Production and characterization of complex folded cellular structures made of sheet metal

• Applicants: Professor Dr.-Ing. Mathias Liewald; Professor Dr.-Ing. Peter Middendorf
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: from 2019 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 427257349

By folding flat semi-finished products, three-dimensional cellular structures can be produced. Folding structures can be used in various technical fields, especially as sandwich core material between two covering sheets. Sandwich construction methods offer the possibility to put rigid, large-area components into effect. These components have considerable weight and material savings compared to conventional monolithic or differential construction methods.Today’s cellular folding structures can only be produced from initial materials with very small sheet thicknesses (s0 ≤ 0.2 mm). In addition to their use as sandwich elements, folded structures with thicker sheet metals offer considerable potential for the industrial use as cladding elements, crash and carrying structures.The cellular folding cores made of sheet metal are based on isometric folded structures. In the initial state, a mostly flat semi-finished product is formed into repeating unit cells by local bending processes around one or more bending axis orientations (BAO). Bending according to DIN 8582 takes an exceptional position, since the formation of local bending axes enables complex shaping of the workpiece (here the core), which enables an extraordinarily application and application-specific component design. The aim of the research project is the production and characterization of complex cellular structures made of aluminium or steel sheet with thicknesses greater than 0.5mm. For this purpose, a workflow is being developed that covers all aspects from the geometric and structural design to the newly developed production technologies and their technological limits to the manufacture and inspection / quality assurance of optimized structures made of sheet metal in the above-mentioned thickness range. The following sub-targets are addressed in particular: - Development and transfer of analytical design methods for folding thicker sheets - Development of methods for pre-structuring sheet metal - Process development for the production of folded sandwich cores - Modelling of the mechanical properties of sandwich panels and definition of process boundariesThe scientific findings of this project on the one hand enable a more precise estimation of the potential of folded structures made of sheet metal as a new type of core material for two-dimensional sandwich applications and on the other hand extend the basic knowledge on the behaviour and processing of sheet metal in complex, previously unfinished isometric forming processes.

• DFG Programme: Research Grants