The high cost of new factory tools makes it impractical for manufacturers to produce totally new designs every year. Completely new designs usually have been programmed on three- to six-year cycles with generally minor refinements appearing during the cycle. In the past, as many as four years of planning and new tool purchasing were needed for a completely new design. Computer-aided design (CAD), testing by use of computer simulations, and computer-aided manufacturing (CAM) techniques may now be used to reduce this time requirement by 50 percent or more. See '
Automotive bodies are generally formed out of sheet steel. The steel is alloyed with various elements to improve its ability to be formed into deeper depressions without wrinkling or tearing in manufacturing presses. Steel is used because of its general availability, low cost, and good workability. For certain applications, however, other materials, such as aluminum, fibreglass, and carbon-fibre reinforced plastic, are used because of their special properties. Polyamide, polyester, polystyrene, polypropylene, and ethylene plastics have been formulated for greater toughness, dent resistance, and resistance to brittle deformation. These materials are used for body panels. Tooling for plastic components generally costs less and requires less time to develop than that for steel components and therefore may be changed by designers at a lower cost.
To protect bodies from corrosive elements and to maintain their strength and appearance, special priming and painting processes are used. Bodies are first dipped in cleaning baths to remove oil and other foreign matter. They then go through a succession of dip and spray cycles. Enamel and acrylic lacquer are both in common use. Electrodeposition of the sprayed paint, a process in which the paint spray is given an electrostatic charge and then attracted to the surface by a high voltage, helps assure that an even coat is '