JP2008176535A - Numerical analysis method in tube making process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of accurately numerically analyzing a tube making process of electric resistance weld tube, including the behavior of an edge part during molding without needing an enormous calculation time. <P>SOLUTION: When the tube making process of electric resistance welded tube is calculated by a numerical analysis method such as finite element analysis, a shell element is used for calculating the whole model including the overall tube making process, and a solid element is used for calculating a partial model on the basis of the obtained calculation results except the thickness direction as constraints. Preferably, the whole model ranges at least from just before a first roll to a roll disposed in an electric resistance welding position, and the partial model is shorter than the longest roll interval. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for efficiently calculating a pipe making process of an electric resistance steel pipe by a numerical analysis method.

  The electric resistance steel pipe is manufactured by a method in which a steel sheet discharged from a coil is roll-formed into a circular cross section using a large number of forming rolls, and the edges are electro-welded. If the molding conditions such as the shape and pressure of each molding roll are not set appropriately, a steel spring springback may occur between the molding rolls, resulting in a step in the ERW weld or reduced roundness. there's a possibility that. Conventionally, the molding conditions of each molding stand have been adjusted mainly by trial and error, but the optimum conditions change depending on the steel type and size of the steel plate. If it can be calculated, the number of trials and errors is reduced, and the cost can be significantly reduced.

  Therefore, in the field of roll forming, numerical calculation using a finite element method has been attempted in order to obtain a guideline for appropriate roll design and line design. For example, as shown in Non-Patent Document 1, only a section of a plate directly under a forming roll is partially modeled with a two-dimensional solid element, and deformation is approximately calculated, as seen in Non-Patent Document 2. In this case, a long plate that spans several stands is modeled and the forming state is simulated.

  However, the analysis using the partial model as in Non-Patent Document 1 has a drawback that it cannot reflect the deformation state of the three-dimensional plate and cannot take in the influence of the roll radius. On the other hand, when a method of analyzing a large-scale three-dimensional model that spans several stands as in Non-Patent Document 2, accurate prediction is possible, but a great amount of calculation time is required.

As a technique for shortening the calculation time, there is conventionally a technique for analyzing using a simple element called a shell element. For example, for a large-scale model using a three-dimensional solid element as shown in Non-Patent Document 2, if this method is used, the calculation time can be reduced to about 1/10. However, this simple element is a technique that approximates the deformation of the material only by deformation at the center plane of the plate thickness, and although it is convenient for evaluating the overall deformation and bending of the plate, the edge of the plate There is a drawback that local deformation in the thickness direction such as crushing or indentation due to rolls cannot be evaluated. These local deformations are important matters that are problematic in the pipe making process.
"Plasticity and processing" Vol. 38, No. 443 (December 1997) 56-60 Proceedings of the 54th Plastic Working Joint Lecture Meeting (November 2003)

  The present invention solves the above-mentioned conventional problems, and does not require enormous calculation time for the pipe making process of ERW steel pipes using multi-stage forming rolls, and also includes the behavior of the edge part during forming. The object of the present invention is to provide a numerical analysis method of a pipe making process which can be numerically analyzed well.

  The present invention made in order to solve the above problems, in calculating the pipe making process of the ERW steel pipe by the numerical analysis method, first, using a shell element for the entire model including the entire pipe making process, Next, a calculation using a solid element is performed for the partial model using the obtained calculation results in directions other than the thickness direction as a constraint condition.

  As a numerical analysis method, a finite element method can be used. Further, the pipe forming process is a roll forming process using a large number of forming rolls, and it is preferable that the entire model includes at least the range from the front of the first roll to the roll arranged at the ERW welding position. However, it is preferable that it is a range shorter than the longest adjacent roll interval. Furthermore, the calculation using the shell element is performed while ignoring the calculation accuracy in the thickness direction, the calculation using the solid element is preferably performed accurately in the thickness direction, the calculation using the shell element is performed by a dynamic explicit method, It is preferable to perform the calculation using the solid element by the static implicit method.

  According to the present invention, first, a calculation using a shell element is performed for an overall model including the entire pipe making process. The calculation using the shell element can analyze the shape at the center of the plate thickness, but cannot analyze the reduction in the plate thickness direction or the collapse of the plate angle. Thus, although the calculation accuracy is inferior, the calculation speed is fast and the entire model can be calculated in a short time. Therefore, if the calculation accuracy in the thickness direction is ignored, the shape of each forming part in the pipe making process can be accurately grasped.

