Study of micro-EDM plasmas

Micro Electrical Discharge Machining (micro-EDM) is a plasma-assisted process for the manufacturing of micro-components in high-hardness conductive materials. The removal of material is the result of a sum of dc discharges, produced within a point to plane system of electrodes immersed in a dielectric fluid, whose electric disruption with the development of plasma-currents can be induced by imposing a threshold voltage. To better understand the interaction between the micro-plasma and the material, we have designed and build an experimental setup for the production of single-discharges, characterized by a constant voltage-current operation point. The device allows the ignition of resistive plasmas in air/water at different pulse-times ($\sim $100--3200 $\mu $s), currents ($\sim $1-20 A for $\sim $75-250 V), polarities and gap-sizes ($\sim $0,5-25 $\mu $m), and the changes in these work conditions can be correlated to the type and size of the craters produced. The micro-plasma electron density $n_{e}$ is measured using the Stark broadening of the H$_{\alpha }$ atomic line. First results give $n_{e} \quad \sim $ 10$^{16}$ -- 10$^{17}$ cm$^{3}$, in agreement with estimates obtained from an electrical circuit model of the discharge.