A thin film thermocouple for measuring cutting temperature and a method of manufacturing the same

Abstract

The application belongs to the field of thin film thermocouple materials, and particularly relates to a thin film thermocouple for measuring cutting temperature and a preparation method thereof. The thin film thermocouple is prepared by combining the thin film thermocouple preparation method of the intermediate frequency reaction magnetron sputtering technology, the direct current magnetron sputtering technology and the multi-arc ion plating technology. The thin film thermocouple is composed of a hard alloy cutter substrate, Si3N4 thin film, NiCr thin film, NiSi thin film and Si3N4 thin film from bottom to top, wherein one end of the NiCr thin film and the NiSi thin film forms a thermal junction at the cutter tip, and the other end is connected with a standard K-type thermocouple wire. The Si3N4 / NiCr-NiS / Si3N4 composite structure thin film thermocouple prepared on the hard alloy cutter can realize the measurement of a maximum thermal end temperature of 600 DEG C, the response time is 0.58 ms, the bonding force with the cutter substrate is up to 20 N, and the thin film thermocouple has the advantages of high upper limit of temperature measurement and fast response speed.

Description

Technical Field

[0001] This invention belongs to the field of thin-film thermocouple materials, specifically relating to a thin-film thermocouple for measuring cutting temperature and its preparation method. Background Technology

[0002] In the field of machining, cutting heat is a crucial factor affecting tool life and the surface quality of the machined workpiece. This is especially true for difficult-to-machine materials such as high-temperature alloys and titanium alloys, which have high strength and poor thermal conductivity. The cutting process generates a large amount of cutting heat, making the workpiece highly susceptible to severe thermal deformation, which makes it difficult to control the dimensional, shape, and positional accuracy. Real-time and accurate acquisition of the tool's cutting temperature is essential for understanding the tool's machining condition and wear level, and is of great significance for guiding machining processes and controlling the machining process.

[0003] Currently, commonly used methods for measuring cutting temperature include natural thermocouples and infrared thermometry. Natural thermocouples only reflect the average temperature of the cutting tool and have a slow response time, exhibiting a certain degree of temperature lag. Infrared thermometry struggles to effectively distinguish different temperature points in areas with similar temperatures on the cutting tool. Thin-film thermocouples, due to their micron-sized dimensions, offer advantages such as small heat capacity, fast response, and accurate temperature measurement. They can be directly applied to various locations on the cutting tool to achieve real-time monitoring of the tool surface temperature distribution. During actual cutting, an insulating layer needs to be added between the thin-film thermocouple and the metal cutting tool substrate to prevent thermoelectric potential loss. Since direct contact between the thin-film thermocouple and the workpiece may lead to wear and failure, affecting the temperature measurement results, and the high temperatures generated during cutting can easily cause oxidation of the thin-film thermocouple, a protective layer needs to be added to the thermocouple surface during use. Most current research focuses on embedded thin-film thermocouples, but this method alters the cutting tool structure, thus affecting cutting performance.

[0004] In the study of directly depositing thin-film thermocouples on tool surfaces, Biermann et al. (Biermann D, Kirschner M, Pantke K, et al. New coating systems for temperature monitoring inturning processes[J]. Surface & Coatings Technology, 2013, 215(Complete):376-380.) directly deposited thermocouple films on tool surfaces without adding a protective layer, which could lead to the thermocouple being easily damaged by chips during the cutting process. Cui Yunxian et al. (Cui Yunxian, Zhang Bowen, Ding Wanyu, Yan Changgang, Liu Yi. Research on intelligent temperature measuring tools for transient cutting[J]. Journal of Mechanical Engineering, 2017, 53(21):174-180.) prepared thin-film thermocouples on tools using SiO2 as the insulating material, but its stability at high temperatures is poor, and it can only achieve a maximum temperature measurement of 300℃, making it difficult to adapt to higher cutting temperatures. Therefore, it is urgent to develop a thin-film thermocouple that can adapt to complex cutting environments. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of traditional cutting temperature measurement methods and to propose a thin-film thermocouple structure and preparation process for measuring the surface temperature of cutting tools.

