Light based 3D printer shapes custom objects from liquid resin

Hayden Taylor, assistant professor of mechanical engineering at the University of California, Berkeley, and senior author of a paper on the technology explained that the printer relies on a viscous liquid that reacts to form a solid when exposed to a certain threshold of light. Projecting carefully crafted patterns of light - essentially "movies" - onto a rotating cylinder of liquid solidifies the desired shape "all at once."

"Basically, you've got an off-the-shelf video projector, which I literally brought in from home, and then you plug it into a laptop and use it to project a series of computed images, while a motor turns a cylinder that has a 3D-printing resin in it," Taylor said. "Obviously there are a lot of subtleties to it - how you formulate the resin, and, above all, how you compute the images that are going to be projected, but the barrier to creating a very simple version of this tool is not that high."

Taylor said that the light based 3D printer is able to create objects that are smoother, more flexible and more complex than those produced with traditional 3D-printers. It can also encase an already existing object with new materials - for instance, adding a handle to a metal screwdriver shaft. "The fact that you could take a metallic component or something from another manufacturing process and add on customisable geometry, I think that may change the way products are designed," he added.

Taylor and the team used the printer to create a series of objects, from a tiny model of Rodin's "The Thinker" sculpture to a customised jawbone model. Currently, they can make objects up to four inches in diameter.

The group claims the technology has potentially significant advantages over other 3D printing techniques – which typically build up 3D objects layer by layer, often leads to a "stair-step" effect along the edges.

The light based 3D printer was inspired by the computed tomography (CT) scans that can help doctors locate tumours and fractures within the body.

CT scans project X-rays or other types of electromagnetic radiation into the body from all different angles. Analysing the patterns of transmitted energy reveals the geometry of the object.

"Essentially, we reversed that principle," Taylor said. "We are trying to create an object rather than measure an object, but actually a lot of the underlying theory that enables us to do this can be translated from the theory that underlies computed tomography."

Besides patterning the light, which requires complex calculations to get the exact shapes and intensities right, the other major challenge faced by the researchers was how to formulate a material that stays liquid when exposed to a little bit of light, but reacts to form a solid when exposed to a lot of light.

The 3D-printing resin is composed of liquid polymers mixed with photosensitive molecules and dissolved oxygen. Light activates the photosensitive compound which depletes the oxygen. Only in those 3D regions where all the oxygen has been used up do the polymers form the "cross-links" that transform the resin from a liquid to a solid. Unused resin can be recycled by heating it up in an oxygen atmosphere, Taylor said.

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