Longitudinal bending control method, device and system in rolling process of high-strength steel square and rectangular pipe

Abstract

The invention discloses a longitudinal bending control method, device and system in the rolling process of a high-strength steel square and rectangular pipe, and the method comprises the steps: S1, introducing an intermediate pass curvature constraint according to a four-boundary condition, and constructing a forming angle distribution function; and S2, optimally distributing the forming angles according to the forming angle distribution function. By the adoption of the technical scheme, the defects of a traditional forming angle distribution mode in high-strength material forming are overcome, the forming precision and quality of direct square pipe forming production are improved, the longitudinal bending defect is reduced, and the production efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of cold bending forming, and in particular relates to a method, device and system for controlling longitudinal bending during a rolling process of a high-strength steel square tube. Background Art

[0002] With the continuous advancement of cold roll forming technology, the requirements for forming precision and quality are becoming increasingly stringent for the production of directly squared tubes. However, traditional angle distribution methods have many limitations when dealing with high-strength materials. Traditional methods often struggle to accurately distribute angles based on material properties, leading to defects such as longitudinal bending during the forming process of high-strength materials. This impacts product quality and production efficiency, making it difficult to meet the current demand for high-quality square tube production. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method, device and system for controlling the longitudinal bending of high-strength steel square tubes during the rolling process, so as to overcome the shortcomings of the traditional forming angle distribution method in the forming of high-strength materials, improve the forming accuracy and quality of directly square tube production, reduce longitudinal bending defects and improve production efficiency.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] The present invention also provides a method for controlling longitudinal bending during the rolling process of a high-strength steel square tube, comprising:

[0006] Step S1: According to the four boundary conditions, the intermediate pass curvature constraint is introduced to construct the forming angle distribution function;

[0007] Step S2: Optimize and distribute the forming angles according to the forming angle distribution function.

[0008] Preferably, in step S1, an adjustment coefficient α related to the material strain hardening exponent is introduced, and an intermediate pass curvature constraint is added on the basis of the four boundary conditions to construct a forming angle distribution function.

[0009] Preferably, the mathematical expression of the intermediate pass curvature constraint is: y″(N / 3)=α×k1 and y″(2N / 3)=α×k2, where y″ represents the second-order derivative of the sixth-order polynomial curve, and k1 and k2 are the curvature constraint coefficients of the intermediate pass.

[0010] The present invention also provides a device for controlling longitudinal bending during rolling of high-strength steel square tubes, comprising:

[0011] The first processing module is used to introduce the intermediate pass curvature constraint according to the four boundary conditions and construct the forming angle distribution function;

[0012] The second processing module is used to optimize the distribution of forming angles according to the forming angle distribution function.

[0013] Preferably, the first processing module constructs a forming angle distribution function by introducing an adjustment coefficient α related to the material strain hardening exponent and adding an intermediate pass curvature constraint on the basis of the four boundary conditions.

[0014] Preferably, the mathematical expression of the intermediate pass curvature constraint is: y″(N / 3)=α×k1 and y″(2N / 3)=α×k2, where y″ represents the second-order derivative of the sixth-order polynomial curve, and k1 and k2 are the curvature constraint coefficients of the intermediate pass.

[0015] The present invention also provides a longitudinal bending control system for a high-strength steel square tube rolling process, comprising: a memory and a processor, wherein the memory stores a computer program run by the processor, and when the computer program is run by the processor, a longitudinal bending control method for a high-strength steel square tube rolling process is executed.

[0016] Based on the four boundary conditions, this invention further introduces curvature constraints for intermediate passes. Combined with the material's strain hardening properties, this method constructs a forming angle allocation function, which is used to optimize the distribution of forming angles. By introducing an adjustment coefficient α, which is related to the material's strain hardening exponent, the forming angle allocation can be dynamically adjusted based on the material's deformation characteristics, improving forming accuracy. Furthermore, the addition of curvature constraints for intermediate passes allows for more precise forming angle allocation, avoiding localized stress concentration and excessive deformation, and improving the forming accuracy and quality of square tubes. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0018] Figure 1 This is a flow chart of a method for controlling longitudinal bending during the rolling process of high-strength steel square tubes according to an embodiment of the present invention;

[0019] Figure 2 Comparison diagram of longitudinal stress under three angle distribution methods;

[0020] Figure 3 Comparison diagram of longitudinal strain under three angle allocation methods;

