JPH0576947A - Working method for bending steel sheet by strip heating - Google Patents

Abstract

PURPOSE:To provide a working method for bending a steel sheet by means of strip heating by which the bending of the steel plate is easily performed by numerically determining a position for the strip heating and the amount of inherent strain. CONSTITUTION:Geometrical information concerning the initial shape of the steel sheet before the bending and the final shape of the steel plate post the bending is inputted; simultaneously the mesh division of a finite element method in accordance with the initial shape is performed; an elastic deformation is forcedly performed from the initial shape to the final shape; after a strain generated in the process is calculated, the calculated strain is separated into in-plane component and out-of-plane bending component; the distribution of each main strain is graphically displayed; for the distribution of the in-plane strain, an area where the main strain from compression is large is selected as the area for heating, and the wire heating is performed in a direction perpendicular to the direction of the main strain; for the bending strain, an area where the absolute value of the bending strain is large is made as an area for heating, and the wire heating is performed in a direction perpendicular to the main direction where the absolute value is the largest to the direction of the strain; a prescribed specific strain is imparted to each; and the above-mentioned steel plate is bent in a prescribed final shape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for bending a steel sheet by linear heating for bending a flat or semi-cylindrical initial shape steel sheet into a curved final shape by using linear heating. , In particular, the relationship between the intrinsic strains required to obtain the final shape is analyzed using the finite element method, and based on the obtained knowledge, the position to be linearly heated and the amount of the intrinsic strains are numerically determined. The present invention relates to a method of bending a steel sheet by linear heating, which achieves that the bending of the steel sheet can be easily performed.

[0002]

2. Description of the Related Art Generally, most of the bending work of a steel plate in a shipyard is performed by linear heating. In this bending by linear heating, linear heating is applied to a predetermined position of a flat plate or semi-cylindrical steel plate, and the in-plane contraction and angular deformation of the plate due to the generated plastic strain are used to achieve the desired three-dimensional The shape is created, and the in-plane shrinkage rate and the amount of angular deformation are determined by the heating position and direction of the linear heating.

[0003]

By the way, in the bending process by the linear heating, the heating position and the heating condition are important, but conventionally, all the bending processes are performed by the intuition and skill of a skilled worker. Came.

However, recently, the problems such as the aging of skilled workers, the decrease in the number of workers, and the difficulty in inheriting the skills have become more prominent, and there is a fear that the processing capacity will decrease.

Therefore, the present invention has been devised in order to effectively solve these problems, and the main purpose thereof is to technicalize the linear heating work which requires skill and requires special skill. It is intended to provide a linear heating method capable of achieving an improvement in processing capacity without doing so.

[0006]

In order to achieve the above object, the first basic invention is to bend a flat plate or semi-cylindrical steel sheet having an initial shape into a final shape having an arbitrary curved shape. In the method for bending a steel sheet by linear heating for the purpose of inputting geometric information on the initial shape of the steel sheet before bending and the final shape of the steel sheet after bending,
Mesh division of the finite element method corresponding to the initial shape,
After forcibly elastically deforming from the initial shape to the final shape and calculating the strain that occurs in the process, the calculated strain is separated into in-plane and out-of-plane bending components, and the main strain distribution of each is displayed graphically. However, for the in-plane strain distribution, a region with a large compression main strain is selected as the heating region, and the direction perpendicular to the direction of the main strain is linearly heated. Is a heating area, the strain direction is linearly heated in a direction perpendicular to the main direction whose absolute value is the maximum, and given a specific intrinsic strain to each, bending the steel sheet into a predetermined final shape. It is to be processed.

[0007]

As described above, according to the present invention, the strain of the steel sheet from the initial shape to the final shape is calculated by using the finite element method, and the position of the steel sheet, the shape of the strain and the magnitude of the strain are calculated. Although it should be given, it can be grasped accurately and easily, so bending work by linear heating is easy and
No special skill or intuition is required for bending.

[0008]

Next, preferred embodiments of the present invention will be described.

