• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2002.05a
• /
• pp.103-107
• /
• 2002

The 2nd forming process of flanging/hemming has recently many interest because it determines external quality of automobile. It is difficult to apply finite element simulation in flanging/hemming due to small element size which needs for expression of bending effect on the die corner and big model size of side door, back door, tank lid and like opening Parts. This paper shows the process of flanging/hemming simulation using finite element model for automotive panels. The explicit finite element program PAM-STAMP$\^$TM/ was used to simulate the flanging and hemming operations.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.9 no.6
• /
• pp.777-787
• /
• 1985

The study is concerned with the analysis of flanging as a sheet metal working process. In terms of mechanics, the flanging process can be divided into two groups, i.e, shrink flanging and stretch flanging. In this study, the shrink flanging process is analyzed by using the proposed energy criterion and the forming limit is found for the process. The forming limit for stretch flanging is also found by employing the neckind theory. Experiments are carried out for both processes. Approximate forming limits are obtained from the experiments. An approximate method to calculate the punch force is proposed and the computed results are compared with the experimental results. It is shown that there are good agreements in forming limits and punch forces between theory and experiments.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2006.06a
• /
• pp.49-54
• /
• 2006

During most of manufacturing processes of auto-body panels, the trimming line should be designed in advance prior to flanging. It is an important task to find a feasible trimming line to obtain a precise final part shape after flanging. This paper proposes a new fast method to find feasible trimming line based on one-step analysis. The basic idea of the one-step analysis is to seek for the nodal positions in the initial blank from the final part, and then the distribution of strain, stress and thickness in the final configuration can be calculated by comparing the nodal position in the initial blank sheet with the one of the final part. The one-step analysis method is able to predict the trimming line before flanging since the desired product shape after flanging can be defined from the final configuration and most of strain paths are simple during the flanging process. Finally, designers can obtain a discrete trimming line from the boundary of the developed meshes after one-step analysis and import it into CAD system in the early design stage. The proposed method has been successfully applied to two basic curve flanging processes demonstrating many advantages.

• Transactions of Materials Processing
• /
• v.15 no.6 s.87
• /
• pp.445-452
• /
• 2006

In most of automobile body panel manufacturing, trimming process is generally performed before flanging. To find feasible trimming line is crucial in obtaining accurate edge profile after flanging. Section-based method develops blank along manually chosen section planes and find trimming line by generating loop of end points. This method suffers from inaccurate results of edge profile. On the other hand, simulation-based method can produce more accurate trimming line by iterative strategy. In this study, new fast simulation-based method to find feasible trimming line is proposed. Finite element inverse method is used to analyze the flanging process because final shape after flanging can be explicitly defined and most of strain paths are simple in flanging. In utilizing finite element inverse method, the main obstacle is the initial guess generation for general mesh. Robust initial guess generation method is developed to handle genera] mesh with very different size and undercut. The new method develops final triangular mesh incrementally onto the drawing tool surface. Also in order to remedy mesh distortion during development, energy minimization technique is utilized. Trimming line is extracted from the outer boundary after finite element inverse method simulation. This method has many advantages since trimming line can be obtained in the early design stage. The developed method is verified by shrink/stretch flange forming and successfully applied to the complex industrial applications such as door outer flanging process.

• 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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1999.03b
• /
• pp.53.1-56
• /
• 1999

Using a new dynamic-explicity program SAIT_STAMP the analysis of forming a front door panel is presented. The analysis consists of 7 processes including drawing trimming flanging and springback. From the analysis results it is shown that adaptive refinement scheme and robust trimming algorithm enable SAIT_STAMP to simulate the multi-stage forming of automotive parts with large and complex geometry.

• Transactions of Materials Processing
• /
• v.10 no.6
• /
• pp.465-470
• /
• 2001

Hole flanging experiments are performed on flat circular plates with a hole in the center and the flangeability and fracture behaviors of TRIP steels and ferrite-Bainite duplex steels were examined. In the hole flanging, deformation by lip and petalling occurs when plates are struck by punches of various shapes and high circumferential strains induced in the target material cause radial cracking and the subsequent rotation of the affected plate material in a number of symmetric petals. In all cases, failure of the plate was due to lip fracture that results from multiple localized neckings that take place around the hole periphery where straining is most severe and a somewhat regular pattern was observed in a fracture shape. The neck characteristics in flange formation and the transition from the lip to petal mode at which fracture occurs were compared with two materials.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2004.05a
• /
• pp.131-134
• /
• 2004

The hub hole is usually formed with a stretch flanging process followed by a blanking process of a hole. Since the hole is made by blanking, the blanked surface is so rough that the formability in the region is rather poor. The emerging task is to identify the formability of the blanked region in the forming simulation and to relate the criterion to the real forming process by experiments. In this paper, the blanked region of a hole surface is modeled by a defected-edge finite element for stretch flanging simulation. The analysis deals with the level of defect in the blanked region in order to identify the formability in the real process. The analysis provides the formability depending on the level of defect and seeks the way to match the level of defect to that of the real surface. The approach makes the analysis possible to deal with the formability of the high strength steel and predict the fracture at the hole surface during the stretch flanging simulation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2000.10a
• /
• pp.49-52
• /
• 2000

The hole flanging experiments are performed on a flat circular plates with a hole in the center and the flangeability and fracture behavior of TRIP steel and ferrite-bainite duplex steel were examined. Over the ranges of conditions investigated, the flangeability of ferrite-bainite duplex steel is better than TRIP steel and the term 'hole flanging capacity' introduced in this study. Fracture behavior of TRIP steel and ferrite-bainite duplex steel was characterized by petal formation at the edge of flange. In case of crack propagation, crack tip diversion that is supposed to be responsible for flangeability occurs more severely on HSLA Steel.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1998.06a
• /
• pp.121-130
• /
• 1998

In order to analyze the forming characteristics of laser welded tailored blanks, laser welded blanks of different thickness and strength combinations were prepared and tensile, stretching, stretch flanging and deep drawing tests were done. The tensile elongation perpendicular to the weld line, stretching and stretch flanging formability decreased with increasing the deformation restraining force (strength ${\times}$ thickness) ratio between two welded sheets. The tensile elongation along weld line reached a value above 90% of the single sheet's elongation. Stretch flanging formability was reduced to approximately 10% of the single sheet value when the deformation restraining force ratio between two welded sheets was increased to two. Weld line movement of deep drawing test specimens was also affected by the strength ratio of the combined sheets, the weld line location and forming conditions. In all forming modes of tailored blanks, excessive weld line movement resulted from strain concentrations at the weaker sheet and resulted in fracture of the weaker side.