Effects of flushing on electrical discharge machining and electro-arc machining

Abstract

Both electrical discharge machining and electro-arc machining are non-contact machining processes, which use high temperatures produced by discharges to erode material. The gap between the tool and the workpiece is usually filled with liquid dielectric medium. Moreover, liquid flushing is commonly used in the machining processes of electrical discharge machining and electro-arc machining. Much research has been conducted to study the effects of flushing on these processes. However, there has been little study on the mechanism of the flushing procedure for these machining processes. In this article, electrical discharge machining and electro-arc machining experiments adopting different polarities and flow rates were designed and implemented. The plasma tunnel and crater morphology were studied. It was found that the plasma tunnel was lengthened, compressed and broken by flushing in the electro-arc machining experiment; however, the electrical discharge machining experiment did not produce this result. Similarly, tailing discharge craters and polarity effects caused by flushing were observed in the electro-arc machining experiment, while no such performances caused by flushing were found in the electrical discharge machining experiment. The flushing in electro-arc machining was able to reduce the material removal rate, tool wear rate and surface roughness simultaneously, while the effects of flushing in electrical discharge machining were inconspicuous. Moreover, the characteristics of the plasma tunnels of the electro-arc machining experiment were similar to those of arcs, which were different from those of the electrical discharge machining experiment. These results help to verify that the electro-arc machining process adopts arcs, while the electrical discharge machining process adopts sparks, during their respective material removal processes.

Electrical arc machining: Process capabilities and current research trends

“…Zhang et al. 4 performed the EAM on W18Cr4V tool steel by varying the flow rate (0–3 L/min) of pure water dielectric. They concluded that too high flushing reduces the MRR and TWR simultaneously.…”

“…Zhang et al. 4 observed that the surface quality in terms of SR improves with the increase in the dielectric flow rate during the EAM of tool steel. Higher flow rate reduces the crater diameter, which in turn reduces the SR. Zhu et al.…”

“…The research available till date shows that researchers have used pulse duration of up to 20,000 µs in the EAM. 4…”

“…In the RMABM, the relative motion between tool and workpiece (such as rotation, vibration, jumping, and shaking) is utilized for the breaking of arc plasma. 4 In the HABM, the tubular or bundled hollow electrode is used and dielectric is fed (Injection or suction mode) in the machining zone through this electrode. The strong hydrodynamic force and turbulence exerted by dielectric elongate, compress and breaks the plasma channel and in this way stationary arc is avoided.…”

Dielectric flow observation at inter-electrode gap in micro-electro-discharge-milling process

“…The dielectric flushed in the gap does not affect plasma tunnel and crater developed in the gap. 12 It is well agreed in the literature that the physics of mEDM process is complex and many contributions have been reported on the analyses of plasma formation, crater mechanism, heat transfer and so on. But very few researchers have used computational fluid dynamics (CFD) approach to simulate and study the machining aspect of a process.…”