A high-precision stress-free bending method for energy storage copper connectors

Abstract

This invention relates to the field of metal bending processing technology, and discloses a high-precision stress-free bending method for energy storage copper connectors. The method includes: bending the copper connector to a pre-calibrated target position using a mechanical actuator; applying a current pulse while maintaining the position; monitoring transient voltage and current in real time during the application of the current pulse, and calculating the transient dynamic resistance change rate; immediately terminating the current pulse when a characteristic peak representing the completion of lattice recrystallization is detected in the rate of change; and finally releasing the mechanical actuator. This invention utilizes the objective law of abrupt changes in resistivity during physical phase transitions of materials to establish a self-terminating process flow. This method can automatically compensate for batch differences in materials and variations introduced by electrode wear, avoiding residual stress introduced by bending.

Description

Technical Field

[0001] This invention relates to a high-precision stress-free bending method for energy storage copper connectors, belonging to the field of metal bending processing technology. Background Technology

[0002] Currently, especially for copper connectors used in high-current energy storage systems, their three-dimensional shape is usually formed by mechanical cold bending. This pure mechanical plastic deformation inevitably introduces residual stress into the material. In the field of metal processing, this residual stress mainly manifests as geometric springback of the workpiece. However, in the field of conductive connections, this stress constitutes a long-term source of failure. During the service life of the workpiece, residual stress will cause stress relaxation and creep of the material, resulting in a decrease in contact pressure at the connection interface, which in turn causes an increase in contact resistance and may eventually develop into thermal runaway.

[0003] To eliminate this stress and ensure forming accuracy, existing processes either rely on complex compensation molds or independent heat treatment annealing processes after forming. However, these methods reveal their limitations when facing the realities of mass production, especially when dealing with fluctuations in the physical properties of raw materials. Copper raw materials from different batches have different physical properties such as hardness and work hardening, leading to the following problems when using fixed process parameters: 1. Purely mechanical compensation bending cannot eliminate stress, and the fixed compensation amount cannot adapt to the springback differences of different incoming materials, resulting in inconsistent geometric accuracy; 2. Using independent heat treatment after forming increases the production cycle and cost, and similarly cannot make fine-tuned process adjustments for the initial stress differences of different batches of incoming materials.

[0004] Besides the limitations imposed by relying on complex physical molds or independent heat treatment processes, existing technologies, even when attempting to introduce electric-assisted heat treatment, generally suffer from fundamental flaws in the logic of process control. For example, Chinese invention patent CN111590076B discloses an electric pulse post-processing method and device for improving the performance of metal components. The core idea of ​​this patent is to process components through multiple processes such as pre-set electric pulse crack arrest, quenching, and tempering. However, its control logic is essentially an open-loop execution mode based on fixed parameters, that is, for specific processing steps, fixed parameters such as current density and pulse duration are pre-set. This method ignores the inherent fluctuations in the physical properties of raw materials (such as different batches of copper) in terms of hardness, conductivity, etc., in actual production, and cannot compensate for the influence of environmental factors such as electrode wear. Fixed process parameters are prone to insufficient or excessive annealing when facing changing processing objects, and cannot fundamentally guarantee the consistency of residual stress relief and geometric accuracy of each product. The process window is narrow and the robustness is poor. Therefore, the technical problem to be solved by this invention is to find a process method that can overcome the differences in physical properties between batches of incoming materials and achieve controllable elimination of residual stress during the bending and forming process, so that the workpiece can obtain a high-precision geometric shape and also have a highly reliable electrical connection foundation. Summary of the Invention

[0005] This invention provides a high-precision stress-free bending method for energy storage copper connectors. Its main purpose is to solve the problem of how to adapt to the differences in physical properties of incoming batches and simultaneously eliminate residual stress during the bending process, so as to balance geometric accuracy and long-term electrical reliability.

[0006] To achieve the above objectives, the present invention provides a high-precision stress-free bending method for energy storage copper connectors, comprising:

[0007] Step 1, mechanical preforming, using a mechanical actuator to bend the energy storage copper connector to the pre-calibrated target position;

[0008] Step 2, self-terminating annealing based on physical state: With the mechanical actuator held in the target position, the pulse power supply is activated to apply a current pulse to the bending area of ​​the energy storage copper connector. During the duration of the current pulse application: the transient voltage and transient current flowing through the bending area are monitored in real time and synchronously; based on the monitored transient voltage and transient current, the transient dynamic resistance change rate of the bending area is calculated in real time; an operating rule for terminating the current pulse is established, which is: continuously judging whether the transient dynamic resistance change rate exhibits a characteristic peak value that characterizes the completion of internal lattice recrystallization of the material; if and only if the characteristic peak value is detected, a pulse termination command is immediately issued to cut off the energy output of the pulse power supply.

[0009] Step 3: Mechanical unloading. After the pulse termination command is executed, the mechanical actuator is controlled to return.

