Theoretical and experimental analysis of plasma radius expansion model in EDM: a comprehensive study

Abstract Electrical Discharge Machining (EDM) is an established non-conventional process, which is particularly efficient for the processing of hard-to-cut materials, in order to obtain high dimensional accuracy and surface integrity. However, in order to determine the appropriate parameters for machining novel materials, it is necessary to investigate the EDM process in depth, both by experiments and numerical models, taking into consideration the fundamental physical phenomena occurring during this process and be able to predict the surface morphology and microstructural alterations under various conditions. One of the challenging issues of EDM simulation models that still remain open is the representation of the evolution of plasma channel radius, for which various approaches have been proposed such as a linear, power law or a more complex piecewise relation, in respect to time. Thus, in this work, the effect of different relations for the plasma channel radius evolution on energy absorption coefficient, Plasma Flushing Efficiency (PFE) and crater morphology is compared under various conditions with a numerical model, which is also compared to experimental data. The results indicate that the energy absorption coefficient is dependent on the plasma column radius function, as slower growth of plasma channel leads to lower absorption coefficient and more efficient material removal, whereas a lower variation and different trends under different conditions were observed regarding PFE values, in respect to the power law exponent. Finally, the crater dimensions were shown to be consistently more narrow and deeper with higher exponents, thus based on actual observations of indicative craters, it was revealed that the appropriate values for the exponent of the power law plasma radius function are below 0.25.