Vol 23, No 3 (2021)

Introduction. Cast iron extremely poorly tolerate thermal welding cycles, and therefore it is necessary to choose carefully the technological parameters. The main parameters of continuous laser welding are: the power of laser radiation, the welding speed, the parameters of the focusing system. The aim of the work is to determine the optimal power and speed of continuous laser welding of cast iron, depending on the geometry of the weld. In this paper, the welding seams obtained on samples of gray alloyed cast iron with a pearlitic metal base, using an LS-1 ytterbium fiber laser, are studied. Research methods. The geometric parameters of the joints were quantified in the program for quantitative analysis and image processing ImageJ. The obtained data were processed by regression analysis. To optimize the process parameters, an orthogonal plan of the passive experiment was developed, including nine experiments in which the factors varied at three equally spaced levels. The quality parameters in the passive experiment were the geometric dimensions of the weld pool and the size of the quenched zone. To solve the optimization problem, we used the methods of gray relational analysis and linear programming. Results and Discussions. The obtained regression models explain a significant proportion of the variance of the dependent variables, the regression coefficients, as well as the models themselves, are statistically significant, which indicates a close linear relationship between the seam geometry and the process parameters. The calculated shape of the weld pool depending on the radiation power and welding speed shows that the required welding seam of the required dimensions can be obtained at various process parameters which allow solving a multi-criteria optimization problem. The gray relational evaluation of the geometric parameters of the seam shows that the most correct parameters in terms of obtaining the seam of the maximum depth with the minimum width, convexity (concavity) and the quenched zone are the minimum power and maximum welding speed. The calculation of the optimal radiation power and welding speed depending on the seam depth showed that welding of small thicknesses is optimally carried out with minimal power, and the seam depth is adjusted by changing the beam speed. Welding of large thicknesses is optimal at high speed, and to increase the depth of the seam, the power must increase.

Introduction. In the manufacturing industry, there is a particular interest in the development of a new type of technological equipment, which makes it possible to implement methods for modifying the parts surface layers by processing it with concentrated energy sources. The combination of two processing technologies (mechanical and surface-thermal operations) in the conditions of integrated equipment makes it possible to neutralize the disadvantages of monotechnologies and obtain new effects that are unattainable when using technologies separately. The use of hybrid machine tools in conjunction with the developed technological recommendations will allow achieving a multiple increase in the technical and economic efficiency of production, resource and energy saving, which in turn will contribute to an increase in the competitiveness of products and the renewal of the technological paradigm. Purpose of work: increasing productivity and reducing energy consumption during surface-thermal hardening of machine parts by exposure to concentrated energy sources under conditions of integrated processing. Theory and methods: studies of the possible structural composition and layout of hybrid equipment during the integration of mechanical and surface-thermal processes are carried out taking into account the main provisions of structural synthesis and the components of metalworking systems. Theoretical studies are carried out using the basic provisions of system analysis, geometric theory of surface formation, design of metalworking machines, finite-element method, mathematical and computer simulation. Mathematical simulation of thermal fields and structural-phase transformations in the case of HEH HFC is carried out in the ANSYS and SYSWELD software packages, using numerical methods for solving the differential equations of unsteady thermal conductivity (Fourier's equation), carbon diffusion (Fick's second law), and elastoplastic behavior of the material. The verification of the simulation results is carried out by conducting field experiments using: optical and scanning microscopy; mechanical and X-ray methods for determining residual stresses. In the study, Uone JD520 and Form Talysurf Series 2 profilograph-profilometers are used to simultaneously measure shape deviations, waviness and surface roughness. Surface topography is assessed using a Zygo New View 7300 laser profilograph-profilometer. The microhardness of the hardened surface layer of parts is evaluated on a Wolpert Group 402MVD device. Results and discussion. An original method of structural-kinematic analysis for pre-design research of hybrid metalworking equipment is presented. Methodological recommendations are developed for the modernization of metal-cutting machine tools, the implementation of which will allow the implementation of high-energy heating by high-frequency currents (HEH HFC) on a standard machine-tool system and ensure the formation of high-tech technological equipment with expanded functionality. A unified integral parameter of the temperature-time effect on a structural material is proposed when the modes of hardening by concentrated heating sources are assigned, which guarantee the required set of quality indicators of the surface layer of machine parts, while ensuring energy efficiency and processing productivity in general. It is experimentally confirmed that the introduction into production of the proposed hybrid machine tool in conjunction with the developed recommendations for the purpose of the HEH HFC modes in the conditions of integral processing of a “Plunger bushing” type part in relation to the factory technology allows increasing the productivity of surface hardening by 3.5 ... 4.1 times, and reduce energy consumption by 9.5 ... 11.3 times.

