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Micro electrical discharge machining (micro EDM) provides an alternative in generating complex 3-D micro features in difficult-to-machine materials. The micro EDM performance depends not only on machining parameters but also on the microstructures and micro-characteristics of materials. The effect of free surface layer of austenitic stainless steel on the micro EDM performance is investigated in this paper. Experiments are carried out by machining multilayer stainless steel workpieces without and with surface treatment (acid pickling and oxidation treatment). Surface layer model is built to demonstrate the increasing influence of surface layer on micro EDM performance when the size of workpiece is decreased. The surface free energies of AISI 304 workpieces are estimated by measuring the contact angles. The results show that the steel workpiece with oxidation treatment has the highest surface free energy and the highest material removal rate compared with those without treatment and with acid pickling treatment. The influence of surface layer of steel workpiece on micro EDM performance is more significant when the discharge energy is lower due to size effects. Taper ratio of machined holes on steel workpiece without treatment is much higher than those of holes on steel workpieces with acid pickling and oxidation treatment. As a conclusion, surface treatment of steel workpiece before machining is an effective method to improve the machining efficiency and machining precision of micro EDM, especially when involving the sub-micro or nano-machining where machining is conducted on the workpiece surface. • Surface layer model in micro EDM has been developed to demonstrate the increasing influence of surface layer with decreasing size of workpiece. • The higher the surface free energy, the higher the MRR, the less the taper ratio of machined hole. • The influence of surface layer of workpiece becomes more significant when the discharge energy is lower. [ABSTRACT FROM AUTHOR]

Electrical discharge machining (EDM) is one of the most promising non-traditional micro-scale machining methods. Because several operating parameters that are insignificant in macro EDM cannot be neglected during micro EDM process, models derived from the macro EDM process may be inappropriate at the micro scale. This paper contains a comprehensive review of size effects in traditional micro-machining and characteristics specific to micro EDM compared to macro EDM techniques. The very concept of size effects in micro EDM is thoroughly defined and three categories of effects are presented: material microstructure, processing parameter and thermal conduction size effects. Future potential research directions on the subject are also summarized. We assert that careful research and precise attention must be given to size effects in micro EDM. Size effect information especially benefits the machining speed and machining precision of micro EDM. [ABSTRACT FROM AUTHOR]

Micro electrical discharge machining (micro EDM) is able to remove conductive material by non-contact instantaneous high temperature, which is more suitable for machining titanium and its alloys compared with traditional machining methods. To further improve the machining efficiency and machined surface quality of micro EDM, the nano particle surfactant mixed micro EDM method is put forward in this paper. Experiments were conducted to explore the effect of nano particle surfactant on the micro EDM performance of titanium alloy. The results show that the material removal rate of micro EDM in dielectric mixed with TiO2 is the highest when open-circuit voltage is 100 V, followed by Al2O3 and ZrO2. Lower tool wear rate can be produced by using dielectric mixed with nano particle surfactant. The taper ratio of micro EDM in dielectric mixed with nano particle surfactant is higher than that in deionized water. The surface roughness Ra of micro EDM in dielectric mixed with TiO2 can be 50% lower than that in deionized water. It is helpful to improve the machining performance by adding surface surfactant in the dielectric of micro EDM. [ABSTRACT FROM AUTHOR]

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 Ra 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 Ra 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. [ABSTRACT FROM AUTHOR]