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1.
A literature review of sheet metal forming errors as well as geometrical dimensions and tolerances (GD&T) shows that the theoretical means for the allocation of process tolerances with respect to GD&T are insufficient. In order to judge the influence of geometrical process errors (e.g., angular errors of bends), two typical sheet metal designs with parallelism and a position tolerance are studied. These case studies comprise a detailed analysis of tolerance chains including angular errors of bends and their positions. The resulting errors are compared with those resulting from length dimensional process errors and conclusions are drawn. 相似文献
2.
Thinning as a failure criterion during sheet metal forming 总被引:1,自引:0,他引:1
B. Sarkar B. K. Jha D. Mukerjee S. Jha K. Narasimhan 《Journal of Failure Analysis and Prevention》2002,2(2):63-64
Thinning during forming is often considered a failure criterion in the metal forming industry. It is believed that a critical
amount of thinning takes place in a sheet metal before failure. In this study, varying widths of low-carbon steel sheets were
punch stretched under laboratory conditions. Thinning during punch stretching was measured at various locations along the
steel sheets. These measurements demonstrated that thinning during forming is not constant, but that it is a function of the
strain path followed by the sheet. Hence, thinning should not be used as a failure criterion during forming of sheet metals. 相似文献
3.
Incremental Sheet Forming (ISF) is a manufacturing technology for individualized and small batch production. Among the opportunities this technology provides there is the possibility of a short ramp-up time and to cover the whole production chain of sheet metal parts by using a single reconfigurable machine set-up. Since recent developments proved that manufacturing of industrial parts is feasible, finishing operations such as flanging and trimming gain importance, which are an integral part of manufacturing process chains of many sheet metal parts. This paper analyses the technological capabilities of performing flanging operations by ISF. Due to the localized forming zone and the absence of surrounding clamping devices, ISF exhibits a different material flow than conventional flanging processes. In this paper, the influence of the tool path characteristics, the flange length as well as the flange radius is analysed in order to establish a process window and to compare it to the process limits of conventional flanging operations. Since geometrical deviations occur when flanging operations are performed by ISF, a new adaptive blank holder is developed, which acts in the vicinity of the forming tool and reduces unwanted deformation outside the primary forming zone. The experimental results show the benefits of the adaptive blank holder with respect to geometric accuracy. The established process window and the adaptive blank holder hence contribute to the applicability of incremental flanging operations, such that ISF can be used for all forming and flanging operations along the process chain. 相似文献
4.
Alexandra Werber Mathias Liewald Winfried Nester Martin Grünbaum Klaus Wiegand Jörg Simon Jürgen Timm Walter Hotz 《International Journal of Material Forming》2014,7(4):395-403
In industrial try-out processes in sheet metal forming usually the forming limit curve is used as failure criterion in order to describe the onset of localized necking. Forming limits, however, are strain-path dependent. Up to today many different approaches how the strain-path dependent behavior of the forming limit curve can be avoided have been published. Best known are the approaches based on forming limit stress curves published by Arrieux, and the approach of Müschenborn published in 1975. An overview over existing failure criteria is given in this contribution. The failure criterion forming limit stress curve as well as several failure criteria based on Müschenborn’s approach will be evaluated with newly recorded experimental data on forming limit curves for non-proportional loading. A new approach, that is in contrast to the two mentioned approaches not based on assumptions but on experimental observations, is presented herein. The suggested approach is presented as failure surface where strains above the surface indicate the onset of localized necking. The failure surface is given as function of the loading mode and the level of effective pre-stretching. Different suggestions how to use and simplify the new approach are given in this paper. The prediction accuracy of the addressed approaches as well as of the newly suggested approach is evaluated by transforming the data of the approaches back into the conventional forming limit curve for several non-linear strain paths. The comparison of the described approaches shows that forming limits for non-proportional loading can be well-predicted with the suggested approach. 相似文献
5.
Maysam Gorji Bekim Berisha Pavel Hora Frédéric Barlat 《International Journal of Material Forming》2016,9(5):573-584
In this study, a model based on a strain localization level to overcome the shortcomings of the well-established Forming Limit Diagram (FLD) in predicting the physical phenomenon of necking is introduced. An optical measurement system was used to capture the strain history of the Nakazima experiment until rupture occurred. In order to measure the fracture strain more accurately, a further method is introduced, which is based on the microscopic measurements of ruptured regions. This model is validated using a 3-point bending test. The results show the ability of the method to predict failure under bending conditions as well. Additionally, failure is investigated based on the pressure sensitivity and the Lode dependency. The results show that the triaxiality at the failure point is independent of the loading path. 相似文献
6.
