The race for volumetric 3D printing is accelerating

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3D Printing Business Media has been tracking efforts to commercialize volumetric 3D printing technology for some time now. We seem to be in a very exciting time – seeing many technological advances in this new technique. Volumetric Additive Manufacturing (VAM), touted as a “near-instantaneous 3D printing technique”, removes the need for the support structures typically required to create complex designs with more standard printing methods and could make it easier to print more and more complex designs while saving time and material.

Volumetric 3D printing with glass

Among the latest efforts using a new laser-based VAM approach, researchers from Lawrence Livermore National Laboratory and the University of California, Berkeley have demonstrated the ability to 3D print microscopic objects in silica glass, as part of of an effort to produce delicate layerless optics that can be built up in seconds or minutes. The results are published in the latest edition of the journal Science.

Dubbed “The Replicator,” after the fictional Star Trek device that can instantly fabricate almost any object, the computed axial lithography (CAL) technology developed by LLNL and UC Berkeley draws inspiration from imaging methods by computed tomography (CT). CAL works by calculating projections from many angles through a digital model of a target object, optimizing these projections by calculation, and then delivering them into a rotating volume of photoresist using a digital light projector . Over time, the projected light patterns reconstruct or accumulate a 3D light dose distribution in the material, hardening the object to points exceeding a light threshold as the resin vat rotates. In an ideal volumetric 3D printing setup, the fully formed object materializes in seconds – much faster than traditional layer-by-layer 3D printing techniques – and then the vat is emptied to retrieve the part.

Combining a new micro-scale VAM technique called micro-CAL, which uses a laser instead of an LED source, with a nano-composite glass resin developed by the German company Glassomer and the University of Freiburg, researchers from UC Berkeley reported the production of solid, complex microstructured glass objects with a surface roughness of only six nanometers with features down to a minimum of 50 microns.

Taking inspiration from CT scans, the Computed Axial Lithography (CAL) 3D printing method uses projected photons to illuminate a syrup-like resin, creating a video of continuous projections as the vial spins. Like a scanner done upside down, the projections combine to form a 3D object suspended in the resin. Here, a CAL system projects light into a photoresist to produce a component. Photo by Hossein Heidari/UC Berkeley

UC Berkeley associate professor of mechanical engineering Hayden Taylor, the project’s principal investigator, said the micro-CAL process, which produces a higher dose of light and hardens 3D objects faster and at higher resolution , combined with the characterized nanocomposite resins at LLNL were found to be “perfectly matched to each other”, creating “striking results in the strength of the printed objects”.

“Glass objects tend to break more easily when they contain more flaws or cracks or have a rough surface,” Taylor said. “CAL’s ability to manufacture objects with smoother surfaces than other 3D printing processes is therefore a big potential advantage.”

“You can imagine trying to create these small, complex micro-optics and microarchitectures using off-the-shelf manufacturing techniques; it’s really not possible,” said Caitlyn Krikorian Cook, LLNL co-author, group leader and polymer engineer in the lab’s materials engineering division, “and being able to print it ready to use. job without having to do polishing techniques saves a significant amount of time. If you can eliminate the polishing steps after the optics are formed – with low roughness – you can print a ready to use part.

A microscopic object 3D printed in silica glass using VAM

Cook and the UC Berkeley researchers said VAM patterned glass could impact solid glass devices with microscopic characteristics, produce optical components with more geometric freedom and at higher speeds, and could potentially enable new functions or products at a lower cost.

Real-world applications could include micro-optics in high-grade cameras, consumer electronics, biomedical imaging, chemical sensors, virtual reality headsets, advanced microscopes, and microfluidics with challenging 3D geometries such as “lab-on-a-chip” applications, where microscopic channels are needed for medical diagnostics, basic science studies, manufacturing of nanomaterials, and drug screening. Additionally, the benign properties of glass lend themselves well to biomaterials, or where there is high temperature or chemical resistance, Cook added.

Upconverting Volumetric Jelly

In other University news, Dan Congreve, assistant professor of electrical engineering at Stanford and former Rowland Fellow at Harvard University’s Rowland Institute, and his colleagues have developed a way to print 3D objects in a stationary volume of resin. The printed object is fully supported by thick resin (imagine an action figure floating in the center of a block of Jell-O) so it can be added from any angle – eliminating the need for support structures . The report on this type of volumetric 3D printing system was published in the journal Nature.

