Cars of the future will be made of ... steel

By Staff -- Purchasing, 2/8/2001

Motor vehicles are made mostly of steel; in fact, steel this year still is 54% of a car's average weight. Over the past decade, a costly and time-consuming engineering effort to reduce vehicle weight has triggered numerous initiatives into alternative materials. Latest research shows, however, that steel will maintain its dominant-material position in the future.

In a year when 16 million light vehicles are manufactured, U.S. automotive assembly plants use 15.1 million tons of steel, three million tons of cast iron, 2.1 million tons of aluminum, 2.1 million tons of plastics, 368,000 tons of copper and brass, 304,000 tons of powder metal parts, 97,000 tons of zinc die castings and 68,000 tons of magnesium castings.

It's no secret that automobile manufacturers are under pressure from consumers and government agencies to produce motor vehicles that perform better, are easier to recycle and repair, create less pollution, and are less expensive, more comfortable, durable, fuel-efficient, maintenance- free and safer. Since 1993, many millions of research dollars have been spent by General Motors, Ford, DaimlerChrysler, national laboratories, universities and suppliers to find advanced alternative materials for future fuel-efficient motor vehicles.

Last March, the Big Three carmakers boasted that new fuel-efficient family-size cars and sport-utility vehicles with significant improvements in gas mileage would be available in 2004 models and be in mass production by 2008. The vehicles would have more aerodynamic designs, use hybrid electric-gas engines, and be made from lighter materials to squeeze out better fuel economy.

However, the Partnership for a New Generation of Vehicles (PNGV) has given steel an unexpected endorsement, saying it will take a new look at lightweighting the heavy metal to create vehicles that can be 20% more economic to operate. In October, PNGV leadership admitted the program wouldn't meet initial lightweighting and affordability targets by relying on available advanced materials.

That's because, without a reduction of 40% in the total weight of the car, PNGV 's lofty fuel economy targets couldn't be achieved. And the material researchers admit they haven't found a way to reduce today's 3,300-lb family sedan to a 1,980-lb automobile capable of 80 miles per gallon without sacrificing affordability, performance or safety. The most difficult challenges are reducing the cost of materials themselves and manufacturing the lightweight parts affordably. The National Academy of Sciences, for example, now says "that while extensive progress has been made in aluminum and composites use, their costs still are not competitive with steel."

According to Andy Sherman, chairman of the PNGV materials technical team: "Most of the steel used for automotive applications costs around 40¢/lb, while most product forms of aluminum and magnesium cost more than $2/lb and extremely lightweight titanium and carbon fiber are more than $8 per pound. Furthermore, manufacturing processes will have to be improved or developed to fabricate lightweight parts and components of these materials affordably and quickly."

For example, a PNGV materials technology team last year designed a combination carbon fiber-reinforced composite and aluminum-intensive vehicle body-in-white (chassis) that is 68% lighter with more than 93% fewer parts than its steel counterpart. Problem: The per-vehicle material costs remain exorbitant, even with projected reductions in assembly costs. "The price of carbon fiber and limited production availability for the material today precludes its use in mass-produced vehicles," notes the U.S. Council for Automotive Research (USCAR).

Carbon fiber composites are attractive to designers because they can be stiffer than steel at one-third the weight. However, carbon fiber composites cost $5-$10/lb, are difficult to fabricate, and are not easy to recycle. "So, realistically, it is unlikely automotive carbon fiber composite structures will be produced for another decade," says Elio Eusebi, head of the polymers department at the General Motors Research & Development Center in Warren, Mich.

The cost of carbon fibers primarily is a function of supply and demand, and supply is limited because worldwide production capacity is only 20 million lb annually. "That is barely one-tenth of the potential demand should automotive and other industries increase their use of the material," says Eusebi. Atop that, carbon-fiber-based composites available today are used almost exclusively in the manufacture of commercial and military airplanes.

