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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - AeroPul (Curved profiles for aerospace applications manufactured by Pultrusion)

Teaser

Summary

Pultrusion allows a highly automated and first of all continuous process for the manufacturing of fibre reinforced parts. It combines the cost advantages of liquid composite moulding (LCM) technologies with a fast and efficient continuous process. Compared to todayâ€™s widely used prepreg technology, the pultrusion technology offers a benefit due to lower material and processing costs, less scrap as well as lower transportation and storage costs.
The state of the art pultrusion technology does not allow the production of parts meeting all the aerospace quality requirements, regarding mechanical properties, fire-smoke-toxicity (FST) properties and process reliability.
This project had the objective to develop continuously manufactured profiles by a pultrusion process for aeronautical applications and to demonstrate the process capabilities (complex geometry, high volume manufacturing rates, application of composites with shorter curing cycles) by pultruding curved parts for potential aerospace applications like a frame-part.

Work performed

A reproducible continuous production process for straight, different reinforced (UD and NCF) fibre composite structures could be demonstrated on basis of the predominantly low deviation of the characteristic mechanical values from the aimed values. The partially higher deviations can be attributed to an increased pore content in the material. When introduced into a series production, process adaptations (e.g. preform guidance system and injection method) lead to an improvement of the material quality. As a result, better material properties compared to the target values can be expected, especially for compressive load. According to the resin manufacturer, the interlaminar shear strength can be increased by additives, which is expected to further improve the mechanical properties.
The flame retardant is identified to influence the stability of the process. Without flame retardant a stable process could be shown and the requirements for smoke and toxicity are met, while the flammability does not meet the requirements of AITM. It is recommended to check the addition of a considerably reduced quantity of the flame retardant for reaching the flammability requirements. The same material quality has been proven for a scale-up in complexity from a flat (t=4mm) to the C-profile (t=2mm). The deviating characteristic values of the profile flanges are expected to reach a reproducible level by adapting the manufacturing process to a series production as described above.
The textile is identified to influence the stability of the manufacturing process for curved profiles. No stable process could be shown. Through a previous successful introduction of a curved profile as a bumper in the series production for automotive application under the leadership of Thomas Technik, a wealth of experience regarding the radius pultrusion is available. Therefore, the issues occurring here in the project Aeropul, can be traced back to the textile preform. During the production of the bumper, the profile is curved in the thickness direction of the laminate, while the curvature of the profile in Aeropul is in the same plane as the textile. This leads to accumulations of the NCF at the inner radius and to excessive pull-off forces. Biaxial and multiaxial fabrics (without any 0Â° direction) could be used in series production and the 0Â° fibres could be added well aligned as rovings to prevent material accumulations.
Limitations of the pultrusion process were identified and analysed in regard to material, geometry, and quality inspection. All achieved information are summed up in a review for technology readiness level 2 and 3.

Final results

Today the continuously manufactured profiles cannot be used in FST-relevant structures. Other structures such as Belly Fairings are still possible applications. The substitution of metallic components by pultruded, weight saving CFRP-components and thus all assumptions based on those substitutions, such as the reduction of CO2 emissions, would be lower than originally assumed at the beginning of the project.
The knowledge gained, creates a new sensitivity regarding influences of additives in general and the choice of textiles for the radius pultrusion process is created. Furthermore, new research topics on the field of pultrusion, like the development of an inline quality-assurance system, which allows a faster development of a suitable process setup.
The research and development conducted makes a contribution to the knowledge for composite manufacturing and especially for the profile production by pultrusion. New applications for pultruded profiles will be established. Even if the reproducibility of the material quality according to strict guidelines of AITM has not been proven yet, the pultrusion technology will open up new paths for other industries as well due to the improved feasibility.
Pultrusion is one of the most automated and continuously working production processes for FRP-structures. Due to a theoretically endless profile production with isothermal temperatures, at least 30% of energy can be saved compared to a typical prepreg autoclave process with different heating cycles. Additionally a cost reduction of recurring manufacturing costs of at least 20% is expected.