The Fused Deposition Modelilng (FDM) process builds parts from the bottom up through the use of a computer controlled print head. The feedstock for the process is a filament of extruded resin, which the machine selectively re-melts and deposits on the prior layer for each cross section of the desired part. The FDM process produces parts in ABS or PC, so they tend to be stronger than parts from other additive processes. However, the parts are sometimes porous and have a pronounced stair-stepping or rippling texture on the outside finish, especially at layer junctions. It may also be difficult to achieve tight tolerances with the process.
Pros: FDM parts are relatively strong and can be good for some functional testing. The process can make parts with complex geometries.
Cons: The parts have a poor surface finish, with a pronounced rippled effect. It is also a slower additive process than SLA or SLS from the standpoint of build time. While FDM can make parts with complex geometries, it gives no insight into the eventual manufacturability of the design.