Numerical analysis of effect of material and processing parameters on thickness distribution during superplastic die bulging of cavity sensitive materials

The superplastic bulging of circular sheets clamped against axisymmetrical cylindrical dies has been analysed numerically by means of a rigid-viscopla stic finite element method, in which four node quadrilateral isoparametric elements are used with a Newton-Raphson non-linear solution scheme. Both ef fects of normal anisotropy and strain hardening in the material are conside red and a modified Coulomb friction law is adopted. At the same time, the y ield criterion suited for the superplastic forming process and the cavity d amage evolution model deduced from continuum damage mechanics are applied t o a finite element formulation. The influences of material parameters (the strain rate sensitivity exponent in, the strain hardening exponent it, the coefficient of normal anisotropy R) and processing parameters (pressure cyc le, lubrication condition, die geometry) on the inhomogeneity of the thickn ess distribution are studied and discussed. A selection of the simulated re sults is compared with the experimental results, with good agreement.