Jan 12, 2016 | By Kira

A team of Northwestern Engineers has developed a new method for 3D printing metal that uses liquid inks and a simple syringe-extrusion technique, much like a regular 3D printer, yet with the ability to create complex and more uniform architectures than previously possible in metal 3D printing. By replacing intense energy sources such as lasers or electron beams, the process is also much cheaper and faster, and works with a much wider variety of metals, alloys, metal mixtures and metal oxides, including potentially the cheapest of them all: rust.

We already know that metal powders are the fastest-growing segment with in the 3D printing materials market, and that 3D printing with metal offers a range of highly-sought out characteristics, including immense strength, reduced weight, biocompatibility and corrosion or thermal resistance, making it ideal for high-demand industries such as aerospace, medical, and more.

However, current metal 3D printing processes aren’t exactly ideal in and of themselves.  As Northwestern explains, conventional methods require focusing a very intense energy source, such as a laser or electron beam, across a bed of metal powder, fusing the powder particles together in a pre-determined pattern to create the final 3D structure. While this method does allow for incredibly strong metal 3D structures to be produced, it has his drawbacks. Mainly: it is prohibitively expensive and time consuming; it does not allow for certain types of architectures, such as those that are hollow and enclosed; and it is limited by the types of compatible metals and alloys that can be used.

Current metal 3D printing processes

Northwestern’s novel method for rapid metal 3D printing, however, promises to be cheaper, faster, and open the doors to entirely new metal materials and structural possibilities. It does so by eliminating the powder bed and energy beam approach, and by uncoupling the two-step process of printing the structure and then fusing its layers.

Instead of the powder bed, Northwestern’s team created liquid inks made from metal or mixed metal powders, solvents, and an elastomer binder. This ink can then be rapidly extruded at room temperature through a nozzle, just like on a regular 3D printer. Once extruded, the liquid inks solidify instantaneously as each layer fuses with the last, enabling large objects to be quickly created and, since they haven’t yet been heated, immediately handled.

The second step is to fuse the powders by heating the already-formed 3D structure in a simple furnace. This process is known as sintering, as the powders are permanently merged without actually being melted. “By uncoupling the printing and the sintering, it appears that we have complicated the process,” said David Dunand, a James N. and Margie M. Krebs professor of Materials Science and Engineering. “But, in fact, it has liberated us as each step is much easier separately than the combined approach.”

In addition to being a more rapid and cost-effective solution, the new metal 3D printing process actually allows for more sophisticated and uniform architectures to be created than what was previously possible with metal 3D printing.

More complicated architectures can be created thanks to the use of biomedical polymers, which allow the 3D object to be highly foldable and bendable before it is actually heated--in this stage, it is known as a 'green body'. They can also be hundreds of layers thick without crumbling. "Other binders don’t give those properties to resulting 3D printed objects. Ours can be manipulated before being fired. It allows us to create a lot of different architectures that haven’t really been seen in metal 3D printing," explained Ramille Shah, assistant professor of Materials and Science Engineering and leader of the study.

Professors Ramille Shah and David Dunand

Secondly, in traditional metal 3D printing, the layer-by-layer laser-heating approach can create localized heating and cooling stresses, resulting in undesirable microstructures and flaws in the finished object. However, heating the entire ‘green body’ at once inside a furnace ensures uniform temperature and densified structures that sinter without warping or cracking.

“To me, as a metallurgist, I’m amazed that the structure does not deform or break apart, despite shrinking extensively during densification,” said Dunand. “That is not something that I see often.”

And since many extrusion nozzles can be used at one time rather than a single laser being used for an entire powder bed, large sheets up to a few meters wide can quickly be 3D printed and folded into 3D structures—the only limitation is the size of the furnace.

If all of this—faster, cheaper, larger, more uniform, and more complex 3D printed metal structures didn’t already seem too good to be true, the Northwestern researchers discovered yet another novel use for their process: it can be used to 3D print with metal oxides, such as rust, by reducing it into metal. While rust is usually seen as undesirable, particularly if you are a car-owner, rust powder is actually lighter, more stable, cheaper and safer to handle than pure iron powders.

With this new process, the researchers could 3D printing with rust and other metallic oxides, and then use hydrogen to turn the ‘green bodies’ into the respective metal before heating and merging the powders inside the furnace. “It might seem like we are needlessly complicating things by adding a third reduction step where we turn rust into iron,” said Dunand. “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.”

This novel metal 3D printing process can be used to 3D print batteries, solid-oxide fuel cells, medical implants, aerospace and aircraft parts, and much more, thus representing an important step towards eventually mainstreaming metal 3D printing.

“This is exciting because most advanced manufacturing methods being used for metallic printing are limited as far as which metals and alloys can be printed and what types of architecture can be created,” said Shah. “Our method greatly expands the architectures and metals we’re able to print, which really opens the door for a lot of different applications.”

The research was published in a paper for the journal Advanced Functional Materials. Postdoctoral fellow Adam Jakus, graduate student Shannon L. Taylor, and undergraduate Nicholas R. Geisendorfer co-authored the paper.



Posted in 3D Printing Technology



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orest wrote at 1/21/2016 11:13:40 AM:

Does not look too different from https://www.kickstarter.com/projects/879356311/filamet-the-metallic-printer-filament-for-artists (I am still waiting for my reward...)

Hugues wrote at 1/12/2016 8:19:19 PM:

Interesting. But would have liked to see printed parts, really

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