Brittle Removal Mechanism of Ductile Materials With Ultrahigh Speed Machining

Abstract

Material removal mechanism depends on the material property and machining parameters during machining process. This paper investigates the brittle removal mechanism of ductile materials with ultrahighspeed machining. Based on the theory of stress wave propagation, the prediction model of critical cutting speed for ultrahighspeed machining is proposed. The predicted critical cutting speed values are then validated with ultrahighspeed machining experiments of Inconel 718 and 7050T7451 aluminum alloy at the cutting speeds range from 50 m/min to 8000 m/min. The experimental results show that fragmented chips are produced above the critical cutting speed of 7000 m/min for Inconel 718 and 5000 m/min for 7050T7451 aluminum alloy. The scanning electron microscopy (SEM) micrographs of fragmented chip fracture surface and finished workpiece surface are analyzed. Large amounts of cleavage steps and brittle cracks are observed on the fragmented chip surface. With the brittle cracks remains, the finished surface quality of ultrahighspeed machining is worse than that of highspeed machining. The results show that the material property undergoes ductiletobrittle transition so the brittle regime machining of ductile materials can be implemented with ultrahighspeed machining. Taking both the machining efficiency and machining quality into account, the ultrahighspeed machining is recommended to apply in rough machining or semifinishing, while highspeed machining is recommended to apply in finishing process. In the end, the definition and essence of ultrahighspeed machining are concluded. This paper is enticing from both the engineering and the analytical perspectives aimed at revealing the mechanism of ultrahighspeed machining and optimizing the machining parameters.