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Design and Fabrication of a Coaxial Nozzle for FDM Filament 3D Printers

Yousefzadeh Kouhbanani, Mohammad Hossein | 2026

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58795 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Mohammadi, Kaivan
  7. Abstract:
  8. In recent years, 3D printing technology has found widespread applications in various industries such as aerospace, medical, and the production of complex parts. Among different 3D printing technologies, coaxial printing has been developed to overcome the limitations of single-material printing and enables the combination of multiple materials to create new properties that are a combination of the individual properties of the materials used. These advantages include the creation of conductive fibers, shock-absorbing structures, and hollow structures. Research indicates that the successful production of coaxial structures mainly depends on three key factors, the compatibility of core/shell material properties, optimization of printing variables, and the design of the coaxial nozzle. Most of the studies conducted have used the DIW method, which, due to the need for ink preparation and pre- and post-processing, faces challenges such as increased costs and time-consuming processes. In this research, to address these issues, FDM technology and the use of filament as an alternative method were proposed. Since PCL has been widely used in previous research, it was chosen as the core/shell material because of its well-established properties and fully studied processing variables. One of the major challenges in coaxial 3D printing is the design of the coaxial nozzle. In this context, an innovative design for the coaxial nozzle was proposed to overcome the limitations of existing nozzles. Internal flow simulation within the nozzle under printing conditions showed that the speed variation at different points at the nozzle tip was less than 3%, and the flow velocity along the nozzle symmetry axis (Y-axis) was more than 40 times greater than the other two directions, indicating symmetrical and uniform conditions at the nozzle tip. Additionally, since the filament melts at the nozzle during the FDM process, thermal analysis of the nozzle was also conducted. The results of the thermal simulation showed that the temperature difference within the nozzle was less than 2%, indicating a uniform temperature distribution within the nozzle. This uniform temperature distribution and stable material flow in the nozzle are crucial for producing coaxial structure. Subsequently, the shell nozzle was manufactured using a CNC machine, and the core nozzle was produced with a lathe. After upgrading the existing FDM printer to a coaxial FDM printer, a three-phase simulation using COMSOL software was performed to optimize the printing speed variables in the coaxial printing process. The results of these simulations led to two mathematical models for predicting the core and shell diameters of the coaxial structure for PCL material. This mathematical model can predict the diameter of the coaxial structure based on printing conditions. Comparing the model with experimental data revealed that the difference between the predictions and experimental results was only about 5%, demonstrating the high accuracy of the model. Finally, due to recent research trends and the introduction of coaxial printing into the MEW domain, the designed nozzle was tested in the MEW process in a simplified manner with separate injection of the core and shell materials. The results showed that the MEW process is capable of reducing the theoretical fiber diameter by approximately 90%. This reduction in diameter can aid in the production of micron-sized fibers and expand the application of coaxial 3D printing in various industries, especially in the medical field
  9. Keywords:
  10. Coaxial Nozzle ; Flow Simulation ; Core-Shell Structure ; Polycaprolactone Composite ; Nozzle Thermal Analysis ; Coaxial Three Dimentional Printing

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