Some metals and metallic alloys, when deformed in particular conditions, manifest exceptional ductility giving tensile elongations of up to 1000%. This behaviour, known as superplasticity , could undergo considerable development in sheet metal production. The aerospace industry has already taken the opportunity of producing complex-shaped objects in a limited number of mechanical operations. It makes use of superplastic characteristics to noticeably reduce the weight and cost entailed in manufacturing some components, including structural ones. To better take advantage of the superplastic characteristics of the material, it is necessary to control the temperature and the strain rate during the manufacturing process. Since the material undergoes significant elongation, it also, necessarily, undergoes extreme thinning. The latter can prove not to be uniformly distributed because of (i) the particular geometry of the manufactured product, (ii) the characteristics of the material used, (iii) the lubrification and (iv) the process parameters adopted. The design stage should take account of the real thickness distribution in order to avoid critical areas. At this stage, thus, it is necessary, not only to design the product, but also to design the process in order to establish the optimum production parameters and to foresee the real geometry of the product. Numerical modelling is used since in the field analysis could prove to be expensive, and, analytical modelling would be limited only to some forms and to the use of largely approximated assumptions. The finite element method can be considered to be the most dependable both for analysing complex geometries, and for taking into consideration all the phenomena involved in the manufacturing process. One of the most delicate operations in this method is sub-dividing the continuum into elements since this discretization can have an influence both on the reliability of the results, and on computational requirements. The objective of this paper is to verify the approximation of the results that can be obtained compared to the different options possible both in terms of element type and number. The production of an axisymmetric cup in commercial aluminium based alloy Al 7475 using blow forming technology was taken as a reference case. Comparison between the results of the different simulations showed a substantial equivalence and a good correspondence to the measured thickness values. Since the computational resources required are very different for the cases examined, it can be stated that the best solution is discretization of the start-off sheet with a row of 55 axisymmetrical four node elements.