• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.363-370
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• 2003

Shrinkage of injection molded parts is different form operational conditions of injection molding such as injection temperature, injection pressure and mold temperature, and mold design such as gate size. It is also various for different resins which have crystalline structure or not. In this study part shrinkage was investigated for various operational condition and resins; PBT for crystalline polymer, and PC and PMMA for amorphous polymer was used in experiment. Crystalline polymer shows higher part shrinkage by about three times than amorphous polymer. Part shrinkage increased as injection temperature and mold temperature increased and injection pressure decreased. Part shrinkage decreased as gate size increased since the pressure delivery is mush easier for large gate size. Part shrinkage according to the gate location was that the position in the part with close to the gate showed large shrinkage and this phenomenon might be occurred by residual stress.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.58-64
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• 2004

The shrinkages of injection molded parts are different in molding operational conditions, resins and additives. The shrinkage of injection molded part for crystalline polymer, PBT (polybutylene terephthalate) has been studied for various operational conditions of injection molding and content of additives. Mica was used as a additive to PBT to examine the part shrinkage according to the mica content. The part shrinkages of mica contained PBT decreased as mica content increases. Higher injection temperature and injection pressure resulted in a lower shrinkage. As mold temperature increases the part shrinkage decreased. The part shrinkage of flow direction was less than that of the perpendicular direction to the flow for both pure and mica contained PBT. However the shrinkage difference between flow and perpendicular to flow directions decreased as mica content increased.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.159-165
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• 2004

The shrinkages of injection molded parts are different in molding operational conditions and mold design. It also differs from resins. The shrinkages of injection molded parts for PBT (polybutylene terephthalate), PC (polycarbonate),and glass reinforced PBT and PC have been studied for various operational conditions of injection molding. The part shrinkage of crystalline polymer, PBT was higher than that of amorphous polymer, PC by about two times. The part shrinkages of both polymers decreased as glass fiber content increases. Higher Injection temperature and lower injection pressure resulted in a higher shrinkage in both PBT and PC resins. As mold temperature increases the part shrinkage of PC decreased. However, the part shrinkage of PBT increased as mold temperature increases. The part shrinkage of both PBT and PC resins decreased as gate size increases since the pressure delivery is mush easier for a larger gate size. The part shrinkage of flow direction was less than that of the perpendicular direction to the flow for both pure and glass fiber reinforced resins. The part shrinkage at the position close to the gate was less than that of the position far from the gate.

• Transactions of Materials Processing
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• v.13 no.6 s.70
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• pp.515-521
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• 2004

The shrinkages of injection molded parts are different in molding operational conditions and mold design. It also differs from resins. The shrinkages of injection molded parts fur PBT (polybutylene terephthalate), PC (polycarbonate), and glass reinforced PBT and PC have been studied for various operational conditions of injection molding. The part shrinkage of crystalline polymer, PBT was higher than that of amorphous polymer, PC by about two times. The part shrinkages of both polymers decreased as glass fiber content increases. Higher injection temperature and lower injection pressure resulted in a higher shrinkage in both PBT and PC resins. As mold temperature increases the part shrinkage of PC decreased. However, the part shrinkage of PBT increased as mold temperature increases. The part shrinkages of PBT and PC resins decreased as gate size increases since the pressure delivery is mush easier for a larger gate size. The part shrinkage of flow direction was less than that of the perpendicular direction to the flow for both pure and glass fiber reinforced resins. The part shrinkage at the position close to the gate was less than that of the position far from the gate.

• Elastomers and Composites
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• v.48 no.4
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• pp.300-305
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• 2013

Part shrinkage in injection molding is inevitable phenomenon. Thus, it is necessary not only study on the reducing part shrinkage but characterization of part shrinkage. In this study, part shrinkage in injection molded 2.5 dimensional annular shaped specimens has been studied using glass fiber reinforced PC. Annular shaped specimens were designed with various sizes of outer diameter and thickness. Injection temperature, packing time and packing pressure were selected for operational conditions. Profile variations of outer and inner diameters of molded specimens for various operational conditions were investigated. Sizes of outer and inner diameters of injection molded specimens were smaller than the sizes of mold. Part shrinkage decreased as outer diameter and thickness increased. Part shrinkage showed anisotropic behavior and it depended upon gate location. Subsequently, molded specimens were not circular but oval in shape, and showed the largest shrinkage in the direction of gate. It was realized that the mold design such as gate design is important to control the shape of molded products.

