Advancements in Micro Wire-cut Electrical Discharge Machining

Abstract

A WEDM process may be called as a Micro WEDM (MWEDM) process when it is used for manufacturing micro parts. The rest underlying theory is same as traditional WEDM. A micro part is machined with good dimensional accuracy and surface finish when the kerf (slot) width becomes considerably smaller compared to that obtainable in conventional WEDM. Truly speaking, the cutting tool in WEDM/MWEDM is not the wire, but it is the pulse (electrical discharge). A minimum kerf is ensured in Micro WEDM, when (i) pulse sizes are made extremely small, (ii) extremely thin wire is used (phi = 20-100 mu m), and (iii) process inaccuracies along with the discharge gap are minimized. It is required for Micro WEDM to maintain the pulse energy in the order of 10(-5)-10(-7) J. Process inaccuracies are minimised by minimising the amplitude of wire vibration and wire lag. Hence, for an MWEDM machine, the following subsystems are modified as compared to a conventional WEDM setup: (a) the machine tool configuration is designed mainly to eliminate stray capacitance or leakage of charges from the gap, (b) the pulse generator produces discharges with pulse energy preferably in the order of 10(-6)-10(-7) J, (c) a pulse discrimination system is installed to avoid arc or other abnormal discharges, (d) a closed-loop controlled proper wire transportation system is needed, (e) the wire diameter should be 20-80 mu m and preferably of tungsten, (f) a suitable oil dielectric is used and lastly, (g) a precise closed-loop controlled servo mechanism is used for gap and work-table feed control to operate at steps at submicron level.