• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1994년도 추계학술대회 논문집
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• pp.80-94
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• 1994

As for axisymmetirc sheet metal forming, a kind of pick-up apparatus for body-wrinkling is deviced. Experiments with both hemispherical and flat headed punches, with various clearances between punch and die, with respect to three kinds of materials each of which has two thicknesses, are performed. Firstly the process of evolution of body-wrinkling is observed. Then the critical blank-holding force (or meridional tensile force) for suppression of body-wrinkling at a specified punch-stroke is measured for all cases mentioned above. An empirical formula for it is proposed. Deformation patterns and stress distributions are analysed by the use of FEM. A simplified critical condition for body-wrinkling is formulated and introduced into the FEM program. And its effectiveness is checked by comparison with the experimental results. Using this FEM system, the governing factors of body-wrinkling are cleared up.

• 한국자동차공학회논문집
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• 제9권3호
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• pp.131-142
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• 2001

A wrinkling is the instability phenomenon influenced by material properties, shape geometry, forming conditions, stress state, etc. The wrinkling is considered as a critical defect in appearance of product. Many wrinkling prediction methods using thickness strain distribution and farming analysis have been proposed. The wrinkling, however, is not easily predicted precisely by these methods. In this study, the region in the biaxial plane stress state is modeled with a rectangular plate introducing the effective dimension, and critical stress values for the wrinkling are calculated. Prediction index for the wrinkling is then evaluated by normalizing the actual stress with respect to the critical stress. In order to show the validity and efficiency of the method proposed, the wrinkling prediction for a squared sheet in the uniaxial tensile stress and auto-body front finder panel is performed.

• 대한기계학회논문집A
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• 제33권3호
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• pp.276-282
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• 2009

Wrinkling in the flange and wall of a deep-drawn part is one of the major defects in sheet metal processes. Wrinkling is influenced by many factors, such as material properties, shape of the body, forming conditions, stress state and thickness, etc. It is difficult to analyze the wrinkling initiation and growth according to the factors because the effects of the factors are very complex and the wrinkling behavior may show wide variation even though small deviation of factors. In this study, the influence of wrinkling parameters, such as material properties (Al1050, Al5052), the blank holding force and the drawing depth on the wrinkling initiation and growth is investigated by using the experimental method and the dynamic explicit finite element analysis. From the results, it is shown that the dynamic explicit finite element method can be used effectively to prevent the wrinkling problems advancely in the deep drawing process. Also, there is a good agreement between the experimental result and the dynamic explicit finite element analysis.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1998년도 춘계학술대회논문집
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• pp.28-31
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• 1998

Wrinkling is one of the major defects in sheet metal products and may be also attributable to the wear of the tool. The initiation and growth of the wrinkles are influenced by many factors such as stress state, mechanical properites of the sheet material, geometry of the body, and contact condition. It is difficult to analyze the wrinkling initiation and growth considering the factors because the effects of the factors are very complex and the wrinkling behavior may show wide variation for small deviation of the factors. In this study, the bifurcation theory is introduced for the finite element analysis of wrinkling initiation and growth, All the above mentioned factors are conveniently considered by finite element method. The finite element formulation is based on the incremental deformation theory and elastic-plastic material modeling. The finite element analysis is carried out using the continuum-based resultant shell elements considering the planar anisotropy of the sheet metal. The proposed method is verified by employing to column buckling problem. And then, the initiation and growth of wrinkling in deep drawing of cylindrical cup are analyzed.

• 소성∙가공
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• 제9권2호
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• pp.128-139
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• 2000

Wrinkling is one of the major defects in sheet metal products and may be also attributable to the wear of the tool. The initiation and growth of wrinkles are influenced by many factors such as stress state, mechanical properties of the sheet material, geometry of the body, and contact condition. It is difficult to analyze the wrinkling initiation and growth considering the factors because the effects of the factors are very complex and the wrinkling behavior may show a wide variation for small deviations of the factors. In this study, the bifurcation theory is introduced for the finite element analysis of wrinkling initiation and growth. All the above mentioned factors are conveniently considered by the finite element method. The finite element formulation is based on the incremental deformation theory and elastic-plastic elements considering the planar anisotropy of the sheet metal. The proposed method is verified by employing a column buckling problem. And then, the initiation and growth of wrinkling in deep drawing of cylindrical cup are analyzed.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 추계학술대회논문집
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• pp.18-21
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• 1999

