CN112638558B - Method for manufacturing steel pipe and press die - Google Patents

Abstract

A method of manufacturing a steel pipe, in which a sheet material subjected to end bending processing at both ends in the width direction is subjected to bending processing three or more times in the width direction to form a formed body having a U-shaped cross section, and the formed body is subjected to press processing to produce After opening the pipe with a weld gap in the longitudinal direction, the weld gap is joined to form a steel pipe. When the width of the plate before end bending is taken as the plate width W, the formed body is formed from the end of the plate width The part away from W/4 has a lightly processed part with a smaller curvature than the other regions or an unprocessed part without bending processing, and press processing so that the shape of the open tube becomes the following shape: U-shaped The range of 20 [%] or more of the plate width W centered on the lowest part of the cross section and the range of 10 [%] or more of the plate width W from the end of the plate width are inscribed on the same diameter or approximately the same diameter as the outer diameter of the steel pipe. radius arc.

Description

Steel pipe manufacturing method and stamping die

technical field

The present invention relates to a method of manufacturing a steel pipe and a press die used in the method of manufacturing the steel pipe.

Background technique

Conventionally, UOE forming technology has been widely used as a technology for forming steel pipes. The UOE forming technology is: first stamping the steel plate into a U-shape, then stamping into an O-shape, and forming a pipe body with a weld gap between the opposite plate width ends in the circumferential direction, that is, an open pipe. After the weld gap portion of the open pipe is butt-jointed by welding to form a steel pipe, pipe expansion for enlarging the diameter of the steel pipe is further performed. However, in the UOE forming technology, in the process of stamping a steel sheet into a U-shape or an O-shape to form an open tube, a large press machine has to be used due to the high pressing force required.

Therefore, when manufacturing steel pipes, as a technique for forming open pipes with a reduced press force, for example, a press bending method in which bending processing is performed on the widthwise end portions of a steel plate to impart a bend to the end portions has been put into practical use. After the section, the steel plate is formed into a substantially circular shape by performing multiple times of 3-point bending punching using a punch and a die supported on the punch support body to form an open tube. On the other hand, the opening amount of the weld gap portion of the open tube formed by the press bending method is larger than the width of the punch support body, but if the opening amount is too large, in order to weld the weld gap portion, they will be opposed to each other. The force required to butt the ends of the plate width to close the weld gap increases, and the equipment for closing the weld gap increases in size. In addition, at the welded part after welding the weld gap part with an excessively large opening amount, a force tending to open the weld gap part acts due to springback, so welding defects are likely to occur. If the force is too large, the welding Partially broken.

Therefore, Patent Documents 1 to 4 disclose techniques for reducing the opening amount of the weld gap portion of the open tube after bending. Patent Document 1 discloses a technique of reducing the width of the punch support by making the joint between the tip of the punch and the punch support freely rotatable, thereby reducing the opening amount of the weld gap portion of the open pipe. Patent Document 2 discloses the technique of providing a space keeping mechanism that restricts the movement of the sheet material in a direction perpendicular to the moving direction of the punch, and that the end of the sheet width does not come into contact with the punch support body, and the final bending During the processing, a large pressure is applied to reduce the opening amount of the weld gap of the open pipe. Patent Document 3 discloses a technique of measuring the gap between the end of the plate width after the final pressing process and the punch support, and reducing the gap as much as possible to reduce the opening amount of the weld gap portion of the open pipe. In addition, Patent Document 4 discloses a technique of determining the amount of reduction by the punch in the final process based on the time when the distance between the end portions of the plate width reaches a predetermined value in the reduction in the final bending process, Therefore, regardless of the difference in shape generated in the previous press-bending process, the opening amount of the weld gap portion of the open pipe can be reduced.

However, in the techniques disclosed in Patent Documents 1 to 4, the opening amount of the weld gap portion of the open pipe cannot be made smaller than the width of the punch support body. Therefore, Patent Documents 5 to 9 disclose techniques for further processing the open tube after press-bending to reduce the opening amount of the weld gap. Patent Document 5 discloses a technique of forming with a small load by hot roll forming a bent steel pipe. Patent Document 6 discloses a technique of disposing a strain detector capable of detecting inclination or strain of a pressing member attached to a slider, and disposing the pressing member in a manner capable of detecting the inclination or strain of the strain detector. When the molding material is stamped into a tubular shape, the pressing part is tilted or moved in parallel and punched according to the amount of inclination or strain of the pressing part to make the strain smaller. forming. Patent Document 7 discloses a technique in which, with respect to the center defined by the longitudinal axis of the upper tool entering the progressively formed sheet, at the left and right, respectively, by performing at least one bending step acting on the inner surface of the sheet with The other bending step is a relatively slight profiling so as to form a slit tube with non-circular preforms, which are then applied at any time from the outside in the pre-lightly preformed areas on both sides of the center Acting pressing force to form a complete slit tube. In addition, Patent Document 8 discloses a technique of imparting plastic deformation to only at least one flat portion of a molded body having a flat portion between portions bent with at least two tube curvatures so as to form a predetermined curvature. A tube with a closed slit. In addition, Patent Document 9 discloses a method of forming an open shape by pressing a molded body provided with a lightly processed portion having a very small curvature compared with other regions or having an unprocessed portion in which bending processing is omitted. When forming a tube, a pressing force is applied without restraining the lightly processed part or the unprocessed part, and the tube with the slit closed is molded. In this pressing, it is preferable to hold the molded body in the mold in a U-shaped posture with the opening facing upward, and to support the molded body at the lowermost end.

