The Research Of Key Technologies Of Plastic Particles 3D Printer Based On Simulation

FDM(Fused Deposition Modeling) has been focused on with the rise of the concept of 3D printing. As a kind of rapid prototyping technology, it has the advantages of fast, light, wide range of use. At present, the fixed diameter wire material is applied. It is melted, and molded by different forms of extrusion. Considering the cost of linear material processing and material variety, in the paper, how to use engineering plastic particles(PLA—Polylactide Acid, etc.) to complete the rapid prototyping is studied; a set of small screw extrusion mechanism was designed, and combined with FDM printer with Delta parallel structure, the purpose of rapid prototyping is achieved.Different from the traditional screw extrusion device, in this paper, the extrusion mechanism is designed to separate the transport process and the melt extrusion process of the granular materials. And to achieve the function of the particles melting and squeezing out, the particles extrusion chamber is established. In order to explore the rule of particle transport and melting, CFD( Computational Fluid Dynamics) simulation software(STAR-CCM+) was used to establish the model of particle feeding, extruding, and melting; the simulation analysis of all stages is done, and the rationality of the model was measured by the experimental verification.The main purpose of research on the feed process is to make particles transport more smoothly, using the discrete element method(DEM — Discrete Element Method) of multiphase flow to model the hopper feed system. Different tilt angles of the conical hopper impact the particle transport space and the gravity that the particles are subjected, the smoothness of particles in the feed stage, depending on several factors: the tilt angles of the conical hopper, the gravity of particles, friction between the particles and between the particles and the walls of the hopper and the like. The tilt angle limits space of particles entrying, the greater impact on the smooth of entrance, so establishing three hopper models of different angles. According to the simulation of particle transport characteristics of the hopper, the two factors gravity and the space that affect conveying efficiency are analyzed. 50 degree angle of the hopper works more stably in the low-speed condition, and has high efficiency.Extrusion chamber and melting chamber influence each other, at the end of the extrusion chamber, particles have the speed at right size, the more uniform distribution of motion the better the particles melting, and the extruding process is more smoothly; on the contrary, the more fluctuations of motion, the more unstable the pressure is, leading to poor printing quality. VOF(Volume of Fluid) method is applied to build PLA particles melting model; the melting chamber at a fixed size, the maximum speed which is allowed to make the particles melt in time is analyzed, the relationship between the speed of particles and the size of melt ing chamber is got. When the size of melting chamber length is 30 mm, the allowable maximum speed of particles is 2mm/s. DEM model and the boundary of "DEM capture the wall" were set, the distribution of particle motion in the extrusion chamber is studied when the rotation of the screw at a specific speed, when the size of the extrusion chamber is 35 mm, the velocity distribution is uniform at the end of extrusion chamber, when the speed distribution suitable, the nozzle will not be blocked easily.Experiments realizes the printing of PLA particles, and the printing quality is improved by adjusting different parameters, when the installation height is from 60 mm to 70 mm, the extrusion temperature is about 220 degrees Celsius, single lap printing shows better. Also a variety of other plastic particles printing experiments are realized; a lot of experiments were taken to get appropriate parameters to ensure the printing quality. At the same time, the models established in the previous section are tested, the data are acceptable in the allowed error range, and they can provide good guidance.