[0006] The technical solution to achieve the purpose of this invention is as follows: a thin-film thermocouple for measuring cutting temperature, comprising a Si3N4 thin film, i.e., an insulating layer, disposed between a metal substrate and a thermocouple layer, a NiCr thin film and a NiSi thin film disposed sequentially on the Si3N4 thin film, one end of the NiCr thin film and the NiSi thin film forming a thermal junction at the tip of the cutting tool and the other end connected to a standard K-type thermocouple wire, and a Si3N4 thin film covering the thermal junction as a protective layer.

[0007] Furthermore, the following steps are included:

[0008] Step (1): Heat the coating machine cavity to 100±10℃ under vacuum and maintain it. Use argon and nitrogen as working gases to grow Si3N4 thin film on the metal substrate by medium frequency magnetron sputtering.

[0009] Step (2): Use tin foil as a mask to form a NiCr electrode shape on the cutting tool, heat it to 150±10℃ under vacuum and hold it, use argon as the working gas, and deposit a NiCr thin film on the insulating layer by multi-arc ion plating.

[0010] Step (3): Use tin foil as a mask to form a NiSi electrode shape on the tool, heat it to 100±10℃ under vacuum and hold it, use argon as the working gas, and deposit NiSi by DC magnetron sputtering to obtain a NiSi thin film.

[0011] Step (4): Use tin foil as a mask to form a protective film shape on the cutting tool, heat it to 100±10℃ under vacuum and hold it, use nitrogen and argon as working gases, and use medium frequency magnetron sputtering to prepare Si3N4 thin film.

[0012] Step (5): Standard K-type thermocouple wire is used as the compensating wire for the thin film thermocouple, and high-temperature resistant graphite conductive adhesive is used to connect the corresponding NiSi and NiSi electrodes respectively.

[0013] Furthermore, in step (1), the Si3N4 thin film is prepared in three segments, with each segment growing for 40±4 min and each segment having a film thickness of 300-350 nm. Then, the sputtering power supply is turned off and waited for 20±5 min before being turned on again. The medium-frequency magnetron sputtering current set for the three segments is 4 A, the total time is 120±10 min, and the total thickness is 1±0.1 μm.

[0014] Furthermore, in step (2), the multi-arc ion plating current is set to 65A, the pulse bias voltage is set to 200V, the duty cycle is 30%, and the thickness of the NiCr film is 500±50nm.

[0015] Furthermore, in step (3), the DC magnetron sputtering current is 2A, the pulse bias voltage is set to 200V, the duty cycle is 30%, the thickness of the NiSi film is 500±50nm, and the NiSi film only overlaps with the NiCr film at the tip to form a hot junction.

[0016] Furthermore, in step (4), a medium-frequency magnetron sputtering power supply of 2A is set, and the thickness of the Si3N4 thin film is 1.2±0.1μm. The Si3N4 thin film serves as a protective layer covering the entire hot junction.

[0017] Compared with the prior art, the significant advantages of this invention are:

[0018] (1) The Si3N4 insulating layer prepared in three sections by medium-frequency reactive magnetron sputtering technology has good bonding force with the cemented carbide blade. It also solves the problem of pinhole defects in single-layer Si3N4 film that cause the thermocouple layer to be conductive with the substrate. Furthermore, the resistance value exceeds the requirements at a high temperature of 600℃.

[0019] (2) The thin-film thermocouple obtained by this invention can accurately measure the temperature at any position on the surface of the cutting tool in real time, compared with traditional temperature measurement methods, without changing the original tool structure. It has strong versatility and is not limited to specific cutting tools or workpiece materials. The Seebeck coefficient reaches 16μV / ℃ in the 0-600℃ range, and the dynamic response time is 0.28ms.

[0020] (3) This invention combines three thin film preparation technologies in a good way, which can realize mass production and has promotion value. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the thin-film thermocouple layer structure of the present invention.

[0022] Figure 2 This is a flowchart of the preparation of a thin-film thermocouple in Example 1.

[0023] Figure 3 The image shows the appearance of the thin-film thermocouple prepared on the tool substrate in Example 1.

