Effect of technological parameters on the process performance of pure Al₂O₃ layer of Ni–Al₂O₃ FGMs by self-induced EDM

Wire electric discharge machining (WEDM) and electrical discharge machining (EDM) promise to be effective and economical methods for the machining of metal matrix composites and conducting ceramic blanks. However, the machining process of Ni–Al₂O₃ functionally graded materials (FGMs) is extremely difficult because the insulating ceramic layer cannot be machined directly by EDM. In this paper, the pure Al₂O₃ layer has been machined by self-induced EDM, using the conductive layers of Ni–Al₂O₃ FGMs to trigger the discharges in the insulating ceramic layer. Machining experiments have been performed to investigate the effects of discharge capacitance, pulse off-time, and charging resistance on the process performance of the pure Al₂O₃ layer using RC-type pulse generator. From the experimental results, the discharge waveform of pure Al₂O₃ layer includes long pulse discharge waveform, in addition to conventional normal discharge of conductive layers. The shape of long pulse discharge waveform can be changed by pulse off-time. The appropriate pulse off-time not only improves the stability of EDM but also increases the material removal rate (MRR). Moreover, it was observed that the MRR increases with increasing discharge capacitance and decreasing charging resistance. The surface roughness increases with increasing discharge capacitance. Finally, a small hole with a depth-diameter ratio of 5, little tapper is machined based on the experimental analysis.