Volumetric 3D printing: A New Approach to AM
3D printing, or additive manufacturing, enables users to produce parts without the geometric constraints of conventional manufacturing processes such as machining or injection molding. The method operates on a layer by layer basis, meaning parts are built from the ground up in slices, each of which is often just a fraction of a millimetre thick.
In recent years, a new approach to 3D printing has emerged, however, and it goes by the name of volumetric 3D printing. Volumetric 3D printing is regarded as the next evolution above sequential 3D printing, and it involves printing from all three directions (axes) at the same time, rather than the conventional layer stacking approach. As such, entire parts can be fabricated in a matter of seconds as opposed to hours, drastically reducing lead times.
The Lawrence Livermore method
One of the first instances of volumetric 3D printing came from a research project conducted by Lawrence Livermore National Lab, in collaboration with UC Berkeley, the University of Rochester, and the Massachusetts Institute of Technology. Using laser-powered, holographic 3D images flashed into the photosensitive resin, the team found that they could build complex 3D components in a fraction of the time when compared to traditional layered printing.
The researchers describe it as overlapping three laser beams to outline an object’s 3D geometry from three different axes, which creates a 3D image of the part suspended in the vat of resin. The laser light, which is at a higher intensity where the beams intersect, is used to blast the resin for about 10 seconds, which is long enough for the geometry to cure. Once the excess resin is drained out of the vat, the user is left with a fully formed 3D part.
Using their revolutionary process, the team printed beams, planes, and struts at a wide variety of angles, as well as lattices and complex curved objects. An added bonus of the method was that it required absolutely no support structures, owing to the lack of overhangs and void printing (gravity isn’t a factor after all). Furthermore, as all of the features within the parts are formed at the same time, they don’t have surface defects or rough textures.
This isn’t to say the technique didn’t have its limitations though, as there are restrictions on the resolutions of parts and on the types of geometries that can be manufactured – parts with extremely complex structures would require lots of intersecting laser beams which pose their own problems. When it comes to the resins used, the chemistry of the polymers also needed to be fine-tuned to improve the mechanical properties of the cured materials.
Xolography on the xube
Volumetric 3D printing very recently came back into the limelight when German start up Xolo announced the launch of its xube system – the world’s first volumetric 3D printer. The company’s proprietary process is called xolography and it works very similarly to the Lawrence Livermore process.
Rather than just multiple intersecting lasers, the xolography approach is a dual-color technique that makes use of photo switchable photo initiators to encourage local polymerization (curing) inside a confined chamber filled with a liquid monomer. Once excited by the photo initiators, the monomer cures into a solid part at the relevant coordinates.
When compared to previously established volumetric printing methods, the xolography technique results in the part resolution about ten times higher than computed axial lithography. The volume generation rate, or print speed, is also about four to five orders of magnitude higher than two-photon photo polymerization. The researchers have stated that they expect this technology to transform rapid volumetric production for objects at the nanoscopic to macroscopic length scales, owing to its extraordinarily high spatial resolution.
It’s clear then that volumetric 3D printing is probably well-suited to printing small-scale objects in the centimeter range. With the available range of resin-based materials, the dental and hearing aid markets could definitely benefit from personalized medical devices with rapid production times. Free form lenses and light conductors in the optics sector could also be major beneficiaries here.
If the technology could be scaled up to larger vat sizes, perhaps in the cubic meter range, it’s safe to say sectors like automotive could see a massive boost in production efficiency. While the prospect is probably sci-fi for the next couple of years, we like to imagine complex decorative dashboard components being printed in a matter of minutes.
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