Method for measuring and controlling springback of impact hydraulic bulging branch pipe

Abstract

The invention provides a springback measurement and control method for an impact hydraulic bulging branch pipe, which comprises the following steps: S1, positioning and mounting a mold, mounting a pipe in the mold, and setting optimal bulging parameters according to the characteristics of the pipe and historical experimental data; s2, parameter setting is conducted based on XTDIC system measurement software, and three-dimensional deformation of the pipe in the bulging process is monitored; s3, marking to obtain three-dimensional coordinates and coordinate displacement of the key point of the bulging part; displacement data are transmitted to a PLC program in real time, and the springback displacement and the direction of the springback displacement are obtained; and a PID control logic is constructed, and the material supplementing amount of the punch is adjusted. According to the method, the PID control algorithm is utilized, according to the calculated error, the mode of continuously obtaining the actual bulging value, generating the control signal and adjusting the material supplementing amount in the control cycle is adopted, accurate springback control is achieved, the pipe forming quality is ensured, the whole process depends on experiments and experience to optimize PID parameters, and the optimal control effect is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of hydraulic bulging processing equipment, in particular to a method for measuring and controlling the rebound of a branch pipe formed by impact hydraulic bulging. Background Art

[0002] With the rapid development of economy and the continuous improvement of lightweight technology, higher precision of pipes is required, and hydraulic bulging technology has become one of the main technologies to achieve lightweight.

[0003] The principle is to use the coordinated effect of the internal hydraulic pressure of the pipe and the axial thrust of the pipe end to make the pipe plastically deform, thereby producing precision (or semi-precision) near-net-shaped parts with light weight, high strength and good rigidity. This technology not only achieves lightweight components and saves raw materials, but also helps to improve the strength and rigidity of parts through work hardening and integrated forming processes.

[0004] However, due to the influence of the mold during the bulging process, the bulging process of the tube cannot be observed, resulting in a series of problems in the forming process, such as springback. Therefore, it is necessary to measure the springback, obtain the law of forming springback, and suppress the springback.

[0005] In view of this, the existing patent document CN116618510 A discloses a method for controlling the forming quality of a hydraulic bulging specimen, which sets the bulging information and initial bulging information of a standard specimen and uses a composite mold of tempered glass and diamond to obtain a bulging specimen of a standard shape. By measuring the propagation time of light in different media in the mold, the bulging height and axial feed amount are obtained in real time to achieve control of the forming quality.

[0006] Analyzing the above patent documents, it adopts a rule-based control method, that is, by comparing the actual bulging height with the preset standard bulging height to determine whether the bulging hydraulic pressure and axial feed distance need to be adjusted. This is an open-loop or semi-closed-loop control method that relies on pre-set parameters and the operator's experience.

[0007] If there are unexpected changes in material properties or external interference during the bulging process, the operator needs to manually readjust the bulging parameters, which results in slow response and reduced control accuracy. For example, if the elastic modulus of the material changes suddenly, the deviation between the actual bulging height and the standard bulging height exceeds expectations, and the rule-based control method cannot be adjusted in time, resulting in reduced product quality.

[0008] Based on this, there is an urgent need to propose a method to quickly identify this deviation, adopt a closed-loop control method, automatically adjust the punch feed amount according to the real-time feedback of the system, achieve more precise control, and suppress rebound by instantly adjusting the punch feed amount. Even when the material properties change, the technical method can maintain product quality. Summary of the invention

[0009] In view of the shortcomings of the prior art, the present invention aims to provide a method for measuring and controlling the rebound of an impact hydraulic bulging branch pipe to solve the problems raised in the above-mentioned background technology.

[0010] In order to achieve the above object, the present invention is implemented through the following technical scheme: a method for measuring and controlling the rebound of an impact hydraulic bulging branch pipe, comprising the steps of:

[0011] S1. Comprehensive preparation and basic settings

[0012] Positioning and installing the mold, installing the pipe in the mold, and setting the optimal bulging parameters according to the characteristics of the pipe and historical experimental data;

[0013] S2. High-precision measurement system configuration

[0014] Based on the XTDIC system measurement software, the parameters are set and the acquisition mode is adjusted to monitor the three-dimensional deformation of the tube during the bulging process. A CCD camera is placed on the side wall and top of the bulging part of the tube, and the image is adjusted according to the mold to capture every change of the tube during bulging.

