For every part that goes into a car, Ford Motor Co. figures it must design and build 1,200 others. Those include jigs to hold the part while it's being drilled, clamps to grab it and move it to the next machine tool, and racks to hold it while it's shipped to the assembly plant. Once the design of the part has been approved, the other 1,200 must be designed--and fast. Who wants to slow the rollout of a new car because a jig to hold a door for painting isn't ready?

Those frustrating for-want-of-a-nail delays don't happen much anymore at Ford. That's because the auto maker, despite its reputation for slow product development, has become a world leader in the field of "rapid prototyping," which means it can make a jig in a jiffy. Rapid-prototyping machines used by Ford and others produce one-of-a-kind pieces--at a price, mf course, far higher than that of a mass-manufactured equivalent. But because the parts can be made so quickly--usually in a matter of hours--rapid prototyping is perfect for the design, marketing, and testing of new products, not to mention all those jigs.

LAYER BY LAYER. The basic concept is the same in all forms of rapid prototyping: Working from a computer-generated design, a machine builds a prototype one thin layer at a time. The layers may be made of plastic resin, paper, or ceramic powder, and are generally 1/100 of an inch thick or less. At that rate, it may take a machine four hours to a day to make a three-dimensional model measuring about a foot on each side. That hardly seems fast, but compared with the days or weeks required by the traditional method--sculpting the model from metal, plastic, or wood--rapid prototyping moves at warp speed.

All big carmakers use this technology to some degree, as do other companies ranging from electronics concerns such as Motorola Inc. to tiny biomedical companies looking to sculpt bone replicas for reconstructive surgery. While most of these outfits choose to become expert in one or another of the rapid-prototyping technologies, Ford has tested and compared a variety of methods, gaining skill in an array of approaches. Says Floyd Roberts, a materials scientist at NASA and chairman of the standards committee for rapid prototyping of the American Society for Testing & Materials: "In terms of their knowledge of the systems out there...Ford is probably second to none."

The auto maker's rapid-prototyping guru is Sean B. O'Reilly, 55, a former Niagara University math professor. O'Reilly is principal engineering specialist in computer-aided manufacturing engineering. Walk through his facilities at Ford's Manufacturing Development Center in Detroit, and you'll see one of almost every type of machine on the market. Inside a machine from 3D Systems Inc. of Valencia, Calif., the industry sales leader, a laser beam zips across a pool of liquid plastic resin, building up a part by fusing the resin into layers of solid plastic. Nearby sits a spool of nylon-like plastic filament, waiting to be fed into a machine from Stratasys Inc. in Eden Prairie, Minn., that will melt and squeeze out the plastic into the desired shape--as if it were hot glue. One machine from DTM Corp. in Austin, Tex., that uses ceramic powder as a substrate is optimistically called a "desktop machining" unit, even though it measures 10 feet by 5 feet by 5 feet.

Between 1987 and 1990, O'Reilly and others in Ford's advanced-manufacturing program, then known as Alpha, tested many approaches. When asked to build a part with rapid prototyping, they did the job using traditional methods at the same time--and kept careful records.

MUSTANG TRIUMPH. Eventually, Ford's regular manufacturing operations saw that rapid prototyping could mean time savings of 60% to 90% and ran to Ford's senior management asking for funds for their own machines. At that point, Alpha stepped forward with documentation on cost savings--generally between 50% and 70% per part. Across all sizes of parts, from large transmission cases to small covers for windshield-wiper motors, Alpha's tests found that rapid prototyping produced an average savings of $10,000 per part in design and manufacturing costs. Even though in some cases rapid-prototyping machines can cost $500,000 each, Alpha's numbers showed that a machine could pay for itself by making just 50 kinds of parts.

One of Ford's first triumphs in this arena came in 1988, when it supplied prototypes of a Mustang engine rocker arm to companies that had earlier expressed interest in supplying the parts. The three-dimensional models helped the suppliers understand better how the part could be manufactured. As a result, all four lowered their bids.

Rapid prototyping still has problems. Because the material shrinks or otherwise distorts when hardening, making the parts to ultra-precise measurements is difficult, as is making repeated parts precisely alike. And prototype parts aren't strong enough for heavy-duty use, such as inside an engine. Those problems will likely be resolved through the use of new raw materials, O'Reilly believes. "I liken the entire industry to personal computers in about 1978," he says. Back then, such companies as Sinclair and Ohio Scientific were introducing the first PCs. Those makers later faded, and the same may or may not happen in rapid prototyping: Today's machine makers are all small startups. But the technology is here to stay.

Instant Sculpture: 3-D Models from Drawings

Rapid-prototyping machines turn pictures into reality. Working off a computer-generated drawing, they build sample parts for use in everything from design to marketing of new products.

1 At Ford's Manufacturing Develop- ment Center in Detroit, designers use a workstation from Silicon Graphics and software from 3D Systems to preview a drawing of a housing for a drive- train that may go into a new 4x4 truck.

2 The design is sent to a rapid-prototyping machine made by DTM. A laser beam builds the part by fusing ceramic powder into a solid, one layer at a time.

3 After about 24 hours, the prototype is lifted out of the machine by Sean B. O'Reilly, Ford's rapid-prototyping guru. The porous surface must be coated with wax or epoxy.

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