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Blanking
is a shearing operation, which involves elastic and plastic deformation and fracture. The material is stressed beyond its ultimate strength between two cutting edges. Ductile fracture develops in three different stages: void initiation, void growth, and hole coalescence. For a given material, fracture depends on temperature and strain rate.
The part edge contains four distinct zones: rollover, shear zone, fracture zone, and burr. See Figure. Depending on material properties and on the punch-die clearance, secondary shear may
occur during material fracture. Rollover and burr are results of the elastic and plastic deformations at the beginning of the blanking operation. An ideal part edge would have almost no rollover, burr, or fracture
zone, thereby showing almost 100% shear.
The formation of the different zones is influenced by a number of parameters such as: material properties and thickness, punch-die clearance, tool
wear, punch velocity, and part geometry.
At the ERC/NSM, FEM simulations for blanking processes have been carried out, and the results have been compared with experimental data. (Reference ERC/NSM-S-96-25)
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