• Design & Manufacturing
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• 제10권1호
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• pp.19-25
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• 2016

Connectors are very important components that transmit electric signals to different parts. It must maintain intensity of the connector to prevent defects from impact and maintain contact to transmit electric signals. Most of the external parts of the connector, which act as the main framework, are formed by injection molding. However, bend deformation occurs for injection molded products due to the residual stress left inside the product after product molding. When the bend deformation is large, it does not come into complete contact when being assembled with other parts, which leads to connector contact intensity not being properly maintained. In result, the main role of the connector, which is to transmit electric signals, cannot be performed. In order to address this problem, this study conducted bend deformation cause analysis through bend deformation analysis to predict and prevent bend deformation of housings and wafers, which are injection molded products of pressure welded connectors that are normally applied in compact mobile and display products. Bend deformation analysis was carried out by checking the charging time, pressure distribution and temperature distribution through wire to board connector wafer and housing injection molding analysis. Based on the results of the bend deformation analysis results, the cause of the bend deformation was analyzed through deformation resulting from disproportional cooling, deformation resulting from disproportional contraction, and deformation resulting from ingredient orientation. In result, it was judged that the effects for bend deformation were biggest due to disproportional contraction for both the pressure welded connector wafer and housing.

• 한국주조공학회지
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• 제27권1호
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• pp.31-35
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• 2007

본 연구에서는 Mg합금의 반응고성형 공정기술을 개발하기 위하여 여러 가지 전단속도와 냉각속도에 따른 Mg합금의 점도와 딕소트러픽 거동을 분석하였으며, 이를 전산모사연구와 비교 검토하였다. 전산모사연구에서는 미세조직과 공정변수를 고려한 반응고 슬러리의 유변학적 거동을 분석하였다. 반응고 온도영역에서의 Mg합금(AZ91D) 슬러리의 점도는 고상율에 따라 지수함수적으로 증가하였으며, 전단속도가 증가하면 감소하는 경향을 나타났다. Mg합금 슬러리의 유변학적 거동을 정확하게 분석하기 위하여 Carreau 모델을 사용하여 ANYCAST 프로그램에서 고압다이캐스팅용 금형으로의 Mg합금 반응고 슬러리의 충진거동을 모사하였다. 전산모사된 결과는 동일한 조건에서의 실제 실험결과와 잘 일치하였다.

• 한국주조공학회지
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• 제35권5호
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• pp.120-127
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• 2015

The effects of Ti, B and Zr on grain refinement and castability were investigated in Al-4wt%Mg-0.9wt%Si-0.3wt%Mn-0.15wt%Fe alloy. Measurement of cooling curve and micro-structure observation were performed to analyze the effects of the addition of minor elements Ti, B and Zr during solidification. The prominence of effect on grain refinement was in increasing order for Ti, Zr and B element. Fine grain size and an increase of the crystallization temperature for ${\alpha}$-Al solution were evident as the amount of addition elements increased in this study. Addition of 0.15wt% Ti was most effective for grain refinement, and the resulting grain size of ${\alpha}$-Al solution for shell mold and steel mold were $72.3{\mu}m$ and $23.5{\mu}m$, respectively. Fluidity and shrinkage tests were perform to evaluate the castability of the alloy. Maximum fluidity length and minimum ratio of micro shrinkage were recorded for 0.15wt% Ti addition due to the effect of the finest grain size.

• 생물환경조절학회지
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• 제19권4호
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• pp.366-371
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• 2010

예냉(2, 4, $8^{\circ}C$)과 저장온도(4, 8, $10^{\circ}C$)가 수출용 딸기 '매향'과 '수경'의 저장성에 미치는 영향을 알아보고자 본 연구를 수행하였다. 2010년 3월 16일에 숙도 70%의 과실을 진주지역 온실에서 수확하였다. 농가의 예냉기에서 3시간 동안 예냉한 딸기를 30분만에 실험실로 수송하였고, 즉시 챔버에 저장하였다. 예냉을 위해 농가 현장에 설치되어 있는 간이 예냉기를 이용하였다. 저장하는 동안 딸기의 무게변화, 경도, 색도, 당도, 잿빛곰팡이병 발생율을 이틀 간격으로 3월 16일부터 3월 30일까지 조사하였다. 두 품종 모두 경도, 당도, 색도는 '매향'보다 '수경'이 높았고, $4^{\circ}C$에 저장 하였을 때 경도와 당도함량이 가장 높았다. 숙도가 진행됨에 따라 경도와 당도는 감소하는 경향을 보였다. 또한 모든 온도처리에서 저장기간이 경과함에 따라 무게의 변화가 감소하였다. 잿빛곰팡이병은 $10^{\circ}C$에 저장하였을 때 발생율이 가장 높았다. 따라서 딸기의 신선도를 장기간 유지하기 위해서는 두 품종 모두 $2^{\circ}C$에 예냉하여 $4^{\circ}C$에 저장하는 것이 효과적인 것으로 판단된다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.225-226
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• 2006

As the technique of high-speed end-milling is widely adopted to machining field. The investigation for microscopic precision of workpiece is necessary for machinability evolution. The environmental pollution has become a big problem in industry and many researcher have investigated in order to preserve the environment. The environmentally conscious machining and technology have more important position in machining process. In the milling process, the cutting fluid has greatly bad influence on the environment. The damaged layer affect mold life and machine parts in machining. In this study, the cutting force, the surface roughness, micro hardness and residual stress is evaluated according to machining environment. Finally, it is obtained that the characteristics of damaged layer in environmentally conscious machining is better than that in conventional machining using cutting fluid.

