A low-temperature processing system for thin-walled parts

Abstract

A low-temperature processing system for thin-walled parts belongs to the field of milling technology for difficult-to-machine alloy thin-walled components, and particularly relates to a low-temperature processing system for thin-walled parts. The present invention provides a low-temperature processing system for thin-walled parts with better working effects. The low-temperature processing system for thin-walled parts of the present invention includes a liquid nitrogen dewar 3.1, and is characterized in that the outlet of the liquid nitrogen dewar 3.1 is connected to the inlet of a low-temperature flow valve 3.3 through a liquid nitrogen delivery hose 3.2, the outlet of the low-temperature flow valve 3.3 is connected to the inlet of an electronic flow control valve 3.4, the outlet of the electronic flow control valve 3.4 is connected to the inlet of a low-temperature pressure reducing valve 3.5, the outlet of the low-temperature pressure reducing valve 3.5 is connected to the inlet of a low-temperature throttle valve 3.6, the outlet of the low-temperature throttle valve 3.6 is connected to the inlet of a low-temperature check valve 3.7, and the outlet of the low-temperature check valve 3.7 is connected to the left-end inlet of a left-turn joint 2.4 on a machine tool spindle box 3.8.

Description

Technical Field

[0001] The present invention belongs to the technical field of milling of difficult-to-machine alloy thin-walled components, and particularly relates to a low-temperature machining system for thin-walled components. Background Art

[0002] Difficult-to-machine components such as thin-walled titanium alloys and nickel-based superalloys have good mechanical properties, with high thermal strength, high specific strength, good corrosion resistance, etc., and are widely used in important fields such as aerospace and military defense. However, due to the poor stiffness and high toughness of the materials of such thin-walled components, and high requirements for dimensional accuracy and geometric tolerances, defects such as burrs, easy deformation, and large dimensional errors will inevitably occur when using the traditional cutting fluid cooling milling process. In addition, this difficult-to-machine material such as titanium alloy has a lower thermal conductivity compared to steel, and the cooling capacity and effect of the cutting fluid are not ideal. When machining at high speed, it is extremely easy to cause serious thermal deformation defects. Especially when using a large milling amount, the machining defects are more serious. The milling defects of thin-walled difficult-to-machine alloy materials are the result of the combined action of heat and force. During cutting, the cooling efficiency should be improved and the cutting force load should be reduced.

[0003] Northwestern Polytechnical University has disclosed a robust process control method for the surface state of precision milling of titanium alloy thin-walled structures and applied for a domestic patent, application number: CN202111129812.2, invention name: Robust process control method for the surface state of precision milling of titanium alloy thin-walled structures. This method compensates for the sudden change in the surface state of the structural part caused by the action of uncontrollable factors during machining by adjusting controllable process parameters, ensuring that the fatigue performance of the structural part reaches the expected effect and improving the dimensional and geometric accuracy of titanium alloy thin-walled structural parts. Jiangsu Xianglin Jiayu Machinery Co., Ltd. has disclosed a chip position cooling device during thin-walled part machining and applied for a domestic patent, application number: CN202121806849.X, patent name: A chip position cooling device during thin-walled part machining. This patent can spray water at the machining position of the thin-walled part during machining through a water spraying interface, thereby achieving a cooling effect. Dalian Dongxing Forging Co., Ltd. has disclosed a cooling device for machining thin-walled annular parts and applied for a domestic patent, application number: CN202022435303.X. Invention name: A cooling device for machining thin-walled annular parts. This device can effectively cool the grinding disc and can continuously grind the inner and outer walls of the thin-walled annular part.

[0004] The above inventions all start from cutting stability, machining error compensation, and using cutting fluid to reduce the temperature in the cutting area to improve the machining defects of thin-walled parts. However, for large cutting amount machining, defects such as high-temperature thermal deformation are still inevitable, affecting the dimensional and geometric accuracy of the workpiece. Summary of the Invention

[0005] The present invention aims at the above problems and provides a low-temperature machining system for thin-walled parts with better working effects.

[0006] To achieve the above object, the present invention adopts the following technical solutions. The low-temperature processing system for thin-walled parts of the present invention includes a liquid nitrogen dewar 3.1. It is characterized in that the outlet of the liquid nitrogen dewar 3.1 is connected to the inlet of a low-temperature flow valve 3.3 through a liquid nitrogen delivery hose 3.2. The outlet of the low-temperature flow valve 3.3 is connected to the inlet of an electronic flow control valve 3.4. The outlet of the electronic flow control valve 3.4 is connected to the inlet of a low-temperature pressure reducing valve 3.5. The outlet of the low-temperature pressure reducing valve 3.5 is connected to the inlet of a low-temperature throttle valve 3.6. The outlet of the low-temperature throttle valve 3.6 is connected to the inlet of a low-temperature check valve 3.7. The outlet of the low-temperature check valve 3.7 is connected to the left-end inlet of a left-turn joint 2.4 on a machine tool spindle box 3.8. The control signal input port of the electronic flow control valve 3.4 is connected to the control signal output port of an ultra-low temperature temperature controller 3.12. A thermocouple 3.13 obtains a temperature signal from the nozzle end of the tool and transmits the temperature signal to the ultra-low temperature temperature controller 3.12 in the form of an electrical signal.

[0007] The right-end inlet of a right-turn joint 2.7 on the machine tool spindle box 3.8 is connected to the outlet of a three-way joint 3.14. The pressure detection port of the three-way joint 3.14 is connected to the inlet of an electric contact pressure gauge 3.15. The detection signal output port of the electric contact pressure gauge 3.15 is connected to the detection signal input port of a PLC control module 3.17 through a wire 3.16. The control signal output port of the PLC control module 3.17 is connected to the control signal input port of a low-temperature solenoid control valve 3.18. The outlet of the low-temperature solenoid control valve 3.18 is connected to the inlet of the three-way joint 3.14. The inlet of the low-temperature solenoid control valve 3.18 is connected to the outlet of a low-temperature flow valve 3.19. The inlet of the low-temperature flow valve 3.19 is connected to the outlet of a CO2 dewar 3.20.

