Fraunhofer IWS revolutionizes aircraft construction

Laser technology Connecting large-volume aircraft structures based on CFRP

2024-08-01 Source: Fraunhofer IWS | Translated by AI 4 min Reading Time

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The Fraunhofer IWS has developed a process called CONTIjoin that is suitable for the continuous processing of fiber-reinforced thermoplastic high-performance laminates. This is expected to make the production of future commercial aircraft faster, more environmentally friendly, and more competitive.

As part of the "Large Passenger Aircraft" (LPA) program, Fraunhofer IWS was the first to demonstrate the welding of long connection seams on large-volume thermoplastic aircraft fiber composite structures using a CO2 laser beam source in the MFFD project.(Image: Clean Aviation) — As part of the "Large Passenger Aircraft" (LPA) program, Fraunhofer IWS was the first to demonstrate the welding of long connection seams on large-volume thermoplastic aircraft fiber composite structures using a CO2 laser beam source in the MFFD project.
(Image: Clean Aviation)

Thermoset polymer matrices play a major role in the design and production of modern aircraft structures in composite construction so far. The use of connectors or adhesive systems for joining these parts is inevitable, thus increasing the overall weight of the aircraft and imposing additional requirements on surface pre-treatment. In contrast, thermoplastic matrices enable joining and forming processes: the polymers can be softened and melted, and thus can also be welded.

An international consortium led by Airbus is researching production technologies for the thermoplastic fuselage of tomorrow. The Fraunhofer Institute for Material and Beam Technology IWS has made a significant step forward towards new eco-friendly aircraft construction concepts. A team of researchers from Dresden provided within the EU program Clean Sky 2 in the project "Multifunctional Fuselage Demonstrator" (MFFD) the evidence for the chipless joining of carbon fiber-reinforced component structures made of thermoplastic.

Within the framework program "Large Passenger Aircraft" (LPA), the team led by Dr. Maurice Langer, group leader Adhesion and Composite Technology at the Fraunhofer IWS, managed for the first time worldwide to use a CO2 laser beam source to demonstrate the welding of long joint seams on large-volume thermoplastic aircraft fiber composite structures outside an autoclave. On the left side of the MFFD, the process approach developed at the Fraunhofer IWS created the final longitudinal seam connection between the upper and lower half of an eight by four meter measuring section of the aircraft fuselage segment made of "Carbon Fiber Reinforced Thermo-Plastics" (CFRTP) — in original size.

For this construction method, Dr. Langer and his team developed the CONTIjoin method. The underlying principle is similar to current laying methods such as automated tape laying (ATL). Significant differences between CONTIjoin and previous laying methods are based on the type of semi-finished products processed and the energy source used: while generally known laying methods are usually limited to the deposition of single-layer, unidirectional tapes or tows (fiber ribbons in Automated Fiber Placement — AFP), CONTIjoin allows co-consolidation of multi-layer, multidirectionally reinforced thermoplastic laminates — already fully consolidated — consisting of up to six individual layers. Currently, the process can realize laminate widths up to a maximum of 360 millimeters.

Direct plasticization of the joining partners

To heat the materials, a CO2 laser is used in combination with high dynamic beam deflection. Due to the wavelength of 10.6 micrometers, direct absorption of the laser radiation by the polymer matrix is achieved (surface heating), while the wavelength of 1.06 micrometers of the typically used fiber lasers is mainly absorbed by the carbon fibers, thus primarily causing volume heating. The surface-near absorption in the polymer matrix thus allows direct plasticization and co-consolidation of the joining partners.

Gallery

As part of the "Large Passenger Aircraft" (LPA) program, Fraunhofer IWS was the first worldwide in the MFFD project to demonstrate the welding of long connection seams on large-volume thermoplastic aircraft fiber composite structures using a CO2 laser beam source.(Image: Clean Aviation)

For the first time in a research project, a fuselage segment made of thermoplastic CFRP materials was produced in original size. This should enable a thorough evaluation of feasibility as well as ecological and economic advantages and disadvantages. The fuselage barrel made of thermoplastic composite material weighs significantly less than the sections commonly used today.(Image: Clean Aviation)

The conceptual elaboration and implementation of the entire plant and control system, including human-machine interface, was based on a self-development of the Fraunhofer IWS. In addition, commercially available system components were used.(Image: Clean Aviation)

An important task was to guide the laminate to be applied continuously with precision and to press it accurately to the aircraft half-shells depending on the width. At the same time, the laser beam was controlled and the temperature in the joint zone was measured pyrometrically.(Image: Clean Aviation)

Gallery with 5 images

A measurement system based on pyrometry continuously feeds the determined temperature data for adjusting the laser power into a control loop in order to ensure a defined temperature distribution across the entire width of the laminate. A segmented consolidation roller system that adapts to the shape was developed to ensure homogeneous force distribution during the pressing of the laminates even on curved substrates. It was found that laminates joined with CONTIjoin reach over 90 percent of the reference strength of a static hot press connection. This results in a major advantage when used for large-volume aircraft structures, as autoclaves and associated tools and aids for these dimensions cause enormous costs.

New classes of materials require innovative manufacturing methods. The declared goal was to reduce the fuselage weight by up to one ton in the Multifunctional Fuselage Demonstrator.

Dr. Maurice Langer

Significant weight saved

The novel process makes the use of mechanical fasteners superfluous and also dispenses with material doublings as in classic riveted overlap joints. The barrel made of welded, thermoplastic composite material thus weighs significantly less than sections common today. The challenge was to process materials such as PAEK, which has a comparatively very high heat form and temperature resistance for plastics. "Traditional manufacturing methods for these materials are often energy-intensive and complicated," explains Dr. Langer. "Therefore, together with project partner Airbus, we have developed a process approach in which we can join parts together outside the autoclave using a staggered shearing technology and at the same time achieve excellent strength properties of this composite." Traditional methods are limited in this respect, especially when it comes to high production rates and large-volume component structures in aviation. Dr. Langer emphasizes: "New material classes require innovative manufacturing methods. The stated goal was to reduce the fuselage weight by up to one ton on the Multifunctional Fuselage Demonstrator."

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Date: 08.12.2025

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Next steps: Increase technology readiness and open up further areas of application

The next step is now to increase the technology readiness level (TRL) and thus take a further step towards qualifying for aviation suitability. Dr. Langer explains: "The developed CONTIjoin technology is not only interesting for aircraft construction, but also for other industries. The developed process solution could thus be interesting not only for aviation but also for applications in shipbuilding, truck and trailer construction as well as rail transport or the further development of modern wind energy plants." One challenge is to establish the acceptance and use of both the thermoplastic composite materials and corresponding processes in the different industries. (jup)