Material Jetting is one of the processes available to build parts in an additive format. Material jetting 3D printers use a printhead that is similar to those found in paper inkjet printers, except that these printheads deposit droplets of material onto a build plate. In most cases, the material is photosensitive resin that will cure under ultraviolet light. In at least one case (XJet), the droplets are metal powders encased in a special liquid.
The dimensional accuracy of parts made through material jetting are considered excellent–± 0.1% is typical–along with very good surface finish. Material jetting is used primarily for prototypes and to make tooling parts for manufacturing.
Each vendor’s material jetting system uses a slightly different process. Thus, in general, the material that will go through the printhead is heated to a specific temperature to achieve the best viscosity. Then, the printhead moves over the build platform and deposits material droplets to the desired locations. Some printheads have hundreds of nozzles for material deposition.
A UV light source is a common way to cure the deposited material, but some vendors choose a deposited chemical to cure the material. And with XJet systems, the deposited material is of such a high temperature that it cools and solidifies once it hits the build table or previous layers.
Material jetting allows users to control the placement of color and even some material properties, such as strength or elasticity. These properties are available because most material jetting 3D printers can print with different materials (as well as different colors) simultaneously.
Binder jetting, which originated at MIT in 1993, is a variation of material jetting. The company known as Z Corporation acquired the technology in 1995. 3D Systems bought Z Corp years later. Now, ExOne is one of the main vendors of this technology.
In binder jetting, droplets of a binding adhesive agent are deposited onto thin layers of powdered material. A variety of binding materials are used: furan binder is typical for sand casting applications, phenolic binder is usually used for sand molds and cores, silicate binder is a more environmentally friendly binder for sand molds and cores, and aqueous-based binder is commonly used for metal powders.
In some cases, the binding material is colored, enabling a part to be built with multiple colors. This is known as ColorJet Printing.
After printing, binder jetted parts are considered to be in a green, or unfinished, state. Most parts have a finish that looks like sandstone and are somewhat porous. So, some form of post processing, including heat treatment, is used to finish the part. One advantage of binder jetting is that most techniques do not involve heat, so residual stress is not introduced to the parts.
The manufacturers that make material jetting systems include:
3D Systems: offers multi-material and binder jetting systems (from its Z Corp purchase).
ExOne: This company uses binder jetting in a number of its additive manufacturing systems. The materials include ceramics, plastics, sand, and some metals.
HP: Uses it inkjet expertise to jet chemical binders and agents onto a thin layer of powder material.
Stratasys: the maker of PolyJet 3D printing, which originated with the Objet company, now a Stratasys brand.
XJet: NanoParticle Jetting (NPJ), which uses a liquid that contains building nanoparticles or support nanoparticles. The main materials are metals and ceramics.
