Investigation of the impact of the short fiber reinforcements on the thermal and mechanical properties of polymer-based composites manufactured by material extrusion

In the recent years, additive manufacturing (AM) has been widely expanded for manufacturing the polymer and polymer-based composite parts. The main drawback of the material extrusion additive manufactured parts is the weaker mechanical properties in comparison to the manufactured parts by the conventional methods. The stated weak mechanical properties are due to the weak adhesion between the deposited layers. The poor adhesion between the deposited layers in material extrusion additive manufacturing process is due to the fact that the previous deposited filament (n-1) is already cooled and solidified. To ensure the appropriate adhesion between the two adjacent filaments, the temperature of the first deposited layer (n-1) has to be high enough to obtain a suitable adhesion to the subsequent layer (n) but in an optimum range to avoid the lack of the dimensional accuracy. Therefore, a precise and local measurement of the temperature on the scale of the diameter of the filaments is necessary. In this study, four important process parameters (liquefier temperature, layer height, print speed, and bed platform temperature) were selected to study their effects on the rheological behavior and temperature evolution of the PA6 and CF-PA6 materials during material extrusion process. Then, the impact of the short/chopped reinforcement on the thermal and mechanical properties of the material extrusion additive manufacturing processed polymer-based composites were studied by comparing the obtained results from PA6 and CF-PA6 parts. In one experiment, it was observed that increasing the liquefier temperature from 220 to 240 °C increased the tensile strength and crystallinity percentage of the manufactured PA6 and CF-PA6 specimens. It was determined that the crystallinity percentages of PA6 and CF-PA6 specimens increased from 12.51 to 14.40% and from 19.97 to 20.51%, respectively. One of the existence effects of carbon fibers is highlighted in the higher crystallinity values of the CF-PA6 specimens comparing PA6 specimens. Finally, a time–temperature-transformation diagram was plotted to determine the processability condition of the utilized materials. It can be helpful for the designers and researchers to find out the optimal material extrusion additive manufacturing process parameters condition for the utilized raw materials.