| Summary: | 碩士 === 淡江大學 === 機械工程學系 === 87 === In this research the mold flow analysis of polymer composites consisting of NYLON 6 filled with 6 mm long Nickel Coated Graphite (NCG) fiber for preventing electromagnetic interference (EMI) is investigated to develop products which prevent EMI by using injection molding process. Initially, the polymer composites extracting technology from the injection screw and metallography analysis method of scanning electron microscope (SEM) is performed to confirm the parameters of injection screw design. Then the visible mold was used for observing polymer composites flow front directly. Several products with EMI shielding effectiveness, including notebook computer housing and ASTM D4935-89 EMI specimen were tested to investigate the influence of mold gating systems and screw speeds on EMI shielding effectiveness of these products. Finally, the MOLDFLOW simulations of fiber filling and orientation were proceeded to compared with the microstructure analysis of fiber orientation to verify the influence of injection parameters on fiber orientation and furthermore, to indicate the difference of simulated results.
From the experimental results, the optical grade screw has better mixing effect than the regular grade screw, but the higher screw speed increases the chance of the breaking fibers. The jetting flow in mold filling is prevented effectively by the compound fan gate design and the higher EMI shielding effectiveness is obtained by using the sprue gate design. Then the EMI shielding effectiveness is reduced with the increasing number of the weld lines on EMI specimens. The trend of the EMI shielding effectiveness of the products using the polymer composites with the NCG long fiber is obviously increased as the EMI test frequency increases. The fiber orientation in the core of the microstructure of the notebook computer housing has wave pattern and transverses to the flow direction. This could be used to explain that the simulated flow front by the MOLDFLOW is matched with experimental results, but the simulated results of fiber orientation is opposite to the experimental results. The EMI shielding effectiveness is influenced by the orthogonal patterns of fiber orientation between the shear zone and core of the microstructures of products. Further study will be focused on the model modification of the simulation software, for example the MOLDFLOW, to consider the influences of the wave pattern and rotating effect caused by the polymer composites with long fibers.
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