[0015] S3. Adaptive control strategy implementation

[0016] Mark the key points of the bulging part of the tube during the bulging process, create displacement intercept points, and calculate the three-dimensional coordinates and coordinate displacement of the key points of the bulging part;

[0017] The displacement data is transmitted to the PLC program in real time to obtain the rebound displacement and its direction;

[0018] Construct PID control logic to adjust the punch feed amount, which performs the following operations:

[0019] According to the characteristics of the pipe and the control requirements, the proportional gain K of the PID controller is pre-set during the pipe bulging process. p , integral gain K i , differential gain K d :

[0020]

[0021] The actual displacement value of the tube bulging is continuously obtained to obtain the control signal, which is applied to the system mainboard. The punch feed amount is adjusted according to the difference between the actual rebound displacement data and the maximum allowable rebound value data:

[0022] If the rebound displacement exceeds the preset maximum rebound value data value, PID control triggers the material replenishment or withdrawal action to effectively control the springback and ensure the forming accuracy. Otherwise, it is considered that the quality of the formed part is good, and a high-quality formed part with uniform wall thickness is directly formed.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. Compared with the existing open-loop or semi-closed-loop control methods, the present invention monitors the displacement changes of the pipe during the hydraulic bulging process through a high-precision XTDIC system and a CCD camera, and transmits the data to the PLC program in real time; secondly, the PLC program automatically sorts and screens the displacement data, calculates the rebound displacement during the bulging process, and compares it with the set maximum allowable rebound value; then, the PID control algorithm is used to automatically adjust the punch feed amount according to the calculated error, that is, the difference between the actual rebound displacement and the maximum allowable rebound value; finally, the actual bulging value is continuously obtained in the control cycle, the control signal is generated, and the feed amount is adjusted, so as to realize the precise control of the rebound and ensure the quality of the pipe forming. The whole process relies on experiments and experience to optimize the PID parameters to achieve the best control effect;

[0025] 2. Compared with the existing equipment such as laser infrared used in the hydraulic bulging process, the XTDIC equipment used in this application can observe the changes in a space. Different from the certain limitations of laser infrared, which can only observe the changes on a certain point, the XTDIC equipment proposed in the present invention can observe the overall changes of the pipe and obtain the dynamic deformation data of the pipe during the whole processing cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The disclosure of the present invention is described with reference to the accompanying drawings. It should be understood that the drawings are only for illustrative purposes and are not intended to limit the scope of protection of the present invention. In the drawings, the same reference numerals are used to refer to the same components. Among them:

[0027] Figure 1 It is a flow chart of a method for measuring and controlling the rebound of a branch pipe during impact hydraulic expansion proposed in one embodiment of the present invention;

[0028] Figure 2 A schematic diagram of a mold structure proposed in an embodiment of the present invention;

[0029] Figure 3It is a structural schematic diagram of a method for measuring and controlling the rebound of a branch pipe during impact hydraulic expansion proposed in one embodiment of the present invention.

[0030] Description of reference numerals:

[0031] 1-punch, 2-tube, 3-mold, 4-CCD camera, 5-computer, 6-motherboard;

[0032] 7-tempered glass, 8-diamond. DETAILED DESCRIPTION

[0033] It is easy to understand that according to the technical solution of the present invention, without changing the essential spirit of the present invention, a person skilled in the art can propose a variety of interchangeable structural modes and implementation modes. Therefore, the following specific implementation modes and drawings are only exemplary descriptions of the technical solution of the present invention, and should not be regarded as the whole of the present invention or as a limitation or restriction to the technical solution of the present invention.

[0034] The present invention is further described in detail below with reference to the accompanying drawings, but is not intended to limit the present invention.

[0035] As an understanding of the technical concept and implementation principle of the present invention, the main purpose of the impact hydraulic expansion branch pipe rebound measurement and control method proposed in the present invention is to solve the problem that the rule-based control method cannot be adjusted in time, thereby causing a decrease in product quality.

