Mar 30, 2017 | By Tess

A team of researchers from the Lawrence Livermore National Laboratory is developing a metal 3D printing method called Direct Metal Writing which could help overcome limitations that exist with powder-based metal 3D printing techniques such as Selective Laser Melting (SLM). Direct Metal Writing, which uses a semisolid metal as its base manufacturing material, is being dubbed “a wholly new approach to metal 3D printing.”

There is no question that metal 3D printing is becoming increasingly appealing to manufacturers, as it enables the creation of complexly structured parts and low-batch production runs, as well as cuts back on material waste. Most metal 3D printing processes currently use fine metal powders as a base material, which are sintered by lasers to build up an object. And while metal powder 3D printing processes have their benefits, some argue that they also have their limits, as many metal 3D printed parts suffer from gaps or defects due to the process.

LLNL researcher Luke Thornley

In an effort to solve these limitations, the Lawrence Livermore National Laboratory has teamed up with the Worchester Polytechnic Institute to create an entirely new metal 3D printing process. Called Direct Metal Writing, the additive manufacturing method involves the extrusion of a semisolid metal, known as a “shear thinning material.” The special metal has been engineered so that it behaves like a solid when it is still, but flows smoothly like a liquid when a force is applied to it.

“We’re in new territory,” said Wen Chen, an LLNL materials 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.” The research study, which has been ongoing for three years, was recently published in the journal Applied Physics Letters.

In short, the process consists of using a metal ingot which is heated until it is in a semi-solid state, at which point it is extruded through a nozzle. The force of extrusion makes the shear thinning material liquid enough to be extruded, but when it is left still, it acts as a solid and hardens as the material cools. According to the researchers, this process reduces the amount of incorporated oxide and residual stress that are put into the 3D printed part.

At the moment, Direct Metal Writing is still far from perfect, as the researchers have a few kinks to work out, including being able to manufacture higher-resolution parts using “industry-friendly” materials like aluminum and titanium. The material they’ve been working with to develop the technology is a bismuth-tin mixture, which works well because of its low melting point (though it did take the researchers some time to get the material mixture just right for smooth extrusion).

“The main issue was getting very tight control over the flow,” said Andy Pascall, an LLNL engineer. “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 are currently looking towards printing with an aluminum alloy which, if successful, could be of great appeal to many manufacturing industries, including aerospace, transportation, and more. The main benefits of Direct Metal Writing would be the elimination of time consuming validation and analyzing processes that 3D printed parts currently have to undergo, as well as higher material efficiency.

The ongoing study is being funded by the Laboratory Directed Research and Development (LDRD) program.



Posted in 3D Printing Technology



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I.AM.Magic wrote at 3/31/2017 9:56:04 AM:

Bismuth and tin for industrial application LOL; good try, call the press when you can print steel and aluminium. best of luck

Chef MechTech wrote at 3/30/2017 8:24:20 PM:

"The main benefits of Direct Metal Writing would be the elimination of time consuming validation and analyzing processes that 3D printed parts currently have to undergo, as well as higher material efficiency." At this stage that's bit of a premature conclusion--the process itself (as it currently stands or even a more mature state still cannot guarantee that the materials was extruded sufficiently to avoid any voids in the build, an in process or post-process monitoring will still be required.

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