Engineering 101

3D Printing 100 Times Faster Using Light

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

While 3D printing could change the game for relatively small manufacturing jobs, producing fewer than 10,000 identical items without the need for a mold costing upwards of $10,000, the most familiar form of 3D printing, which is likened to 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.

Until now.

Researchers from the University of Michigan have successfully tested a method of 3D printing that solidifies the liquid resin using two lights to control where the resin hardens–and where it stays fluid. This enables the team to solidify the resin in more sophisticated patterns. They 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”.

“Using conventional approaches, that’s not really attainable unless you have hundreds of machines,” said Timothy Scott, U-M associate professor of chemical engineering who co-led the development of the new 3D printing approach with Mark Burns, the T.C. Chang Professor of Engineering at U-M.

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

The true 3D approach was necessary to overcome the limitations of earlier vat-printing efforts. For example, the resin solidifying on the window that the light shines through, stopping the print job just as it gets started.

By creating a relatively large region where no solidification occurs, thicker resins–potentially with strengthening powder additives–can be used to produce more durable objects. The method also bests the structural integrity of filament 3D printing, as those objects have weak points at the interfaces between layers.

“You can get much tougher, much more wear-resistant materials,” said Scott.

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, and was demonstrated by printing a block M in a U-M chemical engineering lab in Ann Arbor, MI on December 6, 2018.  This project was co-led by Timothy Scott, associate professor of chemical engineering and Mark Burns, T.C. Chang Professor of Engineering and professor of chemical engineering and biomedical engineering.(Image Credit: Evan Dougherty/Michigan Engineering)
A new way to 3D print developed at the University of Michigan. (Image Credit: Evan Dougherty/Michigan Engineering)

An earlier solution to the solidification-on-window problem was a window that lets oxygen through. The oxygen penetrates into the resin and halts the solidification near the window, leaving a film of fluid that will allow the newly printed surface to be pulled away.

But because this gap is only about as thick as a piece of transparent tape, the resin must be very 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–allowing the resin to 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.

U-M has filed three patent applications to protect the multiple inventive aspects of the approach, and Scott is preparing to launch a startup company.

A paper describing this research will be published in Science Advances, titled, “Rapid, continuous additive manufacturing by volumetric polymerization inhibition patterning.”

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