A method for preventing cracking in metal sheet processing and forming based on micro-area flexible control

Abstract

This invention discloses a crack prevention method for metal plate processing and forming based on micro-area flexible control, specifically relating to the removal of local deformation in metal plate straightening. The method includes a straightening roller and an end flexible roller assembly configured with a straightening device. The end flexible roller assembly includes a coating layer for zoned hardness adjustment and a driving unit. A first stress sensing unit, a second displacement sensing unit, and a third temperature sensing unit are arranged in the contact area between the straightening roller and the metal plate. A geometric boundary model is established based on the three sensing units. Zero-load stress values ​​and initial morphological data are recorded under no-external-load conditions to complete the initial calibration of the device and the model. By identifying the target range of the outer edge region in real time based on the geometric boundary model constructed using multiple sensors during the straightening unloading stroke, and performing segmented unloading timing contact stiffness adjustment within this range, the formation path of continuous tensile stress at the outer edge is blocked to prevent delayed crack initiation.

Description

Technical Field

[0001] This invention relates to the field of local deformation removal technology in metal plate straightening, and more specifically, to a method for preventing cracking in metal plate processing and forming based on micro-area flexible control. Background Technology

[0002] In scenarios where rollers are used to remove localized deformation, such as straightening localized dents in appliance housings or vehicle body panels, existing processes typically utilize small-diameter straightening rollers to load and unload along a circumferential or spiral path within the dented area.

[0003] Due to slight differences in the thickness of the sheet material, and the rigid constraints imposed on local areas by the ribs, folds, and other structures, coupled with the influence of differences in friction and traction, a significant plastic strain gradient is formed between the central area and the outer edge during the straightening process.

[0004] At the moment of unloading, the rebound of the central area and the outer edge is asynchronous. The outer edge will generate an inward folding effect in advance and pull the surrounding material, thus forming a continuous high tensile stress area along the contour of the straightening area. This high tensile stress area is difficult to be directly detected on the surface, but the stress concentration inside and the subtle surface undulations will, under the vibration during transportation or the thermal cycle of coating baking, evolve into the initiation position of delayed cracks.

[0005] Currently, the measures we understand, such as extending the holding time, increasing the roller pressure, overall heating, or secondary straightening, can only change the average stress level or improve the appearance smoothness, but cannot effectively cut off this stress transmission path. At the same time, the fixed roller exit trajectory and constant contact stiffness will cause the energy during the unloading process to further accumulate at the outer edge, thereby strengthening the continuous distribution of this high tensile stress area.

[0006] Therefore, the core problem of the existing technology is that the interaction with the boundary constraints during the straightening and unloading process will inevitably generate a continuous residual tensile stress band at the outer edge of the straightening area. The existing process is difficult to effectively eliminate this hidden danger while ensuring the forming quality, which makes thin sheet parts prone to delayed cracking. Summary of the Invention

[0007] To overcome the aforementioned deficiencies of the prior art, embodiments of the present invention provide a method for preventing cracking in metal plate processing and forming based on micro-area flexible control. By identifying the target range of the outer edge region in real time based on a geometric boundary model constructed using multiple sensors during the straightening and unloading stroke, and performing contact stiffness adjustment of the segmented unloading sequence within this range, the method blocks the formation path of continuous tensile stress at the outer edge to prevent delayed crack generation, thereby solving the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for preventing cracking in metal plate processing and forming based on micro-area flexible control, comprising:

[0009] S1: Configure the straightening roller and end flexible roller assembly of the straightening equipment. The end flexible roller assembly includes a coating layer for zonal hardness adjustment and a drive unit. Arrange a first stress sensing unit, a second displacement sensing unit and a third temperature sensing unit in the contact area between the straightening roller and the metal plate. Establish a geometric boundary model based on the three sensing units. Record the zero-load stress value and initial morphology data under no external load condition to complete the initial calibration of the equipment and the model.

[0010] S2: When the metal plate enters the unloading stroke during the straightening process, the first stress sensing unit and the second displacement sensing unit simultaneously collect stress data and displacement data of the outer edge region and the center region, and calculate the springback phase difference and strain gradient of the outer edge region and the center region based on the collected data, and determine the target range of the outer edge region by combining the calculated values ​​of the geometric boundary model.

[0011] S3: Based on the material parameters and geometric boundary model of the processed metal plate, stress calculation is performed on the data of S2 to generate a distribution map of the crack risk intensity in the circumferential direction of the outer edge region. The location of the crack risk intensity value exceeding the preset threshold and the corresponding time window are located in the distribution map. The target peak value and allowable upper limit of peak reduction to be achieved during the unloading process are output.

[0012] S4: Generate unloading timing control curve based on the distribution map of the outer edge region and the springback phase difference; drive the end flexible roller assembly's coating layer to perform segmented unloading timing adjustment within the target range of the outer edge region; synchronously perform contact stiffness adjustment within the circumferential range of the target range of the outer edge region, decomposing the continuously distributed tensile stress into multiple independent segmented tensile stress zones.

[0013] In a preferred embodiment, in S4, the segmented unloading timing adjustment includes: reducing the contact stiffness of the outer edge region in a first time window to absorb the rebound energy of the region, increasing the contact stiffness of the outer edge region in a second time window to limit the deformation of the region from being transmitted to the surrounding region, and restoring the contact stiffness of the outer edge region in a third time window to maintain the forming size of the region.

