Multi Jet Fusion (MJF) for Cost-effective small series and prototypes.
Multi Jet Fusion (MJF) is one of the more recent additive manufacturing (AM) technologies on the market, and it has a lot of potentials. Hewlett-Packard (HP) developed MJF 3D printing in 2016. It is a type of Binder Jetting 3D printing technology, and HP claims it is faster, cheaper, and produces more functional parts than rival technologies.
Interestingly, over 140 MJF-printed components are present in each Multi Jet Fusion 3D printer.
Similar to SLS (Selective Laser Sintering), MJF 3D printing is a Powder Bed Fusion (PBF) technology that uses a heat source to fuse particles together within a build chamber filled with thermoplastic powder– often nylon or TPU. Its process differs from SLS, however, because Multi Jet Fusion does not use a laser. Rather, it employs an infrared energy source combined with a fusing agent to produce each layer of the part. Its mechanical properties and surface finishes are comparable to SLS, with layer heights of around 80µm, and MJF is slightly faster. MJF 3D printing works as follows: beginning with a computer automated design (CAD) model using HP’s proprietary software, the model is sent to the printer. The machine operator must manually load powder into the chamber.
A powder recoater first spreads a thin layer of powder onto the build plate, and the printer’s ink heads can then start printing the first layer. They do so by selectively jetting a fusing agent (in simple words, a sort of glue) onto the powder, drawing the parts’ layers as they pass. A detailing agent is also jetted around the edges of the objects to enhance their resolution. The fusing and detailing agents are sensitive to heat, and this is how the magic happens: once the print heads deposit the agents, a heat lamp solidifies and consolidates the areas where they are present. Then, the build plate descends slightly, and the powder recoater spreads another thin layer of powder onto the previous layer. The process repeats until all layers are complete.
Following printing, the machine operator must take the parts to a post-processing station for semi-manual cleaning. It is possible to recycle the unused powder for subsequent builds. After the depowdering step, parts undergo a bead blasting process. A high-pressure stream blasts fine glass beads onto the parts to improve surface quality and get rid of any remaining powder.
MJF 3D printed parts are high in resolution and have consistent isotropic mechanical properties, making them suitable for functional, end-use applications. This technology also offers fast turnaround times. In quality and functionality, Multi Jet Fusion is in many ways superior to Fused Deposition Modeling (FDM) and Stereolithography (SLA). Its main competition is SLS. As with SLS and other PBF technologies, MJF parts can be printed without support structures. The unfused powder acts as support itself, enabling complex geometries. Multi Jet Fusion printers are mostly priced for industrial or print-on-demand use, with most models costing in the mid-six figures. HP has, however, recently released several more affordable printers priced at under $100,000.
While MJF printers are generally higher in price than SLS, they may be more cost-effective in other ways. For one thing, infrared light is a more efficient energy source than lasers. Another benefit is slightly better excess powder recycling rates. Excess powder in MJF prints can be recycled in subsequent prints at a rate of around 80%. In SLS, it is typically only possible to reuse about 50%-70% of the material. A further potential advantage of MJF 3D printing over its rivals is speed. According to a white paper by HP, internal testing and simulation matched MJF machines with comparable FDM and SLS systems. Among the findings were that HP’s machines are up to ten times faster than their competitors – although this has not been verified independently.
While HP does offer a few (and expensive) full-color MJF printers, most of their printers produce parts of a dull gray color, characteristic of HP PA12. Hence, MJF may not be suitable for applications requiring parts with bright colors right from the start. Another drawback is the extensive post-processing needed to remove excess powder from printed parts. Not only is this process time-consuming, but the bead blasting process can result in damage to fine details on MJF parts.
Multi Jet Fusion printers primarily use HP PA12 (nylon). Nylon is an engineering-grade material with balanced mechanical properties and fine surface finishes. This plastic also boasts good chemical resistance and can be water-dyed. It is possible to print watertight MJF parts with HP PA12, and the material has a base tolerance of +/- 0.3 mm.
Besides PA12, there are a couple of other options, including PA11 (better for ductile parts) and a polypropylene material (HP High Reusability PP) created by the German chemical company BASF. HP has also announced an Open Platform project in which the company seeks collaboration from partners to develop new materials.
MJF 3D printed parts are generally useful in cases requiring strength and moderate temperature resistance, as in engine housings, bellows, baffles, or jigs and fixtures. Some specific applications are as follows. A prosthetic innovator in Rhode Island, Michael Nunnery, enlisted a local MJF print facility to produce a fully functional prosthetic leg socket for a patient. According to Nunnery, the patient was satisfied with the printed prosthetic, adding, “His old socket was very loose and heavy, and he is happy with the light weight of the material.”
Dutch robotics company Avular calls on HP Digital Manufacturing Network partner Materialise to create on-demand, customized parts for drones. Avular is using the partnership to produce various drone parts, from wiring guides to battery holders. Avular says they appreciate the ability to customize parts on the fly and the fact that they can receive their parts within a week. In Michigan, General Motors opened a 3D printing facility offering MJF capabilities. It is exploiting MJF 3D printers to manufacture HVAV ducts for Cadillac CT4-V and CT5-V manual transmissions, among other use cases.
Considering that HP is rolling out production of more affordable MJF printers, including full-color capabilities, it’s clear that the immediate future of Multi Jet Fusion will be focused on more versatile and accessible printing methods. This includes greater material choice and availability as well, which shows promise given HP’s calls for collaboration, though HP does retain proprietary control over their technology.
One question for the future is how much this technology is patent-protected. Could other companies develop variations of MJF 3D printing, further driving down cost and increasing versatility? Time will tell. For now, HP has clearly produced one of the most exciting recent innovations in additive manufacturing, one of which is sure to have many expanded applications for years to come.
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