Thin film thermocouple temperature measuring cutter with biased hot junction and cutting temperature compensation method

Abstract

The invention relates to a thin film thermocouple temperature measuring tool with a biased hot node and a cutting temperature compensation method. The insulating layer is arranged on the surface of the cutter base body, the first film electrode and the second film electrode are arranged on the surface of the insulating layer, and the protective layer covers the film electrodes. A structure of an insulating layer, two electrodes and a protective layer is formed on the front cutter surface of the cutter; the first thin film electrode and the second thin film electrode form a hot junction on the surface of the cutter, the hot junction is located in a non-contact area outside the boundary of the cutter chip contact area and located in a heat affected field of the cutter chip contact area, and the shortest distance between the hot junction and the boundary of the cutter chip contact area is x; moreover, the thin film thermocouple calculates the cutting temperature Tkey based on a temperature compensation model according to the measurement temperature Tmeasure measured by the hot node and the distance x. According to the method, the hot node wear failure risk is reduced, and the accuracy and stability of cutting temperature measurement are improved on the premise that the response and the signal-to-noise ratio are guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of cutting process temperature measurement and thin film sensor technology, specifically relating to a thin film thermocouple temperature measuring tool with thermal junction bias and a cutting temperature compensation method. Background Technology

[0002] In the aerospace field, difficult-to-machine materials such as titanium alloys are widely used. During machining, their low thermal conductivity leads to concentrated cutting heat, easily causing tool wear and workpiece thermal deformation. Real-time, accurate measurement of cutting temperature is crucial for optimizing machining processes and extending tool life. Thin-film thermocouples, due to their small size, high integration, and fast response speed, have become the preferred solution for cutting temperature measurement.

[0003] Existing thin-film thermocouple temperature measurement technology suffers from two major problems: First, wear and failure of the hot junction: Current solutions often place the hot junction in the blade-chip contact area or near the blade tip, directly involving the hot junction in friction, wear, and oxidation, resulting in short sensor life and a high failure probability. Second, temperature difference errors caused by misalignment: Some solutions attempt to move the hot junction away from the blade-chip contact area to avoid wear, but due to the heat conduction of the blade body and temperature gradient, there is a systematic deviation between the temperature measured at the off-position and the highest temperature in the blade-chip contact area. Without an effective compensation mechanism, the temperature measurement accuracy cannot meet the requirements of precision temperature measurement. Third, balancing reliability and accuracy is difficult: Increasing the thickness of the protective / insulating layer can improve reliability, but it introduces thermal resistance and dynamic errors; at the same time, thin film resistivity, film-substrate adhesion, and thermoelectric performance stability also affect long-term availability. Summary of the Invention

[0004] The purpose of this invention is to provide a thin-film thermocouple temperature measuring cutting tool with a hot junction bias and a cutting temperature compensation method. The tool includes a tool substrate, a SiNx insulating layer disposed on the tool surface, a NiCr thin-film electrode and a NiSi thin-film electrode disposed on the insulating layer to form a hot junction, and a SiNx protective layer covering the electrode layer. The hot junction is located in a non-contact area outside the boundary of the chip-tool contact area on the rake face, thereby reducing the risk of failure caused by chip friction wear and high-temperature oxidation.

[0005] The technical solution to achieve the purpose of this invention is: a thin-film thermocouple temperature measuring tool with hot junction bias, characterized in that it includes a tool substrate, an insulating layer disposed on the surface of the tool substrate, a first thin-film electrode and a second thin-film electrode disposed on the surface of the insulating layer, and a protective layer covering the thin-film electrodes; the tool rake face forms a structure of insulating layer + two electrodes + protective layer.

[0006] The first and second thin-film electrodes form a hot junction on the tool surface. The hot junction is located in a non-contact region outside the boundary of the tool-chip contact area and within the thermally affected field of the tool-chip contact area. The shortest distance from the hot junction to the boundary of the tool-chip contact area is x. Furthermore, the thin-film thermocouple is based on a temperature compensation model and the measured temperature T is determined by the hot junction. measure Calculate the cutting temperature T from the distance x. key The temperature compensation model satisfies the following mapping relationship:

[0007] T key =F(x,T measure, P),

[0008] Where P is the set of cutting conditions and tool-workpiece material parameters.

[0009] Furthermore, the insulating layer and the protective layer are SiNx thin films or Si3N4 thin films;

[0010] The first thin-film electrode is a NiCr thin-film electrode, and the second thin-film electrode is a NiSi thin-film electrode.

