Electro-pulse and liquid nitrogen cooling combined assisted cutting method and device

Abstract

The application discloses an electric pulse-liquid nitrogen cooling composite auxiliary cutting machining method and device. Through electric pulse composite liquid nitrogen cooling auxiliary cutting technology, the influence of control electric pulse, liquid nitrogen related process parameters and workpiece surface layer temperature on the temperature of the tool-chip contact surface is controlled, the friction coefficient of the tool-chip contact surface is taken as a closed-loop feedback index, the workpiece strength can be reduced, the workpiece can be softened, the friction state between the tool-chip can be maximally improved, the tool temperature can be reduced, and the tool life and the workpiece surface quality can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metal processing, in particular to a kind of electric pulse-liquid nitrogen cooling composite assisted cutting processing method and device. BACKGROUND

[0002] Titanium alloy, nickel-based alloy, high-temperature alloy, quenched steel and other functional structural materials are widely used in aviation, civil and other fields due to their superior mechanical and physical properties, but these materials are generally high in strength and hardness, which leads to poor cutting machinability, reducing tool life and workpiece machining quality.

[0003] Patent application No. CN201810193754.1 discloses a hard alloy cutting method based on liquid nitrogen cooling lubrication. The method mixes lubricant with ultra-low temperature liquid nitrogen and sprays it onto the cutting tool used in the hard alloy cutting process. This method uses a small amount of lubricant mixed with ultra-low temperature liquid nitrogen, which can reduce cutting temperature and improve the friction state between tool and chip. However, the strength of the workpiece material is still high, and the tool chipping wear still exists, which limits the further improvement of tool life and the improvement of workpiece surface quality, and the small amount of lubricant still has an impact on the environment.

[0004] Electric pulse assisted cutting technology can produce electroplastic effect on workpiece material through the coupling of thermal and non-thermal effects, which can reduce the strength and hardness of the workpiece. Moreover, electric pulse can reduce the friction coefficient between tool-chip contact surface through electroplastic effect, reduce the cutting zone temperature, and improve the friction state between tool and chip. Therefore, electric pulse assisted cutting technology can effectively reduce the cutting force of difficult-to-machine materials by 20%-30% during cutting process, improve tool life by 20%-30%, and reduce workpiece surface roughness by 20%-30%. However, in the process of electric pulse assisted cutting of difficult-to-machine materials, the thermal effect can increase the temperature of the workpiece surface material by about 200℃, increasing the cutting temperature between tool and chip. This not only causes the high-temperature strength of the tool to decrease, but also causes the plastic deformation of the tool tip of the hard alloy tool, the peeling of the diamond tool from the hard alloy substrate, and the increase of the high-temperature chemical activity of the workpiece material, which aggravates the adhesive wear, peeling wear and diffusion wear of the tool during cutting process. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art and provide an electric pulse-liquid nitrogen cooling composite assisted cutting processing method and device, which can improve the friction state between tool and chip, reduce tool temperature, and improve tool life and workpiece surface quality.

[0006] To solve the above technical problems, the present application adopts the following technical solutions:

[0007] A method for combined electric pulse-liquid nitrogen cooling-assisted cutting includes the following steps:

[0008] S1. Install the workpiece, turn on the electric pulse auxiliary unit, measure the real-time temperature T of the workpiece, and determine whether the temperature T has reached the first temperature threshold T0. If yes, proceed to step S2; otherwise, adjust the electric pulse processing parameters until the real-time temperature T reaches the first temperature threshold T0.

[0009] S2. Start the liquid nitrogen auxiliary unit, measure the real-time temperature T of the workpiece, and determine whether the temperature T is less than or equal to the second temperature threshold T1. If yes, proceed to step S3; otherwise, adjust the electrical pulse parameters until the real-time temperature T is less than or equal to the first temperature threshold T1.

[0010] S3. Measure the cutting force signal during the cutting process and calculate the friction coefficient value μ between the chip and the tool rake face. Determine whether the friction coefficient value μ is between the upper threshold μ1 and the lower threshold μ2. If so, continue cutting and measure the cutting force signal in real time during the cutting process. Repeat step S3 until the machining is completed. Otherwise, adjust the liquid nitrogen machining parameters until the friction coefficient value is between the upper threshold μ1 and the lower threshold μ2.