Patent Documents 10 and 11 disclose a technique for producing a UOE pipe having a product diameter in which the diameter of the inner surface of the press die is different from the outer diameter of the product pipe. The die disclosed in Patent Document 10 is a shape in which only a part of the inner surface of the upper and lower dies is cut off in a horizontal oblong shape. In Patent Document 10, which explains the function of the die, FIG. 3(a) and FIG. 4(a) In , the entire inner surface of the O stamping die is in contact with the O tube. In addition, Patent Document 11 discloses a method of using a mold whose inner surface is formed with a circular arc with a radius larger than the product outer diameter, and whose end faces are ground in advance so that the interval is sufficiently large, and the material is filled in the mold and compressed at a predetermined rate. , and then the formed tube is rotated approximately 90[°], and O punching is performed again to form a circular shape. Also in the first O press step at this time, the steel pipe is in a state of close contact with the entire surface of the mold.

prior art literature

patent documents

Patent Document 1: Japanese Patent Laid-Open No. 2004-82219

Patent Document 2: Japanese Patent Laid-Open No. 2011-56524

Patent Document 3: International Publication No. 2014/188468

Patent Document 4: International Publication No. 2014/192043

Patent Document 5: Japanese Patent Laid-Open No. 2005-324255

Patent Document 6: Japanese Patent Laid-Open No. 2005-21907

Patent Document 7: Japanese Patent Laid-Open No. 2012-250285

Patent Document 8: Specification of US Patent No. 4149399

Patent Document 9: International Publication No. 2016/084607

Patent Document 10: Japanese Patent Laid-Open No. 2003-39115

Patent Document 11: Japanese Patent Laid-Open No. 2002-178026

Contents of the invention

The problem to be solved by the invention

However, in the technique disclosed in Patent Document 5, there is a problem in that the manufacturing cost is remarkably increased when the consumption of thermal energy required for heating is taken into consideration. In addition, this technology may lose its characteristics when using a sheet material manufactured through a heat treatment process in order to achieve a balance of strength, toughness, and weldability. In the technologies disclosed in Patent Documents 6 to 8, since the molding material or the non-circular preform is independently molded at the left and right positions, when the amount of deformation is different at the left and right positions, there is a problem of welding at the welded portion. There is a possibility of a step difference (difference in appearance) formed in the slit gap part or the slit part. In addition, in the above techniques, if one time deformation is to be performed into a desired shape, the deformation may be locally concentrated and the roundness of the steel pipe may be deteriorated, so multiple deformations are necessary, and there is a limit to efficient forming. In addition, in the technology disclosed in Patent Document 9, the radius of the lower mold is larger than the outer diameter of the tube, so the lowermost end of the molded body in a U-shaped posture undergoes bending recovery and deformation in which the gap portion is opened, so there is a problem that the narrow gap cannot be reduced. The interval between seams. In addition, in the technologies disclosed in Patent Documents 10 and 11, since the O tube is pressed in a state where the entire surface of the die is in close contact, as described above, a large-scale machine has to be used due to the need for a high pressing force. Condition of the press.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for manufacturing a steel pipe and a press die capable of efficiently forming a steel pipe with high roundness.

means to solve the problem

In order to solve the above-mentioned problems and achieve the above-mentioned object, in the method for manufacturing a steel pipe according to the present invention, the plate material subjected to edge bending processing at both ends in the width direction is subjected to bending processing three or more times in the width direction of the plate material to be formed into A molded body having a U-shaped cross-section is then press-processed to form a pipe body having a weld gap along its length, that is, an open pipe, and then the weld gap is joined to form a into a steel pipe, the manufacturing method is characterized in that,

When the width of the plate material before the end bending process is defined as the plate width W,

The molded body has a lightly processed portion with a curvature smaller than other regions centered on a portion separated by W/4 from the plate width end or an unprocessed portion in which bending processing is omitted,

In the manufacturing method, the press working is performed so that the shape of the open tube becomes a shape of 20 [%] or more of the plate width W centered on the lowermost part of the U-shaped cross section and A range of 10 [%] or more of the plate width W from the end of the plate width is inscribed on an arc having the same diameter or substantially the same diameter as the outer diameter of the steel pipe.

In addition, the method for manufacturing a steel pipe according to the present invention is characterized in that, in the above invention, the lowest part of the U-shaped cross-section that is inscribed in an arc that is the same diameter or substantially the same diameter as the outer diameter of the steel pipe is The range of 20 [%] or more of the plate width W at the center is defined as A, and the plate from both ends of the plate width is inscribed in an arc having the same diameter or substantially the same diameter as the outer diameter of the steel pipe. When the total range of 10 [%] or more of the width W is set to B, formula (1) is satisfied,

2|A-B|/(A+B)＜0.4...(1)

Among them, |A-B| represents the absolute value of A-B.

In addition, the method for manufacturing a steel pipe according to the present invention is characterized in that, in the above invention, the molded body is placed on the other mold in such a manner that one mold of the pair of molds faces the U-shaped open side of the molded body. , and using the pair of molds to clamp the molded body to perform stamping on the molded body,

The other mold has: in a state where the molded body is placed on the other mold, except for a part that is inscribed on the same outer diameter as the steel pipe centered on the lowermost part of the U-shaped cross-section. The molded body is not in contact with the shape outside the range of the diameter or the shape of an arc substantially the same diameter, and

In the state where the stamping process is completed, a part of the other die is not in contact with the processed surface of the open tube;

The one mold has the following features: in a state where the molded body is placed on the other mold, the molded body does not contact, and

In a state where the press work is completed, there is a part of the one mold on a processed surface that does not come into contact with the open tube.

In addition, the manufacturing method of the steel pipe of the present invention is characterized in that, in the above invention, the radius of the arc portion used is within the range of ±3.5 [%] relative to the radius corresponding to the outer radius of the steel pipe. The die implements stamping processing.

In addition, the method for manufacturing a steel pipe according to the present invention is, in the above-mentioned invention, characterized in that, when pressing the molded body, the center of the press die used for the press working of the molded body is aligned with the center of the molded body. Centers in the width direction coincide.

In addition, the method of manufacturing a steel pipe according to the present invention is characterized in that, in the above invention, the molded body is held in a U-shaped posture with the U-shaped opening side facing upward.

In addition, the stamping die of the present invention is a stamping die used in the method of manufacturing a steel pipe of the above-mentioned invention, and is characterized in that the stamping die includes a pair of pressing bodies for clamping the molded body, and each die can be combined with the The contact surface of the molded body is formed with a radius within the range of ±3.5 [%] relative to the radius corresponding to the outer radius of the steel pipe so that the center of the arc is located at the same position as the machining center of each mold. arc portion,

The central angle of the arc portion in each mold is 70 degrees or more, and the sum of the central angles of the two molds is less than 360 degrees.

