Study: CFRP Window Frames for Commercial Aircraft

In addition to stringers and frames, window frames are an essential part of the fuselage. Aircraft window frames are usually made of aluminum and have an oval-shaped outer contour and a t-shaped cross section.

The use of carbon fiber-reinforced polymers together with a component design specifically for composites makes it possible to reduce the window frame weight by almost 50% while maintaining the same safety margins. This weight reduction goal requires the application of innovative materials and manufacturing technologies that will enable industrial process chains for large quantities.

Schematical structure of a single
sub-preform

Preform manufacture takes on a key position in the process chain. The whole window frame consists of sub preforms which themselves consist of several plies of dry fiber material. The lay-up sequence is determined by stress analysis of the window frame design and this, in turn, determines the fiber orientation and cutting positions. The ring-shaped geometry and different fiber orientations in the preform result in particular requirements for the manufacturing process as all forming steps will influence the properties of the dry performs.

The manufacturing method developed at the CTC GmbH based on dry perform technology enables the application of dry semi-finished products with a ply stacking sequence adapted to the requirements by means of the corresponding textile technology. The developed methods also allow for a high lay-up speeds. Compacting and fixation of the whole preform is carried out in a compacting tool so that the highly compacted preform already exhibits the geometry of the final component.

Prototype CFK-Window Frame

The preforms are then impregnated in an injection process and cured in a thermal oil-heated press. During the design of the RTM tool, care is taken that the necessary compaction is achieved during the lay-up process of the preform.

With the analysis of the described process chain, the potentials for automation of industrial series production were identified. An automation of the entire process chain is necessary for large quantities, whereby partial solutions for an industrialization already exist in the RTM field. The production of large quantities at acceptable costs is only possible with a continuous process chain.