[0011] As a further improvement to the above technical solution:

[0012] In step S3, the friction coefficient μ between the chip and the tool rake face is calculated using equation (Ⅰ).

[0013]

[0014] Where is the tool rake angle, Fy is the axial component of the cutting force, and Fz is the tangential component of the cutting force.

[0015] The second temperature threshold T1 is 200℃.

[0016] As a general inventive concept, the present invention also provides an electro-pulse-liquid nitrogen cooling composite assisted cutting machining device, including an electro-pulse auxiliary unit and a machine tool unit. The electro-pulse auxiliary unit includes an electro-pulse power supply, a first brush, and a second brush. The first brush and the second brush are electrically connected to the electro-pulse power supply, respectively. The first brush and the second brush are arranged opposite to each other on the machine tool unit, and the workpiece is installed between the first brush and the second brush. The machine tool unit includes a cutting tool for cutting the workpiece. The electro-pulse-liquid nitrogen cooling composite assisted cutting machining device also includes a liquid nitrogen auxiliary unit and a main control unit. The machine tool unit is equipped with a force gauge for measuring cutting force signals and a temperature sensor for measuring real-time temperature during cutting. The liquid nitrogen auxiliary unit is used to apply liquid nitrogen to the rake face and flank face of the cutting tool in the machine tool unit. After receiving and processing the output data from the temperature sensor and the force gauge, the main control unit adjusts the electro-pulse parameters of the electro-pulse power supply and the liquid nitrogen machining parameters of the liquid nitrogen auxiliary unit.

[0017] As a further improvement of the above technical solution:

[0018] The liquid nitrogen auxiliary unit comprises a liquid nitrogen source, a nozzle and a delivery pipe for delivering liquid nitrogen from the liquid nitrogen source to the nozzle, and the liquid nitrogen processing parameters of the liquid nitrogen auxiliary unit are controlled by the main control unit.

[0019] The liquid nitrogen processing parameters are temperature and flow rate.

[0020] The main control unit comprises a main control module and a flow rate adjustment module, the flow rate adjustment module is used for controlling the processing parameters of the liquid nitrogen auxiliary unit, and the main control module is electrically connected with the electric pulse power supply, the temperature sensor and the force gauge, is used for receiving and processing the output data of the temperature sensor and the force gauge, and then adjusting the electric pulse parameters of the electric pulse power supply and the liquid nitrogen processing parameters of the liquid nitrogen auxiliary unit.

[0021] The temperature sensor is an infrared temperature sensor, and the force gauge is a three-way piezoelectric force gauge.

[0022] As a general inventive concept, the present application also provides an electric pulse-liquid nitrogen cooling composite auxiliary cutting machining system, comprising the following modules:

[0023] A first measurement control module is used for installing a workpiece, starting an electric pulse auxiliary unit, measuring a real-time temperature T of the workpiece, judging whether the temperature T reaches a first temperature threshold T0, outputting to a second measurement control module if yes, and adjusting electric pulse machining parameters until the real-time temperature T reaches the first temperature threshold T0 if no.

[0024] A second measurement control module is used for starting a liquid nitrogen auxiliary unit, measuring a real-time temperature T of the workpiece, judging whether the temperature T is less than or equal to a second temperature threshold T1, outputting to a third measurement judging module if yes, and adjusting electric pulse parameters until the real-time temperature T is less than or equal to the first temperature threshold T1 if no.

[0025] A third measurement judging module is used for measuring a cutting force signal in a cutting process and calculating a friction coefficient value μ of a chip and a rake face of a tool, judging whether the friction coefficient value μ is between an upper threshold μ1 and a lower threshold μ2, continuing cutting and measuring the cutting force signal in the cutting process in real time until machining is completed if yes, and adjusting liquid nitrogen processing parameters until the friction coefficient value is between the upper threshold μ1 and the lower threshold μ2 if no.

[0026] As a general inventive concept, the present application also provides a computer readable storage medium, wherein a computer program is stored in the computer readable storage medium, and the computer program is used for programming or configuring a microprocessor to execute the electric pulse-liquid nitrogen cooling composite auxiliary cutting machining method.

[0027] Compared with the prior art, the present application has the following advantages:

[0028] The electric pulse-liquid nitrogen cooling composite assisted cutting machining method can not only reduce the strength of the workpiece and soften the workpiece, but also maximize the improvement of the friction state between the tool and the chip, reduce the tool temperature, reduce the surface roughness of the workpiece, improve the tool life and the surface quality of the workpiece, and is clean and environmentally friendly.

