A feasibility study on wire electrical discharge machining of carbon fibre reinforced plastic composites

This paper details preliminary experimental work to investigate the wire electrical discharge machining (WEDM) of unidirectional carbon fibre reinforced plastic (CFRP) composites using a high tensile strength zinc rich coated brass wire (0.25 mm diameter). A fractional factorial L18 Taguchi experimental design was employed to evaluate the influence of varying open gap voltage (120 and 140 V), ignition current (3 – 5 A) as well as pulse on-time (0.8 – 1 µs) and off-time (4 – 8 µs) on material removal rate (MRR), top (Wt) and bottom (Wb) kerf widths as well as workpiece edge damage. The ignition current and pulse off-time were found to be statistically significant factors affecting MRR based on an analysis of variance, with percentage contribution ratios (PCR) of 48.5% and 24.3% respectively. It was observed that MRR, which ranged between 0.43 and 2.41 mm3/min, increased with both ignition current and pulse on-time due to the higher discharge energy generated in the machining gap. No signs of workpiece damage in terms of delamination or surface burning was apparent, despite the higher MRR. Conversely, the larger open gap voltage surprisingly led to reductions in MRR, which was likely due to unstable gap conditions caused by greater levels of residual melted resin within the gap or re-deposition on the workpiece surface. In terms of kerf width, ignition current was revealed as the sole significant factor with respect to the top surface (up to ~ 0.28 mm) having a PCR of 56.6%, while none of the variable parameters had a major effect on the bottom kerf width.