Method for calculating residual stress in plate and strip straightening process under action of bending roller

Abstract

The invention belongs to the technical field of plate and strip straightening, and particularly relates to a method for calculating residual stress in the plate and strip straightening process under the action of a bending roller. The invention discloses a method for calculating residual stress in a plate strip straightening process under the action of a bending roller, which comprises the following steps of: analyzing the influence of internal residual stress of a plate strip under the combined action of straightening inflection and initial residual stress, and taking an average value of the residual stress of the plate strip before straightening and the residual stress of the plate strip after straightening as a tension value in the straightening process; and under the influence of the bending curvature, the plate strip generates plastic deformation, so that the residual stress of the straightened plate strip is redistributed, iteration is carried out until convergence, and the residual stress distribution after straightening is completed is obtained. The method can accurately and quickly simulate the influence of the roller type straightening machine on the residual stress distribution of the plate strip by using different roller bending amounts for straightening, and can better control the manufacturing process and ensure the performance and reliability of the final product by analyzing the change of the residual stress and optimizing the process parameters in the straightening process.

Description

Technical Field

[0001] The invention belongs to the technical field of plate and strip straightening, and in particular relates to a method for calculating residual stress in a plate and strip straightening process under the action of bending rollers. Background Art

[0002] Straightening technology is the post-process of metal sheets and strips, and the straightening process is one of the important links that determine the quality of metal sheet and strip products. With the development of the automobile manufacturing industry, higher requirements are placed on the plate shape and other aspects of metal sheet and strip products. During the rolling process of metal sheets and strips, due to the uneven distribution of rolling pressure in the rolling process and the lateral flow of metal, the longitudinal fiber length of the metal sheets and strips will be unevenly distributed, which will cause residual stress inside the sheet and strip. When the metal fiber is too long and the residual stress is large enough to exceed the threshold of strip instability, the long fiber will become unstable, causing the strip to have a wavy shape.

[0003] Roller straightening machines are generally used to straighten longitudinal wave bends, which means that metal plates and strips are bent repeatedly through two rows of staggered working rollers. During the straightening process, bending rollers are applied to the working rollers to make the roller surface convex, which can improve the poor plate shape. Its working principle is to increase the amount of pressure reduction in places where the longitudinal fibers are short, stretch the longitudinal fibers, flatten the wavy places, form a compressed state, and shorten the long fibers, so as to achieve the purpose of improving the plate shape and reducing the residual stress of metal plates and strips. Due to the lack of research on the mechanism of residual stress change of plates and strips during straightening, there is almost no technical theory to support the setting of convexity in actual production, and it can only be adjusted based on experience. In the existing public literature, there is a study on the influence of roller profile curve on residual stress of plates and strips: "The influence of roller profile curve of straightening roller on residual stress of medium and thick plates" (Material Science and Technology, 2012, 1-6). In this article, the stress increment in the thickness direction is equal to the stress increment of the neutral layer, which has a large error. Summary of the invention

[0004] In view of the above problems, the purpose of the present invention is to provide a method for calculating residual stress in the process of plate and strip straightening under the action of bending rollers. The method is based on elastic-plastic mechanics analysis, and calculates the residual stress distribution after straightening by analyzing the influence of the internal residual stress of the plate and strip under the combined action of straightening, reverse bending and initial residual stress. It can accurately and quickly simulate the influence of straightening by a roller straightening machine using different bending roller amounts on the residual stress distribution of the plate and strip, and help to predict the residual stress distribution and plate shape distribution of the plate and strip after straightening, thereby ensuring the performance and reliability of the final product and improving the straightening effect and efficiency.

[0005] The technical solution of the present invention is: a method for calculating residual stress in a strip straightening process under the action of bending rollers, comprising the following steps:

[0006] S1: Divide the plate and strip into n strips in the width direction and mark them as t1, t2, ..., t n , set the metal strip shape distribution BX, roller shape GX and straightening reverse curvature C w ;

[0007] S2: Determine the initial residual strain ε of the plate and strip c0i and the initial residual stress value σ c0i ;

[0008] S3: Determine C w The corresponding bending deflection δ w , and add it to GX to get the compression deflection δ of each element in the width direction wi , according to δ wi Determine the C corresponding to the i-th element wi ;

[0009] S4: Grant Initial value;