[0010] Preferably, in step two, the real-time calculation of the transient dynamic resistance change rate of the bending region includes: real-time calculation of the transient dynamic resistance of the bending region, the calculation rule of which is: ,in, Transient voltage, It is a transient current. Transient dynamic resistance; based on transient dynamic resistance The transient dynamic resistance rate is obtained from the time series data through difference operations or derivative operations.

[0011] Preferably, before step one is executed, an adaptive batch calibration step is also included; the adaptive batch calibration step includes: acquiring one or more sample energy storage copper connectors of the current production batch; applying an energy-increasing scanning pulse to one or more sample energy storage copper connectors; while applying the scanning pulse, measuring the change in DC resistance of the bending area of ​​the sample energy storage copper connector before and after annealing using the four-point method; determining the pulse energy corresponding to the maximum value of the change in DC resistance, and setting the characteristic peak value of the transient dynamic resistance change rate associated with the pulse energy as the judgment basis for the operating rules in step two.

[0012] Preferably, during the execution of step three, an online quality monitoring step is also included. The online quality monitoring step includes: passively monitoring the acoustic emission signal generated by the energy storage copper connector during mechanical unloading in step three using an acoustic emission sensor; establishing a quality judgment rule, which is: if the amplitude of the acoustic emission signal is lower than a preset benchmark threshold, it is determined that the residual stress of the energy storage copper connector has been eliminated; if the amplitude of the acoustic emission signal is higher than the preset benchmark threshold, it is determined that the residual stress of the energy storage copper connector has not been eliminated.

[0013] Preferably, the current pulse applied in step two utilizes the Joule heating generated by the resistance of the energy storage copper connector itself, causing the metal lattice temperature in the bending area to rise above the recrystallization temperature within milliseconds. After the current pulse terminates, the connector is rapidly cooled due to the heat sink effect of the energy storage copper connector body, thereby completing the transient dynamic annealing. The transient dynamic annealing releases the internal lattice dislocations and residual stresses generated by the mechanical preforming in step one.

[0014] Preferably, the target position for pre-calibration in step one is the encoder reading representing the critical position where the energy storage copper connector has been fully formed but the mechanical force of the mechanical actuator has not yet been released.

[0015] Preferably, the characteristic peak in step two is determined by comparing the real-time value of the transient dynamic resistance change rate with a preset threshold representing the completion of the phase transition.

[0016] Preferably, the real-time and synchronous monitoring in step two is performed by one or more analog-to-digital converters at a preset sampling frequency.

[0017] Preferably, in step two, the application of the current pulse and the monitoring of the transient voltage are achieved by electrodes set on both sides of the bending area.

[0018] Preferably, the mechanical unloading in step three is initiated within a microsecond-level time window after the pulse termination command is executed.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. By using a pre-production calibration step to determine the objective correspondence between the physical properties of a specific batch of copper and the required transient electrical pulse energy by utilizing the change in DC resistance in the bending processing area, the subsequent batch production steps strictly execute this calibrated energy parameter. This method of first diagnosing and calibrating and then executing in an open loop transforms the physical fluctuations of the raw material from an uncontrollable interference variable affecting the final forming accuracy into an input parameter that can be pre-identified and compensated for in the process flow. This makes the final shape consistency of the bending process no longer overly dependent on the high consistency of the raw material.

[0021] 2. This method applies transient electrical pulses within a critical window when the mechanical bending reaches a predetermined position but the mechanical force has not yet been released. This specific timing arrangement utilizes the temporary clamping state of the mechanical mold on the workpiece. In this state, the release of internal stress in the material induced by the electrical pulse is limited to eliminating the mechanical springback tendency of the material, while the macroscopic geometry of the workpiece continues to be guaranteed by the physical position of the mold. When the subsequent mechanical force is unloaded, since the internal stress driving the springback has been eliminated in the clamping state, the workpiece can more faithfully maintain the precise shape given by the mold, achieving high-precision reproduction of the bending angle.

[0022] 3. During the calibration phase, an unconventional technical approach was adopted. Instead of using traditional methods such as measuring bending springback angles or material hardness to deduce process parameters, it introduced electrical parameter measurement methods, specifically measuring the change in DC resistance in the bending region. The degree of stress release within a material is characterized by the use of the intrinsic physical relationship between changes in the microcrystalline lattice structure (stress release) and changes in its macroscopic electrical conductivity. This method provides a more sensitive and easily precise technical basis for the calibration of parameters in metal plastic forming processes, avoiding the complexity and uncertainty that may be introduced during the calibration process of traditional mechanical quantity measurements. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the adaptive batch calibration process of the present invention.

[0024] Figure 2 This is a general framework diagram of the high-precision stress-free bending method of the present invention;

[0025] Figure 3 This is a flowchart illustrating the self-terminating annealing bending process of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the scope of protection of the invention.

