Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Calculation of wheel path for 3+2-axis grinding of brazed carbide profilemill cutters for wood and plastic
No full textBrazed carbide profile mill cutters are widely used in the machining of wood, wood materials, and plastic to form various functional and aesthetic surfaces. Tools of this kind are used in serial and mass production and they are built today using very costly 5-axis grinding machines supported by specialized CAM software that is very expensive too. The paper first developed the possible concept of 5-axis grinding of brazed profile mill cutters using universal diamond grinding wheel shapes. The developed concept of 5-axis grinding served as a basis for the developed approach for 3+2-axis grinding of the brazed formmill cutters which is the essence of this paper. Verification of this set approach of 3+2-axis grinding is performed on a developed functional prototype of a simple 3+2-axis grinder (Axes XYZ are CNC controlled, axes B and C are unpowered axes and have fixed positions during grinding). Based on the established 3+2 grinding strategy complete grinding of a complex profile has been performed on a developed functional prototype. Shape and measures of the cutting edge profile achieved by grinding are inspected on an optical measuring system and showed exceptional results. The established 3+2-axis method of grinding
is an economically successful alternative to costly 5-axis grinding machines, as well as to specialized software, presented in the paper through experimental and practical application
Influence of geometry parameters on shaft's load-carrying capacity
No full textThe load-carrying capacity of shafts is a critical factor in the design and performance of various technical systems, ranging from industrial machinery to all kinds of transmissions. This paper presents a comprehensive study aimed at understanding and quantifying the influence of key factors, including material durability, shaft diameter, surface roughness, stress concentration and the distance between shaft supports, on the load-carrying capacity of the shaft. The load-carrying capacity criterion is the fatigue safety factor. The paper offers a systematic exploration of the influential factors affecting shaft load-carrying capacity, both individually and in combination. The paper concludes by considering the simultaneous influence of all the aforementioned factors. A composite factor is introduced, representing the cumulative effect of material and geometry parameters. This composite factor allows for a holistic approach to shaft design, enabling engineers to make informed decisions that maximize load-carrying capacity while minimizing material usage and manufacturing costs
Programming methods and program verification for 3-axis reconfigurable hybrid kinematics machine
Get PDFThis paper presents programming methods and program verification for the 3-axis reconfigurable hybrid kinematics machine MOMA V3, which represents an educational desktop milling machine with a horizontal position of the main spindle. The paper considers the different programming and program verification methods. For programming used CAD/CAM system PTC Creo, specialized CAM software CUT3D and new programming method based on STEP-NC. Program verification is based on tool path simulation, material removal simulation and virtual machine simulation. The paper presented the virtual machine in the programming system and the virtual machine integrated with the LinuxCNC control system. Final verification was achieved during the testing on machine by machining the selected workpieces which programmed with different programming methods.ISSN: 2620-2832
e-ISSN: 2683-4111 (On-line)
Co-Editors in Chief: dr Miladin Stefanović, dr Slobodan Mitrovi
Linear systems in Gauss-type quadratures for variable-sign weight functions
No full textWe consider a recently proposed Gauss-type quadrature formula with respect to a weight function that changes sign in the interior of the integration interval. An important step in its construction is to introduce a modifier function used to transform the given integral into a sum of one integral that does not cause a quadrature error and the other integral with a property that the points from the interior of the integration interval at which the weight function changes sign are the zeros of its integrand. Determining a modifier function requires solving an associated system of linear equations. For the same integral, different modifier functions can be chosen, and hence different linear systems can be obtained. From a theoretical perspective, only necessary is that the associated system has a solution, but from a computational perspective, it is also important that the associated system is not too ill-conditioned and that the structure of its matrix is as simple as possible. We analyze the conditions under which it is guaranteed to obtain, for instance, a system with a Vandermonde matrix or a system with an identity matrix. We also give examples where systems with an arbitrary matrix are obtained, both those that have and those that do not have a solution
Pressure Distribution in Gas Microbearing Modeled with Fractional Derivatives for all Rarefaction Degrees
Get PDFVelocity slip boundary condition for all Knudsen number values in microbearing gas flow is modeled by fractional derivative. For this purpose, a variant of Caputo derivative with the variable order α which depends on the local value of Knudsen number is applied. Such a universal boundary condition is implemented in the solving procedures of continuity and momentum equations, which leads to the general corrected Reynolds lubrication equation for all rarefaction degrees. An appropriate transformation of the variables enabled obtaining an analytical solution for mass flow rate and pressure distribution in the microbearing. The presented solution is in an excellent agreement with the solutions based on the kinetic theory for all regimes: continuum, slip, transition, and free molecular flow
