Method and device for controlling stress relaxation during tensile straightening of aluminium alloy profiles

Abstract

This application relates to the field of metal profile processing technology, and particularly to a method and apparatus for controlling stress relaxation during tensile straightening of aluminum alloy profiles. The method includes: determining the relaxation time constant for the batch to which the test profile belongs based on stress attenuation data collected during a preset holding period on the test profile; determining the target holding time for the profiles to be straightened in the batch based on the relaxation time constant and a preset target relaxation completion rate; after stretching the profiles to be straightened to a preset strain, controlling the stretching machine to maintain the preset strain and continue for the target holding time; and after the target holding time ends, controlling the stretching machine to reduce the stretching force according to a preset unloading speed until the stretching force is zero. The method provided in this application can solve the problem of determining a holding time that balances stress relaxation completion rate and production efficiency for different batches.

Description

Technical Field

[0001] This application belongs to the field of metal profile processing technology, and in particular relates to a method and device for controlling stress relaxation during tensile straightening of aluminum alloy profiles. Background Technology

[0002] After hot extrusion and online quenching, aluminum alloy profiles exhibit complex residual stress fields due to uneven cooling rates and residual extrusion stress, leading to bending or twisting deformation. To eliminate residual stress and ensure profile straightness, tensile straightening is widely used in industry. This involves clamping both ends of the profile with a tensile machine and applying axial tension, causing slight plastic elongation, thereby reducing residual stress and straightening the profile.

[0003] In the tensile straightening process, after stretching the profile to the target strain, it is usually necessary to maintain that strain for a period of time (i.e., hold-load) to allow the internal stress of the profile to fully decay under constant strain conditions before unloading. In existing tensile straightening processes, the hold-load time is usually set using fixed empirical values. However, due to unavoidable fluctuations in process conditions such as extrusion exit temperature, cooling water temperature, and die wear during the extrusion production of aluminum alloy profiles, the material relaxation characteristics of different batches of profiles vary. Even for the same grade of aluminum alloy, the rate of stress decay over time may differ significantly between different batches. When the fixed holding time does not match the actual stress decay rate of the current batch of profiles, the following two situations will occur: If the holding time is too short, the proportion of the stress amplitude that has been relaxed by the end of the holding time to the total relaxation amplitude will be low, and a large amount of residual stress inside the profile will still not be fully released. After unloading, the residual stress will continue to redistribute over time, causing the profile to gradually bend and deform several hours to several days after straightening, i.e., stress rebound phenomenon, resulting in the finished product straightness exceeding the tolerance; if the holding time is too long, although the stress relaxation is more sufficient, it will reduce the production cycle and affect production efficiency. Therefore, how to determine the holding time that can balance the completion of stress relaxation and production efficiency for different batches is a technical problem in the stress relaxation control of aluminum alloy profile tensile straightening. Summary of the Invention

[0004] This application provides a method and apparatus for controlling stress relaxation during tensile straightening of aluminum alloy profiles, which can solve the problem of how to determine the holding time that can balance stress relaxation completion and production efficiency for different batches.

[0005] In a first aspect, embodiments of this application provide a method for controlling stress relaxation during tensile straightening of aluminum alloy profiles, including: Based on the stress decay data collected during the preset load holding process of the test profile, the relaxation time constant of the batch to which the test profile belongs is determined; wherein, the relaxation time constant is used to characterize the rate at which the stress of the aluminum alloy profile of the batch decays with time under constant strain conditions; the stress decay data is a data sequence of real-time stress changes of the test profile with time during the preset load holding process. Based on the relaxation time constant and the preset target relaxation completion rate, the target holding time of the profiles to be straightened in the batch is determined; wherein, the target relaxation completion rate is used to characterize the proportion of the stress amplitude that is expected to be relaxed at the end of the holding time to the total relaxable amplitude; After stretching the profile to be straightened to a preset strain, the stretching machine is controlled to maintain the preset strain and continue for the target holding time. After the target holding time ends, the tensioning machine is controlled to reduce the tension force according to the preset unloading speed until the tension force is 0; wherein, the preset unloading speed is used to indicate the rate at which the tension force decreases during the unloading process.

[0006] The technical solutions described in this application embodiment have at least the following technical effects: The stress relaxation control method for tensile straightening of aluminum alloy profiles provided in this application determines the relaxation time constant of the batch to which the test profile belongs based on stress decay data collected during a preset holding process on the test profile. The relaxation time constant characterizes the rate at which stress decays over time in the batch of aluminum alloy profiles under constant strain conditions. The stress decay data is a data sequence of real-time stress changes over time in the test profile during the preset holding process. Based on the relaxation time constant and the preset target relaxation completion rate, the target holding time for the profiles to be straightened in the batch is determined. The target relaxation completion rate characterizes the proportion of the stress amplitude expected to be relaxed at the end of the holding period to the total relaxable amplitude. After stretching the profile to be straightened to the preset strain, the stretching machine is controlled to maintain the preset strain and continue for the target holding time. After the target holding time ends, the stretching machine is controlled to reduce the stretching force according to a preset unloading speed until the stretching force is 0. The preset unloading speed indicates the rate at which the stretching force decreases during the unloading process. The method provided in this application performs a preset holding load process on the test profile and collects stress decay data. From this data, a quantitative characterization parameter, namely the relaxation time constant, is determined for the rate of stress decay over time under constant strain conditions in the current batch of profiles. Then, based on this relaxation time constant and the preset target relaxation completion degree, the target holding load time for each profile to be straightened is adaptively calculated. Since the determination of the target holding load time is directly related to the actual stress decay rate of the current batch of profiles, when the stress decay rate changes between batches, the target holding load time is adaptively adjusted accordingly. This ensures that the relaxed stress amplitude at the end of the holding load process always reaches the preset proportion of the expected total relaxable amplitude, allowing the internal stress of the profile to be sufficiently and appropriately attenuated before unloading. This effectively suppresses the aging deformation caused by the continued redistribution of residual stress after unloading. Furthermore, since the target holding load time is calculated and determined based on the actual relaxation time constant of the batch of profiles and the preset target relaxation completion degree: for batches with a smaller relaxation time constant (faster stress decay), the target holding load time is correspondingly shorter; for batches with a larger relaxation time constant (slower stress decay), the target holding load time is correspondingly longer. This achieves adaptive matching between the holding time and the actual relaxation characteristics of each batch of profiles, ensuring that each batch of profiles can reach the preset target relaxation completion degree at the end of the holding time, thus ensuring the stress relaxation effect while avoiding unnecessary extension of the holding time.

