RU2459192C1 - Method for predicting wear resistance of hard-alloy cutting tools - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: standard wear resistance tests are performed during cutting of materials at optimum cutting speed. Tests for the change in value of initial parameter from properties of surface structure formed during manufacture of hard-alloy cutting tool are performed. Reference-correlation "initial parameter - wear resistance" relationship is built. The value of initial parameter of current batch of hard-alloy cutting tools is controlled and wear resistance for current batch of tools is predicted on the basis of the relationship. As initial parameter there used is surface area of hysteresis loop (S) obtained during monitoring of surface thermo-emf with activated and deactivated heating of hot probe with enlargement of the surface area (S) of which the wear resistance rises.

EFFECT: accuracy is improved and labour intensity is reduced during prediction of wear resistance of hard-alloy cutting tools.

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Description

The invention relates to the field of metal cutting and can be used to predict - control the wear resistance of carbide cutting tools in their manufacture, use or certification.

A known method for determining the wear resistance of hard alloys is that the test material is placed in an alternating magnetic field with a strength of the order of 5 Oersteds, the magnetic permeability of the material is measured, and the magnitude of the material’s wear resistance is determined from the calibration graph “magnetic permeability - resistance” [ SU AC 268720, IPC G01N 3/58, BI 1970, No. 14].

One of the disadvantages of the known method is that the measurement does not take into account the influence of the mass and demagnetizing factor of products, which often have different shapes and dimensions, on the magnetic permeability, which leads to a decrease in the accuracy of measurements. In addition, the operational characteristic - wear resistance is controlled by this method by assessing the physical condition using relative magnetic permeability in only one of the components of the hard alloy - cobalt bond. This is because tungsten carbide is a paramagnet and its contribution from magnetization to the total relative magnetic permeability is small. Therefore, using this method, essentially, the relative magnetic permeability of cobalt, its quantity and deformation state are evaluated. Moreover, other properties of the surface and volume of the hard alloy are not taken into account at all, including the cohesive and adhesive state at the phase boundaries and in the volume of the components of the hard alloy, etc. Due to the reasons considered, this method is characterized by low accuracy in assessing the wear resistance of hard alloys.

A known method of controlling the cutting properties of a batch of carbide tools, according to which first they act on each tool (carbide plate) from the batch, a control parameter is recorded, then several tools from the batch are selectively subjected to mechanical wear and the cutting properties of the tools of the entire batch are determined. The impact on each tool is carried out by uniformly distributed pulse heating, a chronological thermogram is recorded, the thermal diffusivity of each instrument is determined as a control parameter, according to the results of a selective wear mechanism depending on the thermal diffusivity, and the cutting properties of the instruments of the entire batch are determined using the obtained dependence [SU AC 1651155, IPC G01N 3/58, BI 1991, No. 19]. The selected initial parameter in this method is the thermal diffusivity. The main disadvantage of this method is that it is very difficult to more or less accurately determine the rate of heat propagation in materials in which free electrons are the heat carriers. Hard alloys are such materials, and their heat transfer is ensured by the movement of electrons. The thermal diffusivity of all hard alloys differs by an insignificant amount. Therefore, it is very difficult to determine the fluctuations (changing the wear resistance) of the thermal diffusivity for one particular grade of hard alloy (they are almost invisible). The latter is fraught with great technical difficulties. The proper provision in this situation of control operations with precise - acting, recording and auxiliary instruments and devices guaranteeing the necessary accuracy will entail a significant increase in the cost of control operations. As a result of this, this control method is not very promising for use in both laboratory and production conditions.

A known method for predicting the wear resistance of a cutting tool, selected as a prototype and consisting in the following. Carry out benchmark tests of cutting tools at an optimal or close cutting speed, conduct tests to change the value of the initial parameter on the properties of the surface polyoxide structure of the hard alloy formed during its heating, build the reference correlation "initial parameter - wear resistance", perform statistical monitoring only initial parameter values for the current batch of carbide cutting tools. After that, wear resistance is predicted for the current batch of tools based on the relationship:

where T (current), min - wear resistance in minutes - the average predicted time of trouble-free operation of carbide cutting tools undergoing tests from the current batch of samples;

T (reference), min - average wear resistance in minutes for carbide cutting tools from a reference batch of carbide products;

τ (reference), ps - the average value of the selected initial parameter obtained by measuring the characteristics of the surface polyoxide structure of carbide cutting tools from a reference batch of carbide products;

τ (current), ps - the average value of the selected initial parameter obtained by measuring the characteristics of the surface polyoxide structure of carbide cutting tools from the current - controlled batch. In this case, the value of the positron lifetime embedded in the surface and near-surface layers of hard alloys and estimating the electron density of their structure is used as the initial parameter. The magnitude of the electron density predict the wear resistance of the manufactured cutting tools [SU AC 2251095, IPC G01N 3/58, BI 2005, No. 12]. The main disadvantage of this method is the high organizational complexity in its implementation. To implement this method, a radioactive source is required. In accordance with the standards for its maintenance, there are high requirements. It is necessary to have a special room for its storage. The measurement of the relevant parameters and the processing of the results obtained can only be performed by specially trained and trained personnel. Using this method, the structure is evaluated at the atomic level and the results are not always compared with the results obtained by wear resistance, leading to an accurate forecast. This method allows you to sort out - to predict the wear resistance of hard alloys, similar in appearance and degree of defective structure. Comparison of structures that differ greatly in appearance and degree of defectiveness gives quite noticeable errors in the forecast of wear resistance of carbide cutting tools. As a result, this method for predicting wear resistance does not quite accurately characterize the operational properties determined by the degree of defective structure, which ultimately reduces the degree of tightness of the correlation between the initial parameter and the wear resistance of cutting tools. Nevertheless, this control method informatively reflects the operational state of the surface structure of the tool material, which is important for establishing a relationship between this characteristic and adhesive wear, which to a large extent depends on the type and degree of imperfection of the surface layer, and it is selected as a prototype.

