By Chris Singleton
From simple component covers to radiator end caps; from intake manifolds to bumper fascia, automotive parts that were once designed and made from metal out of "necessity" are now, owing to advances in...
From simple component covers to radiator end caps; from intake manifolds to bumper fascia, automotive parts that were once designed and made from metal out of “necessity” are now, owing to advances in resin performance and molding technology, made from plastic by choice. Today, the palette of resin technology available to the automotive designer exceeds by many times that which was once available twenty years ago. This accounts for the over 600 percent increase in the use of plastic by weight in today’s cars compared to cars made in 1970.
Polyurethane is seeing new use as a material for exterior components, because of its good aesthetic properties, weatherability, ease of painting and excellent dimensional stability. But the new darling for exterior applications is PET (polyethylene terephthalate), which is being touted for molding everything from mirror housings to large body panels.
While plastic body panels have been in use on a number of foreign and domestic vehicles for some years, one of the more ambitious projects today is DaimlerChrysler’s effort to make PET body panels for a four- to 12-piece car body using a 8800-ton two-platen Husky injection molding machine. DaimlerChrysler has said that PET is the first material the company has worked with that would cost less than steel. Ticona is supplying the glass-filled PET, compounded with a variety of additives.
Another new development, apparently close to commercialization, involves the use of small amounts of “nanocomposite” fillers that may pave the way for thermoplastic body panels (see Canadian Plastics, April 1999). The nanocomposites or clay-reinforcing particles greatly improve the structural properties of the the thermoplastic with no decrease in melt flow. If successfully transferred to the market, this development promises to give automotive stylists greater design freedom than metal and provide significant cost savings for both manufacturers and consumers.
Interiors: more than decorating
Plastic continues on its decade-long trend of metal replacement in auto interior applications. DuPont’s Zytel nylon has successfully replaced the aluminum for the pedal-bracket plate in the Mercedes-Benz A-and S-Class vehicles. The new polymer design reduces assembly and installation costs, eases assembly and reduces weight compared to the die-cast aluminum components normally used, while meeting the NVH (noise, vibration and harshness) characteristics required for cars of this class.
Even though an emergency-braking maneuver can create loads up 8000 N, the glass-reinforced Zytel nylon can withstand the force without exceeding permissible deformation.
Zytel was also used in the Mercedes-Benz line of light trucks to make the world’s first center-bolted thermoplastic rocker cover. Molded of Zytel glass-reinforced nylon, this new application provided a 50 percent cost reduction, 40 percent weight reduction and, as well, lowered noise transmission significantly compared to an aluminum rocker cover. Overcoming concerns for how a centre-bolt design could provide sufficient sealing force on the perimeter seal, the engineers of the new design also improved functionality by including an integrated oil separator, further lowering the assembly cost.
In-mold decorating has for many years been seen as the best way of achieving high quality part decorating for dash control panels and wood-grained dash fascias, such as those in Ford’s Mondeo. Molded from Bayer Corporation’s Makrofol DE 1-4 polycarbonate film and Bayblend T84 polycarbonate/ABS blend resin the process eliminates a secondary process to apply a wood grain ink transfer. Continued development of the process promises new opportunities for automotive designers to explore, such as “extreme” graphics, lettering, etc., in-mold decorated on large plastic body panels molded in color in one step, a process which would not be feasible with metal.
Another product from Bayer, the Baydur 410 IMR polyurethane high-density SRIM system, was used to mold the seat back frame on the 1997 Chevrolet Corvette. The glass-fibre reinforced polyurethane seat replaced tubular steel, trimming 60 percent from the weight of each of the Corvette’s two seat back frames without sacrificing strength.
“This is the first structural, mass-produced polyurethane SRIM seat back frame in the North American auto industry, and probably the first in the world,” says Michael Walkowski, product engineer for Lear Corp. Polyurethane SRIM also allowed supplier Lear Corp. to cut fabrication of the frame to a single step and produce two different frames with the same mold. The IMR-modified Baydur 410 system provided an internal mold release feature that reduced cycle time.
Under-the-hood uses growing
Engineered nylons, of course, are now commonly used in difficult, high heat, under-the-hood applications. In 1972 BASF successfully helped commercialize an injection-molded nylon air intake manifold for Porsche.
Originally, the manifolds were molded in multiple pieces then welded together. Then development of lost core molding technology allowed manifolds to be manufactured as one-piece units. However, due to the enormous capital investment and the required secondary operation to melt out the core, some recent projects have returned to multi-piece configurations. One current manifold used on some Opel cars manufactured in Europe utilizes a six piece design with both vibration welding and snap fit assembly that results in a 50 percent weight savings over conventional aluminum cast manifolds.
Jaguar’s new XK8 sports car has a high-performance nylon air intake manifold with a molded-in fuel rail, made from BASF Ultramid A3HG7 black, 2056 type 66 nylon. The manifold is molded by Siemens using a fusible-core injection molding (FCIM) technique in order to conform to the V-8 manifold’s complex runner angles.
Engineers are continuing to find new uses for nylon in powertrain and chassis applications. The 1999 Jeep Grand Cherokee features the first-ever integrated transfer case/automatic shifter assembly made with engineering thermoplastic. The shifter is molded from VYDYNE 66 nylon resin from Dow Automotive. VYDYNE was chosen for its high strength and rigidity, as well as strong heat and chemical resistance, according to Dave Recktenwald, senior program manager at Dow. The shifter yoke is insert-molded with three separate inserts. Overall the shifter has 18 components, most made of VYDYNE nylon.
BMW’s Z3Roadster has an innovative in-tank fuel management system, incorporating a 12-volt pump and an electronic fuel-level sensor, which fits inside the fuel tank. The fuel pump is housed in an injection molded nylon housing, molded of Ultramid nylon A3W, an un-reinforced nylon 66 supplied by BASF. The housing also contains a molded-in, nylon-mesh filter. Ultramid nylon achieves excellent adhesion to the nylon mesh and retains mechanical properties while immersed in fuel. The one-piece housing/filter is made in an automated two-step process, replacing a previous manual assembly operation.
Fuel efficiency and power train reliability are strong incentives for the industry to continue to push polymers into new applications in the engine compartment. Going into the 1999 Oldsmobile Intrigue, the Delphi-E ignition cassette, molded from DuPont’s Rynite R940 PET polyester, helped not only reduce weight and cost, but also provided more power than traditional ignition systems. The new design also makes for a cleaner, stronger running engine.
Future trends: Opportunities for complete assemblies
Part consolidation helps to reduce system cost and opens new opportunities for molders to provide complete assemblies or system modules. This particular facet of providing complete sub-assemblies is an area that the plastics industry seems to have taken closer to heart than many of the metal stamping and machining suppliers.
The near future will also likely see the introduction of new metal composites and ceramic composite materials that will allow polymer materials continue to capture some of the few remaining under-the-hood applications that
are still beyond current high temperature polymer capability.
Although it seems that today’s automotive engineers need only to challenge the resin makers to develop new applications and it will be done; much development is required in the area of recyclability of plastic automotive parts, both at the processor and the consumer levels. The problems of identifying the material, disassembly and storage of the components and re-compounding into a useable material are likely to take on a role of greater importance into the next century.CPL
Chris Singleton is a member of Canadian Plastics’ editorial advisory board