Producing glass using additive methods has been previously accomplished by printing molten glass but this requires extremely high temperatures and heat-resistant equipment. Powdered ceramic particles that can be printed at room temperature have been sintered to create glass; however, objects produced in this way are not very complex.
A new technique that produces complex glass objects with 3D printing is based on stereolithography using a special resin that contains a plastic, and organic molecules to which glass precursors are bonded. The resin can be processed using commercially available Digital Light Processing technology. This involves irradiating the resin with ultraviolet light patterns. Wherever the light strikes the resin, it hardens because the light-sensitive components of the polymer resin crosslink at the exposed points. The plastic monomers combine to form a labyrinth-like structure, creating the polymer. The ceramic-bearing molecules fill the interstices of this labyrinth.
An object can thus be built up layer by layer. The researchers can change various parameters in each layer including pore size: weak light intensity results in large pores and intense illumination produces small pores. The researchers are also able to modify the microstructure, layer by layer, by mixing silica with borate or phosphate and adding it to the resin. Complex objects can be made from different types of glass or even combined in the same object using the technique.
The researchers then fire the blank produced in this way at two different temperatures: at 600 °C to burn off the polymer framework and then at around 1000 °C to densify the ceramic structure into glass. During the firing process, the objects shrink significantly but become transparent and hard like window glass.
These 3D-printed glass objects are still no bigger than a die. Large glass objects — such as bottles, drinking glasses, or windowpanes — cannot be produced in this way. The aim of the work was to prove the feasibility of producing glass objects of complex geometry using a 3D printing process.