№ 5 (155) (2024)
Materials science in mechanical engineering
MECHANISM OF THE ELECTRIC FIELD EFFECT ON THE PROCESS OF GREY CAST IRON INOCULATION
Аннотация
A diagram of an experimental installation for measuring the electrical resistance of a gray cast iron melt is presented, where a gauge based on a Kelvin double bridge is used. It is shown that the value of the specific electrical resistance of gray cast iron varies depending on the type of conditioning agent. Experimental data on the difference in specific resistivity values for various gray cast iron nucleating agents are presented. Changes in the values of electrical resistance under the influence of electric field treatment of inoculated cast iron melt are also given. Comparison of the strength values of gray cast iron with its values of the electrical resistivity of the cast iron melt after the electrical field exposure showed their simultaneous change. The decrease in the values of the electrical resistance of hot iron due to the electric field exposure is shown and it corresponds to an increment in the strength of inoculated cast iron. The effectiveness of the electric field exposure on the process of inoculation is determined by thermal ionization of the chemical elements included in the conditioning agent. The maximum increase of these parameters after electric field exposure when using FS75 nucleating agent is shown. The mechanism of the influence of an electric field on the cast iron solidification for the inoculation process of FS75, containing 75 % silicon in its composition, is described. The dependence of the efficiency of electric field exposure on the composition of the nucleating agent for gray cast iron is shown. A physical model of the effect of an electric field exposure on the process of cast iron inoculation is found. The possibility of influencing the hydrodynamic situation in the melt of gray cast iron and changing the rate of dissolution of nucleating agent particles by means of electric field exposure is given
Science intensive technologies in mechanical engineering. 2024;(5 (155)):3-8
3-8
Technology and equipment of metal processing by pressure
ISOTHERMAL EXTRUSION IN A CONE-TYPE MATRIX OF A RELAXING MATERIAL
Аннотация
The relations for calculating the deformation mode and force conditions of isothermal extrusion of blanks made of high-strength metallic alloys are proposed. Under isothermal deformation, the material is hardened and softened, which is associated with the manifestation of the viscous properties of the material (creep). In this regard, the state of viscoplasticity is taken on. The deformation state is accompanied by stress relaxation, which is greater the lower the speed (longer duration) of the operation. Based on the mechanics of deformation, the dependence of moulding conditions (deformation, force, damage to the work material) is expressed by analytical relations. The power balance of activity of forces results in a pressure estimation for isothermal exposure. In this case, a discontinuous field of path velocities is used, which consists of a block of deformations and rigid blocks. The blocks are separated by slip surfaces. Deformations occur in the deformation block and on slip surfaces. Since pressing leads to the occurrence of micro-damages, the damage rate of the coating material was estimated. In this case, the criteria of fracture kinetics are used: energy and deformation equations. The damage rate of the material depends on the speed and degree of deformation, or solely on the degree of deformation. For a number of materials, reducing the speed helps to reduce damage and, consequently, the possibility of increasing the degree of shaping of the primary blank. The relations for stiffness analysis of the stress pattern are given, on which the damage also depends. Calculations of the pressure and damage of the material under compaction for blanks made of titanium and high-strength aluminum alloys have been performed. It is shown that at low operation speeds on the appropriate hydraulic forging equipment, the exposure pressure decreases significantly. The aluminum alloy damaging is also reduced, and for titanium it depends only on the degree of forming.
Science intensive technologies in mechanical engineering. 2024;(5 (155)):9-13
9-13
Technologies of mechanical processing of workpieces
TOOL DEGRADATION EFFECT ON ROUGHNESS FACTOR IN THE PROCESS OF PHYSICAL MODELING OF CYLINDRICAL GEAR SHAVING AND ROLLING
Аннотация
The main issues related to the results of an experimental study aimed at modeling of the combined (cutting-deforming) finishing process of a gear processing, i.e. cylindrical gear shaving and rolling, under turning with a special combined cutting-deforming tool, which is a single-tip tool of a cylindrical work, divided into equal working areas. Due to the proprietary exploratory procedure used for prototype process, in one operation of a compact cylindrical work, a gear processing of a sufficiently large batch of horisontal wheels-representatives with average parameters, consisting of several thousand pieces, is simulated on a CNC lathe. The analysis of the results of the experiment was treated, allowing us to obtain information about gear processing of a large batch of gears in laboratory conditions. The roughness parameter of the work on workpiece areas is determined, the boundaries of tool degradation for this parameter are revealed. The revealed pattern of tool degradation appears to be the following: the prevailing wear of the tool occurs along the back surface due to its design feature, i.e. zero angle of its back, aggravated by the technological characteristics of the process (shaving - rolling), in which the back is involved in the surface plastic deformation, in particular, crushing a metal layer under the influence of a significant normal load. This results in frictional load taking place between its back surface and the surface of the proccesed workpiece. Tool degradation along the front surface, accompanied by its tool cutter blunting of its cutting edge, contributes to further deterioration of cutting process conditions (when stock removal of about 0.02 mm), and at the same time increases the proportion of surface plastic deformation (when shaving– rolling). This, as a result, increases the workpiece material share, which should be removed not by cutting, but by surface plastic deformation, thereby further redoubling a wear bit in its back surface.
