MJF and SLS are powder-bed fusion technologies that build dense, isotropic nylon parts directly from a 3D model. Unlike FDM they have no support structures inside cavities and produce parts that, in many cases, replace injection-molded production for low to mid volumes.
How MJF and SLS actually work
Both processes spread a thin layer of polymer powder, then fuse a cross-section of the part. SLS uses a laser, MJF uses a print head dispensing fusing and detailing agents followed by heat lamps. The mechanical results are similar, with MJF generally winning on speed and surface smoothness while SLS retains advantages for some specialty materials.
| Property | MJF (PA12) | SLS (PA12) |
|---|---|---|
| Tensile strength | 48 MPa | 48 MPa |
| Elongation at break | ~20% | ~24% |
| Surface finish (as printed) | Slightly grainy, dark gray | Slightly grainy, off-white |
| Layer thickness | 80 µm | 100-120 µm |
| Typical accuracy | ±0.3 mm or ±0.2% | ±0.3 mm or ±0.2% |
Wall thickness and minimum features
Powder-bed parts can be surprisingly delicate during depowdering. Walls below 0.8 mm warp or break out of the build. For load-bearing geometry, target 1.5 mm or more. Reinforcing ribs improve stiffness without thickening walls and reducing cycle time.
- Minimum wall thickness: 0.8 mm cosmetic, 1.5 mm functional.
- Minimum unsupported pin: 1.0 mm diameter, ≤ 8 mm length.
- Minimum hole diameter: 0.5 mm; for clean threads use ≥ 1.5 mm bores and tap after print.
- Maintain ≥ 0.5 mm clearance between assembled parts to keep them from fusing in the build.
Hollows and escape holes
Hollow sections trap unfused powder. We need at least one escape hole, ideally two opposite each other, to depowder cleanly. A 4 mm diameter is the minimum; 6-8 mm is recommended for any internal volume above 50 cm³.
Hollowing thick volumes can cut part cost by 30-50% on MJF, because we charge by the powder consumed and the build height. Pair it with diamond-cell internal lattices for stiffness.
Tolerances, fits, and assemblies
Plan for ±0.3 mm or ±0.2 percent on each linear feature. For sliding fits add 0.4 mm of clearance, for press fits use a 0.1 mm interference. Mating threads should be tapped or use heat-set inserts; printed threads work for low-load applications only.
Finishing options
| Finish | Cost adder | Best for |
|---|---|---|
| Standard depowdered | Baseline | Internal parts, fixtures |
| Bead blast | +5-10% | Uniform matte cosmetic |
| Vapor smoothing (PostPro) | +15-30% | Sealed, smooth, glossy surface |
| Dye black/gray/blue | +10-15% | Consistent color, hides build lines |
| Spray paint + clear coat | +30-50% | Color critical end-use parts |
When MJF/SLS replaces injection molding
Below ~5,000 units, especially with assembly complexity or custom variants, MJF becomes more cost-effective than steel tooling. The break-even depends on part size and geometry but our quoting engine compares both options whenever the part is feasible.
- Bridge production runs ahead of tooling.
- End-of-life service parts where tooling is no longer economic.
- Customer-specific configurations and small variant families.
- Functional housings, ducts, brackets, and lightweight enclosures.
What to upload
Send STL or 3MF; STEP is also fine and we will mesh it server-side. Include a brief note on intended use (cosmetic, structural, food-contact, etc.) so the platform can recommend the appropriate finish and material option.
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