Characterization of plasma in micro-EDM discharge using optical spectroscopy

This paper presents the spectroscopic measurement of temperature and electron density in the micro-EDM (micro electric discharge machining: μμ-EDM) process. A systematic study using L-18 orthogonal array experiments based on the Taguchi method is conducted to understand the effect of varying process parameters including voltage, current, spark gap and electrode size on the plasma characteristics. The line pair method and the Stark broadening of the HβHβ spectral line are used to compute plasma temperature and electron density, respectively. The spark gap and electrode size are found to have a significant influence on the plasma characteristics. The plasma produced by low-energy discharge in μμ-EDM is more non-ideal, denser, and colder than the high-energy discharge plasma produced in the conventional EDM process. The interparticle distance is roughly equal to the Debye length (λDλD), resulting in more electrostatic interactions between ions.