[0014] In a preferred embodiment, S5 is further included: after unloading, the residual stress value and residual strain distribution of the outer edge region are measured by the first stress sensing unit and the second displacement sensing unit; when the residual stress value is not lower than the preset allowable upper limit, S2 to S4 are repeated for the same metal plate in the preset final stroke until the residual stress value is lower than the preset allowable upper limit; the final unloading timing control curve and contact stiffness adjustment parameters are bound and stored with the geometric boundary model.

[0015] In a preferred embodiment, S1 includes:

[0016] S1.1: Configure the straightening roller and the end flexible roller assembly of the straightening equipment. The end flexible roller assembly includes a coating layer for zoned hardness adjustment and a drive unit. The end flexible roller assembly is arranged at the exit position of the metal plate processing path. The end flexible roller assembly and the straightening roller are coaxially positioned.

[0017] S1.2: A first stress sensing unit, a second displacement sensing unit, and a third temperature sensing unit are arranged along the processing direction and the width direction in the contact area between the straightening roller and the metal plate to form a three-dimensional sensing array, and a mapping relationship between the sensing unit and the coordinate system of the contact area is established so that each data acquisition point corresponds to a unique coordinate position on the surface of the metal plate.

[0018] S1.3: Based on the measurement results of the first stress sensing unit, the normal stress values ​​at each coordinate position of the contact area are obtained and denoted as follows: Based on the measurement results of the second displacement sensing unit, the normal displacement values ​​at each coordinate position in the contact area are obtained and denoted as follows: Based on the measurement results of the third temperature sensing unit, the temperature values ​​at each coordinate position of the contact area are obtained and denoted as follows: ;

[0019] S1.4: Obtained based on S1.3 , and Construct the shape function of the geometric boundary model:

[0020] ;

[0021] in, The x-coordinate represents the direction of metal sheet processing. Represents the ordinate along the width of the metal plate; This represents the first partial derivative of the displacement value in the machining direction; This represents the first-order partial derivative of the displacement value in the width direction; The elastic modulus represents the elastic modulus of the metal sheet material, which is used to characterize the stiffness of the material within its elastic range; The coefficient of thermal expansion represents the thermal expansion coefficient of the metal sheet material, which describes the linear dimensional change of the material with temperature; it is calculated as a morphology function. Used to reflect the deformation effect caused by the curvature change and temperature-stress coupling in the contact area;

[0022] S1.5: Under no external load, collect the stress values ​​at each coordinate position in S1.4. Displacement value With temperature value And calculate the zero-load topographic reference function:

[0023] ;

[0024] Among them, stress value This represents the normal stress value when there is no external load; displacement value. This represents the normal displacement value without external load; temperature value. This represents the temperature value when there is no external load. and These represent the first-order partial derivatives of the displacement value without external load in the machining direction and the width direction, respectively; Used to represent the curvature and temperature-stress coupling reference morphology of the contact area under no external load;

[0025] S1.6: The result obtained in S1.4 Obtained with S1.5 Performing difference operations, we obtain the transformation matrix of the geometric boundary model:

[0026] ;

[0027] in, This indicates the difference in morphology between the contact area under the current processing state and the state without external load; The positive and negative distribution of the mean difference is used to characterize the increasing or decreasing trend of curvature change and temperature-stress coupling effect at each coordinate position; Stored in the geometric boundary model database.

[0028] In a preferred embodiment, S2 includes:

[0029] S2.1: During the unloading stroke of the metal plate straightening process, the first stress sensing unit collects the normal stress values ​​at each coordinate position of the outer edge region and the central region. The second displacement sensing unit collects the normal displacement values ​​at each coordinate position of the outer edge region and the central region. ,in Represents a time variable;

[0030] S2.2: Normal displacement value obtained based on S2.1 Calculate the rebound displacement curves in the outer and central regions respectively. and And calculate using the phase difference:

[0031] ;

[0032] in, This indicates the rebound phase difference between the outer edge region and the central region; and These represent the start and end times of the unloading process, respectively. The curve represents the springback displacement of the outer edge region; The curve representing the rebound displacement of the central region; Inverse cosine function;

[0033] S2.3: Based on S2.1 Calculate the strain gradient distribution in the inner and outer edge regions of the unloading stroke:

[0034] ;

[0035] in, Indicates the end time of the unloading process. At coordinate position The strain gradient; This represents the first partial derivative of the displacement value at that position in the machining direction at the end of unloading; This represents the first partial derivative of the displacement value at that position in the width direction at the end of unloading;

[0036] S2.4: The rebound phase difference obtained in S2.2 The strain gradient obtained with S2.3 As input parameters and generated by S1.6 Perform joint calculations to construct an unloading risk response function:

[0037] ;

[0038] in, Indicates coordinate position The overall risk value of stress concentration is generated during the unloading process; This indicates the effect of the rebound phase difference on the sinusoidal amplitude of the risk; This represents the absolute change in curvature at that location in relation to the temperature-stress coupling effect;

[0039] S2.5: Establish circumferential coordinates along the outer edge region. Boundary curve points for parameters ,exist Obtain the outer normal vector Based on the thickness of the metal plate Define the circumferential position as the radial integration range. Corresponding radial band ; Calculate the risk distribution function:

[0040] ;

[0041] in, Indicates circumferential position Average risk value; Boundary curve points Indicates the circumferential position of the outer edge boundary. Spatial coordinates; external normal vector This represents the external normal vector of the coordinate point; Indicates the radial distance along the outer normal; This represents the comprehensive risk value calculated in S2.4. ,in In the outer edge curve coordinate system, by and At a given point, the coordinates are mapped to a two-dimensional position in the global coordinate system of the metal plate. And use this position as the input for risk value calculation; With risk threshold Compare and extract the satisfied The continuous circumferential interval is used as the initial selection result for the target range of the outer edge region;

[0042] S2.6: Combine the preliminary selection results obtained in S2.5 with... Perform an intersection operation on the local extremum coordinate sets and delete the values ​​in the set. The coordinates of the mid-curvature change amplitude are lower than the preset trigger threshold to obtain the final target range of the outer edge region, and the coordinates of the final target range and its corresponding time window are stored.

