Competitive Cooperation

As the theme of this year’s SAE World Congress, “Succeeding In the Alliance Game”, attests, the automotive industry is becoming less of a collection of independent, competing companies and more of a tight-knit community of inter-linked businesses with common interests and aims.

Yet, as highlights of the show’s plastics-related technology in design, processing and materials make clear, the automotive game is still a competitive one. Important collaborative initiatives such Covisint, L.L.C., the auto industry’s global, independent e-business exchange, are also addressing supplier concerns over the manner in which potentially sensitive or proprietary information will be shared. Warm and fuzzy talk aside, suppliers still understand that the best way to collaborate is to bring something innovative and cost-effective to the table.

BETTER, FASTER DESIGNS

Saturn Corporation set an industry standard by completing development and release of the 2000 model year three-door coupe in under 21 months. David Dean, GE Plastics, and Steven Griffin, General Motors, attribute the accomplishment to advanced CAE analysis, rapid prototyping, accelerated tooling, participation of cross-functional teams and the utilization of injection molded body panels (SAE technical paper 2001-01-0848)*.

Saturn began producing vehicles with thermoplastic exterior body panels in 1990. The panels are made from a MPPO/PA alloy supplied by GE Plastics. Using plastic in place of metal shaved a large amount of time and cost from the build process: injection molding tooling for the coupe’s body panels was obtained in 30 to 38 weeks, compared with the 80 weeks usually required for stamping tooling.

The Saturn design team also eliminated an entire prototype phase for the exterior panels (Table 1). Typically, a design will be prototyped using aluminum or epoxy tooling in order to limit costly changes in production tooling. For the three-door Coupe, however, designs of panels, once approved, went from prototype mock-up to P-20 steel. The process was accelerated by merely updating data from the previous model’s quarter panels in areas in which there were slight modifications. No changes, beyond normal debugging, were made to the molds once they were in production.

Saturn organized a cross-functional team to assess and develop the new assembly process required by the three-door model. Vehicle simulation and dimensional management analysis tools were used to establish assembly methods and assure the General Assembly group that build variation could be maintained at line speed.

In another design innovation, Mazda Motor Corp. has developed a technique to strengthen the body frame with a polymeric structural foam (SAE technical paper 2001-01-0313). Benefits include reduced vehicle weight and improved fuel economy. The structural foam prevents the body frame from collapsing on collision, dramatically increasing frame strength.

The company developed an epoxy-based structural foam with superior compressive and adhesive strength. The foam is expanded and cured by heating during the painting process. Researchers examined the effect of foam filling location and foam thickness on frame reinforcement. The method reduced vehicle weight by about 6 kg compared with steel sheet reinforcement and provided equal crash strength.

THIN-WALL AND TECHNICAL MOLDING ADVANCES

GE Plastics has developed a new method it claims will enable processors to design and mold instrument panel sections from engineering plastics with thinner wall thickness than conventional parts of similar geometry. The technique combines advanced thin-wall design and processing technology derived, in part, from the company’s experience in thin-wall molding for the electronics industry. One of the key advances in the automotive application has been a new specific impact analysis method that more accurately predicts the processing conditions that exist in thin-wall molding.

Another leading-edge molding technology was demonstrated by German-based Oechsler AG. The company manufacturers precision plastic gears and sub-assemblies used in small drives and actuators. Typical automotive applications for these small gear assemblies include mechanisms for positioning mirrors, seats, antennas, power windows and other components which require intermittent adjustments.

According to Dr. Frank Pohlau, development and project manager, the company’s Wave Drive gear system, which is used for transmitting torque in many of these applications, consists of five separate plastic parts: a flex ring, fixed ring, output wheel, wave generator and output wheel. Each part is made of a different resin or colored resin. The parts are made from standard grades of acetal, nylon and PBT. Tolerance for the parts is typically 0.01 mm.