The objective of the proposed method is predicting the wear resistance of carbide tungsten-cobalt (group K) cutting tools is to increase accuracy and reduce the complexity in predicting the wear resistance of carbide cutting tools. Prediction is based on a close correlation between wear resistance and the area of the thermal hysteresis loop obtained by measuring the surface thermo-emf (Seebeck method) during heating and subsequent cooling of the controlled zone. With an increase in the area of the thermal hysteresis loop obtained by measuring the thermo-emf on the surface of cutting inserts made of hard alloys of group K, their wear resistance increases when cutting steels and alloys that cause intense adhesive wear.

The task in predicting the wear resistance of carbide cutting tools of the applicability group K in the proposed method is solved by using the selected initial parameter and includes: testing to change the value of the initial parameter from the properties of the surface structure formed during the manufacturing (hardening) of carbide cutting tools, conducting benchmark tests on wear resistance in the process of cutting materials at an optimum or close to her cutting speed, p the construction of the reference - correlation dependence "initial parameter - wear resistance", statistical control of only the value of the initial parameter for the current batch of carbide cutting tools, the prediction of wear resistance for the current batch of tools based on the relationship:

where a _E and in _E are constant coefficients:

,

,

of them:

Tpt is the current wear resistance in minutes for tested carbide cutting tools from the forecasted current batch of carbide products;

Spt is the current value of the selected initial parameter obtained by monitoring the surface of carbide replaceable cutting inserts from the current - controlled batch of carbide products;

Te ₁ and Te ₂ - wear resistance in minutes for two independent samples of interchangeable carbide cutting tools (inserts) from the reference (previous) batch of carbide products;

S _E1 and S _E2 are the average values of the selected initial parameter obtained by monitoring the surface structure for two samples of carbide cutting tools (plates) samples from the reference (previous) batch of products, characterized in that in order to increase the accuracy of prediction of wear resistance as the initial the parameter uses the value of the area of the hysteresis loop obtained by measuring the surface thermo-emf (Seebeck method) with the heating of the “hot” probe on and off, with an increase in the area of Ora wear resistance of carbide cutting tools, a group of applicability to the increases.

The surface structure of a carbide cutting tool, which is formed in the process of manufacturing a hard alloy, has a great influence on its wear resistance. One of the most important characteristics of the surface structure, which determines the most important physical, mechanical and operational properties of carbide cutting tools of the applicability group K, is heat capacity and thermal conductivity. The latter, in turn, depend on temperature and significantly change as a result of the temperature effect on the surface and the formation of oxide, polyoxide and other structures on it. Surface compositions of various composition and properties in the form of films of various thicknesses, island structures, layered systems of nanoscale size, etc. perform various tasks related to reducing wear of cutting tools. So, for example, oxide and polyoxide structures formed on the surface of hard alloys, in the process of their formation and destruction, play the role of solid lubricant, distribute the movement of heat fluxes on the surface, in the near-surface zone and in the volume of hard alloys, and reduce the level of electrostatic (intermolecular) interaction by the boundaries of the contact of tool and work materials, thereby exerting a decisive influence on reducing wear on carbide cutting tools. Already at the stage of manufacturing hard alloys, a structure is formed on the surface and in the surface layers, which differs significantly from the structure located in the bulk. The surface structure is characterized by a high degree of imperfection, the content in its composition of a high concentration of impurity atoms embedded in the crystal lattice and replacing individual atoms of the main component in the nodes, the presence of edge and screw dislocations, pores and their clusters. Due to the high degree of imperfection, the surface structure has an increased sensitivity with respect to external influences on it. Due to the temperature effect on hard alloys, under the conditions of an open thermodynamic system, the formation of solid solutions and chemical compounds with different composition, structure and properties occurs on the surface and in the surface layers. These formations are formed with the participation of the main components of the hard alloy (tungsten carbides and cobalt bonds), impurities, as well as oxygen, nitrogen, hydroxyl groups, which are part of the hard alloys and come from the surrounding gas environment, respectively. The forming structures have a significant impact on the processes of formation, accumulation and distribution of heat both in the surface plane and in the direction of the deep layers of carbide cutting samples (plates). The process of surface and near-surface structural transformation in hard alloys of the applicability group K, due to thermal exposure, begins at sufficiently low temperatures (20-25 ° C) and is accompanied by a change in their heat capacity and thermal conductivity. The properties manifested during heating and cooling on the surface are closely related to the properties of the volume of hard alloys. In this sense, a stable connection exists between volume and surface. Any changes in surface properties depend on the composition and properties of the bulk structure. The heating of the surface is accompanied by its saturation with oxygen, due to the adsorption of oxygen from the surrounding gas medium and due to diffusion from the bulk structure of the hard alloy. Due to the transformations accompanying this process, the heat capacity of the surface increases, and the thermal conductivity decreases. The heat capacity of the bulk structure decreases, while the thermal conductivity increases. Surface cooling is accompanied by the departure of one part of the oxygen atoms due to disorption into the surrounding gas medium, and the other part due to diffusion, into the bulk structure. In this case, the heat capacity of the surface decreases, and the thermal conductivity increases. The heat capacity of the volume increases, while the thermal conductivity decreases. For each specific carbide structure (cutting insert), the degrees of these transformations both during heating and during cooling are strictly individual. They depend on the composition of hard alloys, the content and properties of the components (including the presence of impurities), the history of their preparation, etc. Oxygen flows from the side of the surrounding gas medium and from the side of the volume of the hard alloy take part in the transformation of the surface when it is heated. The contribution of each stream to surface reconstruction is determined by the chemical potentials at the phase boundaries: the surrounding gas medium — the surface and surface — the gas admixture of the volume. The difference in chemical potential between these phases determines the gradient of the chemical potential and the direction of the resulting flow of oxygen atoms. An approximate picture of the interaction of the surface with oxygen in the surrounding gas environment when it is heated will be as follows: oxygen adsorption by the surface, bond breakage of adsorbate molecules, distribution of atoms on the surface, formation of bonds with surface atoms (atomic layer formation), jumps of oxygen atoms into the surface defective layer - redistribution in the surface layer with the formation of bonds, the incorporation of oxygen atoms into the defective structure of the surface layer from the surface (in the octahedral Kie tungsten crystal lattice voids, as these positions are preferably free of carbon). An approximate picture of the interaction of the surface with volume oxygen can be represented as follows: ionization of the oxygen impurity due to heating, diffusion of impurity atoms to the surface, incorporation of oxygen atoms into the defective structure of the surface layer on the side of the volume (in the tetrahedral voids of the tungsten crystal lattice, since these positions are partially not occupied carbon). The presented process is accompanied by an increase in the surface heat capacity and volume thermal conductivity and a corresponding decrease in the volume heat capacity and surface thermal conductivity. The surface transformation during its cooling is accompanied by oxygen desorption into the surrounding gas medium and diffusion into the bulk structure of the hard alloy. The contribution of each stream to surface degradation is also determined by the chemical potentials at the phase boundaries: the surface is the surrounding gas medium and the surface is volume. The difference in chemical potential between these phases determines the gradient of the chemical potential and the direction of the resulting flow of oxygen atoms. An approximate picture of the mass transfer of oxygen from the surface to the surrounding gas environment will be as follows: weakening and destruction of bonds between atoms in compounds on the surface, decomposition of solid solutions, redistribution of atoms on the surface, the formation of oxygen molecules, desorption of volatile molecular compounds. An approximate picture of the mass transfer of oxygen from the surface to the volume will be as follows: decomposition of compounds formed upon heating of the surface in the surface region, diffusion of oxygen atoms into the structure volume, and the formation of bonds with volume atoms. The presented process is accompanied by a decrease in surface heat capacity and volume thermal conductivity and a corresponding increase in volume heat capacity and surface thermal conductivity.

