№ 10 (172) (2025)

The paper shows the use of projection stereolithographic 3D printing by digital light processing (DLP) to produce VTC-95-1 corundum ceramics. Based on data from thermogravimetric (TG) and differential scanning calorimetric (DSC) analyses, temperature regimes of debinding and clinkering have been developed. It is shown that graded debinding with a heating rate of 0,4...0,5 °C/min and exposures at 300, 375 and 470 °C, as well as subsequent clinkering at 1600 °C, ensured the achievement of a relative density of up to 95 % of the theoretical (3,47 ± 0,02 g/cm3). The water absorption was 0,69 ± 0,19 %, which indicates the predominance of closed porosity in sintered ceramics. The tensile strength during three-point bending of sintered samples ranged from 180 to 250 MPa, depending on the orientation of the layers relative to the loading vector: the maximum values (250 ± 30 MPa) were placed on record when exposed to a load along the printing axis. The Vickers hardness was 850 ± 25 HV. According to the results of the microstructural analysis, it was found that the developed heat treatment mode ensures the complete removal of the polymer binder and provides the production of sintered ceramics with a uniform grain size distribution, with an average grain size of 5,1 microns. Thus, the totality of the results obtained confirms the applicability of the considered additive method for forming the geometry of VTC-95 corundum ceramics.

Studies of special features for the formation of the structure and permanent joints properties during laser welding of 09mn2si sheet steel obtained after narrow-stream plasma cutting with a new PMVR-5.3 type plasma torch without additional machining of the gouging welds are presented. More efficient operation of the gas dynamic stabilization system for PTA of this plasma torch improves the cutting quality and, as a result, increases the absorption coefficients of radiation, penetration and laser welding performance. It is shown that a carbon dioxide laser welding contributes to a weld joint formation having a «dagger» shape and structure with a weld zone and an adjacent heat-affected zone (HAZ) on both sides of the CLW. At the same time, HAZ is heterogeneous in structure and consists of two subzones – overheating and normalization. In the weld zone, an increase in the hardness of the base metal is noted, and the distribution itself is symmetrical with respect to the CLW and fully reflects the location and extent of the crystallization and heat-affected zones in accordance with the data of metallographic analysis. In this case, the maximum value of microhardness is observed near the CLW, where a finely dispersed troostite-type structure is formed during crystallization. It is shown that the developed complex cutting and welding technology does not change the chemical composition of the steel in the weld vicinity. Based on the results of mechanical tests, conclusions were drawn about an increase in strength by about 30...35 % and impact strength with a slight decrease in the ductility of weld-in connections, as well as the absence of microcracks, unwelded spots and stretching of metal when stripping along fusion lines, which proves high quality of laser welding using the proposed technology.

The use of additive technologies in the production of parts for drone aircrafts has a number of advantages. Modern research confirms the need for mandatory verification of the strength properties of UAV components produced using additive manufacturing. This paper presents the results of tests for static bending of composite products obtained on Stereotech Fiber 530 V5 additive installations using three- and five-axis volumetric printing with continuous fiber reinforcement. To study the behavior of reinforced samples under the combined action of bending and interlaminar shear, static bending tests were performed in accordance with State Standard R 56810-2015. Seven groups of samples with different layer arrangements and reinforcement structures with PA6 thermoplastic in the form of a matrix material and reinforcement with Contifiber CPA filament based on Umatex UMT42S-3K filament were produced for testing. Different amounts of reinforcing filament were used for reinforcement. The samples were tested on a universal machine TRM-S 10 A1 with a device for testing three-point bending. The calculated values of the following strength indicators are given: tensile yield strength, interlaminar shear strength, flexural modulus of elasticity and interlaminar shear modulus. Diagrams of sample application of load during static bending tests are presented. It has been proved that the five-axis technology of additive manufacturing of reinforced products makes it possible to achieve an increase in the tensile strength under static bending from 1,5 to 2,5 times and a shear modulus from 2 to 4 times for products manufactured using the technology of five-axis printing with continuous fiber reinforcement of 10...20 % of the volume, compared with non-reinforced printed products and printed products reinforced by traditional three-axis technology.

An analytical solution for the elastic plastic contact strain problem is proposed in relation to the processes of finishing and strengthening machining of long thin-walled pipes by rotary run-in using cylindrical and pseudospheric toroidal rollers. Technological and instrumental support of these processes is viewed. It contributes to the improvement of pipe surfaces quality and eliminates errors in the geometric shape of the cross-section. The conditions for self-feed of pipes being treated are determined. An algorithm has been developed for calculating rational modes of surface plastic deformation of long thin-walled pipes in the Mathcad software package, taking into account their special geometry and increased flexibility, as well as strict requirements for products in terms of accuracy of diametrical size and quality of treated surfaces. The proposed method for calculating some rational technological modes of finishing and strengthening treatment has been experimentally tested on thin-walled pipes (sometimes flattened to 1 mm in diameter) made of 30 steel with a hardness of HB160 with an initial surface roughness of Ra = 1,25...1,6 microns. The pipes were run-in using a 3-roller running-in device at a rotational speed of about 80 rpm with cylindrical rollers. The calculated rollers decline in the shell of the running-in device and the technological parameters of the processing mode made it possible, with a five...eightfold overlap of the initial trace of the tool tip, to ensure not only the conditions for self-feeding of the pipe and high process productivity, but also to obtain the required riveting depths and strain hardening degree for its surface. At the same time, the surface roughness decreased by almost an order of magnitude (to Ra ≤ 0,2 microns) without noticeable traces of undulation and peeling, and the initial out-of-roundness of the pipe section was almost completely prevented. The developed rotary running-in technology for long thin-walled pipes is recommended for wide practical use in machine-building enterprises.

The article presents an assessment of the bearing capacity of oils containing additives based on zinc dithiophosphates (DF-11, DF-11k) and molybdenum dithiophosphates (PAF-4) during friction under boundary lubrication conditions. These additives are key components of modern lubricants, which provide the necessary tribological properties under severe operating conditions. The effect of the metal in the composition of dialkyl dithiophosphates on their tribological characteristics, in particular, on the bearing capacity, was studied. The studies were carried out on a standard four-ball machine using MS-20 petroleum oil as a base medium. To assess the tribological characteristics, the RD50-531-85 method was used, which allows determining the parameters of the linear approximation of the dependence of wear intensity on contact pressure: wear coefficient (k) and bearing capacity p0. This approach provides a more in-depth analysis of the tribological properties of lubricants, taking into account contact pressures during wear. The obtained results showed that zinc-containing additives provide a significantly higher load-bearing capacity of the lubricating layer (1235 MPa for DF-11) compared to the molybdenum-containing additive (1038 MPa for PAF-4). This indicates that they form a stronger and more wear-resistant boundary film. At the same time, the molybdenum-based additive demonstrated better antifriction properties, showing the lowest friction coefficient. Thus, the study shows the difference in the functional action of the additives: zinc dithiophosphates act as highly effective antiwear components that increase the ultimate load, while molybdenum dithiophosphate manifests itself primarily as a friction modifier. The obtained results are important for the targeted development of oil formulations for specific operating conditions.