LAYER BY LAYER, a metal spray gun at Carnegie Mellon University builds up a model of a zinc turbine blade. Photo: Jim Schafer.

Desktop Artisans Personal manufacturing weds design with part fabrication

It used to be that people designed parts, and then they went over to the forge and started hammering

them out," says Emanuel Sachs, a pro­fessor of mechanical engineering at the Massachusetts Institute of Technology. "There was an intrinsic coupling of de­sign and manufacturing because the de­signer really understood how the thing was made."

A new technology, sometimes called desktop manufacturing, promises to make the engineer into an artisan yet again. The increasing power of person­al computers may soon enable engi­neers to "print out" completed parts with the ease of printing an engineer­ing diagram. These systems can pare weeks or months from the laborious process of making prototypes. And they may enable engineers to fabricate real parts for short production runs di­rectly from their computer screens.

The most visible examples of desk­top manufacturing so far are plastic prototypes that allow engineers to eval­uate a part for fit and looks. A Valen­cia, Calif., company, 3D Systems, which is 37 percent owned by pharmaceutical and chemical maker Ciba-Geigy, is the largest seller of desktop manufacturing equipment. It has sold hundreds of ma­chines to produce prototypes from a technique known as stereolithography.

Like a computer printer, the system takes a set of coordinates from a com­puter to control the positioning of an ultraviolet laser. The laser builds up layers of plastic a few thousandths of an inch at a time by tracing successive cross sections of the part onto the sur­face of a bath of liquid polymer, caus­ing it to solidify. The process can pro­duce everything from a prototype of an engine block to a model of a diseased hip bone patterned from data from a medical scanner.

These plastic prototypes are still just a few steps removed from the world of the hobbyist. True, plastics can be cured by a laser to precise accuracies, and sometimes they may even be used as real parts. Many parts, though, are made from metal-and so behave differently than plastics do when they are exposed to heat or vibration. A plastic air mani­fold for a jet engine cannot be subject­ed to a temperature test.

With this in mind, the National Sci­ence Foundation and a group of indus­trial companies are supporting research to make parts and prototypes from a full range of industrial materials, from steel to ceramics. Sachs and his col­leagues at M.LT., with funds from the NSF, General Motors, United Technolo­gies and other major companies, are de­veloping a technique called three-dimen­sional printing. It takes a three-dimen­sional, computer-aided design (CAD) and chops it up into minute slices. A nozzle, similar to the ones used for some types of computer printers, squirts a binder chemical onto a bed of

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142 SCIENTIFIC AMERICAN April 1992

powdered ceramic, stainless steel or an­other metal. After this process is repeat­ed for hundreds of layers, the sehlisoli­dified part is then fired in a furnace.

The M.LT. technology has already been licensed by Soligen, a new Los An­geles company that plans to sell ma­chines to fabricate ceramic molds. Af­ter the ceramic powder has been so­lidified, metal will be cast in the result­ing mold. Known as CAD-Casting, it by­passes the task of manufacturing metal dies for producing wax patterns that are then dipped in a ceramic slurry to create such a mold.

Lee E. Weiss and Fritz B. Prinz of Carnegie Mellon University's Robotics Institute and Engineering DeSign Re­search Center believe they can make metal or other parts with nearly the same material density as those pro­duced through conventional casting and milling. They plan to adapt a technique used in the aerospace industry to spray ceramic coatings onto metal parts. The process uses a low-powered carbon di­oxide laser to cut a series of masks. Then a robot-controlled thermal spray gun deposits a layer no more than 0.005

inch in thickness through openings in the stencil-like masks. Each of the 162

layers that make up a zinc turbine-blade model took six minutes to build.

Researchers at the University of Texas at Austin are exploring the possibility of employing a high-powered, 1,100-

watt carbon dioxide laser to fuse metal or ceramic powders in a system similar to one the university has used with thermoplastics. But, says Joseph]. Bea­man, a professor of mechanical engi­neering, the Austin investigators imme­diately found that "you can't just turn on the laser and take a polymer part and plan to make it in metal."

If technical obstacles can be over­come, desktop manufacturing will has­ten the making of the metal-casting molds and tool dies to mass-produce an engine housing or another part. And researchers believe it could enable man­ufacturers to forgo casting altogeth­er in building small lots of customized parts. The possibilities range from vanes and blades for gas turbine engines to dental fittings, packaging for semicon­ductor chips, spare equipment parts and so on.

It may be as simple as printing a doc­ument from a computer. "When some­one wants a part," Beaman says, "a tech­nician will just grab a bag with powder, walk over and turn on the machine." Then the desktop artisan may be con­strained not by present limits of the manufacturing process but only by what can be visualized within the three di­mensions of a CAD drawing.-Gary Stix

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