Sintering glass

What started off as a course project has developed in to a process of printing glass that is both transparent and structurally sound.

Researchers at the Massachusetts Institute of Technology (MIT) have developed what it claims is the first solid glass 3D printed structures. The high-temperature system retains properties often lost when glass is sintered, a common technique used within the 3D printing sector. The stream of glowing molten glass from the nozzle resembles honey as it coils onto a platform, cooling and hardening as it goes.

Sintering uses tiny particles of material melded together. For many materials including metals and plastics it has been used to great avail as the process puts the material in a molten state at lower temperatures than would be needed otherwise – and therefore uses less energy.

However, sintering glass results in parts that are structurally weaker and often optically cloudy. In addition to the finished properties, the process itself has the major obstacle of needing extremely high temperature to produce molten glass. However, the process developed is reportedly able to retain the properties of strength and transparency.

The concept began as an additive manufacturing course project. Researcher, John Klein, said: “Glass is inherently a very difficult material to work with. Its viscosity changes with temperature, requiring precise control of temperature at all stages of the process. This process could allow unprecedented control.”

However, MIT has used molten glass loaded in to an overhead hopper that during operation extrudes molten glass at a maintained temperature in excess of 1,000°C, far higher than the temperatures normally seen in 3D printing devices.

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. They ended up producing 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.

Associate Professor, Neri Oxman, said: “We can design and print components with variable thicknesses and complex inner features. 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 adds 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?” she asked. “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 researchers are pushing research further in several additional directions. One is by adding pressure to the system — either through a mechanical plunger or compressed gas — to produce a more uniform flow, and therefore a more uniform width to the extruded filament of glass. Another is to look at the use of colours in the glass, which the team has already demonstrated as possible during initial testing and development work.

Klein says the printing system is an example of multidisciplinary work facilitated by MIT’s flexible departmental boundaries — in this case, involving team members from the Media Lab, the Department of Mechanical Engineering, and the MIT Glass Lab.

Justin Cunningham

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