Correlation of keyhole exit deviation distance and weld pool thermo-state in plasma arc welding process

Keyhole behavior is believed to determine the process stability in keyhole plasma arc welding, and thermal state of weld pool is one of the most critical factors to affect keyhole stability. To evaluate the correlation of the keyhole behavior to the thermal state of weld pool, vision observation system is employed to image the keyhole exit. Keyhole exit deviation distance is proposed to characterize the thermal state of weld pool. In the normal fully penetrated keyhole welding process, backside keyhole exit deviates a distance away from the torch axis. When the thermal energy in the weld pool and keyhole is increased by increasing the welding current, decreasing the welding speed or slowing the heat dissipation speed, the keyhole exit deviation distance decreases; when the weld pool thermal energy is decreased, the deviation distance increases. Dynamic performance of the new proposed thermal state factor is sound. Correlation mechanism between the keyhole exit deviation distance and the thermal state is established in view of the dependent relationship of the keyhole leading wall (leading melting side) to the keyhole exit deviation distance. The observation results lay solid foundation for deeply understanding of the keyhole behavior and further control of the keyhole process in plasma arc welding process.