RU2500504C1 - Method of accelerated determination of optimum cutting speed - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to P-grade carbide cutting plates. Proposed method comprises temperature measurements effected in the zone of contact between hard alloy and machined material at different cutting speeds to construct a graphical relationship. Then, constructed graph is used to set optimum cutting speed as that whereat heating temperature in said zone corresponds to temperature whereat wear is formed at chamfer formed in cutting on tool plate cutting wedge rear surface and roughness with the maximum fractal size corresponding to maximum wear resistance.

EFFECT: higher precision, lower labor input.

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Description

The invention relates to the field of processing steels and alloys by cutting and can be used to determine the operating parameter of carbide cutting tools - the optimal cutting speed for their direct use on metal cutting equipment, as well as in the certification and certification of this carbide products.

A known method for determining the optimal cutting speed (AS No. 1028427, IPC3 B23B 1/00, BI No. 26, 1983), based on finding the latter by the selected initial parameter associated with changes in the characteristics of the crystal lattice. The crystal lattice period is chosen as the initial parameter for determining the optimal cutting speed, it is determined at various cutting speeds (temperatures), and the optimum speed is taken to be equal to the highest speed at which the lattice period will be maximum.

The process of determining the parameters of the crystal lattice using diffractometers is complex and time-consuming. The study of changes in the crystal lattice of a carbide cutting insert is carried out after termination of the cutting experiments and special preparation, including its cleaning, possible destruction and the choice of the place of control. Due to the different cooling rates of different areas of the tool material, after the next heating during the cutting process, carried out in the range of 400-800 ° C due to a change in the cutting speed, the probability of an accurate determination of the changes that occur is reduced. Inaccuracies also arise due to the fact that a local - random wear zone of a hard alloy is exposed to the study, the structural parameters of which differ significantly from other adjacent areas due to the uneven distribution of the temperature field at different cutting speeds. Therefore, the obtained results of changes in the parameters of the crystal lattice are very approximate and have an insufficient degree of statistical significance.

A known method for determining the optimal cutting speed (AS 841779, IPC3 B23B 1/00, BI No. 24, 1981), based on the fact that the maximum speed of the cutting tool corresponds to the minimum length of the hardening area on the contact surface of the cutting tool. The choice of the length of the hardening section as the initial parameter is explained by the fact that its dimensions characterize the deformation state of the metal in the contact zone, the nature and gradient of the effective temperature fields, the conditions of interaction of the metal of the contact zone with the front surface of the tool and have a great influence on the wear rate of the cutting part of the tool. The measurement of the size of the hardening area is carried out using a microscope; build a graph of the dependence of the length of the hardening section on the cutting speed. The minimum length of the hardening section on the graph determines the optimal cutting speed.

The main disadvantage of the considered method is the high complexity and low reliability in accurately determining the length of the hardening area due to its small size, averaging 0.1-1.0 mm and significant uncertainty of the position of the boundaries. In addition, the determination of the length of the hardening area on the working surfaces of the cutting wedge using a microscope is characterized by methodological shortcomings, the main of which is that the hardened layer is very heterogeneous in length and depth due to the fluctuation nature of contact stresses acting on the surfaces, varying from the maximum values acting at the cutting edge, to zero at the points of exit of the tribological pair from the contact. Because of this, the lengths of the hardening areas on the contact surfaces of the cutting tool, reflecting quantitative and qualitative changes in the structure of the material, measured using a microscope, as well as other methods, for example, by measuring the microhardness, often do not coincide and even have a different character of change. In view of the reasons considered, large errors are also possible in determining the optimal cutting speed.

There is a method of determining the optimal cutting speed for carbide tools (A.S. No. 1227339, B23B 1/00, B.I. No. 16, 1986), selected as a prototype and consisting in the fact that the vacancy level is selected as the initial parameter defects in the structure of the hard alloy. First, the degree of vacancy defects at various heating temperatures is successively measured. Then the optimum temperature - cutting speed is defined as the highest temperature - the speed at which the minimum value of the vacancy defect level is established in the structure.

The disadvantage of this method is that the degree of minimal vacancy defects does not always correspond to the equilibrium thermodynamic state of the structure, at which the lowest value of the level of free energy of a solid is established, as a consolidating system consisting of individual microvolumes and at which a minimum adhesion intensity is likely to be observed wear (see, for example, Van Buren "Defects in crystals", M., I.L., 1961, 584 pp.). As a result, the minimum wear rate of the cutting tool can occur above or below the set optimum temperature - cutting speed. It follows that the accuracy of this method will not be high enough. In addition, for measurements it is necessary to have a special room equipped with radiation protection, and the service operator needs to undergo special training for working with radioactive sources, which in this case is Na-22. The consequence of the above may be a low level of economic feasibility for using the method according to the closest analogue.

