Dry-EDM milling of micro-scale features with high speed rotating tungsten tube electrodes

Micro electrical discharge milling is an alternative to die-sinking EDM for the machining of three-dimensional micro-structures or cavities with free-form surfaces. An important advantage provided by micro-EDM milling for this purpose is the possibility to use simple pin or tube electrodes with diameters de ⤠500 µm. This reduces the manufacturing costs of the workpiece and decreases the setup time for positioning electrodes. The high density of conventional dielectric fluids and the resulting small working gap cause a severe contamination of the working gap with particles and as a consequence short-circuits and process instability. The use of gaseous dielectrics, like compressed air, leads to enhancements in the flushing conditions and the cooling of the tool and workpiece electrodes. The gas is injected through the tube electrode under high pressure, resulting in high flow velocities and a removal of melted material from the working gap. A new spindle with a maximum rotation speed of n ⤠400,000 rpm was developed by the Institute for Machine Tools and Factory Management IWF of the Technische Universität Berlin for the realization of micro dry-EDM milling with tube electrodes. The high speed rotation of the tool electrode stabilizes the process and increases the material removal rate due to better flushing conditions. This paper presents the equipment and machining results of dry-EDM milling of simple micro-scale features.