On-line determination of the working area on Sinking EDM

Wollenberg, G.
Schulze, H.-P.
Görisch, A.

Technical report for EDM TECHNOLOGY-Volume 4
EDM Technology T R A N S F E R
Otem, UT 94059 U.S.A. 1996

One of the most complicated problems of electrical discharge machining is to consider the variations in the effective working area occurring during machining. In order to roughen, if possible, at the maximum pulse energy without causing edge wear damaging the instrument electrodes, the working area has to be determined as accurate as possible. Another criterion of the efficiency of an area measuring system is the time necessary to determine the area and generate a control signal for the generator.
For very large working areas and their variations a number of methods are available which signal variations at an acceptable accuracy. However, these operations are very uncritical since most technological processes require considerably lower pulse energies so that the critical current density of machining is not reached. The situation is completely different with small working areas, e.g. smaller than 2 cm2. Here, however, even a very small parameter variation may cause exceeding of the critical current density of machining.
In most cases the profile starts with a very small working area which is changing continuously during machining. For this situation, the continuous variation of the area has to be determined and a new generator setting established to ensure minimum machining time for the roughing stage. The comparison of various measuring methods outlined in the following section shows that there are a number of restrictions for the determination of the area. For a universal measuring system, CAD coupling and fuzzy control integration should be considered as well.

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