The promise of 3-D printing is tantalizing: You envision something, draw it with the right software, and then print it in three dimensions—regardless of how many parts it has, how they interlock, or whether they will even be accessible once your creation is completed. With this strategy, anyone can make almost anything. Someday, lots of stuff will be manufactured this way, on demand.
Full realization of that promise remains a long way off, but the bandwagon is rolling. Thousands of machines, ranging from kit-built tabletop models to commercial behemoths capable of printing the body of a small car, are out in the world producing parts. And starting this year, the United States' Defense Advanced Research Projects Agency is planning to put 1000 production-quality 3-D printers in high schools across the United States as part of its Manufacturing Experimentation and Outreach program. Even if you don't have access to one of those machines, you can get a free download of Autodesk 123D, a 3-D computer-aided-design program still in public beta testing, which gives you push-button connections to online 3-D-printing services, of which there are now dozens, if not hundreds. So if you're not already printing objects on a regular basis, there's a good chance that in 2012 you will be.

Many 3-D printed objects are used behind the scenes in the production of something else. Jeff DeGrange of Stratasys, a manufacturer of 3-D-printing machines in Eden Prairie, Minn., came to the company after 20 years in manufacturing R&D at Boeing. So when asked where 3-D-printed parts are being used, he naturally offers as an example aircraft companies that print assembly-jig inserts for holding wing sections and other parts in place for drilling and fastening. He says the companies that manufacture high-performance cars have also begun 3-D-printing molds for carbon-composite panels. Machining or sculpting the complex curves required for these body panels is far too time consuming and expensive to do any other way.

Meanwhile, dental laboratories are using 3-D printing to help fabricate crowns and bridgework, metal¬working companies print molds for casting jewelry and other small objects, and small-¬aircraft manufacturers, such as Piper, have even found that 3-D-printed dies can serve for stamping aircraft parts out of sheet metal. The applications go on and on.

What all these examples have in common is the high cost of conventional production of parts used for tooling or machining. Injection molds can cost thousands or tens of thousands of dollars for a single design, so it often makes sense to spend even hundreds of thousands for a production-capable 3-D printer that can churn out many different plastic shapes with ease. Plastic parts produced by fused-deposition-modeling machines (which spit out liquid plastic to build up the desired geometry) typically have about two-thirds the strength per unit area of injection-molded plastic parts, but that's just fine for most applications.