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2017-07-05 11:02:06
Recent advances make 3D printing a powerful competitor to conventional mass
production
SLOWLY but surely the sole of a shoe emerges from a bowl of liquid resin, as
Excalibur rose from the enchanted lake. And, just as Excalibur was no ordinary
sword, this is no ordinary sole. It is light and flexible, with an intricate
internal structure, the better to help it support the wearer s foot. Paired
with its solemate it will underpin a set of trainers from a new range planned
by Adidas, a German sportswear firm.
Adidas intends to use the 3D-printed soles to make trainers at two new, highly
automated factories in Germany and America, instead of producing them in the
low-cost Asian countries to which most trainer production has been outsourced
in recent years. The firm will thus be able to bring its shoes to market faster
and keep up with fashion trends. At the moment, getting a design to the shops
can take months. The new factories, each of which is intended to turn out up to
500,000 pairs of trainers a year, should cut that to a week or less.
As this example shows, 3D printing has come a long way, quickly. In February
2011, when The Economist ran a story called Print me a Stradivarius , the idea
of printing objects still seemed extraordinary. Now, it is well established.
Additive manufacturing, as it is known technically, is speeding up prototyping
designs and is also being used to make customised and complex items for actual
sale. These range from false teeth, via jewellery, to parts for cars and
aircraft. 3D printing is not yet ubiquitous. Generally, it remains too slow for
mass production, too expensive for some applications and for others produces
results not up to the required standard. But, as Adidas s soles show, these
shortcomings are being dealt with. It is not foolish to believe that 3D
printing will power the factories of the future. Nor need the technology be
restricted to making things out of those industrial stalwarts, metal and
plastic. It is also capable of extending manufacturing s reach into matters
biological.
Adding it up
There are many ways to print something in three dimensions, but all have one
thing in common: instead of cutting, drilling and milling objects, as a
conventional factory does, to remove material and arrive at the required shape,
a 3D printer starts with nothing and add stuffs to it. The adding is done
according to instructions from a computer program that contains a virtual
representation of the object to be made, stored as a series of thin slices.
These slices are reproduced as successive layers of material until the final
shape is complete.
Typically, the layers are built up by extruding filaments of molten polymer, by
inkjet-printing material contained in cartridges or by melting sheets of powder
with a laser. Adidas s soles, however, emerge in a strikingly different way one
that is, according to Joseph DeSimone, the result of chemists rather than
engineers thinking about how to make things additively. Dr DeSimone is the boss
of Carbon, the firm that produces the printer which makes the soles. He is also
a professor of chemistry at the University of North Carolina, Chapel Hill.
Carbon s printer uses a process called digital light synthesis, which Dr
DeSimone describes as a software-controlled chemical reaction to grow parts .
It starts with a pool of liquid polymer held in a shallow container that has a
transparent base. An ultraviolet image of the first layer of the object to be
made is projected through the base. This cures (ie, solidifies) a corresponding
volume of the polymer, reproducing the image in perfect detail. That now-solid
layer attaches itself to the bottom of a tool lowered into the pool from above.
The container s base itself is permeable to oxygen, a substance that inhibits
curing. This stops the layer of cured polymer sticking to the base as well, and
thus permits the tool to lift that layer slightly. The process is then repeated
with a second layer being added to the first from below. And so on. As the
desired shape is completed, the tool lifts it out of the container. It is then
baked in an oven to strengthen it.
Dr DeSimone says that digital light synthesis overcomes two common problems of
3D printing. First, it is up to 100 times faster than existing polymer-based
printers. Second, the baking process knits the layers together more
effectively, making for a stronger product and also one that has smooth
surfaces, which reduces the need for additional processing.
All this, he reckons, makes digital light synthesis competitive with injection
moulding, a mass-production process which has been used in factories for nearly
150 years. Injection moulding works by forcing molten plastic into a mould.
Once the plastic has solidified, this mould opens to eject the part. Injection
moulding is fast and extremely accurate, but making the moulds and setting up
the production line is slow and expensive. Injection moulding is therefore
efficient only when making thousands of identical things.
