Performance Evaluation of Powder Mixed Electric Discharge Drilling for High Aspect Ratio Holes in Aluminium Alloy (AI7075)

Micro or meso holes are used in various applications, such as cooling channels in turbine blades, fuel injection nozzles, rocket injector plates, mold inserts for microfluidic devices, and micro-cannulae in medical devices. Producing these holes in high-strength materials through conventional drilling is challenging due to the significant tool wear, adhesion of chips, and deterioration of hole quality, resulting in distortion of geometrical features and surface quality, thereby leading to the rejection of parts. Thus, electric discharge drilling (EDD) has become the go-to method for creating micro holes. EDD offers several advantages over conventional drilling techniques. Nevertheless, during the drilling of high aspect ratio micro holes using electrical discharge machining, the machining quality deteriorates progressively as the hole depth increases. This is because of the accumulation of debris in the narrow gap area. EDD faces challenges such as high tool wear rate, increase in hole diameter, and taper during drilling of high aspect ratio hole. Therefore, in order to alleviate such problems, powder-mixed electric discharge machining has been explored in this study. A comprehensive study has been conducted, and the results have been compared in terms of Material Removal Rate (MRR), Taper Angle (TA), Tool Wear Rate (TWR), and Over Cut (OC) with and without powder mixed dielectric fluid to achieve high aspect ratio holes possessing better quality. The alumina mixed dielectric fluid was taken with varying concentrations of alumina powder (0, 0.5%, 1%, and 2% g/L) and investigated the effect of alumina powder on the performance characteristics. The performance characteristics have been examined using 1 mm diameter copper for holes with a high aspect ratio of 15. This study revealed that powder-mixed EDM (PM-EDM) showed better results as compared to its counterpart regarding desired upshots such as higher MRR and lower TWR, TA, and OC. With the addition of alumina (0.5% g/L) powder in pure deionized water, the percentage improvement in MRR was about 39 % and TWR, OC and TA were reduced by 57%, 21%, and 39%, respectively.