Machining behaviour modulation of electrochemical milling via manipulation of inter-electrode gap: From electrochemical machining to electrochemical discharge machining

The inter-electrode gap (IEG) is a key factor in electrochemical machining (ECM), which directly governs the electric resistance of machining and affects the flow field. In conventional electrochemical milling, the actual IEG expands with the material removal of the workpiece, which increases the electric resistance and renders the electrolyte flow ineffective in transporting the electrolytic products. In this paper, a sinking push mode for electrochemical milling is proposed to minimise the IEG, thus improving material removal rate (MRR). Under a small IEG, electrochemical discharges are observed and damages the workpiece. Arising from this observation, electrochemical discharges are intentionally introduced to further improve MRR. And the material removal process is transformed from mere ECM to electrochemical discharge machining (ECDM). Furthermore, a novel ECDM-ECM mode is developed to eliminate the recast layer produced by discharge action. In this mode, the machining behaviour from ECM to ECDM can be altered by simply manipulating IEG distribution. Multiphysics simulations coupling electric field and flow field are conducted to better understand the mechanisms of the proposed modes. The IEG distribution, transient current behaviour, MRR, energy efficiency, surface integrity and tool wear are discussed by experiments. The ECDM-ECM mode successfully eliminates the recast layer with high MRR in a single controllable process, demonstrating its potential for producing high quality surfaces with high throughput. • A sinking push mode is proposed to minimise the IEG in electrochemical milling. • Fast electrolyte flow is employed to break potential electrochemical arcs. • Stray corrosion is avoided by achieving a high ending current density. • Machining behaviour from ECM to ECDM can be adjusted by controlling IEG. • A novel hybrid ECDM-ECM mode is proposed to effectively remove the recast layer.