Honeycomb cores have also been used in aerospace carbon fiber composites, such as the structure and blades of Sikorsky Aircraft's S-97 RAIDER helicopters and, reportedly, in the shell of Virgin Galactics' SpaceShip Two. A similar honeycomb sandwich structure is used in some parts of Boeing 787's Dreamliner.
The new material's honeycomb core is covered on both its top and bottom with glass fiber mats, then sprayed with the Baypreg system, which contains a flame retardant and may optionally also contain cut glass fibers. The component is placed in a compression mold while it is still moist and is pressed at a temperature of 130°C. The polyurethane system foams slightly and binds the components together. After about two minutes, the part can be removed from the mold and deburred.
Components as large as four square meters in area can be produced, yet they have excellent dimensional stability, allowing the parts to be installed in the final assembly with a high level of precision. "By using this new material, we can reduce the component’s weight by over 35 percent -- and cut costs by 30 percent," said Jan Kuppinger, a Fraunhofer ICT scientist, in a press release.
Bayer's Baypreg spray system has been used in automotive applications for producing panorama roof modules, spare tire covers, and the floor of a car's trunk. The team optimized the standard fiber spraying manufacturing process by developing a mixing chamber that allows more complex structures to be produced in any required size. The prototype diesel engine housing measures approximately 4.5 meters long and more than 2 meters wide.
The diesel engine housing prototype was produced as part of the PURtrain project, which is funded by the German Federal Ministry of Education and Research (BMBF). The prototype has passed its first strength test; the next step is field tests. If the prototype passes those tests, the team expects the material to also be useful in applications such as roof segments, side flaps, and wind deflectors for automobiles and commercial vehicles.