The cooling system design and the process parameters study for hot stamping
Date Issued
2011
Date
2011
Author(s)
Hou, Chia-Wei
Abstract
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.
Subjects
hot stamping
die cooling system
22MnB5 sheet
flat-shaped dies
U-shaped dies
process parameter
finite element analysis
experimental validation
Type
thesis
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