[0043] In a preferred embodiment, S3 includes:

[0044] S3.1: Elastic modulus based on metal plate material Coefficient of thermal expansion ,as well as , and At the end time of the uninstallation process Calculate the temperature-corrected equivalent stress at each coordinate position:

[0045] ;

[0046] in, Indicates coordinate position Equivalent stress; This represents the normal stress value at the moment unloading ends; This indicates the temperature value at the moment unloading ended;

[0047] S3.2: The result obtained from S3.1 With S1.6 Combined, calculate the crack risk intensity field at the end of the unloading process:

[0048] ;

[0049] in, Indicates coordinate position The crack risk intensity value; This represents the absolute change in curvature at that coordinate position in relation to the temperature-stress coupling effect.

[0050] Will Coordinate position in the global coordinate system The distribution on the surface is arranged in a two-dimensional matrix to generate a distribution map of crack risk intensity;

[0051] S3.3: Establish circumferential coordinates in the outer region and in each circumferential coordinate Define radial band For the distribution map Perform radial integral averaging within this band:

[0052] ;

[0053] in, Indicates circumferential position The average crack risk intensity; Represents the circumferential coordinate system in the outer edge curve coordinate system. and radial distance The determined points are mapped to Then, the crack risk intensity value is calculated for that point;

[0054] S3.4: Will With the preset risk intensity threshold Compare and locate to satisfy The continuous circumferential interval, and combined with S2.2 calculations Determine the unloading time window corresponding to the risk interval; these circumferential intervals, time windows, and their corresponding... The value, serving as the target peak value information for peak clipping control, is output to the unloading timing control curve generation module, while simultaneously recording the allowed peak values. As subsequent control constraints.

[0055] The technical effects and advantages of this invention are as follows:

[0056] 1. By introducing dynamic target range identification based on geometric boundary model, springback phase difference and strain gradient during the unloading stroke, and implementing segmented unloading timing adjustment within this range, the formation path of continuous high tensile stress at the outer edge is effectively cut off, fundamentally reducing the probability of delayed crack occurrence.

[0057] 2. By constructing an integrated geometric boundary model of stress, displacement and temperature through multiple sensing units, the curvature change and thermo-mechanical coupling state can be reflected in real time in the full-plane coordinate system, ensuring that the unloading control is based on the real physical state rather than empirical parameters, thereby improving the pertinence and accuracy of the control.

[0058] 3. By combining spatial risk distribution with temporal unloading characteristics using a crack risk intensity distribution map, it is possible to accurately locate the circumferential range of the outer target area and match the corresponding unloading time window, thereby achieving dual synchronous control of space and time.

[0059] 4. By using a three-time-window contact stiffness adjustment strategy, the rebound energy is dissipated, deformation transmission is blocked, and forming size is locked at different unloading stages, so that the unloading process is continuously controlled at the three levels of energy, path, and size, ensuring both crack prevention and forming quality.

[0060] 5. Introduce a closed-loop detection and parameter reinjection mechanism for residual stress and residual strain, so that the unloading timing control curve and contact stiffness adjustment parameters are continuously optimized in batch processing, forming a reusable control parameter library, improving process stability and cross-batch consistency. Attached Figure Description

[0061] Figure 1 This is a flowchart of the method steps of the present invention. Detailed Implementation

[0062] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0063] Refer to the instruction manual appendix Figure 1 An embodiment of the present invention provides a method for preventing cracking in metal plate processing and forming based on micro-area flexible control, comprising:

[0064] S1: Configure the straightening roller and end flexible roller assembly of the straightening equipment. The end flexible roller assembly includes a coating layer for zonal hardness adjustment and a drive unit. Arrange a first stress sensing unit, a second displacement sensing unit and a third temperature sensing unit in the contact area between the straightening roller and the metal plate. Establish a geometric boundary model based on the three sensing units. Record the zero-load stress value and initial morphology data under no external load condition to complete the initial calibration of the equipment and the model.

[0065] S2: When the metal plate enters the unloading stroke during the straightening process, the first stress sensing unit and the second displacement sensing unit simultaneously collect stress data and displacement data of the outer edge region and the center region, and calculate the springback phase difference and strain gradient of the outer edge region and the center region based on the collected data, and determine the target range of the outer edge region by combining the calculated values ​​of the geometric boundary model.

[0066] S3: Based on the material parameters and geometric boundary model of the processed metal plate, stress calculation is performed on the data of S2 to generate a distribution map of the crack risk intensity in the circumferential direction of the outer edge region. The location of the crack risk intensity value exceeding the preset threshold and the corresponding time window are located in the distribution map. The target peak value and allowable upper limit of peak reduction to be achieved during the unloading process are output.

