Fundamental Machining Characteristics of the In-base-plane Ultrasonic Elliptical Vibration Assisted Turning of Inconel 718

Abstract

Inconel 718 has been widely used in aerospace, petroleum and nuclear industry because of its excellent mechanical properties such as high fatigue strength, good corrosion resistance and strong creep resistance. However, these properties in turn are leading to high cutting force and heavy tool damage in the turning process. Against these problems, the ultrasonic assisted machining was a potential technique since the presence of ultrasonic vibration could decrease the cutting force and cutting temperature, and therefore reduce the tool damage. Nevertheless, in conventional ultrasonic assisted turning, the ultrasonic vibration was superimposed in a single direction along the cutting speed which resulted in the existence of a critical cutting speed and thus limited to the material removal rate. Therefore, this study proposed a novel ultrasonic assisted tuning method in which an ultrasonic elliptical vibration was superimposed to the tool in the base plane. In order to validate the proposed method, experiments were carried out on a CNC lathe attached with an ultrasonic cutting unit involving a rod-shaped Inconel 718 specimen. In addition, a dynamometer was positioned under the cutting unit for measuring cutting forces. A coated carbide insert was installed at the tip of the cutting unit as the cutting tool. The experimental results showed that the cutting force and cutting temperature with ultrasonic vibration were smaller than those without ultrasonic vibration. Particularly, even the cutting speed was beyond the maximum vibration velocity, the cutting force and cutting temperature with vibration were still much lower than those without vibration. In other words, the application of ultrasonic elliptical vibration in the base plane still benefited to the turning of Inconel 718 even when the cutting speed exceeded the max ultrasonic vibration speed.