System and process development for coaxial extrusion in fused deposition modelling

Purpose - This paper aims to design and test a system capable of coaxial fused deposition modelling (FDM) and assess the coaxial fibres produced for their coaxial concentricity. The goal is to achieve concentricity values below the literature standard of 15 per cent. Design/methodology/approach - This research discusses the design of the coaxial nozzle internal geometry and validates the modelling process by using computational fluid dynamics to assess its flow profile. Sequentially, this paper discusses the abilities of current additive manufacturing (AM) technology in the production of the coaxial nozzle. Findings - The methodology followed has produced coaxial fibres with concentricity values as low as 2.89 per cent and also identifies a clear speed suitable for coaxial printing using polylactic acid (PLA) as the internal and external materials. Research limitations/implications - The concentricity of the printed fibres is heavily influenced by the feed rate for the thermoplastic feedstock. This in turn alters the viscosity of the material to be printed, implying that a relationship exists between feed rate and print temperature, which can be further optimised to potentially obtain higher concentricity values. Practical implications - This paper adds reliability and repeatability to the production of coaxially printed structures, the likes of which has numerous potential applications for biological printing. Originality/value - The outcomes of this study will provide an AM platform to alter the paradigm of biofabrication by introducing a new level of versatility to the construction of biofabricated structures.