鋁合金板件溫成形製程之成形性研究

Abstract

由於汽車產業對於輕量化的追求以及鋁合金的高強度重量比，鋁合金在汽車零組件的應用日益增加，而由於鋁合金在常溫下的低成形性，促成產學研各界著重於鋁合金溫/熱成形技術之研究，以提升鋁合金之成形性。雖然溫成形製程能夠改善鋁合金之成形性，但是成形溫度過高會導致強度減損發生，由於成形溫度的限制所以仍有回彈及破裂等成形缺陷待改善。而一般溫成形T6製程，其強度會在烤漆後減損，因此本論文配合國立台灣大學材料系顏鴻威團隊提出的時效成形(Aging Forming, AF)製程進行研究，其相較於溫成形T6製程具備較佳的成形性以及在烤漆後具有較高的強度，彰顯出AF製程的研究價值。然在AF製程之成形溫度範圍內，尚不足以完全避免回彈與破裂缺陷之產生，仍有賴製程工法以及模具設計來克服成形缺陷的問題，此亦是本論文主要之研究目的。 本論文藉由有限元素分析方法，建立鋁合金溫/熱成形製程分析技術，使用學界及業界公認具代表性的U型基礎載具探討鋁合金AF製程的成形缺陷，透過分析溫/熱成形製程參數對於成形性的影響，以及透過具統計學基礎的分析方式如田口實驗法探討模具特徵幾何參數對於成形性的影響，對於回彈及破裂缺陷而言，R角尺寸皆為重要模具特徵幾何參數，最後建立AF製程成形特性資料庫，建立鋁合金溫/熱成形成形製程缺陷分析方法。 在成形缺陷改善方面，本論文透過製程工法以及模具設計兩種方法研究回彈改善效果。在製程工法的部分，透過田口實驗法進行製程工法參數對於回彈改善的敏感性分析，並得出保壓對於鋁合金溫/熱成形製程的回彈具有相當程度的影響性；在模具設計的部分，透過分析截面特徵幾何參數對於回彈改善的影響性，並探討其回彈改善機制，藉以建立模面補償流程。最後進行基礎載具U-hat實驗驗證研究結果，由實驗與模擬比較結果，回彈與實驗結果之誤差在10%內，厚度與實驗結果之誤差在2%內，顯示本論文所建立之CAE模擬分析模型具有可信度，而實驗結果顯示在溫成形製程中增加保壓力與保壓時間可改善回彈，提供鋁合金溫/熱成形成形製程缺陷之改善方針。 本論文對於鋁合金溫/熱成形製程之成形性進行完整的分析，並建立一套改善成形缺陷的分析模式，同時針對鋁合金溫成形製程的回彈缺陷提出創新的模具補償流程，提供未來從事鋁合金溫/熱成形研究及應用之參考依據，促進產學研各界在鋁合金溫/熱沖壓技術的發展。

Due to the pursuit of lightweight in the automotive industry and the high strength-to-weight ratio of aluminum alloys, the application of aluminum alloys in automotive parts is increasing. However, because of the low formability of aluminum alloys at room temperature, industrial and academic efforts have been devoted to the research of warm forming technology greatly nowadays. Although the formability of aluminum alloys can be improved by warm forming process, the higher forming temperature will lead to strength decrease. Owing to the restriction of forming temperature, forming defects such as springback and crack still need to be improved. However, the strength of the warm forming T6 process will deteriorate after paint baking. Therefore, this research investigates the aging forming (AF) process, which is proposed by Prof. Hong-Wei Yan. Compared with the warm forming T6 process, it has better formability and higher strength after paint baking. However, within the forming temperature of the aging forming process, springback and crack still can not be avoided thoroughly. It is necessary to overcome the forming defects by process engineering and die design. The finite element method was utilized to establish the warm/hot forming process simulation model in this thesis. The U-hat drawing, which is regarded as a representative in academia and the industry, was utilized to discuss the forming defects of aluminum alloy aging forming process. This study has investigated the influence on formability of warm/hot forming process parameters. The influence of die geometry on the formability of aluminum sheets has also been discussed by using the Taguchi method. The results reveal that the size of die corner radius has a significant impact on forming defects such as springback and crack. Due to previous effort, a database of AF process forming characteristics has been established. The thesis has established forming defect analysis method for aluminum alloy warm/hot forming process. In terms of improving forming defect, this thesis has investigated springback reduction. In process engineering analysis, the sensitivity of process engineering parameters to the springback reduction was obtained by the Taguchi method. Die holding process has a significant impact on reducing springback of aluminum alloys in the warm/hot forming process. In the die design analysis, the mechanism of springback reduction has been investigated. A die compensation method has been proposed. Experiments have been implemented to verify the simulation results. It is validated that the siumlation model can achieve an accuracy of 90% in predicting springback, and of 98% in predicting the thickness of aluminum alloy sheet. Experimental results also show that increasing the die holding pressure and die holding time in the warm forming process can reduce springback. A design guide for the forming defect improvement in aluminum alloy warm/hot forming process has been established in this study. This thesis presents a comprehensive research on the formability of aluminum alloy warm/hot forming process and establishes analysis procedure to improve forming defects. A novel die compensation procedure for eliminating springback of the aluminum alloy warm forming process has been proposed. This thesis provides valuable references for promoting the development of aluminum alloy warm/hot forming technology in industrial application and academic research.