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ABSTRACT
The present paper presents multi- objective optimization of Wire Electric Discharge Machining process parameters for machining of Ti 6-2-4-2 high strength temperature resistant aerospace alloy, with metal removal rate and overcut as performance characteristics. Box Behnken design and response surface methodology are used to plan and analyze the experiments. Six process parameters viz. Pulse on time, pulse off time, peak current, spark gap set voltage, wire feed and wire tension are taken as process parameters. Analysis of variance and F- test values are utilized to find out most significant parameters and to develop mathematical models. The optimal parameter combinations have been verified by conducting confirmation experiments. Results of confirmation tests show that the developed mathematical models are appropriate for effective machining of Ti 6-2-4-2 alloy using Wire Electric Discharge Machining.
Keywords: WEDM, Ti 6-2-4-2, Box Behnken designs, Response Surface Methodology, Multi Objective Optimization, Metal Removal Rate, Overcut
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1. INTRODUCTION
Titanium and its alloys are considered excellent materials for their applications in aerospace and automobile industries because of their improved mechanical and physical properties like higher strength, strength to weight ratio, toughness, corrosion resistance and oxidation resistance. However, due to these properties, titanium and its alloys are difficult to shape and machine into precise shape and size. Thus, their widespread applications have been hindered by high cost of machining (Aspinwall and Thoe, 1998). During conventional machining of Ti and its alloys, problems such as galling, welding and smearing along the cutting edges of the tool, causing rapid destruction of the cutting tool occurred (Leigh, Schuller and Smit, 2000). Moreover, due to poor thermal conductivity of Titanium and its alloys, most of the heat produced during conventional milling, turning remains concentrated in the cutting zone, which leads to failure of cutting edge and face of the cutting tool. Thus, upper speed limit of machining Ti is of the order of 300-350 SFM (Surface feet/ min). Beyond this range, a thin layer of metal near the surface is severely damaged. The extent of sub surface damage increases with increasing speed (Yang and Liu, 1998).
As conventional machining becomes impractical to machine Ti and its alloys, there is need to use non - conventional machining processes to machine such materials. Wire electrical...