Formability Characteristics of Advanced High Strength Steel Sheets in Hydromechanical Forming
Date Issued
2010
Date
2010
Author(s)
Chou, Yi-Hong
Abstract
Recently, the applications of advanced high strength steel have become more popular in the automotive industry due to the high demand of light-weight vehicles. However, in the stamping of advanced high strength steel sheets, there is a major defect that produces dimension variations of shape geometry such as springback and distortion. Therefore, reducing the springback of advanced high strength steel is an urgent problem at present.
Unlike the traditional stamping process, hydromechanical forming replaces the die with a fluid chamber. This makes the blank able to sustain a uniform pressure, and ameliorate the formability. Hence, the superiority of the hydromechanical forming process on reducing the springback occurred in the forming of advanced high strength steel sheets was examined by both the finite element analysis and experimental approach.
The deformation mechanism of advanced high strength steel sheets in the hydromechanical forming process was studied first using the finite element software PAM_STAMP 2G. The convergence tests of element size, integration points and stamping velocity were discussed. With the established simulation model, the influence on springback with different hydraulic pressure curves were compared, and the simulation results were used to determine the hydraulic pressure curves used in the subsequent simulations.
The basic process parameters of traditional stamping and hydromechanical forming were also generalized, including: steel strength, sheet thickness, holding force, hydraulic pressure, die radius and punch radius. With the use of the finite element simulations on hydromechanical forming, the effects of the process parameters on springback were observed, and the causes of the difference between hydromechanical forming and stamping process were discussed.
The experiments of forming the advanced high strength steel sheets with both traditional stamping process and hydromechanical forming were also conducted in the present study. The consistence of the finite element simulation results and the experimental data confirms the accuracy of the finite element analysis. In addition, both the finite element analysis and the experiments indicate that the springback can be reduced if the hydromechanical forming is applied compared to the traditional stamping process.
Subjects
hydromechanical forming
traditional stamping process
advanced high strength steel
springback
process parameters
finite element analysis
experiments
Type
thesis
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