Vol 22, No 1 (2020)

Introduction. The development of modern engineering necessitates the creation of materials with a combination of properties such as strength, corrosion resistance, heat conductivity, heat resistance, wear resistance, etc. In the manufacture of new types of products with a complex profile, bimetallic materials are widely used. For processing such products, it is advisable to use electrophysical processing methods, one of which is the technology of copy-piercing electrical discharge machining (EDM). Currently, the EDM method is one of the most common methods for processing modern materials. The paper is devoted to improving the efficiency of the EDM of bimetallic materials such as steel-copper. Subjects of research are: unevenness of the material removal of the treated surface, the roughness parameter during the EDM of a steel-copper type bimetallic material under various modes of electric discharge machining. The aim of the work is to increase the efficiency and accuracy of the EDM process of complex-profile bimetallic products electrode tool (ET) with various physical and mechanical properties. Methods. Experimental studies were carried out according to the classical experiment. For the experiments, a copy-piercing electrical discharge EDM machine Smart CNC was used. As a bimetallic processed product, a steel substrate with a deposited coating was used. The base material is steel 09G2S, the surfacing material is M1 copper. As electrode electrodes used: steel 20; duralumin grade D16; copper M2. Results and Discussion. A theoretical model is developed that allows one to calculate the amount of removal of the bimetallic material for steel-copper removal depending on the regimes of EDM and material ET. The convergence of the theoretical model with the results of experimental studies is 15%. An experimental study was made of the wear of ET during the EDM of a bimetallic steel-copper material depending on the modes of EDM and the material of the ET. It is established that during EDM of copper ET in the med and max modes, the wear of ET is minimal and amounts to 0.03 - 0.05 mm, respectively. The roughness parameters are calculated and the treated surface of the bimetallic steel-copper EDM bimetallic material is analyzed at different modes of processing ET with various electrophysical properties.

Introduction. One of the fields of use of deformational cutting (DC) is the manufacturing of meshes from thin sheet materials. The principle of its production consists in finning of both side of the thin sheet in mutually perpendicular directions with a depth of cut more than half the thickness of the sheet. A significant disadvantage of such meshes is the small effective screening area (the ratio of the total area of holes to the mesh area). One of the promising fields of use of meshes obtained by DC is hernioplasty as titanium implants for the treatment of hernias and reinforcement of bone and soft tissues. Implants require an effective screening area of more than 60 %, high compliance with plastic deformations, and a large specific surface area to hold the tissues sprouting into the implant. In the paper, the DC method is considered as an alternative to the existing titanium woven mesh implants, which have an extremely high cost. Work objective is to study the main relationships of obtaining preforms for meshes by the DC method, the features of mesh stretching, and to analyse the resulting shapes and sizes of mesh cells. In this paper the two-sided finning of thin-sheet blanks of  pure titanium VT1-00 with a mismatched direction of finning of opposite sides of the sheet in the range of fins crossing angles of 1.3o-10o with varying the angle of workpiece undercutting and the fin pitch were studied. The analysis of the stretching mechanics for obtaining rhombic, hexagonal, and parallelogram forms of cells was carried out. Results and discussion. The range of fin pitch and crossing angles that ensure the stability of the DC and stretching stability is set. The shape of the cell depends on the length of the fins bonding obtained on opposite sides of the sheet. Increasing the bond length with by a decreasing the crossing angle leads to the transition of the cell shape from rhombic to hexagonal. A cell in the form of a parallelogram is typical for the fins of the opposite sides, which have differences in bending strength. Conclusions: the method of deformational cutting is an alternative of metal punching for through-cutting sheet metal and polymer for its subsequent stretching in order to obtain meshes. The meshes obtained on the basis of DC have a large surface area and an increased ability to plastic deformation. It is justified to obtain the rhombic, hexagonal, and parallelogram forms of mesh cells. The shape of the mesh cell is controlled by selecting the fins crossing angle and the pitch of the fins on opposite sides of the workpiece. The largest cell size and maximum effective screening area of the mesh are provided by meshes with hexagonal cells form at the fins crossing angles on opposite sides of the workpiece less than 3o.

