When it comes to automotive assembly, simpler often means better. Just consider the vibration-damping fuel- and brake-line fasteners that Emhart Teknologies (www.emhart.com) created for BMW. These clips feature a single-material design and take the place of fasteners formerly made from two materials in a more complex, costly manufacturing process.
Fuel-line clips may be a minor component of the car, but fighting vibration and noise around fuel lines is not trivial. Unchecked vibration stresses fluid lines. "It could lead to premature failure," says Christine Yingli Lee, Emhart's automotive research and development director. And noise goes right to the heart of consumer quality perceptions.
According to Lee, previous generations of clips relied on multiple materials to meet OEM requirements for vibration damping and noise reduction, and retention forces. These clips would typically use a rigid thermoplastic, often acetal, to fulfill the force requirements. The clips would also contain an insert of thermoplastic elastomer, which would nestle against the brake or fuel line bundles to absorb any vibration and reduce noise. Fastener manufacturers would bring the two materials together in a two-shot injection molding process that required elaborate tooling.
Emhart engineers found a simpler one-material design in a thermoplastic ether ester elastomer—Hytrel from DuPont Engineering Polymers. At 72 Shore D, Hytrel offered enough rigidity to stand in for the hard thermoplastic while still providing the necessary vibration-damping performance, Lee explains. Emhart engineers then supplemented the material's inherent performance by molding in vibration-absorbing honeycomb sections. The design team then ran extensive FEA analyses to optimize the honeycomb cells for maximum damping.
The resulting clips "equal the performance of the two-piece clips in terms of noise and vibration absorption," says Randy Leedy, Emhart's automotive product manager.
So if the performance only equals that of the earlier design, why bother? Cost is the big reason. Emhart managed to reduce piece-part cost for the fasteners by about 20%, thanks to savings in its tooling and molding costs. And since it's composed of just one material, the new clip also supports European recycling goals. Finally, the new fasteners also weight about 10% less. Emhart last month announced that it would make the clips available in North America too.