Single vision system for simultaneous observation of keyhole and weld pool in plasma arc welding

A common CCD camera was equipped with a specially designed filter to constitute a vision system, which was used to capture the weld pool and the keyhole images during plasma arc welding process. Through image processing and calibration, the shapes and sizes of both the keyhole and the weld pool were measured under different welding conditions. The dynamic variations of the keyhole/weld pool sizes with time and their relations with the main process parameters were experimentally determined. Six stages of the keyhole/weld pool evolution were observed during the whole welding process. The observation results lay solid foundation for optimizing the welding process parameters and implementing process control of plasma arc welding.