Correlation of reflected plasma angle and weld pool thermal state in plasma arc welding process

Keyhole behavior and weld pool thermal state have a great influence on the stability of the plasma arc welding process, detection of the weld pool thermal state plays a very important role. Deviation distance of the keyhole exit was proved to be a candidate parameter to characterize weld pool thermal state. However, such a backside detection method is often limited by space. This research proposed a method to evaluate the weld pool thermal state by the front side reflected plasma angle. The correlation is verified with varying of welding current, welding speed, and plasma gas flow rate. It was found that: before the fully penetrated keyhole is formed, the reflected plasma angle increases with the increase of arc penetration ability; after the fully penetrated keyhole is formed, the reflected plasma angle decreases with the increase of arc penetration ability. In the fully penetrated keyhole welding process, the phenomenon that the reflected plasma angle is positively correlated with the deviation distance of the keyhole exit proves that the reflected plasma angle is related to the weld pool thermal state. This work proposes a new front side detection method to evaluate the weld pool thermal state and lays the foundation for the control of plasma arc welding process.