• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.200-203
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• 2001

Micromolding methods such as micro-injection molding and micro-compression molding are most suitable for mass production of plastic micro-optics with low cost. In this study, plastic micro-optical components, such as refractive microlenses and diffractive optical elements(DOEs) with various grating patterns, were fabricated using micro-compression molding process. The mold inserts were made by ultrapricision mechanical machining and silicon etching. A micro compression molding system was designed and developed. Polymer powders were used as molded materials. Various defects found during molding were analyzed and the process was optimized experimentally by controlling the governing process parameters such as histories of mold temperature and compression pressure. Mim lenses of hemispherical shape with $250{\mu}m$ diameter were fabricated. The blazed and 4 stepped DOEs with $24{\mu}m$ pitch and $5{\mu}m$ depth were also fabricated. Optical and geometrical properties of plastic molded parts were tested by interferometric technique.

• Transactions of Materials Processing
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• v.21 no.1
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• pp.36-41
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• 2012

Gas Assisted Injection Molding is a relatively new low-pressure injection molding technique that provides benefits such as reduced part warpage, excellent surface quality without shrink marks, greater design flexibility, etc. In the gas assisted injection molding process, the injected pressurized nitrogen gas flows through designed gas channels and forms hollow sections within the part. However, due to the characteristics of the gas, the design of the gas channels which are the paths for the injected gas is important in order to avoid defects such as gas blowout, fingering, etc. Therefore, in this study, the gas channel design for gas assisted injection molding of exterior display panels was conducted by examining the results of three CAE analyses. The designed gas channel was verified by conducting tryouts using a 450 ton injection molding machine with 3-stage pressure controlled gas kit. In addition, the hollow shapes which were formed by the gas with the installed gas channels were examined by examining the cross sections of the prototypes that were produced. As a result, it was found that exterior display panels can be produced without any defect by applying the gas assisted injection molding technique.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.2
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• pp.67-74
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• 2009

Injection molding have been used for manufacturing various fields of automotive interior trims for years. The demands on the injection molding technique are grown with the further development of the automobile technique and the design presentations for cost reduction and environment-friendly. This paper shows that multi-component injection conditions are different from general injection, also shows how to optimize part design and mold design and how to manufacturing through the efficient use of multi-component injection in development process using core back system. To fulfill this purpose, all influential process parameters related to the quality of automobile parts were analyzed in terms of the correlation between them. Base on that, a innovative process will be developed by injection engineers to implement it in practice.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.37-42
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• 2007

We present a powder injection molding technique of fabricating cemented tungsten carbide(WC) balls for milling and dispersing nano-powder in this paper. The conventional powder metallurgy approach is investigated to reveal its drawbacks of density non-homogeneity. New procedures of powder injection molding for the homogeneous high-precision WC balls, involving the binding process, powder injection molding process and sintering process, are presented in detail. Each process is investigated empirically and numerically to obtain its engineering information, which can used for process optimization.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.04a
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• pp.269-274
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• 2001

This research covers the development of new technique for composite injection molding of high stiffness Sabot. An analysis of polymer resin is performed by means of making test specimen mold and doing test with accordance of ASTM test guidelines. Structural analysis and simulation of injection molding process are carried out in order not only to estimate but also to predict the characteristics of molding stresses what both product and structure of mold may have. For structural analysis software, Moldflow and LS-dyna are used and universal test machine is utilized for evaluating performance of sabot. Cases of adopting this material to sabot are not announced yet in domestic academic world. In addition to that, materials for polymer-metal mixed injection molding are imported on the whole due to deficient level of domestic technology. Therefore, this new developed injection molding technique using PEI material can make it available to ensure the technology of making mold, injection and design. Finally, this technique may be applicable to another sabot having different radius of warheads from now on.

• Transactions of Materials Processing
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• v.4 no.3
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• pp.204-213
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• 1995

A finite element program is developed to analyze the flow phenomena in SMC compression molding as a viscoplastic model. The calculation of temperature distribution is also carried out by uncoupling the thermal analysis from the flow analysis. SMC molding processes with a flat plate substructure and the one with a T-shaped rib are considered in numerical simulation. The numerical results provide deformed shapes, temperature distribution in a SMC charge, and the forming load. The simulation of compression molding of a flat plate with a T-shaped rib requires a remeshing technique for the whole process.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.4
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• pp.50-55
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• 2014

Currently, flat cover glasses are widely applied to mobile devices. However, for a good design and for convenience of use, curved cover glasses are in demand. Thus, many companies are attempting to produce curved cover glasses using a shaving technique, but the production efficiency is very low. Therefore, a molding technique has been adopted to increase the efficiency of curved glass production systems. For a glass molding system, a uniform temperature distribution of the mold is crucial to produce high-quality curved cover glasses. Before setting the heating conditions of the molding system for a uniform temperature distribution by a thermal analysis, verification is required. Therefore, in this study, temperature measurements were conducted for a prototype molding system and the experimental results were compared with simulation computations. The temperatures of the heating block surface were in good agreement with the computational results for transient and steady conditions.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.444-447
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• 2008

Recently, the need of thin-walled injection molding and enhancement of its productivity is greatly increased. In this study, we designed and manufactured a injection molding system, which can mold a part with the thickness of $500{\mu}m$ and 8 cavity. And processing technique for the multi-cavity injection molding system, which is capable of mass productivity on the plastic parts, was considered. The problems of unbalance/imbalance on the molding process for the multi-cavity mold were predicted by numerical analysis using plastic injection molding commercial code. In addition, controllable system of melt front filling was introduced for a balanced filling using the mold temperature sensor on injection mold. It was shown that balanced filling with the suggested injection molding system was possible for $500{\mu}m$ plastic parts with 8 cavity layout.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.766-771
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• 2001

Gas-assisted injection molding is an innovative low-pressure injection molding technique that can provide numerous benefits such as reduced part warpage, excellent surface quality without sink marks, low injection pressure, and greater design flexibility. However, the adoption of gas-assisted injection molding may cause unexpected defects if the gas channel design is not conducted properly. The objective of this paper is to broaden the understanding of gas-assisted injection molding by summarizing the design procedures and experimental results of the gas-assisted injection molding of a 17" flat monitor front cover. The gas channels were designed by using Moldflow(MF/GAS) simulations and a 450 ton injection molding machine with a 5 stage pressure control gas kit was used in the experiments.

• Design & Manufacturing
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• v.1 no.1
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• pp.17-21
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• 2007

In the manufacture and processing of large plastic materials, product quality is tested and verified through several techniques such as injection processing, residual stress through injection molding and shrinkage. With regards to the injection molding process, common problems such as inconsistent density is seen when different points of the product are discovered to have varying thickness levels. Sink marks in product are then evident. This occurs when there is poor molding conditions caused about by poor runner and packaging systems incorporated into the process. We designed the runner system which is possible balanced filling to cavities using CAE program $Moldflow^{TM}$ and then obtained optimal processing conditions by Taguchi's Robust Design technique.