What's the best thing about plastics? Judging from the recent Innovative Use of Plastics Awards held by the Society of Plastics Engineers Automotive Division, the ability to simplify assembly would be a good answer.
The competition overflowed with examples of how good plastic part design can improve assembly operations by eliminating parts, fasteners, and manufacturing steps. It featured everything from underseat storage drawers that assemble from a single piece of plastic using living hinges to complete front end modules with molded-in brackets and attachment points. Light bars, speaker enclosures, and all-plastic running boards likewise highlighted how plastics can result in simpler assemblies. Here's a more detailed look at how two of the finalists used plastics to make their assemblies more efficient:
Strong fibers cut hinges and brackets. A door inner panel made in a single compression molding process from both glass- and carbon-fiber sheet molding compound (SMC) helped DaimlerChrysler reduce the size of the door hinges on the 2003 Viper. According to Michael Shinedling, a performance vehicles engineer, the superior strength of the carbon-reinforced section of the door allowed the hinge frame to span about half the height of the door—which is in keeping with styling goals. "Usually the hinges have to be spaced much further apart for strength," Shinedling says. The extra strength from the carbon-fiber portion of the door also allowed Viper engineers to downsize a steel reinforcement near the front of the door, which helped contribute to a weight savings of about 6.5 lb. Central to the hybrid door panel was the development of a blended joint between the glass- and carbon-fiber regions. Created during the compression-molding process, the joint encapsulates the carbon-fiber material within its glass-fiber counterpart.
Shinedling points out that the door represents the first use of a carbon-fiber reinforced SMC in a commercial automobile. But the door isn't the only place it's used. "Overall, the 2003 Viper uses nearly 18 lb of carbon-fiber materials," he reports. These include a unique fender support system in which six molded composite panels serve as the attachment points for 34 different exterior and underhood components. These six panels replace 15-20 metal stampings and brackets required by conventional construction for a weight saving of about 40 lb per vehicle.
No glue headlamps. Visteon Corp. showed off an adhesive-free, sealed headlamp assembly for Ford E-150 Econoline. Using a patented integrated molding and assembly method, Visteon bonds the headlamp lens and reflector together inside an injection mold, creating a sealed joint by injecting a clear thermoplastic around the mating surfaces of the headlamp pieces. "We use the headlamp parts themselves as the mold for the bonding plastic," notes Visteon engineer Kelly Herman. In the past, this type of headlamp would be assembled with a two-part urethane adhesive, adding cure time and cost. Other headlamps have been put together with vibration welding. "But both glue and vibration welding can have problems with the 3D geometry of lamps," Herman says. The new in-mold assembly method also saves time and money. Herman estimates that it takes about a quarter as long to make a headlamp, in part because there's no wait for curing before a leak testing step. And the integrated molding and assembly also cuts in-process scrap by 85%.