Automotive lightweighting with alternative materials
By Don Rosato

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Note: This is the second of a four-part series covering (1) automotive lightweighting trends, (2) material advances, (3) process technologies and (4) applications.

INDUSTRY PULSE

What is the important alternative material trend in automotive lightweighting?
  • 1. More carbon fiber-reinforced plastics for structural parts
  • 2. Advanced nylons in under-the-hood applications
  • 3. Growing use of aluminum and magnesium in front-end systems
  • 4. Weight reduction by replacing steel with CFRP, FRP and magnesium, followed by aluminum

Consumer preferences have limited the downsizing options available to automakers, and safety and performance standards have resulted in a very limited ability to reduce weight further with conventional materials. Every potential vehicle lightweighting component is under investigation. Material substitution replacing heavier iron and steel with weight-saving advanced composites and other plastics, aluminum, magnesium and advanced high-strength steel is essential for boosting vehicle fuel economy. Material substitution is dependent on mechanical properties, cost, design and manufacturing capabilities. In addition to reduced fuel consumption, weight reduction enables smaller power plant and energy storage systems, with corresponding cost and/or performance benefits as well as secondary weight reductions in load bearing structures.

Plastic composites and other advanced plastics offer significant lightweighting potential. FRP (fiber reinforced plastics) composites are typically 25-35 percent lighter than steel parts of equal strength. Low- and ultra-low-density SMC (sheet molding compounds) advances are also facilitating weight reductions. New material uses to reduce weight will include:
  • Greater use of plastics/composites in car body panels
  • Long-fiber technology for structural parts
  • More use of CFRP (carbon fiber-reinforced plastics) for structural and other parts as lower cost composites are developed

    CCFRP concept car body frame

  • PC (polycarbonate) and PMMA (polymethylmethacrylate, or acrylic) as glazing including car roofs and rear ends
  • Advanced polyamides (nylons) in under-the-hood applications
  • Foaming/glass bead technology to reduce part density
  • More use of plastic—metal and organic hybrid technology
  • Advances in thin-gauge, high-performance steel

    Advanced high-strength steel (AHSS) sheet

  • Growing use of aluminum and magnesium — More than half of Ford vehicles already have aluminum hoods. The Audi A4 also uses aluminum for its front-impact management system. General Motors, in an industry first, used die-cast magnesium alloy (AE44) for a front engine cradle cast by Meridian Lightweight Technologies Inc. reducing weight 35 percent over the previous aluminum structure. The Magnesium Front End R&D Project undertaken through sponsorship by Canada, China and USA, aims to develop key technologies and a knowledge base for increased use of magnesium in automobiles.
On the component level, weight saved by using alternative materials depends on application/design intent. For example, in a body panel designed for strength and resistance to plastic deformation, 1 kg of aluminum replaces 3-4 kg of steel, whereas for a structural component designed for stiffness to resist deflection, 1 kg of aluminum only replaces 2 kg of steel. In general the weight reduction obtained by replacing steel tends to be greatest for CFRP, FRP and magnesium followed by aluminum. For example, weight savings by different materials used for a car rear floor is as follows:

Material Mass (kg) Weight savings (pct.)
Steel 6.54
Aluminum sheet (5182) 3.38 48%
Polyamide glass fiber (PA 6/6 GF30) 2.87 56%
PP glass fiber (PP GF30) 2.35 64%
Magnesium sheet (AZ31) 2.18 67%

Lightweighting measures are expected to be applied to every car model that is launched in the coming years. Mazda, for example, has set a goal to reduce the curb weight of all its new model cars by 15 percent (up to 220 pounds per car) through material replacement and engineering, redesigning features and shrinking part dimensions. The company is also looking to improve its global corporate fuel economy average by 30 percent by 2015.

Innovative materials combined with new production methods and reinforcing structures will play an important role in reducing vehicle weight. This lower weight not only improves fuel efficiency but also reduces the load on the brakes and suspension systems. The average car contains 15 percent of its total weight, or 360 pounds, of plastics with use in automotive manufacturing accelerating. As the automotive industry gears up to meet new emissions regulations, lightweight plastics will play a critical role. Experts predict that these uses will more than double over the next five years.

Porsche Panamera Sedan lightweighting spatial options


Dr. Donald V. "Don" Rosato serves as president of PlastiSource, Inc. a prototype manufacturing, technology development and marketing advisory firm located in Concord, Massachusetts, USA, and is the author of the Vol 1 & 2 "Plastics Technology Handbook".