• 한국주조공학회지
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• 제37권3호
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• pp.71-77
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• 2017

Casting defects produced during the casting process seriously affect the mechanical properties of the resulting products, reduce the performance capabilities of the product, and also result in economic losses. Therefore, this paper mainly investigates the causes of defects and methods by which to reduce these defects stemming from molten metal flows in a runner system of the type widely used in the sand mold casting process. The flow characteristics of a molten alloy are difficult to observe during the actual casting process. For this reason, a water model was used to observe the flow in the casting process, and the flow in each case was recorded using high-speed cameras as part of the experimental process of this study. Several repetitive experiments were performed to improve the accuracy of the experimental results. The traditional casting system was modified according to the design rules proposed by Campbell, and the system was termed flow-adaptive gating system with a water model. Comparing the flow characteristics of traditional and adaptive gating systems with a water model shows that the bubbles in the water in the latter case are reduced more significantly than in the former case. A ceramic filter system was adapted to the flow-adaptive gating system to minimize the instability of the flow during filling, which occurs as the fluid velocity in the runner increases. In additional, the flow behavior with and without the filter system were compared. The water model system in this work was shown to be able to verify that the adaptation of the filter system brings improvements by stabilizing the flow and reducing the amount of bubbles in the runner system. Moreover, using the flow-adaptive runner system with the filter system leads to considerably stable flows in the runner system.

• 한국공작기계학회논문집
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• 제17권1호
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• pp.7-15
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• 2008

Currently existing high-accuracy and high-speed die sets used in reciprocal press create scratches at the surface of guide posts, steel balls, and bushes due to vertical movement of balls with point-contacts between inner surface of bushes and guide posts. Consequently, accuracy of the die set and the life span of the metal mold are reduced. However, those scratches could reduce the pre-load of the steel ball. This research designed and developed a groove-type die set which improves life span of the die set by eliminating point-contacts of steel balls with guide posts. The guide post consisted of a steel-ball retainer, a steel-ball retainer stopper, a guide bush, a guide pin, a snap ring, and a spring. The steel-ball retainer has 72 holes with 8 columns of 9 holes in each column. The inner surface of the guide bush was grinded(surface roughness: $Ra\;\\;0.2{\mu}m$, accuracy: $0\;{\sim}\;-0.002mm$) after NC turning and heat treatment. Also, a line of small intermediate pocket was processed inside of the guide bush for lubrication and elimination of foreign materials. Guide grooves of steel balls were processed using a wire EDM(Electrical Discharge Machining) after heat treatment. With such a design of the guide post stated above, loads against steel balls could be dispersed greatly by the line contacts through the guide groove between the guide post and the guide bush, and the life span of the guide post could be expanded semi-permanently.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 The 6th International Symposium of East Asian Resources Recycling Technology
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• pp.198-201
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• 2001

Porous structures of aluminum foam have been studied by using return aluminum scrap. The apparent foam shape, foam height, density, pore size and their distributions in various section areas of the experimental samples have been investigated. The sample have been cast into metallic mold, using aluminum foam prepared from a precursor based on pure Al ingot and return aluminum scrap mixed with various amounts of 1-2wt% increasing viscosity and foam agent materials. The process provides for flexibility in design of foam structures via relatively easy control over the amount of hydrogen evolution and the drainage processes which occur during foam formation. This is facilitated by manipulating parameters such as the foaming agent, thermal histories during solidification and mix melt viscosities. A metal for producing the foamed are decomposing a foaming agent in a molten metal such that there is an initial and a subsequent expansion due to foaming agent. It has been found that the Al porous foaming with variation amount of 1∼2wt% foam agent and at 2min holding time, which melting temperature has appeared homogeneous pore size at 650∼700$^{\circ}C$. The compression strength were 10-13 kg/min at 125ppi, and increased by higher pore density. The acoustical performance of the panel made with the foamed aluminum is considerably improved; its absorption coefficient shows NRC 0.6-0.8. It has been found that the Al foam is very preferable for the compactness of the thermal system.

