Fueling improvements: Turning Performance

Using continuous improvement to reach automotive fuel-economy goals.

Today’s passenger cars, on average, generate more horsepower and consume less fuel than ever before. There are some obvious drivers behind this, such as high fuel costs, worry over dependence on foreign oil and environmental concerns. To make autos even more efficient, the U.S. government reached an agreement in 2011 with 13 automakers to begin delivery of 54.5-average-mpg vehicles by 2025, up from 27.8 mpg in 2011.

Courtesy of Steel Market Development Institute

A forged steel output flange mounted on an aluminum-body automatic transmission.

According to the feds, that agreement will potentially save a total of $1.7 trillion in gasoline costs from 2011 to 2025. But how automakers will achieve that goal remains an open question. And what does the agreement mean to part manufacturers—the folks who make a living machining parts for these newfangled cars and light trucks? There’s no easy answer, but one thing is certain—change will continue to be the norm in the automotive world.

Lighter and Stronger

No one disputes the fact that better fuel economy starts with lighter vehicles. It should be a no-brainer, then, to eliminate steel wherever possible in favor of lighter materials, such as aluminum, magnesium and even plastic, right?

Not so fast, said David Anderson, senior director, automotive technical panel and long products program at the Steel Market Development Institute, Southfield, Mich. Anderson explained that steelmakers can produce product that competes on a pound-per-pound basis with aluminum. “One of the programs we recently completed was on a lower control arm,” he said. “The steel control arm matched the weight of an aluminum one, and we were able to produce it at a 35 percent cost savings.”

Anderson cited other programs with similar results, including body enclosures and chassis components.

“We’re seeing 25 to 35 percent weight savings at no additional cost to the OEM,” he said. “There’s a lot of development work going on, especially in the power train: axle shafts, transmission gears and connecting rods. Advanced high-strength steels have multiphase microstructures that help improve elongation and strength at the same time. But you have to consider all of the material’s attributes—its strength and machining costs, as well as the weight. It’s all about power density, which means getting more power from smaller components.”

Modern steelmaking provides lower inclusion content than previous methods and controls the inclusions that do exist so they don’t adversely affect part performance, according to Anderson. But how do inclusions—undesirable defects in metal—affect fuel economy?

Courtesy of Makino

Robotic handling systems for auto parts, such as this one from Makino, offer greater flexibility than dedicated transfer lines.

Courtesy of Steel Market Development Institute

Steel crankshafts, such as this one, offer greater strength than those made of iron.

“Because you’re improving the material properties, you’re able to do more with less material,” he said. “Consider a traditional cast iron crankshaft, like in the Ford V-8 engine. When they went to the V-6 EcoBoost in the F-150 [pickup], they used a steel crankshaft. This is because of the toughness that steel offers and the fatigue and durability performance—they’re now able to give you the same performance on a V-6 as what you had on the V-8, and better fuel economy too.”

Cutting these new steels can be difficult, but the steel industry is addressing it. “We’ve made extensive machining calculations and developed machinability databases to give automakers a feel for the cost impact of new steels,” Anderson said. “We’re also working with cutting tool manufacturers to improve machinability. Automakers need affordable lightweighting, and even though there may be a negative impact on machining costs with these new steels, you end up buying, and machining, less material. Overall, it’s a wash.”

Matt Zalusec, materials group leader for the United States Council for Automotive Research (USCAR), Southfield, Mich., agreed that steel is often the best choice for automotive components. “I anticipate continued progress and use of quenched and tempered steels for driveshafts and halfshafts. We’re using more hardened steels overall, and you’re going to see a lot of the 4000-series high-hardened and deep-hardened steels used for splines and gears. Steel technology is the driver for higher performance in driveline products.”

There’s more to driveline performance than good steel, however. Improved process control is equally important. For example, “At the end of the halfshaft, you have a highly complex gear tooth,” Zalusec said. “That inserts into a mating gear set, which in turn drives the wheel. Continuous improvement comes about through an accurate interface between the two—you cut down on wear with a good marriage between the surfaces and by providing a better lubricating film. If your gear sets aren’t perfectly matched, you get noise, vibration and harshness, or NVH. More and more, we’re trying to figure out how we can make the splines and gears more accurately through better process control and avoid NVH.”

The Alternative

But steel’s not the whole story at USCAR. Zalusec is a contributing member of the United States Advanced Materials Partnership Program (USAMP) on behalf of Ford Motor Co. “We co-collaborate on precompetitive technologies that benefit the automotive industry as a whole,” he said.

Part of this collaboration is research into alternative materials. “As far as the drivetrain goes, you might see couplers and universal joints made from aluminum in the future,” Zalusec said. “And thermoplastic covers and housings will continue to evolve. It’s just a matter of making sure these alternative materials meet the durability, reliability and environmental attributes we need.”

There’s also a potential for use of carbon fiber-reinforced composites. The biggest roadblock to increased CFRC use is cost—carbon fiber alone runs upwards of $9 to $10 per pound. “When you add in the resin and material processing needed to turn it into a usable product, the cost of CFRC runs about 10 times higher than steel,” Zalusec said. “Cutting that in half would be a great target. That doesn’t mean it becomes the material of choice, but carbon fiber, with its high tensile strength and modulus of elasticity, offers a lot of technical merit.”

Carbon fiber sounds cool—after all, high-end sports cars using this stuff are the envy of car enthusiasts everywhere—but is it really practical for vehicles used more for grocery shopping than impressing your friends at the car rally? “The reason people use carbon fiber isn’t so much its strength as its weight,” Zalusec said. “Reducing weight is a good thing, but when you reduce the weight of rotating components—such as carbon fiber driveshafts and brake rotors—you get a bonus. Because the engine now has to put out less horsepower to move a lighter rotational mass, you not only reduce the weight of the vehicle, but can use a smaller (and lighter) engine to power it.”

Does this mean everyone should rush out and buy waterjet machines and special carbon-fiber machining centers? “Not at all,” laughed Zalusec. “Extensive use of carbon fiber in automobile components is still years away.”

Your Father’s Aluminum

There’s no single material solution, however, when it comes to lighter vehicles and improved fuel efficiency. Doug Richman of Kaiser Aluminum Corp., Foothill Ranch, Calif., is the Aluminum Association’s Aluminum in Transportation Group technical committee chairman. Despite his obvious allegiance to aluminum, Richman keeps an open mind.

“I’m in awe of what the steel folks have done when it comes to developing new materials,” he said. He noted that multiple materials will continue to be used in vehicles. “The vehicles of the future will have the best of what all of us can put together, and aluminum will coexist with the advanced steels to make better cars.”

Courtesy of Makino

Automated loading of engine blocks into a pair of Makino a61 horizontal machining centers.

Richman said the next big story with aluminum will be in automobile bodies because the material is dominant and approaching saturation in the power train area.

“We’re seeing a lot of growth in the sheet market: hoods, trunks, doors and the main body structures,” he said, noting that more than 80 percent of all engine blocks today are aluminum, aluminum cylinder heads have a 98 percent market share and transmission cases have long been made from aluminum. “Sure, there are new uses ramping up, such as turbocharger housings and valve train components, but the big aluminum revolution has come and gone.”

Still, Richman said: “Metallurgists are constantly, and even aggressively, trying to improve the fundamental properties of aluminum. And they’ve been quite successful—just look at aerospace aluminums. They’re twice the strength as those used in automotive, but they’re also far more expensive and more costly to machine. As a result, they don’t meet the value proposition needed for mass production of automobiles. Most automotive aluminum grades used today have been in the market for more than 50 years.”