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

Future aircraft manufacturing factories are moving towards more flexible and adaptable manufacturing systems that enable shorter manufacturing cycles, environmental friendliness, energy efficiency, and higher productivity. A global aeronautic trend to face this challenge includes the replacement of metal parts with composite counterparts with emphasis on thermoplastic composites (TPCs) for their unique ability to be recycled, reprocessed, and welded. Aiming to commit to the drastic projected increase in aircraft production rates, WELDER project, focused on the next-generation MultiFunctional Fuselage Demonstrator (MFFD), has promoted the development and investigation of highly integrated and robotized manufacturing technologies that needed to be scaled up from a laboratory to an industrial environment. To contribute to such an advance, resistance welding was investigated in this work and successfully automatized for fuselage components assembly.

Welding investigation, including process maturation, parameter optimization, and scale-up analysis was performed at laboratory using LM-PAEK/CF composites. A resistance welding Heating Element (HE), made of stainless steel metal mesh and embedded in glass fiber scrims, was first designed and manufactured using a hot press. The HE, priorly characterized by electrical analysis, was adopted, in conjunction with a lab-scale welding head, to optimize and define appropriate processing times (welding and cooling), welding power, and pressures for the welding of the composite parts. The welds were characterized by visual inspection, microscopy analysis, and mechanical tests (SLSS tests - AITM 1-0019). Once materials and processes were optimized, they were scaled up to finally perform the welding of the frame couplings into MFFD.

Abstract

Los materiales compuestos termoplásticos (TPCs) están transformando la industria aeroespacial gracias a su alta tenacidad, capacidad de reprocesamiento y reciclabilidad, alineándose con los objetivos de sostenibilidad y reducción de peso estructural para minimizar las emisiones de carbono. No obstante, las técnicas de unión convencionales, como remaches y adhesivos, presentan limitaciones significativas, como la pérdida de integridad estructural debido a perforaciones, el aumento de peso y procesos largos y costosos. La soldadura de TPCs es un proceso de unión para eliminar las superficies diferenciadas de las piezas a soldar mediante una nueva consolidación del material. El entrelazamiento de las cadenas poliméricas resultante en la zona soldada posibilita la transferencia de cargas a través de la interfaz. Esta técnica permite obtener uniones ligeras, sin necesidad de elementos adicionales, y con propiedades mecánicas comparables al material base. FIDAMC trabaja sobre un método de soldadura por inducción para material compuesto termoplástico, bajo el cual han sido fabricadas probetas a partir de paneles planos. Las probetas simulan el pie de un larguerillo soldado a un revestimiento como resultado de la puesta a punto del proceso. Las probetas han sido ensayadas obteniendo propiedades mecánicas por encima del 90% respecto del valor de referencia Este trabajo ha estado apoyado por un modelo numérico creado en COMSOL Multiphysics para modelar y simular la interacción entre los campos electromagnéticos y la distribución térmica a lo largo del material durante el proceso de soldadura.

Abstract

Thermoplastic composite materials present advantages over thermoset materials since they can be re-shaped, which is a benefit in terms of recyclability and sustainability for the aeronautical industry. It is possible to achieve a high level of integration in thermoplastic structures by developing new joining techniques such as welding processes, since the use of traditional methods to join thermoplastic composites is technically complex and results in high costs. Welding is defined as the process of obtaining a new consolidation of the material by integrating differentiated surfaces resulting in the ability of transferring loads through the interface, due to the cross-linking of the polymer chains in the welded area. The quality of welded parts is comparable to the quality of parts consolidated in press or oven processes. There are different welding technologies for thermoplastic composite materials depending on the heat transfer method along the welding interface. FIDAMC, together with Aciturri, has worked on the development of a conduction welding method on thermoplastic composite material, LMPAEK, within the framework of the NEOTAIL project "New Optimized Empennage with Advanced Technologies for Laminarity Integration". The welding process has been set-up on flat panels that represent the integration of the stringer foot on a skin, supported by numerical results of a simplified model made in Abaqus. The welded specimens have been tested obtaining mechanical properties above 80% with respect to the reference value considered. Finally, an omega stringer and a C-section spar have been welded on a skin, as an example of aeronautical application. This demonstrates FIDAMC capability to manufacture parts in thermoplastic composite material with a high level of integration.