• Journal of the Korean institute of surface engineering
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• 제32권3호
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• pp.244-248
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• 1999

Photoelectrodeposition of copper on semiconductive B-doped diamond films was investigated. There are cleasr morphology differences between photodeposited copper and electrodeposited copper. Photoelecrodeposition proceeded as uniform 2-dimensional growth. On the other hand electrodeposition proceeded as scarce random deposition. By applying this effect we have succeeded in forming a conductive pattern on semiconductive B-doped diamond with the aid of a photo-mask. And it was suggested that the surface reforming caused by photoelectrochemical process could be easily detected by the following metal (copper) deosition method, which is demonstrated as 'Diamond photographic phenomenon'.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.209-212
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• 2001

It is known that the mim forming processes show somewhat different phenomena compared with the conventional metal forming processes, namely, the size effect, enhanced friction effect and etc. Such typical phenomena, however, are not predicted by the conventional finite element analysis, which has been an efficient numerical tool to predict the metal forming processes. It is due to the fact that the constitutive relations used does not describe the microstructural characteristics of the materials. In the present investigation, the finite element formulation using the rate-dependent rigid plastic crystal plasticity model of the face-centered cubic materials is conducted to predict the micro mechanical behaviors during the mim forming processes. The finite element analysis, however, provides mesh-dependent solutions for the intragranular deformations. Therefore, the couple stress energy is additionally introduced into the variational principle and formulated within the framework of the rigid plastic finite element method to obtain mesh-independent solutions. Micro deformations of single crystal and bicrystal with various orientations are calculated to show the potential of the developed formulation.

• Design & Manufacturing
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• 제12권3호
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• pp.42-47
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• 2018

Recently, in the surge of global environmental issues, there has been a great attention to lightweight materials in purpose of saving energy. Magnesium alloys not only have low specific gravity, and superb specific stiffness, but are also excellent in blocking vibrations and electromagnetic waves. So demand for this material is getting bigger rapidly throughout the industry. In this study, we examined the improvement of formability of magnesium alloy AZ31 material in warm working. Drawing, bending and shearing process were carried out by varying the forming temperature and the forming speed, and the influence of the variables on each process was studied. In the experiments, the high forming temperature and low forming speed results in high formability in the drawing process and the bending process. In the shearing process, as the forming temperature increases, the length of the fracture decreases.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제33권11호
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• pp.1209-1216
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• 2009

Nano-micro hierarchical structures that nanoprotrusions were formed on the network-type microstructures were fabricated using an ultrasonic vibration forming technology. A commercial ultrasonic welding system was used to apply ultrasonic vibration energy. To evaluate the formability of ultrasonic vibration forming, nickel nano-micro hierarchical mold was fabricated and polyethylene (PE) was used as the replication material. The optimal molding time was 3.5 sec for PE nano-micro hierarchical structures. The molding process was conducted at atmospheric pressure.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 한국소성가공학회 2000년도 춘계학술대회논문집
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• pp.56-62
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• 2000

Semi-solid forming process has some advantages such as successful manufacturing of high quality components with less inner defects suitable for less machining high productivity and energy-saving effect. the thixotropic behavior(solid-like in the unperturbed state and liquid-like during shearing) has been the basis for the semi-solid forming process. The main focus of this article is the investigation of the effect of T6 heat treatment and alloying elements on the mechanical properties in the semi-solid formed products using thixotropic hypoeutectic (A357 and ALTHIX 86S) and hypereutectic(A390) materials. The new methods to produce semi-solid formed components with high quality are also proposed and discussed in terms of a die design and the development of a lubricant.

• The Bulletin of The Korean Astronomical Society
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• 제42권1호
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• pp.55.4-56
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• 2017

Complex organic molecules (COMs) are commonly detected in star forming regions and considered important species since they are seeds of prebiotic molecules. Although COMs form in ice mantles on dust grains, they are preferentially detected in the gas phase. The origin of the gaseous COMs highly depends on the circumstance of each star forming region. Therefore, the distribution of COMs emission reflects the physical and chemical conditions of the region. We present the newly detected COMs, especially methanol emission lines toward two massive star forming regions, G19.61-0.23 and G75.78+0.34 in the Atacama Large Millimeter/submillimeter Array Band 3 observations during the Cycle 2 phase. Multiple transitions of methanol are detected in both regions but show different emission morphology. The origin of the desorption (e.g. shocks or high energy photons) is discussed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.35-36
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• 2009

Development trend and current status were surveyed for pre-heat-treated high strength cold heading quality (CHQ) wire and it's forming technology. Spheroidizing, quenching, and tempering heat treatments are eliminated by adapting the pre-treated wire, which could reduce energy consumption rate and green house gas emission rate during produce parts requiring high strength. There are some challenging problems to expand application area such as enhancing forming tool life, and preventing delayed failure. Domestic research movement concerning the development and application of the new high strength wire was introduced.

• Structural Engineering and Mechanics
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• 제58권4호
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• pp.677-687
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• 2016

On the basis of the energy approach it is reported a development of the yield function and the constitutive equations for the orthotropic material with consideration of the crystal lattice constants and parameters of the crystallographic texture for the general stress state. For practical use in sheet metal forming analysis it is considered different loading scenarios: plane stress and plane strain states. Using the proposed yield function, the influence of single ideal components on the shape of yield surface was analyzed. The six texture components investigated here were cube, Goss, copper, brass, S and rotated cube, as these components are typically observed in rolled sheets from FCC alloys.

• Journal of the Korean Society for Precision Engineering
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• 제16권9호
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• pp.96-103
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• 1999

A kinematically admissible velocity field is derived to analyze the forming load and the extruded length in the extrusion/forging process of trochoidally headed bars from round billets. The forming load and the extruded length are obtained by minimizing the total energy-consumption rate. Experiments are carried out with lead billets at room temperature using trochoidally shaped punches. The theoretical predictions of forming load and extruded length are in good agreement with the experimental results.

• Journal of Institute of Convergence Technology
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• 제3권2호
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• pp.17-21
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• 2013

Hot cross wedge rolling process as an incremental forming has many advantages such as the material usage, the short process time, the automatic equipment line and the low forming load. However, it occurs some defects such as the surface groove, the axis warping and the Mannesmann hole. In this paper, the defect of the Mannesmann hole was carried out. Finite element analysis was utilized to reveal the stress distribution, the rotation of the specimen and the change of section profile. Cross wedge rolling experiment was also conducted on the generation of the Mannesmann hole. It was demonstrated according to the spreading angle with respect to the various types of material. In the view point of metal flow, the smaller forming angle and the larger spreading angle increase opportunities of the defect hole generations.