Simulation Of Metal Forming Research Articles

Simulation of Bulk Metal Forming by Means of Finite Integral Mesh Free Methods

This paper draws from the fundamentals of the finite integral mesh free representation methods and of the rigid-plastic formulation for slightly compressible materials to the main aspects of computer implementation and modelling of bulk-metal forming processes. Fundamental research and development is based on the reproducing kernel particle method (RKPM) and the corrected smoothed particle hydrodynamics (CSPH) method. Special emphasis is placed on a wide range of theoretical and numerical subjects such as discretization procedures, numerical integration of the system matrices derived from the weak form, relief of volumetric locking, geometrical update of the deforming workpiece, and treatment of the frictional contact interface between the workpiece and tooling.

PLF-09: Effect of Force Correction Algorithm Arising from Change of Tool Normal on Sheet Metal Forming Simulation(PLF-II: PLASTIC FORMING AND ADVANCED PRODUCTS)

PLF-09: Effect of Force Correction Algorithm Arising from Change of Tool Normal on Sheet Metal Forming Simulation(PLF-II: PLASTIC FORMING AND ADVANCED PRODUCTS)

Effect of Force Correction Algorithm Arising from Change of Tool Normal on Sheet Metal Forming Simulation

Treatment of contact problems between sheet and tools is one of the most difficult problems to deal with in sheet metal forming simulations. This paper describes a new algorithm for the discretization of the change of the “averaged tool normal” which is calculated by averaging the normals defined on all adjacent elements. The proposed algorithm was implemented into STAMP3D, which is a static explicit program dedicated to sheet metal forming simulations. Simulations of draw bending process were performed and the normalized norm of the non-equilibrated forces due to the change of the tool normals was compared between the original result and the result obtained with the proposed algorithm. It was found that the normalized norm of the non-equilibrated forces was drastically reduced by applying the proposed algorithm. This result shows the improvement of the accuracy of the simulation and the efficiency of the proposed algorithm.

Current Condition and Development of Crystal Plasticity Simulation in Metal Forming

Current Condition and Development of Crystal Plasticity Simulation in Metal Forming

Evolution of Plastic Anisotropy during Deformation of Metal Sheets

Evolution of Plastic Anisotropy during Deformation of Metal Sheets

Numerical modelling and simulation in sheet metal forming

The application of numerical modelling and simulation in manufacturing technologies is looking back over about a 20–30 years history. In recent years, the role of modelling and simulation in engineering and in manufacturing industry has been continuously increasing. It is well known that during manufacturing processes simultaneous the effect of many different parameters can be observed. This is the reason why in former years, detailed analysis of manufacturing processes could have been done only by time-consuming and expensive trial-and-error methods. Due to the recent developments in the methods of modelling and simulation, as well as in computational facilities, modelling and simulation has become an everyday tool in engineering practice. Besides the aforementioned facts, the emerging role of modelling and simulation can also be explained by the growing globalisation and competition of the world market requiring shorter lead times and more cost effective solutions. In spite the enormous development of hardware and software facilities, the exclusive use of numerical modelling still seems to be very time- and cost consuming, and there is still often a high scepticism about the results among industrialists. Therefore, the purpose of this paper is to overview the present situation of numerical modelling and simulation in sheet metal forming, mainly from the viewpoint of scientific research and industrial applications.

Web-based material properties for use with metalforming simulation packages

Commercial pressures are forcing metalforming companies to embrace technologies that enable the development of high value added designs. One of these technologies is metalforming simulation normally based on the finite volume or finite element method.The use of simulation enables innovative designs to be examined and modified before execution. However, the precision of the results from any simulation depends on the quality of the input data. This data must accurately describe every aspect of the forming process being examined and can include the behaviour of the tools, the workpiece and the interface between the two. The mechanical and thermal data required must be valid over the temperature, strain and strain rate ranges applicable to the process. This type of data differs greatly from the data normally available in design handbooks and in many well-publicised databases.This paper demonstrates the importance of accurate material data for simulation and discusses the issues of available data and their relationship with real process temperature and strain rate ranges. In addition, the limitations associated with testing conditions as well as the work being undertaken by Brunel University in conjunction with the UK metalforming industry in developing a web-enabled database of materials properties is discussed.

