David S. Hotter
In the last issue, we looked at underhood applications for advanced plastics in the automotive industry. Be assured that engineers aren’t resting on their laurels when it comes to finding new applications around cars. Automotive interiors and exteriors are two areas receiving more attention lately.
Already the Big Three are talking about using polymers for windows, truck beds, and body work. By successfully molding large, colored body panels, for example, Chrysler hopes to eliminate the most-expensive and time-consuming step in automobile production — painting. The automaker estimates that eliminating painting, along with complex forming and assembly steps such as stamping and welding, will cut the cost of a car in half.
According to a survey conducted last year by DuPont and the Society of Automotive Engineers, reducing development and manufacturing cost is the number one challenge among automotive engineers. And almost half of the respondents identified cost reduction/cost targeting as the industry’s greatest challenge.
Plastics will continue to help engineers push the envelope for more advanced automotive designs, with lower tooling costs than metalworking processes and design flexibilities such as molding complex-shaped fuel tanks that fill the irregularly shaped spaces left behind in chassis designs.
Slim and trim
Automotive exteriors also place demands on plastic materials with wide temperature ranges, corrosive environments, and UV exposure. A recent trend in the industry is to use colored resins and reduce or eliminate paint from exterior components.
GE Plastics, Pittsfield, Mass., offers weatherable Geloy acrylic-styrene-acrylonitrile (ASA) and Xenoy polycarbonate (PC)/polybutylene terephthalate (PBT) resins for molded-in color in place of paint. GE’s conductive Noryl GTX nylon/polyphenylene oxide (PPO) resin eliminates primer on painted components. By using plastics, manufacturers cut production costs by eliminating or reducing paint consumption. Paint reduction, in turn, reduces volatile emissions and makes parts easier to recycle.
Engineers typically specify ASA and PC/PBT resins for exterior components such as cowl-vent grilles, front grilles, mirror housings, pillars, tail-lamp housings, and door handles. These resins resist impact loads, high temperatures, and scratches, remain dimensionally stable, and absorb little moisture. Geloy ASA resins come in both high and low-gloss grades.
Color consistency is critical to resin selection for exterior components. “Trim pieces made of our weatherable resins maintain their color, despite exposure to all types of weather conditions, to maintain consistency with other exterior components on the vehicle,” says Venkatakrishnan Umamaheswaran, industry manager for exterior components at GE Plastics.
In the past, painting exterior components using electrostatics required conductive primer. Now, conductive carbon fibrils in the base resin impart electrical conductivity to plastic parts. Engineers use fewer conductive graphite fibrils to deliver the same amount of conductivity as traditional carbon powder and carbon fiber additives. This improves processibility and physical and mechanical properties such as impact resistance. Fibrils technology was developed by Hyperion Catalysis International, Cambridge, Mass.
“Conductive materials let us eliminate conductive primers and improve the transfer efficiency of spray painting,” explains Umamaheswaran. For molders, this means faster cycle times, using less paint, better finish, and reduced emissions. “In many areas, the Environmental Protection Agency is restricting how much volatile organic compounds (VOCs) a plant can release into the air,” he adds. “Reducing the amount of paint a facility uses could actually let a manufacturer increase production capacity and still stay below the emissions cap.”
Advanced materials also appear on body trim and molding. Aftermarket parts maker Truck & Auto Imaging designs running boards and front air dams (or down spoilers) using the Bayflex 110-50 polyurethane reaction-injection molded (RIM) system from Bayer Corp., Pittsburgh. The material handles the hazards of the road while still letting the manufacturer take advantage of flexible designs and fast cycle times.
“We’ve launched a line of high-quality RIM running boards and spoilers that fill a void in aftermarket body accessories,” says Robert Zeffero, vice president of Truck & Auto Imaging. “Our polyurethane components match the quality level of original equipment better than products made from fiberglass and low-cost thermoformed materials.”
The Bayflex 110-50 polyurethane RIM system is a glass-fiber-reinforced solid elastomer that has rapid demold times, is durable when released from the mold, and exhibits favorable physical qualities. “The Bayflex RIM systems withstands impacts and both hot and cold extremes,” says Zeffero. “Finished products have high memory so that if they do absorb small impacts they bounce right back, plus they don’t crack or chip from road debris, and hold paint well. These qualities are critical, especially when designing components located close to the ground that are subject to a lot of wear and tear.”
Ford also designs body trim from thermoplastic polyurethanes for its Explorer, Windstar, and Ranger models. Supplied by BFGoodrich Specialty Chemicals, Cleveland, Estaloc 60155 resin was specifically developed for softer, yet demanding exterior trim applications requiring a paintable surface.