[0010] S5: Initial residual stress σ C0i Residual stress after straightening The average value is taken as the tensile stress value σ during straightening Fi ;

[0011] S6: Discretize the plate and strip in m parts in the height direction, and determine the stress and strain in the X direction of each unit caused by the bending curvature and tension according to the ideal stress state;

[0012] S7: Determine the elastic recovery and residual strain in the X direction of each unit;

[0013] S8: Take the average value of the residual strain of the i-th element in the height direction as the extension of the element, add it to the initial residual strain to get the residual strain after straightening, and determine the residual stress value σ in the width direction after straightening c1i ;

[0014] S9: Determined residual stress value σ c1i and the initial value of residual stress after straightening Determine the maximum error and determine whether it is less than ξ. If so, output σ c1i and ε c1i , complete the calculation, otherwise let the initial value of residual stress after straightening Equal to the determined residual stress value σ c1i , recalculate from step S5;

[0015] S10: By analyzing the residual stress value σ c1i changes, optimize the process parameters during the straightening process, thereby better controlling the manufacturing process and ensuring the performance and reliability of the final product.

[0016] In step S2, the initial residual strain ε of the plate and strip is determined c0i and the initial residual stress value σ c0i The specific process is:

[0017] ε c0i =10 -5 BX(1)

[0018] σ c0i =Eε c0i (2)

[0019] In the formula, ε c0i is the initial residual strain of the i-th strip element; BX is the plate shape value; σ c0i is the initial residual stress value of the i-th strip element; E is the elastic modulus of the plate and strip material.

[0020] In step S3, it is determined that C w The corresponding bending deflection δ w The specific process is:

[0021]

[0022]

[0023] Where C0 is the original longitudinal curvature of the plate, which is taken as 0; C W is the reverse bending ratio of the working roll; C C is the residual curvature ratio; is the residual deflection ratio; is the elastic-complex deflection ratio; is the total deflection ratio of compression and bending; δ t is the elastic limit deflection; δ w is the total bending deflection; M t is the elastic limit bending moment; B is the width of the material; H is the thickness of the material; σ t is the elastic limit stress value of the material.

[0024] In step S3, if there are bending rollers above and below the straightening roller, the bending deflection δ w Directly add GX to obtain the compression and bending deflection δ of each element in the width direction wi ; If only one row has bending rollers, the bending deflection δ w Adding 0.5 times GX gives the compression deflection δ of each strip in the width direction. wi .

[0025] In the step S4, The initial value of is 0;

[0026] In step S5, the tensile stress value σ during the straightening processFi The values ​​are:

[0027]

[0028] In the formula, σ Fi is the tensile stress value, σ C0i is the initial residual stress, is the residual stress after straightening.

[0029] In step S6, the stress and strain in the X direction of each unit caused by the bending curvature and the tension are:

[0030]

[0031] ε wij =Z j C Wi A t (12)

[0032]

[0033] In the formula, A t is the elastic limit curvature of the plate and strip; ε t is the elastic limit strain of the material; ε wij is the strain caused by bending of the i-th strip element in the width direction and the j-th unit in the height direction; ε zij is the total strain of the i-th strip element in the width direction and the j-th unit in the height direction; Z j The distance between the jth unit and the middle surface of the material, which is negative below the middle surface; σ ij is the total stress of the i-th strip element in the width direction and the j-th element in the height direction.

[0034] In step S7, the elastic recovery and residual strain of each unit in the X direction

[0035]

[0036] ε cij =ε zij -ε tij (16)

[0037] In the formula, ε tij is the elastic strain of the i-th strip element in the width direction and the j-th strip element in the height direction; ε cij is the plastic strain of the i-th strip element in the width direction and the j-th element in the height direction.

[0038] In step S8, the residual stress value σ in the width direction after straightening c1i for:

[0039]

[0040] σ c1i =Eε c1i (18)

[0041] In the formula, ε c1i is the residual strain value of the i-th strip after straightening.

[0042] The technical effect of the present invention is that: the present invention is based on elastic-plastic mechanics analysis, and calculates the residual stress distribution after straightening by analyzing the influence of the internal residual stress of the plate and strip under the combined action of straightening, reverse bending and initial residual stress. It can more accurately and quickly simulate the influence of straightening by a roller straightening machine using different bending roller amounts on the residual stress distribution of the plate and strip, which is helpful to predict the residual stress distribution and plate shape distribution of the plate and strip after straightening, thereby ensuring the performance and reliability of the final product and improving the straightening effect and efficiency.

