Abstract

Rib-AM project aims to contribute to the development of novel in-situ manufacturing technologies applied to large size components of primary structure of aircrafts. Framed in Clean Sky 2, the activities within Rib-AM are set out to develop a leading-edge (LE) concept based on reinforced thermoplastic materials avoiding mechanical joints between the skin and the ribs. Induction Welding (IW) process has been selected for the integration of the ribs into the leading-edge structure. The development of an appropriate IW process methodology, including the introduction of magnetic flux concentrators and new coil designs, are key to assure the quality and structural integrity of the produced joints.

In this research, the mechanical strength of induction welded thermoplastic composites have been evaluated at sample level. Characterization specimens have been obtained by welding: (i) short carbon fiber reinforced polyether ether ketone (SCFR/PEEK), with 10 % carbon content, processed by additive manufacturing – fused deposition modeling; and (ii) multidirectional carbon fiber reinforced polyether ether ketone (CFR/PEEK) laminates processed by oven consolidation. The mechanical characterization of the strength has been carried out by means of the block shear test method. In addition, light optical microscopy has been performed to analyse the SCFR/PEEK - CFR/PEEK interface. Infrared thermography (IRT) has been considered for the non-destructive characterization of the welded joints to evaluate the feasibility of being applied as an inspection method for induction welded structures. IRT results have been validated by X-ray computed tomography.

Abstract

Carbon fibre matrix composites are consolidated in high-demanding industries such as aeronautics and aerospace. Nowadays, thermoset composites are fully integrated on several new aircrafts in production. However, thermoplastic composites are progressively emerging as a better solution due to their end-of-life recyclability and optimized manufacturing process. One of the processes used to manufacture final parts from thermoplastic composite materials is press-moulding, in which a high-temperature heating system is combined with the application of pressure at high speeds. This article studies the optimization of press-moulding process in combination with an Additive Manufacturing (AM) produced metallic mould core. The aim of this study is the manufacturing of a thermoplastic aeronautical part, that would be submitted to real-world performance test. For the press-moulding process, a high-temperature infrared heating system was designed, supported by thermal oil mould heating, this heating system was combined with a mould-pressing process by integrating the system in a commercial injection machine. Regarding the AM tooling, produced by Wire Arc Additive Manufacturing (WAAM) process, was designed to reduce tooling weight, and optimise thermal cycle. Moreover, manufacturing data from WAAM tooling was recorded and compared with that obtained from a symmetrical conventional manufacturing made mould. The analysis shows savings in terms of material and energy consumption, as well as cycle times reduction. The final part metrology study shows indistinguishable results between the press-moulding process carried out using the WAAM tooling and that manufactured through conventional methods.

Abstract

Thermosetting matrix composites are by far the most use composite solutions in the market. Thermosetting matrices are not currently possible to recycle by convenient means, which makes them a poor sustainable solution. In environmental terms, these matrices materials are also more harmful due to gas emissions during the curing process that can be considered harmful to the workers. Thermoset composites also have some disadvantages from the point of view of mechanical behaviour, being less ductile and resistant when compared to thermoplastic matrix composites. Despite the very high viscosity of thermoplastic materials that is a main problem regarding composite processing, they have advantages such as being recyclable, cleaner workspaces and greater availability, as well as a longer shelf life. This paper aims to be a contribution to increase use of thermoplastic matrix composites as alternative to the more traditional thermosetting based composites. First, thermoplastic matrix prepregs were produced in tape form by dipping the fibres into a molten polymer bath. Carbon and glass fibres are used as reinforcement material, testing their combination with thermoplastic polymers and recycled polymers. The use of prepregs is more attractive on the market as the process of mixing and selecting the raw materials is carried out prior to their application in a consolidation process. The prepregs were then processed by pultrusion, which is characterised by its continuous nature, allowing the manufacturing of constant cross section profiles for structural applications. The pultrusion of thermoplastic composites is still a novelty and therefore presents challenges. The determination of the best combination of operational parameters was also conducted in this study. Finally, the produced profiles were subjected to mechanical tests as a way of assessing the quality of the processed composites. The mechanical properties obtained will be compared to those predicted by the application of micromechanical models using experimentally obtained mass fibre fraction content.

