Understanding temperature and contact pressure in hot stamped channels

This paper investigates the temperature and contact pressure conditions in hot stamped channels of boron steel. Hot stamping has been used for many years to produce high strength structural automotive components. The high tensile strengths achievable by hot stamping is beneficial where the intrusion during a vehicle crash is not desirable – e.g. for the vehicle occupant compartment. However, the high blank temperatures and high temperature cycling causes a large amount of wear in the tooling. These conditions have led to high tool failures and die maintenance costs. Thus, understanding the main causes of wear behaviour in the hot stamping process is of high interest to hot stampers. To this aim, a generic 2D thermo-mechanical finite element model of a hat-shaped crash formed hot stamped component was developed (based on the authors previous hot stamp model), and a modified phase transformation model based on Scheil’s additive principle has been applied. The model was created in the finite element software ABAQUS Standard V6.13, including convection and radiation when the component was transferred from furnace to the tool as well as the aircooling process. A USDFLD subroutine was used to model the phase transformation and a HETVAL subroutine was used to model the latent heat. Contact heat conductance was a function of the pressure. The authors have used techniques from their previous work on tool wear estimation for cold stamping to estimate the contact pressure on the tooling, and the amount of sliding that occurs over the tooling, and the corresponding tooling temperature. This data provides a unique data set to understand the wear on the tooling, and will eventually lead to a model for estimating tooling life.