Thermal modeling and experimentation on discharge energy distribution and plasma flushing for a single discharge in EDM of D2 steel

Abstract

An electrical discharge forms a crater on the workpiece surface in the electro-discharge machining. The geometry of the molten cavity is determined by the energy parameters (gap voltage, discharge current, and pulse-on-time), the plasma channel radius, and the energy fraction coming to the workpiece. The plasma flushing efficiency determines the crater geometry with respect to the molten cavity. This work attempted to develop a thermo-physical model to express plasma radius, energy fraction, and plasma flushing efficiency as a function of all three energy parameters: gap voltage, discharge current, and pulse on time. Plasma flushing efficiency is calculated from crater dimensions and recast layer thickness. The plasma radius and energy fraction are estimated by inverse-FEM using measured crater radius, crater depth, and recast-layer-thickness values. The expressions for plasma radius, energy fraction, and plasma flushing efficiency are estimated from the regression equations obtained from the designed data set using the Taguchi method. Validation shows that the error found when predicting the crater radius, crater depth, and recast layer thickness is under 10.71%, 8.84%, and 12.65%, respectively.