Selective Laser Sintering (SLS)
3D Printing
Laser Sintering, commonly referred to as Selective Laser Sintering (SLS), is one of the most adaptable and widely utilized methods in 3D printing. As a build method that itself, SLS allows for the creation of intricate shapes, including solid constructions, lightweight parts, and products tailored for mass customization that cannot be produced through other techniques.
Structures? Not in SLS 3D Printing!
SLS 3D printers utilize a CO2 laser alongside thermoplastic polymer powder to fabricate components. Due to the laser's significant power, it follows a "point-to-point" approach, solidifying an entire cross-sectional area of each layer. Once a layer is finished, a re-coater adds another layer of powder, and the build platform lowers by one layer's thickness.
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Technical Specification
Standard lead time
- Minimum of 4 business days, influenced by the size of parts, quantity of components and finish quality.
- For parts measuring less than 200 x 100 x 100 mm, a minimum of 2 business days is required.
Standard accuracy
- ±0.3% (with a lower limit on ±0.3 mm)
Layer thickness
- 0.12 mm
Minimum wall thickness
- 1 mm, though living hinges can be produced at 0.7 mm.
Maximum build dimensions
- There are no limits on dimensions, as components can consist of multiple sub-parts. Our largest machine accommodates a build area of 350 x 350 x 600 mm.
Surface structure
- Unfinished parts usually exhibit a grainy texture, but a wide variety of finishes is achievable. Laser-sintered components can be sandblasted, colored or impregnated, painted, and coated.
Materials
PA - 12
Nylon Powder composed of Polyamide 12. This strong and flexible plastic offers excellent mechanical properties suitable for fully functional parts.
PA-GF
Polyamide Powder filled with glass particles. Much higher thermal resistance(up to 100 °C)Polyamide. Maximum part dimension600x330x550mm.
SLS Design Guidelines
Wall Thickness
In 3D printing, wall thickness is defined as the distance between one side of your part and the directly opposite side. For the material PA 200, we suggest a minimum wall thickness of 1 mm, although living hinges can be made at just 0.3 mm. Thicker walls provide a robust and solid surface, while thinner walls result in a more flexible and expandable surface. For example, if you design a spring that requires suspension properties, thinner surface walls are ideal, making your part lightweight and flexible. Conversely, increasing the wall thickness yields a sturdier result.
Hollowing
Whenever possible, consider hollowing out your part. This practice helps prevent deformation and discoloration during the printing phase. You can hollow your part without a surface hole, keeping some unsintered powder trapped inside. Alternatively, position one or two holes strategically to allow for easy removal of the trapped powder post-printing. If your part needs to be resealed, design a lid that allows for a 0.5 mm gap between the part and the lid.
For parts with wall thickness exceeding 9 mm, our production team may hollow out the part to mitigate deformation and discoloration. For any part with a wall thickness greater than 20 mm, this process is automatically applied, and the powder will remain inside.
Warpage and Deformities
We strongly advise against designing large, flat surfaces akin to A4 dimensions, as such designs are prone to deformation—a phenomenon known as "warping." Adding support ribs beneath your flat area generally does not solve the issue and can even heighten the risk of deformation. The best approach is to steer clear of large, flat sections.
Interlocking or Moving Parts
You can print interlocking and moving components or single-build assemblies using PA 2200 (SLS). When printing parts together, maintain a minimum clearance of 0.5 to 0.6 mm. This spacing is particularly crucial for chain designs, where maximizing space is beneficial. As parts become more complex, it becomes increasingly challenging for us to clear unsintered powder from the inside once the part is removed from the printer. We recommend consulting your local Customer Support Officer before placing an order for such parts to ensure they are printable and to avoid any issues.
Assembly
For parts intended for assembly, it's critical to allow sufficient space between them. A snug fit in your CAD software may not translate to an accurate fit post-printing, as software does not account for real-world friction. Therefore, always ensure at least 0.6 mm of space between parts. For components with large surfaces or thick walls, you may need to allow even greater separation. In these instances, reach out to your local Customer Support Officer to verify printability.
To enhance the accuracy of your printed parts for assembly, design your files in alignment with the final orientation of the assembled parts.
Strength and Fragility
Several aspects can complicate accurate predictions regarding the polishing process. One factor is the geometry of your part, which may behave differently each time it undergoes tumbling. As a general guideline, maintain wall thicknesses of at least 1 mm throughout your design. We pay careful attention to part placement and orientation in our printers to minimize “weak points” that may arise from layer buildup. However, certain design features may be more susceptible to the effects of the polishing stones. Additionally, the longest dimension of your part should not exceed 200 mm to prevent it from getting stuck during smoothing, while the smallest dimension should be no less than 30 mm to avoid breakage.
