HP’s Multi Jet Fusion (MJF) technology takes a unique approach to building parts from thermoplastic nylon powder, which results in fast build times, improved precision, and consistent mechanical properties throughout the part.
If you’re thinking this process sounds awfully similar to selective laser sintering (SLS), you’re not wrong. But there are some differences between the technologies that should be understood before making your manufacturing selection.
How MJF and SLS Build Parts
Multi Jet Fusion uses an inkjet-style array to selectively apply fusing and detailing agents across a bed of nylon powder. Heating elements fuse the powder into a solid. After a layer is built, a fresh layer of powder is distributed on top of the previous layer and the next phase continues until the part is complete.
The processes first material was an engineering-grade nylon powder, PA 12. Parts produced are durable and suitable for functional testing and end use. Then there was the option of PA 12 40% glass-filled black powder to further strengthen your parts. Now the materials have expanded further to offer materials such as PA11 and TPU's. MJF's accelerated build speed ultimately leads to reduced manufacturing costs.
While both MJF and SLS use powdered material as their starting points, the big difference is how the material is fused to form layers. While MJF uses a fusing agent. SLS uses a laser to melt the material before moving to the next layer, and it also offers a few other material choices. Both allow you to your nylon parts to give an improved, less-rough, finish.
A Side-by-Side Comparison
Although MJF and SLS are comparable in many ways, there are some important differences. Your part requirements such as feature resolution, surface finish, materials, mechanical properties, and colour will ultimately determine the best process for your application.
MJF vs. SLS By the Numbers
| Max. Part Size | Min. Feature Size | Tolerances | Materials Available | Layer Thickness | |
| MJF | 284mm x 380mm x 380mm | 0.5mm | For well-designed parts, tolerances of ±0.25mm (Ultrasint™ TPU-01: ±0.30mm) plus ±0.002mm/mm can typically be achieved. Note that tolerances may change depending on part geometry. | PA 11, PA 12, PA 12 GB, UltrasintTM TPU-01 | 0.08mm |
| SLS | Sizes vary depending on material, view our 3DP Maxmimum Extents for further information. | 0.75mm* / 0.80mm** / 1.0mm*** | Typically, expected tolerances on well-designed parts are +/-0.2mm, plus +0.002mm/mm **** | PA 12, PA 12 CF, PA 12 F, PA 12 GF, PAx, TPU-88A | 0.1 mm |
For PAx Natural (both smooth and vapour smooth), tolerances of ± 0.3mm plus ±0.002mm/mm can be expected (for parts bigger than 200mm in this material, tolerances cannot be guaranteed)
For PA 12 Flex Pure Black, tolerance of ± 0,35mm plus ± 0,002mm/mm can be expected (or else, for bigger parts, ± 0,2% of nominal dimension)
Feature Resolution
Multi Jet Fusion parts will have a finer feature resolution 0.5mm compared to 0.75mm for SLS. Although, it should be noted that SLS has better small feature accuracy of ±0.025mm over ±0.10 for MJF. If a smooth surface finish is a requirement, MJF will be a better choice than SLS. Secondary operations are often recommended for both processes if surface finishes are crucial to your application.
Materials and Colours
Not long ago SLS provided a broader range of materials, however, now the playing field has evened out. Both SLS and MJF provide you with multiple nylon options as well as TPU for elastomeric prototyping to get flexible, lighter-weight parts for demanding environments.
Comparing Common Nylon Materials
| Material Property | SLS PA 12 | MJF PA 12 | MJF PA 11 |
| Tensile Strength | 50 +/- 4 MPa | 49 +/- 4 MPa | 52 MPa +/- 4 MPa |
| E-Module | 2000 +/- 200 MPa | 1900 +/- 200 MPa | 1800 +/- 200 MPa |
| Elongation at Break | 11% +/- 4% | 12% +/- 4% | 30% +/- 5% |
Mechanical Properties
Both processes build parts with highly consistent mechanical properties along all directions of the part’s geometry (aka isotropism). The difference in the fusing process does mean that SLS parts tend to be stronger and more durable than MJF parts, but they also have a rougher surface finish than MJF parts.
Part Size
Another important consideration is part size. SLS provides you a larger build envelope for PA parts, although sizes vary between materials, see our max extents page for further detail. MJF’s build envelope is slightly smaller at 284mm x 380mm x 380mm.
Part Quantities
As mentioned earlier, MJF offers accelerated build speed, which means it can support larger quantities in a shorter time frame. However, with either process, you can get parts in as fast as one day.
More info is a click away. Our design guidelines pages for Multi Jet Fusion and SLS have a lot of helpful information, and so do our applications engineers! You can reach them at [email protected].