The objective of the proposed method is to increase the accuracy and reduce the complexity in determining the optimal cutting conditions (optimal cutting speed) for cutting tools equipped with hard alloys - applicability group P (tungsten - titanium - cobalt hard alloys, etc.).

The solution of the problem in the proposed method is to determine the optimal cutting speed with carbide cutting tools of the applicability group P in the form of cutting inserts, first includes measuring the temperature in the working contact zone of the hard alloy — the material being processed at various cutting speeds with the construction of a graphical dependence, and then using the constructed graphical dependence set the speed at which the heating temperature in the zone of the working contact t Verdoy alloy - the material being processed, corresponds to the temperature of formation on the wear facet formed during cutting on the back surface of the cutting insert, roughness with the smallest fractal dimension, corresponding to the highest wear resistance of the cutting tool.

The processing of materials (steels) that cause intense diffusion wear is carried out, as a rule, by carbide, groups of applicability P by cutting tools subjected to high temperature influences.

There is a direct link between the optimal operating conditions of the cutting tool (optimal speed) and its wear resistance. The optimum speed of operation of the cutting tool provides the greatest wear resistance and economic efficiency. The value of the optimal cutting speed when processing materials that cause intense diffusion wear can be estimated by the degree of development of the roughness of the working surfaces of the cutting insert (fractal dimension).

As measurements and control have shown, the microrelief of the resulting wear surface has fractal properties. This is manifested in the fact that with a decrease in the measurement scale of a rough surface, its area does not tend to a finite limit, but increases exponentially. The main characteristic of fractal surfaces is their fractal dimension. The degree of development of the rough structure (fractal dimension) of the wear surface is closely related to the mechanochemical and electrophysical properties of the surface and the surface layer.

A large influence on the formation of the degree of development of the wear roughness is exerted by the surface and surface hydroxycarbonitride structures formed during cutting on the contact faces. The formation of these compounds, their destruction as a result of diffusion, and the formation of roughness on the contact surfaces of the cutting tool are affected by adsorption processes, its features, and stages.

The magnitude and development of the roughness formed during cutting on the contact surfaces of the cutting insert depends on the composition and structure of the hard alloy, the intensity of adsorption of atoms and oxygen and nitrogen molecules by the contact surfaces of the cutting tool, the composition and properties of the formed oxycarbonitride films.

The fractal dimension of the wear surface is influenced by the size and nature of the porosity of the hard alloy, the composition of carbide grains, the composition and properties of the cobalt binder, the composition and degree of defect of grain and interphase boundaries, the presence of impurities, the sorption properties of the microrelief, the electrical and magnetic properties of the surface and volume. There is a close correlation between the fractal dimension of the rough surface of the wear facet and the wear resistance of a carbide cutting tool of application group P. With a decrease in the development of the roughness of the wear facet on the back surface of the cutting insert and its fractal dimension, the wear resistance of the cutting tool increases. A decrease in the specific surface of the wear facet is accompanied by a decrease in the defectiveness of the structure of the wear material due to the formation of dense hydroxycarbonitride formations on the surface and in the surface layers with a high degree of crystal lattice coherence to titanium carbide. The latter circumstance contributes to a temporary decrease in the adsorption intensity of atoms and molecules of the surrounding gas medium by the wear surface of the cutting tool. The resumption of intense adsorption occurs when the wear surface reaches a sufficient degree of imperfection, which occurs when the degraded layer is separated from the surface. The cutting of materials that cause intense diffusion wear of a tool from a hard alloy of the applicability group P is accompanied by the formation of a surface and surface dense oxycarbonitride layer, a gradual weakening of the bond of this layer with the base, removal of the degraded surface structure, subsequent re-formation of a surface and surface dense oxycarbonitride layer, etc. The destruction of the surface and subsurface layers (weakening of the structure) occurs as a result of sequential local chemical erosion, which manifests itself in the diffusion of oxygen and nitrogen into the deep layers, and the carbon structure of the hard alloy to the surface. This leads to the destruction of a single oxycarbonitride structure and the formation of isolated oxide, nitride and carbide formations. The formation of a dense coherent surface and near-surface oxycarbonitride layer as a result of chemical adsorption of oxygen atoms and molecules leads to a decrease in surface imperfection and, at the same time, to a reduction in the processes of subsequent adsorption of oxygen and oxidation of the faces of the insert. On the one hand, thin oxycarbonitride films intensively formed on the contact surfaces of a carbide cutting tool of application group P withstand high mechanical contact stresses and effectively perform the role of thermal insulation, which reduces wear. On the other hand, the periodic nature of the destruction of the surface hydroxycarbonitride structure - (in the form of separation of thin layers) initiates active oxidation and nitriding, which helps to restore a low fractal dimension. The presented patterns manifest themselves both in the initial and in the period of normal wear and tear. A short-term increase in fractal dimension due to the descent of the degraded layer is eliminated due to the subsequent intensive formation of an oxycarbonitride surface structure due to adsorption of oxygen and nitrogen and upward diffusion of carbon to the surface from the deep layers of hard alloys. The considered mechanism of wear of carbide applicability group P of cutting tools is associated with the process of self-organization of the structure, which consists in the fact that intense gas adsorption occurs when the freshly formed surface is highly defective as a result of separation of the degraded layer. The process of self-organization (the formation of a smooth, undeveloped microrelief) is accompanied by a decrease in the intensity of adsorption of gas molecules and the intensity of the formation of an oxycarbonitride layer. The formed thin and dense oxycarbonitride films, in turn, shield the heat flux directed into the body of the tool material, the mass transfer, both towards the cutting tool and towards the material being processed. The processes considered lead to reduced wear. In addition, with the established procedure for self-regulation of phenomena in the contact zones of the hard alloy and the processed material (the formation of thin and dense hydroxycarbonitride wear-resistant films on the contact surfaces of the cutting tool, their functioning, removal and subsequent formation), an increase in the friction coefficient of the cutting forces and a sharp decrease in the quality of the processed surfaces occur at higher values of parameters - wear criteria characterizing the transition of normal wear to katas roficheskomu.