Abstract

La soldadura ultrasónica continua robótica (cUSW) es una técnica prometedora para unir termoplásticos reforzados con fibra de carbono (CFR-TP), que ofrece alta eficiencia y tiempos de procesamiento rápidos. Sin embargo, mantener la calidad de la soldadura y la robustez del proceso presenta desafíos significativos. Las características de la soldadura, como la resistencia de la unión y el rendimiento a largo plazo, se ven fuertemente influenciadas por parámetros clave durante las fases de generación de calor y consolidación. Comprender las interacciones entre el sistema robótico y el proceso de soldadura ultrasónica es esencial, ya que impactan directamente en la calidad y consistencia de la soldadura. El robot debe controlar con precisión el movimiento del sonotrodo durante la fase de generación de calor para mantener una fuerza constante, precisión de trayectoria y uniformidad de velocidad, asegurando una transferencia de energía eficiente y una fusión uniforme. Durante la consolidación, tanto la velocidad como la fuerza son cruciales, controlando la disipación de calor para reducir la temperatura de la interfaz por debajo del punto de cristalización y prevenir defectos. Para abordar estos desafíos, es esencial la monitorización en tiempo real de los parámetros clave del proceso. La integración avanzada de sensores y las estrategias de control basadas en datos permiten ajustes dinámicos para optimizar las condiciones de soldadura y prevenir defectos. Este artículo explora los desafíos asociados con la soldadura ultrasónica continua robótica de CFR-TP y analiza técnicas de monitoreo y estrategias de control para mejorar la consistencia de la soldadura y la confiabilidad del proceso.

Abstract

The increase in both competitiveness and new environmental regulations has created a need within the transport sector to develop new high value-added and differentiated products in an efficient and sustainable manner. In this context, there is a growing need to develop new multi-material components, understood as dissimilar joints between lightweight metals and thermoplastic composite materials, especially for use in high-stress areas of the component. The use of Fibre-Metal Laminates (FMLs) offers, in addition to improved strength compared to lightweight metal alloys such as aluminum, enhanced resistance to mechanical fatigue and impact when compared to monolithic composite materials, combining the properties of both materials. The development of this type of laminate (FML) has traditionally focused on thermoset composites, which have a limited lifespan due to their inability to be reprocessed, as well as longer manufacturing times. For this reason, the COMIC project has studied different manufacturing methodologies for FMLs with a thermoplastic matrix, achieving lightweight and sustainable components simultaneously. This work presents a study of various surface treatments aimed at increasing the surface energy of the metal, which promotes physical and chemical anchoring between the metal and the composite. Additionally, different FML manufacturing methodologies have been explored, incorporating the various surface treatments. Finally, the optimal parameters and treatments have been selected for the production of FML laminates (PA6-aluminum composite) that maximize interlaminar strength and mechanical performance, with a comparison made against monolithic composite materials.

Abstract

The demand for lightweight and high-strength materials across various industries has driven research into hybrid structures that combine the mechanical advantages of metals with the low weight and strength of carbon fiber-reinforced composites. The use of thermoplastic composites additionally enables disassembly and reuse at the end of the service life. Furthermore, the metal-composite joining process and the thermoplastic CFRP processing could potentially be achieved in a single step, resulting in reduced manufacturing cycle times and overall higher productivity. However, several challenges must be addressed, such as differences in the coefficients of thermal expansion, the influence of the composite processing parameters on the metallic material and its surface treatment, and the potential formation of galvanic couples. This study investigates different manufacturing methods for dissimilar or multi-material joints: automated fiber placement (AFP) and thermoforming. A comparison is presented based on the manufacturing parameters, which were adjusted to maximize joint strength for each process.A cross-sectional optical microscopy analysis was carried out to evaluate the joint interface and the interaction between the surface treatment and the thermoplastic resin matrix layer, which is responsible for the adhesive bond between both components. In addition, mechanical testing was conducted to assess the influence of processing parameters, establishing a joint design route for optimized performance evaluation. The conclusions demonstrate that the polymer layer at the interface plays a key role in compensating for differences in thermal expansion coefficients, leading to enhanced mechanical performance of the joint. The advantages and limitations of each manufacturing method are discussed in this work.

Abstract

Continuous fiber-reinforced thermoplastic composites are emerging as an efficient structural alternative to traditional thermoset materials, thanks to their recyclability, good impact resistance, and suitability for continuous processing. In this work, a manufacturing system was developed based on the thermoplastic pultrusion of unidirectional polypropylene (PP) and carbon fiber (CF) tapes, followed by hot compression molding. This approach enables the production of structural profiles with high fiber alignment and good consolidation. Experimental characterization included tensile, flexural, and impact tests to assess the structural applicability of the manufactured profiles. The results demonstrate a balanced combination of stiffness, mechanical strength, and impact performance, confirming the potential of this system for functional applications in sectors such as mobility or infrastructure, where lightweight, efficient processing, and sustainability are key requirements.