SLS printing

SLS printing – Selective laser sintering

What is SLS printing?
SLS – Selective laser sintering in Hebrew “selective laser sintering” is a production technology that uses a high-power laser to melt small particles of polymer powder into a solid structure based on a three-dimensional model.
SLS 3D printing has been a popular choice for engineers and manufacturers for decades. Low cost per part, high productivity and established materials make the technology ideal for a variety of applications, from rapid prototyping to small or custom production.

Since the powder supports the part during printing, there is no need for dedicated support structures. This makes SLS ideal for complex geometries, including internal features, cross-sections, thin walls and negative features.
Parts produced by SLS 3D printing have excellent mechanical properties, with strength comparable to injection molded parts.
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3D printing with SLS technology occupies a significant market share, but it is not the most dominant compared to other technologies. According to the latest estimates, the general market distribution is as follows:

What is each technology in brief:
FDM is the most common technology, thanks to its low cost and accessibility to private and industrial users.
SLS is widely used in the production of functional parts with high mechanical resistance, mainly for industries such as automobile, medicine and aviation.
SLA is widely used to produce parts with high precision and a smooth finish.
DMLS and SLM are used in the production of metal parts for applications that require high strength, mainly in the aerospace industry.

SLS printing technology is increasingly used in industry thanks to its capabilities for printing complex parts, which ensures its position in the range of applications that require high durability and precision.

Why is there an upward trend in SLS printing?

There has been an upward trend in the use of SLS technology in recent years, and growth continues to be steady. This trend stems from several main factors:

Lower costs of printers and materials – a decrease in the costs of printers and materials used in SLS technology makes the technology more accessible for medium and small companies.

Improvement in printing materials – Continuous development of new printing materials, especially combinations of nylon reinforced with fibers such as carbon fiber and glass fiber, makes SLS more attractive for applications in various industries, such as automotive and aviation.

Expanding Functional Uses – The use of SLS for the production of final parts is steadily increasing, especially in applications that require high durability and precision, as well as for parts with complex geometries that cannot be easily produced by traditional manufacturing methods.

Increase in needs for fast and customized production – the increase in the trend of production on demand and small series also contributes to the growth of SLS, because it provides customized parts at high speed and with excellent quality.

Improvement in technology capabilities – the scientific and technological improvements in the printing processes and the ability to control the mechanical characteristics of the printed parts increase the trust and demand for technology in the medical, aviation, electronics and other industries.

Estimates show that SLS technology is expected to continue to grow by approximately 15-20% per year, at a relatively high rate compared to traditional printing technologies, and to gain momentum as the technology continues to improve and becomes a key tool for flexible and accurate production.

How does SLS printing work?

1) Heating the cell – a preliminary step for printing, depending on the size of the SLS printer cell takes between 1 and 3 hours.
Large SLS printer about 3 hours, small SLS printer about 1 hour.

2) Printing – the powder is spread in a thin layer on a platform inside the construction chamber. The printer preheats the powder to a temperature just below the raw material’s melting point, making it easy for the laser to raise the temperature of specific areas of the powder bed while following the model to solidify a part. The laser scans a cross section of the 3D model. It fuses the particles together mechanically to form one solid part. The unfused powder supports the part during printing and eliminates the need for dedicated support structures. The platform is then lowered one layer into the build chamber, typically between 50 and 200 microns, and the process is repeated for each layer until the parts are complete.

3) Cooling- After printing, the build cell needs to cool slightly inside the print case and then outside the printer to ensure optimal mechanical properties and prevent distortion of the parts.
In small printers about 3 hours, large ones over 6 hours.

4) After processing – the finished parts must be removed from the construction chamber, separated and cleaned of excess powder. The powder can be recycled and the printed parts can be further processed by media blasting or media casting. (Printed SLS parts have a slightly grainy surface finish, but with almost no visible layer lines. For a smoother surface finish, it is recommended to work with media spraying.

SLS printing requires a high level of precision and tight control throughout the entire printing process. The temperature of the powder together with the (incomplete) parts must be controlled within 2°C during the three stages of preheating, melting and storage before removal to minimize heat-induced distortions and stresses.

Raw materials in SLS printing:

There are a variety of SLS printing materials such as:
Nylon 12 (PA12) – the most common material in SLS printing, a durable, flexible and easy-to-process material, suitable for functional parts and prototypes.
Excellent combination of strength, rigidity and chemical resistance.
Excellent for general uses such as end products, connecting devices and industrial parts.
Usually with white powder and dyeing with fabric dyeing materials is required to paint the part from the inside.
In PA12, the flow and absorption are relatively high, in printers it is simpler sometimes to print with black in advance (so it is easier for the laser to burn the material) and no finishing work is required in painting.

Nylon 11 (PA11) – a more flexible material than PA12 and resistant to mechanical damage, especially suitable for parts that require higher resistance such as pipes and flexible bodies.
Occupies a smaller percentage than nylon 12 but is common in applications that require increased flexibility and durability.

Nylon reinforced with glass fibers or carbon fibers – a combination of nylon with reinforced materials to improve strength and rigidity. Suitable for components that require additional durability, such as industrial or engineering parts.
Used mainly in industries that require higher rigidity and durability, such as automobiles and aviation.

TPU (Thermoplastic Polyurethane) – a more flexible and elastic material than nylon, suitable for parts that require flexibility, such as gaskets, upholstery parts, certain medical components and products that require shock absorption.