[0011] Furthermore, the shortest distance x from the hot junction to the boundary of the chip contact area is selected as the minimum distance that makes the hot junction temperature signal meet the preset measurable conditions and the temperature gradient meet the preset gentle conditions. The value range is 2-6 mm, preferably 3-4 mm.

[0012] Furthermore, the hot junction is located on the tool's axis of symmetry.

[0013] Furthermore, the insulating layer has a thickness of 0.6-2.0 μm, the protective layer has a thickness of 0.6-2.0 μm, and the first and second thin-film electrodes have a thickness of 300-800 nm.

[0014] Furthermore, the temperature compensation model F can be any one or a combination of the following: polynomial-response surface model, piecewise function, lookup table interpolation model, regression model, machine learning model, or hybrid model with physical constraints.

[0015] Furthermore, the set P of cutting conditions and tool-workpiece material parameters includes: cutting speed, feed rate, depth of cut, tool geometry parameters, workpiece material thermal properties, tool material thermal properties, cooling method, and convective heat transfer coefficient.

[0016] The above-mentioned method for compensating the cutting temperature of a thin-film thermocouple-based cutting tool includes the following steps:

[0017] Step (1): Determine the shortest distance x from the hot junction to the boundary of the tool-chip contact area through simulation pre-analysis. The simulation pre-analysis includes three-dimensional cutting simulation and tool heat conduction simulation. Extract the temperature distribution curve along the symmetry axis of the tool rake face. Calculate the temperature gradient outside the boundary of the tool-chip contact area in an increasing distance manner. Arrange the hot junction in the area where the temperature gradient meets the preset flat condition and the temperature signal can be measured.

[0018] Step (2): Construct a temperature compensation model: Obtain a model containing (x, T) measure , T key The calibration dataset is used to obtain the mapping relationship T by fitting or training the calibration dataset. key =F(x,T measure , P);

[0019] Step (3): During the cutting process, the temperature T at the hot junction is measured. measure Based on the temperature compensation model, the critical cutting temperature T is calculated and output. key .

[0020] Furthermore, the calibration dataset in step (2) is obtained through any one or a combination of the following: temperature field data obtained from cutting numerical simulation, data calculated by tool heat conduction model, temperature measurement data from cutting experiment, and simulation-experiment fusion calibration data;

[0021] The fitting or training in step (2) includes any one or a combination of least squares fitting, orthogonal experimental parameter optimization, regularized regression, Bayesian regression, or machine learning training.

[0022] The above-mentioned method for preparing a thin-film thermocouple temperature measuring tool includes the following steps:

[0023] S1: Matrix pretreatment;

[0024] S2: Insulating layer is deposited by pulsed negative bias magnetron sputtering;

[0025] S3: The first thin film electrode is deposited using multi-arc ion plating;

[0026] S4: The second thin-film electrode is deposited by DC magnetron sputtering;

[0027] S5: Hot node location arrangement: The hot node is arranged on the tool rake face in a non-contact area outside the boundary of the tool-chip contact area using a mask plate; the shortest distance from the hot node to the boundary of the tool-chip contact area is x; the boundary of the tool-chip contact area is determined by the contact marks on the rake face after cutting.

[0028] S6: Annealing is performed under vacuum or inert atmosphere;

[0029] S7: A protective layer is deposited on the surface of the thermocouple electrode layer by medium-frequency magnetron sputtering;

[0030] S8: Static calibration: Perform static calibration on the thin-film thermocouple temperature measuring tool to obtain the temperature-thermoelectric potential curve and fit it to obtain the equivalent Seebeck coefficient.

[0031] This invention places the hot junction of the thin-film thermocouple outside the boundary of the tool-chip contact area to prevent the hot junction from directly participating in cutting and thus wearing down. To ensure the identifiability and accuracy of the critical cutting temperature obtained through thermal conductivity compensation, the distance x from the hot junction should be as close as possible to the boundary of the tool-chip contact area, placing it within the thermally affected field of the tool-chip contact area, thereby maintaining a high signal-to-noise ratio and low response hysteresis. If x is too large, the temperature attenuates significantly along the tool rake face, leading to attenuation of the measured temperature signal, increased temperature gradient, and exacerbated response hysteresis, making it difficult to reflect the true temperature changes in the tool-chip contact area. Therefore, this invention primarily recommends x to be 2-6 mm, and chooses the smallest possible x while satisfying the requirement of being "outside the contact area boundary".

