University of California, Berkeley
Computed axial lithography for volumetric additive manufacturing with photopolymers
Volumetric additive manufacturing is defined as producing the entire volume of a component or structure simultaneously — rather than by layering — and has been envisioned as a possible way to increase the speed of polymeric additive manufacturing. Until recently, however, no practicable technique existed for creating arbitrary 3D geometries volumetrically. Recently, my group has demonstrated Computed Axial Lithography (CAL), in collaboration with colleagues at Lawrence Livermore National Lab, to meet this need (Kelly et al., Science, 2019, DOI: 10.1126/science.aau7114). CAL essentially reverses the principles of computed tomography (widely used in imaging, but not previously in fabrication) to synthesize a three-dimensionally controlled illumination dose within a volume of photocurable resin. The photosensitive volume rotates steadily while a video projector illuminates the material from a direction perpendicular to the axis of rotation. The illumination pattern typically changes >1000 times per revolution, so that light from many different projection angles contributes to the cumulative dose. Where the dose exceeds a threshold, the resin solidifies and the part is formed.
The CAL printing technique has several potential advantages. Because the component being printed does not move relative to the resin during printing, the printing speed is not limited by resin flow effects, as it can be in layer-by-layer photopolymerization-based printing. The absence of relative motion also allows highly viscous resins or even solid gels to be used as the starting material, so that a wider range of mechanical properties can be achieved in printed components. Because layers are not used in CAL, the surfaces of printed components are very smooth (c. 1–4 µm roughness in preliminary experiments), which may open up new applications. Additionally, it is possible to print objects around pre-existing solid objects that could have been made using a different material or process. This ‘overprinting’ capability suggests applications in mass-customisation for end users.
I will discuss current and future research directions for CAL, in particular the prospects for scaling up the sizes of printed components (from the current 5–10 cm) or scaling down the minimum achievable feature sizes (from the current ~0.3 mm). Some of the ongoing engineering challenges, including resin formulation requirements and projection algorithm needs, will be discussed. Finally, I’ll discuss application areas that may take particular advantage of CAL’s properties.
Hayden Taylor is an Assistant Professor of Mechanical Engineering at the University of California, Berkeley. He holds B.A. and M.Eng. degrees in Electrical and Electronic Engineering from Cambridge University and a Ph.D. in Electrical Engineering and Computer Science from MIT. His research spans the invention, modeling and simulation of manufacturing processes. His group is particularly focused on processes that can be used to fabricate extremely rich and complex, multi-scale geometries, such as are found in semiconductor integrated circuits and biological tissues. Past work has addressed plasma etch, polymer bonding, chemical mechanical polishing, and mechanical exfoliation of van der Waals-bonded solids. He has particular expertise in mechanical lithography processes including micro-embossing and nanoimprint lithography. Current research activities have the following themes: (A) contact mechanics in materials processing, (B) surface engineering for heat and mass transfer, and (C) multi-scale additive manufacturing, including computed axial lithography.
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