SLS Video taken on a Concept Laser M100R (shown at 8x speed)
A very broad overview of one of the most common industry level 3D printing processes
Selective Laser Sintering (SLS), https://en.wikipedia.org/wiki/Selective_laser_sintering, is where things become very difficult both to do and to explain. Entire books can be written on the numerous different methods of powder based 3D printing and no matter how we explain it, not everyone will agree on the manner in which we will describe SLS or other powder based 3D printing techniques. We will very quickly review major concepts and then stress how they apply to MakerSpace USNA. If you have a lot of experience with 3D metal printing, you should probably stop reading here as you will probably not agree with how simply we explain these numerous definitions.
In our simple terms SLS and other powder techniques can be very easily summarized as a process where a powder (which can be a powder of virtually any material including metal, nylon, or others) is laid on a build plate and then a laser (or multiple lasers) sinters (thinking melting is fine for our purposes but whether the material is melted or not is a technical difference) a single layer of the parts. The build plate is then moved down, a new layer of powder is laid down, and the process repeats. In a very big picture sense, SLS is very similar to SLA except rather than a liquid polymer resin, a powder is used.
Now is where the process becomes difficult to explain. There are numerous different definitions used in the 3D printing industry and many are very similar. The major differences are how the powder is heated/sintered/melted and how the powder is laid down. Here are some very simple definitions (some sources will consider these definitions to be overly simplified) :
SLM (Selective Laser Melting). For our purposes SLM and SLS are almost identical so we will offer no explanation on the difference. In the most technical terms “sintering” describes a process that is below the melting temperature of the alloy and is thus, not melting. Similarly this process is sometimes called Direct Metal Laser Sintering (DMLS).
Powder Bed Fusion (PBF). PBF is a broad AM definition that simply describes a process where any powder (could be metal or non-metal) is laid on a build plate (the bed) and is then “fused” into a layer by some heating process. In this definition, SLS and SLM as well as other techniques are specific PBF techniques.
Electron Beam Melting (EBM). For most practical reasons EBM is very similar to SLS with the exception that EBM systems operate at a very high vacuum. EBM and SLS are both PBF techniques were a heat source (electron beam or laser) is used to fuse powders layer by layer.
Directed Energy Deposition (DED). DED systems are very different than PBF systems in that in addition to the heat source being directed to the build plate, the part material is similarly directed to the build plate (vice being on the build plate is in PBF systems). Exampled of DED systems include powder fed systems where the powder is sprayed onto the build plate and wire fed systems where a material is fed through a nozzle similar to a FDM system
For MakerSpace USNA, the only available SLS (or any PBF) process is the Fuse1 Formlabs nylon powder printer (ETA late 2019). Although not part of the MakerSpace currently, USNA does also have a SLS metal powder printer, the M100R Concept Laser printer.
In addition to printing parts via AM, USNA has significant experience characterizing structures made from AM in the Center for Material Characterization. Above left is optical microscopy of AM Ti64 done at USNA and above right is an inverse pole figure map using electron backscatter diffraction of a nickel superalloy. Both images reveal characteristics of the SLS process.