Three researchers from University of Southern California developed a 3D printer prototype which uses metal powder to create metal parts, like in conventional sintering, but without laser systems thanks to a new approach called Selective Inhibition Sintering (SIS). SIS was specifically developed aiming at low-cost sintering 3D printers, where lasers are replaced by piezoelectric printing heads derived by those used in inkjet printers.

Il modello 3D di un oggetto e la sua realizzazione in SIS

3D model (left) and its object made with SIS (right)

Selective Inhibition Sintering is a form of negative printing: the printing head doesn't work on the powder which, once fused, will be part of the final object but on powder that will be discarded. As usual, everything starts with the deposition of a first layer of metal (a bronze alloy, for the Californian prototype). On this layer, the printing head "draws" the boundary of the part section using a liquid chemical solution which is a sintering inhibitor.

After this first layer, the printer deposits a second one and draws on it. Then a third layer, a fourth and so on, until all layers are completed. Next step: powder sintering. The entire object block is bulk sintered in a conventional furnace: powder treated with the inhibitor simply crystallizes, while un-treated powder melts and gives form to the actual object. To reveal it, you have just to remove crystallized powder.

Un modello 3D, il "disegno" tradizionale e quello in SIS, solo per i contorni

3D model, section "drawing" with conventional binding and SIS boundary-only approach

SIS is not the first technology using a chemical solution to "draw" an object for metal sintering. Just to make an example, ExOne is been using this approach in its M-Print and M-Flex 3D printers for years. The difference is that in SIS the printing head deposits a sintering inhibitor, while other approaches usually do the opposite: depositing a sintering catalyst (a binder) on the powder to be fused.

This difference, Californian resarchers explain, gives two important advantages: 3D printing process is faster, because the printing head must "draw" only an object's boundary and not the whole section; fused metal is purer, because is not contaminated by a binder.


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