Y. Tozawa

Prediction of Dimensional Difference of Product from Tool in Cold Backward Extrusion

Abstract The effects of forming stresses and generated heat on the dimensional change of punch, die and work piece during forging are discussed analytically. The change in outer and inner diameter of backward extruded cup is investigated numerically using thermo-elastic-plastic FEM code according to the actual forging sequence, namely extruding, unloading of punch force, and ejection and air cooling of extruded cup. The calculated results of outer and inner diameters of product are in good agreement with the experimental results. The simulation can be used to determine the initial tool dimensions for precision parts in the tool design process of cold forging.

Calculations from texture of earing in deep drawing for FCC metal sheets

Abstract The present study aims to calculate the height at each peripheral position of a cup drawn from polycrystalline sheet using texture data. In the analytical treatment the polycrystalline sheet is simplified to an aggregation of many single crystals with various orientations, and the texture is represented by a three-dimensional crystallite orientation distribution function. The ear is calculated crystallographically using the orientation distribution function as a volume fraction of a certain oriented crystal. In the experiment aluminium, Al-Mg alloy and copper sheets which are treated under various conditions of cold rolling and heat treatment are used. The average textures over the thicknesses of the sheets are measured by the Schulz reflection method. The calculated ears based on the measured textures are compared with the experimental ears for each material. The results show that all the principal features of the ears of drawn cups are predicted satisfactorily by the calculation.

Prediction of Dimensional Accuracy of Cold Extruded Can During Repeating Operation

Summary The change in dimension of the product with increasing the ordinal number of products during repeating operation of backward cold can extrusion, is predicted analytically. The analytical procedure is started with an analysis for plastic deformation of a workpiece, in which the rigid-plastic finite element method is used. Deformation work and frictional work are mostly transformed into heat energy. In order to simulate the temperature distribution in the workpiece and the tool during repeating operation, heat generation is represented by introducing a heat generation distribution function and metal flow is approximated by a step-wise move model. In calculating the temperature distribution in the workpiece and the tool, the finite difference method is used. Deformation of the tool due to both a forming pressure and a temperature change is analyzed by the finite element method. At the completion of each forming, the shape of workpiece is assumed to be the same as that of deformed tool. When the workpiece is knocked out from the die, the workpiece is assumed to become free from the restriction of the tool and the temperature of it goes down to the room temperature. Deformation of the workpiece after knocking out is analyzed by the finite element method and finally the shape of product is obtained. Numerical examples are illustrated. The change in diameter of the extruded can during real repeating operation is predicted satisfactorily by the present analysis.

Calculations of earing in deep drawing for BCC metal sheets using texture data

Abstract The present study aims to calculate the height at each peripheral position of a cup drawn from a polycrystalline BCC metal sheet using texture data. In an analytical treatment, the polycrystalline sheet is simplified by considering it to be an aggregate of many single crystals with various orientations. A three-dimensional crystalline orientation distribution function which is constructed from measured texture data is used as the volume fraction of a particular oriented crystal. The ear is calculated crystallographically by considering both restricted glide and pencil glide. In an experiment four kinds of steel sheets were used. An average texture over a thickness of the sheet was measured by the Schulz reflection method. The calculated ear based on the measured texture was compared with the experimental ear for each sheet. The results show that all principal features of the ear of the drawn cup are predicted satisfactorily by the calculation in which pencil glide is not taken into consideration.

Analytical Approach to Elimination of Surface Micro-Defects in Forging

Initial surface micro-scratches due to cropping, rolling or handling change that cause crack or lap defects during forging and reduce the quality of forged products. Elimination of surface micro-defects in forging is pressing problem in forging industry. A new method of finite element analysis featuring effective meshing and an adaptive remeshing system is applied to clarify the mechanism of the formation or the disappearance of surface micro-defects in forging. V-shaped and rectangular scratches on the surface of billet are simulated under the axisymmetric assumption and the basic deformation of scratch during upsetting and the influence of friction on the deformation of micro-defects are discussed. Shallow V-shaped scratch on the top surface of billet tends to disappear and deep scratch becomes lap defect during upsetting. Defects are more likely to disappear under low friction. It is possible to predict that an initial surface micro-scratch on the billet remain or not as a defect after forging.

