• Polymer(Korea)
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• v.35 no.1
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• pp.1-6
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• 2011

Pressurized high temperature plastic resin flows into the cavity of mold and is solidified in injection molding process. Residual stress is being developed in injection molded part because of high temperature variations and high pressure. Developed residual stress relaxes as time goes. Consequently this makes part deformed and deteriorates quality of product. A measurement method of residual stress for injection molded transparent articles has been investigated using photoelasticity. Light, a composite of electromagnetic waves, is purified into a single wave by a polarized film. When this wave passes through the specimen, birefringence is developed according to the level of residual stress in the specimen and color fringed pattern appears after the second polarized film. Residual stress in the injection molded transparent flat a part has been measured quantitatively using the color fringed pattern. Optical characteristics have been a part also predicted by computer simulation and compared with experimental results.

• Polymer(Korea)
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• v.36 no.2
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• pp.131-136
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• 2012

Residual stress is developed in the injection molded articles during the molding process due to temperature variation and shear stress. The residual stress causes the deformation and warpage in the injection molded parts shortly within several days or after several years. Therefore, the injection molding conditions should be optimized to reduce the residual stress. And residual stress in the part should be also relaxed after molding process to maintain its shape. According to the annealing conditions, such as relative humidity, temperature and time, this study investigates the relaxation of residual stress generated in the transparent injection molded specimens. Through the experimental results, it was realized that the residual stress was relaxed at a relative humidity higher than 50%. Utilizing photoelasticity equipment, it was found that the residual stress was rapidly relaxed near glass transition temperature. Additionally, we recognized that the specimen shrunk along the flow direction but expanded to the perpendicular direction of the flow during the annealing processes, which resulted in the warpage of the specimen.