The speed, composition and thickness of the structures formed on the surface depends on the value of the chemical potential, which in turn is a function of the concentration of oxygen on the surface, in the surrounding gas medium, and in the volume of the hard alloy. The chemical potential (toughness) between the tungsten and carbon in carbide grains located on the surface of the hard alloy and in the bulk, the state of the cobalt binder (thickness, type and degree of defectiveness, magnitude and sign of the stress state, etc.) have a significant influence on the value of the chemical potential. .), the presence of impurities interacting with carbide grains and a cobalt layer, the state of intergranular and interphase boundaries (formation of segregation of impurity atoms, solid solutions, chemical physical compounds).

The process of forming a surface film structure when heating a surface involves at least three stages. At the first stage, the molecules of the surrounding gas medium are captured by the surface, the adsorbed atoms are distributed on the surface and in the near-surface zone due to their diffusion, island films of atomic thickness are formed on the surface of the nuclei, island segregations grow and merge as oxygen arrives. In the second stage, the number of islands on the surface stabilizes, and the resulting ones grow in size. At the third stage, islet formations are combined with the formation of large islet formations and continuous films. There is a critical size and time required to achieve it, at which the forming surface film structure becomes stable and does not undergo significant transformations in the future (upon reaching a stationary temperature state). Similarly to the formation of oxide structures occurs in the surface zone. Both oxygen of the surrounding gas medium and oxygen atoms diffusing from the bulk structure take part in their formation. At the same time, local volume formations are formed in the near-surface zone, which, like germinal surface formations, increase in quantity, unite, and turn into clusters and bulk phases. The process of decomposition of structures on the surface during its cooling includes: the decomposition of solid solutions on the surface, the separation of island clusters from the film structure, the formation of small island systems from clusters, the degradation of islands due to diffusion of oxygen atoms into the volume of the alloy and oxygen desorption into the surrounding gas environment. The degradation of the surface film structure is also multi-stage. After reaching a certain degree of fragmentation of the film structure, the process of its degradation is inhibited and continues at a fairly low rate. Similarly, the decomposition of the oxide structure in the near-surface region occurs, which includes: the release of oxygen atoms from the bulk oxide phase, the formation of a fragmentary structure, its further decay, diffusion of oxygen atoms to the surface and into the volume, desorption of oxygen atoms from the surface and segregation of oxygen atoms in the bulk structure near electropositive impurities and grain boundaries.

