On the optimisation of superplastic forming processes by the finite-element method

This paper presents an original algorithm, with a finite-element interface capability, that can calculate, for superplastic forming processes, the load curve to be applied during forming. The algorithm makes it possible to maintain the maximum strain rate as near as possible to the optimum characteristic value of the material thereby reducing forming time. The proposed algorithm was validated by calculating the optimum pressure curve to be assigned in the case of both a conical-bulging process and a cap-forming one. Parallel experimental activity was carried out using a Pb/Sn-based metallic alloy that is superplastic at room temperature. For both geometries examined, comparison between numerical and experimental results proved to be acceptable. In particular, the relative error was less than 6% for measurements of both the strain–time relationship and the thickness distribution. Different measurements were carried out during each process: the shift in the sheet centre-point for the conical-bulging process and the thickness distribution corresponding to a particular sheet configuration for the cap-forming one.