Numerical Approach for the Modelling of a Sheet Metal Folding Process

Folding is a process of forming cellular structures out of a flat raw material. Through this technology it is possible to create sharp-edged structures with high depths and multiple bending axes and for this reason it is part of the technical origami.Current research work at the IFU focuses on applying this technique to sheet metals with thicknesses between 0.5 - 2mm. These kinds of structures can be used for optically appealing claddings, heat exchangers or sandwich panel core materials. In previous projects, it was shown that it is necessary to pre-crease the bending axis on the flat raw material to achieve a defined folding process. For sheet metals, in particular the embossing of grooves is a promising approach. The general challenges for folding sheet metals are the forming of radii, the hardening effects emerging in the bending axis, and well-ordered design of appropriate tool concept. Also appropriate FEA models are necessary for a sufficient development of this process. The embossing of grooves itself is a bulk metal forming process and, therefore requires volume elements. Folding itself, however, is a forming process of large blanks, which is why simulations based on tetrahedral elements are extremely time-consuming. For this reason, two different models are necessary. The first model, which has integrated volume elements, simulates the folding of single folding cells targeting to detect the interaction of the embossing and the subsequent bending process. In the second model, shell elements are used, with a focus on the effect of the grooves' run rather than the effects of the embossing itself.In this paper, a FEA model for the folding of a mono cell is presented, which shows that a defined folding with small radii for sheet metals with blank thicknesses larger than 0.5mm is possible as well.