More details emerge on UC Berkeley-LLNL new CAL volumetric 3D printing

A few weeks ago we ran a piece describing new volumetric 3D printing approaches and their implications for the additive manufacturing industry. We concluded anticipating that we would hear the term a lot more often in 2019. This supposition was confirmed today as the full paper on the Computed Axial Lithography (CAL) process was published on Science Journal and complemented by an article and video on Nature Journal.

The paper and updated video expand and illustrate the process developed originally within a research project involving UC Berkeley and the Lawrence Livermore National Laboratory among others. The scientits explain that the Computed Axial Lithography (CAL) approach was developed to “free” additive processes from the current constraints: speed, geometry, and surface quality, which are linked to the reliance on material layering.

In order to do this, the scientists demonstrated concurrent printing of all points within a three-dimensional object by illuminating a rotating volume of photosensitive material with a dynamically evolving light pattern. As shown in the video below, this enables printing features as small as 0.3 mm in engineering acrylate polymers, as well as printing soft structures with exceptionally smooth surfaces into a gelatin methacrylate hydrogel.

In addition, the CAL process enables construction of components that encase other pre-existing solid objects, allowing for multi-material fabrication. It does this extremely fast, with printing times of 30–120 s for diverse centimeter-scale objects.

The video below, which appeared on Nature Journal (inaccurately titled “3D Printing with Light” as if previous 3D printing did not involve “light”), shows what this technology is capable of in impressive details.

Real 3D

The authors explain that current AM processes create 3D geometries through repeated one- or two-dimensional unit operations. Such layer-by-layer approaches limit throughput, degrade surface quality, constrain geometric capabilities, increase post-processing requirements, and may cause anisotropy of mechanical performance. By comparison, the formative processes that AM technologies seek to supplant (injection molding, die-casting, investment and lost-wax casting) do not suffer from these issues but are limited by geometry and a generally “analogic” approach to part manufacturing (many parts, all the same).

By comparison, a manufacturing technique capable of simultaneously fabricating all points within an arbitrary three-dimensional geometry would provide a different strategy to address these issues and complement existing AM methods. A method that forms parts volumetrically allows for different ways to integrate multiple components and may widen the material landscape to enhance the functionality of finished parts.

Enter Computed Axial Lithography

The Computed Axial Lithography (CAL) method allowed the researchers to synthesize arbitrary geometries volumetrically through photopolymerization. It provides several advantages over conventional layer-based printing methods: for example, it may be used to circumvent support structures as it can print into high viscosity fluids or even solids. Printing 3D structures around preexisting solid components is also possible. The CAL process is inherently scalable to larger print volumes, and is several orders of magnitude faster, under a wider range of conditions, than layer-by-layer methods.

The CAL manufacturing system selectively solidifies a photosensitive liquid within a contained volume. We delivered light energy to the material volume as a set of two-dimensional images. Each image projection propagates through the material from a different angle. The superposition of exposures from multiple angles results in a three-dimensional energy dose sufficient to solidify the material in the desired geometry. The core concept was inspired by Computed Tomography (hence the name).