Development of an object-oriented finite element program: application to metal-forming and impact simulations

During the last 50 years, the development of better numerical methods and more powerful computers has been a major enterprise for the scientific community. In the same time, the finite element method has become a widely used tool for researchers and engineers. Recent advances in computational software have made possible to solve more physical and complex problems such as coupled problems, nonlinearities, high strain and high-strain rate problems. In this field, an accurate analysis of large deformation inelastic problems occurring in metal-forming or impact simulations is extremely important as a consequence of high amount of plastic flow.In this presentation, the object-oriented implementation, using the C++ language, of an explicit finite element code called DynELA is presented. The object-oriented programming (OOP) leads to better-structured codes for the finite element method and facilitates the development, the maintainability and the expandability of such codes. The most significant advantage of OOP is in the modeling of complex physical systems such as deformation processing where the overall complex problem is partitioned in individual sub-problems based on physical, mathematical or geometric reasoning.We first focus on the advantages of OOP for the development of scientific programs. Specific aspects of OOP, such as the inheritance mechanism, the operators overload procedure or the use of template classes are detailed. Then we present the approach used for the development of our finite element code through the presentation of the kinematics, conservative and constitutive laws and their respective implementation in C++. Finally, the efficiency and accuracy of our finite element program are investigated using a number of benchmark tests relative to metal forming and impact simulations.

Combined implicit/explicit time-integration algorithms for the numerical simulation of sheet metal forming

In order to simulate stamping processes, an explicit method, which is conditionally stable, is generally thought to be the most adapted. Such an algorithm presents the advantage of being noniterative while, the contact configuration evolves rapidly, and the conditional stability is not a disadvantage since time steps must be small enough anyway for an accurate computation. But during the springback simulation, an implicit method, which is iterative, presents the advantage of unconditional stability. The optimal solution is then to have both implicit and explicit methods readily available in the same code and to be able to switch automatically from one to the other. Criteria that decide to switch from a method to another, depending on the current dynamic, have been developed. Implicit restarting conditions are also proposed that annihilate numerical oscillations resulting from an explicit calculation.

Boundary controlled automatic remeshing for 2D simulation of metal forming

During finite element simulation of metal forming processes, the mesh undergoes large distortions leading to inaccurate results and numerical instability in the solution process. In order to overcome this problem, the domain is to be remeshed whenever the quality of the mesh or geometrical representation of the contacting boundary violates the desired criteria. This paper describes a strategy, wherein the mesh density during remeshing is controlled by regenerating the boundary segments dynamically, using a background mesh when mesh distorts above allowable limits. This, in conjunction with an advancing front technique is used for generating the finite element mesh. The background mesh specifies the desired length of boundary segments at different locations as per the geometrical configuration of the deforming body and the die. This gives a possibility of remeshing with one background mesh fixed in space and/or multiple background meshes each attached to one of the dies. This also allows easier user intervention if required. The procedure is applied and demonstrated for 2D metal forming problems with quadrilateral mesh generation based on paving technique.

