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Currently, the metal working in manufacturing industry is growing rapidly, taking in mind that production activities cannot be separated from the use of machinery as a support for its operations. The excessive vibration will reduce the effectiveness of the engine, furthermore the engine will be irreparable. One way to reduce the excessive vibration from rotating shaft system at lathe machine is by using Radial Vibration Damper (RVD). This aims of this study are to reduce the vibration acting on a long thin shaft using RVD and to validate the experiment’s results and simulation’s results using the Independent T-test sample method. The position of RVD which is laid on a long thin shaft was varied. The working frequencies of the lathe machine were 320 rpm, 540 rpm, and 900 rpm. The results show that the simulation results correspond well to the experimental results. The maximum vibration reduction of a long-thin shaft occurred at the working frequency of 900 rpm for both the experimental method and the simulation method. The experimental results presented that the maximum vibration reduction of the shaft in the X-axis direction is 67.51% at point 4 (midspain) and the reduction in the Y-axis is 61.47% at point 3. While, the maximum reduction from simulation method occurred in the X-axis is 65.83% and in the Y-axis is 75.78%. [ABSTRACT FROM AUTHOR]

The cutting stage is an essential step in the process of multi-stage forming of metal sheets. In this work, a robust cutting strategy is thoughtfully described. The cutting strategy involves the following steps: the reading of the cutting line geometry and parameters; the projection of the cutting lines over the blank to cut; the regeneration of the FEM mesh in the vicinity of the projected lines, the removal of the finite elements that were cut off; the smoothing of simulation variables at nodal and gauss-point levels. To validate the proposed procedure, four industrial examples are given including 3D geometries discretized with isoparametric hexahedra and BST shell elements. The results show that the whole process of multi-stage forming of thick metal sheets can be successfully simulated employing this cutting strategy. [ABSTRACT FROM AUTHOR]

The coupling of Finite Element (FE) simulations to mathematical optimization techniques has contributed significantly to product improvements and cost reductions in the metal forming industries. The next challenge is to bridge the gap between deterministic optimization techniques and the industrial need for robustness. This paper introduces a new and generally applicable structured methodology for modeling and solving robust optimization problems. Stochastic design variables or noise variables are taken into account explicitly in the optimization procedure. The metamodel-based strategy is combined with a sequential improvement algorithm to efficiently increase the accuracy of the objective function prediction. This is only done at regions of interest containing the optimal robust design. Application of the methodology to an industrial V-bending process resulted in valuable process insights and an improved robust process design. Moreover, a significant improvement of the robustness (>2σ) was obtained by minimizing the deteriorating effects of several noise variables. The robust optimization results demonstrate the general applicability of the robust optimization strategy and underline the importance of including uncertainty and robustness explicitly in the numerical optimization procedure. [ABSTRACT FROM AUTHOR]

Robustness, optimization and Finite Element (FE) simulations are of major importance for achieving better products and cost reductions in the metal forming industry. In this paper, a metamodel-based robust optimization strategy is proposed for metal forming processes. The applicability of the strategy is demonstrated by application to an analytical test function and an industrial V-bending process. The results of both applications underline the importance of including uncertainty and robustness explicitly in the optimization procedure. [ABSTRACT FROM AUTHOR]

Saving of resources becomes more and more important. Therefore the forging industry tries to develop processes with less flash than the conventional techniques or to avoid flash completely. Currently only simple parts like gears can be forged without flash. In a research project flashless forging processes for crankshafts were developed. In this paper the evolution of the flashless forging process and the process steps will be described. The collaboration research project 'process chain for the production of precision forged high performance parts' has been conducted in the last few years at IPH and is funded by the German Research Foundation (DFG). [ABSTRACT FROM AUTHOR]

Numerical modeling of heat transfer during solidification has become widespread in the foundry industry. This is because it is possible to investigate the effects of adjustment to the casting variables on final casting quality, without having to do costly trial-and-error experiments. After selecting a suitable mathematical model, one has to choose an appropriate discretization method. If the grid is very fine, each type of method yields the same solution. However, some methods are more suitable to some classes of problems than others. The main objective of this paper is to demonstrate the advantages of using a block unstructured grid in combination with a generalized curvilinear formulation in a casting scenario and compare the performance of two discretization methods, finite differences (FD) and finite volume (FV). The validation of the numerical procedure is done by comparison with measurements which experimental set up is also described. A very good agreement of both numerical methods were verified with a slightly advantage for the finite volume method. Block unstructured grids works well with both discretization methods, allows obtain any physical feature in specific positions of the domain and is suitable for parallel computation; in combination with a generalized curvilinear formulation allows avoid geometric complexities and the development of more efficient algorithms. [ABSTRACT FROM AUTHOR]

Time and cost of development are key factors for the success of advanced devices. Device development requires multiple iterations of carefully designed implant splits to optimize device performance and yield. Conventional whole wafer implant splits are both time consuming and costly, due in part to the need to gain adequate statistics with the relatively high wafer to wafer variability of early stage development devices. VMASK, which provides multiple implant conditions on a single wafer, can be applied for a variety of corner splits, such as well, halo, and LDD implants to achieve target device performance and optimize process flow. By reducing the impact of variability from other process steps and the direct reduction in the number of device wafers required by a factor of four, a significant reduction in both wafer cost and cycle time can be achieved. In this paper, the benefits of VMASK were discussed and evaluated in a high volume production foundry fab and applied in the process development. [ABSTRACT FROM AUTHOR]