[0029] The electric pulse-liquid nitrogen cooling composite assisted cutting machining device of the application, the main control unit adjusts the electric pulse parameters of the electric pulse power supply and controls the liquid nitrogen processing parameters of the liquid nitrogen auxiliary unit according to the workpiece temperature, the dynamometer monitors the cutting force in the process of cutting the workpiece by the tool, the main control unit calculates the friction coefficient between the rake face of the tool and the chip according to the cutting force, sends instructions to the liquid nitrogen auxiliary unit, and adjusts the liquid nitrogen processing parameters (such as the liquid nitrogen flow and the nozzle liquid nitrogen output flow) of the liquid nitrogen auxiliary unit in real time, so that the advantages of the electric pulse-liquid nitrogen cooling composite assisted cutting technology are fully utilized. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The electric pulse-liquid nitrogen cooling composite assisted cutting machining method of the application is shown in the process flow chart.

[0031] Figure 2 The control logic diagram of the electric pulse-liquid nitrogen cooling composite assisted cutting machining method of the application is shown in the control logic diagram.

[0032] Figure 3 The overall structure of the electric pulse-liquid nitrogen cooling composite assisted cutting machining device of the application is shown in the overall structure schematic diagram.

[0033] Figure 4 The local enlarged view of A in Figure 3 The local enlarged view of A in

[0034] Figure 5 The local enlarged view of A in Figure 3 The local enlarged view of A in

[0035] The various labels in the figure represent: 1, electric pulse power supply; 2, machine tool unit; 3, first brush; 4, workpiece; 5, temperature sensor; 6, tool; 7, dynamometer; 8, nozzle; 9, second brush; 10, conveying pipe; 11, main control unit; 12, liquid nitrogen source. DETAILED DESCRIPTION

[0036] The detailed implementation of the application will be further described below in combination with the drawings and technical solutions.

[0037] Taking the outer circle turning of a TC4 titanium alloy round bar as an example, the workpiece size is Φ20*150mm, the cutting process parameters are: cutting depth ap=1mm, feed speed f=0.1mm / r, spindle speed n=60m / min; the material of the turning tool is diamond, the rake angle γ0=-6°, and the relief angle ψ=5°.

[0038] The application will be further described below. Unless otherwise specified, the instruments or materials used in the application are commercially available.

[0039] Example 1

[0040] As shown in Figure 1 and Figure 2 A kind of electric pulse-liquid nitrogen cooling composite auxiliary cutting processing method of the application, comprising the following steps:

[0041] S1, install workpiece 4, open electric pulse auxiliary unit, measure the real-time temperature T of workpiece 4, judge whether temperature T reaches first temperature threshold T0 (the embodiment is 60 ℃), if yes, execute step S2, otherwise adjust electric pulse processing parameter until the real-time temperature T reaches first temperature threshold T0;

[0042] S2, start liquid nitrogen auxiliary unit, measure the real-time temperature T of workpiece 4, judge whether temperature T is less than or equal to second temperature threshold T1 (the embodiment is 200 ℃), if yes, execute step S3, otherwise adjust electric pulse parameter until the real-time temperature T is less than or equal to first temperature threshold T1;

[0043] S3, measure the cutting force signal in the cutting process and calculate the friction coefficient value μ of chip and the rake face of tool 6, judge whether the friction coefficient value μ is between upper threshold μ1 (the embodiment is 0.192) and lower threshold μ2 (the embodiment is 0.145), if yes, continue cutting and measure the cutting force signal in the cutting process in real time to repeat step S3 until machining is completed, otherwise adjust liquid nitrogen processing parameter until the friction coefficient is between the upper threshold and the lower threshold.

[0044] The electric pulse-liquid nitrogen cooling composite auxiliary cutting processing method of the application, by electric pulse composite liquid nitrogen cooling auxiliary cutting technology, by controlling electric pulse, liquid nitrogen related process parameters, the influence of workpiece 4 surface layer temperature on the temperature of tool-chip contact surface, with the friction coefficient of tool-chip contact surface as a closed-loop feedback index, not only can reduce the strength of workpiece, soften workpiece, but also can maximize the friction state between tool-chip, reduce tool temperature, reduce workpiece surface roughness, improve tool 6 life and workpiece 4 surface quality, clean and environmental protection.

