FDM is gaining ground in the printing world. It is arguably the most “printer-like” of all methods; it consists of a moving bed (Z-axis) and a print head (X-axis and Y-axis). The print head has a heating element in it; thermoplastic is forced into the print head, melts, and is squeezed out, not unlike toothpaste. The bed is usually cooled so that the plastic hardens soon after being placed down. Again, this is a layer by layer process; some systems can print layers as small as 0.178mm. 

Since it is squeezing out spools of plastic filament, there are different types of plastic available to print with. ABS is the most popular; if you are not familiar, ABS plastic is what LEGOs are made of. It can also print PPSF and PC plastics.

Stratasys, the developer and leading manufacturer of FDM technology, offers FDM systems that not only print parts as large as 36×24x36, but print moving parts. The machine can differentiate between separate objects within a CAD file, allowing you to print, for example, a system of gears that works right out of the machine. You can print objects within other objects, etc.

Support structures are necessary, but the print head contains a second element for extruding support material. Stratasys’ FORTUS systems (expensive) contain a bed of water soluble liquid that you place the models in after they print; the liquid disintegrates all support material from the model.

Advantages

• ABS plastic means durable and functional models.
• Several different material options.
• Prints moving parts.
• Separate support material with removal system.

Disadvantages

• Slow print time compared to some other methods.
• Rougher surface finish than SLA.