• 소성∙가공
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• 제20권5호
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• pp.344-349
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• 2011

Variation of contact pressure causes change of friction coefficient, which in turn changes stress distribution in the sheet being formed and final springback. In the present study, U-draw bending experiments were carried out under constant blank holding force(BHF) and different blank sizes, and finite element analysis was conducted with and without considering contact pressure effect on friction. When the BHF was sufficiently high, the degree of springback was different between constant blank holding pressure condition and that with varying blank holding pressure. Finite element analysis considering the influence of contact pressure effect on friction could explain the occurrence of springback.

• 소성∙가공
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• 제29권5호
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• pp.241-250
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• 2020

In this study, the methodology of the springback prediction of automotive parts applied 3rd generation AHSS was investigated using the response surface model analysis based on a regression model, and the meta model analysis based on a Kriging model. To design the learning data set for constructing the springback prediction models, and the experimental design was conducted at three levels for each processing variable using the definitive screening designs method. The hat-shaped member, which is the basic shape of the member parts, was selected and the springback values were measured for each processing type and processing variable using the finite element analysis. When the nonlinearity of the variables is small during the hat-shaped member forming, the response surface model and the meta model can provide the same processing parameter. However, the accuracy of the springback prediction of the meta model is better than the response surface model. Even in the case of the simple shape parts forming, the springback prediction accuracy of the meta model is better than that of the response surface model, when more variables are considered and the nonlinearity effect of the variables is large. The efficient global optimization algorithm-based Kriging is appropriate in resolving the high computational complexity optimization problems such as developing automotive parts.

• 소성∙가공
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• 제15권4호
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• pp.295-303
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• 2006

Optimization is carried out to determine process parameters which reduce the amount of springback and improve shape accuracy of a deep drawn product in sheet metal forming process. The study uses the amount of stress deviation along the thickness direction in the deep drawn product as an indicator of springback instead of springback simulation. The scheme incorporates with an explicit elasto-plastic finite element method for calculation of the final shape and the stress deviation The optimization method adopts the response surface method in order to seek for the optimum condition of process parameters such as the blank holding force and the draw-bead force. The present scheme is applied to design of the variable blank holding force in an U-draw bending process and the application is further extend ε d to the design of draw-bead force in a front side member formed with advanced high strength steel (AHSS) sheets of DP60. Results show that design of process parameter is well performed to decrease the stress deviation through the thickness and to reduce the amount of springback. The present analysis provides a guideline in a design stage for controlling the springback based on the finite element simulation of the complicated parts.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 제5회 박판성형 SYMPOSIUM
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• pp.61-67
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• 2006

Optimization is carried out to determine process parameters which reduce the amount of springback and improve shape accuracy of a deep drawn product in sheet metal forming process. The study uses the amount of stress deviation along the thickness direction in the deep drawn product as an indicator of springback instead of springback simulation. The scheme incorporates with an explicit elasto-plastic finite element method for calculation of the final shape and the stress deviation. The optimization method adopts the response surface method in order to seek for the optimum condition of the draw-bead force. The present scheme is applied to the design of draw-bead force in a front side member formed with advanced high strength steel (AHSS) sheets of DP60. Results show that design of process parameter is well performed to decrease the stress deviation through the thickness and to reduce the amount of springback. The present analysis provides a guideline in a design stage for controlling the springback based on the finite element simulation of the complicated parts.

• 산업기술연구
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• 제21권B호
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• pp.287-294
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• 2001

This study is aimed to evaluate the springback characteristics of automotive steel sheets through the S-rail forming test and to find the process condition under which springback can be reduced. Die set for the S-rail test has been made according to the dimension of the NUMISHEET '96 benchmark model. Experiment and finite element analysis have been performed on two kinds of automotive steel sheets: mild steel, SPCEN and high strength steel, SPRC. The test results show that the amount of springback is larger on the high strength steel SPRC than on the mild steel SPCEN, and decreases with increasing blank holding force as the case of material flow. And the reduction of friction has the effect of lowering the blank holding force in view of punch force and material flow. It is shown that the strain distribution over the whole specimen and along the specified sections calculated from the finite element analysis coincides with the measured data except local differences.

• 소성∙가공
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• 제21권5호
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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.

• 소성∙가공
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• 제12권1호
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• pp.49-59
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• 2003

To reduce the cost of finite element analyses for sheet forming, a 3D hybrid membrane/shell method has been developed to study the springback of anisotropic sheet metals. In the hybrid method, the bending strains and stresses were analytically calculated as post-processing, using incremental shapes of the sheet obtained previously from the membrane finite element analysis. To calculate springback, a shell finite element model was used to unload the final shape of the sheet obtained from the membrane code and the stresses and strains that were calculated analytically. For verification, the hybrid method was applied to predict the springback of a 2036-T4 aluminum square blank formed into a cylindrical cup. The springback predictions obtained with the hybrid method was in good agreement with results obtained using a full shell model to simulate both loading and unloading and the experimentally measured data. The CPU time saving with the hybrid method, over the full shell model, was 75% for the punch stretching problem.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.62-65
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• 1999

To reduce the cost of finite element analyses for sheet forming a 3D hybrid membrance/sheel method has been developed to study the springback of anisotropic sheet metals. in the hybrid method the bending strains and stresses were analytically calculated as post-processing using incremental shapes of the sheet obtained previously from the membrane finite element analysis. To calculate springback a shell finite element model was used to unload the final shape of the sheet obtained from the membran code and the stresses and strains that were calculated analytically. For verification the hybrid method was applied to predict the springback of a 2036-T4 aluminum square blank formed into a cylindrical cup. the springback predictions obtained with the hybrid method was in good agreement with results obtained using a full shell model to simulateboth loading an unloading and the experimentally measured data. The CPU time saving with the hybrid method over the full shell model was 75% for the punch stretching problem.

• 소성∙가공
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• 제17권2호
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• pp.97-101
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• 2008

Unique constitutive behavior of magnesium alloys as one of hexagonal close packed(hcp) metals has been implemented into the commercial finite element program ABAQUS. The constitutive equations can represent asymmetry in tension-compression yield stresses and flow curves. For the verification purpose, the springback of AZ31B magnesium alloy sheet was measured using the unconstrained cylindrical bending test proposed in Numisheet'2002 benchmark committee. Besides the developed constitutive models, the isotropic models based on tensile and compressive properties were also considered for comparison purpose. The predicted results by the finite element analysis and corresponding experiments showed enhanced prediction capability in springback analysis.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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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.