Investigation of depth error of microgroove in micro-EDM adopting ultrasonic circular vibration (UCV) electrode

The unstable discharge status can greatly reduce the machining accuracy in micro-EDM of microgrooves. In order to solve this issue, a novel micro-EDM method using ultrasonic circular vibration (UCV) electrode was proposed in this study. A sandwich-type UCV electrode driving device with working frequency of 32.85 kHz was developed, and its basic principle was analyzed. Meanwhile, as the discharge gap and electrode wear are also crucial factors affecting the actual machining depth of microgrooves in EDM, this study proposed the concept of erosion depth coefficient, which is further used for the depth error compensation. To better understand the influences of UCV electrode on the machining depth of microgroove, the orthogonal experiments were carried out, and the influences of various process parameters on the erosion depth of microgroove were analyzed through ANOVA. Results showed that compared with the rotating electrode, the UCV electrode can generate larger bottom gap distance during the microgroove milling process, and more even discharge waveforms with complete discharges were observed. Meanwhile, under the same compensation strategy, the ultimate depth error in the case of UCV electrode is less than that in the case of rotating electrode. What is more, as the feed depth has tiny effect on the erosion depth coefficient when UCV electrode is used, the depth error compensation still shows better accuracy with the increase of machining depth. This study verified the feasibility of UCV electrode mode in micro-EDM, and the erosion depth coefficient can provide a new thought for the compensation of electrode wear and discharge gap in the microgroove machining process.