Ongoing miniaturization in various technical fields such as the electronics industry or micro-systems technology requires precise forming processes for the production of small and thin components; for example, thin metal foils are being used in microelectromechanical systems, electronic components, and medical devices. In the same manner as micro bulk-metal-forming processes, metal foils with thicknesses in the range of microns are subjected to so-called size effects. Previous investigations of various metal-forming processes have shown the share of surface grains to be a decisive factor in micro foil forming behaviour. Besides this general size effect, every forming process exhibits specific size effects. In the case of bending processes, large strain gradients are present, influencing the bending parameters and process accuracy (e.g. spring-back). In the present paper, a free bending concept is introduced, which enables the determination of size effects that occur. The mechanical properties and bending behaviour of metal foils with thicknesses ranging from 25 μm to 500 μm are discussed in terms of material properties, microstructure, and foil thickness. Fundamental experiments are performed, providing an experimental basis for future development of theoretical models to describe strain gradient-dependent forming behaviour of foil bending processes. The experimental results are compared with finite element simulations and the strain hardening behaviour is characterized by micro-indentation tests.
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