Stir zone material flow patterns during friction stir welding of heavy gauge AA5056 workpieces and stability of its mechanical properties

Introduction. Friction stir welding and processing are almost identical processes of severe plastic deformation at elevated temperatures. These technologies differ mainly in the purpose of its use: the formation of a hardened surface layer or producing a welded joint. However, it is known that both during welding and during processing of heavy gauge workpieces temperature gradients occur. As a result, the conditions of adhesive interaction, material plastic flow, and the formation of the stir zone change as compared to thin-sheet workpieces with fundamentally different heat dissipation rates. In this connection, the purpose of the work is to determine the regularities of the structure formation and stability of the mechanical properties in different directions in the material of 35-mm-thick aluminum-magnesium alloy samples produced by friction stir welding/processing. Research Methodology. The technique and modes of friction stir welding and processing of AA5056 alloy workpieces with a thickness of 35 mm are described. Data on the equipment used for mechanical tests and structural research are given. Results and discussion. The data obtained show the excess mechanical properties of the processing zone material over the base metal ones in all studied directions. Material structure heterogeneities after friction stir welding/processing of heavy gauge workpieces have no determining effect on the stir zone properties. At the same time, there is no clear correlation between the tensile strength values and the load application direction, nor is there any significant difference in mechanical properties depending on the location of the samples inside the stir zone. The average ultimate tensile strength values in the vertical, transverse, and longitudinal directions are 302, 295 and 303 MPa, respectively, with the yield strength values of 155, 153 and 152 MPa, and the relative elongation of 27.2, 27.5, 28.7 %.

Investigation of complex surfaces of propellers of vehicles by a mechatronic profilograph

Introduction. The technology of investigation of screw propellers complex surfaces, which include the marine and aircraft propellers of vehicles, mechatronic profilers for the implementation of reverse engineering, is considered. A review of the scientific literature shows that at present the problem of monitoring complex surfaces of products at various stages of its life cycle requires further research, since the use of available devices and methods does not always provide the necessary accuracy, technological effectiveness and sufficient information on measurements. The purpose of the work is to develop a new technology for studying complex surfaces of propellers, which include marine and aircraft propellers of vehicles by means of a mechatronic profilograph to implement reverse engineering. Methods. The paper considers the implementation of the innovative technology for studying complex surfaces of propellers using the developed mechatronic profilograph. This ingenious mechatronic profilograph is designed to measure the profile and study the shape of complex surfaces of various products, as well as to determine the geometric and morphological parameters of these surfaces. On the basis of theoretical studies the main design and technological parameters are found and the hyperbolic dependence of the angular rate of the laser sensor movement on the scanning radius is determined for the developed mechatronic profilograph. For example, if a constant pitch of the trajectory along the Archimedes spiral is 2 mm, the value of the sensor angular rate should gradually decrease from the maximum value of 2 rad/s to the minimum value of 0.574 rad/s, i.e. by 3.484 times. Results and discussion. It is revealed that the use of cylindrical coordinates for processing the obtained data by a profilograph is logical and has a number of advantages. An express analysis of the propeller surfaces with rotary symmetry is carried out and differences in the shapes of the surfaces of the propeller blades by deviation values in the longitudinal and transverse directions for different radii are established. On the basis of the experimental data, a two-factor power model describing deviations with a determination coefficient of 0.967 is obtained, according to its analysis, it is clear that on average the angle of deviation in the perpendicular direction to the radius  - increases from 0 to 0.3, and the angle of deviation along the radius  increases from 0 to 5.4.

