A method of obtaining a cut thickness of a ptf material

Abstract

The application discloses a method for obtaining the cutting thickness of PTFE material. At present, there is no accurate cutting thickness calculation and setting method. The application integrates the influencing factors contained in the machining process, comprehensively analyzes the factors such as the surface stress of the PTFE material, the material performance, the cutting condition and the temperature environment, and then accurately calculates the cutting thickness setting value of the PTFE material, so that when the workpiece is cut at the cutting thickness setting value, the actual cutting thickness is close to the expected cutting thickness, thereby improving the machining accuracy and the overall performance. The application greatly matches the expected value and the actual value of the cutting thickness, which is particularly important for the service life and use effect of high-precision flow control components.

Description

Technical Field

[0001] This invention belongs to the field of cutting technology, and in particular relates to a method for obtaining the cutting thickness of PTFE material. Background Technology

[0002] Precise cutting thickness is a fundamental issue in the field of machining, and most errors in the cutting process are caused by plastic deformation. Due to differences in material properties, their elastic moduli vary. The desired cutting thickness h is set as the cutting thickness of the workpiece. d When the machine tool cuts down, the surface will undergo elastic deformation Δx due to the compressive force. After the tool pressure is released, the surface elastic deformation recovers, and the actual cutting thickness is h. d -Δx does not match the ideal value. Currently, there is no accurate method for calculating and setting the cutting thickness. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for obtaining the cutting thickness of PTFE materials. This method can systematically calculate the corresponding accurate cutting thickness according to different working conditions, making it easier to match the expected value of the cutting depth with the actual value in practical applications.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] The present invention discloses a method for obtaining the cutting thickness of PTFE material, as detailed below:

[0006] Step 1: Use the cutting temperature calculated using the empirical formula for cutting temperature as the workpiece surface temperature; the empirical formula for cutting temperature is as follows:

[0007]

[0008] Among them, T s For cutting temperature, C θ v is the cutting temperature coefficient. c f is the cutting speed. z For the feed rate, a p For the depth of cut, a1, a2, and a3 are v. c f z a p The index;

[0009] Step 2: Construct a surface stress calculation formula suitable for PTFE material workpieces:

[0010]

[0011] in, The reference strain rate is taken between 0.01 and 0.1, A is the reference strain rate and the initial yield stress at the reference temperature, B is the strain rate hardening modulus at the initial yield stress, and ε is the strain rate hardening modulus. p For equivalent strain, C is the strain rate strengthening parameter. Where is the equivalent strain rate, n is the hardening exponent, and T is the effective strain rate. s T represents the surface temperature of the workpiece. r The reference temperature is D, and the coefficient for the temperature term is D.

[0012] The hardening index n is related to the workpiece surface temperature T. s The relationship building process is as follows:

[0013] According to the curve equation:

[0014] lnσ temp =ln K+n! lnε

[0015] Where ε is the strain and K is the strength coefficient, the slope dσ at a given strain is obtained. temp / dε, then according to the slope dσ temp / dε and the slope σ of the true stress-strain curve T / ε T Relationship:

[0016] dσ temp / dε=nσ T / ε T

[0017] Transpose the terms to get

[0018] n=dσ temp / dε·ε T / σ T

[0019] Where, ε T For true strain, σ T True stress;

[0020] The strain ε and stress σ were measured. temp After that, the true stress σ T With true strain ε T Through strain ε and stress σ temp It is obtained by calculation using the following formula:

[0021] σ T =σ temp ×(1+ε)

[0022] ε T =ln(1+ε)

[0023] Experiments were conducted at different temperatures to obtain ε at different temperatures. T σ Tand dσ temp / dε, thus obtaining the hardening exponent n at different temperatures. After fitting using the least squares method, the hardening exponent n and the workpiece surface temperature T are obtained. s The relation n = f(T) s );

[0024] Step 3: Based on n = f(T) s Calculate the current workpiece surface temperature T. s The hardening index n value is determined by the current workpiece surface temperature T. s Substituting n into the surface stress calculation formula in step two, we obtain the workpiece surface stress σ. temp ;

[0025] Step 4: Calculate the current workpiece surface temperature T s The elastic modulus below:

[0026] E = E0·(1+25aT) s )

[0027] Where E0 is the elastic modulus at absolute zero, and parameter a is the linear expansion coefficient of PTFE material;

[0028] Step 5: Calculate the elastic deformation:

[0029] Δx=σ temp / E

[0030] Step Six: Calculate the workpiece cutting thickness setting value:

[0031] h = Δx + h d

[0032] Among them, h d Let h be the desired cutting thickness; then the actual cutting thickness of the workpiece is the desired cutting thickness h. d .