Science intensive technologies in mechanical engineering. 2024;(5 (155)):14-24
14-24
ANALYSIS OF METAL-CUTTING MACHINES IN-TENDED SERVICE
Аннотация
The analysis of machining facility used for short-run production, large-scale or mass-production operations has been carried out. Their disadvantages are presented in the work, i.e., in a short-run production, superuniversal machining center units are used, being primarily made for processing techniques, but not for the surface of the part. Such machines, having excessive wide technological and technical capabilities, remain untapped in the workplace, becoming low effective in the application; in mass production, designed process-specialized machines can cover only a small part of the common typical surfaces, that means, there are no machines for making bearing arrangement, in mass production operational machines are designed with no reconfiguration, which makes their application impossible when there is some introduction of changes in the structure of the manufactured part. To eliminate these disadvantages, it is necessary to design specialized machines for manufacturing in all types of production of programme units for parts surfaces. Depending on the type of production, machines should be designed for the manufacture of different groups of surface modules (SM) types. In a short-run production, a large number of types of SM should be manufactured on one machine, and with an increase in the production cycle, the number of SM types manufactured on one machine should decrease. Taking into account the high frequency of sets of bases in manufactured parts, it is necessary to expand the group of specialized machines through their design for the manufacture of sets of bearing arrangements, where the production of their diversity is limited. The machine tool holding for the manufacture of all SM will allow changes to be made to the designing technological processes technique. So, technological operations should be aimed not at machining individual surfaces or groups of surfaces, but at one or more types of SM. This will improve the quality of manufacturing activity for parts production by reducing the number of operations, since one or more SM will be machined and it will reduce the labor intensity of their engineering process due to the use of a data bank of modules of process industries for the manufacture of SM.
Science intensive technologies in mechanical engineering. 2024;(5 (155)):25-30
25-30
Surface layer quality, contact interaction, friction and wear of machine parts
COMPARISON OF TRIBOLOGICAL PROPERTIES OF A DLC JOINTLY WITH STEEL / CERAMICS UNDER DRY FRICTION AND BOUNDARY LUBRICATION
Аннотация
. Studies conducted in the last decade having proven experience of many years of practical use in friction units of various mechanisms and machines used in the national economy, have shown that the effective way to ensure their longevity, reliability and energy conservation is to apply DLC coatings on the friction surfaces of contacting parts in these friction nodes. It has now been established that the effectiveness of the use of these coatings is determined to a large extent by the conditions of their operation and the materials of the contacting parts. In the presented article, friction pairs are compared in terms of anti-friction properties, in which the studied steel samples with an amorphous DLC coating applied to steel through an intermediate layer of titanium aluminitride wear out under conditions of dry friction and film lubrication. Standard balls made of bearing chromium alloyed steel and ceramics based on silicon nitride are used as a wearing coupled element. Tribological experiments are carried out on the well-known laboratory installation KT-2 with an upgraded friction unit, which allows for the contact of a wearing ball with three horizontally positioned rollers, on the cylindrical surfaces of which the coating under study is applied. The article provides an analysis of the results of these experiments. In addition to DLC coating tests, data on tests of uncoated and coated samples with only a layer of titanium aluminitride are provided for comparison. A harder coupled element material can significantly affect the tribological properties, destroying coatings, thereby reducing the positive effects of the antifriction properties of coatings, and even lead to increased wear due to the formed abrasive particles in the friction zone.
Science intensive technologies in mechanical engineering. 2024;(5 (155)):31-39
31-39
Technological support of operational properties of machine parts and their connections
ENGINEERING SUPPORT OF MATING SURFACES OPERATIONAL PROPERTIES IN THE COMPOUND FORMING TOOL ELEMENTS WITH REGARD TO SPECIFIED PRESSMOLD LIFE
Аннотация
Design and technological concepts are viewed at the stages of designing, manufacturing and joining process providing for the required reliability (durability) of mold elements. Recommendations are given for rationing and achieving the parameters of accuracy and quality of mating surfaces, taking into account the formation of the necessary operational properties at the main stages of the product life cycle. The factors that have the greatest impact on ensuring the correct and accurate location of forming tool elements have been elicited. The concept of determining the actual contact area and calculating the scale parameter, which provides a contact interface degree specification for conjugated surfaces, is presented. The hypothesis of the formation of reliability indicators is found, taking into account the manufacturing capability and technical capacity of production with the introduction of correction of the upper and lower dimensional deviations included in the dimension chains and ensuring the pre-set accuracy parameters of the master link.
The analysis of the operating conditions of the studied type of pressmold elements is carried out. The main operational properties that provide the required operating time for shaping part failures are identified and analyzed. Special attention is paid to the study of the structural features of such parts, a comparison of the integral and prefabricated structures is made, and also, contact stresses under the joining operation for the most promising of the latter are calculated for contact interface degree simulation. This will allow developing practical recommendations for any type of compound forming tool for the benefit of basic mechanical properties rate making, accuracy indicators, including deviation allowances in the correct geometric shape, including quality parameters of the surface layer at the designing stage,processing methods dispatch and modes setting at the manufacturing and testing stages and also suggesting the amount of static loading when assembling.
Science intensive technologies in mechanical engineering. 2024;(5 (155)):40-48
40-48