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Simulation of relevant process variables for electrochemical etching

: Neugebauer, Reimund; Knüpfer, H.; Wolf, K.; Roscher, H.-J.

Electromagnetics Academy, Cambridge/Mass.:
Progress in Electromagnetics Research, PIERS 2008. CD-ROM : Cambridge, USA, 2-6 July, 2008
Cambridge, 2008
Progress in Electromagnetics Research Symposium (PIERS) <2008, Cambridge/Mass.>
Fraunhofer IWU ()
elektrochemische Bearbeitung; elektrochemisches Ätzen; Simulation; Prozessparameter; Vibrationsantrieb; Piezoaktor; electrochemical machining; electrochemical etching; simulation; process parameter; vibration drive; piezoactuator

The process of electrochemical etching requires the existence of an electrolytic bath and two electrodes with a certain distance in between, which is called the gap width. For an intensive etching process the gap between the electrodes should vary over short periods. The increase of the gap provides the possibility to rinse the removed material. Material which is ablated by the process of electrochemical etching in an electrolytic bath must be removed by rinsing. A periodic expanding of the working gap between electrode and work piece is essential for an intensive etching process. The duration of the rinsing process should be kept short for the reason of efficiency. Small working gaps lead to high contour accuracy during the etching process itself. The arising process forces reach to kilo Newton range. Thereby, a short circuit between electrode and work piece must be avoided. By the usage of new high dynamic actuators instead of powered drive solutions a profile of the electrode movement could be realized, which is better adapted to the process requirements. This article introduces a Simulinkr model (under simplifying assumptions) for the determination of relations between the movement of the electrode and the arising forces in the working gap. The results are fundamental input data for dimensioning of actuating elements.
State-of-the-art for the adjustment of the gap size is to use a powered drive. A motor-driven tappet provides a sinusoidal curve of the gap width over time. A rectangular-shaped gap over short periods would be optimal. Moreover, the motor-driven approach requires large electrical engine power and high effort for the positioning accuracy of the tiny etching gaps. To overcome these problems high dynamic actuators, for example piezo-stacks, can be used because they can act with relatively high frequency and high accuracy while providing high reaction forces and the necessary stroke. To prove the usability of different actuators simulations were done, which are introduced in the first section. This section also introduces the physical model of the system from which the differential equations and the Simulinkr model are derived. The behavior of the system and conclusions concerning dimensioning of certain input parameters are discussed in the following section. Finally, the last section provides conclusions and an outlook. As the simulations show, the realization of a piezo-based vibration drive is very promising. Since the estimated spring stiffness of the piezo actuator as well as the electrode mass are realistic values, they are retained. The working gap can be forced to be relatively constant caused by the nonlinear system properties and by applying a drive frequency which is advantageous to the resonance frequency. Additionally, a trapezoid excitation performed by the piezo actuator is reasonable to achieve the desired gap shape. The large reaction forces limit the minimal working gap to approximately 10 micrometer at relatively small electrode shell areas. The resulting opened gap should be large enough for the rinsing. The next step is to verify the simulation results by doing measurements of the system. On basis of the results the model can be improved by considering the masses of the actuator and the linear drive as well as its stiffness. Additionally, the shell area can be calculated depending on the gap width and the real dynamic viscosity of the liquid should be used.