With the drive towards implementing Advanced High Strength Steels (AHSS) in the automotive industry; stamping engineers need to quickly answer questions about forming these strong materials into elaborate shapes. Commercially available codes have been successfully used to accurately predict formability, thickness and strains in complex parts. However, springback and twisting are still challenging subjects in numerical simulations of AHSS components. Design of Experiments (DOE) has been used in this paper to study the sensitivity of the implicit and explicit numerical results with respect to certain arrays of user input parameters in the forming of an AHSS component. Numerical results were compared to experimental measurements of the parts stamped in an industrial production line. The forming predictions of the implicit and explicit codes were in good agreement with the experimental measurements for the conventional steel grade, while lower accuracies were observed for the springback predictions. The forming predictions of the complex component with an AHSS material were also in good correlation with the respective experimental measurements. However, much lower accuracies were observed in its springback predictions. The number of integration points through the thickness and tool offset were found to be of significant importance, while coefficient of friction and Young’s modulus (modeling input parameters) have no significant effect on the accuracy of the predictions for the complex geometry. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper is concerned with crashworthiness of auto-body members considering the effect of fabrication. Most auto-body members are fabricated with sheet metal forming process and welding process that induce fabrication histories such as the plastic work hardening, non-uniform thickness distribution and residual stress. Crash simulation is carried out for auto-body members with LS-DYNA3D in order to identify the fabrication effect on the crashworthiness. The analysis calculated crash mode, the reaction force and the energy absorption for crashworthiness assessment with the forming effect. The result shows that the crash analysis with considering the forming history leads to a different result from that without considering the forming effect. The analysis results demonstrate that the design of auto-body members should be carried out considering the forming history for accurate assessment of the crashworthiness.. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Since sheet metal forming has a high percentage contribution in the overall design costs of a new car, this engineering area assisted in the last decades to considerable development efforts. The present challenge is to simulate all the production stages, from the initial blank sheet to the final part ready to assembly. On this particular issue of multi-step deep-drawing simulation, this work presents a new remapping method called Incremental Volumetric Remapping (IVR) developed to minimize the error that occurs, when performing the variable transfer operation between two different meshes. The IVR method is based in a volumetric approach where the calculus of the remapped state variables is obtained by means of a weighted average of the intersection volume between the meshes. The method performance is tested and compared with a standard extrapolation-interpolation, by applying a numerical example of the Numisheet’005 Conference, “The Channel Draw/Cylindrical Cup Benchmark”. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The main goal of this work is to determine the influence of the work hardening model in the numerical prediction of springback. This study will be performed according with the specifications of the first phase of the “Benchmark 3” of the Numisheet’2005 Conference: the “Channel Draw”. Several work hardening constitutive models are used in order to allow a better description of the different material mechanical behavior. Two are classical pure isotropic hardening models described by a power law (Swift) or a Voce type saturation equation. Those two models were also combined with a non-linear (Lemai⁁tre and Chaboche) kinematic hardening rule. The final one is the Teodosiu microstructural hardening model. The study is performed for two commonly used steels of the automotive industry: mild (DC06) and dual phase (DP600) steels. The mechanical characterization, as well as the constitutive parameters identification of each work hardening models, was performed by LPMTM, based on an appropriate set of experimental data such as uniaxial tensile tests, monotonic and Bauschinger simple shear tests and orthogonal strain path tests, all at various orientations with respect to the rolling direction. All the simulations were carried out with the CEMUC’s home code DD3IMP (contraction of ‘Deep Drawing 3-D IMPlicit code’). © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Advanced high strength steels (AHSS) are increasingly being used in the automotive industry to reduce vehicle weight while improving vehicle crash performance. One of the concerns in manufacturing is springback control after stamping. Although computer simulation technologies have been successfully applied to predict stamping formability, they still face major challenges in springback prediction, particularly for AHSS. Springback analysis is very complicated and involves large deformation problems in the forming stage and mechanical multiplying effect during the elastic recovery after releasing a part from the die. Therefore, the predictions are very sensitive to the simulation parameters used. It is very critical in springback simulation to choose an appropriate material model, element formulation and contact algorithm. In this study, a springback benchmark test, the slit ring cup, is used in the springback simulation with commercially available finite element analysis (FEA) software, LS-DYNA. The sensitivity of seven simulation variables on springback predictions was investigated, and a set of parameters with stable simulation results was identified. Final simulations using the selected set of parameters were conducted on six different materials including two AHSS steels, two conventional high strength steels, one mild steel and an aluminum alloy. The simulation results are compared with experimental measurements for all six materials and a favorable result is achieved. Simulation errors as compared against test results falls within 10%. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The “Digital Die Design System” (3DS) international project has been launched following the undesirable lack of reproducibility observed in some Numisheet benchmarks. The main idea behind the project was to repeat the same stamping experiments in different labs or press shops, with exactly the same tools and conditions. In spite of all precautions taken to ensure a good reproducibility of the stamping process, a high level of scatter was found between partners for some geometries and couples of material-lubricant. We discovered that a parameter, not neglected but insufficiently taken into consideration, was responsible for this scatter: it is the ram speed. Thanks to the quantity of recorded data, the examination of results finally drove us to see that, in certain circumstances, small differences of ram speed (i.e. 10 in place of 20 mm/s) were sufficient to strongly modify the level of springback, due to their influence on friction restraining forces. Consequences are discussed in the paper. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Sheet metal forming processes invariably involve non-proportional loading and changes in deformation/loading direction, resulting in a very complex material and structural behaviour. Much of this complexity can be traced back to the reaction of the material microstructure to such loading. In the case of hardening behaviour, for example, the interplay between the direction of inelastic deformation, the orientation of dislocation structures, and the current deformation/loading direction, plays an important role. The purpose of the current work is the formulation, numerical implementation and application of a thermodynamically-consistent material model for anisotropic hardening in such materials taking this interplay into account. Direction- and orientation-dependent quantities are represented in the model with the help of evolving structure tensors. These include the strength of dislocation structures, dislocation polarization, and kinematic hardening. Together with the initial texture-based inelastic flow anisotropy, these govern the evolving anisotropic response of the model to changes in loading direction. To exemplify this, the behaviour of the model subject to typical two-stage loading histories involving monotonic, reversing and orthogonal changes in loading/deformation direction are investigated for various parameter values. These simulations demonstrate clearly the effect of severe and abrupt changes in deformation/loading direction on the hardening behaviour and so on the resulting springback process. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