[0027] This invention provides a high-precision stress-free bending method for energy storage copper connectors. The technical solution involves coupling a high-precision mechanical plastic deformation step, a self-terminating transient annealing step based on real-time monitoring of the material's internal physical state, and a precisely time-controlled mechanical stress relief step. This method utilizes the physical law that the resistivity of a material undergoes a nonlinear abrupt change during the physical phase transition of lattice recrystallization (i.e., residual stress release) in the bending and forming process of metal sheets or profiles. By real-time monitoring of this physical characteristic signal, closed-loop self-terminating control of the annealing energy injection is achieved, thereby ensuring geometric accuracy while avoiding residual stress introduced by cold bending. A preferred embodiment of this high-precision stress-free bending method for energy storage copper connectors includes the following steps: Step 1, mechanical pre-forming. This step aims to use standard tools for metal plastic forming to give the workpiece the desired target geometry. A standardized mechanical actuator, such as a servo press or a multi-station bending machine, drives the forming mold at its end to shape the energy storage copper connector to be processed. The connector (usually a copper plate or rod) is bent to a pre-calibrated target position. It's important to note that this pre-calibrated target position is a critical process parameter, representing the encoder reading at the critical position where the energy storage copper connector has fully reached its final design form, but the mechanical constraint of the actuator has not yet been released. In this state, the workpiece's geometry is constrained by the physical boundaries of the mold, and its interior accumulates a large number of lattice dislocations and residual stress due to plastic deformation. Step two, self-terminating annealing based on the physical state, is crucial to this method. Its purpose is to utilize the window period during which the workpiece is mechanically constrained at the target position, and through transient energy injection, eliminate the internal residual stress generated in step one in situ. In this step, when the control system (e.g., PLC or PAC) confirms that the actuator has accurately reached and maintained the pre-calibrated target position, it immediately triggers the pulse power supply. This pulse power supply applies a high-energy current pulse to the bending area of ​​the energy storage copper connector through electrodes located on both sides. This current pulse utilizes the resistance of the copper material itself to generate Joule heating. ), causing the metal lattice temperature in the bending region to decrease within milliseconds (e.g. to The temperature rises rapidly above the recrystallization temperature, and after the current pulse ends, it cools rapidly due to the heat sink effect of the copper connector body (the unheated area), thus completing a transient dynamic annealing. This annealing process physically releases the internal lattice dislocations and residual stresses generated by mechanical preforming.

[0028] To address the issue of inconsistent processing caused by fluctuations in physical properties (such as hardness and conductivity) of different material batches or electrode wear, this step employs a self-terminating logic based on physical state feedback, rather than relying on fixed pulse duration or energy parameters. Throughout the entire duration of the applied current pulse, this method performs the following sub-steps: A, Real-time and synchronous monitoring via one or more high-speed analog-to-digital converters (ADCs) at a preset high sampling frequency (e.g., Real-time and synchronous acquisition of transient voltage flowing through the bending zone With transient current B, Real-time calculation of transient dynamic resistance change rate; the controller's processing unit is based on the monitored... and The data is first used to calculate the transient dynamic resistance of the bending region in real time based on Ohm's law. The calculation rules are as follows: ,in, Transient voltage, It is a transient current. This is the transient dynamic resistance; subsequently, the controller is based on the transient dynamic resistance. Time series data, through differencing operations (e.g. Alternatively, by performing derivative operations, the transient dynamic resistance change rate can be obtained. C, Establish and execute an operating rule for terminating the current pulse. The physical basis of this operating rule is that when a metallic material undergoes a violent lattice recrystallization (i.e., residual stress is concentrated and released) under Joule heating, the reorganization of its internal microstructure will cause a nonlinear abrupt change in its resistivity. This abrupt change is reflected in the transient dynamic resistance change rate calculated in real time. On the curve, it exhibits a clear characteristic peak; therefore, the operating rule is set as follows: continuously judge the transient dynamic resistance change rate ( Does a characteristic peak appear that characterizes the completion of lattice recrystallization within the material, if and only if the characteristic peak is detected (e.g., by...)? The real-time value is compared with a preset threshold representing the completion of the phase transition to determine the pulse termination command. The controller immediately issues a pulse termination command to cut off the energy output of the pulse power supply. In this way, the actual duration of the pulse or the total energy injected is no longer a fixed input parameter, but a result value determined by the real-time physical state of each workpiece, thereby automatically compensating for the changes introduced by material batch differences and electrode wear. Step 3: Mechanical unloading. After the pulse termination command is executed, that is, after confirming that the residual stress in the bending area has been eliminated in the clamping state, the control system immediately (e.g., within a microsecond time window) controls the mechanical actuator to return (i.e., unload the force). Since the internal residual stress driving the geometric springback no longer exists, the energy storage copper connector can accurately maintain the geometric shape given by the mold in step 1.

