Research On Numerical Simulation And Parameter Optimization On Plasticizing Process Of Injection Molding Screw

Injection molding is a principal method of plastic processing, which occupies an important position in the production of plastic products. With the progress of modern science and technology, and the widely use of composites materials in all fields, peoples’ requirements on plastic products are increasing continuously. As an important stage of injection molding, plasticizing process directly affects the quality of the products, production efficiency and energy consumption level, and its performance depends on whether the design of screw structure or the choosing of molding process conditions is reasonable. Therefore, research on the mechanism and influence factors of plasticizing process, improvement of the evaluation system of the screw plasticizing performance, optimization design of screw structure and process parameters, become the research direction of injection molding technology. The dissertation mainly studied the theories and methods of performance evaluation, numerical simulation and structure parameters optimization design of the melt conveying process in plasticizing process. The organizational structure of the paper is as follows:In the first chapter, the composition, technological process and main parts of the injection molding system were summarized. The research status of theory, experiment, numerical simulation and optimization design on plasticizing process were reviewed, especially in the process of melt conveying. Aiming at the deficiencies of the existing theory and methods, the research purpose and main contents of the dissertation were presented.In the second chapter, evaluation criteria on the plasticizing performance of the injection screw were analyzed. The basic effects of process parameters and screw structure on plasticizing performance and their reference settings were summarized. What’s more, performance evaluation criteria of the screw was put forward, including the increase of plasticizing production and decrease of energy consumption under the precondition of guaranteed plasticizing quality and measurement accuracy.In the third chapter, a rectangular screw groove physical model and Newtonian fluid assumption were established considering the situation of force and movement of polymer melt flow in the screw groove. According to the control equations and constitutive equation of melt flow, a mathematical model was derived to describe the flow and heat transfer characteristics of isothermal Newtonian fluid in the process of melt conveying, including the velocity, pressure, flow rate, energy consumption and etc.In the fourth chapter, by the finite element software FLUENT, the flow and heat transfer characteristics of polymer melt in the screw groove of metering region were simulated and analyzed when processing the material of low density polyethylene(LDPE), using three dimensional non-isothermal non-Newtonian fluid as the analyze model and the derived flow rate functions as velocity boundary. The accuracy of the simulation method was verified by comparing with theoretical model. The difference of injection screw and extrusion screw with the same structure was compared in the process of melt conveying by changing four kinds of different process conditions. It was approved that the influence of the reverse speed of screw on plasticizing process was not ignorable. And the influence of screw speed and backpressure on plasticizing performance was analyzed.In the fifth chapter, by combining the numerical simulation of injection molding with experimental design, orthogonal experimental design for four structure parameters was achieved, including screw pitch, length of metering region, depth of metering region and width of screw arris. According to the range analysis of simulation results, the influence rule and degree of screw structure parameters on melt conveying was analyzed considering the evaluation criteria of plasticizing capacity, energy consumption of per unit weight, ability to build pressure and etc. The optimal structure parameters combination was obtained and its applicability was verified by stress analysis.In the sixth chapter, the main contents and achievements in this work were summarized, and an outlook of the further research was presented.