Analysis of superplastic blow-forming in a circular closed-die

A mathematical mode using the slab method and the finite-difference approach has been proposed in this work to examine the plastic deformation behavior during blow-forming a thin sheet into a circular closed-die. A computer program has been developed also to determine the optimized pressurization profile and the thickness distribution of the product at any instant during the blow-forming process. By using the optimized pressurization profile, the strain rate which corresponds to the maximum m-value can be maintained. The effects of various forming parameters, such as the die entry radius, the friction coefficient, the aspect ratio of the die, the original sheet thickness, etc., upon the optimized pressurization profile, forming time and the thickness distribution of the products are discussed systematically. Furthermore, experiments of superplastic blow-forming in a circular closed-die have been carried out using 8090 Al-Li sheets. It has been found that the thickness distribution of the formed product employing the optimized pressurization profile predicted by this model is more uniform than that using the Ghosh and Hamiltion model.