鋁合金板件沖壓成形之研究

Abstract

近年來，由於消費者對於空間舒適與多功能要求提升，導致代步工具之體積重量不斷增加。然而面對能源危機與日漸惡化的生存環境，減少溫室氣體的排放已成為重要課題，以至於部品輕量化已是各大板金廠發展的目標，而由於鋁合金的比重約為鋼的三分之一，使得許多鋼板逐漸被鋁合金所取代，甚至歐美先進國家皆陸續推出全鋁合金汽車以及遊艇。 鋁合金板件雖然擁有重量輕及耐腐蝕特性，但其成形性較傳統鋼板為差，在沖壓過程中除了容易產生破裂（crack）問題外，鋁合金因較低的彈性係數（elastic modulus）而產生的回彈（springback）缺陷，更使得尺寸精度上的變異難以克服。也因此過去鋼板的設計概念無法直接套用於鋁合金的模具設計，造成板金廠開發時程與成本的耗費。 在沖壓成形上，鋁板大都選用成形性相對較佳的5000與6000系列材料，本論文亦是選用A5083-O與鋁A6181-T4板材作為研究素材，藉以探討不同降伏準則（yield criteria）與硬化準則（hardening rule）對鋁合金板材沖壓成形CAE分析準確性的影響。並經由實際實驗取得材料參數，應用於V型彎曲及U形帽狀（U-hat）引伸成形之CAE模擬分析上，再將板件進行成形實驗，以比對模擬分析結果，提供適於鋁合金板件成形分析之材料模型。 複雜載具方面，本論文選用實際開發之引擎蓋板，探討傳統鋼板與鋁合金板件之成形差異，經由製程參數與模具修正條件的改善，整理各參數對成品拉伸之影響。引擎蓋板選用了A6181-T4材料，由於 經過T4熱處理後的機械性質會隨著時間而有所改變，因此本研究經由實驗取得各時效時間之材料參數，將時效實驗結果應用於CAE模擬分析，並進行實際開模驗證，以比對鋁合金沖壓成形之分析模式。 本研究採用所上述鋁合金板件成形分析模式，進行鋁合金遊艇外板沖壓成形之技術建立。由於遊艇外板屬大面積且局部深抽型特徵，成形時容易產生破裂與皺褶同時存在之缺陷問題，因此目前遊艇外板的製造仍有賴於焊接製程。遊艇外板材料係選用具耐腐蝕性的A5083-O，再針對遊艇外板之成品部份進行特徵歸納及成形性分析，將其難以克服之特徵造型，給予較佳化之餘肉造型（addendums）設計與製程參數，以改善鋁合金遊艇板件之沖壓成形技術問題。

In recent year, customers had raising demands for the coziness of spaces and multi-functions, which makes the sizes and weights of vehicles increased. However, when facing the energy crisis and the deteriorating living environment, it is essential to decrease the emission of greenhouse gases. To produce light-weighted parts then becomes the goal of most sheet metal factories. In European and American countries, some factories have even launched aluminum alloy automotives and aluminum alloy yachts one after another. The weight of aluminum alloy is approximately one-third of steel; as a result, aluminum alloy has gradually substituted for steel. Aluminum alloy bears its own advantages of light-weight and better corrosion resistance, but its formability is inferior to that of steel. In the stamping process, except that aluminum alloy would crack easily, the low elastic modulus makes the aluminum alloy easier to produce a significant springback defect, which would lead to variation of accuracy hard to grapple with. As a result, the design concept of stamping conventional steel sheets cannot be completely applied to the die design of aluminum alloy, which causes the tooling maker to spend more time and money to develop a set of stamping dies. And thus, the computer-aided engineering (CAE)technology becomes even more necessary in helping the die design. It is well known that the material model including the yield criterion and the hardening rule plays an important role in the CAE analysis for predicting the springback. In the present study, the tension-compression reversal tests were conducted to obtain the stress-strain relations and the Bauschinger effect exhibited in the A5083-O and A6181-T4 sheets. The test results were fitted into different yield criteria and work hardening rules used in different finite element software. The finite element simulations were then preformed for V-bending and U-hat drawing of A5083-O and A6181-T4 sheets, and the results of springback and side-wall curl were compared with those obtained from experiments. It can be concluded from the comparison that the material model which includes the Bauschinger effect renders a more consistent results with the experimental data. The formability of stamping an engine hood with A6181-T4 was also examined in the present study. The aging phenomenon of A6181-T4 was first observed from aging tests and the test results were included in the subsequent finite element simulations. In order to investigate the difference of forming characteristics between conventional steel and A6181-T4 in the stamping process of an engine hood, the effects of material properties, such as n-value, r-value and yield stress, on the different forming modes were systematically analyzed by the finite element simulations. In addition, the stamping process of the outer panels of a yacht with A5083-O sheets was developed in the present study to replace the current welding process. Due to the V-shaped deep drawing, the defects of wrinkling and fracture are apt to occurring in the stamping process. In order to avoid the presence of these defects, the deformation mechanism in the stamping process of the yacht outer panels were characterized by the finite element simulations. An optimum die face shape with a proper addendum design was then developed according to the finite element analysis, and an actual stamping die set is scheduled to be manufactured following the suggested die design.