[0043] The following is a further description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The present invention is a flowchart of a method for calculating residual stress during strip straightening under the action of bending rollers according to an embodiment of the present invention.

[0045] Figure 2 It is a schematic diagram of the strip element division and each unit parameter of the embodiment of the present invention.

[0046] Figure 3 This is the residual stress distribution of the plate and strip before and after straightening in Example 2 of the present invention.

[0047] Figure 4 This is the residual stress distribution of the plate and strip before and after straightening in Example 3 of the present invention. DETAILED DESCRIPTION

[0048] Example 1

[0049] like Figure 1 As shown, a method for calculating residual stress during the straightening process of a plate strip under the action of a bending roller comprises the following steps:

[0050] S1: Divide the plate and strip into n strips in the width direction and mark them as t1, t2, ..., t n , set the metal strip shape distribution BX, roller shape GX and straightening reverse curvature C w ;

[0051] S2: Determine the initial residual strain ε of the plate and strip c0i and the initial residual stress value σ c0i ;

[0052] S3: Determine C wThe corresponding bending deflection δ w , and add it to GX to get the compression deflection δ of each element in the width direction wi , according to δ wi Determine the C corresponding to the i-th element wi ;

[0053] S4: Grant Initial value;

[0054] S5: Initial residual stress σ C0i Residual stress after straightening The average value is taken as the tensile stress value σ during straightening Fi ;

[0055] S6: Discretize the plate and strip in m parts in the height direction, and determine the stress and strain in the X direction of each unit caused by the bending curvature and tension according to the ideal stress state;

[0056] S7: Determine the elastic recovery and residual strain in the X direction of each unit;

[0057] S8: Take the average value of the residual strain of the i-th element in the height direction as the extension of the element, add it to the initial residual strain to get the residual strain after straightening, and determine the residual stress value σ in the width direction after straightening c1i ;

[0058] S9: Determined residual stress value σ c1i and the initial value of residual stress after straightening Determine the maximum error and determine whether it is less than ξ. If so, output σ c1i and ε c1i , complete the calculation, otherwise let the initial value of residual stress after straightening Equal to the determined residual stress value σ c1i , recalculate from step S5;

[0059] S10: By analyzing the residual stress value σ c1i changes, optimize the process parameters during the straightening process, thereby better controlling the manufacturing process and ensuring the performance and reliability of the final product.

[0060] In the step S1, the schematic diagram of dividing the strip elements is shown in Figure 2 shown.

[0061] In step S2, the initial residual strain ε of the plate and strip is determined c0i and the initial residual stress value σ c0i The specific process is:

[0062] ε c0i =10 -5 BX(1)

[0063] σ c0i =Eε c0i (2)

[0064] In the formula, ε c0i is the initial residual strain of the i-th strip element; BX is the plate shape value; σ c0i is the initial residual stress value of the i-th strip element; E is the elastic modulus of the plate and strip material.

[0065] In step S3, it is determined that C w The corresponding bending deflection δ w The specific process is:

[0066]

[0067] Where C0 is the original longitudinal curvature of the plate, which is taken as 0; C W is the reverse bending ratio of the working roll; C C is the residual curvature ratio; is the residual deflection ratio; is the elastic-complex deflection ratio; is the total deflection ratio of compression and bending; δ t is the elastic limit deflection; δ w is the total bending deflection; M t is the elastic limit bending moment; B is the width of the material; H is the thickness of the material; σ t is the elastic limit stress value of the material.

[0068] In step S3, if there are bending rollers above and below the straightening roller, the bending deflection δ w Directly add GX to obtain the compression and bending deflection δ of each element in the width direction wi ; If only one row has bending rollers, the bending deflection δ w Adding 0.5 times GX gives the compression deflection δ of each strip in the width direction. wi .

[0069] In the step S4, The initial value of is 0;

[0070] In step S5, the tensile stress value σ during the straightening process Fi The values ​​are:

[0071]

[0072] In the formula, σ Fi is the tensile stress value, σ C0i is the initial residual stress, is the residual stress after straightening.

