Creep-age forming AA2219 plates with different stiffener designs and pre-form age conditions: Experimental and finite element studies

Creep-age forming (CAF) is one of the relatively new forming techniques that has been proven viable for the production of extra-large integral airframe structures. However, experimental studies on forming stiffened structures under creep-ageing conditions remain scarce. In this work, 200 mm × 48 mm integrally stiffened plates of aluminium alloy 2219 have been formed on an end clamp device that has a bending radius of 156 mm and creep-aged at 175 °C for 18 h. Three different stiffener designs, namely the beam stiffened, waffle and isogrid plates, are tested alongside the flat plates. Utilisation of PTFE pocket fillers and intermediate sheets to reinforce and protect stiffeners during forming operation is found effective as demonstrated by the defect-free formed parts with smooth curvature. Springback of the plates ranged from 12.2 to 15.7% in the experimental studies for different stiffener designs. Using the CAF material constants determined for this alloy, corresponding finite element models have been developed and experimentally validated using the measured profiles of the creep-age formed plates. Up to 6.3% difference in springback is observed when forming workpieces with different pre-form age condition alone.