Experimental optimization of micro-electrical discharge drilling process from the perspective of inner surface enhancement measured by shear-force microscopy

The micro-electrical discharge drilling process was studied by means of experiments with the twofold objective of increasing the surface quality while minimizing the drilling time. To characterize the inner surface of micro-drilled holes obtained by EDM a specifically conceived scanning probe microscopy technique was used. Discharge current and pulse duration were used as input parameters with the aim of quantifying the effects of applied spark energies on surface characteristics. 150μm diameter holes were drilled using combinations of process parameters defining spark energies within the range of 3.25μJ and 15μJ. Results showed that the surface texture can be characterized by (i) maximum peak-to-valley distance and (ii) periodicity whose dimensions were related to the adopted spark energy. Standard Rq derived from the measured cylindrical surfaces was found to vary between 240nm and 380nm. Experiments testified that removal rates higher respect to those commonly used in industry can be adopted when followed by a lateral erosion phase at low energy which reduces Rq of 32% without changing the drilling time.