RU2570604C1 - Method of determination of tool strength - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: to determine strength of tool operating as part of press for metals cold work by pressure at work load in plane, perpendicular to treatment plane, coercitive force is measured at most loaded areas of tool during its operation. Measurement is performed treatment plane in directions parallel and perpendicular plane of work load acting on tool. The obtained values are compared with critical values, and current life time of the tool is estimated. For estimation minimum of values of the current life time calculated according to specified equations is used.

EFFECT: as result during determination of the tool strength effect of the tool design and material, degree of wear and work load on the process operation are considered, this increases accuracy of determination.

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Description

The invention relates to mechanical engineering and can be used mainly as a method for reliably determining the durability of a tool operating as part of a press for cold metal forming with a working load on the tool in a plane perpendicular to the processing plane, based on the correlation between magnetic and physical-mechanical properties.

The prior art method for determining the tool life according to the formula proposed by Romanovsky V.P. ("Handbook of cold stamping." - L .: Engineering. Leningrad. Department. 1979. - 782 s., Ill., P. 600):

where s is the thickness of the workpiece material (mm ² ),

σ _in - the tensile strength of the workpiece material (kgf / mm ² ),

and - a coefficient depending on the type of stamp (for example, 16000 universal-prefabricated stamps, 25000 - punch stamps, 30,000 - blanking stamps).

The disadvantage of this solution is that the proposed formula takes into account only the parameters of the workpiece, and is also relevant only under certain industrial and technological conditions, which leads to low accuracy and low efficiency of the known method for determining tool life.

Closest to the claimed prototype is a method of operating a roll, including magnetic flaw detection by measuring the coercive force on the surface of the roll before putting it into operation, operating the roll and writing off, characterized in that it additionally periodically conducts magnetic flaw detection of the roll by measuring the distribution of coercive force over the surface and with the average value of the coercive force exceeding twice the average value of the coercive force before putting into operation, write off the roll or low temperature tempering (RU, application for invention No. 2003108187 A, B21B 28/02, publ. September 20, 2004).

The disadvantages of the prototype include its low accuracy and low efficiency, due to the lack of correlation of the measured indirect parameter - coercive force - with real processing parameters and, as a result, an overestimated margin of safety.

The claimed technical solution was based on the task of creating a method for the most reliable determination of tool life, working as part of a press for cold metal forming with a working load on the tool in a plane perpendicular to the processing plane, which would take into account the influence of the main factors - the design and material of the tool, the design and degree of wear of the equipment, the schedule of workloads of the technological operation, etc.

The technical result of the invention is the optimization of the resource of the tool while eliminating the possibility of an emergency at work.

The task and the claimed technical result are ensured by the fact that in the method for determining the durability of a tool operating as a press for cold metal forming with a working load on the tool in a plane perpendicular to the processing plane, including measuring the coercive force on the most loaded parts of the tool during operation, comparing the obtained values with the critical one and assessing the current tool life, the coercive force is measured in the plane of the ar work in the directions parallel and perpendicular to the plane of the work load on the tool, and as the current resource take the smallest of the calculated values

and

where dN is the current resource of the instrument,

dH _c1 is the difference between the critical value and the value of the coercive force in the most loaded section of the tool working part, measured in a direction parallel to the plane of the tool working load, A / m;

dH _c2 is the difference between the critical value and the value of the coercive force in the most loaded section of the tool working part, measured in the direction perpendicular to the plane of the tool work load, A / m;

Χ ₁ - tensile strength of the workpiece material (MPa),

X ₂ - tensile strength of the tool material (MPa),

X ₃ - the number of resurfacing of the tool,

X ₄ - the number of parts already processed by the tool at the moment,

X ₅ - the thickness of the workpiece sheet (mm),

X ₆ - rated press force (kN).

An analysis of the prior art by the applicant, including a search by patent and scientific and technical sources of information and identification of sources containing information about analogues of the claimed technical solution, made it possible to establish that no analogues were found that are characterized by signs and relationships between them, identical or equivalent to all essential features of the claimed technical solutions, and the prototype selected from the identified analogues (as the analogue closest in terms of the totality of features) made it possible to identify the essential essential (in relation to the technical result perceived by the applicant) distinctive features in the claimed subject matter of the invention set forth in the formula.

Therefore, the claimed technical solution meets the condition of patentability "novelty" under the current law.

