Development And Experimental Research Of Screw Extrusion 3D Printing Equipment For Fiber Reinforced Engineering Materials

3D printing technology is a new manufacturing technology that has developed rapidly in recent years.Fused deposition 3D printing and molding(FDM)has become an indispensable manufacturing means in consumer and industrial fields due to the advantages of simple process,easy molding and material diversity.However,the traditional fused filament fusion 3D printing technology has hindered its wide application in the industrial field due to low molding efficiency and poor strength of the fabricated parts.Screw extrusion 3D printing technology is a new type of fused deposition 3D printing technology proposed in recent years,which has the characteristics of faster molding speed of parts,more diverse molding materials(especially fiber-reinforced composites)and higher strength of molded parts,and has good market potential in the manufacturing and application of engineering parts.In this paper,we developed screw extrusion 3D printing equipment to achieve accurate control of the flow rate of screw extrusion;we prepared carbon fiber reinforced nylon 6(PA6-CF)with high fiber content,and prepared sample parts by screw extrusion 3D printing equipment to study and analyze the mechanical properties of the parts;meanwhile,we 3D printed polyether ether ketone(PEEK-CF)reinforced with high fiber content,and did annealing and hot pressing post-treatment to test the mechanical properties of the parts at room temperature and high temperature environment,and the main research contents are as follows:First,The design of the screw extrusion 3D printing device includes the main frame structure of the 3D printing device,the screw extrusion module,and the flow control module.The flow rate of screw extrusion is analyzed in detail,and experimental tests are conducted on a variety of materials with different physical properties to prove the effectiveness of the flow control.The variation of polymer melt extrusion volume in the screw was investigated under different printing speed,printing temperature and empty driving distance.The flow control device was found to be effective in reducing polymer melt spillage from the nozzle.Solving the flow control of the screw extrusion 3D printing device during the idle portion of the operation improved the print quality of the parts.Second,High-strength PA6-CF composites containing 35 wt.% CF were prepared,and the effects of CF content on the rheological and mechanical properties of PA6-CF composites were investigated in detail.Mechanical tests showed that CF significantly improved the strength of the 3D printed composites.At 25 wt.% CF,the tensile strength reached a maximum strength of169.7MPa,which was 3.2times higher than that of unfilled PA6 and reached more than 90% of the tensile strength of injection molded specimens of the same material.In-depth microstructure showed that the printed specimens retained long carbon fibers(average length over 200μm)with relatively low porosity(2.93% at 25 wt.% CF),which facilitated the achievement of higher mechanical strength.Finally,To meet the molding requirements of specialty polymers and improve the molding quality of printed fabrications,a screw extrusion 3D printing device with chamber temperature is designed and experimentally validated with PEEK-CF composites in this paper.The effects of porosity,CF content and length of the printed specimens,and high temperature environment on the mechanical properties of the 3D printed parts are discussed.It was found that the porosity of the 3D printed specimens increased with increasing CF content.In-depth microstructure showed that CFs were uniformly embedded in the PEEK matrix with an average length of more than 220μm.The long and uniformly distributed CFs allowed PEEK-CF to be fabricated with higher tensile strength,reaching a maximum tensile strength of 190.5MPa.a tensile strength of64.1MPa was maintained in a high-temperature environment at 200°C.Printed test specimens had strengths in excess of 200 MPa after hot press treatment.In this paper,we developed a screw extrusion 3D printing device and verified the effectiveness of the device for printing with PA6 and PEEK materials with high carbon fiber content,and the results obtained from the study have played a positive role in promoting the engineering application of screw extrusion 3D printing.