The method for bending a steel sheet by linear heating according to the present invention is a method for producing a desired three-dimensional shape by utilizing in-plane contraction and angular deformation of the sheet due to plastic strain generated during linear heating.

Therefore, first, the shape of the bending member to be molded and the in-plane shrinkage amount and the angular deformation amount to be given by the linear heating will be described. Fig. 2 shows an example of the case where a partial spherical shell is created from a flat plate, and the position of linear heating and the angular deformation (contraction amount changes in the plate thickness direction) and in-plane contraction (contraction amount in the plate thickness direction). Is uniform).
In the figure, a shows a shape after bending and a heating wire, and b shows a state in which a bending member having a three-dimensional curved surface is cut along the heating wire and is flatly developed. Intuitively, it shows the in-plane reduction amount and the angular deformation amount that the opening amount generated in the cut shown in FIG. As this example shows, in order to create a cylindrical shape having curvature in only one direction, only angular deformation is necessary, but in the case of a partial spherical shell having curvature in two directions,
In-plane shrinkage must also be considered. Therefore, in order to perform plate bending for an arbitrary shape, it is necessary to consciously properly use both in-plane contraction and angular deformation according to the target shape. On the other hand, the amount of in-plane contraction and the amount of angular deformation can be obtained by geometrical calculation if secondary effects such as springback are ignored, and as a method for theoretically creating a linear heating plan. A method based on geometric calculation has already been proposed, and when only in-plane shrinkage is taken into consideration as the intrinsic deformation, the heating position and the amount of shrinkage to be applied can be determined from the geometric conditions.

However, it is generally necessary to properly use both the in-plane shrinkage and the out-of-plane bending specific strain depending on the situation, and the secondary bending of a member that has been subjected to primary bending by roll processing or press processing. There is a limit to the method based on the geometrical calculation considering the correspondence to. On the other hand, the finite element method is superior in that it faithfully simulates the bending deformation, and it is one of the everyday tools in combination with the recent performance improvement of EWS and the like. Therefore, in the present invention, the possibility of a method for determining the position of linear heating and the amount of intrinsic deformation was devised based on elasticity analysis by FEM.

That is, the method for bending a steel sheet by linear heating according to the present invention has been devised based on the above viewpoints, and FIG. 1 is a flow chart showing the heating position and the direction for determining the linear heating. It is a figure.

First, after inputting the initial shape (which may be the shape after the primary bending) and the geometrical information on the final formed shape (step 1), the FEM mesh division corresponding to the initial shape is performed (step 2). Next, to determine the heating position and direction, first, forcibly elastically deform from the initial shape to the final shape, calculate the strain that occurs in the process, and then divide the calculated strain into the in-plane component and the bending component. Then, each principal strain distribution is displayed on the graphic screen (step 3). Next, paying attention to the in-plane strain distribution, select the region where the main strain of compression is large as the heating region, and set the heating direction to be the direction perpendicular to the direction of the principal strain (step 4). Paying attention, a region where the absolute value of bending strain is large is added to the heating region, and the heating direction is perpendicular to the main direction in which the absolute value of strain is maximum (step 5).

Next, to determine the type and magnitude of the intrinsic strain to be applied, the amount of the intrinsic deformation corresponds to the gap when the plate is cut and the plane is developed as shown in FIG. In order to simulate the cut, the elastic modulus of the element in the heating position is set to 1/1000 of that of the other portion (step 6). In this state, when performing elastic analysis of the deformation from the initial shape to the final shape, the strains that were originally dispersed throughout the plate were concentrated in the heated part, and the value was the magnitude of the intrinsic strain or the intrinsic deformation that should be applied by linear heating. Give Then, based on these calculations, linear heating is performed to generate an intrinsic strain, thereby processing into a predetermined final shape (step 7).

Next, an example similar to the bending member of an actual ship will be described as this embodiment.

