• 대한기계학회논문집A
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• 제20권2호
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• pp.488-499
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• 1996

SMC(Sheet molding compound) is a thermosetting material reinforced with chopped fiberglass. The compression molding of SMC was analyzed based on a rigid thermo-viscoplastic approach using a three dimensional finite element program coupled with temperatures. Only the temperature analysis part was tested in this paper by solving one-dimensional heat transfer problem and comparing with the exact solutions available in the literature. Based on this comparison the program was proved to be valid and was further applied in solving compression molding of SMC between flat dies. To investigate the usefulness of a rigid thermo-viscoplastic approach in the compression molding analysis of SMC charge, compression of rectangular shaped SMC charge at plane strain and three dimensionalde formation condition was analyzed under the same condition as given in the literature. From this comparison it was found out that the rigid thermo-viscoplastic approach was useful in analyzing SMC compression molding between flat dies.

• 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.

• 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.

• 소성∙가공
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• 제8권5호
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• pp.498-506
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• 1999

The metal forming processes of aluminum alloy wheel forging at elevated temperature are analyzed by the finite element method. A coupled thermo-mechanical model for analysis of plastic deformation and geat transfer is adapted in the finite element formulation. In order to consider the strain-rate effects on material properties and the flow stress dependence on temperatures, rigid-viscoplasticity is introduced in this formation. In this paper, several process conditions were applied to the dimulation such as die speed, rib thickness, and depth of die cavity. Simulation results are compared, and discussed with each case. Metal flow, die pressure distributions, temperature distributions, velocity fields and forging loads are summarized as basic data for process design and selection of a proper press equipment.

• 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.

• 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.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1995년도 추계학술대회논문집
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• pp.16-29
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• 1995

A full three-dimensional thermo-coupled rigid-viscoplastic finite element method and the currently developed microstructural evolution system which includes semi-empirical mathematical equations suggested by different research groups were used together to form an integrated system of process and microstructure simulation of hot rolling. The distribution and time history of thermomechanical variables such as temperature, strain, strain rate, and time during pass and between passes were obtained FEM analysis of multipass hot rolling processes. Then distribution of metallurgical variables were calculated successfully 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 literature. Consequently, this approach makes it passible 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.

• 대한기계학회논문집A
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• 제24권11호
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• pp.2836-2844
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• 2000

Thickness control of hot-rolled strips has become an important issue in recent years because of the need for improving the quality of the hot-rolled strip. In this study, a modifying method of rolling force set-up with consideration of spread was developed to improve the thickness uniformity at the finishing rolling units in hot rolling. Through the analysis of real production data it was found that the accuracy of the rolling force determined from the finishing mill set-up (FSU) model dominantly governed the thickness uniformity in rolled plates at the front. Based on this analysis , several examples were selected to calculate the spread of rolled plate using three dimensional rigid thermo-viscoplastic finite element program. FE analysis results were used to train the neural network system that can predict the spread hot-rolled plate and the rolling force was modified based on the predicted value of spread. The modified rolling forces were closer to the measured rolling force so it can be expected that the accuracy of thickness uniformity of hot-rolled plate will be improved.