The aircraft industry increasingly relies on composites that combine light weight and excellent mechanical strength. There is an important need to reduce the associated production costs, particularly for very large components such as fuselage requiring very large autoclaves. Scientists launched the EU-funded project 'Optimal tooling system design for large composite parts' (OPTOCOM) to address the challenge. The test case was a double curvature fuselage stiffened panel with co-cured stiffeners of about two square metres in area. Investigators designed a large machine tool for manufacturing. INVAR 36, a 36 % nickel-iron alloy with a very low rate of thermal expansion, was chosen as the material for the tool. A HexPly M21 epoxy matrix system with reinforcing fibres was chosen for the fuselage part. Large complex parts with sharp angles exhibit a phenomenon called springback due to the plastic-elastic nature of the materials. The team sought to accurately simulate the springback that occurs after curing to minimise it and reduce the costs of reworking or assembly. Scientists then created finite element method (FEM) models simulating the distortion and springback during the curing process based on experimental data. They provided good qualitative results and are currently being optimised. Secondly, researchers targeted optimisation of the cure cycle temperature distribution for uniformity in the composite part, lower residual stress and lower energy consumption. The FEM models were used to evaluate and optimise the thermal behaviours of the tooling system in the autoclave to significantly increase speed, lowering costs and energy consumption. The models and experimental evidence confirmed that there is very little deformation of the tool, which is heated and cooled very uniformly. The final tool was designed to be quite adaptable. A cost analysis demonstrated that OPTOCOM outcomes indeed significantly reduce autoclave time, which in turn reduces energy consumption, emissions, and reworking and assembly times. Further optimisation and commercialisation promise important benefits for the competitive position of the EU aerospace industry.
Composite parts, aircraft, autoclave, tooling, fuselage, springback