As more Advanced High-Strength Steels (AHSS) are heavily used for automotive body structures and closures panels, accurate springback prediction for these components becomes more challenging because of their rapid hardening characteristics and ability to sustain even higher stresses. In this paper, a modified Mroz hardening model is proposed to capture realistic Bauschinger effect at reverse loading, such as when material passes through die radii or drawbead during sheet metal forming process. This model accounts for material anisotropic yield surface and nonlinear isotropic/kinematic hardening behavior. Material tension/compression test data are used to accurately represent Bauschinger effect. The effectiveness of the model is demonstrated by comparison of numerical and experimental springback results for a DP600 straight U-channel test. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The FEM simulation of a sheet forming process can be seen as a method for calculating a deterministic vector set of output responses, starting from a vector set of input variables. In the real world, though, most process parameters should be considered as random variables (material properties, lubrication conditions, etc.), with a given statistical distribution. As a consequence, any FEM simulation which is run with nominal values of the input variables does not provide the “true” solution, but only a nominal response, related to a distribution around an expected value. The robustness of a given solution can be evaluated by several methods: sensitivity analysis, Montecarlo method, Response Surface Method (RSM), etc. The sensitivity analysis is usually performed by running one or two simulations for each random variable, setting it at an extreme value. The method does provide a rough measure of the process variability, but it does not usually guarantee a quantitative estimation of the response’s confidence interval. Statistical techniques, such as Montecarlo or RSM are very effective in predicting the true process variation. However, both methods are computationally very expensive, if the problem is complex (e.g., when forming, trimming and springback operations must be simulated for a large part). In the present paper the solution’s robustness of a Numisheet ’05 benchmark case is faced and solved with an approximate and computationally inexpensive method. The purpose of the study is to determine the tolerance interval of the part surface, induced by the random variation of 11 process parameters. The variability is modeled with a joint multinormal distribution. The analyzed response is the geometrical error of the process with respect to a reference “deterministic” geometry. The proposed method provides an upper bound estimation of the tolerance interval, by exploring the boundaries of the ellipsoidal probability density function of the multinormal input. Finally, the effectiveness of the method is tested by running a conventional Montecarlo analysis of the problem. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The exclusion of inherent process variations in the current deterministic design methods for sheet metal forming can lead to very unreliable result that may cause high scrap rate, frequent rework, machine shut down and thus huge loss of profit. In this paper, a general approach is presented to quantify the uncertainties and to incorporate them into RSM model so as to conduct probabilistic based optimization. As an application, deep drawing process of Hishida part is analyzed. Given the blank shape and tooling, a probabilistic design is successfully carried out to find the optimal combination of blank holder force and friction coefficient under the presence of variation of material properties. The result shows that by the probabilistic design, the quality index (average defect rates of wrinkling and fracture) improved (reduced) 42% over the traditional deterministic design. In a mass production environment, the achieved quality improvement is huge. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

