結合微放電與研磨技術之高精度微孔加工研究

Study of Micro-EDM combined with Abrasive Finishing method to Micro-hole

劉弘松(Hung-Sung Liu)

指導教授 ： 顏炳華

國立中央大學/工學院/機械工程學系/博士(2005年)

摘要

高精度的微細孔洞，一直是微細加工技術所追求的目標之一，由於微孔廣泛應用於微閥、微射流口、微感應器、微模具等場合，因此如何使用經濟的方法，來製造高精度的微細孔洞，是本研究的重點。微細放電加工法(micro-EDM)係運用傳統的放電加工原理，以高加工精度、少去除量，微小且穩定能量型態，加工任何導電材料；是製作形狀複雜或硬、脆、韌等難加工材料微細元件的有效方法，這種非接觸式的加工技術經常用來製作孔徑小於100μm的微孔的有效方法之一，但在微細放電加工後，由於工具電極的消耗，會使加工後之微孔形成錐度狀，且微孔的孔壁表面會形成再凝固層、微裂痕與放電坑，孔壁的表面粗糙度不佳，嚴重影響微孔的孔徑尺寸及幾何形狀精度。由於微孔無法以傳統的內圓磨加工法進行加工，因此本研究提出結合微細放電與研磨的精修技術，針對微細放電後表面粗糙度不佳的微孔進行改善研究。
本研究提出的四種研磨精修技術，分別為螺旋研磨法、抖動研磨法、超音波振動研磨法及電解拋光法，針對微細放電後之微孔或異形微孔，進行線上的研磨精修加工，改善微孔的孔壁表面品質。實驗結果顯示，以精修微細圓孔為例，採用螺旋電極研磨法或高頻抖動研磨加工法，孔壁表面均可獲得顯著的研磨效果，表面粗糙度值由研磨前之2.11 Rmax降低至0.85 Rmax，在研磨加工時間上的比較，螺旋電極研磨法約需120分鐘；利用此加工法搭配超音波振動，則加工時間可降至30分鐘，而採用高頻抖動研磨法僅需15分鐘。針對異形微孔；採用超音波研磨法或電解拋光法，由AFM量測表面粗度值顯示，孔壁表面粗度值Rmax由0.957μm(Ra 0.11μm)降至 0.31μm(Ra 0.015μm)；再由SEM的觀察顯示，孔璧表面甚為光平。在研磨加工時間上的比較，超音波振動研磨法約需45分鐘，而電解拋光法僅需5分鐘，即可得到光滑平整的微孔孔壁。

關鍵字

微放電加工 ； 線放電研磨 ； 抖動研磨 ； 電解拋光 ； 微細孔

並列摘要

High precision micro-holes are one of the objectives that can be fabricated by micro machining method. Since micro-holes are widely used in the micro-valve, micro-fluidics, micro-sensor and micro-mould applications, an economical and effective method producing high accuracy micro-holes is focused in this thesis. Based on the traditional electrical discharge machining (EDM) principle, the micro-EDM can be utilized to fabricate conductive materials with high precision, less material remove rate, micro and stable energy state. Micro-EDM is an effective method to produce fine devices with complex shapes. Hard, brittle or tough materials are easily fabricated by this process. This noncontact manufacturing process is frequently used to produce micro-holes with diameter less than 100 ?m. However, micro-EDM will cause recast layer, discharge craters and micro-cracks on the machined surface with poor surface quality. This affects the precision of diameter and the geometric shape. Moreover, owing to the wear of the electrode during the process, not only will the dimension of the machined micro-hole be changed, but also its shape is severely distorted. Unfortunately, the conventional grinding is difficult to refine the machined surface by inserting the micro-tool into the micro-hole. To solve such problems, in this study, some different finishing methods, followed after the micro-EDM process, were developed to produce a superior refined surface of the micro-hole with almost no machining defects.
After the micro-hole is made by micro-EDM, four kinds of finishing methods will be applied to improve the surface quality of the micro-hole. The four finishing methods are helix grinding method (HG), high frequency dither grinding method (HFDG), ultrasonic vibration grinding method (UVG), and electropolishing method (EP). The shapes of the micro-holes investigated in this study are not only the circular type but also the special shape. Experimental results show that the surface roughness of the micro-hole can be well refined without micro-cracks by each of the proposed methods. For the circular shape of the micro-hole, the HFDG takes only 15 minutes to improve the work surface from 2.11 to 0.85 μm Rmax, while the HG and the UVG require 120 and 30 minutes respectively. By using UVG or EP, the surface roughness of the micro-hole with special shape can be improved from 0.957 μm Rmax (0.11μm Ra) to 0.31 μm Rmax (0.015μm Ra), which is measured by AFM. However, the EP takes only 5 minutes, while the UVG requires 45 minutes.

並列關鍵字

dither ； Micro-EDM ； WEDG ； electropolishing ； micro-hole

參考文獻

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