鉬金屬具有高強度、高硬度、高熔點、高熱傳率、良好的導電率及熱膨脹係數小等優點；廣泛應用於需要耐高溫的場合。因為鉬金屬具有優異的機械性質，於是在使用傳統加工法對鉬金屬進行加工時，會造成刀具嚴重磨損。 放電加工法是利用火花放電去除材料，此方法具有不受限於材料強度、硬度、韌性等性質之優點。因此本研究擬定以鉬金屬為工件材料，探討其放電加工之特性。另一方面如同一般金屬，鉬金屬放電表面會形成再鑄層，其中包含了微裂痕與放電坑等缺陷，因此表面粗糙度不佳，會嚴重影響表面的品質，所以本論文利用電解拋光法針對放電後的鉬金屬表面進行加工，並探討電解拋光法對放電表面改善之效果。 由實驗結果顯示，鉬為高熔點的金屬材料，所以工件正極性時需要較大的能量密度或是使用負極性加工，才不會造成電極消耗率遠高於材料去除率。電解拋光部分，可將表面粗糙度Ra與Rmax由原始放電加工面的0.9μm和8.5μm降至0.23μm和1.48μm，改善率Ra與Rmax分別可高達74.4%與82.5%。 Molybdenum is a refractory metal characterized with high melting point、good strength、low coefficient of thermal expansion、good thermal and electrical conductivity. Although it is widely used in high temperature applications, its superior mechanical properties cause it very difficult to be machined into high quality surface on parts. The EDM is a kind of electro-thermal process which removes the material by melting and vaporization routes without directly touching the surface. This study presents an experimental investigation of the machining characteristics of molybdenum by electrical discharge machining (EDM). However as general condition after EDM, the residual microcracks and craters on surface may seriously affect the machined quality. In order to further improve the EDMed surface of molybdenum, the electropolishing (EP) treatment was taken and the effects of process parameters were also analyzed in the second part of study. Experimental results show that the polarity of EDM has a great deal effects on machining of molybdenum. Using positive polarity (+) of workpiece must apply greater energy density to remove material. But using negative polarity (-) of workpiece apply small energy can remove material. The original surface roughness of EDMed molybdenum can be improved from 0.9μm Ra and 8.5μm Rmax to 0.23μm Ra and 1.48μm Rmax, after EP process. It is evident that the EP process is an effective method to enhance the EDM surface quality by improving rate up to 74.4% Ra and 82.5% Rmax.
