Plastics in automotive.
Building on experience
The development of a composite front fender and hood design for the 1995 Lincoln Continental, and for future models, was the result of Ford Motor Co.'s desire for a lighter-weight and more cost-efficient integrated system. Initially, steel and aluminum were considered for the hood, but since The Budd Co.'s Plastics Division was developing the design and production of the Hi-Flex SMC (sheet molding compound) fenders, the decision was made to produce an SMC hood as well. "Suppliers no longer merely produce components designed by the automakers," says Elton Trueman, vice president, Worldwide Commercial Development. Since the fenders and hood are mating parts, placing total design and supply responsibility with one supplier ensured the maximum design integration of the front-end components. Design elements such as radii, clearances, and mating details could be optimized for the application in order to achieve quality, weight reduction, and cost goals. The Budd Co.'s Plastics Division designed the components, directed the steel tooling program, produced production-intent parts, and worked with Ford to process these components through the automaker's assembly plant in Wixom, Mich. It was also necessary to prove that the SMC components would also be compatible with the total assembly system, including Electro-Coat and top-coat painting.
In terms of bottom line benefits, the cost for the SMC fender tooling was only 40% of the projected tooling for steel fenders, and the comparative weight saving was 33%. Cost of tooling for an SMC hood was 23% of what it would have been in steel, and the weight saving was 18%.
Owing to the success of the team approach, the decision was made to proceed on a similar track with the next-generation vehicle. Trueman says that because so much was learned through the design integration efforts, new targets for weight reduction, simplification, quality improvement, and cost reduction have been established for the front-end composite design of the next-generation Continental. "A great deal has been achieved as a result of prior experience of SMC design integration, and it will be obvious in the next-generation Continental in relation to further part and weight reduction and simplified assembly."
Major structural part
The new radiator support for the Ford Taurus and Mercury Sable represents a significant advance in the use of plastics in a major structural part for a high-volume platform. Also developed for Ford by The Budd Co., the polyester SMC structure is manufactured with 40% continuous roving reinforcements. Owens Corning supplies the fiberglass and Alpha/Owens Corning, in Collierville, Tenn., supplies isopolyester for Budd's SMC material. The two-piece design, which satisfies the lower front, cab forward styling theme of the new Taurus/Sable, combines the functions of the radiator support, headlight assembly, grille-opening reinforcement panel, hood latch mounting and hood bumper support, while also controlling the fit and coordination of the fascia, hood, fenders, and lamps. Ken Rusch, advanced projects manager of Budd's Plastics Division, says the modular design reduces complexity and contributes to improved system reliability. "The two-piece SMC structure consolidates 22 metal parts and 27 fasteners and provides significant cost savings (14%) and weight savings (22%) versus a conventional steel design. The design contributes to a significant reduction in the number of operations necessary in the assembly plant."
During vehicle assembly, the upper radiator support is bolted to the front fenders and front body structure and the SMC component proceeds through the E-coat, body prime, and body top-coat paint systems, along with the attached sheet metal structure. Since the thermal expansion coefficient of the SMC is similar to that of the steel, no adjustment is necessary after the paint ovens. In final assembly, the upper radiator support positions the lamps, hood latch, hood bumpers, fenders, and bumper fascia to meet the front-end fit/finish specifications.
The SMC lower radiator support serves as the base for the car's front-end cooling module and the assembly, including the radiator, transmission fluid cooler, oil cooler, air-conditioning condenser, cooling fans, housing, and other hardware. The completed subassembly is installed on the vehicle after the paint and prior to engine decking at the Taurus/Sable assembly plants in Atlanta and Chicago. Upper and lower radiator supports are bolted to each other and incorporate the structure for the hood latch, while contributing to the structural requirements and overall stiffness of the front end. Rusch says that the SMC components meet all front-end performance specifications, including hood slams, hood fly-up loads, torsional and lateral dynamic loads, static load stiffness specifications, and bumper impact requirements.
An industry star
The SMC Automotive Alliance follows the continuing growth of sheet molding compound applications in the 1997 models. More than 90 new SMC components can be found on 29 cars and trucks, representing a 29% increase over 1996. The SMC industry projects a 5% jump in the total poundage used by automakers in 1997, even with the demise of the composite body panels on GM's Chevrolet Lumina, Pontiac Trans Sport, and Oldsmobile Silhouette minivans.
Early projections indicate that about 250 million lbs of SMC will be used in 1997, up from 240 million in 1996. SMC Automotive Alliance chairman Jim Grzelak says that structural components, such as valve covers, grille-opening reinforcements, fascia supports, and cross vehicle beams, represent more than 70% of the new poundage of SMC on the latest car and light truck models. It is a good bet that where the structural composite parts are incorporated into the vehicles, design integration at some level is not far behind.