The usual economies of scale, however, barely apply to 3D printers. Their
easy-to-change software means they can turn out one-off items with the same
equipment and materials needed to make thousands. That alters the nature of
manufacturing. For example, instead of having vast warehouses packed with spare
parts, Caterpillar and John Deere, two American producers of construction and
agricultural equipment, are working with Carbon on moving their warehouses, in
effect, to the online cloud, whence digital designs can be downloaded to
different locations for parts to be printed to order.
Printers made by established producers are improving, too. They are speeding
up, enhancing quality and printing more colours and in a wider variety of
polymers, including rubbery materials. Two of the biggest firms in the
business, 3D Systems and Stratasys, were joined last year by a third American
company when HP, well known for conventional printers in offices, entered the
market with a range of 3D plastic printers costing from $130,000. According to
the latest report by Wohlers, a consultancy, the number of firms manufacturing
serious kit for 3D printing (ie, not hobby printers, but systems priced from
$5,000 to $1m and more) rose to 97 in 2016 from 62 a year earlier. Nor is
purchase always necessary. Whereas many producers sell their machines outright,
Carbon follows a software model and leases them to customers at a price
starting from $40,000 a year. And, like software firms, it updates its machines
over the internet.
New metallica
Printing polymers, which have low melting-points and co-operative chemistry, is
reasonably easy. Printing metals is another matter entirely. Metal printers use
either lasers or electron beams to reach the temperatures needed to melt
successive layers of powder into a solid object. This takes place in multiple
stages: depositing the powder, spreading it and, finally, fusing it.
Such printers can produce extremely intricate shapes, but may need to run for
several days to make a single item. For high-end components used in low-volume
products, such as supercars, aircraft, satellites and medical equipment, this
can, nevertheless, be worth the wait. 3D printing, which is able to create
voids inside objects far more easily than subtractive manufacturing can manage,
increases the range of possible designs. There are cost savings, too. Addition,
which deposits metal only where it is needed, generates less scrap than
subtraction. That saving matters. Many of the specialist alloys used in
high-tech engineering are exotic and expensive.
These advantages have been enough to persuade GE, one of the world s biggest
manufacturers, to invest $1.5bn in 3D printing. In Auburn, Alabama, for
example, the firm has spent $50m on a factory to print fuel nozzles for the new
LEAP jet engine, which it is building with Safran of France. By 2020, the plant
in Auburn should be printing 35,000 fuel nozzles a year.
A kilo saved is a trophy won
Each LEAP uses 19 nozzles, which have new features, such as complex cooling
ducts, that GE says can be created in no other way. The nozzles are printed as
single structures instead of being welded together from 20 or more components
as previous versions were. The new nozzles are also 25% lighter than older
designs, which saves fuel. And they are five times more durable, which reduces
servicing costs.
More such developments are coming. GKN Aerospace, a British firm, recently
signed a five-year agreement with Oak Ridge National Laboratory, in Tennessee,
to find new ways to print large structural aircraft parts in titanium. The
intention is to reduce waste material by as much as 90% and to cut assembly
time in half.
Existing metal printers can be as big as a car, and some cost $1m or more.
What, though, might companies achieve if they had smaller, cheaper metal
printers? Ric Fulop thinks he can make such machines. Mr Fulop is the boss of
Desktop Metal, a firm he co-founded in 2015 with a group of professors from the
Massachusetts Institute of Technology and nearly $100m in cash from investors
that include GE, Stratasys and BMW. The firm s first printers are now coming to
market.
Instead of zapping layers of powder with a laser or an electron beam, Desktop
Metal s machines use a process called bound-metal deposition. This also
involves a bit of cooking. First, the machine extrudes a mixture of metal
powder and polymers to build up a shape, much as some plastic printers do. When
complete, the result goes into an oven. This burns off the polymers and
compacts the metal particles by sintering them together at just below their
melting point. The outcome is a dense metallic object, rather like one that has
been cast the old-fashioned way as a solid chunk of metal. The sintering causes
the object to shrink. But this can be compensated for by printing it a little
larger than required, because the shrinkage occurs in a predictable way.
Desktop Metal makes two sorts of machine. Its Studio system, priced at around
$120,000, is designed for prototypes and small production runs. A full-scale
system costs just over $400,000. By incorporating a conventional metal printer
s multiple production stages into a single sweep of the print head, Desktop
Metal s machines are fast. According to Mr Fulop, they can build and bake
objects at the rate of 500 cubic inches (8,194cm3) an hour. That compares with
about 1-2 cubic inches with a conventional laser-based metal printer, or 5
cubic inches with an electron-beam machine.
