An experimental investigation into the micro-electro-discharge machining behaviour of aluminium alloy (AA 2024)

Abstract

Aluminium (Al) alloys are extensively used in all areas of manufacturing including automotive and aerospace industries due to its lightweight, excellent machinability, good surface finish at high cutting speed, low cutting forces and outstanding tool life. Although Al alloys have excellent machinability with conventional machining processes, electric discharge machining (EDM) and micro-EDM are often used to machine intricate features in Al alloys for plastic injection moulds and electronic applications. Present study aims to investigate the influence of various operating parameters on the micro-EDM behaviour of an important Al alloy AA 2024, commonly known as ‘Duralumin’. The machining behaviour has been investigated by engraving micro grooves on the surface of the AA 2024 using different parameters settings from a resistance-capacitor (RC) type pulse generator. The operating parameters studied were capacitance, resistance, supply voltage, electrode rotational speed and gap control parameters. The micro-EDM machinability of the AA 2024 alloy was evaluated in terms of the material removal rate (MRR), tool wear ratio (TWR), surface roughness (SR) and machining depth of the micro grooves. It has been found that the increase of capacitance and voltage results in increase of discharge energy, causing higher MRR at the expense of higher tool wear and rougher machined surface. On the other hand, too low capacitance and gap voltage result in unstable machining by creating arcing and short-circuiting, which again makes the surface defective in addition to reducing the machining speed. The careful selection of gap control parameters improves the machining stability by reducing the arcing and short-circuiting as well as improves the overall machining performance. For stable micro-EDM with higher machining speed and improved surface finish, the identification of optimum parameters is needed. With this said, the recommended settings of parameters for micro-EDM of AA 2024 were found to be the voltage of 160 V, capacitance of 10,000 pF and resistance of 470 Ω, spindle speed of 720 rpm, gap feed rate of 0.01 mm/s, gap control factor of 50 and gap threshold voltage of 80 %.