The surface integrity of a micro electrical discharge machining (micro EDM) surface represents the surface quality of workpiece. The surface quality of micro EDM can be further improved by clarifying the machining mechanism and optimizing processing technology. In this paper, experiments were carried out to investigate the influence of the tool electrode diameter on the machined surface integrity of micro EDM. The evolutions of the tool diameter on the micro topography, element migration, and surface roughness of workpiece surface machined in pure water and EDM oil were illustrated. The results show that the surface roughness R
a decreases as the tool electrode diameter increased, regardless of the open circuit voltage and dielectric type, owing to the skin effect. The good fluidity and cooling property of pure water and the effect of electrochemical corrosion cause the surface roughness R
a of surface machined in pure water is much larger than that machined in EDM oil. Tool material migrates to the workpiece surface during the micro EDM process, whether pure water or EDM oil is adopted as the working medium. The influence of electrode size on the Cu content of the workpiece surface shows no significant trend. Pure water is more suitable for high efficiency, low-precision micro EDM, while EDM oil is better for high-precision micro EDM.
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