[0073] In step S6, the stress and strain in the X direction of each unit caused by the bending curvature and the tension are:

[0074]

[0075] ε wij =Z j C Wi A t (12)

[0076]

[0077] In the formula, A t is the elastic limit curvature of the plate and strip; ε t is the elastic limit strain of the material; ε wij is the strain caused by bending of the i-th strip element in the width direction and the j-th unit in the height direction; ε zij is the total strain of the i-th strip element in the width direction and the j-th unit in the height direction; Z j The distance between the jth unit and the middle surface of the material, and the distance below the middle surface is negative (see the attached Figure 1 );σ ij is the total stress of the i-th strip element in the width direction and the j-th element in the height direction.

[0078] In step S7, the elastic recovery and residual strain of each unit in the X direction

[0079]

[0080] ε cij =ε zij -ε tij (16)

[0081] In the formula, ε tij is the elastic strain of the i-th strip element in the width direction and the j-th strip element in the height direction; ε cij is the plastic strain of the i-th strip element in the width direction and the j-th element in the height direction.

[0082] In step S8, the residual stress value σ in the width direction after straightening c1i for:

[0083]

[0084] σ c1i =Eε c1i (18)

[0085] In the formula, ε c1i is the residual strain value of the i-th strip after straightening.

[0086] Example 2

[0087] The residual stress calculation method in the process of plate and strip straightening under the action of bending rollers described in Example 1 is used to calculate the residual stress of a certain X plate and strip material in the process of plate and strip straightening under the action of bending rollers. In this embodiment, the elastic modulus of the plate and strip material is 115 GPa, the elastic limit stress is 500 MPa, the plate width is 1000 mm, the plate thickness is 1 mm, and the roller spacing of the straightening rollers is 35 mm. The specific implementation steps are as follows:

[0088] S1: Divide the plate and strip into n strips in the width direction, and mark them as t1, t2, ..., t 50 , set the metal strip shape distribution BX, roller shape GX, straightening reverse curvature C w , as shown in Table 1;

[0089] Table 1 Plate shape, roll shape and anti-bending rate setting parameters

[0090]

[0091] S2: Calculate the initial residual strain ε of the plate and strip c0i and the initial residual stress value σ c0i ;

[0092] ε c0i =10 -5 BX(1)

[0093] σ c0i =Eε c0i (2)

[0094] S3: According to

[0095]

[0096]

[0097] Calculate C w The corresponding bending deflection δ w =1.775, and add it to GX (assuming there are bending rollers above and below) to get the bending deflection of each strip in the width direction δ wi , according to δ wi Calculate the C corresponding to the i-th element wi ;

[0098] S4: Grant Initial value;

[0099] S5: Initial residual stress σ C0i Residual stress after straightening The average value is taken as the tensile stress value σ during straightening Fi ;

[0100]

[0101] S6: Discrete m parts in the height direction of the plate and strip, and calculate the stress and strain in the X direction of each unit caused by the bending curvature and tension according to the ideal stress state, as shown in Table 2;

[0102]

[0103] ε wij =Z j C Wi A t (12)

[0104]

[0105] Table 2 Total strain and total stress of some units

[0106]

[0107]

[0108] a7: Calculate the elastic recovery and residual strain of each unit in the X direction, as shown in Table 3;

[0109]

[0110] ε cij =ε zij -ε tij (16)

[0111] Table 3 Some unit elastic strains and residual strains

[0112] i 5 10 15 20 25 j 1 11 21 31 41 <![CDATA[ε tij ]]> -0.00396 -0.00396 -0.00396 -0.00344 -0.00170 <![CDATA[ε cij ]]> -0.00478 -0.00301 -0.00124 0 0 i 30 35 40 45 50 j 51 61 71 81 91 <![CDATA[ε tij ]]> 0.00004 0.00176 0.00348 0.00396 0.00396 <![CDATA[ε cij ]]> 0 0 0 0.00123 0.00293

[0113] a8: Take the average value of the residual strain of the i-th element in the height direction as the extension of the element, and add it to the initial residual strain to obtain the residual strain ε after straightening c1i , calculate the residual stress value σ in the width direction after straightening c1i ;

[0114]

[0115]

[0116] a9: Calculated residual stress value σ c1i and the initial value of residual stress after straightening Calculate the maximum error and determine whether it is less than ξ. If not, set the initial value of the residual stress after straightening to Equal to the calculated residual stress value σ c1i , return to step S5; if yes, output σc1i and ε c1i ,like Figure 2 shown.