Solitary bumper beam
Design integration played a major role in the development of the injection molded "solitary" bumper beam for the 1997 Saturn coupe. Injection molded from GE Plastics' Xenoy 1102, the new bumper is a single part that replaces the functions of 17 parts on the vehicle's former bumper system. Although bumper systems have traditionally been made of steel and foam, Saturn Corp. began using an aluminum/expanded polypropylene foam system as a high-performance, lightweight alternative to the widely used steel designs. Nevertheless, the aluminum system required separate fascia supports, attachments for park and turn lights, additional steel for corner impacts, and other reinforcements.
Developed by Saturn Corp. and a GE Plastics cross-functional "Bumper Team" of design, process, and market specialists, the new beam mounts under a flexible fascia and includes specially designed molded-in towers that crash upon impact to absorb the energy load. The more integrated solitary Xenoy beam, in addition to the parts consolidation, provides a 3.0-lb weight reduction and meets 5-mph impact tests, surpassing the Federal Motor Vehicle Safety Standards (FMVSS) 2.5-mph impact requirement. It also passes the Insurance Institute for Highway Safety rear pole test, which measures vehicle damage sustained in various types of impact, such as that which occurs when a vehicle backs into a light pole or a parking garage pillar. Finally, the new bumper beam is capable of being recycled and is cost-competitive.
Simpler trim panel
The quest for continually higher forms of integration in the automotive industry can take many forms. The PEF Division of Toray Plastics (America) recently concluded a product development program with the Ford Automotive Components Division's plant in Utica, Mich., for utilization of low pressure molding (LPM) to form door trim panels. The objective was a lighter, more cost-effective adhesive-bonded laminate trim panel for the Ford Taurus and the Mercury Sable. It consists of a polypropylene substrate and an insert-molded trim pad comprising a crosslinked, high-polypropylene-content foamed sheetstock and a vinyl skin. The interior trim panel is produced in a single step, complete with the trim panel and vinyl skin.
PVC foam, the most commonly used alternative, has a density four times higher than the olefin foam, and also requires an additional synthetic backing for adherence of the foam layer to the polypropylene substrate. Because the two materials are from the same chemical "family," adhesion between the polypropylene substrate and the olefin foam is instead readily achieved.
A number of reasons dictated the selection of the olefin foam in place of the more traditional expanded PVC in the application. Its higher tear and compression strength help prevent mechanical damage to the olefin foam during injection and also maintain long-term durability and performance. The olefin's high thermal capabilities (to 400 [degrees] F) prevent melting at the LPM injection temperatures. Also, at roughly one-fourth the weight of expanded PVC at a comparable thickness, the olefin foam offers weight reduction opportunities. Finally, the olefin's ability to adhere to the polypropylene substrate without the use of adhesive or backer fabrics eliminates materials, processing steps, weight, and cost. The new system is also more amenable to in-plant and post-consumer recycling efforts.
A widening trend
The trend toward design integration and modularization in car interiors began with door panels and seats, and is widening to include almost every element of the modern car's "cockpit." One thing leads to another. Change the dimensions of one component, such as an "A" pillar, and suddenly the headliner must be redesigned, which affects the "B" pillar, the door panel, the scuff plates, the floor system, the seat mounts, and so on. Dan Jannette, vice president, Technology Division, Lear Corp., says the modularization trend will continue to expand because it provides "benefits across the board, from reduced assembly labor and floor space, to improved quality, cost-effectiveness, and time-to-market. From an OEM standpoint, design integration at the Tier 1 level makes good business sense."
Lear's structural door design integrates all interior door components into one unit for delivery to the car manufacturer. The assembly includes hardware, such as window lifts and latches, plus decorative trim, wiring, speakers, acoustic components, glass, and interior impact energy-management items. The structural door relieves OEMs of a complex assembly operation and replaces it with an easy-to-install unit, reducing required production space and labor, and netting cost savings, mass reductions, parts consolidation, and packaging efficiency.
Lear has developed a molding technique that eliminates assembly steps to provide a complete door panel. A molded-in-place decorative trim for interior door panels uses a Wood Stock process to bond the component coveting material to the substrate during molding, eliminating the need for mechanical or adhesive bonds. Jannette says two major door panel assembly operations have been integrated, "and since the trim pieces are attached while the panel is being molded, a better fit is achieved."
Lear's Integral Restraint Seat, on the 1997 Buick Park Avenue and LeSabre, consolidates the lap and shoulder belts into the seat. The company also has designed and currently supplies a complete overhead system to Saab in Europe. Shipped on a just-in-time basis, the entire interior ceiling of the car is installed as one piece. The modular headliner includes wiring, assist handles, lighting components, and visors already attached.
