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Micro electro discharge machining of electrically nonconductive ceramics

: Schubert, A.; Zeidler, H.; Wolf, N.; Hackert, M.

Postprint urn:nbn:de:0011-n-1748814 (1.8 MByte PDF)
MD5 Fingerprint: efc52982d1a0cb275932917e10fcf778
Copyright AIP
Created on: 22.9.2011

Menary, G. ; American Institute of Physics -AIP-, New York:
14th International ESAFORM Conference on Material Forming 2011 : 27-29 April 2011, Belfast
New York, N.Y.: AIP Press, 2011 (AIP Conference Proceedings 1353)
ISBN: 978-0-7354-0911-8
ISBN: 0-7354-0911-0
ISSN: 0094-243X
International Conference on Material Forming <14, 2011, Belfast>
Conference Paper, Electronic Publication
Fraunhofer IWU ()
micro electro discharge machining; ceramic; zirconium dioxide; assisting electrode; vibration

EDM is a known process for machining of hard and brittle materials. Due to its noncontact and nearly forceless behaviour, it has been introduced into micro manufacturing and through constant development it is now an important means for producing high-precision micro geometries. One restriction of EDM is its limitation to electrically conducting materials. Today many applications, especially in the biomedical field, make use of the benefits of ceramic materials, such as high strength, very low wear and biocompatibility. Common ceramic materials such as Zirconium dioxide are, due to their hardness in the sintered state, difficult to machine with conventional cutting techniques. A demand for the introduction of EDM to these materials could so far not be satisfied because of their nonconductive nature. At the Chemnitz University of Technology and the Fraunhofer IWU, investigations in the applicability of micro-EDM for the machining of nonconductive ceramics are being conducted. Tests are undertaken using micro-EDM drilling with Tungsten carbide tool electrodes and ZrO2 ceramic workpieces. A starting layer, in literature often referred to as "assisting electrode" is used to set up a closed electric circuit to start the EDM process. Combining carbon hydride based dielectric and a specially designed low-frequency vibration setup to excite the workpiece, the process environment can be held within parameters to allow for a constant EDM process even after the starting layer is machined. In the experiments a cylindrical 120 mm diameter Tungsten carbide tool electrode and Y2O3- and MgO- stabilized ZrO2 worpieces are used. The current and voltage signals of the discharges within the different stages of the process (machining of the starting layer, machining of the base material, transition stage) are recorded and their characteristics compared to discharges in metallic material. Additionally, the electrode feed is monitored. The influences of the process parameters are analysed with regard to the discharge type, electrode wear and process speed. Using the found parameters, micro geometries can be successfully machined into nonconductive Y2O3- and MgO- stabilized ZrO2 ceramic by means of micro-EDM.