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Rise of the Machines | Printing structures

ABC 7082 edit Cropped

Top secret research is going into 3D robot-arm printing of bespoke concrete forms.

Advances in 3D printing are happening at a rapid pace. Glass, metal, plastic and ceramics have all been used in applications from Nasa’s rovers to human body parts. Now the construction industry is hot on the heels of the latest developments, adding concrete to the list. And with exciting results.

Concrete 3D printing is the latest new technology to seemingly promise major changes in the way buildings could be mass produced, with evidence emerging from the United States and China of fully 3D printed houses rising from the ground in a matter of hours.

ABC 7106 edit

ABC 7106 edit

ABB robot designers teamed with Skanska, MTC, Tarmac and Foster & Partners

Here in the UK, contractor Skanska is keen to ensure it is leading the field with its own top secret research into the technology’s more bespoke uses.

With passports verified and phones banned, New Civil Engineer was given a unique insight into this covert laboratory.

“We want to separate ourselves from the competition, so we’re not interested in printing large scale houses with our technology,” says Skanska innovation manager David Lewis. “We’re going after the high value with configurability and lots of different unique products.”

First steps to commercialisation

Loughborough University laid the foundations for the project almost a decade ago with its research into new 3D printing techniques. In November 2014 the first steps  towards commercialisation were taken.

Working with architect Foster & Partners, concrete specialist Tarmac, robot designer ABB, the government-led advanced Manufacturing Technology Centre (MTC) and Skanska, the team embarked on a development programme to create one of the world’s first commercial concrete printing robots.

MTC AMTCVIEW 0006 EDIT small

MTC AMTCVIEW 0006 EDIT small

Research was carried out at the government-led Manufacturing Technology Centre

Like many other 3D printing technologies, the basic technique is to lay material down in lines and build up in layers. But Skanska’s technology differs from its competitors because the concrete dispenser is mounted on a fully articulated robot arm and not an overhead gantry crane, which is limited in its movement. This allows shapes to be built up in ways which cannot be replicated by other, more constrained, systems.

“You can create something which is hollow on the inside or double curve panels,” says Lewis. “At the moment we’re trying to make the process more robust, the printing process and the mixing process.”

One of the fundamental obstacles facing the development team has been the concrete mix design. If it is too liquid, layers could slump into a shapeless mass. If it is too stiff, it loses the ability to be pumped. The rate at which the concrete cures is also key to the design – too fast and the required bond between the layers may not be established, too slow and it will not develop enough strength in time to prevent collapse.Luckily for the team, the initial design for the mix was developed by Loughborough and now only needs to be tweaked for different atmospheric conditions and speeds of printing. As of now, the robot has only been tested indoors. But the team knows the technology will have to perform in a range of environments.

We can print our own shuttering and formwork, and get rid of the three week design and build process

David Lewis, Skanska

Concrete forms are currently being printed with a 9mm diameter nozzle, but Lewis says 10mm, 15mm and 20mm nozzles are all available depending on what the customer might want. The robot arm can achieve impressive speeds of up to 600mm/s, but speed is not the ultimate goal.

Moving away from the mass housing market, the group has a different, bespoke vision for the future of the developing technology. Working with Foster & Partners, the team is using the robot to create geometrically complex panels for buildings – including voids to reduce weight or incorporate services – which could not be made using any other manufacturing technique. Additionally Lewis says each of the panels could easily be printed to be subtly different, a feat which is currently highly costly.

Flexible process

“Our process is a lot more flexible, you can print the components that you cannot precast,” says Lewis. “The precast industry is very good, but there are advantages in being able to print endless variability into the components.”

To do this, instead of using a series of 2D co-ordinates to build up the form, it has brought in robot control specialists Hal Robotics to help it programme the robot in 3D, which allows the printed concrete to incorporate voids, using supporting materials.

“Traditionally you create it in slices and build it up in layers,” says Lewis. “If you’re not bothered about using support material, then the conventional approach with slicing software is fine and straightforward.

“But when you use support material you need to use a more exciting five axis tool approach but unfortunately I can’t talk more about that.”

We want to separate ourselves from the competition, we’re not interested in printing large scale houses

David Lewis, Skanska

For now, these panels are not designed to be structural elements due to the additional testing which would be required. But to create bespoke structural components the team is looking at printing its own formwork.

“A traditional mould on site can make 100 or 1,000 forms, all [forms] the same,” says Lewis. “Not only with this [3D printing method] can you make as many as you like, you can make each one subtly different in design. We can print our own shuttering and formwork, and get rid of the three week design and build process and print our own bespoke formwork on site.

“Being able to have that reconfigurability and being able to change something in the design on the fly is really something we think we can go after. The mould can be printed in a matter of hours and then all it is, is the time it takes to cure.”

Ridging drawback

One area which might be perceived to be a drawback is the ridging on the surface which is created as the concrete is dispensed line upon line. To overcome this, in areas where a different surface finish is desired, Lewis says a subtractive manufacturing technique such as milling or acid etching could be applied by the robot to take away the ridged effect.

“Because we’re using the robot arm, and they’re doing this a lot in the automotive industry, the arm simply rotates round and picks up a milling bit and then just mills everything that it’s just printed,” he says. “It could acid etch or it could fill with filler or it could paint it, it’s just a case of changing the tool.”

When it comes to printing bespoke formwork, he says a design could be printed into the bottom of the mould which would then leave an imprint in the finished object.

Stronger components

Stronger components can also be created by incorporating steel reinforcement into the form. Future testing will look into including fibres in the concrete mix.

“The dream is that construction workers on site with their ipad or tablet, will have the latest revision of the building information modelling (BIM) model and they can press print,” he says. “We’re not that far away from that.”

But the team is not just hoping to get the 3D printing benefits from the project. Lewis says that lessons from the industrialisation of the process is something which can be applied to other problem areas.

“One of the areas is tunnel grouting for example,” says Lewis. “If you could take the 3D printing robot and drive it through the tunnel, the robot could simply articulate its arm and put grout in between the gaps.

 

 

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