The objective of the PUL-AERO project was to design and build a pultrusion line for the production of composite stringers for the aerospace industry.
The PUL-AERO project has developed a two-stage pultrusion line for the production of straight and curved composite profiles, complete with resin injection/recirculation technology, process monitoring/QA and in-line NDT inspection. The process offers the benefits of continuous production, repeatability, low production costs and the potential flexibility to manufacture stringers with different curvatures. This gives the process the potential to provide a cost-effective solution whist meeting stringent aerospace quality standards.
The PUL-AERO pultrusion line has a number of special features:
Separation of the process into two stages
In stage 1, linear heated dies partially cure the resin in order to obtain dimensional stability. Then, in stage 2, a post-forming die introduces any required curvature and fully cures the resin. This design feature offers the potential to create stringers with a range of different curvatures by simply replacing the post-former die, rather than having to reset the whole pultrusion process. Sections may also be removed after stage 1 and post-formed off-line, enabling the production of joggled pultrusions.
A resin injection/recirculation system
Resin injection ensures the correct amount of resin is introduced for complete wetting of the fibres and considerably reduces wastage over a resin bath approach. Sensors in the collector tray monitor the resin temperature and viscosity and only recirculate the resin if specific condition criteria are met, improving the consistency and quality of the pultruded product.
An integrated process monitoring and QA system
The sensors collect information from the line and provide the user with information about the line operation. The output of the system is a complete signature of the process, which can accompany the produced part. This is seen as very attractive by aerospace companies in order to fulfil certification standards.
In-line NDT system
Real time inspection of parts allows any inconsistencies in the manufacturing process to be identified immediately, leading to a reduced scrap rate and early remedial actions. It prevents parts being shipped around the world for inspection only to be rejected, saving both time and money.