May 3, 2017 | By Benedict
Lawrence Livermore National Laboratory scientists have developed a new technique for 3D printing transparent glass. They say the research could change the way lasers and other optical devices are built.
LLNL's new glass 3D printing technique can incorporate different refractive indices in a single flat optic
Although the 3D printing of glass is still in its infancy, there are already competing views on how best to carry out the practice. Look in different places, and you’ll find various experts telling you this and that about how additive manufacturing should (or shouldn’t) be used to create the transparent stuff.
Israeli 3D printer developer MICRON3DP, for example, recently set up its first batch of revolutionary glass 3D printers in-house, and the company says its FDM-style machine can heat molten glass to around 1,000 degrees Celsius before extruding it like plastic.
Other researchers, however, don’t consider this the best way to print glass, and have attempted to use stereolithography-style 3D printing to fabricate the material at lower temperatures.
Now, researchers at LLNL in California think they have cracked it.
They believe that techniques such as FDM and stereolithography 3D printing aren’t capable of fully melding glass filaments—a problem that leads to porous or non-uniform structures. So they have instead created a range of custom glass inks.
Made from concentrated suspensions of glass particles, these inks have highly controlled flow properties, and can therefore be printed at room temperature.
The LLNL researchers say that parts printed with these special inks can then undergo heat treatment, making them denser and removing evidence of the printing process. Once this is complete, the researchers can add an optical-quality polish to make the parts more optically uniform.
“For printing high-quality optics, you shouldn't be able to see any pores and lines, they have to be transparent,” said LLNL materials engineer Du Nguyen.
“Once we got a general formulation to work, we were able to tweak it so the material could merge during the printing process. Most other groups that have printed glass melt the glass first and cool it down later, which has the potential for residual stress and cracking. Because we print at room temperature, that's less of an issue.”
The printed object comes out of the 3D printer opaque, but after drying and heat treatment becomes transparent.
LLNL chemical engineer and project lead Rebecca Dylla-Spears & LLNL materials engineer Du Nguyen
So what can this new glass 3D printing technique be used for? According to the LLNL researchers, quite a lot—and that’s largely thanks to the high resolution afforded by the direct-ink writing process used.
The research could apparently allow scientists to 3D print glass that incorporates different refractive indices in a single flat optic. Usually, special shapes are needed to achieve these lensing characteristics, and making them can therefore be challenging.
“Polishing complex or aspheric lenses is pretty labor-intensive and requires a lot of skill, but polishing a flat surface is much easier,” Nguyen said. “By controlling the refractive index in the printed parts, you alter the bending of light, which enables a lens that could be polished flat.”
Nguyen and his team think that the new 3D printing technique could complement existing optics practices, rather than replace them. Specifically, 3D printing could be used to create composition gradients that don't exist on the market today, while some 3D printed components could be used to reduce the size, weight, or cost of optics systems.
“Optical fabrication research and development is trending toward freeform optics, which are optics that can be made virtually to any complex shape,” said Tayyab Suratwala, LLNL's program director for Optics and Material Science and Technology. “Expanding this to 3D printed optics with compositional variation can greatly increase the capabilities of this new frontier.”
The researchers now plan to try 3D printing high-quality optics and gradient index lenses by varying the composition of the glass. One key challenge will be the creation of Gradient Refractive Index (GRIN) optics, which will require a higher level of understanding and control of the printing process.
The LLNL scientists will also try 3D printing glass for applications outside of optics, such as glass microfluidic devices with complex geometries.
The research, carried out in collaboration with scientists from the University of Minnesota and Oklahoma State University, has been published in Advanced Materials.
Posted in 3D Printing Technology
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