先進高強度鋼板液壓成形特性之研究

Abstract

近年來為了配合車輛輕量化，高強度鋼板的應用逐漸受到重視。然而高強度鋼板在沖壓成形過程中，最大的缺點在於容易產生回彈與扭曲等幾何形狀與尺寸的變異。因此有效降低高強度鋼板之回彈現象，是目前相當需要解決的問題。 板液壓成形採用油壓槽取代母模，使得板件表面受到均勻之靜水壓，對於改善板件引伸成形有相當程度的改善。因此本論文利用有限元素法軟體Pam-Stamp進行模擬，探討板件液壓成形是否可有效改善高強度鋼板之回彈現象。 本論文首先針對板件液壓成形機制進行初步探討，了解成形過程中材料之受力情形。接著建立板件液壓引伸CAE模擬分析模型，進行網格尺寸、厚度方向積分點以及沖壓速度等數值參數之討論。藉由此模擬分析模型，比較各種液壓曲線對於回彈量之影響，並決定後續模擬所使用之液壓曲線。 本論文亦歸納板液壓成形以及沖壓成形之基本製程參數，包括：材料強度、材料厚度、壓料力、液壓壓力、母模R角及沖頭R角，利用所建立之板件液壓CAE模擬分析模型進行比較，觀察各種參數對回彈量之影響，並同時探討板液壓成形和沖壓成形影響回彈量差異之原因。最後利用實驗數據驗證CAE模擬結果之正確性。

Recently, the applications of advanced high strength steel have become more popular in the automotive industry due to the high demand of light-weight vehicles. However, in the stamping of advanced high strength steel sheets, there is a major defect that produces dimension variations of shape geometry such as springback and distortion. Therefore, reducing the springback of advanced high strength steel is an urgent problem at present. Unlike the traditional stamping process, hydromechanical forming replaces the die with a fluid chamber. This makes the blank able to sustain a uniform pressure, and ameliorate the formability. Hence, the superiority of the hydromechanical forming process on reducing the springback occurred in the forming of advanced high strength steel sheets was examined by both the finite element analysis and experimental approach. The deformation mechanism of advanced high strength steel sheets in the hydromechanical forming process was studied first using the finite element software PAM_STAMP 2G. The convergence tests of element size, integration points and stamping velocity were discussed. With the established simulation model, the influence on springback with different hydraulic pressure curves were compared, and the simulation results were used to determine the hydraulic pressure curves used in the subsequent simulations. The basic process parameters of traditional stamping and hydromechanical forming were also generalized, including: steel strength, sheet thickness, holding force, hydraulic pressure, die radius and punch radius. With the use of the finite element simulations on hydromechanical forming, the effects of the process parameters on springback were observed, and the causes of the difference between hydromechanical forming and stamping process were discussed. The experiments of forming the advanced high strength steel sheets with both traditional stamping process and hydromechanical forming were also conducted in the present study. The consistence of the finite element simulation results and the experimental data confirms the accuracy of the finite element analysis. In addition, both the finite element analysis and the experiments indicate that the springback can be reduced if the hydromechanical forming is applied compared to the traditional stamping process.