Fraunhofer CO2 Laser Welds Carbon Fiber Fuselage

Researchers from the Fraunhofer Institute for Material and Beam Technology IWS (Fraunhofer IWS) have demonstrated chipless joining of carbon fiber-reinforced thermoplastic (CFRTP) component structures using a CO₂ laser. According to Fraunhofer IWS, the automated process joined the upper and lower halves of the world’s largest CFRTP fuselage segment, measuring 8 × 4 m.

The work was conducted by an international consortium led by Airbus under the EU program Clean Sky 2 in the project Multifunctional Fuselage Demonstrator. The researchers anticipate the development will lead to savings on time and labor, as well as massive reductions in weight and required materials, leading to faster, more ecofriendly production of future commercial aircraft.

The so-called CONTIjoin process, a combination of CO₂ laser technology and highly dynamic beam shaping, controlled the laser power in real time to keep the temperature in the joining zone constant. At the same time, it enabled the automated adjustment of the beam shape in the welding gap.

Within the framework program “Large Passenger Aircraft” (LPA), Fraunhofer IWS used a CO₂ laser beam source to demonstrate the welding of long joining seams on large-volume thermoplastic aircraft fiber composite structures for the first time. Courtesy of Clean Aviation.

The technology avoids the use of mechanical joining elements and material doubling as with classic riveted overlap joints. Therefore, the hull shell, made of welded, thermoplastic composite material, weighs significantly less than conventional sections.

According to Fraunhofer IWS, the work marks an important step in aircraft construction using new types of thermoplastic high-performance materials, as it enables the production of high-strength and weldable large components. The challenge involved processing materials such as PAEK, a plastic with a comparatively high heat deflection temperature and heat resistance.

“Conventional manufacturing processes for these materials are often energy-intensive and costly," said Maurice Langer, Group Manager Bonding and Fiber Composite Technology at Fraunhofer IWS.

High production rates and large-volume aerospace component structures are limitations in this respect. “New material classes require innovative production methods,” Langer said. “The declared aim of the Multifunctional Fuselage Demonstrator was to reduce the weight of the fuselage by up to one ton.”

Over the operating life of the aircraft, the lower weight and improved integration of the system architecture could significantly reduce overall energy requirements, fuel consumption, and emissions of air pollutants such as carbon dioxide and nitrogen oxides.

According to Langer, the wavelength used by the CO₂ laser system is a distinguisher of the demonstrated process. The CONTIjoin process uses a wavelength of 10.6 μm in the relevant thermoplastic part of the fiber composite material, which means a significantly higher absorption of the laser radiation than the conventionally used fiber lasers with 1.06 μm. “As a result, we can reduce the required energy at the interfaces between the individual components to a minimum and completely eliminate typical following process steps,” Langer said.

Another essential technology component is the “ESL2-100 module”, another in-house development at the Dresden institute. “This enables us to process a wide variety of sensor signals and implement corresponding control algorithms derived from them,” said Peter Rauscher, group manager for high speed laser processing at Fraunhofer IWS. “This offers the possibility to monitor and adaptively control the welding process in real time and would not be possible with conventional control electronics. For example, in addition to controlling the welding temperature along the welding gap, we are also able to take into account the position, width, and curvature of the aircraft half-shells.”

An important task was to continuously and precisely guide the applied laminate and press it onto the aircraft half-shells in a contour-accurate, width-dependent manner. At the same time, the laser beam had to be guided and the temperature in the joining zone recorded pyrometrically. Courtesy of Clean Aviation.

The setup also consisted of two interacting movement units, called end effectors. One end effector served to precisely guide the applied laminate during continuous deposition and press it against the aircraft half-shells. The second end effector ensured laser beam guidance and pyrometric recording of the temperature in the joining zone. Each end effector moved synchronously with the other on its own linear axis system to decouple the transmission of possible vibrations or deformations caused by the pressing of the laminate strips from the laser system's optical beam guidance.

Future work will be conducted with the aim of increasing the technology readiness level toward qualification for aviation suitability. One challenge is establishing the acceptance and use of both the thermoplastic composite materials and the corresponding processes in the various industries.

The researchers will present their results and the system technology at the International Aerospace Exhibition ILA 2024 in Berlin, Germany.