HP Multi Jet Fusion
How it works:
In really simplified terms you can look at Multi Jet Fusion as something between Powder Binding 3D printer and Laser Sintering. The core of the MJF 3D printer is a removable build unit. This unit serves as a space for the actual 3D printing process and at the same time as a container for a 3D printing material.
The build unit is fully detachable from the Multi Jet Fusion 3D printer, and the unpacking of printed parts is done in an additional postprocessing station. The station is also used for filling up the unit with material and for recycling the used material. This makes Multi Jet Fusion much more user-friendly and easy to operate compared to the majority of SLS 3D printers.
Inside the Multi Jet Fusion 3D printer (above the build unit) thermal camera and heating lamps are located. During printing, the lamps keep the material heated slightly below its melting point. Beneath there is a moving scan axis carrying print heads and fusing lamps. The carriage moves from one side of the MJF 3D printer to another. Next, there is a roller with a scraper (used for spreading new layers of material) that moves from front to back.
The 3D printing process:
A screw inside the build unit moves material from bottom container to the upper part of the build unit. There it is spread evenly as a new printing layer on the build platform. Next, the print heads pass above the new layer of material and deposit fusing and detailing agent. The fusing agent is a black substance that absorbs thermal heat. The detailing agent is a substance that evaporates quickly when exposed to heat.
Now, this is where the magic happens. The whole powder in the build unit is constantly kept heated just a few degrees below its melting point. After the detailing and fusing agents are deposited, fusing lamps that are part of the moving scan axis pass above the layer. The additional heat from the fusing lamps gives the black spots a heat kick that melts the powder (the fusing agent absorbs heat). The detailing agent evaporates during this process, ensuring that the powder surrounding the black spots does not melt.
The build platform inside the build unit then moves down by an increment (0,07mm – 0,1mm layer thickness) and another layer is printed. This process repeats until completion of the whole print.
Compared to SLS machines, Multi Jet Fusion 3D printers are much faster. The full volume build is printed in 10 hours, no matter how complex the parts being printed. Because the print heads cover the full width of the build platform, the agents can be deposited on the whole layer in just one pass of the scanning axis. It takes approx. 8 seconds for one layer to be 3D printed and fused. In SLS machines, the laser has to trace the entire surface of the printed parts. So more complex shapes take longer to print.
Currently, the Multi Jet Fusion 3D printers can print from PA 12, PA11, PA12GB, TPU, PP and TPA with more materials similar to the ones used in SLS are coming.
Parts printed with MJF are suitable to be used as end-use parts. This makes Multi Jet Fusion a great alternative to injection molding. Especially in lower volumes (500-1000 parts) and for complex designs that cannot be mass produced by injection molding. Another big plus over injection molding is customisation of 3D printed parts. You can put a unique logo or serial number on every part you print. Or you can alter some specific features of the design to fit a particular customers needs – without needing to produce a different mold which is usually really costly.
Because of using a few similar principles like a Powder Binding 3D printers, the HP Multi Jet Fusion technology is also capable of printing full-color 3D models (HP MJF 580 series 3D Printers).
Also, in the next generation of HP 3D printers, there should be special agents available that can alter different properties of the material being printed. It should be possible to 3D print features that are elastic or for example conductive. This makes MJF very promising technology for both prototyping and end-use production.