Wiping die bending of laminated steel

Laminated steel is a sheet metal product consisting of two steel sheets with a thin, viscoelastic polymeric layer between them. The product integrates structural function with sound and vibration absorbing capabilities. Under bending operations, such as wiping or V-press bending, however, the walls of bent parts develop an undesirable curl and consequently an apparently larger spring-back angle. This work addresses bending of laminated steel strips by wiping and their resulting shape using both experimental and numerical approaches. The experimental results indicate that for the materials and geometry used here, the curl can be reduced somewhat by employing larger punch strokes. In addition, the curl decreases slowly with time over many days due to the viscoelasticity of the polymer layer. The reduction in curl due to both effects, however, is not sufficient to eliminate the problem. A numerical, finite-element model to simulate the experiments was developed and yielded reasonably good agreement with the experiments. A parametric study indicated that the curl decreases with decreasing yield stress and increasing thickness of the steel sheets. Increasing the shear stiffness of the polymer layer from zero leads to increasing curl until a maximum is reached. Further increase yields a slow decrease in the curl.