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Machining of micro rotational parts using electrical discharge machining

Bearbeitung von Mikrorotationsteilen mit Hilfe des elektroerosiven Abtragens
 
: Piltz, S.; Röhner, M.; Uhlmann, E.

Rajurkar, K. P. ; Ex One Company, Irwin/ Pa.:
15th International Symposium on Electromachining. Proceedings : April 23 - 27, 2007, Pittsburgh, Pennsylvania, USA
Lincoln, Neb.: University of Nebraska-Lincoln, Industrial and Management Systems Engineering, 2007
ISBN: 0-9794977-0-1
ISBN: 978-0-9794977-0-4
pp.247-251
International Symposium on Electromachining (ISEM) <15, 2007, Pittsburgh/Pa.>
English
Conference Paper
Fraunhofer IPK ()
mechanisches Bauteil; Rotation (Drehung); Mikrobearbeitung; elektroerosives Abtragen; elektroerosives Schleifen; Drahterodieren; Drahtelektrode; Umfangsgeschwindigkeit; Materialabtragung; Finite Elemente Methode; numerische Strömungssimulation; Wärmeleitung; Hydrodynamik; elektrische Entladung; Oberflächenrauigkeit; Strömungsgeschwindigkeit

Abstract
Micro rotational parts are used in several industrial sectors. Well-known applications are micro shafts of gears, ejector pins in forming tools, pin electrodes for micro ED-drilling or micro stamping dies. Depending on the geometric complexity of micro rotational parts different process variants of micro electrical discharge machining characterized by a rotating workpiece can be used: 1. Wire Electrical Discharge Grinding (WEDG) with fine wire electrodes (50 microns). 2. Electrical Discharge Turning (EDT) with micro structured tool electrode. 3. Cylindrical Electrical Discharge Grinding (CEDG) with micro profiled disk electrode. Characteristic to these process variants is the superimposed relative motion between the rotating electrodes and the feed. This relative motion can be varied in a wide circumferential velocity range to improve the material removal process. The paper gives an introduction to the analysis of electrical, thermal, and hydrodynamic effects (amongst others: FEM and CFD results) influencing the process behavior with respect to technological requirements of micromachining. The investigations about the role of the relative movement according to the process behaviour of Micro Electrical Discharge Machining led to conclusion that several heat-conductive, hydrodynamic or pulse-electric effects must be taken into account. It has been determined, that the relative movement between both electrodes does not cause a premature break down of the spark, but leads to pulsating current. The assumption of a stationary discharge channel can be derived from this. The influence of the relative movement on the heat conduction is, however, only relevant on circumferential speed above v(ind u) = 2 m.s(exp -1) or on discharge duration longer than t(ind e) = 10 micro s, as the FEM-simulations have shown. Optical based measurements of single discharges confirmed the tendency of decreasing crater size with rising velocity of the relative movement. In contrast, the surface roughness produced by series of discharges increases with rising speed. This result led to the further assumption, that improved flushing conditions because of the relative movement effect an increase of the power density and the process efficiency respectively. CFD simulations clarified the increase of the flow rate with rising velocity. But the dielectric fluid flows produce also a substantial change of the hydrodynamic pressure, thus a removal process free of machining forces can no longer be assumed. According to the current state of the investigations the conclusion follows, that a relative movement with high circumferential speed should be used only for removal-intensive machining operations.
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: http://publica.fraunhofer.de/documents/N-76233.html