All About Multi Jet Fusion (MJF) 3D Printing
Learn about this 3D printing technology and its applications.
Multi Jet Fusion (MJF) 3D printing is a high-volume, high-accuracy additive manufacturing technology developed by HP Additive. HP released the MJF printer for commercial use in 2016. MJF is a relative newcomer to the additive manufacturing field when compared to older technologies like SLA (Stereolithography), FDM (Fused Deposition Modeling), and SLS (Selective Laser Sintering). Multi Jet Fusion works by applying a fusing and detailing agent to a thin layer of powder in the shape of the part's cross-section at a specific layer height. A heat source then fuses the powder into the final part. The print bed moves down by the thickness of one layer, typically 80 microns, and the process is repeated.
MJF is used both for functional prototypes and for end-use parts in the aerospace, medical, and consumer products industries. MJF can be used to print watertight electronics enclosures, under-the-hood hardware for cars, and custom medical equipment like prosthetics and dental models.
This article explains how MJF works, the materials used, the advantages, and the minimum feature sizes possible.
How It Works
MJF 3D printing works by applying a thin layer of the material onto the print bed using a recoater. The powder is then heated to just beneath its sintering temperature. Next, a fusing agent is applied to the powder in the shape of the part cross-section. This is applied using multiple nozzles which jet the fusing and detailing agent onto the powder. The fusing agent helps absorb heat during a later process step. A detailing agent is applied to the edges of the part to help create crisper and sharper edges. The detailing agent prevents the molten plastic from bleeding past the part edges. An infrared heat source then passes over the material and sinters the plastic particles together wherever the fusing agent is applied.
Available Materials For MJF
MJF 3D printed parts are most often made from PA12, a common grade of nylon. MJF printers can also print elastomeric parts. The full range of available materials is listed below:
- PA11(Nylon): PA11 is more flexible and tougher than PA12, and as such is better for end-use parts.
- PA12 (Nylon): PA12 has good crack resistance and has the lowest moisture absorption of all the polyamides. Glass-filled variants are also available. PA12 is generally well suited to functional prototypes.
- PP (Polypropylene): Ideal for functional prototypes that can mimic the performance of injection-molded polypropylene.
- TPU01 (Thermoplastic Polyurethane): This material offers a good balance between flexibility and shock absorption, and can be used to create high-resolution features.
- TPU M95A (Thermoplastic Polyurethane): This elastomeric material has excellent abrasion resistance and high elongation at its break strength. Ideal for end-use parts like seals and shoe insoles as well as functional prototypes.
- TPA (Thermoplastic Polyamide): This elastomeric material is a lightweight, highly flexible elastomer. TPA has high elongation in low-temperature environments.
Common Applications for MJF 3D Printing
MJF printing can be used for functional prototypes as well as end-use parts. Some notable applications are listed below:
- Aircraft rudder trim systems
- Custom prosthetics
- Dental implant molds
- Robot end-arm tooling
- Drone frames
- Automotive door-support hinges
- Flexible lattice structures
Benefits of Multi Jet Fusion 3D Printing
Use Multi Jet Fusion 3D printing when you need a technology that is fast and can produce highly detailed, dimensionally accurate features.
Why MJF Is Excellent for the Production of End-Use Parts
MJF 3D printing is excellent for the production of end-use parts since it is a high-volume additive manufacturing technology that was developed especially for this purpose. MJF makes use of nylon and polypropylene powders as raw materials. Both are engineered thermoplastics used in a number of industrial applications. MJF parts also have isotropic properties which is not always the case with other printing technologies such as FDM (Fused Deposition Modeling) and SLS (Selective Laser Sintering). MJF is able to produce highly detailed small features. The use of a detailing agent also ensures a smooth, albeit matte, outer surface finish.
MJF's Dimensional Accuracy
MJF 3D printing can produce parts that only deviate by ± 0.15 % from nominal dimensions with a lower limit of 0.3 mm, after which, the dimensional accuracy is not defined nor guaranteed by the machine manufacturers.
MJF's Maximum Construction Size
The largest of the HP MJF 3D printers is the HP Jet Fusion 5200 series. This machine has a usable build volume of 380 x 284 x 380 mm. Unlike many other 3D printing technologies, MJF can stack parts in the entire printer volume, making maximum use of the available space. This is because MJF parts do not need complex support structures. The powder itself supports the part. In the case of large hollow parts, it may be beneficial to include permanent internal supports for mechanical strength.
MJF and Small Parts
MJF 3D printers can print parts with features as small as 0.1 mm in width. Table 1 below lists some additional minimum feature sizes possible with MJF printing:
| Property | Minimum Size |
|---|---|
Property Layer height | Minimum Size 80 μm |
Property Minimum slit between walls | Minimum Size 0.5 mm |
Property Minimum hole diameter (part thickness of 1mm) | Minimum Size 0.5 mm |
Property Minimum shaft diameter (part height of 10 mm) | Minimum Size 0.5 mm |
Property Minimum feature size | Minimum Size 0.1 mm |
Property Minimum font size for debossed or embossed text | Minimum Size 6 pt |
Table Credit: HP MJF Handbook
Advantages of MJF
MJF is a highly capable 3D printing technology. Some of its key advantages are listed below:
- MJF parts are highly isotropic, with 98% isotropy achievable.
- MJF powder is reusable. Up to 80% of the unused material present in the build chamber during printing can be reused. The remaining 20% may consist of powder that has been oxidized and degraded due to the heat in the printing zone. The detailing agent evaporates during the printing process.
- MJF printers have removable build volumes. This means that the completed parts can be removed from the printer to allow for cooling while another build volume can be installed to maintain production continuity and to enable high volume production.
- No support structures are needed during printing, as the unsintered powder behaves as the part’s support structure.
MJF 3D Printing Water Resistance
Multi-jet fusion parts can be water resistant if designed correctly. HP has tested the IP (Ingress Protection) rating of their commonly used raw materials and has achieved IP66 and IP67 waterproof ratings with them.
The first digit in the IP rating number indicates that MJF parts demonstrate complete protection against the ingress of dust. The second digit, a 6 in this case, means that MJF parts resist water intrusion, while a value of 7 means that parts do not absorb water even when immersed.
MJF vs. SLS 3D Printing
Both MJF and SLS are powder bed fusion printing methods. However, in the MJF process, a print head applies a fusing and detailing agent to the base powder; then the powder is sintered with an infrared energy source wherever the fusing agent was applied. SLS, on the other hand, uses a laser to fuse the powder. The SLS printing process requires support materials to stabilize the part during printing, while MJF does not. For more information, see our guide on SLS vs. MJF 3D Printing.
Summary
To learn more about multi jet fusion and how it can benefit your unique application, contact a Xometry representative.
Xometry provides a wide range of manufacturing capabilities, including 3D printing and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.
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