Improvement of electrochemical drilling deep holes using combinatorial tube electrode with a suitable leading flow structure

Deep holes with high quality are extensively demanded in such industrial applications as aviation. Electrochemical drilling (ECD) is a promising technique for fabricating deep holes in difficult-to-machine materials. However, at the initial machining stage, the electrolyte flow in the inter-electrode gap changes dramatically from expansion flow to converging flow, which may affect the machining process. To address this, a leading flow structure is developed to confine the electrolyte flow when machining the hole entrance, which helps to improve processing stability. A height of 10.0 mm for the leading flow structure is found to be sufficient for ensuring the fine entrance profile and machining stability. Furthermore, the normal tube electrode commonly causes misdistribution of electrolyte flow and current density at the hole bottom, generating defects such as spikes and striations, which limits its application in deep holes requiring a flat bottom. Therefore, a combinatorial tube electrode is proposed to enhance the distribution of flow and electric fields by changing the cross-section at the tube tip, resulting in a defect-free flat bottom. Based on these findings, two typical deep holes, a through hole and a flat-bottomed blind hole, were successfully fabricated with high quality, as so the machining capability and processing stability had been prominently enhanced.