An improved extrusion-based manufacturing system includes one or more extruders, with each extruder containing at least two stages of increasing pressurization. In a preferred embodiment, a first stage of pressurization is created by the motion of a solid wafer of thermoplastic through an orifice...http://www.google.com.au/patents/US5764521?utm_source=gb-gplus-sharePatent US5764521 - Method and apparatus for solid prototyping