Full-factor matrix model of accuracy of dimensions performed on multi-purpose CNC machines

Introduction. One of the main reasons that modern multi-purpose CNC machines do not use the capabilities of multi-tool processing is the lack of recommendations for design in this direction and, accordingly, for adjustment schemes. The study of the possibilities of multi-tool processing on multi-purpose machines is the subject of the work. The purpose of research: The problem of developing full-factor matrix models of dimensional accuracy and its sensitivity to the machining process is considered to increase the machining efficiency while ensuring machining accuracy using the technological capabilities of multi-tool machining on modern multi-purpose CNC machines. For this purpose, full-factor matrix models of the size scattering fields performed on multi-tool double-carriage adjustments have been developed, taking into account the cases of processing parts with dimensions that differ sharply in different directions, which are often encountered in practice, and in this case, the significant influence of the turns of the workpiece on the processing error, especially in directions with sharply different overall dimensions. Results of research: The developed accuracy models make it possible to calculate not only plane-parallel displacements of the technological system for double-carriage adjustments, but also angular displacements around base points, take into account the combined effect of many factors – a complex characteristic of the subsystems of the technological system (plane-parallel matrix of compliance and angular matrix of compliance), the geometry of the cutting tool , the amount of bluntness of the tool, cutting conditions, etc. As a result, based on the developed accuracy models, it is possible to obtain several ways to control multi-tool machining, including improving the structure of multi-tool adjustments, calculating the limiting values of cutting conditions. Based on the developed full-factor matrix models, it became possible to develop recommendations for the design of adjustments and the creation of an automated design system for multi-tool machining for a group of modern multi-purpose CNC lathes. Scope of the results: The results obtained can be used to create mathematical support for the design of operations in CAD-systems provided for multi-tool multi-carriage machining performed on multi-purpose machines. Conclusions: The developed models and methodology for simulating the machining accuracy make it possible to increase the accuracy and efficiency of simultaneous machining, to predict the machining accuracy within the specified conditions.

Structural and mechanical properties of stainless steel formed under conditions of layer-by-layer fusion of a wire by an electron beam

Introduction. As of today, additive technologies are among the most promising methods to manufacture various parts. They allow producing parts of complex shapes and provide their quality structure. The quality of the structure formed depends on numerous parameters: equipment type, its operation mode, materials, shielding medium, etc. Large international companies producing 3D-printers provide technological guidelines for working on it. Such guidelines include the information on the manufacturers of raw materials (printing powders), products their equipment can work with and the operation modes that should be used with such powders. These parameters should be investigated to use it on the domestic equipment developed within the framework of research programs and import substitution programs. The researchers and developers of 3D-printing equipment frequently run into a problem of using currently available raw materials for obtaining parts possessing minimal porosity, uniform structure and mechanical properties similar to that of at least cast blanks. One of the widely used materials for 3D-printing is stainless steel. It has high corrosion resistance, which reduces the requirements to the medium in which 3D printing is carried out. Manufactured stainless steel products have a good combination of strength and plastic characteristics. The aim of the study is to obtain stainless steel specimens possessing minimal number of micro- and macro-defects and uniform structure by the method of wire arc additive manufacturing using an electron-beam setup developed at Tomsk Polytechnic University. The methods to study the AISI 308LSi stainless steel 3D-printed specimens are as follows: XRD analysis, tomography, chemical analysis, metallographic analysis, microhardness testing. Results and discussion. It is established that the AISI 308LSi stainless steel specimens manufactured using the electron-beam 3D-printing setup contain no macro-defects in the bulk of the specimens. There are small microdefects represented by residual gas pores with the dimensions of no more than 5.2 μm. The microstructure of the specimens is formed close to that of coarse-grained cast austenite steels and consists of columnar grains of the γ-Fe austenite matrix and high-temperature ferrite. The interfaces between the wire layers are not pronounced; however, there are small differences in phase composition. Based on the analysis of the results obtained, it is established that the use of electron-beam 3D-printing for the manufacture of parts from AISI 308LSi steel gives a structure similar to cast austenitic steels. Macro-defects do not appear, and the number of gas pores is small.

