Vol 21, No 2 (2019)

Introduction. Threads manufacturing in mass production is based on non-waste methods of plastic deformation. For medium-and small-scale production, methods of thread cutting with taps, dies, thread chasers, thread mills, thread cutters have become widespread. For all known methods of thread cutting, the problem is to obtain threads on the material with high plasticity, especially on thin-walled tubes. A universal method of obtaining threads of various diameters and pitches is threading on lathes using thread cutters. A significant disadvantage of threading by cutters is the multi-pass processing, which significantly reduces productivity. There is a relatively new method of deformational cutting (DC) based on both the cutting process and the process of deformation of the undercut layer. In the article, the modification of the DC method is considered as an alternative to the traditional cutter threading based on the material removal from the thread grooves. The purpose of the work: approbation of the DC method as a method of obtaining threads on ductile metals in one pass of the tool with a minimum amount of material to be removed as a chip. The tasks of the work: theoretical analysis of the process of redistribution of material in the process of DC, identification of the main laws and features of thread formation, analysis of the threads obtained. In this paper, the outer threading of copper tubes by the DC method but having tool feed to the deforming edge is studied. Methods of research are the analysis of geometric parameters obtained threads and metallographic studies, including the measurement of the distribution of hardness on the threaded profile. Results and discussion. For DC uses a special tool that provides the cutting process of the main cutting edge, and eliminates the cutting process on the auxiliary edge, which is deforming edge. In DC process the layer cut by the cutting edge is squeezed out onto the treated surface in the form of a ridge, which takes the final shape of the threaded profile on the next turn of the workpiece. Conclusions: Theoretically justified and experimentally confirmed the designation of processing parameters to obtain a threaded profile of the required geometry. The proposed method of obtaining threads mediate between the methods based on the cutting process (removal of the workpiece material) and the process of plastic deformation. The main difference from conventional thread cutting is that in the process of DC there is a plastic redistribution of the material from the volume of the thread grooves to the volume of the thread ridge. The main difference from the thread rolling is that in DC new surfaces are formed, which is peculiar for the cutting processes. In the structure of the material of the threaded profile there are zones common for both processes of plastic deformation and conventional cutting. The large value of tool rake angle on the cutting edge and improved metal flow conditions on the tool face significantly reduce the load on the workpiece to be processed. In contrast to grooving with a threaded cutter, the proposed process allows threading in a single pass of the tool. In practical terms, the method can be used for single-pass cutting of threads with a cutter on ductile metal.

Introduction. One of the methods for the vibration diagnosis of fatigue cracks in the airframe metal elements is based on the analysis of the monitor objects forced oscillations portraits. The assessment of the reliability of this method in relation to real structures is an urgent task. Objective of the work: to assure the reliability of cracks detecting in metal structures by nonlinear distortions of oscillations portraits. Research technique. With the help of harmonic sources, forced oscillations of the diagnosed structure are created and recorded by acceleration sensors. Initially, the acceleration sensors are placed with condensation in the most loaded areas, which are determined by the calculations results or in vibration tests. Then, the sensors positions can be shifted to the defect locations. The signal of each sensor is represented as an oscillations portrait, the vertical scanning of which is proportional to this signal, and the horizontal one – to the first harmonic of the signal, phase shifted by π/2. Such an oscillation portrait is a circle for a linear dynamic system. The fatigue crack initiation is accompanied by nonlinear distortions of the oscillation portraits because of the collision of its edges and dry friction at the tips. For the numerical evaluation of distortions, the first harmonic is subtracted from the Fourier series for the oscillations portrait; the absolute maximum for the oscillation period is determined in the series remainder, the maximum value related to the first harmonic amplitude and is taken as the distortion parameter. Distributions of the oscillation portraits distortion parameter are built over the surface of the test object. Locations of cracks are determined from the locations of the distortions local maximums. At the same time, the amplitudes of the oscillations of the airframe and the methods of normalizing the distortion parameter changed, electrical interference in the test equipment systems are evaluated. Results and discussions. The reliability of the fatigue cracks detecting by distortions of the oscillations portraits are estimated by the example of the aircraft fuselage metal panel diagnosing. The influence of the panel vibrations amplitude, the method of normalization of the oscillation portraits distortions and the level of electrical interference in the excitation system on the effectiveness of crack diagnosis is established. A method for mathematical processing of distributions of the oscillations portraits distortion parameter, allowing to exclude the initial state of the test object from analysis, to track the dynamics of changes in its state and record the development of each defect separately, to eliminate the influence of the fastening system that can introduce nonlinearities in the test object oscillations is proposed to improve the reliability of defects diagnosis. The result of cracks detection in the aircraft wing ribs in the process of strength tests is presented.

