| 摘要: | 石英具有壓電效應、化學穩定性良好等優異性質，因此廣泛被應用於微機電系統之關鍵零組件。但由於其硬脆特性，若以傳統之加工方式很難在效率與精度二者之間同時兼顧。電化學放電加工是以高溫熔融並且此高溫可加速蝕刻速率的非傳統加工方法，相當適合作為加工石英之製程技術。唯此製程技術中，仍然存在著許多有待釐清且改善的問題，其中氣泡於電極表面生成時的狀態不僅影響氣膜結構的緻密性，同時為影響放電火花效率的重要因素之一；並且氣膜受到氣泡不斷結合、脫離的影響下，使得氣膜處在此動態的環境中，穩定程度受到嚴重的考驗。有鑑於此，透過本論文的研究，逐步釐清、解析、並提供如何增加氣膜穩定性、加工效率的方法，以提升電化學放電加工之性能。 首先，由於不同電極材料的性質皆不相同，必須先針對不同電極材料去各別調整輸入電壓以得到各電極之轉折電壓。除此之外，為了能夠釐清氣泡貼覆於電極表面的狀態，應用不同粗糙度的電極表面進行測試，當電極表面粗糙度大而產生較大的接觸角，將增加成形於電極表面的氣膜厚度；在加工過程中，電極需能承受放電時的高溫，因此碳化鎢電極在連續加工50個微孔後，僅有端面有些微的損耗，而仍然不致於對加工精度造成影響。 另外，在電化學放電加工過程中，氣膜的穩定性及氣膜成形的型態為影響加工精度及加工效率相當重要的關鍵因素，為了增加氣膜的穩定性而提升加工精度，本研究以磁力的輔助提供另一方向的作用力(勞倫茲力)，促使氣泡能快速的脫離電極表面，避免影響氣膜的穩定性。從實驗結果得知，在添加磁力後，加工後孔徑標準差的變異程度減少80.7%，而同時藉由磁力提供氣膜薄化的效果，加工後孔徑縮小達24.6%的改善幅度，明顯的提升加工的穩定性及加工精度。除了提升氣膜的穩定性之外，電化學放電加工於加工深度的限制也是受限於氣膜成形的型態，若以一般常用的圓柱電極應用於加工時，由於圓柱電極的外形其直徑均相同，因此氣膜將填滿電極與工件之間的加工間隙，而阻礙電解液的循環。本研究為了徹底解決此問題，將製作具有多段式直徑之微球狀電極，利用多段式直徑的電極外形，當前端球狀外形(直徑150 μm)進行加工時，後端(直徑100 μm)包覆於電極表面的氣膜厚度將小於加工後的微孔直徑，可避免氣膜阻礙電解液的循環，影響加工效率。從實驗結果得知，在深度500 μm的加工下，加工時間及加工後孔徑與圓柱電極相比較，加工時間縮短了83%，加工後孔徑減少65%，可大幅度的提升加工效率，且在進行通孔加工時，微孔入出口及孔壁皆擁有更佳的形狀精度。 Quartz is the critical material used in MEMS due to its beneficial properties, such as piezo-electric effect and stable chemical properties. However, it is difficult to machine between the efficiency and accuracy using conventional methods. Electrochemical discharge machining (ECDM) is an emerging non-traditional machining process that involves high-temperature melting assisted by accelerated chemical etching. However, the electrochemical reaction affects the coalesce status of gas film in ECDM. The structure of gas film is in turn affected by efficiency and accuracy. Therefore, this research uses different methods to improve the stability of gas film and machining efficiency in ECDM. First, discharge energy varies with tool material of electrode. Different tool materials have different transition voltages, which determine the gas film formation, and hence the hole diameter and average current achieved. Otherwise, Surface roughness of tool electrode is key determinant of gas film formation. Poor surface roughness increases contact angle of gas bubbles adhered on electrode surface, causing them to coalesce and form a thicker gas film, resulting in largest hole diameter machined. During machining process, there is no significant tool wear observed after repeated gravity-feed machining of 50 micro-holes by using tungsten carbide tool electrode. In ECDM process, the stability and formation of gas film is in turn affected by the machining efficiency and quality. In order to improve the stability of gas film structure, this study attempt to use the magnetic effect keeps bubbles move quickly form the tool electrode. According to the experimental results, the stability of standard deviation in hole diameter was increased by 80.7% while hole diameter was also decreased by 24.6%. Besides, both machining efficiency and accuracy were found to worse with increasing machining depth. In particular, the machining gap between the electrode and micro-hole is completely filled up by the gas film when using the cylindrical tool electrode. To solve these problem, this study proposed using a tool electrode with a spherical end whose diameter (150 μm) is larger than that of its cylindrical body (100 μm). In other words, during machining by the spherical end, the thickness of gas film formed on the surface of electrode body would be smaller than that of the micro-hole machined. Comparison between machining depth of 500 μm achieved by conventional cylindrical tool electrode and the proposed spherical tool electrode shows that machining time was reduced by 83% while hole diameter was also decreased by 65%. |
