Estimate of power spectral density of discharge pulses in micro-EDM milling

The power spectral density (PSD) of the voltage and current waveforms acquired during micro-EDM milling experiments are calculated and analyzed. The estimate of the PSD in the frequency domain allows to identify the pulse energy contribution in relation to the dynamics of the erosion process. The first results show that most of the energy released by the micro-EDM generator in the sparking gap during the erosion process is concentrated at the fundamental frequency set by the end-user, which in turns means that the process is stable. However, the contribution to the fundamental frequency is not provided by normal pulses only, but also by arcs. Nonetheless, a relevant number of unpredictable events (arcs and delayed occurrence) leads to several non-negligible subharmonic contribution, which witnesses the presence of inductive currents generated during the erosion process.