• 한국주조공학회지
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• 제14권6호
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• pp.576-589
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• 1994

Water modeling experiments and computer simulation for the predictions of defects of die castings are very important to produce high quality castings with less cost. The relation between the variable air vent system and the characteristics of the fluid flow in the die cavity is studied by using water modeling tests, which give ideas on reasonable designing of die cavity, vent arrangement and gating system. In order to test the water modeling, injection is done by using water containing NaCl. Flow behaviors in cavities are visualized by high speed camera and video tape recorder, and local filling time is measured with electrode sensors. Special attention is paid to the configuration of die cavity. Simulated results by computer are examined and compared with the results of water modeling experiments. There are close correlations between the simulated results and water modeling ones.

• 소성∙가공
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• 제14권4호
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• pp.351-359
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• 2005

The semi-solid processing is now becoming of great interest for the production of various parts by pressure die casting. Also, the rheo-casting has been substituted for thixo-casting, because the rheo-casting can control the solid particles to globular and non-dendritic solid phase. In the rheo-casting process, the important thing is to control the solid particles behavior in semi-solid materials. So in this paper, to control solid particles behavior in semi-solid materials, we experimented about the die filling tests during the semi-solid die casting in 0.3, 0.4, 0.5 and 0, 6 solid fraction. The die filling in semi-solid die casting were simulated by MAGMA soft/thixo module. By the die filling tests and computer simulation, the effect of solid particles behavior in rheology flow had been investigated.

• 소성∙가공
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• 제5권3호
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• pp.239-255
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• 1996

A new forming technology has been developed to fabricate near-net shape products using light metal. A semi-solid forming technology has some advantages compared with the conventional forming processes such as die casting squeeze casting and hot/cold forging. In this study the numerical analysis of semi-solid filling for a straight die shape and orifice die shape in gate pattern is studied on semi-solid materials(SSM) of solid fraction fs =30% in A356 aluminum alloy. The finite difference program of Navier-Stokes equation coupled with heat transfer and solidification has been developed to predict a filling pattern and the temperature distribution of SSM. The programdeveloped in this study gives die filling patterns of SSM and final solidifica-tion region.

• 소성∙가공
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• 제14권1호
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• pp.49-56
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• 2005

In the semi-solid die casting process, an important thing is the flow behavior of semi-solid materials. The flow patterns of the semi-solid material can make the defects during die filling. To control the flow patterns is very important and difficult. In this paper, the flow behavior of the semi-solid A356 alloy material during die filing at various die gate shapes has been observed with the grain size controlled material. The effect of the gate shape on the die filling characteristics was investigated. The filling tests in each plunger stroke were experimented, and also simulated on the semi-solid material die casting process by MAGMAsoft. According to the filling tests and computer simulation, the effect of the gate shape on liquid segregation has been investigated.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 고액공존금속의 성형기술 심포지엄
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• pp.135-147
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• 1997

The production of light metal parts using aluminum is mainly performed by die casting and squeeze casting, which directly fabricate the required shape from the liquid state. However, die casting is subject to defects such as shrinkage porosity and air trapped when molten metal enters the cavity, whilst squeeze casting also has defects due to turbulent flow in the die cavity. Both diecasting and sqeeze casting have inhomogeneous mechanical property in terms of dendritic structure during solidification. Active research has been carried out on semi-solid processing, rather than on conventional process methods such as die casting, which involve various problems. Therefore in this paper, to introduce the fundamental technology for d e design, in die casting and forging process with semi-solid materials, relationship between stress and strain of semi-solid materials, and for producing parts die design has been proposed as parameters of globulization of the microstructure and gate shape. The prevention of various defects to produce sound parts are also introduced.

