| Summary: | 碩士 === 國立高雄應用科技大學 === 模具工程系碩士班 === 101 === Micro EDM (µEDM) provides a non-contact machining process with energy throughput exerting directly at the working zone. Its machining energy can be controlled under a precise small level, therefore, its small removal rate and its precision capability can produce real three dimensional miniature and precision parts for complex molds’ or dies’ features. Conventional micro EDM use cylindrical electrode to achieve drilling and milling, but its efficiency of processing and debris expelling still remains much room for improvement. Some researches were focused on the helical tools in the past decade. Characteristics of micro helical tools and its application to ultrasonic assisted micro EDM processes are studied in this thesis. First of all, this paper is to explore further the characteristics of spiral thread and the practical application of better micro-helical electrode for discharge machining. Secondly, an aero-static table with ultrasonic vibration drive was designed in this thesis, associated with micro helical tools; to achieve ultrasonic vibration assisted micro EDM process. Its ultrasonic frequency is 42.6 KHz; the maximum output power is 95 W. Experimental results showed that the best helical electrode shape with helical groove depth ratio of 30% and pitch in 400 µm is able to achieve highest speed of micro EDM drilling for 0.1mm blind holes. This experiment confirmed such a helical tool without jump motion provides approximately 4.1 times of efficiency than that by cylindrical electrode. And compared to cylindrical electrode with jump motion, the helical tool still presents higher efficiency at 1.1 times efficiency. And the ultrasonic vibration assisted EDM increases the drilling efficiency up to about 13% further. Carefully compensating the wear of micro-tools, the ultrasonic vibration assisted micro EDM milling reveals faster processing time than no vibration assisted case by about 16%, and the surface roughness is also reduced by about 15%. The experiments verified combining the specific helical tool shape with ultrasonic high-frequency vibration assistance, both the micro EDM drilling’s and milling’s efficiency and surface roughness can be improved significantly.
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