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| Editors in charge |
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Anne Katharine Dahl, NTNU |
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Gunnar Sand, SINTEF |
| Editor: |
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Åse Dragland, SINTEF |
| Editorial coordinator |
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Nina E. Tveter, NTNU |
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Spare parts from powder
Tired of waiting for spares for your car? In the future, you will
be able to make some of them quickly and easily yourself, if all goes
well with some Norwegian experiments.
By Svein Tønseth
Imagine a workbench, with a machine that can be filled with various types
of metal powder. From the Internet you download a three-dimensional “blueprint”
that tells the machine what sort of spare part you want. A “layered”
manufacturing process starts inside the machine. Thin layers of metal
powder are laid on top of each other and heated, so that the powder particles
grow together and turn into solid metal. A finished spare part pops out
after a few minutes, or perhaps a few hours, depending on how high it
is.
The idea of such a machine came to Øyvind Bjørke when he
was a professor at what was then NTH in the early nineties; today, he
is head of his own high-technology company in Germany.
He called the process “Metal Printing” and two postgraduate
engineering students developed it further in the course of their doctoral
studies. Now, SINTEF has launched a NOK 40 million, five-year project
to continue the process of development and turn the machine into reality.
– If we are successful, this could revolutionize our way of producing
things, just as the mobile telephone has changed the way in which we communicate,
says research director Odd Myklebust at SINTEF Industrial Management.
The NOK 40 million will go into a strategic institute programme at SINTEF
Industrial Management. The US aircraft and armaments manufacturer Lockheed
Martin want to put a further NOK 10 million into the project, if the Norwegian
Ministry of Defence is willing to recognize such a contribution as part
of a specific buy-back agreement.
The strategic research programme is being funded by the Research Council
of Norway, SINTEF, NTNU and the Norwegian companies SensoNor, Raufoss
and Kongsberg Defence Communications. Industry itself will be the first
market for the new technology, according to Odd Myklebust and Roald Karlsen,
who has a doctorate in Metal Printing and is currently a postdoctoral
fellow at NTNU. Both researchers believe that it will be several decades
before a “domestic” version of the machine reaches the market.
– There are still several technological challenges to overcome, but
we aim to establish a company to manufacture Metal Printing machines within
five years, says Roald Karlsen and with his doctorate in this area he
will be playing a key role in the project.
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Illustration: Roar Øhlander
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More than just spares
There are potential benefits at all “levels”. Karlsen and Myklebust
prophesy that Metal Printing machines will be installed on board space
stations, so that astronauts will be able to produce their own spares.
– This would be cheaper than launching rockets with new components,
says Myklebust laconically. The scientists also believe that the world
will see warships that make their own spares while they are at sea, while
they expect the technology to have other benefits for users ashore:
- Simpler production of components in exotic materials – everything
from aircraft engines to artificial limbs. Such products have to be
manufactured in hard materials and often have complex shapes, making
them difficult to machine by milling or turning, for example.
- More sophisticated electronics: because the products are built up
in layers, it ought to be possible to combine metals (conductors) and
ceramics (insulators) in new ways, which in turn would lead to completely
new electronic components.
- New combinations of materials: changing powder from layer to layer
should make it possible to join materials that cannot be laid on top
of each other at present. The superknife of the future, for example,
could have a relatively soft core and gradually change to harder materials
on the outside. Such a knife would withstand all sorts of abuse without
becoming notched or broken.
- Much faster production of moulds for casting plastics.
But what about you and me? Karlsen and Myklebust believe that Metal
Printing will gradually affect all our lives. The local garage may be
the first place we will see such machines. Today, a brake disc may be
transported halfway around the world before it ends up in the importer’s
spare-parts warehouse. In the future, local workshop could make one
while you wait
The researchers also prophesy that at some time in the future, anyone
who enjoys tinkering with cars will have his own Metal Printing machine
in the cellar. You would be able to make your own water pumps, brake parts
and cogs for the gearbox, for example, not to mention parts for the lawnmower
and the washing machine. If you needed to repair the awning over the living-room
window, you could simply “print out” the bolts you required.
And why not make the right size of spanner while you are at it?
But perhaps this is only something for millionaires?
– It’s clear that the first machines will be expensive. But
we should gradually be able to bring prices down to a level that would
make them attractive for everyone, says Roald Karlsen.
Professor Øyvind Bjerke, the father of the concept, had been producing
objects in plastics using a similar method when he began to play around
with the idea of Metal Printing. During the 1980s, the Americans developed
a machine that builds up plastic models layer by layer, giving product
developers overnight prototypes. On Bjørke’s initiative NTNU
and SINTEF soon acquired a machine of this type.
