Plastics vs Automobile Industry
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Legislative actions such as the Clean Air Act Amendment, the National Energy Policy Act, and potential new corporate average fuel economy (CAFE) standards have resulted in increased emphasis on electric, hybrid, and alternative-fuel vehicles, as well as improved fuel economy of conventional vehicles. The Lightweight Materials Program at the Department of Energy's (DOE) Oak Ridge National Laboratory (ORNL) in Oak Ridge, TN, is aimed at developing new, cost-effective, environmentally sound materials and process technologies to enable the U.S. transportation industry to be more energy efficient through vehicle weight reduction. According to ORNL, 75% of a vehicle's energy consumption is directly related to factors associated with vehicle weight, and it identifies as critical the need to produce safe and cost-effective lightweight vehicles. The Partnership for a New Generation of Vehicles (PNGV) was established in 1993 by the U.S. government, Chrysler, Ford, and GM to achieve three goals: Explore technologies that reduce the time and cost to design and manufacture vehicles. Apply innovations, when commercially viable, to conventional vehicles. Develop a mid-size vehicle with a fuel efficiency of 2.94 L/100 km (80 mpg) while achieving improved recyclability and maintaining performance, utility, safety, and cost of ownership comparable to a mid-size vehicle of 1994. Through PNGV, the three automakers are pursuing a variety of advanced powertrain options, such as fuel cells and various hybrid combinations, to meet the fuel efficiency goal in a pre-production vehicle by 2004. According to the U.S. Council for Automotive Research (USCAR), one of the challenges in integrating these powertrains into vehicles is overcoming their increased weight and complexity as compared to conventional powertrains. To compensate for the increased weight, the weight of other vehicle components must be reduced by approximately 40% to meet the fuel efficiency targets. There has been much research involving material options for vehicle bodies, such as steel, aluminum, and a variety of composites. However, every component and part must be analyzed for potential weight reduction. While the PNGV partners have decades of experience with lightweight body component designs (the Chevrolet Corvette has been made of fiberglass body components since the early 1950s), the most difficult challenges are reducing the actual cost of materials and manufacturing the lightweight parts affordably. According to the DOE's Office of Transportation Technologies (OTT), current materials can reduce vehicle weight by more than 60%. However, OTT believes the cost of these materials, the capability to design with them, and the associated manufacturing processes presently are inadequate to produce safe, durable, recyclable, and affordable cars. The DOE announced in January that it is funding a $1.8 million project at Virginia Tech and Clemson University aimed at the development of low-cost carbon fiber for use in making lightweight automotive parts. The approach to reducing cost is to develop a new polymer (or plastic) to serve as a precursor for the carbon fiber. The new polymer would have to be processed more cheaply than existing polymers and contain a higher percentage of carbon in the final fiber. Carbon fibers are currently produced through a process called pyrolysis, in which a precursor material such as tar-like pitch is chemically changed by heating and subsequently pre-tensioned, or stretched, to obtain the desired properties. The fibers are then ready to be made into a carbon-fiber composite. Currently, carbon fiber suitable for automotive use costs around $8 per pound. The research team hopes to develop a carbon fiber that can be produced for less than $5 per pound. Designers have moved away from plastics as just a direct replacement material, and have begun integrating plastics at the design stage to meet weight reduction requirements while improving safety, performance, corrosion resistance, and fuel economy; exploring new styling potentials; and reducing maintenance. Following are the more innovative examples of how plastics are changing, and have changed, the design of the automobile. Exterior
Substituting a material with another is often a "copy and paste" of the previous solution. In the past, some thermoplastic body panels failed or were not as successful as expected because the characteristics of thermoplastics were not taken into consideration initially. Recent successes owe to the fact that the unique characteristics of the new materials were considered during the early stages of development. Plastic body panels are more resistant to impact damage than metal panels. The three most common plastic systems used for body panels are sheet molding compound (SMC), a thermoset polyester sheet; reaction injection molding (RIM), a thermoset system in which urethane resin is injected into a mold; and thermoplastic systems, including thermoplastic polyolefins (TPO). All three systems use plastics reinforced with glass fiber to add rigidity and structural support. The all-new Mercedes-Benz CL500 is over 227 kg (500 lb) lighter than its predecessor due to a variety of weight-saving materials such as aluminum, composites, and magnesium. The trunk lid is manufactured from a special polyamide blend, a thermoplastic with excellent elasticity. The new material allowed engineers to build the telephone and Tele Aid (Mercedes' automatic call system with GPS) antennae into the lid, a choice that would not have been available with a metal lid because of reception interference. At the other end of the vehicle, the 2000 Ford Focus has a plastic/metal composite grille opening reinforcement (GOR). The structural body component is produced using patented hybrid technology devised and developed by Bayer AG and is the result