While RAPID 2016 was abuzz with the possibilities of HP’s Multi Jet Fusion technology, an equally formidable force at the convention was Israel’s XJet, which occupied a large portion of the showroom floor with its massive liquid metal 3D printer. This was the first time that the machine had been shown in public, and the public was impressed and intrigued with this new NanoParticle Jetting (NPJ) technology, which is unlike anything seen in the industry before.
Using a novel inkjetting technique, XJet’s technology is capable of achieving a level of detail and finish unmatched by other metal printing approaches. Avi Cohen, markets development manager for XJet, described the process in an interview, saying a key component is the nanoparticle ink that is deposited by the machine. The metal is ground into a dust so fine as to produce particles at the submicron level. This is a remarkable feat compared to the atomized metal powders used in powder bed systems, which have particle sizes ranging in the 30- to 45-micron level for selective laser sintering (SLS) platforms and 45 to 100 microns for electron beam melting systems.
Suspended in a liquid carrying agent, the ink is then deposited onto the build plate from standard piezoelectric print heads at a rate of 221 million drops per second, at which point the carrying agent instantly evaporates, leaving only the metal particles. A heating element passes over the layer, applying temperatures of up to 300 °C (572 °F) to fuse the particles together at layers as thin as one micron, a feat rivaling the technology of micro-SLS firm 3D MicroPrint.
The result, Cohen said, is that these parts are fully dense and have no thermal distortions or residual stress associated with powder bed metal printing processes. Cohen added, “Printing in different areas of the tray does not affect the part. The machine also has auto maintenance cameras that monitor the progress of the print and adjusts the jetting level as needed.” At the same time, only the metal necessary for a build job is used, thus limiting waste as much as possible.
Another advantage of the NPJ process, which may not necessarily be considered by casual observers of metal 3D printing, is that the operator of the machine never has to deal with metal powder or the gasses used with powder bed methods. With powder bed metal 3D printing, parts are necessarily handled with rubber gloves and respirators or a sealed chamber with built-in gloves, as if dealing with a radioactive isotope. This is because the material is highly reactive, with a single static charge capable of starting a fire. The inhalation of the powder can also potentially cause irritation, breathing problems and gastrointestinal issues. Cohen explained that, with the XJet platform, there is a much greater level of safety, with no residual metal dust to speak of. The metal ink is stored in sealed cartridges, which are inserted into the machine, ready for printing.
The parts are then put into a conventional sintering oven to produce the final part. While that last step may seem to detract from the possibility of instantaneously creating a finished metal part in one go, it is important to remember the post-processing steps that are not required with XJet’s technology but are required with powder bed machines. As the ink contains submicron particles of metal, the surface finish and detail are so refined that it requires no machining or other subtractive procedure to clear away support structures or remove the print from a metal build plate.
Also key to limiting the post-processing required is the support material used to fabricate intricate metal parts. Without describing the exact chemistry, Cohen explained that the support material does not fuse during the printing process. Instead, when the finished part is placed into the oven, that powder burns away completely, leaving only the printed object.
“The support material here, I think, is actually the bigger story,” Cohen said. “In a powder bed system, if you have a pipe, you will print it standing up because of the support material. If you want to print it on its side, how are you going to clean it? My gosh! So, to avoid this, you’ll change the design to a different shape that doesn't require supports. Then you've changed the design just to fit the machine.”
With NPJ, Cohen said, it doesn't matter how an object is oriented. The software generates supports automatically. In turn, supports can be placed within cavities. Moving parts can even be designed into an object, yielding complete metal assemblies when the job comes out of the oven. The software also compensates for the minimal shrinkage that occurs during the sintering process. Cohen pointed out that the shrinkage is quite small because the metal particles, being nano in scale, are packed so closely together.
The XJet machine is massive, with a build tray of 500 mm x 250 mm x 250 mm in size. When asked if it is possible to 3D print large-scale objects, such as an engine block, Cohen said that that's no problem. The real beauty of the machine is the ability to print very small components while maintaining precision and quality. In this regard, the XJet system could be used to mass produce a large batch of tiny, intricate parts as easily as it could manufacture large, detailed objects. “It was made for the mass production of small and medium parts.”
On the exhibition floor, XJet proved that the machine is indeed real by printing stainless-steel objects live at the event, though some of the prints exhibited were made from silver, as well. Constructing such a system was no easy task, however. Having obtained more than $100 million in funding since being founded in 2007, the XJet team has spent almost 10 years at its facility in the Rehovot Science Park in Israel researching these capabilities, acquiring 55 patents and 66 employees.
The CEO, Hanan Gothait, was the founder of Objet, whose much-marveled-after technology became property of Stratasys when the two companies merged. Therefore, inkjetting is in Gothait’s blood. It is also in the veins of numerous other members of the XJet team, including CTO Dror Danai, who was vice president of sales and business development at Objet, as well as COO Udi Bloch and Vice President of R&D Doron Avramov, both of whom previously worked at HP. Cohen, too, was with Objet and stayed on with Stratasys for sometime after the merger, heading over to XJet just eight months ago.
After 10 years of hard work, the system is just about ready for commercialization. Cohen said that XJet expects to begin taking orders at the beginning of 2017, with a price that competes with existing metal 3D printing technology. When the first units leave the factory, 3D printing may truly evolve from a prototyping technology to a manufacturing technology.