- How does SLS 3D printing work?
- Can SLS 3D printing be used for rapid prototyping?
- Can SLS 3D printing be used for low-volume production runs?
- How does an SLS 3D printer work?
- What are the features of SLS 3D printing?
- What materials are utilized in SLS printing?
- What options exist for SLS post-processing?
- What are the advantages of SLS 3D printing
- What are the disadvantages of SLA 3D printing?
- SLS best practices
Selective Laser Sintering (SLS) is an additive manufacturing process that falls under the powder bed fusion category. In SLS 3D printing, a laser selectively sinters polymer powder particles, melding them together to construct a part, layer by layer. The materials utilized in SLS comprise thermoplastic polymers that come in a granular form.
Generally, SLS presents a flexible alternative, especially if you aim to delay injection molding and its costly initial expenses. It is more cost-effective to test your product or technology before making expensive molds and tools when producing high-quality components in moderate amounts (less than 1,000 units).
Our SLS 3D printing service is ideal for prototyping with functional polymer components, as well as small to medium production runs or end-use parts. To learn more about maximizing SLS performance, please contact firstname.lastname@example.org to speak with an engineer.
How does SLS 3D printing work? #
SLS (Selective Laser Sintering) 3D printing is an additive manufacturing process that utilizes a laser to sinter small particles of polymer powder. Here's a step-by-step breakdown of how SLS 3D printing works:
- Preparing the Machine: The powder bin and the build area of the 3D printer are heated to a temperature just below the melting point of the polymer powder. This ensures that the particles are in a semi-molten state.
- Spreading the Powder: A re-coating blade or roller spreads a thin layer of polymer powder evenly over the build platform.
- Laser Sintering: A high-powered CO2 laser scans the cross-section of the component or layer being printed. The laser selectively fuses the polymer particles together, binding them to form a solid shape based on the 3D model.
- Layer-by-Layer Building: After each layer is sintered, the build platform moves downward by a distance equal to the height of one layer. The re-coating blade then spreads a fresh layer of powder over the previously sintered layer. The process repeats until the entire part is built layer by layer.
- Cooling and Unpacking: Once the printing is complete, the parts remain fully encapsulated within the unsintered powder in the build chamber. The powder bin and the parts must be allowed to cool down before unpacking. This cooling process can take several hours, typically up to 12 hours.
- Post-Processing: After cooling, the parts are carefully removed from the build chamber. They are often covered with excess, unsintered powder, which needs to be removed. This can be done through methods like compressed air blowing or using a blasting media. Once cleaned, the parts are ready for use or can undergo additional post-processing steps like sanding, polishing, or dying to achieve the desired finish.
SLS 3D printing is known for its ability to produce functional, complex parts with excellent mechanical properties. The process offers design freedom, as the unsintered powder acts as support for overhangs and intricate geometries. It is widely used in various industries, including automotive, aerospace, medical, and manufacturing.
Can SLS 3D printing be used for rapid prototyping? #
SLS is an excellent solution for rapidly prototyping functional polymers because it allows for high design flexibility and accuracy. Unlike FDM or SLA 3D printing techniques, it consistently produces parts with mechanical properties that are predictably high. Therefore, SLS can produce models that are almost identical in quality to end-use parts, making it a dependable technology for concept to trial models.
Can SLS 3D printing be used for low-volume production runs? #
SLS 3D printing is highly versatile and can be used as a substitute for injection molding in low-volume production runs. It allows for the production of parts with intricate shapes and geometries, as well as a range of finishes and lead times.
How does an SLS 3D printer work? #
For SLS 3D printing, most process parameters are preset by the manufacturer, with a default layer height of 100-120 microns.
A significant benefit of SLS is that no support structures are required as the unsintered powder offers sufficient support. This allows for the creation of free-form geometries that would be impossible to manufacture with other methods.
