• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1994.10a
• /
• pp.44-54
• /
• 1994

A variational formulation and the associated finite elemet equations have been derived for general three-dimensional deformation of a planar anisotropic rigid-plastic sheet metal which obeys the strain-rate potential proposed by BARLAT et al [13]. By using the natural convected coordinate system, the effect of geometric change and the rotation of planar anisotropic axes are considered efficiently. In order to check the validity of present formulation, a cylindrical cup and a square cup deep drawing test was modeled. good agreement was found between the FE simulation and the experiment. The results have shown that the present formulation for planar anisotropic deformation can be efficiently applied to the analysis of sheet metal working processes for planar anisotropic nonferrous metals.

• Journal of the Korean Society for Precision Engineering
• /
• v.24 no.3 s.192
• /
• pp.91-99
• /
• 2007

Fractures of galvannealed coating layer during actual press forming in automotive applications were observed by scanning electron microscopy in order to understand fracture mechanism. Fracture behaviors of galvannealed coating layer in extra deep drawing quality steels and high strength steels have been studied by performing the tests describing the representative plastic deformation in sheet metal forming such as uni-axial tensile test, compression test, bi-axial test and plane strain test. Growth and direction of cracks were deeply related to the plastic deformation modes and history. The material properties of galvannealed coating layer were investigated by nano-indentation test equipped with Berkovich diamond indentor for the specimens. Hardness and elastic modulus of the coating layer were higher than bared steels and that was the reason for crack of coating layer. Flat friction test and drawbead friction test were performed to observe the effect of the surface morphology on the frictional characteristics. The micro-plasto hydrodynamic lubrication were appeared and played an important role in reducing the coefficient of friction.

• Korean Journal of Materials Research
• /
• v.27 no.11
• /
• pp.597-602
• /
• 2017

In this study, an Al-0.7wt%Fe-0.2wt%Mg-0.2wt%Cu-0.02wt%B alloy was designed to fabricate an aluminum alloy for electrical wire having both high strength and high conductivity. The designed Al alloy was processed by casting, extrusion and drawing processes. Especially, the drawing process was done by severe deformation of a rod with an initial diameter of 12 mm into a wire of 2 mm diameter; process was equivalent to an effective strain of 3.58, and the total reduction in area was 97 %. The drawn Al alloy wire was then annealed at various temperatures of 200 to $400^{\circ}C$ for 30 minutes. The mechanical properties, microstructural changes and electrical properties of the annealed specimens were investigated. As the annealing temperature increased, the tensile strength decreased and the elongation increased. Recovery or/and recrystallization occurred as annealing temperature increased, and complete recrystallization occurred at annealing temperatures over $300^{\circ}C$. Electric conductivity increased with increasing temperature up to $250^{\circ}C$, but no significant change was observed above $300^{\circ}C$. It is concluded that, from the viewpoint of the mechanical and electrical properties, the specimen annealed at $350^{\circ}C$ is the most suitable for the wire drawn Al alloy electrical wire.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1996.03a
• /
• pp.62-72
• /
• 1996

A process model is formulated considering the effect of crystallographic testure developed in forming process. The deformation induced plastic anisotropy can be predicted by capturing the evolution of texture during large deformatin in the poly crystaline aggregate. The anisotropic stiffness matrix for the aggregate is derived and implemented in Dulerian finite element code. As an application , the evolution of texture in rolling, drawing and extrusion processes are simulated . The numerical results show good agreement with reported experimental textures.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.21 no.12
• /
• pp.2055-2067
• /
• 1997

Values of process parameters in sheet metal forming can be estimated by various one-step inverse methods. One-step inverse methods based on deformation theory, however, cause some amount of error. The amount of error is generally increased as the deformation path becomes more complex. As a remedy, a new three dimensional multi-step inverse method is introduced for optimum design of blank shapes and strain distributions from desired final shapes. The approach extends a one-step inverse method to a multi-step inverse method in order to reduce the amount of error. The algorithm developed is applied to square cup drawing to confirm its validity by demonstrating reasonably accurate numerical results. Rapid calculation with this algorithm enables easy determination of an initial blank of sheet metal forming.

