Micro-CAL builds on the computed axial lithography (CAL) that the same team developed three years ago, but scales the process down so that it can create tiny glass objects that exhibit high optical quality, design flexibility and strength.
Unlike current industrial 3D-printing that builds up objects from thin layers of material, CAL prints an entire object simultaneously. A laser projects patterns of light into a rotating volume of light-sensitive material, building up a 3D light dose that then solidifies into the desired shape. The layer-less nature of the CAL process enables smooth surfaces and complex geometries. The latest research, published in Science, explains how the CAL process was effectively shrunk to produce the tiny micro-CAL structures and how glass was added to the materials mix.
“When we first published this method in 2019, CAL could print objects into polymers with features down to about a third of a millimetre in size,” said Hayden Taylor, principal investigator and professor of mechanical engineering at UC Berkeley. “Now, with micro-CAL, we can print objects in polymers with features down to about 20 millionths of a metre. And for the first time, we have shown how this method can print not only into polymers but also into glass, with features down to about 50 millionths of a metre.”
To print the glass, Taylor and his research team collaborated with scientists from the Albert Ludwig University of Freiburg, who have developed a special resin material containing nanoparticles of glass surrounded by a light-sensitive binder liquid. Digital light projections from the printer solidify the binder, then the researchers heat the printed object to remove the binder and fuse the particles together into a solid object of pure glass.
“The key enabler here is that the binder has a refractive index that is virtually identical to that of the glass, so that light passes through the material with virtually no scattering,” said Taylor. “The CAL printing process and this Glassomer-developed material are a perfect match for each other.”
The researchers also discovered that the CAL-printed glass objects had more consistent strength than those made using a conventional layer-based printing process.
“Glass objects tend to break more easily when they contain more flaws or cracks, or have a rough surface,” said Taylor. “CAL’s ability to make objects with smoother surfaces than other, layer-based 3D-printing processes is therefore a big potential advantage.”
The team believes the CAL 3D-printing method offers manufacturers of microscopic glass objects a new and more efficient way to meet customers’ requirements for geometry, size and optical and mechanical properties.
“Being able to make these components faster and with more geometric freedom could potentially lead to new device functions or lower-cost products,” said Taylor.
