A high-precision stress relief and tempering device and process for precision springs

Abstract

The application provides a stress relief high-precision tempering device and process for precision springs, comprising a furnace body, a pulse current power supply, an axial pressing device, an insulating support and a controller. The pulse current power supply is used for electrical connection with the spring. The axial pressing device is used for applying axial constraint to the spring. The insulating support is used for ensuring electrical insulation of the spring from the furnace body when the spring is electrified. The controller is configured to control the pulse current power supply to output a pulse current with a fundamental frequency matched with a characteristic frequency of the spring material to the spring. The axial pressing device is controlled to apply dynamic axial pressure to the spring during the pulse current application, and the dynamic axial pressure varies with the tempering processing stage. The application generates Joule heat effect through the pulse current, and directly affects the dislocation behavior inside the spring material by using the electronic wind effect, so as to eliminate the residual stress of the spring from the micro level, and improve the fatigue life and size precision of the spring.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment technology, specifically relating to a stress-relieving high-precision tempering device and process for precision springs. Background Technology

[0002] The performance of precision springs determines the reliability and service life of aerospace equipment, precision instruments, high-speed machinery, and more. After cold rolling or quenching, springs develop complex residual stress fields, which are eliminated through tempering. However, traditional hot tempering relies on atomic thermal diffusion to eliminate stress. For the complex dislocation entanglement network formed during cold working, thermal activation is insufficient to fully open it, leading to micro-stress concentration areas within the spring, resulting in creep and stress relaxation during use. Furthermore, conventional tempering easily causes carbides to coarsen at grain boundaries, forming "soft spots," and the residual austenite decomposes incompletely, resulting in a significant decrease in the spring's elastic modulus at high temperatures and poor resistance to thermal decay. During the tempering process, springs may deform due to their own weight or improper clamping, and the volume changes during phase transformation are difficult to control precisely, causing critical dimensions such as the spring's free height and coil spacing to exceed tolerances.

[0003] In recent years, scholars have discovered the electroplastic effect—the phenomenon that metallic materials exhibit reduced deformation resistance and increased plasticity under energized conditions. For example, patent CN109932388B, through ingenious experimental design, has demonstrated that pulsed current not only generates Joule heating but also directly influences dislocation behavior (i.e., non-thermal effects) through mechanisms such as electron wind, providing an important theoretical foundation for electro-assisted machining. However, this patent only focuses on the mechanistic study and does not provide a technical solution for applying this effect to actual heat treatment processes.

[0004] Therefore, how to apply pulsed current technology to the overall tempering process of springs to completely eliminate internal residual stress, accurately control microstructure, and precisely lock macroscopic dimensions remains an urgent problem to be solved. Summary of the Invention

[0005] Purpose of the invention: In order to overcome the above shortcomings, the present invention provides a stress-relief high-precision tempering device and process for precision springs. By synergistic effect of pulse current and dynamic pressure, the internal stress of the spring is removed, and the precise control of the spring's microstructure is achieved.

[0006] Technical solution: In order to achieve the above objectives, the present invention provides a stress-relieving high-precision tempering device for precision springs, including a furnace body, a pulse current power supply, an axial pressure device, an insulating support component, and a controller; The pulsed current power supply is used for electrical connection with the spring; The axial compression device is used to apply axial constraint to the spring; The insulating support is used to ensure electrical insulation between the spring and the furnace body when the spring is energized; The controller is configured to control the pulse current power supply to output pulse current to the spring. The fundamental frequency of the pulse current matches the characteristic frequency of the spring material. The characteristic frequency is a frequency range that can resonate or strongly couple with the micro-defects inside the spring. The axial pressure control device applies dynamic axial pressure to the spring during the pulse current application process, and the dynamic axial pressure changes with the tempering treatment stage.

[0007] The furnace body of this invention is equipped with a heating element and a temperature sensor. The furnace body can be evacuated and filled with a protective gas (such as argon or nitrogen) to prevent the spring from oxidizing at high temperatures. A pulse current power supply is electrically connected to the spring and can output a pulse current with specific parameters to the spring.