Thus, changes in thermal characteristics (heat capacity and thermal conductivity) will be facilitated by current changes occurring on the surface and in the volume of hard alloys caused by temperature exposure (heating and cooling), namely: mass transfer of oxygen and various impurity elements from the surrounding gas environment and volume towards the surface and from the surface, increasing or decreasing the degree of adsorption by the surface of atoms and molecules of the surrounding gas medium, changing the selectivity of adsorption, foreign directivity and residual effects during structural transformations on the surface and in the volume, change and redistribution of heat fluxes propagating from the surface (from the place of local external heat exposure). Monitoring of processes occurring on the surface (the formation of adsorption layers, oxide films, nanosized oxide structures, etc.) caused by thermal exposure (heating and subsequent cooling), accompanied by a change in thermal characteristics (heat capacity and thermal conductivity), allows you to quickly and fairly high accuracy to predict the wear resistance of carbide cutting tools (cutting inserts) based on measuring the thermo-emf (Seebeck method).

The measurement of the thermo-emf was carried out using a setup equipped with a measuring table and two probes. The tip of one probe is made of copper, the other of tungsten alloy. The distance between the probes is constant and is 4 mm. The process of measuring the thermo-emf that arises between the probes mounted on a controlled surface (cutting insert) starts from the moment that the heating of the tungsten probe is carried out using a thin nichrome spiral covering this probe. The average heating rate of the tungsten probe is approximately 0.5 ° C / sec. The maximum heating temperature of the tungsten probe reaches 140 ° C. The duration of the measurement process is 4-8 minutes. The measurement of the thermo-emf is carried out continuously in two stages, including the measurement of the thermo-emf when the heating of the tungsten probe is switched on and with the further continuous measurement of the thermo-emf, but with the tungsten probe already turned off (measurement during subsequent natural cooling of the contact zone). Moreover, the measurement time of the thermo-emf during heating (2-4 min) should be equal to the measurement time of the thermo-emf during cooling (2-4 min). As a result of measurements of the surface thermo-emf, a hysteresis loop is obtained - the dependence of the thermo-emf value on the time of heating and subsequent cooling. The higher the growth rate of the thermoelectric power when heated and the more intense the decrease in the thermoelectric power when cooling, the higher the wear resistance of carbide cutting tools of applicability group K when they cut materials that cause intense adhesive wear.

The magnitude of the thermo-emf upon heating depends on the intensity of the increase in the temperature gradient between the copper and tungsten probes. The greater the temperature gradient (the temperature difference between the unheated - “cold” probe made of copper and the heated - “hot” probe made of tungsten alloy) at each next moment of time compared to the previous one with continuous heating - increasing temperature, the more intense the thermo increase emfs from time to time. The temperature gradient between the probes depends on the degree of surface oxidation in the contact (location) area of the tungsten (hot) probe and on the thermal characteristics of oxide films and structures formed on the surface and in the surface layers between the copper and tungsten probes. With an increase in the conversion intensity (oxidation state) of surface oxide films and near-surface oxide structures, the heat capacity of the surface of carbide cutting tools of the applicability group K increases, and the thermal conductivity decreases. Moreover, the ratio between changes in heat capacity, thermal conductivity and density of surface oxide structures is such that their thermal diffusivity, as a result, decreases. The reason for the higher heat capacity of tungsten oxide compounds compared to carbide compounds is a change in the nature of the chemical bonds between atoms. There is an increase in the specific gravity of ionic and covalent bonds with a simultaneous decrease in metal bonds. In this case, the threshold level of thermal energy required for the generation of phonon vibrations of the crystal lattice increases for tungsten oxide, compared with the level of thermal energy necessary for the generation of similar phonon vibrations for tungsten carbide. Similarly, cobalt oxide acquires a higher heat capacity in comparison with pure cobalt as a result of oxidation of the latter. As a result, thermal conductivity, with an increase in the degree of oxidation of the surface and near-surface structure, begins to take place more due to phonon vibrations of the lattice and less due to the motion of free electrons.

If the degree of surface oxidation during heating is higher than the oxidation state of the near-surface zone (external oxidation), then the high temperature gradient between the probes will increase solely due to a decrease in surface thermal conductivity, and decrease due to an increase in volumetric thermal conductivity. If the oxidation state of the near-surface zone is higher than the oxidation state of the surface, then the high temperature gradient will increase due to a decrease in volumetric thermal conductivity, and decrease due to an increase in surface thermal conductivity. A different ratio between the heat fluxes propagating during heating along the surface and directed into the volume of the hard alloy determines the shape of the upper part of the hysteresis loop “thermopower value - time”.

The magnitude of the thermo-emf upon cooling depends on the intensity of the decrease in the temperature gradient between the copper and tungsten probes. The smaller the temperature gradient (the temperature difference between the unheated - “cold” copper probe and the cooled - “hot” tungsten alloy probe), the lower the thermo-emf. In this case, the temperature gradient between the probes depends on the rate of decomposition of oxide and oxycarbide solid solutions, which occurs when the temperature decreases (when cooling with the “hot” probe turned off). The higher the decay intensity, the more intensely the thermal conductivity will increase and the more intensively the decrease in the temperature gradient and, accordingly, the thermo-emf will occur. If the diffusion of oxygen from the tungsten oxide crystal lattice during cooling occurs at a sufficiently high speed and significantly exceeds the rate of thermal compression of the tungsten crystal lattice that occurs during cooling, then the decomposition of surface and surface compounds formed during heating with the participation of oxygen will be unhindered and at a high speed. This is possible only with a low chemical bond strength between the elements of the oxide compound formed at the control stage with the heating of the “hot” probe turned on. With an increase in the conversion intensity (degree of decomposition) of surface oxide films and near-surface oxide structures, the heat capacity of the surface of carbide cutting tools of the applicability group K decreases, and the thermal conductivity increases. The thermal conductivity of the surface to a greater extent will be due to free electrons and to a lesser extent due to phonon vibrations. In this case, the ratio between changes in heat capacity, thermal conductivity and density of surface structures is such that their thermal diffusivity, in the end, increases. The reason for the lower heat capacity of the surface tungsten carbide compounds as compared with oxide compounds is a decrease in the specific gravity of covalent and ionic chemical bonds between atoms while increasing the specific gravity of the metal bond. In this case, the threshold level of thermal energy for tungsten carbide, which is necessary for generating the corresponding phonon vibrations of the crystal lattice, is reduced, compared with the level of thermal energy necessary for the generation of similar phonon vibrations for tungsten oxide. Likewise, cobalt acquires lower heat capacity in comparison with cobalt oxide as a result of reduction of the latter.