[0021] Figure 4 This is an analysis diagram of longitudinal warpage at different spacings based on the work hardening function allocation method;

[0022] Figure 5 This is an analysis diagram of longitudinal warpage under different profile thicknesses based on the work hardening function allocation method;

[0023] Figure 6 This is the finite element model and physical picture of the square tube with longitudinal bending defects;

[0024] Figure 7 To correct the defects, the finite element model and physical diagram of the rear tube are provided;

[0025] Figure 8 The finite element model and physical picture of the square tube with longitudinal warping defect;

[0026] Figure 9 To correct the defects, the finite element model and physical diagram of the rear tube are provided;

[0027] Figure 10 The roll die diagram is assigned considering the work hardening parameter angle for S550GD galvanized material;

[0028] Figure 11 The roller pattern diagram is distributed considering the work hardening parameter angle for S550GD galvanized material. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] Example 1:

[0032] like Figure 1 As shown, an embodiment of the present invention provides a method for controlling longitudinal bending during a rolling process of a high-strength steel square tube, comprising:

[0033] Step S1: According to the four boundary conditions, the intermediate pass curvature constraint is introduced to construct the forming angle distribution function;

[0034] Step S2: Optimize and distribute the forming angles according to the forming angle distribution function.

[0035] As an implementation method of an embodiment of the present invention, the horizontal projection trajectory of the plate end follows a sixth-order polynomial:

[0036] y=ax 6 +bx5 +cx 4 +dx 3 +ex 2 +fx+g

[0037] In the formula, a, b, c, d, e, f, and g are constants. Any point x on the sixth-order curve at the flange end is represented by i, and the corresponding y value is Hcosθi. The boundary conditions are constructed to establish the following set of equations:

[0038]

[0039] Where: N is the total number of passes; H is the plate width; θN / 3 and θ2N / 3 are the bending angles at the N / 3 and 2N / 3 passes respectively; k1 and k2 are the curvature constraint coefficients of the intermediate passes;

[0040] α is an adjustment factor related to the strain hardening exponent of the material and is defined as α=1+0.5×(n−0.1), where n is the strain hardening exponent of the material.

[0041] Substituting the boundary conditions into the sextic polynomial, we obtain a system of equations containing 7 unknowns (a, b, c, d, e, f, g).

[0042]

[0043] Use Python's SymPy library for symbolic calculations to solve the system of equations and obtain the coefficients a, b, c, d, e, f, g of the sextet polynomial.

[0044] import sympy as sp import math

[0045] #define symbol variables

[0046] x = sp.symbols('x')

[0047] a,b,c,d,e,f,g=sp.symbols('abcdef g')

[0048] N,H,theta_N3,theta_2N3,alpha,k1,k2=sp.symbols('NH theta_N3 theta_2N3 alpha k1 k2')

[0049] #Define a sextic polynomial

[0050] y=a*x**6+b*x**5+c*x**4+d*x**3+e*x**2+f*x+g

[0051] #Define seven boundary conditions

[0052] eq1 = y.subs(x, 0) # y(0)=0

[0053] eq2 = sp.diff(y, x).subs(x, 0) # y'(0)=0

[0054] eq3 = sp.diff(y, x, 2).subs(x, 0) # y”(0)=0

[0055] eq4 = y.subs(x, N) - H # y(N)=H <s

[0056] eq5 = sp.diff(y, x).subs(x, N) # y'(N)=0

[0057] eq6 = sp.diff(y, x, 2).subs(x, N) # y”(N)=0

[0058] eq7 = y.subs(x, N / 3) - H * sp.cos(theta_N3) # y(N / 3)=H*cos(theta_N3)

[0059] eq8 = y.subs(x, 2 * N / 3) - H * sp.cos(theta_2N3) # y(2N / 3)=H*cos(theta_2N3)

[0060] eq9 = sp.diff(y, x, 2).subs(x, N / 3) - alpha * k1 # y”(N / 3)=alpha*k1

[0061] eq10 = sp.diff(y, x, 2).subs(x, 2 * N / 3) - alpha * k2 # y”(2N / 3)=alpha*k2

[0062] # Solve the system of equations

[0063] solution = sp.solve((eq1, eq2, eq3, eq4, eq5, eq6, eq7, eq8, eq9, eq10), (a, b, c, d, e, f, g))

