Prediction method for residual stress in roller type straightening process of metal plate

Abstract

The invention belongs to the technical field of plate straightening, and particularly relates to a method for predicting residual stress in the roller type straightening process of a metal plate. In the calculation process, various influences of technological parameters on the straightening process in the roller type straightening process are comprehensively considered, the obtained residual stress value is basically close to an actual value, and the calculation precision is improved. The method is safe, reliable, accurate in calculation, simple and convenient, the straightening residual stress of the metal plate under different straightening technological procedures can be accurately predicted, and the product can be better applied to actual production.

Description

Technical Field

[0001] The invention belongs to the technical field of plate straightening, and in particular relates to a method for predicting residual stress in a metal plate roller straightening process. Background Art

[0002] With the development of economy and society and the improvement of the level of urban modernization, plates, as important materials for social infrastructure, are widely used in bridges, smart factories, shipbuilding, oil platforms, oil and gas pipelines, and high-rise buildings. At this stage, my country's steel is no longer facing competition in terms of output and low prices, but higher requirements in terms of appearance quality and performance quality. Therefore, how to achieve breakthroughs in steel production efficiency and quality is the focus of attention. In actual production, the surface flatness of the plate and the distribution of residual stress are important indicators that determine product quality. In particular, residual stress plays a vital role in the use of plates. When a bridge collapses or mechanical equipment is damaged, in addition to being related to the strength of the material itself, most of it is due to the influence of residual stress on it. Roller straightening machine is an important equipment on the production line to ensure product flatness and reduce residual stress.

[0003] The main purpose of the straightening process is to improve the plate shape and quality. At present, the research on straightening theory mainly focuses on the research of roller system structure, reduction, curvature and residual stress. Among them, the research on residual stress is of great significance to actual production. How to effectively reduce residual stress is directly related to the final quality of the plate.

[0004] At present, the traditional research methods for residual stress in roller straightening process mainly include experimental method, beam bending method and finite element method. The experimental method can only be used for specific processes each time and cannot meet the actual production needs; the beam bending method simplifies the straightening process, but is not suitable for accurate and quantitative calculation of residual stress; the time-consuming finite element method is limited by time and has a large amount of calculation, which is not convenient for actual engineering applications. Therefore, it is necessary to develop a prediction method for residual stress in roller straightening that is short in time, convenient in calculation and has more accurate calculation results. Summary of the invention

[0005] In view of the deficiencies in the prior art, an object of the present invention is to provide a method for predicting residual stress during roller straightening of metal sheets.

[0006] To achieve the above object, the technical solution of the present invention is as follows: A method for predicting residual stress during roller straightening of metal sheets comprises the following steps: Step 1: Determine the process parameters for straightening analysis according to the equipment conditions of a certain straightening process and the material properties of the metal sheet; Step 2: In a straightening zone, the metal sheet is divided into three-dimensional grids in the length, width and thickness directions. units, the width direction is divided into units, the thickness direction is divided into units, and from the length direction units, width direction Start counting from the units; Step 3: Initialize the residual stress in the width direction; Step 4: Initialize the inverse curvature in the width direction and calculate the curvature increment in the length direction; Step 5: Set the strain increment of the center line of the plate thickness and calculate the strain in the thickness direction. Stress distribution of the element, through the thickness direction The stress distribution of each unit has been calculated. Step 6: According to the convergence condition, determine whether the stress and tensile stress in the cross section are equal. If they are equal, proceed to the first step in the length direction. units, widthwise units, up to the width After all units are calculated, enter the length direction. units, widthwise units, the final length direction Units, width direction All calculations for each unit are completed; if they are not equal, reset the strain increment of the plate thickness centerline in step 5 and repeat step 5 until they are equal; Step 7: Enter the next straightening interval and repeat the operations from step 2 to step 6 to obtain the stress distribution of the metal sheet in all straightening intervals; Step 8: Solve the linear equations according to the stress distribution of the metal sheet in all straightening intervals, and correct the strain increment of the center line of the plate thickness of each unit in each straightening interval; Step 9: Recalculate the stress distribution of all straightening intervals according to the corrected strain increment of the plate thickness centerline of each unit in each straightening interval; Step 10: According to the convergence condition, determine whether the stress satisfies the residual stress self-balance principle. If so, output the residual stress calculation result; if not, reinitialize the inverse curvature in the width direction, calculate the curvature increment in the length direction, repeat the operation in step 9 to calculate the stress, and output the residual stress calculation result; Step 11: Solve for the standard deviation of residual stress and complete the prediction.