[0008] As a preferred solution, the left-end inlet of the left-turn joint 2.4 and the right-end inlet of the right-turn joint 2.7 of the present invention are tapered holes.

[0009] As another preferred solution, the temperatures at both ends of the horizontal machining surface of the workpiece of the present invention are set to T1, and the middle is T2. The temperature change satisfies the following formula:

[0010]

[0011] In the formula, y is the calculated set temperature of the nozzle, x is the coordinate in the feed direction, and L is the length of the workpiece in the feed direction, where the tool position before cutting is 10 mm from the starting cutting end of the workpiece.

[0012] The length L of the workpiece is divided into 10 parts. From the above formula, the cooling temperatures y1, y2... y required for each step along the machining feed x direction can be calculated. 10 .

[0013] Meanwhile, the feed time per portion is

[0014]

[0015] where t is the feed time (s), f z is the feed per tooth of the tool (mm / z), z is the number of tool teeth, and n is the spindle speed (r / min).

[0016] The preset nozzle calculated set temperature y that needs to change in real time is input into the ultra-low temperature thermostat 3.12. On the basis of the adjusted temperature T1, T1 is the temperature at the tip outlet where liquid nitrogen and CO 2-雪 mixture appears and reaches the required nozzle temperature; after the tool feeds 10 mm, it enters the cutting state, and then the temperature is regulated starting from the set temperature y1;

[0017] When regulating the temperature starting from the set temperature y1, the temperature state changes according to the parabola characteristic. The thermocouple 3.13 converts the temperature signal into an electrical signal and transmits it to the ultra-low temperature thermostat 3.12. The ultra-low temperature thermostat 3.12 transmits the electrical signal to the servo controller inside it through the PID signal amplifier in the electronic flow control valve 3.4. It drives the servo motor to rotate forward or backward, drives the regulating valve in the electronic flow control valve 3.4 to act through the reducer, opens or closes the valve until the ultra-low temperature thermostat 3.12 reaches the set nozzle temperature requirement, and then the electronic flow control valve 3.4 stops working.

[0018] In addition, the set temperature y1 described in the present invention is -190°C to 153°C, T1 = -190°C, and T2 = -153°C.

[0019] Advantages of the present invention.

[0020] The present invention controls the instantaneous temperature in the cutting area by controlling the liquid nitrogen flow rate, and controls the cutting lubrication performance by controlling CO2.

[0021] For the PLC control module at the CO2 end of the present invention, considering that the solidification temperature of CO2 is higher than that of liquid nitrogen, when the liquid nitrogen pressure exceeds the CO2 pressure, it prevents liquid nitrogen from flowing into the CO2 end circulation pipeline, resulting in CO2 freezing and blocking the pipeline.

[0022] The present invention uses wires to connect the electronic flow control valve 3.4, the ultra-low temperature thermostat 3.12, and the thermocouple 3.13; connects the electric contact pressure gauge 3.15 to the third interface of the three-way joint 3.14 and seals it, and uses a wire 3.16 to connect the electric contact pressure gauge 3.15, the PLC control module 3.17, and the electrical control unit of the low-temperature solenoid valve 3.18; uses the fixture 3.11 to clamp the workpiece 3.10, and uses the tip on the tool holder 3.9 mounted on the spindle box 3.8 to align and cut the workpiece.

[0023] The one-way valve 3.7 of the present invention can prevent CO2 from flowing into the liquid nitrogen pipeline.

[0024] According to the present invention, the temperature state changes according to the parabolic characteristic. The thermocouple 3.13 converts the temperature signal into an electrical signal and transmits it to the cryogenic temperature controller 3.12. The cryogenic temperature controller 3.12 transmits the electrical signal to the servo controller inside it through the PID signal amplifier in the electronic flow control valve 3.4. It drives the servo motor to rotate forward and backward, drives the regulating valve in the electronic flow control valve 3.4 to act through the speed reducer, opens or closes the valve until the cryogenic temperature controller 3.12 reaches the set nozzle temperature requirement, and then the electronic flow control valve 3.4 stops working.

[0025] If the pressure of the liquid nitrogen delivery pipe is greater than the pressure in the CO2 pipeline, the electromagnetic contact in the electric contact pressure gauge 3.15 is activated, and the signal is fed back to the PLC control module 3.17. After processing the signal, the PLC control module 3.17 gives an electrical signal to the cryogenic electromagnetic control valve 3.18 to close the control valve opening and achieve locking to prevent liquid nitrogen from flowing into the CO2 pipeline. After the pressure of the liquid nitrogen pipeline is lowered, the pressure of the electric contact pressure gauge 3.15 returns to the set pressure and the cryogenic electromagnetic control valve 3.18 is controlled by the PLC control module 3.17 to open the pipeline.

[0026] The present invention can input two kinds of coolant (liquid nitrogen + CO 2-雪 ) simultaneously. At ultra-low temperatures, the cutting force will increase, and the elastic modulus of the material will increase significantly. Since the cutting force is related to the cutting lubrication effect, in order to reduce the ratio of the cutting force to the elastic modulus, through the low-temperature processing system for thin-walled parts of the present invention, two kinds of coolant (liquid nitrogen + CO 2-雪 ) can be input simultaneously for mixed cooling, and ultra-low temperature mixed lubrication cooling can be carried out during the milling of thin-walled parts. During ultra-low temperature cooling processing, the stiffness of the cutting area and the lubrication function can be improved simultaneously, the friction force can be reduced, and the cutting load can be alleviated; effectively improve the processing defects of thin-walled parts and improve the milling efficiency of thin-walled parts. Brief Description of the Drawings

[0027] The present invention will be further described below in conjunction with the drawings and specific embodiments. The protection scope of the present invention is not limited only to the description of the following content.