[0033] Preferably, for different cutting speeds, feed rates, and depths of cut, C is obtained by fitting the measured workpiece cutting temperature using the least squares method. θ a1, a2, a3.

[0034] Preferably, the solution process for the initial yield stress A and strain rate hardening modulus B is as follows:

[0035] The PTFE material workpiece was subjected to quasi-static tests under both uniaxial tensile and uniaxial torsion stress states, and three sets of ε values ​​were measured. p and σ temp Substitute the data into the formula:

[0036]

[0037] Thus, a set of initial yield stress A and strain rate hardening modulus B are obtained respectively. The two initial yield stresses A are averaged to obtain the final initial yield stress A, and the two strain rate hardening moduli B are averaged to obtain the final strain rate hardening modulus B.

[0038] Preferably, the strain rate hardening parameter C under compression is obtained by using a linear fitting method through Hopkinson bar experiments. Tension Strain rate hardening parameter C under tensile conditions Comp and strain rate hardening parameter C under torsional conditions Torsion , for C Tension C Comp and C Torsion The mean value is used to obtain the strain rate hardening parameter C.

[0039] Preferably, in the finite element analysis software, the workpiece is elementized, and two points M and N with a distance of l0 are selected in the element. Pressure is applied to the workpiece, so that the element is at t total Within a certain time interval, point M is compressed by pressure F, and point N moves to point N′. Let l1 be the distance between point M and point N′ at this time. Then the equivalent strain rate is... The calculation formula is:

[0040]

[0041] Wherein, the speed at which point N moves is:

[0042] v(t)=(l1-l0) / t total

[0043] Then the equivalent rate of variation is obtained:

[0044]

[0045] Equivalent variability Integral equation to obtain equivalent strain ε P .

[0046] Preferably, the parameters A, B, C, n, and ε are obtained. p , Then, for different workpiece surface temperatures T s Operating conditions, based on the measured workpiece surface stress σ temp Based on this, the temperature term coefficient D is obtained by fitting using the least squares method.

[0047] The beneficial effects of this invention are as follows:

[0048] This invention proposes a surface stress calculation formula applicable to PTFE material workpieces. It integrates various influencing factors during processing, comprehensively analyzing factors such as PTFE surface stress, material properties, cutting conditions, and temperature environment. This allows for precise calculation of the PTFE material cutting thickness setting, ensuring that the actual cutting thickness closely approximates the desired cutting thickness when the workpiece is cut at the set value. This improves machining accuracy and overall performance. Furthermore, this invention can incorporate AI algorithms to repeatedly correct the obtained values, further enhancing accuracy. These algorithms can be integrated into CNC machine tools to autonomously calculate and obtain parameters, resulting in a high degree of consistency between the expected and actual cutting thickness values. This is particularly important for the lifespan and performance of high-precision flow control components. Detailed Implementation

[0049] The present invention will be further described below with reference to the embodiments.

[0050] Currently, the Johnson-Cook constitutive formula (hereinafter referred to as the JC constitutive formula) is commonly used to calculate the surface stress σ of a workpiece. The Johnson-Cook constitutive formula is as follows:

[0051]

[0052] in, The reference strain rate is taken between 0.01 and 0.1, A is the reference strain rate and the initial yield stress at the reference temperature, B is the strain rate hardening modulus at the initial yield stress, and ε is the strain rate hardening modulus. p For equivalent strain, C is the strain rate strengthening parameter. Where is the equivalent strain rate, n is the hardening index, m is the thermal softening index, and T is the thermal strain rate. * Temperatures within the same system;

[0053] T * =(TT) r ) / (T m -T r )

[0054] Where T is the current ambient temperature, T r The reference temperature (when the initial temperature is not defined, it is the temperature of a uniform temperature field applied; when the initial temperature is defined, T) is the reference temperature. r (The initial temperature can be used as a substitute), T m The melting point of the workpiece material (generally in the range of 327 to 342°C).

