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Fast 3-D Method Shapes Objects With Light

Model of The Thinker

Model of Rodin’s The Thinker made with computed axial lithography (Stephen McNally, Univ of California – Berkeley)

1 Feb. 2019. A new three-dimensional printing method harnesses rotating light waves to quickly produce objects at miniature scale on demand with common polymers and hydrogels. A team from University of California in Berkeley and Lawrence Livermore National Laboratory describe their process in yesterday’s issue of the journal Science.

Researchers from the Berkeley nanomanufacturing design lab of mechanical engineering professor Hayden Taylor are seeking better methods for additive manufacturing, the industrial form of 3-D printing, to produce small, complex custom-made items, such as those used in medical devices and aerospace systems. Most of today’s 3-D printing technologies print in layers, sometimes in very small increments, but rarely resulting in completely smooth objects. The technology’s limitations are further evident when producing soft or flexible materials that can bend from their intended shape during the print process, or printing an object that adds to an existing item.

Taylor and colleagues devised an alternative 3-D printing process that shapes objects with light waves beamed into photosensitive liquids that they say addresses these issues. The process the researchers call computed axial lithography — which they nicknamed The Replicator — begins with a 3-D computer model of an item that dissects the object into thin visual slices, similar to computed tomography or CT scans used in medical images.

The image slices are then assembled into a time-sequence video file that drives light beams into photosensitive materials to produce the object. This shaping process also borrows from medical technologies that use CT scans to deliver measured radiation doses for treating cancer. In this case, the light beams release free radicals that oxidize the target material, but are quickly extinguished when exposed to oxygen. The print-shaping method can be fine-tuned with non-oxidizing materials or adding dyes to block the light beams. After shaping the objects, the materials are cured, with excess materials, if any, removed with solvents.

The Berkeley-Livermore team tested their process with highly viscous liquid resins and hydrogels made from common acrylate polymers, like those found in vinyl. The light-beaming hardware likewise uses a commercially-available video projector. The tests show computed axial lithography can produce items as small as 0.3 millimeters. The process enables the team to produce items around existing hard objects with, as an example in their tests, a handle for a screwdriver bit. Most objects are produced in less than a minute.

The researchers further tested computed axial lithography producing complex objects with lattice structures and a model of a lower jaw, including teeth. As a signature item, the team produced a small-scale model of Rodin’s iconic sculpture The Thinker. As currently configured, the process can generate objects as large as 4 inches in diameter.

Taylor says computed axial lithography is more than a production method, but a process that can encourage an entirely new way of approaching product design and manufacturing. “The fact that you could take a metallic component or something from another manufacturing process and add on customizable geometry, I think that may change the way products are designed,” notes Taylor in a university statement. He adds, “I think this is a route to being able to mass-customize objects even more, whether they are prosthetics or running shoes.”

Several of the authors, including Taylor, applied for a U.S. patent on computed axial lithography. The following video demonstrates the process.

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