Vol 22, No 4 (2020)
- Year: 2020
- Articles: 12
- URL: https://journal-vniispk.ru/1994-6309/issue/view/19959
- Description:
Full Issue
TECHNOLOGY
Experimental Study of the Defect Layer on Workpieces, grown by the DMD method
Abstract
Introduction. At this time, new methods of manufacturing workpieces are gaining great popularity, for example, additive technologies. Methods for growing workpieces by sintering a powder with a laser make it possible to manufacture parts of complex shapes that are impossible or rather difficult to obtain by traditional methods, such as casting, forging, etc. However, the details, obtained by means of additive technologies, in particular the DMD method (Direct Metal Deposition), do not correspond with the accuracy requirements. Consequently, such workpieces require further processing by turning, milling or grinding. To design an operation for machining parts, it is necessary to know the machining allowances, the magnitude of errors formed during the blank operation, so that after its removal the processed part meets the requirements of the drawing. The purpose of the work: experimental study of the size of the defect layer in the near-surface layers of generative workpieces made of Stellite 6 and CuAl10Fe4, grown by DMD method, using microstructural methods. In the work, using a microscope, a study is carried out, which consisted in the visual determination of the defective layer, which differs in structure; measuring its size; carrying out a chemical analysis; determining the nature of the change in microhardness. The research method is a microscopic examination of deposited materials Stellite 6 and CuAl10Fe4 (CuAl10Fe4). From the pictures taken with a microscope, it is possible to establish the linear size of the defect layer. Results and Discussion. Vortex formations are found in the melting zone, its chemical analysis is carried out and it is found that the concentration of chemical elements in these areas changes and includes both elements of the powder material and the substrate material. Measurement of microhardness showed that it decreases with depth from the surface of the deposited material to the substrate. Thus, the use of the technique presented in this paper for microscopic studies of the structure, chemical composition and microhardness of workpieces, grown by the DMD method will allow to predict the value of processing allowances in the future, during the designing of mechanical processing operation of generative workpieces.
Obrabotka Metallov / Metal Working and Material Science. 2020;22(4):6-17
6-17
The Limits of Applicability of the Method of Discontinuous Solutions in the Study of Pipe Drawing Processes
Abstract
Introduction . Non-contact deformation of the workpiece material, which occurs along the boundaries of the deformation zone, is one of the main factors determining the energy-power parameters of pipe reduction processes. The most widespread practice in the design of metal forming processes is the method of discontinuous solutions, which makes it quite simple to take into account non-contact deformation in numerical simulation of processes. However, for most processes in the technical literature there are no systematic practical recommendations on the application of this method, which inevitably leads to a mismatch of theoretical principles and practice. The aim of the work is to determine the limits of applicability of the method of discontinuous solutions for processes of faultless drawing of pipes through a conical die, depending on the geometric parameters of the workpiece, tool, as well as the degree of deformation and hardening of the processed material. Research Methods. The model of the deformation zone for the process of flawless drawing is considered in two versions: by the method of discontinuous solutions and taking into account non-contact bends of the pipe wall. From the condition of the balance of the shear forces acting on the conditional shear surface and the bending moments caused by the bending of the pipe wall, under various deformation conditions, the boundary values of the thickness parameter are determined, at which it is advisable to carry out numerical simulation of the drawing processes using the discontinuous solution method. In this case, the calculations are performed separately for two sections of the deformation zone corresponding to the bending of the pipe wall at the entrance to and exit from the die. Results and discussions. The numerical implementation of the obtained dependences showed that at the entrance to the deformation zone, the boundary value of the thickness parameter increases with an increase in the taper angle of the die and the hood for the transition, but decreases with an increase in the anti-tension stress and the thickness parameter of the initial workpiece. At the exit from the deformation zone, the boundary value of the thick-walled parameter increases with an increase in the taper angle of the die and decreases with an increase in the stretch coefficient for the transition and the thick-walled parameter of the initial billet. If the parameter of the thickness of the initial billet exceeds the boundary value, then in numerical modeling it is advisable to use the method of discontinuous solutions. If it does not exceed, then other methods and models should be used. The results of a theoretical study can be used in the design of pipe drawing processes.