• 한국정밀공학회지
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• 제23권9호
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• pp.174-178
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• 2006

Pyramid shape of micro pattern is applied to the light guide panel (LGP) to enhance the uniformity of the brightness of the LCD. The micro pyramids are molded in intaglio on the surface of the LGP. The size of each pyramid is 5$\mu$m $\times$ 5$\mu$m on bottom and the height is about 3.5$\mu$m. The pyramids are distributed on the LGP surface randomly to be sparser where the light comes in and denser at the opposite side as a result of a simulation using lightools$^{TM}$ Based on this design, a silicon pattern master and a nickel stamper are fabricated by MEMS process and electro plating process. Intaglio micro pyramids are fabricated on the 6' of silicon wafer from the anisotropic etching using KOH and the process time, temperature of the KOH solution, etc are optimized to obtain precise shape of the pattern. A Wi stamper is fabricated from this pattern master by electro plating process and the embossed pyramid patterns turns out to be well defined on the stamper. Adopting this stamper to the mold base with two cavities, 1.8' and 3.6' LGPs are injection molded.

• Asian-Australasian Journal of Animal Sciences
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• 제15권9호
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• pp.1294-1299
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• 2002

The study aimed to evaluate the influence of molasses in ensiling cassava and Gliricidia tops, common crop residues in the farming systems of Vietnam. Four levels of sugarcane molasses: 0, 30, 60 and 90 kg per tonne of fresh material, and two storage periods (2 and 4 months) for each of the two plant species: Cassava (Manihot esculenta, Crantz) and Gliricidia (Gliricidia sepium, Jacq.) were allocated in a 4${\times}$2 factorial completely randomized block design with 3 replicates. A total of 48 plastic bags, each one containing 10 kg herbage were used. Based on the colour, smell and mold appearance, all the silages were considered to be acceptable but with more spoiled silages with higher levels of additives. DM of herbages (25.8% and 22.4% in cassava and Gliricidia tops, respectively) were not changed during ensiling and the molasses additive had no significant effect on the silage DM. Contents of CP and NDF in the cassava tops silage decreased significantly with increased level of molasses and storage period, respectively. The mean pH values of non-molasses silages were 4.39 in cassava tops and 4.60 in Gliricidia tops. Increased additive levels significantly reduced silage pH in Gliricidia (p<0.01) but not in cassava tops silage (p=0.10). Longer storage period significantly reduced pH in both silages. The water soluble carbohydrate (WSC) concentrations of cassava tops and Gliricidia tops were reduced by 90 and 80%, respectively, after ensiling. Molasses addition increased significantly the silage WSC concentrations. HCN contents in the fresh cassava and Gliricidia tops were reduced by 68 and 43%, respectively, after 2 months ensiling, and were continuously reduced during storage. A reduction of 25% and 42% in the tannin content of fresh cassava and Gliricidia tops, respectively was found after ensiling. Storage time and molasses additive had little affect on the tannin content. Silage lactic acid concentrations were around 1,0% of DM in cassava and 1.7% of DM in Gliricidia top silages, and no effect of molasses additive and storage time was found. It is concluded that cassava and Gliricidia tops residues can be preserved successfully by ensiling, and only low levels of molasses additive are needed to improve silage fermentation.

• Asian-Australasian Journal of Animal Sciences
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• 제27권6호
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• pp.832-840
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• 2014

This study aimed to investigate the effects of storage duration and temperature on the characteristics of wet brewers grains (WBG) as feeds for ruminant animals. Four storage temperatures ($5^{\circ}C$, $15^{\circ}C$, $25^{\circ}C$, and $35^{\circ}C$) and four durations (0, 1, 2, and 3 d) were arranged in a $4{\times}4$ factorial design. Surface spoilage, chemical composition and microorganism density were analyzed. An in vitro gas test was also conducted to determine the pH, ammonia-nitrogen and volatile fatty acid (VFA) concentrations after 24 h incubation. Surface spoilage was apparent at higher temperatures such as $25^{\circ}C$ and $35^{\circ}C$. Nutrients contents decreased concomitantly with prolonged storage times (p<0.01) and increasing temperatures (p<0.01). The amount of yeast and mold increased (p<0.05) with increasing storage times and temperatures. As storage temperature increased, gas production, in vitro disappearance of organic matter, pH, ammonia nitrogen and total VFA from the WBG in the rumen decreased (p<0.01). Our results indicate that lower storage temperature promotes longer beneficial use period. However, when storage temperature exceeds $35^{\circ}C$, WBG should be used within a day to prevent impairment of rumen fermentation in the subtropics such as Southeast China, where the temperature is typically above $35^{\circ}C$ during summer.

