Multi-scale surface integrity and plasma erosion mechanisms in micro EDM of Nimonic 90 A using SEM–AFM analysis

The most widely applied process for machining nickel-based superalloys is micro-electrical discharge machining (EDM); however, sustaining good surface quality together with high material removal rate continues to be difficult. This paper examines the effects of discharge current (3–9 A), pulse-on time (2–6 µs), and pulse-off time (1–3 µs) on machining characteristics and surface quality of Nimonic 90 A alloy. Cu was used as the electrode in micro-EDM operation in a deionized water. Performance characteristics like overcut, taper angle, tool wear rate (TWR), and material removal rate (MRR) were used to characterize machining performance. Results show that amplification of the plasma channel led to a dramatic increase in the MRR from 0.031 mm 3 /min at 3 A to 0.049 mm 3 /min at 9 A. The overcut follows a non-linear behavior, where amplification of the plasma channel causes overcut to reduce to 0.0158 mm under moderate level parameters and then increase to 0.0175 mm under high level parameters. Precision reduces with increase in taper angle from 0.0024 to 0.0029 as the discharge energy increases. MRR increased from 0.038 to 0.042 mm 3 /min as the pulse-on time increased from 2 to 6 µs and TWR increased to 1.06 mm at 4 µs. It is evident that the decrease of the pulse-off times between 1 µs to 3 µs resulted in a decline of MRR by 0.041 to 0.035 mm 3 /min. Nevertheless, there was an improvement in overcut by 0.022 to 0.010 mm. At high discharge energy, there was a formation of craters with accumulation of debris.