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Resources - Features

Great Designs in Steel 2007 —
So Much Information, So Little Time

The all-day four-track program featured more than 38 technical presentations, many focusing on forming techniques and technologies used to turn advanced high-strength steels into automotive parts.

by Brad F. Kuvin, Editor

The Automotive Applications Committee (AAC) of the American Iron and Steel Institute (AISI) initiated Great Designs in Steel six years ago to assist automotive engineers in using advanced high-strength steel technologies for designing and building safe, affordable, fuel-efficient and environmentally responsible passenger cars, sport utility vehicles and light trucks. Back in 2002 at the first GreatDesigns event, a total of 13 presentations focused on the USLAB (ultra-light steel auto body) project, and just a few papers covered actual production applications, including hydroformed engine cradles and a laser-welded assembly for the Jeep Liberty. I’ve been to nearly all six editions of the seminar, and the evolution of this stellar technology-transfer event has been something to behold. Now boasting four concurrent tracks with discussion of actual applications for manufacturing advanced high-strength-steel (AHSS) parts,many of which focus on stamping, GDIS has become one of the most important events on the annual calendar of many automotive suppliers. Some of the topics covered at GDIS 2007, held March 7 in Livonia,MI:

  • Tailored Coils—A New Process to Further Expand Tailored Applications
  • AHSS Technology in the 2006 Honda Civic • CostModeling of TailoredWelded Blanks
  • Springback Control for Advanced High-Strength Steels
  • AHSS Application Guidelines
  • Steel Content of the Average North American Vehicle

All of the presentations—not just for 2007 but for every GDIS event since 2002—can be viewed online at www.autosteel.org.Here are highlights from just a few of them, to whet your appetites.

Mild Steel’s Disappearing Act

By the year 2015,AHSS will comprise more than 400 lb. per vehicle (up from 149 lb. in 2007) by growing at a rate of 14 percent per year. And, AHSS in the body structure will increase from 11 percent of body weight to 40 percent by 2015. These and other conclusions of AISI market research have been compiled by project consultant Dick Schultz, of DuckerWorldwide, which monitors material use in light vehicles for a variety of organizations, including the AAC. In 1975, Ducker reports that the average North American light vehicle contained 2180 lb. of mild steel. This total shrunk to 1748 lb. in 2007, and will dwindle to 1300 lb. by 2015. In all, says Schultz, 319 lb. of advanced and other high-strength steel, aluminumandmagnesium alloys, as well as plastics, will replace 478 lb. of mild steel, iron and other metal alloys, for a 33-percent metallic-material weight savings over the next eight years. Making this transition, he says, will present many challenges, particularly those related to the enabling technologies of stamping and welding. Schulz called out six specific 2007 vehicles and discussed their body and closure steel content: GMC Acadia, Daimler Chrysler M Class, Ford Expedition, Nissan Altima, Toyota Tundra and Honda CR-V. Among noteworthy findings: The CR-V’s body and closure steel comprises 28 percent dual-phase steel (590-MPa tensile strength), easily leading the way. Honda has been a regular participant in the GDIS proceedings, always proud to discuss its research efforts related to use of advanced high-strength steels, and the 2007 event included a talk by Mark Pafumi fromHonda R & DAmericas, Inc. Pafumi discussed the use of AHSS alloys in the 2006 Civic, which presented Honda engineers with the challenge of improving performance and controlling weight, even as the vehicle grew by 31 mm in overall length, 81 mm in wheelbase, 38 mm in width, and took on a larger engine. Compared to the 2005 model, the use of 590-MPa steel tripled with the 2006 model, and a full 50 percent of the body on the 2006 Civic is of high-strength steel, up from 32 percent in the previous model. Pafumi described several assemblies developed for the new Civic that utilize AHSS, including the front subframe, rear crossmember and the rear parcel tray, designed to control vibration input from the vehicle’s sound system that features a 360- W subwoofer. AHSS also helped the design team create a high-energy-absorbing structure, thanks to use of 590-MPa steel for all critical frame members. There’s also 590-MPa steel in tailor-welded blanks used in the dashboard lower assembly and front sideframe.

The 2006 Honda Civic (right) boasts improved performance and weight control thanks to increased use of high-strength steels. Compared to the 2005 model (left), the use of 590-MPa steel (in purple) tripled with the 2006 model, and a full 50 percent of the body on the 2006 Civic is of high-strength steel, up from 32 percent in the previous model.

 

A Lesson in Dual Phase from Mittal
A cost modeling study by the Tailored Steel Product Alliance shows that by using tailored blanks, the rail shown in this illustration— originally designed of 13 components— can be manufactured from just five components. Comparing costs for each design (to make left and right assemblies) showed the need for 562 spot welds with the 13-component baseline design, and 320 welds for this enhanced design with tailor-welded blanks.

Mittal Steel staff engineer Liang Huang reviewed for attendees four popular dual-phase steels—DP500,DP600, DP780 and DP980— and the typical automotive applications for each. He then focused on the FederalMotorVehicle Safety Standard FMVSS 216, designed to reduce deaths and serious injuries when a vehicle roof crushes into the occupant compartment during rollover crashes.AHSS in the roof structure improves energy absorption in a front crash and improves occupant protection in a side impact. Key structural components studied atMittal included the A- and C-pillars, front and rear header, roof rail, cowl side inner and the roof bow. A newly developed roof-structure design presented by Huang calls for a rollformed roof rail, rear header and roof bow, and the addition of local stiffener beads to a stamped bracket, all of dual-phase alloys. Huang’s team, after verifying manufacturability of critical components using incremental finite-elementanalysis software, found that DP780, TRIP780, DP980 and M900 all are good candidates for key roof-strength components.

 

Analyzing Costs for Stamping Tailored Blanks

In January 2006 several manufacturers of tailored steel blanks joined with a couple of equipment suppliers and six steel companies to form the Tailored Steel Product Alliance (TSPA). Its goals include the promotion of tailored steel products in automotive applications and development of a cost model for comparing conventional stamping with laser-welded blanks. GDIS attendees heard all about the cost-modeling project, which seeks to look at three case studies in depth: a rail, a bodyside inner and a door inner. Processes studied include blanking, stamping, rollforming and assembly, including welding. The baseline rail design featured 13 components, whereas use of laser-welded blanksminimized the rail design down to three tailored blanks and two additional components —13 pieces whittled down to five. Comparing costs for each design (tomake left and right assemblies) showed the need for 562 spotweldswith the baseline design and 320 welds for the enhanced design with tailor-welded blanks. Total unit cost (at a production rate of 275,000 per year) dropped from $127 for the baseline to $105 for the enhanced design. For similar cost data related to the body-side inner redesign, and to access the presentations from GDIS 2007, log on to www.autosteel.org. Stay tuned for news regarding the 2008 edition of GDIS —it’s a can’t-miss event formanufacturers charged with forming and fabricating advanced high-strength steels.

MIM

 



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