[0032] Compared with the prior art, the significant advantages of this invention are:

[0033] 1. The hot junction is located outside the boundary of the tool-chip contact area, reducing wear and damage, and improving the stability and life of the temperature measuring tool;

[0034] 2. The temperature difference between the highest temperature in the temperature measurement zone and the chip contact zone is compensated by a temperature difference compensation model to improve the accuracy of temperature measurement;

[0035] 3. Vacuum annealing can improve the thermoelectric performance of thin-film thermocouples. In the example, the average Seebeck coefficient can be increased from 21.2 μV / ℃ to 23.4 μV / ℃, and the temperature measurement error can be reduced from 3.34% to 1.80%.

[0036] 4. The SiNx protective layer forms a SiO2 / SiOxNy rich surface layer at high temperature, which can prevent further oxygen diffusion and delay oxidation failure. In the embodiment, the upper limit of temperature measurement can be increased from 400 ℃ to 600 ℃. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the thin-film thermocouple layer structure of the present invention.

[0038] Figure 2 The diagram shows the location of the hot junction; (a) is a working diagram of the tool, and (b) is a schematic diagram of the tool.

[0039] Figure 3 The image shows a NiCr-NiSi thin-film thermocouple temperature measuring tool; (a) is a schematic diagram of the tool, (b) is a schematic diagram of the tool connected to the thermocouple, and (c) is a schematic diagram of the tool's working installation.

[0040] Figure 4 Fit a surface plot to the temperature compensation function.

[0041] Figure 5 This is a diagram showing the static temperature measurement performance of the thin-film thermocouple of the present invention. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to the accompanying drawings.

[0043] Example 1: Fabrication of SiNx / NiCr-NiSi / SiNx thin-film thermocouple temperature measuring tool

[0044] 1. Matrix and Pretreatment: YG8 carbide inserts were selected as the tool matrix. Surface defects were removed by sanding, followed by polishing to a surface roughness of approximately Ra 0.1 μm. The sample was then ultrasonically cleaned sequentially with acetone, deionized water, and alcohol for approximately 15 min each, and dried. The sample was placed in a vacuum chamber and evacuated to approximately 5.0 × 10⁻⁶. -3 Pa.

[0045] 2. SiNx insulating layer deposition

[0046] The temperature control system was activated to stabilize the substrate temperature at approximately 50 °C and maintained at this temperature. A glow discharge cleaning process was performed using 150 sccm Ar, and a -1200 V pulsed negative bias was applied to the substrate to remove surface oxides and impurities and improve film-substrate adhesion. Subsequently, a vacuum was evacuated to approximately 5.0 × 10⁻⁶. -3 Pa, 90 sccm Ar and 60 sccm N2 were introduced as working gases, and the intermediate frequency sputtering power supply of 4 A was turned on under a controlled vacuum of 1.6 Pa. A -150 V pulsed negative bias voltage was applied to the substrate to deposit a SiNx insulating layer. The deposition time was 120 min, and a SiNx insulating layer with a thickness of about 1.2 μm was obtained.

[0047] 3. NiCr thin film electrode deposition

[0048] The substrate temperature was stabilized at approximately 100 °C and maintained at this temperature, and a vacuum was drawn to approximately 5.0 × 10⁻⁶. -3 Pa. 100 sccm Ar was introduced, and a multi-arc power supply of 70 A was turned on under a vacuum of 1.6 Pa. A -150 V pulsed negative bias voltage was applied, and a NiCr thin film electrode was deposited on the insulating layer by patterning through a mask. The deposition time was 15-16 min, resulting in a NiCr film thickness of about 600 nm.

[0049] 4. NiSi thin film electrode deposition

[0050] At approximately 100 °C, a vacuum of approximately 5.0 × 10⁻⁶ was created. -3Pa. 100 sccm Ar was introduced to control the vacuum level at 1.6 Pa. The DC sputtering power supply was turned on at 1.5 A and a -150 V pulsed negative bias voltage was applied. NiSi thin film electrodes were deposited through a mask to form a hot junction with the NiCr electrode. The deposition time was 50 min, resulting in a NiSi thin film thickness of approximately 600 nm.

[0051] 5. Hot junction location arrangement

[0052] The hot junction is positioned on the rake face of the tool in a non-contact area outside the boundary of the chip-tool contact zone using a mask. The shortest distance from the hot junction to the boundary of the chip-tool contact zone is x. The boundary of the chip-tool contact zone can be identified and determined by the contact marks on the rake face after cutting.

