• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1992년도 춘계학술대회 논문집 92
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• pp.103-114
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• 1992

Cogging is generally the initial and primary step in the manufacture of practically all large open-die forgings, and consists of forging and ingot by reducing the cross-section and simultaneously enlarging the body. A three-dimensional thermo-viscoplastic finite element model is used to study the distribution of internal stresses and strains of workpiece and temperature of workpiece and die during cogging process. Simulations are carried out on an circular ingot, using v-die and flat die, to study the effects of die configuration, die width, penetration depth, temperature gradient, die overlapping and pass design.

• 대한기계학회논문집A
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• 제27권4호
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• pp.614-622
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• 2003

In this paper, the stress-strain curves of bearing steels at hot working conditions are obtained by hot compression test with a computer controlled servo-hydraulic Gleeble 3800 testing machine and elongations and reductions of area of the bearing steels are also obtained by hot tensile test with a Gleeble 1500 testing machine. Experiments are conducted under the various strain-rates and temperatures and their results are used to obtain the flow stress information. A rigid thermo-viscoplastic finite element method is applied to the multi-stage hot forging process in order to predict temperature distribution of workpiece. The experimental results and the analysis results are used to obtain an optimal hot forging condition.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1995년도 추계학술대회논문집
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• pp.102-108
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• 1995

Internal contact scheme between two free surfaces on one deforming body has been proposed by using the penalty method. It has been imposed to be internal boundary condition on two-dimensional thermo-viscoplastic finite element method so as to analyze one deforming body, which has two free surfaces penetrating each others. Analysis of side pressing with a circular void and a inclined elliptic hole have been carried out in order to verity the proposed contact scheme. A finite element code imposed internal boundary condition has been applied to two-dimensional analysis of free forging of large ingot with a void. Through the analysis, effects of working parameters in order to consolidate voids have been investigated.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 추계학술대회논문집
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• pp.11-16
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• 1997

In this study, the finite element analysis of AA6061 wheel forging processes over hot working range is performed and a thermo-viscoplasticity theory applicable to hot forging is applied for simulation. Aluminum alloy has frequently been utilized to manufacture automobile and aircraft parts due to its various advantages such as lightness, good forgeability, and wear resistance. Several forging conditions are applied to the simulation, such as die speeds, rib thicknesses, and depth of die cavity. The effectiveness of the simulation results is summarized in terms of metal flow, strain distributions, temperature distributions, forging load, which are essential to over all process design.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 춘계학술대회논문집
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• pp.159-164
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• 1997

The optimal conditions were investigated in order to manufacture the light automotive body parts using the semi-solid forging process by the finite element nalysis. Considering about macro-segregation cause to difference of relative velocity between solid phase and liquid phase, solidificational phenomenon cause to heat transfer from die and export of the latent heat, so solid fraction updating algorithm can be proposed. The rigid thermo-viscoplastic finite element analysis was carried out according to die temperature with proposed algorithm, so availability of forming part were understood. The finite element program can be used to the analysis of semi solid forging process.

• 소성∙가공
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• 제9권3호
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• pp.233-241
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• 2000

It is well known that the quality and efficiency of the design of metal forming processes can be significantly improved with the aid of effective numerical simulations. In the present study, a two-and three-dimensional finite element simulation system, CAMP form, was developed for the analysis of metal forming processes in the PC environment. It is composed of a solver based on the thermo-rigid-viscoplastic approach and graphic user interface (GUI) based pre-and post-processors to be used for the effective description of forming conditions and graphic display of simulation results, respectively. In particular, in the case of CAMPform 2D (two-dimensional), as the solver contains an automatic remeshing module which determines the deformation step when remeshing is required and reconstructs the new mesh system, it is possible to carry out simulations automatically without any user intervention. Also, the forming analysis considers ductile fracture of the workpiece and wear of dies for better usage of the system. In the case of CAMPform 3D, general three-dimensional problems that involve complex die geometries and require remeshing can be analyzed, but full automation of simulations has yet to be achieved. In this paper, the overall structure and computational background of CAMPform will be briefly explained and analysis results of several forming processes will be shown. From the current results, it is construed that CAMPform can be used in providing useful information to assist the design of forming processes.

• 대한기계학회논문집
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• 제15권1호
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• pp.190-200
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• 1991

본 연구에서는 고온에 노출되는 열-점소성 거동의 해석을 위해 소성유동, 크 리프, 응력풀림(stress relaxation)등의 거동을 동시에 다룰 수 있는 통일구성방정식 모델에 대해 논하고 적절한 모델을 선정한다. 이 모델은 미소변형이론에 근거한 것 이므로 구조물의 거동을 소변형률(small strain)과 소회전(small rotation)의 범위내 로 가정하여 해석한다.선정된 모델에 대해서 시간변화율 형태의 방정식으로부터 유 한요소법을 통한 수치화와 사용된 구성방정식을 효율적으로 처리할 수 있는 수치해석 법상의 알고리듬을 제안한다. 제안된 알고리즘을 사용하여 유한요소법 전산코드를 적상하고, 작성된 코드를 이용하여 고온에서 하중을 받는 단순보와 국부적으로 심한 가열을 받는 구조물에 적용하여 고전적인 구성방정식으로 복합적인 해석이 어려웠던 열-점소성 거동을 효과적으로 해석할 수 있음을 보인다. 본 논문은 응력해석에 주안 점을 두었으므로 열해석에 관한 상세한 논의는 가급적 생략하기로 한다.

• 대한기계학회논문집A
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• 제26권10호
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• pp.2211-2218
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• 2002

In this study, an optimal design study has been made to determine dimensions of die and multi stress rings for extrusion process. For this purpose, a thermo-rigid-viscoplastic finite element program, CAMPform, was used fur forming analysis of extrusion process and a developed elastic finite element program fur elastic stress analysis of the die set including stress rings. And an optimization program, DOT, was employed for the optimization analysis. From this investigation, it was found out that the amount of shrink fitting incurred by the order of assembly of the die set should be taken into account for optimization when the multi stress rings are used in practice. In addition, it is construed that the proposed design method can be beneficial fur improving the tool life of cold extrusion die set.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.901-904
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• 2002

The cutting thickness of ultra-precision machining is generally very small, only a few micrometer or even down to the order of a flew manometer. In such case, a basic understanding of the mechanism on the micro-machining process is necessary to produce a high quality surface. When machining at very small depths of cut, metal flow near a rounded tool edge become important. In this paper a finite element analysis is presented to calculate the stagnation point on the tool edge or critical depth of cut below which no cutting occurs. From the simulation, the effects of the cutting speed on the critical depths of cut were calculated and discussed. Also the transition of the stagnation point according to the increase of the depths of cut was observed.

• 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.