In addition, the press die of the present invention is characterized in that, in the above invention, the angles of the central angles of the two dies are the same.

In addition, the press die of the present invention is characterized in that, in the above invention, each die has a straight line portion connected to both ends of the arc portion in the arc direction or an arc portion of small curvature smaller than the arc portion.

In addition, the method for manufacturing a steel pipe of the present invention is characterized in that the press die of the above-mentioned invention is used in the method for manufacturing a steel pipe of the above-mentioned invention.

Invention effect

The method for manufacturing a steel pipe and the press die of the present invention have the effect of being able to efficiently form a steel pipe with high roundness.

Description of drawings

FIG. 1 is an external perspective view of a die, a punch, and the like used for forming a molded body having a U-shaped cross section by a press bending method according to an embodiment.

Fig. 2 is a diagram showing a step of forming a molded body having a U-shaped cross section by press bending.

Fig. 3 is a cross-sectional view of a molded body having a U-shaped cross section.

Fig. 4 is a diagram schematically showing a step of performing O punching on a molded body to form an open tube.

Fig. 5 is an explanatory diagram of circular arc portions, straight line portions, and central corners of an upper die and a lower die.

FIG. 6 is a graph showing the relationship between the opening amount of the weld gap portion of the open pipe and the restraint range.

Fig. 7 is a diagram schematically showing the state of deformation when forming an open tube using an upper mold and a lower mold with a constraint range of 0 degrees.

8 is a graph showing the relationship between the confinement range and the roundness of the steel pipe before pipe expansion when the weld gap of the open pipe is closed by welding.

FIG. 9 is a graph showing the relationship between the constraint range and the press load.

FIG. 10 is a graph showing the results of the opening amount of the weld gap portion of the open pipe when the restraint ranges of the upper mold and the lower mold are changed.

11 is a graph showing the results of roundness of steel pipes before pipe expansion formed by welding to close the weld gap portion of the open pipe when the respective constraint ranges of the upper mold and the lower mold are changed.

FIG. 12 is a graph showing the results of the press load when the restraint ranges of the upper die and the lower die are changed.

13 is a graph showing the results of the opening amount of the weld gap when the constrained range of the upper die is the same as that of the lower die and the length of the lightly processed part or the unprocessed part of the formed body after bending is changed. picture.

Fig. 14 shows the roundness of the steel pipe before pipe expansion when the constrained range of the upper die is the same as that of the lower die and the length of the lightly processed part or the unprocessed part of the formed body after bending is changed graph of the results.

FIG. 15 is a graph showing the results of press loads when the constraining range of the upper die is the same as that of the lower die and the length of the lightly processed part or the unprocessed part of the bent molded body is changed.

FIG. 16 is a graph showing the results of the opening amount of the weld gap portion of the open pipe when the radii of the arc portions of the upper die and the lower die are changed.

FIG. 17 is a graph showing the results of the press load when the radii of the arc portions of the upper die and the lower die were changed.

detailed description

Hereinafter, an embodiment of the manufacturing method of the steel pipe and the press die used in the manufacturing method of the steel pipe according to the present invention will be described. Fig. 1 is an external perspective view of a die 1, a punch 2, and the like used for forming a molded body having a U-shaped cross-section by the press bending method of this embodiment. The die 1 is arranged in a conveyance path of a sheet S formed by a plurality of conveyance rollers 3, and is composed of a pair of left and right bar-shaped members 1a, 1b that support the sheet S at two places along the sheet conveyance direction. In addition, the distance e between the rod-shaped members 1a and 1b in the sheet material conveying direction can be changed according to the size of the steel pipe to be finally formed.

The punch 2 can move toward the die 1 or away from the die 1, and is connected to the back (upper end face) of the punch front end 2a with the same width by the downwardly convex punch front end 2a that presses the sheet material S. The punch support body 2b which supports the punch front-end part 2a is comprised. The upper end portion of the punch support body 2b is connected to a drive mechanism (not shown), and a pressing force can be applied to the punch tip portion 2a by the drive mechanism.

Fig. ₂ shows the steps of forming a molded body S1 with a U-shaped cross-section by press bending. It should be noted that this step specifically shows an example of the following situation: For the sheet material S that has been subjected to end bending processing in advance, follow the top-to-bottom sequence in the left column of FIG. Bending and feeding of the sheet material S are performed in the order from top to bottom, and finally the right column in FIG. 2 . In addition, the arrows respectively attached to the punch 2 and the sheet S in FIG. 2 show the moving directions of the punch 2 and the sheet S in each stage.

In order to form the sheet material S into a tubular shape using the sheet material S as a starting material, the sheet material S is first subjected to end bending processing. Compared with the case where the sheet material S is bent using the die 1 and the punch 2, the end bending process is performed on the relatively inflexible plate width end. The wide end is provided with an end bent portion, so that a steel pipe with high roundness can be easily obtained compared to a case where the end bent portion is not provided. It should be noted that the true roundness of the steel pipe is an index indicating how close the cross-sectional shape of the steel pipe is to a circle. The value represented by the ratio. For example, at any length position of a steel pipe with an outer diameter D, divide the pipe into 8 equal parts, 12 equal parts, 16 equal parts or 24 equal parts along the circumference and measure the outer diameter at the relative position, and take the largest of them The diameter and the minimum diameter are denoted as D _max , D _min , respectively, and in this case, the roundness [%] is defined as {(D _max -D _min )/D}×100. The closer the roundness is to 0, the closer the cross-sectional shape of the steel pipe is to a perfect circle.

The sheet material S provided with the end bending processing part is placed on the die 1 shown in FIG. Bending process is performed more than 3 times in the width direction of , and formed into a molded body S ₁ having a U-shaped cross section as a whole.

