Mechanical properties and bending behaviour of metal foils

Abstract

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.

Investigating the influence of crystal orientation on bending size effect of single crystal beams

“…First and second order derivatives in Eq. (10)are calculated at the midpoint of the deformable region.…”

“…It is not only dependent on the thickness of the sheet but also influenced by parameters like grain size, number of grains across the thickness direction, crystal orientation with respect to loading direction etc. [22,16,10,28,45,15,23]. This complexity in size effect makes it difficult to transfer the knowledge (theoretical and practical) of conventional forming operation directly to the micro-forming operation.…”

Analysis of the Size Effect on Springback Behavior in Micro‐Scaled U‐Bending Process of Sheet Metals

“…The interactive effect of grain and specimen sizes are investigated on the flow stress of sheet metal in microforming via the tensile test of pure copper and numerical modeling . In micro‐bending process, the grain size and thickness of sheet metal, especially for the ratio of sheet metal thickness t to grain size d , are the key factors affecting bending force and springback angle . To extensively investigate the size effect in microforming processes, different material constitutive models were proposed to explain the relationship between the deformation behavior of materials and grain size.…”

Effect of Grain Size on Springback and System Energy in Micro V-Bending with Phosphor Bronze Foil

“…They also proposed a constitutive model based on the surface layer model to study the materials' mechanical response, and linked it with springback behaviour. Diehl et al [18] performed free bending test to find that the scatter of springback angles in coarse-grained material was greater than that in the fine-grained one. [9]Recently, increasing numbers of research are focusing on the grain structure [19] and grains' stress-strain state [20,21] to explain the correlation between the grain size effect and springback.…”

“…Previous studies [11,16,18] have proved that the ratio T/D is a wide-applied indicator evaluation parameter for studying the relationship between the the grain size effect and springback. However, it is also found that there is a lack of research on grain size effect when the ratio is around 1 (greater than 1, less than 1 and equal to 1).…”