[0029] To further enhance the robustness of the process, this method includes an adaptive batch calibration step before step one. This step provides a scientific and calibrable basis for the characteristic peaks or preset thresholds in step two (C). The calibration step includes: acquiring one or more sample energy storage copper connectors from the current production batch (e.g., a new copper coil); applying incrementally increasing scanning pulses to the samples; and simultaneously measuring the change in DC resistance of the bending area of ​​the sample energy storage copper connector before and after annealing using a high-precision four-point method while applying the scanning pulses. Materials science principles indicate that The change in resistance is positively correlated with the degree of internal stress release; ultimately, the change in DC resistance is determined. The pulse energy corresponding to the maximum value (i.e., the most fully released stress) and the transient dynamic resistance change rate associated with this pulse energy ( The characteristic peak value of the raw material is set as the basis for judging the running rules in step two C. This method of offline calibration followed by online execution transforms the physical fluctuations of the raw material from an uncontrollable interference variable into a process input parameter that can be pre-identified and compensated for. In another preferred embodiment, to improve the processing quality of the method... In the online monitoring process of step three, this method also includes an online quality monitoring step, which utilizes the following physical principle: if the annealing in step two is insufficient and residual stress remains inside the workpiece, these residual stresses will drive violent lattice dislocation movements within the material during the mechanical unloading (springback) in step three, thereby generating a high-amplitude acoustic emission characteristic signal; conversely, if the annealing is sufficient, the unloading process is acoustically at baseline. Therefore, this monitoring step includes: passively monitoring the acoustic emission signal generated by the energy storage copper connector during mechanical unloading in step three using one or more acoustic emission sensors; and establishing quality judgment rules. If the amplitude of the acoustic emission signal is lower than a preset reference threshold (representing the baseline state), it is determined that the residual stress of the energy storage copper connector has been eliminated (qualified); if the amplitude of the acoustic emission signal is higher than the preset reference threshold, it is determined that the residual stress of the energy storage copper connector has not been eliminated (unqualified). The preset reference threshold can be determined by measuring and statistically analyzing the acoustic emission signal baseline of known qualified samples (e.g., samples confirmed by the adaptive batch calibration step).

[0030] Example 1: In an automated metal forming production line for mass production of automotive energy storage copper connectors, the line faces a typical process consistency challenge. The T2 copper coils (workpieces) used are from two different suppliers. Batch A has a higher degree of cold work hardening, and its yield strength is significantly higher than that of batch B. The standard purely mechanical cold bending forming process used in the production line is based on the material characteristics of batch A, which determines the overbending amount to compensate for springback. When the production line switches to the coil of batch B, the fixed overbending amount leads to overshooting due to the softer material. When the hardness of the material in batch A fluctuates again due to differences within the coil batch, the original compensation amount is insufficient, resulting in excessive geometric springback of the workpiece. This metal forming method, which relies on open-loop prediction, causes inconsistent geometric accuracy and uncontrolled residual stress when faced with fluctuations in the physical characteristics of the incoming material. To address this situation, the production line has implemented a bending method. When an energy storage copper connector from batch A (high hardness) enters the station, the system performs mechanical pre-forming in step one, bending and clamping it at the pre-calibrated target position. Subsequently, the system performs step two, namely self-terminating annealing based on physical state. The controller sends a pulse start signal and, while applying current, transmits the signal through an analog-to-digital converter. real-time frequency monitoring and And solve for the transient dynamic resistance change rate ( Because the workpiece has high hardness and slightly low conductivity, it takes a long time to reach its recrystallization temperature. The controller's algorithm firmware continuously monitors this. Only then was it detected. The curve shows a characteristic peak indicating the completion of lattice recrystallization. The controller determines that the dynamic annealing has been physically completed and immediately issues a pulse termination command to cut off the energy output.

[0031] In the next processing cycle, an energy storage copper connector from batch B (low hardness) enters the same station, and the system performs the exact same step one, clamping it in the same pre-calibrated target position; subsequently, the system performs step two, and when the current pulse is activated, due to the workpiece's low hardness and high conductivity, its Joule heating (… The accumulation rate is faster, the physical phase change inside the material occurs earlier, and the controller's algorithm firmware is in... Subsequently, the occurrence of the characteristic peak was detected, and the controller immediately executed the same operating rules. A pulse termination command was then issued; in the subsequent third step (mechanical unloading), although the durations of the transient dynamic annealing experienced by the two workpieces from different batches differed by nearly [missing information], [missing information]. However, since the annealing process of both is terminated solely by their respective physical phase transformations, they exhibit extremely low and consistent geometric springback during mechanical unloading, and the final forming angle maintains a high degree of consistency with the stress-free state. The method of this invention utilizes a collaborative mechanism, namely, using the mechanical clamping in step one for the electrical measurement in step two. The solution provides a stable boundary for the geometric shape, and then uses the self-terminating logic in step two to read the real physical state of each workpiece in real time, thereby actively and piece by piece adapting to the physical fluctuations of the incoming material. This method no longer attempts to predict a fixed processing parameter, but instead seeks an endpoint of the physical state during the processing, thereby transforming the common interference factor of incoming material fluctuations in metal forming process into a variable that can be contained and compensated for in real time by the process flow.

