• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.9
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• pp.2242-2251
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• 1993

The mesh-based frictional contact model has been developed which does not rely on the spatial derivatives of the tool surface. Only points on the surface are evaluated from the description. which can then be simplified because of the relaxed demands placed on it. The surface tangents, normals, and corresponding derivatives at each finite-element node are evaluated directly from the finite-element mesh, in terms of the connecting nodal positions. The advantages accrue because there is no longer a need for a smooth tool surface to assure reasonable normals and derivatives. Furthermore, it can be shown that the equilibrium equations can only be properly written with a special normal derived from the mesh itself. The validity, accuracy, computation time, and stability of mesh-based contact model were discussed with the numerical examples of rounded flat-top and rough, flat-top rounded punch forming operations. Also, the forming process of a automobile inner panel section was simulated for testing the robustness of new contact model. In the discussion, the superiority of new model was examined, comparing with tool-based contact one.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1129-1137
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• 1990

Based on the formulation which incorporates large deformation and anisotropy, an elastic-plastic finite element code is developed with membrane element to include the contact treatment. For the analysis of the general sheet metal forming process with contact condition, the treatment of contact is considered by employing the successive skew coordinate system. Three kinds of sheet metal forming processes with contact conditions are analyzed; stretching of a square diaphragm with a hemispherical punch, deep drawing of a circular cup and deep drawing of a square cup. Then the computational results are compared with the experiment. The computed loads and the distribution of the thickness strain are in good agreement with the experiment for all cases. However, the computational results of the thickness strain show the effect of bending can not be ignored in the deep drawing process whereas the effect of bending is negligible in stretching.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.10a
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• pp.11-15
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• 2001

본 논문에서는 냉장고를 운반하기 위하여 현재 냉장고 뒷판에 부착된 플라스틱 손잡이를 판금물인 냉장고 뒷판에 성형, 대체하는 연구를 수행하였다. 이 손잡이는 그 형상이 비축대칭으로써 평면변형(Plane STRAIN)과 축대칭변형(axisymmetric)이 좁은 공간상에 공존하는 형태를 띄고 있고 그 성형 깊이가 깊어 성형이 매우 어렵다. 따라서 성형을 가능케 하기 위하여 유한요소 해석을 이용한 형상의 최적설계를 통해 터짐을 방지하고 실험을 통해 주름이 발생하지 않도록 하였다. 현재 부착되어 있는 플라스틱 손잡이의 모양을 단공정으로 성형 시에는 재료의 유입이 원활하지 못하여 파단이 발생함으로 불가능하였다. 그러나 두공정으로 하여 첫공정에서는 축대칭에 가까운 형상으로 원하는 깊이를 얻고 두번째 공정에서 손잡이의 형상을 만들어 줌으로써 성형이 가능하다. 또한 냉장고 뒷판의 형상 변경을 통하여 재료의 유입을 원활히 함으로써 단공정으로의 성형도 가능함을 도출하였다.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03a
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• pp.14-17
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• 1999

The finite element formulation is developed for predicting strain distributions and weld line movements in the forming processes of laser welded blank. The welded zone(WZ) is modelled with several narrow finite elements whose material characteristics are analytically obtained from those of base metals based on the tensile tests. In order to show the reliability and effectiveness of weld element the forming process of hemispherical dome stretching and auto-body door inner panel stamping are simulated FEM predictions show good agreements with experimental observations.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.27-30
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• 2007

In order to measure the friction coefficient used in sheet metal forming analysis, a friction tester was manufactured and friction tests were performed in various forming conditions. Based on the friction coefficients measured, a mathematical friction model was constructed in terms of lubricant viscosity, blank holding force, punch velocity and sheet roughness. In addition, the effect of the number of forming parameters in the calculation of friction coefficient on the accuracy of sheet metal forming analysis was investigated by comparing the punch loads obtained from the FEM simulation, in which the friction coefficients were determined by a few parameters with the experimental measurement.

• Transactions of Materials Processing
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• v.6 no.4
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• pp.300-310
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• 1997

A finite element inverse method is introduced for direct prediction of blank shapes, strain distributions, and reliable intermediate shapes from desired final shapes in axisymmetric multi-step deep drawing processes. This mothod enables the determination of process disign. The approach deals with the Hencky's deformation theory. Hill's second order yield criterion, simplified boundary conditions, and minimization of plastic work with constraints. The algorithm developed is applied to motor case forming, and cylindrical cup drawing with the large limit drawing ratio so that it confirms its validity by demonstrating resonably accurate numerical results of each problem. Numerical examples reveal the reason of difficulties in motor case forming with corresponding limit diagrams.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.4
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• pp.247-255
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• 2016

Sheet metal-forming processes such as stamping, deep drawing, bending, shearing, hydroforming, hydromechanical deep drawing, rubber forming, and incremental forming have been widely used in the automotive, aircraft, and ship-building industries. With the expansion of the automotive industry, research on these processes has been remarkably developed in Korea since the 1980s. Here, we review the history of this research as well as recent trends in sheet metal-forming processes. This overview focuses specifically on the results of research in Korea and on the works of Professor D.Y. Yang, in honor of his retirement.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.26-29
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• 1999

The sectional forming analysis program for analyzing the hydroforming processes of axisymmetric sheet parts was tleveloped. The rigid-viscoplastic FEM formulation based on membrane theory was derived, wh~cta simi~ltaneously solve force equilibrium as well as non-penetration condition. Hill's non-quadratic normal anisotropic yield theory(1979) was used for material behaviour. For describing the liquid pressure iaction, the flexible tool concept was introduced. Isotropic hardening law was also assumed. To verify the \,alidity of the formulation, the stepped cup forming process as well as the hydrostatic bulging test were \imnlated. Simulation results agreed well with Finckenstein and experimental ones.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.549-556
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• 2010

In general, materials that can be used to form elastic pads, such as urethane and rubber, are often used in flexible forming processes by inserting the pads between a blank and flexible die for smoothing the forming surface that is formed by a reconfigurable die. In this study, the effects of the elastic pad on formability in the flexible forming process for sheet metals are investigated by performing numerical simulations. In the simulation, the hyperelastic material model is used, where the urethane elastic pads serve as elastic cushions. Case studies are carried out for elastic materials with different hardness values and thicknesses. The results are used to evaluate formability by comparing the configuration of the deformed blank and its major cross-sectional profiles. It is verified that the elastic pad used in the flexible forming process for sheet materials should be hard and that its thickness should be chosen appropriately.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.118-121
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• 2008

Flexible die is more efficacious than fixed die which is generally used in stretch forming process in view of production cost. Accordingly, in order to verily the validity of the flexible forming process, curved thin skin structure forming analyses using the fixed and flexible die were performed. As results, merit and demerit with regard to the fixed and flexible die were confirmed. The result of the stretch forming process analysis using the flexible die was better than that using the fixed die in view of the elastic recovery. However wrinkles were occurred on the sheet material due to die cavities between the punches in the flexible forming process, thus the solutions against these problems were presented.