• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.2113-2122
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• 1994

The 3-D FEM analysis for simulating the stamping operation of planar anisotropic sheet metals with arbitrarily-shaped tools is introduced. An implicit, incremental, updated Lagrangian formulation with a rigid-viscoplastic constitutive equation is employed. Contact and friction are considered through the mesh-normal, which compatibly describes arbitrary tool surfaces and FEM meshes without depending on the explicit spatial derivatives of tool surfaces. The consistent full set of governing relations, comprising equilibrium equation and mesh-normal geometric constraints, is appropriately linearized. The linear triangular elements are used for depicting the formed sheet, based on membrane approximation. Barlat's non-quadratic anisotropic yield criterion(strain-rate potential) is employed, whose in-plane anisotropic properties are taken into account with anisotropic coefficients and non-quadratic function parameter. The planar anisotropic finite element formulation is tested with the numerical simulations of the stamping of an automotive hood inner panel and the drawing of a hemispherical punch. The in-plane anisotropic effects on the formability of both mild steel and aluminum alloy sheet metals are examined.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2653-2663
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• 1994

The design of sheet metal working processes is based on the knowledge about the deformation mechanism and the influence of the process parameters. The typical geometric process parameters are the die geometry, the initial sheet thickness, the initial blank shape, and so on. The initial blank shape is of vital importance in the most sheet metal forming operations, especially in the deep drawing process, since the forming load and the strain distribution are significantly affected by the shape of an initial blank. The influence of the initial blank shape on a square cup deep drawing process is investigated by the numerical simulation and the experiment. The numerical simulation is carried out by a modified membrane finite element method which takes bending deformation into account. The numerical and experi-mental results show that the initial blank shape have strong influence on the forming load and the strain distribution. The numerical results are compared with the experimental results and other numerical results which are calculated with the membrane theory.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1142-1147
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• 2003

The formability of sheet metal appears better in incremental forming than in conventional forming. in this study, the effect of process parameters - tool type, tool size, feed rate, friction at the interface between tool and sheet, plane-anisotropy of sheet - on the formability was investigated by experiments and FEM analyses. it was found that the formability is improved when a ball tool of a particular size is used with a small feed rate and a little friction. Due to the plane anisotropy, the formability differs according to the direction of the tool movement. in this paper, details of the experimental procedures and the results obtained from the study are discussed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1994.06a
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• pp.147-162
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• 1994

Generally, the forming process of sheet metal is very complex and difficult process because of many variables such as tool geometry, material properties and lubrication. In this view point, the numerical analysis of sheet metal forming process is very difficult. High speed computer is used to model complex sheet metal forming process on a reasonable time scale. The design and development of sheet metal parts in the automotive industry and the need for improved sheet forming process and reduced part development cost have led to the use of computer simulation in tool/die design of sheet metal pressing. HMC(Hyundai Mator Company) has invested to develop programs for analysis of sheet metal forming process with connection of Universities. As a result, several programs were developed. Recently, the commercial software, PAM-STAMP of ESI was installed and is being tried to application of it to the real automotive panels. This article reviews the ongoing activities on development and application of analytical modeling of sheet metal forming at HMC.

• Journal of Ocean Engineering and Technology
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• v.13 no.1 s.31
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• pp.29-38
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• 1999

In this paper the forming simulation of circular bulge by using PAM-STAMP has been performed to estimate the sheet metal forning and the plastic deformation characteristic of circular bulge. The uniaxial tension tests adn bulge tests are carried out for studying the forming characteristics of materials, and also Moire experiment are carried out for measuring the radius of curvature of the bulge and the polar compressive thickness strain. In order to compare the simulation results with the experiment and Hills theory, the relationships between redius of curvature adn polar height of the bulge, between hydraulic pressure and polar height, and between polar compressive thickness strain and polar height, are used. According to this study, the results of simulation and Hills theory are good agreement to the experiment. So, the results of simulation by using PAM-STAMP and Hills theory will give engineers good information to assess the formagbility and plastic deformation characteristic of hydraulic circular bulge test.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.10a
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• pp.16-20
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• 2001