[0053] 6. Vacuum annealing

[0054] The deposited NiCr-NiSi thin-film thermocouple was placed in a tube furnace and evacuated to approximately 0.1 Pa. Ar was then introduced to prevent oxidation. The furnace was heated at a rate of approximately 1 °C / min. The annealing temperature could be selected from 200 °C, 300 °C, 400 °C, or 500 °C, and held at that temperature for approximately 30 min. Subsequently, the thermocouple was cooled to room temperature in the furnace at a rate of approximately 1 °C / min. An annealing temperature of approximately 400 °C was preferred to obtain a higher average Seebeck coefficient and a lower temperature measurement error.

[0055] 7. SiNx protective layer deposition

[0056] A SiNx protective layer is deposited on the surface of the thermocouple electrode layer using medium-frequency magnetron sputtering. The thickness can be comparable to that of the insulating layer (approximately 1.2 μm in the example) to improve high-temperature oxidation resistance and temperature measurement stability.

[0057] 8. Static calibration

[0058] A self-built static calibration platform was used to statically calibrate the thin-film thermocouple temperature measuring tool, obtaining a temperature-thermoelectric potential curve, which was then fitted to obtain the equivalent Seebeck coefficient. In the example, the average Seebeck coefficient after vacuum annealing at 400 °C was approximately 23.4 μV / °C, and the maximum temperature measurement error was approximately 1.80%.

[0059] Example 2: Determination of the distance x between hot nodes

[0060] 1. Before fabricating the temperature measuring tool, a simulation pre-analysis is performed to determine the arrangement distance x of the hot junctions. Specifically, this includes:

[0061] (a) Establish a three-dimensional turning simulation model of TC4 titanium alloy and obtain the thermal load distribution near the tool-chip contact area;

[0062] (b) Based on the thermal load results in (a), a simulation model of tool heat conduction is established, and the temperature field of the tool rake face is solved.

[0063] (c) Extract the temperature distribution curve along the symmetry axis of the tool rake face, and calculate the temperature gradient outside the boundary of the tool-chip contact area in an increasing distance manner;

[0064] (d) Within the region where the temperature gradient is relatively gentle and the temperature measurement signal can be stably acquired, select the minimum distance x that satisfies the condition of being located outside the boundary of the tool-chip contact area. Preferably, x is 2-6 mm. This method ensures that the hot junction is located within the heat-affected field, balancing the hot junction's lifespan with the accuracy of the compensation calculation.

[0065] Simulation comparisons of different values ​​of x show that as x increases, the temperature amplitude at the hot junction decreases, the response delay increases, and the critical cutting temperature error obtained by the temperature difference compensation model increases. Therefore, this invention selects an arrangement strategy that is as close as possible to the boundary of the contact area.

[0066] Example 3: Construction of Temperature Difference Compensation Model and Application of Cutting Temperature Measurement

[0067] 1. Simulation Data Acquisition and Temperature Field Reconstruction

[0068] A three-dimensional turning simulation of TC4 titanium alloy was established to obtain the temperature field in the tool-chip contact area and determine the maximum cutting temperature T. max A tool heat conduction simulation was established, and cutting thermal boundary conditions were applied to the tool model to reconstruct the tool temperature field.

[0069] 2. Isochronous Sampling and Mapping Modeling

[0070] Extract the temperature field curve along the tool's axis of symmetry, and obtain multiple temperature values ​​at equal intervals with a preset step size on the curve to form (x i , T i , T max ) dataset, where x i This represents the shortest distance from the point to the boundary of the chip contact area. Based on the dataset, T is established... max With T i The goodness-of-fit or mapping model can reach 0.99346.

[0071] 3. Online temperature compensation measurement

[0072] Temperature T is measured at the hot junction during the cutting process. measure Based on the distance x from the hot junction to the boundary of the tool-chip contact area and the cutting parameter P, the compensation model outputs the critical temperature T of the tool-chip contact area. key This enables indirect and precise measurement of the cutting temperature of titanium alloys. In the example, the relative error of the cutting temperature measurement is approximately 10%.

Claims

1. A thin-film thermocouple temperature measuring tool with thermal junction bias, characterized in that, The tool comprises a tool substrate, an insulating layer disposed on the surface of the tool substrate, a first thin-film electrode and a second thin-film electrode disposed on the surface of the insulating layer, and a protective layer covering the thin-film electrodes; the tool rake face forms a structure of insulating layer + two electrodes + protective layer; characterized in that: The first and second thin-film electrodes form a hot junction on the tool surface. The hot junction is located in a non-contact region outside the boundary of the tool-chip contact area and within the thermally affected field of the tool-chip contact area. The shortest distance from the hot junction to the boundary of the tool-chip contact area is x. Furthermore, the thin-film thermocouple is based on a temperature compensation model and the measured temperature T is determined by the hot junction. measure Calculate the cutting temperature T from the distance x. key The temperature compensation model satisfies the following mapping relationship: T key =F(x,T measure, P), Where P is the set of cutting conditions and tool-workpiece material parameters.