In order to verify the conformity of the claimed technical solution to the requirement of the patentability condition “inventive step”, the applicant conducted an additional search of similar solutions known from the prior art in order to identify features that match the distinctive features of the claimed technical solution, the results of which show that the claimed technical solution does not follow ( for a specialist) explicitly from the prior art, since the influence of the prior art (as determined by the applicant) does not reveal transformations provided for by the essential features of the claimed technical solution for achieving the technical result perceived by the applicant.

In particular, the claimed technical solution does not provide for the following transformations of the known prototype object:

- addition of a well-known object by any well-known sign, attached to it according to known rules, to achieve a technical result, in respect of which the influence of such additions is established;

- replacement of any sign of a known object with another well-known sign to achieve a technical result, in respect of which the influence of such a replacement is established;

- the exclusion of any sign of a known object with the simultaneous exclusion due to the presence of this sign of the function and the achievement of the usual result for this exclusion;

- an increase in the number of similar features in a known object to enhance the technical result due to the presence of just such signs in the object;

- the implementation of a known object or part of it from a known material to achieve a technical result due to the known properties of the material;

- the creation of an object that includes known features, the choice of which and the relationship between them are based on known rules and the technical result achieved in this case is due only to the known properties of the features of this object and the relationships between them.

Therefore, the claimed technical solution meets the requirement of the patentability condition "inventive step" under applicable law.

The essence of the claimed method is illustrated by graphic materials, where in FIG. Figure 1 shows a diagram of the value of the coercive force in the machining plane in the coordinate system ОХ-ΟΖ, where ОХ is the direction parallel to the plane of the work load on the tool (actually parallel to the front of the press), ΟΖ is the direction perpendicular to the plane of the work load on the tool (actually - perpendicular to the front press).

The coercive force H _c (A / m) is taken as the main controlled parameter, since it is uniquely associated with residual plastic deformation, i.e. with the level of damage to the metal.

From the diagram (in Fig. 1 is an example, a lot of diagrams were obtained during the study), it follows that for a tool working as part of a press for cold metal forming with a working load on the tool in a plane perpendicular to the processing plane, the maximum values of the coercive force are practically in 100% of cases received in the directions of OX and / or ΟΖ, which is taken into account in the claims.

The proposed method is based on the principle of test measurements of the parameters listed in the claims for a specific process of processing a particular part with a specific tool on specific equipment, followed by mathematical modeling of the dependence of the determined parameter — the current (residual) resource of the tool — on the above parameters.

The method is implemented as follows.

1. The value of the coercive force for the tool used for the manufacture of working parts is measured experimentally or according to literature, which corresponds to prefracture during heat treatments recommended by the governing materials (GOSTs, etc.).

2. The current value of the coercive force is measured in the most loaded area of the working part of the tool (determined either by expert data or by calculation by numerical methods).

3. The following data are determined: X ₁ - tensile strength of the workpiece material ("Handbook of cold stamping", 6th edition revised and enlarged. - L.: Engineering. Leningrad. 1971. - 782 s, ill., p. 740-744 or experimentally), MPa, X ₂ — tensile strength of the matrix material (for example, according to “Marochnik steel and alloys” under the editorship of AS Zubchenko - M .: Mechanical Engineering, 1977. - 380 pp. or experimentally ), MPa, X ₃ - the number of resurfacing (from the technological magazine of the workshop), pcs, X ₄ - the number of parts removed from the stamp at the time of the study (from the technological magazine shop), pcs, Х ₅ - thickness of the workpiece sheet (terms of reference), mm, Х ₆ - nominal strength of the press (determined by the standard method, for example, “Cold stamping handbook”, - L .: Engineering. Leningrad. 1971. - 782 s, ill., pp. 22-24, 481), kN.

4. According to the proposed formulas, the current tool life is calculated in two directions (perpendicular and parallel to the front of the press).

5. When the value dN <1 is reached, the tool should be decommissioned by replacing it with a new or restored one.

The reliability of the obtained equations and the adequacy of the model were assessed using the Tail mismatch coefficient and the Fisher criterion (Efimova, M.R. General statistics theory: Textbook / Μ.Ρ Efimova, E.V. Petrova, V.N. Rumyantsev / - M .: INFRA-M, 1996, 340 p.) Theil mismatch coefficient was: for the model in the direction of OX 0.065, in the direction of ΟΖ 0.124. The calculated value of the Fisher test for the model in the direction of the OX axis was 340.90, ΟΖ 7.99, which is more than the theoretical value (7.20), therefore, with a probability of more than 99%, the model is adequate.

