THINK OF AN OBJECT and watch it appear before your eyes. All it takes is a
click of a mouse, a flick of a switch and you can have almost anything, made to
order. Researchers are on the point of creating a magic box that can bring the
stuff of your imagination into the hard-edged material world.
The technical name for this box of tricks is a 3D printer. Where an ordinary
printer lays down a single 2D layer of ink on a sheet of paper, the new devices
can deposit a bewildering variety of materials. They add the extra dimension
simply by printing layer after layer until you have a real, 3D object.
The technology is maturing fast, and 3D printing is already a worldwide hit
with engineers. Make a few quick plastic prototypes and you can instantly tell
whether an innovative space-saving engine part will really fit in as it鈥檚
supposed to. The US Army is developing ways to print out vehicle parts from a
truck-mounted 3D printer, so stranded drivers can pick up vehicle parts made on
the spot. And NASA is about to 3D print in space. Tests in zero-gravity
simulations have been successful, and a 3D printer is awaiting a space shuttle
launch.
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It鈥檚 not just for engineers, either. 3D scanning and printing has enabled
archaeologists to uncover and recreate the skull of an Egyptian mummy without
removing any bandages. Archaeologists can beam the dimensions of a dinosaur bone
from their site straight to museum-bound colleagues, who can print out a copy.
And expectant parents have been given models of their unborn baby. Yes, you can
hold your child while it鈥檚 still in the womb.
These specialised applications are already hard at work, and those of us with
rather more mundane requirements will soon also be sampling the thrills of 3D
printing. 鈥淚n the next five years this will become much more available to the
public,鈥� says Philip Dickens, an expert in 3D printing based at De Montfort
University in Leicester. You could custom design your own crockery in the
morning and download it in time for lunch. Never again will you have to wait six
weeks for a replacement part for the washing machine. Grandma could shop around
for a new pair of glasses on the Internet, punch in her prescription, and have
them made right there in her living room.
The process begins with a computerised map of the object鈥檚 geometry, either
generated from scratch by a computer-aided design (CAD) program or digitised by
a 3D scanner. A slicing algorithm breaks the map into horizontal layers, and
sends the information layer by layer to the printer. Engineers are already using
a wide range of printing techniques to produce their models and casting moulds.
The first to arrive was stereolithography, invented in 1984 by Charles Hall, now
president of 3D Systems based in Valencia, California. In this technique, the
object of desire is formed from a liquid polymer that hardens on exposure to
ultraviolet light. A laser scans across the surface of a vat of polymer, forming
the base layer of the design. This is then lowered just far enough into the
liquid to allow the laser to create the next layer. And so it continues layer by
layer until fabrication is completed.
Cut and paste
Other printing methods include laser sintering, where a thin layer of
powdered material鈥攎etal, ceramic, nylon or a host of other
possibilities鈥攊s fused into a solid by a laser beam that strikes its
target only where the design requires it. As with stereolithography, the
substrate is then lowered slightly. Another powder layer is then deposited and
rolled flat. The process repeats until the whole object is built, and then the
unfused powder is removed, revealing the finished product. Objects can also be
made from thin sheets of material鈥攑aper, plastic, metal or
acrylics鈥攖hat are laser-cut to shape, and glued together.
But the technique most likely to be first into your local electronics store
is 3D ink-jet printing. The familiar 2D version deposits ink, but the 3D ink-jet
lays down droplets of hot, liquid plastic. The plastic hardens as it cools,
building the desired pattern layer by layer. An alternative ink-jet technique,
developed in 1989 by Emanuel Sachs and Michael Cima at the Massachusetts
Institute of Technology, combines sintering, gluing and droplet technologies: it
sprays fine droplets of glue onto specific points on a powder bed, which sticks
the powder together in the right places
(see Diagram). Then another layer
of powder is deposited, rolled flat and glued: the finished product emerges when
the layers are complete and the unglued powder鈥攚hich provides support
while the structure is growing鈥攊s blown away.
The trouble with all of these techniques is that the object can only be made
of a single material鈥攎etal, plastic or whatever. The real power will come
when 3D printers can combine materials, allowing us to create, or recreate,
anything we desire. And this has just come a step closer. Last month Z
Corporation of Burlington, Massachusetts, began selling the first ever colour 3D
printer. Based on MIT inkjet technology, it adds coloured ink to individual
glue drops. The coloured glue seeps into tiny air gaps between the powder
granules, giving colour right through the finished object.
It may not sound like much of an advance, but it鈥檚 only a short step from
combining coloured inks to combining different materials. 鈥淲e suddenly realised
that getting colour into a material is more or less the same as getting another
material inside the material,鈥� says Rik Knoppers of TNO in Delft, the
Netherlands, who came up with the first designs behind the colour printing
technology. Since then, TNO has been going hell for leather towards making
multi-material printing a reality鈥攁s are several of its competitors.
The idea is simple. You just break up the design into a matrix of volume
pixels or 鈥渧oxels鈥�, each specifying exactly which material the printer should
deposit at each point in the design. Implementing it is another matter, though,
because of the sheer quantity of information you have to handle. Ordinary
digital picture files are big enough. But for each voxel of a 3D model you may
have a few million colours to choose from, and on top of that you have to
specify a material from a palette of, say, fifty different substances. The size
of the computer file multiplies alarmingly鈥攁nd that鈥檚 just for the first
layer. Because 3D printing builds an object layer by layer, you might need to
stack thousands of these files to create the end product.
