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標題: | 電化學放電現象與製程應用之研究 Study of electrochemical discharge phenomena and its applications |
作者: | Wen-Yang Peng 彭文陽 |
指導教授: | 廖運炫 |
關鍵字: | 電化學放電加工,玻璃孔加工,石英加工,非導電硬脆材料加工,火花,氣泡,氣膜,臨界電壓, electrochemical dischage machining,optical wafer,quartz,spark,bubbles,gas film,current density, |
出版年 : | 2005 |
學位: | 博士 |
摘要: | 隨著微機電製程與生物科技的發展,光學玻璃(例如,Pyrex)與石英等非導電材料的應用與日遽增。電化學放電加工是非導電硬脆材料加工製程的新興技術,然而針對火花釋放行為的模式仍未有一致明確的解釋,且缺乏解決火花能量密度與被加工材料之間匹配問題的策略,以致實際應用上未有具體的成果。本文目的即在探討細線電極與柱狀電極之電化學放電現象的基本特性,以平均電流密度與脈衝電流的密集度作為火花能量密度的指標,作為製程應用評估的主要依據,並歸納出加工條件的選取原則。由水平細線電極的反應發現臨界電壓與平均電流密度受線極長度、線極材質的影響。以反應的耐壓性而言,30mm以下不銹鋼線有最佳的效果;在增進火花能量密度方面,上沖式液柱有助於穩定包覆線極的氣膜結構,使脈衝電流密度增高,另外,透過電壓作用時間與休止時間的調整,可以增進象徵正常火花釋放的脈衝電流比率達87%左右,然而長度70mm以上的線極,因為平均電流密度在0.04A/mm2以下,形成加工應用的基本障礙,在直徑10mm玻璃與石英圓棒的切片加工測試中,材料移除率在0.24 mm3/min以內,且火花能量受切縫影響較不穩定。綜觀而知,走線式電化學放電加工先天限制較多,較難凝聚出商業技術開發的適當目標。文中發現直立柱狀電極的臨界電壓與電極尺寸及反應面積有正向的關係,平均電流密度則與電極尺寸呈現負相關。直徑2.0mm以內的電極,電極端面的平均電流密度在0.11A/mm2以上,且不受電極沒入深度影響,而電極側面平均電流密度約為電極端面的1/3左右,大致上隨電極沒入深度而遞減。從高速攝影的電極端面的火花釋放資料配合電流波形的變化,發現電壓的上升會導致氣泡群與氣膜結構等形態上的轉變,以及放電柱面積與分佈的變化,直接反應在平均電流的擾動幅度與脈衝電流的峰值大小及密集度等反應特性上。文中定義了「轉折電壓」,代表反應由臨界電流密度的狀態完整過渡到穩定火花釋放的階段,做為加工電壓的參考依據。從轉折電壓發現,200~250Hz的脈衝電源頻率,以及0.7~0.85的衝擊因子,可以獲得較佳的脈衝電流密集度與火花強度。由平均電流密度等基本特性的研究結果,採用柱狀電極進行電化學放電的製程應用。在生物晶片注樣孔加工製程方面,以外徑1.9mm的中空管電極,利用具有較佳脈衝電流密集度與強度的電源參數,先求取各深度最大允許進給率作為實際加工進給率的參考基準,使電極與工件保持適當的間隙,可以獲得無微裂縫而孔徑誤差範圍在±5%的小孔,為了提高連續加工的穩定度,利用電流波形及上湧氣泡週期的分析結果,找到適當的啄鑽參數,成功地加工出Pyrex基板上的36個注樣孔,平均材料移除率為1.48mm3/min。於石英的溝槽銑削加工方面,先找到不同深度之下最大允許進給率,再決定最適進給率。研究發現以直徑1.0mm電極在切深0.5mm與進給率1mm/min時可以獲得最佳的材料移除率1mm3/min。經過連續溝槽的加工,電極端面直徑平均縮小率為0.02mm/min。而直徑2.0mm電極,最佳的材料移除率降為0.2 mm3/min,顯示平均電流密度偏低,在進給率低於0.8mm/min時,溝槽底面產生沙灘紋,必須靠0.02mm切深的精加工製程方能消除。在石英基板薄化製程方面,為了避免電極端面火花能量在加工過程中破壞工件,採用直徑2.0mm電極對0.6mm厚的基板,進行兩次的薄化加工。以0.4mm切深進行第一次的加工,發現電極端面火花造成0.04mm的過度加工(即工件剩餘厚度為0.16mm),以高於轉折電壓10%左右的電壓條件(60V)進行第二次薄化加工,每次0.05mm的下降量,經過來回兩次加工後,所得工件厚度為50μm,可作為高頻震盪器元件的半成品,揭示了利用電化學放電加工製作石英基板局部薄化特徵的可行性。 The optical materials like Pyrex or quartz are more widely used due to the development of MEMS or bio-technology. The newly developed technology, electrochemical discharge machining(ECDM), may be a new procedure for machining these non-conductive brittle materials. But only if the spark mechanism or energy intensity problem is well-solved, will the new method be highly evaluated. This article aims at the erosion energy intensity and the derived material removal rate. The average current density is chosen as the spark density evaluation index. The power source parameters , the electrolyte supply arrangements and so on are investigated to derive the better spark release. For the horizontally-stretched wire electrode, the up-spray electrolyte supply could stabilize the gas film which enhanced the spark release. However the workpiece thickness is quite limited due to the drastic descending of the current density when the wire length is increased. The most inspiring observation of the current release is that the pulse current could be regulated by the power source parameters which means only the proper voltage-on time together with a good voltage-off time can realize tense spark release for a given wire length. For the cylindrical electrode tool with no larger than 2mm diameter, the electrode end area could attain the average current density above 0.11A/mm2. This implies that the electrode end area has more potential for machining application. More detail observations of the bubbles-to-film transformation process is implemented by the high speed photograph system. The gas film is formed at a sudden and the spark spot area is smaller and more evenly distributed when the voltage just reaches the “transition voltage” which symbolizes the stable spark phenomena is obtained. At higher voltage, the spark spot area is larger and more randomly occurred. With respect to the current pulse morphology, the current pulse is narrower and the peak value is smaller at lower voltage or smaller immersed area. The current pulse duration becomes longer and the peak is higher but there is less pulse occurrence within single voltage-on cycle time. This gives a new description of the continuous process concerning the gas film, the spark intensity and the current morphology at different voltage level. These results tell how to decide the parameters in real hole machining process. To conquer the problem of gap maintenance at real machining, a slip-coupling is used to measure the utmost feed rate at certain eroded depth. A 1.9mm diameter hollow copper pipe is verified for stable machining ability to produce 36 holes on the 0.6mm thickness Pyrex wafer without electrode dressing and the hole diameter is satisfied. The cylindrical electrode is then used to thin the quartz wafer by the milling-like process. A locally-thinned wafer structure with minimum thickness of 50μm is successfully produced. This reveals another brand new application of the ECDM process. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/34954 |
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顯示於系所單位: | 機械工程學系 |
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