FDM is the second most widely used rapid prototyping technology, after stereolithography (SLA). A plastic filament, approximately 1/16 inch in diameter fed from a coil supplies material to an extrusion nozzle (in an alternative arrangement, plastic pellets are fed from a hopper). The heated nozzle melts the plastic and controls the flow of the melted plastic. The nozzle is mounted to a mechanical stage, which can be moved in horizontal (X-Y) and vertical (Z) directions. As the nozzle is moved over the table in the defined geometry, it deposits a thin bead of extruded plastic to form each layer. The plastic hardens as it discharges from the nozzle and bonds to the layer below. The entire system is contained in an oven held at a temperature just below the melting point of the plastic.
As with SLA, support structures are required for any overhanging geometries, which are later removed in secondary operations. Several materials are used for this process including a nylon-like polymer and both machinable and investment casting waxes, and more recently, ABS and polyphenyl sulfone.