Fundamental Turning Characteristics of Inconel 718 by Applying Ultrasonic Elliptical Vibration on the Base Plane

Inconel 718, a nickel-based superalloy, exhibits desirable properties over a wide temperature range, and it is widely used in industry. However, Inconel 718 is typically difficult to cut because of its strong work hardening, high temperature tensile strength, and shear strength. To improve the machinability of Inconel 718, this study proposes ultrasonic turning by applying elliptical vibration to the base plane. The principle and features of the ultrasonic elliptical vibration are discussed in detail. Experiments were conducted on a commercial ultrasonic cutting unit installed onto a commercial numerical control (NC) lathe; the cutting forces were found to be lower in the new method than in conventional turning (CT). Microchip particles were observed on both chip and work surface in CT but were almost absent on the surfaces prepared by ultrasonic elliptical vibration assisted turning (UEVT). Furthermore, the cutting tool used in CT developed built-up edge (BUE), and its flank wear became heavier; in contrast, negligible BUE and less flank wear were found on the cutting tool used in UEVT. The theoretical surface roughness of UEVT was calculated and it agreed much well with the measured surface roughness.