The wrinkling of thin sheet metal induced by compressive instability is one of major defects in sheet metal forming processes. compressive instability is influence by many factors such as mechanical properties of the sheet material geometry of the sheet contact conditions and plastic anisotropy. The analysis of compressive instability in a plastically deforming body is rather difficult because the effects of the above-mentioned factors are rather complex and the instability behavior may show swide variations even for small deviations of the factors. in this work the bifurcation theory is introduced for the finite elemental analysis of the instability behavior of a thin sheet with initially sound geometry and property. All the above-mentioned factors are conveniently considered by the finite element method. The instability limit is found by introducing a criterion scheme into the incremental analysis and the post-bifurcation behavior is analyzed by introducing the branching scheme. Wrinkling initiation and growth in the deep drawing process are analyzed.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.14-17
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• 1999

The wrinkling behavior of a thin sheet with perfect geometry is a kind of compressive instability. The compressive instability is influenced by many factors such as stress state mechanical properties of the sheet material geometry of the body contact conditions and plastic anisotropy. The analysis of compressive instability in plastically deforming body is difficult considering all the factors because the effects of the factors are very complex and the instability behavior may show wide variation for small deviation of the factors. In this study the bifurcation theory is introduced for the finite element analysis of puckering initiation and growth of a thin sheet with perfect geometry. All the above mentioned analysis and the post-bifurcation behavior is analyzed by introducing the branching scheme proposed by Riks. The finite element formulation is based on the incremental deformation theory and elastic-plastic material modeling. in order to investigate the effect of plastic anisotropy on the compressive instability a square plate that is subjected to compression in one direction and tension in the other direction is analyzed by the above-mentionedfinite element analysis. The critical stress ratios above which the buckling does not take place are found for various plastic anisotropic modeling method and discussed. Finally the effect of plastic anisotropy on the puckering behavior in the spherical cup deep drawing process is investigated.

• 소성∙가공
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• 제7권4호
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• pp.382-392
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• 1998

Computer simulations and test trials were carried out to obtain the optimal stamping conditions of the die design of the laser welded automotive body. The stamping process including gravity deflection bead calibration binder wrap, forming and spring back was simulated and compared with the results obtained from test trials. The production variables were determined from a preliminary operation and they were investigated in the simulation and the test trials. The formability was tested under the various conditions, such as the initial position of blank, blank holding force, corner radius and the shape of drawbead. Sound products without fracture, wrinkling and excessive weldline movement were produced by applying results obtained this investigation.

• 소성∙가공
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• 제14권1호
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• pp.21-28
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• 2005

This paper is concerned with the quantitative effect of design parameters on a stamped part of the auto-body. The considered parameters in this paper are the blank holding force, the draw-bead force, the blank size which greatly affect the metal flow during stamping. The indicators of formability selected in this paper are failures such as tearing, wrinkling and the amount of springback. The stamping process of the front side inner member is simulated using the finite element analysis changing the design parameters. The numerical results demonstrate that the blank holding force cannot control the local metal flow during forming although it controls the overall metal flow. The modification of the initial blank size considering the punch opening line ensures the local wrinkling and reduces the amount of springback after forming. The restraining force of draw-bead controls the metal flow in the local area and reduces the amount of excess metal. It is noted that the parametric study of design parameters such as blank holding force, the blank size and the draw-bead are very important in the process design of the complicated member.

• Archives of Plastic Surgery
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• 제36권6호
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• pp.767-772
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• 2009

Purpose: Among reasons for reoperations in augmentation mammoplasty, palpable implant, due to thin skin is relatively common, but not easy to correct, especially if thin skin area is wide. The capsule around the implant is a physiologic response to foreign body, naturally formed, and suitable for use as a flap because of its high vascularity. Authors report that capsular flap is very effective and successful method for correction of implant palpability in secondary breast augmentation. Methods: From September 2007 to September 2008, the capular flaps were performed on 5 patients having palpable and wrinkling breast implants due to very thin skin among the cases on whom secondary augmentation mammaplasty had been performed. After the capsular flap was elevated according to thin skin area, the capsular flap was turned down or over to cover the thin skin area and made the thin skin area thick. Results: Post - implant palpable breast wrinkling had been successfully corrected by capsular flaps and breast implants were not palpable any more during the follow - up period(average 9.2 months). All patients who suffered from deformed breast were satisfied. Conclusion: Authors suggest that the capsular flap is a ideal, effective and useful method in management of implant palpability.