Research Team Takes Advantage of Common FFF 3D Printing Defect to 4D Print Plastic Self-Folding Objects

A lot of research has been undertaken regarding 3D printed self-folding structures and 3D printed items that can self-assemble, but a team from Carnegie Mellon University is changing things up in the field by using an inexpensive 3D printer to fabricate flat, self-folding items made from plastic. The researchers, from the university’s Human-Computer Interaction Institute (HCII), have developed 4D printed flat plastic items that fold themselves into predetermined shapes, like a boat, a bunny, and a rose, once they’re heated.

While other research teams have used more unique materials or complex processing technologies to develop 3D printable self-folding materials, the HCII researchers were able to do the same thing with an inexpensive, extrusion-based 3D printer – a MakerBot Replicator 2X – by taking advantage of the common FFF defect of warpage.

Lining Yao, director of the university’s Morphing Matter Lab and an assistant professor in HCII, explained, “We wanted to see how self-assembly could be made more democratic — accessible to many users.”

Materials that self-fold are less expensive, and faster, to produce than solid 3D printed objects. This means that noncritical parts are able to be replaced, or prototypes produced, with structures that only have to approximate a solid object. According to Yao, her team’s self-folding 3D printed plastic objects are representative of a first step towards the possibility of making products like fiberglass boat molds for less money.

Earlier this week, Yao presented the group’s research on their method, dubbed Thermorph, at the Conference on Human Factors in Computing Systems (CHI 2018) in Montreal. Co-authors of the paper, titled “Thermorph: Democratizing 4D Printing of Self-Folding Materials and Interfaces,” include Byoungkwon An, Ye Tao, Jianzhe Gu, Tingyu Cheng, Xiang ‘Anthony’ Chen, Xiaoxiao Zhang, Wei Zhao, Youngwook Do, Shigeo Takahashi, Hsiang-Yun Wu, Teng Zhang, and Yao.

According to the paper’s abstract, “To demonstrate the Thermorph platform, we designed and printed complex self-folding geometries (up to 70 faces), including 15 self-curved geometric primitives and 4 self-curved applications, such as chairs, the simplified Stanford Bunny and flowers. Compared to the standard 3D printing, our method saves up to 60% – 87% of the printing time for all shapes chosen.”

FFF 3D printing lays down a continuous strand of melted thermoplastic filament, which contains residual stress. Once the material cools down and that stress is relieved, the material contracts, which results in warped surfaces, edges, and user annoyance…usually.

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

The team, which also includes members from Duke University, Zhejiang University, Syracuse University, Glodon Company Limited, the University of Aizu, and TU Wien, control this warping process by changing up the speed at which the thermoplastic is deposited to create their self-folding objects. In addition, they also combine rubber-like materials that resist contracting with warp-prone materials.

The objects are removed from the print bed as hard, flat plastic. But, when placed in water that’s been heated enough to make it rubbery and soft, but not too hot to melt it, the materials fold up into predetermined shapes.

The team also had to figure out how to automate the process.

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

Instead of using open source software, the researchers replaced it with their own code, which calculates the print speed and patterns needed to achieve certain folding angles automatically.

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

These first 4D printed examples are quite small, as they were only made on a desktop 3D printer. But the team believes that it’s possible in the future to print larger self-folding objects.

Gu said, “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.”

In addition to boat hulls, Yao says that the team’s self-folding plastic objects could also someday lead to furniture that’s packed flat but folds into its final shape once exposed to a heat gun, and even flat-pack emergency shelters that could fold up in the sunshine.

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[Source/Images: Carnegie Mellon University]