Computer Simulation and Control of Microstructure and Mechanical Properties in Hot Forging

An analytical procedure for predicting the microstructure and mechanical properties of forged microalloyed steels is presented. Empirical relationships between recrystallized grain size, temperature and strain as well as the relationship between austenite grain size and ferrite grain size are obtained. These relations are expressed as an incremental formula and incorporated into thermo-coupled FEM code. By applying this analysis to practical multiple stage hot forging of flange companions or automotive parts made of microalloyed steel, the microstructure and hardness of forged parts can be predicted. The results of these predictions are in good agreement with the experimental results. The simulation is used to investigate the thermo-mechanical processes for forging functional parts with partially fine grain and high hardness.

Effect of Extrusion Conditions on Metal Flow and Microstructures of Aluminum Alloys

Abstract Study of metal flow in extrusion billet is fundamental and useful to understand extrusion technology. Investigation of behavior of extrusion billet skin and microstructure of products is indispensable to maintain qualities of extrusions. In order to research the behavior, experiments and FE analysis of clad billet extrusion were performed. The analytical results of billet skin deformation were similar to that in experiments. Friction between back end of billet and ram affects the deformation of skin and its penetration into billet. Secondly, microstructure of an extruded product is predicted and the condition of recrystallization and grain refnement is revealed.

Optimization of Pass Schedule from the View Point of Shape and Profile of Cold Rolled Strip

Abstract The paper aims at finding analytically an optimum pass schedule for producing strip with uniform thickness across the width and dead flat shape. The profile of strip is calculated by a three-dimensional analysis in which the elastic deformation of rolls and the plastic deformation of strip are considered as one system. The flatness defect is considered as the elastic buckling by the the residual stress which is calculated from the stresses at the exit of roll gap.

Crystallographical Calculation of Earing in Deep Drawing under Various Conditions

Earing in the cup drawing of sheet metals is calculated quantitatively using a crystallographical theory with measured texture data. In the analysis a polycrystalline sheet is simplified to be an aggregate of many single crystals with various orientations, and a crystallite orientation distribution function which is calculated from the measured texture is used as a volume fraction of a certain oriented crystal. The circumferential distribution of radial strain in a flange of a blank being drawn is calculated by considering a restricted glide in a crystal, and then cup height at each peripheral position of a drawn cup is calculated from this distribution of radial strain. For an aluminium, a copper and two steel sheets the calculated cup profiles are compared with experimental ones under various drawing conditions of dimension of a punch, a die and a blank. The result shows that earing in the drawn cup can be predicted satisfactorily by the present calculation for a wide range of drawing conditions and materials.

Prediction of the Bending Moment of Predeformed Sheet from Uniaxial Test Results

Summary The bending moment of a metal sheet, especially of a predeformed sheet, is generally not predictable from the behaviour of the sheet under uniaxial stress condition that is usually determined only by the tensile test, while the sheet bends almost under plane strain condition. In the present study, the behaviours under uniaxial stress condition are first determined not only with the tensile tests but also with a compressive test in the direction of thickness or plane of the predeformed sheet. The procedure o f the compressive tests have been developed by one of the authors and published elswhere. The yield stress of the sheet under plane strain tension and compression are then obtained from the uniaxial stress-strain relations by using an equation which has been proposed by one of the authors, for the calculation of the bending moment. The results calculated are compared with the experimental results for cold drawn sheets of brass and steel or cold rolled sheets of aluminium and steel. The good coincidence between them shows that the bending moments are predicted satisfactorily from the results of the uniaxial tests proposed.