Operating Parameters of Electric Pulse Activation for Internal Tapping-Screw Operations and its Justification

The processes of intensification of thread-cutting opera-tions by electric current have been known since the 70s of the last century. Internal threading operations are associated with the mechanism of plastic deformation, and, accordingly, with high values of forces and torques. This reduces the reliability of the process and requires additional measures to reduce power ten-sion. The use of the energy of short stimulating current pulses makes it possible to solve such problems due to the so-called electro-plastic effect (EPE). It is manifested due to additional stresses that cause an increase in the plasticity of metals in the presence of an electric potential and a temperature field in the de-formation center. At present, there is still no clear understanding of the phys-ical processes that determine the change in the VAT of a metal when an electric current is passed. The article presents an analysis of information in this area, which allows us to establish a number of physical phenomena, which are formed into three theories that explain the essence of EPE in metals: electron-dislocation interaction, joule heating, and magnetoplasticity. A description of experiments and equipment for electro-pulse stimulation of the threading operation is presented. The author offers a number of indicators that evaluate the possibilities of electric pulse action on the formation of internal threads when rolling threads, screwing thread-pressing parts, etc. A system of calculated coefficients evaluating the efficiency of the pulse current, its parameters and modes is established.

Sustainability and tool wear of titanium alloy thread cutting in dry and cryogenic conditions

The article is devoted to the study of the effect of cryogenic cooling on the tool wear in thread turning tests. The tool wear and its influence on the thread accuracy were investigated. Two different grades of titanium alloys were used for comparative purposes. The excellent performance characteristics of titanium alloys pose machining problems, causing high unit forces at the edge of the tool leading to chipping and premature tool failure. In turn, the low thermal conductivity of pure titanium affects the heat distribution in the cutting zone. The heat is not absorbed by the material being machined but accumulates in the tool, causing an increase in diffusion and chemical wear. The results of cutting tests using liquid nitrogen showed lower values of wear on the major and minor tool flank. The edge reduction of the tool was also significantly less during cryogenic machining. The analysis of the formation of wear marks and the blade wear mechanisms was carried out for the tool rake face. The tests were carried out using the SEM method and confirmed by EDS analyses. In order to compare the course of tool wear over time, a mathematical model was developed, which results from the course of phenomena during cutting. It consists of two complementary equations. The first equation is characteristic for the first cutting phase and results from the loads imposed on the blade and aims at thermodynamic equilibrium. It is a period of stable tool operation and constant wear intensity. The second equation concerns crossing the equilibrium point followed by the process of accumulation of elementary wear phenomena. These phenomena accumulate until the blade is completely worn-out. The use of blade wear development models to determine the expected blade life allowed to confirm the beneficial effect of cryogenic cooling on the course of the blade wear process when cutting threads for two different titanium alloys.

Equipment and materials for shock-intermittent cutting

The article considers the shock-intermittent processing method, which is used for cutting blind threads M12x1.5 in nuts made of steel grade X18N9T. Compared to the conventional method, it allows increasing the processing productivity; the durability of the thread taps has increased to 300 holes (with manual thread cutting, the durability of the taps is 100 holes). The method allows mechanizing labor-intensive threading operations. The optimal conditions of processing by this method are determined based on ensuring sufficient strength of the cutting wedge of the tool under repeated loading and, at the same time, creating the most intense impact on the material of the cut layer of the workpiece. The destruction of the processed material on impact most easily occurs at critical deformation rates, which, for instance, equal 60 m/s for corrosion-resistant steel. This leads to an overestimation of the impact pulse values, and consequently, chipping of the cutting edges of the tool. Therefore, for these processing conditions, there is an optimal value of the pulse load transmitted by the spindle to the tool. For threads M10 and M12 with pitches of 1.25 and 1.5 in parts made of steel grades X18N10T, the best results are achieved at loads corresponding to the increment of the dynamic moment of the driven bushing with the tool. At high pulse loads, the durability of the working tool is sharply reduced, and at lower loads, the cutting performance is reduced. One of the positive features of shock-intermittent cutting is the presence of breaks that facilitate the operation of the cutting wedge due to the better penetration of the coolant. Therefore, shockintermittent cutting is carried out at more intensive modes than conventional continuous cutting. However, the tool life does not decrease as a result, but even increases. The relative length of the cutting area, determined by the angle, should be chosen based on the fact that the temperature in the cutting area does not have time to reach its steady value, equal to the cutting temperature during the normal long-duration cutting, carried out continuously.

