3D Printing

New tech boosts 3D printing of metal objects

New tech boosts 3D printing of...
A copper lattice structure created using the new process
A copper lattice structure created using the new process
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A copper lattice structure created using the new process
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A copper lattice structure created using the new process

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

9 comments
Wombat56
Neat, especially the part about chemically reducing the metal oxides with [electrically ionized] hydrogen gas before sintering.
notarichman
compare the output of this process with a cast, welded, formed product for strength, durability, etc. do some testing in other words.
Bruce H. Anderson
This is an example of taking one step back to take several steps forward. Very innovative and (dare I say?) "disruptive."
Island Architect
Interesting that in the now classical way of working with metals things were always done by separate processes. Just think of tempering steel and the purple and the straw. b
pmshah
I think it is brilliant.
JagtygerII
I am curious about the Structural strength of the sintered parts vs solid machined parts and whether alloy steels or other metals, such as Inconel can be used by this method. The only sintering process that I knew about required not only heat but pressure to form the part. Has this been changed?
MD
jagtygurl: sintering is (always) the heating process, the pressure in conventional "powder metallurgy" is used to "form" the "green" part, before it is transformed into a metallic solid in the kiln. NB. in "sintering" nothing actually melts, the products just get hot enough to get "plastic" (gooey) and fuse together, it works with metals, polymers or ceramics, just that the critical temps vary a lot.
MichiganDave
Interesting, and this method is going to be disruptive...just wait 20 years to see the results. 1 question for whomever: how hot does this furnace need to get? Thanks ( in advance ) for your help.
Noel K Frothingham
Please note that the author has acknowledged that this printer output isn't as robust as the original part created by conventional processes. This technology is limited by the available feed stock material. It is not a mature process. The among the first sintered product I encountered were oiled bronze bushings and sleeve bearings used in electric motors. Their porosity of the sintered bronze bearings allowed it to absorb oil and release it gradually, just enough oil to maintain the thin oil film between the bearing itself and the motor shaft. My first total knee replacement used a granular high density polyethylene the as a bearing plate that would act as the meniscus. The second replacement used homogenous polyethylene bearing plate. The granular PE plate had started to deteriorate and crumble after 14 months and was seen clearly on an x-ray.The solid PE plate was still intact after 5 years of use. The granular PE was essentially 'sintered' PE. This goes to show that sintered materials have their place but are not suitable for many applications.