[0032] Example 2: To objectively verify the effectiveness of the method of the present invention in eliminating residual stress and ensuring geometric accuracy when dealing with fluctuations in the physical properties of raw materials, this comparative experiment was conducted. The experimental equipment included: a servo press with a position repeatability of [missing information]. Used to perform mechanical preforming in step one and hold it in a pre-calibrated target position; a pulse power supply system, configured with A sampling rate analog-to-digital converter (ADC) is used for real-time monitoring. and One X-ray diffractometer (XRD), using standard The method used was to measure the residual stress in the bending zone; and a three-dimensional optical scanner was used to measure the actual bending angle of the formed workpiece and calculate the geometric springback angle; the test materials were selected... Thick T2 copper rods were selected, and two batches with different physical properties were chosen: Batch A (Vickers hardness) ) and batch B (Vickers hardness) This represents a common material fluctuation condition in metal forming. The experiment was conducted in three groups, with 10 samples prepared from both batch A and batch B materials in each group. The average values ​​of residual stress in the bending zone and springback angle were measured. Control group 1 (pure mechanical cold bending): The sample was bent to the pre-calibrated target position in step one, and then mechanical unloading in step three was performed directly without applying a current pulse. This group simulated the pure cold bending forming method in the background technology. Control group 2 (open-loop pulse annealing): The sample was held at the pre-calibrated target position in step one. Subsequently, a current pulse with fixed parameters was applied, and the duration of the pulse was fixed at 100%. (This value is taken from the average of the time required for two batches in Example 1); After the pulse ends, mechanical unloading is performed in step three. This group simulates an open-loop electrically assisted molding method without the self-termination logic of this invention; Sample group of this invention (self-termination annealing): The sample is strictly executed according to the complete method, including step one, step two (including sub-steps A, B, and C) and step three. The termination of its current pulse is calculated in real time by the controller based on the transient dynamic resistance change rate ( It is triggered upon detecting the appearance of a characteristic peak.

[0033] Table 1: A comparison of the processing results of different batches of materials using different process methods.

[0034]

[0035] Referring to the experimental data in Table 1, the following objective conclusions can be drawn: The samples from control group 1 (pure mechanical cold bending) all retained more than [a certain percentage] of [something]. The residual stress, and its geometric rebound angle varies significantly depending on the material hardness. Degree vs This reproduces the process consistency problem faced by the background technology; the data from control group 2 (open-loop pulse) shows the limitations of the fixed parameter method, the fixed For batch B (soft material), the energy of the pulse is close to the required value (residual stress). However, for batch A (hard material), this time is insufficient (the time required for this batch in the sample group of this invention is...). This results in insufficient annealing, leaving residual [unclear - possibly a contaminant or residue]. The stress, and its process results fluctuate with material batch variations; the data from the sample group of this invention demonstrate the effect of the self-terminating annealing step based on physical state, as shown in the pulse duration column. This method automatically performs annealing for batch A (hard material). Annealing was performed for batch B (soft material). In the annealing process, the duration is no longer a fixed input parameter, but rather a result value determined by the real-time physical state of the material. Ultimately, both batches of samples in this invention's sample group achieved low and consistent residual stress (both below...). and low and consistent bend rebound angles (both) (Degree), experimental data show that the method of the present invention, by introducing a self-terminating operation rule based on transient dynamic resistance change rate, can automatically compensate for the fluctuations in the physical properties of incoming materials commonly found in the field of metal forming.

[0036] Example 3: This example combines Figures 1 to 3 A high-precision stress-free bending method for an energy storage copper connector is described, such as... Figure 1 As shown, the operator first initiates the batch calibration program through the control system and provides the sample connectors for the current batch. The control system issues instructions to the pulse power supply to set the scanning pulse parameters and applies pulses with increasing energy to the sample connectors. During the pulse application process, the control system, in conjunction with a four-point method measuring device, performs DC resistance measurements before and after annealing. The four-point method measuring device measures the DC resistance before and after the annealing pulse and reports the resistance change to the control system. The control system records the resistance change data and, after the scan is completed, analyzes and determines the maximum resistance change, extracts the corresponding characteristic peak information, and sets the production judgment threshold accordingly. Finally, the process ends when the batch calibration is completed and the parameters are saved. Figure 2 As shown, the process is initiated by the process engineer and mainly includes three core steps. First, adaptive batch calibration is performed, which aims to determine the characteristic peak values ​​for process control for the new batch of copper. This determination is then provided to the core process, namely, the high-precision stress-free bending step. This step includes the complete preforming, annealing, and stress relief core process flow. Finally, to verify the quality of each finished product, an online quality monitoring step can be selectively performed, which confirms the quality of the finished product by monitoring acoustic emission signals. The operation of the high-precision stress-free bending and online quality monitoring steps is managed by the control system PLC / PAC.

