| Summary: | 碩士 === 國立高雄應用科技大學 === 模具工程系 === 100 === Micro EDM provides a non-contact machining process with energy throughput directly into the working zone. Its machining energy can be stably controlled under a precise small level, therefore, its removal rate is small and its precision capability can produce real three dimensional micro parts and precision mold/die features. Conventional micro EDM processes rely on time-consuming Wire Electrical Discharge Grinding (WEDG) to achieve acceptable quality of micro tools and only 2-D contours can be conducted by the horizontal configuration. In this study, a rotational axis augmented to standard WEDG processes with ultrasonic assistance and its applications to efficient dressing are reported. Different inclined angles can be arranged from -15 degree to +15 degree. First of all, an ultrasonic assisted WEDG system (UA-WEDG) is developed for high-speed preparing helix or special profile of micro-electrodes to serve as tools. Significant effects on dressing efficiency by the novel UA-WEDG system were verified experimentally. It was found at least 23% of time saving can be obtained for WC tool electrodes from raw material of 500μm to 50μm in diameter.
Then, micro EDM drilling and milling are conducted with the prepared micro-tools. The machining efficiency and the surface quality of the micro EDM workpiece are major concerns. For micro-drilling with 0.3 mm of SUS 304 thin platelet, the proposed helical tools can reduce the machining time up to 35% over conventional cylinder tools of 100μm diameter. Its expansion of inner holes diameter is also significantly reduced in compared with cylinder tools. Because of its geometric properties, the helical surface contributed to expelling debris from the machining region, especially, in deep-hole drilling or long aspect-ratio machining. But, after considering the wear compensation of micro-tools through series of wear experiments and statistical regression, the novel tools reveals less significant time saving and almost negligible accuracy improvement for a single step EDM milling of a 0.5 x 0.5 area with 0.05 mm depth. Therefore, a novel WEDG mechanism with ultrasonic assisted rotational axis is established and a better configuration with new micro-tools is also introduced into the micro EDM fields.
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