Experimental investigation of micro-EDM hole drilling on Inconel-718 for predicting surface quality characteristics

This study investigates the impact of plasma flushing efficiency (PFE) on solidified white layer thickness (WT) and heat-affected zone (HAZ) depth during micro-hole fabrication using micro-electrical discharge machining (µEDM) of Inconel-718. Temperature distribution was simulated using axisymmetric three-dimensional finite element models. Full factorial designed experiments (four pulse-on time (Ti) and five pulse-current (I) levels) were conducted to validate the simulation results. The results reveal that extending the pulse-on duration increases WT and HAZ depth owing to longer temperature exposure during discharge. In contrast, higher pulse current causes a minor reduction in both WT and HAZ depth, implying a link between plasma behaviour and heat distribution. For constant discharge energy, higher pulse current coupled with shorter pulse-on time leads to a reduction in both surface damage characteristics, potentially due to improved PFE. The finite element model demonstrates good predictive accuracy with average deviations of 9.65% and 12.65%, compared to experimental data for WT and HAZ depth, respectively. This study highlights the effectiveness of FEM modelling in predicting surface integrity in µEDM and provides insights into optimizing process parameters for Inconel-718 machining.