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 p rocess with finite-element methods (FEM). A rigid plastic model was us ed, with the assumption that the material behaved as a membrane, to mo del axisymmetric forms. Such simulations could then be used to optimis e the process, in terms of minimising the forming time required whilst minimising the amount of cavitation damage or retaining acceptable ma terial thickness. To apply the optimisation in practice, and for the g eneration of experimental data, a high degree of process control was r equired. Control of forming pressure is not sufficient for this purpos e 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 wa s possible to reduce the amount of cavitation significantly by applyin g an optimised volume-rate cycle.