Thermoplastics in aircraft construction – less weight, more future

Every gram counts: In aviation, a weight reduction of just one kilogram can save up to 25,000 litres of fuel annually. Plastics can be the key to this. The German Aerospace Center, for example, uses carbon fibre-reinforced thermoplastics to make aircraft fuselages more resource-efficient. Within the framework of the Large Passenger Aircraft project, fundamentally new technologies have even been developed for this purpose.

In an interview with K-MAG, Dr.-Ing. Frederic Fischer talks about the current challenges for aviation, the extent to which the use of plastics and the newly developed manufacturing technologies are more climate-friendly and cost-effective.

Dr Fischer, what challenges is aviation currently facing? To what extent do you address them in the Large Passenger Aircraft project?

Dr.-Ing. Frederic Fischer: Aviation is facing the urgent task of becoming more climate-friendly and sustainable. For decades, we relied on aluminium as the main material. But in today's world, with its increased focus on environmental protection and resource efficiency, this is no longer enough. The Large Passenger Aircraft project aims to reduce fuselage weight by 10 % and running costs by 20 %, which will revolutionise aviation.

In the project, you developed a fuselage component. What is it made of? What are its special features?

Fischer: Our multi-function fuselage demonstrator (MFFD) is made of a special plastic: carbon fibre-reinforced thermoplastic (LM_PAEK). Compared to aluminium, this material is lighter and also has the ability to be reshaped when heat is applied again. This makes repairs and recycling easier.

What impact does the use of CFRP have on sustainability compared to aluminium?

Fischer: CFRP offers numerous advantages over aluminium. Not only is it lighter and thus more fuel-efficient, but it is also recyclable. This leads to less waste and reduced energy consumption over the life cycle of the aircraft.

You have redeveloped some of the technologies and tools used to manufacture the MFFD. To what extent was this necessary and what were they in detail?

Fischer: Our main motivation was to make aviation more sustainable. To achieve this, we had to make the transition from aluminium structures to carbon fibre-reinforced thermoplastics in aircraft production. This transition also required the development of new manufacturing technologies. The three core innovations are:

• Laser-based in-situ fibre deposition: Here we use a robot that precisely heats material strips by means of a laser and deposits them in layers. This technique minimises material waste.
• Continuous ultrasonic welding: Instead of riveting, we use this method to connect the longitudinal reinforcements, the so-called stringers, to the outer skin.
• Electrical resistance welding: We use this method to weld the transverse reinforcements, the so-called formers, to the skin. To do this, a welding element in the joining zone made of carbon fibre is exposed to electricity, which heats it up and melts the components.

By using these technologies, we can fully exploit the advantages of the new materials and significantly reduce the production effort.

What were the individual production steps for the MFFD?

Fischer: The production took place in several specific steps:

1. Fibre deposition: A ceiling-mounted robot used a laser to heat strips of material and lay them down in layers. This formed a laminate of fibre-reinforced plastics.
2. Reinforcement of the outer skin: The next step was to reinforce the finished outer skin with the continuous stringers. They were attached by means of the newly developed ultrasonic welding. A robot with a precise path correction was used for this to effectively join the stringers.
3. Application of the transverse reinforcements: Following this, the transverse reinforcements, our formers, were added by electric resistance welding.
4. Final connection: Finally, the longitudinal and transverse reinforcements were welded together. Due to the confined working space, we combined a standard robot with a smaller lightweight robot to ensure precise welding of the fasteners.

What advantages do these new manufacturing processes bring over conventional methods in terms of production costs and sustainability?

Fischer: Our new manufacturing processes reduce production time by up to 40 %, which brings significant cost savings. Since we have less material waste and can do without the autoclave process, we are also more resource-efficient. Overall, these processes increase both the economic efficiency and sustainability of production.

What happens now with the MFFD shell?

Fischer: After successful completion, the MFFD shell was delivered to Premium Aerotec, where the final machining took place. It will now be transported to the Fraunhofer Institute in Stade for further processing. Finally, Airbus will validate the technologies in Hamburg. These are exciting developments and we look forward to driving progress in this area.