[0024] Figure 4 The temperature resistance characteristic diagram is shown for the silicon nitride insulating layer prepared in Example 1.

[0025] Figure 5 The static performance diagram of the thin-film thermocouple prepared in Example 1 is shown.

[0026] Figure 6 The image shows the dynamic response time of the thin-film thermocouple prepared in Example 1. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings.

[0028] Example 1

[0029] Thin-film thermocouples are fabricated on the surface of a YG8 cemented carbide cutting tool as a substrate, and the process is as follows: Figure 2 As shown, it includes the following steps:

[0030] Step 1: First, mechanically polish the tool surface to a mirror finish, then ultrasonically clean it sequentially in acetone, deionized water, and anhydrous ethanol for 12 minutes each. After cleaning, place the tool in a vacuum chamber and evacuate it to a vacuum level of 5 × 10⁻⁶. -5 The pressure was increased to Pa, then argon gas was introduced at a rate of 150 ml / min, maintaining a constant vacuum of 1.5 Pa. The pulsed negative bias was set to 1200 V with a duty cycle of 30%, and argon ion sputtering pre-cleaning was performed for 15 min. After cleaning, the argon gas and pulsed power supply were turned off, and the vacuum chamber was heated to 100 °C and maintained while evacuating to a base vacuum of 5 × 10⁻⁶ Pa. -3After Pa, argon gas at a flow rate of 80 ml / min and nitrogen gas at a flow rate of 40 ml / min were introduced to maintain the vacuum level of the chamber at 1 Pa. The intermediate frequency current was set to 4 A. The Si3N4 insulating layer was prepared on the tool surface in three segments, each segment taking 40 min. The machine was turned off in the middle and waited for 20 min before being turned on again. The thickness of each segment was 350±20 nm, and the total thickness of the insulating layer was 1100±100 nm.

[0031] Step 2: After the vacuum chamber cools down, remove the tool and ultrasonically clean it in anhydrous ethanol for 10 minutes. Then, wrap the tool with tin foil, leaving the NiCr electrode shape, and place it in the vacuum chamber for evacuation while heating to 150°C and maintaining the temperature; until a background vacuum of 5×10⁻⁶ is achieved. -5 After Pa, argon gas at a flow rate of 120 ml / min was introduced to maintain a vacuum of 2 Pa. The multi-arc power supply was turned on and set to 65 A. The pulse bias power supply was turned on and set to 200 V with a duty cycle of 30%. The coating time was 20 min, and a NiCr thin film with a thickness of 500 ± 20 nm was obtained on the surface of the insulating layer.

[0032] Step 3: After the vacuum chamber cools down, remove the tool and ultrasonically clean it in anhydrous ethanol for 10 minutes. Then, wrap the tool with tin foil, leaving the NiSi electrode shape, and place it in the vacuum chamber for evacuation while heating to 80°C and maintaining the temperature; until a background vacuum of 5×10⁻⁶ is achieved. -5 After Pa, argon gas was introduced at a rate of 120 ml / min to maintain a vacuum of 0.8 Pa. The DC magnetron sputtering power supply was turned on and set to 2 A. The pulse bias power supply was turned on and set to 200 V with a duty cycle of 30%. The deposition time was 40 min, and a NiSi thin film with a thickness of 500 ± 20 nm was obtained on the surface of the insulating layer.

[0033] Step 4: After the vacuum chamber cools down, remove the tool and ultrasonically clean it in anhydrous ethanol for 10 minutes. Then, wrap the tool with aluminum foil, leaving a protective film, and place it in the vacuum chamber to evacuate to a base vacuum of 5×10⁻⁶. -5 After passing through the thermocouple layer, argon gas at a flow rate of 100 ml / min and nitrogen gas at a flow rate of 20 ml / min are introduced. The working vacuum is 1 Pa, the preparation time is 90 min, and the thickness is 1200-1300 nm. A Si3N4 protective layer is then prepared on the thermocouple layer.

