• Transactions of Materials Processing
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• v.15 no.1 s.82
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• pp.42-46
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• 2006

For mass production, usually injection mold has multi-cavity which is filled through geometrical balanced runner system. Despite geometrical balanced runner system, filling imbalances between cavity to cavity have always been observed. These filling imbalances are one of the most significant factors to affect quality of plastic parts. Filling imbalances are results from non-symmetrical shear rate distribution within melt when it flows through tile runner system. It has been possible to decrease filling imbalance by optimizing processing conditions, but it has not completely eliminated this phenomenon during injection molding processing. This paper presents a solution for these filling imbalances by using Runner Core pin (RC pin). The Runner Core pin which is developed in this study creates a symmetrical shear distribution within runner. As a result of using Runner Core pin, a remarkable improvement in reducing filling imbalances was confirmed.

• Journal of Korea Foundry Society
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• v.16 no.6
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• pp.513-522
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• 1996

In the present work, we have investigated the strain-induced melt activation (SIMA) process in Al-8%Si and Al-25%Si alloys. Primary dendrites were transformed into spherical microstrctures by mushy zone heat treatments of the cold-worked alloys. Various processing parameters which govern the sphering of the dendrites have been examined. The result showed that semi-solid alloys having a typically nondendritic spherical microstructure can be easily produced by this method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.6 s.249
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• pp.615-621
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• 2006

Increased application of optical disks requires more improved dynamic stability of rotating disks. In this study, a new concept of controlling the processing conditions of injection molded disks was developed to improve vibration characteristics. The critical speed, which shows stiffness and dynamic stability of disk, is affected by the residual stress distribution; this varies as functions of distance from the gate and processing condition. The critical speed of disk was calculated with the initial stress taken into consideration, which was determined from injection molding simulation. Choosing melt temperature, mold temperature, filling speed and packing pressure as design parameters, critical speed is maximized with the method of response surface. It is shown that the stability of injection molded disk has been improved for the new condition obtained as a result of the study proposed.

• Design & Manufacturing
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• v.1 no.1
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• pp.13-16
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• 2007

Almost all injection molds have multi-cavity runner system for mass production, which are designed with geometrically balanced runner system in order to accomplish filling balance between cavity to cavity during processing. However, even though geometrically balanced runner is used, filling imbalance have been observed. Filling imbalance could be decreased by modifying processing conditions such as injections rate, mold temperature, injection pressure, melt temperature that are related to shear, viscosity. In this study, a series of experiment was conducted to investigate filling imbalance variation when modifying runner layout and polymer and to determine which processing condition influences as the primary cause of filling imbalance in geometrically balanced runner system.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.4 s.193
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• pp.147-152
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• 2007

UV laser ablation of polyimide is a combination of photochemical and photothermal mechanism. Photochemical mechanism is that molecular bonds are broken by photon energy and photothermal is evaporation and melt expulsion. When the laser processing, the etching depth needs to be calculated for prediction of processing result. In this paper, in order to predict the laser etching depth of polyimide by UV laser with the wavelength of 355nm, the theoretical model which includes both the photothermal and the photochemical effect was introduced. The model parameters were obtained by comparing with experimental results. The 3rd harmonic $Nd:YVO_4$ laser system was used in the experiment. From these experimental and theoretical results, the laser ablation of a polyimide was verified to achieve the highest quality microstructure.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.129-134
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• 2004

The development of fabrication processes of polycrystalline-silicon-thin-film transistors (poly-Si TFTs) at low temperatures is reviewed. Rapid crystallization through laser-induced melt-regrowth has an advantage of formation of crystalline silicon films at a low thermal budget. Solid phase crystallization techniques have also been improved for low temperature processing. Passivation of $SiO_2$/Si interface and grain boundaries is important to achieve high carrier transport properties. Oxygen plasma and $H_2O$ vapor heat treatments are proposed for effective reduction of the density of defect states. TFTs with high performance is reported.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.135-136
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• 2006

The shear flow properties have been reported in many cases by manufactures and fabricators. Only this characteristic is sometimes insufficient for the processings to provide a complete picture of the relationship between the processability and the flow behavior when underwent free-surface processes in which the shape and thickness of the extrudate are determined by the rheological properties of the melt, the die dimensions etc. In this paper the methodology of control of elongational flow is discussed in terms of relaxation time control of the polymer melts.

• Proceedings of the Korean Fiber Society Conference
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• 1998.04a
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• pp.20-24
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• 1998

Poly(ethylene 2,6-naphthalate) (PEN) has been known since 1948, when its synthesis was first reported by ICI. Co. In spite of its long history. application of PEN is limited as compared with poly(ethylene terephthalate) (PET). because PEN monomer is very expensive, and PEN exhibits relatively high melt viscosity that is not easy for fiber spinning and injection molding.(omitted)

• Transactions of Materials Processing
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• v.11 no.8
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• pp.641-650
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• 2002

For the production of complicated plastic parts in a cycle, a mold is needed.. The basic tasks of a mold are accommodation and distribution of the resin, shaping and cooling the melt and ejection of the molding. To achieve these goal a mold has several important parts and we classified types of molds. The 6 different major functions of a mold are explained and several types of molds are shown in her. I hope these explanation will help to understand injection molds for a design engineer.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.4
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• pp.144-150
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• 2005

Gas-assisted injection molding (GAIM) process is reducing the injection pressure during mold filling required as well as the shrinkage and warpage of the part and cycle time. Despite of these advantages, this process introduces new parameters and makes the application more difficult because the process interacts between gas and melt during injection molding process. Important GAIM factors that involved in this process include gas penetration design, locations of gas injection points, shot size, gas injection delay time as well as common injection molding parameters, gas pressure and gas injection time. In this study, the experiments were conducted to investigate effects of GAIM process variables on the gas penetration for PP and ABS moldings by changing gas injection point. Taguchi method was used fer the design of experiment. When the gas was injected at cavity's center, the most effective factor was shot size. When the gas was injected at cavity's end, the most effective factor was melt temperature. Injection speed was also an effective factor in GAIM process.