對於放電加工而言,加工表面因為放電融熔所形成的再鑄層,表面布滿放電火花衝擊造成有許多的放電坑 (Crater)與微裂(Microcrack),影響加工表面的品質,因此通常在放電後還要進行拋光後製程,才能達到精密模具的要求。本研究乃提出以電流變液(Electrorheology fluid)作為放電加工液,並添加磨粒結合放電加工與拋光的機制,在同一個製程下進行放電加工以及拋光,開發一個創新式複合加工的新製程。在放電加工的場合下,電極與工件間可達數kV/mm電場,電流變液在這電場下會產生纖維狀的鏈結構,若在電流變液中添加磨粒,配合電極的旋轉速度,將形成一個強力粘附磨粒的拋光刷,而可以對放電加工的表面進行品質改善。實驗結果證實,電流變液並不影響放電加工的基本行為,可以作為EDM之介電液進行放電加工,但是電流變液濃度越高時放電效率會越低。添加適當濃度的電流變液與氧化鋁磨粒(10-10wt%),在放電加工的製程下對工件同時進行拋光,可得到Ra0.06μm之加工表面,使工件達到奈米等級良好的表面粗糙度。
The objective of this study is to develop the combined technology of EDM with ER as work fluid .The surface of workpiece after machining by EDM has a re-casted layer, many micro-craters and cracks. The polishing is usual method to solve this problem, which is performed after EDM and add extra cost. In the study, we proposed a novel method of EDM by using ER (Electrorheological) fluid. In ER fluid the starch particle will gather and become the fibrous chains due to polarization when the electrical field achieves several kV/mm between the electrode and work-piece. And then the fibrous chains become a polishing blush with abrasives such like Al2O3. It is possible to develop the new EDM process to satisfy the fine machined surface in the one process. The experimental results show the ER fluid can work for EDM but decrease D.F. with increasing the ER concentration. We have the good performance Ra 0.06μm with ER -Al2O3(10-10wt%) in the combined process with electrical discharge machining and polishing.