Quadratic programming method in numerical simulation of metal forming process

In this paper, a quadratic programming (QP) model based on a parametric variational principle is proposed for elastic–plastic (EP) finite element analysis of metal forming processes. The contact problem with friction between blank and tools is treated in the same way as in plastic analysis. The penalty factors, which are normally introduced into the algorithm for contact analysis, have a direct influence on accuracy of solution. There is no available rule for choosing a reasonable value of these factors for simulation of metal forming, and they are therefore cancelled through a special technique so that the numerical results can be of high accuracy. The algorithms for contact analysis and plastic analysis are established in one frame and consistent with each other. Compared with the conventional EP FEM, the newly developed method requires no tedious iterative procedures, and has no convergence problems. To apply this method easily to simulation of metal forming, detailed forms of some key matrices or vectors for 2D FEM and 3D FEM are presented, and a parametric loading algorithm for the QP model is developed, which is suitable for QP problem with free variables, and can decrease memory cost by avoiding the introduction of additional slack variables and improve the solution efficiency to some extent. Finally the proposed QP model is validated by two examples, analysis of V-notched tension test and analysis of the drawing of a square box––one of the benchmarks proposed at NUMISHEET93. It can be seen that the accuracy of solution of the new EP FEM based on QP is better than that of the conventional EP FEM based on iteration. To make the new EP FEM more applicable to metal forming industries, It is necessary to develop a more efficient QP algorithm that is suitable for large-scale problems.

Numerical Simulation of Viscoplastic and Frictional Heating During Finite Deformation of Metal. Part I: Theory

This paper is concerned with the numerical simulation of hot metal forming, especially superplastic forming. In this first part, a complete thermo-viscoplastic formulation at finite strains is derived and a unified stress update algorithm for thermo-elastoplastic and thermo-elasto-viscoplastic constitutive equations is obtained. The resulting unified implicit algorithm is both efficient and very inexpensive. A staggered scheme is used for the global resolution of the thermomechanical problem. We will also describe the basis of our thermomechanical frictional contact model. Discussion of computational aspects and efficiencies will be assessed in the second part of this work.

A rigid–plastic hybrid element method for simulations of metal forming

In the present study, the rigid–plastic hybrid element method (HEM) is developed. The rigid–plastic HEM is a mixed approach of the rigid–plastic domain-BEM and the rigid–plastic FEM. Since the compatibilities of velocity as well as velocity’s derivative can be satisfied, the velocity and the derivative of the velocity can be calculated with the same precision with the rigid–plastic HEM. On the other hand, the conventional rigid–plastic FEMs are formulated with single variable (velocity), the velocity and the derivative of the velocity cannot be calculated with the same precision for the rigid–plastic FEMs. A plane strain forging problem is analyzed by the rigid–plastic HEM. Velocity fields and contours of effective strain rate, effective strain, effective stress and shear stress, etc. can be obtained successfully.

Rigid‐plastic hybrid element analyses of the plane strain upsetting

AbstractA rigid‐plastic hybrid element method (HEM) for simulation of metal forming is developed. This method is a mixed approach of the rigid‐plastic domain‐BEM and the rigid‐plastic FEM based on the theory of compressible plasticity. Because the compatibilities of not only velocity but also velocity's derivative between the adjoining boundary elements and finite elements can be met, the velocities and the derivatives of the velocity can be calculated with the same precision for the rigid‐plastic HEM. Then, it is considered that the rigid‐plastic HEM is a more precise method in formulation than the conventional rigid‐plastic FEMs for which the compatibilities of velocity's derivative cannot be met. The plane strain upsetting processes with two friction factors are analyzed by the rigid‐plastic HEM in this article. © 2002 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 18: 726–737, 2002; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/num.10031.

Finite element simulation of metal forming and in-plane crack propagation using ductile continuum damage model

The continuum damage model for ductile damage and ductile fracture is applied to metal forming and crack propagation by finite element method. The highly nonlinear equilibrium equation is formulated in order to include geometric, material nonlinearities and frictional contact condition. The effect of friction on the damage concentration is shown in the upsetting process. Then it is verified that the ductile fracture using this damage model is reasonable by the comparison with the experimental result in CCT specimen. The influence of the hole at the crack tip is shown through the numerical simulations of edge-cracked plates with different hole size. Finally, the strain energy release rate in this damage model is compared with J-integral using ABAQUS to relate the result of damage analysis to the concept of fracture mechanics.