From the presented it follows that the decrease in the development of the roughness of the wear facet and, accordingly, the fractal dimension is closely related to the increase in wear resistance (cutter operating time, up to the established dullness criterion, for example, on the back surface) of the cutting tool. Therefore, the determination of cutting conditions (determination of the optimal cutting speed), taking into account the degree of development of the formed microrelief of the wear surface, is an important step that is closely related to wear resistance and machining performance.

The process of adsorption of gas molecules of oxygen and nitrogen on the contact surfaces of cutting tools of hard alloys of the applicability group P consists of two main stages and is specific in nature. A feature is that strong chemical adsorption occurs at the first stage. Its intensity is associated with a high initial degree of polarization of the wear surface of the hard alloy. The second stage involves continuous physical adsorption. The main active centers of adsorption of gas atoms and molecules are located in the cavities of the resulting microcracks of the wear surface, depressions, open and closed pores. In the internal cavities of the indicated imperfections, the wear-out surface structure of the cutting tool, oxide, nitride and oxycarbonitride dense structures are formed with a high degree of coherence to the base compound of the instrumental composition - titanium carbide. As a result of this, the intensity of heat and mass transfer from the side of the processed material and the surrounding gas medium into the deep layers of carbide material decreases. The latter circumstance limits the erosion and destruction of the instrumental structure and provides an increase in the wear resistance of the cutting tool at the individual stages of its functioning between the outflows of the degraded layer from the wear surface. When processing materials that allow high cutting speeds (not causing intense adhesive interaction) with hard alloy tools of application group P, there are no high tangential stresses, and the coefficient of friction is low. As a result, for cutting tools of the applicability group P there is no need for intensive oxidation of contact surfaces in order to reduce tangential contact stresses. For them, intensive oxycarbonitriding of the wear surface after the degradation of the degraded layer is sufficient and low or moderate oxycarbonitriding of the contact surfaces between the adjacent stages of separation of the degraded structures is sufficient. The surface contact structure of cutting tools for hard alloys of the applicability group P withstands high normal stresses and, at the same time, is subject to destruction from the action of shear stresses. The low development of surface roughness implies the absence of a chamfer of wear on local sites with a large slope to the nominal surface on the microrelief. As a result, the intensity and frequency of cleavage of local oxycarbonitride structures is significantly reduced. An increase in the length of the areas of protrusions and troughs of roughnesses (a decrease in fractal dimension) leads to an increase in the stresses necessary for cleavage formed on the microroughnesses of structures. This ultimately leads then to an increase in the wear resistance of cutting tools. Thus, the lower the development of the roughness of the contact surfaces, the higher the operational characteristics of carbide cutting tools of the applicability group P, when processing materials that cause intense diffusion wear. With a decrease in the development of the roughness of the wear surface, the bond strength of the surface and near-surface structure transformed as a result of oxygen and nitrogen adsorption with the carbide base increases, and the wear resistance of cutting tools is higher. A great influence on the roughness height and its development on the wear facet on the back surface is exerted by the nature of the contact between the tool and the processed material. Carbide groups of applicability P cutting tools are used for processing materials with low adhesive activity with respect to tool material. Such processing can be carried out with high speed and be accompanied by the action in the contact zones of high temperatures and various chemical reactions. Chemical reactions, in turn, are due to the high mobility of the atoms of the reacting components. So, the atoms of the processed material penetrate the structure of carbide material and vice versa. Due to the formation of a chamfer of wear of foreign structures on the surface and in the near-surface region, carbide material degrades, destroys it, and forms a certain surface roughness, which, in turn, can initiate surface adsorption, oxidation, and nitriding. The main objects of concentration of diffusing atoms from the processed material into the structure of the carbide material are surface and bulk defects of the carbide composition. These include primarily open and closed surface pores. At some optimal cutting conditions (temperatures), the objects of oxygen and nitrogen of the surrounding gas medium are the objects of adsorption by the contact surfaces of the carbide cutting tool. The latter are captured by surface defects and form dense and highly coherent compounds (with a high chemical inertness) with the substrate substance (titanium carbide). As a result of this, structures are formed on the surface and in the near-surface region, which are an effective heat-insulating and anti-diffusion screen that limits the penetration of atoms of the processed material into the structure of the hard alloy. The higher the degree of stoichiometry of the resulting compounds, the higher the operational characteristics of the resulting surface and subsurface structures.

