• Proceedings of the KWS Conference
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• 2005.06a
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• pp.91-93
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• 2005

Forming sheet metal by laser-induced thermal stresses (laser forming) has been extensively studied, and the research has focused on two-dimensional geometries using a multi-pass straight line scan. Recently there came out some useful studies or three-dimensional laser forming which is applied to doubly curved shapes. The task of 3D laser forming sheet metal is to determine a set of process parameters such as laser scanning paths, laser power and scanning speed that will make a given shape. New method for laser forming of a doubly curved surface by using geometrical information was proposed and verified by experiments. This method shows good performance in the sense of calculation time and accuracy compared to the inherent strain method.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.1
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• pp.45-50
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• 2011

Hot-Press-Forming (HPF), an advanced sheet metal forming method using stamping at a high temperature of about $900^{\circ}C$ and quenching in an internally cooled die set, is one of the most successful forming process in producing crash-resistant parts such as pillars and bumpers with complex shape, ultrahigh strength, and minimum springback. To optimize conditions of a forming quality in HPF process and secure a safe product without any failures, such as fractures and wrinkling, the simulations based on the coupled thermo-mechanical analysis for a hot-press-formed lower control arm are applied with Taguchi's orthogonal array experiment. Three factor variables - the friction coefficient, blank shape, and hole location for burring - are selected to be optimized. The most effective condition of a forming quality for a hot-press-formed lower control arm is suggested. The simulation results are confirmed with experimental ones.

• Transactions of Materials Processing
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• v.20 no.5
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• pp.377-386
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• 2011

During stamping processes, the air trapped between sheet metal and the die cavity can be highly compressed and ultimately reduce the shape accuracy of formed panels. To prevent this problem, vent holes and passages are sometimes drilled into the based on expert experience and know-how. CAE can be also used for analyzing the air behavior in die cavity during stamping process, incorporating both elasto-plastic behavior of sheet metal and the fluid dynamic behavior of air. This study presents sheet metal forming simulation combined simultaneously with simulation of air behavior in the die cavity. There are three approaches in modeling of air behavior. One is a simple assumption of the bulk modulus having a constant pressure depending on volume change. The next is the use of the ideal gas law having uniform pressure and temperature in air domain. The third is FPM (Finite point method) having non-uniform pressure in air domain. This approach enables direct coupling of mechanical behavior of solid sheet metal and the fluid behavior of air in sheet metal forming simulation, and its result provides the first-hand idea for the location, size and number of the vent holes. In this study, commercial software, PAM-$STAMP^{TM}$ and PAM-$SAFE^{TM}$, were used.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1481-1486
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• 2007

Frictional laws are criticized with emphasis on their application to bulk metal forming simulation in this paper. Coulomb frictional law and constant shear frictional law are investigated in detail in terms of their effect on metal forming process. A friction sensitive bulk metal forming process, a long-pipe simultaneously shrinking and expanding process, is introduced and the problems of the constant shear frictional law are revealed comparing the predictions obtained by the Coulomb frictional law and the constant shear frictional law with the experiments. It is shown that the constant shear frictional law is improper in the case that the normal stress varies very much from position to position and that the normal stress is low compared with flow stress of the adjacent material. It is also shown that the Coulomb frictional constant is more or less affected by the normal stress.

• Design & Manufacturing
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• v.14 no.2
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• pp.49-55
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• 2020

Recently, when a new component of construction equipment is designed, a stamping process capable of producing parts having high appearance quality and precision has been gaining attention. However, in general, as it is developed based on existing parts made by welding metal sheets and tubes, frequent to die modification occurs, which increases the time and cost of developing new parts. Thus, it is necessary to reduce the cost by shortening the die development period. In this study, a stamping process was designed for the urea tank cover, which is a part for excavators, to reduce the die development period through sheet metal forming analysis. The stamping process was designed by determining the blank holding force after selecting the initial blank shape and size. The round value at the corner was modified such that formability is ensured. After selecting process parameters, the thickness reduction rate and spring-back effect were reviewed.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.2
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• pp.55-63
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• 2014

Fractures and wrinkles are two major defects frequently found in the sheet metal forming process. The process has several noise factors that cannot be ignored when determining the optimal process conditions. Therefore, without any countermeasures against noise, attempts to reduce defects through optimal design methods have often led to failure. In this study, a new and robust design methodology that can reduce the possibility of formation of fractures and wrinkles is presented using decision-making theory. A two-attribute value function is presented to form the design metric for the sheet metal forming process. A modified complex method is adopted to isolate the optimal robust design variables. One of the major limitations of the traditional robust design methodology, which is based on an orthogonal array experiment, is that the values of the optimal design variables have to coincide with one of the experimental levels. As this restriction is eliminated in the complex method, a better solution can be expected. The procedure of the proposed method is illustrated through a robust design of the sheet metal forming process of a side member of an automobile body.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.12
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• pp.53-63
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• 1995

In the analysis of metal forming problems, the explicit time integration finite element method, which does not have convergence problems, is frequently used. The present work is to assess the applicability of the explicit time integration finite element method to quasi-static metal forming problems. Compressing analyses of thin-walled tubes and solid cylinders are performed with different loading velocities. The computed buckled profiles of thin walled tubes are compared with the theoretical and experimental ones and it is found that at sufficiently low loading velocity, the explicit time integration finite element method accurately predict quasi-static buckled profiles. When loading volocity is increased, the computed buckled profiles of thin-walled tubes are very sensitive to loading velocity however the computed profiles of solid cylinders are less sensitive to loading velocity. In orther words, the geometrically self-constrained specimens like solid cylinders are less sensitive to loading velocity than the geometrically unconstrained specimens like thin-walled tubes. As a result, it is found that the geometrically self-constrained problems which include the greater part of metal forming problems can be efficiently analyzed with loading velocity control technique.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.182-185
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• 2004

Based on the experimental observation, the mathematical friction model, which is an essential information for analyzing the forming process of sheet metal, is developed considering lubricant viscosity, surface roughness and hardness, punch corner radius, and punch speed. By comparing the punch load found by FEM with a proposed friction model with experimental measurement when the coated and uncoated steel sheets are formed in 2-D geometry in dry and lubricant conditions, the validity and accuracy of the developed friction model are demonstrated.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.7
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• pp.14-19
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• 2000

현재 자본재산업의 기술낙후는 상품의 수출경쟁력 약화의 근원적인 원인이 되어 결국 지속적으로 선진국의 기술종속을 심화시키고 있다. 이러한 자본재 산업의 문제는 현재의 주력 수출상품의 핵심요소부품생산기술의 미비가 큰 원인이며(거의 주요핵심부품 도는 관련기술은 거의 대부분 수입에 의존하고 있음), 같은 논리로 차세대 신기술의 개발을 통한 첨단 상품의 개발도 이에 필요한 핵심요소부품의 생산기술이 뒤를 바쳐 주지 못한다면 결국 10년 후에도 현재와 같은 현상이 되풀이될 것은 분명하다.(중략)

• Transactions of Materials Processing
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• v.13 no.5
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• pp.461-465
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• 2004

Based on the experimental observation, the mathematical friction model, which is an essential information for analyzing the forming process of sheet metal, is developed considering lubricant viscosity, surface roughness and hardness, punch comer radius, and punch speed. By comparing the punch load found by FEM with a proposed friction model with experimental measurement when the coated and uncoated steel sheets are formed in 2-D geometry in dry and lubricant conditions, the validity and accuracy of the developed friction model are demonstrated.