If the degree of decomposition of solid solutions on the surface during cooling is higher than in the near-surface zone, then a low temperature gradient will be achieved due to an increase in surface thermal conductivity, and its decrease will be delayed due to insufficient growth rates of near-surface (bulk) thermal conductivity. If the degree of decomposition of solid solutions during cooling in the near-surface zone is higher than on the surface, then a low temperature gradient between the probes will be achieved due to an increase in near-surface (volume) thermal conductivity, and its decrease will be delayed due to insufficient rates of increase in surface thermal conductivity. A different ratio between the heat fluxes propagating during cooling along the surface and directed into the volume of the hard alloy determines the shape of the lower part of the hysteresis loop “thermopower value - time”.

In the course of the experiments, it was found that the wear resistance of tungsten-cobalt carbide cutting tools of the applicability group K when cutting materials that cause intense adhesive wear is closely related to the shape of the thermo-emf curves obtained as a function of time when monitoring the surface during heating of tungsten probe and its subsequent cooling. As a result, the thermo-emf curves obtained by heating and cooling form a hysteresis loop with a certain area. With an increase in the hysteresis area, the operational characteristics of the cutting insert — its wear resistance — increase. A more intense increase in thermo-emf upon heating can be accompanied by both a more intense and less intense decrease in thermo-emf upon cooling. Also, a less intense increase in the thermo-emf upon heating can be accompanied by both a less intense and a more intense decrease in the thermo-emf upon cooling. Figure 1 shows typical dependences of the thermo-emf obtained respectively upon heating (the upper branch of the OABSD and the lower branch of the DEKMR), which form a hysteresis. With increasing hysteresis area, the wear resistance of carbide inserts increases. Thus, the more intensively the thermoelectric power increases with time (OAVSD curve) during heating and the more intense the thermoelectric power decreases with time (DEKMR curve) when cooling, the higher tungsten carbide plates have higher performance (wear resistance) - cobalt hard alloys (group of applicability K) when they cut materials that cause intense adhesive wear.

The main reasons for the increase in wear resistance of cutting tools of the applicability group K with an increase in the area of the hysteresis loop are: an increase in the efficiency of the polyoxide mass as a solid lubricant, as well as as a heat-shielding and anti-adhesive agent. With increasing oxidation intensity, an oxide (polyoxide) crystal lattice (higher tungsten oxide) is formed with the highest number of planes and “easy” slip directions (most optimal for playing the role of solid lubricant in the contact zone). This oxide has a low density and correspondingly high thermal insulation ability, which protects the hard alloy from thermal destruction. The intense nature of the decomposition of solid solutions upon cooling of the surface (formed upon heating) indicates a low strength of chemical bonds between the constituent elements of the oxides. The latter is a condition for the high polarizability of the oxide (polyoxide) mass and the presence of a high dielectric constant. In turn, the high dielectric constant of the medium (oxide layer) in the contact zone between the cutting and the processed material significantly reduces the level of intermolecular interaction and provides increased wear resistance of the cutting tool.

The formation of the most effective oxide (polyoxide) structure on the surface, which provides the greatest wear resistance of the cutting tools of the applicability group K, depends primarily on the composition and state of the bulk structure of hard alloys, the chemical bond strength of carbides, the distribution of carbide bond strength over the grain volume, the state of bond between carbide grain and cobalt, the presence of controlled and uncontrolled impurities in carbide grain, cobalt at the interface, etc.

Thus, the larger the area of the hysteresis loop obtained by measuring the thermo-emf during heating and subsequent cooling of the tungsten probe, the higher the rate of formation of oxides, the lower the bond strength between the oxide elements, the higher their ability to turn into solid lubricant upon failure, and the higher their thermal insulation properties, their dielectric constant is higher and, accordingly, the wear resistance of carbide cutting tools of the applicability group K is higher when cutting materials that cause intense dgezionny wear.

An essential feature of the proposed method is that in accordance with its methods - without additional costs and technical difficulties, it seems possible to conduct a more objective and accurate assessment of wear resistance - due to the operational analysis and comparison of current controlled and reference parameters obtained in a wide range of cutting conditions and temperatures cutting. The properties of polyoxide films formed in the contact zone during cutting are significantly affected by protective coatings and various surface hardenings, however, and in this case, as the tests showed, a stable correlation relationship is also observed between the wear resistance of cutting tools and the area of the hysteresis loop.