Fig. 3 is a cross-sectional view of a molded body S1 having _a U-shaped cross section. When the width _of the sheet material S before end bending is taken as the sheet width W, as shown in FIG. The /4 part is centered, and the unprocessed part P which omits a bending process is provided. This unprocessed portion P can be provided by increasing the feeding of the sheet material S to omit pressing by the punch 2 . It should be noted that it is also possible to provide _a part of the molded body S1, especially centering on each W/4 part from the end of the plate width, instead of providing an unprocessed part P, but to provide a part with a curvature smaller than that of other parts (compared with other parts). The lightly processed part is given a very small curvature compared to the part. In this case, in the following description, what is necessary is just to replace "unprocessed part P" with "lightly processed part" suitably. The lightly processed portion can be provided by pressing down in such a manner that the amount of pressing applied by the punch 2 is smaller than other portions.

In addition, the shape of the punch 2 shown in FIG. 1 and FIG. 2 is an I-shape in which the width of the punch front end portion 2a in the sheet material conveying direction is the same as the width of the punch support body 2b in the sheet material conveying direction, but The shape of the punch 2 is not limited thereto. For example, the punch 2 may have a substantially inverted T-shaped structure in which the width of the punch tip 2a in the sheet conveying direction is larger than that of the punch support 2b in the sheet conveying direction. When the width of the punch support body 2b in the sheet conveying direction is the same, the sheet can be pressed in one press using the substantially inverted T-shaped punch 2 compared to the case of using the I-shaped punch 2 The larger area of S can reduce the number of pressing.

After the sheet material S is subjected to bending processing by press bending to form a molded body S1 having _a U-shaped cross section, the molded body is formed by using a stamping die including a pair of molds shown in FIG. The S ₁ stamping process is an O-shaped O stamping to form the open pipe S ₂ , which is a pipe body having a weld gap G between the plate width ends facing each other in the circumferential direction.

Next, the procedure _of performing O punching on the molded body S1 to form the open tube S2 will be described with reference to FIG. ₄ . First, as shown in (a) of FIG. 4 , the molded body S1 is set in such a manner that the upper mold ₄ faces the U-shaped open side of the molded body S1 ₍ with the U-shaped open side _of the molded body S1 facing upward). On the lower mold 5, the molded body S1 is clamped by the upper mold ₄ and the lower mold 5. In addition, at the time of press working of the molded body S1, the machining center _of the press die is made to coincide with the center _of the width direction of the molded body S1. Thereby, it is possible to press the plate wide end portion evenly on the left and right sides _of the U-shaped open side of the molded body S1.

It should be noted that, as shown in FIG. 5 , on the surfaces of the upper mold 4 and the lower mold ₅ that can be in contact with the molded body S1, the outer diameter of the formed steel pipe is the same diameter or substantially the same diameter and the center angle The arc portions 4a and 5a of θ are press-worked to be inscribed in an arc having the same diameter or substantially the same diameter as the outer diameter of the steel pipe. For example, the case where the central angle θ is 360 degrees corresponds to the case where 100[%] of the plate width is press-worked into the aforementioned inscribed shape. It should be noted that, hereinafter, the central angle θ of the arc portions 4a, 5a is referred to as a constrained range, and the value obtained by dividing the angle by 360 degrees is inscribed on the same diameter or substantially the same diameter as the outer diameter of the steel pipe. The range of press processing in the shape of an arc of a diameter. The arc center of the arc portion 4a is located at the same position as the machining center _Op4 of the upper die 4, and the arc center of the arc portion 5a is located at the same position as the machining center _Op5 of the lower die 5. In addition, the upper die 4 has linear portions 4b ₁ and 4b ₂ respectively connected to both ends of the arc portion 4a in the arc direction, and the lower die 5 has straight portions 5b ₁ respectively connected to both ends of the arc portion 5a in the arc direction. , 5b ₂ . It should be noted that the upper die 4 and the lower die 5 may have circular arc portions with a smaller curvature than the arc portions 4a, 5a instead of the linear portions 4b ₁ , 4b ₂ , 5b ₁ , and 5b ₂ . It should be noted that, in the present invention, from the viewpoint of improving the symmetry of the finally obtained steel pipe, it is preferable that the straight line portions 4b ₁ , 4b ₂ , 5b ₁ , 5b ₂ connected to the circular arc portions 4a, 5a or small curvature circles The arc portion is symmetrical with respect to the machining centers O _p4 , O _p5 , that is, the centers of the arc portions 4 a , 5 a. In addition, it is preferable to perform press working using a die having an arc portion whose radius is within the range of ±3.5 [%] with respect to the radius corresponding to the outer radius of the steel pipe. The reason for this will be described later.

Next, the molded body S1 sandwiched between the upper die 4 and the lower die 5 is pressed down by the upper die ₄ as shown in FIG. 4( b ) to perform O-pressing. At this time, the portion of the molded body S1 facing the arc portions 4a, 5a of the upper mold ₄ and the lower mold 5 is constrained by the upper mold 4 and the lower mold ₅ , while the unprocessed part P of the molded body S1 is not restrained by the upper mold 4 and the lower mold 5. The mold 4 and the lower mold 5 are constrained. Therefore, the open pipe S2 shown in _{( c} ) of FIG.

In addition, in the method for manufacturing a steel pipe according to the present embodiment, the molded body S1 is press-worked using _a press die including the upper die 4 and the lower die ₅ so that the shape of the open pipe S2 becomes the following shape: The range of 20 [%] or more of the plate width W (corresponding to a central angle θ of 70 degrees or more) centered on the lowest part of the glyph cross-section and 10 [%] or more of the plate width W from the edge of the plate width (corresponding to The central angle θ is 35 degrees or more) inscribed in a circular arc having the same diameter or substantially the same diameter as the outer diameter of the steel pipe.

In addition, in this embodiment, from the viewpoint of improving the shape of the steel pipe finally produced, it is preferable that the inscribed range of the open pipe S2 and the mold be substantially the same size on the upper mold ₄ side and the lower mold 5 side. That is, the range of 20 [%] or more of the plate width W centered on the lowermost part of the U-shaped cross section inscribed in an arc with the same diameter or substantially the same diameter as the outer diameter of the steel pipe is defined as A, and the inscribed When B is the total range of 10 [%] or more of the plate width W of the arc of the same diameter or substantially the same diameter as the outer diameter of the steel pipe from both ends of the plate width, it is preferable to satisfy the formula (1).