The degree of stoichiometry of the resulting compounds is greatly influenced by the composition of carbide grains (including the presence of impurities), as well as the intensity of adsorption of oxygen and nitrogen by the contact surfaces of the surrounding gas medium. The intensity of adsorption by the surface of oxygen and nitrogen, in turn, also depends on the composition and presence of chemical elements - impurities that activate adsorption. With an increase in the composition of titanium carbide, for example, calcium and aluminum, the adsorption intensity of gas elements increases. A thermodynamically equilibrium (stoichiometric) structure is formed. Therefore, the formation of a developed structure and the destruction of the structure of carbide material during cutting are radically reduced. In this case, the diffusion component of integral wear is most significantly reduced.

Thus, the degree of development of the resulting microrelief of wear sites on contact surfaces will depend on the composition of the substrate, the nature of the formed chemical bonds between the surface components of the carbide composition and the adsorbate, and the intensity of brittle fracture occurring in the microvolumes of the surface and subsurface structure of the hard alloy. A large influence on the nature of the destruction of the surface layer and the formation of an undeveloped microrelief, characterized by a low fractal dimension, is exerted by the low value of the coefficients of the fracture intensity formed by the surface and surface hydroxycarbonitride structures on the contact surfaces of the cutting insert. This implies, on the one hand, low crack resistance of the structure, and on the other hand, the effective penetration of oxygen and nitrogen gas molecules into the structure of solid alloys and the formation of protective hydroxycarbonitride structures. The high ability to inhibit formed during the destruction of the surface structure of cracks provides a high degree of surface imperfection of polyoxide and oxycarbonitride films. The surface structures formed on the contact surfaces of the cutting tool contain a low concentration of vacancies, and a high concentration of small and large pores. In titanium oxycarbonitride films, the bulk of the vacancy field is made up of cationic vacancies, and in cobalt oxide films, anionic vacancies. With a decrease in the concentration of both types of vacancies, with a simultaneous increase in their associations (small and large pores), the development of the microrelief during the destruction of surface structures decreases. The latter circumstance is accompanied by a decrease in fractal dimension.

The contact of tool surfaces with the processed material is heterogeneous and not continuous. The surface of the cutting insert is not simultaneously and not equally subjected to transformation due to atmospheric oxygen and nitrogen. The nature of the brittle fracture of the contact surfaces of the cutting insert due to diffusion interaction with the processed material will be determined by the degree of modification of the surface and surface structures that occur when it interacts with the surrounding gas environment. The development of oxidation and oxycarbonitriding, from instantaneous, characterized by the formation of a film consisting of a single layer of atoms, to a multi-stage, characterized by the formation of a multilayer film, is intensified, as a result of the formation of active regions - active centers in the resulting surface and subsurface structure. Active centers have a reduced ionization energy and contribute to the effective capture of adsorbed oxygen and nitrogen molecules and their retention on the surface. The main centers of capture by the instrumental surface of atoms and molecules of oxygen and nitrogen are regions that are heterogeneous in composition in the form of vacancies, impurity atoms, or combinations thereof.

The rate of capture of atoms and molecules of oxygen and nitrogen by the contact tool surface (contact occurs with the processed material) increases with decreasing pressure in the intercontact region (the space between the contacting surfaces). The lower the pressure in the intercontact region, the stronger the capture of atoms and molecules of oxygen and nitrogen penetrating into this region. The capture process occurs in conditions of high competition between various active centers (capture centers) of the surface. The most probable trapping centers are the following structural defects: anionic vacancy in combination with an electron in the structure of the titanium oxide film, cationic vacancy in combination with a hole in the structure of the cobalt oxide film, impurity ion and cationic vacancy in combination with the anionic vacancy in the structure of titanium oxide, impurity ion and anionic vacancy in combination with a cationic vacancy in the structure of cobalt oxide, atomic centers in crystals with monovalent cationic impurities, ions of one and divalent impurities in anio the vacancy in the structure of titanium oxide, the process of transition of an impurity ion from the cationic sublattice to the anionic one, the process of deformation mixing of the cationic and anionic sublattices. The considered static and dynamic active centers have an ionization energy significantly lower than that of the atoms that make up the surface defect-free structure of the hard alloy. As a consequence, these structural defects are actively involved in the implementation of the adsorption process. They contribute to the capture and retention of atoms and molecules of oxygen and nitrogen in the field of action of electronic and atomic forces during the entire period of time necessary for chemical reactions with surface elements, and the formation of a stoichiometric oxycarbonitride landscape on the surface and in the surface region. In the process of destruction of such a structure during the diffusion interaction of the tool surface with the processed material, the wear surface of the contact surface, roughness and its fractal dimension increase slightly for a short time. However, the subsequent intense adsorption of gas molecules reconstructs the structure and recreates its protective properties. As a result, its wear resistance is quickly restored.