[0036] As an embodiment of the present invention, Figure 1 - Figure 2 As shown, a method for measuring and controlling the rebound of a branch pipe during impact hydraulic expansion is proposed, comprising the following steps:

[0037] S1. Comprehensive preparation and basic settings

[0038] The mold 3 is positioned and installed, the pipe 2 is installed in the mold 3, and the basic bulging parameters are set according to the characteristics of the pipe 2 and historical experimental data. Figure 2 As shown, the mold 3 preferably adopts a composite mold structure of tempered glass 7 and diamond 8. The outer surface of the structure is diamond to meet the high strength and light transmittance of the mold, and the inner surface is tempered glass to meet the positioning requirements of XTDIC. In specific implementation, the specific process of setting the best bulging parameters suitable for the forming of the tube 2 includes: installing the tube 2 in the mold, and setting basic bulging parameters according to the characteristics of the tube 2 and historical experimental data; adjusting the basic bulging parameters in the servo circuit system, the basic bulging parameters include axial feed and hydraulic pressure, to meet the forming requirements of the tube 2; determining the best bulging parameters according to the historical experimental and empirical data of the tube 2 to ensure that the tube 2 can be formed normally; and performing an initial functional test to verify the installation accuracy of the mold 3 and the correctness of the servo circuit system setting.

[0039] S2. High-precision measurement system configuration

[0040] It should be noted that, taking the hydraulic bulging test piece forming quality control method proposed in the existing patent document CN116618510 A as an example, the method involves the use of a composite mold of tempered glass and diamond, and the use of light propagation time to determine the distance of the bulging piece. It is understandable that in this process, if the light propagation time measurement inside the mold is subject to any reflection or refraction caused by the ambient light conditions, it will affect the measurement result, resulting in the quality of the formed pipe not meeting the standard, causing material waste or product returns.

[0041] Therefore, in order to solve the above problems and ensure that the three-dimensional deformation measurement of the pipe during the hydraulic bulging process is both accurate and reliable, and to provide high-quality data support for subsequent control and analysis, how to accurately capture and measure the complex three-dimensional deformation of the pipe during the bulging process, ensure the accuracy, consistency and comparability of the measurement data, and how to deal with the impact of environmental changes, such as lighting conditions, on measurement accuracy have become key processing factors in the early stage.

[0042] Based on this, the present invention proposes that after the mold 3 is installed and the basic parameters are set, the parameters are set based on the XTDIC system measurement software and the acquisition mode is adjusted to monitor the three-dimensional deformation of the tube 2 during the bulging process. The specific implementation process includes:

[0043] First, select an XTDIC system suitable for measuring the three-dimensional deformation of the pipe 2. The system must have sufficient measurement range and accuracy to cover all possible deformations of the pipe 2.

[0044] Secondly, according to the expected deformation rate and measurement range of the pipe 2, set the appropriate sampling frequency and resolution to ensure that the sampling frequency can capture the fastest deformation speed and the resolution is high enough to capture the tiny deformation details;

[0045] Thirdly, after setting the sampling parameters, the CCD camera 4 is adjusted, including the focal length, exposure time and white balance, to ensure that the images captured by the CCD camera 4 have sufficient clarity and contrast under different ambient lighting conditions, so that the key feature points in the image can be accurately identified and tracked;

[0046] Next, the image captured by the CCD camera 4 is preprocessed using image processing software, which includes eliminating noise and improving the measurement accuracy of the image, and further improving the image quality by applying filters or edge enhancement techniques;

[0047] In order to ensure the accuracy and repeatability of the measurement data, the XTDIC system and the CCD camera 4 need to be calibrated during the specific implementation, including correcting or compensating the optical components of the system and accurately configuring the internal parameters of the camera, so as to ensure that each measurement can obtain consistent results;

[0048] Finally, to ensure the consistency and comparability of the data, the XTDIC system measurement software is required to be synchronized with the acquisition time of the CCD camera 4. By accurately aligning the timestamps of the two systems, it is ensured that the data collected from different angles and different time points can be accurately compared and merged.

[0049] It is understandable that compared with laser infrared and other equipment, XTDIC equipment can observe changes in a space. Laser infrared has certain limitations and can only observe changes on a certain point, while XTDIC equipment can observe changes in the entire tube. In addition, there are many limitations for laser infrared, ultrasonic and other equipment, and the observation distance and accuracy need to be controlled, but XTDIC does not have these limitations. After setting the parameter accuracy and adjusting the acquisition mode on the XTDIC system measurement software, a CCD camera 4 is placed on the side wall and top of the bulging part of the tube 2, and the image is adjusted for the mold 3. The purpose is to ensure that the camera is accurately aligned with the tube 2, laying the foundation for subsequent automated measurement and real-time control, and capturing every change of the tube 2.

[0050] As an embodiment of the present invention, the sampling frequency of the XTDIC system measurement software in the above steps is set to be adjustable to adapt to the bulging process at different speeds, and the placement position of the CCD camera 4 is adjusted along the bulging part of the tube 2 and around the bulging part of the tube to monitor the bulging of the tube at different angles. The frame rate of the CCD camera 4 is preferably 340FPS, so that the collected data is more precise.

