Composites Improve Surface Quality

Several composite suppliers have developed new technologies that may spur a significant shift in the auto industry away from steel body panels to composite body panels.

The innovative methods eliminate surface quality deficiencies on composite panels that often steer auto makers toward steel or aluminum, even though composites are lighter, corrosion resistant, offer more design freedom and lower tooling costs.

The composite industry's biggest hurdle is a deficiency called “paint pops,” which are craters or bubbles that appear on the surface. Paint pops are caused by air trapped in the composite part's substrate working its way to the surface at the assembly plant during the bake process used to dry paint when high temperatures increase vapor pressures.

Thyssen Krupp Budd has developed a new “Tough Class A” sheet molded composite (SMC) because 70% of paint pops are caused by microcracks — a minute fracture invisible to the naked eye — inflicted during handling or delivery.

The company evaluated resins, additives, catalysts and fillers to make the substrate more robust. It developed a new resin that resulted in a 69% increase in toughness. Thyssen Krupp Budd debuted the new SMC on several Ford Motor Co. products since June and recently completed two prototypes with General Motors Corp.

Ford also is at the forefront of another SMC technology called ultra-violet (UV) cured sealer developed by Meridian Automotive Systems and BASF. The UV cured sealer, which will be used on the Lincoln Aviator front fender when the SUV debuts this fall, replaces the traditional primer as the first coat of a multi-layer coating process used for composites. Featuring a newly created polymer makeup, the sealer is applied to the composite part. UV lights emitting 900 degrees F (482 degrees C) are used to complete, almost instantly, 80% of the curing process. A low-heat oven is used to finish curing the sealer. Traditional processes use an oven for the entire curing procedure. Slow baking leaves the composite more susceptible to cracking.

“With these solutions to address this issue, there will be few limitations for composite use in the automotive industry,” says Dave White, Automotive Composites Alliance chairman and sales director for Meridian Automotive.

Meanwhile, in a reversal of industry trends, Ford is considering switching the composite hood on its current Mustang to aluminum when the next-generation pony car debuts in 2004. The materials swap largely is based on Mustang's production site, say industry insiders.

Mustang presently is built at Ford's assembly plant in Dearborn, MI. But the forthcoming version will be produced at the Ford/Mazda Motor Corp. AutoAlliance Inc. joint venture plant in Flat Rock, MI. AutoAlliance is inexperienced working with SMC panels and has on-site stamping that the company wants to utilize fully, insiders say. Adding Mustang stampings, a source says, would create enough work for a 7-day production schedule. Composite parts typically are molded by suppliers off-site.

Contrary to prevailing trends, the switch to aluminum would add weight to the popular sports car. A typical SMC hood weighs around 15 lbs. (6.8 kg) whereas a finished aluminum hood weighs about 20 lbs. (9.1 kg), according to Ducker Research.

However, the switch from SMC to aluminum might not include all Mustang models. The Mach 1 and SVT Cobra (Terminator) editions began using the Tough Class A SMC recently; the higher-volume GT model may switch to aluminum.