[0055] The thermal softening index m can be calculated using the following formula:

[0056]

[0057] in, and These represent the workpiece material at the same strain rate and at the same in-system temperature T. * Yield stress at reference temperature T r The yield stress at different strain rates was measured. and The average value of the thermal softening index at each strain rate is calculated to obtain the final thermal softening index m.

[0058] The JC constitutive model, being an empirical formula, is subject to significant limitations, particularly the temperature term (1-T). *m If only ambient temperature is considered, since ambient temperature is less affected by processing, while the surface temperature of the workpiece will rise by nearly 100% during processing, and for PTFE, a material with high cleanliness requirements and susceptible to temperature, the surface temperature of the workpiece has a greater impact on the overall structure, the Johnson-Cook constitutive formula is no longer applicable to the calculation of surface stress σ of PTFE material workpieces.

[0059] This invention proposes a surface stress calculation formula more applicable to PTFE material workpieces, and based on this formula, proposes a method for obtaining the cutting thickness of PTFE material, as follows:

[0060] Step 1: As a raw material for ultra-clean machining, PTFE's material properties are significantly affected by temperature. Taking PTFE's coefficient of thermal expansion (CTE) as an example, due to PTFE's high CTE, its expansion volume is relatively large at high temperatures, and its internal structure will change accordingly. In actual machining, the workpiece surface temperature is affected by multiple factors, requiring a suitable theoretical approximation for calculating the workpiece surface temperature. This invention uses the cutting temperature calculated by the empirical formula for cutting temperature as the workpiece surface temperature; the empirical formula for cutting temperature is as follows:

[0061]

[0062] Among them, T s The workpiece surface temperature, also known as the cutting temperature, is C. θ (Unknown) represents the cutting temperature coefficient, v c f is the cutting speed. z For the feed rate, a p For the depth of cut, a1, a2, and a3 (unknown) are v. c f z a p The index. Using range and variance analysis of orthogonal experimental data, the cutting speed v can be obtained. c The cutting temperature is significantly affected; for different cutting speeds, feed rates, and depths of cut, based on the workpiece cutting temperature measured by a temperature sensor, C is obtained by least squares fitting.θ a1, a2, a3; see Table 1 for the orthogonal array.

[0063] Table 1

[0064]

[0065]

[0066] The obtained C θ Substituting a1, a2, and a3 into the empirical formula for cutting temperature, the actual cutting speed ν during machining can be determined. c Feed rate f z Back cut amount a p The surface temperature of the workpiece is obtained.

[0067] Step 2: Surface stress calculation formula applicable to PTFE material workpieces:

[0068]

[0069] Among them, T s T represents the surface temperature of the workpiece. r Here, D is the reference temperature, and D is the temperature coefficient. Due to the low modulus, poor rigidity, poor thermal conductivity, and high coefficient of linear expansion of PTFE material, parameters A, B, C, n, and ε need to be obtained through a combination of experimental, fitting, and finite element analysis. p , Specific values, and then for different workpiece surface temperatures T s (The workpiece cutting temperature measured by a temperature sensor is taken as the workpiece surface temperature T) s Under operating conditions, the surface stress σ of the workpiece is measured using a surface stress tester. temp Based on this, the temperature term coefficient D is obtained by fitting using the least squares method, thus obtaining the formula for calculating the surface stress of PTFE material workpieces with temperature dependence.

[0070] As can be seen from the properties of the surface stress calculation formula, the terms are not coupled, so each parameter can be calculated independently without affecting the final result.

[0071] For the initial yield stress A and strain rate hardening modulus B, the PTFE workpiece is subjected to two stress states in a quasi-static test: uniaxial tension and uniaxial torsion. The surface stress applicable to the PTFE workpiece is then obtained as follows: In uniaxial tensile and uniaxial torsion tests, three sets of ε were measured respectively. p and σ temp Substitute the data into the formula:

[0072]

[0073] Thus, a set of initial yield stress A and strain rate hardening modulus B are obtained respectively. The two initial yield stresses A are averaged to obtain the final initial yield stress A, and the two strain rate hardening moduli B are averaged to obtain the final strain rate hardening modulus B.