The bending member of the actual ship is close to a donut type curved surface having curvatures in two directions as shown in FIG. Tanaka, Yasukawa, Yamauchi, Togo: Study on automation of hull outer panel bending work by universal multi-point press method (1st report: Basic research), Proceedings of the Shipbuilding Society of Japan, 132nd
issue. pp481-501, (1972)), and the range is -1.0 x 10 ^-4 <1 / r <3.0 x 10 ^-4 (1 / mm) 0.0 <1 / R. <3.0 × 10 ⁻⁵ (1 / mm). Considering the similarity rule with experiments, etc., it is better to arrange by parameters t / r and t / R that also consider the plate thickness t, so assuming the plate thickness of the actual ship is 20 mm, the range of parameters is -2 0.0 × 10 ⁻³ <t / r <6.0 × 10 ⁻³ 0.0 <t / R <6.0 × 10 ⁻⁴ . Therefore, two cases included in this range and having t / r = ± 2.5 × 10 ⁻³ t / R = 5.0 × 10 ⁻⁴ will be examined. The dimensions and curvatures thereof are shown in FIG. 4, where (a) is a pillow type having curvatures in the same direction, and (b) is a saddle type having different curvature directions.

First, assuming that the curved surface of the pillow type a is machined from a flat plate, the strain distribution without cutting is calculated. The analysis was performed on 1/4 of the plate in consideration of symmetry. FIG. 5 shows the distribution of the in-plane strain obtained as the calculation result, and the maximum absolute value of the in-plane strain ε ^m is 3.17 × 10 ⁻³ . On the other hand, bending strain is dominated by bending in the short side direction, and strain corresponding to t / 2r = 1.25 × 10 ⁻³ is distributed almost uniformly (not shown). In this case, since the magnitudes of the in-plane strain and the bending strain are of the same order, it is not possible to perform bending with only the in-plane intrinsic strain. Therefore, as is actually done in the field, it is effective to first perform uniform bending in the short side direction with a roll, and then perform linear heating. Therefore, here, consider a process in which a plate formed into a cylindrical shape with a curvature r by primary processing is processed into a pillow shape having a height h ₀ at the center point on the long side of 100 mm. FIG. 6 shows the in-plane strain distribution as the principal strain distribution, and the arrows indicate the direction and magnitude of the principal strain. On the other hand, FIG. 7 shows the distribution of the maximum principal strain on the surface regarding bending strain. Comparing the in-plane and bending strain distributions, the in-plane strain changes greatly on the xy plane, but the bending strain is almost uniform. Also, paying attention to the maximum value of strain, the maximum values of in-plane and bending strain are 3.15 × 10 ^-3 and 2.48 × 10 ^-4 , respectively. In this case, compared with the case of molding from a flat plate. The magnitude of bending strain has decreased and is one digit smaller than the magnitude of in-plane strain. Thus, since the in-plane strain is dominant, the heating position and direction can be determined from the in-plane strain distribution. If the portion where a large compressive strain is generated is heated perpendicularly to the strain direction, the heating region is determined as shown in FIG. The figure shows that the periphery should be heated, leaving the center, which corresponds to the actual work on site. Incidentally, as shown in FIG. 6, a considerable amount of tensile strain is generated at the position along the x-axis at the center of the plate. In order to incorporate the influence of this tensile strain into the intrinsic strain, a part where tension occurs is included in the heating region. Next, deformation analysis was performed assuming that the Young's modulus of the heating region was 1/1000 of the others, and the obtained in-plane strain distribution is shown in FIG. It can be seen that the strain is mostly concentrated in the heating region, and the tensile strain seen in FIG. 6 disappears. Furthermore, the deformation when the strain in the heating region was given to the cylindrical plate as the intrinsic strain was calculated. The results of the plate A, B, the height h _a of the point C, h _b, as shown in FIG. 12 for h _c.

