Leveling process plate shape control method based on improvement of residual stress distribution

Abstract

The invention provides a flatness process plate shape control method based on residual stress distribution improvement. The method comprises the steps that 1, temper mill size parameters, leveling process parameters and strip steel parameters are collected; step 2, establishing a leveling process simulation model based on the parameters acquired in the step 1, and copying to obtain a strip steel simulation model which only retains strip steel and attributes thereof; 3, initial internal stress is applied to the strip steel in the strip steel simulation model; step 4, introducing the strip steel to which the initial internal stress is applied in the strip steel simulation model into the leveling process simulation model in a data transmission mode; 5, carrying out condition setting on the leveling process simulation model, wherein the condition setting comprises pretreatment, grid division, contact type and boundary condition definition and load application; and step 6, performing leveling process simulation to obtain a group of leveling process parameters enabling the residual stress to be minimum, and applying the leveling process parameters to a leveling field to improve the plate shape.

Description

Technical Field

[0001] The invention belongs to the technical field of plate shape control and relates to a plate shape control method in a flattening process based on improving residual stress distribution. Background Art

[0002] Hot-rolled strip can not only be used as raw material for cold rolling, but can also be directly used in the automotive, construction and other industries. High-quality hot-rolled strip has increasingly higher requirements for plate quality. In this context, uneven residual stress is one of the important issues restricting the production of high-quality hot-rolled strip. Residual stress refers to the self-equilibrium internal stress that remains in an object after eliminating external forces or uneven temperature fields. For the strip rolling deformation process, it is necessary that the longitudinal extension length along the transverse direction of the strip is uniform. However, the deformation of the strip in the rolling zone causes its longitudinal extension to be unevenly distributed due to various reasons. When the amount of pressure applied along the width direction is unevenly distributed, the longitudinal extension may be uneven, with the larger part being compressed and the smaller part being stretched, resulting in uneven distribution of longitudinal residual stress inside the strip. When this uneven extension accumulates to a certain extent, it may not immediately cause obvious wavy shapes on the strip surface, but it will form a potential problem, namely, potential flatness defects. This defect may appear after the strip is cut, affecting the processing and use of downstream users; when the residual stress of the strip exceeds the critical stress value of buckling, the strip will buckle and deform, causing obvious wavy shapes on the strip surface, resulting in flatness defects.

[0003] In the field of modern rolling and engineering, the residual stress of strip steel has an important impact on the performance, service life and safety of the structure. In recent years, ABAQUS, as a widely used finite element analysis software, has been widely used in the engineering field with its powerful modeling and analysis functions. ABAQUS can analyze and optimize the internal stress of materials, providing engineers with an effective tool to predict the stress state of materials in the design stage, so as to make corresponding adjustments to meet engineering requirements. However, most of the current finite element simulations of rolling processes based on ABAQUS mainly focus on the adjustment of flattening related parameters, but there is little in-depth discussion on the assignment of initial internal stress and its data transfer. Especially in the optimization of the flattening process, how to reasonably assign the initial internal stress to the material and combine it with data transfer to achieve the best flattening effect is still a problem that needs to be solved. Summary of the invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a flatness control method in a flattening process based on improving residual stress distribution.

[0005] The present invention provides a flatness control method in a flattening process based on improving residual stress distribution, comprising:

[0006] Step 1: Collect the size parameters of the leveling machine, leveling process parameters and strip parameters;

[0007] Step 2: Establish a flattening process simulation model based on the parameters collected in step 1, and copy the strip simulation model that only retains the strip and its properties;

[0008] Step 3: Applying initial internal stress to the strip in the strip simulation model;

[0009] Step 4: The strip steel to which the initial internal stress has been applied in the strip steel simulation model is introduced into the flattening process simulation model by means of data transfer;

[0010] Step 5: Set conditions for the simulation model of the leveling process, including pre-processing, meshing, defining contact types, boundary conditions, and applying loads;

[0011] Step 6: Simulate the leveling process to obtain a set of leveling process parameters that minimize residual stress, and apply them to the leveling site to improve the plate shape.

