The American Iron and Steel Institute has not sat around and waited in recent years for inquiries from auto makers about using advanced steels in new applications.
AISI has been serving up ready-for-production concepts of auto bodies, suspensions and closure panels since the mid-1990s to show auto makers that steel isn't a material mired in 19th century technology as some perceive.
To drive its point home, AISI's latest project is a complete vehicle rather than just components. The Ultra Light Steel Auto Body-Advanced Vehicle Concept (ULSAB-AVC) features two virtual vehicles, a 2-door hatchback and a 4-door sedan, that AISI claims would receive a Five Star crash safety test rating and provide significant fuel efficiency improvements without costing more than comparable vehicles. “Through the ULSAB-AVC program, we are continuing our commitment to an aggressive steel strategy to advance breakthrough technologies in steel design,” says John Mayberry, AISI chairman and chief executive of Dofasco Inc.
Whether or not ULSAB-AVC sees high volume production is debatable, but there is no denying its comprehensive research and notable results. Evaluations for the 4-door sedan predict that it would achieve a fuel economy rating of 52 mpg (4.5L/100 km) with a gasoline powerplant and 68 mpg (3.5L/100 km) with a diesel engine. AISI says the current average for a midsize sedan is 26 mpg (9L/100 km). Vehicle mass for the gasoline/diesel 4-door sedan is 2,200-2,272 lbs. (1,000-1,032 kg). That's 1,100 lbs. (500 kg) less than the current average vehicle mass, AISI claims. Even the Partnership for a New Generation of Vehicles entries from the Big Three weigh more, save Daimler-Chrysler Corp.'s ESX3 (2,250 lbs./1,022 kg)) vs. the ULSAB-AVC 4-door sedan.
Unlike the PNGV models, reasonable pricing isn't sacrificed in AISI's program. Manufacturing cost/selling price for the 4-door sedan gasoline and diesel models is $9,500 and $10,200, respectively. The current industry average is $23,000, AISI research shows.
So how did AISI do it?
Completed at a cost of $10 million, the ULSAB-AVC program uses advanced high-strength steels for more than 80% of the body structure and for 60% of the closures. Based on multi-phase microstructures, AHSS present a significant amalgamation of strength and formability not available in conventional steels.
AISI also employs state-of-the-art manufacturing techniques to reduce mass and enhance performance. The 4-door sedan's body-in-white, for instance, is comprised of just 81 parts via considerable use of tailored blanks, tailored tubes, hydroforming and laser-welding joining technologies that permit parts integration. As a result, it weighs 480 lbs. (218 kg), or 17% less than the average benchmark, AISI claims. “It has a very clean architecture. At 81 parts, it's well below the traditional body structure you'll find right now, and it's well below the space frame structure that the aluminum industry is quoting to be very effective on part design,” Marcel van Schaik, AISI director-materials technologies tells Ward's.
The body side outer is made of a 5-piece tailored blank, which includes both high-strength and advanced-strength steels. “This is a major component in the ULSAB-AVC and a major contributor to reducing the part count — the fact that you are able to have the body side outer a tailor welded blank reduces the part count dramatically,” explains van Schaik.
AHSS and high-tech manufacturing is everywhere on the vehicles, which share 22% of components and have identical front-end architectures. “The front suspension is a double wishbone design, with both wishbones using AHSS tailored blanks,” says van Schaik. “Wheel, instrument panel beam, fuel tank, seat frames, bumper beams and closures all are steel. The closures (hood, doors, deck lid) incorporate high- and advanced high-strength steels, as well as tailor welded blanks and tubular hydroformed components.”
Of the numerous subsystems, the modular fixed-seat concept is perhaps the most interesting. The entire seat structure and trim components are attached to a single seat cross member prior to vehicle installation. The cross member braces the rocker panels — playing an important role in the event of side impact. Crashworthiness also is enhanced by the engine/suspension subframe module, which eliminates the front shock towers for mass reduction. DP steel is used for the module's rails and pyramid-shaped crash packs. Crash loads are transmitted from the pyramids to the rocker and A-pillar. Hydro-formed DP steel longitudinal rails are the spinal column for the entire underbody as well as key crash energy management structures.