[0007] In one possible implementation of the first aspect, determining the relaxation time constant of the batch to which the test profile belongs based on stress attenuation data collected during a preset load-bearing process on the test profile includes: Obtain the inherent material parameters of the test profile; wherein, the inherent material parameters are the ultimate relaxation stress of the test profile that tends to stabilize after being subjected to a first time under the preset strain; During the preset load-bearing process, the real-time stress of the test profile at different times is collected at a preset sampling frequency; For each data acquisition moment, the logarithmic transformation value corresponding to the test profile is obtained by taking the logarithm of the difference between the real-time stress and the ultimate relaxation stress. A linear regression was performed on the time values ​​at each acquisition time and the logarithmic transformation values ​​to obtain the regression slope; The relaxation time constant is determined based on the regression slope.

[0008] In one possible implementation of the first aspect, determining the target holding time for the profiles to be straightened in the batch based on the relaxation time constant and a preset target relaxation completion rate includes: Based on the preset target relaxation completion degree, calculate the target value corresponding to the preset target relaxation completion degree; wherein, the target value is 1 minus the target relaxation completion degree; Calculate the natural logarithm of the target value; The target holding time is determined by taking the negative of the product of the relaxation time constant and the natural logarithm.

[0009] In one possible implementation of the first aspect, the method further includes: When the preset identification conditions are met, the preset load holding process is re-executed on the new test profile to update the relaxation time constant of the batch; wherein, the preset identification conditions include at least one of the following: the number of straightened profiles reaches a preset quantity threshold, the ambient temperature change exceeds a preset temperature threshold, the deviation between the load holding end stress of multiple consecutive straightened profiles and the model prediction value exceeds a preset deviation threshold, a manual trigger command is received, or the alloy grade or cross-section of the profile to be straightened changes.

[0010] In one possible implementation of the first aspect, the method further includes: Obtain the preset maximum allowable hold time; If the target holding time is greater than or equal to the maximum allowable holding time, the target holding time is limited to the maximum allowable holding time, and a warning is issued that the material relaxation is too slow.

[0011] In one possible implementation of the first aspect, determining the relaxation time constant of the batch to which the test profile belongs based on stress attenuation data collected during a preset load-bearing process on the test profile includes: Real-time stress is collected within a preset duration after the load holding time begins; The corresponding ultimate relaxation stress is read from the material database based on the aluminum alloy grade of the test profile. Calculate the difference between the real-time stress and the ultimate relaxation stress at each acquisition time, and take the natural logarithm of the difference to obtain a logarithmic sequence; Using the holding time as the independent variable and the logarithmic sequence as the dependent variable, a linear regression was performed to obtain the regression slope; The relaxation time constant is determined based on the regression slope.

[0012] In one possible implementation of the first aspect, the method further includes: During the load-bearing process, the current real-time stress of the profile to be straightened is collected at preset intervals; Based on the relaxation time constant, the ultimate relaxation stress, and the initial stress of the profile to be straightened, predict the model stress at the current moment; If the deviation between the current real-time stress and the model stress exceeds a preset deviation threshold N times consecutively, the current straightening is stopped and the relaxation time constant is redefined.

[0013] In one possible implementation of the first aspect, the method further includes: When the holding time reaches the target holding time, an unloading command is issued to the stretching machine; wherein, the unloading command is used to instruct the stretching machine to reduce the stretching force according to the preset unloading speed until the stretching force is 0.

[0014] Secondly, embodiments of this application provide an aluminum alloy profile tension straightening stress relaxation control system, applied to an aluminum alloy profile tensioning device, for implementing the aluminum alloy profile tension straightening stress relaxation control method described in any one of the first aspects above. The aluminum alloy profile tension straightening stress relaxation control system includes: The testing unit is used to determine the relaxation time constant of the batch to which the test profile belongs based on the stress decay data collected during the preset load holding process of the test profile; wherein, the relaxation time constant is used to characterize the rate at which the stress of the aluminum alloy profile of the batch decays with time under constant strain conditions; the stress decay data is a data sequence of real-time stress changes of the test profile with time during the preset load holding process. The calculation unit is used to determine the target holding time of the profiles to be straightened in the batch based on the relaxation time constant and the preset target relaxation completion degree; wherein, the target relaxation completion degree is used to characterize the proportion of the stress amplitude that is expected to be relaxed at the end of the holding time to the total relaxable amplitude; The adjustment unit is used to control the stretching machine to maintain the preset strain and continue the target holding time after stretching the profile to be straightened to a preset strain. The control unit is used to control the stretching machine to reduce the stretching force to 0 at a preset unloading speed after the target holding time ends; wherein the preset unloading speed is used to indicate the rate at which the stretching force decreases during the unloading process.

[0015] Thirdly, embodiments of this application provide an aluminum alloy profile stretching device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the aluminum alloy profile stretching and straightening stress relaxation control method described in any of the first aspects above.

[0016] It is understood that the beneficial effects of the second and third aspects mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating a method for controlling stress relaxation during tensile straightening of aluminum alloy profiles according to an embodiment of this application. Figure 2 This is a schematic diagram of linear regression in the stress relaxation control method for tensile straightening of aluminum alloy profiles provided in an embodiment of this application; Figure 3 This is a schematic diagram of triggering preset identification conditions in the stress relaxation control method for tensile straightening of aluminum alloy profiles provided in an embodiment of this application; Figure 4 This is a schematic diagram of the control device and sensor provided in one embodiment of this application; Figure 5 This is a schematic diagram of the stress relaxation control system for tensile straightening of aluminum alloy profiles provided in the embodiments of this application; Figure 6 This is a schematic diagram of the control device of the aluminum alloy profile stretching device provided in the embodiments of this application. Detailed Implementation

[0019] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0020] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0021] In related technologies, after aluminum alloy profiles undergo hot extrusion and online quenching, a complex residual stress field exists inside the profile due to factors such as uneven cooling rate of the cross-section and residual extrusion stress, leading to bending or twisting deformation. To eliminate residual stress and ensure the straightness of the profile, the industry widely adopts a tension straightening process, which involves clamping both ends of the profile with a tensioning machine and applying axial tension to cause a small amount of plastic elongation in the profile, thereby reducing residual stress and straightening the profile.

[0022] In the process of tension straightening, how to determine the holding time that can balance the completion of stress relaxation and production efficiency for different batches is a technical problem in the stress relaxation control of aluminum alloy profile tension straightening.

