Grain Size Effect on Multi-Stage Micro Deep Drawing of Micro Cup with Domed Bottom

A two-stage micro deep drawing system was designed and developed to manufacture a micro cup with domed bottom. The copper blank was annealed at three different conditions to obtain different grain sizes in such a way to study the grain size effect on the deformation behavior and thickness variation of the micro part. To investigate the instantaneous effect and deformation behavior, finite element simulation was used to simulate the whole drawing process. It revealed that the fracture in the place with the thinnest thickness in the micro part drawn from a circle blank with residual stress induced in blanking can be easily happen and the deformation load in the first-stage decreases more than that in the second-stage with the increase of grain size. Moreover, the micro part with a larger grain size has more nonuniform thickness and severer thinning around the punch corner. The surface roughness at the bottom of micro part increases with the grain size. The surface roughness at the wall of it, however, decreases with the deformation stage mainly due to the ironing effect. The research promotes the understanding of grain size effect on multi-stage micro deep drawing and facilitates the development of microforming process.