FEM simulation of multi step forming of thick sheet

A case study has been performed on the forming of an industrial product. This product, a bracket, is made of 5mm thick sheet in multiple steps. The process exists of a bending step followed by a drawing and a flanging step. FEM simulations have been used to investigate this forming process.
First, it has been investigated on a representative section whether shell elements can still be used for a small curvature thickness ratio. The difference between solid and shell elements proved to be acceptable, so shell elements have been used in the subsequent work.
The next topic that will be addressed is the simulation of the combination of two forming steps. The springback of the sheet after the bending step is calculated and the results are transferred as initial condition to the next drawing simulation. Implicit dynamics and gravity are needed for the simulation of the closing of the curved blankholder with a curved product. Element refinement is used, as the radii of the tools in the drawing step are much smaller than in the bending step.
From practice it is known that this product does not fail by necking during drawing but fails at the product radius. Therefore the commonly used FLD in sheet metal forming cannot be used here. Instead fracture criteria are used to assess the failure of this product. A tool modification shows how this forming process can be influenced.