Research On The Forming And Properties Of Metal Materials In 3D Printing By Screw Extrusion

SS304 and Ni₄₅Mn₄₄Sn₁₁ are important structural and functional materials widely used in various aspects of the national economy.With the increasing complexity of component structures,traditional manufacturing methods cannot meet the processing needs.Additive manufacturing,as a new type of manufacturing technology,has attracted the attention of research and development departments worldwide.Currently,selective melting of metal powder using laser or electron beam is commonly used to produce metal parts.The high cost of laser and electron beam equipment and raw materials limits the large-scale application of metal additive manufacturing technology.This article proposes a convenient and efficient metal material 3D printing method,namely,screw extrusion 3D printing method,in response to the realistic demand for low-cost metal additive manufacturing.Using a mixture of metal powder and polymer as raw materials,our self-developed micro single-screw extrusion 3D printer was used to respectively form SS304 and Ni₄₅Mn₄₄Sn₁₁ billets,which were then prepared into well-formed SS304 and Ni₄₅Mn₄₄Sn₁₁-shaped parts through low-temperature dewaxing and high-temperature sintering.Firstly,SS304&PP composite material system and Ni₄₅Mn₄₄Sn₁₁&PP composite material system were prepared.In this composite material,the metal material powder loading is high（up to 90 wt%）,with a low softening temperature.After printing and forming,it can solidify quickly.Additionally,the bonding agent and powder have good wettability,do not react with the metal powder,and exhibit high strength and stiffness at room temperature.Next,SS304-shaped metal samples were prepared using the screw extrusion 3D printing method.Through the study and optimization of printing parameters,the printing process was determined as follows:the printing nozzle temperature was 195℃,the bed temperature was110℃,the extrusion flow rate was 60%,the internal diameter of the printing nozzle was 0.4mm,the interlayer distance was 0.1 mm,and the printing nozzle movement speed was 20 mm/s.The formed billet had a complete shape.By properly adjusting the dewaxing-sintering process,the sample’s maximum density can reach up to 95.78%,and the microstructure is uniform.The maximum tensile strength of SS304 is 484 MPa,and the maximum yield strength is 310 MPa.The shrinkage rate at a pre-dewaxing rate of 60%is approximately 14%.Subsequently,Ni₄₅Mn₄₄Sn₁₁-shaped samples containing microchannels of about 100μm were prepared.It was found that a lower sintering temperature would lead to a higher porosity of the samples.As the sintering temperature increased,the relative density of the samples gradually increased,and the microstructure became more dense and uniform.The optimal sintering temperature was determined to be 960℃,at which the relative density reached as high as 93.59%.XRD analysis revealed the presence of modulated martensite and face-centered cubic austenite,resulting in a significant increase in the phase transition temperature range and the occurrence of partial hysteresis.The maximum magnetic entropy changeΔS_M value of the samples was 1.62 J/kg·K.