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What is SLS 3D Printing?

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Get to the know the basics of selective laser sintering, also known as SLS 3D printing. Find out how SLS printing works, the materials and post-processing options available, advantages and disadvantages of the process, and how the 3D printing technique can benefit you.

What is SLS 3D printing?

SLS 3D Printing 5

 

Selective Laser Sintering (SLS) is an additive manufacturing (AM) technique that belongs to the Powder Bed Fusion family and is often referred to as the plastic counterpart of Direct Metal Laser Sintering (DMLS). It works by selectively fusing powder together layer-by-layer to build a solid object.

SLS is an industrial 3D printing method that is known for building sturdy, durable parts out of established materials (mainly nylon). It is also fast, accurate, and can handle geometric complexity with ease. For these reasons, SLS has been a popular choice among engineers and manufacturers for functional prototypes and end-use low-volume parts for decades.

How does SLS 3D printing work?

Overall, the process involves 3 basic steps: printing, cooling, and post processing.

 

Printing

The SLS 3D printing process takes place primarily in the interior of the 3D printer, called the build chamber. First, a layer of powdered metal is sprayed across a platform located inside the build chamber. Then, the heaters in the printer preheat the powder to a temperature just below its melting point. The lasers come into play next, fusing the powder layer at specific points to form a 3D cross section of the desired build. The powder that is unsintered acts as the structural support for the build.

After the first layer of powder is sintered, the platform is lowered slightly, and another layer of powder is sprayed on. This process is repeated over and over until the build is fully printed.

 

Cooling

Due to the high temperatures involved, after printing, the powder bin must cool before the parts can be unpacked to ensure sure optimal mechanical properties and avoid warping and shrinkage as much as possible. This cooling process can, however, take a considerable amount of time—sometimes up to 12 hours.

 

Post Processing

Once all the layers have cooled, the sintered parts are separated from the unsintered powder, and the excess powder is cleaned and removed to reveal the final 3D-printed object. Further post-processing or surface finishes can then be applied to the final part to improve surface quality or enhance functionality.

Designing parts for SLS

Unlike other additive manufacturing processes, such as Stereolithography (SLA) and Fused Deposition Modeling (FDM), SLS does not require support structures, allowing for greater design freedom. For this reason, it is also one of the easier 3D printing technologies to design for.

While the process has many advantages, it also has its limitations. Staying within a set of geometric recommendations can help ensure better part quality and a successful print. To find out how to design wall thickness, hollow parts, mating parts and more, view our SLS 3D Printing Design Guide.

SLS material options

Nylon

Many sectors, including industrial, prefer nylon (PA) as a material for SLS 3D-printed parts. It has high thermal stability, high wear resistance, and is exceptionally strong. PA comes in three colors: black, white, and beige. But these can be dyed in post processing.

 

Glass Fibers

Filling PA with glass fibers (GF) makes a material that is a great alternative to metal. It increases PA’s thermal resistance to up to 110°C, as well as improves its resistance to wear. If you’re looking for a final product that is more stiff and able to stand up to high temperatures, PA+GF is probably your best option.

 

TPU 

TPU, a rubbery material available in many different colors, differs from nylon and PA+GF in that it is much more elastic and flexible. It’s also smooth to the touch. But it still provides an extraordinarily high amount of durability and strength. Industries such as medical and consumer goods often select TPU as their SLS material of choice.

SLS post processing options

SLS printed parts have a rough, grainy surface structure, that often requires extensive post-processing to achieve a smooth, aesthetic finish. The appearance of SLS printed parts can be improved through various post-processing techniques, including media tumbling or blasting, dyeing and spray painting. Protective coatings, such as watertight coating or a metal plating, can also be applied to SLS components to enhance functionality.

Advantages of SLS

  • Batch Production: With SLS, multiple plastic objects can be printed at the same time. This allows HLH Rapid to produce several batches of parts at once, allowing us to meet large orders from industrial businesses.
  • Greater Design Freedom: SLS prints don’t require support structures, allowing for a lot of extra freedom in the design phase.
  • Functional Parts: SLS parts have good isotropic mechanical properties, making them ideal for functional prototypes and end-use parts.
  • Reusable Powder: Once a print is finish, around 70% of the remaining powder can be reused (aka recycled).

Disadvantages of SLS

  • Prone to Shrinkage and Warping: SLS components – especially large, flat surfaces – are more likely to shrink and warp due to the high temperature experienced during printing.
  • Grainy Surface: SLS printed parts come out grainy and require extensive post processing to achieve a smooth finish, which can be costly.
  • Limited Material Choice: The selection of materials for SLS 3D printing is limited compared to methods like SLA and FDM.

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