Introduction. In modern engineering, there are increasing demands for processing performance, which ensures high quality results for the processed surface of products made of alloyed wear-resistant steels. These steels have high physical and mechanical properties, which makes its machinability with a blade tool rather difficult. For the processing of such products, it is advisable to apply electrophysical processing methods, one of which is the technology of electrical discharge machining (EDM). With the help of EDM, it is possible to process difficult-to-reach deep elements with a complex profile, as well as blind grooves of products made of alloyed wear-resistant steels. The paper deals with effectiveness improvement of EDM processing of complex profile elements of the “Shutter Housing” type parts made of steel 38Cr2Ni2MnA (GOST 8479-70). Subjects of research are the following: the parameter of the roughness of the treated surface; performance and accuracy of steel 38Cr2Ni2MnA EDM with different modes. The aim of the work is to increase the efficiency and accuracy of EDM of blind grooves and elements of a complex profile of products made of alloyed wear-resistant steels. Methods. Experimental studies are carried out according to the method of a full factorial experiment with subsequent regression analysis. For carrying out of experiments, a Smart CNC EDM machine is used. A profile copper electrode is used as an Electrode-tool (ET). ET material is M1 grade copper (GOST 1173-2006). Results And Discussion. Empirical dependences, reflecting the relationship between processing modes, productivity, surface roughness parameter after processing, and the size of the interelectrode gap are established. To ensure the required ratios of the quality of the treated surface with maximum performance indicators, technological recommendations of the EDM of blind grooves and elements of a complex profile of products made of wear-resistant alloyed steel 38Cr2Ni2MnA, which has high rates of wear resistance, are obtained. The dimensions of the profile ET, taking into account the size of the side and end interelectrode gaps, providing the specified EDM accuracy, are calculated.

Introduction. Creating of a new process equipment begins with the development of a draft proposal, i.e. the general concept of the design object. A recent analysis emphasized that it is this stage (including exploratory design, specifications development and draft proposal) that accounts for up to 80% of the process equipment manufacturing and operating cost. With the task being complex itself, the mistakes made at the early design stages lead to a sharp increase in labor costs for their correction. Developing the concept of a future hybrid process equipment is a difficult task to formalize. Since multitask machine complex combine various methods of product processing during geometry generation and changing the surface properties, there is a high probability of compatibility problems of the integrated subsystems and components. This is due to the systems design and layout complexity, harmonization of the multitask machine operating characteristics, compatibility of the machine control principles for solving spatial trajectory tasks and ensuring the accuracy of geometry generation. The purpose of the study is to increase the effectiveness of the initial stages of the hybrid metalworking complexes designing based on the structural synthesis of the machine geometry generation systems and the prediction of their technical characteristics. Methods: Theoretical studies were based on the principles of system analysis, geometric theory of the surfaces formation, design of metal-working machines, as well as finite elements method, mathematical and computer simulation. Results and discussion. We present an original methodology for conducting structural kinematic analysis for exploratory design of hybrid metalworking equipment. Theoretical studies have established that the hybrid metalworking systems design efficiency can be increased 6.092... 18.297 times using the methodology of exploratory design. Since the developed design methodology was approved, we proposed the implementation scheme for the hybrid metalworking process equipment. The use of the proposed hybrid machine will increase the efficiency of metalworking in general: the machine parts manufacturing performance will significantly rise owing to the implementation of surface hardening processes by high-energy heating with high-frequency currents and mechanical processing on the same technological site without intermediate re-installation of the workpieces and tools.

Introduction. Hybrid laser-arc welding (HLAW) is an advanced technique of permanent joint formation. A distinctive feature of this process is the interaction of two heat sources in one melt welding bath. With the help of this type of welding it is possible to weld thick-walled metal workpieces in one pass without cutting edges at high speed. Due to the fact that this welding process involves two heat sources that influence each other in the welding process and form molten pools with different characteristics and different structure after solidification, the study of the relationship between the formation of the weld structure and its mechanical properties is still relevant. Research of welds on the example of structural steel 13Mn6 is an important study in welding engineering. The aim of the work is to investigate the structure and mechanical properties of weld metal formed by hybrid laser-arc welding. Results and discussion. On the basis of the obtained data it is possible to draw a conclusion that the weld metal formed by hybrid laser-arc welding is heterogeneous. The heterogeneity is shown in different directions both in the microstructure and in the results of the microhardness study. Measurements of microhardness inside the weld clearly demonstrate the thermal history of the hybrid laser-arc welding process. The boundary area of the two molten pools has a reduced hardness in comparison to the arc or laser melting zones only. Static tensile tests on the weld metal have shown differences between the arc and laser melt pools. Mechanical test results also demonstrated seam metal anisotropy in mutually perpendicular directions.