[0012] The present invention provides a flatness control method for the flattening process based on improving the residual stress distribution. The initial residual stress of the strip is given by the secondary development of ABAQUS software and finite element simulation is performed in combination with data transmission to simulate the residual stress distribution of the hot-rolled strip after flattening. The residual stress of the strip is extracted by the post-processing function, and compared with the initial state. The residual stress is used as the control target to optimize the flattening process parameters. The flatness quality of the strip is effectively improved, the flatness defects and uneven stress distribution of the strip after flattening are improved, and a reference is provided for improving the process and improving the product qualification rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a flow chart of a flatness control method of a flattening process based on improving residual stress distribution of the present invention;

[0014] Figure 2 It is a steel strip cloud diagram after the initial internal stress of the steel strip is given by the ABAQUS interface SIGINI subroutine in the specific implementation mode of the present invention;

[0015] Figure 3 The residual stress diagram of the upper surface of the strip steel given initial stress in a specific embodiment of the present invention;

[0016] Figure 4 It is the residual stress diagram extracted along the width direction of the strip in the strip simulation model;

[0017] Figure 5 It is a residual stress diagram of the upper surface of the strip steel of the target steel grade after flattening in a specific embodiment of the present invention;

[0018] Figure 6a-6dIt is a residual stress diagram of four equidistant paths extracted along the width direction of the strip after the target steel grade is flattened in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0019] like Figure 1 As shown, a flatness control method for a flattening process based on improving residual stress distribution of the present invention comprises:

[0020] Step 1: Collect the size parameters of the leveling machine, leveling process parameters and strip parameters, specifically:

[0021] Step 1.1: To ensure the accuracy of the calculation results, the geometric model of the leveling machine is established at a ratio of 1:1. The four-roller single-frame leveling machine is used as the prototype, and the model size of the leveling machine is determined by the volume equivalence method according to the leveling machine drawings.

[0022] Volume equivalence means that under the premise of keeping the total volume of the working roll unchanged, the roll body and roll neck of the working roll are regarded as different geometric bodies, and the equivalent diameter of the roll neck is calculated based on the known size of the roll body. This can effectively design and optimize the structure of the roll, thereby improving the simulation efficiency.

[0023] Step 1.2: Collect process parameters at the leveling site, including: pressing amount, bending roller force, front tension, back tension and leveling speed.

[0024] Step 1.3: Using 750L steel, collect the mass fraction of steel composition and elements, strip geometry and strip performance parameters from the hot-rolled strip leveling production line, and obtain stress-strain data through experiments, specifically:

[0025] Step 1.3.1: Collect the geometric dimensions of the strip including strip width and strip thickness; collect the performance parameters of the strip including strip density, Young's modulus and Poisson's ratio.

[0026] In this embodiment, the steel type is 750L, and the composition (content %) is as shown in Table 1.

[0027] Table 1 750L ingredients

[0028]

[0029] The selected strip length is 3m, the width is 1500mm and the thickness is 5mm.

[0030] Step 1.3.2: Take samples of the strip and perform compression tests to obtain the corresponding stress-strain data.

[0031] Step 2: A flattening process simulation model is established based on the parameters collected in step 1, and a strip simulation model is obtained by copying the strip and retaining only the strip and its properties.

[0032] Step 3: Apply initial internal stress to the strip in the strip simulation model, specifically:

[0033] Step 3.1: The potential wave-shaped internal stress distribution of the strip is divided into middle wave internal stress, double-sided wave internal stress, 1 / 4 wave internal stress and edge-middle composite wave internal stress, and the initial internal stress is expressed by the cosine function as follows:

[0034]

[0035] Among them, σ(x) is the initial internal stress applied, x represents the coordinate in the width direction of the strip, x∈[0,B]; A is the internal stress amplitude, in MPa; B is the strip width, in mm; k is the stress distribution coefficient; when A>0, k=1 is a middle wave, k=2 is a 1 / 4 wave; when A<0, k=1 is a double-sided wave, and k=2 is a side-middle composite wave.

[0036] In this embodiment, the strip is given a wave-like internal stress, A=60MPa, k=1.

[0037] Step 3.2: Use the SIGINI subroutine in ABAQUS to assign initial internal stress to the strip steel, and set continuous initial conditions in the flattening process simulation model to improve the accuracy and stability of the simulation.

[0038] Stress is assigned through the SIGINI subroutine, and the cloud diagram of the assigned strip is as follows: Figure 2 As shown in the cloud diagram after analysis and calculation, it can be seen that the middle part is compressive stress and the two sides are tensile stress. After the residual stress on the upper surface of the strip is extracted by ABAQUS post-processing and plotted, the residual stress distribution of the initial strip is as follows: Figure 3 As shown in the figure, it can be seen that the stress distribution of the strip after the subroutine gives the middle wave internal stress is in the shape of a cosine function, which is consistent with the initial internal stress formula and Figure 2 Corresponding. A path is established on the upper surface of the strip, and the residual stress values ​​of the nodes on the path are extracted and plotted. The results are as follows Figure 4 As shown, it can be seen more intuitively that the stress distribution of the strip in the width direction is in the shape of a cosine function.

