Research On Modeling Aspect Ratio Of A Micro Hole Drilled By EDM

Micro electrical discharge machining (micro EDM) is widely used in manufacturing industry as one of the non-contact precision manufacturing methods. However, the mechanism of the limitation of the aspect ratio of a micro hole drilled by EDM is not clear. In the literature review, there is no related paper available to estimate the aspect ratio of a micro hole drilled by EDM. The experimental equipment of micro EDM is also necessary for this study.In this study, a set of vertical micro EDM is developed. A control system with NC function is also developed based on an existing horizontal micro EDM system, which includes modules of manual control, surface detection, spindle rotating control, data display, data record, auto control, etc.In the micro EDM drilling process, it is considered that the dielectric and debris are removed from hole by bubbles. When the aspect ratio of the micro hole reaches a certain value, the bubbles are not effectively removed from hole due to viscous resistance in the narrow discharge gap. The debris concentration in the narrow discharge gap results in abnormal discharges leading to excessive electrode wear, then the drilling speed will decrease or stop. Therefore, it is very difficult to drill a micro hole with high aspect ratio. To understand the mechanism of the limitation of the aspect ratio of a micro hole drilled by EDM, a theoretical model is proposed based on the micro fluid mechanics and surface tension to estimate the aspect ratio of micro hole in normal discharge machining process.Extensive experiment are carried out under two different machining conditions such as deionized water as dielectric and oil as dielectric in this study respectively. Experimental results agree well with the theoretical values, which indicate the proposed model is valid. The difference between the theoretical values and the experimental values might be caused by debris suspended in the dielectric, temperature change and rotating electrode in the discharge gap, which are ignored in the model. This model can be used as the fundament for the optimization of machining parameters for micro hole drilled by EDM.