Obrabotka Metallov / Metal Working and Material Science. 2020;22(4):18-30
18-30
Technological Assurance of Fiberglass Composites Surface Layer Quality during End Milling
Abstract
Introduction. Today fiberglass is one of the most common composite materials. Therefore, its mechanical processing continues to be the subject of many studies. In many scientific publications, the influence of cutting modes and structural and geometric parameters of the tool on the roughness of the machined surface, cutting forces and wear of the cutting tool has been established. The purpose of this work is to study the effect of machining modes on delamination and roughness of fiberglass composites during end milling, as well as testing the hypothesis about the effect of torque on the delamination. The relevance of the study is due to the fact that delamination, along with roughness, has a significant impact on the quality of processing and subsequent assembly of the finished product. A criterion is proposed for assessing the magnitude of the delamination of composite materials during its machining. The results of experimental studies of the torque on the cutter, the relative coefficient of delamination and surface roughness from cutting conditions are presented. Methods: factorial experiment using an experimental assembly developed by the authors based on a piezoelectric torque sensor. The installation allows real-time recording of the change in torque during the milling process, depending on the modes of operation. Results and Discussion. A comparative analysis of the obtained dependences showed that the torque is directly related to delamination. To reduce the delamination, the depth of cut should be decreased, and in order to ensure the specified productivity, the feed and the rotational speed of the cutter should be increased. The presented results confirm the prospects of the developed approach aimed at machining new classes of composite materials.
Obrabotka Metallov / Metal Working and Material Science. 2020;22(4):31-40
31-40
Technological investigation of effect of machining parameter on tool life
Abstract
Introduction. The machinability is typical criteria to be investigated and different authors suggested different parameters describing its quantification. Different parameters i. e. speed, feed, depth of cut, tool work-piece combination, machine types and its condition, cutting fluid, machinist expertise, etc. are contributing directly to the tool life. The selection of the tool for the machining impacts greatly on the economic viability of the machining in terms of energy usage and tooling costs. The method of investigation. The current research emphasis mainly on tool life investigation when machining the mild steel specimens ISRO 50, BIS 1732:1989 at constant cutting speed i.e. 200 m / min. In the industries the mild steel material is commonly used for various products manufacturing. Considering the high demands on productivity and surface finish, machining at 200 m / min is the preferred. The computerized numerical control machine (CNC DX-150) is used for the turning. The four corner insert (TNMG 120408) is used for different machining times i.e. 10, 15, 20 and 25 minutes respectively. The flank wear of the tool is measured with calibrated optical microscope. The temperature of the tool corner during machining is continuously measured for possible impact of temperature on bonding properties of the tool insert and impact on red hardness. Results and discussion. The plot of flank wear vs. machining time will give the value of tool life. The other quality output parameter, such as surface roughness, is measured after machining, indicating surface irregularities in root means square value. Efforts have been made to identify the relationship of tool life, machining time, the quantity of metal removed, surface roughness, and tool bit temperature.