The jelly container approach isn’t entirely new, with MIT and BMW working on another similar technology to produce urethane parts. The key element of the Harvard researchers’ new volumetric 3D printing design is to turn red light into blue light by adding what’s called an upconversion process to resin, the light-reactive liquid used in 3D printers that hardens plastic.

Congreve’s lab specializes in converting one wavelength of light to another using triplet fusion upconversion. With the right molecules in close proximity to each other, researchers can create a chain of energy transfers that, for example, transform low-energy red photons into high-energy blue photons.

The race towards volumetric 3D printing - based on laser and upscaling.  The latest efforts from Harvard, Stanford, Berkeley and LLNL.
Changing the content of the nanocapsules controls the power of red light needed to cure the resin and enables different types of volumetric printing. Two types of printing shown here: scanning and tracing an image using a high power laser (left) and projecting an image all at once using a low power LED (to the right). (Image credit: Dan Congreve/Tracy H. Schloemer/Arynn O. Gallegos)

“I became interested in this upscaling technique in graduate school,” Congreve said. “It has all sorts of exciting applications in solar, bio and now this 3D printing. Our real specialty is in the nanomaterials themselves – designing them to emit the right wavelength of light, to emit it effectively and for them to be dispersed in resin.

Through a series of steps (which included sending some of their materials for a spin in a Vitamix blender), Congreve and his colleagues were able to form the necessary upconversion molecules into distinct nanoscale droplets and coat them in a shell. silica protector. Then they distributed the resulting nano-capsules, each of which is 1000 times smaller than the width of a human hair, throughout the resin.

“Understanding how to make nano-capsules tough was not trivial – a 3D printing resin is actually quite tough,” said Tracy Schloemer, postdoctoral researcher at Congreve’s lab and one of the paper’s lead authors. . “And if those nano-capsules start collapsing, your ability to upconvert goes away. All of your content overflows and you can’t get those molecular collisions that you need.

The race towards volumetric 3D printing - based on laser and upscaling.  The latest efforts from Harvard, Stanford, Berkeley and LLNL.
a–d, Side and top views of our final reference boat print (Benchy) hardened using a single-voxel excitation print, seated on a dime for scale. The scale bar indicates 5 mm. e, f, top and side views of Benchy STL file. Side and top views of the final print show the faithful reproduction of key features. g, h, Top views of Stanford’s logo (g) and gear (h) prints hardened with large-area two-dimensional parallel excitation printing, sitting next to a penny for the scale. Scale bars indicate 5 mm. i, j, microscope images of lines printed in approximately 0.1 ml of resin (i) with light projected through the US Air Force target test mask (j). The scale bar indicates 500 μm.

“What we were wondering was if we could actually print entire volumes without having to go through all those complicated steps?” said Congreve. “Our goal was to just use a moving laser to create a true three-dimensional pattern and not be limited by that kind of layer-by-layer nature of things.”

In 3D printing, the resin cures in a flat, straight line along the light path. Here, researchers are using nano-capsules to add chemicals so that they only react to a certain type of light – blue light at the focal point of the laser that is created by the upconversion process. This beam is scanned in three dimensions, so it prints that way without needing to be overlaid on anything. The resulting resin has a higher viscosity than in the traditional method, so it can remain unsupported when printed.

“We designed the resin, we designed the system so that the red light wouldn’t do anything,” Congreve said. “But that little dot of blue light triggers a chemical reaction that causes the resin to harden and turn it into plastic. Basically it means you have this laser going through the whole system and it’s only at this little blue that you get the polymerization, [only there] do you get the impression that is happening. We just scan that blue dot in three dimensions and wherever that blue dot touches it, it polymerizes and you have your 3D print.

The researchers, which included Christopher Stokes of the Rowland Institute, plan to continue developing the system for speed and refining it to print even finer detail. The potential of volumetric 3D printing is considered game-changing as it will eliminate the need for complex support structures and dramatically speed up the process when it reaches its full potential.

“We’re really just beginning to scratch the surface of what this new technique could do,” Congreve said.

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