What is SLS 3D printing?

Selective Laser Sintering (SLS) is an additive manufacturing process that belongs to the Powder Bed Fusion family. In SLS 3D printing, 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. A SLS 3D printing service is used for both prototyping of functional polymer components and for small production runs. Its versatility makes SLS a great alternative to injection molding for low-production runs.

3D printing technology tree highlighting SLS

How does SLS 3D printing work?

SLS 3D printing uses a laser to sinter small particles of polymer powder. The entire cross-section of the component is scanned, so the part is built solid. The process works as follows:

  1. The powder bin and the build area are first heated to just below the melting temperature of the polymer.

  2. A re-coating blade spreads a thin layer of powder over the build platform.

  3. A CO2 laser then scans the contour of the next layer and selectively sinters—fuses together—the particles of the polymer powder. 

  4. When a 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.

  5. After printing, the parts are fully encapsulated in the unsintered powder. The powder bin must cool before the parts can be unpacked, which can take a considerable amount of time—sometimes up to 12 hours.

  6. The parts are then cleaned with compressed air or another blasting media, then they are ready to use or further post-process. 

How does an SLS 3D printer work? 

Schematic of SLS printer
Schematic of a SLS printer

For use of an SLS 3D printer, almost all process parameters are preset by the machine manufacturer. The default layer height used is 100–120 microns. 

A key advantage of SLS 3D printing 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 free-form 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 laser scanning occurs very rapidly, so it’s actually the re-coating step which determines the total processing time. The machine will have to cycle through the same number of layers regardless of the number of parts. Bin packing may affect lead times of small orders, as operators may wait until a bin is filled before starting a print task.

What are the advantages of SLS 3D printing

  • SLS parts have good, isotropic mechanical properties, making them ideal for functional parts and prototypes.

  • SLS requires no support, so designs with complex geometries can be easily produced.

  • The manufacturing capabilities of SLS is excellent for small to medium batch production.

  • All remaining unsintered powder is collected and can be reused.

What are the disadvantages of SLA 3D printing?

  • Only industrial SLS systems are currently widely available, so lead times are longer than other 3D printing technologies , such as FDM and SLA.

  • SLS parts have a grainy surface finish and internal porosity that may require post processing, if a smooth surface or watertightness are required.

  • Large flat surfaces and small holes cannot be printed accurately with SLS, as they are susceptible to warping and oversintering.

SLS best practices

Is SLS 3D printing right for your part or project? These are the rules of thumb:

  • SLS can produce functional parts from a large range of engineering plastics—most commonly Nylon (PA12).

  • The typical build volume of an SLS system is 300 x 300 x 300mm.

  • SLS parts exhibit good mechanical properties and isotropic behavior. For components with special requirements, additive-filled PA powders are available.

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