[0023] To address the aforementioned issues, this application provides a method and apparatus for controlling stress relaxation during tensile straightening of aluminum alloy profiles.

[0024] In this method, a preset holding load process is performed on the test profiles, and stress decay data is collected. From this data, a quantitative characterization parameter, namely the relaxation time constant, is determined for the rate of stress decay over time under constant strain conditions in the current batch of profiles. Then, based on this relaxation time constant and the preset target relaxation completion rate, the target holding load time for each profile to be straightened is adaptively calculated. Since the determination of the target holding load time is directly related to the actual stress decay rate of the current batch of profiles, the target holding load time is adaptively adjusted when the stress decay rate changes between batches. This ensures that the relaxed stress amplitude at the end of the holding load process always reaches the preset proportion of the total relaxable amplitude, allowing the internal stress of the profile to be sufficiently and appropriately attenuated before unloading. This effectively suppresses the aging deformation caused by the continued redistribution of residual stress after unloading. Furthermore, since the target holding load time is calculated based on the actual relaxation time constant of the batch of profiles and the preset target relaxation completion rate: for batches with a smaller relaxation time constant (faster stress decay), the target holding load time is correspondingly shorter; for batches with a larger relaxation time constant (slower stress decay), the target holding load time is correspondingly longer. This achieves adaptive matching between the holding time and the actual relaxation characteristics of each batch of profiles, ensuring that each batch of profiles can reach the preset target relaxation completion degree at the end of the holding time, thus ensuring the stress relaxation effect while avoiding unnecessary extension of the holding time.

[0025] The stress relaxation control method for aluminum alloy profile tension straightening provided in this application embodiment can be applied to an aluminum alloy profile tensioning device. In this case, the aluminum alloy profile tensioning device is the main body for executing the stress relaxation control method for aluminum alloy profile tension straightening provided in this application embodiment. This application embodiment does not impose any restrictions on the specific type of aluminum alloy profile tensioning device.

[0026] For example, an aluminum alloy profile stretching device may include a stretching machine and a control device, wherein the stretching machine and the control device are electrically connected. The stretching machine includes a left chuck and a right chuck for clamping both ends of the aluminum alloy profile and applying axial tensile force. The control device can control the stretching, holding, and unloading processes of the stretching machine according to the aluminum alloy profile stretching and straightening stress relaxation control method of this application, such as... Figure 4 .

[0027] For example, the control device can be a microcontroller, tablet computer, laptop computer, ultra-mobile personal computer (UMPC), netbook, desktop computer, computing device, or computer, laptop computer, handheld communication device, handheld computing device, etc. connected to a wireless modem.

[0028] For ease of understanding, the technical concepts involved in this application are explained below.

[0029] Stress relaxation refers to the physical phenomenon that the internal stress of a material gradually decreases over time under constant strain conditions. During the load-holding stage of tensile straightening, the profile maintains a constant elongation, but its internal stress gradually decreases over time. This decrease follows an exponential decay law, i.e., σt = σ∞ + (σ0 - σ∞) × exp(-t ÷ τ), where σt is the stress at time t, σ∞ is the ultimate relaxation stress, σ0 is the initial stress at the start of the load-holding stage, and τ is the relaxation time constant.

[0030] The relaxation time constant τ is a physical parameter characterizing the rate at which stress decays over time under constant strain conditions. A smaller τ indicates faster stress relaxation, while a larger τ indicates slower stress relaxation. τ depends on factors such as the alloy composition, heat treatment state, extrusion process conditions (e.g., cooling rate, exit temperature), and holding strain level. The τ values ​​vary significantly between different grades of aluminum alloys, and even within the same grade, variations may exist between different batches due to fluctuations in the extrusion process.

[0031] Ultimate relaxation stress σ∞ refers to the limit value at which the stress of a material stabilizes under a given constant strain condition after a sufficiently long period of loading. It varies with alloy composition and heat treatment state and can be predetermined through offline calibration. Ultimate relaxation stress can be obtained in advance by conducting stress relaxation tests on the aluminum alloy grade of the test profile and stored in a material database. During the formal straightening process, the corresponding ultimate relaxation stress σ∞ value is retrieved from the material database based on the aluminum alloy grade of the test profile. For example, commonly used aluminum alloy grades in the factory (such as 6063, 6061, 6082, 7075, etc.) are sampled. On a laboratory universal testing machine, a standard stress relaxation test is conducted at the same strain level as production (e.g., 0.5% constant strain), with a holding time of at least 60 seconds, until the stress decays to a stable level (attenuation rate less than 0.1 MPa / s). The stable stress value is recorded as σ∞, and the σ∞ values ​​for different grades are entered into the material database, indexed by the alloy grade.

[0032] Relaxation Completion Rate (RCD): This refers to the proportion of relaxation completed to the total amount of relaxation that can be completed during the load holding phase, i.e., RCD = (σ0 - σt) / (σ0 - σ∞). The RCD value ranges from 0 to 1, where RCD = 0 indicates that the load holding has just begun (t = 0), and RCD = 1 indicates that the relaxation has been completely completed (t → ∞).

[0033] Stress rebound: refers to the phenomenon that after a profile is stretched, straightened and unloaded, insufficient holding time leads to inadequate relaxation of internal stress, and residual stress continues to redistribute in the following hours to days, causing the profile to gradually bend and deform.

[0034] To better understand the stress relaxation control method for tensile straightening of aluminum alloy profiles provided in this application embodiment, the specific implementation process of the stress relaxation control method for tensile straightening of aluminum alloy profiles provided in this application embodiment will be described by way of example below.

[0035] Figure 1 This paper presents a schematic flowchart of a stress relaxation control method for tensile straightening of aluminum alloy profiles according to an embodiment of this application. The stress relaxation control method for tensile straightening of aluminum alloy profiles includes: S100, based on the stress decay data collected during the preset load holding process of the test profile, determines the relaxation time constant of the batch to which the test profile belongs. The relaxation time constant characterizes the rate at which the stress of the aluminum alloy profile in the batch decays over time under constant strain conditions. The stress decay data is a sequence of real-time stress changes over time in the test profile during the preset load holding process.

