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In this paper, the factors that affect the accuracy of springback prediction are discussed. Springback predictions of aluminum and high strength steel panels are compared with measurement data. The effect of springback can be reduced or eliminated through process control and die face compensation. The first method involves finding the root causes of springback and eliminating them through process modification. The second method is a direct way to eliminate the springback effect. For large springback with twisting, an incremental compensation is required and the final deviation can be controlled by setting tight convergent tolerance. Stamping production environment can introduce many variables which deviate from engineering condition. The paper shows that material property change within the same grade will cause significant springback variation. This means that the process control is one of the key factors that we have to pay attention to solve springback issue.

A demonstration of the preform anneal process was conducted to form a one-piece aluminum door inner. In preform annealing, the aluminum panel is partially formed, annealed at 350°C to eliminate the cold work (strain hardening) 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. Preform annealing uses non-age hardenable aluminum alloys of the 5xxx series and is suitable for a wide range of interior body panels. A rear door inner panel for a mid-size sports utility vehicle (SUV) was used in this study. This door inner was successfully created in one piece out of AA5182-O sheet with only slight design modifications to the original steel product geometry. The design of the door inner panel was conducted based on finite element analysis and predictions were verified with physical parts using thickness measurements and mechanical testing.

The analysis of localized necking is strongly dependent on the yield function. Numerous yield criteria have been advanced to characterize the plastic deformation of sheet materials. Among them Hill's 1948 and the fourth form of 1979 yield criteria are the most commonly used yield criterion. A new and user-friendly yield criterion was proposed by Hill in 1993, which uses five independent and easily-obtainable material parameters. The present investigation compares these three yield criteria in forming limit predictions based on the M-K approach. The M-K analysis based on Hill's 1993 yield criterion yields forming limit predictions for aluminum in good agreement with experimental data. All three yield criteria are found to provide acceptable predictions for aluminum killed steel.