Automakers are striving to achieve better fuel efficiency, in part to address upcoming government regulations that place stringent greenhouse gas emissions requirements on vehicles. Improved fuel economy is also a compelling selling point for auto dealers, who can appeal to prospective customers’ environmental concerns as well as their wallets by emphasizing better mpg. These factors contribute to why the trend for more plastic in automotive designs will continue.
Today’s average light vehicle contains 332 lb (150 kg) of plastics and composites, 8.3% of its total weight, according to the American Chemistry Council. Plastic is a viable alternative because it can provide considerable weight savings—in some cases, more than 40%—compared to metals such as aluminum while providing the necessary strength and support.
Plastic has historically created other advantages. The use of plastic in automotive body exterior parts allows manufacturers to expand modular assembly practices, reduce production costs, improve energy management, achieve better dent resistance, and use advanced, flexible styling techniques for sleeker, more aerodynamic exteriors.
Traditionally, acrylic has been only used in transparent applications, such as head and taillights. However, the recent use of opaque acrylic has expanded areas in which acrylic is used on a vehicle to include pillars, spoilers, roof and window trim, quarter and body panels, emblems and logos, mirror shells, and lighting lens wraps. Integrating acrylic into these “nontraditional” parts can lead to a number of manufacturing and aesthetic advantages.
First of all, acrylic is a harder material than polycarbonate, so it is more difficult to scratch. If a nick does occur, acrylic has such a deep color and robust, high-gloss surface that minor scratches can be easily polished away. Acrylic’s inherent weather resistance allows it to maintain its appearance throughout a car’s expected life cycle.
Another advantage of acrylic is that it can offer variations in finishes from high gloss to matte, as well as colors. These attributes eliminate the need for a coating, reducing manufacturing costs and eliminating VOC emissions related to the coating process. Not only does this speed production, the lack of paints and coatings allow acrylic to be easily recycled.
In addition, acrylic has a reliable and consistent part appearance out of the mold, which lowers scrap rates, and its light weight can also reduce overall parts count in a vehicle. Proper design is critical, however, for the benefits of acrylic to be realized.
Acrylic must be attached and assembled differently than metal. There must be a matched fit, including proper placement of locating holes. Attachment strategies that firmly hold the part in place by using fastening systems that stabilize the part without applying stress to the acrylic component must be properly implemented as well. Typical fastening systems used with acrylic involve the use of plastic grommets that allow the piece to float securely in place.
A new heat-reflecting acrylic polymer that reflects the sun’s infrared (IR) radiation is expanding the areas in which acrylic can be used in automotive designs. The acrylic can reduce heat buildup by as much as 15 to 20% on dark-colored plastic parts, reducing linear expansion by as much as 22%. Co-extruded plastic parts will have higher dimensional stability, reducing the possibility of warpage or discoloration as a result. Its high IR-reflective properties also can improve driver and passenger comfort by reducing heat buildup, making it a viable alternative for use as a vehicle roof covering or for roof trim applications.
Design engineers rely on plastics as an alternative to metal when developing new vehicles. And new technologies such as these will help ensure this trend continues.
Peter Colburn, Director of Business Development, Innovation & Technology for Evonik Cyro, wrote this article for SAE Magazines.