No 1 (2021)

Additive technologies are among the most rapidly developing areas of modern production. To ensure the progressive movement of additive technologies development in the Russian Federation, it is necessary to provide maximum availability of additive raw materials – spherical metal powders for the domestic enterprises; however, the absence of domestic assemblies to produce such powders hampers the solution of this issue. Peter the Great St. Petersburg Polytechnic University has developed and successfully carried out industrial tests of a plasma atomization system for solid metal feedstocks of various chemical compositions. The paper presents the results of the study of the influence of some technological parameters on the granulometric size, shape, and defect structure of 12H18N9 steel and VG98 alloy powders. The paper includes the results of the research of the influence of such spraying parameters as the current strength and the plasma-forming gas velocity supplied to the plasma generator and the volume of protective gas supplied to the spray torch through the fluidized bed system nozzles located in the midsection of the atomizer spraying chamber. The study showed that by increasing the current strength and the plasma-forming gas velocity, it is possible to reduce the average size of the powder particles; and by changing the volume of the protective gas supply, it is possible to control the particle shape. The analysis of the chemical composition of the obtained powders shows that during the spraying process, there is no loss of alloying elements and the powder composition is the same as the original feedstock compositions. The paper gives the developed modes for the alloy feedstocks spraying, shows the possibility to produce metal powders with the level of the spherical shape factor of 92–96 % and minimal – not exceeding 0.5 % of powder aggregate weight – number of particles with nonmetallic inclusions, external and internal defects.

The authors considered a new method of texture analysis of machined precision surfaces based on using computer optics and the autocorrelation method of processing the images of micro-relief textures under the study. This method is based on a probabilistic comparative evaluation of the unknown texture of the micro-relief under the investigation with the available textures of reference micro-patterns, in which microrelief parameters are determined. The paper proposes an approach to identify the profile surface roughness of a gas turbine engine (GTE) blade after vibro-contact polishing according to the parameters of correlation surface texture. The authors studied the surface micro-geometry of the blade back and pressure side using the optoelectronic complex based on the calculation of the average amplitude of the variable component of an autocorrelation function resulting from computer processing of a surface video image. The application of the electrooptic method for evaluating the surface texture of compressor and turbine blades allows building the surface roughness fields and more deeply analyzing the technology of final processing of the GTE blade feather profile. The relevance and novelty of the study lie in the promising technique to evaluate the surface quality parameters using the electrooptic method. A special feature of this method is the measurement of surface area roughness, while the stylus methods measure the roughness of the surface profile. An important advantage of the proposed method is its application to measure the roughness parameters of a curved surface by a non-contact method, which is advanced since there are surfaces of parts that do not imply being scratched with a diamond needle.

The paper considers the creation and research of a virtual prototype of titanium blanks drilling using the Lagrange and Galerkin method. The developed finite-element models are designed to study the process of mechanical treatment and optimize technological cutting parameters. The paper presents the results of computational investigation of titanium blanks drilling using mathematical modeling programs, which allow complete simulating operating procedures in a computer (digital twin). As a program to simulate the process of removing the allowance from a titanium workpiece, the authors used a multipurpose software product of finite-element modeling and analysis of highly-linear dynamic processes using various Ls-DYNA time integration schemes. The application of the Galerkin method allows adequately describing the drilling process with the introduction of the ultrasonic field energy into a treatment zone, can significantly reduce the duration of experimental research and evaluates the influence of the cutting mode elements and the tool design parameters on the power and energy aspects of the formation of new machine parts surfaces. Both methods are applicable to create various processes of mechanical treatment, however, the Lagrange method is less sensitive to the ultrasonic field energy. The introduction of the ultrasonic field energy into the drilling zone of workpieces made of hard-processing titanium alloys can significantly reduce energy costs. As a result of the simulation, the authors obtained a calculation file containing the simulation process, the solution of which visually reflects the drilling process of a titanium workpiece in a real-life setting with the removal of chips. However, for complete verification of numerical study results, it is necessary to carry out an experimental check and make adjustments to the calculated data.

The author carried out the comparative analysis of elastomers – polyurethane (NPC) and silicone compound (NCOC) modified with carbon nanotubes (MCNT) with a mass content of 1 to 9 %. MCNTs were synthetically produced by the CVD technology using Co-Mo/Al₂O₃-MgO (MCNT1) and Fe-Co/_2,1Al₂O₃ (MCNT2) catalysts. The analysis of experimental study results showed that the lowest specific bulk electrical conductivity (5×10^-10 Cm×cm^-1) was typical for polyurethane elastomer (1 mass. % MCNT synthetically produced using Fe-Co/_2,1Al₂O₃ catalyst). For the silicone elastomer modified with 9 mass. % MCNT1, the specific bulk electrical conductivity was 4×10^-1 Cm×cm^-1. The author identified the parameters of percolation of electrical conductivity model for NPC, NCOC with MCNT1 and MCNT2, taking into account the MCNT packing factor and electrical conductivity critical index. The maximum temperature field uniformity is typical for silicone elastomer with 7 mass. % MCNT2. Nonuniform temperature field in modified polyurethane-based elastomers can be caused by the local MCNT entanglement manifested in the creation of agglomerates or more dense electrically-conductive circuit packing, which, in its turn, results in the decrease in heat power. The heating temperature of nanomodified composites produced from NCOC 1 and NCOC 2 can vary from 32.9 to 102 °С. The author studied the modes of nanomodified elastomers heat generation in the range of 6 to 30 V, compared heat generation in the elastomer-based and ceramics-based samples. The study allowed identifying the best combination of the polymeric matrix and MCNT type. For the electric heater, it is the most efficient to apply silicone compound at the 7 % MCNT concentration and, depending on the feeding voltage level of 12 or 24 V, to use MCNT1 or MCNT2.