Note: This is the third article of a four-part series covering automotive plastics lightweighting (1) trends, (2) material advances, (3) process technologies and (4) applications.
The average car contains 400 pounds of plastics or approximately 14 percent of its total weight, and it is accelerating in car manufacturing. Experts predict that these uses will more than double over the next five years.
For example, Mazda has shaved 220 pounds from the curb weight of its Mazda2 over the previous model. This has been done through material replacement and engineering, plastic process technology refinement, redesigned features and shrunken parts dimensions; and Mazda has continued this weight reduction in its other models.
Weight-saving measures are expected to be applied to every model that launches over the coming years. Innovative materials combined with new process technology 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.
As the automotive industry gears up to meet new emissions regulations, lightweight plastics will play a critical role. Let's take a look at some emerging automotive weight-saving process technologies.
Thermoplastic composite system process development is a good place to start. Thermoplastic materials, with both short- and long-fiber reinforcement, have made a major contribution to lightweighting, replacing innumerable metal production components by equally-capable plastic counterparts.
As these plastic components and materials start to reach their fundamental limits, the next big advance in metal substitution in vehicle construction is expected to succeed only with a technological leap, namely, using continuous fiber reinforcement of injection-molded structures with thermoplastic composites.
To this end, BASF has developed its Ultracom thermoplastic composite system. The Ultracom thermoplastic composite system consists of three elements, namely:
- Continuous fiber-reinforced semifinished products including the following technologies — Ultralaminate: laminates made of woven glass-fiber fabrics, impregnated with Ultramid, polyamide (PA) or Ultradur polybutylene terephthalate (PBT) from BASF. This is better suited to quasi-isotropically loaded hybrid parts with a large surface). Ultratape: unidirectional, reinforced glass or carbon fiber tapes, impregnated with Ultramid or Ultradur polybutylene terephthalate (PBT), This is more suitable for the local reinforcement of injection-molded short glass fiber-reinforced parts. These thermoplastic composites are being enhanced in development cooperation together with TenCate, a fiber-reinforced composites manufacturer, and Owens Corning, a leading supplier of glass fibers.
- Overmolding compounds — the Ultramid and Ultradur overmolding compounds have been specifically developed for use with these laminates. By using the overmolding compounds in combination with the laminates and tapes, it is possible to injection-mold complex parts with high mechanical reinforcement (using continuous fibers at precisely defined locations) while simultaneously incorporating specific functions as the result of overmolding.
- Engineering support — the third component of the Ultracom package is engineering support, based on BASF's Ultrasim simulation tool. BASF has also added at its technical center a fully automated pilot line that combines an injection molding system with automated laminate feeding.
Continuous fiber-reinforced composites based on polyurethane and epoxy resin systems for structural and semistructural applications are also being developed. Working with automotive suppliers, production concepts for thermoplastic composites with continuous fiber reinforcement for body and chassis parts are expected to be developed in the next three years.
The first customer prototype using Ultracom is a rear seat back from Johnson Controls Automotive Seating based on Ultralaminate overmolded with high-impact Ultramid ZG7 COM nylon.
Next, let's consider the automated production of carbon fiber-reinforced plastic hood (CFRP) hood.
The Institut für Kunststoffverarbeitung (IKV), or Institute of Plastics Processing, at RWTH Aachen has developed a prototype CFRP engine hood for the Ford Focus using a gap impregnation process technology with innovative mold technology. The IKV is working in collaboration with the Institut für Kraftfahrwesen (IKA), the Institute of Automotive Engineering, and a number of industry partners.
The processing technology used allows automated production of the engine hood in just 15 minutes. In the process, a preform is inserted into a mold, then impregnated with a liquid resin and finally cured.
The combined fixing and ejection units allow double-sided impregnation of the preform, so complex sandwich parts can be produced in a single step. Rapid impregnation is allowed through creation of a temporary flow gap, followed by the subsequent compression of the impregnated preforms by means of pressing and squeezing.
Institute of Plastics Processing (IKV)
IKV gap impregnation process (top, left) and carbon fiber-reinforced hood (bottom).
Apart from the curved part and stiffening structures, the hood also contains fixing elements for its assembly. Compared with the steel equivalent, the CFRP hood at 5 kilograms is 60 percent lighter.
Industry partners involved in the joint project include the Ford Research Centre in Aachen, Germany; Composite Impulse; Toho Tenax Europe; Evonik Industries; and Henkel. The project is financed by the German State of North Rheine Westphalia (NRW) as part of the Hightech NRW project "Exterior body parts of CRP for large-volume production." The aim is to conclude the project by Q4 with the cycle time-optimized manufacture of the engine hood by the gap impregnation process.
Continuing, the new KIS process technology is cutting auto interior trim-part weight. KIS technology is a new manufacturing process developed by Daimler AG for series production of lightweight interior trim parts. The technology combines intelligent compression and injection-molding processes to achieve weight reductions up to 50 percent.
Pressed components allow a marked reduction in weight, while injection-molded components enable incorporation of ribs to ensure the necessary stability and strength, as well as opening up broad scope for shaping to enable the realization of many different components. In KIS, ribs and attachment points are injected directly onto the pressed carrier while it is still hot.
The starting material for the carrier takes the form of hybrid bonded-fiber fabrics consisting of thermoplastic and reinforcing fibers. Use of the same materials for the bonded fiber fabric and the injection-molding process provides an optimum bond.
The result is both simple functional integration and low wall thicknesses. The first parts for pillar and door trims to be produced with the KIS technology will go into series production in one of the next Mercedes-Benz model lines. When fully exploited in interior trim, weight savings of over 5 kilograms per vehicle are attainable with the KIS technology.
Finally, let's take a look at structural adhesive-bonding advances in the auto sector. Adhesives are set to play a large part in bonding together various material combinations, as a variety of plastic and nonplastic material combinations increasingly play key roles in vehicle lightweighting. The advent of higher-performance structural adhesives means load-bearing parts and components like doors, bumpers and struts can now be bonded and stiffened.
INterlaced Elastomer NetworkS (INES), a recently-launched line of hybrid structural adhesives from Aderis Specialty Adhesives offers high structural and sound-damping performance suitable for automotive parts. The line combines the performance of three adhesive bonding technologies: the resistance/mechanical strength of epoxies; the elasticity provided by polyurethane (PUR) and the fast assembly rate enabled by methyl methacrylate (MMA).
This is the first time a structural adhesive combines elongation, low modulus and high-mechanical performance with high-impact resistance and peel-and-shear strengths over a range of temperatures from minus-80 degrees to 140 degrees C. INES can be used to join a broad range of materials such as treated metals, engineering composites, thermoplastics (e.g., acrylonitrile butadiene styrene, or ABS; and polycarbonate), glass and zinc.
The adhesive has excellent elasticity — 70 percent pure elasticity over an elongation range — in combination with high strength (250 kg/cm² for shear on steel, and up to 100 kg/3.5 cm for peel. These properties offer exceptional technical performance for high-stress bonding applications. Greater use of structural adhesives and aluminum is helping Cadillac reduce overall weight of the ATS and its all-new CTS sedans.
The new Cadillac CTS uses 387 feet of structural adhesives, more than the length of a football field. In addition to reduced weight, the extensive use of adhesive in these Cadillac vehicles provides a damping effect that reduces the transmission of vibration through the body structure with fewer squeak and rattle sounds reaching the driver.