of a collaborative effort with Ford, Visteon Automotive Systems, and Misslbeck. The original concept was for the Focus' GOR to be made of more than 10 welded metal stampings. However, the manufacturing tolerance stack-up of the proposed part exceeded accepted limits. Manufactured from Bayer's 30% glass-filled polyamide, Durenthan, and profiled steel plate, the plastic/metal composite GOR is about 40% lighter than if it had been made entirely of metal. The GOR also provided improved part integration and consolidation, having 26 connections for 15 mating components. Bayer's hybrid technology links the metal and plastic by combining them into one component. The GOR consists of two metal stampings of 220 bake-hardened mild steel with a nominal thickness of 0.5 mm (0.02 in) and heat-stabilized polyamide 6 resin with a nominal thickness of 2.5 mm (0.1 in). The metal stampings are placed in a mold and the resin flows into and around them, mechanically locking to the metal and forming a single integrated unit. The component part maintains dimensional stability after being e-coated and painted. Engineers from Plastic Omnium Auto Exteriors theorize that automobile hoods will be very different in the future-a smaller, removable part with no hinges. Value analysis shows that the opening functionality is very expensive, considering the number of times the hood is opened in a vehicle's life. Given recent advances toward 160,000 km (100,000 mi) distances before major engine tune-up, the value of a highly engineered hinged hood becomes questionable. A painted off-line solution can be realized with a skin in mineral-filled PP and a structure with glass-filled PP. To paint the hood on-line, a hybrid solution can be adopted with the skin in a polyamide/polyphenylene ether (PPE) alloy and a structure in SMC, Plastic Omnium has found. Owens Corning, Bayer, and SIA Adhesives supplied the materials that Cambridge Industries molded for the 2001 Chevy Silverado composite pickup box. The box's outer panels and outer tailgate are made of reinforced reaction injection molded (RRIM) materials, chiefly polyurea with mica filler. The outer panels bolt or snap on for easy removal, repair, or replacement with minimal downtime. The one-piece inner panel and the inside of the tailgate are formed by a high-density, structural reaction injection molding (HD-SRIM) process and consist of Bayer's Baydur 425 internal mold release (IMR) polyurethane system. The Baydur system is combined with various reinforcements to make a structural composite, including both preformable and nonpreformable glass-fiber mats, as well as directed chopped glass-fiber preforms. Scratches on the inside of the box or tailgate can be polished out with a silicone cleanser. The new box reduced the weight of the truck by 22.7 kg (50 lb), with the tailgate alone being 6.8 kg (15 lb) lighter than the current steel tailgate. The 2001 Explorer Sport Trac is Ford's first truck to include an SMC composite box. Molded by The Budd Company with glass fibers from Owens Corning, the material was developed specifically for light trucks. It is a vinyl ester with random glass fibers that produces a part 20% lighter than the traditional steel pickup box. Owens Corning predicts the use of composites for pickup truck boxes to grow from zero today to more than 30,000 t (33,000 ton) annually within the next five years. Cambridge Industries is supplying an SMC tri-door rear closure system (liftgate and cargo doors) on the 2000 Ford Excursion SUV. The SMC system is comprised of inner and outer panels bonded with epoxy adhesive. It allowed for design flexibility such as molded-in retention features for attachment of interior trim components, hinge mounting locating points, and metal reinforcements. Several metal components were eliminated early during product design, such as reinforcements required for the door latch handle attachment. The material exceeds the temperature range requirements in the e-coat paint ovens at Ford's Kentucky Truck Plant, with the tri-door system being 15% lighter than a comparable system made from sheet metal. Tooling costs for the composite system were approximately 75% less than the costs associated with steel doors. Chrysler worked with DuPont (alloy development), A. Schulman (color development), and Build-A-Mold (tooling) to design the injection-molded exterior fascia of the 2000 Dodge Neon. The fascia is made of Surlyn Reflection Series alloy, a DuPont molded-in-color supergloss for exterior trim applications. The new supergloss product is an engineered alloy of ionomer and polyamide resins, resulting in improved colorability and toughness from the ionomer, and scratch resistance from polyamide. Material development was focused on conventional injection-molding processes. However, co-injection molding technology and sheet thermoforming technology and processes are being explored. The DaimlerChrysler Smart micro compact car sold in Europe features interchangeable molded-in color body panels. The panels are supplied by Dynamit Nobel and molded from GE Plastics' Xenoy, a thermoplastic alloy blend of polybutylene terephthalate (PBT) and PC resins. The amorphous PC provides impact resistance and toughness while the crystalline PBT structure provides enhanced chemical resistance and thermal stability to -40°C (-40°F). The functionality of the panels include high impact strength for dent resistance, reduced fuel consumption due to a 50% weight reduction, and inherent corrosion resistance. The alloy blend is characterized by its chemical resistance, a high temperature dimensional stability up to 140°C (284°F), UV resistance, good lubricity, and color retention. The panels offer more than 7 colors to choose from with clearcoat provided by the molder, eliminating the paint shop step from the vehicle's production. Download 0.62 Mb. Share with your friends:
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