[0028] Figure 1 It is a liquid nitrogen + CO2 delivery control system.

[0029] 3.1 - Liquid nitrogen Dewar flask, 3.2 - Liquid nitrogen transfer hose, 3.3 - Cryogenic flow valve, 3.4 - Electronic flow control valve, 3.5 - Cryogenic pressure reducing valve, 3.6 - Cryogenic throttle valve, 3.7 - Cryogenic check valve, 3.8 - Spindle, 3.9 - Tool holder, 3.10 - Workpiece, 3.11 - Fixture, 3.12 - Ultra-low temperature thermostat, 3.13 - Thermocouple, 3.14 - Three-way joint, 3.15 - Electric contact pressure gauge, 3.16 - Wire, 3.17 - PLC control module, 3.18 - Cryogenic solenoid control valve, 3.19 - Cryogenic flow valve, 3.20 - CO2 Dewar flask.

[0030] Figure 2 is the flow - temperature regulation scheme.

[0031] Figure 3 is the PLC module control circuit (LED1 lights up to display the control working state, and LED2 lights up to display the PLC power - on state. Figure 3 The cryogenic solenoid control valve in Figure 1 is the cryogenic solenoid control valve 3.18).

[0032] Figure 4 is liquid nitrogen / CO 2-雪 Internal - spraying integral tool holder.

[0033] 1.1 - Tool holder, 1.2 - Upper bearing, 1.3 - Upper threaded fastening washer, 1.4 - Upper sealing ring, 1.5 - Tool holder outer ring, 1.6 - Lower sealing ring, 1.7 - Lower threaded fastening washer, 1.8 - Lower bearing, 1.9 - Stop washer, 1.10 - Fastening nut, 1.11 - Left blade, 1.12 - Left blade fastening screw, 1.13 - Right blade, 1.14 - Right blade fastening screw.

[0034] Figure 5 is the connection of the integral tool holder to the machine tool.

[0035] 3.8 - Spindle box, 2.2 - Spindle, 2.3 - Left sealing ring, 2.4 - Left swivel joint, 2.5 - Left connecting bolt, 2.6 - Right sealing ring, 2.7 - Right swivel joint, 2.8 - BT40 taper shank part. Specific implementation method

[0036] Such as Figure 4As shown in the figure, the machine tool spindle box 3.8 in the low-temperature processing system of the thin-walled part of the present invention is connected to the low-temperature processing device for thin-walled parts. The low-temperature processing device for thin-walled parts includes a tool holder outer ring 1.5. The upper inner wall of the tool holder outer ring 1.5 expands outward to form an upper sealing ring placement groove and an upper bearing placement groove. An upper sealing ring 1.4 is arranged in the upper sealing ring placement groove. An upper threaded fastening washer 1.3 is arranged at the upper end of the upper sealing ring 1.4 (the outer wall of the washer 1.3 is an external thread, and the central hole of the tool holder outer ring 1.5 is an internal thread. By rotating 1.3, 1.3 moves downward to press 1.4). The upper bearing placement groove is located at the upper end of the upper sealing ring placement groove, and the diameter of the upper bearing placement groove is larger than that of the upper sealing ring placement groove; an upper bearing 1.2 is arranged in the upper bearing placement groove;

[0037] The lower inner wall of the tool holder outer ring 1.5 expands outward to form a lower sealing ring placement groove and a lower bearing placement groove. A lower sealing ring 1.6 is arranged in the lower sealing ring placement groove. A lower threaded fastening washer 1.7 is arranged at the lower end of the lower sealing ring 1.6. The lower bearing placement groove is located at the lower end of the lower sealing ring placement groove, and the diameter of the lower bearing placement groove is larger than that of the lower sealing ring placement groove; a lower bearing 1.8 is arranged in the lower bearing placement groove, and a stop washer 1.9 is arranged at the lower end of the lower bearing 1.8;

[0038] The tool holder 1.1 passes through the central hole of the tool holder outer ring 1.5. The upper outer wall of the tool holder 1.1 has a flange extending outward. The lower end face of the flange is connected to the upper end face of the upper bearing 1.2; A fastening nut 1.10 is screwed on the lower outer wall of the tool holder 1.1, and the upper end of the fastening nut 1.10 is connected to the lower end of the stop washer 1.9;

[0039] A left cutting blade 1.11 and a right cutting blade 1.13 are arranged at the lower end of the tool holder 1.1. The left cutting blade 1.11 and the right cutting blade 1.13 are symmetrically arranged on both sides of the lower end of the tool holder 1.1;

[0040] A left coolant inlet 1.15 is formed by the left side of the tool holder outer ring 1.5 bulging upward, and a right lubricant inlet 1.16 is formed by the right side of the tool holder outer ring 1.5 bulging upward; The left coolant inlet 1.15 and the right lubricant inlet 1.16 are communicated with the coolant channel in the tool holder outer ring 1.5, and the coolant channel is communicated with the left cutting blade 1.11 and the right cutting blade 1.13.

[0041] The present invention is provided with a left coolant inlet 1.15 and a right lubricant inlet 1.16, and two coolants (liquid nitrogen + CO 2-雪 ) can be input simultaneously. At ultra-low temperatures, the cutting force will increase to some extent, and the elastic modulus of the material will increase significantly. Since the cutting force is related to the cutting lubrication effect, in order to reduce the ratio of the cutting force and the elastic modulus, through the low-temperature processing device for thin-walled parts of the present invention, two coolants (liquid nitrogen + CO 2-雪)The hybrid cooling integral external transmission and internal cooling tool holder device performs cryogenic hybrid lubrication cooling during the milling of thin-walled parts, achieving the improvement of the stiffness and lubrication function in the cutting area, reducing friction, and alleviating the cutting load during cryogenic cooling machining; effectively improving the machining defects of thin-walled parts and enhancing the milling efficiency of thin-walled parts.

