Numerical Simulation And Die Design Of Square Tube Polymer Gas-assisted Extrusion

Extrusion technology occupies an important position in the field of polymerprocessing, it is a widely used molding technique, not only used the industry but alsofamily life. The main difficulty and key for extrusion processing is die design,because it affects the shape and the quality of the extrusion products. The designs ofthe traditional die used the tryout method and repair methods, which needed longperiod and high cost. To predict the die shapes of required extrusion products bynumerical simulation and to optimize the structures of the die by analyzing the flowof melt in the extrusion die is important for the design of Profile Extrusion Die. In thethesis, first, use the module of inverse extrusion of polyflow software with PTTViscoelastic model to design shape tube of profile extrusion die and work out theshapes and sizes of exit section extrusion die. The main work is listed below:(1) Introduction the polymer extrusion process and forming theories, andaccording to its flow characteristics, based on the theories of rheology andhydrokinetics etc., Used the shape tube die to study, the mathematical model ofgas-assisted extrusion molding process is established.(2) By PRO/E, GAMBIT three-dimensional modeling software for geometricmodeling and meshing, the shearing stress on the wall of co-extrusion die is set to bezero to replace the function of gas layer，which is used as the kinetic conditions of thewall, the gas-assisted extrusion process numerical simulation of shape tube dieextrusion was performed by using the POLYFLOW software.(3) Obtaining and analyzing the Physical fields such as velocity field,pressurefield and stress field by numerical simulation, and deeply researched the die swell anddistort. It explains gas-assisted extrusion can eliminate extrusion die swell，reduce thedegree of encapsulation so that improve accuracy and quality of products.(4) Analyzing the influence of different process parameters and materialparameters for all kinds of the several flow fields in the die，studying the influencingrules of these factors, Through the analysis that pointed out the changes of differentparameters have produced different degrees influence on each field in extrusion process.(5) Combined numerical simulation with theoretical simulations, analyzed thechange rules of the geometry of the die and flow fields in the die(such as change thelength of slip, die thickness and cross-sectional area of the die to observe the changeof extrusion pressure, speed and shear stress).Worked out the shapes and sizes ofsection extrusion die, then design the square tube gas-assisted extrusion die.