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FDM uses a thermoplastic filament that is melted down and extruded from a print head. Once extruded into a bead, the material is immediately set in the high temperatures of the machine and layered on a platform. The machine head repeats the extruding and melting, layer by layer, until the part is complete. 

The PolyJet process is different in that a carriage jets photopolymers onto the work space, which are then cured by a UV light. After a thin layer is created, the process repeats itself by jetting additional layers until the part is fully formed.

Since the process and materials are different, the characteristics of parts each produces will be different, too. There are a few key things to consider when choosing the right technology:

Application

How will your part be used? PolyJet’s ability to create parts with great intricacy makes it a great choice for concept models.

While PolyJet makes its name with exceptional detail, FDM hangs its hat on the ability to produce durable parts that are ready for end-use applications. If fit and function are critical to your part, FDM may be the best choice.

Material

It is also important to consider what material is needed to satisfy your part’s application. If attention to detail is a crucial component of your part, PolyJet will be able to produce the small features and fine textures you need. PolyJet can also print parts with variety of flexibilities, from rubber-like parts to those that have a more rigid feel.

When printing in FDM, you have the ability to choose from different thermoplastics that can withstand a wide variety of elements, from extreme temperatures to exposure to certain chemicals.

Aesthetics/Surface Finish

The importance of how a part looks when completed largely depends on how the part will be used. For concept modeling and some prototypes, the surface finish and aesthetics can be crucial. If this is the case, PolyJet’s use of multiple materials and attention to detail is often a good option.

And while FDM does not offer the detail PolyJet does, it can still produce parts with complex geometries and intricate components. The FDM process will produce layer lines on parts, but these lines usually do not affect a part’s strength or functionality.

Part Size

The size of your part also needs to be considered when choosing a technology. Both PolyJet and FDM offer similar dimensions for the maximum part size from a single system: PolyJet parts can be built up to 39.3 x 31.4 x 19.6 in. and FDM parts can be built up to 36 x 24 x 36 in.

However, FDM technology allows you to build parts as large as you need them to be. If your part is larger than the FDM dimensions above, the design file can be split into multiple pieces, with each piece built on a separate machine and then bonded together, giving it the strength and functionality as if it was a single part.

Both technologies have their strengths and limitations; it is ultimately up to how the part will be used when determining what technology to choose. If you are looking for high-resolution, ultra-fine parts, PolyJet is a great option. However, if durability and end-use function in extreme conditions is important to you, FDM is your best bet.