Analysis of arc plasma characteristics and energy distribution in EDM based on two-temperature model

Abstract

Arc plasma is the heat source in electrical discharge machining (EDM), it affects the material removal and discharge crater formation directly, so it is necessary to clarify its characteristics. However, it is challenging to understand the physical mechanisms behind each pulse discharge through experimental methods, as it is a transient, multi-physical process that occurs in a very short time and small gap. In this paper, a two-temperature model was proposed to investigate the characteristics of the arc plasma and the energy distribution considering the multi-physics fields in the steady state. In this model, the electrons and the heavy species of the arc plasma were considered separately in the energy conservation equations, so that the temperature of the electrons and heavy species can be calculated separately. Besides, the velocity distribution, pressure distribution, electrical potential distribution, and diameter of the arc plasma, as well as the heat flux distribution and the energy distribution into the anode and cathode were analyzed. Then the variations in arc plasma properties and energy distribution with different discharge conditions were studied. The results showed that, at a lower discharge current, the electron temperature was higher than the heavy species temperature, which means that the arc plasma did not reach a local thermodynamic equilibrium (LTE) state under these discharge conditions. To validate the simulation results, the arc plasma was observed with a high-speed camera, and the diameter of craters on the surface of both the cathode and anode was measured with single-pulse discharge experiments. The experiment results were consistent with the simulation results.