SoylentNews is people
SoylentNews
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[sic] 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.
[...]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.
[...]"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."
More information: Wen Chen et al. Direct metal writing: Controlling the rheology through microstructure, Applied Physics Letters (2017). DOI: 10.1063/1.4977555
(Score: 2, Informative) by Anonymous Coward on Sunday April 02 2017, @06:46PM (1 child)
When you care about the metal being used, you use lost wax casting. 3D-print the object in wax, coat it with something to resist heat, pack it in fine sand, cook out the wax, pour in molten metal, let it harden, and then break it out of the mold.
This is good enough for making hollow jet turbine blades out of single-crystal superalloys. It's good enough for objects to be implanted into the body. (many metals react badly) For cheap projects, an aluminum-zinc alloy or plain old solder can be used.
(Score: 3, Interesting) by mhajicek on Sunday April 02 2017, @06:51PM
Yep. Most applications where porosity would be an issue would not tolerate using their special alloy.
The spacelike surfaces of time foliations can have a cusp at the surface of discontinuity. - P. Hajicek