2|A-B|/(A+B)＜0.4...(1)

Among them, |A-B| represents the absolute value of A-B.

In addition, the meaning of formula (1) will be described later.

In the method for manufacturing a steel pipe according to this embodiment, in order to securely inscribe the open pipe S2 within a predetermined range and obtain a good shape, as shown in FIG. ₅ , it is preferable to For the body S1, in the U _- shaped section, the angles θ ₁₁ and θ ₁₂ formed by the tangent TL ₁ at the central part of the plate width, that is, the W/2 part, and the tangents TL ₂₁ and TL ₂₂ at the W/4 part are More than 35 degrees and less than 90 degrees. In addition, it is preferable that the angle θ formed by the tangent lines TL ₃₁ and TL ₃₂ at the end portions of the sheet width and the tangent lines TL ₂₁ and TL ₂₂ at the W/4 portion of the formed body S ₁ before the press working is ₂₁ , θ ₂₂ is more than 35 degrees and less than 90 degrees. In addition, in order to make the range inscribed on the side of the upper mold 4 and the side of the lower mold 5 the same, it is preferable that the sum of the angles θ ₁₁ and θ ₁₂ formed by the tangent TL ₁ and the tangents TL ₂₁ and TL ₂₂ is the same as that of the tangents TL ₃₁ , TL ₃₂ and The sum of the angles θ ₂₁ and θ ₂₂ formed by the tangent lines TL ₂₁ and TL ₂₂ is substantially the same.

It should be noted that, regarding the above angle, it is necessary to consider the equipment for bending the U _- shaped molded body S1 and the shape _of the mold when processing the U _- shaped molded body S1 into the open tube S2 for the following reasons. If the above angle is too large, the distance between the ends of the plate width will be reduced. If this distance is smaller than the width of the punch support 2b when bending the U _- shaped formed body S1, the U _- shaped formed body S1 cannot be obtained. On the other hand, if the above angle is too small, the distance between the plate width ends of the U _- shaped molded body S1 increases. Therefore, when the U-shaped molded body S1 is placed _on the mold, the plate width ends The distance between the parts will be larger than the opening of the upper mold 4, and the processing force cannot be applied. In addition, the distance between the left and right unprocessed parts P becomes too large, and it cannot be accurately placed on the lower die 5 .

In addition, the molded body S1 is placed on the lower mold ₅ which is the other mold in such a way that the upper mold 4 which is _one mold of the pair of molds faces the U-shaped open side of the molded body S1, and the upper mold is used to In a process in which the die 4 and the lower die ₅ sandwich the molded body S1 to press the molded body S1, the upper die ₄ and the lower die 5 have the following processing surfaces. That is, the lower die ₅ has a processed surface that is 20 [%] or more (equivalent to Outside the range where the central angle θ is 70 degrees or more), the molded body S1 is not in contact, and a part of the lower die ₅ is not in contact with the open tube _S2 in the state where the press processing is completed. In addition, the upper die 4 is provided with a part of the upper die ₄ that is not in contact with the molded body S1 in the state where the molded body S1 is placed _on the lower die ₅ , and is not in contact with the open pipe S2 in the state where the press processing is completed. contact surface.

In addition, in this embodiment, it is preferable that the center of the press die used for the press working _of the molded body S1 coincides with the center _of the width direction _of the molded body S1 when the molded body S1 is pressed. The reason for this is that applying _a force symmetrical to the center of the formed body S1 in the width direction contributes to improving the shape accuracy of the finally produced steel pipe.

In addition, in the present embodiment, it is preferable to hold the molded body S1 in _a U-shaped posture with the U-shaped opening side directed upward. One of the reasons is that it is easy to perform press work in this posture. In addition, another reason is to avoid the possibility of scratching the plate width end portion of the molded body S1 due to the self _- weight of the molded body S1 acting _on the plate width end portion of the molded body S1 if the U-shaped open side is directed downward. or mold.

Here, in this embodiment, when the molded body S1 is _subjected to O-pressing using the upper mold 4 and the lower mold ₅ to form the open tube S2, the center _of the unprocessed portion P in the molded body S1 faces The reason why the pressing force is applied at the portion where the plate width end is separated from W/4 is as follows. That is, regarding the bending moment when the molded body S1 as _a whole is circular, M=F·r·cosφ (F: pressing force, r: radius of the circle) ), the maximum deformation occurs at a position separated by 90 degrees from the pressing part. Therefore, the unprocessed part P is effectively deformed by applying a pressing force to a position separated by 90 degrees from the center of the unprocessed part P, that is, a quarter of the entire circumference. At this time, the bending moment is maximum at a position separated by 90 degrees from the position where the pressing force is applied, and decreases as the position moves away from this position. Therefore, in order to generate sufficient plastic deformation in the unprocessed portion P, it is preferable to apply a pressing force to a portion separated by W/4±0.07W from the center of the unprocessed portion P toward the plate width end.

In addition, in the present embodiment, the center of the unprocessed portion P is provided at a location including a position separated by W/4 from the plate width end portion for the following reason. That is, as described above, although it is desirable to apply the pressing force to a portion separated by W/ ₄ from the center of the unprocessed portion P toward the end of the plate width, in the stage _of forming the molded body S1 into the open tube S2, due to As the shape _of the molded body S1 changes, the contact position between the upper mold ₄ and the molded body S1 changes, and the position where the pressing force is applied also changes. In the case where the unprocessed portion P is provided in the molded body S1 including _a position separated by W/4 from the plate width end, the portion to which the pressing force is applied is always the plate width end _of the molded body S1. The processing portion P is deformed the most. By adopting this method, deformation can be imparted to the unprocessed portion P by one pressing without changing the pressing position. In addition, it is preferable to provide the unprocessed portion P within the range of W/4±0.07W from the end _of the plate width of the molded body S1 at the position where the pressing force is applied.

In addition, in the initial stage of pressing such as Fig. 4(a) and Fig. 4(b), since the end portion of the plate width is in contact with the upper mold ₄ , it is preferable that the unprocessed portion P is provided in the molded body S1. The part that is separated from the part of W/4 from the end of the plate width.

