Instead of accumulating plastic filaments layer by layer, a new approach to 3D printing lifts complex shapes from a liquid tank up to 100 times faster than conventional 3D printing processes, researchers at the University of Michigan have shown.
3D printing could change the game for relatively small manufacturing jobs, producing less than 10,000 identical items, because it would mean that the objects could be made without the need for a mold that cost more than $ 10,000. But the most familiar form of 3D printing, which is how to build 3D objects with a series of 1D lines, has not been able to fill that gap at typical production timescales of a week or two.
"The use of conventional approaches can not really be achieved unless you have hundreds of machines," said Timothy Scott, associate professor of chemical engineering at U-M who led the development of the new 3D printing approach with Mark Burns, T.C. Chang Professor of Engineering at U-M.
His method solidifies the liquid resin using two lights to control where the resin hardens and where it remains fluid. This allows the team to solidify the resin in more sophisticated patterns. They can make a 3D bas-relief in a single shot instead of a series of 1D lines or 2D cross sections. His print demonstrations include a lattice, a toy boat and an M block.
"It's one of the first true 3D printers ever made," said Burns, a professor of chemical engineering and biomedical engineering.
But the true 3D approach is not a simple trick: it was necessary to overcome the limitations of previous deposit printing efforts. Namely, the resin tends to solidify in the window through which the light shines through, stopping the print job just as it begins.
By creating a relatively large region where solidification does not occur, coarser resins, potentially with reinforced powder additives, can be used to produce more durable objects. The method also improves the structural integrity of 3D printing of filaments, since these objects have weak points in the interfaces between the layers.
"You can get much stronger materials and much more resistant to wear," said Scott.
A previous solution to the problem of solidification in the window was a window that lets oxygen pass through. Oxygen enters the resin and stops solidification near the window, leaving a film of fluid that will allow the newly printed surface to be removed.
But because this gap is as thick as a piece of transparent tape, the resin must be very liquid so that it flows fast enough towards the small gap between the newly solidified object and the window when the piece is lifted. This has limited the printing of deposits to small and custom products that will be treated relatively softly, such as dental devices and shoe insoles.
By replacing oxygen with a second light to stop solidification, the Michigan team can produce a much larger space between the object and the window, with a thickness of millimeter, which allows the resin to flow 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 where the light shines. In the Michigan system, there is also a photoinhibitor, which responds to a wavelength different from light.
Instead of just controlling the solidification in a 2D plane, as do current tank printing techniques, the Michigan team can model the two types of light to harden the resin in virtually any 3D location near the lighting window.
U-M has filed three patent applications to protect the multiple inventive aspects of the approach, and Scott is preparing to launch a new company.
An article describing this research will be published in Scientific advances, entitled, "Rapid and continuous manufacture of additives by volumetric polymerization inhibition patterns".
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