Interior Polishing
The small size of polishing stones can lead to them getting stuck in narrow openings. Thus, we recommend ensuring that any openings requiring polishing have a diameter of at least 6.5 mm. This precaution helps avoid blockages inside your model. Also, be aware that the inside of your model will generally be less polished compared to the exterior. In fact, if the holes are smaller than 6.5 mm, the interior could remain unpolished because the stones won't be able to enter.
Rounded Edges
Parts with sharp edges will have those edges rounded off during the polishing process. In contrast, rounded corners and smooth transitions between surfaces will achieve a higher level of polish than their sharp-edged counterparts.
Embossed and Engraved Details
For engraved features or text, we recommend a minimum line thickness of 1 mm, a depth of 1.5 mm, and an overall height of at least 4.5 mm. Embossed text or surface features should be robust enough to withstand production and transport. We suggest a line thickness of at least 0.8 mm, an overall height of a minimum of 3 mm, and a depth of at least 0.8 mm.
File requirements
We accept a variety of file formats, including STL, 3DS, 3DM, OBJ, STP, SKP, SLDPRT, STEP, IGES, and Parasolid.
Please send your design file to sales@voxelwerks.com in one of the formats mentioned above.
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Applications of SLS 3D Printing
SLS applications allow functional prototyping or large production parts in taxing environments. Prototypes with mechanical properties similar to injection-molded parts are used, as well as lightweight designs in complex lattice structures. Certain design applications for SLS below will mark several instructions that will ensure a better quality SLS part.
Application
Design
Axles
- Nylon provides smooth low friction mechanism for low load and velocity applications
- Surface clearance of 0.3 mm is recommended for running axles
- Powder must be removed to ensure smooth running shaft
- Escape holes with the minimum size of 3.5 mm diameter must be included wherever possible
- 2 mm between the running shaft axle and clearance shaft hole is required to allow for powder removal
Integrated Hinges
- Works well with SLS nylon when designed accurately
- Pocket the shape of a trapezoid accepts a semi-spherical ball
- This allows for low friction and decent stability
- 0.2 mm of space between the sphere and pocket is suggested with 0.3 mm clearance between every other gap
- 2 mm between the running shaft axle and clearance shaft hole is required to allow for powder removal
Tanks
- SLS nylon provides chemical resistance
- Executed in custom tank design
- Anything greater than 1 mm is required for the wall thickness
Threads
- SLS produces rough surfaces when increased friction connects the threaded SLS parts together
Living Hinges
- SLS is a printing method that produces functional living hinges
- Anneal the hinges by heating it up and flexing the hinge back and forth
- Hinges should be 0.3-0.8 mm thick and minimum 5 mm in length
Limitations of SLS 3D Printing
SLS applications allow functional prototyping or large production parts in taxing environments. Prototypes with mechanical properties similar to injection-molded parts are used, as well as lightweight designs in complex lattice structures. Certain design applications for SLS below will mark several instructions that will ensure a better quality SLS part.
Product Size
- The size of a part being printed is limited by the size of the nylon containers used in SLS machines
- Average build volumes = 300 mm x 300 mm x 300 mm
- Larger machines offer build volume of 700 mm x 380 mm x 580 mm
Consistency
- Because there are so many layers within printing SLS parts, variations between products may occur within the dimensions and surface quality
- Post processing steps are done manually
- Minor variations may occur such as small colour or coating variations
Surface Finish
- Grainy finish
- Post processing recommended
Benefits of SLS 3D Printing
Laser Sintering is a great option when the geometric complexity of a part makes it difficult to produce through other processes or when the anticipated production volume doesn’t justify the time & expense of tooling.
- Consistency & Reliability - Implementation of stringent, proprietary process controls and procedures for executing builds, maintaining equipment, and handling materials.
- Production Parts - SLS is an affordable means to build durable, stable production parts in low volume. Also effective for high volumes of components when designs are too complex for traditional manufacturing to execute
- Part Consolidation - With the ability to produce complex features, undercuts, and internal features with ease, SLS can consolidate what once was a multi-part assembly into one part. SLS eliminates the need for separate fasteners, mounting components, and adhesives.
SLS vs Injection Modeling
- Function
- Form
- Fit
Injection Molding
SLS
- Injection molding must be removed from a die
- Can not produce undercuts, negative drafts or interior features
- No removal of die required
- Can easily conduct undercuts, negative drafts and interior features
- Costly
- Terminates need for costly tooling
- More affordable for a small series production
- Has the ability to produce sharp edges and exact corners
- Can only produce parts that include a radius of ±0.4 mm at all corners and edges
- Keep in mind that a radius of 0.4 mm on a design will be printed as 0.4 mm
- Stress relief is not offered
- Natural radius offers some stress relief
- Areas of concern require a larger radius than 2 mm
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How Does Laser Sintering Work?
Laser Sintering is a laser-based technology that uses solid powder materials, typically plastics. A computer-controlled laser beam selectively binds together particles in the powder bed, by raising the powder temperature above the glass transition point after which adjacent particles flow together. As the powder is self-supporting, no support structures are necessary.
