What's the difference between Selective Laser Sintering (SLS) and Selective Laser Melting (SLM)? Here's one of the better descriptions I've found that explains it:
"Selective Laser Sintering and Direct Metal Laser Sintering are essentially the same thing, with SLS used to refer to the process as applied to a variety of materials—plastics, glass, ceramics—whereas DMLS refers to the process as applied to metal alloys. But what sets sintering apart from melting or "Cusing" is that the sintering processes do not fully melt the powder, but heat it to the point that the powder can fuse together on a molecular level. And with sintering, the porosity of the material can be controlled.
Selective Laser Melting, on the other hand, can do the same as sintering--and go one further, by using the laser to achieve a full melt. Meaning the powder is not merely fused together, but is actually melted into a homogenous part. That makes melting the way to go for a monomaterial, as there's just one melting point, not the variety you'd find in an alloy. To nutshell it, if you're working with an alloy of some sort, you'll go SLS or DMLS; if you're working with say, pure titanium, you'll go with SLM."
So in lay terms, SLM is stronger because it has fewer or no voids which helps prevent part failure but is only feasible when using with a single metal powder.
Original release: http://www.eurekalert.org/pub_releases/2014-06/dlnl-lrd061614.php