[0036] It is understood that the test profile can be an aluminum alloy profile used to identify the relaxation time constant; for example, it could be a test sample specifically reserved from the production line. The alloy grade, cross-sectional dimensions, and heat treatment state of the test profile should be the same as or similar to those of the officially produced profile. Stress decay data refers to the data sequence of stress changes over time within the test profile during the preset load holding process. This data sequence reflects the stress relaxation behavior characteristics of the material, and the stress decay data can be collected in real time by a force sensor installed on the tensile testing machine. The relaxation time constant τ is used to characterize the rate at which the stress of the current batch of aluminum alloy profiles decays over time under constant strain conditions. The preset load holding process can be the process from the start of the load holding time to the end of the load holding duration. The real-time stress can be the actual stress value of the test profile at various moments during the load holding process.

[0037] For example, real-time stress can be obtained by dividing the tensile force collected by the tension sensor by the cross-sectional area of ​​the profile. The time-stress data pair (ti, σi) is stored in the PLC's data buffer to form stress decay data. For instance, the tensile force value F(ti) is continuously collected at a sampling frequency of 10 Hz (i.e., a sampling period of 100 milliseconds) and converted into real-time stress σ(ti) = F(ti) ÷ A, where A is the cross-sectional area of ​​the profile, which can be obtained from the drawings.

[0038] For example, for each acquisition time, the logarithmic transformation value is obtained by taking the logarithm of the difference between the real-time stress and the ultimate relaxation stress. For instance, the logarithmic transformation model σt = σ∞ + (σ0 - σ∞) × exp(-t ÷ τ) yields ln(σt - σ∞) = ln(σ0 - σ∞) - (1 ÷ τ) × t by taking the logarithm of both sides, thus transforming the exponential relationship into a linear relationship, facilitating subsequent linear regression solutions. The logarithmic transformation value yi = ln(σ(ti) - σ∞) represents the natural logarithm of the difference between the real-time stress and the ultimate relaxation stress at the i-th acquisition time.

[0039] For example, the σ∞ value corresponding to the profile grade is read from the material database, and then yi=ln(σi-σ∞) is calculated for each sampling point.

[0040] Specifically, the preset load holding process can be as follows: after stretching the test profile to a preset strain, the tensile machine is controlled to maintain this preset strain, and real-time stress data is continuously collected at a preset sampling frequency (e.g., 10 Hz). The load holding duration is not less than three times the estimated relaxation time constant (e.g., not less than 20 seconds). The preset strain can be determined according to the aluminum alloy grade and cross-sectional dimensions. For example, for 6063 and 6061 series alloys, the preset strain is 0.3%-1.0%. That is, the preset load holding process is a test process performed online on the production line before the formal straightening load holding is applied to the test profile.

[0041] In some embodiments, a lower limit protection can be set for σi-σ∞, and the data point is removed when σi-σ∞ is less than a preset minimum value (such as 1 MPa).

[0042] Specifically, after obtaining the corresponding logarithmic transformation value, a linear regression is performed on all N data points collected during the load maintenance phase, with the load maintenance time as the independent variable X and the logarithmic transformation value yi = ln(σi - σ∞) as the dependent variable Y. The linear regression model is Y = a + b × X, where a = ln(σ0 - σ∞) is the intercept, and b = -1 ÷ τ is the slope. The regression slope b reflects the rate of change of the logarithmic transformation value over time. Finally, the negative reciprocal of the regression slope b is taken as the relaxation time constant τ.

[0043] For example, the calculation process of linear regression is as follows: First, calculate the sum of independent variables Sx = Σti, the sum of dependent variables Sy = Σyi, the sum of squares of independent variables Sxx = Σ(ti²), and the sum of the products of independent and dependent variables Sxy = Σ(ti×yi). Then, calculate the regression slope b = (N×Sxy - Sx×Sy) ÷ (N×Sxx - Sx×Sx) and the intercept a = (Sy - b×Sx) ÷ N.

[0044] In one possible implementation, please refer to Figure 2S100, Based on the stress attenuation data collected during the preset load holding process of the test profile, determine the relaxation time constant of the batch to which the test profile belongs, including: S110, Obtain the inherent material parameters of the test profile. The inherent material parameters are the ultimate relaxation stress at which the test profile stabilizes after being subjected to a preset strain and held under load for an initial time.

[0045] It is understandable that the inherent parameters of a material can be parameters determined by the material's own properties under specific strain conditions. Specifically, the inherent parameter of a material is the ultimate relaxation stress σ∞ that tends to stabilize after the test profile has been subjected to a sufficiently long load under a preset strain.

[0046] S120, during the preset load holding process, collects the real-time stress of the test profile at different times according to the preset sampling frequency.

[0047] For example, during the preset load holding process, the real-time stress can be obtained by dividing the tensile force collected by the tension sensor by the cross-sectional area of ​​the profile, and the time-stress data pair (ti, σi) is stored in the data buffer of the PLC to form stress decay data.

[0048] S130: For each acquisition time, the logarithmic transformation value corresponding to the test profile is obtained by taking the logarithm of the difference between the real-time stress and the ultimate relaxation stress.

[0049] For example, for each acquisition time, the difference between the real-time stress and the ultimate relaxation stress is calculated. Then, the logarithm of the difference is taken to obtain the corresponding logarithmic transformation value. For example, the logarithmic transformation model σt=σ∞+(σ0-σ∞)×exp(-t÷τ) can be transformed into ln(σt-σ∞)=ln(σ0-σ∞)-(1÷τ)×t by taking the logarithm of both sides, thus converting the exponential relationship into a linear relationship, which facilitates subsequent linear regression solutions. The logarithmic transformation value yi=ln(σ(ti)-σ∞) represents the natural logarithm of the difference between the real-time stress and the ultimate relaxation stress at the i-th acquisition time.

[0050] S140, perform linear regression on the time values ​​and logarithmic transformation values ​​at each acquisition time to obtain the regression slope.

[0051] It is understandable that linear regression is used to find the linear relationship between two variables: the retention time and the logarithmic transformation value.

[0052] For example, using the holding time as the independent variable X and the logarithmic transformation value yi = ln(σi - σ∞) as the dependent variable Y, a linear regression is performed on all N data points collected during the holding period. The linear regression model is Y = a + b × X, where a = ln(σ0 - σ∞) is the intercept, and b = -1 ÷ τ is the slope. The regression slope b is used to reflect the rate of change of the logarithmic transformation value over time.

[0053] S150, based on the regression slope, determines the relaxation time constant.

[0054] For example, the negative reciprocal of the regression slope b is taken as the relaxation time constant τ.

[0055] S200 determines the target holding time for the profiles to be straightened in a batch based on the relaxation time constant and the preset target relaxation completion rate. The target relaxation completion rate characterizes the proportion of stress amplitude expected to be relaxed at the end of the holding time to the total relaxable amplitude.