[0051] like Figure 3 As shown, the present invention also includes step S3, adaptive control strategy implementation

[0052] It is implemented after the high-precision measurement system is configured. The specific steps are as follows:

[0053] First, the XTDIC system and CCD camera 4 are used to synchronously monitor the three-dimensional deformation of the tube 2 during the bulging process: mark the key points of the bulging part of the tube 2 during the bulging process, create displacement intercept points, and calculate the three-dimensional coordinates and coordinate displacement of the key points of the bulging part. The specific implementation process includes:

[0054] Start the XTDIC system and CCD camera 4, perform system self-check and initialization, adjust the position and angle of the CCD camera 4, and ensure that the side wall and top of the bulging part of the tube are completely within the shooting range;

[0055] Before the bulging process begins, the CCD camera 4 is used to capture the original state image of the tube 2, and the captured original state image is preprocessed, such as noise reduction or contrast enhancement or edge detection processing, and predefined key points are marked on the preprocessed image using an image processing algorithm;

[0056] Using the XTDIC system, the three-dimensional coordinates of each displacement intercept point are calculated by triangulation: Where, L is the distance between the CCD camera 4 and the pipe 2, and f x , f y Represented as the coordinates of the key points on the original state image, d x ,d y It is represented by the coordinates of the key points after distortion correction, and X, Y, and Z represent the three-dimensional coordinates of the key points;

[0057] For each displacement intercept point, calculate its displacement during the bulging process: ΔX = X t -X0, ΔY=Y t -Y0, ΔZ=Z t -Z0, where X0, Y0, and Z0 represent the initial three-dimensional coordinates before bulging. t , Y t , Z t Expressed as three-dimensional coordinates at a certain moment; record the three-dimensional coordinates and displacement of each displacement intercept point and update them in real time.

[0058] Secondly, the displacement measured by the system is transmitted to the PLC program of the computer 5 in real time through the measurement software, and the obtained displacement data is stacked, sorted and screened, and the displacement data before and after the unloading pressure is screened out to determine the actual displacement change of the pipe 2 during the hydraulic bulging process; because the bulging and measurement are carried out synchronously, the time is consistent, so the displacement data before and after the unloading pressure is extracted, that is, the displacement of the front pipe and the displacement of the pipe after the pressure is unloaded, and the rebound displacement can be obtained by subtracting them, and the positive and negative directions can be determined. The specific process is:

[0059] a. Filter the collected displacement data to eliminate noise and outliers:

[0060]

[0061] Where D(t) represents the original displacement data at time point t, D f (t) represents the displacement data at time point t after Gaussian filtering, u is the mean of the time series, indicating the center point of the displacement data, and σ is the standard deviation of the time series, indicating the dispersion of the displacement data;

[0062] b. Sort the displacement data by timestamp to ensure the time sequence of the data, and select the displacement data before and after the unloading pressure according to the time node of the bulging process, perform differential calculation on the displacement data before and after the unloading pressure, and obtain the rebound displacement ΔD: ΔD=D(t u )-D(t u-σt ), where t u-σt It is expressed as a short period of time before unloading pressure, D(t u ) represents the moment of pressure unloading, i.e. the starting time point of measuring the rebound displacement;

[0063] c. Determine the rebound trend of the material based on the magnitude and direction of the rebound displacement: The rebound direction angle θ is determined based on the change in the displacement vector. Where D X , D Y Respectively expressed as u , t u-σt The X-axis and Y-axis components of the displacement at the time; the direction of the rebound displacement is calculated as: In the formula, is the displacement at time point t, indicating the displacement from the initial position to the current position, It is expressed as the change in displacement vector, i.e., the difference in displacement vector before and after unloading pressure;

[0064] d. The calculated rebound displacement and its direction are used in the PID controller to adjust the punch feed amount.

[0065] Finally, the PID control logic is constructed, the absolute value of the obtained data is taken, and then it is compared with the maximum rebound value set in the control algorithm, and then the feeding amount of punch 1 is adjusted. If the rebound displacement exceeds the preset maximum value, the main board 6 controls the punch 1 to trigger the feeding or withdrawing action, and adjusts the feeding amount little by little in real time to effectively control the springback and ensure the forming accuracy. Otherwise, it is considered that the quality of the formed part is good, and a high-quality formed part with uniform wall thickness is directly formed.