[0074] The hardening exponent n is highly sensitive to temperature and requires fitting through experiments at different temperatures. Based on the curve equation:

[0075] lnσ temp =ln K+n·lnε

[0076] Where ε is the strain and K is the strength coefficient, the slope dσ at a given strain is obtained. temp / dε, then according to the slope dσ temp / dε and the slope σ of the true stress-strain curve T / ε T Relationship:

[0077] dσ temp / dε=nσ T / ε T

[0078] Transpose the terms to get

[0079] n=dσ temp / dε·ε T / σ T

[0080] Where, ε T For true strain, σ T This is the true stress.

[0081] Strain ε and stress σ temp As temperature changes, strain ε and stress σ are measured. temp After that, the true stress σ T With true strain ε T Through strain ε and stress σ temp It is obtained by calculation using the following formula:

[0082] σ T =σ temp ×(1+ε)

[0083] ε T =ln(1+ε)

[0084] Experiments were conducted at different temperatures to obtain ε at different temperatures. T σ T and dσ temp / dε, thus obtaining the hardening exponent n at different temperatures. After fitting using the least squares method, the hardening exponent n and the workpiece surface temperature T are obtained. s The relation n = f(T) s).

[0085] For the strain rate hardening parameter C, the strain rate hardening parameter C under compression was obtained by linear fitting method through Hopkinson bar experiments. Tension Similarly, the strain rate hardening parameter C under tensile conditions is obtained. Comp and strain rate hardening parameter C under torsional conditions Torsion , for C Tension C Comp and C Torsion The mean value is used to obtain the strain rate hardening parameter C.

[0086] For equivalent rate of variation In finite element analysis software, the workpiece is elementized. Two points M and N, spaced 10 apart within each element, are selected. Pressure is applied to the workpiece, causing the element to... total Within a certain time interval, point M is compressed by pressure F, and point N moves to point N′. Let l1 be the distance between point M and point N′ at this time. Then the equivalent strain rate is... The calculation formula is:

[0087]

[0088] Wherein, the speed at which point N moves is:

[0089] v(t)=(l1-l0) / t total

[0090] Then we get:

[0091]

[0092] For the equivalent strain ε p Equivalent variability Integral equation to obtain equivalent strain ε P .

[0093] Step 3: Based on n = f(T) s Calculate the current workpiece surface temperature T. s The hardening index n value is determined by the current workpiece surface temperature T. s Substituting n into the surface stress calculation formula in step two, we obtain the workpiece surface stress σ. temp .

[0094] Step 4: Calculate the current workpiece surface temperature T s The elastic modulus below:

[0095] E = E0·(1+25aT) s )

[0096] Where E0 is the elastic modulus at absolute zero (generally taken as 500 MPa), and parameter a is the linear expansion coefficient of PTFE material (generally taken as 10 to 12 × 10⁻⁶). -5 / ℃).

[0097] Step 5: Calculate the elastic deformation:

[0098] Δx=σ temp / E

[0099] Step Six: Calculate the workpiece cutting thickness setting value:

[0100] h = Δx + h d

[0101] Among them, h d Let h be the desired cutting thickness. Then the actual cutting thickness of the workpiece is the desired cutting thickness h. d The actual cutting thickness of the workpiece can approach the ideal desired cutting thickness, increasing the accuracy of PTFE material cutting.

