Hydrodynamic arc moving mechanism in EDM of polycrystalline diamond

Polycrystalline diamonds (PCD) are difficult-to-cut materials due to their ultra-hardness caused by the diamond particles sintered in the materials' structure. Electrical discharge machining is a universal nontraditional method to process electrically conductive hard-to-cut materials by using electro-thermal energy without considering the workpiece's hardness and strength. However, due to the high electrical resistivity caused by the non-conductive diamond particles, EDM machining characteristics of PCD are different from those of metals. Dielectric flushing can disturb the position and shape of the plasma channel, resulting in predictable movements of the sparking spot, which provides the possibility of preventing the discharge from being trapped between the non-conductive particles during each single discharge. This paper explored the potential of improving the processability of PCD by utilizing the moving electric arcs formed by dielectric flushing. Mathematical models were established and simulated to investigate the movement behavior of plasma channels in one single-pulse discharge for the first time. A series of experiments were conducted to investigate the theory and validate the assumptions. The results showed that dielectric flushing stretched the plasma channel and changed the spots of the arcs, which increased the material removal rate and improved the consistency of the processed surface topography.