No 2 (2017)
TECHNOLOGY
Features of small holes formation in copper by electrochemical machining in water chloride solutions
Abstract
The problems of the interelectrode gap value assignment at the electrochemical dimensional machining of small holes in copper in chloride solutions with using a hollow cathode- tool with an internal diameter 0,26 mm and external diameter 0,46 mm are considered. It is established that when obtaining holes at small interelectrode gaps (0,05…0,1 mm) with electrolyte jet pressure P = 0,3 MPa, the accuracy of copying the tool is not ensured. This is explained by the fact that the electrochemical dimensional machining of copper in chloride solutions is accompanied by the formation of a hardly soluble CuCl salt on the surface, which prevents electrochemical dissolution of the metal under the cathode-tool end. The accuracy of copying the tool on the machined surface is achieved by increasing the interelectrode gap to 0.2 mm. However, an increase in the interelectrode gap leads to a decrease in the localization of the anodic dissolution process, and, consequently, to a decrease in the rate of hole formation. It is shown that an increase in the pressure of the electrolyte jet to 0,8 MPa at a value of the interelectrode gap from 0,05 to 0,1 mm ensures the accuracy of the hole formation. It is noted that increasing the electrolyte jet pressure intensifies the process of depassivation of the anodic surface, which makes the processing possible at a small value of the interelectrode gap with a high degree of localization of the process. It is established that at interelectrode gap equal to 0,3 mm at P = 0,3 MPa and equal to 0,1 mm at P = 0,8 MPa, it is possible to realize the scheme of electrochemical machining of holes with continuous stabilization of the interelectrode gap due to the displacement of one of the electrodes.
Obrabotka Metallov / Metal Working and Material Science. 2017;(2):6-16
6-16
EQUIPMENT. INSTRUMENTS
Cam mechanism designing with account of the technological load and energy costs
Abstract
The problems of the cam mechanisms designing are discussed. The analysis of scientific literature on this problem indicates that today the synthesis of motion laws is usually performed without account of energy costs. The main criteria including phase angles and laws presented either in the analytic form or as tables of the cam profile are considered. The goal of the present study was to develop the method for synthesis of the motion laws of a cam mechanism with the account of energy costs from the payload, moment of inertia force, elastic forces of the mechanism elements and energy of the slave unit. This study is relevant due to the lack of uniform methodology taking into account energy costs during the mechanism design. A computational model of the slay mechanism of STB loom was used in the study. The values of work used to overcome resistance from the technological load, work from the mechanism inertia forces and energy used for elastic deformations of the mechanism elements were calculated to determine the energy costs of the mechanism. The mathematical package MathCad was used in the calculations. The analysis of the calculation results indicates that certain types of fabrics cannot be produced using existing parameters of the slay mechanism. A method for synthesis of cam mechanisms for technological machines including determination of energy costs from the payload, inertia forces and moment on the slave shaft of the cam mechanism was suggested on the basis of the performed studies. The theoretical studies were tested using a model of a particular machine - STB loom. The motion law of the slay mechanism was synthesized. A new profile of the cam in the form of the radius-vector table was suggested. The obtained results make it possible to discriminate assortment abilities of weaving machines by the values of the technological force and recommend their most efficient operation modes to factories.
Obrabotka Metallov / Metal Working and Material Science. 2017;(2):17-27
17-27
Design and manufacture of decorative metal box
Abstract
The paper deals with the problems of designing and creating one of the types of jewelry - decorative jewelry box made of metal. A detailed description of the sequence of design-engineering - from the choice of subjects to its manufacture - is given. The relevance of the product being developed is proved; the analysis of the product analogues is carried out in terms of artistic and material design. An original sketch of decorative jewelry box corresponding to aesthetic, structural and functional design requirements with a regard to an analysis of the strengths and weaknesses of the existing analogues is developed. The ergonomic factors, suggesting the convenience of use of the product are taken into account when creating jewelry box. The choice of material is justified. On the basis of the material properties the production process is selected. The product weight is calculated and the structural analysis of the pivoted fall joint is made involving Inventor software product. The necessary drawings, the master model for investment casting are made. The decorative jewelry box production process consisting of three main phases: 1) the production of the jewelry box case, 2) applying a decorative coating, 3) assembling of the jewelry box elements is described. Molding technology for the production of a single product is considered. As a result of design-engineering a jewelry box based on the artistic image of the stylized giraffe’s figures with entwined necks is produced. The use of stylized figures of birds and animals for the production of small metal boxes adorned with enamel and precious inserts is a fashion trend at the moment.
