• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1996.10a
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• pp.174-184
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• 1996

Two methods for cold extrusion processes to produce an axisymmetric steel gear blank are investigated for comparing each other. The "classical" forming method consisting of four operations is selected first to be simulated using the rigid-plastic finite element method and uses single-die presses. The other using a fully automated transfer headers can produce the final part without interannealing. The final products must be checked at the design criteria such as area reduction, the extrusion ratio and punch diameter to depth ratio, especially punch buckling by simulations. FEM analysis is performed mainly for strain distribution, both process sequences are proved to have proper charicteristics suitable for each production method in terms of maximum load. Those simulation results will provide good design criteria in the future work to advance the manufacturing process.

• Transactions of Materials Processing
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• v.6 no.6
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• pp.517-526
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• 1997

The purpose of this study is to investigate changes in the wall thickness of tube sinking and working forces by the upper bound method and ABAQUS code. The independent variables are ; workpiece material, original wall thickness of tube, die angle, friction, and reduction of diameter. The results indicate that these five variables are factors of the increase in wall-thickness and working forces. Three variables, a inner tube wall angle and two angles of the velocity discontinuous surfaces, are optimized in this proposed velocity field by the upper bound method. In this method, we can estimate the working forces and final tube thicknesses similar to actual forming process. Optimum process variables which are obtained by upper bound method are used in ABAQUS pre-model.

• Transactions of Materials Processing
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• v.4 no.3
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• pp.267-281
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• 1995

Preform design is one of the critical fields in metal forming. The finite element method(FEM) has been effective in designing preforms and process sequence, for which the backward tracing scheme of the rigid-plastic FEM has been explored. In this work a program using the backward tracing scheme by the rigid-plastic FEM is developed for three-dimensional plastic deformation, which is an extension of the scheme from two-dimensional cases. The calculation of friction between workpiece and die, and handling of boundary conditions during backward tracing require sophisticated treatment. The developed program is applied to upsetting of a rectangular block and to side pressing of a cylindrical workpiece. The results of the two applications show feasibility of the program on three-dimensional plastic deformation.

• Transactions of Materials Processing
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• v.18 no.3
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• pp.251-255
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• 2009

Since fastener bolt for airplane require high specific strength and corrosion resistance, Ti-6Al-4V alloy is widely used. However, the Ti-6Al-4V bolt is generally manufactured by cutting and rolling because of their poor workability. The aim of present work is to develop hot forming technology for high strength Ti-6Al-4V. Various heat-treatments were applied to specimen in order to increase hot-workability and prevent galling with die. Multiple forging were simulated with FE code to determine optimum process parameters including specimen temperature, strain rate, local strain, and thermal shrinkage. Forged samples were heat-treated again to increase their mechanical properties.

• Transactions of Materials Processing
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• v.20 no.8
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• pp.568-574
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• 2011

The combination of tailor welded blank (TWB) and hot stamping often offers improved crash-worthiness and reduced mass of stamped parts in the automobile body. To investigate the formability of laser TWB and the reliability of weld line, the present study used 22MnB5 boron steel sheet of the same thickness and used the Erichsen cupping test at elevated temperatures. The effects of laser direction, die temperature, weld line positions and forming speed on formability(the limiting dome height) were studied and the results were compared with the formability of the base material.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.2
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• pp.58-65
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• 2003

The conventional forming process such as squeeze casting or die casting for fabricating metal matrix composites products have a disadvantage such as non homogenous distribution of reinforcement, weak bonding between matrix and reinforcement and cost increase in parts fabrication. Thixoforming process has been accepted as a new method for fabricating the net shaped metal matrix composites with lightweight and wear resistance. In this paper, the effect of volume fraction and reinforcement sizes on mechanical properties in cylinder liner part of metal matrix composites has been investigated with processes parameters such as pressure and velocity. Moreover, the methods to obtain the thixoforged composites cylinder liner with high quality has been proposed. To evaluate the composites cylinder linear fabricated at the conditions proposed in this study, mechanical properties of fabricated composites cylinder linear were compared with those of commercial composites cylinder linear.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.04b
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• pp.171-177
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• 1995

In this paper, the deformation method for inner and outer races of rollr-bearing bymeans of the warm precision forging is investigated. We adapted the process designsuch as following that, toincrease Die life, reduce heat transfer through conduction and the eccentricity of preform in warm forging of bearing gace, the bottom portion of billet is formed during upsetting process. Then it is backward extruded, and thus obtained ring preform is formed by combined extrusion. Also, we compared it with the froming method in China and Japan, and we have known it is more excellent method. Basides, this forming method is simulated by UBST which is based on the merits of UBET nd FEM. The results show that it is easy to know the exact location of neutral surface through the inspection of streamline during combined extrusion, and the velocity vector distribution along the surface of velocity discontinuity is investigationed. Also the effectiveness of this method is proved by te experiment using model material that is Plasticine.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.186-189
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• 2005

This paper was designed to assess the adhesive properties of hard coatings on non-nitrided and nitrided various tool steels. Estimations of adhesion were done to scratch test which is mainly used in hard coating. The critical load(Lc) between coating and substrate is defined through analysis of frictional load vs. normal load curve, signals of acoustic emission and optical observations. Coatings employed in this study are TiN, CrN and TiAlN, tools as substrates are STD11, STD61 and SKH51. It was classified to substrates with/without nitrided layer and hard coatings on substrate were deposited by arc PVD. Results showed that harder substrates and coatings give higher values of critical loads.

• Transactions of Materials Processing
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• v.6 no.4
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• pp.338-345
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• 1997

The behaviour of alloys in the semi-solid state strongly depends on the imposed stress stage and on the morphology of the phase which can vary from dendritic to globular. To optimal net shape forging of semi-solid materials, it is important to investigate for material behaviour for variation of strain rate. Therefore, to investigate the effect of compression speed on deformation of aluminum alloy with globular microstructure, the compression test for semi-solid aluminum alloy with controlled solid fraction is perform by material test system which is attracted with furance. The behavior of semi-solid aluminum alloy were discussed for the various solid fraction and die speed. The material constants in stress-strain were are also proposed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.05a
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• pp.103-107
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• 2002

The 2nd forming process of flanging/hemming has recently many interest because it determines external quality of automobile. It is difficult to apply finite element simulation in flanging/hemming due to small element size which needs for expression of bending effect on the die corner and big model size of side door, back door, tank lid and like opening Parts. This paper shows the process of flanging/hemming simulation using finite element model for automotive panels. The explicit finite element program PAM-STAMP$\^$TM/ was used to simulate the flanging and hemming operations.