New tech boosts 3D printing of metal objects

A copper lattice structure created using the new process

A copper lattice structure created using the new process (Credit: Northwestern University)

The prospects for 3D printing may have just become a little bit stronger, literally, thanks to a new way of using metallic powders to create structures. A Northwestern University team has shown a new technique using liquid inks and common furnaces rather than more expensive lasers or electron beams.

In addition to being cheaper, the researchers say the process is also faster, more uniform and works with a wide variety of metals, alloys and compounds.

"Our method greatly expands the architectures and metals we're able to print, which really opens the door for a lot of different applications," said assistant professor of materials science and engineering Ramille Shah, who led the study.

Shah created a liquid ink from metal powders, solvents and an elastomer binder that could be printed through a nozzle in much the same way that plastic-based consumer 3D printers function. The printed structures are then sintered, a process in which they are heated in a simple furnace to allow the powders to merge together without melting.

"By uncoupling the printing and the sintering, it appears that we have complicated the process," said team member David Dunand. "But, in fact, it has liberated us as each step is much easier separately than the combined approach."

After an object has been printed with the metallic powders, but before it has been sintered and hardened, it's what is known as a "green body" that remains flexible.

"They're foldable, bendable, and can be hundreds of layers thick without crumbling," Shah explained. "It allows us to create a lot of different architectures that haven't really been seen in metal 3D printing."

The process can also be used to print metal oxides that are cheaper, safer and more stable than some pure metal powders. Green bodies 3D-printed from rust or other metallic oxides can then be turned into their respective metals by using hydrogen before being sintered.

"It might seem like we are needlessly complicating things by adding a third reduction step where we turn rust into iron," Dunand said. "But this opens up possibilities for using very cheap oxide powders rather than corresponding expensive metal powders. It's hard to find something cheaper than rust."

Possible future applications for the new approach include customized, quickly printed metals, batteries, fuel cells, medical implants, mechanical parts and on-site manufacturing.

The research was published in a recent issue of the journal Advanced Functional Materials.

Source: Northwestern University

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