鋁合金板件沖壓成形之回彈分析與改善研究

Abstract

本論文主要探討鋁合金A6061在冷成形製程下透過阻料條設計改善回彈以及透過溫成形製程改善回彈的方式。兩者回彈改善機制並不相同，以阻料條設計而言，是透過後拉伸的方式改善板材內外表面應力不均的現象，進而抑制回彈現象；而溫成形製程則是透過加熱板件使得其材料曲線強度降低，進而使得產生回彈量減小。 在分析上述製程前，先探討鋁合金A6061-O與A6061-T6之材料性質與材料參數，包含A6061-O與A6061-T6之加工硬化指數與塑性應變比值等材料參數，針對材料參數進行成形性與回彈分析，藉此比較鋁合金與鋼材不同材料性質對應之成形性與回彈差異。後續再建立A6061之材料模型，其中包括非等向性之降伏準則參數 (Hill48、Barlat91)，並且探討A6061-O與A6061-T6之包辛格效應(Bauschinger effect)，建立鋁合金A6061-T6之Yoshida模型。 建立上述之材料模型後，透過基礎載具包含V型彎曲、U型帽狀引伸等模具進行回彈模擬分析，驗證前述材料模型之準確性，建立適合鋁合金A6061之回彈分析模型，並且進行後續的回彈改善研究。 針對回彈改善方法，本論文首先探討阻料條改善A6061-T6之回彈， 使用阻料條設計流程建立適合鋁合金A6061-T6之阻料條造型，並使用U型帽狀引伸模具搭配可調式阻料條驗證其阻料條設計，確認其有效改善回彈。另外也探討鋁合金在溫成形製程條件下回彈改善的趨勢，使用V型彎曲溫成形實驗，得到A6061-T6在三溫度製程條件下的回彈改善角度，發現隨溫度升高，其回彈角度有變小的趨勢。並且依照沖頭圓角較大的彎曲成形，其回彈改善比率較大。

This thesis mainly studied the springback improvement methods of the aluminum alloy A6061, including using the drawbead in cold forming process and forming aluminum in warm temperature. These springback improvement methods are not the same diminishing springback mechanism. In terms of drawbead design, drawbead can achieve “post-stretch” effect and unify stress distribution on blank’s upper or lower surface. On the other hand, due to material strength reduced after heating the blank, the springback phenomenon improved. Before analyzation these two process, the material properties of the aluminum alloy A6061-O and A6061-T6 were studied first. The material properties include working-hardening ratio and plastic strain ratio etc…The influence of A6061 material properties in formability and springback had been analyzed, and the differience of formability and springback between aluminum and steel had been discussed. The material model of A6061 has been established, including non-isotropic yield function parameters (Hill48, Barlat91). On the other hand, Bauschinger effect of A6061 had been considered in this thesis, so the Yoshida- Uemori model of A6061-T6 was established. After established the material models, the springback analysis simulations including V-bending and U-hat drawing were conducted in this thesis. With simulations of different material models, the proper material model could be figured out by comparing with experiment data. About springback improvement methods, the drawbead design was studied to eliminate the springback of A6061-T6. The U-hat shape drawing die with drawbead design experiment was conducted to confirm influence of drawbead design on the springback phenomenon. The V-bending warm forming process of aluminum A6061-T6 was also conducted to discuss the springback improvement in three experimental temperatures. The results show that the springback degree decreases when the blank temperature increases, and the ratio of springback improvement increases when the fillet of punch increases.