Finishing of fused deposition modeling parts by CNC machining

Fused Deposition Modeling is a filament extrusion-base Additive Manufacturing process that integrates Computer Aided Design system, material science, Computer Numerical Control and the extrusion process to fabricate physical parts without geometrical limitations. Notwithstanding the wide industrial diffusion of this technology, one of the most limiting aspects is the obtainable surface roughness. In order to comply with the design requirements, often secondary finishing operations are necessary. Several efforts have been done in this field but a lack exists about Computer Numerical Control machining: the anisotropic FDM mesostructure and the particular surface morphology, which strongly depends upon the deposition angle, make very difficult the determination of the machining process parameters. The aim of this work is to develop a methodology able to unlock the possibility to finish FDM parts by Computer Numerical Control machining preserving the surface integrity. The preliminary observations have pointed out that a variable cutting depth is necessary: for this reason it has been defined as a function of the deposition angle. In order to employ commercial CAM software for the machining, the cutting depth function has been used to modify the original virtual model and to provide the finished one necessary for the toolpath generation. The resulting method has been proved on a case study characterized by a complex geometry.