Often referred to as the most common 3D printing method, Fused Deposition Modeling (FDM) or Fixed Filament Fabrication (FFF) (https://en.wikipedia.org/wiki/Fused_filament_fabrication) are synonymous terms and are essentially the process of melting a plastic filament and laying the filament down in sequential layers to build a part.  Although normally associated with simple, cheap, and easy 3D printers, there are several advanced materials and processes that involve FDM.  However, the overall process of FDM is very simple:  a material in filament form is melted and extruded layer by layer on a build plate to build a part from the bottom up.

​

Here are some of the most common terms associated with FDM:

 

• Extruder (or print core) or hot end.  The extruder is usually an easily replaceable part and is the component that heats and melts the filament.  Extruder temperature is a major parameter and is often the most important and limiting settings of any build.  Typical extruder temperatures start at 200 deg C and can get as high as 350 deg C (although most printers cannot get that high).

​

• Build plate.  The build plate is the surface on which the filament is laid and thus where the part is built.  Sticking to the build plate is a major concern and by far the best method to get a part to stick to the build plate is to use a heated build plate which most, but not all, printers have.  Tape or glue can also be used to improved build plate adhesion.  Tape is less commonly used now than it was several years ago.

​

• Nozzle.  The nozzle is the end of the extruder and the point through which the filament is extruded.  Nozzle diameter and nozzle material are major parameters.  Higher nozzle diameters result in increased printing speeds usually at the cost of lower print resolution.  Harder material nozzles (such as steel) are needed for abrasive or more difficult filaments. 

​

• Raft.  A raft is a part added to the designed part to increase build adhesion to the build plate and allow for easy of removal of the part.  Most software packages can add a raft automatically and do not need to added by the user in the design of the part.  Heated build plates often do not require a raft but other similar structures such as brims and skirts are often used.

​

• Supports.  Several paragraphs could be written on supports but in simplest terms a support is what prevents a 3D printer from having to print “in mid air”.  If a part has an overhang, void, or hole a support may be required for the structure to be built.  Printers and software vary on how supports are used and when they are required.  Supports must be removed after the part is printed and this can be a challenging process.

​

• Infill.  Infill is the percent of the part that is solid.  Normal values can range from as low as 10% to 100% although often 20-30% is common.  Lower infill is used to increase printing speed and reduce filament usage at the cost of some structural integrity.  Unlike some other 3D printing techniques, almost all FDM parts are mostly hollow.

​

• Resolution (or layer thickness).  Resolution is directly related to nozzle diameter and inversely related to printing speed, i.e. higher resolution requires longer printing times (often dramatically).  In simplest terms, increasing resolution reduces the thickness of any individual layer and thus "smooths" the part out.  Most USNA research has shown that resolution does not affect material properties other than appearance.

​

In simple terms, FDM is a simple and inexpensive 3D printing technique.  However, there are several advanced FDM printers and materials that can produce good quality in use parts.