Continued...
Shaping components such as commercial aircraft wing skins is a complex operation due to a number of factors, including the physical size of the components. The Airbus A380 wing skins are up to 33 metres long and 2.8 metres wide, with thicknesses that vary abruptly between 3mm and 28mm, due to the minimum weight design criteria of the product. Furthermore, an assembly tolerance of -0, +1mm is required over all areas of the wing skin panels. Given the complexity of the double-curved aerodynamic shape required for these components, this produces an extremely challenging forming operation.
A particular feature of the CAF process is that the initial deformation experienced by the component during deflection to the tool surface is predominantly elastic. This loading is maintained during the heat treatment process (which may be completed using multiple temperatures and dwell periods), which activates creep (stress relaxation) and ageing mechanisms in the component material. When the clamping is removed at the end of the heat treatment cycle, some permanent deformation remains in the component. The amount of elastic deformation that is recovered during this unloading is termed spring-back.
As the temperature time profile used in creep age-forming is solely specified to produce an improvement in mechanical properties of the component material, any retained shape after creep age-forming may be viewed as purely a by-product of a required heat treatment operation.
Delivering a panel to the creep forming tool
Wrapping a wing skin and tool before creep forming in the autoclave
