J. Lechler

Characterisation of the flow properties of the quenchenable ultra high strength steel 22MnB5

Nowadays in the automobile industry more and more high strength steels find their application. For their processing innovative forming technologies, like the non-isothermal hot stamping process, are required. With regard to a reliable numerical process design the knowledge of the thermal and thermo-mechanical properties is essential. Within this paper an experimental setup will be introduced, which enables the determination of the materials flow behaviour according to the hot stamping time-temperature-characteristics. Further results of investigations on the thermo-mechanical flow properties of the quenchenable, ultra high strength steel 22MnB5 in dependency of the temperature, the strain and the cooling rate etc. will be represented.

Determination of tribological conditions within hot stamping

Innovative hot sheet metal forming technologies are gaining an increasing significance in the scope of application of more and more innovative high and ultra high strength steels in the automotive industry. With respect to a numerical process design beside the mechanical and the thermal material characteristics the friction coefficient represents an important input parameter for finite element (FE) simulation. Within the scope of this paper an evaluation method for the determination of the friction coefficient μ for the direct hot stamping process of boron-manganese steels will be presented. Therefore cup deep drawing tests at elevated temperatures following the time-temperature-characteristic of the hot stamping process are carried out. For the calculation of the friction coefficient the approach according to Siebel for the modeling of the maximum drawing force is used.

Interlaboratory Comparison of Forming Limit Curves for Hot Stamping of High Strength Steels

The paper presents the approaches followed by two labs – LFT at the University of Erlangen-Nuremberg (Germany) and DIMEG at University of Padua (Italy) – in evaluating formability limits of 22MnB5 sheets when processed under hot stamping conditions. Details about the two testing apparatuses and the testing procedures are outlined, and the results in terms of Forming Limit Curves FLC compared and critically commented.

Interlaboratory Comparison of Friction Conditions in Hot Stamping Operations

The paper presents results obtained at two labs, on in Germany and one in Italy, in terms of friction coefficient as function of hot stamping process parameters. Even if the testing procedures and analysis tools to evaluate tribological conditions are different for the two labs, both the approaches show a similar trend as regards the friction coefficient dependence from the process parameters.