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Two types of approaches for material definitions and methods for worst case scenarios are explored. The first is from the material specification supplied by the OEM or the alloy producer for the material, which has basic material properties and no specific FLC. The potential exists that any material within the specification can be delivered to the stamping plants. The second is if the material is to be supplied within a narrowed band of material specification with a known FLC. For both cases, there is considerable pressure from product design to use the most formable material possible. However, if a material is delivered outside the FEA testing limits, the results can be catastrophic. A specification is proposed to take advantage of the formability capability to enhance product performance while minimizing stamping plant risk.

A common occurrence in computer aided design is the need to make changes to an existing CAD model to compensate for shape changes which occur during a manufacturing process. For instance, finite element analysis of die forming or die tryout results may indicate that a stamped panel springs back after the press line operation so that the final shape is different from nominal shape. Springback may be corrected by redesigning the die face so that the stamped panel springs back to the nominal shape. When done manually, this redesign process is often time consuming and expensive. This article presents a computer program, FESHAPE, that reshapes the CAD or finite element mesh models automatically. The method is based on the technique of volume morphing pioneered by Sederberg and Parry [Sederberg 1986] and refined in [Sarraga 2004]. Volume morphing reshapes regions of surfaces or meshes by reshaping volumes containing those regions.

The CAE analysis revealed that a stamping component required extremely high yield strength steel in order to pass the safety requirements. However, springback with this component could cause assembly distortions. The formability prediction was compared with the actual nominal die stamping for splits and wrinkles. The predicted free state springback was compared to the measurements. A compensated die was engineered based on the springback dimensions of the free state stamping. Morphing the negative residual surface created the dimensional compensation. Then a new compensated die face was created. A CAE prediction was used to confirm and adjust the compensated die using iterations of predictions and corrections.

The use of aluminum alloys as automotive body materials increases the need for springback control because of their higher yield strength-to-elastic modulus ratios. Math-based tools can be used to predict the amount of springback of sheet metal parts after stamping, and to further compensate the die face, based on the prediction, to reduce springback. In this study, analysis was conducted with LS-DYNA [1] on an aluminum hood inner to verify the accuracy of springback prediction. This was used as a basis for the die face compensation through a morphing procedure [2, 3]. Reasonably accurate springback prediction was obtained in the rear region of the hood inner, while in the front center region, LS-DYNA over-predicted springback. Gravity loading, appropriate mesh size and adaptive level can all affect springback prediction. Material models have a significant effect on springback prediction of this part.

A CAE NASTRAN based analysis along with GM internal software provides the capability to morph math surfaces that represent the clamped state of components in a weld station. These surfaces can clearly show the interference and gaps between mating flanges. Section plots are the method of detecting and dimensioning the weld mismatch. The sheet metal die changes for fitting the flanges together and correcting excessive weld flange gaps or interference are determined. Another morphed CAD model of the corrected stamping shape is sent to the die plant for guiding the die changes.