No 1 (151) (2024)
Materials science in mechanical engineering
STRENGTH CONTROL OF GREY CAST IRON BY ELECTROGRAPHIC METHOD
Abstract
The experimental procedure carried out on a test installation to determine the electrical resistance value in the process of crystallization of cast iron is presented. A scheme of a test installation using a measuring circuit based on the Wheatstone bridge circuit to determine the electrical resistance value of crystallized cast iron is given. Recording measured data over time allowed constructing a graphical dependence of the change in the values of specific electrical resistance during the crystallization of gray cast iron. Experimental data on changes in the values of the specific electrical conductivity of a sample of gray cast iron during crystallization and their relationship to the amount of supercooling of the melt of this alloy are presented. The obtained dependence made it possible to identify on the curve of specific electrical resistivity change under supercooling of cast-iron test sample those areas, which were exposed to the cast-iron melt supercooling. The ratio of the initial and final values of the electrical resistivity under supercooling of cast iron allowed calculating the values of the relative electrical resistivity. Measurements of cast iron strength have shown that they are functionally related to the value of the relative electrical resistivity of gray cast iron, determined by the degree of supercooling of the cast iron melt. The use of this method will make it possible to predict gray cast iron strength and will allow reducing the amount of castings defective in terms of mechanical properties and at the same time increasing foundry production profitability.
Science intensive technologies in mechanical engineering. 2024;(1 (151)):3-6
3-6
Welding, related processes and technologies
HOT FORMING OF WELDED BLANKS OF ALUMINUM ALLOY SHEETS 1565 CHM
Abstract
The details of forming in cold or heated position for welded blanks of alloy 1565chM with a thickness of 8,0 mm, performed by friction stir welding, are viewed. It is found that welded joints of alloy 1565chM with a thickness of 8,0 mm, obtained by friction stir welding have high strength properties together with sufficient toughness. Thus, bending angle of the joints is 165…170 °. The strength factor of the welded joint is 0.96 of the strength of the base metal. At the same time, the temporary resistance of the weld metal exceeds temporary resistance of both: base metal and the welded joint in its value. The 1565chM alloy joints, made by friction stir welding have good formability under cold deformation. This special feature of welded blanks made of 1565chM alloy sheets is explained by the presence of a fine-grained recrystallized structure in a stir zone, which is formed as a result of heat impact and force action of the working tool on the material to be welded. Welding modes providing specified mechanical properties of the joints were used for welding shells (blanks) of gas cylinders (liners). Manufacturing technique for such cylinders includes the following operations: welding of the shell, calibration of the shell, quality control of the weld on the shell, jumping into a hot mold for forming bottoms, welding of fittings and general tightness control. Experiments on forming liners bottoms due to the shell jumping into a heated to 450...500 °C mold have shown that there is an intensive weld metal runout due to differences in the strain capacity of the weld metal and the base metal. This behavior of the weld metal during hot forming can be explained by superductility of the weld metal owing to the presence of a recrystallized ultrafine-grained structure. It was found that starting from a temperature of 400 °C, the relative elongation of the weld metal significantly exceeds the elongation value of the base metal. In case of 450 °C, this difference reaches
72 %. For the weld of the 1565chM alloy, starting from the heating temperature of 540 °C, an abnormal grain growth occurs along the entire weld.
Science intensive technologies in mechanical engineering. 2024;(1 (151)):7-15
7-15
Technologies of mechanical processing of workpieces
THE DEVELOPMENT OF COMPUTER-AIDED PLANNING PRINCIPLES FOR MULTIPRODUCT MACHINING PROCESSES
Abstract
The scientific principles of improving the system of automated planning of technical processes in the conditions of multiproduct machining industries are viewed. The study of modern approaches to automation of design and implementation of machining processes taking into account the production situation, is carried out. The use of the system of automated planning of multiproduct machining processes is justified, because its basic procedure includes a possibility of real-time interaction between subsystems design and implementation of technical processes, where the key place is occupied by a database on the technological capabilities of equipment and tooling. The interrelation of the system of automated planning of multiproduct machining processes with subsystems for assessing production manufacturability, monitoring technological equipment state, control and measuring procedures and assembly, is shown. The principle of designing multiproduct machining processes, generated for a given range of parts, taking into account the condition and capabilities of the production system, is presented. It is proposed to use the value of the total manufacturing time of a given range of parts as a generalized criterion for the efficiency of the production system. Ranking technique of design procedures according to the degree of influence of the decisions made on the generalized criterion of efficiency of the production system, is described. A model, based on genetic algorithms, is characterized, allowing the system being automatically adjusted to the conditions, changing during the design process. As a result, the efficiency of technological preparation of diversified production increases due to the rational distribution of manufacturing process for machining operation of parts to existing production facilities. The development of the work is aimed at increasing the level of design automation of machining processes and obtaining feedback on the current state of the production system.
