Researchers from the Massachusetts Institute of Technology (MIT) have developed a 3D printer capable of producing optically transparent glass objects. The new system, described in the September issue of Journal of 3D Printing and Additive Manufacturing, uses temperatures of more than 1,000ºC to produce glass with light transmission, reflection and refraction that can be controlled.
3D printing has exploded in recent years and it is now possible to print a wide variety of materials, including plastics, metals, and even biological materials. Simultaneously, the cost of 3D printers has fallen sufficiently to make them household consumer items.
The manufacture of glass objects by 3D printing has proven challenging up until now, a major obstacle being the extremely high temperature needed to melt it. One 3D printing method, sintering, whereby tiny particles of glass can be melded together at lower temperatures, has been used before to produce the material. However, the glass products end up structurally weak and optically cloudy, eliminating two of glass’s most desirable attributes: strength and transparency.
The high-temperature system developed by the MIT team retains those properties, producing printed glass objects that are both strong and fully transparent to light. Like other 3D printers now on the market, the device can print designs created in a computer-assisted design program, producing a finished product with little human intervention.
In the present version, molten glass is loaded into a hopper in the top of the device after being gathered from a conventional glassblowing kiln. When completed, the finished piece must be cut away from the moving platform on which it is assembled.
During operation, the system’s hopper as well as an alumina-zircon-silica nozzle which the molten material gets funnelled through, are maintained at temperatures of about 1,038°C, far higher than the temperatures used to 3D print other materials.
One challenge the researchers faced was keeping the filament of glass hot enough so the next layer of the structure would adhere to it, but not so hot that the structure would collapse into a shapeless lump. To solve this issue, they produced three separate components that can independently be heated to the required temperatures: the upper reservoir for the stock of molten glass, the nozzle at the bottom of that chamber, and a lower chamber where the printed object is built up.
‘Glass is inherently a very difficult material to work with,’ said MIT researcher John Klein, adding that the viscosity of glass changes with temperature, and therefore requires precise control during all stages of the process.
This is not the first time glass has been printed in liquid hot form. In June, Israeli company Micron3DP, a manufacturer of 3D printer components, successfully printed transparent glass in a range of different colours, using temperatures between 850 and 1,640ºC. Although not yet commercially available, the company is seeking investment to develop the process further, which according to the company will open up new 3D printing applications within the art industry, medicine, security, architecture, aerospace and many other areas.
Indeed, producing glass through 3D printing may enable new features that were not possible to create using conventional methods, which would open the door for new uses for the material. ‘We can design and print components with variable thicknesses and complex inner features — unlike glassblowing, where the inner features reflect the outer shape,’ explained Neri Oxman, an associate professor at the MIT Media Lab.
‘We can control solar transmittance… Unlike a pressed or blown-glass part, which necessarily has a smooth internal surface, a printed part can have complex surface features on the inside as well as the outside, and such features could act as optical lenses.’
Oxman added that she foresees the process being adapted to create much larger structures: ‘Could we surpass the modern architectural tradition of discrete formal and functional partitions, and generate an all-in-one building skin that is at once structural and transparent? Because glass is at once structural and transparent, it is relatively easy to consider the integration of structural and environmental building performance within a single integrated skin.’
The MIT team is now working on adding pressure to the system – either through a mechanical plunger or compressed gas – to produce a more uniform flow, and thus a more uniform width to the extruded filament of glass. Additional work will focus on the use of colours in the glass, which the team has already demonstrated in limited testing.
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