Method and apparatus for superplastic forming

A method of shaping a metal sheet into a formed product comprising the steps of:

• providing a first and second die member operative to move between a first open position and a second sealed position such that a die cavity is formed;
• providing a preforming punch disposed on one of the die members;
• providing a metal sheet of ductile material;
• providing a blankholder operative to move between a first material loading position and a second material loaded position;
• providing a cushion system engageable with the blankholder and operative to exert a force against the blankholder and the first die member;
• heating the die members and the preforming punch to a predetermined temperature;
• heating the metal sheet to a predetermined material forming temperature;
• moving the first and second die members to the open position and the blankholder to the material loading position;
• placing the metal sheet into the blankholder;
• moving a die member, the blankholder, and the metal sheet until the die member sealed position is reached;
• controlling the amount of material flow into the die cavity as the metal sheet is formed over the preforming punch by adjusting the amount of pressure exerted by the cushion system against the blankholder and the first die member;
• applying gas pressure to the metal sheet after the sealed position is reached and until forming of the product is completed;
• moving the die members to the open position;
• and
• moving the blankholder to the material loading position and removing the formed product.