[0008] This invention generates a Joule heating effect through pulsed current and utilizes its electron wind effect to directly influence the dislocation behavior within the spring material. A controller directs the pulsed current power supply to output a pulsed current to the spring, ensuring that the fundamental frequency of the pulsed current matches the characteristic frequency of the spring material. The characteristic frequency refers to the frequency range that resonates or strongly couples with microscopic defects within the spring (including dislocations, grain boundaries, vacancies, and second-phase particles). Matching the frequency of the pulsed current with the natural vibration frequency of the dislocation segments induces a resonance effect in the spring, thereby generating dislocation slip and eliminating residual stress at the microscopic level. During tempering, an axial pressure device applies axial constraint to the spring, precisely controlling the magnitude of the axial pressure to suppress thermal deformation, ensure geometric accuracy, and utilize stress-induced effects to assist dislocation slip and phase transformation processes. Furthermore, during cooling, thermal contraction is precisely compensated, locking in the final dimensions and ensuring the spring's dimensional accuracy meets design requirements.

[0009] Furthermore, the aforementioned stress-relieving high-precision tempering device for precision springs includes an impedance measurement unit for acquiring the impedance spectrum information of the spring before and / or during the tempering process; the controller determines the characteristic frequency based on the impedance spectrum information and adjusts the fundamental frequency of the pulse current accordingly.

[0010] The impedance measurement unit applies a low-amplitude AC detection signal to the spring. The frequency of the detection signal continuously varies from 1 Hz to 1 MHz, covering the frequency range where micro-relaxation and resonance may occur. During the scan, the impedance measurement unit acquires impedance data at different frequencies, including the real part, imaginary part, impedance amplitude, and phase angle. These data constitute the impedance spectrum of the spring material. The controller processes the acquired impedance data, identifies characteristic frequency peaks related to micro-defects, and ensures that the pulse current always matches the micro-state of the spring material.

[0011] Furthermore, in the aforementioned stress-relief high-precision tempering device for precision springs, the axial pressing device includes an upper pressure head, which is a flexible graphite contact. The flexible graphite contact comprises a graphite block and a built-in preload spring, used to maintain stable electrical contact with the spring end ring at high temperatures. When a pulsed current is applied, the electroplastic effect may cause minute dimensional fluctuations; the preload spring absorbs these fluctuations and maintains stable contact. The upper pressure head is driven by a screw drive mechanism located outside the furnace body. The output end of the screw drive mechanism drives the upper pressure head to move up and down via a drive rod extending into the furnace body. To achieve high-precision dimensional compensation during the cooling stage, a piezoelectric ceramic actuator is connected in series between the screw drive mechanism and the drive rod. The piezoelectric ceramic actuator is electrically connected to the controller and is used to receive controller commands during the cooling stage to apply high-precision dynamic compensation pressure to the spring, counteracting dimensional changes caused by thermal contraction.

[0012] Preferably, the upper pressure head includes a housing with an opening at the lower end, and a graphite block and a preload spring are housed within the housing. The preload spring elastically presses the graphite block against the opening at the lower end of the housing.

[0013] Furthermore, in the aforementioned stress-relieving high-precision tempering device for precision springs, the insulating support includes: The spindle has an insulating coating on its surface for contact with the inner ring of the spring. The mandrel seat is fixedly installed at the bottom of the furnace body and electrically connected to the pulse current power supply. An insulating ring is connected between the mandrel and the mandrel seat to achieve electrical insulation between the two. An annular graphite electrode is disposed on the upper end face of the mandrel seat and is used to contact the lower end ring of the spring to form an electrical connection.

