German scientists from the Karlsruhe Institute of Technology (KIT) have developed a novel process for 3D printing intricate objects in glass using SLA machines. Using a photocurable nanocomposite — in a process not dissimilar from that used for zirconia and ceramics — they were able to create transparent fused silica components at a resolution of just a few tens of micrometres.
3D printed lenses is one of the obvious potential applications for this technology. And whilst Luxexcel produces 3D printed lenses rated for ophthalmic applications, these are printed using an UV-curable acrylic, not real glass which still offers superior optical transparency, better mechanical, chemical and thermal resistance as well as thermal and electrical insulating properties.
The problem is that 3D printing glass has not been without it’s difficulties. Indeed, as the study highlights, the various technologies that have been available thus far have plenty of limitations:
- Using a fused deposition moulding process — where soda lime glass is heated to around 1,000ºC — or a manual wire feeding process — where glass filament is melted with a laser — create components with high surface roughness.
- Inkjet and SLS of glass powders have — at least so far — produced white, non-transparent components.
- Stop-flow lithography — whilst able to shape glass directly — is limited to 2D microstructures.
- Direct laser lithography — with a necessary additional hydrofluoric etching step — has been used but the results are too rough for optical applications and requires extensive post-processing.
You get the picture, glass is tricky to 3D print. Especially if we’re talking about intricate, highly transparent parts.
So, to be able to print glass components, using desktop SLA machines — they cite the Asiga Pico 2 — at a resolution, transparency and structure quality compatible with applications in MEMS, micro-optical and microfluidics, is quite a feat.
In order to achieve this, they used an UV-curable monomer — hydroxyethylmethacrylate (HEMA) — mixed with amorphous silica nanoparticles with an average diameter of 40nm. The study cites HEMA as having been chosen for allowing the dispersion of high amounts of the silica nanoparticles without having to use further additives. This nanocomposite can then be used with the SLA machine using free radical polymerisation. The non-polymerised material is removed by immersing the part in a solvent.
Of course, there’s a catch. The final step of the process involves removing the polymeric matrix through thermal decomposition — in other words by heating the component to 1,300ºC. So whilst a desktop machine can be used to print the components, an industrial kiln is required for the final sintering process.
The study opens up the possibility of creating complex, highly transparent components that are temperature- and chemical-resistant — using existing 3D printing technology — in one of the oldest and most coveted materials on the planet. You just need a really big oven.