[0007] Furthermore, the process parameters of the straightening analysis in step 1 include the number of straightening rollers , straightening roller diameter , straightening roller pitch , straightening roller entrance pressure , straightening roller outlet pressure , metal sheet yield stress , elastic modulus , Poisson's ratio , Metal sheet thickness , Metal sheet width and the initial curvature .

[0008] Furthermore, the specific method for initializing the residual stress in the width direction in step 3 is: ; in, is the residual stress in the width direction, is the width direction coordinate, ±: + represents side wave, - represents medium wave.

[0009] Furthermore, the specific method of initializing the inverse curvature in the width direction in step 4 is: ; in, For the The reverse curvature distribution of the roller along the width direction, For the Roller reduction distribution along the width direction; The specific method for calculating the curvature increment in the length direction in step 4 is: ; in, is the curvature increment in the length direction, is the curvature change between the two straightening intervals, For the The reverse curvature distribution of the roller along the width direction.

[0010] Furthermore, the specific process of step 5 is as follows: Step 5.1: According to the curvature increment in the length direction Set the strain increment at the center line of the plate thickness , specifically: ; in, Indicates the thickness direction Unit in The stress distribution in the direction, Indicates the thickness direction Unit in The plate thickness centerline offset in the direction, Indicates the thickness direction The distance from the element to the center line of the plate thickness; Step 5.2: Calculate the thickness direction Unit in Strain increment in the direction , specifically: ; Step 5.3: Calculate the thickness direction Unit in direction, Stress increment in the direction , , specifically: Within the elastic range: like : ; ; like : ; ; In the plastic range: like : ; ; ; like : ; ; ; Step 5.4: Calculate the thickness direction Unit in direction, Stress distribution in the direction , , specifically: ; ; Step 5.5: Repeat steps 5.2 to 5.4 until the thickness is The stress distribution of each unit is calculated.

[0011] Furthermore, the convergence condition in step 6 is: ; in, Represents the tensile stress in the cross section.

[0012] Furthermore, the linear equations in step 8 are: ; in, Indicates the width direction The stress increment on each element is Indicates the width direction The plate thickness centerline offset on each element, Indicates the width direction The curvature increment over the element, Indicates the width direction The plate thickness centerline strain increment on each element.

[0013] Furthermore, the convergence condition in step 10 is: Direction and The resultant force on the cross section is zero: ; ; The bending moment about the center plane is zero: ; .

[0014] Furthermore, the specific method for solving the residual stress standard deviation in step 11 is: ; in, is the standard deviation of residual stress.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention predicts the straightening residual stress of the metal sheet during the roller straightening process, and the obtained residual stress value is basically close to the actual value. In the calculation process, the various effects of the process parameters on the straightening process during the roller straightening process are comprehensively considered to improve the calculation accuracy. The method of the present invention is safe and reliable, accurate in calculation, simple and convenient, and can accurately predict the straightening residual stress of the metal sheet under different straightening process regulations, so that the product can be better applied to actual production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of eleven-roller straightening provided by the present invention; Figure 2 This is a schematic diagram of dividing a plate into units according to the present invention; Figure 3 This is a comparison chart of the predicted value of the straightening residual stress of the present invention and the actual value at a certain site. DETAILED DESCRIPTION