[0045] In the step S3, the friction coefficient value μ of chip and the rake face of tool (6) is calculated by formula (I):

[0046]

[0047] where is the tool rake angle, Fy is the axial component of the cutting force, and Fz is the tangential component of the cutting force.

[0048] As shown in Figures 3 to 5 The electric pulse-liquid nitrogen cooling composite assisted cutting device of the embodiment comprises an electric pulse assisting unit, a machine tool unit 2, the electric pulse assisting unit comprising an electric pulse power supply 1, a first electric brush 3 and a second electric brush 9, the first electric brush 3 and the second electric brush 9 being connected with the electric pulse power supply 1 respectively, the first electric brush 3 and the second electric brush 9 being oppositely arranged on the machine tool unit 2, a workpiece 4 being installed between the first electric brush 3 and the second electric brush 9, the machine tool unit 2 comprising a tool 6 for cutting the workpiece 4, the electric pulse-liquid nitrogen cooling composite assisted cutting device further comprising a liquid nitrogen assisting unit and a main control unit 11, a dynamometer 7 for measuring a cutting force signal and a temperature sensor 5 for measuring a real-time temperature during cutting being installed on the machine tool unit 2, the liquid nitrogen assisting unit being used for applying liquid nitrogen to rake faces and flank faces of the tool 6 of the machine tool unit 2, the main control unit 11 adjusting electric pulse parameters of the electric pulse power supply 1 and liquid nitrogen processing parameters of the liquid nitrogen assisting unit after receiving and processing output data of the temperature sensor 5 and the dynamometer 7.

[0049] In the embodiment, the main control unit 11 is located in a main control box.

[0050] The electric pulse assisting cutting adopted in the embodiment can not only reduce the strength of the surface layer material of the workpiece 4 through the electroplastic effect, weaken the chipping wear and plastic fracture failure of the tool 6, but also improve the friction state between the tool and the chip, reduce the adhesive wear and peeling wear of the tool 6; the liquid nitrogen cooling can reduce the temperature of the cutting zone and eliminate the influence of the temperature rise caused by the electric pulse on the wear of the tool 6.

[0051] The liquid nitrogen assisting unit can reduce the temperature and the cutting force of the workpiece 4, but causes a large temperature gradient of the cutting tool 6, which causes the tool 6 to easily generate microcracks. Under the premise of reducing the strength and plasticity of the workpiece 4, the temperature (-25℃ to -10℃) and the flow (0.2L / min to 0.6L / min) of the liquid nitrogen are reasonably controlled according to the surface layer temperature of the workpiece to be processed, so that the tool 6 can be prevented from generating microcracks.

[0052] In the embodiment, the workpiece 4 is connected with the electric pulse power supply 1, the strength of the surface layer material of the workpiece 4 is reduced, and the friction state between the tool and the chip is improved; the liquid nitrogen is applied to the rake faces and the flank faces of the tool 6, the influence of the temperature rise caused by the electric pulse on the wear of the tool 6 can be eliminated, and the friction coefficient between the tool and the chip can be further reduced, so that the service life of the tool 6 and the quality of the workpiece are improved.

[0053] In this embodiment, the first brush 3 is connected to the positive pole of the electric pulse power supply 1 through a cable, and the second brush 9 is connected to the negative pole of the electric pulse power supply 1 through a cable. The current of the electric pulse power supply 1 flows from the first brush 3, through the machine tool and the workpiece 4, and out of the second brush 9.

[0054] The liquid nitrogen auxiliary unit includes a liquid nitrogen source 12, a nozzle 8, and a delivery pipe 10 for delivering liquid nitrogen from the liquid nitrogen source 12 to the nozzle 8. The liquid nitrogen processing parameters of the liquid nitrogen auxiliary unit are controlled by the main control unit 11.

[0055] The liquid nitrogen processing parameters are temperature and flow rate. The flow rate includes the output flow rate of the liquid nitrogen source 12 and the output flow rate of the nozzle 8.

