Approach to minimize the distortion of 6xxx-aluminum tailor heat treated blanks in industrial applications

Tailor heat treated blanks (THTB) are a well-known approach to considerably enhance the forming limits of 6xxx-aluminum alloys. This is realized by locally adjusting the mechanical properties with regard to a forming operation using a short term heat treatment. However, the resulting temperature distribution unavoidably leads to distortion of the blank due to thermal expansion of the heated areas. This is challenging for automated processing of THTB since dimensional accuracy and stackability must be assured. In this work the influence of heating parameters, tool design and blank thickness on the distortion behavior of 6xxx THTB are investigated by laboratory experiments. To show that it is in principle possible to predict the distortion behavior in advance, a thermo-mechanical simulation is used to recalculate one of the findings. The results from laboratory experiments are transferred and validated on a near-series heating tool. It is demonstrated that distortion can be minimized and controlled in a way that automated processing of THTB becomes possible.