F. Grosman

Application of a flow stress function in programmes for computer simulation of plastic working processes

Abstract Computer simulation of plastic working processes enables, unavailable so far, getting closer of process model to real conditions. One of elements of computer simulation programme, that decide on accuracy of obtained analysis results, is a flow stress function which should take into account the effect of deformation history as well as current conditions of deformation of a particle surroundings corresponding with finite elements of the analysed area (Fig. 1). Obtaining of correct description of a flow stress function is related both to the mathematical structure of this function as well as to the methodology of experimental determination of flow stresses values. A mathematical form of the function should take into account the physical phenomena occurring in the material that decide about instantaneous value of the flow stress. These phenomena depend on the material and forming conditions as well as on the of history materials technological processes preceding the moment of starting the simulation of plastic working. Experimental determination of flow stress value for defined deformation conditions requires taking into account the phenomena occurring in a studied sample, that cause deviations from the assumed ideal conditions. They depend both on the test type (tension, compression, torsion) and on technical solutions for the test stand. Solutions related to the methodology of flow stress determination will be discussed in further part of the report on the basis of a plastometric torsion test. The types of flow stress functions and problems related to experimental determination of flow stress will be discussed. Moreover, plastic working processes will be classified from the point of view of the choice of the most appropriate description of the flow stress for computer simulation requirements.

Metal flow in the deformation gap at primary swaging

Abstract Taking into consideration technological conditions typical for the real swaging process an analysis of metal flow in the deformation gap has been performed using finite elements method, and assuming flatness of sections. The stress and strain distributions, as well as deformation rates and temperature distributions have been calculated for swaging according to sizing schemes: circle → circle, circle → square and circle → octagon. The obtained results of local strain distribution calculations have been verified experimentally. The local strains were measured using the method of combined rods being swaged in practical conditions. Moreover, the experimental verification of the calculated temperature distributions in the swaged material cross-section has been carried out by comparison with the results of pyrometric measurements of the rod surface temperature. The calculated strain distributions can be used to design efficiently the swaging process because the knowledge of the strain distribution indicates some potential crack nucleation areas and the respective level of acceptable strain limits.

Flow-stress functions for the computer simulation of metal forming

Abstract The problem of the selection of the flow-stress function for metal forming process simulation programmes has been explored in this paper. The set of flow-stress functions has been divided into five groups. Criteria for the selection of the flow-stress function have been proposed. Attention has been paid to the necessity of taking into consideration the principal directions of the strain state in the flow-stress function in the case of interrupted deformation.

The Material Flow Analysis in the Modified Orbital Forging Technology

The main aim of this work is the computer aided design of the new orbital forging process. The finite element model was developed and used in research on possibility of modification of the classical orbital forging technology based on the Marciniak press to obtain more effective process. Obtained numerical results from simulations of the new orbital process are compared with the experimental analysis, performed on the orbital press with the developed device. However, due to the novelty of the developed approach the investigation on direction of material flow during deformation is of particular interest in this work. Direction of material flow and strain path change effect due to incremental character of deformation is analyzed. Obtained results confirm good predictive capability of the FE model and are the basis for the comparison of the two processes and discussion on the effectiveness of the modified incremental forming process.

Application of Incremental Metal Forming for Production of Aircraft Integral Panels

The principle and the potential of an incremental bulk metal forming method is presented in the paper. It can be used for manufacturing of the specific aircraft integral panels in a form of ribbed parts with high surface/thickness ratio. A unique laboratory device has been developed to investigate the effect of process parameters on the material flow and the press load. It utilizes tooling consisting of working rolls, a die and a punch that is divided into a number of segments. The results of preliminary numerical simulations proved that the presented forming method offers significant advantages in comparison with conventional forging.