[0056] The main control unit 11 includes a main control module and a flow rate adjustment module. The flow rate adjustment module is used to control the processing parameters of the liquid nitrogen auxiliary unit. The main control module is electrically connected to the electric pulse power supply 1, the temperature sensor 5, and the force gauge 7. After receiving and processing the output data of the temperature sensor 5 and the force gauge 7, the main control module adjusts the electric pulse parameters of the electric pulse power supply 1 and the liquid nitrogen processing parameters of the liquid nitrogen auxiliary unit.

[0057] The temperature sensor 5 is an infrared temperature sensor 5, and the force gauge 7 is a three-way piezoelectric force gauge.

[0058] The electric pulse-liquid nitrogen cooling composite assisted cutting processing method of this embodiment includes the following steps:

[0059] S1, first, the workpiece 4 is clamped on the machine tool unit 2, the electric pulse auxiliary unit is started, the electric pulse is applied to the workpiece 4, the infrared temperature sensor 5 is placed on the workpiece, and the position of the infrared temperature sensor 5 is followed during processing. Start the infrared temperature sensor 5, measure the real-time temperature T of the workpiece 4, adjust the electric pulse parameters, and determine whether the temperature T reaches the first temperature threshold 60℃. If yes, execute step S2, otherwise adjust the electric pulse processing parameters until the real-time temperature T reaches the first temperature threshold 60℃.

[0060] S2, when the temperature of the workpiece 4 reaches the predetermined temperature T0, the main control unit 11 sends an instruction to the flow rate control module to start the liquid nitrogen auxiliary unit, the liquid nitrogen source 12 outputs liquid nitrogen, the real-time temperature T of the workpiece 4 is measured, and it is determined whether the temperature T is less than or equal to the second temperature threshold 200℃. If yes, execute step S3, otherwise adjust the electric pulse parameters until the real-time temperature T is less than or equal to the first temperature threshold 200℃.

[0061] In this embodiment, during the cutting process, the main control unit 11 receives the temperature signal of the workpiece 4 measured by the infrared temperature sensor 5. When the surface of the workpiece 4 to be processed exceeds 200℃, the main control unit 11 sends an instruction to the electric pulse auxiliary unit to adjust the electric pulse parameters, so that the surface temperature of the workpiece to be processed gradually returns to below 200℃, avoiding the oxidation of the workpiece.

[0062] S3, measuring the cutting force signal in the cutting process and calculating the friction coefficient value between the chip and the rake face of the tool 6, judging whether the friction coefficient value is between the upper threshold value 0.192 and the lower threshold value 0.145, if yes, continuing cutting and repeatedly measuring the cutting force signal in the cutting process until the machining is completed, otherwise adjusting the liquid nitrogen machining parameters until the friction coefficient is between the upper threshold value μ1 and the lower threshold value μ2.

[0063] In the embodiment, when the surface of the workpiece 4 to be machined is not more than 200℃, the main control unit 11 receives the cutting force signal measured by the three-way piezoelectric force gauge 7, calculates the friction coefficient between the chip and the rake face of the tool 6, and sends instructions to the flow control module in real time according to the liquid nitrogen output flow and friction coefficient model, controls the liquid nitrogen output temperature and flow of the special nozzle 8, so as to achieve the optimal machinability of the workpiece, improve the tool life and the workpiece quality; when the cutting machining of the workpiece 4 is completed, the electric pulse power supply 1, the main control unit 11 and the liquid nitrogen source 12 are turned off.

[0064] The electric pulse-liquid nitrogen cooling composite auxiliary cutting machining system of the embodiment comprises the following modules

[0065] The first measurement control module is used for installing the workpiece 4, turning on the electric pulse auxiliary unit, measuring the real-time temperature T of the workpiece 4, judging whether the temperature T reaches the first temperature threshold value 60℃, if yes, outputting to the second measurement control module, otherwise adjusting the electric pulse machining parameters until the real-time temperature T reaches the first temperature threshold value 60℃.

[0066] The second measurement control module is used for starting the liquid nitrogen auxiliary unit, measuring the real-time temperature T of the workpiece 4, judging whether the temperature T is less than or equal to the second temperature threshold value 200℃, if yes, outputting to the third measurement judgment module, otherwise adjusting the electric pulse parameters until the real-time temperature T is less than or equal to the first temperature threshold value 200℃.