Critical conditions for organic thread cutting under electric fields

Critical conditions with electric capillary number are investigated for triggering the on-demand cutting of an organic thread in a microchannel under electric fields.

RELIABILITY INCREASE OF THREAD CUTTING WITH TAP BORERS IN SUPER-SMALL HOLES

The purpose of this work consists in the reliability increase of thread cutting with the use of tap borers in super-small holes of aluminum alloy parts. The investigation methods used are based on classic regulations of the cutting theory, physical-chemical mechanics of materials, reliability theory and methods of statistical analysis. There are revealed the reasons of thread cutting low reliability and tool failure. The effectiveness of edge anode-machining use at thread cutting is researched. On the basis of data obtained there is carried out a calculation of basic indices of thread cutting reliability. A comparative analysis of the processing reliability indices obtained under standard conditions and with the use of the developed circuit of anode-machining is shown, the effectiveness of the latter use is presented. As a result of the investigations carried out there is developed a technology for thread cutting in super-small holes that ensures a considerable increase of reliability and allows excluding hand work during the process.

A Study of Parameters of the Sewing Thread Cutting Process

Sewing thread cutting processes are widely used in semi-automatic machines in the garment industry. The lack of scientifically justified methods for designing mechanisms for thread trimming in semi-automatic sewing machines makes studying these processes a topical issue. There are works that examine cutting free-hanging yarn using scissors. However, these results cannot be used to develop mechanisms for thread trimming in semi-automatic sewing machines for the following reasons: the properties of free-hanging yarn and sewing thread vary significantly, and the cutting conditions for the thread that grips the blade of a movable knife are different as well. Another reason is that as a rule, sewing thread cutting occurs in a limited space, which imposes a significant restriction on the design parameters of knives and affects the cutting process. There are no such restrictions when cutting yarn. Cutting threads by the method of scissors does not provide complete cutting of all the components of the thread if the knife blades are not in tight contact with each other. To ensure complete trimming, a design scheme of cutting was developed, and calculation formulas were obtained for determining the force exerted by the thread on the movable knife, taking into account the mechanical characteristics of the cut thread.

Investigation of Cutting Force in Screw Cutting by Three Axis Controlling Helical Interpolate With a Wireless Communication Tool Holder System

In recent years, the movement of machine tools including 5-axis control machining centers (5 MC) and turning centers has progressed to enable machining at high speeds and high degrees of accuracy. The accuracy of simultaneous three-axis movement at very high feed speeds has increased significantly. Specifically, with the development of control technologies for these machine tools featuring simultaneous three-axis control, the accuracy of helical interpolation motion at high feed speed has achieved a sufficient level to perform processes such as screw cutting with a thread mill tool. Boring machining and pocket machining for difficult-to-cut materials are processing methods that employ helical interpolation movements with an endmill tool, and it is becoming a promising technology in light of recent advancements. Therefore, we looked at screw cutting with a thread mill tool and proposed a novel monitoring method to improve the accuracy of machining the screw by deriving the radial force of thread cutting from three components — two forces in the X and Y directions and torque around the Z axis — using a piezoelectric dynamometer. In this study, we also investigated the accuracy of machining the screw when the pilot hole and screw were drilled at the same time as well as the accuracy when the pilot hole is drilled beforehand. In addition, we monitored the cutting data and X-Y feed motions using a wireless holder and CNC information to construct a smart manufacturing method for machining screws using helical interpolation. As a result, the proposed monitoring method is effective at improving the accuracy of machining screws from various work materials using helical interpolation motion of a thread mill tool.