[0017] In order to facilitate the understanding of the present invention, the present invention will be described more fully below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive. Example

[0018] The straightening equipment used in this embodiment is an eleven-roll straightening machine, such as Figure 1 As shown, the upper rollers of the straightening machine are tilted and pressed down, while the lower rollers are fixed. As long as the pressing amount of the head and tail rollers of the upper rollers is set, the pressing amount of the entire roller system can be determined according to the linear decrease. In each straightening interval, the straightening movement direction is defined as positive, the vertical downward direction is positive, the downward convex deformation curvature is positive, and the bending moment is positive. The specific implementation method of this embodiment is described as follows.

[0019] Step 1: Determine the process parameters of straightening analysis according to the equipment conditions of a certain straightening process and the material properties of the metal sheet. The process parameters of straightening analysis include the number of straightening rollers , straightening roller diameter , straightening roller pitch , straightening roller entrance pressure , straightening roller outlet pressure , metal sheet yield stress , elastic modulus , Poisson's ratio , Metal sheet thickness , Metal sheet width and the initial curvature .

[0020] Step 2: In a straightening interval, the metal sheet is divided into three-dimensional grids in the length, width and thickness directions, such as Figure 2 As shown, the length direction is divided into units, the width direction is divided into units, the thickness direction is divided into units, and from the length direction units, width direction Start counting units.

[0021] Step 3: Initialize the residual stress in the width direction, specifically: ; in, is the residual stress in the width direction, is the width direction coordinate, ±: + represents side wave, - represents middle wave; In this embodiment, the calculation for: .

[0022] Step 4: Initialize the inverse curvature in the width direction and calculate the curvature increment in the length direction; The specific method of initializing the inverse curvature in the width direction is: ; in, For the The reverse curvature distribution of the roller along the width direction, For the Roller reduction distribution along the width direction; The specific method for calculating the curvature increment in the length direction is: ; in, is the curvature increment in the length direction, is the curvature change between the two straightening intervals, For the The reverse curvature distribution of the roller along the width direction.

[0023] This embodiment takes the first unit of the first straightening interval and the first unit of the second straightening interval as examples, and the calculation process is as follows: ; ; ; in, is the inverse curvature of the first unit in the width direction of the first roller, is the reverse curvature of the first unit in the width direction of the second roller, It is the pressure reduction of the first unit of the entrance roller in the width direction.

[0024] Step 5: Set the strain increment of the center line of the plate thickness and calculate the strain in the thickness direction. Stress distribution of the element, through the thickness direction The stress distribution of each unit is calculated. The specific process is as follows: Step 5.1: According to the curvature increment in the length direction Set the strain increment at the center line of the plate thickness , specifically: ; in, Indicates the thickness direction Unit in The stress distribution in the direction, Indicates the thickness direction Unit in The plate thickness centerline offset in the direction, Indicates the thickness direction The distance from the element to the center line of the plate thickness; This embodiment sets ; Step 5.2: Calculate the thickness direction Unit in Strain increment in the direction , specifically: ; In this embodiment, the first unit in the thickness direction (i.e. ) as an example, the strain increment of the first unit in the thickness direction is solved as ; Step 5.3: Calculate the thickness direction Unit in direction, Stress increment in the direction , , specifically: Within the elastic range: like : ; ; like : ; ; In the plastic range: like : ; ; ; like : ; ; ; In this embodiment, the elastic range For example, the solution is that the first unit in the thickness direction is direction, Stress increment in the direction , for: ; ; Step 5.4: Calculate the thickness direction Unit in direction, Stress distribution in the direction , , specifically: ; ; This embodiment takes the first unit in the thickness direction as an example and solves the first unit in the thickness direction. direction, Stress distribution in the direction , for: ; ; Step 5.5: Repeat steps 5.2 to 5.4 until the thickness is The stress distribution of each unit is calculated.

