Selective Laser Sintering – SLS

Selective Laser Sintering, or SLS, is one of the most popular 3D printing technologies commonly used for prototyping and product development. In principle, it’s very much like SLA (stereolithography) – a laser “draws” cross-sections of the printed part on the surface of the raw material.

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However, there is a substantial difference between SLS and SLA: while SLA is limited to a liquid polymer, SLS can use a wide range of powdered materials, from nylon, elastomer and polymer to metal powders.

This makes SLS 3D printers suitable for rapid creation of relatively robust parts that can be used as concept models, functional prototypes (when using materials such as DuraForm PA or DuraForm GF) or even as end-use parts – in dentistry, aerospace and other industries. You may not be able to make a shuttle – but how about printing a drone? Yes, SLS 3D printing technology is being increasingly used in production of unmanned vehicle parts . . . and other, no less interesting, things.

SLS lets you print this . . .

Or this! Well, partially.

If you’re interested in an SLS 3D printer, be prepared to spend a bit of coin on a commercial-grade model, like the EOS 3D printers.

How does Selective Laser Sintering work?

As mentioned, SLS is very similar to SLA. First, a 3D software model of the part is created. Then, it’s converted into an STL file – an industry standard extension file – that stores your 3D model as a set of cross-sections. Next, a laser “draws” one of those cross-sections on the surface of a container filled with raw material – say, titanium powder. Finally, a thin new layer of powder is added on top of the already-drawn cross-section, the laser goes at it again, and, layer by layer, the desired item is produced. The following short video outlines the whole process.

Advantages of SLS

The SLS process has more advantages than SLA printing. First of all, you don’t have to worry about supports. If you want to make a large capital letter T with SLA 3D printing technology, the vertical parts would likely need support. Sometimes this process of creating supports is automated, but sometimes it’s not. Either way, you’ll have to remove the supports later. With selective laser sintering, however, the powder itself may actually act as a support – and this decreases both raw material usage and the time needed to make the part.

Second, SLS, unlike SLA, doesn’t need post-curing or anything of that nature. You may need to heat up the powder to speed up the work of the laser, but that’s it. Since there’s no curing, the finished product won’t lose its shape with time.

Third, flexible snaps and living hinges can be made since SLS parts are flexible. With SLA, the parst are rigid and flexibility is impossible.

SLS is economical and fast, and is great for prototyping. You might think that SLS is the best 3D printing technology there is!

But it isn’t.

Disadvantages of SLS

Yes, selective laser sintering has some disadvantages. Probably the biggest of them is that the fabricated prototypes are porous. This depends on the material used, as well as a few other factors. But generally you can expect an SLS-made part to have a rough, porous surface – and it probably won’t be as strong as a molded part, either. However, SLS parts can be coated to smooth out the surface and make the part stronger.

SLS is a more complex operation, and has more build variables. For this reason, the part might not be printed as accurately as a part made using stereolithography. The complexity of the build variables can make it a little more difficult to get the precise temperatures required, and excess fused material can compromise dimensional accuracy.

Still, SLS is a great 3D printing technology. You can create parts of almost any complexity out of a wide variety of materials, quickly and cheaply. It may not be as precise as SLA, but it’s much more robust, easier to machine, and can be used to create not only concept models, but parts that are very close in properties to a molded piece, depending on the materials used.

So if you’re making a concept model, go with SLA. If you want to make a part for functional testing, or perhaps you need to build a drone from scratch, choose selective laser sintering.