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SLS 3D printing
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
- Polyamide (PA) 6
- Polyamide (PA) 11
- Polyamide (PA) 12
- Thermoplastic polyurethane (TPU)
- Polypropylene (PP)
- Glass-filled nylon (PA-GF)
- Carbon fibre-filled nylon (PA-CF)
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.
Powder collection
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).
Post processing
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.
Rapid Prototyping
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.
There are very few health hazards associated with SLS 3D printing. The powdered raw material typically doesn’t contain any dangerous chemicals, but it consists of extremely fine particles and shouldn’t be inhaled. Open air powder filling and depowdering have historically led to discomfort and dirty clothes amongst operators. Today, there are solutions on the market that minimise (eliminate) the powder issue by ensuring the powder is transferred safely from packaging to the interior of the machine or confines it to a sealed-off area.
Ensuring a powder-free work environment is the first step toward a healthy and clean workplace. Open powder handling systems still require wearing gloves and an air filter mask.
SLS printers can be a significant investment, where the smallest and simplest ones cost some $10 thousand, and the big, industrial machines cost up to fifty times that much. This investment needs to be evaluated against the dramatic benefits of having a local SLS 3D printer.
- Development teams can run iterations with printed prototypes within 24 to 48 hours. Compared to ordering SLS prints from 3D print service companies, this typically saves well over a week per iteration.
- Companies or public institutions producing orthoses will save on material and labour costs. 3D printed orthoses are typically more comfortable to wear and can be offered in days rather than weeks.
- The bigger SLS 3D printers are typically used for the production of plastic products and components, where volumes do not quite motivate the investment in injection moulds.
Some applications require a smooth surface, which typically is achieved by sand-blasting, lacquering or other surface treatment methods. The most suitable post-processing procedure needs to be chosen based on the design, texture and application needs of the printed object.
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.
SLS nylon is a popular choice for bespoke tank design because of its chemical resistance and ability to withstand heat. Coating or lining the tank is a good option to improve water tightness or for harsh fluids like gasoline or solvents. With a wall thickness of at least 1mm, the tank can remove any excess powder. Every SLS 3D printer has a limit when it comes to just how thin walls it can print. These limits are stretched each year with new research and better material. If you plan to print thinner walls than 1 mm, you will probably have to check if this is within the capabilities of the SLS 3D printer you use. Also, with such fine structures, depowdering will need to be executed with care.
It might be difficult to link threaded SLS pieces together because of the rough surface created by SLS printing. SLS nylon is drillable and tappable. To keep your 3D-printed components safe, you can use SLS nylon.
SLS is one of the only technologies of 3D printing that can manufacture live hinges. To anneal SLS hinges, heat the hinge (dipping it in hot water typically works) and then bend the hinge back and forth many times in quick succession. The suggested thickness and length for living hinges are 0.3-0.8mm and 5mm, respectively.
SLS 3D printing generates products that are recognized for their increased stiffness, which is a major requirement in the healthcare industry. Using this method, you may create patient-specific medical gadgets. Orthoses (structures that support damaged, dysfunctional or weak limbs) are a common application. Amputation-replacement limbs and braces are other examples of common applications of SLS 3D printing in surgical models and instruments.
Many industries rely on machinery that depends on plastic replacement parts. Once the supplier of that machinery retires the machine from their assortment, it is just a matter of time before the spare parts become extinct. And from day one, the parts can be prohibitively expensive. This is why many companies look into the possibilities of scanning critical parts and printing them themselves. The big savings are typically found in the avoided downtime awaiting the shipment of spare parts. Another big saving (often overlooked) is the possibility to prolong the lifetime of existing machines.
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.
Cloud software
Our Deep Space software lets you easily place 3D files in the virtual build volume and stack many copies on top of each other while keeping material consumption down.
Materials
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.
Talk to one of our product specialists
