THE leading edge of technology moves in mysterious ways 鈥� sometimes more by luck than judgement. In the mid-1990s, when US aerospace giant Boeing was helping to create the International Space Station, its engineers had to make 50 small plastic boxes, each one a different shape. The engineers reckoned that to make them by a form of injection moulding would take nine months. But time was pressing, so they took a short cut.
To test that their design fitted together and would survive the low pressures of space, the designers used cheap copies of the boxes, planning to fit the real ones later. They made the copies by a process new at the time called rapid prototyping. In this, shapes are designed on a computer screen and fed to a 3D printer which turns the virtual object into reality, building it up a layer at a time by fusing together tiny particles of nylon with a laser. This 鈥渟elective laser sintering鈥�, created the boxes within hours.
What happened next was unexpected. The cheap boxes tested brilliantly, sparking a debate. 鈥淚f they pass the tests, why not use them on the station?鈥� asked Cliff Brampton, a metallurgist at Boeing. The cheap boxes won the day. Today the ISS orbits Earth with 50 oddly shaped boxes created by rapid manufacturing.
Advertisement
Since those early days, printing in 3D has sparked imaginations. 鈥淎nything, anywhere鈥� is the goal. The US army talks of making spare parts for its tanks in remote locations. Futurists have predicted that every home will have a 3D printer, and technology guru Howard Rheingold asks what will happen when the 鈥淣apster for devices鈥� comes along.
So far, though, the consumer revolution has not arrived: 3D printers are certainly cheaper, but still not cheap. A machine that cost $250,000 five years ago, now costs $30,000. Terry Wohler, an analyst at Wohler Associates of Fort Collins, Colorado, likens the falling prices to what happened when desktop computers started replacing mainframes in the 1980s. 鈥淲e don鈥檛 yet have the equivalent of the PC in the rapid prototyping industry but it鈥檚 coming,鈥� he says.
There are already a variety of technologies for 3D printing: those based on ink-jet printers; polymers which harden under UV light; or thin films that form a 3D shape when stacked up (快猫短视频, 30 September 2000, p 24).
But prototyping is one thing; manufacturing another. Designers might build a prototype chair, for example, to check all the bits fit together and that it is comfortable. The prototype has to hold up for only a few hours. But the finalised chair will have to survive years of harsh treatment, and designers do not use materials unless they really understand their properties, such as strength and durability. Only now are the properties of the layered materials made by 3D printers becoming clear.
Once these properties are understood, the technique offers huge promise for producing one-off designs in small quantities. These can cost a fortune to make by conventional means. Boeing now prints 100 different nylon parts for the F-18 fighter, mostly ducting for cooling systems. It has even printed parts of the space shuttle main engines. 鈥淭here are big advantages in the complexity of the parts we can make and weight reduction we can achieve,鈥� says Brampton, who is also chief technology officer for On Demand Manufacturing, a company set up by Boeing to exploit 3D printing.
Laser sintering has also paid off for Siemens Hearing Instruments of Piscataway, New Jersey, which turns out custom-made hearing aids. The company makes a silicone-wax impression of a person鈥檚 ear canal and scans it to create a computer model. A 3D printer then creates a shell of nylon-like polymer to house the electronics. The result is a snug, almost invisible hearing aid. 鈥淏efore this technique everything was done by hand,鈥� says Bill Lesiecki of Siemens, and this risked making small changes that altered the fit of the hearing aid. That is not a problem with 3D printing, Lesiecki says.
Wohler predicts that other markets will emerge to exploit 3D printers, perhaps bringing them to local shopping centres. 鈥淐ompanies that currently offer photocopying services are ideally placed to do this,鈥� he says. When the breakthrough comes, small businesses, schools and even householders will be able to create the objects of their desire at the touch of a button.
Metal: the final frontier
Three-dimensional printers now work with anything from wax to plastics and ceramics. They have even turned out entire electronic circuits, made from conducting, semiconducting and insulating polymers. But the big prize is to find a perfect way to print metals.
As with plastics, the object is built up layer by layer as a laser fuses together tiny particles of a metal, such as steel, coated with a polymer. The laser melts the polymer so the particles stick together. This shape is then heated to burn off the polymer and partially melt the metal particles to create a single metal object. The final step is to fill the voids between the particles with another molten metal, such as bronze.
The big problem here is that the properties of these materials can be difficult to predict and control. 鈥淏ut we are getting the hang of it,鈥� says Cliff Brampton of On Demand Manufacturing. Brampton foresees big profits by supplying complex metal parts needed in small quantities. His company will target the rocket industry, where production runs are counted on the fingers of one hand, and the market for spare parts for ageing aircraft.