F.‐W. Bach A. Roßberg M. Schperktter M. Schaper L. Walden J. Weber 《Materialwissenschaft und Werkstofftechnik》2004,35(7):423-430
The production and processing of sheet metals of high‐strength steels, titanium, aluminum or magnesium alloys is investigated intensively at universities and in the industry. The main emphasis is put for example on the aluminum space frame concept as well as on the succeeding projects of the ULSAB‐study in the field of the steel sheet metals. Within this article the qualification of the above mentioned materials for the application as deep‐drawing materials will be discussed. The aim of the development for new deep‐drawing sheet metals is to decrease the elastic part of the forming, which means to lower the yield point. A high elastic portion would cause a high resilience after the forming of the sheet metals and therefore an increased requirement of force and form error during the forming process. Furthermore the optimized sheet metal material should have a great uniform elongation, so that it can be plastically deformed in a wide range. The beginning of the deformation should be possible at low forming forces but due to the deformation an increase of the hardening should be caused, so that the finished component has high strength. But it is not possible to realize both aims, high strength and great uniform elongation, at the same time. 相似文献
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8.
Markus Bambach 《International Journal of Material Forming》2016,9(3):353-360
In order to use incremental sheet forming (ISF) in an industrial context, it is necessary to provide fast and accurate simulation methods for virtual process design. Without reliable process simulations, first-time right production seams infeasible and the process loses its advantage of offering a short lead time. Previous work indicates that implicit finite element (FE) methods are at present not efficient enough to allow for the simulation of AISF for industrially relevant parts, mostly due to the fact that the moving contact requires a very small time step. Finite element methods based on explicit time integration can be sped up using mass or time scaling to enable the simulation of large-scale sheet metal forming problems. However, AISF still requires dedicated adaptive meshing methods to further reduce the calculation times. In this paper, an adaptive remeshing strategy based on a multi-mesh method is developed and applied to the simulation of AISF. It is combined with subcycling to further reduce the calculation times. For the forming of a cone shape, it is shown that savings in CPU time of up to 80 % are possible with acceptable loss of accuracy, and that the simulation time scales more moderately when the part size is increased, so that larger, industrially relevant parts become feasible. 相似文献
9.
10.
微薄板塑性成形本构关系研究 总被引:1,自引:0,他引:1
尺寸效应的影响使得传统的成形理论和变形机制不再适用于微塑性成形.在考虑尺寸效应对微薄板成形性能影响的基础上,对已有的CuZn36黄铜薄板微拉伸实验结果进行处理,提出了一种研究微塑性成形本构关系的方法.根据弹性和塑性变形过程,分阶段分析了t/d(板厚/晶粒大小)对屈服强度和切线模量的影响,修正了双线性弹塑性本构关系,获得了考虑尺寸效应的微塑性成形本构关系.借鉴宏观增量本构关系,结合微拉伸实验,采用Mises屈服准则和随动强化模型,得出适合微塑性成形的弹塑性增量本构方程,为微塑性成形的理论研究和实际应用奠定了基础. 相似文献
11.
Alexander Govik Ramin Moshfegh Larsgunnar Nilsson 《International Journal of Material Forming》2014,7(3):305-316
In this study a simulation-based sensitivity study is performed in order to investigate the influence of the forming history on the properties of an assembly. In the study the assembly properties are predicted by sequentially simulating the manufacturing process chain of a sheet metal assembly. Several simulations of the assembly stage are performed in which different combinations of forming histories are transferred from the forming stage. It is found that the forming history affects the properties of the assembly and that the residual stress state is the most influential history variable. This demonstrates the importance of utilising the complete final mechanical state of each manufacturing step as the initial condition for the subsequent step in the manufacturing process chain in order to achieve accurate predictions of the assembly properties. Furthermore, if more reliable predictions can be made concerning the manufacturability of a product and its in-service behaviour, more design alternatives can be evaluated during product development while a considerably smaller number of physical prototypes are needed. 相似文献
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13.
M. Hamdaoui G. Le Quilliec P. Breitkopf P. Villon 《International Journal of Material Forming》2014,7(3):337-358
Our approach aims at coupling the ever increasing off-line computing power of mainframe computers with the interactive on-line possibilities of ubiquitous low computing power devices at the early design stages in order to provide insight into the design problems and to search for candidate optimal design points. In the off-line phase, the method under investigation relies on combining an optimized space-filling sampling plan on the design parameter space with extensive finite elements (FE) simulations yielding a learning set of displacement fields. The objective of this paper is the on-line phase. We provide a rigorous mathematical presentation of a family of non-intrusive, bi-level surrogates. We focus on displacement field approximation by Proper Orthogonal Decomposition (POD) combined with kriging interpolation of coefficients. The method is illustrated with two simple, easily reproduced numerical examples of quality assessment of deep-drawing process of a cylindrical cup by on-the-fly plotting forming limit diagrams (FLDs) and related quantities enabling thus to spot improved design points. 相似文献
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15.