FEA simulations have been successfully applied to various sheet metal forming processes to predict formability issues such as fractures, wrinkles, and thinnout; however, they have not achieved the same level of success in the springback predictions. As the former mainly dealt with stretch and the latter with bending, we contemplated that a fundamental underlying problem in the FEA springback predictability may lie with the thin shell theory, as it allows the thickness stress to be neglected and only uses an in-plane stretch and shear to balance the out-of-plane loads. A study was conducted to investigate the problem with channel draw test. Two steels, DP590 and HSLA350, were formed and simulated with same set of tooling and process conditions except for two different drawbead setups, i.e. with and without drawbead restraining force. Two different deformation modes, stretch bending and bending, were produced as a result. The testing and FEA results showed that the FEA simulation could not properly and accurately predict the bending strains. Also, it tended to underpredict the bending deformation while overpredicting the stretch. These findings proved that the inability of thin shell element to predict the bending strain is a major cause for the problematic and inaccurate FEA springback simulations. In order to correctly solve the springback problem with FEA simulations, the thin shell element formulations must be improved to include through thickness stress. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Sheet metal forming software is commonly used in the automotive and sheet metal sectors to support the design stage. However, the ability of the currently available software to accurately predict springback is limited. A sensitivity analysis of the springback behavior of a simple product is performed to gain more knowledge into the various factors contributing to the predictability of springback. The sensitivity analysis comprises both numerical and physical aspects and the most important results are reported in this paper. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The impact of material models on the numerical simulation of springback is investigated. The study is focused on the strain-path sensitivity of two hardening models. While both models predict the Bauschinger effect, their response in the transient zone after a strain-path change is fairly different. Their respective predictions are compared in terms of sequential test response and of strip-drawing springback. For this purpose, an accurate and general time integration algorithm has been developed and implemented in the Abaqus code. The impact of several numerical parameters is also studied in order to assess the overall accuracy of the finite element prediction. For some test geometries, both material and numerical parameters are shown to clearly influence the springback behavior at a large extent. Moreover, a general trend cannot always be extracted, thus justifying the need for the finite element simulation of the stamping process. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

In terms of the intensive similarity between the sheet metal forming-springback process and that of the annealing of metals, it is suggested that the simulation of the sheet metal forming process is performed with the Nonlinear FEM and the springback prediction is implemented by solving the large-scale combinational optimum problem established on the base of the energy descending and balancing in deformed part. The BFGS-SA hybrid SA approach is proposed to solve this problem and improve the computing efficiency of the traditional SA and its capability of obtaining the global optimum solution. At the same time, the correlative annealing strategies for the SA algorithm are determined in here. By comparing the calculation results of sample part with those of experiment measurement at the specified sections, the rationality of the schedule of springback prediction used and the validity of the BFGS-SA algorithm proposed are verified. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Springback or shape change has been one of the major challenges in sheet metal fabrication, particularly with increase application of high strength steel (HSS) and aluminum alloys in automotive stamping. Springback, an elastic material recovery after the unloading of stamping tools, causes variations and inconsistencies of final part dimensions. Minor or mild springback usually can be corrected in the re-strike process. Excessive springback must be corrected so the part will be produced within the given design tolerance and dimension. The commonly used Spring Forward approaches and shape compensations such as over-crown and over-bending are proven effective to alleviate excessive springback. To enhance these approaches, a new strategy of Die Face Engineering (DFE) based processing is proposed to quickly and easily to achieve the maximum allowable compensation using the under cut (or die lock) as the primary criteria. The implementation of the die face compensation through iterative FEA calculation, automatic surface mapping, projection and manual morphing are crucial to meet production environment requirements in terms of generating NC quality CAD surfaces of the compensated or morphed die face. In this paper, the strategy of the die face compensation with the consideration of the under cut criteria is presented. The implementation of various processes to enable user to perform the die face compensation task in a production environment is also discussed. Finally, two examples are shown to demonstrate the implementation of the proposed springback compensation scheme based on the combined CAE/CAD methodology. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Upon unloading after the forming stage, a sheet metal product will spring back due to internal stresses. Springback is a major problem for process-planning engineers. In industrial practise, deformations due to springback are compensated manually, by doing extensive measurements on prototype parts, and altering the tool geometry by hand. This is a time consuming and costly operation. In this paper the application of two compensation algorithms, based on the finite element simulation of the forming process are discussed. The smooth displacement adjustment (SDA) method and the springforward (SF) method have been applied to several industrial products, such as the NUMISHEET 2005 benchmark[sharp/mesh/hash_synonym]1. With the SDA method successful compensations have been carried out. For the SF method some principal problems remain. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Springback is an unquenchable forming defect in the sheet metal forming process. How to calculate springback accurately is a big challenge for a lot of FEA software. Springback compensation makes the stamped final part accordant with the designed part shape by modifying tool surface, which depends on the accurate springback amount. How ever, the meshing data based on numerical simulation is expressed by nodes and elements, such data can not be supplied directly to tool surface CAD data. In this paper, a tool surface compensation algorithm based on numerical simulation technique of springback process is proposed in which the independently developed dynamic explicit springback algorithm (DESA) is used to simulate springback amount. When doing the tool surface compensation, the springback amount of the projected point can be obtained by interpolation of the springback amount of the projected element nodes. So the modified values of tool surface can be calculated reversely. After repeating the springback and compensation calculations for 1∼3 times, the reasonable tool surface mesh is gained. Finally, the FEM data on the compensated tool surface is fitted into the surface by CAD modeling software. The examination of a real industrial part shows the validity of the present method. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Prediction of formability for sheet metal pressings has advanced to a high state of confidence in recent years. The major challenge is now to predict springback and, moreover, to assist in the design of tooling to correctly compensate for springback. This is particularly the case for materials now being routinely considered for automotive production, such as aluminium and ultra high strength steels, which are prone to greater degrees of springback than traditional mild steels. This paper presents a case study based on the tool design for an ultra high strength steel side impact beam. The forming and springback simulations, carried out using eta/DYNAFORM (based on the LS-DYNA solver), are reported and compared to measurements from the prototype panels. The analysis parameters used in the simulation are presented, and the sensitivity of the results to variation in physical properties is also reviewed. The process of compensating the tools based on the analysis prediction is described; finally, an automated springback compensation method is also applied and the results compared with the final tool design. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

