A team of researchers at MIT have recently demonstrated the first ever machine that can print molten glass through a nozzle and make transparent glass objects layer-by-layer according to digital instructions. The most challenging aspect of printing glass is that it must happen at extremely high temperatures. material must be kept at a temperature greater than 1000 deg C to flow well enough to be extruded through a nozzle. To achieve this, the printer needs separate heating systems for each stage of the manufacturing process. The molten glass ink is housed in a crucible above the nozzle, where heating coils maintain the desired temperature. The glass flows from the crucible into a custom nozzle, where separate heating coils keep it hot enough to flow and without sticking to the inside. Finally, objects are built inside a third heating chamber, which is kept just above the temperature at which the glass turns solid. This allows the printed objects to be cooled in a gradual, controlled way so that they don't break. Finding a nozzle suitable for printing glass was a complicated task, according to Peter Houk, head of MIT's Glass Lab. It needed to be made of a material that can both handle high temperatures and resist the glass sticking to it. Instead of the usual, more expensive platinum nozzles the group settled on a custom-made nozzle made of aluminium oxide. The full version of the academic paper which details the research, "Additive Manufacturing of Optically Transparent Glass" is available to download, free of charge, from: online.liebertpub.com/doi/pdfplus/10.1089/3dp.2015.0021
