臺灣博碩士論文加值系統

本文針對微放電加工後工件表面問題進行創新的製程研究。放電加工後的工件表面會產生再鑄層與放電坑，一般都需再經過二次研磨加工，然而在微孔放電加工後再進行二次研磨加工，會因機台本身定位精度不足造成加工誤差，若能將放電與研磨兩種加工製程合併一起，即可解決定位精度問題。故本研究先將電極刀具進行複合電鍍，在電極表面上沉積鑽石顆粒，利用放電所產生的高溫將材料熔融至冷卻的這段時間內，使刀具表面之鑽石顆粒將熔融材料去除來防止再鑄層與放電坑的產生。本方法除了改善重覆定位精度問題，另可達到微孔平直輪廓及精細高品質的加工表面，以滿足業界對高品質表面微孔加工面的需求。
本實驗首先整合鎳-鈷/鑽石電鍍系統與一高速主軸，將已修整之微螺旋刀具電極在不需拆裝下直接於同一微放電機上進行低轉速鑽石複合電鍍。本實驗已證實，在同步放電與研磨加工板厚0.3 mm的SUS304圓孔時，刀具電極製作參數使用Ni-Co/Diamond (5g/l)，並配合電鍍時旋轉速度2 rpm、電流密度為7 ASD、鑽石粒徑6～12μm、電鍍時間5 min時，其鍍層內鑽石顆粒含量達31.77 wt(%)，而鈷含量為11.31 wt(%)。使用此刀具電極配合主軸旋轉速20K rpm、進給速度30μm/min、Z軸進刀深度2 mm時，加工面粗糙度有最好的表現，其值為Ra 0.107μm。而圓孔出入口孔徑差異為9 μm。另由同步微放電研磨加工(μEDMG)全圓孔之表面，發現本製程，可細分為三階段。第一階段: Z軸進刀深度為0~1.0mm時為放電加工打通孔，以及將圓孔尺寸進行擴孔至所需尺寸；第二階段:Z軸進刀深度為1.0~1.5mm時，為粗放電研磨加工，先將再鑄層隆起部分藉由鑽石顆粒拖移拉扯，讓再鑄層較為平坦；第三階段: Z軸進刀深度為1.5~2.0mm時，為細放電研磨加工，將經過粗加工之再鑄層研磨去除。
與本實驗室先前研究結果相比，本文至少報告兩點創新；即製備刀具及推進μEDMG實用可能性。
添加鈷離子作用:增加鍍層耐磨耗性能，與鑽石顆粒含量及分散性。
刀具形式分別從標準微放電用圓柱刀具修整成微螺旋溝槽，增加排屑效果，並進一步設計前端為引導用錐面，其錐面作用為，配合粗/細兩階段放電能量，先將工件加工出一通孔，以利後續細放電研磨。
由於過去μEDMG因使用圓柱電極，且無修整螺旋溝槽，故排屑效果不佳，僅能對板材側壁方向進刀5~10μm進行同步放電研磨製程，無法完成全圓孔之同步放電研磨，而本報告經以上改進，已完成於單一機台單一加工道次之0.33μm微孔之精密加工。
此外，同步放電研磨加工後，由SEM觀察加工面表面形貌，發現並非單純的放電加工或機械研磨機制，另有類似高溫塑性加工的現象。當發生放電現象時，電漿通道所產生的高溫，將金屬表面局部熔融，工件表面因加工液冷卻作用產生放電坑與再鑄層。而刀具電極表面上的鑽石顆粒，將未完全冷卻的再鑄層拉扯、拖移，進而將放電坑隆起處去除，並填平放電坑，因此留下塑性加工之現象。另由於放電脈衝週期短至數微秒，因此在粗放電研磨過程被鑽石顆粒剷起的屑片隆起處，優先再被放電作用，形成非典型的放電坑洞。