  In the present invention, calculation using solid elements is performed for the partial model using the calculation results obtained in the above calculation other than in the thickness direction as constraint conditions. Although the calculation using this solid element has high calculation accuracy and can analyze the reduction in the thickness direction and the crushing of the plate angle, etc., there is a disadvantage that it takes calculation time. However, in the present invention, the calculation is performed for the partial model having a short total length. Therefore, analysis is possible in a short time. In addition, since the calculation result of the entire model is used as a constraint condition, analysis including the influence of the front and rear molding stands is possible. Therefore, according to the present invention, the pipe making process of the ERW steel pipe using the multi-stage forming roll can be accurately predicted including the local deformation such as the end crushing and the indentation due to the roll, and the calculation time is non-patent document 2. Can be reduced to about 1/10 to 1/5 of the conventional method shown in FIG.

  In addition, if the whole model including the range from the front of the first roll to the roll arranged at the ERW welding position is used as in claim 3, an accurate analysis including the entire pipe making process of the ERW steel pipe is performed. If a partial model having a range shorter than the shortest roll interval as in claim 4 is used, the calculation time using the solid element can be shortened. Further, if the calculation using the shell element is performed by the dynamic explicit method as in claim 6 and the calculation using the solid element is performed by the static implicit method, the low calculation cost which is an advantage of the dynamic explicit method can be obtained. In addition, the calculation utilizing the high calculation accuracy, which is an advantage of the static implicit method, can be performed, and both the calculation cost and the calculation accuracy can be achieved.

Preferred embodiments of the present invention are shown below.
FIG. 1 is an overall view of a pipe forming process of an electric resistance steel pipe by roll forming, and FIG. 2 is an explanatory view of a cross-sectional change of a steel plate by each forming roll.

  As shown in FIG. 1, in this embodiment, the steel sheet discharged from the coil is subjected to a breakdown process in which each of the forming rolls B1, B2, B3s, B4, B5s, and B6 passes, and F1s, F2, F3s, While continuously passing through the fin pass process passing through each of the forming rolls F4 and F5, it is gradually processed into a circular cross section as shown in FIG. 2, and is electro-welded at the position of the forming roll of the last SQ. In addition, s means the process by the forming roll arrange | positioned in the board width direction.

  In this way, the steel sheet is formed while sequentially passing through a large number of forming rolls. However, since the steel sheet between the forming rolls has a tension and springback occurs, the final forming roll SQ In order to make a perfect circle at the position and accurately match both edges so that there is no step, partial numerical analysis is insufficient, and numerical analysis including the entire molding process is necessary. However, enormous calculation time is required to analyze the deformation in the thickness direction for all processes.

  Therefore, in the present invention, a numerical analysis of the entire model is performed using a shell element with a low calculation cost, and a three-dimensional deformation history of the steel sheet is calculated. In this embodiment, the numerical calculation is performed using the most common finite element method as the numerical analysis method, but the present invention is not necessarily limited to this, and for example, the boundary element method can also be used. As is well known, the finite element method divides an object into finite elements, represents physical quantities such as deformation, strain, and stress at multiple nodes (nodes) on each element, and solves simultaneous equations to solve the object. This is a technique for obtaining the total deformation and stress.

  The shell element used for the numerical analysis of the overall model in the present invention is an element suitable for finite element modeling of a shell structure composed of a curved outer plate, and has a small number of nodes in the plate thickness direction. However, the calculation accuracy in the thickness direction is poor, but the calculation speed is fast, and it is possible to analyze the shape at the center of the plate thickness using the entire pipe making process of ERW steel pipe as a model.

  Here, the entire model includes at least a range from the front of the first roll B1 to the roll SQ arranged at the electric welding position. More preferably, since the behavior of the steel plate before entering the first roll B1 also affects the roll forming, the starting point of the overall model is set to a range from about 3 times the steel plate width before the first roll B1. By performing the calculation using the shell element for the entire model set in this way, the calculation accuracy in the thickness direction is poor, but the shape of each forming part in the pipe making process can be accurately grasped.

  Next, in the present invention, calculation using solid elements is performed for the partial model using the calculation results obtained by the above calculation other than the thickness direction as constraint conditions. The relationship is as shown in FIG. 3, and a range in which a part is cut out from the entire model is a partial model. However, the previous analysis result is given as the plate edge boundary condition before and after this partial model. Here, the solid model is a numerical model that describes a three-dimensional shape as a solid substance (solid), and it is a numerical model that completely represents the three-dimensional shape, although the amount of data is large and the computational load is heavy. Therefore, it is possible to accurately analyze the thickness direction of the steel plate.

