Last week, the additive-manufacturing community and design aficionados everywhere excitedly welcomed glass to the growing list of 3D printing media. Developed by a team comprising the MIT Media Lab’s Mediated Matter Group, the MIT mechanical engineering department, the MIT Glass Lab, and the Wyss Institute at Harvard University, the additive manufacturing platform G3DP (Glass 3D Printing) can print glass in a variety of shapes, profiles, and colors—and subsequently different optical properties and degrees of opacity.
The resulting objects are breathtaking and dazzling, as is the
group’s experimental and prototyping process as detailed in its paper, “Additive
Manufacturing of Optically Transparent Glass,” published in the September
issue of 3D Printing and Additive
Manufacturing (which recently named
MIT Self-Assembly Lab director Skylar
Tibbits as its editor-in-chief). Moreover, the technology has great implications in the building and construction industries.
Architects stand to benefit from the patent-pending technology in everything from custom glass products with graded mechanical and optical properties to glass building components that can “contain, flow, and control the distribution of gas or liquid media, such as hot or cold air, water, and photosynthetic microorganisms, throughout channel networks and spatial pockets,” says Neri Oxman, director of the Mediated Matter Group. “Mies [van der Rohe]’s glass skyscraper was to us more than an inspiration because at its core is the belief that technological innovation can drive form and function. … [I]n this project, we wanted to explore the possibility of creating architectural building skins that are at once structurally sound, environmentally informed, and have the potential to contain and flow media through them.”
The advantages of 3D-printed, glass-based materials include their hardness, optical qualities, affordability, and availability, the paper's authors write. Conventional, additive printing methods using glass require sintering or SLM (selective laser melting). However, the authors note, the resulting products are opaque, fragile, and exhibit poor mechanical properties. The G3DP leverages the time-tested process of extrusion with molten glass, used by artisans and large-scale manufacturers alike, to “generate structures that are geometrically customizable and optically tunable with high spatial resolution in manufacturing,” Oxman says. “Because we can design and print outer and inner surface textures independently—unlike glass blowing—we can control solar transmittance … [and] continuously vary thickness and as well as internal features.”
After a year and a half of experimentation and tweaking, the team built an aluminum-and-steel printer with a 250-millimeter-square-by-300-millimeter build volume that extrudes a 10-millimeter-diameter glass filament at a build rate of 460 cubic millimeters per second and creates objects modeled in Rhinoceros with a custom Grasshopper script.
The printer consists of two chambers. Heated to approximately 1,040 C (1,900 F), the upper chamber acts as a kiln cartridge, capable of holding enough molten glass to build a single architectural component. The lower chamber serves as a print annealer and is kept at 480 C (896 F), just below the glass annealing temperature of approximately 515 C (959 F), to ensure the cooling printed objects evade thermal shock. (Radiation from the glass heat increases the chamber’s temperature to within the annealing temperature range.)
Users funnel molten soda-lime glass into a crucible kiln in the upper chamber that feeds into a nozzle that deposits a glass bead directly on the build platform inside the print annealer. Three motors controlled by Arduino microelectronics direct the nozzle along the XYZ axes. The flow of glass is initiated by manually heating the nozzle, and stopped by cooling it.
The team experimented with different feed rates, which varied the width of the 4.5-millimeter-tall glass layers, before settling on 6.1 millimeters per second, slightly higher than the natural flow, which resulted in a more uniform output.
Most of the printed objects required post-processing. Sharp edges where the printing terminated and the rough bottom where the objects first made contact with the build platform were ground down. To print objects with sudden and graded changes in hue, the team dropped colored frits into the crucible kiln when it was partially filled with molten glass.
The team also began exploring the potential of printing objects with predetermined optical properties. Polishing the 3D-printed glass resulted in a high degree of transparency while retaining the textured printed surface led to light scattering and the creation of stunning, highly complex caustic patterns when the objects were illuminated.
G3DP's Next Phase
In academia, one's work is never quite done. The research team's wish list of refinements includes improving G3DP’s feeding mechanism to create a continuous flow of molten glass through the printer; automating the start, stop, and cutting process of the glass filament; and using other glass types beyond soda lime.
“The tunability enabled by geometrical and optical variation driven by form, transparency, and even color variation can drive, limit, or control optical light transmission, reflection, and refraction,” Oxman says. The G3DP platform could help lead to "aerodynamic building façades optimized for solar gain, geometrically customized and variable thickness lighting devices ... printable optoelectronics or … channel networks built into the architectural skin containing photosynthetic media for the production of biofuels and electricity," she says. "Think Centre Georges Pompidou without functional or formal partitions [but with] a single transparent building skin that can integrate multiple functions and be shaped to tune its performance."
Several of the G3DP glass objects will appear in an exhibition at the Cooper Hewitt, Smithsonian Design Museum, in New York, next year. Check back for further details.
Research Team: MIT Media Lab's Mediated Matter Group—John Klein (lead researcher), Markus Kayser, Chikara Inamura, Giorgia Franchin, Neri Oxman; MIT’s mechanical engineering department—Michael Stern, Shreya Dave; Wyss Institute—James Weaver; MIT Glass Lab—Peter Houk