Automotive plastics: more challenges - more solutions.
THE BIG BANG
In the evolution of the automotive industry, Charles Haddad, manager, Advanced Engineering Dept., Ford Motor Co., considers Henry Ford's assembly line "Big Bang #1." Between 1909 and 1923, the cost of the Model T dropped from $850 to $260, though the car was essentially unchanged.
Today's critical need, Haddad believes, is a fundamental "single-shot" change in the car's complete architecture-Big Bang #2. His view: While manufacturing methods and performance have thrived with consistent, evolutionary attention, sudden radical changes in the car's basic structural and assembly concepts have been off limits. Haddad's prescription is that the domestic car industry must reposition itself with highly efficient and more profitable products at the low-cost end of the market. He calls for a quantum change that would parallel the enormous effect of Henry Ford's production line innovations.
According to Haddad, the tools, ingredients," and know-how to prevail as a viable industry are available, and an abundance of ideas are lying fallow, including extensive opportunities to maximize design simplicity.
He cites, for example, the Ford Contour concept car's flouting of tradition and its technologically aggressive integration of multiple existing disciplines. Shown in January at the North American International Auto Show in Detroit, the Contour is a potentially cost-efficient, structurally lean, simple in design and assembly, high- or very low-volume production vehicle. Its extruded, adhesive-bonded aluminum space frame; hybrid doors of RIM polyurea (from Mobay) and extruded aluminum door structure and reinforcement beams; hook and loop fasteners (from Velcro); in-mold coating (from Mobay) or use of formed, prepainted sheets (from Avery); single transverse leaf spring suspensions; and center-take-off engine/transmission are among numerous diversions from the beaten track. These leading-edge ideas represent a more eclectic approach to technology utilization. With these concepts, Haddad is confident, new investment and plant costs could be reduced by as much as 50% to help restore competitiveness to the U.S.
The effort may not yet be the Big Bang #2 that Haddad wants, but it is more than just a firecracker.
ON THE AGENDA
Plastics in car design continues moving ahead. More use of different plastics, in 1992 models and beyond, is on Chrysler Corp.'s agenda, say Carol Lindquist, executive engineer, Materials Engineering, and Saad Abouzahr, product development specialist. Rubber-modified polypropylene with molded-in color is a leading contender, as replacement for painted RIM fascias and ABS trim parts in some applications.
The body-in-white, E-coat paint-oven temperatures still set the pace for exterior panels on the high-volume models, to avoid secondary "hang-on" assembly steps. Any preassembled plastics for on-line painting must keep in step with the steel through the high-temperature ovens. Nevertheless, Lindquist and Abouzahr predict that between 1992 and 1994, there will be increasing replacement of sheet metal and die castings by polymers in some power transmission/engine components, body panels, and other parts in Chrysler's high-volume cars.
Speed of delivery was a rule of thumb in the fast development of Chrysler's all-composite V-10, 400 HP Dodge Viper. Originally unveiled as a concept performance car in 1989, the vehicle was the pace car at last spring's Indy 500, and a production vehicle almost identical to the prototype will debut next month. Volume is expected to grow to 3000 to 5000 units per year, from a projection of 200 to 300 vehicles in the 1992 model year. Low-cost, fast-delivery epoxy and nickel-shell epoxy tooling and liquid transfer molding have kept the project on the fast track. Built around a steel chassis, all of the Viper's exterior panels, except the compression molded polyester SMC hood, are resin transfer molded of ICI's Modar A 24 S acrylic. The Viper features more than thirty semistructural parts made of the low viscosity acrylic composite material.
A METHODICAL PATTERN CAFE (Corporate Average Fuel Efficiency) standards, based on total fleet averages, spur weight reduction for all car lines. Peter Beardmore, manager, Materials Science Dept., Research Staff, Ford Motor Co., says that this pressure makes even the larger models, such as the Grand Marquis, Continental, Town Car, and Mark VII, candidates for plastic exterior panels.
Beardmore foresees horizontal hood and deck panels, probably SMC, but even possibly aluminum, appearing on more "specialty" cars throughout the '90s. Lower modulus, flexible SMC, with reduced glass fiber content and expansion coefficients closer to that of conventional SMC, is an evolving technology. Because of existing problems of growth and contraction in mating vertical door and fender panels, Ford is still limiting uses to pilot programs. Since the resin materials are more expensive than steel, applications still depend on the extent of parts consolidation through modular assemblies and function integration.
