微放電複合製程之微型工具製作技術及其精微加工研究

A study on micro-tools fabrication in micro-EDM hybrid process for micro-machining

洪榮洲(Jung-Chou Hung)

指導教授 ： 顏炳華

國立中央大學/工學院/機械工程學系/博士(2007年)

摘要

微放電加工法是以高精度、微加工量、微小且穩定能量，加工微小且形狀複雜或具有特殊機械性質之難加工導電材料的一種有效方法。但微放電加工後，由於工具電極的消耗會使加工後之微結構形成錐度狀，且加工表面會形成再凝固層、微裂痕與放電坑，造成形狀精度不佳。再加上無法以一般傳統研磨加工法對微結構進行精修加工，因此本研究提出新式微放電複合製程精修加工技術，並發展出製作圓柱狀與圓球型等微型工具成形技術，可有效應用於精微模具加工而使模具達到高精度與高品質的表面形狀精度，以符合工業所需。
本研究提出兩種複合製程技術，分別為微工具搭配超音波振動游離磨粒之研磨技術，以及複合電鍍嵌入式磨粒後的微工具成形技術並探討其精微加工特性。首先針對微放電後之微圓孔與方形微孔進行研磨精修加工。實驗結果顯示，採用螺旋電極研磨法或微型圓柱狀研磨工具加工法，微細圓孔孔壁表面均可獲得顯著的精修效果；螺旋電極搭配超音波振動研磨法加工約25分鐘後，表面粗糙度值由研磨前之Rmax 1.35 μm降低至0.58 μm，而採用複合電鍍鎳-碳化矽後的微型圓柱狀工具加工時，表面粗糙度值可由研磨前之Rmax 1.47μm降低至0.46 μm。針對方形微孔而言，採用方柱狀工具搭配超音波振動研磨法，當加工45分鐘後表面粗度值Rmax可由0.96 μm降至0.31 μm。另外，對於微型球面模穴加工則是利用電極末端放電形成微球後，經複合電鍍鎳-鑽石後之微球型工具進行加工測試，可加工出一球面模穴，若搭配游離磨粒加工時，更可獲得Rmax 0.35 μm的微模穴表面。

關鍵字

複合電鍍 ； 超音波振動 ； 微放電加工 ； 微型工具 ； 複合製程 ； 微孔 ； 微模穴

並列摘要

The micro-EDM can be used to machine complex shape conductive hard-to-machine materials with high precision, less material remove rate, micro stable energy. 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, the electrode wear not only will the dimension of the machined structure be changed, but also its shape is severely distorted. Unfortunately, the conventional grinding is difficult to refine the machined shape accuracy by inserting the tool into the micro-hole. To overcome these issues, novel hybrid processes combined with micro-EDM were applied to effectively machine a micro-structure with high accuracy and quality surface.
This study describes two hybrid processes that are micro-tool with ultrasonic vibration free abrasive grinding method and co-deposited micro-tool with grinding method. The circular and square micro-holes are investigated in this study. Experimental results show that the surface roughness of the micro-hole inner-wall can be well refined without micro-cracks and micro-craters by each of the proposed methods. For the circular micro-hole, using a helical micro-tool with ultrasonic vibration grinding method takes only 25 minutes to improve the machined surface from 1.35 to 0.58 µm Rmax, while using a co-deposited micro-tool grinding method can improve the machined surface roughness from 1.47 to 0.46 µm Rmax. By using a square micro-tool with ultrasonic vibration grinding method, the surface roughness of the square micro-hole inner-wall can be improved from 0.96 to 0.31 µm Rmax. Moreover, after EDM spherical forming, a micro-spherical tool is made by Ni-diamond co-deposition. A smooth surface of micro-spherical cavity can be gained using the micro-spherical diamond tool and better one has surface roughness 0.35 μm Rmax can be finished by combining with free abrasive grinding.

並列關鍵字

co-deposition ； ultrasonic vibration ； micro-EDM ； hybrid process ； micro-tool ； micro-hole ； micro-cavity

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