Experimental study of fused deposition modeling parts interference fit

Fused Deposition Modeling (FDM) is an additive manufacturing (AM) technology able to fabricate a physical object, directly from a virtual model, using layer by layer deposition of a thermoplastic filament extruded by a nozzle. Originally born for the fabrication of conceptual and aesthetic prototypes, at present it has become one of the most used AM process in the industry for functional prototypes and low volume production of final parts. The fabrication of functional components brings forward the necessity of the assembly with other components with different properties in term of shape, material and surface quality. One of the most used assembly method involving plastic materials is the interference fit. It consists in components fastening in which the two parts are pushed together, by means a fit force, and no other fastener is necessary. It required the accurate design of the part interference, typically carried out by the designers through diagrams and theoretical formulations supplied by the material manufacturers. At present no theory has been provided for FDM parts since their mesostructure, surface roughness and dimensional deviations are anisotropic and mainly depend upon the deposition angle. In this work the effect of the surface morphology of FDM parts on the assembly and disassembly forces in an interference fit joint is investigated. For the purpose, a design of experiment with a factorial plan has been carried out. A relationship between the real interference and the assembly forces has been found.