[0042] The lower end of the tool holder 1.1 can adopt a standard indexable end mill structure.

[0043] The left blade 1.11 and the right blade 1.13 are diamond blades, which are inclined, and the lower ends of the diamond blades face outward.

[0044] The blade clearance angle of the diamond blade is 25° ( Figure 4 the lower end is marked), reducing the friction with the machined surface.

[0045] The middle part of the left blade 1.11 is fixed to the lower end of the tool holder 1.1 through the left blade fastening screw 1.12, and the middle part of the right blade 1.13 is fixed to the lower end of the tool holder 1.1 through the right blade fastening screw 1.14.

[0046] The BT40 taper shank part 2.8 at the upper end of the tool holder 1.1 is placed in the spindle box 3.8 (a pull stud can be installed at the tail of the BT40 taper shank part 2.8, and the tool holder is clamped and connected by using the internal standard broach device of the spindle 2.2 of the tool clamping cylinder and the spindle box 3.8). A left swivel joint 2.4 is arranged on the left side at the lower end of the spindle box 3.8, and a right swivel joint 2.7 is arranged on the right side at the lower end of the spindle box 3.8. A left sealing ring 2.3 is arranged at the lower end outlet of the left swivel joint 2.4, and a right sealing ring 2.6 is arranged at the lower end outlet of the right swivel joint 2.7;

[0047] The left end inlet of the left swivel joint 2.4 is connected to the left end of the left liquid inlet channel in the left swivel joint 2.4, and the lower end of the left liquid inlet channel is connected to the lower end outlet of the left swivel joint 2.4;

[0048] The right end inlet of the right swivel joint 2.7 is connected to the right end of the right liquid inlet channel in the right swivel joint 2.7, and the lower end of the right liquid inlet channel is connected to the lower end outlet of the right swivel joint 2.7;

[0049] The upper part of the left coolant inlet 1.15 is placed in the lower end outlet of the left swivel joint 2.4, and the left sealing ring 2.3 is placed between the outer wall of the upper part of the left coolant inlet 1.15 and the wall of the lower end outlet of the left swivel joint 2.4;

[0050] The upper part of the right lubricant inlet 1.16 is placed in the lower end outlet of the right swivel joint 2.7, and the right sealing ring 2.6 is placed between the outer wall of the upper part of the right lubricant inlet 1.16 and the wall of the lower end outlet of the right swivel joint 2.7.

[0051] The left turn joint 2.4 is provided with a left vertical connection hole, and the upper end of the left connection bolt 2.5 passes through the left vertical connection hole and is screwed into the left threaded hole at the lower end of the main spindle box 3.8;

[0052] The right turn joint 2.7 is provided with a right vertical connection hole, and the upper end of the right connection bolt 2.9 passes through the right vertical connection hole and is screwed into the right threaded hole at the lower end of the main spindle box 3.8.

[0053] The coolant passage includes a left vertical coolant passage 1.17, a right vertical coolant passage 1.18, a middle horizontal coolant passage 1.19, a middle vertical coolant passage 1.20, a left lower inclined coolant passage 1.21 and a right lower inclined coolant passage 1.22. The upper end of the left vertical coolant passage 1.17 is connected to the left coolant inlet 1.15, and the upper end of the right vertical coolant passage 1.18 is connected to the right lubricating fluid inlet 1.16;

[0054] The lower end of the left vertical coolant passage 1.17 is connected to the left end of the middle horizontal coolant passage 1.19, the lower end of the right vertical coolant passage 1.18 is connected to the right end of the middle horizontal coolant passage 1.19, the middle of the middle horizontal coolant passage 1.19 is connected to the upper end of the middle vertical coolant passage 1.20, the lower end of the middle vertical coolant passage 1.20 is respectively connected to the upper ends of the left lower inclined coolant passage 1.21 and the right lower inclined coolant passage 1.22, the lower end of the left lower inclined coolant passage 1.21 is communicated with the upper end of the left blade 1.11, and the lower end of the right lower inclined coolant passage 1.22 is communicated with the upper end of the right blade 1.13; The left lower inclined coolant passage 1.21 is inclined from the upper right to the lower left, and the right lower inclined coolant passage 1.22 is inclined from the upper left to the lower right.

[0055] The left coolant inlet 1.15 and the right lubricating fluid inlet 1.16 are frustum-shaped ports, and the center of the frustum-shaped port is the liquid inlet passage; The lower end outlets of the left turn joint 2.4 and the right turn joint 2.7 are frustum-shaped grooves corresponding to the frustum-shaped ports.

[0056] The upper threaded fastening washer 1.3 and the lower threaded fastening washer 1.7 adopt glass fiber reinforced plastic washers.

[0057] The upper threaded fastening washer 1.3 and the lower threaded fastening washer 1.7 are provided with twist jacks 1.23. A pair of pliers with a pointed head can be used to insert the head into the twist jack, and then the threaded fastening washer can be twisted, which is convenient for pressing the sealing ring.

[0058] The diameter of the middle vertical coolant passage 1.20 is 3 mm ( Figure 4 lower part is marked) (that is, the inner diameter of the flow channel in the tool shank is 3 mm), and the diameters of the left lower inclined coolant passage 1.21 and the right lower inclined coolant passage 1.22 are less than 2 mm ( Figure 4 lower end is marked) (that is, the diameter of the nozzle is less than 2 mm).

