• Transactions of Materials Processing
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• v.7 no.1
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• pp.12-22
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• 1998

An expert drawbead model is developed for the finite element analysis of stamping processes. The expert model calculates drawbead restraining forces and bead-exit thinnings with the forming condi-tions and drawbead size. The drawbead restraining forces and bead-exit thinnings of a circular draw-bead and stepped drawbead are computed by mathematical models and corrected by the multiple lin-ear regression method based on experimental measurements. The squared drawbead preventing the sheet from drawing-in inside die cavity is assumed to have a very huge drawbead restraining force and no pre-strain just after drawbead. The combined beads are considered as a combination of basic draw-beads such as circular a drawbead stepped drawbead and squared drawbead so that the drawbead restraining forces and bead-exit thinnigs are basically sum of those of basic drawbeads.

• 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.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.1
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• pp.171-177
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• 2008

The characteristics of sheet metal process are little loss of material during process, the short processing time and the excellent price and strength. It has been widely used in autobody, electronic components, aircraftbody, etc. Lancing is a press operation in which a single-line cut or slit is made on part way across the strip stock, without removing any metal. In this paper, we examined the validity of finite element method analysis on the automobile CTR-PLR -L/R stamping process by using the lancing engineering method. As a result, it has shown that the proper lancing engineering method could prevent fracturing by improving sheet metal flow.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.560-563
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• 2008

A condensed model is proposed for the simulation of forming of sandwich sheet with pyramid core. A corresponding finite element analysis for L-type bending is carried out to prove the accuracy and the effectiveness. Simulation results are compared with those of experiment. Deformation shape and post-buckling behavior by simulation are in good agreement with those of experiment for the considerable range of deformation. From the comparison of force-displacement curve, it is shown that the proposed model shows good prediction of the forming force compared to the experiment. Thus, the effectiveness of the proposed method is sufficiently demonstrated.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1119-1128
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• 1990

A numerical method for analyzing non-isothermal, rigid-viscoplastic deformation problems has been presented. As an application, a stretch forming of sheet metals, including temperature effect, has been analyzed by a three-dimensional finite element method. Bishop`s step-wise decoupled method is adopted to solve thermomechanical coupling between deformation and heat transfer. Using the method, the effect of temperature on strain distribution during stretch forming is investigated. By comparison of the non-isothermal results with isothermal analysis, the importance of including temperature effects in the analysis of metal forming problems is emphasized. The predicted results were in good agreement with the existing experimental measurements at the different punch temperatures and dome heights investigated. It is also found that any increase of the punch temperature appeared to postpone the strain localization process by lowering the peak strain in the critical punch-sheet contact region and by normalizing strain distribution within the specimen.

• 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.

• Transactions of Materials Processing
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• v.12 no.4
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• pp.401-407
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• 2003

This paper newly proposes a mesh regularization method for the enhancement of the efficiency in sheet metal forming analysis. The regularization method searches for distorted elements with appropriate searching criteria and constructs patches including the elements to be modified. Each patch is then extended to a three-dimensional surface in order to obtain the information of the continuous coordinates. In constructing the surface enclosing each patch, NURBS(Non-Uniform Rational B-Spline) surface is employed to describe a three-dimensional free surface. On the basis of the constructed surface, each node is properly arranged to form unit elements as close as to a square. The state variables calculated from its original mesh geometry are mapped into the new mesh geometry for the next stage or incremental step of a forming analysis. The analysis results with the proposed method are compared to the results from the direct forming analysis without mesh regularization in order to confirm the validity of the method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.2
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• pp.440-449
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• 1996

Superplastic punch forming of sheets is simulated by a finite element method to obtain the optimal punch speed and the related deformed shapes. The punch forming has an advantage of guaranteeing the desired accuracy inside a product and controlling the thichness of a deformed sheet more accurately than blow forming. The finit element code developed is associated with the contact algorithm and the control algorithm of punch speed for the optimum forming. The simulation demonstrates that the variation of the thichness in a blank sheet affects the punch speed and the final distribution of the thichness in a product. The analysis proposes that a ring-typed thichness controller is very effective in controlling the thichness of a deformed sheet appropriately.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.2
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• pp.193-200
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• 2000

In the sheet metal forming process, the drawbead is used to control the flow of material during the forming process. The drawbead provides proper restraining force to the material and prevents defects such as wrinkling or breakage. For these reasons, many studies for designing the effective drawbead have been conducted. In this paper, the influence of the number of drawbead during the blank forming process will be introduced. For the analysis, the numerical method called the static-explicit finite element method was used. The finite element analysis code for this method has been developed and applied to the drawbead process problems. It is expected that this static-explicit finite element method could overcome heavy computation time and convergence problem due to the increase of drawbeads.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.387-390
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• 2008

Electromagnetic forming (EMF) technology, which is one of the high speed forming methods, has been used for the forming process in various industry fields. Numerical approach by finite element simulation of the EMF process is presented in this study. The implicit code is used to obtain the numerical model of the time-varying currents that are discharged through the coil in order to obtain the transient magnetic forces. In addition, the body forces generated in the workpiece are used as the loading condition to analyze deformation of thin sheet metal workpiece using explicit code. Numerical approach for a dimpled shape by EMF process is carried out and the simulated results of the dimpled shape by EMF are reviewed in view of the deformed shape and formability evaluation.