[0034] The temperature resistance properties of the Si3N4 insulating layer prepared in step one were tested as follows: Figure 4 As shown, the resistance exceeds 10 MΩ at 600℃, meeting the insulation requirements at high temperatures. Mechanical and electrical properties of the prepared thin-film thermocouple were tested, and the film-substrate bonding force was found to be 20 N. The output thermoelectric potential at different temperatures is shown below. Figure 5 As shown, the Seebeck coefficient obtained after fitting is 16 μV / ℃. The dynamic response test is as follows... Figure 6 As shown, the calculated response time is 0.58ms.

Claims

1. A thin film thermocouple for measuring cutting temperatures, characterized by The application relates to a thin-film thermocouple for a cutting tool, which comprises a Si3N4 film (insulating layer) arranged between a metal base and a thermocouple layer, a NiCr film and a NiSi film arranged on the Si3N4 film in sequence, one end of the NiCr film and the NiSi film forms a thermal contact point at a cutting tool tip, the other end is connected with a standard K-type thermocouple wire, and a Si3N4 film covering the thermal contact point as a protective layer.

2. The method of claim 1 wherein the thin-film thermocouple is formed by, The application relates to a thin-film thermocouple for a cutting tool, which comprises a Si3N4 film (insulating layer) arranged between a metal base and a thermocouple layer, a NiCr film and a NiSi film arranged on the Si3N4 film in sequence, one end of the NiCr film and the NiSi film forms a thermal contact point at a cutting tool tip, the other end is connected with a standard K-type thermocouple wire, and a Si3N4 film covering the thermal contact point as a protective layer. The application relates to a thin-film thermocouple for a cutting tool, which comprises a Si3N4 film (insulating layer) arranged between a metal base and a thermocouple layer, a NiCr film and a NiSi film arranged on the Si3N4 film in sequence, one end of the NiCr film and the NiSi film forms a thermal contact point at a cutting tool tip, the other end is connected with a standard K-type thermocouple wire, and a Si3N4 film covering the thermal contact point as a protective layer. The application relates to a thin-film thermocouple for a cutting tool, which comprises a Si3N4 film (insulating layer) arranged between a metal base and a thermocouple layer, a NiCr film and a NiSi film arranged on the Si3N4 film in sequence, one end of the NiCr film and the NiSi film forms a thermal contact point at a cutting tool tip, the other end is connected with a standard K-type thermocouple wire, and a Si3N4 film covering the thermal contact point as a protective layer. The application relates to a thin-film thermocouple for a cutting tool, which comprises a Si3N4 film (insulating layer) arranged between a metal base and a thermocouple layer, a NiCr film and a NiSi film arranged on the Si3N4 film in sequence, one end of the NiCr film and the NiSi film forms a thermal contact point at a cutting tool tip, the other end is connected with a standard K-type thermocouple wire, and a Si3N4 film covering the thermal contact point as a protective layer. In step (1), the Si3N4 film is prepared in three sections, each section is grown for 40+ / -4 min, and the thickness of each section is 300-350 nm; then the sputtering power is turned off and is waited for 20+ / -5 min, and then is turned on again; the middle frequency magnetron sputtering current is set to be 4 A, the total growth time is 120+ / -10 min, and the total thickness is 1+ / -0.1 micron. In step (2), the multi-arc ion plating current is set to be 65 A, the pulse bias voltage is set to be 200 V, the duty cycle is 30%, and the thickness of the NiCr film is 500+ / -50 nm.

3. The preparation method according to claim 2, characterized in that, In step (3), the direct current magnetron sputtering current is 2 A, the pulse bias voltage is set to be 200 V, the duty cycle is 30%, the thickness of the NiSi film is 500+ / -50 nm, and the NiSi film only overlaps with the NiCr film at the cutting tool tip to form a thermal contact point.

4. The production method according to claim 3, characterized by, In step (4), the middle frequency magnetron sputtering power is set to be 2 A, the thickness of the Si3N4 film is 1.2+ / -0.1 micron, and the Si3N4 film covers the whole thermal contact point as a protective layer.

5. The production method according to claim 4, characterized by, ​ 6. The production method according to claim 5, wherein ​

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