The implementation of the method is carried out sequentially, passing through several stages. First carbide cutting tools (cutting inserts) are subjected to control by measuring the thermo-emf. Previously, before measurements, the surfaces of the cutting inserts are cleaned. After that, the measuring head of the device with copper and tungsten probes is placed on any surface convenient for measurement. The copper probe is “cold” and the tungsten probe is “hot”. Copper and tungsten probes are made of wire with a diameter of 2.5 mm. The tungsten probe is heated during surface control using a spiral made of nichrome wire with a diameter of 0.25 mm. The distance between the probes in the control position is 4 mm. The hot probe is heated from an individual power source at a voltage of 20 V. The device is equipped with a digital voltmeter that records the value of the thermo-emf generated when the tungsten probe is turned on and off. A digital voltmeter is connected to a computer through a converter, and continuously recorded data is transmitted to the display. Measurement (fixation) of the thermo-emf was carried out every 15 seconds after turning on the heating on the "hot" probe. The process of measuring the thermo-emf at the heating stage continues for 2-4 minutes. As a result of the measurements, we obtain data for constructing the OABSD curve. After turning off the heating of the “hot” probe, also, every 15 seconds, the thermo-emf is measured (fixed) during cooling. As a result, data for the DECM curve are obtained. As a result, when measuring the thermo-emf of a batch of carbide inserts, with the heating of the "hot" probe on and off, a family of hysteresis curves having one or another area is obtained. Figure 2 presents a diagram of the installation for measuring surface thermal emf.

Then carry out reference tests. For this, a fairly representative sample of carbide (group K) cutting tools (cutting inserts) is made from an existing batch of carbide products and they are tested for their wear resistance during cutting on a metal cutting machine, usually steel or alloy, causing intense adhesive wear. Cutting is carried out at an optimum or close to cutting speed [See, for example, RU 2168394, C27 B23B 1/00 of 06/10/01. Bull. No. 16]. The amount of wear resistance is determined as the uptime for a specified blunting criterion - the wear facet on the back surface (usually 0.2-0.8 mm).

After that, a graph of the reference dependence “wear resistance - the value of the area of the hysteresis loop” is plotted, bounded above, respectively, by the OAVSD curve obtained with the heating of the “hot” (tungsten) probe turned on, and bounded below, respectively, by the DEKMR curve obtained with the heating of the “hot” probe turned off. There is a stable correlation between the wear resistance of cutting tools of the applicability group K and the area of the hysteresis loop. With an increase in the area of the hysteresis loop of controlled cutting inserts (Spt), when they process 12X18H10T austenitic steel, which causes intense adhesive wear, their wear resistance increases. This experimentally obtained dependence is quite well approximated with a high degree of tightness of the correlation relationship by a linear dependence:

And mT = _E · S _T + B _e.

Subsequent control of carbide cutting tools of the current batch of products supplied is based on measuring only the selected initial parameter, namely: the size of the hysteresis loop bounded by the upper curve obtained by measuring the thermo-emf, with the heating of the "hot" probe and the lower curve obtained with measuring the thermo-emf when the heating of the "hot" probe is turned off. Based on the obtained reference relationship "wear resistance (T _E ) - area (S _E )" and formula (1) above, a forecast of the wear resistance of the current batch of carbide products is carried out. The predicted wear resistance may be higher or lower than that obtained from benchmark tests. With an increase in Spt (the average area of the hysteresis loop for a controlled sample), the predicted wear resistance of the inserts in the delivered batch increases.

The proposed method allows to predict with high accuracy the wear resistance of carbide group applicability K cutting tools, when machining steels and alloys that cause intense adhesive wear. The selectivity (focus) of this method for predicting the wear resistance of carbide cutting tools of only the applicability group K significantly increases its accuracy.

Figure 5 presents a graphical correlation dependence of the change in the value of wear resistance (T) of carbide cutting tools of the applicability group K on the size of the area (S).

