• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.217-221
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• 1997

In this study, 3D sheet metal forming analysis program is developed by explicit finite element method. In this program, analysis flow just follows the real engineering process to provide the user intuitive understanding and smooth contact alorithm improves the accuracy of stress prediction. The capability of this program are demonstrated by various examples.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.279-280
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• 2007

In this study, it is investigated that the effect of material properties such as various temperature, forming speed and strain rates on formability and forming limits of Mg alloy sheet in square cup deep drawing. Since the sheet metal forming of Mg alloy is perform at elevated temperature, the effect of strain rates related with the forming temperature and forming speed is very important factor for formability and forming limits. Therefore, the investigation for process variables is necessary to improve formability and forming limits. Also, the effects of strain rate and thickness transformation were studied by the experimental and FE analysis using the square cup deep drawing. The temperature, forming speed, and strain rates were investigated. Forming of Mg alloy takes consider into temperature, proper forming speed and strain-rate the formed parts were good without defects fur forming limits.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.1
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• pp.88-99
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• 1996

The explicit scheme for finite element analysis of sheet metal forming problems has been widely used for providing practical solutions since it improves the convergency problem, memory size and computational time especially for the case of complicated geometry and large element number. The explicit schemes in general use are based on the elastic-plastic modeling of material requiring large computataion time. In the present work, a basic formulation for rigid-plastic explicit finite element analysis of plain strain sheet metal forming problems has been proposed. The effect of some basic parameters involved in the dynamic analysis has been studied in detail. Thus, the effective ranges of parameters have been proposed for numerical simultion by the rigid-plastic explicit finite element method. A direct trial-and-error method is introduced to treat contact and friction. In computation, sheet material is assumed to possess normal anisotropy and rigid-plastic workhardening characteristics. In order to show the validity and effectiveness of the proposed explicit scheme, computations are carried out for cylindrical punch stretching and the computational results are compared with those by the implicit scheme as well as with a commercial code. The proposed rigid-plastic exlicit finite element method can be used as a robust and efficient computational method for analysis of sheet metal forming.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.10a
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• pp.196-201
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• 2001

This study reveals the thin sheet metal process with multi-forming die that the name is progressive die, as a pilotless type, also high precision production part is made. They require analysis of many kinds of important factors, i.e. theory and practice of metal press working and its phenomena die structure, machining condition for die making, die material, heat treatment of die components, know-how and so on. In this study, we designed and constructed a multi-forming progressive die as a bending and drawing working of multi-stage and performed through the try out for thin sheet metal. Out of the characteristics of this paper that nothing might be ever seen before such as this type of research method on the all of processes of thin and high precision production part.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.10a
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• pp.275-281
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• 2001

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 effect of the drawbead shape 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. In result, convergence problem and computation time due to large non-linearity in the existing numerical analysis methods were no longer a critial Problem. Futhermore, this approach could treat the contact friction problem easily by applying very small time intervals. It is expected that various results from the numerical analysis will give very useful information for the design of tools in sheet metal forming process.

• Transactions of Materials Processing
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• v.25 no.3
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• pp.182-188
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• 2016

Flexibly-reconfigurable roll forming (FRRF) is a novel sheet metal forming technology conducive to producing multi-curvature surfaces by controlling the strain distribution along longitudinal direction. In FRRF, a sheet metal is shaped into the desired curvature by using reconfigurable rollers and gaps between the rollers. As FRRF technology and equipment are under development, a simulation model corresponding to the physical FRRF would aid in investigating how the shape of a sheet varies with input parameters. To facilitate the investigation, the current study exploits regression analysis to construct a predictive model for the longitudinal curvature of the sheet. Variables considered as input parameters are sheet compression ratio, radius of curvature in the transverse direction, and initial blank width. Samples were generated by a three-level, three-factor full factorial design, and both convex and saddle curvatures are represented by a quadratic regression model with two-factor interactions. The fitted quadratic equations were verified numerically with R-squared values and root mean square errors.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.40-43
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• 2001

The use ef sheet material for the hydroforming of a closed hollow body out of two sheet metal blanks is a new class of hydroforming process. By using a three-dimensional finite element program, called HydroFORM-3D, the hydroforming process of sheet metal pairs is analyzed. Also the comparison of conventional deep-drawing and hydroforming process was conducted. The simulation has concentrated on the influences of the various forming conditions, such as the unwelded or welded sheet metal pairs and friction condition, on the hydroforming process. This computational approach can prevent time-consuming trial-and-error in designing the expensive die sets and hydroforming process of sheet metal pairs.

• Transactions of Materials Processing
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• v.25 no.5
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• pp.301-305
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• 2016

The manual modification of stamping die has widely been used in order to reduce springback after sheet metal forming. When UHSS (Ultra High Strength Steel) is used in sheet metal forming, the die design considering springback compensation is more difficult because higher strength sheet has more springback. In this study, the optimization method was used in order to design die geometry considering springback compensation after forming of 1.2GPa UHSS. Die geometries were defined as design variables and the springback distance from the die surface was conducted as object function in optimization process. The optimized die geometry considering springback compensation was performed using finite element and optimization analysis. The simulation results such as thickness distribution and springback amount were compared with measured data using 3D optical measurement system (GOM ARGUS, ATOS). And the prediction of springback amount showed a good agreement within test results.

• Transactions of Materials Processing
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• v.8 no.4
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• pp.347-355
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• 1999

The paper is concerned with an improved scheme for application of the blank holding force in order to take account of the thickness distribution in the sheet material of the flange region. The scheme incorporates with a modified membrane finite element method for planar anisotropic materials. The new scheme proposed two coefficients α and βto calculate the compressive stress in the sheet metal due to the blank holding force, which should be determined properly for accurate analysis. The effect of αand βon the blank holding force distribution and the deformed shape is investigated with simulation of rectangular cup deep drawing processes by changing parameter values.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.134-137
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• 2005

In this paper, a continuous contact treatment has been considered during FE-analysis of the sheet metal forming processes. Because the simulation is usually performed stepwise, the status of contact can change suddenly. In case of implicit scheme, the increment of punch stroke can be chosen as large value. For exact assessment of contact force and friction force between die and sheet, the continuous contact treatment is proposed. The virtual surface of sheet metal is modeled by NURBS curves or surfaces in order to calculate exact contact area and penetration depth. From the geometrical evaluation of contact behavior, additional contact pressure is imposed to the element. The deformation of bending process and hydroforming process are analyzed based on this scheme.