Model Based Prediction of Plasma Resistance, and Discharge Voltage and Current Waveforms in Micro Electrodischarge Machining

Abstract

In electrodischarge machining (EDM), the thermal energy causing material removal at the electrodes is given by the electrical energy supplied to the discharge. This electrical energy, also known as the discharge energy, can be obtained from timetransient voltage and current waveforms across the electrodes during a discharge. However, in microEDM, the interelectrode gaps are shorter causing the plasma resistance to be significantly smaller than other impedances in the circuit. As a result, the voltage and current waveforms obtained by a direct measurement may include voltage drop across the stray impedances in the circuit and may not accurately represent the exact voltage drop across microEDM plasma alone. Therefore, a modelbased approach is presented in this paper to predict timetransient electrical characteristics of a microEDM discharge, such as plasma resistance, voltage, current, and discharge energy. A global modeling approach is employed to solve equations of mass and energy conservations, dynamics of the plasma growth, and the plasma current equation for obtaining a complete temporal description of the plasma during the discharge duration. The model is validated against singledischarge microEDM experiments and then used to study the effect of applied open gap voltage and interelectrode gap distance on the plasma resistance, voltage, current, and discharge energy. For open gap voltage in the range of 100–300 V and gap distance in the range of 0.5–6 خ¼m, the model predicts the use of a higher open gap voltage and a higher gap distance to achieve a higher discharge energy.