• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.658-666
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• 1992

In developing computer-aided design technology for optimization of stamping die design, it has been an important issue to treat the frictional constraint acting on the blank holder surface. The main goal of this work is to establish database of draw bead restraint force and clarify friction characteristic for various automotive sheet steels, which is essential in developing friction algorithm that can be used for CAD of stamping die design. Draw bead friction tester is used to evaluate the various parameters that affect the draw restraint force and the coefficient of friction for the cold rolled and the coated sheet steels such as drawing rate, lubricant type, surface property of material, etc.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.06a
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• pp.55-60
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• 2006

Draw-bead is applied to control the material flow in a stamping process and improve the product quality by controlling the draw-bead restraining force (DBRF). Actual die design depends mostly on the trial-and-error method without calculating the optimum DBRF. Die design with the predicted value of DBRF can be utilized at the tryout stage effectively reducing the cost of the product development. For the prediction of DBRF, a simulation-based prediction model of the circular draw-bead is developed using the Box-Behnken design with selected shape parameters such as the bead height, the shoulder radius and the sheet thickness. The value of DBRF obtained from each design case by analysis is approximated by a second order regression equation. This equation can be utilized to the calculation of the restraining force and the determination of the draw-bead shape as a prediction model. For the evaluation of the prediction model, the optimum design of DBRF in sheet metal forming is carried out using response surface methodology. The suitable type of the draw-bead is suggested based on the optimum values of DBRF. The prediction model of the circular draw-bead proposes the design method of the draw-bead shape. The present procedure provides a guideline in the tool design stage for sheet metal forming to reduce the cost of the product development.

• Transactions of Materials Processing
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• v.17 no.4
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• pp.278-283
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• 2008

This paper concerns the die face design for a heat protect panel aided by the finite element forming analysis in order to eliminate the surface defect and to improve the surface quality. The CAE procedure of the stamping process is introduced in order to reveal the reason of surface inferiorities and to improve surface quality. Complicated shape of the product induces the surface inferiorities such as wrinkling due to the insufficient restraining force of the forming blank and the non-uniform contact of the blank with the tools. This paper proposes a new guideline for the die design which includes the modification of tool shapes and addition of the draw-beads on the tool surface for ensuring the increased the restraining force with the uniform contact condition. The effectiveness of the proposed design is verified by the forming analysis and is confirmed by the tryout operation in the press shop. The analysis and test results show that the modified process parameters such as tool shapes and draw-beads can reduce the tendency of wrinkling and improve surface quality.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.53-57
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• 1998

In order to investigate the effects of the variables during the stamping process upon the side wall curl behavior, experiments and finite element analyses were done using a 90 degree draw-bending test. The variables considered were the die radius, the forming speed, the restraint force, the lubrication and the sheet grade. The experiments and simulation conditions were selected according to the design of experiment (DOE) approach. The effects of the restraint force, the lubrication and the forming speed were the same for both high strength and mild steels, but the effects of the die radius on the side wall curl were dependent on the magnitude of the die radius and the sheet grade. A straight side wall was observed for both high strength and mild steels when the die radius was about 2∼3 times of the sheet thickness. It was recommended that the restraint force, the forming speed and the friction be increased in order to reduce the side wall curl.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.6
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• pp.10-18
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• 2008

Metal stamping is widely used in the mass-production process of the automobile industry. During the stamping process, air may be trapped between the draw die and the panel. The high pressure of trapped air induces imperfections on the panel surface and creates a situation where an extremely high tonnage of punch is required. To prevent these problems, many air ventilation holes are drilled through the draw die and the punch. The present work has developed a simplified mathematical formulation for computing the pressure of the air pocket based on the ideal gas law and isentropic relation. The pressure of the air pocket was compared to the results by the commercial CFD code, Fluent, and experiments. The present work also used the Bisection method to calculate the optimum cross-sectional area of the air ventilation holes, which did not make the pressure of the air pocket exceed the prescribed maximum value.

• Transactions of Materials Processing
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• v.11 no.8
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• pp.668-675
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• 2002

The circles deform into various shape during deformation, the major and minor axes of which indicate the direction of the major and minor principal strains. Likewise, the measured dimensions are used to determine the major and minor principal strain magnitudes. This circular grid technique of measuring strains can be used to diagnose the causes of necking and fracture in industrial practice and to investigate whether these defects were caused by material property variation, changes in lubrication, of incorrect press settings. In non-axisymmetric deep drawing, three modes of forming regimes are found: draw, stretch, plane strain. The stretch mode for non-axisymmetric deep drawing could be defined when the major and minor strains are positive. The draw mode could be defined when the major strain is positive and minor strain is negative, and plane strain mode could be defined when the major strain is positive and minor strain is zero. Through experiments the draw mode was shown on the wall and flange are one of a drawn cup, while the plane strain and the stretch mode were on the punch head and the punch corner area respectively, We observed that the punch load of elliptical deep drawing was decreased according to increase of die corner radius and the thickness deformation of minor side was more large than major side.

• Transactions of Materials Processing
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• v.14 no.2 s.74
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• pp.153-159
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• 2005

Design modification of the stamping die for the upper member of a front end module carrier is carried out in order to improve the surface quality of the final product. The small inferiority induced by wrinkling near the wall of the upper member has been inspected after the draw-forming process. The finite element analysis is pursued with the whole geometry in order to consider the complicated shape. The simulation shows that the excess metal is developed by the irregular contact of the blank the tool and it remains after the final stroke. This paper proposes two guidelines for the modification. One is to add the draw-bead near the critical region in order to increase the draw-in force. The other is to modify the tool shape such as the forming shape at the wall in order to absorb the excess metal before the final stroke. Simulation results show that the proposed guidelines both guarantee the improved surface quality.

• Transactions of Materials Processing
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• v.6 no.2
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• pp.152-160
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• 1997

Three-Dimensional finite element analysis is performed using PAM-STAMP for design evaluation of automotive back door inner panel die. Gravity process by blank own weigth, binder-wrap process, and drawing process in the forming operations are sequentially simulated with Virtual Manufacturing Method. The most valuable result in this research is that 3-D FEM analysis can be applied to the design evaluation of draw dies in the die try-out, though effects of mesh size and drawbead resistance force on the try-out, the experimental knowhows about the forming variables such as friction coefficient punch velocity, drawbead force, etc are necessary.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.04a
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• pp.382-386
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• 2001

Die design of bonnet drawing is composed of upper die, lower die and blank holder. It has been performed by checked and re-design method, which cause economic and financial loss. Nowadays, CAD/CAM system is excellent, but Application is low. Therefore, in specific item, drawing die of bonnet outer draw by 3-D Lay-Out. In this study purpose, Bonnet drawing die is designed rapidly, correctly. It's method that shape modify to resemble. This purpose lead to 3-D Lay-Out. It is to react the standard die. In rule relation, input data change all of the shape

• Journal of the Korean Society for Precision Engineering
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• v.19 no.8
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• pp.194-202
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• 2002

Die design of bonnet drawing is composed of upper die, lower die and blank holder. It has been performed by checked and re-design method, which cause economic and financial loss. Nowadays, CAD/CAM system is excellent, but application is low. Therefore, in specific item, drawing die of bonnet outer draw by 3-D lay-out. In this study purpose, Bonnet drawing die is designed rapidly, correctly. It's method that shape modify to resemble. This purpose lead to 3-D Lay-Out. It is to react the standard die. In rule relation, input data change all of the shape.