[0067] The third measurement judgment module is used for measuring the cutting force signal in the cutting process and calculating the friction coefficient value between the chip and the rake face of the tool 6, judging whether the friction coefficient value is between the upper threshold value 0.192 and the lower threshold value 0.145, if yes, continuing cutting and repeatedly measuring the cutting force signal in the cutting process until the machining is completed, otherwise adjusting the liquid nitrogen machining parameters until the friction coefficient is between the upper threshold value 0.192 and the lower threshold value 0.145.

[0068] The computer readable storage medium of the embodiment, the computer readable storage medium stores a computer program, and the computer program is used for being programmed or configured by a microprocessor to execute the foregoing electric pulse-liquid nitrogen cooling composite auxiliary cutting machining method.

[0069] Those skilled in the art can understand that the above description of the computer device is only an example and does not constitute a limitation on the computer device, and can include more or less components than the above description, or combine certain components, or different components, for example, can include input and output devices, network access devices, buses, etc. The processor can be a central processing unit (CPU), and can also be other general-purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor, etc. The processor is the control center of the computer device, which connects various parts of the computer device through various interfaces and lines.

[0070] The memory can be used to store the computer program and / or modules, and the processor realizes various functions of the computer device by running or executing the computer program and / or modules stored in the memory, and calling the data stored in the memory. The memory can mainly include a program storage area and a data storage area, wherein the program storage area can store an operating system, at least one application program required for a function (such as a sound playing function, an image playing function, etc.), etc.; and the data storage area can store data created according to the use of the mobile phone (such as audio data, a phone book, etc.), etc. In addition, the memory can include a high-speed random access memory, and can also include a non-volatile memory, for example, a hard disk, a memory, a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, at least one disk storage device, a flash memory device, or other volatile solid-state memory devices.

[0071] The modules / units integrated in the computer device, if implemented in the form of software functional units and sold or used as independent products, can be stored in a computer readable storage medium. Based on such understanding, all or part of the processes in the above-mentioned embodiment methods can also be completed by a computer program instructing related hardware, and the computer program can be stored in a computer readable storage medium. When the computer program is executed by a processor, the steps of each of the above-mentioned various template labeling based distributed crawler methods embodiments can be implemented. The computer program includes computer program code, which can be in the form of source code, object code, executable files or some intermediate forms. The computer readable medium can include any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signal, electrical signal and software distribution medium, etc.

[0072] Although the present application has been disclosed in the above preferred embodiments, it is not intended to limit the present application. Any person skilled in the art can make many possible changes and modifications to the technical solutions of the present application, or modify equivalent embodiments with equivalent changes, without departing from the scope of the technical solutions of the present application, by using the technical contents disclosed above. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, without departing from the content of the technical solutions of the present application, shall fall within the scope of protection of the technical solutions of the present application.

Claims

1. A method for combined assisted cutting machining using electrical pulse-liquid nitrogen cooling, characterized in that: Includes the following steps: S1. Install the workpiece (4), turn on the electric pulse auxiliary unit, measure the real-time temperature T of the workpiece (4), and determine whether the temperature T reaches the first temperature threshold T0. If yes, execute step S2; otherwise, adjust the electric pulse processing parameters until the real-time temperature T reaches the first temperature threshold T0. S2. Start the liquid nitrogen auxiliary unit, measure the real-time temperature T of the workpiece (4), and determine whether the temperature T is less than or equal to the second temperature threshold T1. If so, execute step S3; otherwise, adjust the electrical pulse parameters until the real-time temperature T is less than or equal to the first temperature threshold T1. S3. Measure the cutting force signal during the cutting process and calculate the friction coefficient value μ of the chip and the rake face of the tool (6). Determine whether the friction coefficient value μ is between the upper threshold μ1 and the lower threshold μ2. If so, continue cutting and measure the cutting force signal during the cutting process in real time. Repeat step S3 until the machining is completed. Otherwise, adjust the liquid nitrogen machining parameters until the friction coefficient value μ is between the upper threshold μ1 and the lower threshold μ2.

2. The electro-pulse-liquid nitrogen cooling composite assisted cutting method according to claim 1, characterized in that: In step S3, the friction coefficient μ between the chip and the rake face of the tool (6) is calculated using equation (Ⅰ): Where γ0 is the tool rake angle, Fy is the axial component of the cutting force, and Fz is the tangential component of the cutting force.

3. The electro-pulse-liquid nitrogen cooling composite assisted cutting method according to claim 1, characterized in that: The second temperature threshold T1 is 200℃.