Synthesis of titanium carbide and titanium diboride for metal processing and ceramics production

Introduction. Titanium carbide and diboride are characterized by high values of hardness, chemical inertness and for this reason are widely used in modern technology. This paper provides information on the synthesis of titanium carbide and diboride by carbothermal and carbide-boron methods, respectively, on the use of titanium carbide as an abrasive and in the manufacture of tungsten-free hard alloys, carbide steels, wear-resistant coatings, as well as titanium diboride in the production of cutting tools and ceramics based on boron carbide The aim of this work is to study the processes of synthesis of highly dispersed powders of titanium carbide and diboride, which are promising for the manufacture of cutting tools, wear-resistant coatings, abrasives and ceramics. Research methods. Titanium oxide TiO2, nanofibrous carbon (NFC), and highly dispersed boron carbide were used as reagents for the synthesis of titanium carbide and diboride. Experiments to obtain titanium carbide were carried out in a resistance furnace, and titanium diboride in an induction furnace. X-ray studies of the phase composition of titanium carbide and diboride samples were carried out on an ARL X-TRA diffractometer (Thermo Electron SA). The determination of the content of titanium and impurities in the samples of titanium carbide and diboride was carried out by the X-ray spectral fluorescence method on an ARL-Advant'x analyzer. The total carbon content in the titanium carbide samples was determined on an S-144 device from LECO. The content of boron and other elements for titanium diboride samples was determined by inductively coupled plasma atomic emission spectrometry (ICP AES) on an IRIS Advantage spectrometer (Thermo Jarrell Ash Corporation). The surface morphology and particle sizes of the samples were studied using a Carl Zeiss Sigma scanning electron microscope (Carl Zeiss). The determination of the particle/aggregate size distribution was performed on a MicroSizer 201 laser analyzer (BA Instruments). Results. The paper proposes technological processes for obtaining highly dispersed powders of titanium carbide and diboride. The optimum synthesis temperature for titanium carbide is 2,000…2,100 oC, and for titanium diboride 1,600…1,700 oC. The content of the basic substance is at the level of 97.5…98.0 wt. %. Discussion. A possible mechanism for the formation of titanium carbide and diboride is proposed, which consists in the transfer of vapors of titanium oxides to the surface of solid carbon (synthesis of titanium carbide) and vapors of boron and titanium oxides to the surface of solid carbon (synthesis of titanium diboride). Due to the high purity and dispersion values, the resulting titanium carbide powder can be used as an abrasive material and for the manufacture of tungsten-free hard alloys, carbide steels, wear-resistant coatings, and titanium diboride powder can be used for the preparation of cutting tools and ceramics based on boron carbide.

Application of digital image processing technique in the microstructure analysis and the machinability investigation

Introduction. The world is at the stage of creating an interdisciplinary approach that will be implemented in metallurgical research. The paper formulates the technique of image analysis in the study of processing at different depths from the mold-metal interface. The purpose of the work. Processing of a cast-iron workpiece within the first 3.5 mm of thickness from the mold-metal interface is a serious problem of solid processing. The study of machinability at different depths is a key requirement of the industry for ease of processing. Machinability will determine a number of factors, including tool consumption, workpiece surface quality, energy consumption, etc. The method of investigation. Image analysis is performed to determine the percentage of graphite in etched and non-etched samples. K-means clustering allows to create a new image from a given one with a clear separation of white and black areas by converting a digital image into a binary image using a threshold value for segmentation. The volume fraction of perlite, the volume fraction of graphite and the average size of graphite flakes in microns are used as input variables for the machinability of cast iron. Results and discussion. The output, that is, the segmented image, will be the input function for calculating the workability index using formulas. Thus, microstructural analysis will help predict the workability index of grey cast iron ASTM A48 Class 20. Using this method and the program, based on the microstructure, it is possible to predict in advance the characteristics of the machining of the part, taking into account possible changes in the casting process itself.