종래에 자동차 차체의 프레스 성형 공정은 설계자의 정성적인 계산이나 다이 (Trial Dic)에 의해 시행 착오 끝에 설계되었다. 그런데, 부정확하게 계산되는 경우가 많아, 아이가 준비된 후 단점이 노출되어 여러 차례 수정 과정을 겪게 되어 시간과 경비를 증대시키는 원인이 되었다. 자동차 회사에서는 이 때문에 금형 설계 단계에서 빠르고 정확하게 금형의 불량을 예측하고 성형성을 정량적으로 평가하기 위한 시스템을 필요로 한다. 그중 비선형 유한요소법(F.E.M)에 의한 시뮬레이션은 정확한 해와 많은 정보를 줄 수 있다는 장점을 가지고 있다. 그러나, 3차원적인 대단히 복잡하고도 치수가 큰 자동차 판넬에 있어서는 수렴성 등의 문제로 적절한 시간 안에 충분한 정밀도를 갖는 해를 구할 수 있는 단계까지는 이르지 못하고 있다.

• Journal of Ocean Engineering and Technology
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• v.12 no.2 s.28
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• pp.57-64
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• 1998

This study is concerned with criterion for membrane to shell conversion in two-dimensional elastic-plastic finite element analysis using membrane/shell mixed element. It is well known that in the sheet metal forming some parts of the sheet deform under almost pure stretching (membrane) conditions, whereas other parts in contact with sharp tooling surfaces can develop significant bending strains. The membrane analysis has a short computational time however, in the membrane analysis the bending effects can not be condidered at all. On the other hand, the shell analysis allows the consideration of bending effects, but involves too much computational time. So Onatel),2), Yang et al3),4) developed the membrane/shell mixed element. Onate introduced the energy ratio parameter and Yang et al introduced the ratio of thickness to radius of curvature as the criterion. In the present study we propose a new criterion by using the angle between both side elements in the nodal point.

• Transactions of Materials Processing
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• v.7 no.3
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• pp.233-245
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• 1998

A new approach has been proposed for the incremental analysis of the nonsteady state large deformation of planar anisotropic elastic-plastic sheet forming. A mathematical brief review of a constitutive law for the incremental deformation theory has been presented from flow theory using the minimum plastic work path for elastic-plastic material. Since the material embedded coordinate system(Lagrangian quantity) is used in the proposed theory the stress integration procedure is completely objective. A new return mapping algorithm has been also developed from the general midpoint rule so as to achieve numerically large strain increment by successive control of yield function residuals. Some numerical tests for the return mapping algorithm were performed using Barlat's six component anisotropic stress potential. Performance of the proposed algorithm was shown to be good and stable for a large strain increment, For planar anisotropic sheet forming updating algorithm of planar anisotropic axes has been newly proposed. In order to show the effectiveness and validity of the present formulation earing simulation for a cylindrical cup drawing and front fender stamping analysis are performed. From the results it has been shown that the present formulation can provide a good basis for analysis for analysis of elastic-plastic sheet metal forming processes.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.89-92
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• 2007

The metallic bipolar plate in PEMFC is widely used for automotive driving because of its advantages, i) high strength, ii) high chemical stability, iii) low gas permeability and iv) applicability to mass production. Especially, the metallic bipolar plate which is manufactured with the sheet metal stamping process can be applied in automotive PEMFC with less volume and weight because of its thin thickness but the formability and springback problems arise in real manufacturing process. The assessment for formability and springback of metallic bipolar plate should be performed before making stamping die sets. In this work, the methodology for determining the allowable draft angle of flow passage is introduced by using finite element analysis. In analysis results, as the draft angle of flow passage increase, the major strain and thinning is increase with exponential function. The allowable draft angle without fracture is presented by fitting the results. Additionally, the staking results with manufactured metallic bipolar plates by stamping process is presented.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.471-476
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• 2001

Milli-structure components ate classified as a component group whose size is between macro and micro scales, that is, about less than 20mm and larger than 1mm. The forming of these components has a typical phenomenon of bulk deformation with thin sheets because of the forming size. In this study, milli-structure rectangular cup drawing is analyzed and measured using the finite element method and experiment. Generally, milli-structure containers or cases like cellular phone vibrator consist of rectangular-shaped drawing to save installation space. A systematic approach is established for the design and the experiment of the forming processes for rectangular milli-structure cases. To verify the simulation results, the experimental investigations were also carried out on a real industrial product. The numerical analysis by FEM shows good agreement with the experimental results in view of the deformation shape of the product.