THE SIMULATION, CONTROL AND OPTIMIZATION OF THE GAS-PRESSURE FORMING OF ALUMINUM-ALLOY SHEET AT ELEVATED-TEMPERATURE

The superplastic forming of Al-4.5% Mg alloy sheet, using gas pressure at elevated temperatures, has been studied. By using suitable models of material behaviour and friction, it was possible to simulate this process with finite-element methods (FEM). A rigid plastic model was used, with the assumption that the material behaved as a membrane, to model axisymmetric forms. Such simulations could then be used to optimise the process, in terms of minimising the forming time required whilst minimising the amount of cavitation damage or retaining acceptable material thickness. To apply the optimisation in practice, and for the generation of experimental data, a high degree of process control was required. Control of forming pressure is not sufficient for this purpose and volume-rate control was used. Good correlation was found between the predictions of the simulation and results from formed parts, and friction was found to be a very important factor in the process. It was possible to reduce the amount of cavitation significantly by applying an optimised volume-rate cycle.