• Elastomers and Composites
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• 제47권4호
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• pp.341-346
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• 2012

사출성형은 고분자성형법 중에서 가장 광범위하게 활용되고 있다. 사출성형은 전형적인 사출성형 외에 가스사출, 물사출, 그리고 사출압축성형 등과 같이 특수한 사출성형방법들이 쓰인다. 사출압축성형은 사출과 압축공정이 합쳐진 것으로 균일한 물성 및 성형의 정밀도를 향상시키기 위하여 사용된다. 또한 사출압축은 잔류응력을 줄이는데도 효과적으로 사용되고 있다. 본 연구에서는 성형품의 형상에 따라 다양하게 나타나는 사출압축성형의 특성에 대해서 컴퓨터 해석을 통해 분석하였다. 성형품에 벽이 있는 제품은 벽의 두께가 압축의 방향과 직각이므로 압축효과가 작게 나타났다. 사출압축성형을 일반사출성형과 비교하였을 때 수축의 균일성 및 수축량 또는 성형수축률이 작게 나타나서 정밀성형에 유리하게 나타났다. 실험계획법을 통해 실제로 제작되고 있는 렌즈에 대해서 최적 사출압축조건을 구하고 이의 결과를 사출성형의 결과와 비교분석하였다.

• 동력기계공학회지
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• 제9권4호
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• pp.83-89
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• 2005

Molding shrinkage is one of the problems to be solved in conventional injection molding. Despite many trying-out has been to solve it, intrinsic cause of shrinkage such as orientation and thermal exchange between melt and mold has not been solved yet. For reducing shrinkage and residual stress on molding, injection compression molding process was invented. In this study, experiments about effects of injection compression molding's parameters on shrinkage of PMMA molding were conducted and compared with conventional injection molding's shrinkage. Before the injection compression molding experiment, molding shrinkage rate was predicted by analyzing pvT diagram and was compared with the results of experiment. The shrinkage rate of injection compression molding was lower than convention injection molding's one which was different from the predicted shrinkage. The reason was observed that the experimental mold was not a proper type for injection compression, flowing backward of melt into nozzle and unreasonable mechanism of injection molding machine.

• Journal of Mechanical Science and Technology
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• 제18권8호
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• pp.1451-1460
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• 2004

A two-stroke Schnurle-type gasoline engine was modified to enable compression-ignition in both the port fuel injection and the in-cylinder direct injection. Using the engine, examinations of compression-ignition operation and engine performance tests were carried out. The amount of the residual gas and the in-cylinder mixture conditions were controlled by varying the valve angle rate of the exhaust valve (VAR) and the injection timing for direct injection conditions. It was found that the direct injection system is superior to the port injection system in terms of exhaust gas emissions and thermal efficiency, and that almost the same operational region of compression-ignition at medium speeds and loads was attained. Some interesting combustion characteristics, such as a shorter combustion period in higher engine speed conditions, and factors for the onset of compression-ignition were also examined.

• 소성∙가공
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• 제13권2호
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• pp.180-187
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• 2004

A computer code was developed to simulate the filling stage of the injection/compression molding process by a finite element method. The constitutive equation used here was the compressible Leonov model. The PVT relationship was assumed to follow the Tait equation. The flow-induced birefringence was related to the calculated flow stresses through the linear stress-optical law. Simulations of a disk part under different process conditions including the variation of compression stroke and compression speed were carried out to understand their effects on birefringence variation. The simulated results were also compared with those by conventional injection molding.

• Advanced Composite Materials
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• 제16권3호
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• pp.207-221
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• 2007

The filling process of resin injection/compression molding (I/CM) can be divided into injection and compression phases. During the resin injection the mold is kept only partially closed and thus a gap is present between the reinforcements and the upper mold. The gap results in preferential flow path. After the gap is filled with the resin, the compression action initiates and forces the resin to penetrate into the fiber preform. In the present study, the resin flow in the gap is simplified by using the Stokes approximation, while Darcy's law is used to calculate the flow field in the fiber mats. Results show that most of the injected resins enter into the gap during the injection phase. The resin injection time is extremely short so the duration of the filling process is determined by the final closing action of the mold cavity. Compared with resin transfer molding (RTM), I/CM process can reduce the mold filling time or injection pressure significantly.

