Papers by Keyword: Sheet Metal Forming

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Authors: M. Bakhshi, A. Gorji, M. Hosseinzade, M. Jamshidi, G. Mohammad-Alinejad
Abstract: Some new sheet hydroforming processes have been introduced during the last few years to increase the application and to overcome some of the limitations in conventional deep drawing. In recent years, the applications of sheet hydroforming have become increased. Nowadays, this technology has been largely accepted by industries for the production of different components with specific characteristics. Despite the advantages of the sheet hydroforming techniques, they have their own disadvantages. In this paper, a new sheet hydroforming technique is presented that improves the applications of the current sheet hydroforming processes. The proposed technique is applied to two complex non-symmetrical industrial parts. It is shown that the new technique can produce the products very well. In addition, it is shown that the forming pressure and load are very low compared with those of other hydrofoming methods.
Authors: Jin Yan Wang, Ji Xian Sun
Abstract: In most FEM codes, the isotropic-elastic & transversely anisotropic-elastoplastic model using Hill's yield function has been widely adopted in 3D shell elements (modified to meet the plane stress condition) and 3D solid elements. However, when the 4-node quadrilateral plane strain or axisymmetric element is used for 2D sheet metal forming simulation, the above transversely anisotropic Hill model is not available in some FEM code like Ls-Dyna. A novel approach for explicit analysis of transversely anisotropic 2D sheet metal forming using 6-component Barlat yield function is elaborated in detail in this paper, the related formula between the material anisotropic coefficients in Barlat yield function and the Lankford parameters are derived directly. Numerical 2D results obtained from the novel approach fit well with the 3D solution .
Authors: Ai Mei Zhang, Zhi Yuan Zhang, Qi Li
Abstract: The sheet metal forming of magnesium alloy is studied. A novel hydro-mechanical deep drawing for magnesium alloy sheets at gradient temperature is proposed on the basis of the study in this domain, the properties of magnesium alloy and the forming characteristics of workpiece in deep drawing. It is indicated that the deep drawing operation should be done in the warm condition and the temperature gradient of workpiece is necessary. The essence why the limited drawing ratio can be improved by means of the new process is demonstrated. The proper temperature gradient can be obtained by the control of the hydraulic during deep drawing operation. Thus the feasibility of the new technology is verified. It plays a solid foundation for solving the forming problem of magnesium alloy sheets and designing the novel setup of hydro-mechanical deep drawing with gradient temperature.
Authors: M.S. Niazi, V. Timo Meinders, H.H. Wisselink, C.H.L.J. ten Horn, Gerrit Klaseboer, A.H. van den Boogaard
Abstract: The global fuel crisis and increasing public safety concerns are driving the automotive industry to design high strength and low weight vehicles. The development of Dual Phase (DP) steels has been a big step forward in achieving this goal. DP steels are used in many automotive body-in-white structural components such as A and B pillar reinforcements, longitudinal members and crash structure parts. DP steels are also used in other industrial sectors such as precision tubes, train seats and Liquid Petroleum Gas (LPG) cylinders. Although the ductility of DP steel is higher than classical high strength steels, it is lower than that of classical deep drawing steels it has to replace. The low ductility of DP steels is attributed to damage development. Damage not only weakens the material but also reduces the ductility by formation of meso-cracks due to interacting micro defects. Damage in a material usually refers to presence of micro defects in the material. It is a known fact that plastic deformation induces damage in DP steels. Therefore damage development in these steels have to be included in the simulation of the forming process. In ductile metals, damage leads to crack initiation. A crack is anisotropic which makes damage anisotropic in nature. However, most researchers assume damage to be an isotropic phenomenon. For correct and accurate simulation results, damage shall be considered as anisotropic, especially if the results are used to determine the crack propagation direction. This paper presents an efficient plasticity induced anisotropic damage model to simulate complex failure mechanisms and accurately predict failure in macro-scale sheet forming processes. Anisotropy in damage can be categorized based on the cause which induces the anisotropy, i.e. the loading state and the material microstructure. According to the Load Induced Anisotropic Damage (LIAD) model, if the material is deformed in one direction then damage will be higher in this direction compared to the other two orthogonal directions, irrespective of the microstructure of the material. According to Material Induced Anisotropic Damage (MIAD) model, if there is an anisotropy in shape or distribution of the particles responsible for damage (hard second phase particles, inclusions or impurities) then the material will have different damage characteristics for different orientations in the sheet material. The LIAD part of the damage model is a modification of Lemaitre’s (ML) anisotropic damage model. Modifications are made for damage development under compression state and influence of strain rate on damage, and are presented in this paper. Viscoplastic regularization is used to avoid pathological mesh dependency. The MIAD part of the model is an extension of the LIAD model. Experimental evidence is given of the MIAD phenomenon in DP600 steel. The experimental analysis is carried out using tensile tests, optical strain measurement system (ARAMIS) and scanning electron microscopy. The extension to incorporate MIAD in the ML anisotropic damage model is presented in this paper as well. The paper concludes with a validation of the anisotropic damage model for different applications. The MIAD part of the model is validated by experimental cylindrical cup drawing wheras the LIAD part of the model is validated by the cross die drawing process.