Obrabotka Metallov / Metal Working and Material Science. 2020;22(4):41-53
41-53
EQUIPMENT. INSTRUMENTS
Influence of Cutting Dynamic on the Selection of the Technological Regimes to Ensure Minimal Wear of Cutting Tools
Abstract
Introduction. The intensity of tool wear, as an increment of wear to the cutting path, characterizes one of the important processing indicators. It is used in the development of algorithms for controlling the cutting process, including the calculation of trajectories in CNC machines. As the cutting speed increases, there is a value at which the wear rate is minimal. It corresponds to the optimal value of heat production in the cutting zone, that is, the power of irreversible transformations of the energy supplied to cutting. Heat production depends on the dynamic system parameters that change along the tool path. In this regard, at the initial stage and during processing, it is necessary to coordinate the control with the properties of the dynamic cutting system. Subject. The paper offers a study and analysis of the relationship between the tool wear rate and the dynamic properties of the cutting process, and on this basis, the definition of technological modes in which the wear rate is minimal. The purpose of this work is to study the dependence of the tool wear rate on the initial and changing dynamic properties of processing along the path, and to create on this basis methods for matching technological modes with the current cutting dynamics to reduce the wear rate. Method and methodology of the work. In this paper, experimental and analytical methods are used to study the evolutionary changes in the properties of the system in relation to the development of tool wear. The developed mathematical models of the cutting system are presented, which differ from the known ones in that the power of irreversible energy transformations of the mechanical system in the interface of the back faces of the tool with the workpiece is additionally modeled. The dependence of the wear rate on the power of irreversible transformations, that is, on a given time interval in the increment of wear, is given. This takes into account the dependence of wear on the dynamic properties of the cutting system, including during its evolution. Results and discussions. It is shown that the properties of evolution are sensitive to small variations in the parameters of the dynamical system. These variations make significant changes in the wear rate. The paper reveals the dependence of wear on the properties of a dynamic system, that is, on its parameters, technological modes, beats, and other perturbations. Conclusions. The disclosure of the dependence of wear resistance on the dynamic properties of the cutting process characterizes new ideas about the factors that affect wear resistance.
Obrabotka Metallov / Metal Working and Material Science. 2020;22(4):54-70
54-70
Development and Research of a Profile Recorder for Measuring Deviations in the Shape of the Surface of Products by Laser Spiral Scanning
Abstract
Introduction. The paper deals with the development of a Profile recorder and measurement of deviations in the shape of the surface of products by laser spiral scanning. Analysis of the scientific literature shows that at present, the issues of monitoring and evaluating deviations in the shape of the surface of products require further research, since the use of well-known devices and methods does not always provide the necessary accuracy, manufacturability and sufficient information content of measurements. The research urgency is caused by the fact that existing methods of measuring form deviations of the surfaces does not allow to define a set of parameters with the required accuracy and submit it to two-dimensional and three-dimensional form. Objective: to develop a new method for evaluating a three-dimensional profile by implementing the method of laser spiral scanning and study the Profile recorder to improve the accuracy and productivity of measuring deviations in the shape of the product surface. Methods. The paper proposes a new method for evaluating a three-dimensional surface profile in order to directly determine the shape of the surface of products, to control the quality of the surface of products, regardless of its location. To implement the method, a Profile recorder of an original design is developed and investigated, which provides measurement of two parameters along the Archimedean spiral. Optimization of the design and the method of presenting information for measuring deviations in the shape of the surface of products are performed. Results and discussion. A method of statistical estimation of equations for describing the shape of metal surfaces based on the use of classical laws is proposed. In the case of a flat surface, deviations from flatness are evaluated: undulation, warping, twisting, convexity, concavity, curvature, etc. A Profile recorder is developed to implement the proposed method. The automated mechatronic device and the proposed method are tested on corrugated surfaces. Various equations obtained as a result of statistical processing were compared with each other, and the equation with the highest coefficient of determination is selected. The Profile recorder in Cartesian coordinates is studied in order to obtain reliable and accurate data for estimating shape deviations. The values of the deflection and the size of the corrugation along the height of the C-9 corrugated sheet are determined by laser spiral scanning.
