Effect of Cutting Speed on Shape Recovery of Work Material in Cutting Process of Super-Elastic NiTi Alloy

Abstract

Increasing use of NiTi alloy products makes it very important to improve the cutting performance of this material. This study presents the effect of cutting speed on radial shape recovery of work material which is supposed to deteriorate the dimension accuracy in cutting process of super-elastic NiTi alloy. The shape recovery of work material was investigated at the beginning of cutting process, during the stable part of cutting process and after feed stops respectively utilizing a high-speed camera and a cutting force dynamometer in orthogonal cutting experiments at various cutting speeds. The mechanism of the shape recovery was investigated by analyzing the crystallization phase state of work material before and after cutting using XRD and measuring the temperature distributions on the end surface of work material during orthogonal cutting experiments using non-reversible temperature indicating paints correspondingly. Results show that at relatively low cutting speed, the temperature of work material near the cutting point did not exceed the threshold temperature of phase transformation, and thus work material generated obvious shape recovery throughout the whole cutting process due to the phase transformation. Increasing cutting speed could increase the temperature of work material; when cutting speed increased to 100 m/min, the temperature of work material near the cutting point exceeded the threshold temperature of phase transformation, thus work material did not generate obvious shape recovery because it could not undergo any form of phase transformation during the stable part of cutting process and after feed stops. Consequently, increasing cutting speed could be proposed as an approach to improve dimension accuracy by inhibiting shape recovery of work material in cutting process of NiTi alloy.