Hybrid coaxial 3D printing with nested-screw mechanism: Optimizing material integration and structural performance for coaxial designs

The emergence of multi-material extrusion systems has opened up new possibilities for 3D printing, spurring research on the combination of diverse materials and structures to enhance part quality and performance. In this work, a nested-screw coaxial co-extrusion 3D printing mechanism was designed for hybrid coaxial structures to address the viscosity matching limitation that is present in traditional coaxial extrusion. The high-viscosity shell material, with 3 wt% added carbon fiber, can be extruded and printed at room temperature. This suggests that the nested-screw can be used to adjust the high viscosity difference between the core and shell materials for co-extrusion. A model for coaxial extrusion was developed to establish appropriate printing parameters for the hybrid integration of materials and structures in coaxial designs. The resulting model for determining the printing parameters of the C-S structure improves dimensional stability and print repeatability. The coaxial printing was also employed to validate the bionic coaxial structure of antlers. The influence of the core-shell material and structure combinations on strength and toughness was thoroughly examined, enabling the optimization of structures with superior strength-toughness combinations. The comparative truss structure tests demonstrated that the core-shell structure enhanced damage absorption by 30.1 % compared to a single-structure design. This confirms the adjustability of mechanical properties in printed systems through a combination of hybrid materials and structure.