Fused filament fabrication of polypropylene: Influence of the bead temperature on adhesion and porosity

Abstract The mechanical properties of the parts produced using fused filament fabrication (FFF) strongly depend on the adhesion strength between beads (FA), which substantially depends on the temperature of the polypropylene (PP) beads during their deposition. In this work, the temperature of the beads was controlled through the adjustment of the nozzle temperature (Tn) and the manufacturing chamber temperature (Tch) in order to control respectively the PP temperature at the nozzle end and the cooling of the PP beads after their deposition. SEM observations revealed an improvement of the coalescence between overlayed beads of different layers and between adjacent beads in the same layer with the increase in Tn. The increase of Tch promotes mainly the coalescence between adjacent beads within the layer. These observations were confronted with uniaxial tensile tests based on a Mode III fracture experiment allowed quantifying the influence of Tn and Tch on the adhesion strength between overlayed beads of different layers. Results reveals a weak increase in FA caused by the increase in the manufacturing chamber temperature from 80 °C to 100 °C, while an increase in the nozzle temperature from 170 °C to 180 °C causes a 145% FA increase. In the same time, this decrease in the manufacturing chamber temperature causes an important increase in porosity and a substantial decrease in the adhesion strength between layers.