A boundary line of manufacturing history cuts across the factory floor of Siemens Hearing Instruments in Piscataway, NJ. On one side, skilled technicians use casting techniques, precision tools, and years of experience to craft the acrylic shells of hearing aids modeled from silicone impressions of actual ear canals.

On the other side of the factory floor, two pizza-oven-sized machines create similar shells from nylon dust. Inside the machines, needles of laser light, guided by digital design files, robotically scan back and forth, cinching paper-thin layers of dust into tough strata of plastic. Four hours and several hundred laser sweeps later, a batch of 80 hearing-aid shells is completed (see “From Dust to Hearing Aids,” bottom). The process saves hours of human labor and produces hearing aids that fit and sound better than traditional ones.

It works so well that Siemens, the world’s largest maker of hearing aids, is completely switching to the technology at several factories. “This whole process allows us to be more accurate and eliminate human error. This is going to change the business,” says William Lesiecki, director of software and e-business solutions for Siemens Hearing Instruments.

Boning Up

In some ways, direct manufacturing is a natural consequence of the relentless pressure to reduce the time it takes to move a product from concept, through design and development, to commercial reality. When computer-aided design and digitally controlled tools began infiltrating factories in the 1970s and 1980s, the stage was set for rapid prototyping, which uses printing technologies to create three-dimensional objects that serve as prototypes for, say, toys or car parts. With prototypes in hand in just hours-rather than the weeks or months hand-carving and casting once took-designers can more quickly refine products, and engineers can quickly detect and correct problems.

The first rapid-prototyping machines used lasers to bind successive layers of a liquid polymer-a process called stereolithography. Later versions used a broader range of raw materials, such as powders that would fuse together when hit by a laser beam. Another leap came in the 1990s, when the method expanded beyond lasers to include printheads that spewed binding liquids onto powders, adding speed and an even greater variety of materials (see “Players in Direct Manufacturing,” bottom). At the same time, the push was on to develop these technologies to the point that they could make finished products, not just prototypes. “In the late 1980s, stereolithography had just come out, and it was very inspiring to see,” says Emanuel Sachs, a mechanical engineer at MIT who developed the printhead method. “What I set out to do was to shift the focus from making prototypes to creating functional parts directly.”

That goal has now been met. On a recent day at the Therics laboratory in Princeton, NJ, two employees in cleanroom suits watched as a car-sized printer made 300 two-centimeter-long chunks of substitute jaw bone. A linear array of eight printheads swept over successive layers of a powder called hydroxyapatite (the major mineral in natural bone), selectively dispensing tiny droplets of an organic binding liquid that would later be burned out during a furnace treatment. Under the relentless sequence of droplets-800 per second-the otherwise formless mass of powder began to take shape. The U.S. Food and Drug Administration approved Therics’s bone substitute in late May, and while it hasn’t yet been used in an implant in humans, it is already in the hands of surgeons who intend to test it soon. As a means of making replacement bone, direct manufacturing has some advantages. Say an accident victim has lost a fragment of arm bone. The piece can be digitally reconstructed using images of the same bone on the other arm. What’s more, the printing technology is able to create pores just 50 micrometers wide, which allow the bone segment, once implanted, to host real cells that make real bone, strengthening and eventually supplanting the implant.

The FDA’s approval of Therics’s directly manufactured bone substitute is a milestone for the manufacturing technology. Indeed, Ranji Vaidyanathan, a materials scientist at Advanced Ceramics Research in Tucson, AZ-which is developing its own printed bone substitutes-expects directly manufactured bone to be common in three to five years. “I would say it will change the way we look at replacement bone,” he says.

Custom Robots

Bone implants presage far broader future applications that will follow improvements in speed, precision, and variety of raw materials. On Demand Manufacturing, which already makes plastic and metallic parts, hopes to offer materials that can perform under the most demanding of conditions, including the furnacelike heat of a rocket engine. The company has developed superalloy powders that can be shaped via direct-manufacturing machines and then baked into complex, superstrong turbine parts. The company is now taking the steps required to qualify the components for use in rockets.

Direct-manufacturing technology is going mobile, too. In a move that might one day have consequences for your local auto garage, the U.S. Army is developing truck-sized mobile units that can fabricate replacement parts-based on digital files or on-the-spot scans-for vehicles and weapons right on the battlefield.

And some are pushing the technology into the realm of robotics and electronics, complete with moving parts. As a first step, John Canny, Vivek Subramanian, and their colleagues at the University of California, Berkeley, are experimenting with ink-jet printing as a method for shaping organic semiconductors and electroactive materials into smart components that change shape in response to a voltage. One long-term vision is an all-polymer custom robot weighing less than one kilogram that could be printed for specific jobs, like fixing wiring in a tight spot on an airplane. But the Berkeley researchers’ initial goals are more modest; Subramanian says they expect to build their first demonstration widget-perhaps a small movable joint-within two years.

The technology could eventually go retail, too. John Wooten, general manager of On Demand Manufacturing, envisions something like a chain of three-dimensional Kinko’s equipped with direct-manufacturing equipment that could replicate pretty much any object that could be scanned or defined in a digital file. “It’s possible to envision a guy with his ‘65 Mustang and a broken window handle going there to have a new handle made,” Wooten says. In a similar vein, Carnegie Mellon’s Bourne foresees new options in personal customization: cell phones, CD players, and all kinds of consumer products with shapes and colors specified by customers.

While these retail applications are still hypothetical, businesses are sprouting to serve manufacturers on a contract basis. Companies like Accelerated Technologies in Austin, TX, and Met-L-Flo in Geneva, IL, accept digital design files and make rapid prototypes-a concept that could evolve into custom-printing products for retail customers. If such a service does materialize, a neighborhood car restorer looking to duplicate a tiny piece of grillwork, or a homeowner replicating old trim, would find it akin to a digital Home Depot, with an infinite virtual stockroom of customized products.