[0025] Step 6: According to the convergence condition, determine whether the stress and tensile stress in the cross section are equal. If they are equal, proceed to the first step in the length direction. units, widthwise units, up to the width After all units are calculated, enter the length direction. units, widthwise units, the final length direction Units, width direction All calculations for each unit are completed; if they are not equal, reset the strain increment of the plate thickness centerline in step 5 and repeat step 5 until they are equal; The convergence condition is: ; in, Represents the tensile stress in the cross section.

[0026] Step 7: Enter the next straightening interval and repeat the operations from step 2 to step 6 to obtain the stress distribution of the metal sheet in all straightening intervals; Step 8: Solve the linear equations according to the stress distribution of the metal sheet in all straightening intervals, and correct the strain increment of the center line of the plate thickness of each unit in each straightening interval; The linear equations are: ; in, Indicates the width direction The stress increment on each element is Indicates the width direction The plate thickness centerline offset on each element, Indicates the width direction The curvature increment over the element, Indicates the width direction The plate thickness centerline strain increment on each element.

[0027] In this embodiment, the plate thickness centerline strain increment on the first unit in the width direction is For example, the solution is .

[0028] Step 9: Recalculate the stress distribution of all straightening intervals according to the corrected strain increment of the plate thickness centerline of each unit in each straightening interval; Step 10: According to the convergence condition, determine whether the stress satisfies the residual stress self-balance principle. If so, output the residual stress calculation result; if not, reinitialize the inverse curvature in the width direction, calculate the curvature increment in the length direction, repeat the operation in step 9 to calculate the stress, and output the residual stress calculation result; The convergence condition is: Direction and The resultant force on the cross section is zero: ; ; The bending moment about the center plane is zero: ; ; Step 11: Solve for the standard deviation of residual stress , complete the prediction; The calculation formula for solving the residual stress standard deviation is as follows: ; in, is the standard deviation of residual stress.

[0029] In this embodiment, the inlet pressure is For example, the solution is It is 4.497MPa.

[0030] According to the method for predicting residual stress in the roller straightening process of metal sheets proposed by the present invention, the model prediction value of the metal sheet used and the actual value of a certain site are statistically analyzed as follows: Figure 3 As shown, by comparing the results, it can be obtained that the residual stress of the metal plate predicted by the present invention is consistent with the actual value, and the residual stress calculation error is within 10%. It can be seen that the residual stress of the metal plate in the roller straightening process predicted by the present invention has higher accuracy and can be better applied in actual production.

[0031] The above description is only for better explaining the embodiments of the present invention, and is not intended to limit the present invention. Any modification or equivalent substitution that does not depart from the spirit and scope of the present invention shall fall within the scope of the present invention.

Claims

1. A method for predicting residual stress during roller straightening of metal sheets, characterized in that: The following steps are involved: Step 1: Determine the process parameters for straightening analysis according to the equipment conditions of a certain straightening process and the material properties of the metal sheet; Step 2: In a straightening zone, the metal sheet is divided into three-dimensional grids in the length, width and thickness directions. units, the width direction is divided into units, the thickness direction is divided into units, and from the length direction units, widthwise Start counting from the units; Step 3: Initialize the residual stress in the width direction; Step 4: Initialize the inverse curvature in the width direction and calculate the curvature increment in the length direction; Step 5: Set the strain increment of the center line of the plate thickness and calculate the strain in the thickness direction. Stress distribution of the element, through the thickness direction The stress distribution of each unit is calculated. Step 6: According to the convergence condition, determine whether the stress and tensile stress in the cross section are equal. If they are equal, proceed to the first step in the length direction. units, widthwise units, up to the width After all units are calculated, enter the length direction. units, widthwise units, the final length direction Units, width direction All calculations for each unit are completed; if they are not equal, reset the strain increment of the plate thickness centerline in step 5 and repeat step 5 until they are equal; Step 7: Enter the next straightening interval and repeat the operations from step 2 to step 6 to obtain the stress distribution of the metal sheet in all straightening intervals; Step 8: Solve the linear equations according to the stress distribution of the metal sheet in all straightening intervals, and correct the strain increment of the center line of the plate thickness of each unit in each straightening interval; Step 9: Recalculate the stress distribution of all straightening intervals according to the corrected strain increment of the plate thickness centerline of each unit in each straightening interval; Step 10: According to the convergence condition, determine whether the stress satisfies the residual stress self-balance principle. If so, output the residual stress calculation result; if not, reinitialize the inverse curvature in the width direction, calculate the curvature increment in the length direction, repeat the operation in step 9 to calculate the stress, and output the residual stress calculation result; Step 11: Solve for the standard deviation of residual stress and complete the prediction.

