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This paper develops a new combined technology to fabricate complex 3D microstructure based on micro milling and micro sinking electro-discharge machining (micro-SEDM). Graphite microform electrode is in-situ prepared by micro milling and subsequently used for micro-SEDM, integrating the advantages of two processes. Material removal rate (MRR) and electrode wear ratio (EWR) are experimentally investigated to determine proper parameters for different micro-SEDM performances. Three different machining strategies including single, double and treble micro-SEDM are adopted to fabricate 3D microstructure. The surface roughness, size accuracy, machining duration and cost of micro-cavities, and electrode wear under different strategies have been compared. The results show that treble micro-SEDM produces superior surface quality with 0.83 μm Ra and size accuracy with ≤ 28.05 μm tolerance. The proposed method broadens the machining flexibility and capability of micro-fabrication techniques. [ABSTRACT FROM AUTHOR]

Abstract: A new micromachining method for the fabrication of micro-metal structures by using micro-reversible electrical discharge machining (EDM) was investigated. The reversible machining combines the micro-EDM deposition process with the selective removal process, which provides the ability of depositing or removing metal material using the same micro-EDM machining system. From the discharge mechanism of micro-EDM, the process conditions of micro-EDM deposition were analyzed firstly. Using the brass and steel materials as a tool electrode, the micro-cylinders with 200μm in diameter and height-to-diameter ratio of more than 5 were deposited on a high-speed steel surface. Then the machining procedure was transformed easily from deposition to selective removal process by switching the process conditions. Different removal strategies including micro-EDM drilling and micro-EDM milling were used in the machining. Micro-holes with 80μm in diameter are drilled successfully in the radial direction of the deposited micro-steel cylinder. Also, a brass square column with 70μm in side length and 750μm in height, and a micro-cylinder with 135μm in diameter and 1445μm in height are obtained by using micro-EDM milling. Finally, the characteristics of the deposited material were analyzed. The results show that the material components of a deposited micro-cylinder are almost the same as those of the tool electrode, and the metallurgical bonding has been formed on the interface. In addition, the Vickers-hardness of 454Hv of the steel deposited material is higher when compared to the hardness of 200Hv of the raw steel electrode. [Copyright &y& Elsevier]