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Construction Corner: 3-D printing method produces moulds for structural elements

0 380 Technology

by Korky Koroluk

We’ve heard a lot about 3-D printing and the effect it may have on the construction industry. But there has been something about the repetitive hype that’s made me uneasy.
Korky Koroluk
Korky Koroluk

We're constantly being told that some new tool or gadget or process will "change forever the way you do..."

But there has always been a caveat: The size of what you wanted to print had to be small enough to fit inside the printer's structure, or was limited by the reach of a robotic arm fitted to the printer.

How, I wondered, could a system with such inherent limitations change the way we do anything? I thought 3-D printing was a neat idea, but there had to be a "eureka moment" when someone wondered "what if?" and in the process created a paradigm shift in the way we think of 3-D printing.

My own eureka moment came last week while reading an article in the Economist, a British magazine that I enjoy because of its excellent coverage of so many things besides economics.

The image accompanying the article was shot looking straight up at the Gothic fan-arch vaulted ceiling of the chapel at King's College in Cambridge. It's a beautiful structure. Each fan is a delicate filigree of the sort one never sees in modern construction. Of course the chapel was finished in 1515 and that filigree is stonework.

The article mentions dryly that such structures "seem to have fallen out of fashion," too complicated for modern methods and requiring skilled labour that would be both scarce and expensive.

Now, in the north of England there is a precast concrete factory equipped with a robotic arm hanging over a wide platform. The arm is mounted on a gantry which lets it move in every dimension covering an area 30 metres long by 3.5 metres wide and 1.5 metres deep. It's called FreeFAB and it uses a specialized wax to print extremely precise moulds for casting concrete panels.

This is no experiment.

Operated by Laing O'Rourke, a construction company, FreeFAB is the first time 3-D printing technology is being used on a big commercial project. Hundreds of the panels are being cast for installation in passenger tunnels as part of Crossrail, which is digging a new east-west railway line across London. It's being billed as Europe's biggest construction project.

What we have come to think of as conventional 3-D printing with concrete involves putting down layers one atop the other to make a thicker panel. But an engineer who has worked with 3-D technology points out that the boundaries between the layers introduce weaknesses that make the panels unsuitable for real buildings.

"These things can peel apart," he says.

FreeFAB sidesteps the problem simply by printing moulds instead of printing structural material directly.

The system was invented by James Gardiner, an Australian architect.

Among its advantages is that it creates far less waste than conventional mould-making processes.

Moulds for precasting are normally made from wood and polystyrene and can only be used to produce a single shape. When that's done, they're scrapped and sent to landfill. But the wax that FreeFAB uses can be melted down and poured back into a tank, ready to be extruded again into a new form. Apparently it took Gardiner three years to find a wax that could be imprinted, milled and recycled.

The system makes it cheaper to produce even complex moulds. Those being made for use in Crossrail are for panels that curve along two different axes. Making one the traditional way would take about eight days, the Economist says. FreeFAB can print one in three hours.

So it's possible that the great promise of 3-D printing in construction may not be producing structural elements; it may be in producing moulds for casting those elements, even if they're imitations of complex 16th century ceilings.

Korky Koroluk is an Ottawa-based freelance writer. Send comments to editor@dailycommercialnews.com.

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