[0059] The distance between the nozzle of the cutter bar and the cutting edge of the low-temperature liquid nitrogen can be shortened to less than or equal to 5 mm ( Figure 4 as marked at the lower end).

[0060] The spraying direction of the nozzle (the left lower inclined coolant channel 1.21 and the right lower inclined coolant channel 1.22) is aligned with the cutting part of the tool tip.

[0061] The left lower inclined coolant channel 1.21 and the right lower inclined coolant channel 1.22 are conical holes. At the same time, standard indexable milling inserts (the left insert 1.11 and the right insert 1.13) can be installed in the insert mounting groove at the end of the cutter bar. The coolant sprays out from the lower ends of the left lower inclined coolant channel 1.21 and the right lower inclined coolant channel 1.22.

[0062] The upper sealing ring 1.4 and the lower sealing ring 1.6 can adopt lip sealing rings.

[0063] The left insert 1.11 and the right insert 1.13 can adopt cemented carbide milling inserts.

[0064] The left end inlet of the left swivel joint 2.4 and the right end inlet of the right swivel joint 2.7 can be connected by means of a sealed pipe thread, and the head of the external hose is a joint that can be screwed with it.

[0065] The outer ring 1.5 of the tool shank can be manufactured by 3D printing, and the material can be fiberglass composite material; at the same time, for the purpose of heat insulation, a layer of 0.5 mm thick polytetrafluoroethylene emulsion is coated on the liquid nitrogen flow channel in the tool shank. During the coating process, the flow channel needs to be kept unobstructed, and after drying, it will adhere to the inner hole of the tool shank and prevent the emulsion from blocking the flow channel.

[0066] The low-temperature machining device for thin-walled parts of the present invention is an integral external rotation and internal cooling tool shank structure. The integral type is relative to the ordinary tool shank. For the ordinary tool shank, the tool shank and the front cutter bar are separated, and the cutter bar needs to be connected to it with a spring collet, which increases the leakage of liquid nitrogen at the connection. The integral structure of the present invention has no leakage.

[0067] The low-temperature machining system for thin-walled parts of the present invention includes a liquid nitrogen Dewar tank 3.1. The outlet of the liquid nitrogen Dewar tank 3.1 is connected to the inlet of a low-temperature flow valve 3.3 through a liquid nitrogen delivery hose 3.2. The outlet of the low-temperature flow valve 3.3 is connected to the inlet of an electronic flow control valve 3.4. The outlet of the electronic flow control valve 3.4 is connected to the inlet of a low-temperature pressure reducing valve 3.5. The outlet of the low-temperature pressure reducing valve 3.5 is connected to the inlet of a low-temperature throttle valve 3.6. The outlet of the low-temperature throttle valve 3.6 is connected to the inlet of a low-temperature check valve 3.7. The outlet of the low-temperature check valve 3.7 is connected to the left-end inlet of a left-turn joint 2.4 on a machine tool spindle box 3.8; the control signal input port of the electronic flow control valve 3.4 is connected to the control signal output port of an ultra-low temperature temperature controller 3.12 (the ultra-low temperature temperature controller 3.12 can adopt an AI-7028 / 7048 multi-channel PID temperature controller); a thermocouple 3.13 obtains a temperature signal from the tool terminal nozzle (i.e., the left lower inclined coolant passage 1.21 or the right lower inclined coolant passage 1.22), and transmits the temperature signal to the ultra-low temperature temperature controller 3.12 in the form of an electrical signal;

[0068] The right-end inlet of a right-turn joint 2.7 on the machine tool spindle box 3.8 is connected to the outlet of a three-way joint 3.14. The pressure detection port of the three-way joint 3.14 is connected to the inlet of an electric contact pressure gauge 3.15. The detection signal output port of the electric contact pressure gauge 3.15 is connected to the detection signal input port of a PLC control module (the PLC control module can adopt a Siemens S7-200 PLC control module) 3.17 through a wire 3.16. The control signal output port of the PLC control module 3.17 is connected to the control signal input port of a low-temperature solenoid control valve 3.18. The outlet of the low-temperature solenoid control valve 3.18 is connected to the inlet of the three-way joint 3.14. The inlet of the low-temperature solenoid control valve 3.18 is connected to the outlet of a low-temperature flow valve 3.19. The inlet of the low-temperature flow valve 3.19 is connected to the outlet of a CO2 Dewar tank 3.20.

[0069] The left-end inlet of the left-turn joint 2.4 and the right-end inlet of the right-turn joint 2.7 are tapered holes.

[0070] The temperatures at both ends of the horizontal machining surface of the workpiece are set to T1, and the middle is T2. The temperature change satisfies the following formula:

[0071]

[0072] where y is the calculated set temperature of the nozzle, x is the coordinate in the feed direction, and L is the length of the workpiece in the feed direction, and the position of the tool before cutting is 10 mm from the starting cutting end of the workpiece.

[0073] The length L of the workpiece is divided into 10 parts. From the above formula, the cooling temperatures y1, y2... y that need to be reached for each step along the machining feed x direction can be calculated. 10 .

[0074] Meanwhile, the feed time for each portion is

[0075]

[0076] where t is the feed time (s), f z is the feed per tooth of the tool (mm / z), z is the number of teeth of the tool, and n is the spindle speed (r / min).

