Materials Driving Lightweighting ChangeDecember 11, 2018
Lightweighting is a concept in the automotive industry referring to building cars and trucks that are less heavy as a way to achieve fuel efficiency and handling.
“Once you reach a certain horsepower level, it gets very expensive to add more power, whereas to take the weight off, it’s generally less expensive,” says Gregory E. Peterson, principal materials engineer for the Michigan Manufacturing Technology Center (MMTC), a consulting organization that helps manufacturers improve profits and performance.
The MMTC and Peterson were asked in 2017 to find a lighter alternative to the C2’s steel frame for the aftermarket sector, and produced a composite frame comprising ultra high-strength steel, aluminum, magnesium and carbon fiber. It weighs 33% (or 89 lb.) less. The frame is also 450% stronger.
At the extreme end, there are the Formula One engineers, creating basically missiles on wheels that can rocket to 62 mph in about 1.7 seconds and weigh less than 2 tons. They are so good at lightweighting they have a minimum weight of 1,618 lb.
At the other end of the spectrum, there are the amateurs with a more low-tech way of lightweighting. For example, removing the backseats to gain a speed advantage against other similar vehicles. Back in the early 2000s that was considered an achievement for some reason. The theory was right on, despite clumsy execution.
Peterson points to the lightweighting rule that a 10% weight reduction leads to a 6% to 7% increase in fuel economy.
But there are easier ways to make cars lighter nowadays than removing key components of a vehicle. Instead, these parts are changing in shape and composition, blending various metals and carbon fiber reinforced plastic, relying on next-gen design software and techniques such as additive manufacturing.
And because of the mass-compounding effect, Peterson explains, when the structure becomes lighter, other elements do as well, from the suspension to the brakes to the tires.
That is why lightweighting has become something of an obsession for the industry. For some, it might be because you want to reduce your carbon footprint, but more likely because governments around the world are demanding it.
Whatever the reason, lightweighting has become a top priority of car makers. The materials and high-tech engineering previously reserved for the Grand Prix can now be had by car owners looking to upgrade to a more fuel-efficient car or electric vehicle. And while the math might be fairly simple, even professional automotive engineers have not yet mastered execution.
Manufacturers are looking for disruptive efficiency gains. They see the Corporate Average Fuel Economy standards getting more stringent, electric vehicles becoming more prevalent, and gas prices in constant flux. At best, lightweighting could potentially reduce vehicle mass by half and boost fuel efficiency by 35%.
Out of necessity, the industry is throwing all of its experience into making lighter vehicle solutions. Innovations in metallurgy, material science and 3D-printing are leading the acceleration.
Below are a couple of materials driving changes from incremental to incredible.
Aluminum provides a 40% to 45% mass improvement over steel.
“The problem is the cost of implementing those materials,” says Alan Taub, the CTO at the LIFT (Lightweight Innovations for Tomorrow) Consortium, a public-private partnership of universities, manufacturers and the U.S. Navy’s Office of Naval Research. Traditional carbon steel is currently priced around $0.40/lb., and aluminum more than doubles carbon steel’s price at $0.88.
LIFT, part of the Manufacturing USA network, exists to find the right lightweight materials and way to implement them in the subsequent manufacturing processes. And the solution must be applicable to at least two industries. They work on transferring innovations found in the lab to the OEMs and Tier 1s who can enact real change. The initiative is as much about economics as it is about metallurgy.
“You want to get in the range of about $2 incremental cost for every pound saved,” Taub explains. “If you’re not in the range of [at least] $2 to $2.50 per pound saved, it’s really not a good value for the customer and there are other technologies you can do.”
This would mean focusing on the engine or aerodynamics, for example. Taub says aluminum sheet now falls within this range, as does the third generation of advanced high-strength steel. The World Steel Association (WSA) says Advanced High-Strength Steel (AHSS) comprises as much as 60% of new auto bodies, and can reduce weight by 25%-39% over conventional steel. Aluminum has less mass than AHSS, but is weaker and is more expensive. An MIT study calculated in 2007 that aluminum structures were 60%-80% more expensive. That was when aluminum was $1.22/lb., though.
AHSS seems to have the edge in emissions when comparing well-to-wheel scores. A life cycle assessment model by the WSA found that AHSS reduced at best 6,600 lb. of CO², while aluminum was 3,300. Even though aluminum is lighter, that reduction equaled a savings of about a third-tank of gas annually. That does not mean aluminum is not a viable option.
“Recycling of aluminum is one-tenth of the energy of getting it out of ground and there’s a lot available,” says Peterson, who works in the same building in Detroit as Taub and supports LIFT’s efforts on behalf of NIST.
The real solution from LIFT’s perspective will be found when the perfect combination of these metals (and plastics and carbon fiber) are implemented. In each scenario they first tinker with the array of prospective materials to create optimal strength, safety and fuel economy. Then they have to ensure the different metals do not negatively interact.
Taub says galvanic corrosion can occur if water gets in between two different metals. This happened with the Statue of Liberty in the 1980s, when her copper exterior and wrought iron supports came into contact after the insulation failed. It required a massive restoration with stainless steel supports. LIFT found a special coating on the multi-metal parts will suffice.
“Carbon fiber has the best potential for lightweighting, but takes a lot of energy,” says Ray Boeman, Oak Ridge National Laboratory’s energy program director. He works at the Institute for Advanced Composites Manufacturing Innovation (IACMI), which is also based in the same building in Detroit’s Corktown neighborhood as LIFT and focuses on making carbon fiber feasible.
Carbon fiber is 55% lighter than carbon steel and can be ten times stronger, but the limiting factor is cost. Despite the price, which could be up to $500/lb., aerospace manufacturers value the performance above all. Half of the Airbus A350 XWB airliner’s total weight is carbon fiber reinforced plastic. Formula One, where expense always comes in a distant second to performance, also relies heavily on the material.
A new low-cost carbon fiber is down to $5/lb., says Lawrence Drzal, Director of the Vehicle Technical Application Area at IACMI. Drzal and his team are now figuring out how to attain the high throughput the auto industry needs. It can take several hours to create one part. The goal is to reach 90 seconds to make a carbon fiber lift gate or hood.
First, a mold must be made and the operator puts the fibers in dry, arranging them in the correct geometry for shape and load bearing, and aligned for the maximum force. Then they close the mold and inject the epoxy at high speed.
The cycle time is limiting CFRP at BMW. The i3 and i8 hybrid sports cars had been made out of CFRP and could get up to 76 mpg, but the new iNext cars produced in Dingolfing, Germany, where the cycle times are 60 seconds, will revert back to a metal frame, adding CFRP at strategic spots.
“Automotive is always looking to cut pennies,” Boeman says. “You don’t need as high performance. They are sort of bookends. We’re trying to move each of those ends closer to the middle and adopt some modified lightweight aerospace systems and figure out how to take out cost.”
ResearchAndMarkets.com predicts the carbon fiber industry will be worth about $6.1 billion in 2023, more than double the 2017 value, and that could reach the hundreds of billions. But for wide use, the auto industry will need a monumental up-shift in skilled labor that can manipulate the carbon fiber.
“The education of people involved in the manufacturing has to be broadened,” Drzal says. Traditionally, you pick up sheet metal, put it in a press, open it and take out the part. With composites, you are concerned with how the fibers are aligned, the thermoset system like epoxy, temperature, and the time exposed to that temperature to achieve the properties you want.
Hitch, John. (2018). “The Road to Lightweighting: The Tech & Materials Leading the Way”. Retrieved from https://www.industryweek.com/technology-and-iiot/road-lightweighting-tech-materials-leading-way.