The Economist UK - 16.11.2019

72 The EconomistNovember 16th 2019

1

B

oat buildingis a long-winded and te-

dious business, even when what is go-

ing down the slipway is a small craft made

from modern materials such as fibreglass,

rather than something nailed together out

of planks of wood. Construct a mould.

Build up layers of resin and glass fibre in-

side that mould. Extract the completed

structure and finish it. All told, it can take

months. That, though, may soon change.

For researchers at the University of Maine

are now in the process of testing an 8-metre

(25-foot) patrol boat that took just 72 hours

to make from scratch (see picture overleaf ).

Their trick was to build the vessel using a

giant 3dprinter.

Since they appeared in commercial

form in the 1990s, 3dprinters have general-

ly been employed in factories to make

small things like prototype models, com-

ponents of jet-engines and dental crowns.

Now, a new generation of outsize printers

is arriving. These are capable of turning out

much bigger objects than previously possi-

ble, and printing them faster.

To print the patrol boat, part of an Amer-

ican army project, the team in Maine

linked up with Oak Ridge National Labora-

tory, in Tennessee, which helped develop

the printing process, and Ingersoll Mach-

ine Tools, in Illinois, which built the prin-

ter itself. The university reckons that for

boat building, a common trade in the state,

large 3dprinters of this sort will dramati-

cally cut the cost and time required to pro-

duce new vessels.

Size matters

Broadly speaking, the biggest object that

can be turned out by a 3dprinter is deter-

mined by the size of the printer itself—and

most printers are not much larger than a

large domestic refrigerator. Over the years

engineers have come up with various ways

of scaling this up a bit, by doing things like

mounting the printing mechanism on a

piece of external scaffolding. But the result

is often a slow and inaccurate device that

turns out things which require a lot of ex-

pensive hand-finishing.

The University of Maine’s printer over-

comes the problem of scale by suspending

the printer’s business end—the nozzle that

extrudes the ink—from a gantry. The ink is

molten thermoplastic resin containing

carbon fibres. Under the control of a com-

puter the nozzle moves horizontally to

build (as is true of any 3d-printing process)

the desired object up layer by layer. After

each layer is complete, the nozzle is raised

slightly to deposit another on top of it until

the object is finished.

And this can be done quickly. The Maine

university printer is able to extrude materi-

al at a rate of 70kg (150lbs) an hour. At the

moment it can make things up to 30 metres

long, 7 metres wide and 3 metres high, but

those dimensions could easily be in-

creased by building a bigger gantry. The

arm carrying the nozzle can also be fitted

with processing equipment, such as an

automated milling head to grind off any

surface imperfections.

Having established the principle, the

university is now looking to change the na-

ture of the composite, to make the process

more environmentally friendly. New Eng-

land’s forestry industry is a potential

source of cellulose fibres that could be in-

Additive manufacturing

Could you print a printing press?

Not yet. But 3D printing can already manage boats and bridges, and will soon

make space rockets—so one day, who knows?

Science & technology

74 Forging rhinoceros horn

74 High-tech rugby

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