關鍵字: 微放電加工、微放電研磨、同步複合製程、Ni-Co複合電鍍、鑽石刀具

This research attempts to achieve a synchronized hybrid process of micro-EDM grinding (micro-EDMG, or μEDMG) on a single machine, it is aimed at saving the secondary precision grinding process after general micro-EDM process in micro-machining fields. First, the micro-tool of tungsten carbide was dressed to 0.3 mm diameter by a WEDG (wire electrical discharge grinding) system, and co-deposited in the nickel electro-plating bath with 6~12 μm of diamond abrasives. A low speed spindle is used for electro-plating, and then, another high speed spindle up to 20 KRPM is adopted to perform synchronous process of micro-EDM grinding. In our previous studies, it had been confirmed the feasibility of the synchronized micro-EDM and micro grinding process with 10 μm of lateral depth into work piece by precision positioning. However, there were severe problems of residual craters and debris accumulation, causing by the secondary discharge between both electrodes.
This study proposes two methods to overcome the defects and increase machining quality compared to the previous researches. One of them is to dress standard cylindrical micro-tool into the helical groove with a short taper, making the spiral grooves serve as the chips pocket to increase debris expelling efficiency. By appending cobalt ion into the plating bath to achieve Ni-Co alloy co-deposition, it is found that both more uniform dispersion of abrasives on the tool’s surface and richer diamond grains and stronger mechanical property in wearing resistance are achieved. By doing so, significant improvement of the precision quality and machining efficiency for such a hybrid process, and the anti-worn out capability of the micro-tool are verified through the conducted surface of micro-holes. Moreover, only one step of processing is required on the same machine and both higher efficiency and better quality by applying micro diamond tools to fabrication of under 0.33 mm micro-holes co-axially and precision circle with 0.3 mm thick of SUS-304 is achieved.
Fabrication conditions of micro diamond tools by Ni-Co co-deposition is conducted under Ni-Co/Diamond bath with 5 g/l of abrasives concentration, 2 RPM of rotation, 7 ASD of current density, and electro-plating interval of 5 min. It was verified from EDS analysis that the diamond amount occupied 31.77 wt(%) and cobalt element occupied 11.31 wt(%). Such a micro-tool with processes parameters of 20 KRPM, 30 μm/min and feeding depth of 2 mm depth achieved the best surface roughness of Ra 0.107 μm. Its diameter difference between entrance and exit also appeared to be the value of 9 μm. From oscilloscope observed EDM waveform and the 10 μm scaled SEM picture of tool’s profile, it is confirmed that synchronous micro-EDMG occurred during the operation processes.
Furthermore, it is found from the machined surface that there are three phases of EDMG processes contributed to this novel strategy. Namely, the first phase during machining depth of 0~1.0 mm along z-direction, it is dominated by micro-EDM drilling with roughing current of 0.5A. There is almost no grinding, or the grinding chips are totally re-discharged again by the second discharge process. The second phase during 1.0~1.5 mm is contributed to rough EDM grinding of the micro holes, some recast layers are pulling-pushed or scratched, and some craters are refilled to some sort of level. There seems some kind of hybrid machining effects around EDM spark’s spot. Finally, the third phase during 1.5~2.0 mm, there are some sort of complete grinding to remove the recast layers and craters to a fine surface in this finishing stage.
Besides, from SEM photo of 1 μm scale, it is found that not only simply EDM or simply mechanical grinding, but also plastic machining regions observed. They are contributed from micro-scale removing mechanism during micro-EDMG processes, in which recast layers are pulling-pushed and scratched to longer chips, and some craters are refilled again. On the other way, due to such a short period of EDM pulse on-time, the shoveled chip by grinding abrasive is the most possible position to be re-discharged again to shape a non-typical EDM crater.

Keywords: micro-EDM (electrical discharge machining), micro-EDMG (micro-EDM grinding), synchronous processes, hybrid Ni-Co co-deposition, Diamond Tool

中文摘要 i
英文摘要 iii
誌謝 v
目錄 vi
圖目錄 viii
表目錄 xi
符號說明 xii
第一章 緒論 1
1.1前言 1
1.2文獻回顧 2
1.3研究目的與方法 7
1.4本文架構 8
第二章 原理與沿革 9
2.1放電加工 9
2.1.1放電加工沿革 9
2.1.2放電加工原理 10
2.1.3微放電加工 12
2.1.4放電加工參數影響 13
2.2複合電鍍 16
2.2.1電鍍與複合電鍍沿革 16
2.2.2電鍍沉積原理 17
2.2.3複合電鍍沉積原理 19
2.2.4電鍍液成分介紹 22
2.3複合微放電研磨原理 25
第三章 實驗設備與規劃 27
3.1實驗設備 27
3.1.1微放電加工機系統 27
3.1.2高、低速主軸系統 29
3.1.3小型複合電鍍系統 32
3.1.4線上刀具電極直徑量測 33
3.1.5檢驗設備 34
3.1.6實驗材料 36
3.2實驗流程 37
3.3實驗方法 38
3.4實驗規劃 39
3.4.1 鎳-鈷/鑽石與鎳/鑽石之複合鍍層對同步微放電研磨之影響 39
3.4.2不同微電極刀具外型之同步放電與研磨性能比較 43
3.4.3同步放電研磨之圓孔加工 45
第四章 合金電鍍鑽石微刀具電極之製備 47
4.1刀具電極修整 47
4.2刀具電極複合電鍍 49
4.2.1鍍浴中不同鑽石微粉濃度對鍍層影響 50
4.2.2添加鈷離子對鍍層影響 51
4.2.3電鍍時刀具電極旋轉速度影響 53
4.2.4電流密度與電鍍時間對鍍層影響 53
4.3微鑽石刀具純研磨性能 56
4.4小結 59
第五章 實驗結果與討論 60
5.1鎳-鈷/鑽石與鎳/鑽石之複合鍍層對同步微放電研磨實驗 60
5.1.1純鎳金屬鍍層與鎳鈷二元合金鍍層之放電性能比較實驗 60
5.1.2鍍浴中不同鑽石微粉濃度對同步放電研磨實驗 63
5.1.3電鍍時電極旋轉速度對同步放電研磨之實驗 71
5.2不同微電極刀具外型之同步放電與研磨實驗 74
5.2.1錐度螺旋電極於鍍浴中不同鑽石微粉濃度之同步放電研磨實驗 74
5.2.2錐度螺旋電極於電鍍時電極旋轉速度之同步放電研磨之實驗 78
5.3同步放電研磨之圓孔加工實驗 81
5.3.1圓孔加工 81
5.3.2圓孔加工效率 90
5.3.3圓孔加工之刀具壽命 102
第六章 結論 108
參考文獻 111
附錄一 (Appendix) 113
作者簡歷 117
 

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