By the time a vehicle program reach

By the time a vehicle program reaches the die-making stage, U.S. car makers have long frozen the nominal dimensions and tolerances. Toyota (and other Japanese automakers), though, still views specifications as targets for die makers to refine. Die makers make the dies as close as they can to the CAD database, stamp out parts, and modify the dies so the body parts fit together (called “functional build”). Manufacturing engineers then set the tolerances based on their understanding of current manufacturing capabilities. Fit and appearance to the customer override concern for exactly matching specifications. The resulting dies, then, define the final specifications for the vehicle, not the CAD database. This example illustrates a belief that a nominal dimension, which appears to be a fixed, single point, really implies a range of acceptable solutions. Die makers have developed a tacit understanding of the range allowed in the design passed on from product engineering.