Carbon/epoxy overbraided, RTM’d spring carrier beam
Munich Composites GmbH (Ottobrunn, Germany) won a JEC Innovation award in the Transportation Category for its carbon fiber air spring carrier part, produced in partnership with transportation giant MAN Truck and Bus AG (Munich, Germany). The project’s goal was to cut suspension weight by using a composite in place of steel.
The air spring carrier beams are attached to the air spring suspension bags, which support the weight of the bus. Each rear axle has two air spring carriers, each weighing 83 kg, and the structure that supports those carriers weighs 53 kg, in a metal design.
Munich Composites developed a prototype replacement carrier beam made by radially overbraiding carbon fiber on a reusable inflatable mandrel. The overbraiding process is robotic, and several robots work together to pull the component mandrel through the braider at exactly the angles necessary to ensure optimum fiber alignment for complex geometries. As it does so, it generates virtually no scrap.
After layup, beams are resin transfer molded, using epoxy, in a fully automated process that results in very low void content, says Martin Stoppel, commercial director for Munich Composites. The resulting hollow, curved 1.6m- long carrier beam weighs less than 16 kg — about 70% lighter than the metal version — allowing an increase in the bus payload of one passenger.
The prototype part is currently undergoing tests on MAN buses to prove its capability and reliability. Stoppel says that the project has resulted in a highly automated and fast process that is scaleable to produce cost-effective carbon-fiber-reinforced transportation parts.
Compared to legacy materials like steel, aluminum, iron and titanium, composites are still coming of age, and only just now are being better understood by design and manufacturing engineers. However, composites’ physical properties — combined with unbeatable light weight — make them undeniably attractive.
Tried-and-true materials thrive, but new approaches and new forms designed to process faster are entering the marketplace.
Fast-reacting resins and speedier processes are making economical volume manufacturing possible.