• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.131-135
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• 2001

Evaluation of microstructural changes during open die forging of heavy ingots is important for process control. The objective of the control of forging parameters, such as shape of the dies, reduction, temperature and sequence of passes, is to maximize the forging effects md to minimize inhomogeneities of mechanical properties. The hot working die steel is produced by using the multistage open die forging. The structure is altered during forging by subsequent processes of plastic deformation, recrystallization and grain growth. A numerical analysis using an rigid visco-plastic finite element model was performed to predict microstructural evolution of hot working die steel.

• Transactions of Materials Processing
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• v.16 no.4 s.94
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• pp.293-298
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• 2007

Recently, there is a need to produce a large forged part for the flight, shipping, some energies, and military industries, etc. Therefore, an open die forging technique of cast ingots is required to obtain higher quality of large size forged parts. Cogging process is one of the primary stages in many open die forging processes. In the cogging process prior to some open die forging processes, internal cavities have to be eliminated for defect-free. The present work is concerned with the elimination of the internal cavities in large ingots so as to obtain sound products. In this study, hot compression tests were carried out to obtain the flow stress of cast microstructure at different temperature and strain rates. The FEM analysis is performed to investigate the overlap defect of cast ingots during cogging stage. The measured flow stress data were used to simulate the cogging process of cast ingot using the practical material properties. Also the analysis of cavity closure is performed by using the $DEFORM^{TM}-3D$. The calculated results of cavity closure behavior are compared with the measured results before and after cogging, which are scanned by the X-ray scanner. From this result, the criteria for deformation amounts effect on the cavity closure can be investigated by the comparison between practical experiment and numerical analysis.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.233-235
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• 2001

Residual stress in the forged parts affects the resistance to mechanical failure, dimensional uniformity, and the service life of the parts. In order to elucidate the development of residual stress in open-die forging process, elasto-plastic finite element analysis was implemented to radial forging process. Super duplex stainless steel SAF 2507 was selected as workpiece material and a series of mechanical tests followed by numerical compensation to deformation heating was conducted to obtain necessary flow data. The residual stress distributions were calculated using commercial 3-D FEM code and the effects of process design were evaluated from selected results.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.176-179
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• 2006

Large tubesheet forgings of the steam generator for the 1,400MW nuclear power plant has been developed. Steam Generator is one of the most important structural part for nuclear power plant. It is manufactured by various steel forgings such as shell, head, torus and tubesheet. These steel forgings have been made by open die forging process. After steel melting and ingot making, open die forging has been carried out to get a good quality which means high soundness and homogeniety of the steel forgings by using high capacity hydraulic press. This paper introduced the forging process development and manufacturing experience of large tubesheet forgings which will be used for the steam generator of 1,400MW nuclear power plant.

• Transactions of Materials Processing
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• v.13 no.2
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• pp.142-147
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• 2004

Three-dimensional rigid-plastic finite element analysis has been performed to optimize open die forging process to make round bar. In the round bar forging, it is difficult to optimize process parameters in the operational environments. Therefore in this study, finite element method is used to analyze the practice of open die forging, focusing on the effects of reduction, feeding pitch and rotation angle for optimal forging pass designs. The soundness of forging process has been estimated by the smoothness and roundness of the bar at various combination of feeding pitches and rotation angles. From the test result, process conditions to make round bar having precise dimensional accuracy have been proposed.

• Transactions of Materials Processing
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• v.21 no.5
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• pp.319-323
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• 2012

In order to predict the internal void closing behavior in open die forging process, multiple scale modeling has been developed and applied. The huge size difference between ingot and inner void makes it almost impossible to simultaneously model the actual loading conditions and the void shape. Multiple scale modeling is designed to integrate macro- and micro- models effectively and efficiently. The void closing behavior was simulated at 39 different locations in a large ingot during upsetting and cogging. The correlation between the closing behavior and variables such as effective plastic strain and maximum compressive strain was studied in order to find an efficient measure for predicting the soundness of the forging.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.79-83
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• 2008

We carry out three-dimensional simulation of pore closing processes during upsetting in open die forging. Several pores on a plane section of a cylindrical material are traced at the same time and the results of hydrostatic pressure and effective strain are discussed to reveal the parameters affecting pore closing phenomena. Five different sizes of pores are also investigated by simulation to reveal the pore size effect in pore closing during upsetting. AFDEX 3D is employed for this study.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.627-632
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• 2001

Nimonic 80A superalloy with high-temperature strength and high corrosion-resistance is used in jet engine for aircraft, gas turbine for power plant and marine diesel engine, etc. To develop the manufacturing process of exhaust valve for large diesel engine using Nimonic 80A, various mechanical tests, such as hot compression, microstructure and hardness test have been performed. This results effectively used to set the reasonable forging conditions while hot forging of Nimonic 80A superalloy. Open die and closed die forging experiments are carried out from ESR ingot and finally get a good shaped exhaust valve product.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1513-1516
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• 2003

A crank throw, which is one of the crankshaft part for a large diesel engine is manufactured by closed die forging or open die forging. For the purpose of improvement of productivity the open die forging is usually adopted these days. However it has disadvantage of low yield ratio compare to closed die forging. To overcome this problem, the material properties for hot top and bottom zones of ingot are investigated to utilize them to the product and a modified forging process to reduce the material loss of ingot body through forging analysis according to forging factors(a , R, Ø$\sub$B/, Ø$\sub$D/) is suggested.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1992.03a
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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.