• 소성∙가공
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• 제19권5호
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• pp.296-304
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• 2010

It is still needed to study the effect of process conditions on the final properties of injection-molded parts for producing precision optical products. Especially, the optical anisotropy, i.e., birefringence, is a significant factor to affect the function of many optical components. In the present study we have focused on the effect of holding and compression processes on the birefringence remaining in the transparent disc by examining the gap-wise distribution of birefringence and extinction angle. As a result, two extra birefringence and extinction peaks near the center in thickness direction showed the effect of holding pressure, which came from the flow in packing stage. However, more uniform birefringence distribution than injection-only cases could be found in injection/compression cases. Depends on the process condition even the flow reversal could be found from the distribution of extinction angle. Finally, graphical representation of optical indicatrix was added for better understanding the final structure of injection-only and injection/compression cases.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.589-592
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• 2005

Molding shrinkage s variation is one of the problems to be solved in conventional injection molding. Despite many trying-out has been to solve these, intrinsic causes of shrinkage such as orientation and thermal exchange between melt and mold has yet not solved. For reducing shrinkage and residual stress on molding, injection compression molding process was invented. In this study, experiments about effect of injection compression molding's parameters on shrinkage of molding were conducted with PMMA and compared with conventional injection molding's shrinkage. Before the injection compression molding experiment, molding shrinkage rate was predicted by analyzing pvT graph and was compared with the results of experiment. The shrinkage rate of injection compression molding was lower than convention injection molding' one but was different from the predicted shrinkage. The reason was observed that experiment mold as not positive type, flowing backward of melt into nozzle and unreasonable mechanism of injection molding machine.

• 소성∙가공
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• 제22권1호
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• pp.48-53
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• 2013

As the adoption of injection molding technology increases, injected-molded optical products require higher dimensional accuracy and optical stability than ever before. In the present study, four kinds of molding methods, i.e., conventional injection molding (CIM), injection/compression molding (ICM), rapid heat and cooling the mold(RHCM) and rapid injection/compression molding (RICM) were selected in order to investigate the optical anisotropy of a 7 inch Light Guide Plate(LGP) by examining the gap-wise distribution of birefringence and the extinction angle. The results indicate that the compression process can decrease flow-induced birefringence over the whole region and that rapid heating can decrease the birefringence level better than conventional molding. In addition, for the combination of compression and rapid heating a reversal flow was detected from the distribution of the extinction angle near the gate.

• 대한기계학회논문집A
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• 제26권11호
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• pp.2355-2363
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• 2002

The accompanying paper, Part 1, has presented the physical modeling and basic numerical analysis results of both the flow-induced and thermally-induced residual stress and birefringence in injection molded center gated disks. The present paper, Part II, has attempted to investigate the effects of various processing conditions of injection/compression molding process on the residual stress and birefringence. The birefringence is significantly affected by injection melt temperature, packing pressure and packing time. Birefringence in the shell layer increases as melt temperature gets lower. The inner peak of birefringence increases with packing time and packing pressure. On the other hand, packing pressure, packing time and mold wall temperature affect the thermally-induced residual stress rather significantly in the shell layer, but insignificantly in the core region. Injection/compression molding has been found to reduce the birefringence in comparison with the conventional injection molding process. In particular, mold closing velocity and initial opening thickness in the compression stage of injection/compression molding process have significant effect on the flow-induced birefringence, but not on tile thermal residual stress and the thermally induced birefringence.

• 한국연소학회:학술대회논문집
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• 한국연소학회 제26회 KOSCO SYMPOSIUM 논문집
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• pp.27-32
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• 2003

Diesel-Fueled HCCI(Homogeneous Charge Compression Ignition) Engine is an advanced combustion process explained as a premixed charge of diesel fuel and air is admitted into the cylinder and compression ignited. It has possibility to reduce NOx by spontaneous auto-ignition at multiple points that allows very lean combustion resulting in low combustion temperatures. Also PM could be reduced by the premixed combustion and no fuel-rich zones. But HCCI couldn't be realized because of the difficulties in vaporizing the diesel, control of combustion phase directly. To solve these problems, new fuel injection strategy, explained as the pilot fuel injection to promote ignition near TDC following the main fuel injection at the extremely advanced timing, is applied during the compression ratio is varied from 18.9:1 to 27.7:1 This is not a pilot fuel to promote the ignition but also the direct control method of the combustion phase. Experimental result shows the pilot fuel injection promote the ignition and the compression ignition of the HCCI engine is achieved as compression ratio becomes higher. Also there is an optimal pilot fuel injection timing for the HCCI combustion. NOx is reduced more than 90% compared to DI-Diesel case but PM and THC emission needs more investigation.