• Journal of the Korean Society for Precision Engineering
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• v.18 no.12
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• pp.145-151
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• 2001

The dimensional accuracy of the cold forged part is depended on the elastic characteristics of the die. To increase the stiffness of the prestressed die, the first stress ring of the tungsten carbide alloy (WC) is considered. For the design, Lame's equation is used. Diameter ratios and interferences have been determinated by maximum inner pressure without yielding of materials. The design of the prestressed die has been compared with the conventional one. For the comparison, the FE-analysis using ANSYS has been performed. The results indicate that the prestressed die with the high stiffness can be obtained by the using the high stiffness material as the first stress ring.

• Transactions of Materials Processing
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• v.8 no.1
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• pp.108-115
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• 1999

In this paper, the analysis of cold forging in final state has been performed by using rigid-plastic FEM. For the analysis, the geometry and flow stress of the workpiece are required. One method to obtain the geometry is measurement of that made from experimet. To evaluate the flow stress, average effective strain is calculated from the load-stroke diagram by using energy method. The numerical test performed to show the validity of propose method. The analysis of PFIR, the precision forging of spurgear with inside relif, is performed.

• Transactions of Materials Processing
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• v.3 no.1
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• pp.3-17
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• 1994

The semi-solid metal forming for vigorously agitated semi-solid alloys has been widely studied over the last decade. Metal forming processes are now being developed using alloys in the semi-solid state, among them are rolling, forging, extrusion, and die casting. Some of these are now employed commercially to produce a components and are also used to fabricate metal matrix composites. The semi-solid materials can be processed either directly during solidification and for this purpose mechanical stirring was demonstrated to produce a highly solidification. This paper is concerned with the influence of processing parameters on limitations of semi-solid forming.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.237-240
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• 1999

The elastic stress analysis of the die for helical gear forging has been calculated by using the nodal force at the final stage obtained from the rigid-plastic finite element analysis. In order to obtain more precise gear products. the elastic analysis of the die after release of punch and the elastic spring-back analysis of product after ejection have been performed and the final dimension of the computational product has been in good agreement with that of the experimental product.

• Journal of the Korean Society for Precision Engineering
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• v.5 no.2
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• pp.33-42
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• 1988

In a large scale oil hydraulic system having repeatedly operated actuator, such as a large scale forging press, pressure surges often due to the recombination of oil column in a return line attached to the downstream side of a directional control valve. Expecially, the pressure surges appear very severe ones at a certain valve operating frequency. These pressure surges restrict the operating frequency of the hydraulic system. But related reports on the above mentioned phenomenon are rarely to be found. In this study, therefore, the authors investigate the exact reason why such severe pressure surges occur at a certain range of valve operating frequency. The study is performed by experiment and numerical computation on the relationship between pressure surges and valve operating frequency.

• Journal of the korean Society of Automotive Engineers
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• v.14 no.1
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• pp.13-24
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• 1992

1) 1/2 Scale Model 실험과 실제품 성형실험을 통하여 정밀 냉간단조에 의한 Tripod Slide Housing의 제조공정 설계기술을 확립하고, 4단계 성형공정으로 시제품 제작에 성공하였다. 2) Triod Slide Housing을 성형할 수 있는 4단계(전방압출, Heading, 후방압출, Ironing)의 금형을 설계 및 제작하여 시제품 생산에 적용하고, 관련 필요기술을 축적하였다. 3)XC 48 등 중,고탄소강의 소둔 실험을 통하여 소둔 조건에 따른 구상화율 및 경도의 변화에 대한 연구를 수행함으로써, 고탄소강의 냉간단조시에 필요한 최적 소둔 조건에 응용할 수 있는 자료를 축적하였다.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.9
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• pp.156-164
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• 2001

Two-dimensional solidification analysis during rheology forming process of semi-solid aluminum alloy has been studied. Two-phase fluid flow model to investigate the velocity field and temperature distribution is proposed. The proposed mathematical model is applied to the die shape of the two types. To calculate the velocity and temperature fields during rheology forming process, the earth governing equation correspondent to the liquid and solid region are adapted. Therefore, each numerical models considering the solid and liquid region existing within the semi-solid material have been developed to predict the deflect of rheology forming gnarls. The Arbitrary Boundary Maker And Cell (ABMAC) method is employed to solve the two-phase flow model of the Navier-Stokes equation. Theoretical model on the basis of the two-phase flow model is the mixture rule of solid and liquid phases. This approach is based on the liquid and solid viscosity. The liquid viscosity is pure liquid state value, however solid viscosity is considered as a function of the shear rate, solid fraction and power law curves.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.7
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• pp.735-742
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• 2014

A self-piercing rivet (SPR) is a mechanical component for joining dissimilar material sheets such as those of aluminum alloy and steel. Unlike conventional rivets, the SPR directly pierces sheets without the need for drilling them beforehand. However, the regular SPR can undergo buckling when it pierces a high-strength steel sheet, warranting the design of a helical SPR. In this study, the joining and forging processes using the helical SPR were simulated using the commercial FEM code, DEFORM-3D. High-tensile-strength steel sheets of different strengths were joined with aluminum alloy sheets using the designed helical SPR. The simulation results were found to agree with the experimental results, validating the optimal design of a helical SPR that can pierce high-strength steel sheets.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.5
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• pp.57-63
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• 2009

Interface friction in blanking dies, cold forging and extrusion of aluminum alloys is a major cause of inefficient process. This paper describes an investigation of femtosecond laser texturing for reduction of interface friction on sliding surfaces in forming process. Femtosecond direct writing technology was used to fabricate a laser micro-machined die and to create microgroove patterns with varying size and density on metal forming dies. A systematic approach to find the optimum parameters and computer simulation comparison of friction coefficients are provided to study the relation of friction coefficients and die profiles. In metal forming tests, the effectiveness of various laser-machined patterns for enhancing interface lubrication is determined.

• Transactions of Materials Processing
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• v.16 no.2 s.92
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• pp.132-137
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• 2007

A double roll rotary forming equipment is presented in this paper. The equipment is developed for joining the socket with the ball of a concave piston assembly with its geometrical tolerance requirements satisfied. The equipment is composed of a lathe, a double roll system and a roll pressing unit driven by the hydraulic system. The workpiece rotates by spindle chuck of the lathe while the double roll system approaches perpendicularly to the central line of the workpiece. The equipment is successfully applied to precision joining of the ball and the socket fur the concave piston assembly of a high pressure hydraulic pump.