Metal Flow Prediction Research Articles

On the Friction Conditions in FEM Simulations of Cold Extrusion

Friction is a very important issue for calculating the punch force and energy consumption in cold extrusion. FEM simulations are commonly used to investigate this process, but the choice of the friction’s model and set-up parameter have influence on the results. In this work FEM simulations of cold forward extrusion of rods were performed using the commercial code DEFORMTM in axisymmetric 2D deformation mode with Lagrangian formulation considering Tresca’s friction model and two parameters as set-up: constant friction factor m or constant frictional shear stress τ. Over the deformation stages of the process, the influence of the friction parameters on the simulated force-displacement curves was analyzed. In addition, metal flow prediction and the profile of the actual frictional stress at the billet-container interface were studied. For the investigated tooling geometry and dimensions, it was found that for low levels of friction (m ≤ 0.1), both parameters can be suitably used to study the forming process, since they provided similar force-displacement curves and metal flow prediction. For higher levels of friction, the use of □ as input provided most stable and reliable results, since in this case, the simulated force-displacement curves agreed very well with experimental result, the effective frictional stresses values were more constant, and the relative frictional stresses resulted closest to the input value.

Numerical simulation of hot forging process in production of axisymmetric automobile parts

The finite element method and the DEFORM software were used for the plastic metal flow prediction of ring shaped parts. Various parameters that affect the forging operation are the material characteristics like material strength, ductility, deformation rate, temperature sensitivity and frictional characteristics of the workpiece, preform design, die design and die material. Numerical simulation has been done for axisymmetric automobile parts. The procedure of numerical modeling contains all simulations phases like the movement of preform from inductor to the tool, placement and setting of preform piece inside the tool before the blow in order to get as good result as possible. These techniques are used to reduce the amount of input material for forgings, extend the lifetime of forging dies, and prevent defects in forged components.

Calculation Method of Numerical Drawbead Properties for Improvement of Metal Flow Prediction Accuracy in Sheet Metal Forming Analysis

Calculation Method of Numerical Drawbead Properties for Improvement of Metal Flow Prediction Accuracy in Sheet Metal Forming Analysis

Metal flow prediction during sheet-metal punching process using the finite element method

In this study, part springback and metal flow caused by punch penetration into a sheet was investigated by punching circular test specimens with concentric circular tools. Strain gauges were bonded on the upper surface of the specimens at radial distances varying from 2 mm to 10 mm from the cutting edge of the punch. The experiments were used to validate a finite element model (FEM) valid for numerical simulation of sheet-metal punching processes. Damage and crack propagation were taken into account by means of an elastoplastic constitutive law. The main difficulty encountered in simulating this operation is describing the behaviour of the sheet continuously from the beginning of the operation up to the total rupture. The choice of a behaviour law is crucial, since each successive step in the whole process has to be described accurately. In this investigation, an elastoplastic behaviour law coupled with damage was retained to describe the progressive damage accumulation in the workpieces. During the analysis, the initiation of a crack is assumed to occur at any point in the structure where the damage reaches its critical value Dc. The crack propagation is simulated by the propagation of a completely damaged area. This is taken into account in the FEM by a decrease in the stiffness of the broken elements. The numerical results obtained by the simulation were compared with the experimental ones in order to verify the validity of the proposed FEM.

The Significance of Experiment in the Finite Element Analysis of a Pulley Forming Process

For reasons of cost and weight, light gauge sheet is used wherever possible for metal fabrications. In sheet metal forming the process is to gather the metal into defined areas. The pulley forming process is no exception and is achieved by superimposing axial loads on top of radial loads using a pressure-controlled tailstock. Whilst the headstock-mounted tooling is fixed, that part held on the tailstock can be powered axially under controlled pressure. This pressure is governed by the width of the workpiece which changes during the forming process. Experiments have been designed to provide an understanding of the pulley forming process and to verify numerical models. The latter has been taken the form of finite element simulations to enable prediction of metal flow, tool forces and potential sources of defects and failures. There are three objectives for conducting the experiments which have been investigated in this paper: 1. providing data to define the movements of the forming tools for the finite element model, including displacements and velocities, 2. understanding the effects of the pulley forming operation on the flow of material, and 3. validating the finite element model.

