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Enhanced Mould for Thermoplastic Fuselage in and out of Autoclave Consolidation

Periodic Reporting for period 1 - EMOTION (Enhanced Mould for Thermoplastic Fuselage in and out of Autoclave Consolidation)

Reporting period: 2019-09-01 to 2021-02-28

EMOTION – Enhanced Mould for Thermoplastic Fuselage in and out of Autoclave Consolidation

The EMOTION project provides a tool that enables the production of high volume half-shells from thermoplastic fibre composite. The tool is planned to be used in the CS2 joint project STUNNING.
Composite strucutres are used for latest airliner generation. Further improvement for the airframe lightweight structure shall be achieved by using thermoplastic based composite materials. While the use of carbon fibers as strong and stiff material remains the same, the matrix materials shall be changed to thermoplastics. This change is also motivated by potential improved end-of-life properties, e.g. meaning improved recycability.
Thermoplastic composite structures are stacked from several thinn plies which need to be consolidated to a solid and strong material. Consolidation means that a pressure of up to 10 bars and temperatures up to 400°C is applied to the stacked material. Doing that, a shape defining tool is required which resists the temperature and pressure applied by an autoclave.

The challenge to be solved by EMOTION research consortium is the temperature resistance while consolidation process. The composite material is positioned at room temperature but later on heated up to 400°C. The tool material (typically metal) as well as the composite material will expand and shrink during that operation. The difference in thermal behaviour causes the challenges. In worst case the metal tool resists the temperature, but the manufactured composite strucutre is affected by wrinkles, like a badly ironed shirt. Wrinkles reduces the strength of a composite material therefore a solution must be found to keep the reinforcing fibers perfectly aligned.

Lightweight structures are essential for the environmental friendly operation of airliners and in general mobility providers. Less weight, means more passenger or freight can be transported at same CO2 footprint. Even new propulsion technologies like electric or hydrogene based ones come up the structural weight need to be optimized. The range and capacity of an airliner will depend on its structural weight.

But not only a tool for manufacuting in autoclave is considered wihtin EMOTION project. The next step focused on energy efficient and waste reduced manufacturing, is under research.
Overall the project objective is, the improvement of environmental friendly production and operation of aviation by use of advanced materials.
The initial design phase was dominated by the search for the most suitable tool material. The challenge lies in low thermal expansion in the temperature range of 350 to 400°C, where the thermoplastic matrix is liquid and the carbon fibre can be easily deformed. A special Ni alloy offers the best properties here. However, this alloy is not or very rarely used for larger components.
The most important task of the tool design at the project partner ALPEX was to work out a solution in which only the tool surface can be made of this special alloy, but the substructure can be made of less expensive steel. A multi-material design with a relatively thin tool shell was developed. Technical risks such as welding of the Ni alloy, spot welding of different steels to attach tension rods to the skin and process-safe (vibration-free) milling had to be secured by trials.
The tool was successfully built by the EMOTION consortium during the first project period and is close to finalisation. The new tool design was produced to the best of our knowledge, supported by preliminary tests at TUM, and must prove its suitability in the associated STUNNING project. With a tool length of approx. 8m and a diameter of approx. 4m, the tool weighs approx. 35t. It will be transported by heavy goods vehicle from the project partner Ostseestaal to the site in Stade, where the topic manager NLR will manufacture a fuselage shell.
In parallel research activities were launched to support the design of the multi material tool, but also to prepare solutions for an enhanced tool version. To improve the economic and environmental performance an integrated heating and cooling need to be evaluated. Next steps for this development route can be defined as soon as learning from the large full-scale tool are available.
A special Ni alloy is being used for the first time for tooling to consolidate fibre composites. If the good results of the laboratory tests are also confirmed on a full-scale basis, large shell components made of thermoplastic fibre composite material can also be produced from unidirectional individual layers in the highest quality. This step allows further optimisation of aircraft structures, weight savings and improvement of eco-efficiency.

The use of costly special alloys requires a new tool design in which the base structure can still be made of low-cost steel. While the tool base is allowed to expand during heating, the tool surface must be kept geometrically within tight tolerances. Stiffness on the one hand and flexibility between components that expand differently must be taken into account in the tool design and are the key to manufacturing high quality fibre composite components.

EMOTION extends the kowledge and capability to design and manufature tools capable for high temperature thermoplastic composites usable in highest challenging aerospace applications.
Geometry measurement by laser tracker of the full scale EMOTION tool after first assembly