the decisive detection of laser welding defects and for the stable formation of sound welds since laser welding has been applied in several industries. The objective of this research is to obtain a fundamental knowledge of in-process monitoring and availability of adaptive control for laser spot and seam welding of pure titanium with a pulsed Nd:YAG laser beam. The reflected light and heat radiation from the laser-irradiated area were monitored in synchronism with 20,000 F/s high-speed video observation of a molten pool. With respect to in-process monitoring, it was found that the reflected light was sensitive to the molten area formation and the heat radiation had clear correlation to the molten pool sizes for respective laser powers. Moreover, the heat radiation intesity had a quick response to the rapid change of laser peak power, and then the correlation between the heat radiation and the molten pool size was maitained in the designed laser power. As for adaptive control, spatters and pores were drastically reduced by controlling laser peak power and pulse duration according to the obtained features of the heat radiation-monitoring signal.