[0064] # Assume parameter values <0000e153>N_val = 9

[0066] H_val = 100

[0067] theta_N3_val = sp.rad(37) # Assume theta_N3 is 37 degrees

[0068] theta_2N3_val = sp.rad(68) # Assume theta_2N3 is 68 degrees

[0069] alpha_val = 1.05

[0070] k1_val = 1.0

[0071] k2_val = 1.0

[0072] # Substitute parameter values to calculate coefficients

[0073] a_val = solution[a].subs({N: N_val, H: H_val, theta_N3: theta_N3_val, theta_2N3: theta_2N3_val, alpha: alpha_val, k1: k1_val, k2: k2_val})

[0074] b_val = solution[b].subs({N: N_val, H: H_val, theta_N3: theta_N3_val, theta_2N3: theta_2N3_val, alpha: alpha_val, k1: k1_val, k2: k2_val})

[0075] c_val = solution[c].subs({N: N_val, H: H_val, theta_N3: theta_N3_val, theta_2N3: theta_2N3_val, alpha: alpha_val, k1: k1_val, k2: k2_val})

[0076] d_val = solution[d].subs({N: N_val, H: H_val, theta_N3: theta_N3_val, theta_2N3: theta_2N3_val, alpha: alpha_val, k1: k1_val, k2: k2_val})

[0077] e_val = solution[e].subs({N: N_val, H: H_val, theta_N3: theta_N3_val, theta_2N3: theta_2N3_val, alpha: alpha_val, k1: k1_val, k2: k2_val})

[0078] f_val=solution[f].subs({N:N_val,H:H_val,theta_N3:theta_N3_val,theta_2N3:theta_2N3_val,alpha:alpha_val,k1:k1_val,k2:k2_val})

[0079] g_val=solution[g].subs({N:N_val,H:H_val,theta_N3:theta_N3_val,theta_2N3:theta_2N3_val,alpha:alpha_val,k1:k1_val,k2:k2_val})

[0080] #Calculate the bending angle for each pass

[0081] angles=[]for iin range(N_val+1):

[0082] x_val=i

[0083] y_val=a_val*x_val**6+b_val*x_val**5+c_val*x_val**4+d_val*x_val**3+e_val*x_val**2+f_val*x_val+g_val

[0084] theta_val=math.degrees(sp.acos(y_val / H_val))

[0085] angles.append(theta_val)

[0086] #Output the bending angle of each pass for i,theta in enumerate(angles):

[0087] print(f"Pass {i}: {theta: .2f}°")

[0088] Where yi is the y-coordinate at the i-th pass, calculated using the above sixth-order polynomial.

[0089] By solving this system of equations, we obtain the specific values ​​of each coefficient and thus determine the forming angle distribution function. During the cold roll forming process, the horizontal projection trajectory of the sheet metal end can be approximated as an arc. At each pass i, the vertical distance of the horizontal projection of the sheet metal end is yi, and the width of the square tube is H. The forming angle θi at that pass is then calculated using the following formula:

[0090] θi=arccos(yi / H)

[0091] Refine control strategy

[0092] The adjustment coefficient α related to the material strain hardening exponent is introduced so that the forming angle distribution can be dynamically adjusted according to the deformation characteristics of the material, thereby improving the forming accuracy.

[0093] Refined process control

[0094] Adding curvature constraints in the intermediate passes makes the forming angle distribution more refined, avoids local stress concentration and excessive deformation, and improves the forming accuracy and quality of square tubes.

[0095] Introduction of curvature constraints

[0096] Traditional four-boundary conditions primarily consider constraints such as the starting point, end point, slope, and curvature, but these conditions are typically only applied at the beginning and end of the forming process. In contrast, the improved boundary conditions retain these constraints while also introducing curvature constraints at intermediate passes (such as at 1 / 3 and 2 / 3 of the total number of passes). These intermediate curvature constraints allow for more precise control of stress and strain distribution during the forming process, preventing local stress concentration and excessive deformation.

[0097] Mathematical expression of curvature constraint

[0098] In the set of seven boundary conditions, the newly added curvature constraint is:

[0099] y″(N / 3)=α×k1

[0100] y″(2N / 3)=α×k2

[0101] Where y″ represents the second-order derivative of the sixth-order polynomial curve, reflecting the curvature of the curve at that point. k1 and k2 are the curvature constraint coefficients of the intermediate passes, which are used to control the curvature magnitude at the intermediate position. By introducing these constraints, the degree of bending during the forming process can be more accurately adjusted, avoiding longitudinal bending defects caused by excessive local curvature.

