Daniel Berglund, Krister Amundsson, and Lars-Olof Hellgren:
Hot stamped components with soft zones-simulation and validation of material properties and product performance
Hot stamping, soft zones, simulation, validation, microstructure, mapping, crashworthiness
Simultaneous forming and quenching is a method for manufacturing low weight and ultra high strength components.
The process is often referred to as hot stamping or press hardening and is mainly used for producing passive safety components, such as side impact beams, bumper beams and different types of reinforcement components.
Controlling the deformation and avoiding extensive strain localization and cracks around critical areas are important issues when designing an automobile structure for different crash conditions. One method for controlling the buckling and deformation is to use weaker areas by changing the thickness of the component or by reducing the yield and tensile strength of the material.
In this work, a method has been developed to control the cooling rate and, thereby, the mechanical properties of the components during hot stamping. The tensile strength of the material is less than half of that of fully hardened material and the strain-to-failure is increased by factor two. The transition zone from soft to fully hardened material is 10 - 20 mm depending on application. Numerical methods such as the finite element (FE) method are often used in simulations of manufacturing processes and component functionality. A thermomechanical hot stamping simulation has been performed on a beam to predict mechanical properties and the simulated result is compared with measured material hardness. The predicted microstructure after hot stamping is used to estimate mechanical flow stress properties. The estimated properties are exported and mapped to a model with a different discretisation for use in crash analysis. The simulated deformation behaviour during a four-point bending test at high velocity with the predicted material properties from forming is validated by experiments.
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