[0067] S4: Generate unloading timing control curve based on the distribution map of the outer edge region and the springback phase difference; drive the end flexible roller assembly's covering layer to perform segmented unloading timing adjustment within the target range of the outer edge region; synchronously perform contact stiffness adjustment within the circumferential range of the target range of the outer edge region, decomposing the continuously distributed tensile stress into multiple independent segmented tensile stress zones.

[0068] For S4, it needs to be explained that when generating the unloading timing control curve, firstly, the risk value of each circumferential position in the crack risk intensity distribution diagram of the outer edge region is correlated with its corresponding springback phase difference, and the start time and duration of contact stiffness adjustment during unloading are determined based on the springback phase difference. Subsequently, at each circumferential position within the target range of the outer edge region, the contact stiffness is reduced, increased, and restored in sequence according to the magnitude of the risk value, so that the springback energy is dispersed in time and segmented in space. Finally, the contact stiffness adjustment actions at each circumferential position within the target range of the outer edge region are synchronized as a whole, so that the originally continuously distributed tensile stress is decomposed into several independent and non-transmittable segmented tensile stress zones, thereby reducing the risk of crack propagation along the outer edge.

[0069] In S4, the segmented unloading timing adjustment includes: reducing the contact stiffness of the outer edge region in a first time window to absorb the springback energy of the region, increasing the contact stiffness of the outer edge region in a second time window to limit the deformation of the region from being transmitted to the surrounding region, and restoring the contact stiffness of the outer edge region in a third time window to maintain the forming size of the region.

[0070] It should be noted that the execution and division of the three time windows of S4 are as follows: In the first time window, the drive unit reduces the hardness of the coating layer within the target range of the outer edge region to the preset unloading start stiffness in order to reduce the contact stiffness; the start condition is that the time point corresponding to the rebound phase difference reaches the unloading start time and the absolute value of the displacement velocity exceeds the set threshold; the end condition is that the absolute value of the displacement velocity drops below the threshold or the residual energy indicator drops below the allowable upper limit, so that the rebound energy is absorbed within this window and does not accumulate in the circumferential direction.

[0071] In the second time window, the driving unit increases the hardness of the coating layer in the same outer edge region to the preset limit stiffness to improve the contact stiffness. The start condition is that the first time window ends and the strain gradient increment still exceeds the set threshold. The purpose of the execution is to block the deformation from being transmitted laterally to the surrounding area in the middle of the unloading. The end condition is that the strain gradient increment falls back to within the threshold or the dynamic change of the geometric boundary model enters the stable range at the circumferential position.

[0072] In the third time window, the drive unit restores the hardness of the coating layer to the nominal process stiffness in order to restore the contact stiffness. The start condition is the end of the second time window and the residual stress indication and residual strain distribution simultaneously meet the upper limit of the allowable range. The purpose of the execution is to stabilize the forming size at the end of the unloading process and avoid subsequent springback. The end condition is the arrival of the nominal process time or the dimensional deviation converges to the allowable range.

[0073] The mechanism of the above three-segment division is as follows: the first time window is used to dissipate instantaneous rebound energy, the second time window is used to cut off the deformation transmission path, and the third time window is used to lock the final geometric dimensions; the three are jointly controlled by event triggering and time constraints to ensure that the unloading process in the outer edge region is continuously controlled in terms of energy, path and size.

[0074] It also includes S5: After unloading, the residual stress value and residual strain distribution of the outer edge region are measured by the first stress sensing unit and the second displacement sensing unit; when the residual stress value is not lower than the preset allowable upper limit, S2 to S4 are repeated for the same metal plate in the preset final stroke until the residual stress value is lower than the preset allowable upper limit; the final unloading timing control curve and contact stiffness adjustment parameters are bound and stored with the geometric boundary model.

[0075] It should be noted that in the formula structure involved in this scheme, dimensionless terms can be used as proportional or structural adjustment factors. When combined with quantities with units, they only play a role in numerical scaling and do not introduce new physical dimensions. Therefore, they will not change or confuse the overall unit system. This combination of "dimensionless terms and terms with units" can be understood as a composite structural expression commonly used in mathematical physics modeling. It conforms to the principle of dimensional consistency and has a clear physical interpretation basis.

[0076] Secondly, in the formula structure of this scheme, if multiple variables with different physical units are involved, including but not limited to time, mass or energy variables, their joint appearance is to express the collaborative modeling relationship of multiple physical mechanisms. Each variable can form a unified structure through function mapping, ratio combination or normalization adjustment, with clear units and clear meaning. The overall expression conforms to the principle of dimensional consistency and the conventional formula of engineering modeling.

[0077] In this solution, constants, weights, adjustment factors, threshold parameters, proportional coefficients, etc., are all adjustable control parameters for different application environments. Their values ​​depend on the target equipment configuration, data input characteristics, and performance optimization goals. During the implementation phase, they are set to converge within a reasonable range through model verification, performance constraints, or engineering calibration. Although these parameters do not have a unique preset value, they have clear adjustment logic and calculation paths. They belong to the deterministic setting process in engineering implementation. The purpose of this setting is to ensure that the solution is both universally adaptable and reproducible and operable, without affecting its technical clarity and feasibility.

[0078] S1 includes:

[0079] S1.1: Configure the straightening roller and the end flexible roller assembly of the straightening equipment. The end flexible roller assembly includes a coating layer for zoned hardness adjustment and a drive unit. The end flexible roller assembly is arranged at the exit position of the metal plate processing path. The end flexible roller assembly and the straightening roller are coaxially positioned to ensure that the straightening roller and the end flexible roller assembly form a continuous contact line during the processing.

