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SLS was commercialized by the DTM Corporation. In many respects SLS is similar to SLA except that the laser is used to sinter and fuse powder rather than photocure a polymeric liquid. The first step convert the solid model of the part (usually STL files) and decompose it into slices.

Inside the SLS machine, a thin layer of fusible powder is laid down and heated to just below its melting-point by infrared heating panels at the side of the chamber. Then a laser sinters and fuses the desired pattern of the first slice of the object in the powder. Next, this first fused slice descends, the roller spreads out another layer of powder, and the process repeats.

In comparison with SLA, this process can rely on the supporting strength of the unfused powder around the partially fused object. Therefore, support columns for any overhanging parts of the component are not needed. This allows the creation of rather delicate, lace-like objects. Nevertheless hand-finishing is still needed to improve the inevitable stair-stepping.

Also, SLS parts have a rough, grainy appearance from the sintering process and it is often preferable to hand smooth the surfaces. Another difficulty is maintaining the temperature of the powder at a few degrees below melting. This is done with the infrared panels: but maintaining an even temperature over a large mass of powder requires long periods of stabilization before sintering by the laser can be started.

Click below to view a quicktime movie of the process, taken from the DTM Corporation website.