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Abstract
The bonding quality among polymer filaments in the fused deposition modeling (FDM) process determines the integrity and mechanical properties of resultant prototypes. This paper investigates the bond formation among extruded acrylonitrile butadiene styrene (ABS) filaments in the FDM process. Thermal analysis of the FDM process resulted in an estimation of the cooling profile of the extruded filaments. Sintering experiments were carried out to evaluate the dynamics of bond formation between polymer filaments. Quantitative predictions of the degree of bonding achieved during the filament deposition process were made. The model was used to estimate the effects of different manufacturing parameters in the FDM process. Results suggest that better control of the cooling conditions may have strong repercussions on the mechanical properties of the final part fabricated using the FDM process.
Keywords: Freeform Fabrication, Laminated Object Manufacturing, Polymer Sintering, Thermal Analysis, Acrylonitrile Butadiene Styrene (ABS), Rapid Prototyping
Introduction
The fused deposition modeling (FDM) machine is a computer-numerical-controlled (CNC) gantry machine carrying double miniature extruder head nozzles. The machine fabricates prototypes by extruding a semi-molten filament through a heated nozzle in a prescribed pattern onto a platform. As the material is deposited, it cools, solidifies, and bonds with the surrounding material. The formation of the bonding in the FDM process is driven by the thermal energy of the semi-molten material. The FDM prototypes are orthotropic composites of polymer filaments, partial bonding between filaments, and voids (Figure /). The quality of the bond formed between individual filaments depends on the growth of the neck formed between adjacent filaments (wetting) and on the molecular diffusion and randomization at the interface. The bond formation process can be modeled following approaches similar to those used to describe polymer welding, where the issue of molecular diffusion dominates. It can also be viewed as a sintering process for which the wetting phenomenon is also of importance.
The overall properties of the prototype can be modeled by the lamination theory (Mallick 1993). At the macro level, the properties are studied as laminates of bonded laminas (Figure /). At the micro level, the properties of each lamina are functions of the properties of the filaments, the quality of the bonds between filaments, and void density. Methods have been proposed to model the lamina...