汽車結構件熱沖壓成形之製程參數分析

Abstract

由於國際間日益重視環保節能與提高汽車安全性，如何有效提升汽車結構強度並減輕車體重量，已成為各大車廠追求之目標。目前各大車廠多採用先進高強度鋼板(Advanced High Strength Steel, AHSS)作為結構件之用料，而為了開發更高強度之汽車構件，產學研各界近年來皆均致力於發展熱沖壓製程，以求強度達到1200MPa以上之結構件，增加汽車安全性。本論文即是針對熱沖壓製程，探討有限元素法之分析模式以及各製程參數對熱沖壓成形之影響。 本論文首先針對熱沖壓製程進行文獻之蒐集，了解目前熱沖壓製程之發展與研究現況，並歸納各文獻所使用之板材與模具材料性質。隨後針對熱沖壓製程進行有限元素法分析模式之建立，包含板材出爐空冷熱傳分析、板材熱沖壓成形分析，以及板材模內淬火分析等，藉由有限元素法分析可掌握各階段板材與模具之溫度歷程，並確保板材淬火後之金相組織達到強度要求。同時本研究亦進行U型模具熱沖壓循環製程實驗，探討循環製程下板材與模具之溫度變化，以及驗證熱沖壓限元素法模擬之準確性。 此外，本論文亦以汽車結構件A柱作為實際載具進行熱沖壓製程之研究，藉由前述所建立之熱沖壓限元素法分析模式進行A柱之製程分析，探討兼顧冷卻效率與加工成本之較佳化冷卻系統配置方式，並分析不同製程參數對於板材成形性與淬火特性之影響。 本論文所建立之熱沖壓分析模式已由U型模具循環熱沖壓實驗進行驗證，實驗所得之板材與模具溫度歷程與模擬相符，可將此分析模式應用於實際熱沖壓構件之量產製程設計，提升業界於熱沖壓成形領域之製程技術。

Due to the demand for fuel consumption reduction and automobile safety improvement, the automobile industry takes a lot of efforts to increase vehicle structural strength and decrease its body weight effectively. One way to achieve these targets is to use advanced high strength steels. However, the formability and shape controllability are the two main problems that are difficult to overcome. Another method is to use the hot forming process, which would result in better formability and less springback effects. Therefore, the latter method has become more popularly applied in the automotive industry. This thesis focuses on the hot forming studies, investigating the latest developments in the hot forming process and related material properties. In order to employ the finite element analysis to explore the hot forming process, this thesis set up a simulation model to examine the temperature history of blank and tools in the hot forming process, which includes hot blank air cooling, hot forming, and quenching. To validate the accuracy of the finite element analysis, U-shaped tools were designed for the cyclic hot forming experiments with thermal couples embedded in the die and punch to measure the tool temperature history for comparison. With the constructed finite element model, the hot forming process of the automobile structural parts A-pillar was also investigated in this thesis process, including cooling system design, process parameter analysis, and formability analysis. An optimum hot forming process for the A-pillar was then proposed. The research results obtained in this thesis could provide a reference for the future study on the hot forming process.