Using exhaust gas mass flow rate to control superplastic forming

摘要

A forming die which includes a die cavity contains a forming blank composed of a metallic alloy having superplastic properties. The forming pressure in a pressurized space adjacent the forming blank is regulated by a pressure regulator. The volume of the die cavity is determined, as is the mass of gas initially contained in the die cavity at the beginning of the forming cycle. The total forming time is empirically determined. The average gas mass flow rate that will be exhausted from the die cavity is calculated by dividing the total mass of gas initially contained in the die cavity by the total forming time. A gas mass flow meter fluidly communicates with the die cavity and measures the mass flow rate of the gas displaced by the forming blank and exhausted from the die cavity. The gas mass flow meter is continuously monitored during the forming cycle or a gas mass flow rate signal is fed back to the pressure regulator. The forming pressure is regulated by the pressure regulator so that the gas mass flow rate exhausted from the die cavity approximates the predetermined average gas mass flow rate.