Material Witness - composite materials for Chinese car

Automotive Industries,  June, 1999  by Gerry Kobe

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The plastic-bodied Paradigm car may prove that designing for the material makes its own economic and engineering case.

When Michael Van Steenburg was a student at Texas A&M, he spent one Christmas break working free of charge for a firm in Austin that was building a composite-bodied, mid-engine sports car. By the end of the break, the owner of the company fired his mold makers and engineers and put Van Steenburg in charge of the whole project.

From these humble beginnings, Van Steenburg is now founder and CEO of San Antonio-based Automotive Design and Composites Ltd., and is in charge of all the development work on the Paradigm car, an all-plastic vehicle funded by Chinese investors. Aimed at developing markets, the Paradigm will begin production in the first quarter of 2000.

"I started thinking about the things they do in engineering school that most students just look at as games," he says. "Things like building a bridge out of spaghetti may seem pointless at the time, but it tells you that you can design a structure with any material providing you design for the material."

Van Steenburg let cost be the primary driver for his choice of materials and process for Paradigm, leading him to precolored thermoplastic body panels and thermoforming technology.

"Thermoforming this type of material has been done in other industries for years," says Tony Bernardo, automotive business director for material supplier BASF's plastic materials group. "The Paradigm body is actually a co-extruded three4ayer sheet with an acrylic cap for scratch resistance and high gloss. Beneath that there is a layer of our Luran S, an ASA plastic that provides heat resistance and weatherability. And on the bottom is a layer of Terluran, an ABS formulation that is there for structure."

The resulting body panels fall short of a true Class-A surface but are more than acceptable for their intended emerging nations sales target. Bernardo says BASF also has a paintless film material that could be applied to Paradigm's panels in the molding process to make the finish on par with a painted surface and therefore acceptable to the U.S. market.

Equally as exotic as Paradigm's body panels is a newly revised pultruded plastic chassis that is made using a fire-retardant, Dow-supplied vinylester resin with reinforcing fibers from BTI.

"Our current chassis is in its fourth iteration," Van Steenburg says. "Initially we molded a chassis in the conventional way using stitch-bonded fiberglass. It weighed 384 pounds and came in at a cost of just over $1,300. I wasn't satisfied with that, so we looked at other technologies and we started exploring pultrusions. Ultimately, we came up with a pultruded vinylester chassis weighing just 80 pounds, at a cost of just $600."

Pultrusions have a much better fiber-to-resin ratio, making them both stronger and lighter. A pultruded section is actually made under pressure by pulling fibers through a six-foot die. The fibers are compressed tightly at the same time they are saturated with resin, and are fully cured by the time they come out of the die. The pultrusions are made at a rate of 65 inches per minute with an amazing 75,000-psi tensile strength. A typical plastic frame member made with this process has twice the strength of steel, and one-fourth the weight, Van Steenburg says.

Low cost drove the choice of materials, which in turn drove the manufacturing process. Van Steenburg claims all of the tooling for bob the Paradigm chassis and body cost a mere $100,000. He says that means the manufactured cost on each car will dip as low as $6,500 when production volumes reach just 30,000 units. Additionally, Van Steenburg has tried to engineer the scrap on the vehicle to compliment the percentage of re-grind material that can be put into the basic resin. In that way, any scrap generated in the process of building the car can be ground up and reused, making the scrap rote virtually zero.

With a plastic-intensive interior and even plastic chassis components, Paradigm is plowing new ground for automotive use of composites. But as Van Steenburg admits, that project has been in the works for two years. The really cutting-edge stuff is yet to come.

COPYRIGHT 1999 Cahners Publishing Company
COPYRIGHT 2000 Gale Group