On top of all this, because the materials used by Desktop Metal s printers are
already employed in other industrial processes they are, according to Mr Fulop,
80% cheaper than some specialist 3D-printing powders. And they require less
finishing to remove rough surfaces. Improvements such as these can change the
economics of manufacturing (see article).
Printing a bit of you
One of the earliest adopters of additive manufacturing was the medical
industry. For good reason; everybody is different, and so, therefore, should be
any prosthetics they might need. As a result, millions of individually sculpted
dental implants and hearing-aid shells are now printed, as are a growing number
of other devices, such as orthopaedic implants. The big prize, however, is
printing living tissue for transplants. Though this idea is still largely
experimental, several groups of researchers are already using bioprinters to
make cartilage, skin and other tissues.
Bioprinters can work in several ways. The simplest use syringes to extrude a
mixture of cells and a printing medium, a method similar to that used by a
desktop printer in plastic. Others employ a form of inkjet printing. Some
medical researchers are trying a form of 3D printing called laser-induced
forward transfer. In this, a thin film is coated on its underside with the
material to be printed. Laser-pulses focused onto the film s upper surface
cause spots of that material to detach themselves and land on a substrate
below. Sometimes, though, the third dimension needs a helping hand. Certain
printers therefore impose the desired shape by printing cells directly onto a
pre-prepared scaffold, which dissolves away once the cells have proliferated
sufficiently to hold their own shape.
Anthony Atala and his colleagues at the Wake Forest Institute for Regenerative
Medicine, in North Carolina, have printed ears, bones and muscles in this way,
and have implanted them successfully into animals. The crucial part of the
process is ensuring the printed tissue survives and then integrates with the
recipient when transplanted. Some types of tissue, such as cartilage, are easy
to grow outside the body. Infusing nutrients into the medium they are kept in
is sufficient to sustain them, and they tend to take well when transferred to a
living organism. More complex structures, though, like hearts, livers and
pancreases, require a blood supply to grow beyond being tiny slivers of cells.
Dr Atala and his colleagues therefore print minute channels through their
structures, to let nutrients and oxygen diffuse in. This encourages blood
vessels to develop. The next step, probably within a few years, will be to test
such bioprinted material on people.
All clever stuff. But what was missing in bioprinting, reckoned Erik Gatenholm
and Hector Martinez, two biotechnology entrepreneurs, was some form of
standardised bio-ink . So, in January 2016, they founded a firm called Cellink
to commercialise bioprinting materials developed at the Chalmers University of
Technology, in Gothenburg, Sweden.
Cellink s ink is made from nanocellulose alginate, a biodegradable material
containing wood fibres and a sugary polymer found in seaweed. Researchers first
mix their cells into the bio-ink and then extrude the result as a filament from
which the desired shape is constructed. The company has gone on to develop
tissue-specific bio-inks that contain growth factors needed to stimulate
particular types of cells, including stem cells. These are cells that can
proliferate to produce any of the cell types that form a particular tissue. If
the stem cells in question are obtained from the patient into whom the
transplant will later be inserted, that will reduce the risk that the
transplant will be rejected.
In addition to making bio-ink, Cellink has also launched its own range of
printers. These are sold at a discount to universities in return for research
feedback. That provides a good picture of what is going on. In particular, says
Mr Gatenholm, advances are being made in printing tissues for drug testing. One
is to employ a patient s own cancer cells to print multiple versions of his
tumour. Each can then be challenged with a different drug, or mixture of drugs,
to help determine what treatment will work best. For actual transplantation, Mr
Gatenholm suggests that cartilage, followed by skin, are likely to be the first
tissues printed for such use. Organs that need blood vessels will follow.
Bioprinting, then, looks set to become a new manufacturing industry albeit one
located at medical centres and operating in sterile conditions that more
resemble a laboratory than a production plant. But even the less esoteric forms
of 3D printing, those involving plastics and metals, will transform what a
factory is. The 3D print shops of the future will still have some workers. But
those will mainly be hardware and software engineers. And they are more likely
to be wearing white coats rather than overalls.