臺灣博碩士論文加值系統

傳統放電加工放電效率比一般機械加工低，為提升加工效率因而產生超音波輔助放電技術。但過去超音波振動常見作用於工件，因此，本文提出一種刀把式迴轉超音波輔助放電加工主軸，其振動不同於其他振動工件方式，採錐狀彈性筒夾可夾持如直徑3~6mm的圓棒做上下振動和高速迴轉輔助放電加工，形狀與工件如SKD61模具鋼做24kHz的相對運動。本文首先探討超音波震盪電源之輸出電壓(代表功率)對材料移除率、電極消耗率、放電深度影響，並利用田口方法L18直交表規劃放電加工實驗，控制因子分別為超音波振動(Un)、放電電流(Ip,5~15 A)、脈衝時間 (τon,50~150μs)、休止時間(τoff,50~150μs)伺服間隙(SV,10~30段)、排渣高度(Jp,0.2~3.2mm) 、主軸轉速(N,180~900rpm)，並以信號雜訊比(S/N)與變異數分析(ANOVA)的分析，探討放電加工材料移除效率、電極消耗率、表面粗糙度等品質特性，並提出優化之加工參數組合與確認實驗。
研究結果發現超音波輸出電壓(功率)與材料移除率成正比，隨著放電深度越深，超音波振動越能發揮排除碎片的效果而提升加工效率，而全功率的超音波放電移除率比一般放電加工至少提昇41%；並觀察放電波列圖，發現超音波振動可減少放電延遲時間，使單位時間內放電脈波數增加，另空化作用加速氣泡與屑渣排出並使加工狀態更穩定。另由L18田口品質調查超音波輔助(U-EDM)與迴轉超音波(RU-EDM)對放電加工的品質與效能，發現影響材料移除率主要顯著因子共同為放電尖峰電流、脈衝時間、超音波振動。單純振動放電時，影響電極消耗率主要顯著因子為脈衝時間、超音波振動，而迴轉式超音波放電則為電流與脈衝時間。影響表面粗糙度主要顯著因子為電流與排渣高度。另由變異數分析(ANOVA)探討優化加工參數，建議欲達到最大加工效率應開啟超音波振動與設置放電電流15A與脈衝時間100μs。另開啟超音波搭配放電電流10A與脈衝時間150 μs即可大幅降低電極消耗率至0.037%。U-EDM參數之表面粗度可輕易達到Ra2.0μm以下，並且電流越低越好，調整至電流5A與脈衝時間150μs，則U-EDM及RU-EDM雖未比一般放電細，優化加工參數後表面粗糙度可達到1.32μm與1.47μm。若採0.5A搖動細修一道次則可迅速達Ra0.52μm以下。

Machining efficiency of convntional Electrical Discharge Machining (EDM) is much lower than that of milling/drilling processing, and it is still the main issue for EDM during the last decades. In the past, hybrid processes of combining EDM and ultrasonic vibration (U-EDM) was verified to be an optional mean for higher speed EDM. But most of them exerted vibration effect on the workpiece, and there was still lack of comprehensive understanding of the ultrasonic assisted effect on such a U-EDM processes.
This thesis proposed a rotary ultrasonic assisted EDM (RU-EDM) spindle combined with ultrasonic transducer of 24 kHz frequency and tapered spring clamp for various tools, such as rod electrodes of from 3 to 6 mm diameter. The research topics started from investigation of the ultrasonic amplitude effects (through exerted) on EDM removal rate (MRR), relative tool wear rate (TWR), and federate of EDM depth for the SKD61 steel. Secondary, Taguchi method is adopted as the design of quality experiment for main performance of MRR, TWR and the surface roughness (SR). Besides the ultrasonic vibration, the other main control factors include the peak current, pulse on-time, off-time, jumping height of tool, servo gap, rotating speed, and ultrasonic output voltage. Each control factor is assigned three operation levels from experience and advice from machine builder. The signal-to-noise ratio (S/N) is measured from outcome of the arranged L18 orthogonal array. After that, the ANOVA analysis and F-test of MRR, TWR and SR are calculated to evaluate the most significant factors; also the optimum operational parameters are chosen based upon this analysis and are further verified through confirmation experiments.
It is found that MRR is in proportional to the ultrasonic voltage (related to its output power and amplitude), and the deeper the EDM goes through, the more significant of ultrasonic assistance is observed. The increasing rate of MRR can be at least 41% in compared to the conventional EDM. Through the waveform and pulses train, the EDM ignition delay is reduced and the discharge frequency is significantly increased by the assistance of ultrasonic vibration. It was found ultrasonic device causes turbulent flow and cavitation among dielectric (accelerate the bubble rising and particles movement) resulting in improvement of EDM stability and better debris expelling efficiency.
From Taguchi method, the significant factors for MRR are verified as peak current, pulse on-time and the ultrasonic assistance. For simply U-EDM, the significant factors for TWR are pulse on-time and the ultrasonic assistance, but for RU-EDM, they are shifted to peak current and pulse on-time, while the ultrasonic assistance is of no significance. Significant factors for SR are peak current and jump height.
From the ANOVA analysis, it is suggested that 15A of current and 100 μs of on-time can achieve the highest MRR of 67.4 mg/min, and furthermore, about 109.5 mg/min with 30A. The least percentage TWR by U-EDM and RU-EDM are reduced to 0.037% and 0.049 %, respectively by on-time of 150 μs and 10A of current, and with 540 rpm RU-EDM. The surface roughness of vibration EDM can easily achieve to under Ra 2.0 μm, and the minimum SR are verified to be 1.32 μm and 1.47 μm by U-EDM and RU-EDM confirmation tests, respectively.with the secondary process of finishing by 0.5A, orbital U-EDMT can further rapid achieve Ra 0.52μm .Therefore, high performance rotary ultrasonic assisted electrical discharge machining processes are investigated and compared in this thesis and some fundamental mechanism are studied and verified.

