Experimental Investigations on Machinability Characteristics of Medical Grade NiTiNOL Shape Memory Alloy

Abstract

NiTiNOL (Nickel-Titanium) shape memory alloys (SMAs) are ideal replacements for newlinetitanium alloys used in biomedical applications because of their superior shape memory newlineand superelasticity properties. The machining of NiTiNOL alloy is challenging, as it is difficult to cut material. Hence, in the current research, the experimental studies on machinability aspects of medical-grade NiTiNOL SMA during wire electric discharge machining (Wire EDM) using plain brass, zinc-coated brass and diffusion annealed coated (X-type and A-type) wire electrode materials have been carried out. Pulse time (Ton), pause time (Toff), wire feed (WF) and servo voltage (SV) are chosen as varying input process variables. The effects of their combinational values on output responses such as surface roughness (SR), material removal rate (MRR) and tool wear rate (TWR) are studied through response surface methodology (RSM) based developed models. The suitability of the developed models was verified through analysis of variance (ANOVA), and the adequacy of the models was checked through confirmatory experiments. newline newlineThe surface quality of the samples machined with zinc-coated brass and diffusion annealed A-type wire electrode materials is found to be better than those machined with plain brass and diffusion annealed X-type wire electrode materials. The MRR attained through zinc-coated brass wire is higher when compared to the machining of NiTiNOL with other three wire ectrode materials. The tool wear rate performance of coated and diffusion annealed wire lectrodes are better compared to plain brass wire. The surface of the machined NiTiNOL amples was characterized by large craters, colossal debris and prominent micro-cracks when machined with a higher pulse time of 125 and#956;s and lower spark gap set voltage of 20 V. amples machined with diffusion annealed coated electrodes showed lesser cracks and craters compared to machining with plain brass and zinc coated brass electrode materials. newline newline