Selective Laser Sintering (SLS)
3D Printing Design Guidelines

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.

 

   

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

 

Feature	Description
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 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.

Material	Benefits
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

 

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
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

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 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

 

 

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