Design Around Powder, Heat, and Cleaning
SLS design rules are different from FDM and resin rules because the part is supported by unfused powder. That removes many support concerns, but it adds new priorities: powder escape, thermal stability, minimum feature size, packing, surface texture, and post-processing.
Design Around Powder, Heat, and Cleaning
SLS design rules are different from FDM and resin rules because the part is supported by unfused powder. That removes many support concerns, but it adds new priorities: powder escape, thermal stability, minimum feature size, packing, surface texture, and post-processing.
Good SLS design begins with the finished function. A clip, duct, housing, hinge, fixture, and wearable part need different wall thickness, radii, clearances, and cleaning access. The best rule is the one tied to the part’s use.
Wall Thickness
Walls need enough thickness to survive printing, depowdering, finishing, and use. Very thin walls may flex, distort, or break during cleaning. Very thick walls can hold heat and raise cost. Many service bureaus publish process-specific minimums, so the final number must match the supplier.
For functional nylon parts, even wall sections and rounded transitions are safer than abrupt thick-to-thin changes. If a feature is loaded, make it thicker at the root and use fillets instead of sharp internal corners.
Clearances and Moving Parts
SLS can print interlocking and moving assemblies, but clearance still matters. Powder must be able to leave the gap, and surfaces need room after blasting, dyeing, or tumbling. A CAD-perfect joint often becomes a fused or gritty joint in the real part.
Use larger clearances for moving parts than for fixed alignment features, and test joints before committing to a production batch. For high-wear joints, metal pins, bushings, or inserts may be better than printed-on-printed contact.
Hollowing and Powder Escape
Hollowing can reduce cost and weight, but only when powder can be removed. Escape holes must be large enough, reachable, and placed where they do not weaken the part. Long internal passages may need several openings or a split design.
If the part cannot be cleaned, hollowing becomes a problem rather than a savings. For sealed functional parts, a solid or partly solid design may be more predictable even if it uses more material.
Text, Details, and Surface Finish
Raised text usually survives better than engraved micro-detail, but both need enough size to remain visible after cleaning and finishing. SLS surfaces have a fine powder texture, so tiny cosmetic details can blur.
Place critical labels where they are easy to clean and inspect. If branding or serial numbers must be sharp, consider larger features, post-machining, inserts, labels, or another marking method.
Batching and Orientation
SLS has fewer support constraints, but orientation still affects heat, surface consistency, accuracy, and packing. Parts packed together must leave enough spacing for powder flow and thermal behavior. A dense build is useful only if the parts remain clean and stable.
For repeated parts, keep orientation consistent across batches so measurements and finish are comparable. Changing orientation can change the practical tolerance of holes, walls, and surfaces.
Engineer-Level Checklist
Before release, confirm wall thickness, fillets, clearance, powder escape, finish allowance, material choice, and inspection points. For production, define what dimensions are critical and which surfaces can accept normal SLS texture.
The strongest SLS designs are simple where they need to be controlled and complex where the process provides real value. Use freedom for ducts, lattices, part consolidation, and custom geometry, not for avoidable fragility.
FAQ
Does SLS require support design?
No conventional supports are usually needed, but the design still needs powder escape, wall thickness control, and thermal stability.
Can SLS print moving assemblies?
Yes, but gaps must be large enough for powder removal and post-processing effects.
What is the most overlooked SLS design rule?
Powder removal is often overlooked. Hollow parts and internal channels need realistic cleaning paths.
