Matt Sullivan, a retired soldier, still has trouble explaining his right leg to strangers.
The shiny chrome surface, embossed with the lightning bolt logo of his beloved San Diego Chargers, covers the calf area of his prosthetic leg, the result of a roadside bomb in Afghanistan in 2010.
At the naval hospital where he was recovering from his wounds and the resulting surgery, Sullivan ran into entrepreneur Scott Summit, who suggested a solution to covering the metal rod that protruded conspicuously from his knee.
Summit's firm, Bespoke Innovations, uses an obscure process known as 3-D printing to make durable thermoplastic leg coverings, or fairings. By digitally scanning the surviving leg to match its shape and form, Bespoke produces curved panels resembling soccer shin pads that cover the artificial limb. You can often tell a person has a prosthetic leg by the way the pants leg flaps, Sullivan says. "Having that symmetry now, you can't tell the difference."
Thanks to the Internet and declining hardware costs, 3-D printing — once a specialized process used sparingly by industrial companies for prototyping — is becoming more common among design hobbyists and entrepreneurs such as Summit.
The consumer market's embrace of the technology has been swift. Sales for all 3-D printing products and services worldwide grew 24% to $1.33 billion in 2010, fueled in part by a fast-growing market of do-it-yourselfers, says industry research firm Wohlers Associates.
The firm also estimates sales will continue to post "strong double-digit growth" in the next several years, reaching about $3.1 billion by 2016 from an estimated $1.6 billion this year.
Here's how 3-D printing generally works: Once a product is designed on software, the file is sent to a special 3-D printer that contains a spool (or cartridge) of a material — typically, plastic, metal or ceramics — in a fine powder or gel-like texture. Like printing on paper, the 3-D printer lays down successive layers of the material and builds up until an object emerges. It's then cleaned, painted or cooled.
"It's like a hot glue gun. Think of it as building from strings of spaghetti glue," explains Jim Kor, a Canadian engineer who has printed the exterior panels of a fuel-efficient concept car, the Urbee, with the help of Stratasys, a Minnesota company that is a 3-D printing technology pioneer.
Traditional manufacturing, involving injection molding or die casting, generally produces better results for making parts in large volumes. Experts caution that 3-D printers, particularly entry-level models, can produce rough finishing and imprecise details, and raw materials may be expensive.
But proponents say the technology enables on-demand parts production, eliminates assembly lines, reduces inventory and is a speedier process for making objects or parts that don't require precise detailing.
The technology is already prevalent in industrial manufacturing. Boeing prints some air duct parts for its planes. Invisalign's teeth aligners are printed, as are hearing aid shells by Starkey Laboratories in Minnesota.
"You have freedom of creation. You can do almost anything," says Terry Wohlers of Wohlers Associates.
Some innovators are determined to prove that theory. Anthony Atala, a professor at the Wake Forest University School of Medicine, is something of a cult figure in 3-D printing with his research on printing human organs. Using living human cells and a special gel that binds them, he has printed a human bladder that is in a clinical trial.
Big Ideas, Small Scale
3-D printing has bred a cottage industry of entrepreneurs who see business opportunities in making products for customers — jewelry, toys, home decor and clothing — who otherwise have no access to customized, small-scale manufacturing.
Want to make a toy robot for your third-grader? MyRobotNation.com, which specializes in 3-D-printed toy robots, has design software and a product ordering page on its website.
Need a good use for a mountain of Lego Duplo blocks? Thingiverse.com, a website where product designers share their designs for others to use, features small plastic connectors that link the blocks to toy train sets. Using the connector, Duplo blocks can be built as a bridge tower or train depot.
Thingiverse founder Bre Pettis says the Duplo connectors may be the most unusual objects on his site. The 15,000 designs attest to the creativity and diversity of interests of its users, he says. "The possibilities are endless."
The emergence of hobbyists has been a blessing in new sales possibilities for printer makers. Printer prices vary widely, ranging from sub-$1,000 models that require assembly at home to $500,000 products used by industrial companies. 3-D printers and raw materials are generally purchased online or through resellers.
But printer prices are coming down as makers increasingly eye the casual-user market. Company 3D Systems created much buzz at the recent Consumer Electronic Show with Cube, a desktop 3-D printer aimed at home users. At $1,300, it's one of the cheapest fully assembled printers, says CEO Abe Reichental.
He says a third of the company's 2011 research-and-development budget was poured into the consumer market. "We think that's the big part of the future," he says. "The technology is finally affordable."
Fueling the popularity of 3-D printing is the fact that the software, once intimidating to casual hobbyists, is becoming cheaper and easier to use. You no longer need to spend hundreds of dollars for high-end computer-aided design software. Some websites — 3DTin, Tinkercad, Google's SketchUp and Autodesk's 123Dapp.com — allow users to design directly online. Sites such as MyRobotNation.com require little design skill.
Software is improving in other areas, as well. Bespoke's Summit says scanning an amputee's surviving leg once required a heavy scanner, and was a cumbersome and costly task.
But Bespoke recently switched to a new Autodesk program that allows scanning with a simple point-and-shoot camera. "It went from exotic wizardry to common camera. And it's made the process a lot easier," Summit says.
Another catalyst for the do-it-yourself movement is the variety of software and printer plans available online for individuals to use and modify as they see fit. RepRap, a free desktop 3-D-printer kit that users have downloaded to build their own printers, is one example.
Three years ago, Pettis founded MakerBot, a company that makes printers based on RepRap's designs. It has sold about 10,000 printers in the U.S. since 2009, he says.
Fast Results for Small Orders
3-D printing has also fueled a boom in small businesses, such as Shapeways and Ponoko, that promise customers quick-turnaround printing for small orders.
Sarah Stocker and her business partner, Mark Danks, opened MyRobotNation last year to leverage their work experience in the video gaming industry. On their site, customers can log on to design robots and order a finished product — ranging from 2-inch ($18) to 6-inch ($170) — that are 3-D printed. "It's basically like playing a video game," Danks says.
Entrepreneurs with limited resources, such as designer Jeff Bare, are increasingly using online service companies such as Shapeways, which prints uploaded designs and lets members open virtual stores on the site where they pay a fee for each item they sell.
Bare, a furniture designer by day, began designing a cover for the iPad three months before it was introduced in April 2010. With an estimate of iPad dimensions, he printed a prototype. After making adjustments, he was ready to sell his covers when iPad was launched. The first cover, made of polyimide (nylon-based plastic), sold a month later for $30.
Bare is one of 120,000 users of Shapeways, based in New York. Shapeways printed 750,000 products last year, ranging from jewelry (a popular category) to phone accessories. "In China, you have to order thousands. (Here), you can order one or two," says Shapeways CEO Peter Weijmarshausen. "The risk of doing business goes down to absolutely zero."
Despite its potential, 3-D-printing technology does not yet pose a serious threat to traditional manufacturing.
When you look closely, printing traces are visible on items printed by low-end printers, Wohlers says, and 3-D printing isn't ideal for large-volume orders that need to be turned around quickly. While printer prices are coming down, the materials cost is still "relatively expensive," says Autodesk CEO Carl Bass. For example, ABS plastic — used often for its durability — when packed into spools of a 3-D printer can be "a couple of hundred times more expensive" than the raw material, Bass says.
Despite the technology's shortcomings, its proponents liken it to the microwave oven in the early '80s, a curious appliance not quite ready for prime time but with the potential to become indispensable.