Modelling of overlapping craters in micro-electrical discharge machining

The availability of theoretical and empirical models to predict the machining performance measures of the micro-electrical discharge machining (micro-EDM) process helps in process optimization. However, assumptions made during model development greatly affect the ability and accuracy of such models in process performance prediction. In this work, a new heat conduction analysis using an expanding circular heat source with time varying heat flux as the thermal loading condition is reported for a single electrical discharge erosion model for micro-EDM. Furthermore, a new approach for predicting the machining performance measures of micro-EDM by considering the effects of multiple discharges is also proposed. The heat conduction analysis allowed the plasma flushing efficiencies (PFEs) in micro-EDM to be determined. For discharge energies of 1.6 µJ, 3.4 µJ and 14.6 µJ, the PFEs at the anode were 19%, 23% and 33%, respectively. In addition, the multiple discharge approach generated lower and upper bounds of Rmax values for micro-EDM, which represents the range of Rmax values that may exist on the machined surface. A comparison with the measured Rmax values of surfaces machined at discharge energies of 3.2, 5.5 and 10.4 µJ showed good agreement, thus validating the proposed multiple discharge approach.