Apr 25, 2018 | By David

A team of researchers based at Carnegie Mellon University have made use of 3D printing technology to create an impressive range of self-folding 3D objects. Their Thermorph 3D printing method exploits a common flaw in 3D printing, which is warpage in a plastic object after it is printed. This allowed the team to use a relatively basic desktop FDM 3D printer to build their self-folding objects, making their approach much more affordable than similar approaches for 3D printing self-folding "4D" objects that have been developed in the past.

When an object is 3D printed, there will be residual stress left within its structure from the process. When the object cools, this stress is relieved in a way that makes the thermoplastic contract, leading to warped edges and surfaces. The Thermorph technique works by precisely controlling this process, varying the speed at which thermoplastic material is deposited and combining warp-prone materials with rubber-like materials that resist contracture.

The objects are printed flat, and then placed into hot water to trigger the controlled warping process. In this way the flat objects can transform into any number of different 3D objects with shapes that are pre-determined in the design phase. Examples that the team has created so far include a rabbit, a rose and a boat. The geometric shapes that they printed often had up to 70 faces.

The 3D printing system that the team used for the Thermorph structures was a basic one, but they made use of advanced software they built specifically for this task. Replacing the printer’s open-source code, they implemented a program that can automatically determine the exact print speeds and 3D patterns that are necessary to achieve particular folding angles and realize specific shapes.

"The software is based on new curve-folding theory representing banding motions of curved area", said Byoungkwon An, a research affiliate at Carnegie Mellon’s Human-Computer Interaction Institute. "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."

The team believes that their Thermorph approach could save between 60 and 87 percent of the printing time required for all of the shapes that they tested out in their study. It has so far only been demonstrated on smaller objects, but in future it could be scaled up to have many useful applications for a number of different fields. Products such as flat-pack furniture could be 3D printed in a way that allows them to quickly assume their final shapes with the help of a heat gun. Emergency shelters could also be shipped flat and then folded into the appropriate shape under the warmth of the sun. The cost and speed of the technique means it could also be useful for printing prototypes or noncritical parts, such as molds for boat hulls and other fiberglass products.

Thermorph was a collaborative effort, and the CMU researchers worked with researchers from Zhejiang University, Syracuse University, University of Aizu, and TU Wien. Lining Yao, assistant professor in CMU’s Human-Computer Interaction Institute and director of the Morphing Matter Lab, will be presenting the research at CHI 2018, the Conference on Human Factors in Computing Systems. This is held April 21-26 in Montreal, Canada.



Posted in 3D Printing Application



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