[0037] like Figure 3 As shown, starting with the energy storage copper connector to be processed, which may come from different batches of copper, an adaptive batch calibration step is first performed. That is, before production, a scanning pulse is applied to the new batch of samples to measure the change in DC resistance. It is certain that it can make To maximize the release of stress, the pulse energy is fully utilized, and its corresponding characteristic peak information is extracted. This information serves as the threshold for characteristic peak judgment and is input into the core process. The first step of the core process is: mechanical pre-forming, where the connector is bent to the pre-calibrated target position and placed in a clamped state, providing a stable geometric boundary for transient annealing. Next, the process proceeds to step two: self-terminating annealing based on physical state, where current pulses are injected into the bending area while the transient dynamic resistance change rate is monitored in real time. When a characteristic peak representing the completion of recrystallization appears, the annealing is automatically terminated. Then, the process proceeds to step three: mechanical unloading, where the mechanical constraint is released after the residual stress has been eliminated, and the workpiece is precisely maintained in the target shape without geometric springback, thereby obtaining a high-precision, stress-free energy storage copper connector. To achieve 100% piece-by-piece quality verification, an online quality monitoring step can be further performed. During mechanical unloading, the signal is passively monitored by an acoustic emission sensor. If the signal amplitude is lower than the benchmark threshold, the residual stress is determined to be eliminated and qualified; otherwise, it is determined to be unqualified.

[0038] Example 4: This example provides a method for determining the target location for pre-calibration ( ) and transient dynamic resistance change rate ( The characteristic peak judgment criteria include the calibration procedure for preset thresholds; in a specific calibration scenario, for a batch of T2 copper rods, the diameter is... The initial hardness is It will be bent into Angle, calibration is performed on a configuration with a powerful sensor (range) precision ) and displacement sensor (range) resolution The process is performed on a servo press that integrates a pulse power supply system and monitoring unit for performing a physical state-based self-terminating annealing step; the target position is first pre-calibrated ( For calibration, three samples from this batch were selected, and calibration was performed without applying a current pulse. The machine performs a purely mechanical bending process on the material at a certain speed, while simultaneously recording the displacement-load curve of the press. Analyzing this curve, the machine identifies the critical point where the load reaches its peak and begins to decrease, but the displacement has not yet reversed (i.e., springback has not occurred). The displacement sensor reading corresponding to this critical point is designated as the pre-calibrated target position for this batch of material at this bending angle. By analyzing the curves of three samples, the bending angle of this batch of materials was determined. for Next, an adaptive batch calibration step is performed to determine the criteria for identifying characteristic peaks. Five more samples from this batch are then taken and the following operations are performed sequentially: the samples are mechanically pre-formed to the calibrated... ( And hold; apply a peak current to the first sample. Duration The initial scan pulse is generated, and during the pulse application process, its data is recorded according to steps A and B in steps two. , Data and real-time calculation Immediately after the curve and pulse ends, the change in DC resistance in the bending region is measured using the four-point method. For the second sample, while keeping other conditions constant, the duration of the scan pulse was increased. to Record its Curve and measurement after annealing Repeat this process, applying the following durations to subsequent samples sequentially: , , The scanning pulses were recorded. curves and .

[0039] Analysis obtained Data sequence ( to ),Discover It increases with increasing pulse energy (time), but reaches its maximum during pulse duration. Time (corresponding) ), The increment slowed down, and in Time (corresponding) When saturation is reached, select the one that produces the maximum. value( The pulse condition corresponding to ) ) and its records The curve serves as a reference; regarding this reference... The curve is analyzed by first applying a five-point smoothing digital filtering algorithm to process high-frequency noise, and then identifying the positive peak with the clearest shape and highest amplitude on the filtered curve, recording the peak height ( ). ) and the time of peak occurrence ( Approximately Based on this peak information, a judgment criterion is established for the operation rules in step two C. One specific method is to set a preset threshold to the calibration peak height. times, that is In subsequent mass production, when the (filtered) data is monitored in real time... The value exceeded for the first time At that time, the controller issues a pulse termination command. Through this calibration procedure, the parameters for this material batch and bending task are determined. Position parameters and The basis for quantitative judgment of characteristic peaks.

