|dc.description.abstract||This study investigates the influence of injection molding process parameters on fiber orientation and mechanical properties of short glass fiber reinforced polyoxymethlene (POM/GF) composites. Filling time, melt temperature, mold temperature and packing pressure were considered as the controllable factors during the injection molding process. Taguchi experimental design, ANOVA analysis and principle component analysis were adopted in order to optimize the process conditions. Moreover, the fiber orientation and fracture surfaces were observed with a scanning electron microscope (SEM).
Two distinct layers existed in the cross section of the POM/GF tensile specimen. The fibers in the frozen layer were parallel to the tensile direction, while those in the core layer were perpendicular to the tensile direction. In addition, three distinct layers existed in the cross section of wear specimens. The fibers in the frozen and the core layer were perpendicular to the melt flow direction, but the fibers were parallel to the melt flow in the intermediate layer.
The tensile strength and friction coefficient increased with the amount of glass fiber. The friction coefficient and the wear volume loss also depended on the sliding direction. The specimen with sliding direction paralleling the melt flow had low friction coefficient and wear volume loss. To obtain the best tensile strength and tribological properties POM/GF composites, the injection molding conditions were as follows: filling time 1.5 s, melt temperature 215℃, mold temperature 75℃, and packing pressure 65 MPa.
Though the fiber-avulse and the fiber-snap were the major fracture mechanisms of frozen layer, the fiber-breakage and the pull-out were the major fracture mechanism of the core layer for the tensile specimens. In addition, SEM photographs revealed that peel-off and grooves were the major wear mechanisms of the neat POM. Grooves, debris, cracks and debonded fibers were the major wear mechanisms of the POM/GF composites.
With respect to the optimum injection molding process of POM/25wt.% composites, it was found that the most influential factor depended on the target mechanical property. For a multi-response case with the tensile strength, elongation, and friction coefficients (P-type), the optimal injection molding process conditions were filling time 1.5 s, melt temperature 215℃, mold temperature 75℃, and packing pressure 65 MPa. Moreover, the most influential factor was packing pressure, and its contribution was 50.99%.