Reinventing metal 3-D printing with new direct writing process

March 31, 2017
Lawrence Livermore scientist Luke Thornley helped engineer the semisolid metal, a bismuth-tin mixture, that can be extruded through the nozzle of a specially designed 3D printer. Credit: Kate Hunts/LLNL

Metal 3-D printing has enormous potential to revolutionize modern manufacturing. However, the most popular metal printing processes, which use lasers to fuse together fine metal powder, have their limitations. Parts produced using selective laser melting (SLM) and other powder-based metal techniques often end up with gaps or defects caused by a variety of factors.

To overcome the drawbacks of SLM, Lawrence Livermore National Laboratory researchers, along with collaborators at Worchester Polytechnic Institute , are taking a wholly new approach to metal 3-D printing with a process they call direct metal writing, in which semisolid metal is directly extruded from a nozzle. The metal is engineered to be a shear thinning material, which means it acts like a solid when standing still, but flows like a liquid when a force is applied. The results of the ongoing three-year study were published in February in Applied Physics Letters .

"We're in new territory," said lead author Wen Chen, an LLNL scientist. "We've advanced a new metal additive manufacturing technique that people aren't aware of yet. I think a lot of people will be interested in continuing this work and expanding it into other alloys."

Instead of starting with metal powder, the direct metal writing technique uses an ingot that is heated until it reaches a semi-solid state—solid metal particles are surrounded by a liquid metal, resulting in a paste-like behavior, then it's forced through a nozzle. The material is shear thinning because, when it's at rest, the solid metal particles clump up and cause the structure to be solid. As soon at the material moves, or is in shear, the solid particles break up and the system acts like the liquid matrix. It hardens as it cools, so there's less incorporated oxide and less residual stress in the part, the researchers explained.

While encouraged by their success in printing test pieces, the researchers cautioned the method is still in its early stages and will need more work to achieve higher resolution parts with more industry-friendly metals, such as aluminum and titanium. In the paper, the team produced parts using a bismuth-tin mixture, which has a low of less than 300 degrees Celsius. The process took numerous iterations to get right, as researchers ran into the problem of dendrites—fingers of solid metal that would get stuck in the nozzle.

"The main issue was getting very tight control over the flow," said LLNL engineer Andy Pascall. "You need precise control of the temperature. How you stir it, how fast you stir it, all makes a difference. If you can get the flow properties right, then you really have something. What we've done is really understand the way the material is flowing through the nozzle. Now we've gotten such good control that we can print self-supporting structures. That's never been done before."

The researchers said the latest study will provide accurate operating conditions for printing with metal directly from a nozzle. They're already moving onto aluminum alloys, a metal that would be more attractive to industries such as aerospace and transportation, but will present challenges because of its higher melting point.

Unlike other metal 3D printing techniques that use lasers to fuse metal powder, the direct metal writing approach incorporates an ingot that is heated until it reaches a semi-solid state before it's forced through a nozzle. As it cools, the material hardens to form a 3D metal structure. Credit: Lawrence Livermore National Laboratory

"Being able to print parts out of in this way is potentially important," said staff scientist Luke Thornley, who worked on engineering the material. "So much of the work that goes into validation and analyzing for defects would be eliminated. We can use less material to make parts, meaning lighter parts, which would be big for aerospace."

Explore further: Nanoparticles improve melting and solidification for manufacturing processes

More information: Wen Chen et al. Direct metal writing: Controlling the rheology through microstructure, Applied Physics Letters (2017). DOI: 10.1063/1.4977555

Related Stories

Solid Concepts 3D prints world's first metal gun (w/ Video)

November 8, 2013

(Phys.org) —3D printing company Solid Concepts has announced that it has 3D printed the world's first metal gun—other guns printed using 3D printers have been made of plastic. Representatives for Solid Concepts say they ...

Researchers outline physics of metal 3-D printing

January 15, 2016

While the most common method of metal 3D printing is growing exponentially, moving forward from producing prototypes to manufacturing critical parts will be possible only by reaching a fundamental understanding of the complex ...

Lower-cost metal 3-D printing solution available

February 10, 2015

3D printing of plastic parts to prototype or manufacture goods is becoming commonplace in industry, but there is an urgent need for lower-cost 3D printing technology to produce metal parts. New substrate release solutions ...

Recommended for you

Gravitational waves may oscillate, just like neutrinos

September 21, 2017

(Phys.org)—Using data from the first-ever gravitational waves detected last year, along with a theoretical analysis, physicists have shown that gravitational waves may oscillate between two different forms called "g" and ...

Detecting cosmic rays from a galaxy far, far away

September 21, 2017

In an article published today in the journal Science, the Pierre Auger Collaboration has definitively answered the question of whether cosmic particles from outside the Milky Way Galaxy. The article, titled "Observation of ...

New technique accurately digitizes transparent objects

September 21, 2017

A new imaging technique makes it possible to precisely digitize clear objects and their surroundings, an achievement that has eluded current state-of-the-art 3D rendering methods. The ability to create detailed, 3D digital ...

Physicists publish new findings on electron emission

September 21, 2017

Even more than 100 years after Einstein's explanation of photoemission the process of electron emission from a solid material upon illumination with light still poses challenging surprises. In the report now published in ...

Rapid imaging of granular matter

September 21, 2017

Granular systems such as gravel or powders can be found everywhere, but studying them is not easy. Researchers at ETH Zurich have now developed a method by which pictures of the inside of granular systems can be taken ten ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

24volts
5 / 5 (1) Apr 01, 2017
I certainly hope they are moving on to something else. I don't want anything made from bismuth and tin.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.