Material Jetting

Material jetting (MJ)

Material jetting also uses photopolymers, but instead of a vat, MJ jets droplets of material layer by layer from a nozzle onto the build surface in a similar fashion to 2D ink jet printers.

Initially, the liquid is heated to roughly 30-60°C to reach an optimum viscosity for jetting the liquid. The print head travels over the build surface, depositing droplets of liquid. The material is then cured by a UV light to solidify and harden the photopolymer. This process is repeated layer by layer. Deposition of droplets in this way results in less waste than either SLA or DLP.

MJ requires support structures for any overhangs and usually doesn’t require post curing, unlike SLA, due to smaller layer heights.

Benefits and Limitations

Potentially the largest attraction to MJ is that multiple nozzles can be set up which then jet different plastics (of different colourings of plastic) to either give different properties or colour to different sections of a print. Different colourings can also be mixed to give specific hues. In addition, it’s common for support structures to be made from a secondary dissolvable material that can be removed by either pressurised water or an ultrasonic bath. Dissolvable support structures like this can leave no mark once removed, maintaining high quality surface finish.

Other benefits include lower waste than SLA or DLP due to using jetted droplets rather than a vat (as mentioned earlier). Also, print quality is very high, meaning MJ has very smooth surface finishes and dimensionally accurate prints.

MJ shares some of the same disadvantages as SLA and DLP, such as the properties of the plastic making it unsuitable for many applications due to the brittle nature of printed objects. Polymers used are also photosensitive and break down over time and, finally, printing is expensive.