3D folding materials

Self-folding materials made using cheap 3D printer

Image credit: Carnegie Mellon University

Researchers at Carnegie Mellon University, Pennsylvania, have used an inexpensive 3D printer to produce flat plastic items that, when heated, fold themselves into predetermined shapes, such as a rose, a boat and a bunny rabbit.

Professor Lining Yao, assistant professor in the Human-Computer Interaction Institute and director of the Morphing Matter Lab, said these self-folding plastic objects represent a first step towards creating future products such as flat-pack furniture that could assume its final shape using only a heat gun. Emergency shelters for use in areas of natural disaster or military conflict could also be shipped flat and folded into shape under the warmth of the sun.

Yao has dubbed this new method ‘Thermorph’.

Self-folding materials are quicker and cheaper to produce than solid 3D objects, making it possible to replace noncritical parts or produce prototypes using structures that approximate the solid objects. Moulds for boat hulls and other fiberglass products could also be inexpensively produced using these materials.

Other researchers have explored self-folding materials, but typically have used exotic materials or depended on sophisticated processing techniques not widely available. Yao and her research team were able to create self-folding structures by using the least-expensive type of 3D printer - an FDM printer - and by taking advantage of warpage, a common problem with these printers.

“We wanted to see how self-assembly could be made more democratic - accessible to many users,” Yao said.

FDM printers work by laying down a continuous filament of melted thermoplastic. These materials contain residual stress and, as the material cools and the stress is relieved, the thermoplastic tends to contract. This can result in warped edges and surfaces.

“People hate warpage,” Yao said, “but we’ve taken this disadvantage and turned it to our advantage.”

To create self-folding objects, she and her team precisely controlled the process by varying the speed at which thermoplastic material was deposited and by combining warp-prone materials with rubber-like materials that resist contracture.

The objects emerged from the 3D printer as flat, hard plastic. When the plastic was placed in water hot enough to turn it soft and rubbery, but not hot enough to melt it, the folding process was triggered.

Whilst the team used a 3D printer with standard hardware, the researchers replaced the machine’s open-source software with their own bespoke code which automatically calculates the print speed and patterns necessary to achieve particular folding angles.

“The software is based on new curve-folding theory representing banding motions of curved area. The software based on this theory can compile any arbitrary 3D mesh shape to an associated thermoplastic sheet in a few seconds without human intervention,” said Byoungkwon An, a research affiliate in HCII.

“It's hard to imagine this being done manually,” Yao said.

The early folded-object examples produced by the team are at a desktop scale, but making larger self-folding objects appears feasible.

“We believe the general algorithm and existing material systems should enable us to eventually make large, strong self-folding objects, such as chairs, boats or even satellites,” said Jianzhe Gu, HCII research intern.

Research into foldable materials and objects has increased in popularity in recent years as the cost and flexibility of 3D printing has become cheaper and more appealing.

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