Beardmore predicts near-term application of structural composite components, such as cross members and bumper beams, that do not require integration into larger structures, and which will provide production experience. Pilot programs will examine replacement of larger segments of the steel structure, with emphasis on part integration. However, even given steady progress, Beardmore's view is that structural composite replacement of steel body structures probably will not materialize during this decade.
Resin transfer molding (RTM) and SRIM are the front-running processes for large structural composite parts, but higher process automation and reproducibility are needed. The millionth part must be the same as the first one, and performance/cost must be as good or better than that of the technology it would replace. "Structural composites absorb energy differently than metals," Beardmore says, "and a substantial time on the learning curve is needed before large leaps forward can be prudently taken. Fatigue and durability are not as much an issue as energy absorption. But significant changes are anticipated as experience is gained, and specifications for weight reduction and performance tighten."
CONSORTIUM FOR LEARNING
To accelerate the structural composites learning process, the Composites Research Consortium was established in 1988. Its board includes two executives each from Chrysler, Ford, and General Motors (GM); the purpose of this unconventional joint venture is the equal sharing of newly acquired, precompetitive data and technology. It was the first automotive-related consortium to be set up under the guidelines of the National Cooperative Research Act of 1984, which was formulated by Congress to encourage R&D by U.S. industries.
Elio Eusebi, department head, Polymers Dept., GM Research Laboratories, this year's chairperson, says the consortium has been unusual in its ability to break down the traditional walls of secrecy between the Big Three. Advantageous use of the cooperatively generated knowledge is a function of the private efforts of the individual companies.
The ultimate goal of the consortium (which has a 12-year legal life), is to develop the design, data, and production infrastructure for a cost-effective, all-composite production vehicle. "We may not entirely accomplish that goal in the time frame," Eusebi says, "but that is where we are conceptually headed."
Intercompany groups are assigned specific tasks. In materials, a test procedures manual is the first set of guidelines for composite suppliers and researchers. Providing uniform test requirements based on modified ASTM procedures, the manual primarily covers tensile, compression, and shear testing; guidelines for fatigue and creep testing are expected to be developed soon.
Development of more cost-effective, high-volume processing capabilities is a primary area. More efficient preform production is a key factor. Consortium teams are working on automated preform methods, and, in conjunction with the National Institute of Standards and Technology, on flow in preforms. One group is investigating coring for lightweight hollow sections; a model, involving tooling, capital equipment, and part costs, has been developed.
In energy management, the consortium is looking at types of composite structure and the effects of interfaces between matrices and reinforcements; conducting crush tube tests; and designing crush simulation software.
On a front-end composite design for a Ford Escort, a preform's parts were decreased from more than thirty glassfabric lay-ups to four random- and braided-glass RTM shapes. Now being assembled into a vehicle for crash testing, the redesign cuts preform production time from two days to less than five minutes.
RAISING THE STANDARD
The GM 200 APV minivan all-plastic-body program expresses GM's commitment to plastics. Fred Kulka, system manager, Body Exterior, GM 200 Program, says that surface finish was the critical concern: "By raising the standards on exterior appearance of the SMC surfaces, we set in motion many associated factors, including changes in the SMC formulation, modifications in the low-profile additives to reduce waviness, improvements in press technology by incorporation of vacuum in the compression molding to eliminate porosity, and prodding our suppliers to get better. That was the only way the all-plastic-body APV could have made it to the production line, by a lot of engineering and manufacturing sweat.
"The growth of plastics is inevitable, because the writing is on the wall with tighter CAFE standards and the need for continued weight reduction," Kulka continues. Beyond those pressures, plastics are now recognized for the inherent design flexibility they offer in response to changing market requirements. "GM is now comfortable with plastics for exterior panels, for example," Kulka says. "We have moved ahead in the learning process and are not afraid to use them anymore. But changes to plastics and composites still will be measured, and there will be more hybrids than radical switches from steel.