Next, the case of molding the saddle mold b from a cylinder will be described. First, similarly to the pillow type a, the strain when deformed from a cylinder to a saddle type was analyzed. Since the bending strain distribution has the same absolute value as that of the pillow type and the sign is opposite, only the in-plane strain distribution is shown in FIG. Based on this strain distribution, the heating region was determined as shown in FIG. 11, the intrinsic strain was calculated, and the deformation when the intrinsic strain was applied was analyzed. The result is shown in FIG. 12 together with the case of the pillow type. Examining the shape obtained by applying the intrinsic strain based on Table 1, the amount of deformation to be further applied to the cylinder, that is, h ₀ is 100 mm, whereas in the case of the pillow type, the height error at each point is The shape is within about 8 mm.
On the other hand, in the case of the saddle type, the error is rather large, and the value is 17-
It is 27 mm. This indicates that the forming error may be relatively large depending on the case, but the method devised here can be an effective method for actual plate bending.

As described above, the present invention elastically analyzes the deformation from the initial shape to the desired final shape using the finite element method, and determines the position of linear heating from the main direction and magnitude of in-plane and out-of-plane bending strains. By determining the direction and the direction, it is possible to accurately and easily grasp what position, what shape, and what kind of strain should be applied to which position of the steel sheet. Is unnecessary.

[0020]

In summary, according to the present invention, since bending of a steel sheet by linear heating can be easily performed, there are problems that the skilled worker is aging, the number of workers is reduced, and it is difficult to inherit the skill. It has an excellent effect that it can be eliminated and the processing capacity can be further improved.

[Brief description of drawings]

FIG. 1 is a flowchart showing an embodiment of the present invention.

FIG. 2 (a) is a perspective view showing a shape and a heating wire after bending, and FIG. 2 (b) shows a state in which a bending member having a three-dimensional curved surface is cut along the heating wire and flattened. It is a top view.

FIG. 3 is a partially enlarged view showing a part of a bending member of a donut-shaped actual ship.

4A is a perspective view showing a pillow-shaped member, and FIG. 4B is a perspective view showing a saddle-shaped member.

FIG. 5 is a diagram showing a distribution of in-plane strain of the pillow-shaped member obtained as a calculation result.

FIG. 6 is a diagram showing an in-plane strain distribution of a pillow-shaped member as a main strain distribution.

FIG. 7 is a diagram showing the distribution of the maximum principal strain on the surface with respect to the bending strain of the pillow-shaped member.

FIG. 8 is a diagram showing a heating region of a pillow-shaped member.

FIG. 9 is a diagram showing an in-plane strain distribution of a pillow type member.

FIG. 10 is a diagram showing only the in-plane strain distribution of the saddle type member.

FIG. 11 is a diagram showing a heating region of the saddle-shaped member.

FIG. 12 is a table showing the results of calculating the deformation when the strain of the heating region is applied to the cylindrical plate as the intrinsic strain.

Front page continuation (72) Inventor Yukio Ueda 11-1 Mihogaoka, Ibaraki City, Osaka Prefecture, Research Institute for Welding Engineering, Osaka University (72) Inventor Eiichi Murakawa 11-1, Mihogaoka, Ibaraki City, Osaka Prefecture, Welding Engineering Laboratory, Osaka University

Claims (1)

[Claims] 1. A method of bending a steel sheet by linear heating for bending a plate-shaped or semi-cylindrical steel sheet having an initial shape into a final shape having an arbitrary curved surface shape,
Enter geometric information about the initial shape of the steel sheet before bending and the final shape of the steel sheet after bending, and perform mesh division of the finite element method corresponding to the initial shape to force elasticity from the initial shape to the final shape. After deforming and calculating the strain that occurs in the process, the calculated strain is separated into in-plane components and out-of-plane bending components, and each main strain distribution is displayed graphically and compressed for in-plane strain distribution. The area with a large main strain of is selected as the heating area and linearly heated in the direction perpendicular to the direction of the main strain, and for the out-of-plane bending distortion, the area with a large absolute value of the bending strain is set as the heating area. Linear heating characterized by linearly heating the direction perpendicular to the main direction, which has the maximum absolute value in the strain direction, and imparting a specific intrinsic strain to each, and bending the steel sheet into a specific final shape. To Bending method of that steel sheet.