Cost-conscious carmakers keep on looking hard for inexpensive manufacturing processes that will make plastics practical for widespread structural use. A typical car body contains about 200 parts. Composites could cut that to 10 parts, researchers believe today. But hurdles remain, including the relatively long cycle times for plastics, questions on plastics' crash-energy management characteristics, and recycling considerations.
One process being developed at Ford Motor Co. - liquid composite molding - is stirring opitimism. The process is aimed at replacing the more conventional and widely used sheet molding compound process in making large parts. Development is being done with input from the Big Three automakers, resin and glass suppliers, and other.
Bob Mull, director of the Consortium called the partnership for a new generation of vehicles program at Ford, calls the work critical to the achievement of a car that gets 80 miles per gallon. To reach that fuel economy target, vehicle weight must be reduced by as much as 40 percent, he said.
"Liquid composite molding uses low molding pressure and precisely oriented continous reinforcing fibers that allow for larger, higher performance structures to be manufactured than can be made with the sheet molding process," said Alan Taub, manager of material science at the Ford Reasearch Laboraty in Dearborn, Mich. Ford uses about 85 million pounds of composites annually, 60 million pounds of which are SMC.
"Liquid composite molding is a high-tech method we hope to have perfected for high volume by the year 2000. It will be a rapid, high-performance, low-cost technique for production of large, lightweight, integrated body structures," Taub said.
He said automation in making performs is key. Another important element is for continuous fibers to be oriented as cost-effectively as possible.
The automation of perform making has been a chief goal of the composites consortium since its founding in 1988 as the first of the Big Three's 13 non-competitive consortia.
Taub said researchers are looking for cycle times of two to four minutes per part. Today, in comparison, large structrual components are limited to rates of about 30 per day, he said.
The molding pressures involved in liquid composite molding range from 100-500 pounds per square inch, compared with 1,500-3,000 psi for SMC. Savings are anticipated from reduced tooling costs, increased parts integration and faster production with fewer machines.
"In volumes below 100,000, in fact, liquid composite molding is projected to be cost-competitive with steel on a fully accounted basis," said Carl Johnson, composite group leader in the materials science department.
Johnson said he expects to use the process with glass or graphite fibers and that it could allow the vehicle body structure to be molded in as few as five mogor components.
A major target is the use of the composites for primary structural components such as cross members, which support the transimission and tie together the vehicle's frame rails. The cross member is a convenient research target because it is a simple bolt-on part that during testing should have