"There are no generic answers as to whether thermoplastics or thermosets are better for vertical exterior panels. The answer must come from the particular model car, its projected production volume, the plant in which it will be built relative to specific assembly procedures, the curing temperature of the paint system, and the economical volume crossover point in comparison with steel. The unseen decision making process is very complex. In the final analysis, the material must justify itself in the performance/cost framework of the specific application."
As designers become more sophisticated in coping with the "fit and finish" effects of thermal expansion and contraction, for example, they are becoming better able to compensate for "material growth" conditions they would have rejected a few years ago. Kulka implies that this capability could bring lower-cost materials, such as thermoplastic olefins, into the vertical panels arena, thus increasing the alternatives now available. Finally, he muses, "the steel people are not sitting on their hands, so things will continue to be interesting."
A LEADING CONTENDER
Requirements for fit-and-finish stability, Class A surface, and mechanical properties make SMC the leading contender at Ford Motor Co., with potential for expanded use as exterior panels on production cars, according to Al Murray, manager, Advanced Technology Office, Plastic and Trim Products Division.
Ford has been conservative regarding plastic exterior panels as replacements for steel. An initial entry was the SMC hood as a running production part on the Aerostar compact van since 1986; it represents about a 30% weight saving over steel. Extending the application to the full-size 1992 Econoline van, with a similar projected annual production of more than 200,000 vehicles, is a significant expansion in the amount of SMC used and an extension of the technology. Produced in a 60-second cycle time, the Aerostar and Econoline hoods are adhesive-bonded laminates of inner and outer SMC panels. The previous need for costly and time consuming finishing has essentially been eliminated by control of formulations, and molding, priming, and bonding processes. In 1992, a full-size series F pickup truck, with flareside fenders in SMC, will be available.
Based on ongoing pilot programs, Ford plans to expand use of SMC to other car lines in the near future. The targets are basically larger luxury cars with projected volumes of less than 200,000, and where CAFE fuel efficiency standards strongly mandate weight reduction. "Other plastic materials do not yet meet our on-line painting and fit-and-finish requirements for body panels," Murray says. "The SMC panels can survive the body-in-white electrocoats and retain the critical dimensional margins."
Ford would prefer a more flexible and lower density material than conventional SMC for vertical body panels. Development continues on SMC formulation to retain dimensional stability, repeatability, and surface finish, while adding desired flexibility and resilience. Ford also continues to evaluate improving technology with other plastics for vertical panels.
Today's car interior reflects a high degree of sophistication in use of materials, parts integration, and styling to create an atmosphere of "family room" comfort, convenience, and security. Much has already been achieved in the development of "flow-through" designs, in which the instrument panel, console, and doors blend smoothly together to provide a comfortable, highly efficient cockpit-type enclosure, notably in sporty mid-size vehicles. There is an increasing effort to respond to often subtle customer perceptions regarding ergonomics, functionality, performance, and quality. In this context, Lou Chmura, executive engineer, Product Engineering, Vehicle Interior Systems, Plastic and Trim Products Division, Ford Motor Co., says that with every new interior design, there is increased sensitivity to customer-perceived quality. This sensitivity drives the continuous emphasis on details such as fit-and-finish of contiguous parts and elimination of squeaks and rattles from mounted panels and other elements. "The current challenge," Chmura says, "is to enhance the styling creativity we see in today's car interiors. We expect that future car interior designs will become increasingly more coordinated, requiring implementation of a single fully integrated concept, rather than assembling a set of segmented elements. Design pressures continue to force interior components to accommodate such items as passenger-side air bags and strengthened door panels that will meet pending side-impact standards. Company acceptance standards are becoming more stringent, manifesting themselves, for example, in such things as improved panel grain matching and an even greater perception of quietness."
Chmura does not foresee radical swings in specific material usage in the car interiors in the next few years. Relative to the structural composites, and citing the experience with the growth of plastic fuel tanks, he predicts a methodical evolutionary development as possible replacements for steel in the instrument panel structure.
Finally, Chmura emphasizes that recyclability, as a mounting environmental issue, will require much greater attention to the problem of sorting the diverse materials and assembly processes that are now used. "Design for efficient recycling is rapidly becoming one of the big issues of the day. In our company, and in the industry, serious attempts are being made to resolve these problems and to respond without adverse impact on cost and quality."
