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3D printing at UM
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.

3D Printing With Two Lights Build Speed by a Factor of 100

New 3D printer uses two lights to make complex shapes rather than just flat layers.

Rather than building up plastics layer by layer, a new approach to 3D printing developed at the University of Michigan lifts complex shapes from a vat of liquid at up to 100 times faster than conventional 3D printing processes.

3D printing could change the way small manufacturing jobs producing fewer than 10,000 identical items are done. It would also mean the objects could be made without the need for a mold costing upward of $10,000. But the most familiar form of 3D printing, which is sort of like building 3D objects with a series of 1D lines, hasn’t been able to fill that gap on typical production timescales of a week or two.

The new method solidifies liquid resins using two lights to control where the resin hardens and where it stays fluid. This lets the team solidify resin in more sophisticated patterns. It can make a 3D bas-relief in a single shot rather than in a series of 1D lines or 2D cross-sections. Their printing demonstrations include a lattice, a toy boat, and a block M.

The method was developed to overcome a problem associated with traditional 3D printers: Resin tends to solidify on the window the laser shines through, stopping the print job just as it gets started. The Michigan approach creates a relatively large region where there’s no solidification. This lets thicker resins with strengthening powder additives be used to make more durable objects. The method also improves the structural integrity compared to filament 3D printing, as those objects have weak points at interfaces between layers.

An earlier solution to the solidification-on-window problem was a gap that let oxygen through. Oxygen penetrates the resin and prevents solidification near the window, leaving a film of fluid that will let the newly printed surface be pulled away. But because this gap is only about as thick as a piece of transparent tape, the resin must be runny to flow fast enough into the tiny gap between the newly solidified object and the window as the part is pulled up. This has limited vat printing to small, customized products that will be treated relatively gently, such as dental devices and shoe insoles.

By replacing the oxygen with a second light to halt solidification, the Michigan team can produce a much larger gap between the object and the window—millimeters thick—letting resin flow in thousands of times faster.

The key to success is the chemistry of the resin. In conventional systems, there is only one reaction. A photoactivator hardens the resin wherever light shines. In the Michigan system, there is also a photoinhibitor, which responds to a different wavelength of light.

Rather than merely controlling solidification in a 2D plane, as current vat-printing techniques do, the Michigan team can pattern the two kinds of light to harden the resin at essentially any 3D place near the illumination window.

UM has filed three patent applications to protect the multiple inventive aspects of the approach, and researchers are preparing to launch a startup company.

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