[0056] It can be understood that the target relaxation completion rate can be the proportion of the stress amplitude expected to be relaxed at the end of the load hold to the total relaxable amplitude, and its value ranges from 0 to 1. For example, the target relaxation completion rate R = (σ0 - σt) ÷ (σ0 - σ∞), where σt is the stress at time t. When t = 0, σt = σ0, and the target relaxation completion rate R = 0; when t = ∞, σt = σ∞, and the target relaxation completion rate R = 1. The target load hold time can be the length of the load hold time required to achieve the target relaxation completion rate, and the unit is seconds.

[0057] For example, the target relaxation completion rate R can be read from the process parameter configuration pre-stored in the PLC. The target relaxation completion rate R ranges from 0.7 to 0.95. Subtracting the target relaxation completion rate from 1 yields the target value. The target value reflects the proportion of stress amplitude that has not yet been relaxed to the total relaxable amplitude. For example, when R = 0.85, the target value = 1 - 0.85 = 0.15, indicating that 15% of the relaxable stress amplitude has not yet been relaxed. When R = 0.90, the target value = 0.10, indicating that 10% of the relaxable stress amplitude has not yet been relaxed. According to σt = σ∞ + (σ0 - σ∞) × exp(-t ÷ τ), when σt reaches the target stress σ1, we can obtain exp(-t / τ) = 1 - R = target value. Taking the natural logarithm of both sides of the equation, we get -t / τ = ln(target value), thus transforming the exponential relationship into a linear relationship, which facilitates the solution of the target holding time.

[0058] For example, the relaxation time constant τ calculated in step S100 and the natural logarithm of the target value ln(1-R) ​​calculated in step S200 are substituted into the formula for calculating the target load holding time: t target time = -τ × ln(1-R) ​​to obtain the target load holding time.

[0059] Specifically, when σt reaches the target stress σ1 (i.e., σt = σ1), σ1 = σ∞ + (σ0 - σ∞) × exp(-t ÷ τ). Then, a phase shift separates the stress term from the exponential term: σ1 - σ∞ = (σ0 - σ∞) × exp(-t ÷ τ). Dividing both sides by the total relaxation amplitude, we obtain the residual stress ratio: (σ1 - σ∞) ÷ (σ0 - σ∞) = exp(-t ÷ τ). The previously calculated 1 - R = 1 - (σ0 - σ1) ÷ (σ0 - σ∞) = (σ1 - σ∞) ÷ (σ0 - σ∞) is equal to exp(-t ÷ τ) = (σ1 - σ∞) ÷ (σ0 - σ∞), thus we can obtain exp(-t / τ) = 1 - R = the target value.

[0060] It should be noted that the calculation of the target holding time t is independent of the initial stress σ0. That is, regardless of how the initial stress σ0 of each profile fluctuates (due to differences in incoming materials), the target holding time t depends only on the relaxation time constant τ and the target relaxation completion degree R, and is unrelated to σ0. This characteristic makes the method of this application have good robustness, without the need to readjust the calculation method of the holding time for each profile.

[0061] For example, when τ=6.54 and R=0.85, the target load holding time t = -6.54×ln(1-0.85) = -6.54×ln(0.15) = -6.54×(-1.8971) = 12.41 seconds. When τ=8.2 seconds and R=0.80, the target load holding time t = -8.2×ln(1-0.80) = -8.2×ln(0.20) = -8.2×(-1.6094) = 13.20 seconds. When τ=5.0 seconds and R=0.90, the target load holding time t = -5.0×ln(1-0.90) = -5.0×ln(0.10) = -5.0×(-2.3026) = 11.51 seconds.

[0062] In one possible implementation, S200, based on the relaxation time constant and a preset target relaxation completion rate, determines the target holding time for the profiles to be straightened in the batch, including: S210, Calculate the target value corresponding to the preset target relaxation completion degree based on the preset target relaxation completion degree. The target value is 1 minus the target relaxation completion degree.

[0063] It can be understood that the target relaxation completion rate can be the proportion of the stress amplitude that is expected to be relaxed by the end of the load hold period to the total relaxable amplitude, and its value ranges from 0 to 1, for example, it can be 0.80, 0.90, etc. The target value is used to reflect the proportion of the stress amplitude that has not yet been relaxed to the total relaxable amplitude.

[0064] For example, subtract the target relaxation completion from 1 to obtain the target value.

[0065] S220, calculates the natural logarithm of the target value.

[0066] For example, according to σt=σ∞+(σ0-σ∞)×exp(-t÷τ), when σt reaches the target stress σ1, we can obtain exp(-t / τ)=1-R=target value. Taking the natural logarithm of both sides of the equation, we can obtain -t / τ=ln(target value), thus transforming the exponential relationship into a linear relationship.

[0067] S230, the negative of the product of the relaxation time constant and the natural logarithm is determined as the target hold-up time.

[0068] It can be understood that the relaxation time constant τ calculated in step S100 and the natural logarithm of the target value ln(1-R) ​​calculated in step S200 are substituted into the formula for calculating the target load holding time: t target time = -τ × ln(1-R) ​​to obtain the target load holding time.

[0069] S300, after stretching the profile to be straightened to the preset strain, controls the stretching machine to maintain the preset strain and continue for the target holding time.

[0070] It is understandable that controlling the stretching machine to maintain the preset strain can be achieved by switching the stretching machine to the position holding mode after the preset strain has been reached, keeping the clamp position stationary, and thus maintaining a constant strain in the profile. The continuous target holding time can be achieved by waiting in the position holding mode until the holding time reaches the target holding time determined in step S200.

[0071] S400 controls the tensioning machine to reduce the tensile force to 0 according to a preset unloading speed after the target holding time ends. The preset unloading speed indicates the rate at which the tensile force decreases during the unloading process.

[0072] It is understood that unloading can be achieved by slowly reducing the tensile force to zero after the load holding period, allowing the profile to return to its free state. The preset unloading speed can be adjusted according to the profile's cross-sectional stiffness and length. In one specific embodiment, for 6063-T5 aluminum alloy profiles, the preset unloading speed is 20 MPa / s.

[0073] With this setup, this application achieves the matching of the holding time with the actual relaxation characteristics of each batch of profiles by online identification of the relaxation time constant and adaptive calculation of the target holding time based on the constant, thus balancing the stress relaxation completion rate and production efficiency.

