Abstract:
There exists a powerful need in the composite industry for more versatile ways to manufacture high performance fibre-reinforced plastics. In prosthetic manufacture a leg socket can commonly cost $7000USD, but uses only $200USD of base materials. The rest of the cost is dominated by labour and tooling. In this work, an extruder for the purpose of additively manufacturing long-fibre reinforced thermosets has been developed. The concept is novel and uses air pressure to force a UV-cured resin formulation out of an orifice containing fibre. Upon extrusion, UV lights cure the resin. The concept is versatile, it has the potential to extrude any UV cured resin with any type of fibre including but not limited to kevlar, carbon, glass, aramid, or optical fibre and even electrical wire. Results indicate the method can achieve volume fractions of 30% or higher at volume extrusion rates significantly higher than conventional thermoplastic 3D printing. Models were developed based on viscous flow equations in an annulus geometry. Agreement was found between predictions and experimental data, but nonlinearity was present which remains unexplained. The mechanical design of the extruder is progressed. It is small and light enough to be used on a standard 3D printing gantry. A closed-loop fluid level control system actuated by air pressure has been implemented. The method was demonstrated to be capable of reacting quickly with a high degree of reliability. The method functioned without problems across a wide range of pressures and feed rates. Tensile testing and microscopy of extruded filament was conducted. Properties exceeded those used in current prosthetic manufacture. Achieved ultimate tensile strength, with a long infusion chamber, was up to 93% of the theoretical value of 909.3MPa at the extruded volume fraction. Difficulty was encountered with cure systems during printing. The opacity of carbon fibres required a high degree of surface cure in order for the deposited filament to hold shape, which caused problems with cured resin fixating to the nozzle. Resin rheology must be studied and a cure system developed before the concept can be employed to print parts. However, the feasibility was demonstrated and method shows significant promise in reliability, versatility, print speed and material performance.