Thermoplastic olefin (TPO) continues to grow in auto design. The major poundage is in fascias, mostly at the expense of RIM polyurethane. The material, however, is still playing catch-up with the European cars, where over 70% of front and rear fascias are made of rubber-modified polypropylene. In North America, the penetration in 1990 in fascias was about 20%. This compares with a penetration of about 4% in 1985. Other uses of TPO in 1990 was for air dams, cladding, rub strips, wheel flares, air ducts, and interior parts.
D&S International and Himont Advanced Materials, the big domestic hitters in TPO, see the material's growth reflecting the quest for lower-cost functionality. Robert Gerlach, D&S automotive market manager, points to a new expertise in design and molding, and an expanded product range, largely resulting from enhanced compounding and compatibilizing. The range of flexural moduli, about 35,000 to 200,000 psi in 1985, has spread to 10,000 to 350,000 psi. Also, advancement from a fractional to a 10 melt index range up to a 35 melt index provides easier-flow materials that widen processing windows and retain impact properties.
D&S has developed a precolored TPO that, when covered with a PPG weatherable glossy clearcoat, has demonstrated that it does not peel off on exposure to Florida sunlight for two years. Previously, the colored fascias have been limited to dull finishes.
TPO is also trying to expand into exterior vertical and horizontal body panels. One route, Gerlach says, could be coinjection, using a TPO skin and any of a wide range of solid or foamed core materials. The degree of stiffness or resilience could be up for grabs, depending on the recipe. D&S is involved in specific proprietary "partnerships" and programs with OEMS.
John Harvey, marketing manager, Transportation, Himont Advanced Materials, credits reactor-grade TPO resins and new glass-reinforced materials for the steadily improving market share of the propylene-based materials. Himont has actively participated in a number of new programs, some recent ones being the Chevrolet Cavalier fascias, Peterbilt bumpers, Ford Sable/Taurus and Dodge Caravan claddings, Cadillac STS rocker panels, and GMC truck grilles. The company will have various applications on twelve 1992model-year American-made cars.
To meet standards relating to side-impact collisions, Arco Chemical development programs with automakers include Dytherm SMA copolymer, Arpro resin, Dylite expandable polystyrene, and new urethane foam products. A new Dylark (378P20) resin, with improved long-term thermal aging, expands the material's potential for instrument panels and trim parts, headliners, and other interior uses.
All exterior body panels on the Lotus Elan-projected annual volume of about 3000 cars-are of Ashland Chemical's Arotran RTM resin system. Other current uses include the Chevrolet Corvette removable hardtop roof and the Ford Aeromax 120 heavy-duty truck hood. The Phase Alpha unsaturated polyester SMC resin system continues to be used for many of the body panels for GM's line of composite-body minivans, and for the Chevrolet Corvette, the Ford Aerostar liftgate, and various medium- and heavy-duty truck hoods.
Three new Arotech thickenable vinyl ester resins, which balance strength and controlled shrinkage, are developed for valve covers, oil pans, structural parts, and inner reinforcements for body panels.
At its Tarrytown, N.Y, assembly plant this year, GM changed over to Pliogrip 9000 primerless structural adhesive for bonding the outer panels of the minivan to the steel space frame, eliminating the need for solvent-wipe priming.
BASF Corporation Plastic Materials is developing side-impact systems using bolsters molded of Elastoflex polyurethane foam. The relatively ductile, rigid foam does not shatter when impacted. Also under investigation is an air bag of Elastollan thermoplastic polyurethane, an Ultramid nylon steering wheel, and Elastofoam flexible polyurethane foam for the wheel's resilient air bag cover.
In a manufacturing process developed by the Versatrim Division of Atoma International, Inc., doors for GM's 1991 Oldsmobile 98 are delivered "just in time." Substrates for the door panels use a specially developed rigid, reinforced BASF Elastolit SR polyurethane foam system. Another Versatrim line will make door assemblies for the 1992 Olds 88.
Dow Plastics says that a 1992 GM platform is expected to utilize an instrument panel cluster shroud, with molded-in air duct, made from Pulse 880 BG blowmolding grade resin.