It鈥檚 a stiff challenge. If you鈥檙e going to put different materials inside the
solid, you need to know exactly where each material should be deposited, which
creates a huge data handling problem. Knoppers won鈥檛 reveal how far TNO has got,
and his competitors are equally secretive. 鈥淣obody鈥檚 done it yet, but people are
probably close to it now,鈥� Knoppers says.
And the problems don鈥檛 end with the quantities of data. All the printing
processes involve heating and cooling, and where dissimilar materials are used,
differing expansion rates can wreak havoc by pulling them apart as they cool.
鈥淲e are busy trying combinations of metals and ceramics, but there is a big
problem with shrinkage鈥攖hey break off each other,鈥� says Knoppers. He is
now working through the many possible combinations of different types of
ceramics and metals in search of a combination that stays together. What the
developers of these techniques would like, however, is a deeper understanding of
the fundamental nature of bonding, to avoid having to work out a special set of
tricks for every new process they develop.
Even better would be to avoid putting dissimilar materials together in the
first place. It might be possible to create new materials, with previously
unknown properties. 鈥淎fter all, it鈥檚 not that we want to use steel and ceramics;
we just want to have a material with certain properties for doing certain
things,鈥� Knoppers says.
That鈥檚 exactly the approach that Stephen Danforth and his colleagues at
Rutgers University in New Jersey are following. Over the past five years they
have 3D-printed electronic components from ceramic materials that can be
insulating, semiconducting or fully conducting, depending on their exact
composition. That provides almost everything that鈥檚 needed from modern
electronics systems, and the materials can all be laid down together in a single
print run. The technique could be used, for instance, to print out a new
motherboard for your computer. You could custom design your new board by picking
options from a menu on a website, pay for it online and download the design.
Then, satisfied with the result, you press Print and have the latest in ceramic
electronics installed in less time than it would have taken to drive to the
shops.
Danforth鈥檚 group has now begun to use ceramics to 3D-print electromechanical
components such as sensors and actuators. They can print features as small as
0.2 millimetres, and hope to halve that minimum size over the next couple of
years. 鈥淲e鈥檙e looking at writing circuit elements: things that would serve as
capacitors, resistors, conductors and even battery materials,鈥� Danforth
says.
Such new-found abilities promise to transform the manufacturing industry.
Instead of buying a factory-made component, you will be able to design it using
a CAD program and then send the design straight to the printer鈥攚hich might
be beside your desk, or in a customer鈥檚 office halfway across the world. Then
out pops your carefully constructed object of desire. The shopping public could
soon be cutting out both the manufacturer and the delivery firm from the retail
process. 鈥淚 don鈥檛 think there鈥檚 any doubt in anyone鈥檚 mind that these
3D-printing techniques are going to revolutionise manufacturing,鈥� says
Danforth.
Printing techniques such as laser deposition can not only provide instant
spare parts. They can also make them stronger than the cast or forged originals,
because the printer can carefully arrange the microstructure of the metal. The
product can be lighter, too. Computer programs could minimise the weight of an
axle, for example, by working out exactly where the metal ought to go. This
optimum design may turn out to have a fiendishly complex internal structure
that鈥檚 hard to make by conventional means. With 3D printing that limitation
disappears. 鈥淕eometric complexity is largely irrelevant,鈥� Danforth says. 鈥淵ou
can design the internal and external geometry of a part, and its electrical,
mechanical and thermal properties exactly how you want them to be.鈥�
Researchers who were once only concerned with making quick prototypes and
models are now realising they can bypass the factory and turn out the finished
product from the engineer鈥檚 office鈥攐r from the back of a truck. The US
Army has already demonstrated this by printing spare parts for its vehicles. The
Army can get its troops pretty much anywhere in the world within a few days, but
it can鈥檛 ship specific spare parts for its vehicles anywhere near as quickly.
That problem could be solved with a 3D printer mounted on the back of a truck,
loaded with metallic powder and able to receive CAD instructions delivered over
a satellite link. The armoured car can have its new cylinder head, and the tank
can have its track links replaced, both parts coming straight from the same
machine.
Danforth believes these techniques will soon be available for ordinary
consumers too. Commercial 3D ink-jet machines are currently selling for around
拢30,000. This is clearly out of the range of most casual buyers. But
Dickens says he knows of a number of companies who are looking at mass-producing
3D printers for less than 拢1000 apiece. 鈥淭hey could be available within a
couple of years if one of the companies decided to go for it,鈥� he says.
What鈥檚 needed for this to happen is a 鈥渒iller application鈥濃�攐ne that
will turn 3D printers into something that everyone wants to buy. When asked to
predict what that will be, the experts all turn into a kid鈥檚 best friend. Never
mind the huge implications for high-tech industry, 3D printing is being hailed
by many as the 鈥淪anta Claus machine鈥�. 鈥淭oy manufacturers will put their file of
Mickey Mouse on the Internet and people will simply pay to download it,鈥� says
Chris Ryall of Warwick University.
It could even mean an end to the tears and heartache when a new toy breaks.
鈥淭hey will be able to download and print a new one,鈥� says Kloppers. Ian Campbell
of Nottingham University agrees. 鈥淵ou could end up with very low-cost
3D-sculpting systems that a kid could sit and play about with, creating any
shape they wanted to,鈥� he says.
In fact you can do it now. Send the fruits of your imagination to
ToyBuilders.com and they will be turned into reality in a few hours. The toy and
games manufacturers Hasbro, which makes Pok茅mon toys, already has a whole
department dedicated to 3D printing. The toy manufacturers must be rubbing their
hands together at the prospect. Collecting cards to swap with your friends will
soon be so last century. Come on kids, get online: gotta 3D print them all.