Effect of tube-electrode inner structure on machining performance in tube-electrode high-speed electrochemical discharge drilling

Film cooling holes are required in many crucial and widely used structures. The creation of good film cooling holes requires machining at high speeds with high accuracy and good surface quality. For this purpose, a promising hybrid machining method combining electrical discharge machining and electrochemical machining, called tube-electrode high-speed electrochemical discharge drilling (TEHECDD), has been proposed, which can be used for machining difficult-to-machine superalloys. In TEHECDD, the flushing condition is considered as an important element. To improve the flushing condition and further enhance the machining performance, improved tube-electrode structures, obtained by varying the inner diameter and inner shape, are introduced. In this study, different inner structures are designed for the tube electrodes, whereby the mechanism of the enhanced TEHECDD performance for different tube-electrode inner shapes are analysed and the effects of different tube-electrode inner structures on the machining performance are investigated. The results show that an increase in the tube-electrode inner diameter results in a higher material removal rate, smaller average bore diameter, and smaller taper angle. However, for the single-hole tube electrode, a larger inner hole results in the formation of a residual cylinder. Thus, the double-hole and multi-hole tube electrodes are proposed and found to be effective in removing the residual cylinder. Finally, it is verified that the tube electrodes with improved inner shapes can be used to further enhance the machining performance. The double-hole tube electrode is confirmed to have the optimal structure.