Feasibility study of high-efficiency self-excited vibration cutting for roughing Inconel 718

In the roughing stage of aero-engine superalloys, improving material removal rate can improve overall production efficiency, which is crucial for solving the problems of large blank machining allowance, long machining time, and high cost. To address this issue, this paper proposed a high-efficiency self-excited vibration cutting (SVC) method for roughing Inconel 718. On one hand, this study designed a self-excited vibration turning tool holder, and revealed the tool wear reduction mechanism based on the achieved tool motion trajectory. On the other hand, this paper experimentally investigated the tool wear, machining efficiency and machined surface integrity for SVC in comparison with conventional cutting (CC), to verify the feasibility of SVC for Inconel718. The experimental results show that, compared to CC, SVC can extend tool life by up to 400% at the same machining efficiency and the machining efficiency for SVC can be increased by up to 350% at the same tool life by increasing the cutting speed and the cross-sectional area of the cutting layer. In addition, the study characterized the surface integrity for both SVC and CC in terms of surface morphology, micro-hardness, subsurface metallographic structure, and residual stress. SVC produces periodic ridges along the cutting speed direction on the machined surface. The surface micro-hardness for SVC gradually decreases with the increase of cutting speed, and the hardening rate decreases from 40.21% to 34.0%. While CC shows a different behavior, and its micro-hardness increases with the increase of cutting speed, and the hardening rate increases from 14.64% to 25.23%. The depth of the plastic deformation layer on the machined surface of SVC is deeper than that of CC, and its maximum depth increases by 123.3%. The residual stress of the SVC machined surface is compressive stress, which gradually decreases with the increase of cutting speed (−418.8 to −266.62 MPa), while the residual stress of the CC machined surface at different cutting speeds is tensile stress, which gradually increases with the increase of cutting speed (7.71–74.03 MPa).