熱沖壓汽車結構件特徵造型之成形性研究

Formability Study of Characteristic Shapes in Hot Stamped Automotive Structure Parts

李政勳(Jeng-Shiun Lee)

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(2015年)

https://doi.org/10.6342/NTU.2015.10513

摘要

摘要
燃油消耗問題成為環保議題的重點討論要素，除了造成環境資源的損耗，溫室氣體的排放也會衍生全球氣候變化，因此節能減碳成為現今全球工業界致力發展改善之趨勢，而汽車產業亦紛紛投入低油耗之輕量化汽車結構設計。但現今車廠常用之先進高強度鋼，隨鋼種強度提高，於常溫沖壓容易產生回彈、扭曲及成形性低等不利於產品設計開發之缺陷，熱沖壓成形製程即因應而生。透過高溫成形，上述成形缺陷可獲得大幅改善；而後續之模內淬火，可使板材組織轉變為高強度之麻田散鐵，其抗拉強度可達1470MPa，使汽車結構件可採用更薄之鋼板藉以達到輕量化之目標。
熱沖壓成形製程中首先必須確保前段熱成形無成形缺陷之產生，藉由有限元素分析，於產品開發前有效預測產品特性以及製程分析將有利於熱成形設計。而特徵造型設計即為各款式汽車結構件開發源頭，如能事先歸納各類載具之特徵造型，並找出不同造型參數下特徵造型對熱沖壓汽車結構件成形性之影響，將可提供模具設計與開發之參考依據。
本論文首先藉由文獻與車廠資訊蒐集，瞭解熱沖壓汽車結構件之使用現況與製程技術之應用，結合實際汽車載具分析結果進行整理與歸納特徵造型種類，透過簡化設計探討特徵造型參數對成形性之影響性，並探討不同成形結果之主要原因。所探討造型種類包含U形基礎載具、高低落差造型與M形特徵造型。
本論文亦應用實驗設計方法分析幾何參數對特徵造型之影響，藉由分析結果說明不同參數之敏感性，同時反應造型之最佳化設計。透過交互作應影響說明理論設計與實際分析結果之差異性，以提供造型優化設計的概念。
為驗證所提出的造型設計之參考性，本論文藉由實際U形基礎載具模擬與實驗進行比對，其中主要進行厚度分析，並由實驗量測結果驗證模擬之準確性。
本論文已建立熱沖壓汽車結構件特徵造型設計與分析模式，未來將可透過造型整合技術應用於實際熱沖壓汽車載具開發，進行更深入之研究探討，以完備車輛造型生產技術發展。

關鍵字：熱沖壓成形、特徵造型、U形基礎載具、高低落差造型、M形特徵造型、實驗設計法、最佳化、交互作用

關鍵字

熱沖壓成形 ； 特徵造型 ； U形基礎載具 ； 高低落差造型 ； M形特徵造型 ； 實驗設計法 ； 最佳化 ； 交互作用

並列摘要

Abstract
Fuel consumption has become an important factor in environmental issue. In addition to causing the loss of environmental resources, gas emission has also led to greenhouse effect and global climate change. Therefore, the automotive industry has been devoted in the development of lightweight car body structure, and the advanced high strength steel (AHSS) is being widely adopted for manufacturing the structural parts. However, by increasing the strength of steels leads to the low formability, high tendency to springback and twisting defect. A hot stamping process therefore becomes an effective solution to cope with the difficulties mentioned above. In addition, due to the transformation of microstructure from austenite into martensite during the die-quenching process, the ultimate strength of the production part can reach up to 1,470MPa with thinner sheet blanks.
In the hot stamping process, a defect-free production part must be assured during the hot forming operation so that the subsequent die quenching operation can be resumed. To examine the formability of sheet blank in the hot forming operation, the geometric features of the production part play an important role on the presence of defects. Therefore, in this thesis the characteristic geometries that affect the formability of sheet blank were identified and classified following a detailed review and generation from the popular hot stamping parts, such as A-pillar, B-pillar and side sill. Three types of characteristic geometries: U-hat, Stepped-shape, and M-shape were then sorted and collated. The geometric parameters that may affect the formability of sheet blank were also determined. The method of design of experiment (DOE) was then adopted to analyze the sensitivity of each parameter on the formability of sheet blank. The finite element software PAM_STAMP 2 G was employed to conduct the hot forming simulations. The relations between each parameter and formability and the interaction of each parameter on the formability were established according to the finite element simulation results based on the DOE.
A hot stamping experiment for manufacturing a U-hat part was also implemented to examine the validity of the relations between geometric parameter and formability constructed in this thesis. The measured thickness distributions of the formed part and those predicted by the finite element simulations are consistent quite well. The validity of the relations between geometric parameter and formability constructed in this thesis is then confirmed.
The method of approach for the characteristic geometry analysis and the relations between geometric parameter and formability constructed in this thesis could be a valuable reference for the future study of hot stamping process.

Keywords：Hot stamping, characteristic geometric shape, formability, U-hat, stepped-shape, M-shape, design of experiment, finite element analysis, experimental validation.

並列關鍵字

Hot stamping ； characteristic geometric shape ； formability ； U-hat ； stepped-shape ； M-shape ； design of experiment ； finite element analysis ； experimental validation

參考文獻

[1]H. Engels, O. Schalmin, and C. Bollenhagen, “Controlling and monitoring of the hot-stamping process of boron-alloyed heat-treated steels”, New Development in Sheet Metal Forming Technology, pp. 135-150, 2006.

[2]A. Naganathan, “Hot Stamping of Manganese Boron Steel(Technology Review and Preliminary Finite Element Simulations)”, Master thesis, The Ohio State University, 2010.

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

[4]B. Yang, D. Zhang, Z. Chang, R. Ge, Z. Wang, and Y. Zhang, “Optimized Design and Numerical Simulation of B-pillar Reinforcement Panel by Hot Stamping Steel”, Advanced Materials Research, Vol. 1063, pp. 309-313, 2015.

[5]H. S. Choi, B. M. Kim, K. J. Nam, S. Y. Ha, S. H. Cha and C. G. Kang, “Development of Hot Stamped Center Pillar Using Form Die with Channel Type Indirect Blank Holder”, International Journal of Automotive Technology, Vol. 12, No 6, pp. 887-894, 2011.