Investigation on EDM Plasmas Using Time and Spatially-Resolved Optical Emission Spectroscopy

Abstract

Electrical discharge machining (EDM) is a well-established non-conventional manufacturing process. The underlying working principles of EDM relay on interactions of electric discharge plasmas with the electrodes material and dielectric in micrometer gaps. Key aspects of the process, such as material removal mechanisms, are strongly related to this complex interaction. Therefore, observation of small gaps plasma-material interactions can help to better understand this particular EDM process, supply new boundary conditions for existing models, and lead to more sophisticated processing. Different methods of analysis have been used to study and explain the physics of EDM discharges. In the present work, spatially-resolved high-speed optical emission spectroscopy is used to analyze emission spectra from small gap discharges under different conditions. Results on the plasma expansion in function of time as well as time resolved profiles of plasma components and of different plasma parameters are obtained and interpreted. Optical emission spectra supported by emission spectra simulations suggest that the center of the micro discharge is dominated by highly ionized species, whereas single ionized and atomic species are more uniformly distributed over the whole plasma. Furthermore, the spatially-resolved measurements shows that the center of the plasma is not in thermodynamic equilibrium, probably field emission leads to an ion-enhanced FE driven Townsend discharge in the small gaps.