A Study of Distortion in Stamping of Advanced High Strength Steel Sheets
Date Issued
2010
Date
2010
Author(s)
Wei, Hua-Zuo
Abstract
With technology advancing, the performance and equipment of automobile are improved, and the demand for the automobile body structural parts is also increased. To cope with the energy crisis problem and the rising importance of collision regulations, reducing weight and increasing strength of an automotive structure are the goals for the major car manufacturers at present. Although the use of light metal such as magnesium and aluminum are alternatives to achieve the purpose of light weight, the price of these metals is relatively higher than that of steel. Therefore, the advanced high strength steel with the characteristics of high strength and low cost are applied to the automobile industry gradually.
Despite the high strength and low cost characteristics borne by the advanced high strength steel, the formability is much poorer than that of traditional low strength steels. In the stamping process, the advanced high strength steel is not only easy to produce cracks and wrinkles, but also is difficult to overcome the variations of dimensional accuracy caused by springback, sidewall curl and distortion after forming. Hence, the implementation of CAE simulation technology to assist the die design of stamping advanced high strength steel sheets has become a popular trend in both the automotive and the tooling industries.
In order to improve the accuracy of CAE simulation analysis, different yield criteria and work hardening criteria were first discussed in the present study. Then the CAE simulations were performed to examine the stamping processes for some simple shapes, such as V-bending and U-hat bending with the use of Hill 48 and Barlat yield criteria. The convergence tests were conducted to identify the sensitive simulation parameters and an optimum set of parameters was established. The simulation results were then compared with the experimental data to investigate the effect of different yield criteria on the occurrence of springback and sidewall curl.
The forming of an S-rail shape was also examined by the finite element analysis in the present study. The benchmark experimental data published in the International Conference NUMISHEET in 1996 was adopted to verify the accuracy of the finite element simulation results. The influences of process parameters on distortion were further discussed, and the deformation mechanism of distortion was investigated as well. Finally, the methods of ameliorating distortion were analyzed, including the drawbead design and blank holder force. The results obtained in the present study could be valuable references to the future research in the stamping of advanced high strength steel sheets.
Subjects
advanced high strength steel (AHSS)
stamping
springback
sidewall curl
distortion
yield criteria
Type
thesis
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