Total car coverage with PET molded body panels

Take a good look at the two concept vehicles shown here--the Plymouth Pronto Spyder and Dodge Intrepid ESX2. Both have more in common with the ubiquitous 2-liter soda bottle than with past Chrysler vehicles. They are, in fact, the pioneers of the OEM's patented manufacturing process in which body panels are entirely injection molded. Borrowing from lessons learned with its Composite Concept Vehicle (CCV), Chrysler is forging ahead with its Extended Enterprise partners--Ticona (materials), Ashland Chemical (adhesives), Cascade Engineering (molder), Husky (molding machines), and Paragon and Weber (tooling)--to create PET panels for these vehicles.

Steve Leyrer, Ticona program director for Chrysler's large injection molded parts project, spoke to IMM recently about the program. "Chrysler is looking at a way to develop a structural body that is entirely plastic on top of a metal frame that houses the engine and suspension," Leyrer says. "It is committed to translating the technology developed for the CCV, with four molded, adhesively bonded PET parts, into other vehicles."

PET has not been one of the traditional materials of choice for large automotive panels, according to Leyrer. Glass-reinforced PET has been traditionally too brittle for this application, exhibiting brittle fracture at nearly all temperatures. But Ticona's Impet Hi formula is impact modified to reduce fracture concerns even at -20C. Chrysler is using a proprietary grade based on this formula, which is both UV stable and impact modified. The body panel grade will also be precolored by Ticona
at its Florence, KY color matching lab.

We asked Leyrer how the Ticona-developed PET material meets long-term creep requirements. (Creep tests measure how much dimensions change vs. time when a constant load is placed on a part.) This has been a hindrance to using plastic body panels in the past--the tendency for creep strength to fade over time. "Long-term creep doesn't seem to be a problem," he answers. "Chrysler has developed a tremendous amount of computer sophistication in terms of virtual modeling. It was one of the first to embrace computer technology, and the simulations have proven that dimensional changes over time are acceptable. Also, all of the creep data generated by Ticona indicate the same."

Structurally speaking, plastics need greater thickness to meet the level of strength and stiffness that metals afford. Yet Chrysler designers have found a way to add structural integrity without adding undue thickness. "It's a combination of design-for-stiffness and materials technology," Leyrer says. Sources at Chrysler confirm that the multipiece design gains additional stiffness over a true unibody. On the material side, both tensile and flexural strengths have been boosted along with an increase in impact strength.

Specifics on the two new concept vehicles explain why PET panels make sense. For the Intrepid ESX2, the six plastic panels weigh 50 percent less than today's Intrepid, which requires 80 steel pieces. Chrysler sources also confirm the cost savings--20 percent less unit cost--as a significant motivation to making the change.

Design flexibility is another key benefit to plastic panels. The Pronto Spyder, for example, echoes the fluid lines of Porsche's 911 or Volkswagen's Carmen Ghia. Yet cost savings on the panels would allow Chrysler to offer the sports car to consumers at about half the price of today's sleek roadsters, according to company sources.

Tom Tremont, chief designer for Pacifica (Chrysler's design studio), confirms that the PET technology has the potential to reduce manufacturing costs by 80 percent over conventional methods using steel. Additional cost considerations are detailed below.

Contact information
Ticona
Edison, NJ
Phone: (800) 833-4882