[0102] Optimization of forming process with curvature constraint

[0103] By introducing curvature constraints in the intermediate passes, the forming angle distribution function can better adapt to the material's deformation characteristics, ensuring a smooth and uniform forming process. For example, during the forming of S550GD material, due to its high yield strength and low strain hardening exponent, the material is more susceptible to localized stress concentrations during the forming process. By adjusting the curvature constraint coefficients k1 and k2 in the intermediate passes, these localized stresses can be effectively controlled, resulting in a more reasonable forming angle distribution and reducing the occurrence of longitudinal bending defects.

[0104] Practical Application of Curvature Constraints

[0105] In practical applications, the values ​​of the curvature constraint coefficients k1 and k2 can be adjusted and optimized based on specific process requirements and material properties. For example, for high-strength materials (such as S550GD), the curvature constraint coefficient can be appropriately increased in the intermediate passes to increase local rigidity and reduce stress concentration during the forming process. For materials with good ductility, the curvature constraint coefficient can be appropriately reduced to allow for greater local deformation.

[0106] Verification of curvature constraints

[0107] Finite element simulation and experimental verification can be used to evaluate the impact of curvature constraints on the forming process. In the finite element simulation, it can be observed that the introduction of curvature constraints in the intermediate passes leads to a more uniform distribution of stress and strain, and a significant reduction in local stress peaks. In the experiment, the effectiveness of curvature constraints in improving forming quality can be verified by measuring the geometric deviation and defect level of the formed parts.

[0108] To address the problem of high-strength steel square tubes being prone to longitudinal bending defects during the rolling process due to their high material strength and significant strain hardening properties, the present invention introduces an adjustment coefficient α related to the material strain hardening exponent and adds an intermediate pass curvature constraint on the basis of four boundary conditions to construct a forming angle allocation function to optimize the forming angle allocation. Starting from theoretical analysis, the present invention conducts in-depth research on material properties, process parameters, and stress-strain distribution during the forming process, and proposes a forming angle allocation method based on the material strain hardening properties. Through theoretical analysis and defect research of this method, it is found that it can effectively reduce the occurrence of longitudinal bending defects. On this basis, the present invention proposes a series of targeted measures, such as dynamically adjusting the forming angle allocation and adding intermediate pass curvature constraints, to improve forming accuracy and quality. The method of the present invention can dynamically adjust the forming angle allocation according to the material properties, is suitable for the rolling production of high-strength steel square tubes, is innovative and practical, and can be widely used in the production and manufacturing of high-strength steel square tubes in the field of cold bend forming.

[0109] Examples:

[0110] Taking the direct production of square tubes made of a certain high-strength material as an example, the material is first subjected to tensile tests, etc. to obtain its strain hardening characteristic parameters and establish a stress-strain relationship model. Then, the approximate angle range of the forming process is determined based on the four boundary conditions. On this basis, combined with the actual production process, the appropriate curvature constraint value of the intermediate pass is set. The material characteristic data, four boundary conditions and intermediate pass curvature constraint conditions obtained above are substituted into the pre-constructed forming angle distribution function model and solved to obtain the optimized forming angle distribution results for each pass. Actual production is carried out according to this angle distribution scheme, and the production roller drawings and roller pattern are as follows. Figure 9 、 10 As shown, compared with the traditional method, it can effectively reduce the longitudinal bending defects of square tubes, improve the dimensional accuracy and surface quality of products, shorten the production cycle and improve production efficiency.

[0111] The angle function forming method based on the work hardening index is compared with the traditional four-boundary conditions and the angle allocation method with 10 angle increments as shown in Table 1:

[0112] Table 1

[0113]

[0114] Comparing the three forming methods, it can be found that the longitudinal strain and longitudinal stress generated by the work hardening parameter distribution function are lower than those of the other two methods, e.g. Figure 2 and Figure 3 Comparison of longitudinal stress and strain under three angle distribution methods.

[0115] Secondly, for the method based on the work hardening parameter allocation function, the rolling mill parameters are adjusted and optimized to obtain the optimal method. Through this method, the spacing between the frame arches is adjusted and it is found that too large a spacing will lead to an increase in warpage, such as Figure 4 The longitudinal warping analysis diagram under different spacings based on the work hardening function distribution method. At the same time, according to the different thickness of the profile, it is analyzed that the increase of the profile thickness will aggravate the longitudinal warping of the square tube. Figure 5 Analysis of longitudinal warpage under different profile thicknesses based on the work hardening function distribution method.

