Researchers at The Hebrew University of Jerusalem (HUJI), Israel, have developed a method in which flat wooden shapes produced by 3D printers can be programmed to self-transform into complex 3D shapes. In the future, this process could be used to produce wooden products that could be exported to a destination and then dried to form the desired final shape.
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What is 3D printing?
3-Dimensional (3D) printing is an additive technology that is used to manufacture 3D objects using a computer-created design. Typically, the items are made by laying down many thin layers of material in succession. This additive process enables the production of complex shapes using less material than conventional manufacturing methods.
How would a self-morphing technology work?
Wood is a very durable and malleable material. This material is used for various applications, such as for making furniture. Wooden furniture is made by carving, bending, sawing or pressing. But the only problem is that it’s too expensive. That’s why researchers programmed flat wooden shapes to self-morph into complex 3D shapes.
The inspiration for this new research came from nature. Wood, for instance, can change its textures and shapes. But due to variations in fibres within the wood, it wraps and shrinks unevenly. “Warping can be an obstacle, but we thought we could try to understand this phenomenon and harness it into a desirable morphing,” said Doron Kam, a Graduate Student at HUJI.
Previously, the researchers had been printing flat sheets that could self-morph into 3D shapes after a stimulus, such as a change in moisture content, temperature or pH. As these sheets were made from synthetic materials, such as elastomers and gels, they wanted to work with natural materials.
Previously, the research team developed water-based ink known as wood flour that contained wood waste microplastics with cellular nanocrystals and xyloglucan, which are natural binders extracted from plants. They used this ink in 3D printers. When the researchers were trying out different compositions with the ink, they found that the pathway in which the material was placed by the printer’s nozzle affected the final printed product as moisture started to evaporate from it. For example, a flat disc printed as a series of concentric circles dries and shrinks to form a saddle-like structure like a Pringles chip. A disc printed as a series of rays coming from a central point turns into a dome-like structure.
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Researchers discovered that the printing speed was another factor that altered the final shape of the printed wood product since shrinkage occurred perpendicular to the wood fibres in the ink. The shrinkage occurred in all directions as the slower rate of printing causes the fibres to orient themselves randomly. This shrinkage was more directional when the printing rate was faster.
The scientists produced several structures by altering print speed and pathway. They noticed that stacking two rectangular layers resulted in a helix when the material dried. They could even control whether the helix spiraled clockwise or anti-clockwise by programming the speed, printing pathway and stacking.
Further refinement allowed the research team to combine domes, saddles, helices and designs to produce complicated objects such as tables or chairs. The ultimate goal is to ship wood products directly to the consumers, which could reduce shipping costs and volume. “Then, at the destination, the object could warp into the structure you want,” said Kam.
Researchers are also investigating whether the morphing process could be made reversible. “We hope to show that under some conditions we can make these elements responsive — to humidity, for example — when we want to change the shape of an object again,” said Eran Sharon, Professor at HUJI.
The researchers presented their results at the fall meeting of the American Chemical Society (ACS).