Polymer Honeycomb Structures Target Aircraft Engines

French materials company PlastiCell has developed aninteresting new technology, creating more design opportunity. Honeycomb cellsmade from high-performance plastic film provide significant strength andstiffness.

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

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

The honeycomb structures are made via two steps - formingthin APTIV film sheets to create semi-hexagonal shapes, and sequential stackingof sheets and welding with a laser along lines at the contact points to achievemelt-bonding.

Core blocks made in this way can be machined to shapebefore molding by a variety of processes. Finished structures are produced bypress molding pre-formed and pre-heated composite skins onto the honeycomb in aforming tool. The honeycomb cores conform to the mold geometry due to thecombination of the pressure inside the mold and the temperature of the matingsurfaces. The result is excellent bonding between the core and the skins.

"Unlike traditional honeycombs, which are produced withadhesive systems, the PlastiCell process uses laser welding to join the APTIVfilm layers within the honeycomb matrix. This maintains the performanceproperties 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 forthe surface skins must fulfill the aircraft industry standards for flameperformance, smoke and toxicity, as well as offering mechanical performance andlow weight," says Didier Padey, market development manager France for VictrexPolymer Solutions.

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

PEEK-based honeycomb is also said to provide numerous otheradvantages, including impact resistance. Unlike an aluminum or thermosettinghoneycomb, PlastiCell's honeycomb will not remain deformed by accidentalimpacts during machining or assembly of the part, or due to the material's hightemperature performance. The honeycombs can operate continuously up to 428F, athermoformable honeycomb core allows for the production of parts with shortcycle times using an autoclave-free process.

There is no sizeconstraint as it is possible to make an endless honeycomb using PlastiCell'smanufacturing process. Part size limitation is dictated by the hydraulic pressplaten size. Flat and curved parts can be made using this process and theflexibility of the thermoplastic honeycomb allows it to be formed intocylindrical shapes. Additionally, parts can be permanently laser marked forproduct identification and traceability.