[0080] S1.2: The first stress sensing unit, the second displacement sensing unit, and the third temperature sensing unit are uniformly arranged in the contact area between the straightening roller and the metal plate along the processing direction and the width direction to form a three-dimensional sensing array, and a mapping relationship between the sensing unit and the coordinate system of the contact area is established so that each data acquisition point corresponds to a unique coordinate position on the surface of the metal plate.

[0081] S1.3: Based on the measurement results of the first stress sensing unit, the normal stress values ​​at each coordinate position of the contact area are obtained and denoted as follows: Based on the measurement results of the second displacement sensing unit, the normal displacement values ​​at each coordinate position in the contact area are obtained and denoted as follows: Based on the measurement results of the third temperature sensing unit, the temperature values ​​at each coordinate position of the contact area are obtained and denoted as follows: ;

[0082] S1.4: Obtained based on S1.3 , and Construct the shape function of the geometric boundary model:

[0083] ;

[0084] in, The x-coordinate represents the direction of metal sheet processing. Represents the ordinate along the width of the metal plate; This represents the first partial derivative of the displacement value in the machining direction; This represents the first-order partial derivative of the displacement value in the width direction; The elastic modulus represents the elastic modulus of the metal sheet material, which is used to characterize the stiffness of the material within its elastic range; The coefficient of thermal expansion represents the thermal expansion coefficient of the metal sheet material, which describes the linear dimensional change of the material with temperature; it is calculated as a morphology function. Used to reflect the deformation effect caused by the curvature change and temperature-stress coupling in the contact area;

[0085] S1.5: Under no external load, collect the stress values ​​at each coordinate position in S1.4. Displacement value With temperature value And calculate the zero-load topographic reference function:

[0086] ;

[0087] Among them, stress value This represents the normal stress value when there is no external load; displacement value. This represents the normal displacement value without external load; temperature value. This represents the temperature value when there is no external load. and These represent the first-order partial derivatives of the displacement value without external load in the machining direction and the width direction, respectively; Used to represent the curvature and temperature-stress coupling reference morphology of the contact area under no external load;

[0088] S1.6: The result obtained in S1.4 Obtained with S1.5 Performing difference operations, we obtain the transformation matrix of the geometric boundary model:

[0089] ;

[0090] in, This indicates the difference in morphology between the contact area under the current processing state and the state without external load; The positive and negative distribution of the mean difference is used to characterize the increasing or decreasing trend of curvature change and temperature-stress coupling effect at each coordinate position; The data is stored in the geometric boundary model database as input parameters for subsequent calculation of rebound phase difference and generation of unloading timing control curves.

[0091] S2 includes:

[0092] S2.1: During the unloading stroke of the metal plate straightening process, the first stress sensing unit collects the normal stress values ​​at each coordinate position of the outer edge region and the central region. The second displacement sensing unit collects the normal displacement values ​​at each coordinate position of the outer edge region and the central region. ,in Represents a time variable;

[0093] S2.2: Normal displacement value obtained based on S2.1 Calculate the rebound displacement curves in the outer and central regions respectively. and And calculate using the phase difference:

[0094] ;

[0095] in, This indicates the rebound phase difference between the outer edge region and the central region; and These represent the start and end times of the unloading process, respectively. The curve represents the springback displacement of the outer edge region; The curve representing the rebound displacement of the central region; The inverse cosine function is used to convert cosine values ​​into corresponding phase angles. The significance of the inverse cosine function in the formula is that the definition of the rebound phase difference is based on the cosine similarity between the displacement curves of the outer edge region and the central region. By converting it into the actual angle difference through inverse cosine, it can directly reflect the degree of asynchronous time between the two rebound processes.

[0096] S2.3: Based on S2.1 Calculate the strain gradient distribution in the inner and outer edge regions of the unloading stroke:

[0097] ;

[0098] in, Indicates the end time of the unloading process. At coordinate position The strain gradient; This represents the first partial derivative of the displacement value at that position in the machining direction at the end of unloading; This represents the first partial derivative of the displacement value at that position in the width direction at the end of unloading;

[0099] S2.4: The rebound phase difference obtained in S2.2 The strain gradient obtained with S2.3 As input parameters and generated by S1.6 Perform joint calculations to construct an unloading risk response function:

[0100] ;

[0101] in, Indicates coordinate position The overall risk value of stress concentration is generated during the unloading process; This indicates the effect of the rebound phase difference on the sinusoidal amplitude of the risk; This represents the absolute change in curvature at that location in relation to the temperature-stress coupling effect;

[0102] S2.5: Establish circumferential coordinates along the outer edge region. Boundary curve points for parameters ,exist Obtain the outer normal vector Based on the thickness of the metal plate Define the circumferential position as the radial integration range. Corresponding radial band ; Calculate the risk distribution function:

[0103] ;

[0104] in, Indicates circumferential position Average risk value; Boundary curve points Indicates the circumferential position of the outer edge boundary. Spatial coordinates; external normal vector This represents the external normal vector of the coordinate point; Indicates the radial distance along the outer normal; This represents the comprehensive risk value calculated in S2.4. ,in In the outer edge curve coordinate system, by and At a given point, the coordinates are mapped to a two-dimensional position in the global coordinate system of the metal plate. And use this position as the input for risk value calculation; With risk threshold Compare and extract the satisfied The continuous circumferential interval is used as the initial selection result for the target range of the outer edge region;

[0105] S2.6: Combine the preliminary selection results obtained in S2.5 with... Perform an intersection operation on the local extremum coordinate sets and delete the values ​​in the set. The coordinates of the mid-curvature change amplitude are lower than the preset trigger threshold to obtain the final target range of the outer edge region. The coordinates of the final target range and their corresponding time windows are stored for subsequent generation of unloading timing control curves.

