Formability Analysis Predictions for Preform Annealing of Aluminum Sheet 2011-01-0533
It is important to understand the accuracy level of the formability analysis for any new process so that correct predictions can be made in product and die design. This report focuses on the formability analysis methodology developed for the preform anneal process. In this process, the aluminum panel is partially formed, annealed to eliminate the cold work from the first step, and then formed to the final shape using the same die. This process has the ability to form more complex parts than conventional aluminum stamping, and has been demonstrated on a complex one-piece door inner and a complex one-piece liftgate inner with AA5182-O3. Both panels only required slight design modifications to the original steel product geometry. This report focuses on the formability analysis correlation with physical panels for the liftgate inner, considering both full panel anneal in a convection oven and local annealing of critical areas. For the full panel convection anneal, the mechanical properties are reset to the original incoming properties after annealing, assuming that all cold work has been eliminated. For the local annealing, the mechanical properties are reset to the original incoming properties only for the elements that have been heat treated, assuming a sharp transition zone between the annealed area and the cold worked area. The predictions made in the analysis were verified with physical parts using thickness measurements and mechanical testing. In addition, white light scanning dimensional analyses were compared to springback predictions.