Molten aluminum deposition method trades resolution for speed and scale. Is it worth it?
It’s the essential dilemma of 3D printing: resolution versus speed. Balancing them isn’t always simple, but sometimes faster really is just better. That seems to be the guiding principle for a team of MIT researchers, who have developed a new metal additive manufacturing technique they’ve dubbed liquid metal printing (LMP).
By depositing molten aluminum into a bed of 100-micron glass beads, the researchers have been able to 3D print metal objects at ten times the speed of comparable metal additive manufacturing (AM) processes. The trade-off, of course, is resolution.
“Our process rate is really high, but it is also very difficult to control,” explained lead author Zain Karsan in a press release. “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.”
The aluminum is held in a graphite crucible while molten material is gravity-fed through a ceramic nozzle into the print bed. “Molten aluminum will destroy just about everything in its path,” Karsan explained. “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.”
The researchers experimented with various materials for the print bed before settling on the glass beads, including graphite powders and salt. The beads have the dual benefit of being able to withstand the high-temperature molten metal and act as a neutral suspension to cool parts quickly.
Liquid Metal Printing vs Wire Arc Additive Manufacturing
According to Karsan and the team, the resolution of LMP is roughly on par with wire arc additive manufacturing (WAAM), since both require significant post-processing. However, they also argue for an additional advantage of LMP over WAAM besides speed: the singular thermal cycle of a print.
WAAM involves melting and cooling the workpiece repeatedly, which makes it more susceptible to cracking and warping. Keeping the aluminum molten throughout the build reduces the chances of structural issues occurring due to remelting.
To demonstrate the capability of LMP, the research team printed aluminum frames and parts for tables and chairs. They also showed that parts made using LMP can stand up to post-process machining, including precision boring and thread milling.
“This is a completely different direction in how we think about metal manufacturing that has some huge advantages,” said associate professor and co-author Skylar Tibbits. “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.”
While there are still hurdles to clear in terms of consistency and reliability, LMP could radically change the metal AM landscape, not to mention metal manufacturing and fabrication more broadly.
The research is published in the proceedings of ACADIA 2023: Habits of the Anthropocene.