Creativity and economy

Plastics Engineering, Sept, 1989 by Victor Wigotsky

CREATIVITY AND ECONOMY

Plastics continue to respond to the changing needs of the automotive industry. The 1990 models, and those on the drawing boards, reflect the growing tendency of management and designers to look to plastics for economical, creative car designs. Steady advances in materials and productivity, and the many proven applications, have shown that increased plastics usage can be a major route to meeting diverse industry goals.

FENDER FIELD TEST

Chrysler Motors will evaluate more than 400 Dodge Caravan CV minivans fitted with reinforced thermoplastic front fenders. An 18-month field test with a major fleet customer, Xerox Corp., could be a prelude to high-volume production, perhaps in the early 1990s. In vehicles shipped nationwide to more than 25 Xerox service facilities, the program will check fender durability in varied geographies, climates, and traffic.

Molded of polyethylene terephthalate (PET) supplied by Du Pont and reinforced with glass flake and fiber, the fenders have withstood the high-temperature E-coat paint bake cycles that steel body parts on Chrysler minivans routinely endure during manufacturing.

In another application, the first such use of the technology in the U.S. auto industry, selected 1990 models--the Chrysler Le Baron coupe, convertible, and sedan; Dodge Daytona, Spirit, and Shadow; and Plymouth Acclaim and Sundance--will be equipped with 5-mph bumpers with self-restoring elastomeric energy-absorbing units.

The Du Pont Hytrel unit, a molded hollow cylinder that surrounds the bumper system's sliding central member, is more versatile, simpler, and lighter than hydraulic designs. When the bumper is struck, the cylinder compresses and buckles so that the stored energy then returns the bumper system to its original position.

Dwayne Trimpe, manager, Organic Materials, and Leo Ang, supervisor, Exterior Plastic Applications, Chrysler Motors, report that fascias with molded-in color are being considered. Pigmented fascias would be gray or other dark colors to contrast with body colors. Possible use of polypropylene foam, or materials such as Arco's Dylark, also are being evaluated for the bumper systems.

Under-the-hood efforts include replacement of metal valve covers by thermoplastics or thermosets, including higher-heat ABS and vinyl esters. Chrysler's Jeep sport utility vehicles already have Du Pont Rynite valve covers.

Chrysler has not identified a need to move to higher-temperature interior materials and is maintaining its traditional approach, says John Fillian, supervisor, Interior Plastic Applications. However, the company is preparing for possible future requirements. Use of solar-controlled glass, to screen out radiation for parts that function in the -20 [degrees] F to 175 [degrees] F range, is being explored. Glass suppliers are providing materials that absorb ultraviolet and infrared radiation.

Fillian also expects more emphasis on color concentrates, rather than precolored materials, for possible cost advantages and inventory reduction. More responsibility for color matching is being shifted to the molder level. In addition to the continued pressure to eliminate paint requirements for interior trim, Chrysler is pressing suppliers to take on more product testing.

RIGID MOUNT SYSTEM

The new front and rear 5-mph systems for the 1990-1/2 Ford Escort add bumper area while saving weight and cost. Ed Kure, executive engineer, Exterior Systems, and Paul Guy, executive engineer, New Technology R&D, Ford Plastics Products Div., say that Mazda, designer of the vehicle, subcontracted the development of a rigid mount bumper system to the Plastics Products Div. Replacing the current mount, the design cuts weight about 20% and cost by 10%. Compared with a foam absorber, with fascia and reinforcement, the weight saving can be 10% to 30%.

With an adhesive-bonded GE Xenoy fascia and Xenoy reinforcement beam directly mounted to the car frame, impact energy is absorbed by the plastic structure; shock absorbers or foam is not required. The evolutionary design reflects improved understanding of the plastic material and the impact dynamics. A key to success is that the car bodies are now more dimensionally precise, so that interface elements are not needed to assure proper margins between mating parts.

Ford's Plastics Products Div., especially in light of Corporate Average Fuel Economy (CAFE) standards, is evaluating the car exterior for more opportunities for plastics, including fenders, hoods, and deck lids for 1993 models. Paint-curing cycles tend to be shorter than GM's or Chrysler's and so require a higher temperature--370 [degrees] F--for primers and topcoats.

Ford is checking materials from different suppliers. In one program, reaction injection molded (RIM) polyurea and a thermoplastic, such as GTX, are being studied. Any degradation of flushness or margins, compared with steel, is not acceptable, and plastic panels will not be introduced until differences in expansion and contraction can be compensated for by design. Ford has no present plans for plastic vertical panels in production cars.