- 學位論文
高強度汽車結構件沖壓成形之扭曲現象分析
An Analysis of Distortion in the Stamping of High Strength Automotive Structural Parts
摘要
在高強度鋼板之沖壓成形製程中，除了傳統鋼板成形會產生之破裂、皺褶外，最主要的是必需解決回彈、側壁捲曲及扭曲等缺陷，其中又以扭曲(distortion)現象影響零件整體尺寸差異最為深遠，將降低整車裝配精度並提高焊接難度，且難以掌控其扭曲的方向與大小，為汽車工業沖壓製程中之最大難題。為了克服這些問題，國際間產學研各界均使用有限元素法進行模具設計與分析，以減少板金成形過程中之回彈量。 在過去研究當中，雖然已經對有限元素模擬參數進行最佳化之收斂性分析，但對於提升預測回彈準確度仍不足。因此，本論文針對描述材料受力行為之材料模型進行探討，配合參考NUMISHEET 1996年國際會議之Benchmark實驗數據進行S-rail模擬驗證，提出較適用於高強度鋼板沖壓成形扭曲現象模擬分析之材料模型。 本論文亦針對扭曲現象相當明顯之汽車結構件-A柱，進行開發設計。首先以成形性分析確實掌握產生成形缺陷之因素，並建立模面餘肉造型設計以解決之。在回彈現象方面，藉由造型歸納，整合A柱之扭曲量、UV夾角與尾端扭轉角，並完成回彈模面補償之設計。 針對高強度鋼板沖壓成形之有限元素法模擬，本論文經由實際測試驗證，確定Barlat降伏準則加上考量包辛格效應之Yoshida-Uemori材料模型可有效提升有限元素模擬分析之準確性，且較適用於高強度鋼板沖壓成形扭曲現象分析。而本論文針對A柱開發所建立之有限元素分析模式與模面設計以及模面回彈補償技術，可供日後開發複雜造型高強度結構件沖壓成形製程之設計參考依據。
並列摘要
The common defects present in the stamping of conventional steel sheets are fracture and wrinkling. However, the occurrence of springback, side-wall curl and distortion makes it more difficult to be solved in the stamping of advanced high strength steels. Among these problems, distortion plays a critical role in influencing the overall size difference of parts, resulting in the difficulty in welding and assembly process of the automobile parts. In order to cope with this dilemma, the finite element analysis is employed to help the tooling design so as to reduce the springback in the sheet forming process. Although previous studies have endeavored to establish the optimum simulation parameters, the accuracy in the prediction of springback is yet to be improved. Accordingly, this thesis investigates the optimum material model that describes the material behavior best to raise the accuracy of the finite element simulations on the prediction of springback and distortion. With the use of the optimum material model, this thesis examined the distortion occurred in the stamping of advanced high strength steel sheets and conducted the die design for stamping an automotive structural part, particularly an A-pillar, which possessed a complex shape. The formability of the A-pillar without any die addendum design was studied first to identify the potential defects that might occur in the stamping process. The fracture and wrinkle defects were then eliminated by an optimum die face design with the use of the finite element analysis. In addition, this thesis also constructed the fundamental concepts on the die face design that could compensate for springback and distortion. Since the springback and distortion behave in a non-linear pattern, this thesis also endeavors to establish a design guideline for the die compensation on spingback and distortion to minimize the shape variation occurred in the stamping process. The distortions occurred in an S-rail published as a benchmark in the 1996 NUMISHEET conference and the actual stamping of an A-pillar with DP590 steel sheet were compared to the finite element simulation results with the optimum material model adopted. The comparison reveals that the material model that uses the Barlat 91 yield criteria and the Yoshida-Uemori hardening model renders a better prediction on springback and distortion presented in the stamping of advanced high strength steel sheets. Also the consistency between the production A-pillar and the finite element simulation results confirms the efficiency of the die compensation design guideline developed in this thesis.