Polymer composites are made by mixing various additives of nano / micro-scale inside the polymer matrix, and are produced by methods such as FFF, injection-molding, and etc. with excellent mechanical properties such as corrosion resistance, elasticity, lightness, and easy to manufacture. However, due to the limitations of low properties, it is being used limitedly, and various studies are being conducted to improve the physical properties. An understanding of additive alignment is required to improve the properties of composite materials. In general, the flow of suspension inside mold results in additive alignment, and in the direction of alignment, the effect of improving the properties can be confirmed by cutting the product. However, during the composite production manufacture, it is difficult to intuitively understand the effect of the flow field inside the mold on additive alignment.
The paper first performed a flow visualization analysis and CFD analysis of the polymer composite material in a channel inserting an orifice that mimiced the injection molding process. Flow visualization experiments were performed inside molds with orifice of various shapes. Additive alignment angles according to the mold position were analyzed using a composite material that mixed carbon fiber with a diameter of 7um and a length of 77um in polydimethylsiloxane (PDMS). The analyzed additive alignment angle was compared to the flow field calculated inside the channel with the same shape as the flow visualization experiment with CFD analysis. The orifice inserted inside the mold increases the shear rate, extension rate inside the channel, which has been shown to improve the angle in the direction in which the additive is perpendicular to the flow.
Orifice has a significant effect on changes in additive alignment and was applied to additive manufacturing methods based on the results. Flow visualization experiments were performed on nozzles with orifice inserted to improve the mass properties in the through-layer direction of the output filament. Unlike injection molding, carbon fiber was mixed in polydimethyloxane (PDMS) at high viscosity to laminate, and additive angles were analyzed for mold interior and extruded. In addition, the analyzed additive alignment angle was CFD analysis for the same shape to observe the flow field change. The inserted orifice made a drastic change to the shear rate, extension rate, and the angle of the additive changed due to its effect, but it showed a different tendency compared to the injection mold cases. In addition, the change in additive alignment in the nozzle has shown to be similar to additive alignment after the extrusion at the nozzle outlet. When an orifice, etc. is inserted inside the nozzle, the flow field inside the channel changes, and the sudden change in shear / extension rate is considered to be the cause of the perpendicular alignment of additive alignment. In addition, if the additive alignment is controlled inside the nozzle, the additive alingment can be contolled in a desired direction to control and enhance physical properties of an injection molded or a FFFprocessing products.