[0077] The preset value that needs to change in real time (10 y values y1, y2... y are successively set in the ultra-low temperature thermostat 3.12 10 , obtained from formula (1), and the calculation t in each formula (2) changes once), the calculated set temperature y of the nozzle is input into the ultra-low temperature thermostat 3.12. Based on the adjusted temperature T1, T1 is the temperature at the tip of the tool where liquid nitrogen and CO 2-雪 mixture appears and reaches the required nozzle temperature; after the tool feeds 10 mm for a certain time, it enters the cutting state, and then the temperature is regulated starting from the set temperature y1;

[0078] The temperature regulation starting from the set temperature y1 changes the temperature state according to the parabola characteristic (the parabola characteristic temperature change state is a non-linear temperature change process, smoother than the linear change, preventing the large temperature change gradient from increasing the workpiece cooling change speed and causing uneven cooling. When conducting the optimized cooling temperature experiment for thin-walled parts, the temperature measured at the temperature measurement points at the same step length positions on the cutting surface is fitted into a parabola-like curve). The thermocouple 3.13 converts the temperature signal into an electrical signal and transmits it to the ultra-low temperature thermostat 3.12, and the ultra-low temperature thermostat 3.12 transmits the electrical signal to the servo controller inside it through the PID signal amplifier in the electronic flow control valve 3.4. It drives the servo motor to rotate forward or backward (when the servo motor rotates forward, the opening of the electronic flow control valve 3.4 decreases, the flow rate decreases, and the temperature rises; conversely, when the servo motor rotates backward, the temperature drops. Let K be the temperature collected by the actual thermocouple. When |y - K| > 5°C and y - K > 0, it rotates forward, and conversely, when y - K < 0, it rotates backward; when |y - K| ≤ 5°C, it stops working, that is, the adjustment accuracy is less than or equal to 5°C). It drives the regulating valve in the electronic flow control valve 3.4 to open or close through the reducer until the ultra-low temperature thermostat 3.12 reaches the set nozzle temperature requirement, and then the electronic flow control valve 3.4 stops working.

[0079] The set temperature y1 is -190°C to 153°C, T1 = -190°C, T2 = -153°C.

[0080] In the present invention, for the adapters 2.4 and 2.7, during machining, it is necessary to ensure the perpendicular accuracy of the horizontal and vertical tapered hole axes to the end face (during machining, the end face and the bottom face are machined based on the principle of mutual reference to ensure their perpendicular accuracy, and then the tapered hole is drilled with the end face or the bottom face as the reference to ensure the perpendicular accuracy of the tapered hole to the end face and the bottom face). At the same time, when installing them on the machine tool spindle box, it is necessary to ensure the dimensional accuracy and parallel accuracy between the vertical tapered hole axes of the two adapters and the axis of the spindle 2.2 (since the perpendicularity between the end face of the spindle box and the spindle tapered hole in the assembly of the CNC milling machine is very high, and the two adapters with a relatively high-precision bottom face are installed on the end face of the spindle box 3.8, the parallel accuracy between the vertical tapered hole axis and the axis of the spindle 2.2 can be ensured. Then, the dimensional accuracy between the adapters 2.4 and 2.7 and the axis of the spindle 2.2 is ensured by the threaded holes of the mounting screws 2.5 precisely drilled on the end face of the spindle box 3.8 in advance).

[0081] The fixture 3.11 can adopt an existing conventional pressing plate.

[0082] The low-temperature machining device for thin-walled parts of the present invention is a high-efficiency, high-quality, and low-damage milling machining equipment for weakly rigid alloy materials.

[0083] For the externally transmitted and internally cooled integral tool holder, its tool shank (the thinnest part of the tool holder at the lower end of the fastening nut 1.10 is the tool shank) and the tool holder body are integrally designed and manufactured, without a spring collet (the spring collet is a conventional structure in the art), and the assembly solves the problem of the transmission and leakage of liquid nitrogen in the tool holder (the spring collet has no seal and needs to be disassembled frequently).

[0084] The present invention controls the instantaneous temperature in the cutting area by controlling the liquid nitrogen flow rate and controls the cutting lubrication performance by controlling CO2.

[0085] The device for the flow and control of liquid nitrogen outside the tool holder can refer to the previously authorized invention patent - a hole milling device (ZL201910319180.2).

[0086] For the PLC control module at the CO2 end, considering that the solidification temperature of CO2 is higher than that of liquid nitrogen, when the liquid nitrogen pressure exceeds the CO2 pressure, it is necessary to prevent the liquid nitrogen from flowing into the CO2 end circulation pipeline, resulting in the freezing of CO2 and blocking the pipeline.

[0087] The working process of the present invention will be described below with reference to the accompanying drawings.

[0088] As Figure 4As shown, first press the upper sealing ring 1.4 into the outer ring 1.5 of the tool holder, then screw in the upper threaded fastening washer 1.3, and then install the upper bearing 1.2 to ensure that the outer ring of the bearing is fully installed. Install the tool holder 1.1 along the open end of the upper bearing 1.2 of the outer ring 1.5 of the tool holder, ensuring that the innermost shoulder of the tool holder 1.1 is in close contact with the end face of the inner ring of the upper bearing 1.2; then install the lower sealing ring 1.6, lower threaded fastening washer 1.7, lower bearing 1.8, and stop washer 1.9 in sequence along the other end of the outer ring 1.5 of the tool holder, and finally screw in the fastening nut 1.10; fix the left blade 1.11 and the right blade 1.13 to the tool bar tail at the end of the tool holder through the left blade fastening screw 1.12 and the right blade fastening screw 1.14.

[0089] As Figure 5 shown, install the left sealing ring 2.3 and the right sealing ring 2.6 into the left adapter 2.4 and the right adapter 2.7 respectively, and then install the assembled left adapter 2.4 and right adapter 2.7 onto the spindle box 3.8 with the left connecting bolt 2.5 and the right connecting bolt 2.9; install the BT40 taper shank part 2.8 at the tail of the assembled integral tool holder 1.1 into the spindle box 3.8, and at the same time install the two coolant inlets of the outer ring component of the integral tool holder 1.1 into the left adapter 2.4 and the right adapter 2.7 to realize the connection between the integral tool holder 1.1 and the spindle box 3.8.