An example of a method for predicting the wear resistance of carbide cutting tools. First, carbide cutting inserts made of VK4 obtained from a sample from the previous (reference) batch of products are first wiped with an alcohol solution and subjected to control by measuring the surface thermal emf (Seebeck method). The thermo-emf after turning on the heating for the “hot” probe was measured for 4 minutes every 15 seconds. During this time, the “hot” probe was heated to 120-140 ° C. After turning off the heating for the “hot” probe, the thermo-emf was also measured for 4 minutes and also every 15 seconds. The thermo-emf values obtained for the first sample of cutting inserts, consisting of 10 pieces, amounted to; first plate: 0; thirty; 72; 118; 156; 180; 202; 220; 236; 246; 258; 266; 272; 278; 282; 286; 290; 274; 228; 202; 176; 158; 135; 123; 109; 97; 87; 80; 72; 64; 58; 51; the conditional area of the hysteresis loop (S1 μV × s) was 17483; second plate: 0; 28; 68; 108; 136; 172; 192; 214; 230; 242; 254; 262; 266; 274; 279; 284; 287; 272; 226; 192; 173; 156; 133; 121; 107; 95; 86; 77; 70; 62; 56; fifty; 47; the conditional area of the hysteresis loop (S2) was 16530; third plate: 26; 64; 102; 134; 164; 184; 206; 223; 236; 247; 256; 264; 270; 276; 279; 288; 270; 241; 200; 171; 154; 131; 119; 104; 93; 85; 75; 68; 60; 54; 49; 40; the conditional area of the hysteresis loop (S3) was 16095; fourth plate: 0; 26; 62; one hundred; 132; 162; 182; 203; 220; 234; 243; 253; 262; 268; 274; 272; 278; 250; 220; 190; 168; 148; 128; 115; 101; 90; 81; 72; 64; 58; 53; 48; 45; the conditional area of the hysteresis loop (S4) was 14378; fifth plate: 25; 60; 94; 124; 150; 170; 190; 204; 218; 229; 238; 245; 252; 258; 263; 266; 240; 217; 188; 160; 138; 122; 108; 96; 85; 77; 70; 63; 56; 52; 46; 44; the conditional area of the hysteresis loop (S5) was 14220; sixth plate: 0; 24; 58; 92; 116; 138; 154; 169; 182; 192; 200; 207; 213; 218; 223; 227; 232; 215; 185; 161; 139; 125; 114; 99; 87; 77; 72; 66; 58; 55; 46; 40; 37; the conditional area of the hysteresis loop (S6) was 13920; seventh plate: 0; twenty; 46; 76; 98; 116; 134; 151; 164; 177; 186; 197; 204; 208; 214; 218; 220; 197; 170; 154; 129; 123; 108; 93; 85; 75; 70; 60; 56; 54; 45; 39; 35; the conditional area of the hysteresis loop (S7) was 13283; eighth plate: 0; 19; 45; 72; 93; 102; 126; 146; 158; 171; 183; 198; 200; 206; 210; 214; 216; 208; 167; 148; 125; 119; 104; 91; 83; 68; 67; 56; 54; 53; 43; 37; 34; the conditional area of the hysteresis loop (S8) was 11760; ninth plate: 0; 19; 44; 70; 92; 110; 124; 144; 156; 167; 175; 184; 190; 196; 200; 205; 208; 199; 160; 146; 123; 112; one hundred; 87; 78; 66; 62; 55; fifty; 45; 41; 36; 33; the conditional area of the hysteresis loop (S9) was 10073; tenth plate: 0; eighteen; 42; 67; 90; 108; 123; 138; 149; 159; 167; 174; 180; 185; 189; 193; 195; 185; 154; 136; 120; 105; 92; 83; 74; 63; 60; 54; 48; 44; 40; 34; 32; the conditional area of the hysteresis loop (S10) was 9225. The average value of the area (S _E1 ) of the hysteresis is 13696.7 μV × sec. The thermo-emf values obtained for the second sample of cutting inserts, consisting of 10 pieces, amounted to; first plate: 0; thirty; 80; 123; 165; 201; 230; 254; 272; 289; 303; 315; 325; 333; 341; 348; 352; 325; 284; 248; 216; 190; 167; 150; 135; 121; 109; 99; 89; 81; 74; 67; 60; the conditional area of the hysteresis loop (S1, μV × s) was 21840; second plate: 0; 27; 63; 102; 140; 174; 201; 224; 243; 260; 272; 282; 288; 291; 294; 300; 305; 296; 258; 220; 195; 160; 142; 130; 116; one hundred; 92; 84; 74; 66; 58; 54; 48; the conditional area of the hysteresis loop (S2) was 18263; third plate: 0; 26; 61; 98; 134; 164; 188; 211; 229; 243; 254; 263; 271; 278; 282; 286; 290; 274; 228; 202; 176; 154; 135; 119; 105; 95; 84; 76; 69; 61; 56; fifty; 46; the conditional area of the hysteresis loop (S3) was 17040; fourth plate: 0; 25; 59; 96; 130; 160; 184; 203; 221; 237; 247; 256; 267; 272; 274; 276; 278; 252; 219; 188; 168; 150; 128; 115; 102; 90; 81; 72; 65; 59; 53; 49; 44; the conditional area of the hysteresis loop (S4) was 16313; fifth plate: 0; 24; 56; 92; 124; 150; 170; 190; 204; 218; 229; 238; 245; 252; 258; 263; 266; 248; 215; 186; 166; 148; 124; 108; 96; 88; 78; 71; 64; 58; 52; 48; 42; the conditional area of the hysteresis loop (S5) was 14963; sixth plate: 0; 23; 53; 80; 108; 132; 150; 169; 186; 198; 210; 220; 228; 235; 241; 246; 251; 236; 208; 184; 158; 138; 120; 107; 94; 86; 76; 70; 63; 57; 51; 47; 40; the conditional area of the hysteresis loop (S6) was 13965; seventh plate: 0; 22; fifty; 78; 106; 130; 148; 166; 178; 189; 198; 207; 213; 218; 223; 228; 230; 225; 206; 182; 156; 136; 118; 106; 92; 84; 74; 66; 62; 55; fifty; 46; 38; the conditional area of the hysteresis loop (S7) was 11093; eighth plate: 0; 21; 47; 74; 96; 118; 132; 150; 160; 173; 184; 192; 200; 206; 212; 215; 218; 205; 183; 158; 135; 119; 108; 94; 85; 78; 72; 69; 59; 53; 48; 45; 36; the conditional area of the hysteresis loop (S8) was 10988; ninth plate: 0; twenty; 45; 70; 93; 112; 129; 144; 156; 167; 175; 184; 190; 196; 200; 295; 208; 199; 174; 150; 129; 112; 102; 88; 78; 72; 64; 55; fifty; 46; 42; 38; 34; the conditional area of the hysteresis loop (S9) was 10313; tenth plate: 0; 19; 42; 67; 90; 108; 123; 138; 149; 159; 167; 174; 180; 185; 189; 193; 195; 183; 157; 138; 120; 105; 95; 83; 74; 68; 60; 54; 48; 44; 40; 36; 32; the conditional area of the hysteresis loop (S10) was 9750. The average value of the hysteresis area (S _E2 ) is 14452.8 μV × s.

