Papers by Keyword: Forming Limit Diagram (FLD)

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Authors: Dong Won Jung, Dong Hong Kim, Bong Chun Kim, Dae Lim Ko, Duc Toan Nguyen
Abstract: The products manufactured by the Sheet metal process are widely used in automobile and aircraft industries due to their high strength and superior surface characteristics. In this study, to improve the formability of the lamp-can, forming process was conducted using the Lancing engineering method. Lancing process is a press operation in which the work-piece is sheared and cut with one strike of the die to be a single-line cut or split, without removing any metal. Finite element method (FEM) was used to predict and investigate the improvement of formability of a lam-can with lancing process. As a result, it is believed that the Lancing process used in lamp-can forming would be helpful in the development of high-quality forming products because it can make material flow run well.
443
Authors: Rong Shean Lee, Ta Wei Chien
Abstract: This paper presents a new method concerning testing formability in sheet metal forming, especially focuses on clarifying the divergence of the experiment and a variety of theoretical predictions on biaxial tensile state. Up to now, there are many different fracture criteria appeared. All researches have presented their experimental data which could justify the criterion they presented. However, the experimental results and predictions in the first quadrant of the forming limit diagram (FLD) often diverge. Today, limiting dome height test is commonly used for FLD experiment, but specimens are rubbed and bended during the test, both influencing the experimental results.In order to provide for convincible experimental data, this paper presents a new experimental method to establish the first quadrant of FLD. In this method, cruciform biaxial tensile specimen and biaxial tensile apparatus have been developed. The proposed specimen has the feature of thickness reduction and contour design to ensure the fracture location is in the central region, so that accurate biaxial tensile state can be obtained. Through this method, there is an opportunity to obtain the whole FLD using uniaxial tensile testing machine, which is a low-cost alternative in compared with limiting dome height test. Besides, the experimental results can be utilized to clarify the divergence between various theoretical predictions and experimental results in the first quadrant of the FLD.
275
Authors: Zhu Tao Shao, Qian Bai, Jian Guo Lin
Abstract: Solution heat treatment, forming and in-die quenching (HFQ) is a patented process to form complex shape metal components at a high efficiency and a low cost. Conventional experiment approaches to determine forming limit curves (FLCs) at different strain paths are not applicable for the HFQ forming process. A novel biaxial tensile test rig is designed to overcome the difficulties and determine the FLCs at high temperatures based on the commercial Gleeble machine. This test device employs the circle plate and connecting rod mechanism in order to achieve different strain states, such as uniaxial tension, plane strain and biaxial tension. Resistance heating and air cooling are adopted to obtain an isothermal environment and to control cooling rates in Gleeble respectively. The designs of the cruciform specimen for this test are also introduced in this paper.
241
Authors: Duc Toan Nguyen, Tien Long Banh, Dong Won Jung
Abstract: In order to predict forming limit curve for stainless steel sheet, the modified maximum force criterion (MMFC), introduced by Hora et al (1996 A prediction method for ductile sheet metal failure in FE-simulation Proc. Numisheet’96 Conf. pp 252–256), was adopted follow Swift’s hardening law. After comparing with experimental results, the improvement of MMFC model for FLD’s prediction were proposed based on Swift’s hardening law by representing work hardening coefficient as a function of strain ratio (β). The proposed MMFC model shows in good agreement between FLD’s computational and experimental result for stainless steel sheet. The results of proposed MMFC model also show that the stress-strain curves of sheets materials are difference at each strain ratio.
916
Authors: Jung Han Song, Geun An Lee, Hye Jin Lee, Nak Kyu Lee, S.H. Kim, K.T. Kim, K.D. Park, J.H. Jang
Abstract: This paper is concerned with formability of AZ31B magnesium alloy sheets at various temperatures. In order to acquire the forming limit curve for quantifying the formability of the magnesium alloy sheet, hemispherical punch forming tests are performed under various temperatures. The initial shape of the blank is rectangular and six different types of specimens are used with their length along the rolling direction of 175mm and widths along the transverse direction of 25, 50, 75, 100, 120 and 175mm. With the equipment of on a SIMADZU 100-ton universal testing machine, hemispherical punch forming tests are performed and a forming limit diagram is constructed at the temperature of 100°C, 200°C and 250°C. FE analyses of hemispherical punch forming tests are also conducted by considering ductile failure model in order to compare the forming limit curve obtained from the experiment and numerical analysis. The comparison examines problems in the current material model and it suggests a future research direction.
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Authors: Q. Situ, Mukesh K. Jain, M. Bruhis
Abstract: Forming limit diagram (FLD) is a measure of the formability of a sheet material. The major-minor strain pairs that are closest to the neck on multiple specimens of various strain paths are utilized to construct a boundary between safe and unsafe zones. The challenge to obtain the FLD is the determination of incipient necking. Three approaches to determine the limit strains have been investigated and compared in this research in order to establish the optimal one for implementation: (1) commonly used Bragard criterion ( 1)e Br with periodic grids; (2) tracking the region of large local strains from strain history to locate the instance when critical major strain ( 1)e cr happens; (3) post-processing of strain history to locate the inflection in the major strain rate curve 1 max (e&&) at the onset of localization. The last criterion of inflection in strain rate 1 max (e&&) carries both a numerical and a physical meaning towards developing an understanding of flow localization, formability and fracture.
