超音波振動於鋁合金成形加工的摩擦效應研究

Abstract

本論文之目的在於研究超音波振動於成形加工之摩擦效應。研究中主要以超音波振動抽拉與超音波振動端面壓縮兩種製程，在模具與工件之相對速度兩極端化的加工特性，分析比較超音波振動所產生摩擦機制的影響，進而推論超音波振動對於其他成形加工可能產生的摩擦影響。 論文中研究分為四個主題，包括超音波振動實驗設備設計製作、超音波振動於高溫端面壓縮影響、超音波振動端面壓縮摩擦影響和超音波振動抽拉有限元素分析。研究中，首先利用溫度補償與冷卻系統之設計，克服超音波設備於高溫下實驗之困難點。並利用此設備進行超音波振動高溫端面壓縮實驗，實驗發現超音波振動於常溫或高溫均能有效降低端面壓縮時之成形力量，而降低之成形力亦隨溫度上升而減少。研究中並以端面壓縮製程，探討超音波振動於平行加工方向所產生的摩擦影響。由修正壓縮實驗證實，在無摩擦的效應下，超音波振動仍然能有效降低鋁合金的成形壓縮力。而由環壓縮試驗的結果顯示，超音波振動會造成介面摩擦力增加。同時超音波振動修正壓縮實驗之溫度量測顯示，超音波振動會造成材料溫度上升。 最後，探討抽拉鋁線時，以超音波振動方向平行和垂直於工件與模具相對速度的效應。利用有限元素模擬分析，分別進行CD、AUD與RUD之有限元素模擬。由實驗與模擬結果顯示，於AUD和RUD兩種情況下，當抽拉速度低於一臨界速度時，抽拉力伴隨模具振動週期而變動，且變動振幅隨抽拉速度減少而增加；而RUD之臨界抽拉速度高於AUD。在臨界抽拉速度時，超音波振動作用的摩擦效應將消失。 綜合以上超音波振動端面壓縮與超音波振動抽線的研究，可推論一般成形加工時，超音波振動產生的摩擦效應均與「介面間距變動摩擦效應」及「溫度效應」有關，而此兩種效應對於產生摩擦效應的影響程度，則依成形加工型態而有所不同。本研究已完成超音波振動於成形加工的摩擦影響的定性分析研究，未來將進一步定量分析這些摩擦效應在成形加工的比重程度，以便應用於一般成形製程。

The purpose of this dissertation is to investigate the frictional effect of ultrasonic-vibration during forming of aluminum alloy. This study analyses ultrasonic-vibration drawing and ultrasonic-vibration upsetting, which are extreme cases to each other in terms of relative speed between die and workpiece, to explore the frictional effect of superimposing ultrasonic-vibration during forming processes. The study focuses on four subjects: the set up of an ultrasonic vibration hot upsetting system, the influence of ultrasonic-vibration on hot upsetting, the frictional effect of ultrasonic -vibration during upsetting, and the experiment and simulation of ultrasonic-vibration drawing. In this study, a cooling mechanism was used on an ultrasonic vibration hot upsetting system to overcome high-temperature forming difficulty at the beginning. The effects of ultrasonic-vibration on the upsetting of aluminum alloy was then explored using this system. Results show that the ultrasonic-vibration can significantly reduce the compression force during hot upsetting and the reducing effect of compression force decreases while the temperature increases. Furthermore, upsetting process was used to explore the frictional effect by superimposing an ultrasonic-vibration parallel to the direction of forming. Experimental results of extrapolated compression test also indicate that ultrasonic-vibration can reduce the compressive force when friction is eliminated. The consecutive results of the hot ring compression test and temperature measurements during ultrasonic-vibration on upsetting reveal that increasing temperature by ultrasonic–vibration may reduce the flow stress and increase the interfacial friction. Finally, The ultrasonic-vibration drawing experiments and finite element analysis were performed for CD, AUD and RUD to explore the relative speed effect of workpiece and die by superimposing ultrasonic-vibration parallel as well as perpendicular to the relative speed. For both AUD and RUD, the drawing force fluctuated with the die vibration when drawing speed was below the critical drawing speed and the fluctuation amplitude tended to increase with the decrease of drawing speed. When drawing speed reaches a critical value, the fluctuation of drawing force disappears. On the other hand, results reveal that the critical drawing speed of RUD is higher than AUD and the frictional effect of ultrasonic-vibration vanishes when the interfacial gap speed is zero. From above studies we may conclude that the frictional effect induced by ultrasonic-vibration should associate with both the effect of interfacial gap variation and the temperature increase in general forming processes. The weighting of these two effects depends on the type of forming process. Following this qualitative study, quantitative analysis on the frictional effects of ultrasonic-vibration will be proceeded in the future to be applied in practical forming processes.