Breakthrough phenomena in drilling micro holes by EDM

Abstract

Although electrical discharge machining (EDM) is widely used in the manufacturing industry for drilling small through-holes, the phenomena occurring at the moment the tool breaks through the workpiece are not yet fully understood. In order to gain further insight into this matter, an approach based on processing the gap voltage signal is proposed in this study. This approach enables to analyse how variations in the flushing mechanism of the debris particles affect the discharging behaviour during the last stage of the drilling process. The experimental results indicate that the maximum duration of the time intervals in which the arcs and short circuits occur suddenly increases once the tool first breaks through. Conversely, the average duration of the time intervals in which the open circuits occur shows a decreasing trend after the breakthrough, even though the total amount of time spent in open-circuit state increases. On the basis of the observed phenomena, possible solutions for detecting the completion of the through-hole's drilling process are discussed. A strong influence of the parameter regulating the servo feed on the occurrence of arcs, short and open circuits has been also observed. An optimised drilling strategy to reduce the amount of time spent in breakthrough stage is proposed and experimentally tested. This strategy allows to reduce the time for the tool electrode to completely breakthrough by about 60%.