[0014] Furthermore, the aforementioned stress-relief high-precision tempering device and process for precision springs includes an online insulation monitoring module. This module detects the circuit's insulation resistance to ground during the gap in the pulse current application and cuts off the pulse current power supply when the insulation resistance falls below a preset threshold. The online insulation monitoring module operates during the gap in the pulse current application (millisecond level), and the specific process is as follows: The pulsed current is typically applied at a certain frequency, with a brief gap between adjacent pulses. The online insulation monitoring module utilizes this gap for detection without affecting the normal application of the main pulse. A low-voltage DC detection signal is applied to the electrodes and mandrel circuit. The current in the detection circuit is measured, and the insulation resistance to ground is calculated according to Ohm's law. When the insulation resistance falls below a preset threshold, an insulation fault is identified. Before the next pulse arrives, the pulsed current power supply is immediately cut off, and an audible and visual alarm is triggered. Simultaneously, fault information is recorded for operator troubleshooting. This design achieves real-time monitoring and active protection of the insulation status, preventing equipment and workpiece damage due to insulation failure and ensuring the long-term reliability of the equipment.

[0015] A high-precision tempering process for stress relief of precision springs using the above-mentioned apparatus includes the following steps: S1 acquires the impedance spectrum information of the target spring through the impedance measurement unit, and determines at least one characteristic frequency f based on the impedance spectrum information; S2: During the process of heating the spring to the preset tempering temperature and / or after reaching the preset tempering temperature, a pulse current is applied to the spring through a pulse current power supply; the fundamental frequency of the pulse current matches the characteristic frequency f. S3: During the application of pulsed current, the axial pressure is dynamically adjusted according to the tempering stage, and the tempering process is completed under the condition of applying axial constraint to the spring through the axial pressure device to eliminate stress.

[0016] Furthermore, in the aforementioned high-precision tempering process for stress relief of precision springs, step S1 includes: S11: Apply a low-amplitude AC detection signal with continuously varying frequency to the spring and collect impedance data at different frequencies; S12: Based on the impedance data, identify at least one characteristic frequency peak f0 related to dislocation vibration or grain boundary relaxation; S13: Perform temperature drift correction on the characteristic frequency peak f0 according to the preset tempering temperature T to obtain the target frequency f_target(T); In step S2, the fundamental frequency of the pulse current is set to the target frequency f_target(T).

[0017] Because the physical properties of materials, such as resistivity and elastic modulus, change with temperature, the characteristic frequency f0 measured at room temperature will drift during high-temperature tempering. The actual frequency at high temperature may be out of tune with the resonant frequency of microscopic defects in the material, reducing the processing effect. Temperature drift correction ensures that the frequency of the pulse current remains matched with the microscopic state of the spring material throughout the entire tempering temperature range.

[0018] Furthermore, in the aforementioned high-precision tempering process for stress relief of precision springs, step S3 includes: S31: Apply a first pulse current and a first axial pressure. The current density of the first pulse current is greater than that of the second pulse current, and the first axial pressure is less than that of the second axial pressure. The first pulse current is a high-density narrow pulse current, and the first axial pressure is a low-pressure constraint. The electron wind of the high-density pulse current is used to quickly open the tangled dislocations formed by cold working, promoting dislocation slip and recombination.

[0019] S32: Switch to the second pulse current and adjust the axial pressure to the second axial pressure; the second pulse current is a lower density pulse current and increases the axial pressure. The appropriate axial pressure generates a stress field at the grain boundary, promotes carbide nucleation, inhibits grain growth, maintains fine grain structure, assists in volume change during phase transformation, reduces internal stress, controls the decomposition process of residual austenite, and induces the dispersion precipitation of nanoscale carbides.

[0020] S33: Turn off the pulse current, start the cooling system, and simultaneously apply dynamic compensation pressure to the spring during the cooling process to counteract the dimensional changes caused by thermal contraction. The dynamic compensation pressure is calculated based on real-time temperature feedback to ensure that the spring's free height remains unchanged before and after cooling.

[0021] The working principle of dynamic compensation pressure is as follows: By monitoring the spring temperature in real time, the theoretical thermal contraction is calculated based on the material's coefficient of thermal expansion, and a piezoelectric ceramic actuator applies a corresponding axial compression displacement to the spring, ensuring that the spring remains near its target length during cooling. Specifically, when the temperature drops by ΔT, an unconstrained spring would contract by ΔL = α·L·ΔT; this invention applies axial pressure through a piezoelectric actuator, causing the spring to undergo a compression deformation of ΔL_comp, satisfying ΔL_comp = ΔL, thereby counteracting the effect of thermal contraction and achieving dimensional locking.

