Machinability of Ti-5Al-2.5Sn for electro-discharge machining: an experimental investigation
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Sådhanå (2020)45:238 https://doi.org/10.1007/s12046-020-01479-y
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Machinability of Ti-5Al-2.5Sn for electro-discharge machining: an experimental investigation THRINADH JADAM and SAURAV DATTA* Department of Mechanical Engineering, National Institute of Technology, Rourkela 769008, India e-mail: [email protected] MS received 20 October 2019; revised 1 July 2020; accepted 29 July 2020 Abstract. Present work attempts to investigate machinability of Ti-5Al-2.5Sn for Electro-Discharge Machining (EDM). Extent of machinability is determined through material removal efficiency, tool wear rate, and surface integrity of the EDMed specimen of Ti-5Al-2.5Sn. Detailed analysis of surface morphology followed by study of surface topographical features including surface roughness, crack density, thickness of the recast layer, foreign material migration, metallurgical phase, residual stress, and micro-indentation hardness are carried out. Disappointing morphology is noticed for EDMed work surface at higher values of peak current as well as pulse-on time values. It is experienced that occurrence of surface cracks depends on recast layer thickness. As compared to ‘as received’ workpiece exhibiting compressive residual stresses, tensile stresses are found induced after performing EDM operation. Similar phenomenon is experienced in case of tool electrode. EDM operation improves microhardness of the machined surface. For Ti-5Al-2.5Sn, such improvement is nearly three times than that of ‘as received’ work material. During EDM operation on Ti-5Al-2.5Sn, titanium carbide is formed over tool as well as work surface. Formation of such hard carbides may degrade machining efficiency. Keywords. Ti-5Al-2.5Sn; Electro-discharge machining (EDM); surface integrity; crack density; recast layer; residual stresses.
1. Introduction Titanium (Ti) and Ti-alloys are extensively used for aerospace, and biomedical applications due to their excellent properties such as high strength-to-weight ratio, high temperature stability, appreciable biocompatibility, and high corrosion as well as wear resistance. In spite of increased utility of titanium alloys, capability to produce parts with high productivity, and superior quality becomes challenging. During conventional machining of Ti-alloys, following problems may arise. • While machining, cutting tool gets deformed due to strength, and hot hardness of the workpiece. • While machining (of titanium alloys), abrasive sawtooth edges are, often, formed due to its high dynamic shear strength. These abrasive saw-tooth edges promote notching of cutting tools. • During machining, machine tool chatter, and excessive tool wear are incurred. • Extremely high temperature is localized at tool-tip due to poor thermal conductivity of the work material.
*For correspondence
• Due to generation of huge cutting temperature, welding of cutting tool edge to workpiece takes place. Thus, formation of ‘Built-Up-Edge’ (BUE) deteriorates surface finish, and affects component integr
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