Wrench printed by SIS (Photo Credit: 3DPrint.com)

Many consider the affordable 3D printing of metal to be a breakthrough that would allow greater adoption of additive manufacturing for end-use parts. According to 3Dprint.com, researchers at the University of Southern California are working on a novel approach to that end: Selective Inhibition Sintering (SIS) which inhibits powder from melting, instead using it a mold:

"Using this new technique, a machine first lays down a layer of metal powder on a print bed. At this point a commercial piezoelectric printhead deposits a liquid solution which acts an an inhibitor, preventing the metal that it is sprayed upon from melting once it’s heated. The printhead, which is similar to that found in an inkjet printer, only sprays in an area which represents the boundary of the actual print. Where this solution is sprayed, the metal clumps together and hardens. Layer by layer, more metal powder is deposited, and more of the inhibiting agent is sprayed onto the print bed. The boundary of the object slowly is built up, with metal powder inside. It basically becomes a mold filled with pristine metal powder. When complete the entire print is then melted at a high temperature, leaving behind a solid object encased inside the inhibitor shell, which is then easily removed."

SIS is being touted as an affordable alternative to other metal printing processes because:

It relies on printhead technology which is seen as cheaper
It builds only the boundary of an object and is therefore faster.
Unused powder can still be reclaimed since the inhibitor is made from sucrose which can be dissolved in water.

While not yet perfected - part shrinkage and inhibitor application problems have occurred - researchers are encouraged by their preliminary results.