Investigation of Tribological Conditions within Partial Hot Stamping

The importance of lightweight construction in modern car bodies is motivated by current challenges like reducing the fuel consumption and increasing safety standards. Besides the substitution of common steel grades with aluminum alloys and high strength steels, hot stamping has been established for producing safety relevant components. By using hot stamped parts, the fuel consumption can be reduced while improving the crash performance due to the substitution of conventional steel grades by hot stamped high strength steels with thinner sheet thickness. Partial hot stamping represents a variation of direct hot stamping and provides the opportunity of adjusting the final mechanical properties by altering the tool temperature. Thus, the passenger safety can be further improved by producing structural components with tailored properties considering the final requirements. Finite-element (FE) simulation plays an important role for the design of partial hot stamping processes due to thermo-mechanical interdependencies taking place during the forming. In order to achieve an accurate modelling of the process, reliable input parameters are necessary. Currently, hot stamping processes are modelled assuming a constant friction coefficient due to the knowledge gap regarding the tribological behavior within hot stamping. For the experimental investigation of the tribological conditions under direct hot stamping conditions, a hot strip drawing test rig is used within this study. The influence of tool temperature on the friction is examined for varied workpiece temperatures, contact pressures and drawing velocities. The experiments are performed with AlSi coated 22MnB5. For analyzing friction and wear mechanisms, the surfaces of the specimens are characterized.