Overview of XJET’s NPJ powderless AM technology
Haim Levi, VP Manufacturing and Defense industries
In 2016, XJet Ltd., the Ceramics and Metal Additive Manufacturing company, announced the introduction of its innovative NanoParticle Jetting technology (NPJ), a platform which relies on inkjet print heads to deposit layers of a liquid material infused with ceramics/metal nanoparticles.
Haim Levi, Vice President of the Manufacturing and Defense markets at XJet, is a seasoned additive manufacturing expert who points out the features and benefits that make NPJ stand out from other metal and ceramic AM systems currently on the market.
Our NPJ (Nano Particle Jetting) technology is based on direct jetting of the build material which can be either ceramics or metals, using inkjet printing heads and liquid dispersion containing vast amount of suspended nano particles of material. There is no exposed powder in the process at any time, the build chamber is operating in normal atmosphere, with no Inert gas, high pressure or vacuum needed, and at normal temperature. Therefore, the whole process is highly safe and simple with no need for special uniforms, complex filtering and sieving systems, with costly removal of residual powders.
Another major difference from common powder bed technologies, is that we are using two different materials simultaneously — one is the build material, the other is the support material. We do not build support structures, instead we just fill out all the voids, cavities, overhangs and undercuts with the support material, which is fully dissolved automatically later on. The immediate benefit is that there are no restrictions on the geometry of the part usually imposed by support considerations, and in addition the support cleaning process is fast, simple and hands-free.
Layer thickness is typically 8-10 microns, meaning that very good surface finish is achieved right out of the process, even in inclined and curved surfaces. Along with the fact that we use Nano particles of material we do reach high level of accuracy of +/- 50 microns on dimensions of up to 50mm, while for larger dimensions we reach tolerances of +/- 100 microns . Minimum feature size is typically 100-200 microns.
The final effect of these capabilities is the real near-net- shape parts produced, minimizing the commonly required post processing steps, thus saving much time and lowering production costs significantly.
As for the process itself, there are 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 build and support materials simultaneously, each from its dedicated nozzles. After jetting the liquid droplet, containing the material nano particles, it falls onto the hot building tray (250°C) and upon landing the liquid evaporates leaving behind just the particles coated with a small amount of bonding agent. This allows them to bond to each other in all three dimensions, creating a cross section layer composed of areas belonging to the part and areas filled by support. This process proceed layer by layer till the job is fully done. Typical job can include many parts, either identical or completely different, allowing for high productivity when filling out the full tray area with parts.
By the end of the printing process, we move the whole tray or any individual part to the cleaning vat filled with water-based solvent that dissolves all the support material away, leaving the parts clean and ready for sintering.
In the oven the parts undergo a typical cycle of sintering according to the material, which is standard industrial process.
It is well known that sintering process create some shrinkage of the part. Since we use Nanoparticles, which fill out the part volume to high packing level, and the minimal amount of bonding agent present, we achieve significantly lower level of shrinkage compared with other technologies including classic ones. This shrinkage is isotropic, accurate, repeatable and predictable so that we do take it in considerations when preparing the part for production.
We strongly believe that our NPJ technology has huge potential. It is the only technology existing now that could one day print multi-materials at the same time, creating a real digital alloys voxel by voxel, resulting in new materials we have not yet seen before. It won’t be easy, and there are some big hurdles on the way, but there are some innovative solutions we have already started to explore. This is the future.
