Abstract
Due to the ongoing endeavors to reduce CO2 emissions in the energy sector, particularly through advancements in electric mobility, the demand for thin metallic components is currently increasing. This demand is notably apparent for bipolar plates, which are used in fuel cells. The production of these bipolar plates requires high-precision hollow embossing of thin metallic foils with thicknesses below 100 µm. Even minor variations in this process can result in forming defects and undesirable springback in produced parts. A robust design of manufacturing processes for bipolar plates therefore necessitates the implementation of accurate finite element analysis (FEA), since this is crucial for predicting material behavior during and after the forming process. However, the precision of such simulations is heavily dependent on the material models employed. For this reason, the study presented in this paper specifically focused on the numerical modeling of high-precision hollow embossing of bipolar half-plates. For this purpose, a comprehensive material characterization of a 1.4404 stainless-steel foil with a thickness of 0.1 mm was conducted first. Moreover, an experimental laboratory geometry and a corresponding laboratory tool for the hollow embossing of miniaturized bipolar half-plates was developed in order to enable a comprehensive evaluation of the simulation results. The validation and assessment of widely used material models for metal forming in LS-Dyna, exemplified by MAT_036 Barlat ’89 and MAT_133 Barlat 2000, were effectively demonstrated through experimental forming tests. These tests confirmed distinct performance differences between the two material models concerning springback and thinning. Importantly, it was confirmed that the simpler MAT_036 model exhibits high accuracy in predicting both springback and thinning, emphasizing its effectiveness in capturing relevant deformation properties during the hollow embossing process.
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