• Journal of the Korean Society for Precision Engineering
• /
• v.32 no.11
• /
• pp.945-952
• /
• 2015

In drawing sheet metal, the blank holding force is applied to prevent wrinkling of the product and to add a tensile stress to the material for the plastic deformation. Applying an inappropriate blank holding force can cause wrinkling or fracture. Therefore, it is important to determine the appropriate blank holding force. Recent developments of the servo cushion open up the possibility to reduce the possibility of fracture and wrinkling by controlling the blank holding force along the stroke. In this study, a method is presented to find the optimal variable blank holding force curve, which uses statistical analysis with consideration of the nonlinear deformation path. The optimal blank holding force curve was numerically and experimentally applied to door inner parts. Consequently, it was shown that the application of the variable blank holding force curve to door inner parts could effectively reduce the possibility of fracture and wrinkling.

• Design & Manufacturing
• /
• v.14 no.1
• /
• pp.22-29
• /
• 2020

The analysis was carried out using the press molding analysis program by applying six parameters such as material type change, material thickness, friction coefficient, r_p, r_d and blank holder pressure. As a result of CAE analysis of the soft material DC04 and the relatively hard material HX300LAD, the thickness of the punch R part of the soft material was significantly reduced. The flange portion is greatly increased in thickness in the hard material by the compression action. As a result of considering the deformation amount of 0.6mm, 1.0mm, 1.5mm according to the material thickness, the influence of the thickness is considered to be very small. In case of the material thickness of 0.6mm, the rate of change increases due to the deep drawing depth relative to the material thickness. The sizes of the punches R and die R have the greatest influence on the change in thickness of the material in drawing molding, the smaller the punch R, the thinner the edges of the product, The larger the R of the die, the greater the material thickness of the flange portion. As the coefficient of friction and the blank holder pressure increase, the frictional force of the flange portion increases, which increases the radial force in the drawing process and increases the thickness change of the flange portion.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.2
• /
• pp.450-455
• /
• 2017

A shield connector is an automotive electrical component that is used to connect electrical wiring in a vehicle. This part is made by progressive pressing using a phosphor bronze material with high electrical conductivity. The shape of the product is not complicated, but plastic forming techniques are required, such as deep drawing and bending, as well as shearing techniques such as piercing and notching. The finite element method was used to model the process. The strip layout design stage of the progressive die makes it possible to examine the thickness change, the stability of the forming process, and the spring-back. As a result of this analysis, it is possible to predict the correction values for the tendency of cracks, wrinkles, and incomplete plastic deformation, and to identify possible problems in advance. As a countermeasure against the forming error caused by the drawing process analysis, the drawing shape was modified and applied in the process design. For effective material utilization, a 3D strip layout was designed using an optimized blank shape based on nesting. The results improve the crack stability and spring-back of shield connector products produced through progressive pressing.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1997.03a
• /
• pp.179-182
• /
• 1997

One-step inverse methods based on deformation theory causes some amount of error. The amount of error is generally increased as the deformation path is more complex. As a remedy, a new three dimensional multi-step inverse method is introduced for optimum design of blank shapes and strain distributions from desired final shapes. The approach extends a one-step inverse method to a multi-step inverse method in order to reduce the amount of error. The algorithm developed is applied to square cup drawing to confirm its validity by demonstrating reasonably accurate numerical results.

• Transactions of Materials Processing
• /
• v.15 no.6 s.87
• /
• pp.459-466
• /
• 2006

Trimming line design plays an important role in obtaining accurate edge profile after flanging. Compared to the traditional section-based method, simulation-based method can produce more accurate trimming line by considering deformation mechanics. Recently, the use of a finite element inverse method is proposed to obtain optimal trimming line. By analyzing flanging inversely from the final mesh after flanging, trimming line can be obtained from initial mesh on the drawing die surface. Initial guess generation fer finite element inverse method is obtained by developing the final mesh onto drawing tool mesh. Incremental development method is adopted to handle irregular mesh with various size and undercut. In this study, improved incremental development algorithm to handle complex shape is suggested. When developing the final mesh layer by layer, the algorithm which can define the development sequence and the position of developing nodes is thoroughly described. Flanging of front fender is analyzed to demonstrate the effectiveness of the present method. By using section-based trimming line and simulation-based trimming line, incremental finite element simulations are carried out. In comparison with experiment, it is clearly shown that the present method yields more accurate edge profile than section-based method.