Prediction Of Aspect Ratio Of A Micro Hole Drilled By Micro EDM

Micro holes are widely industrial products such as fuel nozzles. Micro electrical discharge machining (EDM) drills micro holes with various advantaged characteristics such as no mechanical contact between the electrode and workpiece and regardless of strength of workpiece material over other processes. However, in the process of micro holes drilling by micro EDM, It was found that the machining speed slows down and even stops when the aspect ratio reaches a certain value. The theoretical model to describe the relationship of the aspect ratio of micro hole and its related process parameters is rarely published.Based on the energy and frequency of electrical discharges, a theoretical model is proposed to predict the aspect ratio of micro hole in normal discharge machining process in micro EDM to understand the mechanism of the limitation of the aspect ratio of a micro hole drilled by EDM.60holes are drilled under different conditions to verify this model. Experimental results match the theoretical ones well within the error of9.79%. The reasons causing the relative errors are analyzed theoretically and experimentally.In the process of micro holes drilling by micro-EDM, the planetary movement of electrode is applied to achieve high aspect ratio of micro hole. To obtain the maximum machining efficiency, it is necessary to select proper parameters for planetary movement of electrode. This paper proposed a theoretical model to calculate the velocity of electrode planetary movement in XY plane. It was found that the optimal material removal rate (MRR) can be achieved when the scale factor, k, is set within range of0.36±0.03. This model has been verified by experimental results.All drilling experiments and electrode preparation were conducted using the numerical control program developed by myself.