János Prohászka

The effect of electrode material on machinability in wire electro-discharge machining

Abstract Reported in the present paper are the requirements of the materials used for WEDM electrodes that will lead to the improvement of WEDM performance. Experiments have been conducted regarding the choice of suitable wire electrode materials and the influence of the properties of these materials on the machinability in WEDM, the experimental results are presented and discussed.

Fabrication of aluminium/copper bimetallics by explosive cladding and rolling

Abstract In the present paper the authors report on the fabrication of bimetallic components consisting of aluminium and copper plates by explosive cladding and subsequent rolling. Such components are used extensively in the electrical and ship-building industries as well as in vessel design, replacing components made from solid materials. The effect of the cladding and the rolling parameters on the sound fabrication and the micro-structural properties of the resulting bimetallics is evaluated in terms of “surface integrity”, i.e. surface topography, microhardness variation and metallurgical changes through the thickness of the cladded/rolled plates, and the existence and/or intensification of particular defects encountered in such processing.

EDS Investigation of Fe–Al intermetallic compounds

Steels are often coated with other metallic materials to obtain better surface properties. In several cases this layer is made by hot dip methods. ()wing to the concentration gradient between the base metal and the layer, phase transformations occur in the diffusive interface layer. These phase transformations, of course, influence the kinetics of the coating process and the properties of the coating itself. The aim of this work was to clarify the characteristic features of the aluminium coating process in connection with the phase transformations in the diffusive interface layer. The development of the compound layer, its microstructure and phases were investigated in order to determine the effect of the carbon content of the base metal.

The Role of an Anisotropy of the Elastic Moduli in the Determination of the Elastic Limit Value

Most structural materials demonstrate very strong anisotropy in their properties. Due to this, during the elastic deformation of polycrystalline materials , there are very large differences between stresses loading of crystallites, which have different g ain orientation. The consequence of the large differences in stress values is that at the beginning of the plastic deformation only some of the crystallites deform plastically. In different materials the anisotropy determines in which crystallites the plastic deformation will commence. This phenom enon is especially significant at the alternative loading; because of this some crystallites deform only elastically while others deform elastically and plastically as well. In these cases the failures (c acks) start in the last crystallites. Introduction All textbooks dealing with the mechanical properties of metals and lloys treat the crystal orientation dependency of elastic moduli. However, the effect of this ani otropy regarding the assembly materials characteristics in practice are hardly taken in consideration, except at great plastic deformation, then the discussion of textured materials devel oped at the following recrystallization. The earing effect is also attributed to the anisotropy. Fig.1 presents the changing of a few mechanical properties of cold-rolled copper as functions of the rolling direction [1]. At the same time, Fig. 2 presents the earing property of the materials during deep dr awing [2]. The anisotropic character of metals and alloys appear in all the mechanical properties of metals used in practice, nonetheless, these are difficult to indica te in the behaviour of polycrystalline metals. This anisotropic behaviour is a main cause of the scatter of the measured values of mechanical properties. For example: the measured res ults of the fatigue effect, described in most technical books, everywhere are mentioned as having only stati stical value. This is presented in Fig. 3. The measuring results of similar samples, made of the same material and loaded under the same circumstances show a wide range, which in the case of fatigue cycles to failure over 300-600%. Such a measuring range is shown in Fig. 4, presenting the results for the steel of ASTM 7075-T6. In the diagram it is visible, for example, that at a load of 300 MPa the measured values belonging to a failure probability of 10% and 99% indicate a difference near to of an order of magnitude on the same scale. From the same figure, it also becomes relevant that at a load of 200 MPa, the above-mentioned failure probabilities differ from each other by two orders of magnitude. Altogether, using the results of the fatigue measurements the following conclusion can be drawn: the bigger the loading amplitude, the less the scatter of the measured values, and vice-versa. 15 30 45 60 75 90 105 120 135 150 165 100 110 120 130 Rm E E -m od ul us , [ G P a] Angle to rolling direction, [degree] 160 170 180 190 R m , [ M P a]

Modifications of Surface Integrity during the Cutting of Copper

Abstract The required extreme surface quality of metallic parts made necessary investigation of different features of surface formed crystallites in polycrystalline materials. Every surface crystallite has different crystal plane orientation, so its reaction to the machine tool during cutting differs from that of other crystallites. These differences are reflected in the features of surface finish, especially when the surface is mirror like. The reason is that orientation of the crystallite determines the plastic and elastic deformation both of the machined surface and the chip. Elastic deformation perpendicular to the surface depends on the perpendicular compressive stress caused by the tool and Youngs modulus, perpendicular to surface. After the passage of the tool, the elastic deformation disappears and its former values result in different levels of crystallite surfaces. Differences are determined by the orientation dependence of the Youngs modulus. The ratio of highest to lowest modulus for copper is about 3, whereas for tungsten it is 1. The most important features of crystal structure and the reasons that cause deviations in surface finish in the machining of copper are reported.

The effect of magnetic field on the recrystallisation of ferromagnetic material with special respect regarding its anisotropy

Abstract The properties of soft magnetic material used as transformer sheets strongly depend on the orientation of its crystallites. These thin sheets are manufactured by cold rolling followed by the final technological process (i.e. recrystallisation). The magnetic properties are determined by this last recrystallisation process. In the following rows it will be shown that if the recrystallisation is achieved in a magnetic field the new nuclei having orientation 〈0 0 1〉 have the greatest opportunity to form if the intensity of the magnetic field is higher than that required reaching magnetic saturation.

Effect of Microstructure on the Mirror-Like Surface Quality of FCC and BCC Metals

The microstructure of machined metals changes near the tool-affected zone. This paper presents some new results concerning mirror-like surface cutting of aluminum, copper and tungsten. The microstructure of aluminum and copper represents polycrystalline mild metals with face centered cubic (FCC) crystal structure. Examination of a mirror-like surface by optical microscopy, scanning electron microscopy (SEM), electron backscattered diffraction and atomic force microscopy revealed that grain boundaries and twin boundaries were present, which separates two domains for different crystal orientation. The Youngs modulus that depends on orientation can change considerably on these boundaries and, consequently, the value of elastic deformation of the layer under the machined surface. This effect modified the roughness. Ultraprecision machining of tungsten, which is a body centered cubic (BCC) metal, proved useless using diamond and/or boron-nitride tools. Since tungsten is a very brittle metal at room temperature, its ductile to brittle transition temperature is much higher. Therefore, in contrast to normal cutting, the material that is incapable of plastic deformation will cause brittle fracture of the chip and bad surface quality.