[0022] Furthermore, in the aforementioned high-precision tempering process for stress relief of precision springs, a temperature sensor monitors the temperature change rate of the spring's micro-regions. When the temperature rise exceeds a threshold, the pulse current duty cycle is reduced, and the preset duty cycle is restored after the temperature rise recovers. The decomposition of residual austenite is an exothermic reaction, which can lead to an abnormal increase in the temperature of the spring's micro-regions. If the temperature is too high, it can cause the precipitated carbides to coarsen. By dynamically adjusting the pulse current duty cycle, local overheating can be effectively suppressed, maintaining the uniformity of the microstructure.

[0023] Furthermore, in the aforementioned high-precision tempering process for stress relief of precision springs, in the second stage, the axial pressure applied to the spring is an alternating pressure synchronized with the pulsed current, and its frequency is consistent with the fundamental frequency of the pulsed current. The alternating pressure and the electron wind of the pulsed current form a synergistic effect, promoting dislocation slip. This can generate small stress fluctuations at the grain boundaries, which is conducive to the uniform nucleation of carbides, avoids dislocation pile-up under static pressure, and improves the uniformity of phase transformation.

[0024] As can be seen from the above technical solution, the present invention has the following beneficial effects: ① The present invention is used for a high-precision stress-relief tempering device and process for precision springs. By setting the fundamental frequency of the pulse current to a frequency range that matches the characteristic frequency of dislocation vibration in the spring material, precise coupling of electrical energy and dislocation motion is achieved. The non-thermal effect (electron wind effect) of the pulse current is used to directly act on the dislocations, enabling them to obtain sufficient energy to overcome pinning and slip, thus eliminating residual stress at the microscopic level and improving the mechanical properties and service life of the spring.

[0025] ② This invention achieves precise control of microstructure through power-coordinated control and latent heat feedback regulation of phase change, enabling carbides to be dispersed at the nanoscale and reducing elasticity attenuation rate.

[0026] ③ This invention achieves precise control of spring dimensions by using the rigid constraint of the axial pressing device to dynamically compensate for pressure, thereby improving the dimensional accuracy of the spring and ensuring that the spring dimensions meet the requirements of precision instruments.

[0027] ④ This invention acquires the microscopic state information of the spring in real time through the impedance measurement unit and makes dynamic corrections based on the tempering temperature, so that the process parameters can be adjusted in a personalized manner for different materials and different batches, thereby improving the adaptability of the device. Attached Figure Description

[0028] Figure 1 This is an internal schematic diagram of the stress-relieving high-precision tempering device for precision springs according to the present invention. Figure 2 for Figure 1 The enlarged view shown below; Figure 3 This is a flowchart of the stress-relief high-precision tempering process for precision springs according to the present invention.

[0029] In the diagram: 1. Furnace body, 2. Pulse current power supply, 3. Axial pressure device, 31. Graphite block, 32. Preload spring, 4. Insulating support, 41. Mandrel, 42. Mandrel seat, 43. Insulating ring, 44. Annular graphite electrode, 5. Controller. Detailed Implementation

[0030] Example 1 like Figure 1-2 The apparatus shown is a stress-relieving high-precision tempering device for precision springs, comprising a furnace body 1, a pulse current power supply 2, an axial pressure device 3, an insulating support 4, and a controller 5. The pulse current power supply 2 is used for electrical connection with the spring; Axial pressure device 3 is used to apply axial constraint to the spring; The insulating support 4 is used to ensure electrical insulation between the spring and the furnace body 1 when the spring is energized; Controller 5 is configured to control the pulse current power supply 2 to output pulse current to the spring. The fundamental frequency of the pulse current matches the characteristic frequency of the spring material. The characteristic frequency is the frequency range that can resonate or strongly couple with the micro-defects inside the spring. The axial pressure control device 3 applies dynamic axial pressure to the spring during the pulse current application process, and the dynamic axial pressure changes with the tempering treatment stage.

