Abstract: The energy distribution on anode and cathode electrodes during near dry electrical discharge milling (ED-milling) process is studied and a thermo-fluid coupling physical model that predicts the crater size is proposed. The crater radius formed under different machining conditions is measured, and the least squares method is used to deduct the relationship between the crater radius and the pulse duration as well as the discharge current. By assuming a series of different energy distribution ratio and then comparing the simulation results based on the assumed ratio with the experimental results, the energy distribution ration the anode and the cathode is about 0.29 and 0.025 separately. Furthermore, the feasibility of this model is verified by comparing the simulated crater diameter with the measured value. The experiments and analysis results both show that the ratio of energy distributed on the anode is much greater than that on the cathode. This result can explain why work piece positive polarity is preferred in near dry ED Milling and can achieve a relative higher material removal rate than negative polarity machining. The discharge erosion model can not only be used to predict the material removal rate and surface roughness, but also useful the processing parameters optimization to improve the performance and economic of near-dry electrical discharge milling. Furthermore, this model can be generalized for the mechanism analysis of other electrical bischarge machining (EDM) processes.

Key words: Crater, Electrical discharge-milling, Energy distribution ratio, Thermo-fluid coupling model