Dimensional analysis and ANN simulation of chip-tool interface temperature during turning SS304

Introduction. During machining, the resulting temperature has a wider and more critical impact on machining performance. During machining, the power consumption is mainly converted into heat near the cutting edge of the tool. Almost all the work performed during plastic deformation turns into heat. Researchers have put a lot of effort into measuring the cutting temperature during machining, as it significantly affects tool life and overall machining performance. The purpose of the work: to investigate the temperature of the chip-tool interface, taking into account the influence of cutting parameters and the type of tool coating during SS304 turning. The chip-tool interface temperature is measured by changing the cutting speed and feed with a constant cutting depth for uncoated and PVD single-layer TiAlN and multi-layer TiN/TiAlN coated carbide tools. In addition, an attempt is made to develop a model for predicting the temperature of the chip-tool interface using dimensional analysis and ANN simulating to better understand the process. The methods of investigation. Experiments are carried out with varying the cutting speed (140-260 m/min), feed (0.08-0.2 mm/rev) and a constant cutting depth of 1 mm. The chip-tool interface temperature is measured using the tool-work thermocouple principle. The Calibration Setup is designed to establish the relationship between the produced electromotive force (EMF) and the cutting temperature during machining. Statistical dimensional analysis and artificial neural network models have been developed to predict the temperature of the chip-tool interface. Tangential cutting force and chip attributes such as chip width and thickness are also measured depending on the cutting conditions, which is a prerequisite for dimensional analysis simulation. Results and Discussion. A tool made of TiAlN carbide with PVD coating had a lower temperature at the chip-tool interface than a tool with TiN/TiAlN coating. It has been observed that the chip-tool interface temperature increases prominently with the cutting speed, followed by the chip cross-sectional area and the specific cutting pressure. However, a lower cutting force was observed when using a carbide tool with a multi-layer TiN/TiAlN coating, which can be attributed to a lower coefficient of friction created by the front surface of this tool for flowing chips. On the other hand, the greatest cutting force was observed in uncoated carbide tools. It was noticed that the developed models allow predicting the temperature of the chip-tool interface with an absolute error of 5%. However, the lowest average absolute error of 0.78% was observed with the ANN model and, therefore, can be reliably used to predict the chip-tool interface temperature during SS304 turning.

Enhanced assessment of technological factors for Ti-6Al-4V and Al-Cu-Mg strength properties

Introduction. The strength of construction materials when used under cyclic loads is of great importance in design engineering. A significant number of factors that affect the fatigue resistance have predetermined the creation of numerous methods that consider such influence. Nondestructive methods that are based on the connection of the physical degradation of material with strain properties enable evaluating experimentally the fatigue properties of materials. Purpose of study: the analysis of the processes of energy dissipation and strain accumulation during the inelastic cyclic strain of samples, using the VT6 (Ti-6Al-4V) titanium alloy and the D16 (Al-Cu-Mg) aluminum alloy before and after the technological impact. The work experimentally investigates the physical processes of degradation of the VT6 and D16 alloy samples that accompany the process of fatigue failure in materials with homogeneous and inhomogeneous stress-strain states in the concentrator (in the form of a hole and a weld). Typical modes are used to reach the fatigue testing that determine the critical stress in a material sample – the stress at which physical properties (temperature, strain) change without reaching the fatigue failure of samples. Critical stress amplitudes in the cycle, based on the data obtained during the experiment and the results of mathematical simulation, are compared. The effect of stress concentrators on critical loads that a detail can withstand after a unit operation is estimated by the finite-element method (FEM). As a result, the effect of the operational and technological factors on critical stress determined by strain and temperature is estimated. Comparative tests of the VT6 and D16 alloy samples with and without stress concentrators showed that the amplitudes of critical stress decrease by more than 30% in comparison with the ones that are without stress concentrators. The low-cycle fatigue tests of the D16 alloy samples are carried out. Mathematical simulation of the cyclic strain of the samples is carried out using MSC.Marc package. The results of the cyclic loading tests, which show that the characteristics of the technological process reduce the amplitudes of the critical stress of the VT6 and D16 alloys and affect the fatigue properties of the D16 aluminum alloy, are discussed. Mathematical simulation corresponded positively to the experimental data. Such correspondence indicates the possibility of conducting qualitative numerical assessments of the beginning of the inelastic strain accumulation process in structures with stress concentrators under the cyclic stress and the increasing stress amplitude, using the typical sample made of hardening elastoplastic material.