The material’s formulation lets molders fill and pack molds using lower pressures. This prevents parting-line flash, reduces cycle time, resists part sink out of the mold, and provides improved surface aesthetics. In addition, the resin has a lower specific gravity than conventional reinforced engineering thermoplastics, helping to reduce weight.
“The durability and lot-to-lot consistency of Estaloc 60155 have improved our process,” says Albert LaFlamme, vice president of manufacturing at Automotive Moulding Co., Warren, Mich. “The material’s wide processing window lets us set up machines to create shorter cycle time with less flash and part sink.”
Estaloc 59010 resin has moldability qualities that are less-prone to molded-in stress. Components made with it are more flexible, which makes them easier to assemble around vehicle contours. Engineers formulated the polyurethane compound with paintability in mind so that no adhesion promoter or primer is required.
In the driver’s seat
Look around the inside of a car and you’ll see many examples of plastic resins used for interior components such as instrument panels (IPs) and door trim. Automobile manufacturers have used plastic instrument panels for several years to consolidate multiple parts and also form complex geometries. However, there’s more to it than just choosing a resin, particularly when designing IPs for luxury vehicles that carry high consumer expectations.
Ford meets those high expectations associated with its Expedition and Navigator models using Magnum 344CC acrylonitrile-butadiene-styrene (ABS) resin from Dow Chemical Co., Midland, Mich. Engineers chose the material for its performance at high temperatures, versatility in molding different surface finishes, and resistance to scratches and marring.
“The original concept called for a single console component that would be appropriate for both vehicles with minimal modifications,” says Tom Feige, application development engineer for the Dow Automotive division of Dow Chemical. “Specifications only allowed minor cosmetic changes to upscale the IP for the Navigator, using the same tooling and material to minimize production costs.”
The consoles use the same grade of ABS resin in three different finishes: Molded-in color, soft-touch paint, and covered with vinyl and leather substrates. Workers apply wood-grain trim to the Navigator console as an accent to differentiate it from Expedition consoles.
IPs for the 1998 Chrysler Concorde and Dodge Intrepid sedans will be made of Noryl EM6100F, an impact-resistant PPO resin manufactured by GE Plastics. Chrysler teamed with molder Textron Automotive, Troy, Mich., to develop the soft, padded IPs. Once manufacturing and assembly requirements were set, GE Plastics customized a resin to meet the needs of both Chrysler and Dodge.
“Engineering resins increase customer satisfaction by outperforming lower-grade thermoplastics, which saves manufacturers money by avoiding warranty claims,” explains Robert Florence, IP industry manager at GE Plastics. “As temperatures vary, so does the stiffness of the IP. Lower-grade materials exhibit greater dimensional changes with temperature shifts which increase noise, vibration, and harshness levels, leading to warranty claims from annoyed car owners.”
Noryl resin also helps slash manufacturing costs because its heat resistance lets manufacturers mold thinner-walled parts that don’t require metals supports to eliminate warp. Noryl components also resist scuffing, provide tighter dimensional tolerances, and don’t need secondary operations such as surface treatments.
One of the challenges in molding interior trim components is matching the resin color with other interior parts. In response, M.A. Hanna Engineered Materials, Norcross, Ga., produces a Controlled Color Natural line of impact-modified polypropylene compounds. The polymers, natural-colored base resins, were developed in partnership with M.A. Hanna Color. The compounds’ natural hues don’t vary, giving engineers a more consistent, predictable blend with color concentrates. The product line also reduces production costs by eliminating the need to order and store expensive precolored resins.
“To produce interior trim components for one vehicle model, a molder must warehouse numerous polypropylene resins with the same additives mix, but in different colors,” says T. Michael McCormack, automotive industry manager at M.A. Hanna Engineered Materials. “Controlled Color Natural resins are so consistent that molders can add less-expensive color concentrates directly at the injection-molding machine.”
In automotive sun-visor applications, Controlled Color Natural compounds provide the heat deflection and tensile strength specified by the molder. In the past, molders used unfilled polypropylene that warped and twisted during extreme temperature changes. This warping sometimes caused the visor door to remain open and the mirror light on, which drained the car battery, and also pulled the visor away from the headliner.
Specially formulated Controlled Color Natural compounds meet heat-deflection, tensile-strength, and flexural-modulus specifications. They also let molders avoid expensive retooling that would have been necessary for using a material that required higher pressure and faster injection speeds than polypropylene. With color concentrates from M.A. Hanna, the molder meets part-to-part repeatability with a 100% color match, and reduces warehouse stock of precolored polypropylene resin.