Abstract
This paper investigates theoretically the sensitivity of spark location measurement in EDM processes and gives useful information which can contribute to improvement of the measuring sensitivity. The spark location measurement is carried out with the branched electric current method, in which the discharge current is supplied to the electrode through several branched wires, and each spark location is obtained from the ratio of the branched currents. The calculated calibration curve which relates each spark location to the distribution of the branched currents is obtained from the finite-difference analysis of the electric potential distribution in the electrode considering the contact resistance of the feeding points where the branched wires are connected to the electrode. In the course of the analysis, the influences of the contact resistance at the feeding points, the shape of the electrode, and the feeding position on the sensitivity, are studied and the following conclusions are obtained : (1) Although the contact resistance at the feeding points cannot be neglected, it is possible to get the calculated calibration curve which coincides well with the measured calibration curve by taking the contact resistance, which is measured experimentally, into account. (2) A hollow electrode is more effective to improve the sensitivity when a thicker electrode is used. (3) It is possible to get a higher and more uniform sensitivity by feeding the current at the top of the hollow electrode rather than at the bottom.
