| Recently, with the continuous development of the plastics industry, the automobile industry, the Aero-Space industry and household appliance industry, large-scale plastics are got more and more extensively attention and application, which put forward higher request for design and manufacturing of large-scale molds and plastics. Large-scale plastic is mainly manufactured by injection molding, the major deflects for a injection-molded part such as automobile bumper with the characteristic of long strip and large curved face are warp, sink mark and weld lines.The self-interference flow(SIF) in the cavity is a beneficial flow status for injection molding, which shares the same principle with dynamic injection molding, that is improving the morphology of the solid state and properties of the plastic by controling the flow staus of the melt in the cavity. Compared with dynamic injection molding, SIF is generated by the construction itself without extra devices.For a complicated engineering problem like the optimization of process parameters of large-scale plastic injection molding, the experiment design method is a kind of scientific, reasonable and valid tool.By Taguchi Methods, quality indexes of injection-molded plastics can be optimumed, and optimal experiment factor levels and optimal experiment conditions can be given with the least times experiment, furthermore the most important experiment factor can be determined.The thesis is concerned mainly on the project of "The digitized manufacture of car's large precise complex injection mold", which is a key industries project of the Guangdong province.SIF and Taguchi Methods are introduced to solve injection molding deflects of Automobile bumper.In our research, based on our research results of SIF, a kind of new pouring model is designed and created for the injection molding of bumper. As a result of that, the flow status of melt in the cavity is changed and the property of the part is improved. Then, injection molding process parameters are further optimumed by Taguchi Methods, and a set of optimal process parameters is obtained.This paper mainly includes contents as follows:1. To analyze and research the specific law of SIF by CAE simulation, analyze melding mechanism and interference mechanism of two steams of melt of SIF, and analyze factors of formation and influence of weld lines when two steams of melt from self-interference gate meld together, then draw a conclution.2. By analyzing CAE simulation results, compare and induce the influence of CFP pouring mode and SIF pouring model on quality indexes of injection-molded parts, to verify the influence by injection molding these two kinds of sample and testing their mechanical properties.3. Introducing SIF into the injection molding of complex large-scale thin plastic, changing gate form and structure, improving flow status of melt and the morphology of the solid state, improving product quality.4. With the aid of Taguchi Methods, setting process parameters combined with actual production condition to obtain optimumed molding process by CAE simulation, then confirming the results by CAE.The CAE simulation results show whether weld lines form when two steams of melt of SIF meld together depends on the distance between the two small gate, and has nothing to do with gate size, injection speed, material property, gate shape and gate location on the wall surface. SIF can effectively improve mechanical properties of plastics, the tensile strength raise 10% in the direction vertical to pouring direction. Compared with CFP samples, the impact strength of SIF samples are obviously improved, the impact strength in some regions is promoted to more than 100%. The optimal combination of process parameters is found by Taguchi Methods.By confirmation experiments of CAE(Moldflow) simulation, the usefulness and credibility of Taguchi Methods was confirmed. |
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