Despite the potential benefits of lighter weight and durability resulting from corrosion resistance, advanced composites are not recognized as a material of choice in the near term for automotive applications. Significant changes on a broad spectrum would be required to make advanced composites attractive for widespread commercial use in cars and trucks. The principal barrier is the high cost of the raw and converted materials when compared to existing options, and the perception that even with volume production in yet-to-be-perfected processing methods, the costs would still be too high.
The general economic assessment has stalled research on significant immediate requirements, such as the design and engineering data base which would enable producers to employ advanced composites with acceptable risk, and the development of the processing technologies which would permit manufacture of components in the tens of thousands of units per year.
Nevertheless there are opportunities for advanced composites in specific components in the commercial automotive sector. In specialty vehicles of several types, produced in small numbers appropriate to manufacturing rates for advanced composites, these materials have an opportunity to demonstrate their performance benefits, apart from the requirements of the competitive marketplace.
The world automotive market is dominated by three major manufacturers in North America, a so-called "Big Five" in Japan, and a slightly more fragmented market in Europe, where producers are less dominant in market share but formidable in their technologies. The business is global, rapidly changing, a significant source of horizontal and vertical employment, and intensely competitive. Management must continually balance the demand to invest in research and development in numerous technologies in order to appeal to consumers and respond to competition, with the demand to be the efficient, low-cost producer.
At the time of this study, the benefits of advanced composites have not outweighed the expense of their development for widespread use.
Advanced manufacturing of what we may call engineered composites is, however, a different story. That is, the industry worldwide is investing in process improvements for the molding of polymer composites using forms of conventional E-glass in mid-level performance resins, both thermoplastic and thermoset. Although these materials do not meet the definition set out in the scope of this study, a thorough assessment seems to require mention of these advances in manufacturing. In the long term, these may lead to evolutionary development of advanced composites applications for the commercial market.
The first high-volume, true automotive application of aerospace technology is the driveshaft developed by the Spicer U-Joint Division of Dana Corporation. Following an earlier driveshaft introduction on 1985 Ford Econoline van models, the Spicer product on General Motors pickup trucks enjoyed a demand three times that of projected sales in its first year (1988). At approximately one pound of carbon fiber per unit, 250,000 lbs. of carbon fiber were consumed by this application in 1988. Volume has continued to grow well in excess of light truck growth rates during the 1988-92 period.
Despite the success of the technical and production aspects of the part, economics limit the growth of this application. Essentially, the graphite driveshaft is limited to longer-bodied truck vehicles, which require a two-piece shaft in steel. When the part length is less than 58 inches, a one-piece steel shaft is substantially less expensive than the one-piece composite unit. In the GMC truck potential of 500,000 units annually, the composite eliminates a multi-piece driveline, thus reducing assembly time, inventory cost, maintenance, and part number complexity. In addition, the composite assembly is 60% lighter than its two-piece predecessor, delivering a 20-lb. weight saving per vehicle, offering better fuel economy and mileage. Other benefits are the elimination of warranty associated with center bearings, noise and vibration dampening in the passenger compartment, corrosion- resistance, and custom design of driveshaft performance based on model use and power train system.
Production begins with a seamless aluminum tube. A proprietary vinyl ester resin, with both glass and graphite continuous fiber, is then pultruded over the tube in pultrusion equipment purpose-designed by the Morrison Molded Fiber Glass Company (MMFG) -- formerly a unit of Shell Oil Company (now an independent company), Bristol, VA. It is the composite formulation which is responsible for eliminating the center bearings. The part is engineered with an isolation barrier between the tube, and graphite fiber eliminates electrolytic galvanic corrosion.
Production rate and economics for the Spicer unit are not available. In 1985, competitors estimated that full production would demand one unit, or five to six feet per minute. A mid-1980s study by a filament-winding manufacturer, however, revealed interesting cost analyses: contemplating a unit three and one-half inches in diameter, 60 inches long, capable of 5,000 RPM, 2,500 lb.-ft. ultimate torsion load, and a volume of 100,000 driveshafts per year, a 24% reduction in carbon fiber price would lower the cost of the assembly by only 2%. Assuming carbon fiber at $17/lb., and epoxy resin to meet boil and ultimate torque tests, the materials bill was $6.57. Completing analyses, with slightly different dimensions and some variation in materials, gave total part cost at $60 to $133 per unit.
The panel learned in an interview with a planning official of Toyota that the company has licensed driveshaft technology from a European unit of the Spicer/Dana organization. But the company has no plans to introduce the advanced composite driveshaft in production models.
RTM Panel. A second advanced composite production component, although at a low volume, is the structural panel which covers the torsion box running between the two seats of the Dodge Viper. Called the "Top-of- Tunnel" or "T-o-T," it is molded by resin transfer by Dow-United Technologies Composite Products, Inc. This component consists of skins of ñ45ø woven graphite fabric, and a core of continuous strand fiberglass mat. The advanced composites part of 3.1 lbs. replaced a steel part with an estimated weight of 10 pounds.