[0031] The furnace body 1 of this invention is internally equipped with a heating element and a temperature sensor. The furnace body 1 can be evacuated and filled with a protective gas (such as argon or nitrogen) to prevent the spring from oxidizing at high temperatures. A pulsed current power supply 2 is electrically connected to the spring and can output a pulsed current with specific parameters to the spring. The pulsed current power supply 2 uses an IGBT module to construct a full-bridge inverter circuit, with adjustable output parameters: current density 0-200A / mm², pulse width 10-1000μs, frequency 0-500kHz, and duty cycle 0-100%. The power output terminal is connected to the upper pressure head 31 and the annular graphite electrode located on the mandrel seat via a 50Ω coaxial cable.

[0032] This invention generates a Joule heating effect through pulsed current and utilizes its electron wind effect to directly influence the dislocation behavior within the spring material. A controller 5 controls the pulsed current power supply 2 to output a pulsed current to the spring, ensuring that the fundamental frequency of the pulsed current matches the characteristic frequency of the spring material. The characteristic frequency refers to the frequency range that resonates or strongly couples with microscopic defects within the spring (including dislocations, grain boundaries, vacancies, and second-phase particles). Matching the frequency of the pulsed current with the natural vibration frequency of the dislocation segments induces a resonance effect in the spring, thereby generating dislocation slip and eliminating residual stress at the microscopic level. During tempering, an axial pressure device 3 applies axial constraint to the spring, precisely controlling the magnitude of the axial pressure to suppress thermal deformation, ensure geometric accuracy, and utilize the stress-induced effect to assist in dislocation slip and phase transformation processes. Furthermore, during cooling, thermal contraction is precisely compensated, locking in the final dimensions and ensuring the spring's dimensional accuracy meets design requirements.

[0033] As a further preferred embodiment, the device includes an impedance measurement unit for acquiring the impedance spectrum information of the spring before and / or during the tempering process; the controller 5 determines the characteristic frequency based on the impedance spectrum information and adjusts the fundamental frequency of the pulse current accordingly.

[0034] The impedance measurement unit applies a low-amplitude AC detection signal to the spring. The frequency of the detection signal continuously varies from 1 Hz to 1 MHz, covering the frequency range where micro-relaxation and resonance may occur. During the scan, the impedance measurement unit acquires impedance data at different frequencies, including the real part, imaginary part, impedance amplitude, and phase angle. These data constitute the impedance spectrum of the spring material. The controller 5 processes the acquired impedance data, identifies characteristic frequency peaks related to micro-defects, and ensures that the pulse current always matches the micro-state of the spring material.

[0035] As a further preferred embodiment, the axial pressing device 3 includes an upper pressure head, which is a flexible graphite contact. The flexible graphite contact includes a graphite block 31 and a built-in preload spring 32 for maintaining stable electrical contact with the spring end ring at high temperatures. When a pulsed current is applied, the electroplastic effect may cause slight dimensional fluctuations, which the preload spring 32 can absorb to maintain stable contact. The graphite material can withstand temperatures up to 3000°C in an oxygen-free atmosphere, and its conductivity and compressive strength actually increase with increasing temperature.

[0036] As a further preferred embodiment, the insulating support 4 includes: The spindle 41 has an insulating coating on its surface for contact with the inner ring of the spring; the insulating coating is a ceramic insulating and thermally conductive coating.

[0037] The mandrel seat 42 is fixedly installed at the bottom of the furnace body 1 and electrically connected to the pulse current power supply 2; An insulating ring 43 is connected between the mandrel 41 and the mandrel seat 42 to achieve electrical insulation between the two. An annular graphite electrode 44 is disposed on the upper end face of the mandrel seat 42 and is used to contact the lower end ring of the spring to form an electrical connection.