[0066] In one embodiment of the present invention, the specific implementation process of constructing the PID control logic includes:

[0067] When the system has processed the data, it will transfer the data to the set PLC program, automatically sort the data, extract the displacement before and after the unloading pressure, and perform a subtraction process. First, set an allowable error for pipe 2, that is, the maximum value of rebound. According to the characteristics of pipe 2 and control requirements, the proportional gain K of the PID controller is pre-set during the expansion process of pipe 2. p , integral gain K i , differential gain K d :

[0068]

[0069] Where u(t) represents the output of the PID controller and e(t) represents the error, that is, the difference between the set value and the actual value.

[0070] Secondly, the actual displacement value of the tube 2 during expansion is continuously obtained to obtain a control signal, and the control signal is applied to the main board 6 of the system. The measured specific actual value is compared with the maximum value, and the difference between the actual rebound displacement data and the maximum allowable rebound value data is calculated to determine whether operations such as material replenishment and material return are needed. It should be noted that because the control parameters set in the above formula 2 are determined optimal values, when the actual value is substituted, it will be determined whether it is too large. If it is too large, the replenishment amount of the punch 1 is controlled to replenish forward, so as to achieve the size of suppressing the rebound.

[0071] Based on the above technical concept, it can be understood that according to the response of the tube 2 to the bulging, the parameters of the PID controller need to be adjusted to obtain a better control effect, and the parameter adjustment of the PID controller usually requires experiments and experience to determine the optimal value.

[0072] In one embodiment of the present invention, since the normal forming of the tube must be ensured during the bulging process, in order to ensure that the tube 2 will not burst, in addition to controlling the feeding of the punch 1, a program specifically controlling the internal pressure can be designed to control the cavity volume during the bulging process of the tube 2. By changing the cavity volume to reduce the internal pressure, it is ensured that the tube 2 will not burst.

[0073] The technical scope of the present invention is not limited to the contents in the above description. Those skilled in the art can make various deformations and modifications to the above embodiments without departing from the technical idea of ​​the present invention, and these deformations and modifications should all fall within the protection scope of the present invention.

Claims

1. A method for measuring and controlling the rebound of a branch pipe during hydraulic bulging, characterized in that: Includes steps: S1. Comprehensive preparation and basic settings Positioning and installing the mold, installing the pipe in the mold, and setting the optimal bulging parameters according to the characteristics of the pipe and historical experimental data; S2. High-precision measurement system configuration Based on the XTDIC system measurement software, the parameters are set and the acquisition mode is adjusted to monitor the three-dimensional deformation of the tube during the bulging process. A CCD camera is placed on the side wall and top of the bulging part of the tube, and the image is adjusted according to the mold to capture every change of the tube during bulging. S3. Adaptive control strategy implementation Mark the key points of the bulging part of the tube during the bulging process, create displacement intercept points, and calculate the three-dimensional coordinates and coordinate displacement of the key points of the bulging part; The displacement data is transmitted to the PLC program in real time to obtain the rebound displacement and its direction; Construct PID control logic to adjust the punch feed amount, which performs the following operations: According to the characteristics of the pipe and the control requirements, the proportional gain K of the PID controller is pre-set during the pipe bulging process. p , integral gain K i , differential gain K d : The actual displacement value of the tube bulging is continuously obtained to obtain the control signal, which is applied to the system mainboard. The punch feed amount is adjusted according to the difference between the actual rebound displacement data and the maximum allowable rebound value data: If the rebound displacement exceeds the preset maximum rebound value data value, PID control triggers the material replenishment or withdrawal action to effectively control the springback and ensure the forming accuracy. Otherwise, it is considered that the quality of the formed part is good, and a high-quality formed part with uniform wall thickness is directly formed.

2. The method for measuring and controlling the rebound of a branch pipe during impact hydraulic expansion according to claim 1 is characterized in that: In step S3, when the displacement data is transmitted to the PLC program in real time, the specific process of obtaining the rebound displacement and its direction includes: stacking and sorting the obtained displacement data, screening out the displacement data before and after the unloading pressure, so as to determine the actual displacement change of the pipe during the hydraulic bulging process; extracting the displacement data before and after the unloading pressure, subtracting them to obtain the rebound displacement, and judging the positive and negative directions.

