3-D finite element modelling of the forging process with automatic remeshing

doi:10.1016/0924-0136(91)90048-J

Journal of Materials Processing Technology

Volume 27, Issues 1–3, August 1991, Pages 119-133

https://doi.org/10.1016/0924-0136(91)90048-J Get rights and content

Abstract

The purpose of this paper is to illustrate the interest of using a finite element program to simulate the forging process of industrial parts. The forge3 code, which can simulate hot forging of industrial parts, is presented: thermo-mechanical formulation, numerical resolution. It is well known that, in an updated lagrangian approach using a convective mesh, the degeneracy of the mesh occurs very rapidly and stops the simulation. An automatic mesh generation procedure for 3-D complex geometries has been developed with which it is possible to create the initial mesh of the billet as well as to remesh it after its degeneracy. This technique enables to simulate the whole forging process of complex industrial parts using quadratic tetrahedra. In order to show the effectiveness of the method, the example of the forging of a tripod has been computed. The simulation results show that the computation can be carried out using the described remeshing procedure and that it can be applied with success to even more complex geometries.

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The cracks formed in the hot deformation are typical defects caused by plastic capacity limitations. For tested steels, the fracture behavior is associated with temperature, strain rate, and stress state. In this study, a highly crack-sensitive steel with Nb micro-alloying is selected as the research material to establish the fracture criterion considering the above factors comprehensively. First, compression and tension experiments are performed, and various specimen geometries are designed to produce different stress states in the tests at different temperatures and strain rates. Second, the critical stroke of these tests is extracted, and corresponding calculations are completed using the finite element method (FEM). The loading paths of stress states are independent of temperature and strain rate; however, they differ when distinct specimen shapes are considered in the tests. Third, a high–temperature Mohr–Coulomb criterion, which is applicable at elevated temperatures, is established by considering the effects of temperature, strain rate, and stress states on fracture. Finally, some examples of compressive and tensile tests are employed for verifying the formulated fracture criterion. By comparing the FEM and experimental results, it is found that the fracture criterion could accurately describe the fracture behavior during hot deformation with distinct stress paths.
Modeling large viscoplastic strain in multi-material with the discrete element method
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Dissociating material and mesh motions, with an Eulerian [3–5] or an Arbitrary Lagrangian-Eulerian [6–8] kinematical description of the materials. Sequentializing a large distortion in smaller steps, periodically re-generating a Lagrangian mesh [9]. Super-imposing discontinuities description on top of a continuous framework, using additional discontinuous arbitrary shape functions [10,11] or a set of punctual Lagrangian markers, representing material phases [12,13] or interfaces [14].
In this paper, the Discrete Element Method (DEM) is used as a tool to phenomenologically model large compressive viscoplastic strain in metallic composites. The model uses pairwise attractive and repulsive forces between spherical particles. Large packings of particles collectively cope with the prescribed strain, the changes of neighbors model the irreversible strain in the material. Using the proposed calibration method of the model parameters, the macroscopic behavior mimics perfect plasticity in compression, with a strain rate sensitivity approximating a viscoplastic Norton law.
The error on flow stress and volume conservation is estimated for single material. Three bi-material geometrical configurations are built: parallel, series and spherical inclusion. Macroscopic metrics (flow stress and shape factor of inclusion) are confronted to Finite Element Method (FEM) simulations.
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Mesh-independent data point finite element method (MDP-FEM) for large deformation elastic-plastic problems - An application to the problems of diffused necking
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Yoon and Yang [5] performed rigid-plastic finite element analysis with remeshings. We can find the progresses of remeshing technique in the field of finite strain analyses in literature (Coupez, Soyris and Chenot [6], Lee, Yoon and Yang [7], Dyduch, Habraken and Cescotto [8], Petersen and Martins [9], Hamel, Roeandt, Gacel and Schmit [10], Kwak, Cheon and Im [11], Kwak, and Im [12]). We can also find applications of adaptive remeshing techniques in the context of strain localization analysis in literature such as Ortiz et al. [13], Pastor, Peraire and Zienkiewicz [14], Lee and Bathe [15] and Zienkiewicz, Pastor and Huang [16].