Utilizing the entire build volume is crucial when printing with SLS, particularly for small-batch productions. Laser scanning is swift, so the re-coating step actually determines the overall processing time. Irrespective of the number of parts, the machine will have to cycle through the same amount of layers. Bin packing may impact lead times for small orders because operators might delay beginning a print task until a bin is full.
The bond strength between layers in SLS 3D printing is high, resulting in parts with almost isotropic mechanical properties.
The mechanical properties of SLS specimens printed with standard polyamide powder (PA 12 or Nylon 12), the most commonly used material in SLS, are presented in the table below and compared to the properties of bulk nylon.
|X-Y direction||Z direction||Bulk PA12|
|Tensile Strength||48 MPa||42 MPa||35–55 MPa|
|Tensile Modulus||1650 MPa||1650 MPa||1270–2600 MPa|
|Elongation at break||18%||4%||120–300%|
SLS components exhibit exceptional tensile strength and modulus similar to that of the bulk material, but are more brittle, resulting in significantly reduced elongation at break. However, they are more brittle due to the internal porosity of the final product, resulting in a lower elongation at break.
Shrinkage & Warping
SLS parts can shrink and warp. As the newly sintered layer cools, its dimensions decrease, and internal stresses build up, causing the underlying layer to pull upwards.
It's worth noting that SLS typically has 3 to 3.5% shrinkage, but machine operators consider this during the build preparation phase and adjust the design's size accordingly.
Large, flat surfaces are more susceptible to warping. The problem can be somewhat reduced by orienting the part vertically on the build platform. However, the best practice is to minimize the thickness of the flat areas and introduce cutouts to the design to decrease the part's volume. This approach will also lower the part's overall cost since less material will be used.
Oversintering happens when unsintered powder around a feature fuses due to radiant heat, resulting in a loss of detail in small features like slots and holes. As a general rule, you can print slots wider than 0.8mm and holes with diameters larger than 2mm in SLS without worrying about oversintering. For more DFM tips, check out our article on how to design parts for SLS 3D printing.
Since SLS requires no support material, parts with hollow sections can be easily and accurately printed.
This reduces the weight and cost of a part due to the use of less material. To remove the unsintered powder from the inner sections of the component, escape holes with a minimum diameter of 5mm should be added to the design. We suggest at least two escape holes be included.
If a high level of rigidity is required, parts should be printed solid. Alternatively, a hollow design can be made without escape holes. This will trap any tightly packed powder within the part, increasing its mass and providing additional support against mechanical loads without affecting the build time.
An internal honeycomb lattice structure may be incorporated into the hollowed interior, similar to the infill patterns utilized in FDM, to enhance component stiffness. This method of hollowing a part may also decrease warping.
What are the features of SLS 3D printing? #
The vital features of SLA are outlined in the table provided below.
|Characteristics||Selective Laser Sintering (SLS)|
|Materials||Thermoplastics (usually nylon)|
|Dimensional accuracy||± 0.3% (lower limit of ± 0.3 mm)|
|Typical build size||300 x 300 x 300mm (up to 750 x 550 x 550mm)|
|Common layer thickness||100–120 µm|
What materials are utilized in SLS printing? #
The most commonly utilized SLS material is Polyamide 12 (PA 12), also known as Nylon 12, with a price of around $50-$60 per kilogram of PA 12 powder. Though not as widely used, other engineering plastics such as PA 11 and PEEK are also available.
Polyamide powder can also be infused with various additives to enhance the produced SLS part's mechanical and thermal behavior. These additives include carbon fibers, glass fibers, or aluminum. However, materials filled with additives are usually more brittle and can behave highly anisotropically.
