金屬板材圓杯拉伸成形極限之分析

本文採用動態顯函有限元素法，結合材料彈塑性理論，發展出一套增量型彈塑性大變形之三維顯性動態有限元素分析程式，並利用九節點元素來定義模具外形，亦發展出彈性棒元素來處理料片與模具之接觸問題，將此彈性棒與三維實體元素偶合後，進行金屬板材圓杯拉伸成形製程之分析，並探討圓杯拉伸成形之沖頭負荷與衝程之關係、厚度分佈、變形歷程、成形極限，及探討位移增量、彈性棒面積和質量密度於動態顯函解法上之影響，其目的是為了瞭解料片在拉伸過程中，不同條件對工件成形性之影響與變形行為。本文設計一組含引伸扣緣之圓柱形沖模來進行圓杯拉伸成形實驗，以探討圓杯拉伸成形之破裂情況與厚度變化情形，進而得到圓杯拉伸成形極限。經數值分析與實驗結果比較得知，在拉伸過程中，其料片之圓弧轉角會受到最大拉伸應力，此拉伸應力會使得圓弧轉角的厚度明顯的薄化。數值分析之結果皆可合理的模擬實驗結果，故本動態顯函有限元素分析程式可合理的模擬圓杯拉伸成形製程。

關鍵字

動態顯函有限元素；彈性棒；實體元素；拉伸；成形極限

並列摘要

The objective of this study was to observe the deformation when the work pieces were stretched under various conditions. The study applied an analytical program model which integrated dynamic explicit finite element and elasto-plastic theory. The nine-node element was also adopted to define the tool surface geometric characteristic. An elastic bar element was developed to handle the contact problems. After coupling the elastic bar to the solid element in the finite element model, the analysis of three-dimensional stretching proceeds and the simulation results included the relationship between punch load and punch stroke, the various thickness of the work pieces, the deformation history, the forming limit, and effect of displacement increment, elastic bar area and mass density in the dynamic explicit solution. A set of drawbead cylindrical-cup tools was designed to explore the forming of blank in arc corner and the variation of thickness so as to achieve the maximum stretching stress, which significantly thinned the thickness of arc corner. The simulation results show good agreement with the experiments that can be used to verify the reliability and accuracy of the elasto-plastic finite element program in this study.

並列關鍵字

Dynamic Explicit Finite Element ； Elastic Bar ； Solid Element ； Stretching ； Forming limit

參考文獻

1. Qin, S., Shang, H. M., Tay, C. J. and Mo, J., “Stretching during axisymmetrical forming of sheet metal,” Journal of Materials Processing Technology, Vol. 63, pp.117-122 (1997).

2. Lim, T. C., Ramakrishna, S. and Shang, H. M., “Simulation stretch forming and deep drawing in axisymmetrical sheet forming,” Journal of Materials Processing Technology, Vol. 97, pp.82-87 (2000).

3. Chakrabarty, J., Lee, W. B. and Chan, K. C., “A new theoretical model for predicting limit strains in the punch stretching of sheet metals,” Journal of Materials Processing Technology, Vol. 91, pp.257-263 (1999).

4. Siegert, K., Rennet, A. and Fann, K. J., “Prediction of the final part properties in sheet metal forming by CNC-controlled stretch forming,” Journal of Materials Processing Technology, Vol. 71, pp.141-146 (1997).

5. Huang, Y. M. and Liu, C. H., “An analysis of the square-cup stretching process,” Journal of Materials Processing Technology, Vol. 49, pp.229-246 (1995).

國際替代計量

金屬板材圓杯拉伸成形極限之分析

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