The researchers at Lawrence Livermore National Laboratory (LLNL) always impress with their many 3D printing innovations. Their expertise is especially apparent when it comes to their work with materials, from carbon fiber, advanced stainless steel, and other metals to reactive materials and metamaterials with shape memory behavior.
Last year, a team of researchers from LLNL developed a method for 3D printing glass using direct ink writing and published a paper on their work. The organization’s method differed from FFF 3D printing because the glass could be 3D printed at room temperature out of an ink formulated from concentrated silica particle suspensions.
LLNL has been building on this innovative research, and researchers have now successfully 3D printed optical-quality glasses that, for the first time, are on the same level as currently available commercial glass products.
“Additive manufacturing gives us a new degree of freedom to combine optical materials in ways we could not do before. It opens up a new design space that hasn’t existed in the past, allowing for design of both the optic shape and the optical properties within the material,” explained LLNL chemical engineer Rebecca Dylla-Spears, the project’s principal investigator.
It can be hard to make sure that glass 3D printed from the molten phase will give its desired optical performance, since the material’s refractive index is so sensitive to its own thermal history. But, the researchers explained that by depositing their material – a slurry of silica particles – in paste form, and then heating the whole print, glass is formed that allows for a uniform refractive index. This will entirely get rid of any optical distortion that could degrade its function.
“Components printed from molten glass often show texture from the 3D-printing process, and even if you were to polish the surface, you would still see evidence of the printing process within the bulk material. This approach allows us to obtain the index homogeneity that is needed for optics,” Dylla-Spears said. “Now we can take these components and do something interesting.”
The LLNL glass research team was supported by a Laboratory Directed Research & Development project, and they recently published a new paper on their work, titled “3D Printed Optical Quality Silica and Silica-Titania Glasses from Sol-Gel Feedstocks,” in Advanced Materials Technologies.
In the study, the LLNL engineers and scientists describe how they were able to successfully 3D print small test pieces, using the special ink they developed, with properties that are, as the organization puts it, “within range of commercial optical grade glasses.”
The abstract reads, “A method for fabricating optical quality silica and silica–titania glasses by three‐dimensional (3D) printing is reported. Key to this success is the combination of sol–gel derived silica and silica–titania colloidal feedstocks, direct ink writing (DIW) technology, and conventional glass thermal processing methods. Printable silica and silica–titania sol inks are prepared directly from molecular precursors by a simple one‐pot method, which is optimized to yield viscous, shear‐thinning colloidal suspensions with tuned rheology ideal for DIW. After printing, the parts are dried and sintered under optimized thermal conditions to ensure complete organic removal and uniform densification without crystallization. Characterizations of the 3D‐printed pure silica and silica–titania glasses show that they are equivalent to commercial optical fused silica and silica–titania glasses. More specifically, they exhibit comparable chemical composition, SiO2 network structure, refractive index, dispersion, optical transmission, and coefficient of thermal expansion. 3D‐printed silica and silica–titania glasses also exhibit comparable polished surface roughness and meet refractive index homogeneity standards within range of commercial optical grade glasses. This method establishes 3D printing as a viable tool to create optical glasses with compositional and geometric configurations that are inaccessible by conventional optical fabrication methods.
Dylla-Spears explained that the team’s custom inks, which are aimed at forming silica and silica-titania glasses, allow them to precisely tune the mechanical, optical, and thermal properties of the glass.
While the small optics they printed in simple shapes were only a proof of concept, Dylla-Spears said that the team’s technique could one day be applied to any kind of device that uses glass optics, resulting in optics with compositional changes and geometric structures that aren’t possible to achieve with traditional manufacturing methods. As an example, their 3D printed gradient refractive index lenses could be polished flat to replace the expensive polishing techniques that are typically used for curved lenses.
Now that the researchers have achieved 3D printed optical-quality glasses that are on par with commercial glass products, they have filed a patent on the technique, and are already seeing interest from some large-scale glass manufacturers. As for next steps, they are starting to work on controlling material properties in order to make gradient refractive index lenses, by mixing and patterning various material compositions.
Study authors include former LLNL researcher Joel F. Destino, now a chemistry professor at Creighton University, and LLNL researchers Nikola A. Dudukovic, Michael A. Johnson, Du T. Ngyuen, Timothy D. Yee, Garth C. Egan, April M. Sawvel, William A. Steele, Theodore F. Baumann, Eric B. Duoss, Tayyab Suratwala, and Dylla‐Spears.
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