• 대한기계학회논문집A
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• 제26권9호
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• pp.1923-1930
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• 2002

In this paper, we present modeling and simulation of microlens formation by means of a deep X-ray lithography followed by a thermal treatment of a PMMA (Polymethylmethacrylate) sheet. According to this modeling, X-ray irradiation causes the decrease of molecular weight of PMMA, which in turn decreases the glass transition temperature and consequently causes a net volume increase during the thermal cycle resulting in a swollen microlens. In this modeling, the free volume theory including the relaxation process during the cooling process was considered. The simulation results indicate that the modeling in this study is able to predict the fabricated microlens shapes and the variation pattern of the maximum heights of microlens which depends on the conditions of the thermal treatment. The prediction model could be applied to optimization of microlens fabrication process and to designing a micro mold insert for micromolding processes.

• 한국주조공학회지
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• 제24권2호
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• pp.94-100
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• 2004

Gas porosity which is a common defect in aluminum alloy casting, is also thought to be severer in aluminum alloy castings produced by lost foam process due to the pyrolysis of the polystyrene foam pattern during pouring. Fundamental experiments were carried out to evaluate the effect of process variables such as the melt treatment, the cooling rate and pouring temperature on the density and mechanical properties in A356.2 castings with simple bar shape. The density of grain refined specimen was slightly lower than that of degassed one, but was higher than that of no treated one and that of shot ball packed specimen was higher than the other specimens. The tensile strength and elongation were in the ranges of $200{\sim}230MPa$ and $0.5{\sim}1.5%$ respectively. The density and hardness of lost foam cast specimens decreased with increase in pouring temperature.

• 한국기계가공학회지
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• 제12권6호
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• pp.30-36
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• 2013

An FFD(flexible fine die) is an embossed mold that consists of a thin plate ranging from 0.6 to 3 mm in thickness. FFDs are primarily used for cutting LCD films and F-PCB sheets. In the high-speed micro-milling process of flexible fine dies, the lubrication and cooling of the cutting edges is very important from the aspect of eco machining and cutting performance. In this paper, a comparative study of tool wear and surface roughness between cutting fluid and hybrid lubrication for eco-machining of FFD was conducted for processes of high-speed machining of highly hardened material (STC5, HRC52). Especially, the incorporated fluid method for eco machining, in which the cutting performances can be simultaneously measured, was introduced. The machining results show that hybrid lubrication, instead of conventional cutting fluid, leads to excellent tool wear and surface roughness and represents the proper conditions for eco micro-machining of flexible fine dies.

• Design & Manufacturing
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• 제17권1호
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• pp.1-5
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• 2023

In multi-material injection molding, since two or more materials with different process conditions are used, it is essential to maximize process efficiency by operating the cooling or heating system to a minimum. In this study, Liquid silicone rubber (LSR) that can be cured at a low temperature suitable for the multi-material injection molding was selected and the cure behavior according to the process conditions was analyzed through differential scanning calorimetry (DSC). Dynamic measurement results of DSC with different heating rate were obtained, and through this, the total heat of reaction when the LSR was completely cured was calculated. Isothermal measurement results of DSC were derived for 60 minutes at each temperature from 80 ℃ to 110 ℃ at 10 ℃ intervals, and the final degree of cure at each temperature was calculated based on the total heat of reaction identified from the Dynamic DSC measurement results. As the result, it was found that when the temperature is lowered, the curing start time and the time required for the curing reaction increase, but at a temperature of 90 ℃ or higher, LSR can secure a degree of cure of 80% or more. However, at 80 ℃., it was found that not only had a relatively low degree of curing of about 60%, but also significantly increased the curing start time. In addition, in the case of 110 ℃, the parameters were derived from experimental result using the Kamal kinetic model.

• Applied Microscopy
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• 제26권2호
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• pp.235-241
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• 1996

Amophization and decomposition behaviour in $Mg_{62}Cu_{26}Y_{12}$ alloy prepared by melt spinning method and wedge type metal mold casting method have been investigated by a detailed transmission electron microscopy. Amorphous phase has formed in melt-spun ribbon. In the case of the wedge type specimen, however, the amorphous phase has formed only around the tip area within about 2 mm thickness. The remaining part of the wedge type specimen consists of crystalline phases, $Mg_{2}Cu\;and\;Cu_{2}Y$. The supercooling for crystallization behaviour of the amorphous $Mg_{62}Cu_{26}Y_{12}$ alloy, ${\Delta}T_x$ has been measured to be about 60 K. Such a large undercooling of the crystallization bahaviour enables formation of the amorphous phase in the $Mg_{62}Cu_{26}Y_{12}$ alloy under the cooling rate of $10^{2}K/s$. The amorphous $Mg_{62}Cu_{26}Y_{12}$ has decomposed into crystalline phases, $Mg_{2}Cu\;and\;Cu_{2}Y$ after heat treatment at $170^{\circ}C\;and\;250^{\circ}C$.