Automotive-grade aluminum still costs up to five times as much as steel on a per-pound basis, and polymer composite-based sheet molding compounds still cost at least twice as much. Other new materials such as metal foams and aerogels may hold potential for automotive applications, but their high cost currently keeps them a long way from being ready for production vehicles.

So, it's back to the drawing board-with steel as the key material for the chassis, the supporting frame of a car, and the exterior hoods, roofs and fenders, plus the powertrain, suspension and exhaust systems. As long ago as 1998, steel-industry-funded engineering studies proved a body in white could be produced with new grades of lighter steels that cut 25% off the weight of a 1994-model family sedan. Now, the research group is looking to drop another 10% in weight.

In fact, the steel industry's UltraLight Steel Auto Body (ULSAB) program now is working to develop by the end of this year an innovative front-end module and efficient front and rear suspension systems, packaged in a lightweight steel structure. Additional research is studying the suitability of steel-aluminum composites and lightweight steel laminates (which are steel-plastic-steel "sandwiches").

ULSAB actually is a design and engineering consortium of almost three-dozen steel companies who have funded a series of projects by Porsche Engineering Services Inc. of Troy, Mich. In 1998, the initial ULSAB report presented automakers with designs for a lightweight steel platform that met PNGV specifications at a 25% weight reduction. Then there was ULSAS , the UltraLight Steel Auto Suspension, and ULSAC , the UltraLight Steel Auto Closure, program. The latest, ULSAB-AVC , the UltraLight Steel Auto Body-Advanced Vehicle Concepts project, aims to meet projected crash safety requirements for 2004. That's why ULSAB-AVC 's work includes the body structure, closures, suspension, engine cradle and all structural safety-relevant components.

ULSAB-AVC will present advanced concepts to help automakers use steel more efficiently and provide a steel-based structural platform for achieving anticipated, significantly improved fuel efficiency optimized environmental performance regarding emissions, source reduction and recycling, and high-volume manufacturability at an affordable cost. "The completion of the early ULSAB project challenged the conventional wisdom that steel auto bodies are necessarily heavy," says Murray of PNGV 's materials technical team.

So, the ULSAB-AVC project is keying on steel-based suspension and powertrain systems, notes Edward Opbroek, the Middletown, Ohio-based program director. "The engine bay package layout is based on a fully operational front-end module that incorporates engine, gearbox, front suspension, radiator and steering rack, mounted on a single cradle and bolted to the body structure," he says. This design allows for removal of the entire powertrain/suspension system in a single unit for servicing. So, Porsche Engineering is working to incorporate quick-release connections for power, heating, hydraulics and steering systems.

Why materials are key

The major market trend in the advanced materials market is the need for lighter vehicles due to the demand for future vehicles with reduced emissions and expanded fuel consumption, says automotive materials analyst Joerg Dittmer at Frost & Sullivan in Mountain View, Calif. "The main competitive issue for manufacturers is the ability to supply materials that reduce vehicle weight at a lower cost than the competition," he adds. "It is also necessary to provide strong, long-lasting materials to replace current materials," adds colleague Inge Matthey, "so, advanced material manufacturers must meet automakers' demands on issues such as price, weight, recycling, quietness and safety."

Through PNGV , the Big Three automakers are pursuing a variety of advanced powertrain options, such as fuel cells and various hybrid combinations, to improve fuel efficiency in future models. However, the new powertrains will weigh more than conventional lead-acid battery-based powertrains. To compensate for the increased weight, the automakers must reduce the weight of other vehicle components.

That's because the goal for the 2010-model is 2,000 lb or less. By comparison, the 2000-model typical family sedan weighed almost 3,300 lb. So, much of the lightweighting research involves materials-steel, aluminum, magnesium, advanced powder metal-based parts, plastics, composites and ceramics-for use in vehicle bodies, structural members and even components and parts as small as fasteners.