Pareto Optimization as the Basic for Selecting Robotic Mechanic Assembly Technologies
Get PDFThe task of selecting robotic mechanic assembly technologies (RMAT) is considered as a multi-criteria optimization task, which in this formulation is solved on the set of previously obtained solutions regarding the selection of RMAT. The purpose of the paper is to increase the efficiency of technological preparation of robotic mechanical assembly production of machine and instrument engineering due to a new approach to the selection of RMAT using Pareto optimization and the peculiarities of the selection task formulation. The novelty consists in the further development of a science-based approach to solving multi-criteria selection task, based on the first proposed formalisms of the specified process, which reflect the peculiarities of the selection task formulation, its meaningful essence and the content of the Pareto optimization method. The practical value of the research lies in the proposed engineering- acceptable approach to solving applied multi-criteria selection tasks on the example of RMAT selection, which is invariant to the statement of the selection task, the dimension of the task, and its meaningful essence. The methods of discrete optimization, fuzzy multi-criteria selection of alternatives, and the Pareto optimization method were used for the research. The main results of this work consist of the development of formalisms and the demonstration of the efficiency of the proposed approach for the applied task of RMAT selection. The peculiarity of the developed approach is the combination of Pareto optimization, performed on a discrete set of local criteria. Directions for further research are presented
NUMERICAL MODELLING OF POOL AND FLOW BOILING IN TWO-PHASE SYSTEMS OF STEAM GENERATORS
No full textBoiling is an effective heat transfer process for cooling surfaces. It has been widely investigated due to its application in thermal and nuclear power engineering, as well as in various equipment in refrigeration and process industry. The complexity of the boiling process is reflected in the fact that multiple bubbles grow at heated wall and different micro/nano conditions affect heat transfer mechanisms in contact of superheated liquid and heated wall. In the literature, numerical modelling of pool boiling is based on common mechanistic wall heat flux partitioning approach, where all boiling mechanisms such as single-phase convection, quenching and evaporation exist in the same control volume. In these models, the exact location of bubbles are not known, so authors cannot predict important boiling quantities such as void fraction distribution in the pool and the wall temperature under the bubble. The pool boiling model presented in this paper overcomes the mentioned shortcomings. This model simulates discrete bubble nucleation sites, a corresponding two-phase mixture pattern over heated wall surface and, due to the applied conjugate heat transfer modelling, enables insight into transient temperature field at the heated wall surface (Figure 1).
The numerical procedure takes into account the conjugate heat transfer coupling [1,2] and it considers the influence of the liquid film thickness in the two-phase mixture at the wall surface on the heat flux. Therefore, the developed method predicts boiling curves and two-phase mixture dynamics in the pool boiling, along with temperature transients in the heated wall. The pool boiling model is validated against experimental conditions and showed that the model can predict the void fraction distribution in the pool as well as the mean wall temperature [1], [2].
The second model presented in this paper is flow boiling model [3]. Numerical simulations of the flow conditions of the two-phase mixture on the secondary side of the steam generator are performed due to the efficiency and safety of different types of the steam generators [4]. Therefore, for its reliable operation, it is necessary to look in detail at all flow and thermal effects that occur. Today, during the development and design of steam generators, more and more complex requirements are set for generating steam on heating surfaces that are exposed to high values of heat flux. Such conditions can lead to a critical heat flux, which is accompanied by thermal and mechanical damage to the heating wall material or dryout and loss of the heat sink on the cold fluid side. Based on computer simulations of boiling, it is possible to investigate complex mechanisms that affect parameters and equipment during steam generation. The model presented here is validated with two experimental installations of vertical steam generators, one with freon as working fluid and the other with water. The void fraction distributions for these two steam generators are presented in Figure 2
MODELLING OF THREE-DIMENSIONAL THERMAL-HYDRAULICS OF HORIZONTAL STEAM GENERATOR
No full textThe horizontal steam generators (HSGs) are applied in the VVER nuclear power plants equipped with the pressurized water reactor (PWR). The HSG transfers heat from the nuclear reactor coolant to the feedwater, which is heated and evaporated on the HSG shell side. The HSG heat transfer area is composed of the horizontal U-tube bundles connected to the hot inlet header and cold outlet header, which are both positioned vertically. The boiling feedwater flow in the large volume of the HSG shell side is self-organized in complex natural circulations loops. Experimental investigation of the two-phase flow on the HSG shell side is difficult in real operational conditions. However, sophisticated two-phase flow models enable numerical simulation and analyses of these complex conditions, and the obtained results supports design of reliable operation and nuclear power plant safety.