In this paper, a method to carry out the finite strain elastic-plastic analysis using a remeshing technique is presented. When the remeshing is performed, deformation history dependent physical quantities that are stored at the integration points of finite elements need to be transferred to those of the refined finite elements. Such operations are generally performed based on the shape functions of the finite elements. A typical procedures are that i) the strain history dependent quantities are assigned at the nodal points and ii) interpolations are performed by the shape functions. Such processes assume that the sizes and the arrangements of finite elements change moderately after the remesh. We are aiming at developing a methodology that allows drastic changes in mesh arrangements and sizes and in even kinds of finite elements when the remeshing is carried out. We propose a method that the deformation history dependent physical quantities are stored at points independent of the finite element mesh. They move along with the deformation of the solid. The physical quantities at the points evolve in a Lagrange manner. We name such points to be Mesh-independent Data Points (MDPs). The MDPs take the function to store the physical quantities whereas the finite element mesh takes that of performing the numerical integration. Necessary variables are mapped between the MDPs and the finite element. We call proposed technique to be MDP-Finite Element Method (MDP-FEM). This paper describes the concept of the MDP-FEM and numerical implementations are discussed first. Then, the analyses of diffused necking of tensile bars are presented for a demonstrative purpose.
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Hot forging can be defined as a metal shaping process in which a malleable metal part, known as a billet or workpiece, is worked to a predetermined shape by one or more processes such as hammering, upsetting, pressing, and so forth where the workpiece is heated up to about 75% of its melting temperature. The process begins with a cast ingot, which is heated to its plastic deformation temperature, then forged between dies to the desired shape and size. During this forging process, the cast, coarse-grain structure is broken up and replaced by finer grains, achieved through the size reduction of the ingot. Usually, the product is additionally heat treated after it is hot forged.
Modeling of Hot Forging
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Hot forging can be defined as a metal shaping process in which a malleable metal part, known as a billet or workpiece, is worked to a predetermined shape by one or more processes such as hammering, upsetting, pressing, and so forth where the workpiece is heated up to about 75% of its melting temperature. The process begins with a cast ingot, which is heated to its plastic deformation temperature, then forged between dies to the desired shape and size. During this forging process, the cast, coarse-grain structure is broken up and replaced by finer grains, achieved through the size reduction of the ingot. Usually, the product is additionally heat treated after it is hot forged.
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The first generation of two-dimensional finite element computer programs was produced in this period. The second result was due Coupez et al. [7] who opened the possibility of effectively and automatically simulating the whole forming of complex three-dimensional industrial parts from beginning to the end. The approach was exclusively based on the utilization of tetrahedral elements due to robustness, versatility and availability of three-dimensional meshing algorithms based on Delaunay tessellation.
All-hexahedral meshing and remeshing algorithms giving support to finite element modeling of manufacturing processes require continuous development for improving its overall robustness and applicability. This paper draws from a previous all-hexahedral algorithm presented by the authors and proposes new developments related to the construction of adaptive core meshes and processing of multi-objects that are typical of manufacturing applications.
Along with the aforementioned improvements there are other developments that will also be presented due to their effectiveness in increasing the robustness of all-hexahedral algorithms. These include identification and simplification of boundary features, reconstruction of vertices and edges with minimum element distortion, smoothing of nodal points along edges and topology based mesh repair procedures to ensure completeness of edge representation.
The presentation is enriched with examples taken from pure geometry and metal forming applications, and a resistance projection welding industrial test case consisting of four different objects is included to show the capabilities of selective remeshing of objects while maintaining contact conditions and local geometrical details that are critical for electro-thermo-mechanical numerical simulations.

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Section 3. Forging analysis3-D finite element modelling of the forging process with automatic remeshing

Abstract

Int. J. Mech. Sci.

Int. J. Mech. Sci.

J. Comput. Physics

Comp. Meth. in Appl. Mech. Eng.

Comp. Meth. Appl. Mech. Eng.

Int. J. Eng. Sci.

The plastic deformation of metals

Metallurgica

Theoretical prediction of plastic flow in the hot rolling including the effect of various temperature distribution

J. Iron Steel Inst.

New solutions to rigid-plastic deformation problems using a matrix method

Trans. ASME, J. Eng. Ind.

Flow of plastic and visco-plastic solids with special reference to extrusion and forming processes

Int. J. Num. Meth. Eng.

Finite element formulation for the analysis of plastic deformation of rate sensitive materials on metal forming

Calcul par éléments finis de l'évolution d'une inclusion dans une matrice déformée uniformément

Simulation by material flow in closed-die forging by model techniques and rigid-plastic FEM

Section 3. Forging analysis
3-D finite element modelling of the forging process with automatic remeshing