FITCoW

The FITCoW project enables the manufacture of large composite components with complex geometries without the use of an autoclave. 

Clean Sky 2’s FITCoW project has designed, manufactured, scale tested and implemented a tooling system that can reduce the recurring costs of low-volume composite component production. FITCoW supports Clean Sky 2’s OPTICOMS (Optimised Composite Structures for Small Aircraft) project, whose aim was to design a wing-box using automated fabrication, integrated structures, large structural bonding, and novel tooling procedures.

A wing-box is the load-carrying structure which connects the wings to the aircraft’s fuselage, and when produced in composite materials is traditionally fabricated by joining multiple parts together using rivets, bolts, and/or adhesive. Rivets and bolts are reliable and can be easily inspected but can cause deterioration of the composites. Adhesive saves weight but is prone to contamination of the parts’ joining surfaces, resulting in the need for pre-treatments such as grinding, abrasive blasting, or laser treatment. 

All of these aforementioned extra steps increase time and costs — and that’s where the environmental benefit of FITCoW comes in. In contrast to the conventional manufacturing approach, the key energy-saving advantage of FITCoW (and by extension, OPTICOMS) was to produce structures using an ‘out-of-autoclave’ (OOA) process, meaning that an autoclave (a type of high-energy-consuming industrial oven used for curing composites) would not be required. Curing is the phase within the manufacturing process when the raw materials (carbon fibres and bonding resin, a type of adhesive) are combined and solidified to produce the final product.

But FITCoW’s benefits go even further. FITCoW’s process is ‘co-curing’, meaning that multiple parts are simultaneously combined as the bonding resin cures. This brings the advantage of enabling the integration of several sub-assemblies and design of components with complex features, resulting in less parts and mechanical fasteners to hold them together. This in turn translates into further aircraft weight savings, reduced fuel burn and lower emissions. These integrated structures cut costs by approximately 50%.

To achieve these advantages the FITCoW tooling system successfully addressed various challenges. One example was to ensure the process would be compatible with a variety of fabrication methods, including ‘automated tape lay-up,’ ‘automated fibre placement, and ‘manual lay-ups’ — so that the process could be applicable and beneficial when used in other manufacturing scenarios beyond its use in the OPTICOMS project. This was achieved by manufacturing the tool out of Solvay LTM 12, a material pre-impregnated with bonding resin which can be cured in five hours at 70° C while having a 200° C service temperature (the temperature at which the manufactured part operates once installed into the aircraft and is used during flight).