A thermoplastic filament is supplied to an extrusion nozzle which heats the material passed it’s glass transition temperature. Once heated, the material is extruded (or dispensed ) onto the build plate layer by layer.
The Fused Deposition Modelling style of printing regained popularity after a patent expired, which allowed it to become a large open source project in a community called RepRap. It is also known as Fused filament fabrication.
The material is hardened immediately after being pushed out of the nozzle and more material can then be built onto it. The nozzle is computer controlled to follow a specific tool path based on a model designed on a Computer Assisted Drawing software.