According to the ASTM standard terminology definition, material jetting is a process in which droplets of build material are selectively deposited onto a build bed to develop a three-dimensional object. Many of the 3D printers from Stratasys Ltd do a variation of material jetting that the company refers to as PolyJet technology. These 3D printers are the Objet24, Objet30 Pro, Objet Eden260V, Objet Eden350/350V, Objet Eden500V, Objet260 Connex, Objet350 Connex, Objet500 Connex, and Objet1000.
PolyJet technology involves multiple print nozzles jetting one or more liquid photopolymers onto a build tray, which are cured with UV light. With some of the model materials, the 3D printer also jets a gel-like support material for overhangs and complex geometries. This support material is easily removed by hand and with water.
In 2007, Objet introduced its Connex multi-material 3D printing capability. It jetted two materials at the same time and even mixed and composed them to produce up to 14 different and unique material characteristics in one 3D-printed part.
Using material jetting, these printers can deliver more than 100 materials and digital material combinations, including rigid to rubber-like, opaque to transparent and ABS-simulating performance.
Compared to other processes, the PolyJet or material jetting process delivers precise, accurate parts with a smooth finish. Layers can be thin to print fine details and deliver smooth surface finishes. However, some of the materials may not handle heat well, as they are not a true plastic. Other materials will handle heat and deliver high strength too.
FDM materials are known for their strength and they handle high temperatures well. However, objects made through this process tend to show stair-stepping “ridges.”
Stereolithography
 materials are popular, precise, water resistant, and range in cost from low to high. But these materials are not true plastic.
And laser sintering
 materials are durable; handle chemicals and high temperatures but they typically have a rough finish.
The PolyJet materials are available with a variety of characteristics. Some are rigid and opaque and come in blue, black, white, and gray colors. Some are rigid and transparent. Some are rubber-like and range from translucent to gray and black with varying Shore A values. Polypropylene-like materials, and various dental and medical materials, including a transparent bio-compatible material suitable for prolonged skin contact and mucosal membrane contact of up to 24 hours are also available.
To achieve this impressive range of materials, these 3D printers mix and compose two base materials together to create a range of composite materials, known as Digital Materials. The printers use two cartridges. Depending on the material you wish to work with, you select a material from a computer menu, such as VeroBlack, TangoPlus, and so on. The 3D printer software determines which material from the cartridges goes into each of the 798 nozzles of the print head. The print head then deposits the materials, a drop at a time, fabricating a digital material on the fly to create the part. So, for example, by jetting both a rigid and rubber-like material together you can produce a range of different materials with variable Shore A values, or varying color shades.
With this ability to both mix and compose materials and of course, print separate different material elements within the same model, you can accurately simulate complex assembled products. For example, it’s possible to print a pair of transparent eyeglasses with rubber over-molded nose and ear supports—all in a single print job—or a car wheel with a rigid hub and rubber-like tire, or a hair brush with a rigid white body and black rubber-like bristles—all seamlessly grown together within a Connex 3D printer.
Until now, all of these material developments have occurred within the realms of standard plastics simulation. Digital Materials allow you to also create hybrid composites that feature the best properties of two base materials so you can create engineered plastics. This means that you are no longer limited to prototypes that look and feel like the end product, these prototypes can function like the end product.
Leslie Langnau
llangnau@wtwhmedia.com
