Analysis method for straightening using simple straightening analysis model

Abstract

To provide an analysis model capable of roughly reproducing influence of bending and unbending on damage values and distribution of the damage values due to straightening in a relatively short time.SOLUTION: A method for creating a deformation analysis model for straightening a round-bar steel material by bending and unbending, comprises: a step of setting geometric information to arrange a convex die with a convex curved surface and a concave die with a concave curved surface in contact with a one-way curved round-bar steel material from above and below along the curvature of the round-bar steel material; a step of moving at least one or both of the concave die and convex die vertically to press down and clamp the round-bar steel material; and a step of performing a straightening operation to move the concave die and the convex die in opposite directions along directions perpendicular to a longitudinal direction and a vertical direction while the round-bar steel material is still being pressed down. Therefore, the method can acquire numerical change in an object to be analyzed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an analysis method suitable for analyzing the straightening process of steel bars and the like using a simple analysis model. [Background technology]

[0002] Since the straightening process for steel bars generally involves bending and unbending, the reduction applied to the steel bar is not very large. However, when trying to achieve a greater straightening effect with two-roll straightening using concave and concave rolls, a slightly larger reduction may be applied. This can cause cracks to form in the center of the steel bar. Hereinafter, this type of crack will be referred to as "Mannesmann cracking."

[0003] Mannesmann cracking is evaluated using an integral ductile fracture equation (hereinafter referred to as "damage value") derived from strain, stress, etc. The damage value can be derived using CAE.

[0004] Mannesmann cracking is generally a problem that occurs mainly in rotary rolling, rolling, etc. Therefore, in rotary rolling and rolling, cracking is sometimes evaluated using a damage value.

[0005] On the other hand, in the analysis of the straightening process, although residual stress is analyzed, Mannesmann cracking has not been considered.

[0006] For example, Non-Patent Document 1 is a document that models the two-roll straightening process and performs a simple analysis of the residual stress of a wire rod using a three-dimensional elastic-plastic finite element method to evaluate the straightening process. However, no consideration is given to reduction, and there is no mention or suggestion of Mannesmann cracking. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Yanagibashi et al., "Effect of bending plasticity rate and number of repetitions on straightness in two-roll straightening - Study on straightening and residual stress in wire rods (3rd report)", Plasticity and Processing, Vol. 46, No. 537, pp. 972-976 (Published by the Japan Society for Technology of Plasticity) Summary of the Invention [Problem to be solved by the invention]

[0008] The reason why Mannesmann cracking has not been studied is that it has not been a significant problem in the straightening process and has not been a publicly known issue. Therefore, there has been no precedent for evaluating Mannesmann cracking by deriving a damage value, and in fact, no existing analysis has taken into account the application of reduction during straightening.

[0009] There have been cases where damage values ​​have been calculated using rotary rolling. However, the straightening process behaves completely differently from rotary rolling in that bending and unbending are performed simultaneously with reduction, so it is impossible to apply the results as is. This is because it was completely unknown and unknown how bending and unbending processes would affect damage values.

[0010] To evaluate the effect of bending and unbending on damage values ​​and Mannesmann cracking during actual straightening processing, an analytical model that mimics the actual straightening process must first be created and analyzed. However, in CAE for straightening, due to the small amount of contact and the long contact length, a fine mesh must be cut into the long material. This increases the number of meshes, which results in a long analysis time. Therefore, even if it is used for analysis, it is not easy to implement.

[0011] Therefore, the present invention aims to provide a method that can roughly reproduce, in a relatively short time, the influence of bending and unbending on damage values ​​and the damage value distribution due to straightening. That is, the present invention aims to obtain appropriate analysis results by making it possible to roughly reproduce the damage value distribution in concave-concave two-roll straightening in a relatively short time. [Means for solving the problem]

[0012] (Reasons for establishing the analytical model of the present invention) The main reason that analysis of straightening takes so long is that it is necessary to use a long steel model. Because the contact length between the steel bar and the roll is long during straightening using an actual machine, in order to represent the steady state part, it is necessary to create a steel model that is sufficiently long compared to the contact length. As the steel length increases, more mesh must be cut, which makes the analysis more complex and takes a long time. However, if the mesh is reduced and made coarse, not only will the calculation accuracy decrease, but it may also be possible that the analysis becomes impossible.

