Cutting performance and surface integrity for rotary ultrasonic elliptical milling of Inconel 718 with the ball end milling cutter

Ultrasonic assisted milling (UAM) has been demonstrated excellent cutting performance for nickel-based superalloy machining. However, the machining quality improvement achieved by traditional UAM is limited at high cutting speed. Rotary ultrasonic elliptical milling (RUEM) is an unconventional cutting method recently proposed for high quality and efficient machining of difficult-to-cut alloy, breaking the cutting speed limit for UAM. In order to verify the feasibility of this method in thin-walled curved surface machining, the ball end milling cutter was adopted in feasibility experiments of RUEM on Inconel 718 with the evaluation of cutting force, surface integrity and tool wear. The results indicate that compared with conventional milling (CM) without ultrasonic vibration assistance, the cutting force reduction reaches 31.33% in RUEM. The material strength enhancement was obtained in RUEM with the disturbed strengthening phases of Inconel 718. RUEM achieved 728.65 MPa of surface compressive residual stress and 140 mu m depth of compressive residual stress layer beneath the machined surface simultaneously, while CM provided tensile residual stress field near the machined surface. Moreover, the tool flank wear status was significantly improved in RUEM. These results demonstrate that various machinability benefits of Inconel 718 are obtained by RUEM, which is a promising method for nickel-based superalloy thin-walled structure finish machining.