MEMS-Based Micro-Electro-Discharge Machining (M$^{3}$ EDM) by Electrostatic Actuation of Machining Electrodes on the Workpiece

This paper reports a micro-electro-discharge machining technique that is enabled by electrostatic microactuators. The 18-$\mu\hbox{m}$-thick movable copper electrodes that serve as machining tools are microfabricated directly on the surfaces of the workpiece and operated in dielectric machining fluid. A dc voltage of 80–140 V applied between the electrode and the workpiece through a resistance–capacitance pulse generation circuit is leveraged to electrostatically pull in the electrodes toward the workpiece, inducing a breakdown and spark discharge. The discharge lowers the gap voltage and releases the electrode, which is pulled in again as the capacitor is recharged through the resistor. This pull-in and discharge cycle is self-sustained to perform the removal of the workpiece material. The electrode's displacement of $\sim\!\! 30\ \mu\hbox{m}$ is measured at the machining/actuation voltage of 100 V. Micromachining of stainless steel is implemented using the planar electrode with $1.6 \times 1.03\hbox{-mm}^{2}$ area, achieving the removal depth of 20 $\mu\hbox{m}$. The double-layer electrodes that have electroplated microstructures with high-contrast patterns on the backside of the electrodes are developed to demonstrate custom micromachining. A dynamic characteristic of the built-in capacitance of the devices, which is used to form the pulse generation circuit, as well as their mechanical response during the machining process, is theoretically analyzed with the experimental results.$\hfill$ [2008-0299]