[0039] Step 4: The strip steel to which the initial internal stress has been applied in the strip steel simulation model is introduced into the flattening process simulation model by means of data transfer, specifically:

[0040] Step 4.1: Save the strip ODB file given the initial internal stress in the strip simulation model.

[0041] Step 4.2: Open the flattening process simulation model and create a node set or unit set of the strip in the Model module.

[0042] Step 4.3: Define the geometry and mesh, and ensure that the mesh and nodes of the strip in the flattening process simulation model and the strip simulation model are consistent.

[0043] Step 4.4: Define the predefined fields, navigate to the Load module, select the node set or element set created previously, and the required increment corresponding to the initial ODB file.

[0044] Step 4.5: Use the stress data of the strip ODB file to transfer the initial stress state to the strip in the flattening process simulation model.

[0045] Step 5: Set the conditions for the simulation model of the leveling process, including pre-processing, meshing, defining contact types, boundary conditions, and applying loads, specifically:

[0046] Step 5.1: Divide the strip steel in the flattening process simulation model into 5mm×5mm×1mm grids. The vertices of the grids are nodes. Select the C3D8R network type.

[0047] Step 5.2: The contact types provided by ABAQUS can be divided into three categories: single-surface contact, node-surface contact, and surface-surface contact; select the contact surface type and set it to automatic surface contact.

[0048] Step 5.3: Setting appropriate tension can effectively control the material entry speed and position, reduce the warping or distortion of the material, and improve the flattening effect. In the flattening process simulation model, the bending roll force is achieved by applying force to the roll neck. The tension is applied to the front and rear sections of the strip in the form of node force. The specific conversion formula is:

[0049] Nodal force = force per unit area × force area / number of nodes on the force surface.

[0050] Step 5.4: Limit the freedom of movement of the upper and lower working rolls to ensure that they can only perform rotational movement.

[0051] Step 6: Simulate the leveling process to obtain a set of leveling process parameters that minimize residual stress, and apply them to the leveling site to improve the plate shape. Specifically:

[0052] Step 6.1: According to the experience of the leveling process parameters on site, set the adjustment range of each process parameter.

[0053] Step 6.2: Take one of the five flattening process parameters as a variable and the other process parameters as constants to simulate the flattening process and extract the residual stress of the strip after flattening in the flattening process simulation model. The extraction results are as follows: Figure 5As shown, the process parameters as variables are continuously updated to minimize the residual stress of the strip after flattening. The above process is repeated to loop through all flattening process parameters. When the maximum number of iterations is reached, the iteration is stopped to obtain a set of optimal flattening process parameters that minimize the residual stress of the strip after flattening.

[0054] Step 6.3: For the strip with the smallest residual stress after flattening, take multiple paths with equal distances along the width of the strip and extract the residual stress of the nodes on each path. The results are as follows: Figure 6a-6d As shown, verify whether it complies with the stress self-balance law. Figure 6a-6d The residual stress of the four paths extracted along the width direction of the strip is equal to the distance between the four paths. After leveling the figure, the residual stress of the four paths extracted is less than the initial residual stress of 60MPa.

[0055] Step 6.4: Compare the minimum strip residual stress after simulation with the initial internal stress of the strip. If the residual stress of the strip is reduced and homogenized after the flattening process simulation, the optimal flattening process parameters are applied to the flattening site.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the concept of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A flatness control method for a flattening process based on improving residual stress distribution, characterized in that: include: Step 1: Collect the size parameters of the leveling machine, leveling process parameters and strip parameters; Step 2: Establish a flattening process simulation model based on the parameters collected in step 1, and copy the strip simulation model that only retains the strip and its properties; Step 3: Applying initial internal stress to the strip in the strip simulation model; Step 4: The strip steel to which the initial internal stress has been applied in the strip steel simulation model is introduced into the flattening process simulation model by means of data transmission; Step 5: Set conditions for the simulation model of the leveling process, including pre-processing, meshing, defining contact types, boundary conditions, and applying loads; Step 6: Simulate the leveling process to obtain a set of leveling process parameters that minimize residual stress, and apply them to the leveling site to improve the plate shape.

2. The flatness control method of the flattening process based on improving residual stress distribution according to claim 1, characterized in that: The step 1 is specifically as follows: Step 1.1: Take the four-roller single-frame leveling machine as the prototype and use the volume equivalent method to determine the model size of the leveling machine according to the leveling machine drawing; Step 1.2: Collect the leveling process parameters at the leveling site, including: pressing amount, bending roller force, front tension, back tension and leveling speed; Step 1.3: Using 750L steel grade, collect the steel grade composition and element mass fraction, strip geometric dimensions and strip performance parameters from the hot-rolled strip leveling production line, and obtain stress-strain data through experiments.