2. The method for predicting residual stress during roller straightening of metal sheets according to claim 1, characterized in that: The process parameters of the straightening analysis in step 1 include the number of straightening rollers , straightening roller diameter , straightening roller pitch , straightening roller entrance pressure , straightening roller outlet pressure , metal sheet yield stress , elastic modulus , Poisson's ratio , Metal sheet thickness , Metal sheet width and the initial curvature .

3. The method for predicting residual stress during roller straightening of metal sheets according to claim 2, characterized in that: The specific method for initializing the residual stress in the width direction in step 3 is: ； in, is the residual stress in the width direction, is the width direction coordinate, ±: + represents side wave, - represents medium wave.

4. The method for predicting residual stress during roller straightening of metal sheets according to claim 3, characterized in that: The specific method for initializing the inverse curvature in the width direction in step 4 is: ； in, For the The reverse curvature distribution of the roller along the width direction, For the Roller reduction distribution along the width direction; The specific method for calculating the curvature increment in the length direction in step 4 is: ； in, is the curvature increment in the length direction, is the curvature change between the two straightening intervals, For the The reverse curvature distribution of the roller along the width direction.

5. The method for predicting residual stress during roller straightening of metal sheets according to claim 4, characterized in that: The specific process of step 5 is as follows: Step 5.1: According to the curvature increment in the length direction Set the strain increment at the center line of the plate thickness , specifically: ； in, Indicates the thickness direction Unit in The stress distribution in the direction, Indicates the thickness direction Unit in The plate thickness centerline offset in the direction, Indicates the thickness direction The distance from the element to the center line of the plate thickness; Step 5.2: Calculate the thickness direction Unit in Strain increment in the direction , specifically: ； Step 5.3: Calculate the thickness direction Unit in direction, Stress increment in the direction , , specifically: Within the elastic range: like : ; ； like : ; ； In the plastic range: like : ; ； ； like : ; ； ； Step 5.4: Calculate the thickness direction Unit in direction, Stress distribution in the direction , , specifically: ； ； Step 5.5: Repeat steps 5.2 to 5.4 until the thickness is The stress distribution of each unit is calculated.

6. The method for predicting residual stress during roller straightening of metal sheets according to claim 5, characterized in that: The convergence condition in step 6 is: ； in, Represents the tensile stress in the cross section.

7. The method for predicting residual stress during roller straightening of metal sheets according to claim 6, characterized in that: The linear equation system in step 8 is: ； in, Indicates the width direction The stress increment on each element is Indicates the width direction The plate thickness centerline offset on each element, Indicates the width direction The curvature increment over the element, Indicates the width direction The plate thickness centerline strain increment on each element.

8. The method for predicting residual stress during roller straightening of metal sheets according to claim 7, characterized in that: The convergence condition in step 10 is: Direction and The resultant force on the cross section is zero: ； ； The bending moment about the center plane is zero: ； 。 9. The method for predicting residual stress during roller straightening of metal sheets according to claim 8, characterized in that: The specific method for solving the residual stress standard deviation in step 11 is: ； in, is the standard deviation of residual stress.

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