[0074] In one possible implementation, please refer to Figure 3 The stress relaxation control method for tensile straightening of aluminum alloy profiles also includes: When the preset identification conditions are met, the preset load holding process is re-executed on the new test profiles to update the relaxation time constant of the batch. The preset identification conditions include at least one of the following: the number of straightened profiles reaches a preset quantity threshold, the ambient temperature change exceeds a preset temperature threshold, the deviation between the load holding end stress of multiple consecutive straightened profiles and the model prediction exceeds a preset deviation threshold, a manual trigger command is received, or the alloy grade or cross-section of the profile to be straightened changes.

[0075] It is understandable that the relaxation time constant τ of the material may drift due to the slow changes in extrusion processes and cooling conditions over time. Therefore, the pre-identification step can be periodically re-executed to update τ. The preset identification conditions can be the judgment conditions that trigger the recalculation of the relaxation time constant, including at least one of the following: the number of straightened profiles reaches a preset quantity threshold; the ambient temperature changes beyond a preset temperature threshold; the deviation between the end-of-load stress of multiple consecutive straightened profiles and the model prediction exceeds a preset deviation threshold; a manual trigger command is received; or the alloy grade or cross-section of the profile to be straightened changes.

[0076] For example, the default value for the preset quantity threshold is 100 pieces, meaning that re-identification is automatically triggered after every 100 profiles are produced. The default value for the preset temperature threshold is ±5℃, meaning that re-identification is triggered when the ambient temperature changes by more than 5℃. The default value for the preset deviation threshold is 8%, meaning that re-identification is triggered when the deviation between the load-bearing end stress of three consecutive profiles and the model prediction exceeds 8%.

[0077] In one possible implementation, the stress relaxation control method for tensile straightening of aluminum alloy profiles also includes: S500, obtain the preset maximum allowable load time.

[0078] It is understandable that the maximum allowable holding time can be a pre-set process constraint parameter, used to prevent the holding time from being too long due to material abnormalities (such as an excessively large τ value), which would affect the production cycle.

[0079] For example, the maximum allowable holding time can be preset according to the actual situation, such as 30s, 40s, 1min, etc.

[0080] S600, when the target holding time is greater than or equal to the maximum permissible holding time, limits the target holding time to the maximum permissible holding time and issues a warning that the material relaxation is too slow.

[0081] It is understandable that when the calculated target holding time is greater than or equal to the maximum allowable holding time, it indicates that the current material relaxation rate is too slow and the expected relaxation completion cannot be achieved within the allowable holding time. In this case, the target holding time should be limited to the maximum allowable holding time, and a prompt message should be sent to the operator through the HMI. The operator can then decide whether to continue production or adjust the process parameters based on the prompt.

[0082] For example, the maximum permissible holding time t can be 30 seconds. Assuming a batch of profiles has τ=15 seconds and R=0.85, then the target holding time t = -15 × ln(0.15) = 15 × 1.8971 = 28.46 seconds. This value is less than the maximum permissible holding time of 30 seconds, therefore the target holding time is set to 28.46 seconds. Assuming another batch of profiles has τ=20 seconds and R=0.85, then the target holding time t = -20 × ln(0.15) = 20 × 1.8971 = 37.94 seconds. This value is greater than the maximum permissible holding time of 30 seconds, therefore the target holding time is limited to 30 seconds, and a warning is issued on the HMI indicating that material relaxation is too slow and the holding time has reached its limit.

[0083] In one possible implementation, S100, based on stress attenuation data collected during a preset load-bearing process on the test profile, determines the relaxation time constant of the batch to which the test profile belongs, including: S601 collects real-time stress within a preset duration after the load holding time begins.

[0084] For example, real-time stress can be obtained by dividing the tensile force collected by the tension sensor by the cross-sectional area of ​​the profile, and the time-stress data pair (ti, σi) is stored in the data buffer of the PLC to form stress decay data.

[0085] S602, reads the corresponding ultimate relaxation stress from the material database based on the aluminum alloy grade of the test profile.

[0086] For example, the σ∞ value corresponding to the profile grade is read from the material database.

[0087] S603, calculate the difference between the real-time stress and the ultimate relaxation stress at each acquisition time, and take the natural logarithm of the difference to obtain the logarithmic sequence.

[0088] For example, for each acquisition time, the difference between the real-time stress and the ultimate relaxation stress is calculated. Then, the logarithm of the difference is taken to obtain the corresponding logarithmic transformation value. The logarithmic transformation values ​​corresponding to each acquisition time are combined into a logarithmic sequence.

[0089] S604 uses the holding time as the independent variable and the logarithmic sequence as the dependent variable to perform linear regression and obtain the regression slope.

[0090] For example, using the holding time as the independent variable X and the logarithmic transformation value yi = ln(σi - σ∞) as the dependent variable Y, a linear regression is performed on all N data points collected during the holding period. The linear regression model is Y = a + b × X, where a = ln(σ0 - σ∞) is the intercept, and b = -1 ÷ τ is the slope. The regression slope b is used to reflect the rate of change of the logarithmic transformation value over time.

[0091] S605, based on the regression slope, determines the relaxation time constant.

[0092] Specifically, the negative reciprocal of the regression slope b is used as the relaxation time constant τ.

[0093] In some embodiments, after determining the relaxation time constant, the method further includes: calculating the goodness-of-fit R² for quality assessment. Specifically, first, the predicted value ŷi = a + b × ti is calculated, then the total sum of squares = Σ(yi - ȳ)² (where ȳ is the average value of yi), and the residual sum of squares = Σ(yi - ŷi)², so R² = 1 - residual sum of squares ÷ total sum of squares. If R² is less than 0.95, it indicates poor fitting quality, possibly due to material abnormalities or data problems, and an alarm should be triggered and an investigation should be conducted. If R² is greater than or equal to 0.95, it indicates good fitting quality, and the calculated τ is reliable. The calculated τ is stored in the current batch parameter register as the control basis for subsequent formal straightening.

[0094] In one possible implementation, the stress relaxation control method for tensile straightening of aluminum alloy profiles also includes: S700 collects the current real-time stress of the profile to be straightened at preset intervals during the load-bearing process.

[0095] For example, during the load holding process, the current real-time stress σ of the profile to be straightened is collected at preset intervals (e.g., 1 second).

[0096] S800 predicts the model stress at the current moment based on the relaxation time constant, the ultimate relaxation stress, and the initial stress of the profile to be straightened.

