Selective Laser Sintering (SLS) is an Additive Manufacturing process that belongs to the Powder Bed Fusion family. In SLS, a laser selectively sinters the particles of a polymer powder, fusing them together and building a part layer-by-layer. The materials used in SLS are thermoplastic polymers that come in a granular form.
SLS 3D Printing is used for both prototyping of functional polymer components and for small production runs, as it offers a very high design freedom, high accuracy and produces parts with good and consistent mechanical properties, unlike FDM or SLA. The capabilities of the technology can be used to its fullest though, only when the designer takes into consideration its key benefits and limitations.
How does SLS work?
Here is how the SLS fabrication process works:
- The powder bin and the build area are first heated just below the melting temperature of the polymer and a recoating blade spreads a thin layer of powder over the build platform.
- A CO2 laser then scans the contour of the next layer and selectively sinters (fuses together) the particles of the polymer powder. The entire cross section of the component is scanned, so the part is built solid.
- When the layer is complete, the build platform moves downwards and the blade re-coats the surface. The process then repeats until the whole part is complete.
- After printing, the parts are fully encapsulated in the unsintered powder and the powder bin has to cool down before the parts can be unpacked. This can take a considerable amount of time (up to 12 hours). The parts are then cleaned with compressed air or other blasting media and are ready to use or further post process.
Characteristics of SLS
In SLS almost all process parameters are preset by the machine manufacturer. The default layer height used is 60-120 microns.
A key advantage of SLS is that it needs no support structures. The unsintered powder provides the part with all the necessary support. For this reason, SLS can be used to create freeform geometries that are impossible to manufacture with any other method.
Taking advantage of the whole build volume is very important when printing with SLS, especially for small batch productions. A bin of a given height will take about the same time to print, independent of the number of parts it contains. This is because the re-coating step determines the total processing time (laser scanning occurs very rapidly) and the machine will have to cycle through the same number of layers.