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28 May 2024
Major European consortium led by Airbus joined upper and lower halves of the world's largest composite fuselage segment.
Researchers in Europe say that they have successfully laser-welded two halves of an 8-meter-long section of fuselage made from carbon-reinforced fiber - suggesting that it will be possible to make ultra-lightweight passenger aircraft using the approach.
Completed by a large international consortium led by Airbus and featuring multiple Fraunhofer institutes, the demonstration is said to provide a proof of concept for the chipless joining of carbon fiber-reinforced thermoplastic (CFRTP) component structures with a carbon dioxide laser.
Dynamic beam shaping
Working under the “Multifunctional Fuselage Demonstrator” (MFFD) project, part of the European Union’s wider “Clean Sky 2” research program, the team at Dresden’s Fraunhofer Institute for Material and Beam Technology (IWS) say that the novel construction method and process would enable a massive reduction in weight, material, and time.
They used a CO2 source to weld long seams on large-volume thermoplastic aircraft fiber composite structures outside of an autoclave, in what is thought to be a world-first achievement.
“On the left side of the MFFD, the process approach developed at Fraunhofer IWS produced the final longitudinal seam joint between the upper and lower fuselage halves of an eight by four meter section of the aircraft fuselage segment made of carbon-fiber reinforced thermoplastics – in full scale,” reported group manager Maurice Langer and his colleagues.
“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.”
Laser wavelength critical
The team in Dresden, which is due to report its findings at next week’s International Aerospace Exhibition (ILA 2024) in Berlin, also said that the 10.6 µm CO2 laser wavelength plays a critical role, thanks to much higher optical absorption than with 1 µm-emitting fiber lasers that are now widely used in industrial welding.
Using a laser means that mechanical joining elements and material doubling with classic riveted overlap joints is not required, so the the hull shell made of thermoplastic composite material weighs significantly less than conventional sections.
“This 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,” noted the IWS team.
“Conventional manufacturing processes for these materials are often energy-intensive and costly,” added Langer. “Together with our project partner Airbus, we have therefore developed a process that allows us to join components outside the autoclave using a stepped shaft technology, while at the same time achieving excellent strength properties for this composite.
“New material classes require innovative production methods. The declared aim of the MFFD was to reduce the weight of the fuselage by up to one ton.”
Over the operating life of the aircraft, the significantly lower weight would significantly reduce overall energy requirements, fuel consumption, and related emissions.
“With the CONTIjoin process developed at Fraunhofer IWS, we have succeeded in taking an important economic and ecological step for future aircraft development and related applications,” Langer said.
Overlap joints
One of the key elements of the project was to join the upper and lower shells of the aircraft body step-wise, by continuously placing several laminate straps on top of each other, automatically positioned in a stepped geometry on the surfaces of the half-shells.
“The resulting overlap joints restore the initially interrupted force flow of the fiber composite material between the half-shells and form a reliable load-transferring joint,” explains the IWS team.
The higher absorption of the CO2 source also means that the required energy at the interfaces between the individual components can be reduced to a minimum, which is said to eliminate follow-up processing steps that are typically required.
Another key development is said to be the IWS team’s “ESL2-100 module”, developed in-house at the Dresden facility.
According to Peter Rauscher, the IWS group manager for high-speed laser processing, this enables a wide variety of sensor signals to be interpreted, so that corresponding control algorithms can be implemented.
“This offers the possibility to monitor and adaptively control the welding process in real time, and would not be possible with conventional control electronics,” Rauscher said. “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.”
Future plans will look to advance the Technology Readiness Level (TRL) of the approach, towards qualification for the aviation industry and beyond.
“The CONTIjoin technology developed is attractive for aircraft construction and other industries,” Langer pointed out. “In addition to aviation, the solution could also be interesting for applications in shipbuilding, truck and trailer construction, as well as in rail transport or in the further development of modern wind turbines.”
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