Founded in 2007, Israel’s XJET has promised big things since its founding and it has not disappointed. In 2016, the metal and ceramics 3D printing company debuted its innovative NanoParticle Jetting technology (NPJ), a platform which relies on inkjet print heads to deposit layers of a liquid material infused with metal nanoparticles. Excitingly, XJET’s NPJ technology has proven to not only be useful for metal 3D printing, as it also has applications in printing technical ceramics.
Wanting to know more about the innovative additive manufacturing platform, we spoke to Haim Levi, Vice President of Manufacturing and Defense markets at XJET, and a seasoned additive manufacturing expert to see what sets NPJ apart from other metal and ceramic AM systems currently on the market.
“There are a few major things that are different with NanoParticle Jetting than other technologies,” Levi explains. “First of all, we do not utilize powder at all, we work with liquids that contain either metal or ceramic nanoparticles. The printing unit is the same for both materials,” he adds, noting that switching from one material to the other on the same system does require quite a bit of manual work, including cleaning the machine, recalibrating it, etc.
“The second difference is that we are working with two different materials—one is the build material, the other is the support material—and we jet them together at the same time. The result of these two differences is that we achieve real freedom of design as well as near-net shape parts, meaning that the post-processing required is minimal. Because we work with nanoparticles, we can achieve high accuracies and highly detailed parts because we control every nanoparticle that we put on the building tray.”
The accuracies that XJET’s NPJ technology is capable of achieving are indeed impressive. For part dimensions up to 50 mm, Levi says the system has an accuracy of +/- 50 microns, while for larger dimensions it can still reach tolerances of +/- 100 microns. Minimum feature size is also 100 microns.
“We work with very thin layers of about 8-10 microns, meaning that we achieve very good surface finish, even for inclined surfaces,” Levi adds. “Altogether, it means that the amount of finishing required is minimized. Many times there’s no need for finishing at all.”
Delving further into the NPJ process, Levi explains: ”The process works like this: we have twenty-four inkjet printing heads covering the whole area of the printing tray. These heads are moving back and forth across the whole build area and they jet the two materials simultaneously. The principle is similar for both materials: when the nanoparticle liquid is jetted out of the nozzle, it falls onto a hot building tray (250°C). Once it hits the surface, all the liquid evaporates leaving behind just the particles with a small coating of bonding agent. This allows them to bond to each other in all three dimensions.”
Say goodbye to support structures
Another key difference between NPJ and other additive manufacturing processes is that it does not rely on support structures in its build process. “We do not build support structures, because we fill out all the voided cavities with the support material,” Levi elaborates. “Layer by layer we print the whole job—which is not necessarily one part, it can be as many parts as will fit on the tray.”
“By the end of the printing process, we have a job ready. From there, we take the whole tray or the individual parts and put it in a vat of solvent. The solvent, which is very mild, non-irritant and non-hazardous, dissolves all the support material away, leaving behind a part ready for sintering. This is real freedom of design that allows designers and engineers to create any geometry without being restricted by support structure considerations.”
Once the printed part has had its support material dissolved away, the remaining print—whether metal or ceramic—is then placed in an oven where it undergoes a sintering process. According to Levi, the sintering process can take anywhere from 12 to 14 hours, depending on the material used.
“There is shrinkage in the sintering oven, but due to the fact that we work with nanoparticles, there is very little air and bonding agent, meaning that the shrinkage that we achieve with ceramics is only about 16.7%, which is considered very low. Another interesting point is that we can achieve high levels of isotropy and the shrinkage is the same in all three dimensions. Overall, the process is very accurate, predictable and repeatable.”
Another advantage of working with NanoParticle Jetting is the process’ safety. “Because there is no powder around, the process is very safe. There’s no need for filters or safety masks,” he says. “The only thing users have to do is put the container of liquid material into the machine in the right place. Moreover, the build chamber has no gas in it, there’s no vacuum, no pressure and no high temperatures.”
In other words, compared to most powder-based AM systems, XJET’s NPJ technology does away with many of the safety risks brought on by working with metal powders directly. In terms of ceramics, other systems tend to use slurry materials, so the safety discrepancy is not quite as drastic.
Finally, Levi reinforces that the company’s NPJ technology has huge potential for the future. “It is the only technology existing now that could one day be used to print multi-materials at the same time,” he says. “It won’t be easy, and there are some big hurdles—like determining what to do about the different thermal expansion coefficients of different metals—but there are solutions. We have already started working on it. This is the future.”