2. The thin-film thermocouple temperature measuring tool according to claim 1, characterized in that: The insulating layer and the protective layer are SiNx thin films or Si3N4 thin films; The first thin-film electrode is a NiCr thin-film electrode, and the second thin-film electrode is a NiSi thin-film electrode.

3. The thin-film thermocouple temperature measuring tool according to claim 1, characterized in that: The shortest distance x from the hot junction to the boundary of the chip contact area is selected as the minimum distance that makes the hot junction temperature signal meet the preset measurable conditions and the temperature gradient meet the preset gentle conditions. The value range is 2-6 mm, preferably 3-4 mm.

4. The thin-film thermocouple temperature measuring tool according to claim 3, characterized in that: The hot junction is located on the tool's axis of symmetry.

5. The thin-film thermocouple temperature measuring tool according to claim 1, characterized in that: The insulating layer has a thickness of 0.6-2.0 μm, the protective layer has a thickness of 0.6-2.0 μm, and the first and second thin film electrodes have a thickness of 300-800 nm.

6. The thin-film thermocouple temperature measuring tool according to claim 1, characterized in that: The temperature compensation model F is any one of the following or a combination thereof: polynomial-response surface model, piecewise function, lookup table interpolation model, regression model, machine learning model, or hybrid model with physical constraints.

7. The thin-film thermocouple temperature measuring tool according to claim 1, characterized in that: The set P of cutting conditions and tool-workpiece material parameters includes: cutting speed, feed rate, depth of cut, tool geometry parameters, workpiece material thermal properties, tool material thermal properties, cooling method, and convective heat transfer coefficient.

8. The method for compensating the cutting temperature of a thin-film thermocouple temperature measuring tool according to any one of claims 1-7, characterized in that, Includes the following steps: Step (1): Determine the shortest distance x from the hot junction to the boundary of the tool-chip contact area through simulation pre-analysis. The simulation pre-analysis includes three-dimensional cutting simulation and tool heat conduction simulation. Extract the temperature distribution curve along the symmetry axis of the tool rake face. Calculate the temperature gradient outside the boundary of the tool-chip contact area in an increasing distance manner. Arrange the hot junction in the area where the temperature gradient meets the preset flat condition and the temperature signal can be measured. Step (2): Construct a temperature compensation model: Obtain a model containing (x, T) measure ,T key The calibration dataset is used to obtain the mapping relationship T by fitting or training the calibration dataset. key =F(x,T measure ,P); Step (3): During the cutting process, the temperature T at the hot junction is measured. measure Based on the temperature compensation model, the critical cutting temperature T is calculated and output. key .

9. The method according to claim 8, characterized in that: In step (2), the calibration dataset is obtained through any one or a combination of the following: temperature field data obtained from cutting numerical simulation, data calculated by tool heat conduction model, temperature measurement data from cutting experiment, and simulation-experiment fusion calibration data; The fitting or training in step (2) includes any one or a combination of least squares fitting, orthogonal experimental parameter optimization, regularized regression, Bayesian regression, or machine learning training.

10. The method for preparing the thin-film thermocouple temperature measuring tool according to any one of claims 1-7, characterized in that: Includes the following steps: S1: Matrix pretreatment; S2: Insulating layer is deposited by pulsed negative bias magnetron sputtering; S3: The first thin film electrode is deposited using multi-arc ion plating; S4: The second thin-film electrode is deposited by DC magnetron sputtering; S5: Hot node location arrangement: The hot node is arranged on the tool rake face in a non-contact area outside the boundary of the tool-chip contact area using a mask plate; the shortest distance from the hot node to the boundary of the tool-chip contact area is x; the boundary of the tool-chip contact area is determined by the contact marks on the rake face after cutting. S6: Annealing is performed under vacuum or inert atmosphere; S7: A protective layer is deposited on the surface of the thermocouple electrode layer by medium-frequency magnetron sputtering; S8: Static calibration: Perform static calibration on the thin-film thermocouple temperature measuring tool to obtain the temperature-thermoelectric potential curve and fit it to obtain the equivalent Seebeck coefficient.

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