3D printing transparent glass

Researchers at Massachusetts Institute of Technology, MIT, have developed the technology to allow 3D printing of transparent glass objects, an option that was previously off-limits to standard 3D printers. Writing in the Journal of 3D Printing and Additive Manufacturing [DOI: 10.1089/3dp.2015.0021], Neri Oxman, Peter Houk, John Klein and Michael Stern and their colleagues explain how the extremely high temperatures needed to melt glass have until now precluded the use of this age-old material in a 3D printer without resorting to sintering, which produces structurally weak and optically cloudy objects.

The high-temperature system developed at MIT produces strong and transparent objects 3D printed from a computer-assisted design. Molten glass from a glassblowing kiln is poured into a hopper at the top of the printer. The molten glass at just over 1000 Celsius is extruded though a nozzle pouring like honey from a jar on to the printing platform from which the object will later be cut. The hopper, nozzle and printing chamber are all held at high temperature throughout the printing process.

Klein explains that the original concept emerged from a teaching course on additive manufacturing and has taken a lot of trial and error to achieve success. “Glass is inherently a very difficult material to work with,” Klein explains: Its viscosity changes with temperature, requiring precise control of temperature at all stages of the process. The new 3D printing process gives the researchers unprecedented control over the glass objects that might now be produced, Oxman adds.

“We can design and print components with variable thicknesses and complex inner features - unlike glassblowing, where the inner features reflect the outer shape,” Oxman explains. “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.”

Houk cites several other directions in which they might now push the research. One is adding pressure to the system - either by using a mechanical plunger or compressed gas - to allow them to make the flow more uniform and so produce a uniform width to the extruded filament of glass. The team will also investigate adding colored glass, something they have already demonstrated to a limited extent in their tests.

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the bestselling science book "Deceived Wisdom".