N. Chandra 《International journal for numerical methods in engineering》1988,26(9):1925-1944
A finite element velocity method for analysing the superplastic sheet metal forming process is presented. This method is developed from the principle of virtual work and is based on the use of isoparametric continuum elements. The large inelastic deformation of the superplastic material is modelled as the behaviour of an incompressible non-linear viscous flow material. The contact and friction problem is solved by using the compatibility load step method, which is an extension of an earlier work. The finite element method is applied to selected problems to illustrate the applicability of the solution procedure. 相似文献
16.
An elastic-plastic thin shell finite element suitable for problems of finite deformation in sheet metal forming is formulated. Hill's yield criterion for sheet materials of normal anisotropy is applied. A nonlinear shell theory in a form of an incremental variational principle and a quasi-conforming element technique are employed in the Lagrangian formulation. The shell element fulfills the inter-element C
1 continuity condition in a variational sense and has a sufficient rank to allow finite stretching, rotation and bending of the shell element. The accuracy and efficiency of the finite element formulation are illustrated by numerical examples. 相似文献
17.
K.-C. Liao J. Pan S. C. Tang 《International journal for numerical methods in engineering》1998,41(3):559-584
Three phenomenological yield criteria are adopted to describe the plastic behaviour of sheet metals with normal plastic anisotropy. The sheet metals are assumed to be elastic-plastic, rate-sensitive and incompressible. A rate-sensitive thin shell finite element formulation based on the virtual work principle is derived for the three yield criteria. The effects of the yield surface shapes based on the three yield criteria with the same value of the plastic anisotropy parameter R on the strain distribution and localization are investigated under a hemispherical punch stretching operation and a plane strain rawing operation. The results of the simulations show that the yield surface shape, in addition to the plastic anisotropy parameter R, controls the punch force, strain distribution and strain localization for the punch stretching operation. However, the yield surface shape does not affect the punch force and the strain distribution significantly for the plane strain drawing operation. © 1998 John Wiley & Sons, Ltd. 相似文献
18.
Both increased weight reduction and improved passive safety have been simultaneously required for components of new vehicle generation. Thus, advanced high strength Dual Phase (DP) steels have been progressively used when making automotive parts. During each sheet metal forming process the high strength steels exhibit distinct springback effect, which is governed by strain recovery of material after load removal. The springback is variably sensitive to materials and process parameters. Considering springback occurred in a formed part is significant for designing tools and dies. In this work, both experiments and Finite Element Analyses (FEA) of a U-shape forming test were performed and compared for investigating the springback effect. Two DP steels (JSC590R and JSC780Y) with different strengths and a mild steel (JSC270C) were taken into account. The planar anisotropic material model according to Hill’s 1948, Barlat’s yield 2000, and Yoshida–Uemori kinematic hardening model were applied in the simulations. Various mechanical testing as hydraulic bulge test, disk compression test, and in particular cyclic test under tension and compression load were carried out in order to determine required materials parameters of the models. Obviously, steel with higher yield and tensile strength definitely showed an increasing in magnitude of both springback and curling. All presented material models restricted ability to predict springback effect of the examined steels, although the Yoshida–Uemori criterion provided more accurate results than other ones. The model is therefore preferred for describing the strain recovery mechanism of high strength steels, while parameter determination plays a decisive role. The cyclic test was verified to successfully describe the kinematic behaviour of material. 相似文献
19.
J. W. Cho D. Y. Yang W. J. Chung 《International journal for numerical methods in engineering》2002,53(10):2311-2327
A simplified scheme for considering the thickness stress of shell elements induced by contact is presented which improves the accuracy of sheet metal forming analysis. The yield function formulated on the basis of plane stress conditions is modified to incorporate the effect of transverse normal stress induced by contact forces acting on shell elements and return mapping routine is used to update in‐plane stresses at each time step. The transverse normal stress distributions in the thickness direction are determined using the analytic solution of the cylindrical tube under the internal pressure. As numerical examples, uni‐axial compression, bi‐axial tension and bending tests are treated. The problem of cylindrical cup drawing is also calculated. Each result is compared with the results obtained by the analysis using ABAQUS continuum elements. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
20.
为探明高强钢冲压成形过程中的粘模机理,利用数值模拟与工艺试验相结合的方法系统评估了其宏观粘模行为.以高强钢SPFC590为研究对象,采用方盒拉深成形工艺,基于FEM-Archard磨损模型研究了弯曲-拉深复合变形模式下界面压力与滑移距离对粘模行为的影响规律.研究结果表明,方盒拉深过程中模具的宏观粘模行为主要集中在界面压力较大的拉深圆角与弯曲直边相接处附近,并随着拉深次数的增加(即滑移距离的增大),粘模量不断增大且不断向拉深方向扩展.同时,基于FEM-Archard磨损模型得到的粘模评估结果与方盒拉深试验结果相一致. 相似文献