“For performance reasons we need to hold extremely precise, tight tolerances,” says Pohlau. “If the parts are out of round by as little 0.05 mm you can get a 30 percent reduction in power.”

Pohlau says the gears are made on hydraulic injection molding machines. The key to molding these precision parts, he reports, is tooling; especially the precise location of gating.

The critical feature of the design of the Wave Drive gear system is an ellipse-shaped driving core that is firmly connected with the input shaft. The driving core is rotating in a flexible pulsator wheel. Due to the rotary motion of the elliptical core an elastic ring gear is, via the pulsator wheel, continuously deformed and thus in mesh with a stationary toothing located in the housing. As several teeth are engaged at the same time, the system generates a high power density. The drive mechanism also operates without play, has a small number of bearing points and is produced more cost-effectively by injection molding. Oechsler’s 50 mm Wave Drive is commercialized in a reduction ratio of 49:1.

SPECIALTY MOLDERS TAP LUCRATIVE NICHES

Another German company, Starlim-Sterner, manufactures seal housings and connectors from liquid silicone rubber and thermoplastic materials. The parts are co-molded in molds of 16 to 32 cavities on two-component Engel injection machines. Two separate injection units are required because the thermoplastic material melts in the range of 70 to 80C, whereas LSR melts at about 200C.

According to sales manager Karl Grossalber, the parts are produced without flash or sprues, which in turn saves time and cost of finishing operations.

“To get parts without flash there can be no more than one degree variation in the temperature of the melt at injection,” he notes. Grossalber also reports that flash-free seals made of LSR require venting lines as narrow as 0.005 mm in diameter.

One of the main advantages of LSR is its stability across a wide temperature range. LSR costs about 30 percent more than competitive materials, but Grossalber contends the material more than covers the higher initial cost in reduced cycle time and elimination of secondary operations. North America currently accounts for about 20 percent of Starlim-Sterner’s total sales.

“By and large in these types of applications solid silicone is used in North America,” Grossalber says. “In Europe LSR is the standard.”

United Plastics Group, based in Westmont, IL, exhibited its multi-slide injection molding capability. The process produces small, complex parts economically and with high precision. Denis Davidson, president of UPG’s industrial/automotive division, says multi-slide injection molding is a superior alternative to conventional micro molding methods because it is able to run all thermoplastics, including high-end engineering resins, and there is less waste as a result of reduced runner size.

A microcellular polyurethane from Hyperlast Ltd. is used in a variety of applications to control noise, shock and vibration. Autothane microcellular polyurethane spring aids are used to improve the handling characteristics of the new Mazda Tribute sport utility vehicle. The components are used in both the front and rear suspension units.

Autothane engineered polyurethanes exhibits excellent fatigue resistance und
er cyclic dynamic deformation, minimal bulging under compression and progressive load deflection characteristics. The material’s progressive spring rate stiffness and increased damping capability result from a controlled closed-cell distribution within the polymer matrix.

GE Plastics has introduced a new alloy described as a fit between polyolefins and engineered resins.

The alloy, Noryl PPX, gives automotive OEMs and suppliers a high-end polyolefin-type material that can maintain its shape at high temperatures. It is targeted for bumper fascias, front-end modules and underhood components.

Noryl PPX combines previously incompatible particles of polyphenylene ether PPO resin with a base polypropylene using new patent-pending technology.

A Canadian team of researchers studied the feasibility of using oriented polypropylene rods as a replacement for metal in side impact beam applications (SAE technical paper 2001-01-0309). The study, which was performed by Frank Maine, president of SHW Technologies, as well as a group from the Royal Military College of Canada, found that an O-PP beam with an outside diameter of 6 cm and an inside diameter of 3.5 cm exhibited comparable stress-strain behavior to metal during scaled down testing, but a load failure 30 percent less than a steel beam. The group believes the results should encourage further research to validate the design of an oriented polymer side impact beam.

*To order technical papers mentioned in this report, contact the SAE at 724-776-4841.

Table 1