[0106] S3 includes:

[0107] S3.1: Elastic modulus based on metal plate material Coefficient of thermal expansion ,as well as , and At the end time of the uninstallation process Calculate the temperature-corrected equivalent stress at each coordinate position:

[0108] ;

[0109] in, Indicates coordinate position Equivalent stress; This represents the normal stress value at the moment unloading ends; This indicates the temperature value at the moment unloading ended;

[0110] S3.2: The result obtained from S3.1 With S1.6 Combined, calculate the crack risk intensity field at the end of the unloading process:

[0111] ;

[0112] in, Indicates coordinate position The crack risk intensity value; This represents the absolute change in curvature at that coordinate position in relation to the temperature-stress coupling effect.

[0113] Will Coordinate position in the global coordinate system The distribution on the surface is arranged in a two-dimensional matrix to generate a distribution map of crack risk intensity;

[0114] S3.3: Establish circumferential coordinates in the outer region and in each circumferential coordinate Define radial band For the distribution map Perform radial integral averaging within this band:

[0115] ;

[0116] in, Indicates circumferential position The average crack risk intensity; Represents the circumferential coordinate system in the outer edge curve coordinate system. and radial distance The determined points are mapped to Then, the crack risk intensity value is calculated for that point;

[0117] S3.4: Will With the preset risk intensity threshold Compare and locate to satisfy The continuous circumferential interval, and combined with S2.2 calculations Determine the unloading time windows corresponding to these high-risk intervals; determine these circumferential intervals, time windows, and their corresponding... The value, serving as the target peak value information for peak clipping control, is output to the unloading timing control curve generation module, while simultaneously recording the allowed peak values. As subsequent control constraints.

[0118] It should be noted that this solution was developed based on the delayed cracking caused by continuous tensile stress in the outer edge region during the straightening and unloading process.

[0119] Through the device layer design of "configuring the straightening roller and end flexible roller assembly of the straightening equipment", the "coating layer and drive unit for zonal hardness adjustment" are arranged at the processing path exit and coaxially positioned with the straightening roller. Subsequently, the first stress sensing unit, the second displacement sensing unit and the third temperature sensing unit are arranged in the contact area between the straightening roller and the metal plate, and a one-to-one correspondence between the contact area and the surface coordinates is established. The geometric boundary model is constructed with the zero-load stress value and the initial morphology data as the baseline to obtain the dynamic change of the current state relative to the reference state. The reason for adopting this starting point is that the generation of continuous tensile stress is closely related to the geometric change of the plate surface and the thermo-mechanical state coupling. Only by synchronously mapping stress, displacement and temperature to a unified geometric boundary model can the "where is sensitive" and "when is unfavorable" be jointly characterized in the subsequent unloading section, avoiding coarse control based solely on empirical parameters.

[0120] The implementation steps and operation mechanism follow a chain-like closed loop of "perception-inference-allocation-execution-verification-reinjection": When the metal plate straightening process enters the unloading stroke, the first stress sensing unit and the second displacement sensing unit simultaneously collect stress data and displacement data of the outer edge region and the central region, calculate the rebound phase difference and strain gradient of the two, and jointly analyze the results with the dynamic changes of the geometric boundary model, thereby screening the "outer edge region target range" in the outer circumferential direction;

[0121] To ensure that the target range has both instability tendency and geometric sensitivity, the scheme samples point by point on the outer edge curve coordinates and maps them back to the global coordinates. The unloading risk is averaged in the plate thickness direction and intersected with the local extrema of the geometric boundary model. Regions with high risk but insufficient geometric change are eliminated to obtain an executable space window.

[0122] Subsequently, based on the equivalent stress magnitude after material parameter correction, the aforementioned spatial window is mapped to the crack risk intensity distribution map. The circumferential peak value in the distribution map is paired with the springback phase difference to form the time and space constraints of the unloading timing control curve. The execution layer completes the segmented unloading timing adjustment by the end flexible roller assembly.

[0123] The first time window reduces the contact stiffness within the target area of ​​the outer edge region to absorb the rebound energy of the region and dissipate the energy peak at the beginning of unloading; the second time window increases the contact stiffness to limit the deformation of the region from being transmitted to the surrounding region and to block the stress continuity along the circumferential and radial directions; the third time window restores the contact stiffness to maintain the stability of the forming dimensions of the region and avoid introducing new dimensional deviations at the end.

[0124] The three windows mentioned above are executed synchronously and in coordination within the circumferential range of the target area in the outer edge region, so that the originally continuously distributed tensile stress is cut into mutually independent segmented tensile stress zones. After unloading, the first stress sensing unit and the second displacement sensing unit verify the "residual stress value and residual strain distribution". If the residual index in the target area of ​​the outer edge region is not lower than the "set allowable upper limit", then the "data acquisition-range determination-time shaping" process is repeated in the final unloading stroke of the same plate until the standard is met. The qualified "unloading time control curve" and "contact stiffness adjustment parameters" are associated and stored with the geometric boundary model for subsequent batch initialization, thereby forming a transferable parameter library.

