Features of Controlling the Process of EDM Cutting with a Thin Wire Electrode
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ures of Controlling the Process of EDM Cutting with a Thin Wire Electrode B. L. Ovsyannikova, * and A. B. Shvetsovab, ** a
Moscow Polytechnic University, Moscow, 107023 Russia bOOO ELGES, Moscow, 119602 Russia *e-mail: [email protected] **e-mail: [email protected]
Received March 25, 2019; revised June 6, 2019; accepted June 7, 2019
Abstract—An electric discharge micromachining experiment is described. The features of electroerosive cutting of parts by a wire electrode-tool with a diameter of 7–20 μm were studied. The results are interpreted using the developed mathematical model of the EDM cutting process, accumulating available experimental data on the EDM process dynamics with a nonrigid wire electrode. The problem of the stability of microprocessing with a thin wire when using the discrete feed of the electrode tool is investigated. The ways to achieve the maximum cutting speed under given conditions are determined. Keywords: electroerosive processing, microprocessing, cutting, electrode-tool, stiffness, dynamics, control, mathematical model, stability DOI: 10.3103/S1068375520040110
INTRODUCTION The reason for the research, whose results are given in this article, was the initially unsuccessful attempt to produce thin grooves in copper billets using electroerosion cutting with a thin wire electrode tool (WET) and, further, wire-cut electrical discharge machining (WCEDM). Similar operations are used for the manufacture of miniature precision parts both in electronic technology and in other high-tech fields. We conducted testing of cutting modes on the mock-ups of equipment designed for WCEDM. For the manufacture of grooves, WET made of tungsten with a diameter of 8 μm was used. The supply of WET was carried out using a step drive. Initially, the step size was 1 μm, while tracking systems were used to track the position of the WET guides using an optical feedback system and a feed-rate stabilization system with peak voltage feedback on the interelectrode gap (IEG) on the principle of “forward, stop, retraction.” The experiments showed high process instability. Regular occurrence of short circuits (SC), self-oscillations in the stabilization system of the feed rate and, as a result, low cutting speed were observed. The purpose of this work is to elucidate the causes of the emerging instability of the WCEDM process and develop measures to overcome the problems encountered in managing the processing method.
REVIEW OF PROBLEMS IN CONTROLLING THE EDM CUTTING PROCESS AND STATEMENT OF THE RESEARCH PROBLEM We will clarify the preliminary parameters of the investigated process. In the general case, the diameter of a tungsten or molybdenum WET lies in the range of 7–20 μm. WCEDM is characterized by special electrical modes. The pulse duration is in the range of 0.01– 1 μs, and the discharge energy is 0.01–0.5 mJ. The pulse repetition rate can reach 200 kHz or more. Such processing parameters are characterized by very small values of the distances between the electrodes and small WET tension forces. The task of controlling the
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