To reduce weight and increase fuel efficiency and safety, more and more automotive sheet stamping parts are being made of aluminum and high strength steels. Forming of such materials encounters not just reduced formability but also dimensional quality problems. Springback prediction accuracy and compensation effectiveness have been the major challenge to die development, construction and tryout. In this paper, the factors that affect the accuracy of springback prediction are discussed, which includes the effect of material models, the selection of element size, and the contact algorithms. Springback predictions of several automotive aluminum and high strength panels are compared with measurement data. The examples show that the prediction correlates with measurement data in both springback trend and magnitude. The effect of springback on final product can be reduced or eliminated through process control and die face compensation. The process control method involves finding the root causes of springback and eliminating them through process modification. The geometrical compensation of die surface is a direct way to eliminate the springback effect. The global scaling compensation method is normally limited to parts with relatively small springback. For large springback and twisting, a new approach is discussed, which takes into account of the effect of deformation and springback history. The compensation is achieved iteratively by solving a system of non-linear equations. Production dies were cut to the compensated surface, which shows that the die compensation is an efficient way to reduce springback-induced geometry deviation. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Stretch bending is commonly used to shape thin-walled extrusions in aerospace and automotive industries. The extrusions are pre-stretched and bent over rigid curved dies. Effective application of this process demands sufficient knowledge of how different parameters influence the final shape of the product. Numerical simulation is an effective approach to investigate these issues presently. However, the validity of simulation result depends strongly on a precise description of the mechanical behavior of the material. Due to crystallographic texture caused by the extrusion process, aluminium extrusions exhibit significant plastic anisotropy which need be described by advanced constitutive model. In this work stretch bending of aluminum extrusions is simulated by using different anisotropic criteria (Hill quadratic, Barlat three-parameter). The influence of two yield criteria on predicting maximum die force immediately before unloading, permanent sagging and vertical springback displacement in the middle section of extrusion are compared. Maximum die force and springback calculated by two yield criteria are found to be almost same. Permanent sagging is obviously underestimated by two yield criteria, however, prediction by Barlat three-parameter is closer to experiment than one of Hill quadratic yield criterion. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

