light based 3d printing

3D printer fashions objects from light to create superior models to traditional methods

Image credit: uc berkley

Scientists have developed a new type of 3D printer that uses light to transform gooey liquids into complex solid objects in only a matter of minutes.

The team of University of California Berkeley (UCB) researchers nicknamed the machine ‘Replicator’, after the ‘Star Trek’ device that can materialise any object on demand.

The 3D printer can create objects that are smoother, more flexible and more complex than anything currently possible with traditional 3D printers.

The new process can also encase an existing object with new material - for instance, adding a handle to a metal screwdriver shaft - which current printers struggle to do.

The technology has the potential to transform how products from prosthetics to eyeglass lenses are designed and manufactured, the researchers said.

“I think this is a route to being able to mass-customise objects even more, whether they are prosthetics or running shoes,” said Hayden Taylor, assistant professor of mechanical engineering at UCB.

“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.”

Most 3D printers, including other light-based techniques, build up 3D objects layer by layer. This leads to a ‘stair-step’ effect along the edges. They also have difficulties creating flexible objects because bendable materials could deform during the printing process and supports are required to print objects of certain shapes, such as arches.

The new 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 entire desired shape 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,” said Taylor. “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 and the team used the printer to create a series of objects, from a tiny model of Rodin’s ‘The Thinker’ statue to a customised jawbone model. Currently, they can make objects up to four inches in diameter.

“This is the first case where we don’t need to build up custom 3D parts layer by layer,” said Brett Kelly, who co-first authored the paper on the printer. “It makes 3D printing truly three-dimensional.”

The new printer was inspired by the computed tomography (CT) scans that can help doctors locate tumors and fractures within the body.

CT scans project X-rays or other types of electromagnetic radiation into the body from all different angles.

“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 liquid that you don’t want to cure is certainly having rays of light pass through it, so there needs to be a threshold of light exposure for this transition from liquid to solid,” Taylor said.

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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