Fabrication of ZrB₂–SiC–graphite ceramic micro-nozzle by micro-EDM segmented milling

The micro-nozzle is an important component of the micropropulsion system for accelerating the gas flow. However, the 3D ceramic micro-nozzle is difficult to machine due to its small complex structure and high hardness of material. In this study, micro-electrical discharge machining (EDM) segmented milling is proposed to fabricate the ZrB₂–SiC–graphite ceramic micro-nozzle. To improve the machining efficiency and reduce the electrode wear, the micro-nozzle is machined using two tool electrodes with different diameters. The inlet and outlet segments of micro-nozzle are machined by the large diameter electrode, and the throat segments are fabricated with the small diameter electrode. The effects of layer thickness, tool electrode feedrate and electrode diameter on machining performances are investigated in preliminary experiments, and the proper machining parameters are determined. The processing tool-path is planned for producing the micro-nozzle with consideration of the dimension error induced by the machining gap. The micro-nozzle with the conical convergent section and parabolic divergent section is successfully machined, exhibiting high processing efficiency and machining accuracy. It is demonstrated that the proposed micro-EDM segmented milling method is feasible for fabricating the ZrB₂–SiC–graphite ceramic micro-nozzle. (paper)