The effectiveness of the interaction of oxygen and nitrogen molecules with a wearing tool surface is estimated using the accommodation coefficient. The accommodation coefficient is a measure of the efficiency of capture of adsorbed molecules by the surface and a measure of heat transfer between the adsorbent and the adsorbate. The coefficient of accommodation. It is used to assess the degree of filling of the surface with adsorbed atoms and molecules. With an increase in the composition of hard alloys, for example, calcium and aluminum, the capture rate of atoms and molecules of oxygen and nitrogen by the heated (during cutting) wear surface increases. The result of a high degree of accommodation of adsorbed atoms and molecules is the formation of an effective oxycarbonitride structure, the degradation of which leads to the formation of a low-rough and undeveloped microrelief having a low fractal dimension and high wear resistance.

The process of surface diffusion of trapped atoms and molecules of oxygen and nitrogen is one of the main stages in the implementation of effective adsorption. In the process of diffusion, atoms and molecules find thermodynamically optimal positions in the surface and near-surface structures. A decrease in the surface energy of the carbide cutting tool of the applicability group P, with an increase in the diffusion mobility of the adsorbate, accompanied by the formation of equilibrium surface hydroxycarbonitride formations leads to a decrease in the intensity of chemical interactions of the carbide material with the material being processed. In this case, the tangential stresses decrease in the contact zone, the development of the wear surface decreases, and the fractal dimension of the microrelief decreases. A great influence on the diffusion mobility of atoms and molecules of oxygen and nitrogen is exerted by metallic impurities that are part of hard alloys (calcium, aluminum). With an increase in the concentration of these impurities (in the range of acceptable values), the diffusion rate of oxygen and nitrogen increases.

The lowest rough surface on the rear edge of the insert - the wear facet is formed at a certain optimum temperature corresponding to the optimal cutting speed. Below and above the optimum temperature operating in the contact zone on the rear surface of the cutting tool, the development of the microrelief of the wear surface is higher, and the fractal dimension is larger than that obtained at the optimum cutting speed. At temperatures below optimal, (high adhesive activity), the high development of the microrelief of the wear surface and the high fractal dimension are due to the insufficiently high intensity of the formation of hydroxycarbonitride structures and their low operational characteristics (low shielding ability from diffusion manifestations and thermal effects). This is due to the low activity of adsorption processes. As a result, the contact surface of the cutting wedge is substantially free of oxycarbonitride films. The latter circumstance leads to intense intermolecular interaction of the carbide and the material being processed, and the wear surface is partially covered by a metal-like layer of the material being processed. Active areas with metal layers are subjected to high-frequency cyclic loads due to periodic "micro-welding" with the processed material and, as a result, are separated from the contact surface of the cutting tool. Depreciation in this case is significantly intensified, and the wear surface itself is significantly disordered with the presence of deep depressions and high protrusions and a significant development of the microrelief.

At temperatures (speeds) higher than optimal, high roughness and development of the microrelief of the wear surface of the cutting insert, as well as a high fractal dimension, are due to the intense formation of oxycarbonitride films, their melting and intense sublimation. This is due to the high activity of diffusion processes, the high rate of chemical transformations on the surface, and the high rate of evaporation of the formed structures. As a result of this, a microrelief is formed in the friction zones, which contributes to the growth of tangential contact stresses and the average coefficient of friction. In this case, a strong intermolecular interaction also arises between the processed and carbide material, which leads to intense “fusion” at the local points of the contacting objects, which proceeds to an expanded and then to continuous interaction. The latter leads to a significant increase in shrinkage of the chips, an increase in cutting force, intensive wear. The elements of the rough structure of the wear facet of the cutting insert in this case are formed as a result of plastic shifts of parts of the structure of the hard alloy, and the development of the microrelief is significantly increased. Depreciation, at the same time, begins to bear, increasingly, a plastic character. In this case, the fractal dimension of wear roughness rises sharply.

