The Audi A6 Avant is a showcase of leading-edge composite applications, including the first ever composite coil spring.
Sogefi, a developer of flexible components for suspension systems based in Milan, Italy, patented the composite coil spring, which weighs 40 percent less than steel springs.
It’s made with a filament winding composite lost core molding process using a proprietary epoxy resin developed by Hexion. Ropes of fiberglass impregnated with epoxy, additive and hardener are wrapped around an aluminum core. Additional fibers are wrapped around the core at alternating angles of plus and minus 45° to the longitudinal axis. Following polymerization in a curing oven, the core is removed and then recycled.
It takes about 10 minutes to make a part. Up to 80,000 parts per year can be made by the Tier One molder, S.Ara Composite, a Sogefi unit in France.
Audi says that approximately half the weight of the spring is unsprung, which helps vehicle responsiveness. No coating is required since the material is corrosion free.
Christoph Bayerlein, Audi development suspension systems specialist, says: “The GFRP springs are very high strength, and we are confident that they can withstand stone chips that might otherwise penetrate a conventional steel spring coating and cause degradation over time. This is because the glass fibers are about 1.5 mm below the surface, so we do not expect any issue of fatigue behavior to adversely affect the composite springs if there is some surface damage.”
For now the composite springs are only used on the models designated “Ultra”, but Audi says it plans to expand their use. Other car manufacturers are also exploring use of the composite springs. No cost data has been divulged.
Allevard Rejna, the research arm of the Sogefi Group, says that weight savings from use of the composite springs can go as high as 70 percent.
The Audi A6 also uses continuous fiber-reinforced polyamide composite in an infotainment system carrier structure.
KraussMaffei developed a fully automated manufacturing cell with a custom handling system and a heating unit placed directly above the mold platen for prototype development. The resin partner was Lanxess.