Exploring the feasibility of novel coated wires in wire EDM of Ti-6Al-4 V aerospace alloy: a case of multi-pass strategy

Abstract

Wire electric discharge machining (WEDM) is a thermoelectrical process wherein workpiece surface integrity still remains a concern due to process-generated thermal damage. Recent developments in WEDM, such as the use of novel coated wires and multi-pass strategy, present opportunity for reducing this thermal damage and improve surface integrity. Available literature shows that only uncoated wires have been used with multi-pass cutting strategy. Present work reports on the integrated benefits of coated wires with multi-pass cutting technique while employing three coated wires, namely brass core Zn coated, Broncocut Type X (Cu core-ZnCu50 coating) and Topas Plus X (Cu core-double Zn-rich layer coating), to machine superalloy Ti-6Al-4 V in view of its extensive aerospace applications. Five output responses involving workpiece surface roughness, over cut, cutting speed, material removal rate and recast layer thickness have been assessed. Each experiment constituted one rough pass followed by two trim cuts with each cut taken at offset/input parametric settings appropriate for the individual cut type. For comparison purposes, baseline experiment was conducted with uncoated brass wire using the same input parameters employed for rough and rough plus trim cuts for other coated wires considering the fact that rough cut is intended for high material removal, while trim cuts focusing on better surface integrity. Results show that Topas Plus X wire outperformed other wire types investigated in this work. Up to 8% reduction in Ra value, up to 31% increase in cutting speed, up to 26% higher material removal rate (in rough cut) and up to 40% lesser recast layer thickness have been obtained with Topas X wire. Though coated wires resulted in much better performance otherwise, however, higher “overcut” was observed for all coated wires when compared with the simple brass wire. Also, trim cuts that succeeded the rough passes produced crack-free surfaces.