A three-dimensional analysis of the universal beam tandem rolling process: Part I. Deformation analysis

A three-dimensional analysis for the universal beam tandem rolling process is presented. The deformation analysis is carried out based on the upper bound theorem and a three-dimensional continuous velocity field is proposed. In the present study, the major factors are taken into account, such as the effects of tension, the non-contact deformation of the web and the uneven distribution of the flow velocity in the lateral direction in both the flange and web deformation zones, the special deformation mechanism of a wide flange beam in universal pass, cross-flow between flange and web parts of the section and so on. Satisfactory results compared with experimental results were obtained, with good convergence, in the prediction of metal flow, flange spread, and web forward-slip under both forward and backward tensions.

New Model of Flour Stress under Cold-Forming Conditions

Prediction of flow stress under forming conditions is commonly based on an explicit formulation of the flow stress model: The flow stress is in this case expressed as a function of strain, strain rate, temperature, more seldom of structure. Such formulations make it difficult to predict the flow stress under forming conditions for different strain paths and also when the strain rate and/or temperature varies during the deformation. This paper is aimed at describing a new model of strain hardening applied in metal forming analysis. This model allows better prediction of flow stress under cold forming conditions. The application of the incrementally formulated flow stress model is exemplified for prediction of metal flow, loads and temperature distribution in cold forming processes (cold rolling, wire drawing, cold forging).

Arbitrary Lagrangian‐Eulerian thermomechanical finite‐element model of material cutting

AbstractAn arbitrary Lagrangian‐Eulerian model is described for the prediction of metal flow in a steady‐state forming process. The formulation is shown to be capable of dealing with free surface and boundary friction; the coupling with thermal effects is also considered. The numerical techniques are based on the finite elements for spatial discretization of the momentum equation and on an explicit integration scheme for discretization relative to time. The mass and energy equations are integrated by a finite‐volume method. Details on the application to an orthogonal cutting process are given in the final Section of the paper.

Metal flow in compression of tubular parts: predictions made with different computer programs and effect of flow stress data

The study deals with the comparison of three different FEM (finite element method) based codes for simulating the upsetting of a tubular shape. The geometry of this specific part was selected to be very sensitive to variations in flow stress or to errors in the mathematical formulation of metal flow. The results of the study indicated that the available FEM codes are capable of handling two dimensional isothermal and nonisothermal forming problems with reasonable accuracy, provided the input data on flow stress, friction, and heat transfer are also reasonably accurate. Inaccuracies in these data, especially in flow stress, may cause considerable errors in the prediction of metal flow as well as forming loads.

Investigation into Lubricated Extrusion of Round Tubes through Streamlined Dies Considering the Plastic Flow

In cold lubricated extrusion of round tubes the material properties and surface quality of the extruded products are influenced by the die profile. Streamlined dies induce less redundant work and render desirable distribution of strength. In the present general analysis the shapes of the die and the mandrel are expressed by continuous functions. A new general kinematically admissible velocity field for the metal flow is proposed which permits the prediction of metal flow. The upper-bound extrusion pressure is found by using the upper-bound theorem. The grid distortion is computed tracing metal flow along the stream lines. The effective strains are computed to know the workhardening pattern of the extruded tube products. Experiments have been carried employing A12024 as working material. The effect of process parameters such as area reduction, die length, tubular shape ratio (thickness to outer diameter) and friction condition etc. on extrusion power and metal flow has been studied extensively. The theoretical predictions both in extrusion load and metal flow have been shown to be in good agreement with the experimental results. The suggested streamlined dies are shown to be effective for extrusion of round tubes rendering less extrusion power and desirable flow patterns.

A Numerical Method For Simultaneous Prediction of Metal Flow and Temperatures in Upset Forging of Rings

In this study, the interdependence between temperatures and metal flow during upset forging of rings has been investigated. An improved upper-bound analysis has been developed to predict metal flow and temperatures during ring compression. The metal flow and temperatures are considered to influence each other and are estimated at small discrete steps of deformation. Good correlation was found between predicted profiles of the bulged ring surfaces and the experimental results. The analysis and the experimental data show the effects of (a) friction on temperatures, (b) time of contact between the ring and the dies on temperatures and metal flow, and (c) ram speed upon metal flow and temperature. The simulation of the ring test, presented in this paper, is expected to allow a more precise interpretation of experimental results obtained in ring compression tests, especially in warm and hot deformation ranges.