Study on material removal mechanism and control strategy of multi-axis fast ED-milling

Abstract

Diffuser-shaped film cooling holes, which have been used extensively in advanced aero-engines, are usually machined by electrical discharge machining (EDM) by means of drilling and die-sinking approaches in a sequence. However, this sequential machining on different types of machine tools suffers from low machining efficiency and accuracy severely. To cope with this problem, a multi-axis fast ED-milling method that uses tubular electrodes and high-pressure inner flush is proposed for various diffuser machining, such that the fabrication of diffusers can be realized on a single machine tool, is developed in this paper. However, the material removal mechanism and proper control strategies in this machining method are yet not fully investigated. To address this issue, with a dedicated observation platform, single-pulse discharge experiments were firstly carried out to achieve a better understanding of the gap discharge phenomena. The observation results imply that a high-pressure inner flushing can significantly promote the expelling of molten material from a molten pool as well as the evacuation of debris from a discharge gap. After that, characteristics of this machining method such as the electrode wear behavior and the gap discharge state variations were analyzed. Based on the analytical results, a dedicated electrode wear compensation strategy was proposed. Machining tests indicate that the new method guarantees rather higher machining efficiency and comparable surface quality in contrast with layer-by-layer fast ED-milling.