U.S. automaker General Motors (GM, Detroit, Mich.) got lots of kudos and positive press when it debuted the new Volt concept electric car in Detroit at the North American International Auto Show in early January. As well it should. The vehicle marks General Motors’ return to the electric vehicle market since the much-maligned demise in 2003 of the EV1, the company’s previous foray into battery-powered motoring.
The question now is whether this vehicle will morph from concept to commercial production. GM, predictably, was coy about the production future of the Volt, and much speculation centered on the robustness of the battery technology the vehicle would require to travel the predicted 40 miles per charge. Another consideration is the production viability of the hood and door panels. The panels feature an unusual compression-molded composite sandwich panel: a core of Azdel Superlite low-density glass mat thermoplastic (LD-GMT), developed by Azdel Inc. (Forest, Va.), with a matrix of GE Plastics’ (Pittsfield, Mass.) Noryl PPX, a thermoplastic olefin that alloys polyphenylene ether (PPE) and polypropylene (PP), to create a resin with 30 to 50 percent higher modulus than thermoplastic polyolefins (TPOs) currently in use. Panel facesheets feature continuous glass fiber-reinforced PP. Dubbed HPPC, the combination reportedly gives the parts sufficient elongation, stiffness and high-temperature resistance for exterior body applications. The components on the display, however, were developed for offline painting. If and when the Volt goes into production, the hood and doors would be made from an HPPC sandwich designed for online painting, consisting of a Superlite core with a matrix of Valox iQ resin and fiber-reinforced skins made with Azdel’s Xenoy iQ resin — both resins derived from 85 percent post-consumer waste reclaimed from 20-oz bottles made of PET (polyethylene terephthalate).
Derek Buckmaster, market director for body panels at GE Plastics, says HPPC was used in the doors and hood because they are less challenging than fenders, for example, from a contour and dimensional perspective. He adds that the Volt uses 110 lb/50 kg of thermoplastics, including not only the hood/door composites but unreinforced materials in the rear deck lid, roof and fenders as well. All told, this saves about 60 lb/27.2 kg, compared to existing cars of comparable size, and represents a new level of vehicle recyclability.
The challenge, Buckmaster notes, is cycle time. The best time clocked so far on HPPC parts is just under four minutes, using RocTool’s (Le Bourget du Lac, France) Cage System inductive mold-heating technology. Cost requirements for a production vehicle, however, will demand a two-minute cycle. “We continue to be optimistic,” says Buckmaster, noting that the feedback from HPPC’s debut on the Volt has been encouraging. (HPPC and RocTool’s inductive heating are profiled in this issue’s “Inside Manufacturing” article; see "Learn more," at right).
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Low-density GMT-cored sandwich construction and novel inductive mold-heating strategy are a viable option for horizontal body panels.