FDM

Fused deposition modeling (FDM) builds solid objects by extruding molten thermoplastic through a moving nozzle onto a build platform. The material cools and solidifies immediately, bonding to the layer beneath. The nozzle traces a pattern in the horizontal plane, then the platform lowers and the process repeats. This stacking of thin layers, typically 0.1 to 0.3 mm thick, forms the complete part from the bottom up.

The most common feedstock materials are polylactide (PLA) and acrylonitrile butadiene styrene (ABS). PLA is easier to print, melts at around 190, 220 degrees Celsius, and produces less warping. ABS requires higher temperatures (240, 250 degrees Celsius), demands a heated build platform to avoid cracking as it cools, and yields tougher, more chemically resistant parts. Specialty polymers like nylon and carbon-fiber reinforced composites are available but demand more precise machine control and higher extrusion temperatures.

The built part emerges with visible layer lines and internal voids where support material once filled overhanging geometry. Support structures are necessary for any feature that extends horizontally beyond the material below; they are printed from the same or a water-soluble polymer and removed afterward. The trade-off between material efficiency and part strength is constant: denser infill patterns (60, 100 percent) create stronger parts but consume more material and extend print time; sparse infill (10, 20 percent) saves material but produces brittle shells.

FDM excels at producing functional prototypes, jigs, fixtures, and low-volume end-use parts where dimensional tolerances need not be extremely tight. Typical dimensional accuracy is ±0.5 mm for features larger than 10 mm. Surface finish is rough compared to injection molding or CNC machining, with visible striations along the direction of travel. Wall thickness, nozzle diameter (usually 0.4 or 0.6 mm), and layer height all interact to determine the minimum feature size the machine can resolve.

The method is also called extrusion-based 3D printing and fused filament fabrication (FFF), the latter being an open-source variant. FDM sits in the lower-cost and lower-speed end of the additive manufacturing spectrum, competing with stereolithography (SLA) for prototype speed and with injection molding for small-batch production. Unlike SLA, which uses liquid resin and UV light, FDM requires no wet chemical disposal and produces dry, inert parts immediately after printing.