It is known that the crystallographic texture affects very much the mechanical properties of sheet metals. In this paper, rolled aluminum alloy sheets are considered as target materials. Typical texture components usually observed in rolled aluminum alloy sheets are the deformation textures of Cu, Brass and S, and the recrystallization textures of Cube and Goss. First, the effects of these components on mechanical properties, such as variations of Lankford’s r-value for different tensile directions and forming limit strains, are investigated using full crystal plasticity analyses. In general, the most appropriate volume fractions of the texture components for a user-defined particular requirement, e.g. the smallest possible in-plane anisotropy, or the largest possible formability for a particular strain path, are unknown. Then, a texture optimization strategy is considered, i.e. a genetic algorithm is adopted to solve texture optimization problems. We describe a genetic algorithm with real-valued genes, which is called the real-coded GA. This algorithm is used to search for optimum textures that satisfy the requirements of smallest possible in-plane anisotropy and largest possible formability in biaxial stretch, as examples, to verify the efficiency of the method. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The paper presents a few recent contributions brought by the authors in the field of the formability of aluminum alloys. A new concept for calculating Forming Limit Diagrams (FLD) using the finite element method is presented. The article presents a new strategy for calculating both branches of an FLD, using a Hutchinson - Neale model implemented in a finite element code. The simulations have been performed with Abaqus/Standard. The constitutive model has been implemented using a UMAT subroutine. The plastic anisotropy of the sheet metal is described by the Cazacu-Barlat and the BBC2003 yield criteria. The theoretical predictions have been compared with the results given by the classical Hutchinson - Neale method and also with experimental data for different aluminum alloys. The comparison proves the capability of the finite element method to predict the strain localization. A computer program used for interactive calculation and graphical representation of different Yield Loci and Forming Limit Diagrams has also been developed. The program is based on a Hutchinson-Neale model. Different yield criteria (Hill 1948, Barlat-Lian and BBC 2003) are implemented in this model. The program consists in three modules: a graphical interface for input, a module for the identification and visualization of the yield surfaces, and a module for calculating and visualizing the forming limit curves. A useful facility offered by the program is the possibility to perform the sensitivity analysis both for the yield surface and the forming limit curves. The numerical results can be compared with experimental data, using the import/export facilities included in the program. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Since the multi-scale finite element analysis (FEA) requires large computation time, development of the parallel computing technique for the multi-scale analysis is inevitable. A parallel elastic/crystalline viscoplastic FEA code based on a crystallographic homogenization method has been developed using PC cluster. The homogenization scheme is introduced to compute macro-continuum plastic deformations and material properties by considering a polycrystal texture. Since the dynamic explicit method is applied to this method, the analysis using micro crystal structures computes the homogenized stresses in parallel based on domain partitioning of macro-continuum without solving simultaneous linear equations. The micro-structure is defined by the Scanning Electron Microscope (SEM) and the Electron Back Scan Diffraction (EBSD) measurement based crystal orientations. In order to improve parallel performance of elastoplasticity analysis, which dynamically and partially increases computational costs during the analysis, a dynamic workload balancing technique is introduced to the parallel analysis. The technique, which is an automatic task distribution method, is realized by adaptation of subdomain size for macro-continuum to maintain the computational load balancing among cluster nodes. The analysis code is applied to estimate the polycrystalline sheet metal formability. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The influence of strain paths (loading history) on material formability is well known in sheet forming processes. Sophisticated experimental methods are used to determine the entire shape of strain paths of forming limits for aluminum AA6016-T4 alloy. Forming limits for sheet metal in as-received condition as well as for different pre-deformation are presented. A theoretical approach based on Arrieux’s intrinsic Forming Limit Stress Curve (FLSC) concept is employed to numerically predict the influence of loading history on forming severity. The detailed experimental strain paths are used in the theoretical study instead of any linear or bilinear simplified loading histories to demonstrate the predictive quality of forming limits in the state of stress. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The present work aims at analyzing a comparative study between the strain-based forming limit criterion (FLD) and the stress-based forming limit criterion (FLSD), under linear and complex strain paths. The selected material is an AA5182-0 aluminium alloy. Some relevant remarks about stress-based forming limit criterion concept are presented. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The effects of changing strain paths on forming limit stresses of sheet metals are investigated using the Marciniak-Kuczynski model. Forming limits are analyzed for proportional loading and two types of combined loadings: combined loading which includes unloading between the first and second loadings and that which includes an abrupt strain path change without unloading between the first and second loadings. The forming limit stress curves in stress space calculated for the combined loading with unloading are in good agreement with those calculated for the proportional loading, while the forming limit curves in strain space are strongly dependent on the strain paths. The forming limit stresses calculated for combined loading with an abrupt strain path change, however, do not coincide with those calculated for proportional loading. The strain path dependence of the forming limit stresses is discussed in detail. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Commodity thermoplastics such as polypropylene and polyethylene are gaining more attention from the automotive industries for applications requiring weight and cost savings. In order to assess the feasibility of employing thermoplastic tubes for subsequent forming into automotive structural components, first an establishment of the forming limits (or the forming limit diagram) for these materials is required. An analytical model, which is able to predict the forming limits for thermoplastic tubes, is useful from the perspective of examining the effect of material properties on the forming of a given shape without numerous experimental forming trials. Knowledge of the forming limits for these materials is also useful in die design as well as process control. Since thermoplastics such as polypropylene are temperature and strain rate dependent, the proposed analytical model would be able to predict the effect of temperature and strain rate on the resulting forming limits for the tube along various loading paths. Preliminary results from the model indicate that thermoplastic tubes formed at elevated temperature undergo larger strains in both the hoop and axial directions of the tube prior to localized necking. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Line die forming simulation and validation create tremendous business values for automotive die developments and production stamping while they pose a great technological challenge to stamping CAE community. GM Manufacturing Engineering Die Center has developed an integrated line die analysis technology to validate die lines as a productionized business process. In this process, a finished stamping body panel can be streamline analyzed with required time, accuracy, and quality. This paper presents critical issues in line die analysis, discusses technical challenges in production applications and software development, and finally demonstrates the impact of line die forming simulation and validations on automotive body styling and tooling developments. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

An increasing use of combining more than one process step is noticed for coupling crash simulations with the results of forming operations — mostly by inheriting the forming history like plastic strain and material hardening. Introducing a continuous failure model allows a further benefit of these coupling processes; it sometimes can even be the most attractive result of such a work. In this paper the algorithm CrachFEM for fracture prediction has been used to generate more benefit of the successive forming and crash simulations — especially for ultra high strength steels. The choice and selection of the material grade in combination with the component design can therefore be done far before the prototyping might show an unsuccessful crash result; and in an industrial applicable manner. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The punchless piercing is a process that uses highly pressurized fluid instead of the conventional punch to make holes into the sheet metal. This process has many advantages over the conventional method for piercing various shaped holes into very thin strips of metal, composite, etc. An important cost advantage comes from not having to use a punch. Another important advantage comes from the top quality of pierced holes produced by punchless piercing, as no secondary finishing process will be needed for removing burrs typically found in conventional cutting processes. The ABAQUS/Explicit FEM code coupled with Lemaitre damage model has been used to more precisely characterize the punchless piercing process. The formulation adopted for this purpose focuses on the development of an efficient stress integration algorithm and development of a user material subroutine (VUMAT). For verification, the computed results have been compared with those of the experimental results in the literature and shown to be in good agreement with each other. The results obtained from this work are expected to be of significant interest to automotive and aerospace industries interested in using the punchless piercing process. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