Obrabotka Metallov / Metal Working and Material Science. 2017;(2):28-37
28-37
MATERIAL SCIENCE
Formation of mechanical properties of low alloy steel surface under thermomechanical treatment
Abstract
Detection of physical mechanisms of formation and evolution of structure-phase states and dislocation substructures in steels is one of the important problems of condensed-state physics and modern material science because it forms the basis of development and formation of effective methods for increasing the service characteristics of articles. Experimental investigations of structures and phase states being formed in a cross-section of articles as a result of thermomechanical treatment are very significant for understanding the physical nature of transformations as they make it possible to change structure and mechanical characteristics purposefully. Thermomechanical treatment of low carbon steel 09G2S (0.09 wt.% C, 2 wt.% Mn, 1 wt.% Si) is done by rolling of H-beam DP 155 and forced water cooling in the process of rolling on rolling mill 450 open joint-stock company “Evraz - Western Siberian metallurgical combine” By methods of physical material science the investigations of structure-phase states, defect substructure mechanical and tribological properties of H-beam surface from steel 09G2S being formed as a result of thermomechanical hardening in the process of rolling on rolling mill. The qualitative correspondence of change in microhardness and scalar dislocation density along the cross-section of H-beam has been established. The processes were analyzed and the analysis of mechanisms contributing to the formation of nano-dimensional cementite phase in the conditions of thermomechanical treatment of low-alloy steel was done. It was shown that the cementite particles were formed: - in dispersion of cementite plates of pearlite colonies by its cutting with moving dislocations; - in dissolution of cementite plates of pearlite colonies and its repeated precipitation on dislocations, boundaries of subgrains and grains; - the decomposition of solid solution of carbon in α-iron occurring in the conditions of “self-tempering” of martensite loads to formation of particles precipitated in the volume of martensite crystals on dislocations and at boundaries of martensite crystals. - in diffusion γ → α transformation in the conditions of high degree of deformation and high temperatures of treatment a dispersion of lamellar pearlite structure is observed. It is established that the phenomenon of increase in hardness of steel surface layer is a multi-factor, morphologically multi-component one and is determined by the nature of γ → α transformation.
Obrabotka Metallov / Metal Working and Material Science. 2017;(2):38-44
38-44
Spark Plasma Sintering of the mixtures of metallic powders and metal matrix composites: peculiarities of the structure formation and properties of the sintered materials
Abstract
The peculiarities of the behavior of the powder mixtures of metals and metal matrix composites during Spark Plasma Sintering (SPS) using Ti3SiC2-Cu, Fe-Ag, NiO-Ni, Cu2O-Cu, and Fe-Al systems as examples are analyzed in the work. The physical and chemical aspects of the formation of contacts between composite agglomerates obtained by mechanical treatment of the powder mixtures in a high-energy ball mill and the possibilities of the SPS method for the production of metal matrix composites combining different strengthening mechanisms are discussed. In the Ti3SiC2-Cu composites obtained by mechanical milling and SPS, the copper matrix remains in the nanocrystalline state, and the total contribution of dislocation and grain boundary strengthening is greater than the contribution of dispersion strengthening. Microstructural studies of the sintered Ti3SiC2-Cu and Fe-Ag compacts show that during SPS of mechanically milled powders, areas of inter-agglomerate contacts can experience melting. In the systems capable of interfacial interactions, the latter preferentially occur at the inter-agglomerate contacts. The conditions for the efficient reduction of oxide films present on the surface of metallic particles during the SPS using a partially oxidized copper powder containing Cu2O and a partially oxidized nickel powder containing NiO are examined. It is found that under the SPS conditions commonly used in the consolidation practice of metallic powders, elimination of oxide films present on the surface of metallic powders is due to chemical reduction of the oxides by carbon. It is experimentally shown, that reactive pressureless SPS can produce porous materials of high open porosity.
