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Selective laser sintering (SLS) is a powder-bed 3D-printing process: a laser selectively bonds powdered material, usually a polymer such as nylon, one layer at a time to form a part. In polymer SLS, loose powder around the part supports many overhangs, so separate support structures are generally unnecessary. The finished part still needs to be cleaned of loose powder, and it may need additional finishing.
How selective laser sintering works
- A digital 3D model is divided into thin cross-sections.
- A layer of powder is spread across the build area.
- A laser scans the regions specified by the first cross-section, bonding the powder there.
- The build platform advances, a fresh powder layer is spread, and the laser bonds the next cross-section. The cycle repeats until the part is complete.
- The part is removed from the powder bed, and loose powder is cleaned away.
Because the surrounding powder supports the part as it is built, polymer SLS can form many overhangs without separate sacrificial supports. That does not mean every shape is practical: powder trapped in enclosed cavities or behind small openings can be difficult to remove.
What “sintering” means in SLS
Introductory descriptions do not always use the same word for what the laser does. Some say it “sinteres” the powder; others describe the process as fusing or melting it. Siemens explains sintering as heating particles enough for atomic diffusion and bonding without fully melting them. The precise behavior depends on the material and process, so “selectively bonds or fuses the powder” is a useful general description.
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Polymer SLS should not be confused with selective laser melting of metal powder. The names are similar, but they do not make the processes interchangeable.
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Materials used for SLS
Polyamide, commonly called nylon, is a widely used SLS material; PA12 is a common example. Fraunhofer ILT also identifies PA11, TPU, PLA, and PCL among materials it is developing or qualifying for SLS. These examples do not mean every printer can use every powder: compatible materials depend on the machine and process.
What SLS is useful for
SLS is used for functional prototypes, customized one-off parts, and small batches. It can also suit production applications when the material, part requirements, equipment, and process are a good fit. Its ability to form complex geometry—including internal features and undercuts—can be useful when a part would be difficult to make with a process that needs separate supports.
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SLS is not universally the cheapest or best manufacturing choice. A practical comparison should consider the part’s material and properties, geometric complexity and support needs, surface finish and post-processing, machine build capacity, and production quantity.
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- Powder removal: Loose powder must be cleared after printing. Narrow openings and enclosed spaces can make cleanup difficult.
- Shrinkage and warping: Parts can change shape as they are made, so geometry and process settings matter.
- Surface finish: An SLS part’s surface may differ from an injection-molded counterpart, particularly if it receives no post-treatment.
- Feature size and flat areas: Limits depend on the particular system and material. The University of Texas at Austin lab advises considering feature size and large flat areas; its 0.5 mm feature guidance applies to the system described on its page, not to SLS universally.
Build capacity depends on the machine
For one concrete example, the University of Texas at Austin lab lists its Sinterstation system with a 380 × 330 × 450 mm build volume, 100 μm layer thickness, and nylon 12 material. These are specifications for that lab system, not standard or industry-wide SLS figures.
Quick Recap
Best Value
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