Preliminary Evaluation on the Influence of Gas Counter Pressure on the Process Flow Characteristics, Molecular Orientation and Qualities of Injection Molded Parts.
| Autor: | Sung-Wei Huang, 黃松煒 |
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| Rok vydání: | 2012 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 Although injection molding is the most cost-effective way for the production of plastic components for industrial needs, it is subjected to restriction in process characteristics. So as the other innovation process including gas-assisted injection, microcellular foam injection, co-injection, etc.. When hot melt flows within the narrow gap of mold cavity, it induces highly orientated polymer molecular chain. Moreover, due to the fountain flow effect,hot melt is brought to the mold surface and become frozen resulting in the flow-induced residual stress. Both factors contribute to the warpage formation significantly and make the high accurate dimension not easily achieved. In this study, the various polymer material (PP, PS), and product thickness(0.6mm, 1.2mm), and flow rate (5, 10, 15, 20, 30 cm3/s) were discovered with the developed technology of gas counter pressure (GCP). The conventional and GCP molding were be performed to investigate the associated influence on part shrinkage, mechanical property, crystallinity and the shape of melt front cross-section. Finally, the gas-assisted molding of filling characteristics was conducted through the visualization method, transparent mold and high speed camera. As from the results, the GCP had two effects in conventional injection molding (CIM). One is the restriction of molecular orientation, and the other is counter holding effect. In the results of shrinkage, the experimental and simulated both showed the shrinkage would be reduced under GCP of condition. In the experimental results, the average reducing ratio were from 0.0293% to 0.1188% in paralleled flow direction, 0.0173% to 0.0668% in perpendicular flow direction. In the results of elastic module, the degree would be enhanced with GCP of condition, and the average increasing ratios were from 0.1529% to 0.9617%. In the results of tensile strength, due to the holding effect of GCP, the average increasing ratios of PP resin were 0.1937% (0.6mm) and 4.6014%(1.2mm) respectively. The average decreasing ratios of PS resin was 1.8994%,because of the restricted molecular orientation. In the results of crystallinity, the average decreasing ratios were 1.987% (0.6mm) and 2.560% (1.2mm)respectively. From the results of SEM diagram, the profile of melt-front would be obviously flatted with GCP. In the visualized molding case, the penetration of gas-assisted injection molding (GAIM) would directly affect by GCP. The conventional GAIM results of penetrated length and area were respective 2.44 and 2.28 times, than GAIM combined with GCP. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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