By: Hamza Malik, 02/11/2018

Multi-jet Modeling (MJM) is a 3D printing process in which an acrylic polymer flows through Nano-jets to harden and copy the geometry of the 3D-model the user inputs into the printer. The material is hardened and cured by being exposed to UV lights. Support material geometry also flows through the jets  during the print to fill any empty spaces in the model. This support material is a low melting temperature wax that can be separated easily by placing in an oven. This process is referred to as being "hands free" and is one thing that separates MJM from other additive manufacturing methods.

MJM has many applications, some of the most notable being aerospace, dentistry, and medical. One main benefit of MJM is that because there is one large printhead that moves along the whole build platform, the amount of time of the print is the same for any number of parts. MJM printers are popular in office spaces because of their relatively low costs and the printers ability to be easily cleaned. 

Picture showing different part of the multi-jet modeling printer. Build material for MJM is usually acrylic polymer while support material is wax.

Picture of MJM printer; good visualization of nanojets

The history of additive manufacturing dates back to 1986 where the first stereolithography technology was patented by Charles Hull. The rapid advancement of technology during 1985-2010 allowed for many 3D printing technologies to develop. Hull formed the 3D Systems Corporation which created the Actua 2100 in 1996, its first printer that used an inkjet printing mechanism that deposited material layer by layer. In January of 2008 3D Systems released the ProJet HD3000 a multi-jet modeling (MJM) machine still sold today. As printers are advancing in technology, precision and speed are increasing, two factors very important in MJM. 

• MJM is used in applications such as aerospace, medical, jewelry, and dental. 
• MJM is also very useful for functional prototypes, jigs and fixtures, manufacturing tooling, and production parts. 
• Due to the support material being a low melting temperature wax, MJM is very convenient in that the process is to take separate the part is just heating and pulling. 
• Fine feature detail, high resolution, low prices, and being easy to clean make it a process that is perfect for office settings
• An example of tolerances for the OBJET EDEN250 MJM 3D Printer are:  20μm for Y-print axis, 40μm for the X-print, and 90μm for the Z-print. These tolerances for the different directions are all max differences of actual size of the part and size of the model rendered to print. 
• The shortcomings of MJM are in material options and speed of printing. SLA is the alternative to MJM when special materials and speed  are necessary to consider.
• SLA is capable of printing materials that are stronger than what is possible with MJM.
• MJM has the capability to producer finer build layers when compared to SLA

MJM Printed denture guides

MJM Printed drill; multiple parts printed and attached

MJM Printed part to show fine details of the structure

• The first step of the MJM process is to upload a 3D model which is sliced and analyzed to figure out geometries of support material relative to part material. 
• When the print is initialized, the print head moves back and forth while part material is flowed out through nano-jets to accurately create the geometries of the sliced model. This material is usually an acrylic polymer which is exposed to UV light and hardened immediately. 
• At the same time the material is being jetted out, a support material is also being jetted out to fill in spaces of the model. 
• Each layer of material and support material build on top of each other as the print head is moving laterally on the build platform and slowly increasing the thickness of the material by moving up with each layer that is completed. 
• The last step of the process is for the user to separate the support material and the part material by putting the two in an oven and removing after the wax has been melted (~1 Hour). Wipe off any excess wax and the part is finished. 
• This process can be done with one person who creates and uploads the model.

• Typical Multi-jet modeling printers range from $20,000 to $120,000 
• Some exmaples are the Projet3500 HDMax starts at $70,000 and the HP JetFusion 540 starts at $50,000
• Refills for part material being about $600 while the wax material refills are about $400. Rinsing solution refills can cost up to $100. 
• No special skills required to multi-jet model, only simple training on interface and limitations