3. The flatness control method of the flattening process based on improving residual stress distribution according to claim 2, characterized in that: The volume equivalence method is specifically: Volume equivalence means that under the premise of keeping the total volume of the working roll unchanged, the roll body and roll neck of the working roll are regarded as different geometric bodies, and the equivalent diameter of the roll neck is calculated based on the known size of the roll body.

4. The flatness control method of the flattening process based on improving residual stress distribution according to claim 2, characterized in that: The step 1.3 is specifically as follows: Step 1.3.1: Collect the geometric dimensions of the steel strip, including the steel strip width and steel strip thickness; collect the performance parameters of the steel strip, including the steel strip density, Young's modulus and Poisson's ratio; Step 1.3.2: Take samples of the strip and perform compression tests to obtain the corresponding stress-strain data.

5. The flatness control method of the flattening process based on improving residual stress distribution according to claim 1, characterized in that: The step 3 is specifically as follows: Step 3.1: The potential wave-shaped internal stress distribution of the strip is divided into middle wave internal stress, double-sided wave internal stress, 1 / 4 wave internal stress and edge-middle composite wave internal stress, and the initial internal stress is expressed by the cosine function as follows: Wherein, σ(x) is the initial internal stress applied, x represents the coordinate in the width direction of the strip, x∈[0,B]; A is the internal stress amplitude, in MPa; B is the strip width, in mm; k is the stress distribution coefficient; when A>0, k=1 is a middle wave, k=2 is a 1 / 4 wave; when A<0, k=1 is a double-sided wave, k=2 is a side-middle composite wave; Step 3.2: Use the SIGINI subroutine in ABAQUS to assign initial internal stress to the strip steel, and set continuous initial conditions in the flattening process simulation model to improve the accuracy and stability of the simulation.

6. The flatness control method of the flattening process based on improving residual stress distribution according to claim 1, characterized in that: The step 4 is specifically as follows: Step 4.1: Save the strip ODB file given the initial internal stress in the strip simulation model; Step 4.2: Open the flattening process simulation model and create a node set or unit set of the strip in the Model module; Step 4.3: Define the geometry and mesh, and ensure that the mesh and nodes of the strip in the flattening process simulation model and the strip simulation model are consistent; Step 4.4: Define the predefined fields, navigate to the Load module, select the node set or element set created previously, and the required increment corresponding to the initial ODB file; Step 4.5: Use the stress data of the strip ODB file to transfer the initial stress state to the strip in the flattening process simulation model.

7. The flatness control method of the flattening process based on improving residual stress distribution according to claim 1, characterized in that: The step 5 is specifically as follows: Step 5.1: Divide the strip steel in the flattening process simulation model into 5mm×5mm×1mm grids, the vertices of the grids are nodes, and select the C3D8R network type; Step 5.2: The contact types provided by ABAQUS can be divided into three categories: single-surface contact, node-surface contact, and surface-surface contact; select the contact surface type and set it to automatic surface contact; Step 5.3: Setting appropriate tension can effectively control the material entry speed and position, reduce the warping or distortion of the material, and improve the flattening effect. In the flattening process simulation model, the bending roll force is achieved by applying force to the roll neck. The tension is applied to the front and rear sections of the strip in the form of node force. The specific conversion formula is: Nodal force = force per unit area × force area / number of nodes on the force surface Step 5.4: Limit the freedom of movement of the upper and lower working rolls to ensure that they can only perform rotational movement.

8. The flatness control method of the flattening process based on improving residual stress distribution according to claim 1, characterized in that: The step 6 is specifically as follows: Step 6.1: According to the experience of the leveling process parameters on site, set the adjustment range of each process parameter; Step 6.2: Take one of the five leveling process parameters as a variable and the other process parameters as constants, simulate the leveling process and extract the residual stress of the strip after leveling in the leveling process simulation model, continuously update the process parameters as variables to minimize the residual stress of the strip after leveling, repeat the above process to loop through all leveling process parameters, and stop the iteration when the maximum number of iterations is reached to obtain a set of optimal leveling process parameters that minimize the residual stress of the strip after leveling; Step 6.3: For the strip with the smallest residual stress after flattening, take multiple paths with equal distances along the width direction of the strip, extract the residual stress of the nodes on each path, and verify whether it conforms to the stress self-balance law; Step 6.4: Compare the minimum strip residual stress after simulation with the initial internal stress of the strip. If the residual stress of the strip is reduced and homogenized after the flattening process simulation, the optimal flattening process parameters are applied to the flattening site.

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