[0097] For example, based on the relaxation time constant τ, the ultimate relaxation stress σ∞, and the initial stress σ0 of the profile to be straightened, the model stress at the current moment is predicted as σ(t) = σ∞ + (σ0 - σ∞) × exp(-t ÷ τ).

[0098] S900: If the deviation between the current real-time stress and the model stress exceeds the preset deviation threshold N times consecutively, the current straightening is stopped and the relaxation time constant is redefined.

[0099] For example, the current real-time stress σ is compared with the model stress σ(t), and the deviation is calculated as: |current real-time stress σ - model stress σ(t)| ÷ σ(t) × 100%. If this deviation exceeds the preset deviation threshold (e.g., 10%) for N consecutive times (N can be 5, 6, 7, etc., e.g., N=5 times), it indicates that the model parameters are no longer applicable (there may be a sudden change in the incoming material). At this time, the current straightening should be stopped and an alarm should be triggered, and the relaxation time constant should be re-determined.

[0100] In one possible implementation, the stress relaxation control method for tensile straightening of aluminum alloy profiles also includes: When the holding time reaches the target holding time, an unloading command is issued to the stretching machine. The unloading command instructs the stretching machine to reduce the tensile force at a preset unloading speed until the tensile force is 0.

[0101] For example, when the holding time reaches the target holding time, an unloading command can be issued to the stretching machine to control the stretching machine to reduce the stretching force according to the preset unloading speed until the stretching force is 0.

[0102] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0103] Corresponding to the stress relaxation control method for aluminum alloy profile tensile straightening described in the above embodiments, this application also provides a stress relaxation control system for aluminum alloy profile tensile straightening, wherein each unit of the system can realize each step of the stress relaxation control method for aluminum alloy profile tensile straightening. Figure 5 The diagram shows a structural block diagram of the stress relaxation control system for tensile straightening of aluminum alloy profiles provided in an embodiment of this application. For ease of explanation, only the parts related to the embodiments of this application are shown.

[0104] Reference Figure 5 The stress relaxation control system for tensile straightening of aluminum alloy profiles includes: The testing unit is used to determine the relaxation time constant of the batch to which the test profile belongs, based on the stress decay data collected during a preset load holding process. The relaxation time constant characterizes the rate at which the stress of the aluminum alloy profile in a batch decays over time under constant strain conditions. The stress decay data is a sequence of real-time stress changes over time in the test profile during the preset load holding process.

[0105] The calculation unit is used to determine the target holding time for the profiles to be straightened in a batch, based on the relaxation time constant and the preset target relaxation completion degree. The target relaxation completion degree characterizes the proportion of stress amplitude expected to be relaxed at the end of the holding period relative to the total relaxable amplitude.

[0106] The adjustment unit is used to control the stretching machine to maintain the preset strain and continue the target holding time after stretching the profile to be straightened to the preset strain.

[0107] The control unit is used to control the stretching machine to reduce the tensile force to zero according to a preset unloading speed after the target holding time has ended. The preset unloading speed indicates the rate at which the tensile force decreases during the unloading process.

[0108] It should be noted that the information interaction and execution process between the above systems / units are based on the same concept as the method embodiments of this application. For details on their specific functions and technical effects, please refer to the method embodiments section, and they will not be repeated here.

[0109] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units is merely an example. In practical applications, the above functions can be assigned to different functional units as needed, that is, the internal structure of the system can be divided into different functional units to complete all or part of the functions described above. The functional units in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0110] This application also provides an aluminum alloy profile stretching device. Figure 6 This is a schematic diagram of the control device for an aluminum alloy profile stretching device provided in one embodiment of this application. Figure 6 As shown, the control device 6 in this embodiment includes: at least one processor 60 ( Figure 6 Only one is shown in the image), at least one memory 61 ( Figure 6 (Only one is shown in the image) and a computer program 62 stored in the at least one memory 61 and executable on the at least one processor 60. When the processor 60 executes the computer program 62, it causes the control device 6 to perform the steps in any of the above embodiments of the aluminum alloy profile tension straightening stress relaxation control method, or causes the control device 6 to perform the functions of each unit in the above system embodiments.

[0111] For example, the computer program 62 may be divided into one or more units, which are stored in the memory 61 and executed by the processor 60 to complete this application. The one or more units may be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of the computer program 62 in the control device 6.

[0112] The aluminum alloy profile stretching device may include a stretching machine and a control device 6, wherein the stretching machine and the control device 6 are electrically connected. The stretching machine includes a left chuck and a right chuck for clamping both ends of the aluminum alloy profile and applying axial tensile force. The control device 6 can control the stretching, holding, and unloading processes of the stretching machine according to the aluminum alloy profile stretching and straightening stress relaxation control method of this application. The control device 6 may include, but is not limited to, a processor 60 and a memory 61. Those skilled in the art will understand that... Figure 6 This is merely an example of control device 6 and does not constitute a limitation on control device 6. It may include more or fewer components than shown, or combine certain components, or different components, such as input / output devices, network access devices, buses, etc.

[0113] The processor 60 can be a Central Processing Unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor.

[0114] In some embodiments, the memory 61 may be an internal storage unit of the control device 6, such as a hard disk or memory of the control device 6. In other embodiments, the memory 61 may be an external storage device of the control device 6, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc., equipped on the control device 6. Furthermore, the memory 61 may include both internal storage units and external storage devices of the control device 6. The memory 61 is used to store operating systems, applications, bootloaders, data, and other programs, such as the program code of computer programs. The memory 61 can also be used to temporarily store data that has been output or will be output.

[0115] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps in any of the above method embodiments.

[0116] This application provides a computer program product that, when run on an aluminum alloy profile stretching device, enables the aluminum alloy profile stretching device to perform the steps described in any of the above method embodiments.

[0117] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments of this application can be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include at least: any entity or device capable of carrying the computer program code to the aluminum alloy profile stretching device, a recording medium, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, such as a USB flash drive, a portable hard drive, a magnetic disk, or an optical disk.

[0118] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0119] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0120] In the embodiments provided in this application, it should be understood that the disclosed aluminum alloy profile stretching device / aluminum alloy profile stretching straightening stress relaxation control system and aluminum alloy profile stretching straightening stress relaxation control method can be implemented in other ways. For example, the embodiments of the aluminum alloy profile stretching device / aluminum alloy profile stretching straightening stress relaxation control system described above are merely illustrative. For instance, the division of units is merely a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the displayed or discussed mutual coupling or direct coupling or communication connection may be through some interfaces, devices, or units, and may be electrical, mechanical, or other forms.