第一章 緒論
1.1前言
1.2 研究動機
1.3 研究目的
1.4文獻回顧
1.5專利搜索
1.5.1震動工作台與超音波加工裝置
1.5.2超音波振動複合加工具
1.5.3用於超音波輔助式迴轉機械加工的工具單元
1.5.4同軸驅動超音波主軸
1.5.5放電加工機
1.6本文架構
第二章 基本原理介紹
2.1 放電加工
2.1.1放電加工基本原理
2.1.2 放電加工去除機制
2.1.3 放電加工參數
2.1.4放電加工特性
2.2超音波加工
2.2.1 超音波加工基本原理
2.2.2超音波加工的材料去除機制
2.2.3 超音波加工的優缺點
2.2.4 超音波錐體及變幅桿的種類
2.2.5超音波振盪器
2.2.6迴轉式超音波加工(RUM)
2.2.7超音波振動輔助放電加工(U-EDM)
2.3田口品質工程
2.3.1田口實驗設計法
2.3.2田口方法設計基本步驟。
2.3.3直交表
2.3.4品質特性與信號雜訊比(S/N比)
2.3.5變異數分析
第三章 實驗設備與方法
3.1實驗設備
3.1.1放電加工機
3.1.2超音波主軸與夾持連結器
3.1.3迴轉超音波主軸
3.1.4變頻器
3.1.5超音波電源供應器
3.1.6哈伯立式水冷機
3.1.7 TOMAS精密表面輪廓儀
3.1.8 日本AND GR-200電子分析天平
3.1.9 表面粗糙度測定儀
3.1.10 超音波清洗機(Elma Ultrasonic Cleaner LC30H)
3.1.11 示波器與電壓隔絕器
3.2實驗設計規劃
3.2.1電極與工件材料
3.3.2超音波輸出功率(電壓)影響
3.3.3田口實驗設計方法
3.3.量測方法
3.3.1材料去除率(Material removal rate，MRR)：
3.3.2電極消耗率(EWR)： 48
3.3.3相對電極消耗率(Tool wear rate，TWR)：
3.3.4表面粗糙度(Surface roughness，SR)：
3.4實驗流程
第四章 結果與討論
4.1超音波輸出功率(電壓)影響
4.1.1超音波輸出功率(電壓)對材料移除率影響
4.1.2超音波輸出功率(電壓)對相對電極消耗率影響
4.1.3超音波輸出功率(電壓)對表面粗糙度影響
4.1.4超音波振動放電對加工深度之影響
4.1.5超音波振動放電加工波形與討論
4.2超音波振動輔助放電加工-田口方法L18直交表調查
4.2.1 材料移除率分析
4.2.2 相對電極消耗率分析
4.2.3 表面粗糙度分析
4.2.4 驗證實驗
4.2.5細修加工分析實驗
4.3迴轉超音波振動輔助放電加工-田口方法L18直交表調查
4.3.1 材料移除率分析
4.3.2 相對電極消耗率分析
4.3.3 表面粗糙度分析
4.3.4 驗證實驗
第五章 結論
第六章 未來展望
參考文獻
附錄一
簡歷

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