In order to determine the optimal cutting speed, short-term resistance tests of cutting tools of the applicability group P are performed when cutting steels or alloys that cause intense diffusion wear at various processing temperatures (speeds). The magnitude of the fractal dimension (the degree of development of the roughness of the wear facet) depends little on the cutting time and substantially depends on the temperature (cutting speed). As a criterion for the informative operation of each specific cutting tool (cutting insert), the cutting time at each temperature (cutting speed) for 2-5 minutes is taken. Shorter cutting times are used for processed materials that cause more intense diffusion wear (e.g., high carbon steels), and longer cutting times are taken for processed materials that cause less intense diffusion wear (e.g., low carbon steels). At the same time, using a special highly sensitive pyrometer during the cutting process, the temperature in the cutting zone is determined. The fractal dimension of the roughness of the wear facet on the back surface of the tested cutting tools is measured using a non-contact three-dimensional profilometer. After tests and measurements, graphs of the dependence of temperature on cutting speed and the magnitude of the fractal dimension on temperature are constructed. Finally, on the basis of the obtained dependence of the fractal dimension on temperature and temperature on the cutting speed, the optimal cutting speed is determined at which the minimum fractal dimension is formed on the wear facet of the back surface of the cutting tool. For hard alloys of titanium - tungsten - cobalt group (applicability group P), the smallest fractal dimension on the back surface of the wear facet during processing of materials that cause intense diffusion wear forms approximately in the temperature range from 850 to 900 ° C. Moreover, with an increase in the composition of hard alloys of a certain grade (applicability group P) of calcium and aluminum impurities, the temperature region at which the smallest fractal dimension of the microrelief of the wear surface is observed shifts toward higher temperatures and vice versa. The optimal processing conditions for cutting steels or alloys are selected based on the temperature at which the optimal rough microrelief is formed on the wear surface (with the smallest fractal dimension). All actions to take measurements to identify the fractal dimension on the wear surface of the cutting inserts are simple and easy, and, in comparison with analogues and prototype, have higher accuracy in determining the optimum temperature and, accordingly, cutting speed.

The proposed method has high accuracy in determining the optimal cutting conditions (cutting speed), and therefore, the high efficiency of using carbide cutting tools in the processing of materials that cause intense diffusion wear. This, as shown, is achieved by using the optimum temperature (speed) as an informative parameter, at which a roughness with the smallest fractal dimension is formed on the wear facet of the back surface of the cutting wedge. Using the proposed method, it is possible, based on the results of evaluating the fractal dimension, to calculate the most economically feasible processing modes (cutting speed) when cutting materials that cause intense diffusion wear of the cutting tool.

The morphology of the wear surface was studied using a non-contact three-dimensional profilometer MICRO MEASURE 3D station of the French company STIL. The profilometer works as follows. A light beam with a diameter of 2 μm illuminates the examined surface with pulses with a frequency of 30 Hz, 100 Hz, 300 Hz, or 1000 Hz. The frequency of light pulses is selected depending on the intensity of the light reflected from the surface and depends on the state of the surface (roughness, gloss and blackness). To examine the wear surface of T30K4 carbide inserts, a frequency of 100 Hz should be selected. It provides the most accurate reproduction of the examined wear profile. A beam of light generated by a halogen lamp. Then, it is transmitted through the fiber optic conductor to the sensor, where it is formed into a beam. The height of the protrusions and depressions is determined from the difference in the intensities of the incident and reflected light. The surface roughness is calculated from a verified profile registered (installed) on a segment of a certain length. The profiler is equipped with a digital camera that allows you to magnify ten times the image of a worn surface. Therefore, using the camera, you can visually select the location of the examination. Processing of the obtained profiles was carried out using the computer program Maunta ins Map Universal v.2.0.13, which is included in the equipment of the profilometer. Based on the measurement of roughness in the automatic mode, in accordance with the computer program, the value of the fractal dimension was determined.

Roughness control and determination of fractal dimension were determined on the wear facet located on the back surface of the cutting insert in its central region. For all controlled cutting inserts, the coordinates of the diagnostic location should be the same.

Using the proposed method, it is possible, based on the results of evaluating the fractal dimension of the microrelief of the worn surface, as a result of short-term resistance tests, to determine the optimal cutting speed for cutting tools of the applicability group P, for a batch of hard-alloy products manufactured by an enterprise or delivered to a metal processing enterprise. The optimal cutting speed was determined for the cutting inserts from two batches received from the enterprise - manufacturer.

Figure 1 shows the dependence of the change in average temperature on the cutting speed:

curve 1 - for carbide cutting inserts from the first batch of samples;

curve 2 - for carbide cutting inserts from the second batch of samples.

Figure 2 presents the dependence of the changes in the fractal dimension of the microrelief of the wear surface on the rear edge of the cutter on the temperature (speed) of cutting:

curve 1 - for carbide cutting inserts from the first batch of samples;

curve 2 - for carbide cutting inserts from the second batch of samples.

Figure 3 presents a diagram of the choice of location for monitoring the surface roughness, the results of which determine the fractal dimension:

position - 1 - cutting insert,

position - 2 - cutting edge,

position - 3 - chamfer of wear on the rear surface,

position - 4 - plot diagnostics (path scan beam).

