Despite being one of the earliest 3D printing processes, selective laser sintering (SLS) remains a strong option for prototyping and low volume production in engineering. This overview outlines the key advantages and disadvantages to help you decide if SLS suits your outsourced manufacturing needs.
But first, it helps to understand how SLS works, as this explains why it is ideal for some projects and why others may be better served by a different 3D printing process.
What Is the SLS 3D Printing Process?
An SLS machine uses a laser to fuse each layer of the part into a heated bed of nylon based powder. After each layer is sintered, a recoater spreads the next layer of powder across the bed. The process repeats layer by layer until the build is complete.
What Are the Advantages of Using SLS?
SLS is reliable, precise and one of the fastest ways to produce prototypes and low volume batches. It offers distinct advantages over other processes:
1. No Support Structures
Unlike other 3D printing processes, SLS does not need support structures because unused powder fills voids and supports overhangs, making the build self-supporting.
This enables the design of hollow spaces, overhanging features and very thin sections. Parts with complex internal components or channels can be built without support structures, provided design guidelines are followed to allow effective removal of remaining powder. For complex designs, it is a good option and you do not need multiple parts to achieve this.
2. High Productivity
SLS is among the fastest 3D printing technologies because the laser scans quickly and the powder needs only a short exposure to fuse. Multiple parts can be tightly nested in the build chamber with minimal clearance to maximise build volume, so more parts are produced in less time.
3. Excellent Mechanical Properties
SLS produces strong interlayer bonding, so parts show near isotropic properties. Tensile strength, hardness and elongation at break are similar across the x, y and z axes.
This makes printed parts a viable alternative to injection moulded components for prototyping and low volumes. With nylon based materials, parts also provide good chemical resistance.
4. Ideal for Dying and Colouring
SLS parts have a porous surface, which can be an advantage or a disadvantage depending on the application. This makes them well suited to dyeing or colouring.
5. Reduced Product Development Time
Like other 3D printing processes, selective laser sintering enables cost effective prototyping early in the design cycle because it requires no tooling and minimal set up.
For low volume production, the same machine can produce end use parts, so engineers can test and iterate within days and move to production quickly.
What Are the Disadvantages of SLS Printing?
Like any manufacturing process, SLS has disadvantages, and there are occasions when alternatives may be better, such as another 3D printing process, CNC machining or injection moulding.
You may find that some drawbacks are minor in practice, and others can be addressed through post processing.
1. Fewer Materials
SLS offers a more limited material selection. At Protolabs we supply flexible TPU and PA 12 Flex, tough PA 12 40% glass filled and PA 12 carbon filled, plus a general purpose PA 12 White. Most projects use nylon based materials (polyamides), which are engineering grade plastics suitable for a wide range of applications. Nylon is widely available and relatively cost effective.
2. Rough Surface and Porosity
The porosity that makes SLS parts good for colouring also results in a relatively rough surface. As built parts are not watertight and have lower impact strength, so they can be brittle.
If these factors are critical, they can be mitigated with a post processing technique called vapour smoothing. This process produces a smooth, leakproof surface and can improve mechanical properties such as impact strength and elongation at break.
3. High Shrink Rate
SLS powder is exposed to high temperatures during sintering. As the part cools it shrinks, which can reduce dimensional accuracy compared with some other additive processes. Depending on geometry, shrinkage can be as high as 3 to 4%.
Allow for SLS shrinkage in the design by adjusting the model volume accordingly. Contraction during cooling can introduce stress that warps or distorts sharp edges and corners.
Read more about the 7 mistakes to avoid when designing 3D printed parts to help prevent these issues.
4. Higher Waste Than Other Additive Manufacturing
A key advantage of additive manufacturing is low material waste. However, SLS produces more waste because the powder bed is preheated so it will sinter with minimal laser exposure.
This can cause particles in the loose powder bed to partially fuse, reducing the quality for reuse. In practice, some unused powder can be recycled, but a proportion will be waste.
What Are the Typical Applications for SLS Printed Parts?
Selective laser sintering (SLS) is an industrial 3D printing process suited to rapid prototyping and manufacturing functional production parts. We manufacture SLS parts in nylon-based materials and thermoplastic polyurethane.
SLS is a strong choice when you need durable parts with heat and chemical resistance, flexibility and good dimensional stability. It is also cost effective for higher volumes of 3D printed parts.
A number of industries use SLS parts, with common applications including jigs and fixtures, housings, snap fits and living hinges.
Depending on your requirements, SLS may or may not be the right choice for your next project. At Protolabs we offer multiple additive manufacturing processes plus injection moulding and CNC machining, and can advise on the best technology for your needs.
Get a Quote
Ready to choose SLS for your part? Upload your part design to receive an instant quote with material options and recommendations.