Alumide (nylon with aluminum powder) – a mixture of nylon and aluminum that provides a metallic finish and enables the production of durable parts with a metallic appearance, especially suitable for applications that require high thermal and mechanical stability.

Other advanced materials – there are also more chemically or heat resistant polymers, such as PPS (Polyphenylene Sulfide), intended for specific industries such as automobiles, aviation and space, where resistance to high heat and chemicals is required.
In general, there is a problem with changing printing materials in a printer, sometimes requiring half a day or more (depending on the printer), so it is important to make sure what material you need and to check with the subcontractor that they do have the material you are requesting.

The percentage of uses in industry

Advantages over MJF

MJF (Multi Jet Fusion) printing can also be printed with Nylon 12, but the printing method is injection molding and not powder.
Advantages of SLS over MJF:
1. Lower costs in solid (non-hollow) products
2. Variety of colors – SLS is easier to dye since its natural shade is white, unlike MJF, which is gray (dyeing is done by absorbing liquid).
3. Part weight – a slight advantage for SLS assuming we are printing the exact same product.
Features that are pretty similar:
1. There are no large differences in the product’s accuracy. From the measurements of the products, the results are quite similar.
2. There are no large gaps in product strength assuming that there is not a very high percentage of recycled material used in SLS.
3. The finishing process is pretty much the same in both.

SLS printing prices for a variety of materials

Nylon 12 (PA12) – For simple functional products, the final price is in the range of 1000-1,800 NIS per kilogram .
Nylon 11 (PA11) – a more durable nylon suitable for specific uses, its price ranges from 1,200-2,200 NIS per kilogram .
Nylon reinforced with glass or carbon fibers – these products, due to their strength and durability, will range from 1,500-2,400 NIS per kilogram .
TPU (thermoplastic polyurethane) – flexible products with prices ranging from 1,500-2,400 NIS per kilogram , depending on the required flexibility and durability.
Alumide (nylon with aluminum powder) – products with a metallic or heat-resistant finish reach a higher range of 2,200-3,500 NIS per kilogram .
These prices do not include finishing.

Other factors affecting the price:

Quantity : Large orders will lower the price per kg, while individual products are more expensive due to individual production and processing costs.
Finish level : additional processing, such as polishing, painting or manual processing, can add an additional cost.
Geometric complexity : parts with complex geometries are more expensive because of the long printing time required.

The cost of a finished product in SLS printing is relatively high, but very profitable in projects that require high mechanical durability, design flexibility and quality finishing.

PA12 main features:

Ultimate Tensile Strength X (MPa): 50
Tensile Modulus X (MPa): 1850
Elongation at Break, X/Y (%): 11
Elongation at Break, Z (%): 6
Heat Deflection Temperature @ 0.45 MPa (°C): 171
Notched Izod (J/m): 32

Strength data comparison table between SLS printing materials

Printable file:

Any CAD software or 3D scan data can be used to design your model, and it will be exported in a 3D printable file format (STL, OBJ or 3MF). Each SLS printer includes software with fine-tuned print settings that help you orient and arrange models, as well as estimate print times and lay out the digital model into layers for printing. After the setup is complete, the print preparation software sends the instructions to the printer via a wireless or cable connection.

Highlights for product design in SLS printing

Wall thickness: This refers to the thickness in any direction on smooth walls or geometries. The minimum wall thickness allowed is 0.762 mm – 0.508 mm
When the thin wall is supported on both sides it can be thinner and without support a little thicker.
Gaps: This refers to the distance between two features. It is important to consider the channel spacing when designing 3D printed nylons because the sintering process can merge two features that do not relate to the channel spacing. We recommend minimum channel gap sizes of 0.762mm.
Fringe: Designs that have a feature such as a counter hole. Your dimension may drop below the minimum feature size at the far end of the hole. This may result in a truncated or rounded feature that is not generated properly. Similar to the wall thickness, we recommend making sure the measurements are at least 0.762mm – 0.508mm

After all pre-printing tests are completed, the device is ready to print. SLS 3D prints can take from several hours to several days, depending on the size and complexity of the parts, as well as the density of the parts. Thanks to the high power laser.
Depends on SLS printer size and printer cell size.

After printing is finished, the build cell needs to cool down a bit in the print case before moving on to the next step. The build cell can then be removed and a new cell inserted to run another print.

Then, the build chamber with the printer parts needs to be further cooled before post-processing to ensure the optimal mechanical properties and avoid distortion of the parts. This may take up to half the printing time.
After the build has cooled, the finished parts can be removed from the build chamber and extracted from the unbridled powder.

After the parts are extracted, media spraying is a critical step for fully dusting SLS 3D printed parts and achieving a smooth, dust-free finish. This will remove the loose powder and clean the semi-filtered surface armor from your printed parts.

In conclusion

3D printing with SLS technology (selective laser sintering) offers an advanced and efficient solution for the production of precise and durable parts while allowing the design of complex geometries without additional support structures. This technology is particularly suitable for rapid prototyping and small, customized production series, and provides parts with mechanical durability similar to that of cast parts.
The technology occupies between 10-15% of all 3D printing jobs on the market.

When designing parts for SLS printing, it is recommended to maintain a minimum wall thickness of 0.5-0.8 mm and gaps of at least 0.76 mm between adjacent features, to maintain accuracy and prevent unwanted blending between features.

SLS printing percentage deviation ranges from ±0.3% to ±0.5% depending on part size and print settings, with small parts benefiting from higher accuracy around ±0.1mm. Thanks to its strength, durability and uniform finish quality, SLS technology provides high value to the customer with High quality functional parts.
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