Carbide cutting inserts were obtained from two different batches of the manufacturer.

An example of the method "Determination of the optimal cutting speed". The implementation of the method is performed in such a sequence.

First, carbide cutting inserts made of T30K4 alloy (group of applicability - P) are sampled from two different batches.

Then, the selected cutting inserts are subjected to short-term wear tests. As the material being processed, structural steel 45 or another material is used that causes intense diffusion wear. For the criterion of informative operation of the cutting insert (cutting tool) take the cutting time at each temperature (cutting speed) for 3 minutes Tests are carried out at various average temperatures of the contact zone — various cutting speeds in the range from 160 to 190 m / min, the cutting depth and feed are taken, respectively, t = 1.5 mm; S = 0.2 mm / rev The average cutting temperature during short-term tests when cutting steel 45 is measured using a highly sensitive pyrometer (it is possible using the natural pair method followed by calibration). The dependency graph "cutting temperature - cutting speed" is built taking into account the statistical data obtained during testing using a computer program. After testing the cutting inserts (each was tested for 3 minutes), the tested carbide cutting inserts examine the roughness of the wear facet and determine the fractal dimension. The fractal dimension of the microrelief of the wear facet was determined on the cutting inserts, after they were tested at the selected cutting temperature (speed). The final average temperature and average fractal dimension were obtained by examining four plates. The scale similarity coefficient in determining the fractal dimension was taken constant.

At a cutting temperature of 812 ° C, the fractal dimension of the microrelief of the wear facet for four tested inserts from the first batch of carbide inserts was 1.50; 1.48, 1.52, 1.50. The average fractal dimension was 1.50. At a cutting temperature of 825 ° C, the fractal dimension of the microrelief of the wear facet for the four tested inserts was 1.35; 1.37; 1.33; 1.35. The average fractal dimension was 1.35. At a cutting temperature of 850 ° C, the fractal dimension of the microrelief of the wear facet for the four tested inserts was 1.23; 1.21; 1.25; 1.23. The average fractal dimension was 1.23. At a cutting temperature of 870 ° C, the fractal dimension of the microrelief of the wear facet for the four tested inserts was 1.20; 1.18; 1.22; 1.20. The average fractal dimension was 1.20. At a cutting temperature of 875 ° C, the fractal dimension of the microrelief of the wear facet for the four tested inserts was 1.21; 1.20; 1.22; 1.21. The average fractal dimension was 1.21. At a cutting temperature of 900 ° C, the fractal dimension of the microrelief of the wear facet for the four tested inserts was 1.26; 1.25; 1.27; 1.26. The average fractal dimension was 1.26. At a cutting temperature of 925 ° C, the fractal dimension of the microrelief of the wear facet for the four tested inserts was 1.44 1.45; 1.43; 1.44. The average fractal dimension was 1.44. At a cutting temperature of 935 ° C, the fractal dimension of the microrelief of the wear facet for the four tested inserts was 1.56; 1.54; 1.58; 1.56. The average fractal dimension was 1.56.

At a cutting temperature of 818 ° C, the fractal dimension of the microrelief of the wear facet for four tested inserts from the second batch of carbide inserts was 1.50; 1.47; 1.53; 1.50. The average fractal dimension was 1.50. At a cutting temperature of 825 ° C, the fractal dimension of the microrelief of the wear facet for the four tested inserts was 1.38; 1.36; 1.40; 1.38. The average fractal dimension was 1.38. At a cutting temperature of 850 ° C, the fractal dimension of the microrelief of the wear facet for the four tested inserts was 1.16; 1.14; 1.18; 1.16. The average fractal dimension was 1.16. At a cutting temperature of 875 ° C, the fractal dimension of the microrelief of the wear facet for the four tested inserts was 1.11; 1.12; 1.10; 1,11. The average fractal dimension was 1.11. At a cutting temperature of 880 ° C, the fractal dimension of the microrelief of the wear facet for the four tested inserts was 1.10; 1.11; 1.09; 1.10. The average fractal dimension was 1.10. At a cutting temperature of 900 ° C, the fractal dimension of the microrelief of the wear facet for the four tested inserts was 1.13; 1.14; 1.12; 1.13. The average fractal dimension was 1.13. At a cutting temperature of 925 ° C, the fractal dimension of the microrelief of the wear facet for the four tested inserts was 1.26; 1.24; 1.28; 1.26. The average fractal dimension was 1.26. At a cutting temperature of 940 ° C, the fractal dimension of the microrelief of the wear facet for the four tested inserts was 1.50; 1.48; 1.52; 1.50. The average fractal dimension was 1.50.

