M.J.M. Barata Marques

Upper bound analysis of plane strain rolling using a flow function and the weighted residuals method

This paper presents an innovative approach for analysing plane strain rolling. The approach is based on a solution resulting from the combination of the upper-bound method with the weighted residuals method. The upper bound method is applied to estimate the rolling torque and to model the material flow within the region of deformation between the rolls. The weighted residuals method is utilized for obtaining the distribution of stress, the roll separating force and the normal contact pressure along the surface of the rolls. Coupling between the two methods is made by using the upper bound distribution of the strain-rate in conjunction with the rate form of the Levy–Mises constitutive equations to determine an approximate distribution of the stress field by means of the weighted residuals method. The main advantage of this approach over classical upper bound solutions, is the possibility of solving stress equilibrium everywhere throughout the plastically deforming workpiece and on its surface. Such an analysis ensures a complete description of all the variables with interest to the rolling process. The validity of the proposed approach is discussed by comparing the theoretical predictions with experimental data found in the literature. Copyright

Model3—A three-dimensional mesh generator

Abstract A three-dimensional mesh generation program is presented. The program is based on the isoparametric superelement generation. These superelements consist of 20-node hexahedral elements specified by the user. Subdivision into a mesh of eight-node hexahedral elements is automatically performed according to the grading initially specified. A bandwidth reduction algorithm is incorporated in the program in order to optimize finite element core requirements. The program is written in FORTRAN and a glossary of terms and the program listing are provided.

Theoretical and experimental analysis of axisymmetrical deep drawing

Abstract The paper deals with the use of the code ABAQUS in the analysis of axisymmetric cup deep drawing. The selected cases take into account the different friction effects at the punch/sheet, die/sheet and holder/sheet interfaces. Coulomb frictions law is assumed. The true stress-true strain curve of the cup material was obtained from tensile tests on AISI 304 stainless steel. The tests were performed in an universal testing machine and the deformations were calculated from grids impressed on the specimens. To validate the computational results, experimental work was carried out. Hemispherical cup deep drawing tests were performed in a double effect hydraulic press. Punch and holder loads, as well as the punch displacement were recorded by a data acquisition system during the deep drawing operation. Radial and hoop strains were measured from grids impressed in the blank by an electrochemical process. Computational results, punch force-punch displacement curve and strain distributions are discussed and compared with the experimental ones.

An algorithm for remeshing in metal forming

Abstract Finite element analysis of non-stationary large plastic deformation processes, present several difficulties concerning the progressively distortion of the mesh. The difficulties can be solved with a proper remeshing technique. The basic idea of remeshing is to generate a new mesh over the old distorted mesh, with all the history dependent variables being properly transferred from the old to the new one. The paper presents an algorithm to perform remeshing. A practical example, concerning axisymmetric closed die forging, is presented in order to show the application of the algorithm now proposed.

A study of bi-metal coins by the finite element method

Abstract A two-dimensional finite-element program, based on a rigid-plastic formulation has been used to simulate the joint of a bi-metal coin. Several geometric joint profiles have been analyzed and theoretical predictions of the joining load, the deformed grid patterns, the velocity field and the strain field are presented. The strength of the joint has been checked experimentally by measuring the separating load. Experiments have been performed on prototypes with different joint profiles in order to obtain the load necessary to separate the center of the coin from the outer ring. The results obtained have been compared with those found for two bi-metal coins currently produced, and show that the joint profiles proposed presently are suitable for industrial purposes.

Towards nett-shape manufacturing of tubular components

This paper summarizes the results of work-in-progress research with a self developed two-step radial extrusion technique in which a simple preforming operation has been added to the conventional radial extrusion process. The proposed technique requires only simple modifications of the tool. Finite element models conditioned from previous experiments in aluminum served as a design tool for elaborating the process sequence and tool geometry which prevents the development of certain flow failures occurring in the traditional radial extrusion. Metal experiments were performed to test the tool design. As a result, it was possible to verify that the range of shapes that can be produced starting from a tube has been extended. Comparisons between theoretical predictions and experimental measurements obtained for a typical flanged component are provided for material flow, geometrical profile, effective strain distribution and required forming load. Finally the potential of the two-step radial extrusion technique is illustrated for the radial extrusion of a closed die shaped component.

The PLAST3 system and its application to the simulation of an open die forging operation

Abstract Modelling large three-dimensional metal forming deformations with the finite-element program PLAST3 is presented. The program utilises the penalty constrained method, based on the rigid-plastic flow formulation. The structure and main capabilities of this program are described. The post-processing unit PLAPOST3 utilized for the analysis of the simulation results in a graphical form is presented also, this unit being written in LISP language inside a commercial CAD package. A sample solution supported by experimental work carried out with an aluminium alloy at room temperature is included. Theoretical and experimental results are analysed, good agreement between them being found.

Plarmsh3—a three-dimensional program for remeshing in metal forming

Abstract The finite element analysis of metal forming processes usually present several difficulties owing to the progressive distortion of the mesh. Some of these difficulties can be solved with the utilisation of a proper remeshing technique. The basic idea of remeshing is to generate a new mesh over the old distorted mesh, with all the history dependent variables being properly transferred from the old to the new one. This paper presents a solution to perform three-dimensional remeshing, based on the parametric inversion technique. Special emphasis is placed on the computer implementation of this technique. In the last part of the paper the authors provide an example in order to show the application of the model now proposed.

Effect of chip-breaker geometries on cutting forces

Abstract In this paper a method for predicting cutting forces is described. The model considers the indentation or ploughing effect and the presence of a parallel-groove type chip breaker. The technique is based on the measurement of the chip-breaker geometry and the calculation of the effective side-rake angle. The indentation effect, the dynamic shear stress and the cutting forces are determined from experimental studies. The proposed model is applied to the machining of martensitic stainless steels using coated carbide tools. Finally, the experimentally-measured cutting forces are compared with theoretically-predicted values.

Finite-element simulation of powder-metal forming

Abstract A two-dimensional finite-element computer program, bulk2pm , has been developed to perform the simulation of sinter-forming processes. The code allows the analysis of the forming of complex parts and gives the distribution of the principal field-variables, including the density. The paper describes the finite-element flow formulation for powder-metal forming. The constitutive equations of porous materials are presented and the formulation is shown to be equivalent to the penalty approach used in the modeling of dense-material forming. Contact problems that emerge from the high deformations suffered by the workpiece and the complexity that tools can present are considered also. A simple but efficient re-meshing scheme is included also for the simulation of large plastic-deformation processes. A numerical example concerning the axisymmetric closed-die forging of a porous material is presented, in order to show the application of the finite-element code.