FIG. ₆ is a diagram showing the relationship between the opening amount of the weld gap G of the open pipe S2 and the restraint range. It should be noted that the relationship between the amount of opening and the restraint range shown in FIG. 6 is that after welding _both ends of the open pipe S2, the shape of the expanded pipe is corrected with a pipe expansion ratio of 1 [%] to form a tensile strength of 630 [MPa], outer diameter 660.4[mm], pipe thickness 40.0[mm] steel pipe.

The molded body S1 after bending is formed into the following shape: _an unprocessed part P with a length of W/12 is provided at each part of W/4 from the plate width end parts on both sides thereof, and a part at the center part of the plate width The angle θ ₁₁ and θ ₁₂ formed by the tangent and the tangent at the W/4 part away from the end of the plate width is 75 degrees, and the tangent at the end of the plate width and the tangent at the W/4 part The formed angle θ ₂₁ and θ ₂₂ is 75 degrees. This is the shape when the molded body S1 is clamped by the upper mold 4 and the lower mold ₅ having the same constraint range. In addition, the pressing amount is configured so that the distance of the W/ ₂ portion connecting the open pipe S2 is equal to the diameter before pipe expansion (the reduction amount in O punching makes the longitudinal diameter coincide with the diameter before pipe expansion). It can be seen from FIG. ₆ that the opening amount of the weld gap G of the open tube S2 becomes smaller as the constraining range is larger.

Fig. 7 is a diagram schematically showing the deformation state when the upper mold ₄ and the lower mold 5 with a constraint range of 0 degrees are used to form the open pipe S2. When the constraint range of the upper mold 4 and the lower mold 5 is 0 degrees, the upper mold 4 is in contact only with both ends _of the molded body S1, and the lower mold 5 is in contact with only the central part _of the molded body S1. In the embodiment, the arc portions 4a, 5a are formed as arcs having a diameter 1.16 times the outer diameter of the steel pipe. As shown in (a) of FIG. 7 , the diameter of the arc portion 5 a of the lower mold 5 is larger than the diameter of the steel pipe, so that only the 6 o'clock part is in contact with the lower mold ₅ when the cross section of the molded body S1 is regarded as a clock. Therefore, as shown in (b) of FIG. 7 , in the O punching, bending recovery to fit the arc portion 5 a of the lower die 5 occurs at the ₆ o’clock portion of the molded body S1 and its vicinity, and the radius of curvature becomes greater than the pipe diameter. Therefore, after O punching, the opening amount of the weld gap G of the open tube S2 shown in _{( c} ) of FIG. .

FIG. ₈ is a graph showing the relationship between the confinement range and the roundness of the steel pipe before pipe expansion when the weld gap G of the open pipe S2 is closed by welding. According to Figure 8, it can be seen that in the case of a constraint range of 60 degrees, the roundness becomes worse compared with the case of a constraint range of 0 degrees, and when the constraint range is increased, the roundness becomes better, and when the constraint range is 70 When the constraint range is 0 degree or more, the roundness becomes better than when the constraint range is 0 degree. In addition, it can be seen that the roundness is the best when the constraint range is 100° to 110°.

FIG. 9 is a graph showing the relationship between the constraint range and the press load. It can be seen from FIG. 9 that the press load increases as the constraint range increases. Therefore, when the restraint range is increased, although the opening amount of the weld gap G of the open tube _S2 is reduced, the press load is increased according to the press load, and the press equipment is enlarged. Small constraints. For example, in order to make the press load less than 90 [%] when the upper die 4 and the lower die ₅ constrain the entire periphery of the molded body S1 by the upper die 4 and the lower die 5, the constraining range of each of the upper die 4 and the lower die 5 is 180 degrees. Just set it below 150 degrees.

FIG. 10 is a graph showing the results of the opening amount of the weld gap G of the open pipe S2 when changing the restraint ranges of the upper die ₄ and the lower die 5 . Fig. 11 shows the roundness of the steel pipe before pipe expansion formed by closing the weld gap G of the open pipe S2 by welding while changing the restraint ranges of the upper mold ₄ and the lower mold 5 graph of the results. FIG. 12 is a graph showing the results of the press load when the constraint ranges of the upper die 4 and the lower die 5 are changed. It should be noted that, in Figs. 10 to 12, steel pipes with the same tensile strength of 630 [MPa], outer diameter of 660.4 [mm], and tube thickness of 40.0 [mm] as those in Fig. 6, Fig. 8 and Fig. 9 are used as objects. , the horizontal axis is the average value of the constraint ranges of the upper mold 4 and the lower mold 5 , and the icons in the figure are changed corresponding to each constraint range of the lower mold 5 . In the figure, for example, "lower 60 degrees" indicates that the constraint range of the lower mold 5 is 60 degrees.

According to Fig. 10, it can be seen that, regardless of the respective constraint ranges of the upper mold 4 and the lower mold 5, if the average value of the constraint ranges of the upper mold 4 and the lower mold ₅ increases, the opening amount of the weld gap G of the open pipe S2 decreases. small. In addition, as can be seen from FIG. 11 , when the restraint range of any one of the upper die 4 and the lower die 5 is smaller than 60 degrees, the roundness of the steel pipe deteriorates. Therefore, although the restraining ranges of the upper die 4 and the lower die 5 are not necessarily equal to the upper die 4 and the lower die 5, in order to obtain a shape with good roundness of the steel pipe, it is desirable to combine the upper die 4 and the lower die 5 The constraint ranges are all set to exceed the 60-degree constraint range. In addition, it can be seen from FIG. 12 that the greater the average value of the constraining ranges of the upper die 4 and the lower die 5, the greater the press load. Therefore, in the case where the upper limit of the allowable press load has been set, the range of the average value of the constraint ranges of the upper die 4 and the lower die 5 that can be applied is determined corresponding to the upper limit of the press load. .