Introduction. Macroscopic residual stresses (RS) are one of the key metal mechanical state parameters, which largely determines products and structures operational life. Surface plastic deformation (SPD) hardening treatment creates in the surface layer (SL) favorable compressive RS and significantly increases the fatigue life both before and after the fatigue cracks appearance. In this area of knowledge, the problem of high complexity and laboriousness of the experimental determination of RS, as well as the problem of calculating residual stresses under complex non-monotonic types of loading, which include most of the methods of mechanical processing, remains relevant. The research purpose is to develop the theory of formation and increase the reliability of calculations of residual stresses in the processing of SPD based on the model of a strengthened elastic-plastic body. Results and discussion. The paper presents the SPD process simulation results and RS tensor components calculations. The model is made using the finite element method based on the conceptual framework of the mechanics of technological inheritance (TI), taking into account the effect of the strengthened body. It is established that the highest compressive residual stresses values are typical for the axial component, and the extremum can be located both on the workpiece surface and at some distance from it. The depth of compressive residual stresses distribution is about 3 mm with a depth of distribution of significant in magnitude stresses of about 7 mm. The hardened body influence on the residual stresses distribution is performed. The obtained result corresponds to the idea that the hardened metal, which have an increased yield stress limit, allows the larger RS values presence. The tendencies of changes in the distribution of the components of the RS tensor over the depth of the SL, depending on the main parameters of the SPD processing mode: tension and profile radius of the roller, are revealed.

Introduction. Knowledge of the temperature field in the vicinity of a piecework/tool contact can be useful in optimizing the metalworking process. Infrared thermography is a convenient way to obtain the temperature distribution. This method is widely used in a heat control. It seems reasonable to find out the applicability of the method of infrared thermography to determine the temperature distribution character in the piecework/tool contact. It is of scientific interest to compare the temperature distribution obtained using a thermal imager and thermocouples in the model piecework/tool contact. It has been suggested that the sliding of a steel rod against a steel ring can serve as approximation of a sliding of a steel ball smoothing the surfaces of metal parts. The contact temperature can be changed using electric current. The purpose of the work is to study the features of temperature distribution along the axis of a steel rod, sliding against steel counterbody under the influence of electric current using infrared thermography and using thermocouples. Experimental details. The hardened steel of the St3 grade (AISI steel 1020; Fe - 0.2% C) with the hardness HB274 served as a model counterbody. The sliding electrical contact was carried out without lubricants according to the pin-on-ring slip scheme at a pressure of p = 0.13 MPa and a sliding speed of v = 5 m/s. Steel 45 (50 HRC) served as a counterbody. The temperatures were measured with thermocouples attached to the rod by spot welding and with FLIR A655 sc thermal imager. Results and discussion. It was shown that the temperature distribution along the rod axis was non-linear with relatively high (up to 600 K/cm) temperature gradients in the contact zone under sliding electrical contact if the temperatures were measured with a thermal imager. Measurement of temperatures on the rod axis with thermocouples under the same conditions showed a linear temperature distribution with low (about 100 K/cm) temperature gradients in the contact zone. Current passing through the rod in the absence of slip was also accompanied by a linear temperature distribution. It was assumed that the nonlinearity of the temperature field during its imaging with a thermal imager was due to the difficulty of setting the correct value of the emissivity. This coefficient depends on the presence of oxides, roughness and other state parameters of the radiating surface. The lateral surface of the sample with a high temperature in the area of the sliding contact had a state different from that of the same lateral surface in the zone of attachment of the sample to its holder. Therefore the emissivity set for the state of the surface in the slip zone of the sample did not correspond to the state of the surface in the zone of the sample holder. Possible values of the emissivity (about 0.7) corresponding to a contact temperature of about 400 °C were obtained by experimentally estimating of convective and radiative heat-transfer coefficients. It was noted that the exact temperature field can be determined using a thermal imager only after time-consuming calibration of the emissivity and preparation of the sample surface. It was concluded on the limited possibility to apply infrared thermography under piecework/tool sliding contact and it was offered to carry out the thermal control of the same contact using thermocouples.