Analysis of superplastic sheet-metal forming in a circular closed-die considering non-uniform thinning

A mathematical model using the finite-difference method and considering non-uniform thinning in the free bulged region has been proposed in this work to examine the plastic deformation behavior of the sheet during blow-forming in a circular closed-die. Optimized pressurization profiles 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 corresponding to the maximum m-value is maintained during the blow-forming 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 systematically. Furthermore, experiments on superplastic blow-forming in a circular closed-die were carried out using 8090 Al-Li sheets. It is found that the thickness distribution of the formed product employing the optimized pressurization profile predicted by this model is more uniform than that by the previous model considering uniform thinning in the free bulged region. (C) 1997 Elsevier Science S.A.