Coaxial additive manufacturing of continuous carbon fiber composites

Additive Manufacturing (AM) or 3D Printing, is an emerging technique which produces complex and detailed parts layer by layer. Fused deposition modelling (FDM) is one of the most commonly used AM technique due to its wide usage areas and its low cost. However, FDM applications are generally restricted to prototyping because the process is limited with certain thermoplastic polymers. The thermoplastics used in this process could be inadequate due to their weak mechanical properties. Parallel with the recent developments, there is an emerging need for mechanically stronger and durable parts to broaden the application areas of AM as a functional end-parts. To increase the mechanical performance and usability of the printed parts, composite printing can be used. With the inclusion of the continuous carbon fiber reinforcement to the thermoplastic polymers in a composite form, 3D printed parts could meet the needs by providing increase in the mechanical performance. This thesis aims to present FDM based coaxial additive manufacturing of continuous carbon fiber reinforced thermoplastic (PLA) composites for improving the mechanical properties of the 3D printed parts compared to pure thermoplastic materials. The effect of embedding continuous carbon fiber as a reinforcement and PLA, in the form of a pellet, as a thermoplastic matrix material is examined experimentally. A special coaxial nozzle, which supplies the continuous carbon fiber and PLA pellets separately, is developed for printing continuous carbon fiber reinforced thermoplastic composites. After the 3D printing process, the tensile and flexural (3-point bending) mechanical tests are conducted. Also, to improve the bonding of the continuous carbon fiber with the thermoplastic polymer, oxygen plasma, which is one of the surface treatment technique, is implemented as pre-processing operation. In addition, as a post-processing technique, a microwave post-processing is used to enhance the bonding of the printed samples and improve the mechanical properties. Scanning electron microscope (SEM) and optic microscope are used for the visual characterization of the printed composite samples. The results from the mechanical tests showed that continuous carbon fiber reinforced PLA composite resulted in higher tensile and flexure test values than pure PLA. However, adhesion problems were observed, which is one of the main problems with carbon fiber usage in 3D printing, and this limits the much more improved mechanical properties