Experimental and numerical investigation into material removal mechanism of fast ED-milling

Abstract

Fast electrical discharge milling (fast ED-milling) has become a promising technology in the manufacturing industry for machining complex structures such as diffuser-shaped film cooling holes. However, the mechanism of the efficient removal of materials in this technology is not yet fully understood. To gain a further insight into this matter, an experimental investigation on the morphology of discharge craters including the absolute material removal volume per discharge, material residual volume per discharge, and directionality, is firstly carried out. The obtained results imply that a high-pressure inner flushing can significantly promote the expelling of molten material from a molten pool and is a fundamental reason why fast ED-milling can be of higher machining efficiency than regular ED-milling. To explore the mechanism behind, a novel thermal-fluid coupling model is developed to simulate the evolution process of the molten material under the effect of a flow field. The results of numerical simulation show that during a discharging, the molten material moves along the workpiece surface towards the outlet of a gap channel and solidifies at the side of a crater that is away from the electrode center. Another interesting finding is that an inappropriately high flushing pressure can result in a low machining efficiency because the severe heat convection will consume a large part of the heat generated by a discharge. This well explains the phenomenon that occurred during the experimental investigation.