[0013] The straightening process that causes Mannesmann cracking involves applying pressure reduction and bending / unbending to a rotating steel material. Therefore, even for short steel materials, the analysis model of the present invention was developed based on the idea that the stress / strain history during straightening can be roughly estimated, and consequently the damage value can also be roughly estimated, if three elements are known: (i) rotation of the steel material, (ii) radial pressure reduction of the steel material, and (iii) bending / unbending of the steel material in the longitudinal direction.

[0014] For example, when a round steel bar is rolled with a plate-shaped die, a radial pressure is applied to the rotating steel. If the steel and the plate-shaped die surfaces are curved, bending can be applied at the same time, resulting in a process that satisfies all of the above (i), (ii), and (iii). Therefore, we thought it would be possible to roughly reproduce the strain and stress of straightening even when using relatively short steel bars.

[0015] Therefore, the first means for solving the problems of the present invention is a method for creating a deformation analysis model of a round steel bar material by bending and unbending, in which a round steel bar material curved in one direction is used as an analysis object, and this is divided into a finite number of pieces that can be handled, and the numerical changes are analyzed by the finite element method. The method is a method for creating a deformation analysis model of a round steel bar material by bending and unbending, in which a line segment connecting the centers of gravity of the end faces of a round steel bar material curved in one direction is defined as a center of gravity line segment, and the direction when a perpendicular line is drawn from point P on the steel side farthest from the center of gravity line segment to the center of gravity line is defined as the upward direction, and the downward direction is defined as the opposite direction to the upward direction, and the method is a method for creating a deformation analysis model of a round steel bar material curved in one direction by using a convex die having a convex curved surface and a concave ... This method for creating a deformation analysis model comprises the following steps in order: a first step of setting geometric information so that a concave die with a planar curved surface is positioned against the round steel bar so that it follows the curvature from above and below; a second step of moving at least one or both of the concave and convex dies in an up and down direction to clamp the round steel bar so as to press it down; and a third step of performing a corrective processing operation by moving the concave and convex dies in opposite directions along directions perpendicular to the longitudinal direction and the up and down direction while still in the pressed down state. This method makes it possible to obtain numerical changes in the object to be analyzed.

[0016] The second means is a method for creating a deformation analysis model described in the first means, in which the radius of curvature of the curve not including point P is R1, the radius of curvature of the curve including point P is R2, and the radius of curvature of the convex surface of the convex die, R3, and the radius of curvature of the concave surface of the concave die, R4, are modeled to satisfy R1=R2=R3=R4 among the curves formed by the side of the round bar steel material formed by the cut surface of the round bar steel material, which is formed by a plane including the center of gravity line of the round bar steel material and point P.

[0017] It is desirable that the radii of curvature in the longitudinal direction of the die having a convex surface, the die having a concave surface, and the steel material are all equal.

[0018] The third means is a method for creating a deformation analysis model according to either the first or second means, characterized in that the deformation analysis model satisfies 0.1≦H / R, where R1=R2=R3=R4=R and the length of the center of gravity line segment is H.

[0019] The fourth means is a deformation analysis model characterized in that R1 = R2 = R3 = R4 = R, and when the length of the centroid line segment is H, H / R ≤ 0.4 is satisfied, and it is the method for creating the deformation analysis model according to the first to third.

[0020] Another means of the present invention is a prediction method for predicting the influence of straightening processing on a steel bar to be predicted using the deformation analysis model of the present invention. The diameter D of the steel bar to be predicted real and the radius of curvature R of the upper roll of the straightening machine up The ratio R up / D real is such that R / D, which is the ratio of the radius of curvature R of the deformation analysis model and the distance between the intersection of the perpendicular line dropped from point P to the centroid line and the curve not including point P and point P to D, satisfies R up / D real < R / D. This is a method for predicting the influence of straightening processing on a steel bar to be predicted by analyzing the numerical change obtained using the deformation analysis model by the finite element method.

Effect of the Invention

[0021] When using the analysis model of the present invention, even without using a model that reproduces a long steel bar straightened by two rolls similar to the actual machine, using a model in which a more compact round steel bar is clamped from above and below by a curved die and pressed and slid, the deformation analysis of the straightening process can be processed in a shorter time. Therefore, the strain and stress applied to the steel bar can be efficiently grasped, and the trend can be quickly estimated.

