MIT demonstrates rapid Additive Manufacturing with liquid metal process
February 21, 2024
Researchers from the Massachusetts Institute of Technology (MIT), Cambridge, USA, have developed an Additive Manufacturing technique able to rapidly manufacture large-scale parts with liquid metal in just minutes.
The Liquid Metal Printing (LMP) technique involves depositing molten aluminium along a predefined path into a bed of tiny glass beads. The metal then hardens into a 3D structure. The MIT researchers have stated that this technology is more efficient and at least 10X faster than comparable metal Additive Manufacturing processes.
In a recent study, the researchers demonstrated the procedure by additively manufacturing aluminium frames and parts for tables and chairs which were strong enough to withstand post-processing machining. They showed how components made with LMP could be combined with high-resolution processes and additional materials to create functional furniture.
“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 and scale, and also repeatability and energy consumption, are all important metrics,” stated Skylar Tibbits, associate professor in the Department of Architecture and co-director of the Self-Assembly Lab, who is senior author of a paper introducing LMP.
Tibbits is joined on the paper by lead author Zain Karsan SM ’23, who is now a PhD student at ETH Zurich; as well as Kimball Kaiser SM ’22 and Jared Laucks, a research scientist and lab co-director. The research was presented at the Association for Computer Aided Design in Architecture Conference and recently published in the association’s proceedings.
Process speed
Drawing on previous work with rubber, the researchers built a machine that melts aluminium, holds the molten metal, and deposits it through a nozzle at high speeds. Large-scale parts can be manufactured in just a few seconds; the molten aluminium cools in several minutes.
“Our process rate is really high, but it is also very difficult to control; it is more or less like opening a faucet. You have a big volume of material to melt, which takes some time, but once you get that to melt, it is just like opening a tap. That enables us to print these geometries very quickly,” Karsan explained.
The team chose aluminium because it is commonly used in construction and can be recycled cheaply and efficiently. Bread loaf-sized pieces of aluminium are deposited into an electric furnace, “which is basically like a scaled-up toaster,” Karsan added. Metal coils inside the furnace heat the metal to 700ºC, slightly above aluminium’s 660ºC melting point.
The aluminium is held at a high temperature in a graphite crucible, and then molten material is gravity-fed through a ceramic nozzle into a build bed along a preset path. They found that the larger the amount of aluminium they could melt, the faster the building process can go.
“Molten aluminium will destroy just about everything in its path. We started with stainless steel nozzles and then moved to titanium before we ended up with ceramic. But even ceramic nozzles can clog because the heating is not always entirely uniform in the nozzle tip,” Karsan said.
By injecting the molten material directly into a granular substance, the researchers don’t need to use supports to hold the aluminium structure as it takes shape.
Process optimisation
They experimented with a number of materials to fill the 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 aluminium, act as a neutral suspension so the metal can cool quickly.
“The glass beads are so fine that they feel like silk in your hand. The powder is so small that it doesn’t really change the surface characteristics of the printed object,” Tibbits said.
The amount of molten material held in the crucible, the depth of the 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 additively manufactured first, since the amount of aluminium 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 that will be deposited into the print bed at a given time.
Because the nozzle pushes into the glass bead powder, the researchers can’t watch the molten aluminium as it is deposited, so they needed a way to simulate what should be going on at certain points in the Additive Manufacturing process, Tibbits explained.
They used LMP to rapidly produce aluminium 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 manufactured aluminium parts and other components, like wood pieces.
Moving forward, the researchers want to keep developing the machine so they can enable consistent heating in the nozzle to prevent material from sticking, and also achieve better control over the flow of molten material. But larger nozzle diameters can lead to irregular builds, so there are still technical challenges to overcome.
“If we could make this machine something that people could actually use to melt down recycled aluminium 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 said.
“At Emeco, we come from the world of very analog manufacturing, so seeing the Liquid Metal Printing creating nuanced geometries with the potential for fully structural parts was really compelling,” stated Jaye Buchbinder, who leads business development for the furniture company Emeco and was not involved with this work. “The Liquid Metal Printing really walks the line in terms of ability to produce metal parts in custom geometries while maintaining quick turnaround that you don’t normally get in other printing or forming technologies. There is definitely potential for the technology to revolutionise the way metal printing and metal forming are currently handled.”
Additional researchers who worked on this project include Kimball Kaiser, Jeremy Bilotti, Bjorn Sparrman, Schendy Kernizan, and Maria Esteban Casanas. The research was funded, in part, by Aisin Group, Amada Global, and Emeco.
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