Selective Laser Sintering: Everything You Need To Know About SLS 3D Printing

Selective Laser Sintering is one of the main 3D printing technologies used, and has been around since the late 1980s. Along with fused deposition modeling and stereolithography, SLS has dominated rapid prototyping and low number manufacturing for decades. Since the patents expired recently however, many have speculated whether low-cost alternative SLS 3D printer machines will take off, such as Formlabs’ Fuse 1, to rival the industrial 3D printers.

Selective Laser Sintering: Explained

Estimated reading time: 4 minutes.

History of Selective Laser Sintering

Selective Laser Sintering was developed by the now Dr. Carl R. Deckard whilst he was still an undergraduate at the University of Texas. The development was with his professor at the same, Joe Beaman. After developing the process, Dr. Deckard went on to start up Desk Top Manufacturing (DTM) which was later sold to 3D printing giant 3D Systems in 2001 for a reported $45 million.

selective laser sintering
A news report from the 1990s when Selective Laser Sintering was still in its infancy.

Setting up an SLS 3D Printer

To 3D print, you firstly require a 3D CAD modeling program. Using this program you can create the 3D CAD file, before converting it into an appropriate file for 3D printing such as an .STL file. Then, you can send this file to your 3D printer to print the model/part.

Selective Laser Sintering Process

The Selective Laser Sintering process involves tiny particles of powder material (which can be polymers, ceramics, glass etc) being fused together via heat from a high power laser. A thermal source is used to fuse the powder particles together at a specific location on the build platform to develop a solid, 3D printed part.

A recoating blade is used to apply and smooth the powder on the build platform as the part is made. The part is therefore encased in powder when printing.

The process begins with a high power CO2 laser beam which scans the area which it has been programmed to sinter. This laser selectively sinters this powder and solidifies a section of the part just below the powder’s melting point. This continues across the whole layer of the part until that layer is finished.

selective laser sintering
The Selective Laser Sintering Process illustrated.

The recoating blade then deposits another lauer of the powdered material (layer size on an SLS 3D printer is usually 0.1mm) before the laser scans the surface again. The platform moves down one layer height after each layer has been produced, which is repeated layer-by-layer until the 3D part has finished being produced.

This process is like SLA in that a laser is focused on a specific point, and the platform moves after each layer has been finished. It is also like fused deposition modeling in that parts are completed layer-by-layer through the melting of a material, though FDM uses plastic filaments instead of powder.

Post-processing with Selective Laser Sintering

The key difference between Selective Laser Sintering and other plastic 3D printing technologies is that there are no need for supports. This is because the part is encapsulated in the material powder and does not need supports to remain stable. This is a major advantage over techniques such as Fused Deposition Modeling and Stereolithography.

selective laser sintering
An operator removes a part 3D printed using selective laser sintering.

Once finished, a part created through Selective Laser Sintering has to be left to cool before it can be taken out. This takes roughly 50% of the total print time on average.

Another important factor to take into account with Selective Laser Sintering is the shrinkage and warping that can take place. This is worse with long, flat parts, but can be remedied by producing them at an angle. Most SLS 3D printers have a heat chamber which somewhat counters the shrinkage though.

Selective Laser Sintering Materials

Materials used with Selective Laser Sintering are polymers such as nylon and PA (polyamide). Polyamide is mostly used as it is has a good chemical resistance, and is stable and strong. These powders cost around $50-60/kg. The colors are also limited, though parts can be dyed after printing to produce other colors. Metals can be used in a process similar to Selective Laser Sintering, called DMLS (Direct Metal Laser Sintering).

When choosing your powder materials, it is important to think about which types of powders you want. Finer powders produce a smoother part surface but create issues with handling and recoating, whereas coarser powders create parts which are easier to handle, but have a less attractive finish.

selective laser sintering
A guitar created with selective laser sintering.

SLS 3D Printers

Selective Laser Sintering is usually thought of as an industrial 3D printing process, rather than an affordable, low-cost technique such as FDM. This has been the case since 3D Systems, EOS and Stratasys produced the leading SLS 3D printer machines in the 1990s. However, there are more affordable SLS 3D printers around such as the VIT by Natural Robotics, the Fuse 1 by Formlabs, and the Sinterit Lisa.

SLS 3D printers have an average build volume of 300 x 300 x 300 mm. Larger Laser Sintering 3D printers can print up to 750 x 550 x 550 mm however. Shrinkage of the part should also be expected with SLS. This can usually be estimated at around 3-3.5%, and is mostly random. Most SLS 3D printers are accurate to around 100 microns, though this depends on each 3D printer.

sls 3d printer
The Sintratec Kit takes around 4 days to assemble, and is the first desktop selective laser sintering SLS 3D printer kit.

Selective Laser Sintering Applications

Selective Laser Sintering has applications is the production and prototyping of functional parts. This is because SLS is known for having very good accuracy and is able to print very complex geometries. The fact that multiple parts can be created simultaneously in the build platform means Selective Laser Sintering is good for low run part production.

Industries which use Selective Laser Sintering include the aerospace industry, prosthetics, hearing aids, dental implants, and more. SLS is also a preferred production method in the production of hollow parts such as pipes.

Advantages and Disadvantages of Selective Laser Sintering

Selective Laser Sintering Advantages

  • Best for producing strong, functional parts with complex geometries.
  • High level of accuracy (though not as high as stereolithography).
  • Doesn’t require supports, saving printing and post-processing time.

Selective Laser Sintering Disadvantages / Limitations

  • Very expensive. The machines can often cost $250,000+, and the materials cost $50-60/kg. In addition, the machines required skilled operators to use.
  • Cool-down time of 50% of print time can mean up to 12 hours of waiting. This leads to longer production time.
  • Parts have a grainy surface without any post-processing.

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