Micro-electrical Discharge Machining of Large Aspect Ratio Blind Micro-holes Using a Novel Self-Flushing Technique

Due to the debris accumulates in the central areas of the inter-electrode gap (IEG) and being difficult to evacuate in the micro-electrical discharge machining (micro-EDM) process, achieving a large aspect ratio (AR) for blind micro-holes remains a significant challenge. Based on our previous research on debris secondary flow distribution theory in micro-EDM, we propose a novel self-flushing technique using a center-slotted tool electrode to enhance debris evacuation in the central regions of the IEG. A simulation model was developed to analyze the motion and distributions of debris under the self-flushing technique operation. A simulation model was developed to analyze the motion and distribution of debris under the operation of the self-flushing technique. The results indicated that a secondary flow effect occurred within the IEG, concentrating most debris at the center. In comparison to the conventional solid cylindrical tool approach, the debris evacuated through the central slot pathway with the self-flushing effect. Experiments were undertaken to validate the model and the experimental results were well matched with the simulation. Furthermore, the machining efficiency was improved by 73.1% using the self-flushing technique. The slot position and width of the slotted tool electrode and speed of rotation was also shown an important contribution to the effectiveness of self-flushing. A blind micro-hole with an impressive AR of 27.42 (corresponding to a depth of 5.41 mm and an entrance diameter of 197.3 μm) was successfully drilled. This represents the highest AR reported to date for Ti6Al4V alloy using micro-EDM. This novel self-flushing technique is innovatively solved the challenge of difficulty in exhausting debris that accumulated in the center IEG due to the secondary flow effect. It is concluded that the novel self-flushing technique is highly transferrable to process a large AR blind micro-hole on Ti6Al4V alloys.