Visualization of dynamic keyhole behavior in waveform-controlled plasma arc welding

Abstract

To overcome the shortcomings of conventional plasma arc welding (PAW), the “controlled pulse keyholing” strategy is proposed and the waveform-controlled keyhole PAW system is developed. To deeply understand the dynamic behaviors of keyhole in this novel PAW process, it is essential to measure and monitor the dynamic variation information of the keyhole geometry in real time. In this study, a vision system is developed to acquire the images of the keyhole from the underside of the workpiece. When a fully penetrated keyhole (open keyhole) is formed, clear keyhole images are captured. Both CCD camera and an efflux plasma voltage sensor are used to measure and characterize the keyhole shape and size during the waveform-controlled PAW process. The dynamic variation features of keyhole shape in a pulse cycle are visualized. The phenomena of “one keyhole in each pulse” and periodic partial-open keyhole transformation are experimentally sensed. The observation results lay solid foundation for controlling keyhole stability and optimizing the process parameters in keyhole plasma arc welding.