Abstract: The restrained superplastic bulging of axisymmetrical circular sheets is numerically simulated by using a rigid visco plastic FEM of large deformation. During the treating of friction boundary condition for die workpiece interface,frictional stress( f ) is given by f=A mk(k=/3) according to friction law of constant factor A m and frictional stiffness matrix is directed. The advantage of this method is that global stiffness matrix has symmetry. By adjusting reasonably the intial velocity guess and deceleration coefficient for iterations, the calculation unstability is avoided,which is caused due to the change of boundary condition after the metal sheet attaches the die. The influence of the ratio HP/RD (HP and RD are height and width of the die), the rate sensitivity exponent m , the friction factor A m on attaching die process is studied in detail. The effects on inhomogeneity of thickness distribution are discussed as well.

Key words: superplasticity, forming techniques, finite elementmethod, analogies.