This normative design process has been central to automobile design for decades. Although it ,
has generally served the automakers well, it also has some limitations. In particular, this strategy is
unfriendly to innovations such as the introduction of new materials in a vehicle design. The
advantages of a new material stem directly from the fact that it offers a different combination of
performance characteristics than does a conventional material. If the design characteristics are
specified in terms of a past material, however, that material will naturally emerge as the “best”
future material for that design. In other words, if a designer says, “Find me a material that is at
least as strong as steel, at least as stiff as steel, with the formability of steel, and costing no more
than steel for this design that I derived from a past steel design,” the obvious materials choice is
steel.Materials Selection CriteriaFive key factors affect the auto designer’s selection of materials: manufacturability and cost,
performance, weight, safety, and recyclability.Manufacturability and Cost
A typical mid-size family car costs about $5 per pound on the dealer’s lot, and about $2.25 per
pound to manufacture. Of the manufacturing cost, about $1.35 goes to labor and overhead, and
$0.90 for materials, including scrap.^4 The reason cars are so affordable is that steel sheet and cast
iron, the dominant materials, cost only $0.35 to 0.55 per pound. Advocates of alternative
materials such as aluminum and composites are quick to point out, however, that the per-pound
cost of materials is not the proper basis for comparison, but rather the per-part cost for finished
parts. Although they may have a higher initial cost, alternative materials may offer opportunities
to reduce manufacturing and finishing costs through reduced tooling, net shape forming, and parts
consolidation. In addition, a pound of steel will be replaced by less than a pound of lightweight
material. Nevertheless, the cost breakdown given above suggests that, if finished parts made with
alternative materials cost much more than $1.00 per pound, overall vehicle manufacturing costs
will rise significantly.^5 This severe constraint will be discussed later.
For comparison, the per-pound and per-part costs of alternative materials considered in this
study are given in table 3-1, along with the expected weight savings achieved by making the
substitution. On a per-pound basis, glass fiber-reinforced polymers (FRP), aluminum, and graphite
FRP cost roughly 3 times, 4 times, and 20 times as much as carbon steel, respectively.^6 Because
these materials are less dense than steel, however, fewer pounds are required to make an
equivalent part, so that, on a part-for-part basis, the difference in raw materials cost relative to
steel is 1.5 times, 2 times, and 5 times, respectively.^7 High-strength steel costs 10 percent more
(^4) Frank Stodolsky et al., "Lightweight Materials in the Light-Duty Passenger Vehicle Market: Their Market Penetration Potential and Impacts,”
paper presented at the Second World Car Conference, University of California at Riverside, March 1995. 5
1bid
(^6) National Materials Advisory Board, Materials Research Agenda for the Automotive and Aircraft Industries, NMAB-468 (Washington, DC:
National Academ 7 y Press, 1993), p. 34.
Assuming currentcomposite manufacturing technology.