• 대한금속재료학회지
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• 제48권4호
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• pp.363-368
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• 2010

N,N'-diphenyl-N,N'-bis(3-methylphenyl)1-1' biphenyl-4,4'-diamine (TPD) hole-transporting layers were deposited using a continuous slot-die coating method on ITO/PET flexible substrates. It is crucial that the substrates have a very smooth surface with a RMS roughness of less than 2 nm for the deposition of semiconductor nanocrystals or Quantum Dots. The parameters of the slot-die coating, including the solution concentration of the TPD, the gap between the slot-die and the substrates, and the coating speed were controlled in these experiments. To obtain full coverage of the TPD films on the ITO/PET substrates (40 mm wide and several meters long), the injection rates of the TPD solution were increased proportional to the coating speed of the flexible substrates. Additionally, the injection rates must be increased as the gap distance changes from 400 to 600 ${\mu}m$ at the same coating speed. A RMS surface roughness of less than 2 nm was obtained, in contrast to bare ITO/PET substrates, at 13 nm, as the coating speed and gap distance increased.

• 기술사
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• 제30권6호
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• pp.144-152
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• 1997

Development of diamond wheel with fine grains and multi-pore structures were newely attempted to be studied in this paper. Wheels, that are employed for the smooth and mirrow finishing of die materials such as tungsten carbide alloy using tool and die materials, must have both performances to remove tool marks efficiently and to contact elastically with curved surfaces. Diamond abrasive grains were bonded firmly by a melamine to prevent the decrease of machining efficiency due to grain sinking within the bond materials. Also, highly foamed structures were developed to increase the flexibility of the wheel, and to induce active self-sharpening by increasing contact pressure between the wheel and work sufaces. In this paper, melamine-bonded diamond wheels are trial manufactured, then the forming method of wheels are explained.

• Journal of Magnetics
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• 제19권2호
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• pp.106-110
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• 2014

$Nd_{12.5}Fe_{80.6}B_{6.4}Ga_{0.3}Nb_{0.2}$ HDDR-treated powder was compacted by hot-pressing using different configurations of dies and heating rates. The die configurations were especially different in terms of the evacuation system that was used in heating for hot-pressing. The coercivity in the compacts was influenced by the evacuation system of the die and heating rate. In spite of the identical hot-pressing temperature and heating rate, coercivity was radically reduced above $600^{\circ}C$ in the compacts prepared in the closed-type die compared to that in the compacts prepared in the open-type die. The coercivity in the compacts prepared in the closed-type die decreased with increasing heating rate and the value further increased when extreme high heating rate was employed. $Nd_{12.5}Fe_{80.6}B_{6.4}Ga_{0.3}Nb_{0.2}$ HDDR-treated powder contained a significant amount of residual hydrogen (approx. 1500 ppm) in the form of $Nd_2Fe_{14}BH_x$ hydride. The dramatic coercivity decrease in the compact prepared in the closed die is attributed to the disproportionation of $Nd_2Fe_{14}BH_x$ hydride. High coercivity is mainly due to the effective desorption of hydrogen or the suppression of hydrogen-related disproportionation upon hot-pressing.

• 한국분말재료학회지
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• 제11권5호
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• pp.363-368
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• 2004

In the present study, the focus is on the analysis of the effect of the mold dimensions on the temperature distribution of a die during plasma activated sintering. The temperature distribution of a cylindrical mold with various dimensions was measured using K-type thermocouples. The temperature homogeneity of the die was studied based on the direction and dimensions of the die. A temperature gradient existed in the radial direction of the die during the plasma activated sintering. Also, the magnitude of the temperature gradient was increased with increasing sintering temperature. In the longitudinal direction, however, there was no temperature gradient. The temperature gradient of the die in the radial direction strongly depended on a ratio of die volume to punch area.

• 소성∙가공
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• 제10권2호
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• pp.111-114
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• 2001

A new, simple method to determine the die shape using a streamline in extrusion is presented. This method assumes that a billet deforms naturally to minimize the energy input for the given process condition. Then, an optimal die shape can be determined along a streamline. Extrusion operations with two types of materials, strain-hardening material and strain-rate hardening material, are examined using this method. Predictions with the proposed method are compared with those by the previous optimizing model to show its efficiency.