• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2000년도 춘계학술대회논문집 - 한국공작기계학회
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• pp.618-623
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• 2000

In order to increase the porductivity of electrical parts, manufacturing processes using progressive dies have been widely used in the industry. Motor cores have been fabricated using progressive stacking die with the lamination procedure for better electro-magnetic property. for the proper design of a process, a prediction of the process is required to obtain many design parameters. In this work, rigid-plastic finite element analysis is carried out in order to simulate the lamination this work, rigid-plastic finite element analysis is carried out in order to simulate the lamination process of the motor core. The effects of the embossing depth and the amount of deviation are investigated and compared with experiments. The forming process can then be predicted successfully from the results of analyses, which enables to design appropriately the die and the process.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 추계학술대회논문집
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• pp.24-27
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• 1997

In the present work, rigid-plastic continuum elements employing the shape change and anisotropic effects are derived for the purpose of applying more realistic blankholding force condition in three-dimensional finite element analysis of sheet metal forming process. In order to incorporate the effect of shape change effectively in the derivation of finite element equation using continuum element for sheet metal forming, the convected coordinate system is introduced, rendering the analysis more rigorous and accurate. The formulation is extended to cover the orthotropic material using Hill's quadratic yield function. For the purpose of applying more realistic blankholding force condition, distributed normal and associated frictional tangent forces are employed in the blankholder, which is pressed normal and associated frictional tangent forces are employed in the blankholder, which is pressed against the flange until the resultant contact force with the blank reaches the prescribed value. As an example of sheet metal forming process coupling the effect of planar anisotropy and that of blankholding boundary condition, circular cup deep drawing has been analyzed considering both effects together.

• 한국정밀공학회지
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• 제7권2호
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• pp.28-38
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• 1990

The study is concerned with the theoretical and experimental investigation of axisymmetric fluid pressure-driven hydroforming of sheet metal by forming over the die cavity. The rigid-plastic finite element method is employed to calculate the stress and strain distribution. The effect of blank size and die radius is also studied in the finite element analysis. Experiments are carried out for hydroforming of cold-rolled steel sheets under various process conditions. The computational results are compared with the experimental results for the forming pressure vs. pole displacement relations and strain distributions. Comparison has shown that theoretical predictions by the finite element method are in good agreement with the experiment with the experimental observations. Thus, it is shown that the rigid-plastic finite element method is effectively used in the analysis of axisymmetric fluid pressure-driven hydroforming process.

• 한국정밀공학회지
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• 제15권7호
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• pp.129-138
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• 1998

The objective of this study is to demonstrate the ability of a computer simulation of microstructural evolution in hot forging of C-Mn steels. The development of microstructure is strongly dependent on process variables and metallurgical factors that affect time history of thermodynamical variables such as temperature, strain. and strain rate during deformation. Then finite element method is applied for the prediction of microstructural evolution, and it should be coupled with heat transfer analysis to consider the change of thermodynamical properties during forming process. In this study, Yada's recrystallization model and rigid-thermoviscoplastic finite element method are employed in order to analyze microstructural evolution during hot forging process. To show the validity and effectiveness of the proposed method, experiments are accomplished and the results of experiments are compared with those of simulations.

• 한국정밀공학회지
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• 제14권9호
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• pp.90-100
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• 1997

A full three-dimensional thermo-coupled rigid-viscoplastic finite element method and the currently developed microstructural evolution system which includes semi-empirical equations suggested by different research groups were used together to form an integrated system of process and micro- structure simulation of hot rolling. The distribution and time histroy of the momechanical variables such as temperature, strain, strain rate, and time during pass and between passes were obtained from the finite element analysis of multipass hot rolling processes. The distribution of metallurgical variables were calculated on the basis of instantaneous thermomechanical data. For the verification of this method the evolution of microstructure in plate rolling and shape rolling was simulated and their results were compared with the data available in the literature. Consequently, this approach makes it possible to describe the realistic evolution of microstructure by avoiding the use of erroneous average value and can be used in CAE of multipass hot rolling.

