摘 要
本論文為使用高功率超音波輔助振動線切割放電之線電極，對工具鋼SKD61工件進行切槽加工研究，並探討線切割加工參數如開路電壓、超音波功率，脈衝放電時間、伺服電壓之差異，於加工品質特性包括有加工時間、材料移除率、加工槽寬度及表面粗糙度等，並利用光學顯微鏡，觀察有無超音波輔助加工對再鑄層生成之影響。
實驗結果顯示，當超音波輔助振動線電極時因振幅的關係所以兩極間之間隙也會有週期性的變化，當兩極間隙變小時突破絕緣的能量也較小，因此在相同的加工參數下加入超音波輔助後，適當的加工參數組合下，相較於無超音波輔助加工時，加工時間平均縮短了4.2 %，以及材料移除率平均增加了7.5 %。
於超音波輔助加工的情況下，脈衝放電時間與伺服電壓對加工時間及材料移除率有顯著之影響，對加工後之加工槽寬度與表面粗糙度值的影響不明顯。於再鑄層的生成觀察中，在有無超音波輔助加工的情況下，再鑄層厚度皆會隨著開路電壓增加而變薄，而具超音波輔助加工相較於無超音波輔助加工產生之再鑄層厚度更薄，且能夠得到最薄的再鑄層厚度為1.358 μm。

Abstract
The study focused on applying ultrasonic vibration assisted wire electrical discharge machining to cut grooves on SKD61. The processing parameters, such as open voltage, ultrasonic power level, pulse on time, servo voltage, were selected to perform the experiments. The influence of each parameter on machining time, material removal rate, kerf width and surface roughness were inspected. The optical microscope is used to observe the effect of ultrasonic assisted processing on the formation of the recast layer.
The experimental results showed that the gap between the wire electrodes and workpiece changed periodically when the wire electrodes vibrated due to ultrasonic amplitude. When the machining gap became smaller, the power to break through the insulation also became smaller. With a proper combination of processing parameters, the processing time was shortened by an average of 4.2 % and the material removal rate was increased by an average of 7.5 %, when compared with non-ultrasonic assisted processing.
In the case of ultrasonic assisted machining, the pulse on time and servo voltage had significant effect on the processing time and material removal rate, but not on the kerf width and surface roughness values. We also observed that increasing the open circuit voltage reduced the thickness of the recast layer whether it was ultrasonically assisted or not. The thickness of the recast layer produced from ultrasonic assisted processing was even thinner, with the thinnest thickness of the recast layer being 1.358 μm.

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