Apparatus, methodology, and modeling for continuous in-situ impregnation of dry carbon fiber tows with thermoplastic polymers for use in additive manufacturing

Abstract

A novel co-extrusion system for continuous fiber reinforced thermoplastic composites was designed, fabricated, and tested. This new process, called In-Situ Impregnation, is a pultrusion process that impregnates continuous dry fiber reinforcement tows in-situ with thermoplastic for applications ranging from additive manufacturing using robotic manipulation to automated fiber placement. The performance goal was to design a co-extrusion system that directly uses raw materials (thermoplastic pellets and rolls of carbon fiber tow) instead of ‘prepreg’ tow in an effort to streamline and cut costs in advanced composites manufacturing and deliver fully customizable fiber orientation. Analytical and computational modeling was conducted to describe the flow rate of polymer through the system, impregnation of the fibers with polymer, heat transfer and temperature uniformity of the die system, friction and fiber tensioning, and the interfacial shear strength between the polymer and the fibers. Multiple experiments were conducted on the working pultrusion system varying polymer, exit geometry, die temperature, and volumetric flow rate of polymer from a thermoplastic screw extruder to gather process-ability and validate the models. A new test method was developed to evaluate the relative interfacial shear strength of a carbon fiber tow (bundle) and thermoplastic polymer, which was tested experimentally and results were obtained for the three polymers used. Microscopy techniques were employed to estimate the degree of impregnation and fiber volume fraction based on cross sections of the resulting composite tows. Future work includes commercialization of the technology, automation of the manufacturing system, and publishing the work in peer reviewed academic journals.