Analysis of discharge pulses in micro-EDM milling of Si3N4-TiN composite workpiece by means of power spectral density (PSD)

In this paper, the acquired voltage waveforms monitored during micro-EDM milling experiments were evaluated by means of the power spectral density (PSD) method. The spectral analysis was performed to address the following significant issue: the effective contribution of the normal discharges to the energy density at the operation frequency in relation to pulse waveform and duration, discharge conditions and workpiece materials. This method showed that since normal pulses do not have same time evolution in every acquisition window, their spectral content at the operation frequency changes. This variation depends on the duty cycle and on the fulfillment of the discharge condition mainly due to electrical properties of the workpiece material. The spectral performance of the micro-EDM milling experiments was also carried out by means of Q factor (which estimates the losses). All the analyses pointed out that a higher number of normal pulses does not always guarantee the highest energy density delivered at the set process frequency.