熱沖壓成形之冷卻系統設計與製程參數研究

The cooling system design and the process parameters study for hot stamping

侯佳緯(Chia-Wei Hou)

指導教授 ： 陳復國

國立臺灣大學/工學院/機械工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.02738

摘要

由於近年來環保意識之提升，汽車業為了降低油耗並提升行車安全性，全球各大車廠目前均致力於採用高強度鋼板以達減輕車體重量之目的，然高強度鋼板在沖壓成形過程中容易產生回彈、扭曲等難以預測之現象，導致生產時程較長。因此，熱沖壓成為近年新開發之製程，由組織之淬火相變，使板金產品之強度可達到1600MPa以上，且熱成形可解決回彈以及扭曲之問題，是未來汽車結構件重要之成形技術。
本研究針對熱沖壓製程之冷卻系統進行探討。首先蒐集目前文獻之材料性質參數，然後使用平板模具進行冷卻系統之設計，針對冷卻系統的幾何配置進行循環負載模擬，從中獲得不同設計下之模具穩態溫度，並探討不同設計對於板材之影響，將平板模具所歸納之結果應用於U型模具中，探討冷卻系統設計於U型模具之適用性，並藉由模擬U型成形之熱沖壓過程，探討成形過程中製程參數可能產生之冷卻問題。
本論文藉由平板循環負載模擬，獲得不同冷卻系統設計之穩態模具溫度，從中找尋使板材完全轉換為麻田散鐵之設計範圍，提供未來冷卻系統設計之參考依據；並藉由U型模具之成形模擬探討出壓料力、側壁接觸狀況、板材支撐銷，在成形過程中對板材冷卻影響性，其結果可提供未來模具設計之參考。
本論文使用有限元素軟體進行模擬，最後進行22MnB5板材之熱沖壓實驗，藉由比對實驗與模擬之板材厚度分佈、模具之溫度歷程、板材硬度以及金相結果與模擬結果進行比對，證明模擬結果之可信度。

關鍵字

熱沖壓成形 ； 模具冷卻系統 ； 22MnB5板材 ； 平板模具 ； U型模具 ； 製程參數 ； 有限元素模擬分析 ； 實驗驗證

並列摘要

In order to save the fuel consumption and increase the automobile safety, the car makers take a lot of efforts to reduce the weight of an automobile. UHSS (ultra-high strength steel) is then widely used to increase the strength of car body structure, and reduce the car weight. In the application of UHSS, hot stamping is a new process developed in recent years. The strength of stamped part can reach 1600MPa through the phase transformation by quenching in the hot stamping process. Also the defects of distortion and spring-back can be reduced significantly by hot forming.
The properties of the products made by hot stamping are dominated by the cooling rate during the quenching process. Therefore the design of cooling system is crucial in this process. In order to find the steady temperature under different cooling designs, the finite element simulations were performed with the use of the DEFOEM software to study the cooling system design in a cyclic production condition. The cooling system employed in a flat-shaped tooling was examined first and the optimum design parameters were then applied to a U-shape model.
With a proper set of cooling system design parameters provided, the effects of blank holder force and contact condition at side wall on the cooling condition in a U-shape die were then investigated in this study by the finite element simulations. In order to validate the efficiency and the accuracy of the finite element analysis, both flat-shaped and U-shaped tools were designed and manufactured to conduct the actual hot stamping processes with the use of 22MnB5 sheets. The microstructure and mechanical properties of the hot stamped parts were examined by the metallographic analysis and micro-hardness. The experimental data agree well with those obtained from the finite element simulations. The research results obtained in the present study could provide as a reference for the cooling system design of a hot stamping die.

並列關鍵字

hot stamping ； die cooling system ； 22MnB5 sheet ； flat-shaped dies ； U-shaped dies ； process parameter ； finite element analysis ； experimental validation

參考文獻

[1] K. Mori, S. Maki and Y. Tanaka, “Warm and Hot Stamping of Ultra High Tensile Strength Steel Sheets Using Resistance Heating”, CIRP Annals Manufacturing Technology, 54, pp. 209-212, 2005.

[2] T. Svec, M. Gruner and M. Merklein, “FE-Simulation of the Heat Transfer by Defined Cooling Conditions During the Hot Stamping Process”, Key Engineering Materials, 473, pp. 699-706, 2011.

[3] C. Wang, B. Zhu, Y. Zhang, J. Shi and H. Dong, “Hot-Stamping Process Simulation and Optimize Research for Collision Beam of Automobile Door”, Advanced Materials Research, 201-203, pp. 3-8, 2011.

[4] Z. Zhang, Z. Ye, Y. Zhang and J. Li, “Numerical Analysis on Hot Stamping of B Pillar Reinforcement of Automobiles”, Advanced Materials Research, 97-101, pp. 282-285, 2010.

[5] Z. Xing, J. Cui, H. Liu and C. Li, “Numerical and Experimental Investigation into Hot Stamping of High Strength Steel Sheet for Auto B Pillar Reinforced Panel”, Advanced Materials Research, 129-131, pp. 322-327, 2010.