Real-time wireless monitoring of workpiece material and debris characteristics in micro-electro-discharge machining

Wireless signals are generated with each discharge in micro-electro-discharge machining (mu EDM), providing an opportunity to directly monitor discharge quality. Unlike traditional methods of monitoring progress in machining, which rely on electrical characteristics at the discharge supply terminals, this method is less affected by parasitics. 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 Cu backing layer, 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 defined the transition. As debris accumulate in the discharge gaps, shifts in the wireless spectra can also indicate spurious discharges that could damage workpiece and tool. For example, when copper micromachining became debris dominated, the 800-850 MHz band dropped 4 dBm in signal strength with a 2.2 dBm average drop across the full 1 GHz bandwidth.