DETROIT, Dec. 15, 2010 - A joint project of the United States Automotive Materials Partnership LLC (USAMP) and Auto/Steel Partnership (A/SP) using structural optimization techniques within a car’s passenger compartment has shown good potential for no-compromise vehicle lightweighting.
USAMP, a subsidiary of the United States Council for Automotive Research LLC – whose members are Chrysler Group LLC, Ford Motor Co. and General Motors Co. and A/SP – made use of computer modeling to validate a potential mass savings of 15 to 20 percent in a preproduction sedan when advanced high-strength steels and design variations were selectively applied.
The Future Generation Passenger Compartment – Validation project utilized advanced high-strength steel for parts typically made of conventional steel for the passenger compartment of a production-viable, four-door, five-passenger sedan. By applying new load paths (in this case, transverse tubes that directly absorb side impact forces) within the front seat, the results showed that using high-strength steel lowered mass and weight considerably without compromising the passenger compartment’s structural integrity or crashworthiness. Manufacturing feasibility evaluations also supported the design and use of the high-strength steels as acceptable for high-volume manufacturing.
Joe Polewarczyk, project co-chair and lead engineer in General Motors Advanced Technology development, said the project showed some real potential gains while proving out the process as well. “Originally, we hoped to build a prototype vehicle, but due to costs, we focused our efforts on a pre-production model of a production sedan, which already had passed all the rigor of production-vehicle tests.”
The project’s virtual process was based on simultaneously optimizing geometry, grade and gauge – or shape, steel quality and steel thickness – to reduce mass. Optimization techniques were used to determine the best structural load paths and section shapes and the best material grades and gauges for the new geometries. The study also evaluated the effects of continuous joining.
The results included adding two new load paths, while incorporating many grade increases and gauge decreases. In addition, the new design met structural criteria of the baseline, even at various seat locations, and achieved further improvement with continuous joining, resulting in a mass reduction – and corresponding weight reduction – of approximately 15 to 20 percent.
Starting at a baseline mass of 264.7 kg or about 582 pounds, the USAMP – A/SP optimized design saved 39.8 kg or nearly 88 pounds, and with maximum adhesive (spot weld with adhesive bond versus spot weld with laser welds), the mass savings increased to 54.7 kg or approximately 120 pounds. These kinds of savings would have a positive impact on improving a vehicle’s fuel economy.
“In addition, we achieved cost parity,” Polewarczyk added. “We used a higher grade steel, but we used less, so in essence, it was cost neutral.”
Although the project used advanced high-strength steel, Polewarczyk said other lightweight materials such as aluminum or carbon fiber also could be tested. However, those two, as examples, would likely be more costly to produce and have different forming and joining requirements.
With this validation project completed, team members are sharing the project’s results within their companies, allowing each USCAR OEM to determine if, how and when they would use the design process for production.
“We need to increase public awareness of the process and get the design engineers to embrace it in order to harness its full capability, particularly when results show some real potential gains,” Polewarczyk said. “Plus, in this case, every little bit of weight and mass savings helps.”
Founded in 1992, USCAR is the collaborative automotive technology organization for Chrysler Group LLC, Ford Motor Company and General Motors Company. The goal of USCAR is to further strengthen the technology base of the domestic auto industry through cooperative research and development. For more information, visit USCAR’s website at www.uscar.org.
About Auto/Steel Partnership
Formed in 1987, the Auto/Steel Partnership is a consortium of the Steel Market Development Institute’s Automotive Applications Council, Chrysler Group LLC, Ford Motor Co. and General Motors Co. that leverages the resources of the automotive and steel industries to pursue research, validation and education that helps automakers enhance vehicle safety and fuel economy, and improve design and manufacturing. For more news, visit the Auto/Steel Partnership’s website at www.a-sp.org.
Deanna LorinczSenior Director, CommunicationsSteel Market Development InstituteTel: 248.945.4763