This paper presents a comprehensive numerical modelling approach for simulation of three-dimensional thermal-hydraulics of horizontal steam generator (HSG). The model incorporates governing equations including the continuity equations, momentum conservation equations and energy conservation equations. Two separate fluids are observed: the reactor coolant flowing through the generator tubes and the feedwater on the shell side [1]. For the shell side, a two-phase model is employed to separately account for liquid and steam phases, with closure laws utilized to fulfil governing equations. The numerical simulations are conducted using the in-house program 3D-ANA, which enables detailed analysis and visualization of flow phenomena within the steam generator. Through this approach, the complex interplay between flow dynamics, heat transfer, and phase change phenomena within the steam generator is captured with high fidelity. Results obtained from numerical simulations are verified through comparison with experimental measurements. The proposed numerical framework provides valuable insights into the complex behaviour of horizontal steam generators, facilitating the optimization of design and operational parameters to enhance efficiency and safety in nuclear power plants.
The investigation of the three-dimensional thermal-hydraulics of horizontal steam generators has yielded results indicative of notable congruence with experimental data. The calculated predictions demonstrate a high degree of similarity with observed phenomena, suggesting the reliability of the employed modelling techniques (Fig. 1). Crucially, the findings assure the operational safety of the HSG, as evidenced by the absence of local dry-outs within tube bundles and the maintenance of moderate liquid and steam phase velocities that do not lead vibration-induced instabilities (Fig. 2). These outcomes underscore the robustness of the analytical framework employed and emphasize the imperative of rigorous thermal-hydraulic assessments in ensuring the integrity and efficiency of steam generator systems
A comparative study on the slow pyrolysis of Miscanthus (Miscanthus×giganteus Greef et Deu.) cultivated on agricultural and contaminated soils: Assessment of distribution of final products
No full textThis study aims to investigate the slow pyrolysis behavior of uncontaminated (MSC-I - reference) and heavy metals contaminated (MSC-R) samples with heavy metals from the tailings of a Pb-Zn-Cu flotation mine, consisting of whole stems of Miscanthus. Physicochemical properties of raw materials were investigated through instrumental characterization techniques (Atomic Absorption Spectrometry (AAS), Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR) spectroscopy, and X-ray diffraction (XRD)), while the pyrolysis process was monitored by simultaneous thermal analysis techniques (thermogravimetry (TG) – derivative thermogravimetry (DTG)), coupled with Mass spectrometry (MS), for evolved gas analysis. After determination of the lignocellulose content (cellulose, hemicellulose, and lignin) and extractive of the MSC-I and MSC-R samples, it was found that Pb, Zn, Fe, and Mn in MSC-R lead to very fast decomposition of extractive fraction, which facilitates their distribution in formed bio-char, together with lignin char-participation, acting catalytically. It was established that a much greater fraction of extractives decomposition products and non-volatile heavy metals are incorporated in MSC-R bio-char increasing its yield (23 %), compared to MSC-I bio-char yield (21.5 %). It was identified that MSC-R has increased production of H2, CO, and CO2, while decreased production of CH4, influenced by Fe (Fe has a significant positive effect on CO2 evaluation during MSC-R pyrolysis, enhancing decarboxylation process). It was established that CH4 reforming reactions catalyzed by iron additionally affect methane reduction, and increase production of H2, compared to the reference sample. Isoconversional kinetic analysis showed that pyrolysis reactions profile was strongly conditioned by the presence of heavy metals, such as Cd, Pb, and Zn, because they affect the modification of biomass lignocellulosic structure. Also, it was found that small amounts of Cd present in MSC-R can increase pyrolysis activation energy of three pseudo-components, and inhibit their deoxygenation, thus increasing yield of bio-char.Grant No᾽s. 451-03-66/2024-03/200026, 451-03-65/2024-03/200105 and 451-03-66/2024-03/20001
OPTICAL METHODS APPLIED FOR TESTING PIPE RING SPECIMENS
No full textThe Optical methods can be highly useful for analysing Pipe Ring Tensile Specimens (PRTS) since they offer an accurate and non-destructive method of evaluation. Optical technologies have several uses, such as Digital Image Correlation method (DIC method), thermal imaging camera, and 3D scanning. The DIC method is used to measure stresses and full-field displacements. DIC analyses a speckle pattern that is applied to the surface of the specimen and can provide detailed information on strain distribution, deformation gradients, and likely failure spots. An infrared thermal imaging camera can be used to detect defects in pipe specimens, such as
fractures or delamination, by tracking the distribution of surface temperatures. Temperature anomalies can indicate areas of intense stress or material degradation. A 3D scanner is a device that uses the shape, size, and texture of physical objects to digitise them into three-dimensional digital representations. The investigation focused on five distinct PLA PRTS. The study describes how to evaluate PLA PRTS using DIC method, thermal imaging camera, and a 3D scanner. The evolution of strain was monitored using the 3D Digital Image Correlation approach. Using a thermal imaging camera, the temperature field change in the PRTS was investigated during the test. In order to verify the cross-sectional shape of the PRTS after a fracture, 3D scanning was performed on each specimen