Science intensive technologies in mechanical engineering. 2024;(1 (151)):16-22
16-22
INVESTIGATION OF MODE ELEMENTS EFFECT AND THE INFLUENCE OF MILLING CUTTER TEETH SPACE ON TECHNOLOGICAL PARAMETERS AND TEMPERATURE FIELD OF WORK ON A THIN-WALLED PARTS WORKPIECE
Abstract
When machining workpieces of thin-walled parts, the temperature field differs from the field, which is formed during massive workpieces treatment. The reason for this is that machining of a thin-walled billet is interfered with its surface, being opposite to the one under machining. It has a significant effect on the temperature field, since the intensity of heat removal from this surface into the environment is significantly less than heat removal into the underlying layers of a massive material blank. In this regard, the problem of finding a rational mode of the machining process of thin-walled workpieces is relevant. The aim of the study is to determine the effects of the elements of the milling mode of thin-walled workpieces and milling cutter teeth space on the technological parameters of the milling process of titanium alloy workpieces and to develop recommendations for choosing this milling mode. For this purpose, a numerical modeling of the technological parameters of the milling process of blanks of massive workpieces and thin-walled parts made of titanium alloy, was performed experiencing various combinations of feed to the milling cutter tooth, cutting speed and milling cutter teeth space. When machining a thin-walled workpiece, due to less intense heat removal from the cutting zone into the workpiece, the temperatures in the areas of chip contact with the front surface of the tooth, the back surface of the tooth with the workpiece and the temperature of the workpiece itself are higher than when in a massive workpiece treatment. The patterns of changes in the parameters of the milling process of thin-walled workpieces depending on the feed, cutting speed and the milling cutter teeth space are established. With a larger tool stepover, the average and maximum temperatures in the areas of chip contact with the front surface of the tooth and the back surface of the tooth with the workpiece are lower in most of the combinations of mode elements used. Equations that establish the effect of feed on the milling cutter tooth, cutting speed and spacing of teeth on the parameters of the machining are obtained. The results of the study will allow choosing a rational milling mode and spacing of teeth in the work on workpieces of thin-walled parts made of titanium alloy.
Science intensive technologies in mechanical engineering. 2024;(1 (151)):23-29
23-29
Surface layer quality, contact interaction, friction and wear of machine parts
MICROGEOMETRIC PARAMETERS EFFECT OF THE SPHERICAL ROLLER SURFACE ON BEARING SOUND PRESSURE AND VIBRATION
Abstract
In a production environment of JSC UPC Volzhsky it is shown how to increase the vibration discharge of bearings with conical rollers due to the use of rollers with the specified microgeometric parameters of the spherical surface made in the general production flow. The sphere is formed under the combination of rough grinding, finish grinding and final grinding using an assembled abrasive tool consisting of three rolls of various characteristics. It was found that in a bearing, with sequential replacement of rollers, where sphere roughness varies in the range of 0.10 Ra ≤ 0,.20 microns for rollers with roughness Ra ≤ 0,10 microns, the average value of the microgeometric parameters of the roller sphere in bearings (Ra, undulation W, deviation of circularity Δ) decreases by 2,4 – 4,3 times. The impact assessment of bearing rollers set having different parameters of the microgeometry of the spherical roller end on the sound pressure and vibration of the bearing was carried out. It was found that with an increase in the number of rollers with microgeometric parameters of the sphere closer to the lower edge of the tolerance field, the values of the overall vibration level, the vibration level in the third frequency band and the sound pressure level of the bearing improved. A statistical analysis of these parameters was carried out. The significance of the analyzed factors and conditions for increasing the vibration discharge of the bearing while ensuring processing modes within the framework of the current technological process are determined. Correlation and functional relationships between the average values of the microgeometric parameters of rollers spheres in bearings and the parameters of sound pressure and vibration were found.
Science intensive technologies in mechanical engineering. 2024;(1 (151)):30-40
30-40
FRACTAL DIMENSION OF A DISCRETE CONTACT
Abstract
. Contact interaction ability rating for engineering surfaces and their fractal models is carried out. Fractal models describe roughness component geometry properly, they are adequate to the initial engineering surfaces and possess a random component when modeled, which makes it possible to generate a new surface with the desired geometric parameters at all times, allowing the study of the contact interaction of surfaces to be carried as many times as necessary. When solving contact problems of rough surfaces for simplification of calculations, the replacement of the initial contact with the interaction of a smooth surface with a surface having an equivalent roughness, necessary to be determined, is usually used. The paper outlines the principles of finding the fractal dimension of engineering surfaces, as well as an equivalent surface in contact with a smooth one, when the conjugation of both is equivalent to the contact of the initial surfaces. At the same time, it is shown in this work that for anisotropic initial surfaces there are completely different parameters of contact interaction in different directions of their combination, which must be taken into account in the analysis and modelling. The fractal dimension of the equivalent surface was done using the well-known "perimeter-area" method, which, when determining the contact parameters, including the fractal dimension, allows taking into account the direction of the processing traces. Thus, this paper presents a method for determining the fractal dimension of both the surface and the fractal object, and also a contact spots map, an area ratio turndown for the actual contact area to the area of the maximum spot is shown as well, a procedure for estimating the fractal dimension necessary to determine the parameters of the contact interactions of rough surfaces, is proposed.
Science intensive technologies in mechanical engineering. 2024;(1 (151)):41-48
41-48