Prediction and control of cavity growth during superplastic sheet forming with finite-element modeling

Superplastic forming is used widely in the aviation and aerospace industry, but the microstructure variation, especially the cavity growth, has a negative influence on the service properties of the parts. Therefore, the microstructure variation, and especially the cavity growth, and its influences on the flow stress have been studied, the superplastic constitutive equation with the cavity growth and the grain growth then being deduced and applied to the finite-element formulation. In addition, a three dimensional viscoplastic finite-element program using a constant triangular membrane has been developed and applied to predict the cavity growth and its distribution and to calculate the optimum back pressure-time cycle to control the cavity growth. At the same time the experiments with and without the calculated back pressure have been carried out, the results of which agree well with the calculated results. (C) 1998 Elsevier Science S.A.