Recent standards set by the U.S. National Highway Traffic Safety Administration, effective for the 1999 model year, require additional protection for passengers' heads, such as extra padding in headliners and pillars in cars and light trucks The new standards will undoubtedly affect the way interiors are designed and delivered, including headliners, pillars, dashboards, visors, seats, and airbag locations, says Jannette.
Lear developed and began supplying Volvo in 1995 with what it says was the world's first integrated side-impact seat and is developing ways to integrate airbags into door panels, headliners, and "B" pillars. Jannette adds that with the advanced sensor technology available today, side-impact airbags could be integrated into just about any part of a vehicle's interior side wall. Cost-effective improvements follow directly from an overall approach that looks at the entire interior as a unit, as a modular system, rather than as individual components.
Lear has an "acoustic team," acting as a liaison between the automaker and other suppliers, to ensure that overall acoustic goals are met. The team has complete program management responsibility for an upcoming production vehicle. Eventually, according to Lear, interiors may be viewed by car manufacturers as one component, with one supplier responsible for the design, engineering, production, assembly, and delivery of an entire interior module. "We have already developed an entire floor system complete with carpet, scuff plates, and wiring," says Jannette. "Applying this concept to an entire interior, or complete engine or total suspension system, may not be far off. Conceptually, car makers could have five or six pieces to assemble."
Jaguar's new XK8 sports model, equipped with the high-performance AJV8 engine, includes the first composite air-fuel manifold that integrates the fuel passages into the manifold's body, instead of using a discrete fuel raft that is bolted on the outside of the manifold (for a photo, see PlastiConcepts, p. 11). Siemens Automotive's Integrated Air-Fuel Modules Division, which produces the new manifold by the lost-core method at its facility in Telford, England, says it represents an example in a continuing, evolutionary integrated design process that started a few years ago.
In 1993, Siemens introduced North America's first seamless plastic manifold, made by the lost-core method, on Chrysler's 2.0 liter engines for the Dodge/Plymouth Neon. The initial nylon 6/6 manifold served as the main building block for the company's continuing development of a fully integrated air-fuel module (IAFM). David Geran, director of business development, says this planned evolution is now partially realized with the current integration of the fuel rail, and will be further implemented in the near future by the integration of injectors, pressure regulators, sensors, emission controls, and other air induction components on or into the manifold body.
By 2000, it is anticipated that 25% of new vehicles will include the plastic-based air-fuel modules with some form of integration. In a further stage in this process of the IAFM evolution, according to several programs at OEMs under development now, it is expected that a "smart module" will extend the integration through incorporation of electronics for engine management or other control functions into the module itself.
Geran also says that while integration concepts are in development for larger, more complex air-fuel handling components like the throttle body housing, fuel rail, air filter, and engine electronic control unit, of perhaps greater significance is the fact that composites will facilitate the integration of a wide variety of brackets, clips, housings and air, emission, or fluid passages on or into the manifold body. These smaller, less exotic, but also lower-risk examples of integration will probably lead to greater cost savings to the OEMs in the long run than the "bigger ticket" items.
Symmetry makes sense
The 1997 Jeep Wrangler's instrument panel, molded of Mytex engineered polypropylene (EPP) from Exxon Chemical, has a symmetrical design that accommodates either left-hand or right-hand steering, making it easier to market the Wrangler anywhere in the world. This feature alone has saved Chrysler substantial design, engineering, tooling, and manufacturing costs. The hard-panel design uses molded-in color to avoid costly painting as well as foam-and-skin coveting costs. Other benefits are EPP's high heat and ultraviolet resistance, excellent noise attenuation properties, and recycling potential.
A highly integrated instrument panel for Chrysler's Dodge Dakota truck consists of a three-piece monocoque plastic, vibration-welded structure that replaces the typical retainer, air delivery ducts, steel beams, and reinforcements. The instrument panel is injection molded of Dow Plastics' Pulse 830 thermoplastic material. Support for the passenger side airbag and packaging for the electrical harness and other components are also integrated into the simplified design.
As noted in an SAE paper by David Chapman and Darin Evans of Dow and Jeff Soncrant of Chrysler Corp., the design has saved $1.5 million in tooling costs, lessened the number of parts by 50%, and reduced unit weight by 2.5 kg. Labor costs and the number of assembly operations have obviously also dropped.
The Dakota instrument panel is the result of an ongoing cooperative program involving Chrysler, Textron Automotive Corp., and Dow Plastics that is aimed at optimizing materials science, parts consolidation, engineering, performance, and overall cost factors - another example of where the automobile industry is heading as it enters its second century.
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|Title Annotation:||synthetic polymers in cars|
|Article Type:||Cover Story|
|Date:||Sep 1, 1996|
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