UltraLight Steel Auto Body Uses Real World Production Process To Show Manufacturing Feasibility
10 September 1997
UltraLight Steel Auto Body Uses Real World Production Process To Show Manufacturing Feasibility
DETROIT, Sept. 10 -- With Phase II of the UltraLight Steel
Auto Body (ULSAB) project moving toward completion, one of the project's major
goals of demonstrating manufacturing feasibility is proving to be well within
reach.
In addition to showing the untapped potential of steel to contribute to
lightweight vehicle design, ULSAB is confirming that its use of leading edge
material and processing technologies is practical for high volume
manufacturing.
Proof of manufacturing potential rests on the successful forming and
fabrication of the first set of parts and their assembly into a body-in-white
test unit.
The ULSAB project demonstrates the feasibility of high volume production
but does not preclude production at lower volumes. Ensuring the parts were
designed to production intent manufacturing specifications required the early
involvement of the design engineers, steel manufacturers and component
fabricators. This cooperative effort -- and the shared goal of mass savings
without sacrificing safety or performance -- enabled the project partners to
constantly exchange information to optimize development of the entire body-
in-white. This exchange resulted in a streamlined design and fabrication
process.
Importance of early involvement
This partnership was crucial in anticipating and addressing the unique
processes and applications ULSAB employs, including high strength steels,
tailored blanks, hydroforming and steel sandwich material.
High strength steel
ULSAB uses high strength steel and ultra high strength steel for more than
90 percent of the body structure. One challenge posed by these steels is that
they form differently than the mild steel with which many component
fabricators are accustomed. High strength steel has greater springback and
requires different draw angles so each different grade must be treated as a
unique material. High strength material specifications range from 210 to 800
MPa yield strengths with thickness ranges from 0.65 mm to 2.0 mm.
Tailored blanks
ULSAB's body side outer is one of several parts that employs a fully laser
welded tailored blank with different thicknesses and grades of steels.
Careful placement of the seams in the tailored blank was critical for
minimizing weight and facilitating forming. This consideration was especially
important in the body side outer because of its complexity, its size, its use
of high strength steels and the inclusion of a class A surface quarter panel.
Nearly half of the ULSAB mass consists of tailored blank parts.
Hydroforming
To minimize weight and maximize structural performance, the project
partners designed the tube from which the hydroformed side roof rail was
created with an unusually thin gauge relative to its outside diameter. The
project partners had to develop methods for both manufacturing and forming
this critical tubular part, which provides a unique load path for the body
structure.
Steel sandwich
Again, to minimize weight, the program specified the skins of the steel
sandwich material for the dash panel insert and spare tire tub to be
extraordinarily thin. This requirement tasked the project partners' ability to
provide the width required. Additionally, steel sandwich has different forming
characteristics than regular sheet steel, requiring the project partners to
treat it differently in the dies.
Manufacturability prediction and validation
Forming simulation
To help ensure that the designs created through the collaborative effort
were feasible, the project partners performed forming simulation analysis on
the most complex parts. Forming simulation was performed using finite element
methods to show locations of strains and material thinning. The project
partners then used this information to identify areas of unacceptable strain
and recommend product design and tooling adjustments accordingly.
Circle grid strain analysis
To ensure the parts were formed to production standards, the project
partners employed circle grid strain analysis. This technique requires
etching circles on the blank surface and then measuring the circle distortions
after forming. The measurements obtained are then plotted on a forming limit
diagram to discover and address the sites that fall outside acceptable
production limits. After completion of tool development, circle grid analysis
is also used to confirm that the parts are indeed feasible for, full volume
production.
Tooling
Once the analysis had proven the manufacturability of parts, ULSAB began
building and validating tools for parts fabrication. All stamping tools in
this program are "soft" tools made of material such as kirksite and built to
production intent standards. Tools used in hydroforming are "hard" tools and
made of steel. In both cases, part fabrication tolerances and quality
standards were maintained the same as intended for full volume production.
Parts fabrication
Upon completion of tooling, the component fabricators stamped the parts
and evaluated them using circle grid strain analysis to confirm that they were
formed to full volume manufacturing standards. Parts have been fabricated to
meet the original goals and specifications of the project, a fact that has
been substantiated through the assembly of these parts into the first ULSAB
body-in-white test unit.
Next steps
This test unit is being used to validate the mass and static stiffness of
ULSAB. Results from the test unit will be used to refine parts, further
optimizing the body design. Refined parts will be produced and assembled into
ULSAB bodies-in-white demonstration hardware. In Spring 1998, the project
will conclude with presentations of the demonstration hardware, along with
in-depth summaries of the assembly techniques, engineering analyses, physical
test results and economic analysis.
The Automotive Applications Committee (AAC) of American Iron and Steel
Institute focuses on advancing the use of steel in the highly competitive
automotive market. With offices located in Detroit, the AAC fosters
cooperation between the automobile and steel industries and was instrumental
in the formation of the Auto/Steel Partnership.
American Iron and Steel Institute is a non-profit association of North
American companies engaged in the iron and steel industry. The Institute
comprises 49 member companies, including integrated and electric furnace
steelmakers. It also includes 155 associate and affiliate members who are
suppliers to or customers of the steel industry. For more news about steel
and its applications, view American Iron and Steel Institute's web site at
http://www.steel.org.
This release and other steel-related information are available for viewing
and downloading at American Iron and Steel Institute/Automotive Applications
Committee web site at http://www.autosteel.org. Saving the releases as a
text-only file is recommended to avoid formatting difficulties.
SOURCE American Iron and Steel Institute
