Structural design and heat transfer analysis of twin-screw extrusion 3D printer

Multi-material fused deposition 3D printing has the unique ability to maintain complex shapes and add special properties. However, the narrow selection of consumable materials, low printing efficiency, and poor performance of the finished products limit the application scope of this technology. In this paper, we propose a twin-screw extrusion 3D printing system that can print a variety of powdered or granular materials, including environmentally friendly biomass particles, metal particles, and thermoplastics, and that enables the mixing of heterogeneous materials. Then we investigate the heat transfer and rheological properties of the system’s material extrusion process. Through the coupled thermal-fluid-solid multi-physical field simulation of the nozzle system, we qualitatively and quantitatively study the transport law and thermal flow field distribution characteristics of the material within the extrusion system, analyze the transport and melting mechanism of the hot melt in the runner during the extrusion process, and obtain the mechanism of the influence of the structural design parameters and the 3D printing process parameters on the transient flow field characteristics and mixing performance. When the screw’s outer diameter is 20 mm and the speed range is 5–25 r/min, the nozzle extrusion flow rate is 2.45–20.15 mm³/s, and the printing efficiency is 3–4 times that of traditional wire printing. The flow field characteristic parameters are optimal when the screw lead is 24–36 mm, and the material extrusion effect is best when the rotational speed is 8–15 r/min. The heat flow field distribution in the extrusion system is stable, the speed distribution is reasonable, and the temperature field distribution is uniform. There is no solution reflux or overflow at the nozzle, the nozzle is not blocked, and the material can be extruded at constant temperature and pressure. The strength of the twin-screw is within the allowable range, the mixing performance is good, and the material can be transported forward with positive displacement. The maximum thermal deformation of the nozzle is 0.09861 mm, which is much smaller than the maximum deformation precision of 0.2 mm, indicating that the screw and nozzle are reasonably designed. The simulation proves the reasonableness of the calculation results.