• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 추계학술대회 논문집
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• pp.113-116
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• 2001

Finite element analysis programs have been for metal forming process design They will become more and more important in understanding forming process For large-scale forging analysis problems, the performance of a linear equation solver is very important for the overall efficiency of the analysis code. With problem size increased, the computation time needs to be reduced, which is spent on setting the system of algebraic equations associated with finite element model Many matrix solvers have been developed and used usefully in finite element program for this purpose.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.418-421
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• 2003

Specimens of Ti-10Ta-10Nb have been hot upset forged after heating to either the $\alpha$+$\beta$ and $\beta$-phase field. The variety temperatures (At 650, 700, 750, 800, 85$0^{\circ}C$) and strain rates (At 0.001, 0.01. 0.1, 1, 10 $s^{-1}$ ) were used. On the basis of flow stress data obtained as a function of temperature and strain rate in compression, a processing map for hot working has been developed. At strain rates lower than about 0.1 $s^{-1}$ and almost temperatures, processing efficiency exhibited high, but at 0.001 $s^{-l}$, and temperature 80$0^{\circ}C$, low because the Shear band has occurred. On the basis of the processing map, the optimum processing routes available for hot working of this material are outlined.d.

• 소성∙가공
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• 제8권2호
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• pp.188-199
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• 1999

Semi-Solid Forming Process(Thixoforming, Rheocasting) is a novel forming process which has some advantages compared with conventional die casting, squeeze casting and hot/cold forging. In this study. Thixoforming process was selected as analysis processing in terms of billet handling and easiness of automation process. The Thixoforming process consists of reheating process of billet, billet handling, filling inot the die cavity and solidification of SSM part. In filling process, two rheology models which were Newtonian and Non-Nettonian model (Ostwald-deWaele)were verified with experimental results. The Ostwald-deWaele model shows the good agreement to the real flow and filling phenomena in die cavity. To give a boost the economical efficiency of Thixoforming process and to ensure the good forming result, reheating device coupled die set was proposed and the initial billet temperature for system that was found from experimental resluts. This study presents an overview of application of numerical analysis for simulation of semi-solid metal forming process to reduce the lead time for development of manufacturing part in industrial field.

• 소성∙가공
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• 제19권4호
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• pp.248-252
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• 2010

In this paper, three-dimensional finite element analysis of thread rolling process of a 12 point flange head bolt is conducted using a rigid-plastic finite element method based metal forming simulator AFDEX 3D. A whole sequence of cold forming processes of a long shaft bolt composed of four forging stages and final thread rolling process is simulated to reveal the mechanism of thread formation. A mesh density control function is applied near the major plastic deformation region to achieve computational efficiency. It has been shown both numerically and experimentally that longitudinal lengthening or shortening is negligible in thread rolling.

• 소성∙가공
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• 제17권2호
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• pp.117-123
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• 2008

In this study, optimum processing condition of rolled AZ31 Mg alloy was investigated by utilizing processing map and constitutive equation considering microstructure evolution(dynamic recrystallization) occurring during hot-working. A series of mechanical tests were conducted at various temperatures and strain rates to construct a processing map and to formulate the recrystallization kinetics in terms of grain size. Dynamic recrystallization(DRX) was observed to occur at a domain of $250^{\circ}C$ and 1/s(maximum dissipation-efficiency region). The effect of DRX kinetics on microstructure evolution was implemented in a commercial FEM code followed by remapping of the state variables. The volume fraction and grain size of deformed part were predicted using a modified FEM code and were compared with those of actual hot forged part. A good agreement was observed between the experimented results and predicted ones.

• 한국공작기계학회논문집
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• 제14권6호
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• pp.125-131
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• 2005

The purpose of this study is an optimization of gate valve made by forging method instead of welding method. In this study, we propose an optimal shape design to improve the mechanical efficiency of gate valve. In order to optimize more efficiently and reliably, the meta-modeling technique has been developed to solve such a complex problems combined with the DACE (Design and Analysis of Computer Experiments). The DACE modeling, known as the one of Kriging interpolation, is introduced to obtain the surrogate approximation model of the function. Also, we prove reliability of the DACE model's application to gate valve by computer simulations using FEM(Finite Element Method).

