TECH FRONT
in a cheaper, faster, and more uniform process. The North- western team also demonstrated that the new method works for an extensive variety of metals, metal mixtures, alloys, and metal oxides and compounds.
elastomer binder, Shah was able to rapidly print densely packed powder structures using a simple syringe-extru- sion process, in which ink dispenses through a nozzle, at room temperature.
Despite starting with a liquid ink, the extruded material instantaneously solidifi es and fuses with previously extruded material, enabling very large objects to be quickly created and imme- diately handled. Then, with collaborator David Dunand, the team fused the powders by heating the structures in a simple furnace in a process called sintering, where powders merge together without melting.
Instead of one laser slowly working its way
A copper lattice structure created with Northwestern Engineering’s new 3D printing process.
“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 Ramille Shah, assistant professor of materials science and engineering, who led the study. “Our method greatly expands the architectures and metals we’re able to print, which really opens the door for a lot of different applications.”
Conventional methods for 3D printing metallic structures
are both time and cost intensive. The process takes a very intense energy source, such as a focused laser or electron beam, that moves across a bed of metal powder, defi ning an object’s architecture in a single layer by fusing powder particles together. New powder is placed on top of the previous layer, and these steps are repeated to create a 3D object. Any unfused powder is subsequently removed, which prevents certain architectures, such as those that are hollow and enclosed, from being created. This method is also sig- nifi cantly limited by the types of compatible metals and alloys that can be used. Northwestern Engineering’s new method completely bypasses the powder bed and energy beam approach as well as uncouples the two-step process of printing the structure and fusing its layers. By creating a liquid ink made of metal or mixed metal powders, solvents, and an
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AdvancedManufacturing.org | March 2016
across a large powder bed, Shah and Dunand’s method can use many extrusion nozzles at one time. Their method potentially can quickly 3D print full sheets that are meters wide and can be folded into large structures. The only limitation is the size of the furnace. The research is described in a paper pub-
lished in the journal Advanced Functional Materials. Post- doctoral fellow Adam Jakus, graduate student Shannon L. Taylor and undergraduate Nicholas R. Geisendorfer also co-authored the paper.
Self-Adaptive Material Heals Itself A
n adaptive material invented at Rice University (Hous- ton) combines self-healing and reversible self-stiffening
properties.
The Rice material called SAC (for self-adaptive compos- ite) consists of what amounts to sticky, micron-scale rubber balls that form a solid matrix. The researchers made SAC by mixing two polymers and a solvent that evaporates when heated, leaving a porous mass of gooey spheres. When cracked, the matrix quickly heals, over and over. And like a sponge, it returns to its original form after compression. The labs of Rice materials scientists Pulickel Ajayan and Jun Lou led the study that appears in the American Chemi- cal Society journal ACS Applied Materials and Interfaces. They suggested SAC may be a useful biocompatible mate- rial for tissue engineering or a lightweight, defect-tolerant structural component.
Other “self-healing” materials encapsulate liquid in solid shells that leak their healing contents when cracked. “Those
Image courtesy Northwestern University
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