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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.
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| 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. |
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A Lesson in Dual
Phase from Mittal
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| 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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Precision
Metalforming Association, 6363 Oak Tree Blvd., Independence, OH 44131-2500