Authors: Hua Liu, Kai Yong Jiang, Bin Liu, Ping Lu
Abstract: This paper proposes a fast and convenient method to inverse the material performance parameters in stamping forming. This method effectively combined with the FEM and the genetic algorithm. The reverse objective function was constructed with the thickness which is easily measured from the stamped parts, and then a genetic algorithm was programmed; The thickness-sensitive material performance parameters can be acquired through the orthogonal experiment, then these material parameters can be inversed by the self-programming genetic algorithm. Finally, a stamping case proves this method is precise, rapid and valid.
Authors: Zhi Ren Han, Qiang Xu, Ze Bing Yuan
Abstract: An experimental study is conducted to explore a new method to calculate the strain in axisymmetric workpiece forming. When designing deep drawing die for an axisymmetric workpiece, the principal strain during the forming is needed to estimate formability and to decide whether the forming is finished in one pass. Strain calculation is a difficult task, so an ideal same area method used to calculate the strain for an axisymmetric workpiece along with a correction same area method considered thickness reduction rate is proposed here. The deep drawing test for an axisymmetric workpiece is used to obtain the strain along circumference and generatrix direction. The strain along the two directions calculated by the ideal same area method and correction same area method is compared with experimental results. The results show that ideal same area method can be used to calculate the strain during the forming process for an axisymmetric workpiece and the result from correction same area method is close to the experiment.
Authors: Zeng Tao Chen, Rahul Datta
Abstract: We propose a new critical void volume fraction (fc) criterion that identifies the onset of void coalescence based on the stress state of the material as compared to the definition of the phenomenological criterion by Tvergaard and Needleman [1], where void coalescence is predicted based merely on a constant value for critical void volume fraction. The new fc criterion is obtained using the finite element analysis of the unit cell model of clustered voids. Validation of this new criterion is done by implementing the new coalescence criterion into the Gurson-Tvergaard-Needleman (GTN) [1-3] model and simulating the ductile fracture experiment of a series of angularly notched sheet samples of dual phase (DP), advanced high strength steels (AHSS). A methodology has been devised to construct a stress triaxiality-based void coalescence criterion. Validation of the methodology has been performed using tensile tests of angularly notched samples of DP490 AHSS. Experimental data is compared with FE simulations in order to verify the dependency of void coalescence on stress triaxiality.
Authors: Liu Ru Zhou
Abstract: According to sine law, a vertical wall square box can’t be formed by NC incremental sheet metal forming process in a single process, rather, it must be formed in multi processes. A vertical wall square box can be considered to consist of corners and straight sides. Straight sides and corners affect each other and the effect is different in various square boxes. The effect depends on the ratio r/B of the corner radius r and straight side width B. The smaller r/B, the larger the effect of straight side on corner is. In this case, the deformation in the straight sides isn’t even, and the metal of the corner is compressed and gradually piled up. With the increase of r/B, the deformation becomes more uniform. The tool path with gradually reduced corner radius is adopted to overcome this question. A vertical wall square box with small corner radius is successfully formed.
Authors: Xiang An Yang, Feng Ruan
Abstract: Nature of springback in sheet metal forming was analysed in the study, two stress-based objective functions were established to evaluate springback respectively from the stress point of view in an optimization problem aimed to reduce springback. To evaluate springback more comprehensively, multi-objective functions including a stress-based and a strain-based objective function were applied. Results show that when acting in conjunction with strain-based objective function, objective function which is defined on stress component deviation through thickness direction has perfect performance, while objective function which is defined on equivalent stress deviation through thickness direction would work well only when degree of plastic deformation is large for the stamped part. To evaluate the influence of stress position on springback, the parametric coordinate of integration point in thickness direction was also employed as weight factor for those two stress-based objective functions. Accuracy of the proposed two objective functions was also compared with the traditional objective function which is defined on the corresponding nodal distance of the shape before and after unloading.
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