[0038] As a further preferred embodiment, the device includes an online insulation monitoring module for detecting the circuit-to-ground insulation resistance during the gap in the application of the pulse current, and cutting off the pulse current power supply 2 when the insulation resistance is lower than a preset threshold. The online insulation monitoring module operates during the gap in the application of the pulse current (millisecond level), and the specific process is as follows: The pulsed current is typically applied at a certain frequency, with a brief gap between adjacent pulses. The online insulation monitoring module utilizes this gap for detection without affecting the normal application of the main pulse. A low-voltage DC detection signal is applied to the electrode and mandrel 41 circuit. The current in the detection circuit is measured, and the insulation resistance to ground is calculated according to Ohm's law. When the insulation resistance is lower than a preset threshold, an insulation fault is identified. Before the next pulse arrives, the pulsed current power supply 2 is immediately cut off, and an audible and visual alarm is triggered. Simultaneously, the fault information is recorded for operator troubleshooting. This design achieves real-time monitoring and active protection of the insulation status, preventing equipment and workpiece damage due to insulation failure and ensuring the long-term reliability of the equipment.

[0039] Example 2 This embodiment employs the tempering apparatus of Embodiment 1 to achieve a high-precision tempering process for stress relief of precision springs, such as... Figure 3 As shown, it includes the following steps: S1: Obtain the impedance spectrum information of the target spring through the impedance measurement unit, and determine at least one characteristic frequency f based on the impedance spectrum information; S2: During the process of heating the spring to the preset tempering temperature and / or after reaching the preset tempering temperature, a pulse current is applied to the spring through the pulse current power supply 2; the fundamental frequency of the pulse current matches the characteristic frequency f. S3: During the application of pulsed current, the axial pressure is dynamically adjusted according to the tempering stage, and the tempering process is completed under the condition of applying axial constraint to the spring through the axial pressure device 3 to eliminate stress.

[0040] As a further preferred embodiment, step S1 includes: S11: Apply a low-amplitude AC detection signal with continuously varying frequency to the spring and collect impedance data at different frequencies; S12: Based on the impedance data, identify at least one characteristic frequency peak f0 related to dislocation vibration or grain boundary relaxation; S13: Perform temperature drift correction on the characteristic frequency peak f0 according to the preset tempering temperature T to obtain the target frequency f_target(T); In step S2, the fundamental frequency of the pulse current is set to the target frequency f_target(T).

[0041] Because the physical properties of materials, such as resistivity and elastic modulus, change with temperature, the characteristic frequency f0 measured at room temperature will drift during high-temperature tempering. The actual frequency at high temperature may be out of tune with the resonant frequency of microscopic defects in the material, reducing the processing effect. Temperature drift correction ensures that the frequency of the pulse current remains matched with the microscopic state of the spring material throughout the entire tempering temperature range.

[0042] As a further preferred embodiment, step S3 includes: S31: Apply a first pulse current and a first axial pressure. The current density of the first pulse current is greater than that of the second pulse current, and the first axial pressure is less than that of the second axial pressure. The first pulse current is a high-density narrow pulse current, and the first axial pressure is a low-pressure constraint, which is 0.5% to 2% of the spring's ultimate load. The high-density pulse current's electronic wind force rapidly opens up the tangled dislocations formed during cold working, promoting dislocation slip and recombination.

[0043] S32: Switch to the second pulse current and adjust the axial pressure to the second axial pressure; the second pulse current is a lower density pulse current, and the axial pressure is increased to 30%~70% of the spring working load. By providing appropriate axial pressure, a stress field is generated at the grain boundary, which promotes carbide nucleation, inhibits grain growth, maintains fine grain structure, assists in volume change during phase transformation, reduces internal stress, controls the decomposition process of residual austenite, and induces the dispersion precipitation of nanoscale carbides.

[0044] S33: The pulse current is turned off, the cooling system is started, and dynamic compensation pressure is applied to the spring during the cooling process to counteract the dimensional changes caused by thermal contraction. The dynamic compensation pressure is calculated based on real-time temperature feedback to ensure that the free height of the spring remains unchanged before and after cooling. The working principle of the dynamic compensation pressure is as follows: by monitoring the spring temperature in real time, the theoretical thermal contraction is calculated based on the thermal expansion coefficient of the material, and the piezoelectric ceramic actuator applies a corresponding axial compression displacement to the spring, so that the spring always remains near the target length during the cooling process. Specifically, when the temperature drops by ΔT, if there is no constraint, the spring will contract by ΔL = α·L·ΔT; this invention applies axial pressure through the piezoelectric actuator, causing the spring to produce a compression deformation of ΔL_comp, and satisfying ΔL_comp = ΔL, thereby counteracting the effect of thermal contraction and achieving dimensional locking.

