Development of a hot stamped channel section with axially tailored properties - experiments and models

In this work, the in-die heating (IDH) tailored hot stamping (THS) process is considered, in which the forming tool is partitioned into zones that are either cooled or heated. Four configurations of THS rails were formed: a non-tailored configuration using conventional room temperature tooling and three tailored configurations in which one-half of the rail was formed in tooling that was heated at different temperatures (in the range 400-700 degrees C). Micro-hardness measurements confirmed that THS can be used to form an axial crush member that contains tailored properties along its length. The as-formed parts exhibited a Vickers hardness of 430-484 HV in zones formed in cooled tooling, 235-280 HV in zones formed in tooling that was heated to 400 degrees C and 190-215 HV in zones that were formed when the die set was heated to 700 degrees C. Numerical models of the THS process were developed using the Akerstrom material model in LS-Dyna. As part of the modelling, the activation energies for each phase were calibrated using an LS-OPT routine. The resulting hardness predictions were compared with experimental data to assess the accuracy of the LS-OPT routine. The predicted hardness distributions in the components were quite accurate (usually within 10%, but as high as 16% in some cases).