The Viper model appeared as a prototype at the January 1989 auto shows. Introduction of the model by the first quarter of 1992 was considered an innovation by Detroit. In some respects it was Chrysler's answer to the GM Corvette; the entire 1992 production run of 300 units was sold out within one month. Five thousand units are to be produced in 1993. The body skin consists of 35 fiberglass/acrylic panels molded by two conventional RTM suppliers, although the hood will be converted to SMC when full production levels are reached.
Fiber Glass/Epoxy Springs for Heavy Trucks and Trailers. Fiber glass/epoxy springs for heavy trucks and trailers became commercial in the U.S. in 1992, after several years of lab and over-the-road testing. The Delco Chassis Division of General Motors in Dayton, Ohio molds the single-leaf springs with unidirectional fiber glass in a specially-formulated epoxy. The design, materials, and process are similar to those for the original "Liteflex" spring introduced on the 1981 Corvette. The big difference, of course, is size. A fiberglass/epoxy spring for heavy-duty trucks and trailers is 3.5 feet long and 3 inches thick, but weighs only 22 pounds - about one-third as much as steel.
The absence of comparable manufacturing and use in Japan was attributed by a research source in Tokyo to different demands from the domestic truck market. Since the benefits for such parts in the Japanese market are not great, the exhaustive testing and evaluation in advance of use have not been undertaken.
Rocker arm covers, suspension arms, wheels, and engine shrouds are examples of automotive applications which have been prototyped with ACM. But design refinements such as precise fiber orientation, or the use of integral ribs, have shown that E-glass composites in lower cost resins can be used to make these articles more cost-effectively.
Filament-Wound Fuel Tanks. A European pioneer in all-composite compressed natural gas (CNG) cylinders put its first units in service in 1989. These were thermoplastic-lined units, with carbon fiber/epoxy overwrap. Since that time international developments have proceeded, with at least a dozen major composites entities contributing to development of the technology and toward the adoption of International Standards Institute specifications. No consensus has been reached on material combinations. In addition to the advanced fibers and resins within the scope of this report, steel, aluminum, and E-glass are still contenders for various elements of a viable CNG cylinder. This report does not discuss the numerous production, size, weight, performance, and cost issues which are affecting fuel tank research at this time.
Several companies in North America are in commercial production of at least partially-advanced composite CNG tanks in the hundreds of units for municipal bus and utility truck contracts. World-wide, there are half a million to 800,000 such tanks on the road, according to the International Association for Natural Gas Vehicles.
Although a U.S. Department of Transportation standard exists to support this use of composites, the American National Standards Institute (ANSI) draft standard and the ISO document do not fully accommodate all-polymeric composite material systems.
Electrical Vehicle Body Components and Assembly Units. Electrical vehicle body components and assembly units such as battery trays would appear to be suitable uses for advanced composites. The lightest possible weight is desirable in this application. Yet strength-to-weight ratio is not an exclusive concern. Cost and proven manufacturability also influence materials selection decisively. Advanced composites would seem to have a role only when high specific strength is required for a specialized function.
The cost-driven reality of even the experimental applications was evident in a visit to research facilities of Mitsubishi Kasei.
This pre-eminent supplier had no automotive advanced composites to discuss, but did offer an excellent example of advanced process development with transportation applications.
In cooperation with funding from an environmental group and an electric utility, Mitsubishi Kasei has perfected the conceptual elements for one-shot molding of the entire body and platform for an electric motor scooter. Candidate resin materials for this application would be polyurea, an epoxy-polyurethane blend, or other thermosets suitable for reaction-injection molding (RIM). The reinforcement would be conventional E-glass, unless it were determined later in commercial development that "patches" of higher-performance reinforcements were required at points of exceptional stress on the frame. The accomplishment demonstrated by this program is the feasibility of molding a very complex structural part, in only several minutes cycle time, using only a single resin injection port, and without preform "drift" within the mold.
While this project showed world-class development capability, it cannot be said that the RIM process demonstrated is advanced beyond the research work published by Ford Motor Company in cooperation with Dow Chemical, relative to structural cross- members for automotive use, or beyond the research on bumper beam assemblies that has been completed by the U.S. Automotive Composites Consortium. Like the latter, the Mitsubishi Kasei technology has produced parts which meet apparent physical performance requirements, but the scooter bodies have not been put into commercial production.
A number of uses for advanced composites in the automotive sector are being developed for modular or stand-alone components which could be retro-fitted to existing vehicles (an example is tanks for compressed natural gas [CNG] as an alternative fuel). Other applications which should be noticed are specialty parts for prototype transportation whose commercial future is uncertain (examples in this category are components for electric vehicle bodies).
The relative absence of advanced composites from the Japanese automotive scene does not indicate disinterest in advanced technologies for cars generally. At one of the "heavy industry" interviews, the panel was shown visuals of aluminum honeycomb-core panels stamped for use as monolithic, configured floor pans for conventional passenger cars. The host research team said this structural part is in production for a low-volume model which is having a very good reception in the domestic market.