111
Authors: Fung Huei Yeh, Ching Lun Li, Kun Nan Tsay
Abstract: This paper presents an explicit dynamic finite element method (FEM) in conjunction with the forming limit diagram (FLD) to analyze the forming limit for the various arc radii of punch in micro deep drawing of square cup. In the present study, the tensile test and friction test are performed to obtain the material parameters of the electro-deposited copper foil according to the ASTM standards. Importing these properties, the numerical analysis is conducted by the explicit dynamic FEM. The FLD in numerical simulation is used as the criterion of the forming limit in micro deep drawing of the square cup. The forming limit, deformed shape, punch load-stroke relationship, height of cup and thickness distribution of square cup, are discussed and compared with the experimental results. It shows that a good agreement is achieved from comparison between simulated and experimental results. When the arc radii of punch increase with Rp=0.2, 0.5 and 0.8mm, the limit drawing ratio increases from 1.90 to 2.03 and 2.10. The forming limit of square cup increases with an increase of the arc radii of punch. From this investigation, the results of this paper can be used as reference in the relative researches and applications of micro forming.
660
Authors: Fung Huei Yeh, Ching Lun Li, Kun Nan Tsay
Abstract: This paper presents an explicit dynamic finite element method (FEM) in conjunction with the forming limit diagram (FLD) to analyze the forming limit for the SPCC foil in micro deep drawing of square cup. In the present study, the tensile, anisotropic and friction test are performed to obtain the material parameters of the alloy foil according to the ASTM standards. Importing these properties, the numerical analysis is conducted by the explicit dynamic FEM. The FLD in numerical simulation is used as the criterion of the forming limit in micro deep drawing of the square cup. The forming limit, punch load-stroke relationship, deformed shape and thickness distribution of square cup, are discussed and compared with the experimental results. It shows that a good agreement is achieved from comparison between simulated and experimental results. The limit drawing ratio in micro deep drawing of square cup is 2.08 in this paper. From this investigation, the results of this paper can be used as reference in the relative researches and applications of micro forming.
344
Authors: Tomaz Pepelnjak, Aleš Petek, Karl Kuzman
Abstract: The determination of the forming limit diagrams (FLDs) for sheet metal can be influenced by testing parameters and a chosen testing procedure. Many different tests have been applied and recent work has resulted in some guidelines to decrease the influence of the testing method and the expertise of an individual laboratory. In the last years some methods have been developed which tend to be independent from the individual expertise, but comprehensive experimental work is still indispensable to obtain the material’s necking and failure limit. The experimental work could be omitted by prediction of the FLD with numerical simulations. The paper presents a methodology to determine the whole area of the FLD for sheet metal in a digital environment. The material thinning has been analysed with the finite element simulation using the ABAQUS program. The Marciniak testing procedure has been chosen to determine the FLD. The thickness strain as a function of time as well as first and second time derivation of the thickness strain have been analysed for the critical specimen areas where the onset and propagation of necking occur.
697
Authors: Bruce W. Williams, Lucian Blaga
Abstract: There is the requirement to describe the asymmetric and anisotropic deformation behaviour of hexagonal closed packed (hcp) alloys, including wrought magnesium and titanium. Magnesium and to limited extent, titanium, alloys are candidate materials for weight and emission reduction in the automotive industry. Predicting the deformation response of hcp alloys is challenging to the complexity and number of potentially operative deformation mechanisms which can drastically change with temperature, deformation rate, and chemistry. In this work, the constitutive material response is described using various asymmetric/anisotropic yield criteria, specifically designed to describe the deformation response of hexagonal close packed (hcp) materials. These models allow the size and shape of the yield surface to evolve with plastic strain. The Marciniak-Kuczynski (M-K) approach is utilized to predict the forming limit in the form of forming limit diagrams (FLD). The degree of asymmetry and anisotropy is varied in the predictions to quantify their effects on the forming limit response. The numerical FLD predictions are compared to FLD which have been experimentally determined for AZ31B magnesium and Grade 1 CP titanium sheet alloys. For CP titanium alloys, it was found that it was important to capture the asymmetry and anisotropy of deformation to capture the forming limit response. For AZ31B formed at 200 °C, it was important to capture the strain-rate sensitivity of the material, more so than the asymmetry and anisotropy of deformation, for predicting the forming limit behaviour. The combination of experimental data and predictive models developed in this work are intended to characterize the forming behaviour of various lightweight sheet alloys without the requirement for excessive experimental data, and to ultimately aid in the selection of lightweight sheet metals for multi-material vehicle design.
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