|Polyamide 12 (PA 12)||+ Good mechanical properties|
+ Good chemical resistance
- Matte, rough surface
|Polyamide 11 (PA 11)||+ Fully isotropic behavior|
+ High elasticity
|Aluminium-filled nylon (Alumide)||+ Metallic appearance|
+ High stiffness
|Glass-filled nylon (PA-GF)||+ High stiffness|
+ High wear & temperature resistance
- Anisotropic behavior
|Carbon-fiber filled nylon (PA-FR)||+ Excellent stiffness|
+ High weight-strength ratio
- Highly anisotropic
What options exist for SLS post-processing? #
SLS (Selective Laser Sintering) 3D printing produces parts that typically require post-processing to achieve the desired final properties and surface finish. Here are some common options for SLS post-processing:
- Powder Removal: After the SLS printing process, the parts are often covered in unsintered powder. The excess powder can be removed manually by brushing or using compressed air. Care should be taken to ensure all residual powder is removed from intricate geometries.
- Thermal Debinding: In some cases, SLS parts may require thermal debinding, especially when using metal or ceramic powders. This process involves heating the parts in a controlled environment to remove any binder material present in the printed part.
- Sintering: Sintering is a critical step in SLS post-processing for achieving the final material properties. It involves subjecting the printed parts to elevated temperatures to fully fuse the particles together, increasing their density and strength. The sintering process varies depending on the material used, and it can be done in specialized furnaces or ovens under controlled conditions.
- Support Removal: SLS parts often have built-in support structures that need to be removed after printing and sintering. Support removal can be done manually by breaking or cutting away the supports, or by using solvents or other techniques to dissolve the supports selectively.
- Surface Finishing: SLS parts may have a rough or grainy surface finish after printing. Various techniques can be employed to improve the surface quality, such as sanding, polishing, or media blasting. Additionally, chemical treatments, such as dyeing or coating, can be applied to achieve specific aesthetic or functional requirements.
- Post-Machining: For achieving precise dimensions or intricate features, post-machining processes like CNC milling or turning can be used on SLS parts. This allows for further refinement or modification of the printed parts.
Each post-processing step may vary depending on the specific material used and the desired final properties of the SLS parts. It's important to consider the requirements of the application and consult with experts or service providers to determine the most suitable post-processing methods for your SLS-printed parts.
What are the advantages of SLS 3D printing #
SLS (Selective Laser Sintering) 3D printing offers several advantages that make it a popular choice for various applications:
- Material Versatility: SLS can work with a wide range of materials, including various thermoplastics, metals, and ceramics. This versatility allows for the production of functional parts with different mechanical, thermal, and chemical properties. SLS is particularly known for its ability to handle high-performance materials such as nylon, glass-filled nylon, and flexible elastomers.
- Design Freedom: SLS enables the creation of highly complex geometries and intricate designs that may be difficult or impossible to achieve with traditional manufacturing methods. The unsintered powder acts as self-supporting during the printing process, allowing for the production of overhangs, undercuts, and internal cavities without the need for additional support structures.
- No Need for Tooling: SLS 3D printing is an additive manufacturing process, which means it eliminates the need for expensive and time-consuming tooling. This significantly reduces the production lead time and cost, making it suitable for rapid prototyping and low-volume production.
- Strong and Durable Parts: SLS prints produce parts with excellent mechanical properties, including high strength and durability. The sintering process fuses the powdered material particles together, resulting in solid, dense, and robust parts that can withstand demanding applications.
- Batch Production and Part Consolidation: SLS allows for the simultaneous printing of multiple parts within the build chamber. This makes it suitable for batch production, reducing production time and increasing efficiency. Additionally, SLS can enable part consolidation, where multiple components can be combined into a single printed part, reducing assembly requirements and improving overall structural integrity.
- Functional Prototyping and End-Use Parts: The strength, durability, and material options available in SLS make it well-suited for functional prototyping and the production of end-use parts. SLS prints can withstand real-world testing and perform in functional applications, making it a valuable tool for product development and manufacturing.
Overall, the advantages of SLS 3D printing, including material versatility, design freedom, and strong parts, make it a versatile and reliable manufacturing solution for a wide range of industries and applications.
