MIT's new liquid metal printing can build chairs in minutes

However, LMP is not without its limitations. The technique sacrifices resolution for speed and scale. While it can print components that are larger than those typically made with slower additive techniques, and at a lower cost, it cannot achieve high resolutions.

In a recent study, the researchers demonstrated the procedure by printing aluminum frames and parts for tables and chairs which were strong enough to withstand postprint machining. 

They showed how components made with LMP could be combined with high-resolution processes and additional materials to create functional furniture. LMP is suitable for some applications in architecture, construction, and industrial design, where components of larger structures often require less fine details. It could also be used for rapid prototyping with recycled or scrap metal.

One method for printing with metals common in construction and architecture, called wire arc additive manufacturing (WAAM), can produce large, low-resolution structures. Still, these can be prone to cracking and warping because some portions must be remelted during printing. LMP, on the other hand, keeps the material molten throughout the process, avoiding some structural issues caused by remelting.

How LMP works

“This is a completely different direction in how we think about metal manufacturing that has some huge advantages. It has downsides, too. But most of our built world — the things around us like tables, chairs, and buildings — doesn’t need extremely high resolution. Speed, scale, repeatability, and energy consumption are all important metrics,” says Skylar Tibbits, associate professor in the Department of Architecture and co-director of the Self-Assembly Lab, senior author of a paper introducing LMP.

The researchers built a machine that melts aluminum, holds the molten metal, and deposits it through a nozzle at high speeds. Large-scale parts can be printed in a few seconds, and the molten aluminum cools in several minutes. The team chose aluminum because it is commonly used in construction and can be recycled cheaply and efficiently.

The researchers experimented with several materials to fill the print bed, including graphite powders and salt, before selecting 100-micron glass beads. The tiny glass beads, which can withstand the extremely high temperature of molten aluminum, act as a neutral suspension so the metal can cool quickly.

The amount of molten material held in the crucible, the depth of the print bed, and the size and shape of the nozzle have the biggest impacts on the geometry of the final object. For instance, parts of the object with larger diameters are printed first since the amount of aluminum the nozzle dispenses tapers off as the crucible empties. Changing the depth of the nozzle alters the thickness of the metal structure.

To aid in the LMP process, the researchers developed a numerical model to estimate the amount of material deposited into the print bed at a given time.

Perfecting the process

Because the nozzle pushes into the glass bead powder, the researchers can’t watch the molten aluminum as it is deposited, so they needed a way to simulate what should be going on at certain points in the printing process, Tibbits explains.

They used LMP to rapidly produce aluminum frames with variable thicknesses, which were durable enough to withstand machining processes like milling and boring. They demonstrated a combination of LMP and these post-processing techniques to make chairs and a table composed of lower-resolution, rapidly printed aluminum parts and other components, like wood pieces.

LMP is a faster and greener alternative to conventional methods and could revolutionize the metal manufacturing industry. However, it is still in its early stages and needs further development before being widely adopted.

“If we could make this machine something that people could actually use to melt down recycled aluminum and print parts, that would be a game-changer in metal manufacturing. Right now, it is not reliable enough to do that, but that’s the goal,” Tibbits says.