Then, tests are carried out on the wear resistance of carbide cutting tools - carbide cutting inserts of the VK4 brand, which have passed the control stage by measuring the surface thermo-emf. As the processed material was used austenitic steel 12X18H10T. The cutting speed during the tests was chosen equal to 70 m / min. The feed rate and depth of cut were respectively 0.23 mm / rev and 1.5 mm. Cutting was carried out without cooling. As a blunting criterion, the wear of the insert along the rear surface, equal to 0.6 mm, was taken. Resistance for samples of 10 pieces of the first reference sample was: 38.5; 37.5; 37.0; 35.5; 35.0; 34.0; 33.0; 32.0; 31.0; 30.0 minutes The average value was 34.35 minutes. Resistance for samples of 10 pieces of the second reference sample was: 42.5; 39.0; 38.0; 37.5; 36.0; 34.0; 32.0; 31.5; 31.0; 30.5 minutes The average value was 35.20 min.

The measured and calculated characteristics of the thermo-emf were compared with the wear resistance of carbide cutting tools obtained by cutting steel 12X18H10T. According to T (wear resistance of carbide cutting tools) and S (hysteresis loop area), a graph of the reference, correlation dependence "wear resistance (T _E ) - hysteresis loop area (S _E )" was built. The points obtained by comparing T and S for both samples fit quite accurately into the general direct relationship “T _E (wear resistance) - S _E (area)”, which indicates a high correlation between wear resistance and the area of the hysteresis loop (reflecting the intensity of surface oxidation - OAVSD curve and polarization intensity - relative permittivity growth - DEKMR curve). Figures 3 and 4 show the values of the hysteresis loop area for VK4 cutting inserts, respectively, for the samples 1 and 2 subjected to control by measuring the surface thermo-emf, with the "hot" probe turned on and off.

To predict the wear resistance of carbide cutting inserts in the subsequent current (manufactured or obtained) and intended for consumption batch of samples, only the hysteresis loop area is tested according to the readings of the thermo-emf measured on the surface. According to the results of measuring the thermo-emf, the area of the hysteresis loop for 10 cutting inserts made of VK4 hard alloy from the delivered (current) batch was: 12100; 13,200; 14500; 14950; 16,250; 17065; 18970; 19040; 19560; 20750. The total average value (S) for this value was 16639 units. Based on the average value of (Spt) obtained by measuring the thermo-emf on the surface of carbide cutting inserts from VK4 of the current batch, and formulas (1) find (Tpt) - the average predicted wear resistance of carbide cutting inserts from VK4 for the current batch of delivered products. As a result, the predicted value of wear resistance from the calculations, for the controlled current batch of products, averaged 34.70 min, which is below the level of wear resistance of the reference (previous) batch of cutters. Control tests carried out during cutting showed that the average wear resistance of the cutting inserts was 36.40 min. The latter confirms the accuracy of the forecast. When predicting wear resistance for the current batch of carbide tools, there is no need for expensive and time-consuming wear tests conducted on metal cutting machines. The method has a high forecast accuracy. This is due to the close relationship between the properties of carbide cutting tools (wear resistance) and the properties of hard alloys to generate an effective polyoxide structure on the surface when heated - a solid lubricant with high dielectric constant. Figure 5 shows the correlation dependence of predicting the wear resistance of carbide cutting tools from VK4 (applicability group K), when cutting chrome-nickel steel 12X18H10T, on the size of the hysteresis loop area obtained during their control.

Due to the comparison of the data on the forecast of wear resistance obtained in accordance with the prototype and the proposed method, as well as as a result of control experimental studies of wear resistance performed in the process of cutting austenitic steel, it was found that the results obtained in accordance with the prototype differ from the control tests by 15- 20%, while the results obtained by the proposed method differ only by 5-10%.

Thus, the proposed control method - predicting the wear resistance of carbide cutting tools can be used with sufficiently high economic efficiency in enterprises manufacturing or consuming carbide products.

Claims (1)

A method for predicting the wear resistance of carbide applicability groups of K cutting tools according to the selected initial parameter, including carrying out benchmark wear tests in the process of cutting materials at an optimum or close cutting speed, testing to change the value of the initial parameter from the properties of the surface structure formed during the manufacture of carbide cutting tool, the construction of the reference - correlation dependence "initial parameter - wear bone "statistical control only parameter values starting from the current batch of carbide cutting tools, wear forecast for the current batch of instruments based on the relationship:

where a _E and in _E are constant coefficients:

of them:
T _PT (min) is the current wear resistance in minutes for carbide cutting tools (inserts) that have been tested from the forecasted current batch of samples;
S _PT (μV · s) - the current value (hysteresis loop area) of the selected initial parameter obtained by monitoring the thermophysical properties of the surface of carbide cutting tools (inserts) from the current (controlled batch);
Te ₁ and Te ₂ (min) - wear resistance in minutes for two samples of interchangeable carbide cutting tools (inserts) from the reference batch of carbide products;
Sе ₁ and Sе ₂ (μV · s) are the values of the initial parameter (hysteresis loop area) for two samples of carbide cutting tools (inserts), obtained by surface control of carbide cutting inserts from the reference batch of received (sent) products, characterized in that, in order to improve the accuracy of predicting wear resistance, the area of the hysteresis loop - S obtained by monitoring the surface thermo-EMF with the heating probe turned on and off is used as the initial parameter cheniem area (S) which increases wear resistance.

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