SMC and BMC composite valve covers of Dow's Derakane vinyl ester resin, first seen in 1990 and 1991 models, including a range of Ford engines, are active items. More complex fascia designs that incorporate lighting and other components are on the drawing boards. Spectrim HT30 and HT55 polyurea, offering dimensional stability and mineral fillers that do not sacrifice surface appearance, are among the candidates.
OVERBRAIDED FUEL LINES
Du Pont Automotive Products' fuel lines of Teflon PTFE fluoropolymer, overbraided with steel, are used in a number of 1992 Ford models. Air bag deployment doors of DYM 100 polyester elastomer are on at least two 1992 Ford vehicles. Nomex aramid pressboard heat shields are in three engine applications on the 1992 full-size Dodge Ram van. A prefilled clutch hydraulics system has pistons of Kevlar aramid fiber and master and slave cylinder bodies of Zytel glass-reinforced nylon. It is standard on 1992 manual shift vehicles for a North American automaker; variations of the system are on 1992 GM light duty trucks, the Dodge Viper, and Jeep Z-J. The 1992 Pontiac Bonneville SE and Pontiac SSE/SSEi feature front and rear fascias of Bexloy V and a front air dam of weatherable, high gloss Bexloy W. The new model Plymouth Laser/Mitsubishi Eclipse has a ground effects package of a reinforced low-expansion Bexloy V. A late 1992 high-volume car will use fenders of Bexloy K550. Du Pont says the material can withstand electrocoat ovens.
Now THE TOUGH ONES
"The easy jobs are done," says Joseph Reed, general manager, GE Plastics Automotive Team. "Further big gains in weight reduction and quality improvement must be achieved by aggressive programs, such as modular design, for example." Reed mentions modular doors, containing exterior and inner panels and core. The key is to respond to renewed interest in weight and cost reduction.
A new lightweight air injection pump uses Fortron PPS 4184L4, from Hoechst Celanese Corp., Engineering Plastics Division, for the housing and impellers; Vandar thermoplastic alloy 4206Z for the power distribution box's top and bottom enclosures on some 300,000 1992 luxury sedans and pickup trucks; and Vandar thermoplastic elastomer for more than a million air bag enclosures in 1992 cars.
An experimental program aims at sound/vibration reduction with high modulus reinforced thermoplastics in suspensions. In other programs, a single-part fuel rail, injection molded of Fortron PPS, replaces eight stainless steel parts; and metal fuel tank filler necks are replaced by Celcon acetal copolymer. Bumper fascias of Vandar semirigid thermoplastic are used on several luxury models.
LNP Engineering Plastics currently is developing new Stat-Kon composite materials to dissipate static charge buildup in a fuel injection system, including fuel lines, filters, and fuel filler necks. Lower-cost Lubricomp composites for bushings and wear rings, as replacement for steel or more expensive composite materials, also are being developed.
STABLE MOLDED COLOR
Among Mobay Corp.'s development efforts is a light-stable polyurethane or polyurea that would allow molded-in contrasting colors, to counter TPO's advances mainly in the low-end market. The objective is to prevent degradation in sunlight, and thus avoid secondary painting, by building in compatible stabilizers.
Robert Kirk, business director, Polyurethane Division Automotive Group, says the industry is also working on chemical and processing technology to provide Class A SRIM horizontal body panels to compete with SMC. Experimental hoods molded of glass mat encapsulated with polyurethane look promising.
RIM polyurethane and polyurea maintained approximately a 65% share of a total fascia market in 1990 of 200 million lbs. Some new GM models are scaling up to polyurea fascias for improved stiffness, dimensional stability, and processability. Front fascias on the Firebird and Camaro F cars are being carried over from 1991 to 1992 and 1993. The Pontiac Bonneville and the Buick LeSabre H-car front and rear fascias, RIM polyurethane in late 1991 models, have been upgraded to RIM polyurea for 1992; Olds Royale fascias, formerly thermoplastic, have also been converted to RIM polyurea. Front fenders on the 1993 F cars will be changing from sheet steel to polyurea.
THE ROAD TO DISCOVERY
The expanding capabilities and diversity of plastics, combined with the increased knowledge necessary for their use, are reflected in many significant applications in all cars. Many more are sure to come. Thus plastics are playing a major role in helping a beleaguered but dynamic automotive industry on the road to new discoveries of its potential.
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|Date:||Oct 1, 1991|
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