Claims

1. A method for obtaining the cutting thickness of PTFE material, characterized in that: Specifically as follows: Step 1: Use the cutting temperature calculated using the empirical formula for cutting temperature as the workpiece surface temperature; the empirical formula for cutting temperature is as follows: Among them, T s For cutting temperature, C θ ν is the cutting temperature coefficient. c f is the cutting speed. z For the feed rate, a p For the depth of cut, a1, a2, and a3 are ν. c f z a p The index; Step 2: Construct a surface stress calculation formula suitable for PTFE material workpieces: in, The reference strain rate is taken between 0.01 and 0.1, A is the reference strain rate and the initial yield stress at the reference temperature, B is the strain rate hardening modulus at the initial yield stress, and ε is the strain rate hardening modulus. p For equivalent strain, C is the strain rate strengthening parameter. Where is the equivalent strain rate, n is the hardening exponent, and T is the effective strain rate. s T represents the surface temperature of the workpiece. r The reference temperature is D, and the coefficient for the temperature term is D. The hardening index n is related to the workpiece surface temperature T. s The relationship building process is as follows: According to the curve equation: ln σ temp =ln K+n·lnε Where ε is the strain and K is the strength coefficient, the slope dσ at a given strain is obtained. temp / dε, then according to the slope dσ temp / dε and the slope σ of the true stress-strain curve T / ε T Relationship: dσ temp / dεnσ T / ε T Transpose the terms to get n=dσ temp / dε·e T / s T Where, ε T For true strain, σ T True stress; The strain ε and stress σ were measured. temp After that, the true stress σ T With true strain ε T Through strain ε and stress σ temp It is obtained by calculation using the following formula: s T =s temp ×(1+e) e T =ln(1+ε) Experiments were conducted at different temperatures to obtain ε at different temperatures. T σ T and dσ temp / dε, thus obtaining the hardening exponent n at different temperatures. After fitting using the least squares method, the hardening exponent n and the workpiece surface temperature T are obtained. s The relation n = f(T) s ); Step 3: Based on n = f(T) s Calculate the current workpiece surface temperature T. s The hardening index n value is determined by the current workpiece surface temperature T. s Substituting n into the surface stress calculation formula in step two, we obtain the workpiece surface stress σ. temp ; Step 4: Calculate the current workpiece surface temperature T s The elastic modulus below: E=E0·(1+25aT s ) Where E0 is the elastic modulus at absolute zero, and parameter a is the linear expansion coefficient of PTFE material; Step 5: Calculate the elastic deformation: Δx=σ temp / E Step Six: Calculate the workpiece cutting thickness setting value: h=Δx+h d Among them, h d Let h be the desired cutting thickness; then the actual cutting thickness of the workpiece is the desired cutting thickness h. d .

2. The method for obtaining the cutting thickness of PTFE material according to claim 1, characterized in that: For different cutting speeds, feed rates, and depths of cut, C is obtained using the least squares method based on the measured workpiece cutting temperature. θ a1, a2, a3.

3. The method for obtaining the cutting thickness of PTFE material according to claim 1, characterized in that: The solution process for the initial yield stress A and strain rate hardening modulus B is as follows: The PTFE material workpiece was subjected to quasi-static tests under both uniaxial tensile and uniaxial torsion stress states, and three sets of ε values ​​were measured respectively. p and σ temp Substitute the data into the formula: Thus, a set of initial yield stress A and strain rate hardening modulus B are obtained respectively. The two initial yield stresses A are averaged to obtain the final initial yield stress A, and the two strain rate hardening moduli B are averaged to obtain the final strain rate hardening modulus B.

4. The method for obtaining the cutting thickness of PTFE material according to claim 1, characterized in that: The strain rate hardening parameter C under compression was obtained through Hopkinson bar experiments using a linear fitting method. Tension Strain rate hardening parameter C under tensile conditions Comp and strain rate hardening parameter C under torsional conditions Torsion , for C Tension C Comp and C Torsion The mean value is used to obtain the strain rate strengthening parameter C.

5. The method for obtaining the cutting thickness of PTFE material according to claim 1, characterized in that: In finite element analysis software, the workpiece is elementized. Two points M and N, spaced 10 apart within each element, are selected. Pressure is applied to the workpiece, causing the element to... total Within a certain time interval, point M is compressed by pressure F, and point N moves to point N′. Let l1 be the distance between point M and point N′ at this time. Then the equivalent strain rate is... The calculation formula is: Wherein, the speed at which point N moves is: v(t)=(l1-l0) / t total Then the equivalent rate of variation is obtained: Equivalent variability Integral equation to obtain equivalent strain ε P .

6. A method for obtaining the cutting thickness of PTFE material according to any one of claims 1 to 5, characterized in that: Obtain parameters A, B, C, n, ε p , Then, for different workpiece surface temperatures T s Operating conditions, based on the measured workpiece surface stress σ temp Based on this, the temperature term coefficient D is obtained by fitting using the least squares method.

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