от вершины реза.The microrelief was measured at the center of the wear facet. The scan line was at a distance (vertical) of 0.5h mm from the cutting edge and at a distance (horizontal) $$\frac{\mathrm{one}}{3}b=\frac{\mathrm{one}}{3Sin\phi }t\text{mm}$$

from the top of the cut.

The scan length was 0.58 mm. Where b, t and h, respectively, the length of the cutting edge, the depth of cut and the height of the formed bevel. The main angle in terms of φ during cutting was 60 °. The measurement scheme is presented in figure 3.

According to the results of tests and measurements of cutting inserts from samples of the first and second lots, the dependences were built: “cutting temperature - cutting speed”, “fractal dimension - cutting temperature”. From the graph of the dependence “fractal dimension - cutting temperature” for the first batch of cutting inserts it follows that at a temperature of 870 ° C the fractal dimension acquires the smallest value. Below and above the indicated temperature, the value of the fractal dimension has a larger value than it reaches at the optimum temperature.

From the graph of the dependence “cutting temperature - cutting speed” is determined - at the optimum temperature at which the lowest value of the fractal dimension value is reached - the optimal cutting speed. In a specific example, the optimal cutting speed was 175 m / min. At this cutting speed, the greatest wear resistance of the cutting tool of the applicability group is achieved - P, from the first batch of cutting inserts, with the greatest productivity of the cutting process.

From the dependency diagram “fractal dimension - cutting temperature” for the second batch of cutting inserts it follows that at a temperature of 880 ° C the fractal dimension acquires the smallest value. Below and above the indicated temperature, the value of the fractal dimension has a larger value than it reaches at the optimum temperature.

From the graph of the dependence "cutting temperature - cutting speed" is determined by the optimal temperature at which the lowest value of the fractal dimension value is reached - the optimal cutting speed. In a specific example, the optimal cutting speed was 179 m / min. At this cutting speed, the greatest wear resistance of the cutting tool of the applicability group is achieved - P, from the second batch of cutting inserts, with the greatest productivity of the cutting process.

As a result of comparative resistance tests of cutting tools from the first and second batch of cutting inserts at a cutting speed of V = 177 m / min, feed s = 0.2 mm / rev, t = 1.5 mm and with a criterion for blunting on the rear surface h = 0.6 mm, it was found that the wear resistance of cutting tools from the second batch of cutting inserts having a lower fractal dimension of the roughness of the wear surface is higher than the wear resistance of cutting tools from the first batch of cutting inserts having a higher fractal dimension Nost wear surface roughness.

It was found that the lowest wear rate of cutting tools corresponded to their operation at a cutting speed corresponding to that temperature in the contact zone at which the smallest value of the fractal dimension of the wear surface roughness at the rear edge of the cutting wedge is observed.

Thus, the sequence in determining the optimum cutting speed is as follows. First, from the graph of the dependence "fractal dimension - cutting temperature" determine the temperature at which the lowest value of the fractal dimension of the surface roughness of the wear is observed, then, using the graph of the dependence "cutting speed - cutting temperature" and, based on the existing cutting temperature at which the smallest value of the fractal dimension value, determine the optimal cutting speed.

Durability tests carried out at various cutting speeds, a constant feed of 0.20 mm / rev and a cutting depth of 1.5 mm showed that it is with a cutting speed of 175 m / min, corresponding to a temperature of 870 ° C in the contact zone for the first a batch of cutting inserts and, at a cutting speed of 179 m / min — the corresponding temperature in the contact zone of 880 ° C — the minimum wear rate is observed for the second batch of cutting inserts. The optimal cutting speeds obtained for the first and second lots of carbide cutting inserts by the method, in accordance with the prototype, were, respectively: 178 and 182 m / min. Conducted persistent tests showed that at these cutting speeds there is an increased wear rate of carbide cutting tools, compared with their operation at cutting speeds obtained by the proposed method. Moreover, as a result of statistical processing, it was found that the coefficient of variation of wear resistance according to the proposed method for the first batch of cutting inserts was 0.22; for the second 0.25. According to the prototype, respectively, 0.24 and 0.29. This indicates a greater variation in the wear resistance of cutting tools operated at a cutting speed determined by the prototype and the preferred nature of the selection of the optimal cutting speed by the proposed method. As a result, the wear resistance of cutting tools of both batches of carbide inserts operated at cutting conditions determined using the prototype turned out to be lower compared to inserts operated at cutting modes in accordance with the proposed method.

Claims (1)

A method for determining the optimum cutting speed with carbide cutting tools of the applicability group P in the form of cutting inserts, including first measuring the temperature in the contact zone tool - the processed material at various cutting speeds with the construction of a graphical dependence, and then, using the constructed graphical dependence, setting the optimum cutting speed as speed at which the temperature of the heating in the area of the working contact instrumental processed material It exists a temperature at which the wear on the chamfer formed on the rear surface of the cutting wedge during cutting, is formed with a roughness lower fractal dimension corresponding to the highest wear resistance of the cutting tool.

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