[0022] The diameter D of the steel bar to be predicted by the actual machine real and the radius of curvature R of the upper roll of the two-roll straightening machine up The ratio R up / D real is such that R / D, which is the ratio of the radius of curvature R of the deformation analysis model and the distance between the intersection of the perpendicular line dropped from point P to the centroid line and the curve not including point P and point P to D, satisfies R up / D real < R / D, it is possible to appropriately evaluate the bending deformation applied to the straightening process of the actual machine. [Brief explanation of the drawings]

[0023] [Figure 1] This is a structural image (original image is in color) of an example of a simple correction model proposed by the present invention. [Figure 2] Schematic diagram of the definition of curvature and direction in the present invention [Figure 3] This is an example of the damage value distribution in the analysis of the simple correction model proposed by the present invention (the original figure is in color). [Figure 4] For comparison, an example of damage value distribution in an analysis of two-roll straightening on an actual machine is shown (the original figure is in color). DETAILED DESCRIPTION OF THE INVENTION

[0024] As mentioned above, the straightening process that causes Mannesmann cracking involves applying pressure and bending / unbending to a rotating steel material. Therefore, even for short steel materials, if three elements are present: (i) rotation of the steel material, (ii) radial pressure reduction of the steel material, and (iii) bending / unbending of the steel material in the longitudinal direction, it is possible to roughly estimate the stress / strain history during straightening, and consequently, the damage value. Figure 1 shows an example of a simple straightening model that satisfies elements (i) to (iii) by reproducing the action of sliding and kneading a round steel bar (1) between plate-like dies (2, 3) arranged above and below.

[0025] (Reason for R1=R2=R3=R4) When considering the cutting surface of the steel material on a plane including the center of gravity line and point P, R1 to R4 are as follows: R1: The radius of curvature of the curve formed by the side surface that does not include point P. R2: The radius of curvature of the curve formed by the side including point P. R3: radius of curvature of the convex surface of the convex die, R4: the radius of curvature of the concave surface of the concave die; If all the curvature radii are the same after defining the above, the reduction amount and the curvature radius of the steel material being processed will be constant. Therefore, by changing these values and performing analysis, it becomes possible to evaluate the transition of damage values according to the amount of reduction and the magnitude of bending.

[0026] (Reasons why 0.1 ≤ H / R is desirable) R: Curvature radius in the longitudinal direction, H: Length of the steel material When this is the case, the condition of 0.1 ≤ H / R becomes a condition that defines the minimum value of the steel material length. In the correction process, the inventor found that the strain and stress are significantly different between the end part and the steady part. If the steel material is too short, the strain and stress of the end part and the steady part do not separate and are significantly different from the strain and stress during correction. Therefore, it is necessary to make the steel material length satisfy 0.1 ≤ H / R so that the strain and stress of the steel material end part and the steady part can be reproduced.

[0027] (Reasons why H / R ≤ 0.4 is desirable) R: Curvature radius in the longitudinal direction, H: Length of the steel material When this is the case, H / R ≤ 0.4 is a condition that defines the maximum length of the steel material. If the steel material is too long, the time required for analysis becomes too long, and thus the relatively short-time analysis, which is the object of the present invention, cannot be achieved. Therefore, H / R ≤ 0.4 is set.

[0028] From these viewpoints, it is preferable that H / R satisfies 0.1 ≤ H / R ≤ 0.4.

[0029] (R up / D real (Reasons why <R / D is desirable) When considering the cutting plane of the steel material in the plane containing the center of gravity line and point P, R: Curvature radius in the longitudinal direction, D: Vertical distance between the curved point containing point P and the curve not containing point P, When this is the case, if there is a correction process as the object, R up : Curvature radius of the upper roll, D real : Steel material diameter, then, R up / Dreal <It is desirable to satisfy R / D.

[0030] This condition defines the radius of curvature in the longitudinal direction of the steel material. Generally, in concave-convex two-roll correction, the curvature (the reciprocal of the radius of curvature) of the upper roll is larger than that of the lower roll. Therefore, the curvature of the steel material in the concave-convex two-roll correction process is at most equal to the curvature of the upper roll, and by changing the roll angle etc., although the curvature can become smaller, it will not become larger. Thus, R up / D real <By satisfying R / D, bending similar to the assumed correction process can be applied.

