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

Full paper on Computed Axial Lithography method published in Science Journal

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.

Computed Axial Lithography
CAL volumetric fabrication. (A) Underlying concept: patterned illumination from many directions delivers a computed 3D exposure dose to a photoresponsive material. (B) Schematic of CAL system used in this work. (C) Sequential view of the build volume during a CAL print. A 3D geometry is formed in the material in less than a minute. (D) The 3D part shown in (C) after rinsing away uncured material. (E) The part from (D) painted for clarity. (F) A larger (40 mm-tall) version of the same geometry. (G) Opaque version of the geometry in (F), using crystal violet dye in the resin. Scale bars: 10 mm.

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.

Computed Axial Lithography
Parts fabricated by CAL.
(A) A highly complex geometry (dental model). (B) Same part as in (A) painted for clarity. (C) Complex lattice geometry with fine features as small as 0.3 mm and internal voids. (D) “Ball-in-a-cage” geometry: an example of a disconnected part printed without solid support structures. Part is suspended in uncured material. (E) Part in (D) removed from uncured material and painted for clarity. (F) Bridges with unsupported spans up to 25 mm. (G and H) Airplanes with sharp wing tips and overhanging wings. (I and J) Donut printed in highly deformable GelMA hydrogel, showing a smooth, layer-less surface finish. (K) Smooth sphere without layering artifacts. (L) Component with smooth planar and convex curved regions. Scale bars: (A, B, L) 10 mm; (C, G to K): 5 mm (C inset: 1 mm); (D, E): 2 mm.

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).

Computed Axial Lithography
CAL enables over-printing of 3D geometries around pre-existing solid components. A convex occlusion allows access from the half space (A and B), permitting delivery of the projections needed to cure custom geometries around the occlusion. (C and D) Example of a screwdriver handle printed using CAL to encase a metallic shaft (scale-bars: 10 mm).
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Davide Sher

Since 2002, Davide has built up extensive experience as both a technology journalist and communications consultant. Born in Milan, Italy, he spent 12 years in the United States, where he received his undergraduate degree from SUNY Stony Brook. He is a senior analyst for US-based firm SmarTech Publishing focusing on the additive manufacturing industry. He founded London-based 3D Printing Business Media Ltd. (now 3dpbm) which specializes in marketing, editorial and market analysys&consultancy services for the additive manufacturing industry. 3dpbm publishes 3D Printing Business Directory, the largest global directory of companies related to 3DP, as well as several editorial websites, including 3D Printing Media Network and Replicatore.

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