  In the present invention, in order to reduce the burden of numerical calculation using the solid model as much as possible, it is desirable to shorten the length of the partial model. The optimum length of the partial model necessary to fully reproduce the three-dimensional plate shape when formed with a roll is considered to be related to the diameter of the pipe to be formed and the roll diameter, but at least the longest roll If the range is shorter than the interval, the deformation between the previous roll and the next roll can be reproduced, so that sufficient accuracy can be obtained. Therefore, the length of the partial model is preferably less than this. On the other hand, if the length of the partial model is shortened too much, the error in numerical analysis when passing through the forming roll increases, and the original purpose cannot be achieved. For this reason, it is preferable to set the partial model to be at least half the minimum roll diameter that may be subject to direct roll restraint.

  If calculation using this partial model is carried out for each forming stage, it is possible to accurately analyze the reduction in the plate thickness direction and the crushing of the plate angle, etc., and a step occurs in the ERW weld after roll forming, Whether or not there is a possibility that the roundness is reduced can be verified only by numerical calculation.

  Analysis methods include a dynamic explicit method and a static implicit method. The dynamic explicit method is a method for analyzing the dynamic behavior of a structure by explicitly solving the equation of motion. The calculation speed is fast and there is no guarantee of accuracy, but a solution can always be obtained. On the other hand, the static implicit method solves a static balance equation implicitly by performing convergence by iterative calculation of the solution, and the calculation speed is slow and the solution is not necessarily obtained but the solution can be obtained. The accuracy is high.

  Therefore, the calculation of the whole model using shell elements is performed by the dynamic explicit method, which is inferior in accuracy but high in calculation speed, and the calculation of partial models using solid elements is performed at a low calculation speed but with high accuracy. This is preferable because the advantages of each solution can be utilized, so that both the calculation speed and the calculation accuracy can be achieved.

As described above, according to the present invention, the pipe making process of the ERW steel pipe using the multi-stage forming roll does not require enormous calculation time and includes the behavior of the edge part at the time of forming with high accuracy. Numerical analysis is possible. For this reason, according to this invention, it becomes possible to grasp | ascertain the optimal forming conditions including the roll shape in the pipe making process of an ERW steel pipe, without repeating trial and error using an actual installation.
Examples of the present invention are shown below.

  Numerical analysis was performed on a case where a steel pipe having a diameter of 90 mm and a thickness of 8 mm was formed by a pipe forming line including a roll stand as shown in FIG. 4, and the analysis time of the present invention was compared with that of the conventional method. This pipe forming line is composed of a total of 11 stages including 4 stages of upper and lower rolls, 4 stages of side rolls, and 3 stages of fin pass rolls. The intervals between the stands are as shown in the figure, and the total length of the line is 3600 mm. As shown in FIG. 5, the maximum diameter of the portions where the forming rolls contact the steel plate is the diameter D of each forming roll. In this embodiment, each roll has D = 200 mm.

Case 1 is a model similar to the large-scale model described in Non-Patent Document 2, and uses solid elements. The plate length in the plate passing direction of the model was 1500 mm.
Case 2 has the same plate length as Case 1 and uses the elements as shell elements.
Case 3 is an analysis method according to the present invention, and analysis was performed with a solid element having a plate length of 300 mm using the deformation history of the plate from the analysis result of case 2 as a boundary condition.
The results are summarized in Table 1. According to Case 3, the same calculation accuracy as in Case 1 can be analyzed in 1/6 the calculation time of Case 1.

It is a general view of the pipe making process of the ERW steel pipe by roll forming. It is explanatory drawing of the cross-sectional change of the steel plate by each forming roll. It is explanatory drawing of the relationship between a whole model and a partial model. It is explanatory drawing of the pipe making line made into the analysis object of an Example. It is explanatory drawing of each forming roll.

Claims (6)

  When calculating the pipe making process of ERW steel pipe by numerical analysis method, first the calculation using shell elements is performed for the whole model including the whole pipe making process, and then the obtained calculation results other than the thickness direction are restrained conditions. As a numerical analysis method of the pipe making process, characterized in that the calculation using a solid element is performed for the partial model.   2. The numerical analysis method for a pipe making process according to claim 1, wherein the numerical analysis method is a finite element method.   The pipe forming process is a roll forming process using a large number of forming rolls, and the entire model includes at least a range from the front of the first roll to the roll arranged at the ERW welding position. Or the numerical analysis method of the pipe making process of 2.   The numerical analysis method of a pipe making process according to any one of claims 1 to 3, wherein the partial model is in a range shorter than the longest adjacent roll interval.   The numerical analysis of a pipe making process according to claim 1 or 2, wherein the calculation using the shell element is performed ignoring the calculation accuracy in the thickness direction, and the calculation using the solid element is performed accurately in the thickness direction. Law.   3. The numerical analysis method for a pipe making process according to claim 1, wherein the calculation using the shell element is performed by a dynamic explicit method, and the calculation using the solid element is performed by a static implicit method.

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