• Transactions of Materials Processing
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• v.12 no.4
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• pp.348-357
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• 2003

In order to construct the extrusion die surface of arbitrarily shaped sections, an automatic surface construction method based on NURBS surface and area mapping method is proposed in the present work. A center point fur area mapping is determined by introducing the mapping concept based on constant area proportionality between original billet and final product. The characteristic points of inlet profile are determined using the traditional area mapping method and the root finding numerical method. The inlet and outlet profiles are precisely described with NURBS curves using the characteristic points of entry and exit sections. For the construction of NURBS surface, an interpolation method for the pre-determined two section curves has been developed to be used in the generation of interior control points and weights. To show the validity of the proposed method, automatic die surface generation is carried out for the several kinds of shaped sections.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.42-45
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• 2007

Recrystallization behavior during ingot-breakdown process of Alloy 718 was investigated with finite element analysis and experimental approaches. In order to analyze microstructural changes during the cogging process of an Alloy 718 ingot, the side-pressing and heat treatment tests were performed at different temperatures and ram speed. From the side-pressing and heat treatment test results, it was found that microstructural changes during hot forging of Alloy 718 ingot greatly influenced on a close interaction between dynamic and static-recrystallization behaviors. A recrystallization model of Alloy 718 was used to predict the complex microstructural variation during continuous heating and forging processes of the cogging, and the predicted grain size and its distribution were compared with the actual cogged Alloy 718 billet.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.3098-3107
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• 1994

The central burst defects, so-called chevroning, in wire drawing are analyzed by the rigid-plastic finite element method. The occurrence of central burst defects in wire drawing is estimated by the distribution of the hydrostatic pressure around the central part of the workpiece. It has been possible to obtain numerical boundaries which, in reduction in area vs. semicone angle plane, divide the safe and the danger zones, depending on friction factors and material properties. Based on the results of the analysis, it is suggested that the previous criterion derived from the upper bound analysis should be modified for better prediction of the defects. The back tension and the billet with a spherical hole on the central axis are also included in the analysis of the defects.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 2006.05a
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• pp.197-200
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• 2006

본 논문은 철강공장의 연주공정에서 만들어진 빌렛 소재의 관리를 위해 사용되는 소재 관리문자를 실시간으로 인식하기 위한 빌렛 소재 관리문자 인식용 비전시스템 개발 결과에 대해 기술한다. 빌렛 재질의 단면에 마킹된 소재 관리문자는 소재가 다음 공정으로 이동하기 전에 공정상에서 실시간으로 인식된다. 문자인식 시스템은 영상획득을 위한 카메라 시스템, 영상을 장거리로 고속 전송하기위한 영상전송 시스템, 기존 시스템과의 인터페이스를 위한 입. 출력 장치로 구성된다. 개발된 문자인식 시스템을 실제 철강공장에 설치하여 운용테스트를 실시했다. 테스트 기간 중에 시스템의 내구성과 신뢰성을 검증하고 최종적으로 문자 인식률을 검증했다. 개발된 시스템에 대해 현장 테스트 결과 실험실 수준과 비슷한 수준의 인식률을 가졌다.

• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.594-596
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• 2000

Induction Heating is utilized in a large and ever-increasing number of application. The most prominent of these are billet heating, heating treating. metal melting. In this paper, we are modeling of the inductor and calculating of the circuit parameters is described. Analyzed by finite element method and then Inductor's characteristic analysis was studied and perform the test of temperature distribution.

• ETRI Journal
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• v.37 no.5
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• pp.1012-1022
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• 2015

Conventional cryptographic algorithms are not sufficient to protect secret keys and data in white-box environments, where an attacker has full visibility and control over an executing software code. For this reason, cryptographic algorithms have been redesigned to be resistant to white-box attacks. The first white-box AES (WB-AES) implementation was thought to provide reliable security in that all brute force attacks are infeasible even in white-box environments; however, this proved not to be the case. In particular, Billet and others presented a cryptanalysis of WB-AES with 230 time complexity, and Michiels and others generalized it for all substitution-linear transformation ciphers. Recently, a collision-based cryptanalysis was also reported. In this paper, we revisit Chow and others's first WB-AES implementation and present a conditional re-encoding method for cryptanalysis protection. The experimental results show that there is approximately a 57% increase in the memory requirement and a 20% increase in execution speed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.2
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• pp.96-103
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• 2011

Rotor grip is used as a component of rotor system in unmanned helicopter. Instead of usual machining, hot forging process has been considered to improve its proof stress against repeated loading conditions and crash in the farm-field. Die design and forming analysis have been performed according to the conditions such as billet volume, flash, cavity filling, and the distribution of damage during the forming by using FE analysis. In the results of analysis, the possibility of structural failure in the model has not been found because its maximum effective stress is much lower than yield strength of the titanium alloy. In the forging die design, flash has been allowed because of low production in the industrial field. Preform design was studied by using FE-analysis, and its optimal dimension was obtained in the hot forging of rotor grip with titanium alloy.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.2
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• pp.114-120
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• 2008

This study is to compare and analyze the material flow, deformation characteristics, and forming load of flange by means of similitude experimental method of model material using plasticine. In order to find optimal forming conditions, prototype experiments were designed to investigate forming characteristics of general-purpose flange under various working conditions. As a result of prototype experiments, billet thickness and gap-height ratio was found to be the most influential experimental parameter in flange forming. Forming loads from prototype experiments were compared to the results of finite element analysis after conducting estimation of forming loads of real material. Results of prototype experiments based on model material techniques are expected to be used as a basic data of die design f3r the development of products and process.

• Proceedings of the KIEE Conference
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• 2000.11b
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• pp.287-289
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• 2000

Induction heating is utilized in a large and ever-increasing number of application. The most prominent of these are billet heating heat treating, metals joining, and metal melting. In these day, heating roll, a kind of induction heating, is widely used in curing of coatings and fiber industry. In this paper, at first, treated that heating roll's characteristics equation. The second, analysis of magnetic flux and eddy currents distribution using FEM.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.56-57
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• 2006

Porosity in spray-formed materials is an important issue, but the formation of porosity is not completely understood. The paper gives some examples picked from literature, which show some general correlations between process parameters and porosity. To improve the understanding of porosity formation it is necessary to know more about the conditions of the droplets and the deposit at the point of impingement. Determining the impact conditions is a challenge because usually they are not constant with time and some values are difficult to measure. Our experiments show a strong correlation between the deposit surface temperature and the porosity. The average impact angle weighted by the local particle mass flux is also an important parameter.