Numerical analysis of the heat-pressure characteristics in ultrasonic vibration assisted plasma arc

The ultrasonic vibration assisted plasma arc welding process was developed to enhance the welding efficiency while the underlying mechanism of ultrasonic interaction with plasma arc is not yet elucidated. In this study, a numerical model of ultrasonic vibration assisted plasma arc is proposed, which takes into account the influence of plasma flow velocity on the ultrasonic propagation as well as the macro- and micro-effects of ultrasound on the heat-pressure characteristics of the plasma arc. The calculation results show that the plasma flow velocity affects the ultrasonic field in the plasma arc, resulting in a significant increase in the sound pressure near the workpiece surface. Ultrasound can increase the thermal conductivity of plasma and reduce the electric conductivity of plasma. The acoustic radiation force is at the same order of electromagnetic force, while the acoustic energy is five orders of magnitude lower than Joule heat. Under the comprehensive action of ultrasonic vibration, the plasma arc pressure and current density on the anode surface are increased so that the keyholing/penetrating ability of the plasma arc is enhanced. The model is validated by comparison of predicted and measured arc pressure and current density on the anode surface.