Introduction. The efficiency of processing on metal-cutting machines is evaluated by the reduced cost of producing a batch of parts while ensuring the required quality. In modern production, parts are usually made on CNC machines. Today the CNC program and the trajectories of the machine tool actuators match each other with high accuracy, which, however, does not yet guarantee quality and efficiency of production. The definition of the CNC program is based on the knowledge base of rational modes, tools, coolant and etc. during processing. This base reflects some averaging over the set of machines, tools and processing conditions, and does not take into account changes in the properties of the dynamic system in the process of cutting. Subject. The paper deals with the synergistic matching of external control (CNC programs) and cutting dynamics (internal control). The internal control factors can be set a priori, as well as determined as a result of the influence of irreversible energy transformations in the cutting zone. The purpose of the work is to determine the law of controlling the trajectories of the machine's executive elements in such a way that, with changing properties of the dynamic cutting system, the required surface quality of the part and minimizing the intensity of tool wear are ensured during the processing of the part. Method and methodology. Mathematical simulation of the controlled dynamic system, which properties change due to the a priori set laws of variation of subsystem parameters, as well as changes in the cutting properties conditioned by the power of irreversible energy transformation is presented. Consideration of the power of irreversible energy transformations is necessary for predicting back-edge wear, changes in dynamic coupling parameters, and evolutionary restructuring of cutting dynamics. Results and Discussion. The regularity of matching the CNC program with the changing properties of the cutting process, which allows increasing the processing efficiency while ensuring the required quality of parts, is disclosed. A number of properties of the dynamic cutting system caused by changing trajectory of the longitudinal feed rate of the tool during processing of the shaft, the stiffness change of which is given, are revealed and analyzed.

Introduction. The practical significance of non-stoichiometric titanium carbides TiCх in various fields of technology and in medicine is expanding. In this regard, it is important to investigate both methods of obtaining titanium carbide powder and its properties in a wide range of stoichiometry. One of the effective ways to influence the physical and mechanical properties of powder systems is its mechanical treatment. Under shock-shear action, which is realized during processing in a ball mill, mechanical energy is transferred to the powder system, as a result of which it is ground, centers with increased activity on newly formed surfaces are formed; phase transformations, crystal lattice deformation, amorphization, formation of defects, etc. are possible. The aim of this work is to study the effect of low-energy mechanical treatment in a ball mill on the structure, phase composition and parameters of the fine crystal structure of non-stoichiometric titanium carbide powder obtained by reduction of titanium oxide with carbon and calcium. Materials and methods. Powder of titanium carbide TiC, obtained by calcium carbonization of titanium oxide was investigated. The powder was treated in a drum type ball mill. The structure of the powders before and after treatment was studied using the Philips SEM 515 scanning electron microscope. The specific surface area was determined by the BET method. The phase composition and parameters of the fine crystal structure of powder materials were investigated by X-ray analyzes. Results and discussion. It was established that an increase of the time of mechanical treatment in a ball mill of a non-stoichiometric titanium carbide powder TiC0.7 leads to an increase in the specific surface area of the powder from 0.6 to 3.4 m2 / g, and the average particle size calculated from it decreases from 2 μm to 360 nm. It is shown that in the process of treatment of the non-stoichiometric titanium carbide TiC0.7 powder, its structural phase state changes. Powder particles consist of two structural components with different atomic ratio of carbon to titanium: TiC0.65 and TiC0.48. Mechanical treatment of titanium carbide powder leads to a decrease in the microstresses of the TiCx crystal lattice and the size of coherently diffracting domains (CDD) from 55 to 30 nm for the TiC0.48 phase. For the TiC0.65 phase, with an increase in the duration of mechanical treatment, as well as for TiC0.48, the size of CDD decreases, and the level of microdistortions of the crystal lattice increases. This indicates that in the process of mechanical treatment, not only the grinding of powder particles occurs, but also an increase in its defects.

Introduction. Reducing the level of damage accumulation during pressure treatment of materials at elevated temperatures in creep and close to superplasticity modes in the manufacture of parts can significantly increase its service life in the cold state. Finding temperature and power conditions leading to a reduction in damage of material during the production process and operation is an important task. The purposes of the work: 1) to show the possibility of using the Sosnin-Gorev creep and damage model for alloys with a non-monotonic dependence of strain at fracture on diagrams with creep curves; 2) to carry out comparative analysis of damage accumulation under conditions of uniaxial tension at constant stress and at constant strain rates for alloy with such a dependence. Research methods. Used scalar damage parameter is equated to the normalized deformation, i.e. to the ratio of the current strain to the fracture strain. To find the coefficients of relations creep and damage, the similarity of the creep curves in the normalized values “normalized strain – normalized time”, i.e. the presence of single normalized curve of damage accumulation is checked. The least squares method is used to approximate the experimental data. Numerical integration methods are used for comparative analysis of deformation modes. Results and discussion. Determination of the parameters of the creep and damage equations by the method of a single normalized curve is carried out on the example of experimental data for steel 12Kh18N10T  (12Cr18Ni10Ti) at 850 °C, which has a minimum of fracture strain in diagrams with creep curves. Analysis of the static and kinematic modes of deformation for studied material showed that damage accumulation in both cases is practically the same for stresses close to the stress at which this minimum is reached. If the stresses are lower, then the lower level of damage accumulation will be in the kinematic mode; if the stresses above the minimum value, then the static mode will lead to a lower level of damage accumulation. Application. The obtained results can be useful when choosing rational modes of forming structural elements from alloys with a non-monotonic dependence of the fracture strain on stress, as well as in evaluating it for long-term strength during operation.