F. Eberl, Alcan Rhenalu, Issoire Cedex, France; G. Campanile, Alenia Aeronautica, Naples, Italy; V. Galota, Alenia Aeronautica, Turin, Italy

Summary:

In order to reduce cost, welding is an attractive process for the assembly of integral primary structures such as fuselage panels. Thanks to new weldable alloys and optimised design, welding is also of great interest for weight reduction. The welding is affected by distortions and residual stresses that can be reduced but not avoided by the new welding processes as the laser beam welding. Age creep forming applied to these welded structures is expected to be able to recover most of the distortions due to stress relaxation, so that the final result shows improved quality with increased reproducibility of the formed and welded panels. Moreover the possibility to perform the welding of stringers on the flat skin allows a cost reduction in terms of tooling and process, in fact the tooling system is simpler, the forming phase (by stretching or rolling) is avoided and welding process is easier and more repetitive.

Alenia Aeronautica has developed, in the frame of the research project AGEFORM supported by the European Commission (EU project AGEFORM, Fifth Framework Program, G4RD-CT-2002-00743), an activity to evaluate the age-formability of sheets (in the range 2.0-5.5 mm thickness) of Alcans’ new weldable alloys 6056-T78 and 2022-T8. The influence of laser beam welded stringer and friction stir welded butt joints on panel formability has been studied. For this purpose integral welded sub-component panels have been designed, manufactured and formed utilising autoclave and vacuum bag tooling. On the basis of sub-components forming results, a full-scale panel demonstrator, representative of a fuselage panel of a large commercial aircraft, has been formed on a reconfigurable radius variable tool. Also influence of ageforming process on mechanical and corrosion properties of alloys has been evaluated.

The results have confirmed that the age creep forming process is useful applicable to low thickness integral welded structures as fuselage panels with advantages in terms of reduction of distortions induced by welding process and reduction of manufacturing costs.