• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.02a
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• pp.76-83
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• 2002

The injection molding of the plastic optics is basically same as the conventional molding except it requires very intricate control of all the molding processing parameters. In the plastic optics, the problem of injection molding is the shrinkage. The shrinkage must be removed and predicted. This shrinkage is becoming more important than any other problems in precision molding because it can affect the focal length of a lens or the total performance of the optical system. This study focused on avoiding the shrinkage that the mold design allows for the optics. In making mold, the surface accuracy(P-V) of the lower and lower mold are $0.201{\mu}m\;and\;0.434{\mu}m$ respectively. A surface roughness(Ra) is below $0.02{\mu}m$ due to selecting the appropriate tools and using the injection molding machine in high degree. In injection molding of the plastic lens, mold temperature, resine temperature and injecting pressure are important process parameters. Injection molding process is carried out according to varying mold temperature and injecting pressure. As a result P-V(peak to valley) of spheric lens is $3.478{\mu}m$ and that of aspheric lens is $1.786{\mu}m$.

• Design & Manufacturing
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• v.6 no.1
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• pp.90-94
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• 2012

Recently, injection molding process became more popular than ever to produce large quantities of high precision products. Extensive studies have been conducted for reducing the residual stresses and birefringence in injection-molded optical products. Flow-induced and thermally-induced stresses and birefringence have been found as two main sources during injection molding process. Generally, quantitative value of birefringence can be measured with polarizing microscope using the compensator. However, it is difficult to measure low order retardation with microscope, so developing a measurement system for low order optical path difference is in need. In the present paper, a system using Photo Elastic Modulator (PEM) is demonstrated to measure low phase retardation in injection-molded products.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.8
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• pp.164-173
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• 2001

The configuration of injection molded part can be classified into primary feature and supplementary feature. Even though supplementary features such as ribs, snap fits and bosses make mold more complicated, which cause the increasement of the mold cost, supplementary features should be attached to primary features because of assembly, reinforcement, moldability and other functional purposes. But it is not easy for novice designers to design them appropriately because of the profound knowledge related to Injection molding. In this paper, the intelligent design tool called ISFD(Intelligent Supplementary Feature Designer) which supplies easy, simple, time and cost-effective design method has been studied and developed. A knowledge-based design system is a new tool which enables the concurrent design and CIM with integrated and balanced design decisions at the initial design stage of injection molding.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.543-548
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• 1994

This is the paper on the development of assemnly automation and visual inspection system for smart card reader connector. The automation consists of 3 main process injection, assembly and inspection. During the injection, the main pin of a reel. transferred under uniform tension, is cut with an injection interval and positioned precisely to an injection mold by roll feeder after injection. The main base is stacked to a magazine for main pin's exact positionning to a mold . For last effective production, The turn table and pick & place are driver with gears and came by a single monter. We developed the small parts handling technigue for stable supply of micro ist pin and 2nd pin and could determine the orientation and position of those pins. For reliable inspection, We used the vision system which examins the guality of arranged pins with a CCD camera. The connector models which can be manufactured with this system are 8 pin and 10 pin type. The user can select the connector model for production and adjust the torerable error range during the inspection of arranged pins.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.7
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• pp.111-115
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• 2008

This paper describes the optimization of injection molding conditions to minimize sink marks. Sink marks, which refer to a small depression on the surface opposite a thick wall thickness, are often encounted in injection molded plastic parts. Part geometry, material properties and processing conditions during injection molding can affect the sink mark depth. 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. By actual injection molding using optimized mold and molding conditions, it confirmed that sink mark depth decreased zero compared to 1mm level in the conventional mold and process.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.74-77
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• 2009

Demands for high quality and productivity of precision mechanical parts are increasing greatly nowadays due to the rapid growth of information technologies and convergence industries. Therefore, core technologies for fabrication of precision mechanical parts are the fundamental issues, which are the precision machining, micro powder injection molding technologies, MR polishing, micro polymer processes, micro actuation modules and so on. These technologies are directly related to the mass production of high functional devices and machineries. Therefore, this study investigates the fabrication technologies of micro precision molds for advanced devices for possible commercialization in a near future.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.4
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• pp.118-127
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• 2003

An effective tool management system is one of the keys to maximizing the benefits of a computer integrated manufacturing (CIM). Tool management systems, however, are often tailored to the requirement of a highly automated system. Therefore, a different approach is needed for small and medium sized mold shops. This work deals with the implementation of tool management system for milling operations in small and medium sized CIM environment of injection mold production. In this paper, a distributed management approach is proposed for efficient tool management in relatively small machining shops in mold industry. And the design and the functions of the developed system are described.

• 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.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.457-460
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• 2000

Injection molding is the most widely used process for the industrial forming of plastic articles. During an injection molding process of composites, the fiber-matrix separation and fiber orientation are caused by the flow of molten polymer/fiber mixture. As a result, the product tends to be nonhomogeneous and anisotropic. Hence, it is very important to clarify the relations between separation·orientation and infection molding conditions. So far, there is no research on the measurement of fiber orientation using image processing. In this study, the effects of fiber content ratio and molding condition on the fiber orientation-angle distributions are studied experimentally. Using the image processing method, the fiber orientation distribution of welding parts in injection-molded products is assessed. And the effects of fiber content and injection mold shapes on the fiber orientation in case of fiber reinforced polymeric composites are studied. experimentally.

• Korea-Australia Rheology Journal
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• v.19 no.3
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• pp.171-176
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• 2007

LCD-BLU (Liquid Crystal Display-Back Light Unit) of medium size is usually manufactured by forming numerous dots with $50{\sim}300\;{\mu}m$ in diameter by etching process and V-grove shape with $50\;{\mu}m$ in height by mechanical cutting process. However, the surface of the etched dots is very rough due to the characteristics of the etching process and V-cutting needs rather high cost. Instead of existing optical pattern made by etching and mechanical cutting, 3-dimensional continuous micro-lens of $200\;{\mu}m$ in diameter was applied in the present study. The continuous micro-lens pattern fabricated by modified LIGA with thermal reflow process was tested to this new optical design of LGP. The manufacturing process using LIGA-reflow is made up of three stages as follows: (i) the stage of lithography, (ii) the stage of thermal reflow process and (iii) the stage of electroplating. The continuous micro-lens patterned LGP was fabricated with injection molding and its test results showed the possibility of commercial use in the future.