[0125] This scheme directly breaks down the triggering conditions of continuous tensile stress into three controllable quantities: spatially, it relies on the geometric boundary model to lock the target range of the outer edge region; temporally, it uses the springback phase difference to determine the start time and duration; and in terms of intensity, it uses the distribution map of crack risk intensity to determine the target and upper limit of peak reduction. The three together act on the contact stiffness adjustment of the flexible roller assembly at the same end, so that the device, data and control are coupled and executed under the same coordinate and the same timing, avoiding the implementation ambiguity caused by parameter drift and inconsistent terminology.

[0126] In practical applications, this solution does not change the arrangement of the main frame and rollers. It only introduces zoned adjustable contact stiffness and matching unloading timing control at the end of the unloading process, thus enabling it to be embedded in existing production lines. At the same time, all thresholds, allowable upper limits, and coordinate mappings are based on the aforementioned sensor acquisition and benchmark calibration, ensuring that the source is clear and the repeatability is verifiable.

[0127] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preventing cracking in metal plate processing and forming based on micro-area flexible control, characterized in that, include: S1: Configure the straightening roller and end flexible roller assembly of the straightening equipment, wherein the end flexible roller assembly includes a coating layer for zoned adjustment of hardness and a drive unit; A first stress sensing unit, a second displacement sensing unit, and a third temperature sensing unit are arranged in the contact area between the straightening roller and the metal plate, and a geometric boundary model is established based on the three sensing units. S2: When the metal plate enters the unloading stroke during the straightening process, the first stress sensing unit and the second displacement sensing unit simultaneously collect stress data and displacement data of the outer edge region and the center region, and calculate the springback phase difference and strain gradient of the outer edge region and the center region based on the collected data, and determine the target range of the outer edge region by combining the calculated values ​​of the geometric boundary model. S3: Based on the material parameters and geometric boundary model of the processed metal plate, stress calculation is performed on the data of S2 to generate a distribution map of the crack risk intensity in the circumferential direction of the outer edge region. The location of the crack risk intensity value exceeding the preset threshold and the corresponding time window are located in the distribution map. The target peak value and allowable upper limit of peak reduction to be achieved during the unloading process are output.

2. The method for preventing cracking in metal plate processing and forming based on micro-area flexible control according to claim 1, characterized in that: It also includes S4: generating an unloading timing control curve based on the distribution map of the outer edge region and the springback phase difference; driving the end flexible roller assembly's coating layer to perform segmented unloading timing adjustment within the target range of the outer edge region; and synchronously performing contact stiffness adjustment within the circumferential range of the target range of the outer edge region, decomposing the continuously distributed tensile stress into multiple independent segmented tensile stress zones.

3. The method for preventing cracking in metal plate processing and forming based on micro-area flexible control according to claim 2, characterized in that: In S4, the segmented unloading timing adjustment includes: reducing the contact stiffness of the outer edge region in a first time window to absorb the springback energy of the region, increasing the contact stiffness of the outer edge region in a second time window to limit the deformation of the region from being transmitted to the surrounding region, and restoring the contact stiffness of the outer edge region in a third time window to maintain the forming size of the region.

4. The method for preventing cracking in metal plate processing and forming based on micro-area flexible control according to claim 3, characterized in that: It also includes S5: After unloading, the residual stress value and residual strain distribution of the outer edge region are measured by the first stress sensing unit and the second displacement sensing unit; when the residual stress value is not lower than the preset allowable upper limit, S2 to S4 are repeated for the same metal plate in the preset end stroke until the residual stress value is lower than the preset allowable upper limit. The final unloading timing control curve and contact stiffness adjustment parameters are bound and stored with the geometric boundary model.

5. The method for preventing cracking in metal plate processing and forming based on micro-area flexible control according to claim 4, characterized in that: S1 includes: S1.1: Configure the straightening roller and the end flexible roller assembly of the straightening equipment. The end flexible roller assembly includes a coating layer for zoned hardness adjustment and a drive unit. The end flexible roller assembly is arranged at the exit position of the metal plate processing path. The end flexible roller assembly and the straightening roller are coaxially positioned. S1.2: A first stress sensing unit, a second displacement sensing unit, and a third temperature sensing unit are arranged along the processing direction and the width direction in the contact area between the straightening roller and the metal plate to form a three-dimensional sensing array, and a mapping relationship between the sensing unit and the coordinate system of the contact area is established so that each data acquisition point corresponds to a unique coordinate position on the surface of the metal plate. S1.3: Based on the measurement results of the first stress sensing unit, the normal stress values ​​at each coordinate position of the contact area are obtained and denoted as follows: Based on the measurement results of the second displacement sensing unit, the normal displacement values ​​at each coordinate position in the contact area are obtained and denoted as follows: Based on the measurement results of the third temperature sensing unit, the temperature values ​​at each coordinate position of the contact area are obtained and denoted as follows: ; S1.4: Obtained based on S1.3 , and Construct the shape function of the geometric boundary model: ； in, The x-coordinate represents the direction of metal sheet processing. Represents the ordinate along the width of the metal plate; This represents the first partial derivative of the displacement value in the machining direction; This represents the first-order partial derivative of the displacement value in the width direction; The elastic modulus represents the elastic modulus of the metal sheet material, which is used to characterize the stiffness of the material within its elastic range; The coefficient of thermal expansion represents the thermal expansion coefficient of the metal sheet material, which describes the linear dimensional change of the material with temperature; it is calculated as a morphology function. Used to reflect the deformation effect caused by the curvature change and temperature-stress coupling in the contact area; S1.5: Under no external load, collect the stress values ​​at each coordinate position in S1.