4. An electro-pulse-liquid nitrogen cooling composite assisted cutting machining device, comprising an electro-pulse auxiliary unit and a machine tool unit (2), wherein the electro-pulse auxiliary unit comprises an electro-pulse power supply (1), a first brush (3) and a second brush (9), the first brush (3) and the second brush (9) being electrically connected to the electro-pulse power supply (1) respectively, the first brush (3) and the second brush (9) being arranged opposite to each other on the machine tool unit (2), and a workpiece (4) being mounted between the first brush (3) and the second brush (9), wherein the machine tool unit (2) comprises a cutting tool (6) for cutting the workpiece (4), characterized in that: The electrical pulse-liquid nitrogen cooling composite assisted cutting device also includes a liquid nitrogen auxiliary unit and a main control unit (11). The machine tool unit (2) is equipped with a force gauge (7) for measuring cutting force signals and a temperature sensor (5) for measuring real-time temperature during cutting. The liquid nitrogen auxiliary unit is used to apply liquid nitrogen to the rake face and flank face of the tool (6) of the machine tool unit (2). After receiving and processing the output data of the temperature sensor (5) and the force gauge (7), the main control unit (11) adjusts the electrical pulse parameters of the electrical pulse power supply (1) and the liquid nitrogen processing parameters of the liquid nitrogen auxiliary unit.

5. The electro-pulse-liquid nitrogen cooling composite assisted cutting device according to claim 4, characterized in that: The liquid nitrogen auxiliary unit includes a liquid nitrogen source (12), a nozzle (8), and a delivery pipe (10) for delivering liquid nitrogen from the liquid nitrogen source (12) to the nozzle (8). The liquid nitrogen processing parameters of the liquid nitrogen auxiliary unit are controlled by the main control unit (11).

6. The electro-pulse-liquid nitrogen cooling composite assisted cutting device according to claim 5, characterized in that: The liquid nitrogen processing parameters are temperature and flow rate.

7. The electro-pulse-liquid nitrogen cooling composite assisted cutting device according to claim 4, characterized in that: The main control unit (11) includes a main control module and a flow regulation module. The flow regulation module is used to control the processing parameters of the liquid nitrogen auxiliary unit. The main control module is electrically connected to the electric pulse power supply (1), the temperature sensor (5) and the force gauge (7). It is used to receive and process the output data of the temperature sensor (5) and the force gauge (7) and then adjust the electric pulse parameters of the electric pulse power supply (1) and the liquid nitrogen processing parameters of the liquid nitrogen auxiliary unit.

8. The electro-pulse-liquid nitrogen cooling composite assisted cutting device according to claim 4, characterized in that: The temperature sensor (5) is an infrared temperature sensor, and the force measuring instrument (7) is a triaxial piezoelectric force measuring instrument.

9. A composite assisted cutting system of electrical pulse-liquid nitrogen cooling, characterized in that: Includes the following modules: The first measurement and control module is used to install the workpiece (4), turn on the electric pulse auxiliary unit, measure the real-time temperature T of the workpiece (4), and determine whether the temperature T reaches the first temperature threshold T0. If so, it outputs to the second measurement and control module; otherwise, it adjusts the electric pulse processing parameters until the real-time temperature T reaches the first temperature threshold T0. The second measurement and control module is used to start the liquid nitrogen auxiliary unit, measure the real-time temperature T of the workpiece (4), and determine whether the temperature T is less than or equal to the second temperature threshold T1. If so, it outputs to the third measurement and judgment module; otherwise, it adjusts the electrical pulse parameters until the real-time temperature T is less than or equal to the first temperature threshold T1. The third measurement and judgment module is used to measure the cutting force signal during the cutting process and calculate the friction coefficient value μ of the chip and the rake face of the tool (6). It judges whether the friction coefficient value μ is between the upper threshold μ1 and the lower threshold μ2. If so, it continues to cut and measures the cutting force signal during the cutting process in real time until the machining is completed. Otherwise, it adjusts the liquid nitrogen machining parameters until the friction coefficient value is between the upper threshold μ1 and the lower threshold μ2.

10. A computer-readable storage medium storing a computer program, characterized in that, The computer program is used to be programmed or configured by a microprocessor to perform the electro-pulse-liquid nitrogen cooling composite assisted cutting method according to any one of claims 1 to 3.

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