The use of new materials and complex part geometries poses significant challenges for modeling and finite element simulation of deep drawing processes. Due to the complexity and size of the models used, deep drawing simulation using solid continuum finite elements has proved to be too expensive in industrial engineering practice. However, small thickness to length ratio of sheet metal parts are typically computed using dimensionally reduced finite element formulations. Dimensional reduction and model assumptions provide noticeable simulation time and resource savings at the cost of solution quality. A method to obtain a realistic three-dimensional stress state without a complete nonlinear strictly three-dimensional forming analysis is being developed. The solution enhancement scheme has been efficiently applied to press force and elastic springback computations in industrial models involving up to 1.5 million degrees of freedom. The scheme is being developed and implemented as an add-on to commercial FE-Software.

The extrusion of the whole shell mesh is performed with a subsequent three-dimensional stress state reconstruction. The deep drawing simulation using solid elements took more than ten times longer than the shell element analysis together with the subsequent stress state reconstruction.

Fig. 1: Mesh conversion for a three-dimensional stress-state reconstruction

Fig. 2: Result of a three-dimensional forming analysis (left), reconstructed three-dimensional stress-state (right)

In this project, A method to resolve a true three-dimensional stress-state in nonlinear analyses while saving computational cost is based upon a model-adaptive coupling technique. The solid elements can be used in areas where shell elements do not provide reliable results. The rest of the computational domain can be discretized using shell elements. A consistent shell-to-solid coupling is applied at the interfaces between the two different element types.

Fig. 3: Coupled springback simulation of a metal strip