一種線上加速度精密電解法於倒錐微孔噴嘴成形研究

Abstract

本研究旨在開發「加速度精密電解加工技術(Acceleration Precision Electro-Chemical Machining, A-PECM)」，目的在成形具有倒錐造型的噴嘴微孔，應用於如生醫方面的藥物塗佈、汽車工業的柴油引擎及半導體產業的濕式蝕刻等的噴嘴用途。實驗之初，先行開發一部「桌上型精微電解加工系統」，並提出「同位電解法(In-situ ECM)」，使精微鑽孔與精微電解兩製程能在同軸心條件下，精準對位創成。微孔電解所用電極係為直徑 0.1 mm的實心碳化鎢圓軸。為獲得高可控制性的電場分佈，實驗規劃以環氧樹脂絕緣法(Epoxy resin isolation)進行周面絕緣，只讓端部裸露導電。為獲得精密的倒錐微孔，本研究提出「加速度精密電解加工技術」電極於微孔內以一固定的加速度，由下而上進給，經由電極進給速度緩增，使微孔孔壁的電場強度由大逐漸變小，故孔壁的金屬溶解率(Metal Dissolution Rate, MDR)隨之緩降，進而創成倒錐微孔。並且，微孔中的電解液採由下而上的方向流動，以維持電解液濃度的一致性，使成形具高一致性孔壁的倒錐微孔。實驗結果顯示，電極以加速度1.0及2.0 m/s2於孔內進給時，可創造出0.09及0.02錐率的倒錐微孔，且微孔的表面粗糙度Ra小於 0.8 m，符合商用(柴油引擎)噴嘴微孔的標準。成形的倒錐微孔接以「二流體噴嘴」進行測試，發現在氣體壓力0.12 MPa及液體壓力0.04 MPa條件下，因錐孔兩端直徑的差異，能使錐率0.02和0.09的微孔分別獲得23°及31°的霧化角度，證實本研究所提出的「加速度精密電解加工法」，著實能成形精密倒錐微孔，此項技術深具商業化價值。

This study presents the development of an Acceleration Precision Electro-Chemical Machining (A-PECM) technology to create a micronozzle with an inverted tapered microhole which is applied for the pharmaceutical coating in the biomedicine, fuel injector spray in the diesel engine, and wet etching process in the semiconductor industry. To exactly align between the drilled microhole and the ECM’s microelectrode, an in-situ ECM (Electro Chemical machining) is proposed in this study and set up on the developed tabletop micro-electrolytic machining system. A solid tungsten carbide rod with  0.1 mm in diameter is employed as the microelectrode during ECM process. To obtain an electric field distribution with highly controllable, a peripheral insulation where the periphery of the microelectrode is clothed by the epoxy resin only leaving the end exposed to conduct electricity is recommended in this experiment. The A-PECM process, by which the electrode is fed from the bottom to the top in the hole with a constant and slow acceleration, is conducted on the tabletop micro-electrolytic machining system. The electrode’s feed-rate is gradually increased resulting in the electric field strength of electrolysis is gradually decreased which means the metal dissolution rate (MDR) is gradually reduced, thus creating an inverted tapered microhole. Moreover, the electrolyte maintains the consistency of the electrolyte concentration and flows designed from the bottom to the top of the microhole, thereby produces the microhole with highly uniform hole-wall. Experimental results show that the microholes with the 0.09 and 0.02 inverted taper rate can be precisely finished when using the acceleration of 1.0 and 2.0 m/s2, respectively. The surface roughness with Ra<0.8 m on the hole-wall can be finished which meets the demand for the commercial (diesel engine) nozzle microhole. The formed inverted tapered microholes were tested through a "two-fluid nozzle". It was found that the atomization angles of 23° and 31° can be successfully achieved when using the microholes with an inverted taper rate of 0.02 and 0.09, respectively and the conditions of gas pressure of 0.12 MPa and liquid pressure of 0.04 MPa. It is confirmed that the proposed A-PECM process canindeed form precision inverted tapered microhole, and this technology has great commercial value.