Since mid-1999, for example, the automotive and aluminum industries have been researching whether the light metal can be used as a steel substitute. The so-called "Auto Aluminum Alliance" is working to develop standardized testing methods to evaluate aluminum sheet for end-product quality assurance and is studying the possible use of tailor welded blanks (which are aluminum stampings) as a way to reduce manufacturing costs.

In fact, engineers are researching new manufacturing processes that would cut significantly the production cost of automotive aluminum sheet metal. Since aluminum has one-third the density of steel, it is an attractive candidate material for high-quality, lower-cost aluminum sheet. "Unfortunately, a pound of aluminum sheet used for door panels, hoods and even entire auto bodies currently costs four to five times as much per pound as steel sheet," says Al Murray, PNGV 's technical director for the materials technical team. "This higher cost, coupled with the fact that aluminum components are frequently more expensive to manufacture than steel, means aluminum-intensive vehicles are substantially more expensive as mass production vehicles."

Aluminum use has risen to 246 lb per car on average in 2000 from 159 lb in 1990 and is expected to surpass plastic and plastic-based composites in the 2001 model year to become the third-most-used material in light vehicles after iron and steel. However, most of aluminum growth has come from expanded use of engines, castings, wheels and stamped fenders and hoods. Little movement has been made toward mass-produced chassis or structural components made from aluminum. The only commercial "all-aluminum" car, the Audi A2, has a body shell that weighs 43% less but still costs twice as much as a comparable steel body shell. The A2, the second aluminum-body and spaceframe car to be built by the Audi subsidiary of Volkswagen, is a small, moderately priced car marketed in three models in Europe.

That's why even consultant Richard Schultz of Ducker Research Co. in Bloomfield Hills, Mich., (a former aluminum industry executive) says the light metal probably won't displace steel-dominant material in North American-made cars for at least the next 25 years.

There has been a lot of publicity over the car industry's planned conversion to aluminum engines over the next decade. These so-called engines of tomorrow are expected to replace today's cast iron engines and also use more magnesium, powder metals, plastic and other lightweight materials in their smaller components, including cam covers, camshafts, valvetrains, manifolds, bearing caps and oil pans.

However, Schultz says the battle of the future in material dominance still will center on issues relating to the body-in-white-chassis and such hang-on parts as doors, hoods and fenders. "The major battle between aluminum and steel will be waged over auto body sheet," he says. "Steel will maintain its share because aluminum costs, while becoming feasible for volume production, currently remain too high on a per-vehicle basis," he adds. "At the same time, steel bodies under development will weigh at least 10% less than their current counterparts; new steel closure panels will weigh 5%-10% less than current closure panels, depending on the component; and the total cost for the steel required to make a body-in-white with closures will decline over time due to optimized designs using high-strength steels."

Program manager Opbroek says ULSAC began as a concept development program, which produced innovative concept designs for doors, hoods, decklids and hatches that are up to 32% lighter than benchmarked averages and 10% lighter than best-in-class, while meeting stringent structural performance targets. The ULSAC project, in fact, "wound up demonstrating the effective use of high-strength steel and ultra-high-strength steel in tailored blanks and hydroformed tubes in producing lightweight, structurally sound steel automotive closure panels that can be easy and affordable to make in high volume," he says. (Hydroforming is a new manufacturing technology that uses the force of water or hydraulic fluids to shape parts from steel sheets.)

Interestingly, steelmakers and automakers agree it will be important to balance the progress in metallurgical advances with formability needs. Other technical issues to be addressed involve welding of certain types of high-strength steels, further development of laser-welded body assembly (including laser-welding of two-sided galvanized high-strength steels and, as hydroformed tube gains ground, single-side spot welding of steel sheet to tube. Inevitably, because of North American economies of scale, there will be a move to develop hybrid materials. For example, Sherman, of the PNGV materials technical team, says steel eventually will be joined to such light alloys as aluminum.