• 대한토목학회논문집
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• 제30권3D호
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• pp.271-278
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• 2010

반강성 포장은 공극률이 큰 개립도 아스팔트 혼합물의 공극에 시멘트 페이스트를 침투시켜 아스팔트 포장의 연성과 콘크리트 포장의 강성을 동시에 이용하는 포장형식이다. 반강성 포장은 콘크리트 포장에 비해 평탄성이 좋고 주행에 의한 진동이나 소음을 저감할 수 있으며, 아스팔트 포장에 비해 소성변형이 적고 온도저감 효과가 있는 것으로 알려져 있다. 본 연구에서는 반강성 덧씌우기 포장을 시험시공하여 반강성 포장의 온도저감 효과를 조사하였고 시편을 제작하여 옥외에서 온도 및 중량을 측정하여 반강성 포장의 온도저감 및 보수 효과를 확인하였다. 상용 3차원 유한요소해석 프로그램인 Abaqus 6.8로 반강성 포장과 아스팔트 포장을 구조해석하여 하중재하 위치에서의 수평 및 연직방향 응력과 변형률을 비교하고 다층탄성해석 프로그램 Bisar 3.0으로 검증하였다. 구조해석 결과를 바탕으로 피로균열을 예측하여 반강성 포장과 아스팔트 포장의 공용성을 비교하였다.

• 소성∙가공
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• 제8권1호
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• pp.47-56
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• 1999

The governing functional in plastic deformation has to satisfy the incompressibility constraint. This incompressibility constraint imposed on velocity fields can be removed by introducing either Lagrange multiplier or the penalty constant into the functional. In this study, two-dimensional rigid plastic FEM programs using these schemes were developed. These two programs and DEFORM were applied in a cylinder upsetting and a closed die forging to compare the values of load, local mean stress and volume loss. As the results, the program using Lagrange multiplier obtained a more exact and stable solution, but it took more computational time than the program using the penalty constant. Therefore, according to user's need, one of these two programs can be chosen to simulate a metal forming processes.

• 대한기계학회논문집A
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• 제28권10호
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• pp.1492-1499
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• 2004

In this paper, defect formation in ring rolling is revealed by computer simulation of ring rolling processes. The rigid-plastic finite element method is employed for this study. An analysis model having relatively fine mesh system near the roll gap is used for reducing the computational time and a scheme of minimizing the volume change is applied. The formation of the central cavity formation defect in ring rolling of a taper roller bearing outer race and the polygonal shape defect in ring rolling of a ball bearing outer race has been simulated. It has been seen that the results are qualitatively good with actual phenomena.

• Structural Engineering and Mechanics
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• 제10권1호
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• pp.27-36
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• 2000

The Oktalok nodal connection system is an aesthetic and efficient system. It has been widely used throughout Australia. The paper will briefly introduce the concept and application of the Oktalok nodal system. The existing design method is based on the assumption that the joints are pin-ended, i.e., the rotational stiffness of the joints is zero. However the ultimate capacity of the frame may increase significantly depending on the rotational stiffness of the joints. Stiffness tests and finite element simulations were carried out to determine the rotational stiffness of the Oktalok joints. Column buckling tests and non-linear finite element analyses were performed to determine the member capacity of columns with semi-rigid end conditions. A simple formulae for the effective length factor of column buckling is derived based on the above experimental and theoretical investigations.

• 한국정밀공학회지
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• 제22권8호
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• pp.100-107
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• 2005

The objective of the study is to improve the quality of wheel bearing hub by the rigid-plastic finite element analysis and the response surface methodology. The rigid-plastic finite element codes, AFDEX-2D and DEFORM-3D, were used to analyze the two-dimensional and three-dimensional forging processes, respectively. The response surface analysis is used to find the minimum underfill by the variation of design variables such as the height of billet after upsetting and punch angles of blocker dies. The metal flow of forged product shows good agreement with the results from 2D and 3D analysis. Also, the quality of the wheel bearing hub has been improved by the optimization of design variables and the machining time has been reduced by the machining allowance.