• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.337-344
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• 1989

The upper bound elemental technique (UBET) is used to simulate the bulk flow characteristics in axisymmetric closed die forging process. Internal flow inside the cavity is predicted using a kinematically admissible velocity field that minimizes the rate of energy consumption. Application of the technique includes an assessment of the formation of flash and of degree of filling in rib-web type cavity using billets with various aspect rations. The technique considering bulging effect is performed in an incremental manner. The results of simulation show how it can be used for the prediction of forging load, metal flow, and free surface profile. The experiments are carried out with plasticine. There are good agreements in forging load and material flow in cavity between the simulation and experiment. The developed program using UBET can be effectively applied to the various forging problems.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.11
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• pp.63-68
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• 2000

The purpose of this paper is to compare the forging effects according th the shape of preforms of cup shaped powder forging product, and extend the application of powder forging technology to more complicated cup-shaped products like pistons. In order to this, preforms are provided by compacting, sintering, and machining in various shapes, then forged to final shape of products. The workability for sintered aluminium powder material is examined. Density and strain loci of forged products are compared, and the most effective shape of preform is proposed. The preform for a piston of 50mm in diameter is provided and hot forged to final product.

• Transactions of Materials Processing
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• v.21 no.1
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• pp.13-18
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• 2012

During warm forging, materials are formed in the temperature range of $300^{\circ}C\sim900^{\circ}C$. In this temperature range, the friction between the forging die and the material is very high and has a negative effect on the forming process causing severe die wear and possible defects in the component because of stick-slip. Thus, lubrication characteristics are a very important factor for productivity during warm forging. In this paper, ring compression experiments were conducted to estimate the friction factor between the die and the materials as the main factor in characterizing the lubricant. Also, ring tests using normal graphite power as a lubricant coating system were compared with tests using nano graphite powder. The results confirm that the nano graphite is superior to the normal graphite in view of its lubricating effect. In addition, the friction factor (m) was estimated with respect to the amount of the nano graphite content in the lubricant. With 10 % nano graphite the friction factor had the lowest value as compared to other amounts. It can be concluded that the amount of the nano graphite in the coating system can be optimized to obtain the best lubrication condition between the die and the material using ring test experiments.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.257-257
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• 2008

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.9
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• pp.1400-1413
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• 1997

Semi-solid forging(SSF) process of A356 aluminium alloy has been studied to assess the effect of process variables on the component integrity. Semi-solid material(SSM) was fabricated by mechanical and electro-magnetic stirring process. The fabricated SSM by using mechanical stirring process has been carried out on cooling rate of 0.022.deg. C/sec 0.0094.deg. C/sec and stirring speed n=600, 1000 rpm, respectively. The fabricated SSM by using electro-magnetic stirring process is supplied by Pechiney. The holding time and temperature in the semi-solid state before forging also affects the globular microstructure of alloy. Therefore, the influence of these two parameters is discussed in terms of the microstructure of alloy. The SSF process has been conducted with three different die temperatures($T_{die}$=250.deg. C, 300.deg. C, 350.deg. C) and two kinds of gate types(straight gate and orifice gate). This paper is to investigate the influence of gate shapes of die on filling phenomena in SSF process more deeply. The mechanical properties of forged components were also investigated for variation of process conditions such as die temperature, gate shape and SSM.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.119-123
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• 2009

In this paper, effects of major design parameters of cold forging dies on die mechanics are quantitatively investigated with emphasis on shrink fit using a thermoelastic finite element method. A ball-stud cold forging process found in a cold forging company is selected as a test process and the effects of die insert material, shrink fit, dimension of ring, partition of die inert and clamping force on effective stress and circumferential stress are analyzed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.172-175
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• 2003

Thermomechanical behavior of Al-Mg-Si alloys have been studied to investigate the effect of microstructural features such as pre-existing substructure and distribution of particles on the deformation characteristics. The controlled compression tests have been carried out to get the basic information on how the alloy responds to temperature, strain amount and strain rate. Then hot forging of Al-Mg-Si alloys has been carried out and analyzed by the comparison with the compression tests. Microstructural features after forging have been discussed in terms of the thermomechanical response of Al-Mg-Si alloys. As already well mentioned, we have found that the deformation of Al-Mg-Si at the elevated temperature brought the recovered structure on most conditions. In a certain time, however, abnormally large grains have been found as a result of deformation assisted grain growth, which means that hot forging of Al-Mg-Si alloys could lead to a undesirable microstructural variation and the consequent mechanical properties such as fatigue strength.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.106-110
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• 2001

A effective and accurate method of hot-forging process is essential to the design of optimized dies as well as workpiece of intial shape. the former is achieved by a proper forging sequence with invokes serious problem like excessive load and die wear, die failure, underfilling and lap defects. the latter is achieved by a proper preform design of case I, case II, case III. metal forming processes of aluminum-alloy forged at an effective strain and temperature are analyzed by the finite element method. the non-isothermal analysis have been compared with optimized in terms of preform shape.

• Transactions of Materials Processing
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• v.16 no.6
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• pp.452-456
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• 2007

Cold forging technology of a gear product is being interested in the dimensional accuracy, high stiffness and reduction of stress concentration. Especially it is needed to avoid the damage due to extremely high local pressure. Therefore it is important to reduce the high pressure in die design of cold forging. In this study, single die insert type and splitted die insert type are considered to recognize the notch effects in the die of sprocket forming. The stress concentration has been released at the notch area by the cushion effect in the splitted die insert.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.11
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• pp.2749-2761
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• 2000

Densification, grain growth, and phase transformation of nanocrystalline ceramic powder were investigated under pressureless sintering, sinter forging, and hot pressing. A constitutive model for densification of nanocrystalline ceramic powder was proposed and implemented into a finite element program (ABAQUS). A grain growth model was also proposed by including the effect of applied stress on grain growth when phase transformation occurs. Finite element results by using the proposed models well predicted densification behavior, deformation, and grain growth of nanocrystalline titania powder during pressureless sintering, sinter forging, and hot pressing. Finite element results by using the proposed model also well predicted experimental data in the literature for densification behavior of nanocrystalline zirconia powder during pressureless sintering and sinter forging.