- 學位論文
先進高強度鋼板沖壓成形扭曲現象之研究
A Study of Distortion in Stamping of Advanced High Strength Steel Sheets
摘要
隨著科技進步，汽車性能及配備日益提升，針對車體結構件的要求也相對提高，而為了因應能源危機的問題及碰撞法規的重視，降低車身重量及增加車身強度已成為目前各大車廠努力的目標。雖然使用鎂合金及鋁合金等輕金屬可達到減重的目的，但其價格昂貴。因此，具有高強度且低成本特性的先進高強度鋼板逐漸被廣泛地應用於汽車工業上。 先進高強度鋼板雖然有高強度低成本的優點，但其成形性較差，在沖壓製程中除了容易產生破裂及皺褶問題之外，成形後的回彈(springback)、側壁捲曲(sidewall curl)與扭曲(distortion)等缺陷造成產品尺寸精度上的變異更是難以克服。因此，導入CAE模擬分析技術以輔助板金沖壓模具設計，已是未來的趨勢。為了提高CAE模擬分析之準確率，本論文首先將探討不同降伏準則及加工硬化準則，再將其應用於基本造型沖壓成形CAE模擬分析技術上，包括V型彎曲成形及U型帽狀引伸成形。本論文以Hill 48及Barlat兩種降伏準則進行模擬分析，並針對具有影響性的模擬參數進行收斂性測試以取得最佳的參數設定值，再將模擬結果與實驗結果作比對，探討不同降伏準則對模擬回彈、側壁捲曲的影響性。 本論文同時選用S-rail成形作為探討扭曲現象之模型，並以NUMISHEET 1996年國際會議之Benchmark實驗數據驗證使用有限元素軟體模擬分析S-rail型成形的可信度，然後進一步探討一般參數及造型參數對扭曲的影響性，並研究其扭曲機制。最後，本論文整理、歸納並分析改善扭曲缺陷的方法，包括阻料條的設計與壓料力的設計。本論文之研究成果可提供先進高強度鋼板沖壓成形分析者作為模具設計及CAE模擬分析技術之參考。
並列摘要
With technology advancing, the performance and equipment of automobile are improved, and the demand for the automobile body structural parts is also increased. To cope with the energy crisis problem and the rising importance of collision regulations, reducing weight and increasing strength of an automotive structure are the goals for the major car manufacturers at present. Although the use of light metal such as magnesium and aluminum are alternatives to achieve the purpose of light weight, the price of these metals is relatively higher than that of steel. Therefore, the advanced high strength steel with the characteristics of high strength and low cost are applied to the automobile industry gradually. Despite the high strength and low cost characteristics borne by the advanced high strength steel, the formability is much poorer than that of traditional low strength steels. In the stamping process, the advanced high strength steel is not only easy to produce cracks and wrinkles, but also is difficult to overcome the variations of dimensional accuracy caused by springback, sidewall curl and distortion after forming. Hence, the implementation of CAE simulation technology to assist the die design of stamping advanced high strength steel sheets has become a popular trend in both the automotive and the tooling industries. In order to improve the accuracy of CAE simulation analysis, different yield criteria and work hardening criteria were first discussed in the present study. Then the CAE simulations were performed to examine the stamping processes for some simple shapes, such as V-bending and U-hat bending with the use of Hill 48 and Barlat yield criteria. The convergence tests were conducted to identify the sensitive simulation parameters and an optimum set of parameters was established. The simulation results were then compared with the experimental data to investigate the effect of different yield criteria on the occurrence of springback and sidewall curl. The forming of an S-rail shape was also examined by the finite element analysis in the present study. The benchmark experimental data published in the International Conference NUMISHEET in 1996 was adopted to verify the accuracy of the finite element simulation results. The influences of process parameters on distortion were further discussed, and the deformation mechanism of distortion was investigated as well. Finally, the methods of ameliorating distortion were analyzed, including the drawbead design and blank holder force. The results obtained in the present study could be valuable references to the future research in the stamping of advanced high strength steel sheets.