in the near future, however, with increasing policy emphasis on auto recycling around the world
(see recycling section below).Manufacturability
Steel vehicles are constructed by welding together body parts that have been stamped from
inexpensive steel sheet materials. Over the years, this process has been extensively refined and
optimized for high speed and low cost. Steel tooling is expensive: an individual die can cost over
$100,000 dollars, and with scores of dies for each model, total tooling costs maybe several tens
of millions of dollars per vehicle. A stamped part can be produced every 17 seconds, however,
and with production volumes of 100,000 units or more, per-part costs are kept low.
Aluminum-intensive vehicles have been produced by two methods: by stamping and welding of
aluminum sheet to forma unibody structure (a process parallel to existing steel processes); and by
constructing a “space frame” in which extruded aluminum tubes are inserted like tinker toys into
cast aluminum nodes, upon which a sheet aluminum outer skin can be placed.An advantage of the stamped aluminum unibody approach is that existing steel presses can be
used with modified tooling, which keeps new capital investment costs low for automakers and
permits large production volumes. Ford used this method to produce a test fleet of 40 aluminum-
bodied Sables; as did Chrysler in the production of a small test fleet of aluminum Neons.^8 The
Honda NSX production vehicle was also fabricated by this method.
The aluminum space frame approach was pioneered by Audi in the A8, the result of a 10-year
development program with Alcoa. Tooling costs are reportedly much less than sheet-stamping
tools, but production volumes are inherently limited; for example, the A8 is produced in volumes
of about 15,000 units per year. Thus, per-part tooling costs for space frames may not be much
different from stamped unibodies.
Manufacturability is a critical issue for using composites in vehicle bodies, particularly in load-
bearing structures.^9 Although composite manufacturing methods exist that are appropriate for
aircraft or aerospace applications produced in volumes of hundreds or even thousands of units per
year, no manufacturing method for load-bearing structures has been developed that is suitable to
the automotive production environment of tens or hundreds of thousands of units per year.
The most promising techniques available thus far appear to be liquid molding processes, in
which a fiber reinforcement “preform” is placed in a closed, part-shaped mold and liquid resin is
injected.l0 The resin must remain fluid long enough to flow throughout the mold, thoroughly
wetting the fibers and filling in voids between the fibers. It must then “cure” rapidly into a solid
structure that can be removed from the mold so that the process can be repeated. A vehicle
(^8) Jack Keebler, "Light Waits," Automotive News, Mar. 14, 1994.
(^9) Large volume production methods for inexpensive, low-performance composites such as sheet molding compound, are well established for low-
load-bearing parts such as fenders, hoods, and tailgates. However, such composites do not have sufficient strength and stiffness to enable their use in
theload-bearing parts of the vehicle structure. 10 U.S. Congress, Office of Technology
Assessment, Advanced Materials by Design, OTA-E-35 1 (Washington DC: U.S. Government Printing
Office, June, 1988), p. 155.