[0090] As Figure 1 shown, use the liquid nitrogen delivery hose 3.2 to connect the liquid nitrogen dewar 3.1, cryogenic flow valve 3.3, electronic flow control valve 3.4, cryogenic pressure reducing valve 3.5, cryogenic throttle valve 3.6, and cryogenic check valve 3.7 in series, and then connect them to the tapered hole of the adapter ( Figure 5 the adapter 2.4 in ) on the machine tool spindle box 3.8; then use the liquid nitrogen delivery hose 3.2 to connect the CO2 dewar 3.20, cryogenic flow valve 3.19, cryogenic solenoid control valve 3.18, and tee joint 3.14 in sequence, and finally connect them to the adapter ( Figure 5 the adapter 2.7 in ) on the machine tool spindle box 3.8; connect the electronic flow control valve 3.4, cryogenic temperature controller 3.12, and thermocouple 3.13 with wires; connect the electric contact pressure gauge 3.15 to the third interface of the tee joint 3.14 and seal it, and connect the electric contact pressure gauge 3.15, PLC control module 3.17, and the electrical control unit of the cryogenic solenoid control valve 3.18 with wires 3.16; use the fixture 3.11 to clamp the workpiece 3.10, and use the cutting edge on the tool holder 3.9 installed on the spindle box 3.8 to align and cut the workpiece.

[0091] 1) Use the fixture 3.11 to position and clamp the thin-walled workpiece 3.10.

[0092] 2) Insert the tapered shank of the tool holder 1.1 into the machine tool spindle 2.2. At the same time, align the two tapered holes on the outer ring 1.5 of the tool holder with the tapered holes with sealing rings of the adapter 2.4 and the adapter 2.7 installed on the spindle box 3.8. Use the pull stud and the tool clamping cylinder to install and fix the tool holder device on the machine tool spindle 2.2.

[0093] 3) Unscrew the valve on the CO2 Dewar tank 3.20, check the CO2 delivery pipeline to ensure that there is no leakage in each component on the series pipeline, and set the pressure rating of the electric contact pressure gauge 3.15. At the same time, the check valve 3.7 can prevent CO2 from flowing into the liquid nitrogen pipeline.

[0094] 4) Unscrew the valve on the liquid nitrogen Dewar tank 3.1, check the liquid nitrogen delivery pipeline to ensure that there is no leakage in each component on the series pipeline. After spraying for 1 minute, use a cryogenic thermometer to measure the temperature at the tip of the tool. At the same time, adjust the valve on the Dewar tank 3.1 to obtain the stable outlet temperature required for the tool.

[0095] 5) Wait until liquid nitrogen and CO 2-雪 mixture (the mixing ratio is liquid nitrogen: CO 2-雪 = 2:1 to 8:1. By replacing the connector of the liquid nitrogen delivery hose 3.2 with different inner diameters externally connected to the right adapter 2.7, the flow rates of liquid nitrogen and CO 2-雪 can be controlled proportionally) and reach the required nozzle temperature T1, then the machine tool tool is in the state of waiting for processing.

[0096] 6) Due to the non-uniformity of the stiffness of the machined plane of the difficult-to-machine alloy thin-walled component, that is, the stiffness difference at both ends, the relative stiffness is relatively larger towards the middle. In order to obtain a high-quality and uniform machined surface, the reasonable change of the workpiece surface stiffness should be achieved by controlling the cooling temperature, thereby improving the overall machining deformation defect. In order to make the temperature change uniform and the change satisfy the parabolic trajectory, that is, first decrease and then increase. For example, the temperature at both ends is set to T1 and the middle is T2. The temperature change satisfies the following formula

[0097]

[0098] where y is the nozzle temperature, x is the coordinate in the feed direction, and L is the length of the workpiece in the feed direction. The position of the tool before cutting is 10 mm from the starting cutting end of the workpiece.

[0099] Divide the workpiece length L into 10 parts. From the above formula, the cooling temperature y1, y2... y 10 .

[0100] At the same time, the feed time for each part is

[0101]

[0102] where t is the feed time (s), fz $f_z$ is the feed per tooth of the cutting tool (mm / z), $z$ is the number of teeth of the cutting tool, and $n$ is the spindle speed (r / min).

[0103] 7) Input the preset nozzle temperature that needs to change in real time in step 6 into the ultra-low temperature thermostat 3.12. Based on the temperature $T_1$ adjusted in step 5, after the cutting tool feeds 10 mm, it enters the cutting state, and then the temperature is regulated starting from the set temperature $y_1$. Specifically, the temperature state that changes according to the parabolic characteristic converts the temperature signal into an electrical signal by the thermocouple 3.13 and transmits it to the ultra-low temperature thermostat 3.12. The ultra-low temperature thermostat 3.12 transmits the electrical signal to the servo controller inside it through the PID signal amplifier in the electronic flow control valve 3.4. It drives the servo motor to rotate forward and backward, drives the regulating valve in the electronic flow control valve 3.4 to act through the reducer, opens or closes the valve until the ultra-low temperature thermostat 3.12 reaches the set nozzle temperature requirement, and then the electronic flow control valve 3.4 stops working.

[0104] 8) If the pressure of the liquid nitrogen delivery pipe is greater than the pressure in the CO2 pipeline, the electromagnetic contact in the electric contact pressure gauge 3.15 is activated, and the signal is fed back to the PLC control module 3.17. After the PLC control module 3.17 processes the signal, it gives an electrical signal to the low-temperature electromagnetic control valve 3.18 to close the control valve opening to achieve locking and prevent liquid nitrogen from flowing into the CO2 pipeline. After the pressure of the liquid nitrogen pipeline is lowered, the pressure of the electric contact pressure gauge 3.15 returns to the set pressure and the low-temperature electromagnetic control valve 3.18 is controlled by the PLC control module 3.17 to open the pipeline.