[0045] As a further preferred embodiment, a temperature sensor monitors the temperature change rate of the spring micro-region. When the temperature rise exceeds a threshold, the pulse current duty cycle is reduced, and the preset duty cycle is restored after the temperature rise recovers. The decomposition of residual austenite is an exothermic reaction, which can cause an abnormal increase in the temperature of the spring micro-region. If the temperature is too high, it can lead to coarsening of the precipitated carbides. By dynamically adjusting the pulse current duty cycle, local overheating can be effectively suppressed, maintaining the uniformity of the microstructure.

[0046] As a further preferred embodiment, in the second stage, the axial pressure applied to the spring is an alternating pressure synchronized with the pulsed current, and its frequency is consistent with the fundamental frequency of the pulsed current. The alternating pressure and the electron wind of the pulsed current form a synergistic effect, promoting dislocation slip. This can generate small stress fluctuations at the grain boundaries, which is conducive to the uniform nucleation of carbides, avoids dislocation pile-up under static pressure, and improves the uniformity of phase transformation.

[0047] Example 3 The apparatus of this invention is used to temper 65Mn precision springs. The spring specifications are: mean diameter 20mm, wire diameter 2.5mm, free height 50mm, effective number of coils 8, cold-rolled state.

[0048] S1: The spring is mounted on the insulating support 4, and a sweep frequency detection signal of 1Hz to 1MHz is applied to the spring through the impedance measurement unit. The controller 5 analyzes the impedance spectrum and detects a dislocation resonance characteristic peak at the characteristic frequency f0 = 12.8kHz. Temperature drift correction is performed based on the preset tempering temperature of 380℃ to obtain the target frequency f_target = 12.5kHz.

[0049] S2: Furnace 1 is evacuated and filled with argon gas, then heated to 380℃. During the heat preservation stage, pulsed current power supply 2 applies a first pulsed current: frequency 12.5kHz, duty cycle 30%, current density 80A / mm²; axial pressure device 3 applies a first axial pressure of 20N. This process lasts for 5 minutes, utilizing the electron wind effect of the high-density pulsed current to open tangled dislocations.

[0050] S3: Switch to the second pulse current: frequency 12.5kHz, duty cycle 20%, current density 30A / mm²; axial pressure increased to 150N, set to alternating pressure at the same frequency as the pulse current. During this period, the temperature of the spring micro-area is monitored by a temperature sensor. When the residual austenite decomposition causes excessive temperature rise due to heat release, the duty cycle is automatically reduced from 20% to 10%, and restored after the temperature rise recovers. This stage lasts for 15 minutes.

[0051] S4: Turn off the pulse current and start the cooling system at a cooling rate of 15℃ / min. Simultaneously, the piezoelectric ceramic actuator 33 applies dynamic compensation pressure based on real-time temperature feedback, ensuring the spring's free height remains within the range of 50.00±0.02mm. After cooling to below 50℃, the pressure is released, completing the process.

[0052] Testing revealed that the residual stress of the spring decreased from the initial 850 MPa to 45 MPa, the free height deviation was controlled within ±0.02 mm from ±0.30 mm, the microstructure showed a dispersed distribution of nano-scale carbides, and the elastic decay rate was reduced by more than 70% compared to traditional tempering. This process takes approximately 40 minutes, representing a 30% improvement in efficiency compared to traditional tempering (60 minutes).

[0053] The above embodiments are exemplary and are intended to illustrate the technical concept and features of the present invention, so that those skilled in the art can understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A stress-relieving high-precision tempering device for precision springs, characterized in that: Furnace body (1), pulse current power supply (2), axial pressure device (3), insulating support (4) and controller (5); The pulse current power supply (2) is used to be electrically connected to the spring; The axial pressure device (3) is used to apply axial constraint to the spring; The insulating support (4) is used to ensure electrical insulation between the spring and the furnace body (1) when the spring is energized; The controller (5) is configured to control the pulse current power supply (2) to output a pulse current to the spring, wherein the fundamental frequency of the pulse current matches the characteristic frequency of the spring material, and the characteristic frequency is a frequency range that can resonate or strongly couple with the micro-defects inside the spring. The axial pressure control device (3) applies dynamic axial pressure to the spring during the pulse current application process, and the dynamic axial pressure changes with the tempering stage.

