ANALYSIS OF SUPERPLASTIC SHEET-METAL FORMING IN A CIRCULAR CLOSED-DIECONSIDERING NONUNIFORM THINNING

A mathematical model using the finite-difference method and considerin g non-uniform thinning in the free bulged region has been proposed in this work to examine the plastic deformation behavior of the sheet dur ing blow-forming in a circular closed-die. Optimized pressurization pr ofiles during the blow-forming process are obtained by this model, the use of which the strain rate at the pole of the free bulged region co rresponding to the maximum m-value is maintained during the blow-formi ng process. The effects of various forming parameters, such as the die entry radius, the friction coefficient, the aspect ratio of the die, etc., upon the optimized pressurization profile, the forming time and the thickness distribution of the products, are discussed systematical ly. Furthermore, experiments on superplastic blow-forming in a circula r closed-die were carried out using 8090 Al-Li sheets. It is found tha t the thickness distribution of the formed product employing the optim ized pressurization profile predicted by this model is more uniform th an that by the previous model considering uniform thinning in the free bulged region. (C) 1997 Elsevier Science S.A.