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Pioneered by Stratasys in 1988, Fused Deposition Modeling (FDM) is a useful process for rapid prototyping of small mechanical parts. It can produce robust parts relatively quickly, quietly, and cheaply. It also has no toxic chemical by-products; an FDM system can be operated in an office environment and does not have to be relegated to the machine shop.

An FDM system consists of one or more nozzles mounted on a 3-axis movable stage. A plastic filament is fed into the nozzle, where it is melted and deposited at the X-Y co-ordinates specified by a CAD database. Just as in SLA, one layer of material is created at a time. Once a layer has been fully deposited, the stage moves up to begin the next one. The process is repeated until the part is complete, at which point it is allowed to cool and harden.

The primary materials used in FDM are ABS, casting wax, and nylon. Parts created by FDM using ABS are stronger and less expensive to produce than most of those done by SLA. FDM falls behind SLA when it comes to dimensional accuracy and surface finish, however.

For cases where durability and speed are more important than surface finish and tolerances, FDM is a good candidate. Other processes to consider are stereo lithography, 3D printing, and selective laser sintering (SLS).

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