Influence of the parameters of deforming cutting on the features of the resulting slotted filter structures

Introduction. Slot filters are in demand in petrochemical, machine-building, food, mining and other industries. DC is an edge cutting machining method based on undercutting and plastic deformation of the workpiece’s surface layer without its removal in the form of chip. DC stands out from the other slot structure forming methods for its capability of obtaining fine filters (slot width upwards of 20 µm) while maintaining relatively high productivity rate and being waste-free. Nevertheless, patterns of through slots cutting by means of DC had virtually not been investigated previously. The purpose of the work is to establish the influence of the main parameters of deformational cutting, namely feed and depth of cut, on features of through slots obtained, as well as identifying combinations of parameters that ensure the production of structures suitable for filtration. Method of investigation consisted of experiments on through-cutting of corrugations stamped on copper strips and a visual analysis of the structures obtained. Cutting through the corrugations by DC was conducted on a lathe while using a special attachment – a barrel which workpiece corrugated strips were wrapped around and fixed on with tension. Results and discussion. The resulting typical structures obtained under different combinations of depth of cut and feed are systemized and divided into the following groups: “0” – the absence of the through cut; “1” – uniform slots; “2” – “twinning” (pairwise convergence of slot walls), “3” – stripping of every second slot wall; “4” – non-regular or complete stripping of slot walls; “5” – uniform slots with a continuous burr (“skirt”) formed along the slot row on the internal side of the corrugation; “6” – uniform slots with a “skirt” opened incompletely. In the range of feeds 0.2 ... 0.4 mm/rev with increasing cutting depth, there is a transition from structures of group “1” to structures of group “2”, and the greater the feed, the greater the maximum depth of cut, at which uniform slots remain. Group “1” is assigned to the area of structures suitable for filtration applications, although it is characterized by the formation of individual burrs on the inner side of each slot. At lower feeds (up to 0.2 mm/rev) with further increase of the depth of cut another group of structures potentially suitable for filtering purposes is reached: groups “5” and “6”. With the “skirt” formed, individual burrs next to each slots are absent, and the shape of slots is cleaner. With a decrease in feed, the width of the resulting slots decreases. The least tool feed value, at which uniform slots are obtained, is 0.05 mm/rev which corresponds to 19 µm slot width. Establishing the causes of “twinning” and the formation of “skirts” requires further investigation.

Study of the stress-strain and temperature fields in cutting tools using laser interferometry

Introduction. The efficiency of the metalworking processes highly depends on the performance of the implemented cutting tools that can be increased by studying its stress-strain state and temperature fields. Existing stress analysis methods either have a low accuracy or are inapplicable for research during the operation of the tools made of materials with high mechanical properties. In addition, the study of temperature fields using known methods is difficult due to the small size of the cutting zone, high temperatures, and a heavy temperature gradient appearing during metal cutting. The purpose of this study is to develop new experimental methods for measuring the stress-strain and temperature fields in the cutting tool during its operation using laser interferometry. The methods include: obtaining interference fringe patterns using an interferometer with the original design, obtaining the tool deformation field during the cutting process by recording the changes in interference fringe patterns using a high-speed camera, processing fringe patterns with the separation of deformations caused by heating and cutting forces, and calculating temperature fields and stress distributions using mechanical properties and the coefficient of thermal expansion of the tool material. The advantages of the developed methods include: applicability under real operating conditions of the cutting tool, ability to study the non-stationary stress-strain state and temperatures during an operation, and achievement of a high spatial resolution and a small field of view for the investigated surface. Results and Discussion. The experimental study confirmed the efficiency of the methods. The results of the study included the fields of stresses and temperatures obtained during the orthogonal cutting of heat-resistant steel with a tool made of cemented tungsten carbide WC-8Co. The developed methods can be used to study the cutting tool efficiency at close to real conditions and in obtaining boundary conditions for the study stress-strain state of a workpiece material near the cutting zone.