Fused Deposition Modelling (FDM) is a rapid prototyping process to produce three dimensional solid objects directly from a CAD model. The machine is basically a CNC-controlled robot carrying a miniature extruder head. By feeding the head with a plastic wire, solid objects are built „string by string".
The FDM system from Stratasys, USA, consists of the main 3-D Modeller unit, a slicing software and a workstation. The process starts with the creation of a part with a CAD system as a solid or surface model. The model is then converted into an .STL file and send to the FDM slicing software. There, the .STL file is sliced into thin cross sections of a desired resolution, creating an .SLC file. Supports are created if required by the geometry and sliced as well. The sliced model and supports are converted into an .SML file that contains actual instruction codes for the FDM machine. The FDM machine follows the principle of a three axis NC-machine tool. A nozzle, controlled by a computer along three axes, guides the specific material that is melted by heating. The material leaves the nozzle in a liquid form, which hardens immediately at the temperature of the environment. For this reason, it is fundamental for the FDM process that the temperature of the liquid modelling material is balanced just above the solidification point. A spool of modelling filament with a diameter of 1.27 mm feeds the FDM head, it can be changed to a different material in less than 1 minute. Within the building of the desired object the material is extruded and then deposited in ultra thin layers from the lightweight FDM machine layer-by-layer. Recently, Stratasys changed ist working principle by using a double extruder head (similar to Sanders). One nozzle carries the build material the other carries a support wax which can easily be removed afterwards. This allows more complex parts to be built.