[0040] Example 5: In a continuous production run, an online quality monitoring step is used to verify the quality of each energy storage copper connector processed using the method of this invention. When a workpiece completes the self-terminating annealing in step two and enters the mechanical unloading stage in step three, an acoustic emission sensor (frequency response range) installed near the fixture... Signal acquisition begins. For a workpiece whose annealing process meets expectations, the amplitude of the acoustic emission signal generated during the stress relief process is lower than a calibrated reference threshold (e.g., ...). The system determines that the workpiece is qualified; however, the simulated single-pulse power supply output energy is insufficient (e.g., below the rated energy). A sample was processed under fault conditions. Due to insufficient annealing, the residual stress was high. When the sample was subjected to mechanical unloading in step three, the acoustic emission sensor detected an amplitude of [value missing]. The system detects a sudden signal whose amplitude exceeds a reference threshold, and determines that the workpiece is unqualified and issues an alarm. This online quality monitoring step provides a non-destructive, piece-by-piece quality verification method for the metal forming process.

[0041] Example 6: This example further describes the adaptive batch calibration procedure, explaining how to determine the DC resistance variation of different material batches ( The pulse energy corresponding to the maximum value, and how to correlate this energy with the transient dynamic resistance change rate ( The characteristic peak value is used as a basis for judging subsequent production; in a calibration scenario, two T2 copper plate samples from different suppliers were obtained, labeled as batch C and batch D, respectively, and their initial Vickers hardness was respectively and They need to be bent into the same shape. The angle connector and calibration equipment are the same as in Example 3; firstly, the pre-calibrated target positions of batches C and D are obtained through purely mechanical bending calibration. and Subsequently, energy-increasing scanning pulse calibration was performed on samples from batch C. Five samples were selected, all pre-formed to... And maintain, applying peak current sequentially. The durations are respectively The scanning pulses are used to measure the change in DC resistance in the bending region after each pulse. to The measurement results show When the pulse time reaches The growth then slowed down, When the maximum value is reached , and hour A slight decrease (possibly due to other effects from overheating), therefore the optimal pulse time for batch C (corresponding to the maximum) was determined. )for retrieval Pulse corresponding The curve records, after filtering, identify the peak height of the main peak. Set the production threshold for batch C to be [value]. .

[0042] A similar calibration process was performed on samples from batch D (higher hardness), pre-forming to... And maintain, apply peak current The durations are respectively The scanning pulse was measured. to Data analysis revealed exist When the maximum value is reached ,exist hour There was no significant increase; the optimal pulse time for batch D was determined to be... retrieval Pulse corresponding The curve records, after filtering, identify the peak height of the main peak. Set the production threshold for batch D as follows: Through this adaptive batch calibration process, the optimal batch size for achieving maximum stress release was determined for two batches of copper with different physical properties. The pulse energy (time) corresponding to the given energy was determined, and the pulse energy at that energy level was extracted. The characteristic peak information of the curve is converted into specific threshold parameters, which are used for the self-terminating annealing control of step two C on the production line for each batch of parts. This calibration procedure enables the method of the present invention to quantify the physical differences of different incoming materials into specific process control parameters.

[0043] To further verify the necessity of the "self-termination based on physical state" technical feature in the method of this invention from another engineering practice perspective, the following comparative example 1 is added, which simulates an open-loop control strategy based on fixed energy input that a person skilled in the art may adopt.

[0044] Comparative Example 1: This comparative example aims to simulate an engineering attempt to solve batch variation problems by precisely controlling the total energy input, rather than by real-time status feedback. The equipment, materials (T2 copper rods from batches A and B), and all operational procedures except for step two are strictly consistent with the test group using the method of the present invention described in Example 2. The core difference of this comparative example is that the annealing control logic in step two is replaced by an open-loop fixed energy pulse control strategy. The specific execution process is as follows: First, process calibration is performed. Five samples of batch B material with softer physical properties are selected, and current pulses with different total energies are applied to them (achieved by adjusting the product of peak current and duration). After the pulse ended, the residual stress was measured using an X-ray diffractometer. The calibration results showed that when the total injected energy was 150 joules (J), the residual stress of batch B samples could be stably eliminated to below 15 MPa. Therefore, 150 J was set as the fixed process parameter for subsequent batch production. Subsequently, this fixed 150 J energy injection setting was applied to the sample processing of batch A (Vickers hardness 110 HV) and batch B (Vickers hardness 95 HV), respectively. Ten samples were prepared for each batch. After mechanical pre-forming in step one and holding at the pre-calibrated target position, the pulse power system was configured to accurately deliver 150 J of electrical energy to the bending area and then terminate the output. Then, mechanical unloading in step three was performed. The test results are recorded as follows.