[0117] Example 3

[0118] The residual stress calculation method in the process of plate and strip straightening under the action of bending rollers described in Example 1 is used to calculate the residual stress of a certain Y plate and strip material in the process of plate and strip straightening under the action of bending rollers. In this embodiment, the elastic modulus of the plate and strip material is 115GPa, the elastic limit stress is 500MPa, the plate width is 1000mm, the plate thickness is 1mm, and the roller spacing of the straightening rollers is 35mm. The specific implementation steps are as follows:

[0119] S1: Divide the plate and strip into n strips in the width direction and mark them as t1, t2, ..., t 50 , set the metal strip shape distribution BX, roller shape GX, straightening reverse curvature C w , as shown in Table 4;

[0120] Table 4 Plate shape, roll shape and reverse curvature setting parameters

[0121]

[0122] S2: Calculate the initial residual strain ε of the plate and strip c0i and the initial residual stress value σ c0i ;

[0123] ε c0i =10 -5 BX(1)

[0124] σ c0i =Eε c0i (2)

[0125] S3: According to

[0126]

[0127]

[0128] Calculate C w The corresponding bending deflection δ w =1.775, and add it to GX (assuming there are bending rollers above and below) to get the bending deflection of each strip in the width direction δ wi , according to δ wi Calculate the C corresponding to the i-th element wi ;

[0129] S4: Grant Initial value;

[0130] S5: Initial residual stress σC0i Residual stress after straightening The average value is taken as the tensile stress value σ during straightening Fi ;

[0131]

[0132] S6: Discrete m parts in the height direction of the plate and strip, and calculate the stress and strain in the X direction of each unit caused by the bending curvature and tension according to the ideal stress state, as shown in Table 5;

[0133]

[0134] ε wij =Z j C Wi A t (12)

[0135]

[0136] Table 5 Total strain and total stress of some units

[0137]

[0138]

[0139] S7: Calculate the elastic recovery and residual strain of each unit in the X direction, as shown in Table 6;

[0140]

[0141] ε cij =ε zij -ε tij (16)

[0142] Table 6 Partial unit elastic strain and residual strain

[0143] i 5 10 15 20 25 j 1 11 21 31 41 <![CDATA[ε tij ]]> -0.00396 -0.00396 -0.00396 -0.00396 -0.00353 <![CDATA[ε cij ]]> -0.00647 -0.00582 -0.00476 -0.00272 0 i 30 35 40 45 50 j 51 61 71 81 91 <![CDATA[ε tij ]]> 0.00003 0.00303 0.00396 0.00396 0.00396 <![CDATA[ε cij ]]> 0 0 0.00111 0.00243 0.00322

[0144] S8: Take the average value of the residual strain of the i-th strip in the height direction as the extension of the strip element, and add it to the initial residual strain to obtain the residual strain ε after straightening c1i , calculate the residual stress value σ in the width direction after straightening c1i ;

[0145]

[0146] σ c1i =Eε c1i (18)

[0147] S9: Calculated residual stress value σ c1iand the initial value of residual stress after straightening Calculate the maximum error and determine whether it is less than ξ. If not, set the initial value of the residual stress after straightening to Equal to the calculated residual stress value σ c1i , return to a5; if yes, output σ c1i and ε c1i ,like Figure 3 shown.

