Experimental and Numerical Investigations of Machining Ti-6Al-4V Spur Gears Using WEDM Process

Abstract

The technological developments in the non-conventional machining processes have made it more suitable, accurate and time-saving than the conventional ones. Wire electric discharge machining (WEDM) is one of the novel machining methods that involves machining of metals with intricate geometries through better surface finish and accuracy by the help of electrical sparks. It has wide range of applications in cutting and finishing of complex shaped components used in many industries such as electrical, automobile, electronics, biomedical, aerospace etc. We know that gears are extensively used in such industries for smooth transmission of power, which need appropriate finishing and machining operations to obtain better dimensional accuracy to mesh together with each other. So, different types of gears in large number are machined by wire EDM process to obtain desired qualities. Titanium gears are used in various engine applications such as rotors, hydraulic system components, aerospace and differentials due to its better mechanical properties than other metals. Titanium being a hard metal is difficult to machine by conventional methods due to its chemical reactivity having a tendency to weld with the cutting tool. Non-conventional cutting methods such as ultrasonic machining, electrochemical machining have also been explored for commercial machining of Titanium but found to have their own limitations; owing to low machining efficiency and poor geometrical accuracies involved with these methods. Wire EDM is a suitable candidate for machining of Titanium, and its applications in this context need a proper investigation. Titanium has reduced thermal conductivity (16.3 W/m-K) as compared to medium carbon steel (43 W/m-K), due to which a higher amount of heat is accumulated at the machining zone. As Wire EDM is a non-contact process, almost all these problems may be addressed. The present research deals with the manufacturing of spur gear made of Titanium alloy, Ti-6Al-4V machined with wire EDM to obtain optimized settings at different working conditions. Experimental investigations are carried out by varying four input factors i.e. pulse on time, pulse off time, wire feed rate and servo voltage at three different levels each. The experimental results confirmed that with the increase in the pulse on time, the response parameters i.e. MRR, kerf width, surface roughness and wire wear rate also increases machined by all the three wire electrodes (Uncoated brass wire, Brass wire with diffused coated zinc, Brass wire with rich coated zinc). The output responses for WEDM and the gears have been optimized and predicted using TOPSIS based GA and ANFIS technique respectively in order to get optimized settings. The
microstructural analysis and measurements have been carried out for both the machined workpiece and the wire surface at the obtained optimized settings. The numerical modeling is accomplished using ANSYS® for both the workpiece and the wire. The experimental results of the conventional WEDM are also compared with that obtained from ultrasonic vibration assisted (UVA) wire EDM giving vibration to the workpiece in order to study the effects of process parameters on different responses. The results confirmed that UVA-WEDM can be successfully employed to machine gears due to its higher machining rate neglecting the surface roughness of the gear.