• 한국기계가공학회지
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• 제17권4호
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• pp.76-82
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• 2018

3D formed Electrical Discharge Machining (EDM) and hole EDM were conducted for die and mold manufacturing with electrodes which were made by mechanical machining and wire EDM. It is difficult to machine the hardened material after heat treatment and quenching with traditional machining. The only method of machining hardened material is die-sinking EDM. In this research, hole EDM was conducted for heat-treated cold-worked tool steel (SKD11) for use as a die material. The EDM surfaces were analyzed by pulse-on time and peak current of EDM current, according to the machining conditions of EDM. The EDM surface profiles were affected by the peak current. The contribution of each factor is peak current (91.63%) and pulse-on time (0.93%). The best surface roughness was obtained with a $130{\mu}s$ pulse-on time and a 14.2 A peak current. With uniform EDM processing, the surface deteriorated with increasing pulse-on time and peak current. The thickness of the solidified layer induced by EDM was increased as the peak current, crater shapes, and erupted shapes of EDM surfaces were increased. Therefore, microcracking gaps induced by surface tension were increased.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.159-160
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• 2006

A novel approach to the manufacture of biocompatible ceramic scaffold for tissue engineering using micro-stereolithography system is introduced. Micro-stereolithography is a newly proposed technology that enables to make a 3D micro structure. The 3D micro structures made by this technology can have accurate and complex shape within a few micron error. Therefore, the application based on this technology can vary greatly in nano-bio fields. Recently, tissue-engineering techniques have been regarded as alternative candidate to treat patients with serious bone defects. So many techniques to design and fabricate 3D scaffolds have been developed. But the imperfection of scaffold such as random pore size and porosity causes a limitation in developing optimum scaffold. So scaffold development with controllable pore size and fully interconnected shape have been needed for a more progress in tissue engineering. In this paper, bone scaffold was developed by applying the micro-stereolithography to the mold technology. The scaffold material used was HA(Hydroxyapatite) nano powder. HA is a type of calcium phosphate ceramic with similar characteristic to human inorganic bone component. The bone scaffold made by HA is expected, in the near future, to be an efficient therapy for bone defect.

• 비파괴검사학회지
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• 제33권1호
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• pp.73-79
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• 2013

본 실험에서는 NIMAX재료를 3차원 측정기 및 백색광간섭계를 이용, 진원도 측정과 표면조도 측정을 하여 다음과 같은 결과를 얻었다. 절삭특성은 재료의 경도가 큰 관계로 2F의 조건보다 4F의 조건에서 낮게 나타났으며, 주축 회전수 및 공구 이송이 낮을수록 양호하게 나타났다. 3차원 측정기를 통한 진원도 측정은 절삭분력과 같은 4F 조건에서 양호하게 나타났으며, 주축회전수 1,700 rpm, 공구이송속도 85 mm/min의 조건에서 진원도는 양호한 결과를 보였다. 가공면의 표면거칠기는 2F 조건보다 4F의 조건에서 양호하게 나타났으며, 주축회전수 1,700 rpm, 공구이송속도 55 mm/min의 조건에서 Ra $0.4025{\mu}m$값을 보였다.

• 폴리머
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• 제35권1호
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• pp.1-6
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• 2011

사출성형은 고온의 수지를 고압으로 금형에 충전하고 냉각하여 제품을 만드는 공정으로 큰 온도차이와 고압에 의해 성형품에 잔류응력이 형성된다. 이러한 잔류응력은 시간이 지남에 따라 이완되면서 제품에 변형을 일으켜 형상 품질을 저하시킨다. 본 연구에서는 광탄성 장치를 이용하여 투명한 사출성형품의 잔류응력을 측정하는 방법을 연구하였다. 빛은 전자파처럼 진행하는데 편광필름을 통과하면 하나의 파장만이 진행하게 된다. 그 파장이 시편을 통과하면서 시편에 존재하는 잔류응력 때문에 복굴절이 형성되고 두 번째 편광필름을 통과하면서 다양한 색의 패턴을 보이게 된다. 이 색의 패턴을 이용하여 사출성형으로 제작된 사각평판의 잔류응력을 정량적으로 측정하였다. 또한 컴퓨터 해석을 통해 사출성형품의 광학적 특성을 예측하였으며 실험과 비교하였다.