It's always about the cost, according to the engineers. And cost is the issue when they try to deal with magnesium, the lightest of the structural metals. North America already uses more magnesium die-castings than the rest of the world combined, but only eight pounds are used per motor vehicle because cost and other technical challenges limit more widespread use. Automotive applications of magnesium currently include instrument panel assemblies; seat structures; brake, clutch, accelerator and steering wheel assemblies; valve and cam covers; intake manifolds and manifold covers; transmission cases and covers; pistons; and various brackets and housings.

Magnesium's chief advantage is that it's only one-quarter the weight of steel and two-thirds the weight of aluminum. But it is significantly more expensive than the other structural metals; in fact, it's twice the cost of aluminum and 14 times costlier than steel. This, plus concerns about adequate availability, has adversely affected its growth for automotive applications. That's why the Automotive Materials Partnership group within USCAR is trying to learn how to improve the performance (hardness, tensile strength, fatigue and creep strength) of magnesium alloys and manufacturing costs when fabricating mill products.

What about plastics, composites?

The use of plastics-often as a steel substitute-has grown by almost 9% in the past decade. It's estimated that 4.6 billion lb were used by North American automakers last year. About 249 lb of plastics and plastic-based composites were in the average 2000-model automobile. That's still less than 8% of the total weight, but industry insiders project further gains in the years ahead. Industry insiders believe plastics will choose suitable applications-such as nylon-based intake manifolds, high-density polyethylene-based fuel systems, and thermoplastic polyolefins for fascia, instrument panels and door panel skins.

For example, LDM Technologies Inc. of Auburn Hills, Mich., has developed a low-cost, injection-molded energy absorber for front and rear bumpers made of high-density polyethylene to replace expanded polypropylene foam at a 79% cost savings. The absorber consists of injection-molded cones as a barrier between the fascia and steel rail on body systems. Ford Motor Co. and General Motors Corp. will use the LDM absorber for bumpers in nearly 300,000 2002 model vehicles.

The American Plastics Council (APC) notes that since plastic components weigh 50% less than their steel counterparts, future automobile components can be substantially lighter while retaining needed strength. Bill Windscheif, chairman of the automotive group of the American Plastics Council, projects that the average weight of plastics and elastomers in automobiles will reach 263 lb in year-2002 models because of innovative new manufacturing technologies.

For example, McCord Winn Textron in Manchester, N.H., created a complex blow-molded shape of Profax SD613, a compounded polypropylene material from Montell USA Inc. of Wilmington, Del., to replace five individual components in the 2000 models of the Dodge Durango sport-utility vehicle and Dakota pickup. The five parts-the radiator fan shroud, coolant reservoir, front washer reservoir, rear washer reservoir, and rear washer reservoir fill funnel-were merged into a single assembly, providing a piece price reduction to DaimlerChrysler of more than $1.50 per vehicle and a weight savings of 1.2 lb.

The 2001 Chrysler and Dodge minivans are the first in their class to feature a thermoplastic bumper beam that exceeds the 2.5-mile-per-hour federal impact standard. Mark White, market development manager at GE Plastics' automotive group in Southfield, Mich., says "the functions of the traditional steel or aluminum beam and impact-absorbing foam have been integrated into one high-performance, lightweight, injection-molded system that also passes the federal impact test at five mph." The bumper was developed by GE Plastics along with Nascote Industries. It is being molded with Xenoy 1103 resin, a blend of polycarbon-ate/polybutylene (PC/PBT), which means it has high strength for good impact resistance. Also, it weighs 11.4 lb, which is eight lb less (or 41%) than the stamped steel bumper it is replacing.

However, a study conducted for the Bumper Project Group of the American Iron and Steel Institute ( AISI ) found that steel will grow from 76% of the market in 1997 to 91% in 2004 while aluminum will slide from 6% to 1.4% and plastics will slip from 18% to 7.6%. Reason: Manufacturers are increasing their use of lightweight, high-strength and ultra high-strength steels that are cheaper to make than plastic or aluminum bumpers.

Just what is PNGV?

U.S. Automobile Materials Partnership