Effect of processing conditions on the bonding quality of FDM polymer filaments

Purpose - The purpose of this paper is to investigate the mechanisms controlling the bond formation among extruded polymer filaments in the fused deposition modeling (FDM) process. The bonding phenomenon is thermally driven and ultimately determines the integrity and mechanical properties of the resultant prototypes.Design methodology approach - The bond quality was assessed through measuring and analyzing changes in the mesostructure and the degree of healing achieved at the interfaces between the adjoining polymer filaments. Experimental measurements of the temperature profiles were carried out for specimens produced under different processing conditions, and the effects on mesostructures and mechanical properties were observed. Parallel to the experimental work, predictions of the degree of bonding achieved during the filament deposition process were made based on the thermal analysis of extruded polymer filaments.Findings - Experimental results showed that the fabrication strategy, the envelope temperature and variations in the convection coefficient had strong effects on the cooling temperature profile, as well as on the mesostructure and overall quality of the bond strength between filaments. The sintering phenomenon was found to have a significant effect on bond formation, but only for the very short duration when the filament's temperature was above the critical sintering temperature. Otherwise, creep deformation was found to dominate changes in the mesostructure.Originality value - This study provides valuable information about the effect of deposition strategies and processing conditions on the mesostructure and local mechanical properties within FDM prototypes. It also brings a better understanding of phenomena controlling the integrity of FDM products. Such knowledge is essential for manufacturing functional parts and diversifying the range of application of this process. The findings are particularly relevant to work conducted on modeling of the process and for the formulation of materials new to the FDM process.