The workings and usage of SLS 3D printing
Selective Laser Sintering, commonly known as SLS, is an additive manufacturing process that falls under the category of Powder Bed Fusion. SLS 3D printing has garnered the trust of engineers and manufacturers in many fields due to its capacity to generate robust, functional components with complex geometries.
In this guide, you’ll learn the basic principles of Selective Laser Sintering, and the various systems and materials that are currently on the market.
Contents in this guide
What is SLS 3D printing?
Selective Laser Sintering is a 3D printing technique that uses a laser beam to fuse together microscopic particles of polymer powder, layer by layer, to form a solid structure – a fused 3D part.
Since its inception, SLS 3D printing has become one of the most sought-after techniques to generate 3D parts. It has applications across many industries – bridge manufacturing, fast prototyping, small-batch manufacturing, and bespoke manufacturing – mainly due to its robustness. With SLS 3D printing, you can print functional prototypes, spare- or service parts and even finished products.
Recent advancements in technology, materials, and software have made SLS printing a core component in many industries.
Model of the SLS 3D printing process.
What materials are used for SLS printing?
The most common materials for SLS printing are polyamides (PA), also known as Nylon, like PA 11 or PA 12. These two materials have slightly different mechanical properties. PA 12 is tough and more widely used while PA 11 is more ductile. For specific and very demanding applications, there are other technical polymers.
Various additives can be used in the polyamide powder to improve a component’s mechanical and thermal properties. Carbon fibres, glass fibres, and aluminium are examples of additions. With additions, the component tends to be harder and more anisotropic in behaviour.
SLS 3D printing materials include
Aurora SLS powders
How does SLS 3D printing work?
The SLS method of 3D printing uses a laser beam to sinter tiny particles of polymer powder. It solidifies a cross-section of the component, and layer by layer the whole cross-section is scanned to construct a robust part. The procedure is explained step-by-step below.
The File's Design and Preparation
When designing your model, you can use a CAD program or 3D scan data, and save it in a file format that is compatible with 3D printing, usually STL or OBJ.
Every SLS printer comes with a software application that allows you to choose the printing parameters, orient and organise models, calculate print times, and slice the digital model into layers. After the initial setup, the print preparation software uses a wireless connection (or sometimes a cable connection) to communicate the instructions to the printer. However, some of the new entrants to the SLS market have SLS printers with software that simplifies the set-up dramatically, thereby eliminating the need for separate operators, enabling every user to choose settings by themselves and saving time.
3D models being prepared for printing.
SLS 3D printer being loaded with powder.
Get the Printer Ready to Go
Different systems have different workflows for getting the printer ready for use. Traditional SLS systems require a substantial amount of training, tools, and physical labour to prepare and maintain them. However, some new SLS 3D printers are exceptionally simple to operate even for a complete layman.
Next, the machine needs to be loaded with powder. This can be a messy (and potentially hazardous) experience unless you choose a printer that has solved the powder-handling challenge via packaging that integrates completely with the SLS 3D printer, making powder-filling both convenient and safe.
After all of the preprint checks are made, the machine is ready to start printing. SLS 3D printing can take anywhere from a few hours to several days, depending on the size, intricacy, and density of the components. Printing takes place in an adapted atmosphere, at temperatures just below the melting point of the powder and the construction of the printer. The exact temperature varies but generally isn’t very far away from 200 °C.
Once the printing process is complete, the build chamber needs to cool down so that the appropriate mechanical characteristics in the printed object can be achieved. Stressed cooling down results in warping of thin parts and other unwanted effects. The cooling down time is roughly the same as the print time itself.
Camera live stream showing the sintering process.
A printed part being depowdered using Wematter’s Density.
Part Recovery and Depowdering
The next step is to take the final components out of the build chamber and somehow remove the unsintered powder from the inner sections of the printed object. This can be an entirely manual (and very dusty) process at a cleaning station, but modern solutions involve using either compressed air or a media blaster in a closed-off cabinet.
Compared to other methods of 3D printing processes, the post-processing of SLS components involves significantly less time and effort. Due to the absence of support structures, it is straightforward to scale up and produces results that are reliable across batches of components.
In the process of cleaning the parts from unsintered powder, the surplus powder is collected and recycled. However, since the powder has been exposed to high temperatures, it suffers from minor degradation. To ensure the quality of the following print jobs, it is common to replace a share of the powder with brand new material to ensure successful printing. Maintaining a higher share of reused powder saves costs and the environment.
Over time, a good SLS 3D printer can save on costs for powder. As a purchaser of SLS 3D printers, you may wish to discuss the quota of virgin vs recycled powder your prints are going to need before deciding which printer to buy.
Parts being extracted from the powder bed.
SLS 3D printed part treated with vapor smoothing (right).
After cleaning, often referred to as depowdering, the 3D-printed parts are ready to be used. However, to achieve the finest quality parts, there are a few key points to consider.
Graininess is a characteristic of all SLS 3D printing by default. If you want your SLS components to have a smoother surface quality, media blasting or media tumbling could be used. Coating, electroplating, spray painting, and lacquering are some methods that can be used to create the desired colour, finish, and surface structure.
Examples of such methods include water resistance (coating) and conductivity (electroplating).
When should you use SLS 3D printing?
Here are a few use cases for SLS 3D Printing.
SLS is an excellent rapid prototyping method for functional polymers due to its high degree of design freedom and precision. Unlike other 3D printing methods (like FDM or SLA), it generates products with consistent, high mechanical qualities. If you’re looking for a way to make components that are just as good as the final product, this is the best option for you.
Small series production
Compared to injection moulding, SLS 3D printing is an excellent choice for low to mid-volume manufacturing. Complex forms and geometries may be produced with SLS, as well as a broad range of finishes and lead times.
SLS and FDM, a comparison
Functional prototypes for industrial use
Limitations of SLS 3D Printing
SLS additive manufacturing is one of the most commonly used 3D printing processes. However, it does have certain limitations. These are a few things to keep in mind:
The types of materials that may be used in SLS AM are limited. Plastic polymers and ceramics are all suited for the technique, but nylon is the most prevalent.
Examples of design applications for SLS 3D Printing
Many industries use SLS 3D printing as an integrated method of product development. The following are some components produced using SLS 3D printing.
SLS nylon and correctly designed integrated hinges can be a winning combination. When a semi-spherical ball is placed inside of a trapezoid-shaped pocket, friction is reduced and stability is increased. A space of 0.2 mm should be maintained between the sphere and the pocket for best results. A clearance of 0.3 mm is suggested between every other gap.
A complete ecosystem for SLS 3D printing
SLS 3D printer
The Gravity SLS 3D printer and its ecosystem can be placed almost in any environment and is easy to get started with regardless of previous additive manufacturing experience.
We offer one of the broadest ranges of SLS powder for additive manufacturing, covering everything from really soft materials to ones made really stiff with fiber reinforcement.