[0045] For samples from batch B (consistent with the calibration reference material), the annealing effect was acceptable, with the final measured average residual stress being 13.8 MPa and the average bending springback angle being 0.2 degrees. However, during process monitoring, it was found that due to the lack of real-time insight into the internal state of the material, the fixed energy input posed a slight risk of overheating for some individual samples with lower hardness. For samples from batch A (with higher hardness and different resistivity), the limitations of the fixed energy input were fully exposed. Since the energy threshold required for sufficient recrystallization of batch A material is higher than 150J, the energy injection is significantly insufficient. The final measured average residual stress is as high as 58.6MPa, and the average bending springback angle reaches 1.2 degrees. Its geometric accuracy and stress state are seriously deviating from the technical requirements. When performing mechanical unloading in step three, even a weak acoustic emission signal higher than the background noise can be detected by high-frequency acoustic sensors due to stress concentration release. This indicates that the lattice dislocations inside the material underwent violent movement at the moment of unloading. The experimental results of this comparative example show that even if an open-loop strategy with precise control of total energy input is adopted, it is not possible to effectively cope with the changes in the process window caused by the fluctuation of the physical properties of raw materials. Fixed energy parameters may be applicable to one batch of material, but will cause insufficient or excessive annealing process defects for another material with different physical properties.

[0046] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high-precision stress-free bending method for energy storage copper connectors, characterized in that, Comprising: Step one, mechanical preforming, bending the energy storage copper connector to a pre-calibrated target position by a mechanical actuator; Step two, self-terminating annealing based on physical state, in the state that the mechanical actuator is kept at the target position, starting a pulse power to apply a current pulse to the bending area of the energy storage copper connector, and within the duration of the current pulse application: real-time and synchronously monitoring the transient voltage and transient current flowing through the bending area; based on the monitored transient voltage and transient current, real-time solving the transient dynamic resistance change rate of the bending area; establishing an operating rule for terminating the current pulse, the operating rule is: continuously judging whether the transient dynamic resistance change rate appears a characteristic peak value representing the completion of the material internal lattice recrystallization, and only when the characteristic peak value is monitored, issuing a pulse termination instruction to cut off the energy output of the pulse power; Step three, mechanical unloading, after the pulse termination instruction is executed, controlling the mechanical actuator to return; And, in step two, the real-time calculation of the transient dynamic resistance change rate of the bending area includes: Wherein, is the transient voltage, is the transient current, is the transient dynamic resistance; based on the time series data of the transient dynamic resistance , the transient dynamic resistance change rate is obtained by difference operation or derivation operation; The characteristic peak value in step two is determined by comparing the real-time value of the transient dynamic resistance change rate with a preset threshold value representing the completion of phase change.

2. The high-precision stress-free bending method of the energy storage copper connecting piece according to claim 1, characterized in that, Before step one is executed, an adaptive batch calibration step is further included; The adaptive batch calibration step includes: obtaining one or more sample energy storage copper connectors of the current production batch; applying scanning pulses with increasing energy to the one or more sample energy storage copper connectors; while applying the scanning pulses, using the four-point method to measure the change amount of the direct current resistance of the sample energy storage copper connector bending area before and after annealing; determining the pulse energy corresponding to the maximum change amount of the direct current resistance, and setting the characteristic peak value of the transient dynamic resistance change rate associated with the pulse energy as the judgment basis of the operating rule in step two.

3. The high-precision stress-free bending method of the energy-storing copper connecting piece according to claim 1, characterized in that, During the execution of step three, an online quality monitoring step is further included; the online quality monitoring step includes: passively monitoring the acoustic emission signal generated by the energy storage copper connector during the mechanical unloading in step three through an acoustic emission sensor; establishing a quality judgment rule, the quality judgment rule is: if the amplitude of the acoustic emission signal is lower than a preset reference threshold, it is determined that the residual stress of the energy storage copper connector has been eliminated; if the amplitude of the acoustic emission signal is higher than the preset reference threshold, it is determined that the residual stress of the energy storage copper connector has not been eliminated.

4. The high-precision stress-free bending method of the energy-storing copper connecting piece according to claim 1, characterized in that, The current pulse applied in step two is to generate Joule heat using the resistance of the energy storage copper connector itself, so that the metal lattice temperature of the bending area rises above the recrystallization temperature within milliseconds, and then quickly cools down due to the heat sink effect of the energy storage copper connector body after the current pulse is terminated, thereby completing the transient dynamic annealing, which releases the internal lattice dislocation and residual stress generated by the mechanical preforming in step one.

5. The high-precision stress-free bending method of the energy-storing copper connecting piece according to claim 1, characterized in that, The pre-calibrated target position in step one is a critical position encoder reading representing that the energy storage copper connector has been completely formed but the mechanical force of the mechanical actuator has not been released.

6. The high-precision stress-free bending method of the energy-storing copper connecting piece according to claim 1, characterized in that, The real-time and synchronous monitoring in step two is performed by one or more analog-to-digital converters at a preset sampling frequency.

7. The high-precision stress-free bending method of the energy-storing copper connector according to claim 1, characterized in that, In step two, the application of the current pulse and the monitoring of the transient voltage are realized through electrodes arranged on both sides of the bending area.

8. The high-precision stress-free bending method of the energy-storing copper connecting piece according to claim 1, characterized in that, The mechanical unloading of step three is initiated within a microsecond time window after the execution of the pulse termination command.

Images