Making a concept composite floor structure for sedans is one thing, but the engineers and companies involved with the Automotive Composites Consortium also wanted to make sure the concept could fit into existing auto-manufacturing lines.
“Our goal is to develop manufacturing methodologies that each [automaker] would then take forward for their use,” said Libby Berger, a staff researcher in General Motors's research and development center.
So as part of the nearly six-year project to develop a structural composite automotive underbody, the members of the consortium also developed a process to attach it to a steel body structure.
Berger discussed the underbody project during the Society of Plastics Engineers Thermoset TopCon conference Jan. 24-25 in San Antonio. Detroit-based General Motors Co., Ford Motor Co. and Chrysler Group LLC were all part of the cooperative investigation, along with Continental Structural Plastics Inc., Multimatic Inc. and the Department of Energy's Oak Ridge, Tenn., laboratory, as part of the U.S. Council for Automotive Research program to investigate new technology.
The consortium and USCAR have cooperated on other auto-production concept projects in the past, including lightweight vehicle bodies and recycling initiatives. With the composite underbody, the group focused on one part of the body, rather than the entire vehicle — the center flooring structure of a current-model large sedan.
The current center underbody, or floor pan, is made of 14-16 individual steel components. ACC focused on replacing that with one composite part that could be produced in a 21/2-minute cycle. Berger admitted the team did not quite hit the cycle target, but the final component reduced weight by more than 20 pounds and still met extensive crash and structure requirements.
The team looked at a variety of processes and materials for the composite part before landing on a multilayer, sheet molding compound fabric, using long-glass-fiber reinforcement for most of the part and a chopped structural SMC for reinforcing ribs.
Coming up with the material and the design was only part of the work, though. The researchers had to determine how to install the system in an existing auto assembly line, which normally relies on spot welding to attach the underbody to the frame.
Their solution was to attach two narrow strips of steel to the composite with adhesives, then weld the steel connections to the frame, Berger said.
There is no guarantee that the concept will ever make it into production, although there is interest. The coalition focuses on developing projects to a pre-production state. It is then up to individual automakers to decide whether to take the project further. If the concept does move forward, though, Berger warned it could take three to five more years of development.
“If you're going to develop a new material, you've got to plan on it taking a long time,” she warned. “At this point, the technology has gone back to the [carmakers] and it's up to them to take it further.”