A National Centre for Metalforming Simulation in the UK

This paper examines the unique work being undertaken in the UK to ensure the continued competitiveness and advancement in capabilities of the companies that make up the UK metalforming industry. The work is a partnership between commercial metalforming simulation package vendors, universities and the industry through its main trade association the Confederation of British Metalforming. In examining the present activities, a case is made for a National Centre for Metalforming Simulation.

Towards standard benchmarks and reference data for validation and improvement of numerical simulation in sheet metal forming

The last decade has witnessed many advances and a lot of improvement in FE codes for simulation of sheet metal forming processes. Such advances could be followed mainly by benchmarks proposed in Numisheet conferences. It was possible to notice that the scatter of results among numerical codes has decreased so significantly that recently scattering of experimental results among different corporations was evident. However in order to pursue further developments and validate numerical results it is fundamental to have reliable reference experimental data. This is one of the objectives of a current IMS project called 3DS-Digital Die Design System. In this paper such objectives are presented as well as some of the proposed benchmarks. It is intended to show part of the developed work concerning tool design and manufacturing methodology. Also an experimental case study about the use of piercing holes in parts and the use of counter-punch is presented. Finally some simulation results are also shown concerning one of the proposed benchmarks.

Concepts for Integrating Plastic Anisotropy into Metal Forming Simulations

Modern metal forming and crash simulations are usually based on the finite element method. Aims of such simulations are typically the prediction of the material shape, failure, and mechanical properties during deformation. Further goals lie in the computer assisted lay-out of manufacturing tools used for intricate processing steps. Any such simulation requires that the material under investigation is specified in terms of its respective constitutive behavior. Modern finite element simulations typically use three sets of material input data, covering hardening, forming limits, and anisotropy. The current article is about the latter aspect. It reviews different empirical and physically based concepts for the integration of the elastic-plastic anisotropy into metal forming finite element simulations. Particular pronunciation is placed on the discussion of the crystallographic anisotropy of polycrystalline material rather than on aspects associated with topological or morphological microstructure anisotropy. The reviewed anisotropy concepts are empirical yield surface approximations, yield surface formulations based on crystallographic homogenization theory, combinations of finite element and homogenization approaches, the crystal plasticity finite element method, and the recently introduced texture component crystal plasticity finite element method. The paper presents the basic physical approaches behind the different methods and discusses engineering aspects such as scalability, flexibility, and texture update in the course of a forming simulation.

Modeling the Bauschinger effect for sheet metals, part II: applications

The modified Chaboche and ANK model proposed in Part I are implemented into second order accurate user material routines for ABAQUS/Explicit and /Standard. A criterion to detect a load reversal for ANK model is also proposed. They are applied to investigate the role of Bauschinger effect in the simulation of sheet metal forming and springback prediction under multi-cyclic loading conditions. Reverse cup drawing and draw-bead tests are simulated and results are compared with available experimental data. The ANK model predicted the maximum punch forces more accurately with a correct trend for the reverse cup drawing process. The draw-bead test simulation results with the ANK model show encouragingly good comparisons with measured data. An accurate modeling of the Bauschinger effect appears to be more important when multiple cycles of bending and reverse bending loading conditions are expected.

533 A stable and fast new contact search algorithm for FEM simulation of metal forming process

The treatment of contact problems is one of the most difficult problems in the simulation of sheet metal forming. Although many contact search algorithms have been proposed over the last decade, most of these algorithms are for the global search and robust algorithms for the local search are scarce. In this paper, a new stable and fast contact search algorithm for the local search is proposed in the framework of a static explicit FEM approach. This algorithm uses the relative displacement vector for contact search for free nodes and the normal projection onto tool elements for updating the position of contact nodes and as the result, no dead zone problem occurs. Furthermore, no iteration is required in this algorithm and it leads the contact search more stable and accurate. A simulation example using this algorithm is also included.