• Introduction

    SLS (Selective Laser Sintering) is a powdered based fusion technology which requires a laser beam to sinter polymer powder, building parts layer by layer. Powder located in the overflow bin is heated at high temperatures, where a recoating blade deposits an extremely thin layer of the powdered material (0.1 mm) onto the build platform. The building platform then scans an entire cross-section which moves the platform down one layer thickness in height. Powder that has been unsintered will stay in the same spot to support subsequent layers getting rid of the need for support structures. The recoating blade adds another layer of powder on top of the layer that has already been scanned. The laser beam then sinters the cross-section part onto the previously solidified cross-section. This operation is repeated until parts a fully completed. SLS  is necessary for users who are looking for a solution in producing functional products with complex geometries This technology has little to no restrictions compared to other 3D printing technologies.

    Through following these Selective Laser Sintering (SLS) 3D printing design guidelines your parts should come out as intended, but for additional questions and complex problems be sure to reach out to a member of our engineering team.

     

    Selective Laser Sintering PA 2210 Material   Selective Laser Sintering PA 3200 Material

  • Feature Designs

    When designing for SLS, consider the following recommendations to improve the overall quality and finish of your product.

     

    FeatureDescription
    Wall thickness 0.7 mm (PA12) – 2.0 mm (carbon filled polyamide)
    Hole Size Holes should exceed a 1.5 mm diameter
    Escape Holes Minimum of 3.5 mm diameter

     Escape holes are necessary to remove unsintered powder

    Minimum Feature Size Minimum size recommended = 0.8 mm
    Embossed details Minimum height is 1 mm
    Engraved Details Minimum depth of 1 mm
    Text Assure the following rules apply for text readability

     Minimum font height = 2 mm (font size 14) for every direction

     Sans serif font should be utilized for readability

    Connecting/Moving Parts 0.3 mm = moving parts

     0.1 mm = connections

    Supported Walls 0.7 mm
    Tolerances ± 0.3 mm or ± 0.05 mm/mm (whichever is greater)

     

  • Materials

    Materials that are offered with SLS are almost endless. A majority of them are polyamide based, which means it is synthetic thermoplastic polymers. This is also known as nylon. Below presents SLS’s most frequently used materials being printed and their benefits/properties.

    MaterialBenefits
    PA12 Good dimensional stability

     Good wear resistance

     High chemical resistance

     Mechanical properties that can be compared to injection moulded polyamide

    PEBA (TPA) Rubber-like

     Strong

     Flexible

    Alumide (Polyamide filled with aluminium) High stiffness

     Post-processing abilities

    Carbon filled polyamide High stiffness

     High strength

    Glass filled polyamide High stiffness

     Wear resistance

    PA11 High impact resistance

     Elongation at break

     Environmentally friendly

    PEEK Well mechanical properties

     High temperature resistance

     

    Selective Laser Sintering PA 3200 Material

  • Applications

    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.

     

    ApplicationDesign
    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

    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

  • SLS VS. Injection Molding

    Compared to injection molding, SLS parts are often used as prototypes to determine the following three forms of design:

    1. Function
    2. Form
    3. Fit

    Later, these designs will be manufactured using injection molding. The main differences between SLS and injection molding are as followed.

    Injection MoldingSLS
     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

     

    Selective Laser Sintering PA 2200 Material

  • Limitations

     

    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