An improved Sheet Hydro-forming process was put forward, which was researched in the Institute of Metal Research (Chinese Academy of Sciences) and Aalborg University jointly. In this paper, the effects of local constraints on the sheet deformation were researched experimentally. For this case, the local constraints include rigid tools (movable die) and surface roughness of the movable die, especially around the shoulder of the movable die. Finally, ASAME system and FEM are used to analyze the forming process to explain some results that were found in the experiment. In the simulation, the effects of the friction between the movable die and the blank and the movable die on the deformation of the blank are investigated in detail by using the FEM code LS-DYNA. For the sheet hydroforming with local constraints, the contact between the sheet and the dies affects the material flow and the fracture of the sheet can be avoided. Moreover, the forming limit of sheet metal can be remarkably improved. This process meets the need of the deformation of complicated parts as well as forming of low-formability and light-weight materials, such as aluminum lithium alloys and magnesium alloys. The die can be replaced with other die of various shapes, and can also be made of very cheap materials. Thus complex-shaped sheet parts can be formed with less expensive tool systems. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper reports a novel extension of the stress-based flow limit curve approach. A conventional strain-based FLC is converted into a stress-based FLC using the method proposed by Stoughton. This stress-based FLC is then transformed into the XSFLC by casting the stresses in terms of the invariants — effective stress and mean stress that are the variables that constitute the XSFLC. This curve is used in conjunction with LSDYNA finite element simulations that use eight-noded solid elements to predict the onset of necking in tubular hydroforming. The particular case of straight tube hydroforming of ENAW 5018 aluminum alloy tubes is considered. The XSFLC is able to predict the internal pressure at the onset of the neck and the final failure location in the tube with remarkable accuracy. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The wide spectrum of recent improvements in hydroforming deep drawing processes is descried here briefly. New accomplishments were seemingly achieved as soon as the sheet forming industry has found their cost-effectiveness. Some fundamental results and their physical motives are presented, based on an idealized limit-analysis formulation (lower bound approach in this case). The mathematical complexities frequently encountered in more precise solutions are thus avoided, though they had been established as (partially) appeared in the reference list. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

In comparison to the commonly applied technology of tailored blanks the concept of patchwork blanks offers a number of additional advantages. Potential application areas for patchwork blanks in automotive industry are e.g. local reinforcements of automotive closures, structural reinforcements of rails and pillars as well as shock towers. But even if there is a significant application potential for patchwork blanks in automobile production, industrial realization of this innovative technique is decelerated due to a lack of knowledge regarding the forming behavior and the numerical modeling of patchwork blanks. Especially for the numerical simulation of hydroforming processes, where one part of the forming tool is replaced by a fluid under pressure, advanced modeling techniques are required to ensure an accurate prediction of the blanks’ forming behavior. The objective of this contribution is to provide an appropriate model for the numerical simulation of patchwork blanks’ forming processes. Therefore, different finite element modeling techniques for patchwork blanks are presented. In addition to basic shell element models a combined finite element model consisting of shell and solid elements is defined. Special emphasis is placed on the modeling of the weld seam. For this purpose the local mechanical properties of the weld metal, which have been determined by means of Martens-hardness measurements and uniaxial tensile tests, are integrated in the finite element models. The results obtained from the numerical simulations are compared to experimental data from a hydraulic bulge test. In this context the focus is laid on laser- and spot-welded patchwork blanks. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The article reports on a study to benchmark springback prediction capability of various software and skills of users on an underbody part mostly dominated by bending effect. The simulation process of stamping a cross member panel consists of three operations: forming, trimming and springback. In this benchmark, participants are allowed to use either physical beads or line beads in forming simulation. The information of physical bead geometry and bead centerlines is provided in the Nastran mesh file and IGES file.

The article reports on a study to benchmark springback prediction capability of various software and skills of users on a complex inner body panel. The simulation process of stamping a deck lid inner panel consists of three operations: forming, trimming and springback. Participants during the study are not allowed to move the tooling position in the x-y plane. In this benchmark, participants can use either physical beads or line beads in the forming simulation. The information for the physical bead geometry and bead centerlines is provided in the math files.

In stamping practice, springback of the blank is often compensated by developing the shape of the blank, which provides the targeted shape after its springback. In this paper we attempt to address the root cause of springback phenomenon dictated by residual stresses in the blank after completion of the stamping process. New process of springback calibration has been developed based upon the idea of elimination of elastic residual stresses in stamped blank. This technology attempts to address the issues of sheet material variability and stamping process variations, which make geometrical compensation more difficult. Simple set of experiments demonstrated that formed blank can be clamped to the targeted shape and then subjected to pulsed electromagnetic field. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The increase demand for stronger, lighter and economic sheet metal products, make the Hydromecanical deep drawing process lately more and more popular. The Hydromecanical process is used in almost all types of sheet metal parts from home appliances and kitchenware to automotive and aviation industries. Therefore, many common materials were tested and characterized by their ability to sustain large strains via the well known Forming Limit Diagram (FLD). The aim of this work is to examine the forming capability if the Hydromecanical process in production of hemisphere parts made of materials commonly used in the aviation and aerospace industries. Experimental procedures were carried out to assess their ductility through FLD and the Forming Limit Carve (FLC).Two type of material sheets were tested herewith for demonstrating the procedure: commercial pure titanium and stainless steel 316L. A numerical simulation of the Hydromecanical process was examined and compared to self made Hydromecanical deep drawing of hemispherical parts. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Springback prediction has become a major focus in sheet metal forming. Validation of finite element codes for springback prediction require accurate property data and a more complete understanding of the residual stresses that are involved. To provide experimental data for these calculations, neutron and X-ray diffraction measurements were carried out to determine the through-thickness distribution of residual stresses in test specimens of several steels and AA6022-T4 alloy. The techniques are able to provide true spatial resolutions of approximately 0.1 mm for strain measurements at wall thicknesses of ≈1 mm. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The use of X-ray diffraction to measure residual stress in a crystalline material is well known. This method is currently being reapplied to the surface measurement of in situ stresses during biaxial straining of sheet metal specimens. This leads to questions of precision and calibration of the method through plastic deformation. Little is known of the change, with plastic work, in the X-ray elastic constants (XECs) that are required by the technique for stress measurement. Experiments to determine the formability of various materials using this stress measurement technique in conjunction with a typical Marciniak test (with the Raghavan variation of specimen shapes) have been performed assuming a constant value for XECs. New results of calibration experiments are presented which admit the possibility of variation of the XECs with plastic strain history and initial texture of the material. Adjustment of the data from the previously performed formability experiments is shown. Additionally, various phenomena are captured including initial yielding, change of XECs with plastic strain level (both with uniaxial and biaxial strain histories), and some of the effects of texture on the technique. This technique has potential application in verification of the assumptions made during other standard testing methods (in-plane biaxial specimen geometries and bulge testing), verifying stress predictions from finite element analyses (i.e. benchmarking experiments such as BM3), analysis of stress states in localized deformation (yield point effects), and tracking of the effect of prestraining on material formability through the process of multistage forming. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