4. Displacement value With temperature value And calculate the zero-load topographic reference function: ； Among them, stress value This represents the normal stress value when there is no external load; displacement value. This represents the normal displacement value without external load; temperature value. This represents the temperature value when there is no external load. and These represent the first-order partial derivatives of the displacement value without external load in the machining direction and the width direction, respectively; Used to represent the curvature and temperature-stress coupling reference morphology of the contact area under no external load; S1.6: The result obtained in S1.4 Obtained with S1.5 Performing difference operations, we obtain the transformation matrix of the geometric boundary model: ； in, This indicates the difference in morphology between the contact area under the current processing state and the state without external load; The positive and negative distribution of the mean difference is used to characterize the increasing or decreasing trend of curvature change and temperature-stress coupling effect at each coordinate position; Stored in the geometric boundary model database.

6. The method for preventing cracking in metal plate processing and forming based on micro-area flexible control according to claim 5, characterized in that: S2 includes: S2.1: During the unloading stroke of the metal plate straightening process, the first stress sensing unit collects the normal stress values ​​at each coordinate position of the outer edge region and the central region. The second displacement sensing unit collects the normal displacement values ​​at each coordinate position of the outer edge region and the central region. ,in Represents a time variable; S2.2: Normal displacement value obtained based on S2.1 Calculate the rebound displacement curves in the outer and central regions respectively. and And calculate using the phase difference: ； in, This indicates the rebound phase difference between the outer edge region and the central region; and These represent the start and end times of the unloading process, respectively. The curve represents the springback displacement of the outer edge region; The curve representing the rebound displacement of the central region; Inverse cosine function; S2.3: Based on S2.1 Calculate the strain gradient distribution in the inner and outer edge regions of the unloading stroke: ； in, Indicates the end time of the unloading process. At coordinate position The strain gradient; This represents the first partial derivative of the displacement value at that position in the machining direction at the end of unloading; This represents the first partial derivative of the displacement value at that position in the width direction at the end of unloading; S2.4: The rebound phase difference obtained in S2.2 The strain gradient obtained with S2.3 As input parameters and generated by S1.6 Perform joint calculations to construct an unloading risk response function: ； in, Indicates coordinate position The overall risk value of stress concentration is generated during the unloading process; This indicates the effect of the rebound phase difference on the sinusoidal amplitude of the risk; This represents the absolute change in curvature at that location in relation to the temperature-stress coupling effect; S2.5: Establish circumferential coordinates along the outer edge region. Boundary curve points for parameters ,exist Obtain the outer normal vector Based on the thickness of the metal plate Define the circumferential position as the radial integration range. Corresponding radial band ; Calculate the risk distribution function: ； in, Indicates circumferential position Average risk value; Boundary curve points Indicates the circumferential position of the outer edge boundary. Spatial coordinates; external normal vector This represents the external normal vector of the coordinate point; Indicates the radial distance along the outer normal; This represents the comprehensive risk value calculated in S2.

4. ,in In the outer edge curve coordinate system, by and At a given point, the coordinates are mapped to a two-dimensional position in the global coordinate system of the metal plate. And use this position as the input for risk value calculation; With risk threshold Compare and extract the satisfied The continuous circumferential interval is used as the initial selection result for the target range of the outer edge region; S2.6: Combine the preliminary selection results obtained in S2.5 with... Perform an intersection operation on the local extremum coordinate sets and delete the values ​​in the set. The coordinates of the mid-curvature change amplitude are lower than the preset trigger threshold to obtain the final target range of the outer edge region, and the coordinates of the final target range and its corresponding time window are stored.

7. The method for preventing cracking in metal plate processing and forming based on micro-area flexible control according to claim 6, characterized in that: S3 includes: S3.1: Elastic modulus based on metal plate material Coefficient of thermal expansion ,as well as , and At the end time of the uninstallation process Calculate the temperature-corrected equivalent stress at each coordinate position: ； in, Indicates coordinate position Equivalent stress; This represents the normal stress value at the moment unloading ends; This indicates the temperature value at the moment unloading ended; S3.2: The result obtained from S3.1 With S1.6 Combined, calculate the crack risk intensity field at the end of the unloading process: ； in, Indicates coordinate position The crack risk intensity value; This represents the absolute change in curvature at that coordinate position in relation to the temperature-stress coupling effect. Will Coordinate position in the global coordinate system The distribution on the surface is arranged in a two-dimensional matrix to generate a distribution map of crack risk intensity; S3.3: Establish circumferential coordinates in the outer region and in each circumferential coordinate Define radial band For the distribution map Perform radial integral averaging within this band: ； in, Indicates circumferential position The average crack risk intensity; Represents the circumferential coordinate system in the outer edge curve coordinate system. and radial distance The determined points are mapped to Then, the crack risk intensity value is calculated for that point; S3.4: Will With the preset risk intensity threshold Compare and locate to satisfy The continuous circumferential interval, and combined with S2.2 calculations Determine the unloading time window corresponding to the risk interval; these circumferential intervals, time windows, and their corresponding... The value, serving as the target peak value information for peak clipping control, is output to the unloading timing control curve generation module, while simultaneously recording the allowed peak values. As subsequent control constraints.

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