The newest member of GM's family of sheet molding composites (SMC) can take what's dished out in the worst neighborhoods, despite a lean build without a trace of flab. The cryptically named SMC 3374 (after the technical spec that defined its properties) is stiff enough to work as a structural part - even in the heat-intensive environment of the engine compartment - but still shaves off critical pounds.
This innovative product from GM R&D's Materials and Process
Laboratory reduces the weight and number of parts in a car.
The upshot? Better mileage, increased durability, and the
option of added features for car buyers. No, using SMC doesn't
make much difference in the driving experience, but it does
free engineers and designers to use the weight- and parts-savings
elsewhere. Lightening a Buick LeSabre hood by 2 pounds may
not sounds like much, but "it allows the engineer to use that
2 pounds wisely somewhere the consumer will see it," says
Hamid Kia, GM R&D
Senior Staff Research Engineer.
Dbl-Lite SMC, an older cousin of SMC 3374, helped cut 41 pounds from the 1997 Chevrolet Corvette, which reduced the bulk of the car's doors, hoods and wheel housings, and allowed designers to beef up other components. After this success, the platform group told the researchers they'd like to use more SMC, but needed a material that could handle the demanding environment around the engine.
Kia and GM R&D Staff Scientist
Harry
Mitchell spent the next two years refining the recipe
for SMC, tinkering with the known properties of all the ingredients
to come up with a formula that would have sufficient flexure
and tensile strength to resist the heat. "We had some idea
of the keys to turn and changes to make, but it's not a straightforward
process," says Mitchell.
That wasn't the only challenge. Like scaling up a recipe from family-sized to family reunion-sized, working out the formulation for production took a lot of adjustment. "It's fairly easy to make the formulation in the lab," says Kia, "but to make it so that any supplier in any factory could reproduce it is more difficult."
A piece of SMC 3374 is rigid and hard, like old-fashioned Bakelite plastic, but it doesn't shatter and splinter. The plastic itself is tougher than Bakelite, and a layer of embedded glass fibers insures that it stays together even after a sharp impact. "Where it breaks, you see the glass fibers," says Kia. "You'd have to bend it back and forth several times to really pull it apart."
Although plastic body parts have become commonplace, most still require a steel inner frame and fasteners or adhesives to be stiff enough to use as a structural part. But not SMC 3374 - it can stand alone.
The new SMC replaced steel in the front-end support of the 2000 Buick LeSabre, 2000 Pontiac Bonneville, and 2001 Oldsmobile Aurora with significant savings. Using SMC for the part, which supports the headlights and spans the front of the radiator, reduced the weight about 25 percent, according to Jim Schoenow of GM Car Group's engineering and development operations in Flint.
GM plans to use almost 2 million pounds of SMC 3374 in its 2000 and 2001 vehicles, and engineers throughout the company are talking about new ways to use it in various brands. But the next big thing may be an addition to the SMC family: a cosmetic-grade SMC good-looking enough to appear next to steel on the vehicle's exterior.
By Diane Kightlinger
