Note: This is the third article of a three-part series covering automotive lightweighting (1) trends, (2) material/process advances and (3) applications.
Every car model that is launched in the coming years is expected to include lightweighting measures.
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 parts dimensions. The company is also planning to improve its global corporate fuel economy average by 30 percent by this year.
The industry move toward alternative fuels such as diesels, hybrid vehicles, turbo systems and electric-only cars is similarly increasing plastics opportunities. Metal is also increasingly replaced by plastics in under-the-hood applications.
Let's start with a compact plastic exhaust component that saves weight and reduces sound. Faurecia's Emissions Control Technologies, in partnership with automaker Renault in its EOLAB prototype vehicle project, partially reworked the exhaust design to introduce plastic materials that are lighter than their steel counterparts.
Faurecia engineers replaced the acoustic function of the rear muffler with a plastic resonator and a gas separation system that can keep the temperature below 200 degrees C, which is the maximum temperature resistance of the plastic.
The lower temperature allows integration of a Helmholtz resonator molded from glass fiber-reinforced polyamide (PA) into the exhaust system. PA has a density six times lower than that of steel, enabling a 50 percent weight reduction compared with a steel resonator.
Not only is it lighter, but the Helmholtz resonator also effectively muffles low frequencies and reduces the humming sound inside the cabin to enhance the comfort of the occupants. Faurecia has also worked on reducing the thickness of the steel components used in the exhaust system and has successfully slimmed some internal parts down to just 0.6 millimeters.
This new, compact exhaust system has allowed Renault to make additional weight savings of up to 2.3 kilograms compared with conventional exhaust systems.
Supplier Röchling Automotive is also developing a plastic muffler for exhaust systems. Besides a weight reduction of approximately 30 percent, the solution made of plastic provides numerous options for adjusting the sound and reducing the noise level. The use of plastic also has advantages for the design of components with improved aerodynamics and makes it possible to adapt components cost-effectively to the design of the rear end of the vehicle.
Next let's take a look at a PA gear-shift module that replaces metal and outperforms materials such as polyphenylene sulfide (PPS) or polyetherether ketone (PEEK). Long glass fiber polyamide, Grivory HT1VL-50X from EMS-Grivory, featuring high stiffness and creep resistance at high temperature is being used to replace metal for an Audi gear-shift module, a seven-gear dual clutch transmission produced by FTE Automotive.
Grivory HT1VL-50X is a surface-optimized Grivory HT1 with special long glass fiber (LGF) reinforcement. The material is characterized by high stiffness and strength as well as excellent resistance to oils and chemicals. Grivory HT1 maintains its excellent mechanical properties even at high temperatures. It also provides good dimensional stability and low tendency to creep.
Grivory HT1VL-50X has higher stiffness and strength values, increased energy absorption and notched impact strength, a higher heat deflection temperature and strikingly increased creep resistance. In addition, the long glass fibers are more evenly oriented in an injection-molded component, which greatly reduces directional dependency of the material properties.
Continuing, let's examine composite leaf springs for the new Volvo XC90. Benteler SGL Composite Technology GmbH has successfully fabricated a composite automotive leaf spring using a specially developed resin transfer molding (RTM) process. Compared to conventional steel leaf springs, these composite leaf springs are up to 65 percent lighter, for a weight saving of 4.5 kilograms.
Henkel AmericaPlast News
Fiber-reinforced composite leaf spring (left); rear axle of Volvo XC90 with composite leaf spring (right).
Henkel AG developed the process for RTM of glass-fiber-reinforced leaf springs for cars that uses a polyurethane (PUR) matrix resin. The resin, Loctite MAX 2, is said to cure significantly faster than the epoxy products usually employed in the RTM process.
Due to its low viscosity, the PUR resin penetrates and impregnates the fiber reinforcement more easily and with less fiber displacement, thus enabling short injection times and shorter overall cycle times. The Loctite MAX 2 has an exceptionally high stress-intensity factor, which is a measure of toughness. The toughness has a positive effect on the fatigue behavior under load.
Leaf springs in cars are constantly subjected to dynamic loading under driving conditions, so the use of flexible materials with a high fatigue tolerance prolongs component life.
Finally, let's quickly scrutinize the metal competition in automotive lightweighting that is not standing still development-wise. For example, aluminum and advanced high-strength steel (HSS) are cutting vehicle weight and improving safety. A blend of aluminum and new HSS are finding their way into hoods, roofs, frames, engine blocks, cylinder heads, truck boxes and other components driven by a need to reduce weight to improve fuel efficiency.
The 2015 Chevy Colorado pickup uses a combination of HSS, with yield strengths of more than 188,000 psi (pounds per square inch), to cut weight and improve safety. Chevrolet's new Colorado pickup employs such steels throughout its frame; the A and B pillars get the highest-strength alloys. In addition to the HSS in the cab frame, the Colorado employs advanced steels in its pickup box and its box frame.
Similarly, aluminum is applied to its hood, front-steering knuckles, cylinder heads and engine blocks (for both its four- and six-cylinder engines). As a result, according to Chevy, the Colorado is 880-1,400 pounds lighter than direct competitors. For most automakers, advanced HSS are still a more likely choice than aluminum, largely because steel is still cheaper and better understood than aluminum.
Chevrolet
2015 Chevy Colorado pickup — high-strength steel components.