Obrabotka Metallov / Metal Working and Material Science. 2020;22(4):71-81
71-81
Justification of the Flow Characteristics of the Recuperator for the Thermal Preparation of Machinery and Equipment Units
Abstract
Introduction. Machines and equipment in its composition may contain hydraulic systems to ensure the functioning of the main and auxiliary systems. It is known that a common disadvantage of hydraulic systems and drives is the dependence of the viscosity of the applied fluids on temperature. A noticeable part of technological machines and equipment is located in unheated or poorly heated industrial premises and a change in the viscosity of working fluids with a decrease in the ambient temperature can significantly affect the parameters of technological processes. An important factor in ensuring the stability of the technological processes parameters is the degree of preparation of machines and equipment for operation at low temperatures or in conditions of fluctuating temperature conditions. In this regard, the question arises of ensuring the required temperature of technical fluids before turning on machines and equipment, and maintaining the required thermal regime during the operation of its units and assemblies. One way to solve this problem is to use external heat sources. Various heat exchange devices can serve as such sources. In the heat exchange device, the heat carrier is heated, which is then fed into the heat exchange jacket of the machinery and equipment units. Both liquid and gaseous media are used to heat the coolant in the heat exchanger. In the latter case, the heat exchanger is called a recuperator. The efficiency of the recuperator is determined by its design and flow characteristics. There are methods for the analytical determination of both the design and flow characteristics of the recuperator, but these methods are quite laborious. The use of computer simulation of thermal processes makes it possible to successfully solve the calculation problem, and also significantly reduces the design time of heat exchangers. The aim of the work is to substantiate the flow characteristics of the recuperator for maintaining the thermal regime through computer simulation. The research method is computer simulation of thermal processes, which is implemented using the SolidWorks software package from Dassault Systems and its Flow Simulation application for simulating thermal processes in scientific research and engineering. Results and discussion. Simulation carried out in stationary and non-stationary modes made it possible to determine the effect of pump performance on the temperature of the coolant at the outlet of the recuperator. It is found that when the heat carrier flow rate is more than 20 l/h, its temperature does not reach the required values, despite the fact that the gases leaving the recuperator have a significant residual temperature. The efficiency of the recuperator is assessed by determining the exergy efficiency. Based on the data obtained, the most preferable are the pump productivity values lying in the range from 4 to 20 l/h.
Obrabotka Metallov / Metal Working and Material Science. 2020;22(4):82-93
82-93
MATERIAL SCIENCE
Influence of Technology of Hot Forming of Plates from Aluminum Alloys Al-Cu-Li-Zn and Al-Zn-Mg-Cu on Resistance to Fatigue Fracture
Abstract
Introduction. One of the primary objectives in the development of promising aircraft products is to reduce the weight of the aircraft structure. This problem can be solved by applying new low density materials such as aluminum alloys alloyed with lithium (for example, Al-Cu-Li-Zn) in the design of parts. The use of these materials in aircraft construction is limited by the processing technology, which must be such as not to damage the material and not reduce its strength properties. Such technologies include processing by pressure with heating, when creep processes are activated and the material passes into a state close to superplasticity. The purpose of the work: assessment of the effect of pressure shaping of aluminum alloys Al-Cu-Li-Zn and Al-Zn-Mg-Cu in creep mode on strength. The paper investigates the influence of the technology of pressure shaping of aluminum alloys Al-Cu-Li-Zn and Al-Zn-Mg-Cu on the resistance to fatigue failure. The work uses a method that allows to determine the ultimate stresses using diagrams of the accumulation of irreversible deformations; method of forming thick plates (40 mm) in the creep mode. The previously selected optimum temperatures for forming the plates are used. A non-contact coordinate measuring system is used to perform surface inspection after shaping. Fractography of the fracture of samples of alloy Al-Cu-Li-Zn and Al-Zn-Mg-Cu after fatigue failure is performed. Mathematical modeling of the deformation process of plates in creep mode is carried out in the MSC.Marc package. As a result, a conservative evaluation of the endurance limit for aluminum alloys Al-Cu-Li-Zn and Al-Zn-Mg-Cu is obtained. The shaping of thick plates in the creep mode is carried out. More than 80% of the board surface is formed with a deviation of less than 1 mm from the target size. Fatigue tests of samples made of molded panels of alloys Al-Cu-Li-Zn and Al-Zn-Mg-Cu are carried out, fatigue curves are plotted. The fractography of the surface of the fatigue fracture showed the presence of oxides in the samples of alloy Al-Cu-Li-Zn, in contrast to alloy Al-Zn-Mg-Cu. The results of fatigue tests are discussed, showing that the characteristics of the technological process of shaping and heat treatment do not deteriorate the fatigue properties of the investigated alloys. Comparative tests show that alloy Al-Cu-Li-Zn has higher fatigue characteristics. Mathematical modeling show that the use of the Boyle-Norton steady-state creep law is not enough to describe the process of plate forming. The necessity of setting the inverse problem of creep age forming is noted, where the coordinates of the punches of the loading device should act as boundary conditions.
