Note: This is the first article of a three-part series covering automotive lightweighting (1) trends, (2) material/process advances and (3) applications.
The global shifts in automotive manufacturing haven't slowed plastics innovation and the adoption of new plastic materials. In 2006, Japan passed the U.S. to become the world's largest car manufacturer. This position changed again when in 2009 when China overtook Japan for this top position with a current 35 percent market share in vehicles produced, while U.S. production has gone to 25 percent in the last five years.
Vehicle weight has actually been increasing as OEMs continuously add car features, and reversing this growing weight spiral has become a top priority. Over the past 15 years, cars have not become lighter, but are rather some 30 percent heavier.
The VW Golf, for example, which weighed 800 kilograms at its launch in 1974, now weighs 1,200 kilograms. Thus, material producers, car manufacturers, suppliers, processors and various institutes and associations have taken up the challenge of reducing automotive vehicle weight.
Center for Automotive Research
Car front hood weight reduction comparison.
Plastics are helping to shed weight without compromising the safety and comfort features mainly responsible for the upward weight spiral. Cost-efficient plastic manufacturing solutions can also help to consolidate parts and reduce the number and scope of processing steps while reducing weight of the finished component or system.
The replacement of metal material by engineering thermoplastics, fiber-reinforced composites and hybrid composites in the automotive core structure, body or power train offers significant weight reduction potential. Greater reductions can be achieved in structural components such as underbody covers, dashboards, roof, front-end or door modules.
Material combinations allow for a variety of tailor-made solutions. By using different thermoplastic matrix materials (polypropylene, polyoxymethylene or acetal, thermoplastic polyurethane, etc.) and embedding various fibers (glass, carbon, etc.) along with the use of additives, material properties can be tailored to suit specific requirements.
The use of composites also allows key components to be integrated into structural elements eliminating metal and processing steps to reduce both weight and production costs. Volkswagen, for example, has advanced and commercialized the use of long-fiber reinforced thermoplastics (LFRT) Celstran for the large-format dashboard of its Golf Plus, allowing the passenger airbag to be completely integrated into structural components.
Let's take a look at some examples of trendsetting automotive lightweighting technologies.
Take, for example, the composite carbon-fiber tailgate. The composite tailgate from Faurecia featured on the Peugeot 208 Hybrid Air 2L, a low-energy concept car, comprises a combination of plastic and carbon fiber, reducing weight by 35 percent, or 7 kilograms.
The "semi-structural" design consists of a skin and a lining with a thickness of 1.5 millimeters to prevent torsion. This eliminates the need for additional strengtheners in flat areas by optimizing the direction of the carbon fibers in relation to the forces acting upon them.
The stiffness and reduced density have also made it possible to remove one of the two tailgate stabilizers to further reduce weight. A groove is also molded into the lining to accommodate the electrical cables and reduce the number of fasteners.
Other advantages of Faurecia's technology include:
- Removal of interior trim components as a result of the quality of the carbon-fiber material, which can be painted directly
- Reduction in the number of parts to be assembled
- Ability to produce more complex shapes than with parts made of metal or glass, such as the rear window
Also, worthy of note is the "low-cost carbon-fiber project" (FORCE) launched by the Plateforme de la Filière Automobile (PFA) in France that will make carbon-fiber composites more affordable in the next eight years.
Next, let's look at a wood-cellulose composite car part that took first place in the environmental category of the recent November 2014 SPE Automotive Innovation Awards: an injection-molded cellulose fiber composite console armrest, developed for Ford by Johnson Controls and Weyerhaeuser.
Weyerhaeuser's THRIVE, which incorporates cellulose fiber into thermoplastic composites, can replace a variety of fiber-reinforced and fiber-filled thermoplastics in applications including automotive parts. Ford is looking to make extensive use of the new cellulose-fiber reinforcement composite.
Green Car Congress/Ford Motor
Cellulose-fiber PP console armrest underside (left) and top cover/underbody.
Key Attributes of THRIVE composites are:
- Neutral color readily absorbs colors/dyes for full color flexibility
- Odorless (passes stringent automotive interior tests)
- Lower specific gravity than glass fiber by 6 percent
- Excellent moldability with lower cycle time
- Excellent tensile and flexural properties
- Attractive system economics
- Consistent quality
Ford is using THRIVE cellulose-reinforced polypropylene (PP) for the center console armrest of its 2014 Lincoln MKX. Ford has been using the material in several prototype parts, but this is the first application in a production vehicle.
The base polymer is a 35 MFI PP reinforced with 20-40 percent specially engineered cellulose fibers, plus small amounts of coupling additives. Ford's biomaterials research team has found that Weyerhaeuser's cellulose/plastic composites meet the car company's requirements for stiffness, durability and temperature resistance.
In addition, components weigh about 10 percent less than glass-reinforced plastics and can be produced 20-40 percent faster and with less energy, because it can be molded at lower temperatures. Weyerhaeuser plans to develop composites with other plastics and bio-derived polymers.
Weyerhaeuser development partner Interfacial Solutions has developed proprietary technologies to improve moisture resistance of high natural-fiber-content composites at room and elevated temperatures. Interfacial Solutions has also developed a moisture scavenger technology that eliminates the need for predrying natural fibers and other moisture sensitive plastics prior to processing.