An example implementation of the claimed method for determining the tool life.

The die matrix is made of material X12MF (GOST 5950-2000). For this material, we conducted experimental studies on samples of this steel. The samples were subjected to heat treatment (similar to the working parts of dies):

- preheating to 650-700 ° C;

- final heating to 950-1050 ° C;

- quenching in oil;

- vacation 170-190 ° C for 1.5 hours in air.

The strip was cut into elements with dimensions of 80 × 300 × 150 mm mechanically. Elements were cut into blanks for making samples. When cutting, the orientation of the samples with respect to the main directions of the initial strip was observed. During the experiments, the certified KIM-2M device was also used.

For measuring the coercive force on samples according to GOST 12119.3-98 “Methods for the determination of magnetic properties and electrical properties. The method of measuring the coercive force in an open magnetic circuit ”the following requirement is imposed on the test object - the ratio of the length of the test object to the square root of the cross-sectional area must be at least ten. All test samples corresponded to him. The following measurement parameters were applied - demagnetization current 155 mA, 3 magnetization pulses.

The coercive force (A / m) was measured in two mutually perpendicular directions (parallel and perpendicular to the plane of the working load on the tool, or, in production terminology, parallel and perpendicular to the direction of the broach), as well as after testing the samples for crack resistance (near the fracture zone) for determining the value of the coercive force corresponding to the moment of prefracture.

Statistical processing of experimental data:

Determination of sample characteristics (Wentzel E.S. Probability Theory. M .: Nauka, 2003. - 576 s, p. 110)

1. The average value of the investigated value

where n is the number of measurements; H _ci is the value of each of the measurements.

2. Dispersion

3. The standard deviation

4. Range of change (range)

5. Nominal value

where H _Cmin , H _Cmax are the minimum and maximum values of the coercive force according to the measurements.

6. The coefficient of variation

6. The coefficient of relative asymmetry

7. The coefficient of relative dispersion

(среднее значение по (1)); σ_H=839 (среднеквадратичное отклонение по (3)); 2Δ=3014 (размах по (4)); H_CH=6914 (номинальное значение по (5)); k_V=11,93% (коэффициент вариации по (6); k_T=0,08 (коэффициент относительной асимметрии по (7)); α=1,67 (коэффициент относительного рассеяния по (8)). Для выборки Н2 (параллельно направлению протяжки) - $$\overline{H_c}=6675$$

; σ_H=956; 2Δ=5618; H_CH=5864; k_V=17,32%; k_T=0,25; α=1,20. Для выборки Н3 (предразрушение) - $$\overline{H_c}=8077$$

; σ_H=429; 2Δ=1507; H_CH=8003; k_V=5,31%; k_T=0,10; α=1,71. Полученные данные сведены в Таблицу 1. Очевидно, что все выборки соответствуют нормальному распределению (Фиг. 2), для которого обязательно выполнение следующих условий (Вентцель Е.С. Теория вероятности. М.: Наука, 2003. - 576 с, стр.110):For sample H1 (perpendicular to the direction of broaching), $$\overline{H_c}=7027$$

(average value according to (1)); σ _H = 839 (standard deviation according to (3)); 2Δ = 3014 (range according to (4)); H _CH = 6914 (nominal value according to (5)); k _V = 11.93% (coefficient of variation according to (6); k _T = 0.08 (coefficient of relative asymmetry according to (7)); α = 1.67 (coefficient of relative scattering according to (8)). For sample H2 ( parallel to the direction of broaching) - $$\overline{H_c}=6675$$

; σ _H = 956; 2Δ = 5618; H _CH = 5864; k _V = 17.32%; k _T = 0.25; α = 1.20. For sample H3 (pre-destruction) - $$\overline{H_c}=8077$$

; σ _H = 429; 2Δ = 1507; H _CH = 8003; k _V = 5.31%; k _T = 0.10; α = 1.71. The obtained data are summarized in Table 1. It is obvious that all the samples correspond to the normal distribution (Fig. 2), for which the following conditions are mandatory (E. Wentzel, Probability Theory. M .: Nauka, 2003. - 576 s, p. 110 ):

For a normal distribution, the probability density distribution curve is described by the following equation (E. Wentzel, Probability Theory. M .: Nauka, 2003. - 576 s, p. 112)

A probability density distribution graph is shown in FIG. 2 An analysis of the probability density distribution graphs showed that the primary (for intact operational loading of the material) and secondary (corresponding to the pre-fracture) Gaussian curves are located extremely close to each other. This is because the X12MF steel is destroyed by almost a brittle mechanism.

