Journal of Machinery Manufacture and Reliability最新文献

The processes of inertia and linear friction welding of heat-resistant nickel alloys VZh-175, EP-742, and EP-741 are discussed. The programs developed for analyzing the characteristics for linear and inertia friction welding are analyzed. The developed finite-difference models of the temperature field are also described, the main features of which are the movement of the friction boundary, which simulates the process of upsetting. The analysis of the kinematic, force, energy, and temperature characteristics of linear and rotary friction welding cycles is carried out. Comparison of linear and rotary welding cycles by 14 characteristics showed that the most informative in terms of data transfer are the upsetting rate and the upset value, the temperature at the joint, the specific thermal power, work on upsetting the unit volume, and the coefficient of friction.

The issue of structural synthesis of kinematic chains of spherical parallel mechanisms with linear drives is considered. Screw calculus is used to analyze the mobility of chains. Possible structures of chains, including three and four passive rotary kinematic pairs, are successively investigated. It is shown that, if there are three rotary pairs in the chain, the synthesis of a spherical mechanism with linear drives is impossible, and the use of chains with four rotary pairs for this purpose is possible if there is a planar dyad in the chain, including a driving prismatic pair and two rotary pairs.

In the calculation of a thin shell taking into account the transverse shear deformation based on the Timoshenko hypothesis, the results of the elastic–plastic stress state are compared using the constitutive relations in two variants with implementation of the step loading method. In the first variant, the constitutive equations are obtained by differentiating the relations of the plasticity deformation theory with the unchanged metric of the deformation process. The cumbersomeness of expressions is emphasized even with an unchanged metric of the deformation process. In the second variant, the constitutive equations at the loading step are obtained using the hypothesis of a proportional relationship between the components of deviators of the stress and strain increments without dividing the strain increments into elastic and plastic parts. A quadrangular fragment of the middle surface of the shell with kinematic nodal unknowns in the form of displacements and their first derivatives is adopted as a finite element. The efficiency of the developed constitutive equations for taking into account physical nonlinearity is shown using the example of calculation of the shell.

The dependences for calculating corrections for surface roughness crimpling of parts are proposed. The presented dependences allow one not only to determine the crimpling rate of the surface roughness at the time of joint formation, but also to limit the roughness rate to form the required contact area. Considering that Ra is standardized for critical surfaces of parts and Rz must be used to calculate the crimpling rate, the dependences for converting Ra to Rz are clarified. A comparative table is compiled confirming the correctness of the calculations in the range of Ra = 0.1–2.5 μm. Using the example of calculating and selecting a force fit, it is shown that different fits are obtained: ∅30H8/y8 with permissible values of surface roughness of the hole and shaft, and when using those specified in the drawing, ∅30H9/z9.

Based on study of the nominal operating modes of the bearing assemblies of the middle bridge of a 6 × 4 wheeled truck, a characterization of their thermal state has been obtained. The applicability of digital thermodiagnostics technology has been proven based on the diagnostic criteria established.

The relevance and significance of the concept of digital twins in the field of mechanical engineering, as well as their impact on production processes, are discussed. The goals and objectives of the study are defined, including the analysis of the conceptual apparatus, the use of digital twins at various stages of the product life cycle, and the assessment of their advantages and disadvantages. Phenomenological models of material damage management, their classification, and examples of successful application in real situations are examined. The requirements for the creation of a digital twin format are set out, including its structure and main components. Particular attention is paid to damage management issues and possible approaches to their solution, as well as to the assessment of the effectiveness of the proposed solutions. The conclusion highlights the importance of integrating digital technologies and provides recommendations for the implementation of digital twins aimed at increasing production efficiency, reducing costs, and improving product quality. Prospects for further research in this area include the development of analysis algorithms, the introduction of artificial intelligence, and the creation of digital model standards.

The nesting of semifinished and finished products made of titanium alloys by laser cutting is discussed. The world market of consumers and manufacturers of laser processing systems is studied. Experimental work is carried out on full-scale samples of hot-deformed plates and stampings. The productivity and quality indicators of the cutting plane surface are assessed. The results of studies of the quality indicators of the cutting plane surface and near-surface heat-affected zones are presented.

In mechanical engineering, the processes of cast blank production compete with the processes of metal forming. This competition intensifies when comparing the properties of structural materials such as steel and aluminum-based alloys. Based on the results of research and a comparative analysis of various solutions, a technological scheme of horizontal plunger die-casting, free filling of the mold cavity with liquid metal, and the application of high pressure to the crystallizing metal is developed. The option of casting and applying pressure aimed at suppressing ring-shaped casting shrinkage is considered. The advantages and disadvantages are determined. The possibilities of expanding the scope of application are named. The requirements for the equipment design and for the control means, process regulation and control are determined.

The results of theoretical studies aimed at justification of the stress–strain state of the high-load friction units in a MMS-70×23 Gidrofol mill for raw-material self-grinding at the first grinding stage are presented; the mill has a volume of 80 m³ and plain bearings restored by gas-thermal spraying. The operation of the coated plain bearing–rotating trunnion system has been demonstrated. The main directions of theoretical studies have been formulated and the directions of further experimental studies have been justified.

The existing types of drives for hydraulic emergency rescue tools used to perform special work during fires and to eliminate the consequences of road accidents are considered. The main shortcomings of existing drives have been identified. A new drive design is proposed and described, in which compressed air from the cylinders of gas and smoke protection breathing apparatus is used as an energy source. A three-dimensional model of the designed drive is presented. The main technical parameters of the developed design and the results of tests of the prototype are presented.