Fabrication of microstructures with mirror surfaces by wire electrochemical micromachining of stainless steel 304 using NaNO3-ethylene glycol

Microstructures with superior surface quality have been becoming more and more important in many fields. Various methods have been exploited to fabricate high quality microstructures. Among those approaches, wire electrochemical micromachining (WEMM) is an effective and efficient way to manufacture micro components. Generating passive film on the workpiece is an alternative to improve surface quality in WEMM, which necessitates a delicate selection of electrolyte. NaNO 3 solution as a passive electrolyte is beneficial to obtain good surface quality, but it barely takes effect in WEMM. Herein, an attempt is made to combine ethylene glycol (solvent) and NaNO 3 (solute) to investigate its influences on surface quality in WEMM of stainless steel (304 SS). Electrochemical measurements reveal that 304 SS is subjected to secondary passivation in 1 mol/L NaNO 3 -ethylene glycol. X-ray photoelectron spectroscopy analysis indicates that the compositions of the passive films formed at various potentials are not exactly the same. Both the secondary passivation and the passive films make dramatic contributions to the improvement of the machined surface quality. Experimental results demonstrate that surface roughness achieved with ethylene glycol is Ra = 0.034 μm, noticeably smaller than that with traditional acid solutions. Finally, microstructures with ultra-smooth surfaces are fabricated on the 304 SS plate.