What are the disadvantages of SLA 3D printing? #
SLA (Stereolithography) 3D printing has several disadvantages that are important to consider:
- Limited Material Selection: SLA 3D printing is primarily limited to photopolymer resins. While these resins offer a range of properties, the material selection is not as extensive as other 3D printing technologies like FDM or SLS. This can restrict the suitability of SLA for certain applications that require specific material properties.
- Post-Processing Requirements: SLA prints usually require post-processing to remove excess resin and support structures. This can involve time-consuming and manual steps such as rinsing, cleaning, and potentially curing the prints under UV light. Post-processing can add to the overall production time and labor costs.
- Fragility of Prints: SLA prints are generally more brittle compared to parts produced using other 3D printing technologies like FDM or SLS. The printed parts can be more prone to breaking or cracking under stress or impact.
- Limited Size and Build Volume: SLA printers typically have smaller build volumes compared to other 3D printing technologies. This limits the size of parts that can be produced in a single print. Additionally, scaling up the size of SLA prints can be challenging and may require additional considerations to ensure proper curing and dimensional accuracy.
- UV Sensitivity and Color Fading: SLA prints are often sensitive to prolonged exposure to UV light. Over time, the prints may experience color fading or discoloration if exposed to direct sunlight or certain environmental conditions. This can impact the aesthetics and longevity of the printed parts.
- Higher Cost: SLA 3D printers and the associated resins tend to be more expensive compared to other 3D printing technologies. The higher cost of equipment, materials, and post-processing requirements can make SLA less cost-effective for certain applications or when producing large quantities of parts.
It's important to weigh these disadvantages against the specific requirements of your project to determine if SLA 3D printing is the most suitable choice for your needs.
SLS best practices #
When working with SLS (Selective Laser Sintering) 3D printing, there are several best practices that can help ensure successful and high-quality prints. Here are some key guidelines to consider:
- Material Selection: Choose the appropriate SLS material for your specific application and requirements. Different materials have varying properties, such as strength, flexibility, and heat resistance. Consider factors like mechanical performance, compatibility with post-processing steps, and desired aesthetics.
- Part Orientation: Optimize the orientation of your parts within the build chamber. Consider factors like the geometry, support requirements, and heat distribution. Orienting the parts properly can minimize warping, improve surface finish, and reduce the need for support structures.
- Wall Thickness: Design your parts with appropriate wall thickness to ensure structural integrity. Thin walls may be prone to breakage, while overly thick walls can lead to excessive heat retention and increase print time. It's important to find the right balance based on your material and application.
- Support Structures: Carefully analyze the need for support structures in your design. While SLS allows for self-supporting geometries, certain features may still require supports. Minimize support usage to reduce post-processing efforts and optimize part quality. Consider incorporating self-supporting design strategies, such as gradual overhangs or adding structural features to support critical areas.
- Powder Handling: Follow proper procedures for handling and storing the powdered material. Ensure cleanliness and avoid contamination, as foreign particles can affect print quality. Proper powder recycling and sieving can help maintain powder quality and reduce material waste.
- Cooling and Unpacking: Allow sufficient time for the printed parts and the powder bed to cool down before unpacking. Premature unpacking can cause distortion or damage to the parts. Follow manufacturer guidelines for cooling times to ensure optimal results.
- Post-processing Considerations: Understand the specific post-processing requirements for your chosen material. This can include steps like thermal debinding, sintering, support removal, and surface finishing. Follow recommended guidelines and use appropriate equipment and techniques to achieve the desired final properties and surface quality.
- Iterative Design and Testing: Utilize the advantages of SLS for rapid prototyping and design iteration. Test and evaluate the performance of your printed parts to identify potential improvements and optimize your design for functionality and efficiency.
- Collaboration and Expertise: Engage with experienced SLS service providers or consult with experts in the field. They can provide valuable insights, troubleshooting assistance, and guidance to ensure the best possible results with SLS printing.
By following these best practices, you can enhance the quality, reliability, and efficiency of your SLS 3D printing process and achieve the desired outcomes for your projects.
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