The evaluate of laser welded tailor and tubular blanks formability for automotive vehicle elements stamping

The laser welded blanks and tubes take wide range in application as materials for forming of automotive vehicle elements. The heterogeneity of structure and properties in laser weld area has an effect on welded blanks behavior in the plastic forming process. For quantitative evaluation of this heterogeneity influenced on plastic strain course, necessary is to determine characteristics of laser welded blanks mechanical properties. It has a particular meaning in accomplishing selection of proper laser joined sheets and tubes sets, allowed to receive designed quality of presswork. It is difficult to find a universal method of those kinds of welded blanks drawability evaluation, more when joining elements are made of different materials. In this paper are pointed out the important issues at elaborating of those kinds welded blanks drawability evaluation, with special include laser welded tubes drawability evaluation for hydroforming process. Besides, there are presented examples of laser welded sheets and tubes, which are research program objects at Department of Process Modeling and Medical Engineering of The Silesian University of Technology. There is presented research capabilities of designed and built laboratory stand for tubes hydromechanical bulging.

Numerical and Experimental Investigation of the Innovatory Incremental-Forming Process Dedicated to the Aerospace Industry

The main goal of this work is development of the incremental-forming (IF) process for manufacturing integral elements applicable to the aerospace industry. A description of the proposed incremental-forming concept based on division of large die into a series of small anvils pressed into the material by a moving roll is presented within this article. A unique laboratory device has been developed to investigate the effects of process parameters on the material flow and the press loads. Additionally, a developed numerical model of this process with specific boundary conditions is also presented and validated to prove its predictive capabilities. However, main attention is placed on development of the process window. Thus, detailed investigation of the process parameters that can influence material behavior during plastic deformation, namely, roll size and roll frequency, is presented. Proper understanding of the material flow to improve the IF process, as well as press prototype, and to increase its technological readiness is the goal of this article. Results in the form of, e.g., strain distribution or recorded forging loads are presented and discussed.

The Potential and Application Areas of Forging Aided by Shear Stress

The paper demonstrates the potential of unconventional metal forming method that consists in introducing shear stress at the die/workpiece interface during compression. In practice it can be realized by induction of reciprocating, vertical motion of a punch that adheres strongly to a workpiece. To estimate an effect of the method on the material flow, a relevant finite element model has been developed and the selected results of numerical simulations are presented in the paper. In comparison to the conventional forging, forming aided by shear stress is able to provide a number of benefits such as significant increase of local strains, lower press loads and the opportunity to control the strain distribution in the workpiece volume. Perspectives for continuation of the studies as well as possible application areas of forging aided by shear stress are discussed in the summary.

The impact of compression with oscillatory torsion on the structure change in copper

The influence of compression with oscillatory torsion on the copper structure and force parameters are presented. The compression with oscillatory torsion method, developed in the Faculty of Materials Science and Metallurgy at the Silesian University of Technology, is used to achieve severe plastic deformation resulting in homogeneous ultrafine-grained structure of metals. The deformation resistance of copper for various torsion frequency and compression rate is presented. The results of microstructural observations by using LM (light microscope) and TEM (Transmission Electron Microscope) technique are displayed as well. The geometrical parameters of structure elements and their misorientation angles were characterized by using TEM method. Application of compression with oscillatory torsion was found to cause a remarkable decrease of deformation resistance as compared to compression without torsion. Plastic flow localized in shear bands was observed. Structures with large misorientation occur in microbands areas. The banded structure formed during compression with oscillatory torsion consists of well-formed, elongated subgrains.

The Effect of Compression Aided by Additional Shear Stress on Microstructure of Composites Reinforced with Ceramic Particles

The paper presents a new method for processing of cast composites reinforced with ceramic particles in order to improve the microstructure homogeneity and material properties. The presented forming method consists in compression aided by additional shear stress that is caused by transverse motion of a punch. As a result, severe plastic deformation can be obtained in a workpiece. A series of experiments was conducted for previously cast Al-Mg-Cu matrix composites containing 15% reinforcement in a form of the mixture of SiC and glassy carbon particles. It was found that the applied method allows to refine the particles and to obtain a good-quality bonding on the particle-matrix interface.