Fundamental Investigation of EDM Plasmas, Part I: A Comparison between Electric Discharges in Gaseous and Liquid Dielectric Media

Abstract

Electric discharge machining (EDM) in liquid dielectric media is a well-stablished manufacturing process. Dry EDM (DEDM) has been proposed as an environmentally friendlier alternative to the EDM process in oil dielectric. The working principles of EDM and DEDM are based on interactions of electric discharge plasmas with electrodes materials, which is a poorly understood phenomenon. Therefore, optimization of EDM processes is still based on empirical methods and recipes. The investigation performed in the present work uses a collisional-radiative (CR) model for advanced optical emission spectroscopy interpretation of EDM plasmas performed in oil and air as dielectric media. This analysis is additionally supported by electrical parameter and high-speed imaging measurements. These applied plasma diagnostics allow, for the first time, a detailed comparison of EDM discharge plasmas in very different dielectric media. Emission spectra simulated by the CR model give indications on several EDM discharge properties, such as density of electrons, fraction of different ionic states and plasma composition. The emission spectra simulations indicate that EDM discharges performed in oil and air have very similar electron temperatures, while the electron densities are substantially different. In addition, the fraction of EDM plasma components is estimated quantitatively, indicating that plasmas in air are mostly composed of the electrodes materials, whereas EDM plasmas in oil are dominated by species originated from the dielectric medium.