Obrabotka Metallov / Metal Working and Material Science. 2017;(2):45-54
45-54
Effect of a continuous and gas-cyclic plasma nitriding on the quality of nanostructured austenitic stainless steel
Abstract
Plasma nitriding is an effective method of the austenitic stainless chromium-nickel steels hardening. Usage of the low-energy electron beams (to 1 keV), that is typical for plasma generator, provides smaller loss of energy then usage of gas discharges. Low-energy electron beams allow change current density and ion energy independently of one another without using additional external heating devices. The lack of ion-plasma nitriding is deterioration of nitrided surface quality. Nanostructured deformation processing could be applied before nitriding with the aim of increasing growth rate of nitrided layer and reduction of nitrided surface roughness. In the paper, the influence of combined processing including nanostructuring frictional treatment by sliding indentor and following continuous and gas-cyclic plasma nitriding in electron-beam plasma at a temperature of 450 °С and 500 °С on hardening and surface quality of austenitic steel AISI 321 (0.04 wt.% С; 16.77 wt.% Cr; 8.44 wt.% Ni; 1.15 wt.% Mn; 0.67 wt.% Si; 0.32 wt.% Ti; 0.31 wt.% Cu; 0.26 wt.% Mo; 0.12 wt.% Co; 0.12 wt.% V; 0.04 wt.% P; 0.03 wt.% Nb; 0.005 wt.% S; and Fe for balance) is studied. It is established that friction treatment leads to occurrence of 95 vol. % α´ strain-induced martensite and increasing of microhardness to 780 HV0.025 on nitrided surface. On the nanostructured by frictional treatment surface of metastable austenitic steel AISI 321 (in contrast to nitrided coarse-grained steel) after continuous plasma nitriding in electron-beam plasma pore formation and intensive blistering is observed. Blistering is characterized by forming of steam blows and surface blowout. Obvious blistering appears due to advanced nitrogen diffusion into nanostructured surface with α´ stain-induced martensitic structure. Improvement in quality of the nitrided steel surface, hardened by frictional treatment (decreasing of blistering, pore formation and roughness), is achieved by means of: 1) gas-cyclic plasma nitriding is carried out at the conditions of periodic alternation nitriding semicycles in mixture of argon and nitrogen and denitriding (without nitrogen supply); 2) nitriding temperature decreasing from 500 °С to 450 °С. However after gas-cyclic plasma nitriding of nanostructured surface lower micro-hardness level (1 160…1 200 HV0.025) then after continuous nitriding (1 370…1 450 HV0.025) is observed.
Obrabotka Metallov / Metal Working and Material Science. 2017;(2):55-66
55-66
Influence of nonmetallic inclusions on the fracture resistance of steel under fatigue dynamic compression conditions
Abstract
Impact machines are one of the most productive types of equipment for the rock destruction. They provide high drilling speed but generally have low durability and reliability. Modern researches show that the process of mining machines parts fracture often is initiated by nonmetallic inclusions and internal defects in the structure of steel. However, nowadays the question concerning the degree of the influence of the nonmetallic inclusions morphology, size, shape and distribution on the steel fatigue failure resistance is still not clear. The traditional approach to solving the problem of the inclusions influence on steel properties requires the preparation of a significant number of experimental samples, so mathematical modeling is a promising method for assessing the influence of nonmetallic inclusions. The purpose of the research was to estimate the stresses intensity field near nonmetallic inclusions under the influence of cyclic compressive stresses and to develop recommendations for the usage of steels with various impurities for the impact machines parts manufacture. The effect of nonmetallic inclusions under dynamic loading conditions was evaluated in several stages. At the initial stage, using the methods of metallographic and microspectral analysis, the size, shape and morphology of nonmetallic inclusions in ten melt of 45 steel were determined. The obtained results were used as input data for the software package ANSYS Workbench 15.0 for calculating the stress field intensity the near inclusions. The reliability of the obtained mathematical models was checked by measuring the internal stresses by the X-ray diffraction analysis with ARL X'TRA diffractometer. Metallographic studies have shown that the main types of inclusions in the steel are point oxides, whose size can reach up to 100 microns and plastic sulphides up to 1.mm in length. The results of numerical simulation show that under dynamic compression conditions an application of the approach in which the inclusion is assumed to be mechanically equivalent to the pore or crack is incorrect. Under the dynamic compression condition near the pores and low-strength inclusions in the base material regions with a high level of local stresses are formed. The maximum value of the equivalent stresses was revealed near the elongated defects in the case of their orientation perpendicular to the action of the external force. Stress distribution near hard and strong oxides inclusions is significantly different. The maximum stresses are localized in the inclusion, while the stress magnitude is insignificant in the boundary region between the inclusion and base material. To verify the reliability of the data of the numerical experiment, XRD analysis was used for zonal stresses measuring. The results of X-ray diffractometry confirm the assumption that under compression conditions the presence of pores in the steel and plastic low-strength inclusions leads to a 50 % increase of local stresses of the main material near the defects. The stress level near the solid high-strength inclusions in the base material is 20 % lower than the average level. The results of the research show that it is desirable to make the details of impact machines using the steels whose structure contains inclusions which hardness exceeds the hardness of the matrix or apply high-purity steels with a low content of nonmetallic inclusions.
Obrabotka Metallov / Metal Working and Material Science. 2017;(2):67-78
67-78