Influence of ion-rich plasma discharge channel on unusually high discharging points in reverse micro electrical discharge machining

Different discharges occurring during machining in micro electrical discharge machining (MEDM) and its variants, viz. reverse MEDM (RMEDM) and wire EDM, affect the shape, size, surface roughness, and surface integrity of the generated surface. Of these different discharges, there are certain discharges with unusually high discharging points (well above open circuit voltage) during machining that have not been analysed till date. This study primarily aims in understanding the physical phenomenon behind occurrences of these unusual discharges specific to RMEDM process. This understanding should also hold good for MEDM and other electric discharge-based machining processes. A numerical model was developed taking into account the movement of ions and electrons in the dielectric during machining. The model predicted that the presence of ions only in the plasma discharge channel for a very short period of time during machining leads to occurrences of these unusually high discharging points (~170% of open circuit voltage, OCV) which was also verified from experiments (162-164% of OCV).