It is necessary to determine the life of the die matrix for cutting-punching the details of the washer from 10 kp material GOST 16523-97, material thickness 1 mm, outer diameter 15 mm, inner 8 mm. The matrix material is steel X12MF.

Constant Parameters:

А/м - принимается средним по выборке экспериментальных данных (табл.1).Χ ₁ - tensile strength of the workpiece material, taken equal to 320 MPa (sheet material from steel 10 kp GOST 16523-97), X ₂ - tensile strength of the matrix material, taken 1364 MPa (steel X12MF with the above heat treatments - experimental studies of the authors), X ₅ - the workpiece sheet thickness is 1 mm (technical specifications), X ₆ is the nominal press force, we take 250 kN (calculated and selected according to the standard procedure for the cutting-punching operation) - the cut area is 72.22 mm ² , the cut resistance is 270 MPa, therefore technological power will be By cutting the shear area to shear resistance, it will be 195 kN. The press is selected by force with a margin of 1.25 the closest from a series of presses. We select a press with a rated force of 250 kN, the critical value of the coercive force, at which the tool loses its operational properties, $$H_{\mathrm{from}}^{\mathrm{to}R}=8077$$

A / m - is taken as the average of the sample of experimental data (Table 1).

Variable Parameters:

X ₃ - the number of resurfacing of the tool, at the initial moment we accept 0 for the new stamp;

X ₄ - the number of parts already processed by the tool at the current moment, at the initial moment we accept 0 for a new stamp;

N _s1 - the difference between the critical value and the value of the coercive force in the most loaded section of the working part of the tool, measured in a direction parallel to the front of the press, A / m;

H _c2 - the difference between the critical value and the value of the coercive force in the most loaded section of the working part of the tool, measured in the direction perpendicular to the front of the press, A / m

According to the proposed formulas, the tool resource is determined in the directions ОХ and ΟΖ. The direction of the OH is parallel to the front of the press, ΟΖ is perpendicular to it. The matrix is made and located so that the direction of the broach (in the manufacture of the matrix) corresponds to the direction of OX.

The results are summarized in Table 2 and confirm the possibility of industrial application of the claimed technical solution.

Based on the foregoing, we can conclude that the task is to create a method for the most reliable determination of tool life, working as part of a press for cold metal forming with a working load on the tool in a plane perpendicular to the processing plane, which would take into account the influence of the main factors - the design and material of the tool, the design and degree of wear of the equipment, the schedule of workloads of the technological operation, etc. - resolved, the claimed technical result — optimization of the tool’s life while eliminating the possibility of an emergency at work — has been achieved, and the technical solution — the method for determining tool life — is industrially applicable and meets the criteria of the invention of “novelty” and “inventive step” under applicable law.

Claims (1)

A method for determining the durability of a tool used in a press for cold metal forming with a working load on a tool in a plane perpendicular to the processing plane, including measuring the coercive force on the most loaded parts of the tool during operation, comparing the obtained values with the critical value and evaluating the current tool life, characterized in that the coercive force is measured in the processing plane in the directions parallel and perpendicular to the plane of the working load narrow to the tool, and to assess the current resource of the tool use the smallest of the values of the current resource of the tool, calculated by the following formulas:

and

where dN is the current resource of the instrument,
dH _c1 is the difference between the critical value and the value of the coercive force in the most loaded section of the tool working part, measured in a direction parallel to the plane of the tool working load, A / m;
dH _c2 is the difference between the critical value and the value of the coercive force in the most loaded section of the tool working part, measured in the direction perpendicular to the plane of the tool work load, A / m;
X ₁ - tensile strength of the workpiece material (MPa),
X ₂ - tensile strength of the tool material (MPa),
X ₃ - the number of resurfacing of the tool,
X ₄ - the number of parts processed by the tool at the current moment,
X ₅ - the thickness of the workpiece (mm),
X ₆ - rated press force (kN).

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