| In injection molding, weldlines form because of the presence of holes, inserts and multiple gates and an abrupt change in geometry that divide the polymer melt during flow in the mold and then the melt meet again. Despite weldlines form in filling, its construction, shape and property is related to injection processing. The weldlines can not only influence appearance of parts, but also markedly influence mechanics. At present, most researchers mainly take into account that processing conditions in molding have influence on weldlines and performance of parts, however, few researcher investigates flow morphology of melt. Mainly work of this dissertation is to study different geometry of mold cavity and processing conditions that have influence on performance of weldlines by numerical simulation method and experiment. The details of the dissertation are as followings:(1) We design diffom inserts, for instance, circle, square and diamond that form different weldlines based on analyzing weldlines formation mechanism, and then the forming process of weldlines in molding is studied by numerical simulation. Results indicate that the processes of meeting somewhat like two melt fronts directly impinge. Reunited melt almost can't move, the orientation that is induced by the fountain flow is unable to relax.(2) There is a hole behind inserts that have more complex shape when meeting of melt again, and then reunited melt can move slowly. That will help molecule at weldlines area to cross interface and relax, which can greatly increase the strength of weldlines.(3) The material we used is Low-Density Polyethylenecrystal (LDPE) that belongs to crystal polymer. We use Taguchi DOE to design experiment of processing parameters (Melt injection pressure/Melt temperature/Packing pressure/Mold temperature/Melt injection speed), and find out which processing parameters have more influence on the strength of weldlines for plastics injection molding. At last we make use of Signal-to-Noise (S/N) to...
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