Obrabotka Metallov / Metal Working and Material Science. 2020;22(4):94-109
94-109
Effect of Friction Stir Welding Mode and its Direction Relative to the Rolling Direction of 2024 Alloy on the Structure and Mechanical Properties of its Weld Joints
Abstract
Introduction. Friction stir welding conditions determines character of thermomechanical impact on welded material, so a critical alteration of even one of condition parameters can result in formation of defects and strength decrease of welded joint. Also an important factor is an orientation of welded material relative to a welding direction since it determines kinetics of material deformation and consequently its final structure and properties. Research efforts of friction stir welding properties generally consist in analysis of final properties of obtained weld joints and its correlation with parameters of welding condition. But to solve a problem of obtaining of weld joints with strength and quality, it’;s also important to estimate a welded material resistance to deformation from welding tool impact which could be achieved by monitoring a number of parameters directly in process of welding. The purpose of the work is to research an impact of welding condition parameters and an orientation of welded material’;s structure on friction stir welding process behavior and also on structure and strength of weld joints of 2024 aluminum alloy. Results and discussion. By monitoring the torque and welding force, it is shown that as the tool penetration force increases, the material's resistance to deformation increases. When welding is longitudinal to the direction of base metal rolling a torque and a welding force parameters decreases in value of 5-20%. An increase of welding speed provides a growing of material resistance to welding tool movement, at that, a direction of welding doesn’;t have a significant impact. With an increase of welding tool rotational speed, a material resistance to deformation decreases, a welding temperature grows and it results in growing of material’;s plasticization degree and in improvement of its mass transfer conditions. It is also shown that the welding conditions, which allows welding the 2024 alloy at a temperature of 450 – 500 ºС, provides the degree of plasticization of the material, at which welded joints with a high-quality structure and high mechanical properties are obtained. In this conditions a direction of welding in relation to the direction of base metal rolling has an impact: when welding is longitudinal to the direction of rolling the tensile strength of weld joints reaches a value of 92%, and when welding is transverse - 95% of base material tensile strength.
Obrabotka Metallov / Metal Working and Material Science. 2020;22(4):110-123
110-123
The Influence of the Rolling Direction of AA5056 on the Microstructure and Properties of Weld Joints obtained by Friction Stir Welding
Abstract
Introduction. Heat emission and plastic deformation during friction stir welding (FSW) cause profound changes in the microstructure and structural properties of weld joints. The grain size, crystallographic texture evolution and second-phase precipitate are the most important microstructural changes during welding of aluminum alloys, which largely influence the strength properties of weld joints. In addition to process-dependent parameters (instrument sump force, its rotation frequency, and travel rate) of the FSW process, a significant factor, determining the properties of the obtained weld joints, is also a mutual orientation of structural elements of the weld material and the direction of the instruments impact on the material during welding. In this regard, the purpose of the work is to analyze the combined influence of the direction of the initial rolling and the instrument pressure during FSW on the structure and properties of weld joints from the AA5056 aluminum alloy. Methods. Research methods are mechanical tests for statistical tension, microhardness as well as metallographic analysis of the structure of welded joints. Results and discussion. As a result, it is established that at low values of the axial force on the instrument (7 kN), defects such as the joint line and voids are observed in welded joints both rolling and transverse directions. When the load increases from 8 kN to 12 kN, defect-free weld joints with enhanced mechanical properties form. It is determined that the rolling direction of AA5056 during FSW does not influence the structure and tensile strength of the weld joints, but it influences the relative elongation and microhardness. It is shown that in the stir zone of the weld joint, obtained by FSW in the transverse direction of AA5056 flats, the relative elongation is 1.3-2 times greater, and the microhardness is by 4-10% greater than that in the stir zone of weld joints, obtained by FSW in the rolling direction of AA5056 flats.
