Abstract
NiTiNOL (Nickel–Titanium) shape memory alloys (SMAs) are ideal replacements for titanium alloys used in bio-medical applications because of their superior properties like shape memory and super elasticity. The machining of NiTiNOL alloy is challenging, as it is a 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 (WEDM) using zinc coated brass wire as electrode material have been carried out. Pulse time (Ton), pause time (Toff), wire feed (WF), and servo voltage (SV) are chosen as varying input process variables and 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. Modified differential evolution (MDE) optimization technique has been developed and the convergence curve of the same has been compared with the results of differential evolution (DE) technique. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrography (EDS) analysis are carried out to study the surface morphology of the machined alloy. SV is found to be more influential process parameter for achieving better MRR with minimal SR and TWR, followed by Ton, Toff, and WF. The WF has good impact on reduced SR and TWR responses and found to be least significant in maximizing MRR.
Highlights
Shape memory alloy (SMA) known as smart alloy or memory alloy has its prominence since last few decades
The tissues in the body respond to the implants and the response is dependent on surface texture of the machined implant biomaterial
The machining using wire electric discharge machining (WEDM) is the primary process of material removal, where the surface roughness (SR) may range from 1 to 5 μm based on the WEDM machine setting
Summary
Shape memory alloy (SMA) known as smart alloy or memory alloy has its prominence since last few decades. Sharma [12] performed the optimization studies on WEDM for porous Ni40 Ti60 alloy and established the relations between peak current, pulse time, pause time, and servo voltage using response surface methodology (RSM) based central composite rotatable design. They concluded that a single cut operation is sufficient in WEDM of NiTi alloy. There are other types of NiTiNOL apart from industrial grade, which are termed as medical grade because of their characteristics such as biocompatibility, elastic deployment, thermal deployment, kink resistance, and fatigue resistance along with its shape memory and super elastic behavior These medical grade NiTiNOL SMAs are hard and difficult to cut materials.
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