• Transactions of Materials Processing
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• v.21 no.5
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• pp.305-311
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• 2012

One of the main methods of building LNG tankers uses the Moss spherical tank design since it can be precisely analyzed with respect to reliability and safety of construction by stress analysis. Aluminum alloy 5083 is generally used in the Moss spherical tank design for the wall in constructing the LNG tanker. This aluminum alloy does not have low temperature brittleness, but has good corrosion resistance, good weldability, and excellent material properties for the application. The Moss spherical tank is constructed with several sections of A5083 thick plate with curved surfaces, which are welded together. It is essential to predict the amount of springback for the deformed thick plates in design to insure a reliable construction because the structure needs to be assembled into a perfect sphere. Unless the initial construction meets the design, there are additional processing costs for reworking to meet the specifications as well as a cost penalty paid to a consumer. In this paper, FE analyses were conducted to predict the amount of springback for various forming conditions and forming processes. The various forming processes were evaluated with respect to reducing springback and compared with the conventional forming process used for curved surfaces of thick Al plate.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.08a
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• pp.13-20
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• 2003

The implicit, finite element analysis program for analyzing the springback in the warm forming process of aluminum alloy sheets was developed. For the description of planar anisotropy in warm forming temperatures, Barlat's yield function is employed, and the power law type constitutive equation is used in terms of working temperatures fur the depiction of work hardening in high temperatures. Also, Jetture's 4-node shell elements are introduced for reflecting the mechanical behavior of aluminum alloy sheet and the non-steady heat balance equations are solved for considering heat gain and loss during the forming process. For the springback evaluation, Newton-Raphson iteration method is introduced for overcoming the geometric nonlinearlity problem. In order to verify the validity of the FEM program developed, the stretching bending and springback processes are simulated. Though springback analysis results are slightly bigger than experimental ones, they have the same trend of the decreasing springback as the forming temperature increases.

• Transactions of Materials Processing
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• v.21 no.7
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• pp.441-446
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• 2012

A sequential coupled field analysis of electromagnetic free bulging was performed by using FEM. A 2D axi-symmetric electromagnetic model based on the magnetic vector potential is proposed for the calculation of magnetic field and Lorentz's forces. The Newmark integration method is used to calculate the transient dynamic plastic deformation of sheet during free bulging. In the finite element model, the effect of sheet deformation on the electromagnetic field analysis is taken into consideration. In order to confirm the sequential electromagnetic-mechanical coupling analysis, an experiment with an electromagnetic forming apparatus was conducted. The results showed that the final bulge height of the sheet predicted from the proposed method is in good agreement with experimentally measured height.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.3
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• pp.493-503
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• 1998

The sectional forming analysis considering bending effects from the geometrically deformed shape of two linear membrane finite elements(called super element) was performed under plane strain assumption for analyzing forming processes of an arbitrarily shaped draw-die. For the evaluation of bending effects, the bending equivalent forces are calculated from the bending moment computed using the changes in the interior angle at the middle node of super element, and are agumented to the membrane stretch forces. In order to verify the validity of the bending formulation, the simulation results for the stretch, draw, and bend sections were compared with membrane analysis results and measurements.

• Transactions of Materials Processing
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• v.20 no.2
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• pp.124-131
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• 2011

A flexible stretch forming process is useful for small quantity batch production because various shape changes of the flexible die can be achieved conveniently. In this study, the design variables, namely, the punch size, curvature radius and elastic pad thickness, were quantitatively evaluated to understand their influence on sheet formability using statistical methods such as the correlation and regression analyses. Forming simulations were designed and conducted by a three-way factorial design to obtain numerical values of a shape error. Linear relationships between the design variables and the shape error resulted from the Pearson correlation analysis. Subsequently, a regression analysis was also conducted between the design variables and the shape error. A regression equation was derived and used in the flexible die design stage to estimate the shape error.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1630-1633
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• 2003

Hair pin bending machine is pipe forming machine consisting of heat exchanger product system. Hair pin produced by these machine is pathway of refrigerant and play a important role improving the performance and productivity of heat exchanger. The core technology of hair pin bending machine is forming the straight pipe into U-type without any defaults. Therefore, this paper study the relation between the pipe bending forming and the shape and position of mandrel using the elastic-plastic finite element analysis and provide a foundation technology for which developing the hair pin bending machine. The results are followed 1. Mandrel located in front of rotating center of bending die minimized the circular shape variation of copper pipe. 2. Diameter change of mandrel hardly effect the pipe shape.

• Design & Manufacturing
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• v.10 no.2
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• pp.12-17
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• 2016

Recently, lightweight material is attracting attention as a solution to the problem of fuel efficiency and increasing the need for development. CFRP has been attracting attention as lightweight materials for automobile because it has a high specific stiffness and specific strength compared to steel material. CFRP have a wide range of mechanical properties depending on the laminate condition. In this paper, study on the forming analysis of double-dome model was performed considering CFRP prepreg laminate condition and coefficient of friction. After forming analysis, the result has compared with wrinkling area and vertical strain of fiber to the laminated condition. And then compared with inflow of blank to the laminate condition. Through this paper, we propose the forming analysis methods of CFRP material.

• Transactions of Materials Processing
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• v.13 no.6 s.70
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• pp.490-496
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• 2004

Springback comes from the release of external loads after forming. The control of phenomenon is especially important in the sheet metal forming since there are no other practical methods available to correct the dimensional inaccuracy from springback. Therefore the accurate prediction before the die machining has been a long goal in the field of sheet metal forming. The am of the present study is to enhance the prediction capability of finite element (FE) analysis for the springback phenomenon. For this purpose FE analysis for V-bending has been carried out with the commercial programs, LS-DYNA. The FE analysis results have been validated through the comparison of experimental. The experimental results measured directly by the strain gauge have given the confidence to FEA.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.06a
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• pp.781-782
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• 2008

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.301-306
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• 2009

High strength steels are widely used for lightweight automobile parts and the control of springback is very important in sheet metal forming. The object of this study is to develop the forming process for stair type side sill made of high strength steel, DP780. Stair type side sill with local formed area and geometry change area can improve stiffness and design freedom but there are a few studies for forming process. The forming technology considered in this paper is form type process, which have many advantages for farming of high strength steel compared with draw type process. Finite element analysis is carried out to predict formability and springback. It is shown that angle calibration of die is essential for reducing springback, and local forming involving bead is effective to control springback also. The effectiveness of local forming and angle calibration is verified by experimental.