Wireless Monitoring of Workpiece Material Transitions and Debris Accumulation in Micro-Electro-Discharge Machining

Wireless signals are inherently generated with each discharge in micro-electro-discharge machining (¿EDM), allowing direct observation of discharge quality. While traditional methods of monitoring machining quality rely on electrical characteristics at the discharge supply terminals, the wireless method provides more accurate information because it is less affected by electrical parasitics in the supply loop and by spatial averaging. The depth location of a metal-metal interface can be distinguished in the wireless signal. This is useful for determining the stop depth in certain processes. For example, in machining through samples of stainless steel into an electroplated copper backing layer, the metal transition is identified by a 10-dBm change in wireless-signal strength for the 300-350-MHz band and a 5-dBm average change across the full 1-GHz bandwidth. As debris accumulate in the discharge gaps, shifts in the wireless spectra can also indicate spurious discharges that could damage the workpiece and tool. For example, when copper micromachining becomes debris dominated, the 800-850-MHz band drops 4 dBm in signal strength, with a 2.2-dBm average drop across the full 1-GHz bandwidth.