一般認為超音波加工相較於雷射加工、放電加工…等，是精度較差的加工法。但是超音波加工有重複性高與易加工脆性材料之優點。因此，若要發展超音波應用於高精度且高穩定之切削，不只要有穩定的共振頻率及振動位移，還要考慮整體系統的穩定性，以達到精密之需求。其中，變幅桿所產生的振動變化都會直接影響到加工品質與精度大小。是故，本研究將搭配有限元素分析，從中取代業界在設計上常用的實驗試誤法，並利用實驗驗證，探討不同形狀與不同材質時的振動行為對於變幅桿穩定性影響，探討變幅桿接合時易產生的不穩定因素。
我們設計鋁合金為變幅桿的主要材質，其具有高韌性；但是為了增加變幅桿的可替換性，在不同材質介面處的接合，會因為材料波傳特性不同而產生最大振幅的位移下降及負載電流上升；在不同形狀方面，會因截面積的縮小變化，其位移會上升；而變幅桿接合刀具或是換能器時，其接合界面越多越不穩定。實驗中嘗試使用不同的接合力矩，得到接合力矩約36N-m時有助於增強介面的接合，使波的傳遞穩定。且我們利用脈衝波速量測儀與密度試驗所得到的材料參數輸入到有限元素分析中，其有限元素分析與實際驗證誤差在0.3%之內，分析準確性高。
超音波加工法中，常需要透過變幅桿來放大振幅，但大部分有錐度之變幅桿設計，使得加工面積被侷限，所以為了達到大範圍的加工，就需要製作大面積變幅桿。因此，本實驗模擬了數種不同形狀之變幅桿，但變幅桿邊長超過1/4波長時，即會產生振幅不均之現象，所以研究利用複合式切槽法來克服振幅不均的問題。
實驗結果顯示，變幅桿邊長越長時，其端面振動位移會因離中心位置越遠，其振動位移會越小，若設計固定面積尺寸為60mm×20mm來實驗。從模擬中可看出在未改善前振幅不均達40%，而分別加入單切槽、雙切槽或雙切邊時，其振幅可改善至20%內，若使用複合式切槽法時，振幅可改善至10%內。而實際實驗使用800瓦功率透過複合式切槽法，經由量測驗證方形變幅桿振幅改善不均勻至2%。

The Ultrasonic Machining is a less precise processing method than other conventional processing methods. That is because technical problem appear on the application of ultrasonic machining, such as the resonant frequency, displacement and the vibration of the horn that would influence micrometer-level cutting of ultrasonic machining. In this research, we used the finite element method to analyze some factors and demonstrate the simulations. Some factors were analyzed in the simulations, are including observation of different geometries and different materials of horns; simulation of the interface behaviors of horn, transducer and tool, while the waves conducted between them. The result of the simulation would be compared to experiment result. We hope the result of this research could give some contribution for developing the high precision and high stability of the ultrasonic machining.
The results reveal that the material’s data, which were got by pulse wave velocity measurement system and were analyzed by finite element method, show 0.3% deviation compare to experiment. Furthermore, the transducers are aluminum alloy. If we connect with other horns to increase the strength, the different materials of horn and transducer would create the decline of displacement and ascendant current load; if the horns have different shapes, the decrease of the cross-sectional area of horns will increase the displacement distance; the more interface of transducer, horn and tools will introduce unstable phenomena. Lastly, the connective strength about 36N-m of transducer and horn would generate the stability frequency of wave’s transmission.
Furthermore, the non-uniform amplitudes of the large volume horn were detail discussed. The experiments simulate several shapes of the horn. When the volume horn is over than 1/4 waves, the horn creates the non-uniform amplitudes phenomena. Then the Composite grooving method is used to overcome the non-uniform amplitudes phenomena.
We design the 60mm×20mm volume horn, the results reveal that the amplitudes have about 40% irregularities. If we used single notch, double notch and dual trimming of the horn to improve the amplitudes, it just decreased less than 20% irregularities. Lastly, we used composite grooving method which reveals the best results of 10% irregularities. The experiment results demonstrated that using composite grooving method on the large volume of square horn, reveals the best uniformity of the horn.

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