A novel printing technique for glass structures
NCCR Bio-Inspired Materials researchers at ETH Zürich have developed a novel stereolithographic approach to print transparent glass structures in three dimensions using available hardware technology, allowing for the production of customized objects.
Stereolithography, one of the most common three-dimensional printing technologies, comprising several advantages over traditional processing approaches: mass-customization, high complexity and little-to-no waste material. However, this technique has so far remained limited for the processing of functional glass structures. The ETHZ researchers chose to tackle 3D printing of glass structures using conventional digital light processing (DLP) printers. This way, geometries with far greater complexities are achievable compared with commercial glass manufacturing techniques.
Stereolithography was invented in the mid-1980s as the first 3D printing technology, but due to limitations of the available material chemistries, it has only recently been established as a widespread additive manufacturing method. During the process, layers of a liquid resin are sequentially solidified through UV light exposure to form a 3D object. However, only dedicated acrylate-based resins are available for printing of transparent objects, resulting in limited thermal and chemical stability. Glass manufacturing on the other hand dates back to Egyptian times. But despite the invention of glass-blowing in the ancient world, and the recent mechanization of blowing and casting processes, glass manufacturing remains labor intensive. Even if automation and process innovations have increased the reproducibility, properties and quality of glass products, the symmetric and predominantly flat geometries achieved through these approaches remain limited compared to the intricate shapes that can be produced by glassblowers. In the context of glasses, stereolithography has the potential to reconcile the automation of the modern industrial process with even higher geometric complexity than that attained by artisan labor.
The NCCR researchers from the Complex Materials group succeeded in printing transparent glass objects with arbitrary geometric complexity by combining multicomponent glass precursors and acrylate monomers. To achieve high printing resolution, the researchers relied on the phase separation of the liquid resins. Spinodal decomposition - the mechanism through which a solution of two or more components can separate into phases with entirely different chemical compositions and physical properties - during photopolymerization generates a morphology that is eventually stopped by the polymerization process. The scientists found that the phase separation enables the printing of truly complex 3D geometries through the formation of a continuous polymer network that is strong enough to withstand the mechanical stresses of the printing process. In a subsequent heating treatment, the complementary ceramic network is strengthened and its organic counterpart is burned off leaving a porous ceramic body. The final step sees the object heated at temperatures just below the melting point of glass, yielding a dense, transparent glass object. Additionally, the researchers discovered that by spatially controlling the grey-scale intensity of the digital light projection, the rate of polymerization can be also tuned on a voxel basis (the 3D equivalent of a computer screen pixel), which has an effect on the densification kinetics of the part during the final phase.
A rich variety of inorganic precursors can potentially be structured into porous or dense glasses and glass-ceramics using this additive manufacturing technique. With the high-resolution, complex geometries and locally tunable structure of the multicomponent glasses demonstrated in this work, the proposed 3D printing platform presents a step towards combining the high level of automation offered by modern digital fabrication processes with the accurate control over shape and chemistry traditionally achieved by manual labor to create glass objects.
Because readily available precursors and a commercial desktop printer and oven were used, it should be easy for the broader additive manufacturing and open source communities to adopt this new material, and digitally design and create glass components. The technology could therefore be a potential game-changer in the glass manufacturing industry by allowing small scale production of customized glass objects.
Reference: Moore, D. G.; Barbera, L.; Masania, K.; Studart, A. R. Three-dimensional printing of multicomponent glasses using phase-separating resins. Nat. Materials, 2020, 19, 212–217.