Obrabotka Metallov / Metal Working and Material Science. 2020;22(4):124-136
124-136
Multiphase Cu-Ti Coatings coated by Plasma Vacuum-Arc deposition on Cu-Be Alloy С17200
Abstract
Introduction. Deposition of hard intermetallic coatings is an efficient technology to improve operating characteristics of Cu-Be alloys. PVD of coatings is widely used for surface engineering of constructive materials, deposition of wear and corrosion resistant surface layers. Multiphase and multicomponent coatings are considered as the most efficient hard coatings for surface engineering. In this research, Ti-Cu coatings are deposited by a vacuum-arc plasma-assisted method on hardened BrB2 bronze (alloy C17200) at a temperature of 320 – 330 oC. Processing resulted in ageing of Cu-Be alloy and surface hardening of material. The aim of the research is to analyze the microstructure, phase composition, and tribological properties of Cu-Be alloys modified with plasma-activated PVD coatings based on titanium, with the subsequent development of an effective technology for surface engineering and improvement of the mechanical properties of Cu-Be alloys. Results and discussion. Plasma-assisted PVD of Cu-Ti coatings on the surface of tempered C17200 alloy at 320 – 330 oC resulted in formation of multiphase coatings, consisting of Cu, Ti, CuTi and CuTi2 components. X-ray analysis revealed development of ageing process in Cu-Be alloy which resulted in formation of CuBe inclusions. Wear resistance of modified blocks is investigated. The main mechanism of modified blocks wearing is cracking of the coating with further formation of fine debris of base Cu-Be material. Wear debris is significantly smaller then debris of С17200 alloy without coating. Surface microhardness of blocks processed at 320 –330 oC is comparatively high (540 HV0.02 - 530 HV0.02). Wear resistance of blocks subjected to surface engineering is comparatively low probably because of small thickness of the coating (< 8 µm) and insufficient hardness of matrix material.
Obrabotka Metallov / Metal Working and Material Science. 2020;22(4):137-150
137-150
Effect of Mechanical Activation of the Powder Mixture on the Structure and Properties of Boro-Aluminized Low-Carbon Steels
Abstract
Introduction. Boro-aluminizing is one of the most effective ways to improve the performance properties (corrosion resistance, heat and wear resistance) of low-carbon steels. Solid-phase methods of thermochemical treatment (TCT) are carried out from saturating mixtures based on powder materials. Preliminary mechanical activation of these powders is one of the ways to improve the properties of the resulting diffusion layer. The purpose of this work is to determine the effect of preliminary mechanical activation of the powder mixture on the structure and properties of the boro-aluminized layer on the surface of low-carbon steels. Methods: The paper considers the results of research on the preliminary mechanical activation of the saturating mixture in the TCT of low-carbon steels (for example, St3 and 3Kh2V8F) based on powdered boron and aluminum carbide. The results of experiments on preliminary mechanical activation of the saturating mixture are shown, and the dependence of the particle size of the initial mixture on the duration of mechanical activation is established. Samples of steels with a diffusion layer after TCT are obtained. It is found that the process temperature has a significant effect on the thickness of the layers obtained. With an increase in temperature from 950 ° C to 1050 ° C on St3 steel samples, the layer thickness increases from 120 to 150 μm, on 3Kh2V8F steel samples – 105 and 140 μm with a holding time of 2 h and 4 h, respectively. The microstructure of the obtained samples is investigated; dependence diagrams of the microhardness distribution on the depth of diffusion layers are shown. The distribution of Al over the depth of the resulting boro-aluminized layer is established. As additional studies, the saturation capacity of the mixture after a single application in the TCT process is studied. Results and discussions. The principal possibility of using mechanical activation in TCT to obtain diffusion layers with specified strength characteristics is established. An increase in the duration and temperature of TCT in mechanically activated mixtures leads to an increase in the aluminum content in the layer.
Obrabotka Metallov / Metal Working and Material Science. 2020;22(4):151-162
151-162