The effects of pressure control technique on hot gas blow forming of Mg AZ31 sheets

The forming pressure-time schedule is critically important in high temperature gas blow forming of sheet materials. Forming pressure controls the strain rate that influences necking and thickness distribution uniformity in the formed component. In this work, the effects of forming pressure control technique; constant pressure versus constant strain rate, on the superplastic forming of Mg AZ31-H24 sheets at 400 °C are investigated. Experiments and detailed finite element simulations that incorporate a phenomenological microstructure based constitutive model for forming a cylindrical cup are conducted. Sheet thickness distribution across the formed part and the deformation progress are examined in details. The results clearly reveal that for the same forming time required to fully form the cup, the constant forming pressure control technique acts as a variable strain rate forming procedure that yields to a more uniform thickness distribution when compared to the constant strain rate control technique. However, it should be noted that the initial strain rates for forming at constant pressure are of extreme importance as high initial strain rates that exceed 10−2 s−1 might cause rupture.