M. D. Hanna, GM Reserach and Development Center, Warren, MI; F. G. Lee, General Motors, Warren, MI

Summary:

In Superplastic Forming Process (SPF), thickness distribution and forming time is the key for the optimum process design to produce good quality parts of uniform thickness. In this investigation, a parametric study was conducted to determine how the design features and forming parameters affect part thinning and forming time. Explicit formulas, describing the maximum percent thinning and the forming time for channel parts formed by the SPF process as a function of eight designs and forming parameters, were derived. Thinning of the channels was influenced most by the component aspect ratio (height versus width) and entry radius at top of the channel forming tool. The forming time was most influenced by strain rate, aspect ratio and tool bottom radius. A design domain can be established to avoid excessive thinning. The analysis enables accurate prediction of the thickness distribution and are good approximations of those obtained physical experiments.