In addition, in Fig. 11, the difference between the upper and lower constraint ranges is 30 degrees and the difference is 29 [%] of the average value of the upper and lower constraint ranges, that is, upper 90 degrees/lower 120 degrees, upper 120 degrees/lower 90 degrees In some cases, the roundness after welding and before pipe expansion is very excellent at 1.5 [%] or less. On the other hand, although the difference between the upper and lower restraint ranges is 30 degrees, but the difference is large and is 40[%] of the average value of the upper and lower restraint ranges, that is, upper 90 degrees/lower 60 degrees, after welding and pipe expansion The previous roundness was 2.0 [%], which was slightly worse. As described above, a good shape can be obtained by reducing the difference between the upper and lower constraint ranges. That is, in the present invention, the difference between the upper and lower constraining ranges is preferably smaller than 40 [%] of the average value of the upper and lower constraining ranges, more preferably 30 [%] or less. In addition, it is preferable to make the difference between the upper and lower constraint ranges smaller than 30 degrees. Regarding the relationship between the difference between the upper and lower restraint ranges and the average value of the upper and lower restraint ranges, in other words, inscribed in the arc with the same diameter or substantially the same diameter as the outer diameter of the steel pipe and centered on the lowermost part of the U-shaped cross-section The range of 20 [%] or more of the plate width W is defined as A, and 10 [%] or more of the plate width W from both ends of the plate width that is inscribed in an arc that is the same diameter or substantially the same diameter as the outer diameter of the steel pipe When the total range of is B, it is preferable to satisfy the formula (1).

2|A-B|/(A+B)＜0.4...(1)

Among them, |A-B| represents the absolute value of A-B.

FIG. 13 shows the weld gap G in the case where the constraining range of the upper die 4 is the same as that of the lower die 5 and the length L _of the unprocessed portion P of the formed body S1 after bending is changed. A plot of the results of the splay of . FIG. 14 shows the steel pipe before expansion when the constraining range of the upper die 4 and the constraining range of the lower die 5 are the same, and the length L _of the unprocessed portion P of the formed body S1 after bending is changed. A plot of the roundness results for . FIG. 15 is a graph showing the results of the press load when the constraining range of the upper die 4 and the constraining range of the lower die 5 are the same, and the length L _of the unprocessed part P of the formed body S1 after bending is changed. picture. It should be noted that, in FIGS. 13 to 15 , the angle formed by the tangent at the central portion of the plate width and the tangent at the W/4 portion, which is a portion away from the end of the plate width by W/4, is θ ₁₁ , θ ₁₂ , when the angles formed by the tangent line at the end of the plate width and the tangent line at the W/4 portion are set as θ ₂₁ , θ ₂₂ , so that all the above angles have the same value, and correspond to the unprocessed part P varies in width. In addition, the horizontal axis represents the average value of the constraint range of the upper mold 4 and the constraint range of the lower mold 5 .

According to Fig. 13, it can be seen that no matter what the length L _of the unprocessed part P of the molded body S1 and the angles θ ₁₁ , θ ₁₂ , θ ₂₁ , and θ ₂₂ formed by the tangents are, the constraint range of the upper mold 4 and the lower mold The larger the average value of the constraint range of 5, the smaller the opening amount of the weld gap G. In addition, it can be seen that when the average value of the constraint range of the upper mold 4 and the constraint range of the lower mold 5 are the same, the longer the above-mentioned length L is. The smaller the angles θ ₁₁ , θ ₁₂ , θ ₂₁ , and θ ₂₂ formed by the long and tangent lines, the smaller the opening amount. 14 and 15, it can be seen that when the average value of the restraint range of the upper die 4 and the restraint range of the lower die 5 is the same, there is basically no difference in the roundness _of the steel pipe and the stamping load. The difference caused by the length L of the unprocessed part P and the angles θ ₁₁ , θ ₁₂ , θ ₂₁ , θ ₂₂ formed by the tangents. As described above, when the average value of the constrained range of the upper die 4 and the constrained range of the lower die 5 is the same, by increasing the length L _of the unprocessed part P of the molded body S1, the angle _θ11 formed by the tangents is increased. _{. _ _ _} Amount of opening.

FIG. 16 is a graph showing the results of the opening amount of the weld gap G of the open pipe S2 when the radii of the arc portions of the upper die ₄ and the lower die 5 are changed. FIG. 17 is a graph showing the results of the press load when the radii of the arc portions of the upper die 4 and the lower die 5 are changed. It should be noted that, in FIGS. 16 and 17 , the central angle of the arc portions 4a, 5a of the upper die 4 and the lower die 5 is set to 45 degrees, and the radius of the arc portions 4a, 5a, that is, the radius of the arc portion, is changed. , A steel pipe with a tensile strength of 630 MPa, an outer diameter of 660.4 [mm], and a pipe thickness of 40.0 [mm] was pressed by O punching so that the longitudinal diameter was consistent with the diameter before pipe expansion. In addition, the abscissa of Fig. 16 and Fig. 17 is the ratio of the radius of the arc portion to the outer radius of the steel pipe (the radius corresponding to the outer diameter of the steel pipe), which is greater than 1.0 when the radius of the arc portion is greater than the outer radius of the steel pipe. When the radius is smaller than the outer radius of the steel pipe, it is less than 1.0.

As shown in FIG. 16 , when the radii of the arc portions of the upper mold 4 and the lower mold 5 are equal to the outer radius of the steel pipe (the horizontal axis in FIG. 16 is 1.0), the opening amount of the weld gap G is the smallest. On the other hand, if the radius of the arc portion of the upper mold ₄ and the lower mold 5 is larger than the outer radius of the steel pipe, as shown in FIG. The radii of the arc portions of the upper mold 4 and the lower mold 5 increase, and the opening amount of the weld gap G increases. In addition, if the radius of the arc portion of the upper mold 4 and the lower mold 5 is smaller than the outer radius of the steel pipe, bending recovery deformation occurs at the end of the arc portion 4a, 5a of the upper mold 4 and the lower mold 5, so as the arc portion The radius decreases and the opening amount of the weld gap G increases. As mentioned above, although it is ideal that the radius of the arc portion of the upper die 4 and the lower die 5 is the same as the outer radius of the steel pipe, the radius of the arc portion of the upper die 4 and the lower die 5 is equivalent to the outer radius of the steel pipe. When the radius is ±3.5 [%], the opening amount of the weld gap G is suppressed to 40 [mm] or less.

