Search

The ZrB-SiC-graphite composite is a promising engineering material for ultra-high temperature applications. However, the fabrication of micro-hole in this ceramic composite is difficult due to the high hardness. This paper presents micro-electrical discharge machining (EDM) drilling of the ZrB-SiC-graphite composite using the micro sheet-cylinder tool electrode to improve the machining efficiency and quality of micro-hole. The micro-hole is firstly drilled by the sheet segment of electrode under the high capacitance, and then finish drilling is conducted using the cylinder segment of electrode under the low capacitance. The material removal rate, surface roughness, surface microcracks, debris, and material removal mechanisms are investigated. It is found that the material is removed by melting/evaporation and thermal spalling during micro-EDM of the ZrB-SiC-graphite composite, and the thermal spalling effect produces the large size irregular debris. The electrode with the sheet shape can significantly increase the machining efficiency compared with the electrode with the cylinder shape. Furthermore, the surface roughness is reduced in finish drilling with the low capacitance. The experiment results of micro-holes machined by the sheet-cylinder electrode demonstrate that the presented method can improve the machining efficiency, surface quality, and machining accuracy. [ABSTRACT FROM AUTHOR]

Tool electrode wear varying with different materials in electrical discharge machining (EDM) is unavoidable, thus inevitably reducing the machining quality and accuracy of microstructures. To convert this disadvantageous phenomenon into a beneficial process, the paper proposed a wear-variation EDM (WV-EDM) approach to fabricate a laminated disc electrode (LDE) with stable-shape micro channels on the outer edge surface; this electrode was subsequently used to machine micro grooves on workpieces by EDM. The WV-EDM formation of the LDE, the relationship between relative volume wear rate of the disc foils and the machining depth, and flow field distribution in the machining gap of the LDE during processing were investigated. The results show that the method proposed herein could reliably produce LDEs with stable micro channels on the outer edge surfaces that could subsequently be employed to continuously machine micro groove arrays with the same machining depth on the same material workpiece by EDM, and especially LDE reshaping was unnecessary. Additionally, the "pump effect" of the vortex, located in the flow field between micro channels on the LDE and workpiece, was beneficial for debris removal. Using the proposed method, micro groove arrays and columnar microstructures were successfully fabricated on Ti–6Al–4V alloy workpieces. [ABSTRACT FROM AUTHOR]