New Additive Manufacturing Method Uses Light to Prevent Resin From Curing Against Vat

A new approach to 3D printing uses two-color irradiation of resin formulations that contain both a photoinitiator and a photoinhibitor to perform vat-printing up to 100 times faster than conventional 3D printing processes, said a team of University of Michigan researchers. In the team’s approach, photopatterned polymerization inhibition volumes generated by irradiation at one wavelength spatially confine the region photopolymerized by a second concurrent irradiation wavelength. This allows control over where the resin hardens and where it stays fluid, enabling the resin to solidify into more complex patterns. The inhibition volumes created using this method enable localized control of the polymerized region thickness to allow 3D structures to be printed using a single exposure.

A new way to 3D print, developed at the University of Michigan, uses two lights to control the solidification of resin, enabling complex shapes to be pulled from a vat at 100 times the print speed of conventional 3D printers. Courtesy of Evan Dougherty.

The researchers’ approach overcomes a limitation that can stop a vat-printing job just as it’s getting started — that is, the solidification of the resin on the illumination window. In previous systems, the solidification-on-window problem was solved by allowing oxygen through the window. The oxygen would penetrate the resin and halt its solidification near the window, leaving a film of fluid that would allow the newly printed surface to be pulled away. However, for this technique to succeed, the resin had to flow quickly into the tiny gap between the newly solidified object and the window while the printed part was being pulled away. This limited vat-printing to small, customized objects designed for relatively light use, the researchers said.

The researchers’ method replaces oxygen with a wavelength of light, which produces a larger gap between the object and the window than oxygen, allowing resin to flow in much faster. Because the resin is composed of a photoinhibitor as well as a photoactivator, the new method can pattern the light to harden the resin at essentially any spot near the illumination window.

By creating a relatively large region where no solidification occurs, thicker resins — potentially with strengthening additives — could be used to produce more durable objects, the researchers said. They believe that their method could provide greater structural integrity than filament 3D printing, as objects created using filament printing can have weak points at the interfaces between the layers. “You can get much tougher, much more wear-resistant materials,” professor Timothy Scott said about the U-M team’s approach.

Using the new method, the team was able to make a 3D bas-relief in a single shot rather than in a series of 1D lines or 2D cross-sections. It demonstrated the ability to 3D-print a lattice, a toy boat, and a block “M.”

“It’s one of the first true 3D printers ever made,” said professor Mark Burns.

The university has filed three patent applications, and Scott, who with Burns co-led the development of the new approach to additive manufacturing, is preparing to launch a startup company.

The research was published in Science Advances (https://doi.org/10.1126/sciadv.aau8723).

A new way to 3D print uses a photoinhibitor in the resin and light of a specific wavelength to prevent the resin from curing against the vat. Curing is controlled by the light intensities of both UV and the inhibition light. Courtesy of the University of Michigan.