3. The method for measuring and controlling the rebound of a branch pipe during impact hydraulic expansion according to claim 1, characterized in that: In step S2, the specific process of parameter setting based on the XTDIC system measurement software includes: selecting an XTDIC system suitable for measuring the three-dimensional deformation of the pipe; setting the appropriate sampling frequency and resolution according to the expected deformation rate and measurement range; adjusting the focal length, exposure time and white balance of the CCD camera to ensure image clarity and contrast; using image processing software to pre-process the image captured by the CCD camera to eliminate noise and improve measurement accuracy; calibrating the XTDIC system and CCD camera to ensure the accuracy and repeatability of the measurement data; and synchronizing the acquisition time of the XTDIC system measurement software and the CCD camera to ensure data consistency and comparability.

4. The method for measuring and controlling the rebound of a branch pipe during impact hydraulic expansion according to claim 3 is characterized in that: The sampling frequency of the XTDIC system measurement software is adjustable to adapt to bulging processes of different speeds, and the placement position of the CCD camera is adjusted along the periphery of the tube bulging part to monitor the tube bulging at different angles. The frame rate of the CCD camera is 340FPS.

5. The method for measuring and controlling the rebound of a branch pipe during impact hydraulic expansion according to claim 1, characterized in that: The mold adopts a composite mold structure of tempered glass and diamond; In step S1, the specific process of setting the best bulging parameters suitable for the forming of the tube includes: installing the tube in the mold and setting the basic bulging parameters according to the characteristics of the tube and historical experimental data; adjusting the basic bulging parameters in the servo circuit system, the basic bulging parameters include axial feed and hydraulic pressure, to meet the forming requirements of the tube; determining the best bulging parameters according to the historical experimental and empirical data of the tube to ensure that the tube can be formed normally; and performing an initial functional test to verify the mold installation accuracy and the correctness of the servo circuit system setting.

6. The method for measuring and controlling the rebound of a branch pipe during impact hydraulic expansion according to claim 1, characterized in that: The specific process of obtaining the three-dimensional coordinates and coordinate displacement of the key points of the bulging part includes: Before bulging begins, a CCD camera is used to capture the original state image of the tube, the captured original state image is preprocessed, and predefined key points are marked on the preprocessed image using an image processing algorithm; Using the XTDIC system, the three-dimensional coordinates of each displacement intercept point are calculated by triangulation: Where L is the distance between the CCD camera and the pipe, f x ,f y Represented as the coordinates of the key points on the original state image, d x ,d y It is represented by the coordinates of the key points after distortion correction, and X, Y, and Z represent the three-dimensional coordinates of the key points; For each displacement intercept point, calculate its displacement during the bulging process: ΔX = X t -X0, ΔY=Y t -Y0, ΔZ=Z t -Z0, where X0, Y0, and Z0 represent the initial three-dimensional coordinates before bulging. t , Y t , Z t Expressed as three-dimensional coordinates at a certain moment; The three-dimensional coordinates and displacement amount of each displacement intercept point are recorded and updated in real time.

7. The method for measuring and controlling the rebound of a branch pipe during impact hydraulic expansion according to claim 2, characterized in that: The specific process of judging the positive and negative directions includes: The collected displacement data is filtered to eliminate noise and outliers: Where D(t) represents the original displacement data at time point t, D f (t) represents the displacement data at time point t after Gaussian filtering, u is the mean of the time series, indicating the center point of the displacement data, and σ is the standard deviation of the time series, indicating the dispersion of the displacement data; The displacement data are sorted in heaps according to the timestamps to ensure the time sequence of the data. The displacement data before and after the unloading pressure are screened out according to the time nodes of the bulging process. The displacement data before and after the unloading pressure are differentially calculated to obtain the rebound displacement ΔD: ΔD = D(t u )-D(t u-σt ), where t u-σt It is expressed as a short period of time before unloading pressure, D(t u ) represents the moment of pressure unloading, i.e. the starting time point of measuring the rebound displacement; According to the magnitude and direction of the rebound displacement, the rebound trend of the material is determined: the rebound direction angle θ is determined according to the change of the displacement vector. Where D x , D Y Respectively expressed as u , t u-σt The X-axis and Y-axis components of the displacement at the time; the direction of the rebound displacement is calculated as: In the formula, is the displacement at time point t, indicating the displacement from the initial position to the current position, It is expressed as the change in displacement vector, i.e., the difference in displacement vector before and after unloading pressure; The calculated springback displacement and its direction are used in the PID controller to adjust the punch feed amount.

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