主動式氣膜輔助電化學放電鑽孔加工之研究

Abstract

電化學放電加工法常用於對玻璃這類非導電硬脆材料進行加工，但是利用電化學放電進行鑽孔加工仍然有許多地方需要克服，例如鑽孔深度、加工速度和加工後孔的錐度。本文主要是於中空管狀電極內施打空氣，使孔內電解液受到空氣擾動，促使電解液進入加工孔內，研究目的在於觀察於中空電極內施打空氣對電化學放電鑽孔加工所造成的影響。實驗結果顯示，由於施打的空氣氣泡向上漂浮，改變電極側面局部絕緣層厚度，而無法產生較穩定的絕緣氣膜，降低電極側面放電火花發生的機會，故能獲得較小的擴孔量與較佳的孔錐度，但卻因為電極側面放電不均勻的關係，使得孔壁粗糙度下降。鑽孔加工過程中，未施打空氣之電極端面放電火花多為點狀分布，火花面積較小，個別放電柱出現的時間間隔短，持續時間也短；在中空電極內施打空氣時，電極端面之放電火花面積較大且較旺盛；所施打之空氣有助於在電極底部形成較為完整之絕緣氣膜，使同一時間內產生大量之放電柱，且由於空氣的導入，也有助於排渣，故能提升加工速度。此外，施打的空氣往液面漂浮時，會造成加工孔內電解液的擾動，有助於電解液流入孔內，故能提高加工深度。就整體而言，於中空管狀電極內施打適當流量的空氣，將能達到增加鑽孔深度、提高加工速度與改善孔之錐度的效果。

Electrochemical discharge machining (ECDM) is usually used to machine non-conductive brittle materials such as glass, but it still has a lot of problems such as the machined depth, the machining rate and the taper. In this study, a hollow tube electrode was conducted and the air was injected through it. The electrolyte in the hole would be disturbed by the injected air and flow deep into the hole. The purpose of the paper is to investigate the effect of the injected air during electrochemical discharge drilling process. The experimental results showed that the injected air would affect the local thickness of the gas film around the side of the electrode and made it unstable. As a result, the unstable gas film made sparks hardly take place around the side of the tube electrode, and the reaming and the taper would be less as compared with that when machining without injecting air into the tube electrode. But the surface roughness inside the wall would be worse because sparks around the side of the electrode could not appear uniformly. Injecting air into the hollow tube electrode contributes to form much evener gas film under the bottom of the electrode, so sparks under the electrode would be much stronger and take place in a larger area. Besides, injecting air into the hollow tube electrode would induce a scavenging effect, and the machining time would be reduced. The electrolyte in the hole would be disturbed by the injected air and penetrates into the hole much deeper; the machined depth could be increased at the same time. In conclusion, injecting air into the hollow tube electrode could improve the machined depth, the machining rate and the taper.