[0031] (Example) Two-roll analysis by an actual machine as a comparative example (rolling reduction rate 3%, R up / D real =29.4) and analysis by a simple model as an example of the present invention (rolling reduction rate 3%, R / D = 30.0, H / R = 0.3) were compared for the analysis results. In the analysis example, R = 600, D = 20, and H = 180. Also, the steel material was mesh-divided into about 45,000 and used for the analysis.

[0032] The required time until the damage values at the end and steady parts could be analyzed was 77 hours when a model assuming two-roll processing by an actual machine was analyzed by a computer using the finite element method. That is, this time is the time required until the steel material with a length of 600 mm was mesh-divided into about 45,000 and the vicinity of the tip of the steel material passed through the correction roll.

[0033] On the other hand, when analysis processing was performed by a computer using the simple deformation analysis model of the present invention example, the required time was 15 hours, and the processing time was significantly shortened and the efficiency was improved.

[0034] Fig. 3 shows an example of the damage value distribution by the analysis of the simple correction model of the present application. Also, Fig. 4 shows the state of the damage value distribution when analyzing two-roll correction of an actual machine as a comparative example. Both analysis results confirmed that the damage value was high in the center of the steel material. In addition, both analyses confirmed that the damage value had a maximum value near the edge of the steel material, and that the damage value decreased as the steady state approached.

[0035] Therefore, even when using the simplified analysis model of the present invention, a damage value distribution similar to that obtained by two-roll analysis of an actual aircraft can be obtained. Therefore, even when analysis is performed using a simpler method in a short amount of time, analysis can be performed with the same level of accuracy as previous analysis methods, making the present invention a method that can be implemented more efficiently. [Explanation of symbols]

[0036] 1. Curved steel member in a simplified model 2. Simplified model of a plate-shaped die with a convex surface 3. Simplified model of a plate-shaped die with a concave surface 4 Simple model end 5. Simple model steady state part 6 Actual straightening model end 7. Actual straightening model stationary section

Claims

1. A method for creating a deformation analysis model of straightening a round steel bar by bending and unbending, in which a round steel bar curved in one direction is used as an analysis object, the analysis object is divided into a finite number of manageable pieces, and numerical changes are analyzed using the finite element method, The line segment connecting the centers of gravity of the end faces of the round steel bar curved in one direction is defined as the center of gravity line segment. The direction when a perpendicular line is drawn from point P on the steel side farthest from the center of gravity line to the center of gravity line is defined as the upward direction, If downward is the opposite direction to upward, For round steel bars curved in one direction, A convex die having a convex curved surface and a concave die having a concave curved surface are used. a first step of setting geometric information so that the round steel bar material is arranged in contact with the curve from above and below; a second step of pressing down and clamping the round steel bar by moving at least one or both of the concave die and the convex die in a vertical direction; a third step of performing a correction processing operation in which the concave die and the convex die are moved in opposite directions along a direction perpendicular to the longitudinal direction and the up-down direction while the die is kept in the pressed state; A method for creating a deformation analysis model that is equipped with the above steps in order and that enables acquisition of numerical changes in the object to be analyzed.

2. Among the curves formed by the side of the round steel bar material, which are formed by the cut surface of the round steel bar material, which is formed by a plane including the center of gravity line of the round steel bar material and point P, The radius of curvature of the curve that does not include point P is R 1 and, The radius of curvature of the curve including point P is R 2 and, and R, the radius of curvature of the convex surface of the convex die. 3 and, R is the radius of curvature of the concave surface of the concave die 4 But, R 1 =R 2 =R 3 =R 4 The deformation analysis model creation method according to claim 1 , wherein the deformation analysis model is modeled as satisfying the following:

3. R 1 =R 2 =R 3 =R 4 =R, When the length of the center of gravity line segment is H, 3. The method for creating a deformation analysis model according to claim 2, wherein the deformation analysis model satisfies 0.1≦H / R.

4. R 1 =R 2 =R 3 =R 4 =R, When the length of the center of gravity line segment is H, 4. The deformation analysis model creating method according to claim 3, wherein the deformation analysis model satisfies H / R≦0.4.

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