電化學加工製作微電極錐度改善之研究

Abstract

在微細加工的領域中，微放電加工中的線放電研磨法常用於製作微細電極，利用線放電研磨法將長2mm之微電極ψ0.3mm製作成ψ0.1mm，需耗時25分鐘以上。去除量小、加工速度緩慢等是需要克服的問題。而微電化學加工相對來說具有許多優勢，例如高的材料移除率、無加工變質層、無熱變形、無毛邊及良好的表面品質，且製程相對簡單，可節省設備經費，並可提升微電極之加工效率。但一般使用電化學加工製作微電極，會產生錐狀及底部針尖狀的電極，其應用在微放電鑽孔加工上，會產生嚴重的錐孔問題。故本文主要著重在改善電極外觀輪廓以降低電極錐度。本研究提出兩種方法，第一種方法是將ψ0.3mm的碳化鎢電極末端沒入壓克力盲孔中，對電極底部絕緣。以此法進行微電化學加工，可製作出ψ0.05mm、長3mm以上之電極，且明顯降低微電極之錐度，將總加工時間控制在5分鐘內。第二種方法為噴流式電化學加工，將電極間距控制在0.05mm以下，製作出ψ0.08mm、長2mm之電極，除了明顯降低微電極之錐度外，加工時間更縮小至2分鐘。本研究成功利用電化學加工法製作出與線放電研磨法形狀相同之微電極，除克服電極錐度問題外，並大幅提升製作電極之加工效率，對於製作微電極來說是一個明顯較有效率的製程。

Wire Electro-Discharge Grinding (WEDG) process is commonly used to fabricate the microelectrodes. Generally, it would take more than 25 minutes to fabricate a 2mm length microelectrode from the diameter of 300μm to 100μm. So the low material removal rate and the time consuming of the WEDG process are the problems to overcome. Moreover, by the Micro-ECM (Micro Electrochemical Machining) process, though the high material removal rate, bright surface finish, no stress or burrs, no tool wear and ability to improve the efficiency of microelectrode could be obtained, the fabricated microelectrode would have a taper angle and a needle tip. It would cause a serious tapering problem when this electrode is used to fabricate the hole by micro-EDM drilling. Thus, this study is focused on the developing a method of fabricating a micro tungsten carbide electrode by Micro-ECM with an insulated blind hole which is made of PMMA material in the end of the electrode to reduce the taper angle. Experimental results show that a 3mm length tungsten carbide rod was fabricated from the diameter of 300μm to 50μm with no tapering, and the consuming time is less than 5 min. Another method of flushing Micro-ECM process was also proposed. During the flushing Micro-ECM process, under the condition of the inter-electrode gap less than 50μm, a 2mm length microelectrode could be fabricated from the diameter of 300μm to 80μm. The consuming time could even be controlled within 2 min. In conclusion, fabricating the microelectrode with the developed method, the taper angle could be reduced and also apparently improve the efficiency.