Effects of bypass current on physical field and thermal decoupling in hybrid variable-polarity plasma arc

In this study, we address the influence of bypass current on physical quantities relevant to a hybrid variable-polarity plasma arc (HVPPA). Although bypass current is known to decouple heat transfer, the decoupling effect, which is important for process parameter design, has not been quantified. Therefore, we perform a numerical parametric study at a constant gas flow rate and using a torch structure parameterized by the bypass and plasma arc currents. We develop a coupled transient magnetohydrodynamic finite element model in a three-dimensional face-symmetric configuration implemented in ANSYS FLUENT. The heat flux caused by electronic thermal motion and cathode sheath voltage empowerment of a cold cathode material is established in the modeling of an alternating current arc for the first time. The model reveals that the bypass current influences the temperature distribution of the hybrid arc and total heat flux of the base metal. The degree of heat transfer decoupling of the HVPPA is defined by the heat flux transferred to the base metal, which decreases as the bypass current increases. Moreover, the degree of decoupling differs between the electrode positive and negative phases. This signifies the importance of choosing the current ratio between the plasma and bypass arcs in the metal manufacturing process. The agreement between the fusion lines obtained from the experiment and simulation is analyzed to verify the accuracy of the calculations in this study.