Experimental investigation of magnetohydrodynamic effect in electrochemical discharge machining

Electrochemical discharge machining (ECDM) which is also known as spark assisted chemical engraving (SACE) is a machining process to machine non-conducting and brittle materials. Micro-ECDM presents several desirable properties featuring high flexibility, smoothly machined surfaces, and high drilling speed comparing with other micromachining technologies. The unstable gas film around the tool electrode in which the electrical discharges take place is unpredictable as the machining depth increases, resulting in inaccurate geometry and inconsistent machining. The material removal rate is significantly decreased due to insufficient electrolyte flow around tooltip in the hydrodynamic regime. These are the serious drawbacks of the process that need to be improved. This paper presents an analytical analysis of the magnetohydrodynamic (MHD) effect in the ECDM process. The mechanism of the magnetohydrodynamic effect in electrochemical discharge machining was investigated. The high-speed camera was used to record the formation of a gas film on the tool electrode with and without magnetohydrodynamics effect. The experimental results showed that the MHD effect induced by the magnetic field improved electrolyte circulation and higher machining efficiency was achieved. Furthermore, it was observed that the thickness of the gas film was decreased. The radius of the machined hole is reduced from 528 mu m to 430 mu m while the machining time was decreased from 50 to 16 s. The counter resistant feeding method and magnetic field can be applied simultaneously by the newly designed set-up. This hybrid method made significant enhancement in accuracy and throughput of the drilling process, as well as improving the roundness of the machined hole.