While 3D printed objects typically take less time to fabricate than objects created with more traditional methods of manufacturing, they’re not always made as quickly as we want them to be. On the plus side, we now have the ability to create parts with designs and geometries that weren’t possible before; however, when it comes right down to it, the layer by layer methods typically used in additive manufacturing still take hours, or even days, especially if the part is especially complicated. The researchers at Lawrence Livermore National Laboratory (LLNL) in California have worked to develop faster methods of metal 3D printing before, and have now turned their attention to a novel one-step 3D printing approach that can create parts much faster than established methods, in a technique reminiscent of other research into holographic methodologies for additive manufacturing.
LLNL researchers teamed up with collaborators from MIT, the University of Rochester, and UC Berkeley to develop what they call volumetric 3D printing, which flashes laser-generated, hologram-like 3D images into photosensitive resin. The team received program funding from Laboratory Directed Research and Development (LDRD), and recently published a paper on their new method, titled “One-step volumetric additive manufacturing of complex polymer structures,” in the journal Science Advances; co-authors include Maxim Shusteff, Allison E.M. Browar, Brett E. Kelly, Johannes Henriksson, Todd H. Weisgraber, Robert M. Panas, Nicholas X. Fang, and Christopher M. Spadaccini.
According to the abstract, “Two limitations of additive manufacturing methods that arise from layer-based fabrication are slow speed and geometric constraints (which include poor surface quality). Both limitations are overcome in the work reported here, introducing a new volumetric additive fabrication paradigm that produces photopolymer structures with complex nonperiodic three-dimensional geometries on a time scale of seconds.”
The method works by overlapping three laser beams, which define the geometry of the object being printed, from three separate directions – this creates a 3D image, which is suspended in a vat of resin. The light from the lasers has a higher intensity at the point where the beams intersect, and it is turned on for roughly ten seconds in order to cure the part. Then, the researchers drain the excess resin out of the vat to reveal a fully formed, 3D printed object.
“The fact that you can do fully 3D parts all in one step really does overcome an important problem in additive manufacturing. We’re trying to print a 3D shape all at the same time,” said LLNL researcher and lead author Shusteff. “The real aim of this paper was to ask, ‘Can we make arbitrary 3D shapes all at once, instead of putting the parts together gradually layer by layer?’ It turns out we can.”
The team’s volumetric 3D printing method creates parts much faster than other polymer-based methods; in fact, it’s faster than most of the commercial 3D printing methods readily available on the market.
“It’s a demonstration of what the next generation of additive manufacturing may be. Most 3D printing and additive manufacturing technologies consist of either a one-dimensional or two-dimensional unit operation. This moves fabrication to a fully 3D operation, which has not been done before,” explained LLNL engineer Spadaccini, in charge of LLNL’s 3D printing efforts. “The potential impact on throughput could be enormous and if you can do it well, you can still have a lot of complexity.”
Volumetric 3D printing has more speed, flexibility, and geometric versatility than other methods, with a lower cost. The research teams believes that the framework of the method will “open a major new direction of research in rapid 3D printing.”
Other 3D printing methods have a hard time spanning structures without support to hold them up; the research team’s volumetric 3D printing process doesn’t have this issue. They demonstrated what the process was capable of by using it to create lattices, beams, planes, angled struts, and curved objects, which can be 3D printed with layering artifacts. According to Shusteff, if they apply a light source with higher power, volumetric 3D printing could create objects at an even higher rate of speed, and fabricate extra-soft materials, like hydrogels, which won’t be damaged by the method’s fluid motion. In addition, Shusteff notes that it is the only 3D printing technique that works even better in zero gravity.
“This might be the only way to do AM that doesn’t require layering. If you can get away from layering, you have a chance to get rid of ridges and directional properties. Because all features within the parts are formed at the same time, they don’t have surface issues,” said Shusteff.
“I’m hoping what this will do is inspire other researchers to find other ways to do this with other materials. It would be a paradigm shift.”
However, volumetric 3D printing is not foolproof – additional engineering and polymer chemistry are necessary to improve the properties of the resin so they can print more stable structures. Since the laser beams grow without changing through space, specific types of geometry and part resolutions are restricted from forming.
Spadaccini explained, “If you leave the light on too long it will start to cure everywhere, so there’s a timing game. A lot of the science and engineering is figuring out how long you can keep it on and at what intensity, and how that couples with the chemistry.”
Multiple intersecting laser beams would be needed to fabricate very complex structures, which the researchers said can “limit the process.”
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