A Demonstration of Local Heat Treatment for the Preform Annealing Process

The preform annealing process is a two-stage stamping method for shaping non age-hardenable (i.e. 5000 series) aluminum sheet panels in which the panel is heat treated in between the two steps to improve overall formability of the material. The intermediate annealing heat treatment eliminates the cold work accumulated in the material during the first draw. The process enables the ability to form more complex parts than a conventional aluminum stamping process. A demonstration of local annealing for this process was conducted to form a one-piece aluminum liftgate inner panel for a large sport utility vehicle using the steel product geometry without design concessions. In prior work, this process was demonstrated by placing the entire panel in a convection oven for several minutes to completely anneal the cold work. However, the use of local annealing at critical areas of the panel via induction heating coils reduced the cycle time of the annealing step from 20 minutes to less than 15 seconds. This liftgate inner panel was successfully formed in one piece with AA5182-O sheet, which was not possible with conventional stamping.