Effects of the dielectric flow rate of internal washing on micro-EDM drilling performance

Electro discharge machining technology is becoming increasingly important in micromachining thanks to its ability to ensure high precision without exerting force on each piece of conductive material. The main applications are injector holes in the automotive sector, the cavities necessary for film cooling in the aeronautical field and also in the electronics and medical fields. Usually, when high aspect micro holes are executed, internal washing through tubular electrodes is advised to facilitate debris evacuation from the machining zone. The internal washing pressure of the dielectric has to be set by the operator. Investigations into the effects of internal washing pressure were made in this work. Dielectric pressure was varied for electrodes of different diameters and materials. The performances were evaluated in terms of machining time, removal rate, tool wear ratio and geometrical indicators. It was found that machining time was connected to the dielectric flow rate, which affected the level of debris contamination in the dielectric. The dielectric flow rate depends on the internal washing pressure, the internal diameter of the electrode and the electrode length. The material removal rate was always higher for the low flow rates for all of the electrode diameters and materials that were tested. The electrode wear was also influenced by the dielectric flow. With low pressures, a larger amount of debris remained in the machining zone, and the change in the dielectric characteristics made the formation of discharge easier. This phenomenon improved the material removal rate but also increased the electrode wear. A connection between the contamination level and the overcut was also found. A visual investigation of both the electrode tip and the internal hole surfaces supported the assumption about the effects of debris on drilling performance.