FDM (Fused deposition modeling), or FFF(Fused Filament Fabrication), is the most widely used 3D Printing technology. Most installed 3D printers are FDM printers. It is often the first technology people are exposed to.
For desktop or consumer 3d printers, FDM printer is the most popular in the world now. So if you want to get into 3d printing, a FDM printer should be the first choice. And you must know the principle and working process clearly.
Fused deposition modeling(FDM) is a method of additive manufacturing. In the process, layers of materials are fused together in a pattern to create objects. The material(filament) is melted in the printer’s nozzle just past its glass transition temperature, and then extruded in a pattern next to or on top of previous extrusions, creating objects layer by layer.
For FDM 3d printer, there are single extrude or multiple extrudes. But the principle and working process is the same.
Materials used in Fused Deposition Modeling(FDM) technology
There are many filaments can be used on FDM printer now, for example, ABS, Conductive, HIPS, Nylon, PEEK, PET, PETG, PLA, TPU, PC, PVA, ULTM, WOOD, Ceramics, Wax, etc. And the most popular filament is diameter 1.75 mm.

Working process of Fused Deposition Modeling
1. Heat the nozzle until it reaches the desired temperature. The filament will be fed to the extrusion head and then it will be melts in the nozzle.
2. The extrusion head can move in the X,Y and Z directions. The extrusion head extrudes melted material in very thin strands .The material is deposited layer-by-layer on the platform, and then will be cool and solid.
3.When one layer is finished, the build platform will move down (on some machines, the extrusion head moves up) and a new layer will be deposited. This process repeats until the part is completed.
Watch the FDM process on Youtube.
Read <3d printing technology types> to get more knowledge about printing technology.