| Plastic products have been widely used in our daily life and the improvement andoptimization of injection molds have been continually promoted. As the demand for plasticparts of high strength, high quality and low cost is growing, people also require the injectionmold which has higher fatigue life and higher cooling efficiency. The production efficiencyand production costs of plastic parts are determined by injection mold fatigue life. How todesign an injection mold with reasonable structure and take into account both design life andthe improvement of cooling efficiency are urgent problems of mold industry. According to thefracture phenomenon of PET(Polyethylene terephthalate) preform mold cavity in injectionmolding process, the research contents are as follows,(1) First of all, the fracture type and failure mechanism of mold cavity were analyzed, whichwas based on plastic molding process characteristics and fractography theory. Atheoretical foundation for the fatigue analysis and structural optimization has been laid;(2) Heat exchange, thermal distortion and thermal stress of mold cavity were analyzed,which was based on heat transfer theory and mechanics of materials. The heat transfercoefficients of cooling water was calculated and provided as essential data for finiteelement analysis. S-N curve was numerically simulated based on theory of fatiguestrength, which provided material data for fatigue analysis;(3) Combined with the actual production of PET preform mold cavity, the three-dimensionalheat conduction, thermal stress and fatigue life analysis were conducted. The analyticalresults and the actual life were compared to verify the feasibility of the finite elementmethod and provide an analysis method for optimizing the mold cavity structure;(4) An optimization design of mold cavity based on fracture reason was carried through anda fatigue life simulation was analyzed by finite element analysis software. At the sametime, optimized injection mold cooling channels in order to improve the coolingefficiency;(5) Established the three-dimensional model of preform, injection system, as well as thecooling system based on Moldflow. The runner balancing analysis and cooling analysiswere conducted, which obtained the optimization structure of mold cavity;(6) Studied the factors affecting the fatigue life of the mold cavity and proposed severalmethods to improve the fatigue life of injection mold.According to analysis above, optimization design of mold cavity and cooling channels arrangement have been carried out, aiming at longer fatigue life and better cooling efficiency.The analysis and optimization results have been validated and achieved good results. |
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