[0148] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for calculating residual stress during strip straightening under bending rollers, characterized in that: The following steps are involved: S1: Divide the plate and strip into n strips in the width direction and mark them as t1, t2, ..., t n , set the metal strip shape distribution BX, roller shape GX and straightening reverse curvature C w ; S2: Determine the initial residual strain ε of the plate and strip c0i and the initial residual stress value σ c0i ; S3: Determine C w The corresponding compression deflection δ w , and add it to GX to get the compression deflection δ of each element in the width direction wi , according to δ wi Determine the C corresponding to the i-th element wi ; S4: Grant Initial value; S5: Initial residual stress σ C0i Residual stress after straightening The average value is taken as the tensile stress value σ during straightening Fi ; S6: Discretize the plate and strip in m parts in the height direction, and determine the stress and strain in the X direction of each unit caused by the bending curvature and tension according to the ideal stress state; S7: Determine the elastic recovery and residual strain in the X direction of each unit; S8: Take the average value of the residual strain of the i-th element in the height direction as the extension of the element, add it to the initial residual strain to get the residual strain after straightening, and determine the residual stress value σ in the width direction after straightening c1i ; S9: Determined residual stress value σ c1i and the initial value of residual stress after straightening Determine the maximum error and determine whether it is less than ξ. If so, output σ c1i and ε c1i , complete the calculation, otherwise let the initial value of residual stress after straightening Equal to the determined residual stress value σ c1i , recalculate from step S5; S10: By analyzing the residual stress value σ c1i changes, optimize the process parameters during the straightening process, thereby better controlling the manufacturing process and ensuring the performance and reliability of the final product.

2. According to claim 1, a method for calculating residual stress during the straightening process of a plate strip under the action of a bending roller is characterized in that: In step S2, the initial residual strain ε of the plate and strip is determined c0i and the initial residual stress value σ c0i The specific process is: e c0i =10 -5 BX (1) s c0i =Ee c0i (2) In the formula, ε c0i is the initial residual strain of the i-th strip element; BX is the plate shape value; σ c0i is the initial residual stress value of the i-th strip element; E is the elastic modulus of the plate and strip material.

3. According to claim 1, a method for calculating residual stress in the process of strip straightening under the action of bending rollers is characterized by: In step S3, it is determined that C w The corresponding compression deflection δ w The specific process is: Where C0 is the original longitudinal curvature of the plate, which is taken as 0; C W is the reverse bending ratio of the working roll; C C is the residual curvature ratio; is the residual deflection ratio; is the elastic-complex deflection ratio; is the total deflection ratio of compression and bending; δ t is the elastic limit deflection; δ w is the total bending deflection; M t is the elastic limit bending moment; B is the width of the material; H is the thickness of the material; σ t is the elastic limit stress value of the material.

4. According to claim 1, a method for calculating residual stress during the straightening process of a plate strip under the action of a bending roller is characterized in that: In step S3, if there are bending rollers above and below the straightening roller, the bending deflection δ w Directly add GX to obtain the compression and bending deflection δ of each element in the width direction wi ; If only one row has bending rollers, the bending deflection δ w Adding 0.5 times GX gives the compression deflection δ of each strip in the width direction. wi .

5. According to claim 1, a method for calculating residual stress in the process of strip straightening under the action of bending rollers is characterized by: In the step S4, The initial value of is 0.

6. According to claim 1, a method for calculating residual stress in the process of strip straightening under the action of bending rollers is characterized by: In step S5, the tensile stress value σ during the straightening process Fi The values ​​are: In the formula, σ Fi is the tensile stress value, σ C0i is the initial residual stress, is the residual stress after straightening.

7. According to claim 1, a method for calculating residual stress in the process of strip straightening under the action of bending rollers is characterized by: In step S6, the stress and strain in the X direction of each unit caused by the bending curvature and the tension are: ε wij =Z j C Wi A t (12) In the formula, A t is the elastic limit curvature of the plate and strip; ε t is the elastic limit strain of the material; ε wij is the strain caused by bending of the i-th strip element in the width direction and the j-th unit in the height direction; ε zij is the total strain of the i-th strip element in the width direction and the j-th unit in the height direction; Z j The distance between the jth unit and the middle surface of the material, which is negative below the middle surface; σ ij is the total stress of the i-th strip element in the width direction and the j-th element in the height direction.

8. The method for calculating residual stress during the straightening process of a plate strip under the action of a bending roller according to claim 1, characterized in that: In step S7, the elastic recovery and residual strain of each unit in the X direction e cij =e zij -e tij (16) In the formula, ε tij is the elastic strain of the i-th strip element in the width direction and the j-th strip element in the height direction; ε cij is the plastic strain of the i-th strip element in the width direction and the j-th element in the height direction.

9. The method for calculating residual stress during the straightening process of a plate strip under the action of a bending roller according to claim 1, characterized in that: In step S8, the residual stress value σ in the width direction after straightening c1i for: s c1i =Ee c1i (18) In the formula, ε c1i is the residual strain value of the i-th strip after straightening.

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