2. The stress-relieving high-precision tempering device for precision springs according to claim 1, characterized in that: It includes an impedance measurement unit for acquiring the impedance spectrum information of the spring before and / or during the tempering process; the controller (5) determines the characteristic frequency based on the impedance spectrum information and adjusts the fundamental frequency of the pulse current accordingly.

3. The stress-relieving high-precision tempering device for precision springs according to claim 1, characterized in that: The axial pressing device (3) includes an upper pressure head, which is a flexible graphite contact. The flexible graphite contact includes a graphite block (31) and a built-in preload spring (32) for maintaining stable electrical contact with the spring end ring at high temperatures.

4. The stress-relieving high-precision tempering device for precision springs according to claim 1, characterized in that: The insulating support (4) includes: The spindle (41) has an insulating coating on its surface for contacting the inner ring of the spring. The mandrel seat (42) is fixedly installed at the bottom of the furnace body (1) and electrically connected to the pulse current power supply (2); An insulating ring (43) is connected between the mandrel (41) and the mandrel seat (42) to achieve electrical insulation between the two. An annular graphite electrode (44) is disposed on the upper end face of the mandrel seat (42) for contacting the lower end ring of the spring to form an electrical connection.

5. The stress-relieving high-precision tempering device for precision springs according to claim 1, characterized in that: It includes an online insulation monitoring module for detecting the circuit-to-ground insulation resistance during the gap in the pulse current application and cutting off the pulse current power supply when the insulation resistance is lower than a preset threshold (2).

6. A high-precision tempering process for stress relief of precision springs implemented using the apparatus described in any one of claims 1-5, characterized in that: Includes the following steps: S1: Obtain the impedance spectrum information of the target spring through the impedance measurement unit, and determine at least one characteristic frequency f based on the impedance spectrum information; S2: During the process of heating the spring to a preset tempering temperature and / or after reaching the preset tempering temperature, a pulse current is applied to the spring through the pulse current power supply (2); the fundamental frequency of the pulse current matches the characteristic frequency f. S3: During the application of pulse current, the axial pressure is dynamically adjusted according to the tempering stage, and the tempering process is completed under the condition that the spring is axially constrained by the axial pressure device (3) to eliminate stress.

7. The process according to claim 6, characterized in that: Step S1 includes: S11: Apply a low-amplitude AC detection signal with continuously varying frequency to the spring and collect impedance data at different frequencies; S12: Based on the impedance data, identify at least one characteristic frequency peak f0 related to dislocation vibration or grain boundary relaxation; S13: Perform temperature drift correction on the characteristic frequency peak f0 according to the preset tempering temperature T to obtain the target frequency f_target(T); In step S2, the fundamental frequency of the pulse current is set to the target frequency f_target(T).

8. The process according to claim 6, characterized in that: Step S3 includes: S31: Apply a first pulse current and a first axial pressure, wherein the current density of the first pulse current is greater than that of the second pulse current, and the first axial pressure is less than that of the second axial pressure; S32: Switch to the second pulse current and adjust the axial pressure to the second axial pressure; S33: Turn off the pulse current, start the cooling system, and apply dynamic compensation pressure to the spring during the cooling process to counteract the dimensional changes caused by thermal contraction.

9. The process according to claim 8, characterized in that: Step S32 includes: monitoring the temperature change rate of the spring micro-area through a temperature sensor, reducing the pulse current duty cycle when the temperature rise exceeds a threshold, and restoring the preset duty cycle after the temperature rise recovers.

10. The process according to claim 8, characterized in that: In the second stage, the axial pressure applied to the spring is an alternating pressure synchronized with the pulse current, and its frequency is consistent with the fundamental frequency of the pulse current.

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