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Morgen E. Peck

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Printing a Home: The Case for Contour Crafting

Evolving technology could soon fabricate a two-story structure in a day

Published: Thursday, January 19, 2012 - 14:19

It can take anywhere from six weeks to six months to build a 2,800-square-foot, two-story house in the United States, mostly because human beings do all the work. Within the next five years, chances are that 3-D printing (also known by the less catchy but more inclusive term additive manufacturing) will have become so advanced that we will be able to upload design specifications to a massive robot, press print, and watch as it spits out a concrete house in less than a day. Plenty of humans will be there, but just to ogle.

Minimizing the time and cost that goes into creating shelters will enable aid workers to address the needs of people in desperate situations. This, at least, is what Behrokh Khoshnevis, a professor of engineering and director of the Center for Rapid Automated Fabrication Technologies, or CRAFT, at the University of Southern California, hopes will come of his inventions.

A rendering of contour crafting in action (Credit: Contourcrafting.org)

 “Initially it will be most beneficial to developing countries to eradicate their slums,” says Khoshnevis. “Next is emergency-shelter construction, when war or natural disasters uproot thousands of people. [It] can build much cheaper and much faster, and can produce dignified housing rather than tents and boxes.”

Khoshnevis says his system could be ready two years from now, but it may end up on the moon before we see it in Haiti or Somalia. In late November, NASA awarded a grant as part of the NASA Innovative Advanced Concepts (NIAC) to Khoshnevis and his collaborators as a possible way to build lunar structures. The team’s next step is to test the process at the Desert Research and Technology Studies (D-RATS) facility in Arizona.

Contour crafting

Khoshnevis calls his technique “contour crafting,” and it operates on roughly the same principle as consumer 3-D printers like MakerBot’s Thing-O-Matic. His robot pours out a trail of viscous concrete while tracing along the footprint of a wall. As the nozzle sweeps back and forth, the layers rapidly build, with the lower ones hardening enough to support the increasing weight. Its speed puts construction workers to shame.

“We are talking about a technology that can build a square foot of wall in less than 20 seconds,” Khoshnevis says. At that rate, contour crafting can put together a whole room in just an hour.

It took awhile to figure out how to make a printer that could build large objects at that speed. Most 3-D printers—those that make shapes using plastics—build in tiny layers, often only 0.01 mm thick. The number of layers determines the resolution of the object. Just like the pixels in a digital camera, where the more you have, the more accurate the product will be. But when Khoshnevis tried building from such thin layers, the process took too long to be useful.

Eventually, he found that he could build with much bigger layers, more than an inch thick, if he used a tool to smooth out the concrete as it flowed from the nozzle. Ultimately, he attached two swiveling trowels that let him remold the concrete into any angle.

Other robotic fixtures could be added to the printer, giving it the capability to install plumbing and electrical wiring. A gripper would place support beams and lay out a layer of metal over the top of the walls to create a base for the ceiling and roof.

Printing a cube or an octopus

Size is now the only thing holding back the technology. “We have a machine that can build a structure about 23 feet long, about 7 feet high, and about 15 feet wide at this point,” says Khoshnevis.

He estimates that a full-scale printer would break down into three pieces and be small enough to fit onto a flatbed truck. All construction would happen on site. First, a designer would bring a digital blueprint for the house on a thumb drive and plug it into the printer while workers loaded it with concrete. Once the printer was activated, humans would play a supporting role, laying out supplies for the robotic gripper arm and preparing fresh batches of concrete. Humans would also install the windows and doors, since the task is so easy it’s not worth automating, says Khoshnevis.

Not only will it be faster, 3-D printing could enable architects to design in completely new ways.

“There are definitely interesting implications,” says Sean Bailey, an architect and artist in New York. “Whereas traditional fabrication techniques require additional resources as complexity increases, 3-D printers are not bound to this logic.” With a 3-D printer, it takes the same amount of time and money to turn a glob of concrete into a cube as it does to turn it into an octopus, says Bailey.

As masonry has become more of a specialized, and therefore expensive, skill, curvy architecture has become more difficult to produce. However, 3-D printing could bring back some of these shapes.

“There are numerous shapes that you can make with contour crafting that cannot be made by conventional construction, such as doubly curved surfaces, which would be extremely cost-prohibitive to build by current methods,” says Khoshnevis.

This article first appeared in TXCHNOLOGIST.


About The Author

Morgen E. Peck’s default image

Morgen E. Peck

Morgen E. Peck is a contributor to IEEE Spectrum, Txchnologist, Innovation News Daily, and Scientific American. Her last article for Txchnologist looked at the challenges of building a house on Mars.

Txchnologist is an online magazine sponsored by GE. Every week, we offer an optimistic, but not utopian, take on the future and humanity’s ability to tackle the great challenges of our era through industry, technology and ingenuity.


Printing a home with reinforcement

Why couldn't reinforcement be added as part of the "printing" process.  Automated concrete pipe plants draw wire to the correct gauge, automatically size and weld the reinforcement cages, place them in the "forms", place the concrete and move the finished product to the loading dock.  Rather than trying to scale up a miniature "3-d printer", it might be more helpful to go to an actual automated production plant to see how real concrete products are made; and then, figure out how to adapt a universal production controller to existing methods.  It would save a lot of reinventing the wheel, and, would result in a much better quality concrete product.

Printing a Home

In regards to it's use to provide housing following natural disasters (Haiti was mentioned), how will this structure, made of unreinforced concrete, withstand the next earthquake?


Recapitulating History?

It seems to me that I've seen this same idea before...there is a film clip that I remember from the 1950s or early '60s lauding the advantages of automated fabrication of concrete housing. I even remember a large rig similar to that pictured here, using some sort of cast-in-place technology with heavy automation.

I wish that I could find a link to that old clip; it would be interesting to compare to this new technology to the old one.