Key Takeaways
- MJF and SLS both produce strong nylon parts without supports.
- MJF offers fine detail and consistent properties; SLS is widely available.
- Both excel at functional, complex geometry.
- Choose by finish, throughput, and material options.
HP Multi Jet Fusion (MJF) and traditional laser-based SLS are the two dominant powder-bed fusion processes for PA12 nylon. Both produce support-free, isotropic, production-grade parts. Both use PA12 powder beds. But they differ fundamentally in how the powder is fused — and those differences translate into real engineering and business tradeoffs. Understanding them helps Indian engineers and procurement teams specify the right process for each project.
How the Processes Differ
SLS uses a CO₂ or fibre laser that traces the cross-section of each layer, selectively sintering powder grains point by point. Build speed is limited by laser scan speed. Surface roughness is Ra 8–12 µm as-printed. Part packing in the build chamber is typically 10–20% density.
MJF uses an inkjet array to selectively deposit a fusing agent (a dark ink that absorbs IR radiation) and a detailing agent (a bright ink that reflects IR, creating sharp boundaries) across the entire layer at once, then exposes the layer to a uniform IR lamp. The entire layer fuses simultaneously rather than point-by-point. Build speed is 3–4× faster than SLS for equivalent part volume. Surface roughness is Ra 4–8 µm as-printed — noticeably smoother.
Mechanical Properties Comparison
| Property | SLS PA12 | MJF PA12 |
|---|---|---|
| Tensile strength (XY) | 48–52 MPa | 48–50 MPa |
| Tensile strength (Z) | 42–48 MPa | 46–50 MPa |
| Elongation at break | 10–20% | 15–25% |
| Heat deflection (0.45 MPa) | 175°C | 175°C |
| Isotropy ratio (Z/XY) | 88–93% | 96–99% |
| Surface roughness (as-printed) | Ra 8–12 µm | Ra 4–8 µm |
MJF achieves slightly better isotropy (the Z-direction properties more closely match XY), which matters for fatigue applications where load direction is variable. Both processes meet the PA12 specification for REACH and RoHS.
Colour and Appearance
SLS PA12 parts come off the machine as natural off-white/beige. They can be dyed any colour. MJF PA12 parts come off the machine as grey (from the carbon-based fusing agent that remains in the material). MJF parts can be dyed but the underlying grey base shifts colours — achieving true white or light colours is not possible without painting. For black or dark-coloured parts, MJF has an advantage as the base colour is already grey and black dye penetrates uniformly.
If colour is important to your application, specify SLS for light or custom colours, MJF for black/dark or where colour is not critical.
Cost and Lead Time
MJF's higher throughput generally translates to lower cost for high-volume or time-sensitive production runs. For small batches (1–10 parts), the economics are similar. MJF machines cost significantly more to purchase, so service bureaus amortise this into pricing — MJF parts can be more expensive per gram at low volumes, cheaper at high volumes.
Layer X currently runs SLS (EOS and third-party systems). For customers who specifically need MJF output characteristics (smoother surface, faster lead time for large batches), we can advise on process selection and partner network access.
When to Choose Each
| Requirement | Choose SLS | Choose MJF |
|---|---|---|
| Light or custom colour parts | ✓ | |
| Maximum isotropy (fatigue parts) | ✓ | |
| Smoother as-printed surface | ✓ | |
| Established certification history | ✓ | |
| High volume, fast turnaround | ✓ | |
| Smaller batch, lower MOQ | ✓ |
Contact Layer X to discuss PA12 nylon process selection for your next production run. We can provide samples from both SLS and MJF processes for comparison testing before you commit to a production order.