Development of an innovative additive manufacturing equipment containing a co-rotating twin screw extrusion unit

• Ano de defesa: 2022
• Autor(a) principal: Justino Netto, Joaquim Manoel
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Blendas poliméricas; Customized design; Fabricação com pellets fundidos; Fused pellet fabrication; MEX; Polymer blends; Processo aditivo por extrusão; Projeto customizado; Protótipo; Prototype
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/18/18163/tde-26012023-181116/

The development of an innovative 3D printer containing a co-rotating twin screw extrusion unit (Co-TSE) is presented in this work. Material extrusion additive manufacturing (MEX) has been traditionally implemented by filament-based 3D printers with narrow commercial offer of materials. Since the mid-2000s, research efforts have been applied to develop MEX technologies that accept pellets or powders as raw material. The typical solution, based on single screw extrusion, enabled expanding the range of applicable materials, reducing printing costs, and increasing the deposition rates, but have limited process flexibility and mixing capacity. The new design combines a miniaturized modular Co-TSE operated under starve-fed conditions with a benchtop Cartesian platform, and accepts material in powder or micro-pellet form. As with industrial Co-TSE machines, the output and screw rotation speed can be set independently, and its dispersive and distributive mixing capacity can be fine tuned according to a given manufacture. Screw-assisted MEX was investigated in a systematic literature review, revealing the main design advantages, limitations and technology development workflow. The new equipment was developed in three major iterations, starting from the determination of the screw geometry to the simulation of the extrusion process, to ascertain whether the appropriate thermomechanical environment for polymer processing could be created by the proposed design. A functional prototype was built at the end of the third iteration. Extrusion tests were performed under different operating conditions, using polypropylene and a 90/10 wt% polypropylene/polystyrene blend. Two screw configurations were used, with and without kneading discs, to assess the response of the extrusion unit in terms of flow characteristics and mixing performance. The results showed that the mixing elements determine the starting melt position, and the average residence times, as well as the shearing levels which, in turn, affect the homogenization effectiveness. The screw configuration and rotation speed do not affect the output, which depends only on the feed rate. Preliminary deposition tests were conducted to determine the feasible printing parameters. A standard tensile test specimen, a square scaffold and a multicolored rectangular box were successfully printed, validating the innovative design. The mechanical properties of printed test specimens were within the expected values. The blend specimens showed na increase in the Young\'s module and ultimate tensile strength (1417 ± 101 MPa and 32 ± 1 MPa, respectively), accompanied by a significant decrease in the elongation at break (23 ± 6 %) due to the presence of the PS phase. The Co-TSE AM system not only eliminates the dependency on filamentary feedstock but combines polymer compounding and 3D printing in a single processing route. This represents a significant step towards the availability of a more versatile equipment that can be customized according to the required processing tasks and/or intended application. Future research avenues include using this printer to integrate into a single step the manufacture and printing of polymer blends, bio-composites, and bio-nanocomposites for personalized medical applications.