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3D Printing of Continuous Glass Fibre Reinforced Polypropylene Composites.

Kuiper, Stef (2022) 3D Printing of Continuous Glass Fibre Reinforced Polypropylene Composites.

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Abstract:In 3D printing, a filament is extruded and pressed into layers, which determine the product’s geometry. 3D printing with continuous fibre reinforced thermoplastic (CFRT) composites makes it possible to produce complex shapes, where stiffness and strength are provided by the fibres. These composites are applied in, among others, the biomedical, aerospace, wind energy and automotive industries. Current CFRT printers mostly mix a polymer with fibres during printing, or deposit fibres in a print by using a separate nozzle. However, with these techniques relatively low fibre volume fractions can be reached. A possibility to attain a higher fibre volume fraction is to print with a single towpreg where the fibres have already been impregnated in a previous pulltrusion process. Literature has shown that voids are one of the main problems when printing with CFRTs which are influenced by several printing mechanics. It is clear that print parameters such as layer height, print speed and print temperature can influence the amount of voids, but it is unclear how and especially an optimum for the combination of material and process used is not known yet. Additionally, while separate researches have shown that parts of the geometry of the nozzle used to deposit the material can influence the structure of a printed part, it is unclear how the microstructure is affected by various nozzle shapes. The main goal of this research was to investigate the influence of these print parameters and nozzle geometry on the microstructure and ultimately mechanical strength of a printed continuous glass fibre (GF) reinforced polypropylene (PP) beam. First, a GF/PP towpreg with a fibre volume fraction of 34% was used to test the influence of ten different nozzle geometries on the microstructure of the extrudate. Filament was extruded through the nozzle, embedded in epoxy and analysed using a microscope, ImageJ, and Matlab. A GF/PP towpreg with a fibre volume fraction of 42.5 % was used to test the influence of print layer height, print speed and print temperature on the microstructure of and mechanical strength of printed beams. Additionally, ten different nozzle geometries were chosen to be used to print beams with. These beams were analysed under a microscope to investigate how the nozzle geometry could influence the resulting microstructure of a printed beam. Based on these experiments, optimum print parameters were found. It was found that a layer height lower than 0.6mm and higher than 0.75mm was sub-optimal for printing and resulted in beams unsuitable for carrying any mechanical load. Increasing the print speed led to weaker beams, but also increased the surface roughness and led to a lot of protruding fibres from the beams. Increasing the temperature during printing led to a decrease in viscosity during extrusion. This decrease in viscosity allowed many of the fibres to detach from the main filament, which again resulted in a very rough extrudate and many protruding fibres. A print technique of printing two shell tracks and depositing a third track between the two gave the most print accuracy combined with a high mechanical strength. Lastly, it was found that a nozzle geometry with a constant cross section close to the diameter of the filament was the optimum nozzle to print with. Using these optimum printing parameters, a beam with a short beam shear strength of 19.34 MPa was printed.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:54 computer science
Programme:Mechanical Engineering MSc (60439)
Link to this item:https://purl.utwente.nl/essays/93877
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