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2018년도 추계학술발표대회
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• pp.641-644
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• 2018

열간 자유 단조는 고온으로 가열한 강피에 압력을 가하여 원하는 형상을 빚는 공정이다. 가열로에서 여러 개의 강피를 동시에 가열하며 목표 온도에 도달하면 꺼내어 다음 공정을 진행한다. 이때 가열로에 투입하는 소재의 조합과 후단 공정을 위해 소재를 꺼내는 순서가 가열로의 에너지 효율에 영향을 끼친다. 본 논문에서는 열간 자유 단조의 에너지 효율을 높이기 위한 비용 예측 모형 기반 작업 계획 최적화 방안을 제안한다. 유전 알고리즘을 이용하여 가열로 강피 조합을 최적화하며 각 설비별 작업 할당 규칙에 따라 전체 작업 계획을 수립한다. 시뮬레이션 기반으로 후보 작업 계획을 평가하여 계획을 최적화 하며 이를 위해 각 설비별 공정 소요 시간 및 에너지 사용량 예측 모형을 이용한다. 예측 모형은 공정 데이터를 기반으로 기계 학습 알고리즘을 적용하여 학습한다. 또한 주기적인 재계획을 통해 예측의 불확실성으로 인해 작업의 진행이 계획대로 이루어지지 않는 문제점을 해결하고자 한다.

• 정보과학회 논문지
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• 제44권5호
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• pp.486-495
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• 2017

협업 필터링(CF, Collaborative Filtering)은 추천을 수행하기 위해 필요한 비용(시간/공간 복잡도 등)이 현실 데이터에 적용하기에는 한계가 있다. 평점 빈도 가중치 기반의 Baseline Predictor(RFWBP, Rating Frequency Weight-based Baseline Predictor)는 정확도가 기존의 방법과 근사하며, 비용을 크게 줄일 수 있는 효율적인 방법 중 하나이다. 그러나 효율성을 고려해 RFWBP만 사용할 경우, 1)학습을 수행하지 않기 때문에 발생되는 오차를 감소시킬 수 없고, 2)적합한 추천 목록을 작성하기 위한 조건이 없기 때문에 모두 추천했다. 본 논문은, 제시된 문제를 해결하기 위한 BBP(Bias-Based Predictor)를 제안한다. BBP는 Bias를 보정하여 오차의 범위를 감소시킴으로써 1)을 해결했고, 선호에 적합한 추천 목록 작성을 위한 몇 가지 Case를 정하고, 추천 목록을 구성함으로써 2)를 해결하였다.

• 소성∙가공
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• 제22권5호
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• pp.258-263
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• 2013

The deformation behavior of NIMONIC 80A was studied in the high temperature range of $900{\sim}1200^{\circ}C$ and for strain rates varying between 0.02 and $20s^{-1}$ via the hot compression test. Processing maps for hot working were constructed on the basis of the power dissipation efficiency using a dynamic material model. The results showed that the strength during hot compression increased with increasing strain rate and decreasing temperature. At low strains, the processing map of NIMONIC 80A did not reveal any instability domain regardless of the strain rate and temperature. However, at high strains, the processing map exhibited an instability domain at a low strain rate of $0.2s^{-1}$ and within a temperature range of $900{\sim}960^{\circ}C$. In the instability domain, the deformed microstructure exhibited shear bands and carbide precipitation while, in the safe domain, full recrystallization occurred.

• 한국자동차공학회논문집
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• 제6권5호
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• pp.104-110
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• 1998

In automotive industries, various processes for the cost reduction have been investigated lively. As one of them, powder metallurgy becomes influential. Compared to other methods used for he manufacture of steel components the Powder metallurgy process is competitive primarily due to the small number of production steps to reach the final geometry and thereby also the energy-efficiency. In this paper, to alter present forging process into powder metallurgy process by which the automotive clutch disc spline hub is manufactured machining process, the mechanical properties of sintered materials is investigated by specimen test. Selecting the 3 kinds of materials-SMF 4040, SMF 9060 and DHP-1, their properties according to heat treatment such as carburizing -tempering and plasma-nitrodizing are compared. By result of specimen test - tensile test, compression ring test, Impacting test, measurment of hardness, and microstructure analysis - we concluded that SMF 9060 and carburizing-tempering heat treatment is an optimal material and heat treatment method for the spline hub. It will be able to reduce manufacturing cost and weight.