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July 1, 2013

Lightening Up

Weight loss is a major trend for the metals and materials industries. And not just for aircraft and automobiles.

Light weighting” is a process of reducing the weight and mass of products to achieve increased fuel efficiency, easier portability or reduced shipping cost, while maintaining or upgrading performance. 

The most publicized initiatives have been in the automotive industry, where light weighting helps meet the increasingly stringent U.S. Corporate Average Fuel Efficiency standards. Industry experience shows each 10% cut in vehicle weight improves fuel economy by as much as 7%. For all-electric vehicles, every 2.2 pound reduction in mass increases the vehicle’s driving range by about 1.8 miles per charge. 

Many other industries are also moving in this direction, often using advanced metals to do the job. Consumer electronics manufacturers of earphones, iPods, speakers, laptop computers and cameras are improving portability and durability with new materials. Military equipment and weapons are lighter to carry and easier to deploy without degrading combat objectives. And agricultural equipment, such as combines and tillers, need to be wider for large-scale operations, but they must also be lighter to keep from crushing and compacting soil, which interferes with crop growth.

 

The Key Industries: Aerospace 

The most publicized initiatives have been in the automotive industry, where light weighting helps meet the increasingly stringent U.S. Corporate Average Fuel Efficiency standards.

(Photo courtesy of the Steel Market Development Institute)

 

As a matter of physics, anything that flies can do so more economically if it weighs less. Perhaps the most recent commercial aircraft light weighting effort produced the Boeing 787, with its use of composites, especially carbon fiber reinforced plastic (CFRP) for its skin and other components. CFRP is good under tension, as when the fuselage is pressurized. Boeing says CFRP also reduces maintenance and metal fatigue. 

The airframe of the 787 contains 50% composites such as CFRP and 20% aluminum, according to Boeing. For comparison, the Boeing 777 contains 12% composites and 50% aluminum. With its light weighting and other design improvements, the 787 gets 20% better fuel efficiency than similarly sized, conventional aircraft, according to Boeing. 

Other aircraft show similar results. The Airbus A350 XWB family of long-range commercial aircraft contain more than 50% composites such as CFRP, and are 25% more fuel efficient than conventional aircraft due to the weight reduction, improved aerodynamics and new-generation engines.

A new steel/polymer sandwich material is under development at Thyssen Krupp Steel Europe in Essen, Germany. (Photo courtesy of ThyssenKrupp AG)

Military Weapons and Equipment

While fuel economy is the reason behind most light weighting initiatives, the military also needs the full range of its equipment to be easily transportable. BAE Systems, Inc., based in Arlington, Virginia, produces the 8,256 pound M777, a 155 mm towed gun using titanium and aluminum alloys so it is light enough to be towed by a Humvee or carried by a helicopter. It is the first 155 mm Howitzer weighing less than 10,000 pounds, according to BAE Systems’ website. 

The new gun uses parts made from titanium plate, sheet, extrusions and castings, says Marty Procko, North America commercial director at RTI International Metals, Inc. in Pittsburgh, Pennsylvania. RTI is a supplier of titanium components for the M777. The new design and materials reduced the weight of this type of weapon by about 7,000 pounds, he says. 

Soldiers in combat move quicker and react faster when carrying lighter weapons. The M240L 7.62 mm medium machine gun uses titanium components to deliver the same performance as the earlier version M240B, but at 21.8 pounds, it is 5 pounds lighter.

Military vehicles also get light weighting treatment, replacing cast iron brake drums with lighter ones. In the Stryker armored vehicle, an aluminum and ceramic metal-matrix composite brake drum weighs 45% less than the cast iron version, saving 250 pounds per vehicle, according to the U.S. Army Tank Automotive Research, Development and Engineering Center.

 

Agricultural Equipment

Light weighting in agricultural equipment not only improves fuel economy, but also can increase productivity and allow equipment to operate more benignly in the fields. Lighter equipment towed behind a tractor helps reduce soil compaction, and lighter irrigation booms are less likely to sink in the mud, says Scott Cedarquist, director of standards and technical activities, American Society of Agricultural and Biological Engineers in St. Joseph, Michigan. 

The redesign of the reaping arm for a harvester increased its width from eight to 12 row units, reduced the machine’s weight by 12%, and cut material and assembly costs, according to steel maker ArcelorMittal in Luxembourg. 

In addition, a towed container, or skip, redesigned with high-strength steels reduced its weight by 22%, allowing a higher payload, according to ArcelorMittal. The redesign also reduced its cost by 15%.

 

ThyssenKrupp engineers designed a roof module lighter by 38% than a comparable conventional steel roof. (Photo courtesy of ThyssenKrupp AG)

(FSV), a steel-intensive electric concept car design from WorldAutoSteel, the automotive group of the World Steel Association in Brussels, Belgium. The FSV design contains more than 90% HSS and AHSS, according to Krupitzer. Current vehicles are “about halfway there,” he says. 

