A multi-region model for numerical simulation of micro bulk forming

Due to the small billet size in micro forming, each grain, especially that on the surface layer, has direct influence on the deformation behavior of the billet. The multi-region model was proposed for simulating the micro bulk forming process in this paper. The object in the model is divided into three different regions: the inner polycrystal region, the grain interior of the surface region and the grain-boundary layer in the surface region. Each surface grain has different orientation. Depending on the Hall–Petch formula, which is applicable to describe polycrystal materials, and introducing scale parameters, the constitutive equation of each region is deduced based on the unidirectional compression tests data of the copper specimen. Using the multi-region model, the coining process with micro feature is simulated to investigate the size effect in micro forming. Moreover, an experiment of coining process with micro-feature is performed to verify the correctness of the multi-region simulation model. The experimental results show a good agreement with those in numerical simulation.