[0121] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0122] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for controlling stress relaxation during tensile straightening of aluminum alloy profiles, characterized in that, The method includes: Based on the stress decay data collected during the preset load holding process of the test profile, the relaxation time constant of the batch to which the test profile belongs is determined; wherein, the relaxation time constant is used to characterize the rate at which the stress of the aluminum alloy profile of the batch decays with time under constant strain conditions; the stress decay data is a data sequence of real-time stress changes of the test profile with time during the preset load holding process. Based on the relaxation time constant and the preset target relaxation completion rate, the target holding time of the profiles to be straightened in the batch is determined; wherein, the target relaxation completion rate is used to characterize the proportion of the stress amplitude that is expected to be relaxed at the end of the holding time to the total relaxable amplitude; After stretching the profile to be straightened to a preset strain, the stretching machine is controlled to maintain the preset strain and continue for the target holding time. After the target holding time ends, the tensioning machine is controlled to reduce the tension force according to the preset unloading speed until the tension force is 0; wherein, the preset unloading speed is used to indicate the rate at which the tension force decreases during the unloading process.

2. The method for controlling stress relaxation during tensile straightening of aluminum alloy profiles as described in claim 1, characterized in that, The determination of the relaxation time constant of the batch to which the test profile belongs, based on stress attenuation data collected during a preset load-bearing process, includes: Obtain the inherent material parameters of the test profile; wherein, the inherent material parameters are the ultimate relaxation stress of the test profile that tends to stabilize after being subjected to a first time under the preset strain; During the preset load-bearing process, the real-time stress of the test profile at different times is collected at a preset sampling frequency; For each data acquisition moment, the logarithmic transformation value corresponding to the test profile is obtained by taking the logarithm of the difference between the real-time stress and the ultimate relaxation stress. A linear regression was performed on the time values ​​at each acquisition time and the logarithmic transformation values ​​to obtain the regression slope; The relaxation time constant is determined based on the regression slope.

3. The method for controlling stress relaxation during tensile straightening of aluminum alloy profiles as described in claim 1, characterized in that, The step of determining the target holding time for the profiles to be straightened in the batch based on the relaxation time constant and the preset target relaxation completion degree includes: Based on the preset target relaxation completion degree, calculate the target value corresponding to the preset target relaxation completion degree; wherein, the target value is 1 minus the target relaxation completion degree; Calculate the natural logarithm of the target value; The target holding time is determined by taking the negative of the product of the relaxation time constant and the natural logarithm.

4. The method for controlling stress relaxation during tensile straightening of aluminum alloy profiles as described in claim 2, characterized in that, The method further includes: When the preset identification conditions are met, the preset load holding process is re-executed on the new test profile to update the relaxation time constant of the batch; wherein, the preset identification conditions include at least one of the following: the number of straightened profiles reaches a preset quantity threshold, the ambient temperature change exceeds a preset temperature threshold, the deviation between the load holding end stress of multiple consecutive straightened profiles and the model prediction value exceeds a preset deviation threshold, a manual trigger command is received, or the alloy grade or cross-section of the profile to be straightened changes.

5. The method for controlling stress relaxation during tensile straightening of aluminum alloy profiles as described in claim 1, characterized in that, The method further includes: Obtain the preset maximum allowable hold time; If the target holding time is greater than or equal to the maximum allowable holding time, the target holding time is limited to the maximum allowable holding time, and a warning is issued that the material relaxation is too slow.

6. The method for controlling stress relaxation during tensile straightening of aluminum alloy profiles as described in claim 2, characterized in that, The determination of the relaxation time constant of the batch to which the test profile belongs, based on stress attenuation data collected during a preset load-bearing process, includes: Real-time stress is collected within a preset duration after the load holding time begins; The corresponding ultimate relaxation stress is read from the material database based on the aluminum alloy grade of the test profile. Calculate the difference between the real-time stress and the ultimate relaxation stress at each acquisition time, and take the natural logarithm of the difference to obtain a logarithmic sequence; Using the holding time as the independent variable and the logarithmic sequence as the dependent variable, a linear regression was performed to obtain the regression slope; The relaxation time constant is determined based on the regression slope.

7. The method for controlling stress relaxation during tensile straightening of aluminum alloy profiles as described in claim 2, characterized in that, The method further includes: During the load-bearing process, the current real-time stress of the profile to be straightened is collected at preset intervals; Based on the relaxation time constant, the ultimate relaxation stress, and the initial stress of the profile to be straightened, predict the model stress at the current moment; If the deviation between the current real-time stress and the model stress exceeds a preset deviation threshold N times consecutively, the current straightening is stopped and the relaxation time constant is redefined.

8. The method for controlling stress relaxation during tensile straightening of aluminum alloy profiles as described in claim 1, characterized in that, The method further includes: When the holding time reaches the target holding time, an unloading command is issued to the stretching machine; wherein, the unloading command is used to instruct the stretching machine to reduce the stretching force according to the preset unloading speed until the stretching force is 0.

9. A stress relaxation control system for tensile straightening of aluminum alloy profiles, characterized in that, An aluminum alloy profile stretching device is used to implement the aluminum alloy profile stretching and straightening stress relaxation control method as described in any one of claims 1 to 8, wherein the aluminum alloy profile stretching and straightening stress relaxation control system comprises: The testing unit is used to determine the relaxation time constant of the batch to which the test profile belongs based on the stress decay data collected during the preset load holding process of the test profile; wherein, the relaxation time constant is used to characterize the rate at which the stress of the aluminum alloy profile of the batch decays with time under constant strain conditions; the stress decay data is a data sequence of real-time stress changes of the test profile with time during the preset load holding process. The calculation unit is used to determine the target holding time of the profiles to be straightened in the batch based on the relaxation time constant and the preset target relaxation completion degree; wherein, the target relaxation completion degree is used to characterize the proportion of the stress amplitude that is expected to be relaxed at the end of the holding time to the total relaxable amplitude; The adjustment unit is used to control the stretching machine to maintain the preset strain and continue the target holding time after stretching the profile to be straightened to a preset strain. The control unit is used to control the stretching machine to reduce the stretching force to 0 at a preset unloading speed after the target holding time ends; wherein the preset unloading speed is used to indicate the rate at which the stretching force decreases during the unloading process.

10. A stretching device for aluminum alloy profiles, characterized in that, The method includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the method as claimed in any one of claims 1 to 8.

Images