[0116] After adjustment, compared with the original solution, the longitudinal warping defect of the square tube has been improved. Figure 6 、 7 Figures 8 and 9 show the finite element model and actual image of a square tube with longitudinal bending defects, and the finite element model and actual image of a square tube after the defects are corrected. Figures 8 and 9 show the finite element model and actual image of a square tube with longitudinal warping defects, and the finite element model and actual image of a square tube after the defects are corrected.

[0117] This method comprehensively considers material properties, process parameters, and the stress-strain distribution during the forming process. By introducing intermediate pass curvature constraints and combining them with the material's strain hardening characteristics to optimize forming angle distribution, it provides a more accurate and efficient forming angle distribution scheme for the production of directly squared tubes. This method is particularly effective when processing high-strength materials, significantly improving the quality and precision of formed parts. It is highly innovative and practical, and can be widely applied to the production of high-strength square tubes in the cold-formed field.

[0118] Example 2:

[0119] The embodiment of the present invention further provides a device for controlling longitudinal bending of a high-strength steel square tube during a rolling process, comprising:

[0120] The first processing module is used to introduce the intermediate pass curvature constraint according to the four boundary conditions and construct the forming angle distribution function;

[0121] The second processing module is used to optimize the distribution of forming angles according to the forming angle distribution function.

[0122] As an implementation of an embodiment of the present invention, the first processing module constructs a forming angle distribution function by introducing an adjustment coefficient α related to the material strain hardening exponent and adding an intermediate pass curvature constraint on the basis of four boundary conditions.

[0123] As an implementation method of an embodiment of the present invention, the mathematical expression of the intermediate pass curvature constraint is: y″(N / 3)=α×k1 and y″(2N / 3)=α×k2, where y″ represents the second-order derivative of the sixth-order polynomial curve, and k1 and k2 are the curvature constraint coefficients of the intermediate pass.

[0124] Example 3:

[0125] An embodiment of the present invention also provides a longitudinal bending control system for a high-strength steel square tube rolling process, comprising: a memory and a processor, wherein the memory stores a computer program run by the processor, and when the computer program is run by the processor, it executes a longitudinal bending control method for a high-strength steel square tube rolling process.

[0126] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for controlling longitudinal bending during rolling of high-strength steel square tubes, characterized in that: include: Step S1: According to the four boundary conditions, the intermediate pass curvature constraint is introduced to construct the forming angle distribution function; Step S2: Optimize and distribute the forming angles according to the forming angle distribution function.

2. The method for controlling longitudinal bending during rolling of high-strength steel square tubes according to claim 1, wherein: In step S1, the forming angle distribution function is constructed by introducing an adjustment coefficient α related to the material strain hardening exponent and adding an intermediate pass curvature constraint on the basis of the four boundary conditions.

3. The method for controlling longitudinal bending during rolling of high-strength steel square tubes according to claim 2, wherein: The mathematical expression of the intermediate pass curvature constraint is: y″(N / 3)=α×k1 and y″(2N / 3)=α×k2, where y″ represents the second-order derivative of the sixth-order polynomial curve, and k1 and k2 are the curvature constraint coefficients of the intermediate pass.

4. A device for controlling longitudinal bending during rolling of high-strength steel square tubes, characterized in that: include: The first processing module is used to introduce the intermediate pass curvature constraint according to the four boundary conditions and construct the forming angle distribution function; The second processing module is used to optimize the distribution of forming angles according to the forming angle distribution function.

5. The device for controlling longitudinal bending of high-strength steel square tubes during rolling process according to claim 4, characterized in that: The first processing module constructs a forming angle distribution function by introducing an adjustment coefficient α related to the material strain hardening exponent and adding an intermediate pass curvature constraint on the basis of the four boundary conditions.

6. The device for controlling longitudinal bending of high-strength steel square tubes during rolling process according to claim 5, characterized in that: The mathematical expression of the intermediate pass curvature constraint is: y″(N / 3)=α×k1 and y″(2N / 3)=α×k2, where y″ represents the second-order derivative of the sixth-order polynomial curve, and k1 and k2 are the curvature constraint coefficients of the intermediate pass.

7. A longitudinal bending control system for high-strength steel square tube rolling process, characterized in that: include: A memory and a processor, wherein the memory stores a computer program executed by the processor, and when the computer program is executed by the processor, the method for controlling the longitudinal bending of a high-strength steel square tube during rolling is executed as described in any one of claims 1 to 3.

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