Investigation On Particle Flow And Melting Characteristics In Screw Extruder Based On 3D Printing

Fused deposition modeling is widely used in industrial production due to its advantages of convenient operation and low cost.The traditional FDM 3D printer have several disadvantages,such as unsatisfactory mechanical properties of final product and big brittleness of the filament.The screw extrusion device which is fed with pellets can solve these problems.The particle flow and melting characteristics in the screw extrusion device lead to important impact on the quality of final product,but the related research is still not sufficient.Therefore,the screw extrusion device applied in fused deposition modeling is researched.Particularly,the particle flow behaviors in the solid conveying zone and the melting and flow processes in the melting zone are investigated by numerical simulation and experimental research.Firstly,the mathematical model of the screw extrusion device is established.Discrete element method is applied in the simulation of the solid conveying zone,and a directional constant torque model is added to the particle motion equation to consider rolling resistance.In addition,the contact force is calculated using a linear spring dashpot model.Finally,conservation equations and the viscosity model are established,while a Syamlal-O’Brien drag model is adopted to describe the interphase momentum exchange.The experimental platform of the screw extrusion device is set up based on single-chip control technology,and the experimental study on the particle flow characteristics of the solid conveying zone is carried out.The corresponding numerical simulation is conducted based on discrete element method.Meanwhile,experiment and simulation results are compared to check the model.The results show that under both the intermittent feeding mode and continuous feeding mode,the mass flux of pellets increases with the increase of screw rotation speed,and the particle filling rate decreases accordingly.Meanwhile,the relative deviation of particle mass flux in the continuous feeding mode is smaller than that in the intermittent feeding mode,indicating that continuous feeding mode is more suitable for 3D printing.Three different kinds of granular materials is applied in this study: polylactic acid,polyurethane and polypropylene.The flow characte ristics in the solid conveying zone are simulated base on discrete element method.Meanwhile,the influence of rolling friction between particles and rolling friction between the particles and wall on the particle flow characteristics are investigated.The flow parameters analyzed in the simulation include particle mass flow,velocity distribution,collision frequency,etc.The results show that the mass flux of three kinds of particles decreases owing to the increase of the rolling friction coefficient between the particles and wall,and the relative standard deviation of velocities increases accordingly.The total torque increases with the increase of rolling friction coefficient.Moreover,the tendency of the torque caused by the contact force and rolling friction is identical with that of the total torque.With the increase of the rolling friction coefficient between particles,the mass flux of three kinds of particles decreases first and increases later,and the tendency of the total torque and collision frequency is identical with that of the mass flux.Finally,based on the Euler-Euler multiphase flow model,the melting behavior and flow characteristics of pellets in the melting zone are simulated.Firstly,experimental results in the reference are compared with simulation results to verify the rationality of the model,and the grid independence is verified later.The results show that the melting time of single particle decreases with the increase of heating temperature,and the magnitude of temperature decrease is smaller.As the initial particle inlet velocity increases,the melting time decreases,and the particle solid fraction is smaller at the same moment.