What is volumetric 3D printing and why it could mean the end of additive manufacturing

Also known as holographic or tomographic printing, it could be the next evolutionary step

Progress moves fast in the 3D printing industry. So much so that new, disrupting technologies are announced almost every month. However, they can’t all be disrupting and revolutionary. So it happens that when a truly disruptive new approach to 3D printing is announced it may go somewhat unnoticed – or fully understood for its importance. That may have happened when LLNL researchers first announced and presented volumetric 3D printing last year. But exactly what is volumetric 3D printing?

Even if it was a project from top institutions such as LLNL, MIT, UC Berkeley and the University of Rochester, it may have seemed like just another fascinating yet somewhat far-fetched innovation to a consolidated process. However, a recent email exchange with a student from Professor Colosimo’s Additive Manufacturing course at Milan’s Polytechnic University – who has been researching this topic – led us to finding two more recent announcements that seem to indicate that it is much more than that. Volumetric 3D printing, also known as holographic 3D printing or tomographic 3D printing, may just be the next evolutionary step in 3D printing and the first “true” three-dimensional form of printing.

Just last week, bioprinting leader CELLINK announced the development of a new – not so affordable – $1.2 million holographic bioprinter, the Holograph-X. A couple of weeks earlier, researchers from the Ecole Polytechnique Fédérale de Lausanne published a paper on “Volumetric 3D Printing of Elastomers by Tomographic Back-Projection“.

They described the process as “inspired by computed tomography (CT) scans in biomedical imaging. In computed tomography, a series of X-ray radiographs of a patient or object are acquired from different angles. These radiographic projections are then processed with a tomographic algorithm in order to reconstruct cross-sectional images of the scanned object. The cross-sectional images represent the distribution of absorbed X-ray dose inside the object.

In tomographic 3D printing – they explain – the principle of CT scans is used in reverse. First, a digital model of the desired object is loaded. Based on this model, cross-sectional images of the object are generated (voxelization). Then, projections from a set of many angles from 0 to 360° are calculated using any tomography algorithm such that when all these projections are displayed into a homogeneous volume of absorbing material, the cumulative absorbed dose distribution due to the projections reproduces the shape of the three-dimensional object inside the material. If a liquid photopolymer is used as a target material and visible light is used for the projections, locations inside the photopolymer where a high dose of light was applied will solidify whereas other locations remain below the solidification threshold.”

What implications for additive manufacturing?

All 3D printing today is actually a type 2D printing repeated along the Z axis. Volumetric 3D printing approaches are actually printing in all three dimensions at the same time. In this sense, it seems like the natural evolution of 3D printing.

Ironically, volumetric 3D printing may evolve into something that can no longer be considered a type of additive manufacturing and for sure it would not be a type of ALM (additive layer manufacturing) as some refer to it. Not only there would be no layers (as there are no layers in continuous DLP technologies or in 2PP processes) but there may no longer even be anything built additively as parts could all be solidified at the same time. More likely, some volumetric processes may still have a degree of additive manufacturing, but in three dimensions: starting from the center and building outwards.

Being able to 3D print from all spatial dimensions at the same time could be instrumental in producing complex organs, as CELLINK infers with the new Holograph-X system. This would enable better and more functional vascularity and multi-cellular-material structures. More generally this approach may be ideal for very complex multi-material structures which could also be one of the primary challenges in its adoption.

The technology shown by LLNL and by Lausanne researchers is stereolithographic (or self-stereolithographic as they refer to it) and this family of processes almost always works with a single material. Other questions concer whether volumetric 3D printing could ever be applied to thermoplastics and metals. In both cases, the question is whether it could be applied to material extrusion and powder bed fusion processes.

Volumetric PBF and material extrusion?

Powder bed fusion would be excluded for now mainly because it would likely require way too much energy to be able to control it. Even if researchers were able to develop a volumetric powder bed fusion process for polymers (perhaps an evolution of EOS’s LaserProFusion), it would still take many years before even beginning to consider applying it to metals (although EOS’ CEO Adrian Keppler did tell us it would theoretically be possible at formnext)

Other possibilities are polymer and metal extrusion and deposition (DED/LMD). One could theoretically deposit molten plastics and metals from more than one deposition head at the same time but they would not be able to extrude upwards, unless they were in a zero gravity environment, in space. At least in that sense, the bioprinter that was just sent to the ISS may have some more answers for us.

Since we are venturing in the realm of long-term possibilities, one final possibility for metal volumetric 3D printing would be a MIM-based stereolithographic process. One could theoretically use a process similar to that developed by LLNL on mixtures of photopolymers (binders) and metal powders. While it still remains to be seen how the process would work on a thick, non-transparent material, it also must be considered that such MIM-based stereolithographic processes have just recently been implemented in “traditional” layer based 3D printing and it will take a lot more research to evolve them into a volumetric 3D printing approach.

On the other hand, once someone thinks of something new and it works, progress moves pretty fast in 3D printing. We will likely hear the term volumetric 3D printing a lot more than a couple of times next year.