Clarification of material removal mechanism in fast ED-milling - part II: Numerical simulation

To investigate the underlying mechanisms behind the observed phenomena presented in the Part I paper, by considering the observation results and actual processing conditions of fast ED-milling, this study develops a novel thermal-fluid coupling model to numerically simulate the evolution process of the molten material under the influence of a flow field. Throughout an in-depth investigation into the material removal process, as well as the velocity and pressure distribution within the discharge gap, it has been found that in fast ED-milling, the molten material expelled from the molten pool accounts for 58.6% of the total volume. The molten material is primarily removed by the high-pressure flushing fluid during pulse interval, with the driving force behind material removal arising from the hydrodynamic force and the large pressure difference between the electrode centre and discharge locations. Furthermore, to investigate the effects of the flow field on machining stability during a consecutive-pulse discharge process, a particle tracing model was established to simulate the debris evacuation process. The simulation results show that inner flushing can markedly reduce the amount of residual debris within the discharge gap, which is a fundamental reason for the high stability of fast ED-milling. Another interesting finding is that the effective internal flushing pressure for high-speed electrical discharge milling is approximately 0.21 MPa, and flushing pressures exceeding it can not lead to a significant improvement in debris evacuation.