These machines are fed with computerized drawings of objects divided up
into thin layers, and are filled with liquid plastic that solidifies when
it is exposed to light. A laser beam draws and hatches each layer inside
the machine to form the model. But how to get from there to a machine
that build up metal objects layer by layer? Quite a few people put their
minds to this problem, and some manufacturers are already on the market
with such machines - equipment that “draws” with laser light,
but in which the liquid plastic is replaced by powdered metal.
According to Karlsen, two variants of the process are already on the
market: one of them requires a special powder, which limits the range
of materials that can be used. In the other, the powder particles are
covered with a binder. This means time-consuming post-treatment, and in
may cases other processes that mean that the final product is a combination
of materials rather than being homogeneous.
But Oyvind Bjerke thought things through in a different way, and was able
to avoid these limitations.
First, he abandoned the laser altogether. Instead, he wanted to have a
movable plate that would be capable of attracting a very thin layer of
metal powder by means of electrostatic forces. The layers would be formed
because the plate would have tiny chargeable points acting as conductors
that attract the powder. The plate would then carry the layers to a construction
board and place them on top of each other while they were heated up, surrounded
by a supporting powder.
During the mid-90s he recruited Jim Bakkelund and Roald Karlsen as doctoral
students. Bakkelund was the first to start; he retained the idea of exploiting
electrostatic forces, but with a new “twist”. He took the “works”
out of a photocopier, including the photoreceptor; a plate which take
up a charge when it is brought close to a power sources. It also loses
its charge when it is illuminated, though it retains it wherever it has
remained in shadow. When a page in a photocopier is illuminated, the text
casts a shadow on the photoreceptor. Where it has remained dark it absorbs
toner powder. The photoreceptor is then carried to the fresh page, on
which it deposits its powder.
Would it be possible to use the same method with metal powder, and repeat
the whole process layer by layer? Bakkelund constructed an experimental
using the components of the photocopier. Then he and Karlsen began to
carry out their tests. Late one evening they were given the encouragement
they needed.
Box of tricks
In a low-ceilinged windowless room Roald Karlsen tells us all about it.
The experimental machine stands in front of us in a brown timber chest.
The photoreceptor, a brownish plate, is fixed underneath a thin 20 x 20
cm aluminium plate that can be moved along a set of rails.
The receptor’s route starts above the “charging station”,
which consists of a practically invisible Wolfram wire, which is there
to charge up the photoreceptor. Its next stop is a small light-box which
fires off short pulses of light. On top of the light-box lies a glass
plate, on which the doctoral students laid their paper “shadows,
In the final version the glass plate will be replaced by a programmable
screen.
The third stop is a “powder bed”, on which they placed a layer
of powdered iron. Time and again they changed the test conditions, opened
the chest and were disappointed. But late one evening, they removed the
photoreceptor and saw that it was covered in powder, in just the shape
it ought to be.
– This was Jim’s area. He managed to show that layers of powder
can be built up in any form, explains Roald Karlsen.
– Now, the next challenge will be to transfer the powder to the building
board. For the time being, we don’t have a completely adequate method
of freeing the powder from the receptor as we wish. This is one of the
blocks we hope to put into place in the course of this new project, says
Karlsen.
He concentrated on the final link in the process. Then he placed layer
after layer of metal powder one on top of the other and heated up each
layer by passing an electric current through it. Metal Printing is not
a matter of smelting, but rather of sintering, a process that takes place
below the melting point of the metal powder. In sintering, the atoms migrate
through the lattice in the crystalline matrix of the metal, building bridges
of material between individual particles and transforming the powder into
solid metal. The researchers still do not know how they are going to heat
up the powder to sinter it in the final version. This is another problem
which is due to be solved when scientists from three SINTEF institutes;
Industrial Management, Materials Science and Electronics and Cybernetics,
as well as several doctoral students at NTNU, start the main research
project.
The method chosen by Karlsen turned each layer of powder into metal in
less than a second, at the same time as it sintered itself to the previous
layer. – Even under the microscope it was impossible to see where
one layer became the next, he says.
On the way out of the modern research building behind the local sports
stadium I meet senior research scientist Odd Myklebust again.
– Most people raise their eyebrows when I say that in the future
we may be able to make spare parts for our cars at home, he says. –
So I usually mention the head of one of the biggest electronics companies
in the world. Some years ago he was talking about computers, and he said
that he couldn’t imagine them in people’s homes….
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