 

The New Materials: Steel

In the last decade, automakers have increased their use of a wide variety of high-strength steel (HSS) and advanced high-strength steel (AHSS) for different applications within their vehicles.

With stronger steels, you can make parts lighter and lighter, says Ronald Krupitzer, vice president of the automotive market for the Steel Market Development Institute (SMDI) in Southfield, Michigan, and steel companies are adding stronger and stronger grades to their portfolios.

The long-range objective is typified by the FutureSteelVehicle (FSV), a steel-intensive electric concept car design from WorldAutoSteel, the automotive group of the World Steel Association in Brussels, Belgium. The FSV design contains more than 90% HSS and AHSS, according to Krupitzer. Current vehicles are “about halfway there,” he says.

 

Aluminum

In the automotive marketplace, the use of aluminum has grown over the past 40 years, and is now the No. 2 material used in car manufacturing, says Kevin Lowery, director of corporate communications at Alcoa in Pittsburgh, Pennsylvania.

Model year 2009 cars contained, on average, 327 pounds of aluminum, and model year 2012 cars contained 343 pounds, a 5% increase, according to Alcoa. 

The aluminum content is expected to be 550 pounds per vehicle by 2025, representing 16% of the total vehicle weight. 

New aluminum components in automobiles and other applications will be mainly the familiar series 5000 and series 6000 alloys, Lowery says. However, his company has developed a new technology to improve adhesive bonding to aluminum that will allow the same joining performance as spot welding, but with faster assembly at a lower cost. This Alcoa 951 surface treatment will be available by the end of 2013 as a mill-applied pretreatment on sheet and other forms, Lowery says. It has been licensed to Chemetall in Frankfurt, Germany, in an exclusive global distribution agreement, making it available throughout the aluminum industry.

 

Magnesium

Magnesium is the least-dense structural metal, about one-fourth the density of steel. Widely used in electronics housings and similar applications, magnesium has attracted attention as a light weighting metal in the automotive industry. Magnesium made up 10 pounds per vehicle in 2005, but could reach 350 pounds by 2020, according to Magnesium Vision 2020, a report from United States Council for Automotive Research.

The United States Automotive Materials Partnership, part of the U.S. Council for Automotive Research, sponsored by Chrysler, Ford and GM, estimates those 350 pounds of magnesium will replace 500 pounds of steel and 130 pounds of aluminum per vehicle, for an overall weight reduction of 15%.

Magnesium use has been limited by its difficult formability, says Ray Decker, chief technical officer at nanoMAG in Livonia, Michigan. In the past, most magnesium parts have been cast or machined. However, nanoMAG has developed magnesium sheet that can be formed into 3-D parts, Decker says.

 

Titanium

Material and fabrication costs run several times higher for titanium than other structural metals. Otherwise, titanium would be a candidate for light weighting in many more applications, since it is less dense than steel and stronger, depending on grade. Currently, however, it is widely used in aerospace applications, most recently as part of the shift to the use of carbon-fiber-reinforced plastic in aircraft.

On the Boeing 787, titanium has replaced aluminum in some components, especially for use with CFRP. The 787 airframe contains approximately 15% titanium, a significant increase from the 7% to 10% in the 777 airframe. 

 

Metal-Based Composites

Composites, combining metals with other materials, are also on the horizon. A new steel/polymer sandwich material is under development at ThyssenKrupp Steel Europe in Essen, Germany. This new composite could save weight and cost, especially in large body parts such as roofs, doors and hoods. ThyssenKrupp engineers designed a roof module that’s 38% lighter than a comparable conventional steel roof. The sandwich consists of steel sheets 0.008 to 0.010 inches thick, bonded to a polymer core 0.016 to 0.039 inches thick. The material is stiff enough, however, to hold its form  in use, according to the company. 

Historically, light weighting has been driven by the pursuit of greater fuel economy in aircraft and automobiles. But, higher-strength and lighter metals are now making many products more rugged, more portable and higher capacity. New alloys and forming and bonding processes may now offer manufacturers the means to achieve these product improvements without increasing cost. 

Consumers, governments and manufacturers are also starting to pay more attention to the total environmental effect of all kinds of products. The entire product life cycle is receiving scrutiny from the mining, refining and formulating of the raw material, to disposal at end of life. Metals particularly can have a clear advantage in any life-cycle impact analysis, as they are extremely recyclable. Thus, they will continue to be a mainstay of manufacturing as total cost of ownership and life-cycle evaluations become key elements in any materials consideration.


Barbara Donohue is a freelance writer and editor of various marketing communications tools and technical documentation. She is also a mechanical engineer with 15 years of industry experience.