Measurement of dynamic keyhole behaviors in controlled-pulse plasma arc welding

The developed novel variant process of controlled-pulse keyholing plasma arc welding is able to effectively extend the suitable process parameters window, and is of great application potential in joining high-performance metals with medium thickness. To fully understand the underlying thermo-physical mechanisms of this welding process, it is critical to measure and monitor the dynamic variation of the keyhole status in each pulse cycle of the welding current. The experimental sensing system and technique of the dynamic keyhole behavior in controlled-pulse keyholing plasma arc welding are introduced. Under the action of controlled-pulse current waveform, both heat input and keyhole's establishment and closure are actively controlled through adjusting the dropping slopes at the trailing edges of the pulse current, so that complete keyhole formation and full penetration are ensured. The sequential images of the keyhole exit are captured by the vision sensor during the controlled-pulse keyholing plasma arc welding. The information on the shape, size and deviation distance of the keyhole exit is extracted based on the image processing and calibration. It presents the transient variation of the keyhole dimension and location relative to the torch axis during the cyclic process of keyhole establishing-expanding-contracting-closing in each pulse. The research results lay solid foundation for the process optimization of the controlled-pulse keyholing plasma arc welding. © 2013 Journal of Mechanical Engineering.