[0105] In the present invention, the main manifestations of the milling deformation of thin-walled parts are the deflection and rotation angle of the machined end. According to material mechanics, the deflection and rotation angle are affected by the cutting force load (proportional) at the cutting end and the material elastic modulus (inversely proportional). At the same time, the cutting force will increase at ultra-low temperatures, and the material elastic modulus will increase significantly. Since the cutting force is related to the cutting lubrication effect, in order to reduce the ratio of the cutting force and the elastic modulus, the present invention uses a liquid nitrogen + CO 2-雪 The hybrid cooling integral external transmission and internal cooling tool holder device performs ultra-low temperature hybrid lubrication cooling during the milling of thin-walled parts, and simultaneously improves the stiffness and lubrication function of the cutting area, reduces the friction force, and reduces the cutting load during ultra-low temperature cooling machining.

[0106] The present invention can be applied to difficult-to-machine thin-walled materials. Cut the thin-walled materials into regular rectangular blocks, clean the surface of the workpiece with strong wind, and position and clamp the workpiece on the workbench of the numerically controlled machine tool that can be linked according to the positioning rules.

[0107] It is understandable that the above specific description of the present invention is only for the purpose of illustrating the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those of ordinary skill in the art should understand that the present invention can still be modified or equivalently replaced to achieve the same technical effects; as long as the use requirements are met, they are all within the protection scope of the present invention.

Claims

1. A low-temperature processing system for thin-walled parts, including a liquid nitrogen dewar (3.1), characterized in that The outlet of the liquid nitrogen Dewar (3.1) is connected to the inlet of the cryogenic flow valve (3.3) through a liquid nitrogen delivery hose (3.2). The outlet of the cryogenic flow valve (3.3) is connected to the inlet of the electronic flow control valve (3.4). The outlet of the electronic flow control valve (3.4) is connected to the inlet of the cryogenic pressure reducing valve (3.5). The outlet of the cryogenic pressure reducing valve (3.5) is connected to the inlet of the cryogenic throttle valve (3.6). The outlet of the cryogenic throttle valve (3.6) is connected to the inlet of the cryogenic check valve (3.7). The outlet of the cryogenic check valve (3.7) is connected to the left-end inlet of the left-turn joint (2.4) on the machine tool spindle box (3.8). The control signal input port of the electronic flow control valve (3.4) is connected to the control signal output port of the ultra-low temperature temperature controller (3.12). The thermocouple (3.13) obtains a temperature signal from the nozzle end of the tool and transmits the temperature signal to the ultra-low temperature temperature controller (3.12) in the form of an electrical signal. The right-end inlet of the right-turn joint (2.7) on the machine tool spindle box (3.8) is connected to the outlet of the three-way joint (3.14). The pressure detection port of the three-way joint (3.14) is connected to the inlet of the electric contact pressure gauge (3.15). The detection signal output port of the electric contact pressure gauge (3.15) is connected to the detection signal input port of the PLC control module (3.17) through a wire (3.16). The control signal output port of the PLC control module (3.17) is connected to the control signal input port of the cryogenic solenoid valve (3.18). The outlet of the cryogenic solenoid valve (3.18) is connected to the inlet of the three-way joint (3.14). The inlet of the cryogenic solenoid valve (3.18) is connected to the outlet of the cryogenic flow valve (3.19). The inlet of the cryogenic flow valve (3.19) is connected to the outlet of the CO2 Dewar (3.20).

2. The cryogenic machining system for thin-walled parts according to claim 1, characterized in that The left-end inlet of the left-turn joint (2.4) and the right-end inlet of the right-turn joint (2.7) are tapered holes.

3. The low-temperature processing system for thin-walled parts according to claim 1, wherein the workpiece The temperatures at both ends of the horizontal machining surface are set to T1, and the middle is T2. The temperature change satisfies the following formula: In the formula, y is the calculated set temperature of the nozzle, x is the coordinate in the feed direction, and L is the length of the workpiece in the feed direction. The cutting tool position before cutting is 10 mm from the starting cutting end of the workpiece. Divide the workpiece length L into 10 parts. From the above formula, the cooling temperatures y1, y2…y that need to be achieved for each step length along the machining feed x direction can be calculated. 10； At the same time, each feed time is where t is the feed time (s), f z is the feed per tooth of the tool (mm / z), z is the number of teeth of the tool, and n is the spindle speed (r / min); The preset nozzle calculation set temperature y that needs to change in real time is input into the ultra-low temperature thermostat (3.12). On the basis of the adjusted temperature T1, T1 is the temperature at the tool tip outlet where liquid nitrogen and CO 2-雪 mixture appears and reaches the required nozzle temperature; after the tool feeds 10 mm, it enters the cutting state, and then the temperature is regulated starting from the set temperature y1; The temperature is regulated starting from the set temperature y1, and the temperature state changes according to the parabola characteristic. The thermocouple (3.13) converts the temperature signal into an electrical signal and transmits it to the ultra-low temperature temperature controller (3.12). The ultra-low temperature temperature controller (3.12) transmits the electrical signal to the servo controller inside it through the PID signal amplifier in the electronic flow control valve (3.4). It drives the servo motor to rotate forward or backward, drives the regulating valve in the electronic flow control valve (3.4) to act through the speed reducer, opens or closes the valve until the ultra-low temperature temperature controller (3.12) reaches the set nozzle temperature requirement, and then the electronic flow control valve (3.4) stops working.

4. The thin-walled part low-temperature processing system according to claim 3, characterized in that The set temperature y1 is -190 °C to 153 °C, T1 = -190 °C, and T2 = -153 °C.

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