High Strength Steels (HSS) have been widely used in automotive industry for structural components thanks to their high specific strength. The main problem connected to these materials, that is their limited ductility at room temperature, can be overcome by operating at elevated temperatures. In this context, hot stamping has proven to have great potential of competitiveness: in order to exploit all their potential advantages the whole process chains as well as thermal and mechanical parameters are to be very accurately designed. Numerical simulations of the process represent a powerful tool in doing that, even if they need a great mount of data about material behaviour and boundary conditions. Particularly, the knowledge of the friction coefficient and the effective Heat Transfer Coefficient (HTC) between punch and workpiece has to be as accurate as possible for a realistic process simulation. The present work focuses on the experimental investigations related to the determination of heat transfer coefficients in the case of hot stamping of high strength steels. A new experimental set-up was developed to evaluate the heat transfer between the sheet and the punch at different values of applied pressure. During the test, the sheet is heated up above austenitization temperature, held in temperature to reach homogeneous thermal conditions, and then processed. The identification of the effective punch/workpiece HTC was done employing an FE model of the test combined with an inverse analysis technique. Both steels and ceramics were utilised as die materials: the W300 hot working tool steel, that is the one currently employed in industrial operations, and Zirconium dioxide. Experiments results show that, when applying Zirconium dioxide as die material, the heat transfer is much lower compared with the steel. Therefore, Zirconium dioxide inserts can become an alternative to tool steel, when zones made of different microstructures have to be realized on the hot stamped component.

Investigation of die materials in hot stamping operations

GHIOTTI, ANDREA;PELLEGRINI, DANIELE;BRUSCHI, STEFANIA
2010

Abstract

High Strength Steels (HSS) have been widely used in automotive industry for structural components thanks to their high specific strength. The main problem connected to these materials, that is their limited ductility at room temperature, can be overcome by operating at elevated temperatures. In this context, hot stamping has proven to have great potential of competitiveness: in order to exploit all their potential advantages the whole process chains as well as thermal and mechanical parameters are to be very accurately designed. Numerical simulations of the process represent a powerful tool in doing that, even if they need a great mount of data about material behaviour and boundary conditions. Particularly, the knowledge of the friction coefficient and the effective Heat Transfer Coefficient (HTC) between punch and workpiece has to be as accurate as possible for a realistic process simulation. The present work focuses on the experimental investigations related to the determination of heat transfer coefficients in the case of hot stamping of high strength steels. A new experimental set-up was developed to evaluate the heat transfer between the sheet and the punch at different values of applied pressure. During the test, the sheet is heated up above austenitization temperature, held in temperature to reach homogeneous thermal conditions, and then processed. The identification of the effective punch/workpiece HTC was done employing an FE model of the test combined with an inverse analysis technique. Both steels and ceramics were utilised as die materials: the W300 hot working tool steel, that is the one currently employed in industrial operations, and Zirconium dioxide. Experiments results show that, when applying Zirconium dioxide as die material, the heat transfer is much lower compared with the steel. Therefore, Zirconium dioxide inserts can become an alternative to tool steel, when zones made of different microstructures have to be realized on the hot stamped component.
2010
Proceedings of IDDRG: Tools and Technologies for the Processing of Ultra High Strength Steels
9783851251081
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/2472785
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