Polymer Honeycomb Structures Target Aircraft Engines

French materials company PlastiCell has developed an interesting new technology, creating more design opportunity. Honeycomb cells made from high-performance plastic film provide significant strength and stiffness.

One target application is aircraft OEMs that are trying to dramatically reduce weight, like the Boeing Dreamliner 787 which remains about 8 percent above its projected weight.

The cells are made from Victrex APTIV^™ film, which are thermoformed into shape in combination with fiber reinforcement. No adhesives are used. Because they consist only of PEEK polymer, any scrap and end-of-life parts can be fully recycled, providing further advantages over traditional phenolic/aramid fiber and aluminum-based honeycombs.

The honeycomb structures are made via two steps — forming thin APTIV film sheets to create semi-hexagonal shapes, and sequential stacking of sheets and welding with a laser along lines at the contact points to achieve melt-bonding.

Core blocks made in this way can be machined to shape before molding by a variety of processes. Finished structures are produced by press molding pre-formed and pre-heated composite skins onto the honeycomb in a forming tool. The honeycomb cores conform to the mold geometry due to the combination of the pressure inside the mold and the temperature of the mating surfaces. The result is excellent bonding between the core and the skins.

"Unlike traditional honeycombs, which are produced with adhesive systems, the PlastiCell process uses laser welding to join the APTIV film layers within the honeycomb matrix. This maintains the performance properties of the base film and this is what makes this solution so ideal," says Marc Le Monnier, founder and manager of PlastiCell.

"The thermoplastic film used for the honeycomb and for the surface skins must fulfill the aircraft industry standards for flame performance, smoke and toxicity, as well as offering mechanical performance and low weight," says Didier Padey, market development manager France for Victrex Polymer Solutions.

Victrex PEEK meets these requirements and also offers chemical resistance, high temperature performance, hydrolysis resistance, and also has wear resistance when compared with other high-performance engineering polymers.

PEEK-based honeycomb is also said to provide numerous other advantages, including impact resistance. Unlike an aluminum or thermosetting honeycomb, PlastiCell's honeycomb will not remain deformed by accidental impacts during machining or assembly of the part, or due to the material's high temperature performance. The honeycombs can operate continuously up to 428F, a thermoformable honeycomb core allows for the production of parts with short cycle times using an autoclave-free process.

There is no size constraint as it is possible to make an endless honeycomb using PlastiCell's manufacturing process. Part size limitation is dictated by the hydraulic press platen size. Flat and curved parts can be made using this process and the flexibility of the thermoplastic honeycomb allows it to be formed into cylindrical shapes. Additionally, parts can be permanently laser marked for product identification and traceability.