Design And Experimental Study Of Screw 3D Printer Based On FDM

As a new manufacturing technology,additive manufacturing technology has shown a diversified development trend since its inception,and has shown significant advantages in personalized customization and processing of complex structural products.Fused Deposition Molding(FDM)technology,as one of the main categories of additive manufacturing technology,which is popular for its low equipment cost,low pollution and strong environmental adaptability.However,FDM printing technology has a single type of material and its shape must be a wire with certain strength.These problems limit its further application.In order to solve these drawbacks,domestic and foreign scholars have applied the traditional screw extruder to 3D printing,but the screw production mode is slightly rough compared with 3D printing,which is a fine processing,and it is easy to appear nozzle blockage,extrusion instability and other phenomena.In addition,the heating process of screw is longer,and the fluctuation of temperature also has an impact on material fluidity.In this paper,we designed a compound screw 3D printer,which solves the problems of blockage of extrusion nozzle,bad match between extrusion speed and printing speed,and difficult fine adjustment of extrusion speed.The research contents and results are as follows:(1)Studying on extrusion swelling,hysteresis and the dependence of polymer material viscosity on temperature and shear rate in the process of screw 3D printing,which provided a reference for the design of screw 3D printer and the optimization of printing parameters.(2)Structural design of screw 3D printing machine.The whole machine structure is divided into three parts: plastic melt extrusion,transmission and mechanism frame.The plastic melt extrusion part is the focus and innovation point of this paper.The problem of high pressure and easy blockage of nozzle is solved through the design of compound screw.In order to match the extrusion speed and printing speed correctly,a storagecylinder is designed in the middle of horizontal and vertical screw.The design of transmission part and structure frame is improved on the basis of the existing desktop computer to meet the printing requirements.(3)Servo motion control and temperature control system of workbench and extrusion part are improved on the basis of existing printers,which are compiled and uploaded to printers through Ardino control board.In the melt plasticizing part,the screw rotation is realized by PC+PCI1240 motion control card,and the screw speed can be adjusted by modifying the library function of the package in the board.The temperature control adopts fuzzy PID control to improve the response speed of the temperature control system,reduce the temperature overshoot,and automatically adjust the PID parameters according to different printing environments.(4)Using POLYFLOW to simulate the flow field in the horizontal screw,the distributions of pressure field,velocity field and shear velocity field are obtained,and the simulated extrusion speed is compared with the theoretical extrusion speed.The results are not very different.The time required for filling the storage cylinder is predicted,which provides a reference for the design of the rear barrel structure.(5)The PLA was modified by PCL with high toughness and MWCNTs with high strength to solve the problem of brittle fracture in the process of printing.Tributyl citrate(TBC)was used as the interface compatibilizer to improve the interfacial adhesion between PLA and PCL,and anionic surfactant sodium dodecylbenzene sulfonate(SDBS)was used to reduce the agglomeration of MWCNTs.Finally,the modified materials and screw 3D printing equipment are tested and printed respectively.