One of the principal foundations of mathematical theory of conventional plasticity for rate-independent metals is that there exists a well-defined yield surface in stress space for any material point under deformation. A material point can undergo further plastic deformation if the applied stresses are beyond current yield surface which is generally referred as “plastic loading”. On the other hand, if the applied stress state falls within or on the yield surface, the metal will deform elastically only and is said to be undergoing “elastic unloading”. Although it has been always recognized throughout the history of development of plasticity theory that there is indeed inelastic deformation accompanying elastic unloading, which leads to metal’s hysteresis behavior, its effects were thought to be negligible and were largely ignored in the mathematical treatment. Recently there have been renewed interests in the study of unloading behavior of sheet metals upon large plastic deformation and its implications on springback prediction. Springback is essentially an elastic recovery process of a formed sheet metal blank when it is released from the forming dies. Its magnitude depends on the stress states and compliances of the deformed sheet metal if no further plastic loading occurs during the relaxation process. Therefore the accurate determination of material compliances during springback and its effective incorporation into simulation software are important aspects for springback calculation. Some of the studies suggest that the unloading curve might deviate from linearity, and suggestions were made that a reduced elastic modulus be used for springback simulation. The aim of this study is NOT to take a position on the debate of whether elastic moduli are changed during sheet metal forming process. Instead we propose an approach of modeling observed psuedoelastic behavior within the context of mathematical theory of plasticity, where elastic moduli are treated to be constant. In the context of this investigation we refer psuedoelastic behavior in the most general sense as any deviation from linearity in the unloading curve. The non-linearity leads to a hysteresis loop upon reloading. The approach is based on the non-conventional theory with a vanishing elastic region as advanced by Dafalias and Popov. The treatment is purely phenomenological where we don’t distinguish between macroscopic plasticity and micro-plasticity. The macroscopic uniaxial stress-strain curve is used to define effective plastic response in the same manner as classical plasticity theory except that the nonlinearity during unloading and reloading are incorporated into plasticity. It is shown that such models can be easily formulated within the context of elastoplasticity without violating any physical mechanisms of deformation. Springback for a plane strain bending model is used to demonstrate the potential effect if such a model is applied. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Forming Limit Diagram (FLD) has been proved to be a powerful tool for assessing necking failures in sheet metal forming analysis for majority of stamping operations over the last three decades. However, experimental evidence and theoretical analysis suggest that its applications are limited to linear or almost linear strain paths during its deformation history. Abrupt changes or even gradual deviations from linear strain-paths will shift forming limit curves from their original values, a situation that occurs in vast majority of sequential stamping operations such as where the drawing process is followed by flanging and re-strike processes. Various forming limit models have been put forward recently to provide remedies for the problem, noticeably stress-based and strain gradient-based forming limit criteria. This study presents an alternative path-independent forming limit criterion. Instead of traditional Forming Limit Diagrams (FLD) which are constructed in terms of major - minor principal strains throughout deformation history, the new criterion defines a critical effective strain [variant_greek_epsilon]* as the limit strain for necking, and it is shown that [variant_greek_epsilon]* can be expressed as a function of current strain rate state and material work hardening properties, without the need of explicitly considering strain-path effects. It is given by [variant_greek_epsilon]* = f(β, k, n) where β = d[variant_greek_epsilon]2/d[variant_greek_epsilon]1 at current deformation state, and k and n are material strain hardening parameters if a power law is assumed. The analysis is built upon previous work by Storen and Rice [1975] and Zhu et al [2002] with the incorporation of anisotropic yield models such as Hill’48 for quadratic orthotropic yield and Hill’79 for non-quadratic orthotropic yield. Effects of anisotropic parameters such as R-values and exponent n-values on necking are investigated in detail for a variety of strain paths. Results predicted according to current analysis are compared against experimental data gathered from literature and good agreements are achieved. This provides a powerful validation for this approach. The new criterion retains all the advantages of the traditional FLDs since it’s still constructed in the strain space. Its relationship with stress-based forming limit criteria is discussed. It is believed that the approach is especially suitable for production stamping CAE analysis since the strain rate state at any material point during forming deformation is readily available from FEA simulations. It can be easily embedded in forming simulation software or alternatively deployed as a post-processing function for forming simulations. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]