Introduction. Tool vibrations accompanying the cutting process are largely related to the long-established regenerative effect, which significantly affects the dynamic characteristics of the metal cutting process, which is indicated in numerous foreign publications of leading European specialists in the field of Metalworking. In the works of some Russian scientists specializing in the analysis of metal cutting processes on metal-cutting machines, the position of the existence of an optimal cutting speed that provides the best quality of the processed surface and the greatest tool life is considered. Therefore, the paper considers the question of the probable connection of this optimal speed with the regeneration of tool vibrations during metal turning. Objective: the possibility of assessing the influence of the regenerative effect on the dynamics of the processing process is considered, without taking into account additional influences on the process, both from the machine side and from the cutting process itself, in order to determine the existence of optimal cutting modes. The study investigated: a mathematical model describing the dynamics of tool vibrations in the conditions of metal processing on machines of the turning group, while only the case of longitudinal turning of the product is considered. Research methods: on the basis of mathematical modeling of the dynamic cutting system, three variants of the possible behavior of the processing process are considered, taking into account the influence on the regeneration of tool vibrations, the period of rotation of the spindle with the part fixed in it. As the first case, a neutral variant in which this period is not associated with the carrier frequency of the speed of axial deformations of the tool is considered. The second option determined the optimal speed of rotation of the spindle, which completely coincided with the carrier frequency of the speed of axial deformations of the tool. The third option shows the worst-case version of the spindle rotation speed, which makes the spindle oscillation period such that the regenerative effect is maximized. Results and discussion. The results of modeling are presented, revealing the dynamics of the system, taking into account the three options selected for the specified spindle speed of the machine. The results of research show that even in the simplest description of cutting forces, the dynamics of the system is quite complex, which is significantly affected by the regenerative effect revealed in the work. The numerical experiment confirms the theory proposed in the paper about the existence of an optimal processing speed, in terms of the influence of tool vibration regeneration on the cutting process. The results obtained are in line with well-known domestic works devoted to the practical analysis of the possibility of building optimal cutting systems and link them with the work of leading European experts in the field of dynamics of metal processing processes.

Introduction. Morphological changes in the free surface of materials during loading are interesting from a fundamental and practical point of view. In the first case, through the deformation relief, scientists judge the processes taking place inside the material, identify the deformation mechanisms, analyze the change in the stress-strain state, etc. In the second case, the deformation relief is an undesirable phenomenon, because it worsens fatigue resistance, adhesion, leads to cracking and reduces other physical and mechanical properties of machine parts. In addition, on the basis of the deformation relief, scientists try to evaluate the residual life of the machine parts. Today, industry uses materials in various structural conditions. The microstructure of the metal (the presence or absence of grains and grain boundaries, grain size, texture, crystallographic orientation, etc.) has a significant effect on the nature of the course of plastic deformation and the morphology of the deformed surface. The purpose of the work is to study the influence of the material structure on the evolution of the surface morphology during deformation. For this purpose, nickel samples in a single-crystal, polycrystalline, and ultrafine-grained state are investigated. The methods of investigation are mechanical compression tests, confocal laser scanning microscopy. Quantification is carried out using standardized three-dimensional roughness parameters. Results and Discussion. The paper shows the influence of the internal structure of the material on the evolution of the morphology of the deformation surface. Changes in the strain relief are discussed in terms of the prevailing strain mechanisms for each structural state of the material. It is shown that using three-dimensional roughness parameters, one can evaluate the presence of potential stress concentrators on the surface. It is determined that the presence of deep sharp depressions is most inherent in the material in a polycrystalline state. The results of the work can be useful for a reasoned choice of the microstructure of the material in the manufacture of machine parts and for mathematical modeling of the behavior of metals under load.

Introduction. At present, the methods of additive manufacturing technologies for obtaining metallic materials of different chemical and phase composition are being actively developed. Wire technology is based on the electron-beam melting method and is one of the most promising technologies that allows, in addition to obtaining complex shaped components, to create materials with unique gradient layered structure. But such technologies allow obtaining products with the structure of cast unhardened material with a coarse crystalline structure and irregular component distribution of the used material. In order to achieve a homogeneous structure of the obtained materials, as well as to strengthen the material and refine the grains, it is possible to use additional friction stir processing, which can change the distribution of polymetallic sample components with the formation of the structure, which is not achievable by any available methods. From the above, the problem of grain refinement, material hardening and obtaining a homogeneous structure during the polymetallic materials manufacturing from similar and dissimilar metals and alloys is an important one at present. In this paper, a combination of additive electron-beam manufacturing and friction stir processing techniques is used to solve this problem. The approach consists in the effect of the severe plastic deformation method on the gradient transition of a polymetallic product fabricated by additive manufacturing. The aim of this work is to study the macrostructural regularities of polymetallic samples formation by the additive electron-beam manufacturing method, which forms mechanical mixtures (Cu-Fe), solid solutions and intermetallic compounds (Cu-Al) in the contact zone. The peculiarities of bimetal samples formation from similar and dissimilar metals, obtained by additive method, and regularities of structural changes in materials of Cu-Fe system after hybrid additive-thermomechanical processing are investigated in the work. The research methods are optical and scanning electron microscopy as well as analysis of micromechanical properties by the microhardness measurement in different sections of the obtained samples. Results of the study. The structural changes in the materials obtained by additive method depending on the polymetallic material phase types are revealed. The received data indicate a uniform distribution of the polymetallic sample components in the structural gradient zone, which do not form intermetallic phases and solid solutions in the contact zone. The regularities of plastic deformation and fragmentation in the Cu-Fe system (copper М1 - steel 321) after friction stir processing were determined using scanning electron microscopy, micro-X-ray spectral analysis and optical microscopy. The data obtained demonstrate the formation of metal flows in the stir zone towards the contour of the tool. The material layers have different grain size, peculiarities of copper and steel particles distribution, and also chemical elements distribution regularities. On the edges of the stir zone there is excessive mixing into the upper material layers from the underlying steel layers. In the stir zone there is a heterogeneity of structure that occurs in the distribution of individual layers, their thickness, grain size and volume fraction of different phases.