• Elastomers and Composites
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• v.38 no.4
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• pp.295-302
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• 2003

The amount of shrinkage of injection molded parts is different from operational conditions of injection molding such as injection temperature, injection pressure and mold temperature, and mold design such as gate size. It also varies depending on the presence of crystalline structure in resins. In this study, part shrinkage was investigated for various operational conditions and resins. Poly(butylene terephthalate) (PBT) for crystalline polymer, and polycarbonate (PC) and poly(methyl methacrylate) (PMMA) for amorphous polymers were used. Crystall me polymer showed higher part shrinkage by about three times than that of amorphous polymers. Part shrinkage increased as melt and molt temperatures increased, and injection pressure decreased. Part shrinkage decreased as gate size increased since the pressure delivery is mush easier for larger gate sizes. Part shrinkage at the position close to the gate was larger than that or the position far from gate. This phenomenon might be occur by difference of residual stress.

• Elastomers and Composites
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• v.50 no.3
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• pp.184-188
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• 2015

There is a need for light weight and high stiffness characteristics in the building structure as well as aircraft and cars. So fiber reinforced plastic with the addition of reinforcing agent such as glass fiber, carbon fiber, aramid fiber is utilized in this regard. In this study, mechanical strength, flow property and part shrinkage of glass fiber and carbon fiber reinforced PA6 were examined according to reinforcement content such as 10%, 20%, and 30%, and reinforcement type. The mechanical property was measured by a tensile test with specimen fabricated by injection molding and the flow property was measured by spiral test. In addition, we measured the part shrinkage of fiber reinforced PA6 that affects part quality. As glass fiber content increases, mechanical property increased by 75.4 to 182%, and flow property decreased by 18.9 to 39.5%. And part shrinkage decreased by 52.9 to 60.8% in the flow direction, and decreased by 48.2 to 58.1% in the perpendicular to the flow direction. As carbon fiber content increases, mechanical property increased by 180 to 276%, flow property decreased by 26.8 to 42.8%, and part shrinkage decreased by 65.0 to 71.8% and 69.5 to 72.7% in the flow direction and the direction perpendicular to the flow respectively.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.308-311
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• 2004

Nowadays, plastic industry has needed to produce parts that require high precision and quality. To make a high precision and quality part, before injection molding, plastic material is investigated about their properties such as shrinkage, warpage, etc. In this study, experiments were conducted with PA6(polyamid) to figure out shrinkage behavior according to three type aspect ratio of samples. The injection speed that affects on shear rate, molecular orientation within plastic part was determined as main variable of experiment. As a result of experimental study, part shrinkage had a tendency to be decreased by increasing injection speed and aspect ratio of samples.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.11 s.176
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• pp.210-217
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• 2005

A curl distortion induced by shrinkage during stereolithography polymerization process is analyzed with the classical lamination theory. Test parts of different layer thickness and part thickness are manufactured and their deformations are measured with CMM. Curl distortion is generated by the differential shrinkage of the layers, where the total shrinkage includes the shrinkages due to solidification and the change of temperature. It is shown that the curl distortion increases exponentially with decreasing the total thickness of the part, whose smaller layer thickness induces larger curl distortion. It is verified that only a part of the total shrinkage plays a role in generating the curl distortion.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.3 no.3
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• pp.46-51
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• 2004

Nowadays, plastic industry has needed to produce parts that require high precision and quality. To make a high precision and quality part, before injection molding, plastic material in investigated about their properties such as shrinkage, warpage, etc. In this study, experiments were conducted with PP(polypiopylene) to figure out shrinkage behavior according to three type aspect ratio of samples. The injection speed that affects on shear late, molecular orientation within plastic part was determined as main variable of experiment. As a result of experimental study, part shrinkage had a tendency to be decreased by increasing injection speed and aspect ratio of samples.