The second-generation 2004 Dodge Durango SUV and Dakota pickup feature an automotive industry first – the use of plastic for structural support of a sheet metal body panel at the body-in-white stage.
Chrysler Group engineers wanted to reduce the expense and complexity involved in using a support bracket that was stamped and welded together in multiple steps from steel, then coated for corrosion resistance. The bracket, located between the inner and outer door panels, supports the driver- and passenger-side exterior mirrors.
Sandeep Vijaywargiya, Chrysler Group truck products engineer, thought of DuPont first to help resolve the challenge through innovative use of materials technology. Together they identified DuPont™ Rynite® PET as the prime candidate due to its resistance to creep, load, torque and its ability to take brutal e-coat oven temps of 350 degrees for an hour. The result – a mirror housing bracket that provides significant savings on the cost of each part by eliminating costly multiple steps in the manufacturing process, eliminating the need for an additional welding cell on the assembly line and significantly reducing EHPV (engineering hours per vehicle) in the plant.
The new part simply snaps in place quickly and accurately during assembly, assuring it will stay in place until the mirror is bolted on. It also weighs 86 percent less than the equivalent part in steel. The part is molded and supplied to the Chrysler Group by Mayco Plastics, Sterling Heights, Michigan.
"The weight, cost and EHPV savings alone make this a breakthrough application," Vijaywargiya said. "The fact that this is the first use of plastic to reinforce non-crash body panels opens up a whole realm of possible automotive applications."
"Rynite® is one of the few plastics able to manage the extremes of this application," said Dino Tres, DuPont design programs manager. "The part appears small, but is critical in performance and is needed as a material combination of structural strength, stiffness, dimensional stability and extreme heat resistance with no warp."
Structural strength is vital in supporting the oversize side mirrors appropriate to a large sport utility or pickup. Any flex in this crucial part of the door would show up as annoying vibrating images in the mirror.
The material also had to resist weather and harsh chemicals and withstand durability testing, including a torture test that slams the vehicle door 50,000 times.
Rynite® doesn't absorb moisture, so it won't warp even when exposed to water infiltration. Rynite® thermoplastic polyester resin unites the best properties of reinforced polyethylene terephthalate (PET) with easier moldability.
According to Chrysler, Chrysler Group truck products engineers Vijaywargiya, Joe Rozenbaum and John Rodomski have applied for a patent relating to this new use for engineering plastic – citing the precise snap-fit assembly method for the mirror bracket, the bracket design and application of DuPont™ Rynite® and other PET resins as a reinforcement for body panels.
For more information on polyethylene terephthalate, click here.