彎管製程中，製程缺陷如管材彎曲破裂、管件減薄亦或是滑管現象等，在彎管產業界中是極為重要的加工前參考資訊。而在預估板材成形能力中，成形極限圖是最常被使用的資訊，本文透過建立成形極限圖了解材料成形資訊，並套用至彎管製程中，預測彎管之破管現象。
本文所研究之彎管材料為不鏽鋼429，吾人對其進行材料試驗，獲得相關參數，並以兩種不同幾何形狀之試片進行拉伸試驗直到試片破裂，求得極限拉壓應變與平面拉壓應變。接下來透過延性破壞準則來建立成形極限曲線，預測材料破壞之極限應變。為了驗證其準確性，吾人利用LS-DYNA對上述兩種不同幾何形狀之試片進行拉伸至破裂之模擬，確認破裂位置與應變數值是否相符。在建立成形極限圖後，本研究將其匯入了前處理軟體DYNAFORM建模並以LS-DYNA計算模擬，探討管件在彎曲過程中的缺陷，包括減薄、破壞、皺褶與滑管現象，並預測破壞處確切夾角位置與破壞發生時之管材彎曲角度等。模擬結果與實際彎管互相比對過後，驗證了模擬結果之準確性。
本研究結果顯示，原型條件之模擬可預測破壞發生在準確彎曲範圍之內。此外，藉由對於破裂點應力應變變化之觀察，發現增加壓模速度可改善管件外壁減薄，延遲材料發生破壞，但也會對內壁造成更劇烈之皺褶現象。另外，透過後處理軟體觀察管件與夾模、壓模之相對速度，可以判斷管件與模具之間的滑管現象。此外，藉由分析，設置助推裝置可明顯改善管件成形性，延後破壞發生。本研究將成形極限圖配合有限元素分析，對彎管製程之缺陷進行分析，可做為加工前之參考。

This study predicted the crack of tube in bending process by establishing forming limit diagram (FLD). By establishing FLD and then imported it into the finite element software DYNAFORM, we could discuss the stress and strain during the process and then analyze the defect of the rotary bending process. Through the comparison between the simulation and the actual bending process, it is confirmed that the simulation is able to predict the accurate range of the bending angle when crack occurs and also the cracked area.
Furthermore, by the analysis, it is clear that increasing the speed of the press die can decrease the thinning rate, thus improve the formability of the tube. But the more speed of the press die increased, the more trend that wrinkling would have occurred inside of the tube. Besides, by observing the related speed between the die and tube, sliding between the die and tube could be determined. In addition, through the analysis of the simulation, bending with pushing device could also improve the formability of the tube, delaying or even prevent the happening of crack.

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