However, according to Fig. 17, it can be known that the stamping load increases as the radius of the arc portion decreases, especially in the case of a small radius of the arc portion, it is also necessary to consider the load of the stamping machine to determine its radius.

[Example 1]

Preparation After edge bending of a steel plate with a width W of 1928 [mm], a length of 1000 [mm], a thickness of 40 [mm], and a tensile strength of 635 [MPa] by beveling with an edge milling machine Formed body S ₁ obtained by performing press bending. Next, the upper die 4 and the lower die 5 of various restraint ranges _were used for the molded body S1, and a press machine of 30 [MN] was used to carry out O-pressing to mold the molded bodies A and B. Table 1 and Table 2 show the shapes of molded bodies A and B. It should be noted that the letters A and B at the beginning of "No." in Table 1 and Table 2 indicate the shape of the molded body (molded body A, B), and the numbers after the letters A and B indicate the upper mold 4 and the lower mold 5 combinations of constraint ranges.

Table 1 shows the following molded body A: As condition A, centering on the W/4 part from the plate width end, an unprocessed part is provided at a width of 160 [mm] (W/12), and the plate width end The angles θ ₂₁ and θ ₂₂ formed by the tangent at the center of the plate width and the tangent at the W/4 portion are 65 degrees, and the angles θ ₁₁ and θ ₁₂ formed between the tangent at the center of the plate width and the tangent at the W/4 portion are 73 degrees. Table 2 shows the following molded body B: as condition B, centering on the W/4 part from the end of the plate width, with a width of 321 [mm] (W/6) (width twice that of condition A ) set the unprocessed part, the angle θ ₂₁ and θ ₂₂ formed by the tangent at the end of the plate width and the tangent at the W/4 part are 59 degrees, and the angle between the tangent at the central part of the plate width and the tangent at the W/4 part The formed angle θ ₁₁ and θ ₁₂ is 61 degrees. The moldings A and B are symmetrical with respect to the straight line connecting the center of the plate width end and the 1/2 plate width, and Table 1 and Table 2 show the values of the 1/2 plate width. In addition, the reduction amount at the time of O punching is such that the distance between the outer surface side of the W/2 portion and the outer surface side of the plate width end portion becomes 654 [mm].

_In addition, after measuring the opening amount of the open pipe S2 after O stamping of the molded bodies _A and B, the weld gap G of the open pipe S2 was welded to form a steel pipe with an outer diameter of 654 [mm], and then The diameter was measured at 8 places at intervals of 22.5 degrees, and the difference between the maximum and minimum diameters was obtained. In Table 1 and Table 2, the die shape (constraint range), press load, opening amount, and roundness are collectively shown. The roundness at this time is a numerical value obtained by dividing the difference between the maximum and the minimum by the outer diameter of the steel pipe (the average value of all measured values of the above-mentioned diameters).

It should be noted that, in the case of the welding machine used in this example, the opening cannot be closed when the opening amount after O punching exceeds 40 [mm]. Both ends and the center of the pipe axial direction are temporarily welded, and then full-length welding of the weld gap G is performed. In addition, regarding the roundness, 2.5 [%] before pipe expansion was set as a pass standard. This is because if the roundness before pipe expansion is 2.5 [%] or less, the roundness after pipe expansion can be made a good value of 1.0 [%] or less.

[Table 1]

[Table 2]

In Nos. A1 to A7, A9, and A10 in Table 1 and Nos. B1 to B7, B9, and B10 in Table 2 within the scope of the examples of the present invention, the opening amount was small and the roundness was also good. In particular, when the constraint range is 90° to 110°, the roundness is 1.0 [%] or less even without pipe expansion. In addition, the smaller the average value of the constraint range, the smaller the punching load.

On the other hand, in No.A8 and A11 in Table 1 and No.B8 and B11 in Table 2, where the constraint range of the upper mold 4 and the lower mold 5 is a combination of 60 degrees and 90 degrees, although the amount of opening is small, they are true circles. degree of deterioration. In addition, in No.A12 to A16 in Table 1 and No.B12 to B16 in Table 2, where the average value of the constraint range is 60 degrees or less, the amount of opening is large. In particular, No.A15 and A16 in Table 1, and No. In .B16, the roundness cannot be measured because the welded part after welding the weld gap part G is broken.

Also, in the case of using the molded body B whose width of the unprocessed part is larger than that of the molded body A, compared with the case of using the molded body A, the pressing load and the roundness are substantially the same, but the opening amount is smaller.

The embodiment to which the present invention is applied has been described above, but the present invention is not limited to the description and drawings constituting a part of the disclosure of the present invention based on the present embodiment. That is, other embodiments, examples, applied techniques, and the like obtained by those skilled in the art based on the present embodiment are all included in the scope of the present invention.

[Example 2]

Prepare to press after end bending a steel plate with a plate width of 1639 [mm], a length of 1000 [mm], a plate thickness of 31.8 [mm], and a tensile strength of 779 [MPa] using an edge milling machine. Formed body S ₁ obtained by bending. Next, the molded body S1 was O-pressed with _a press machine of 30 [MN] using the upper die 4 and the lower die 5 of various constraint ranges, thereby molding the molded bodies A and B. Table 3 and Table 4 show the shapes of the moldings A and B. It should be noted that the letters A and B at the beginning of "No." in Table 3 and Table 4 indicate the shape of the molded body (molded body A, B), and the numbers after the letters A and B indicate the upper mold 4 and the lower mold 5 combinations of constraint ranges.

Table 3 shows the following molded body A: As condition A, centering on the W/4 part from the plate width end, an unprocessed part is provided at a width of 137 [mm] (W/12), and the plate width end The angles θ ₂₁ and θ ₂₂ formed by the tangent at the center of the plate width and the tangent at the W/4 portion are 65 degrees, and the angles θ ₁₁ and θ ₁₂ formed between the tangent at the center of the plate width and the tangent at the W/4 portion are 72 degrees. Table 4 shows the following molded body B: As condition B, centering on W/4 from the end of the plate width, the width is 273 [mm] (W/6) (width twice that of condition A) Set the unprocessed part, the angle θ ₂₁ and θ ₂₂ formed by the tangent at the end of the plate width and the tangent at the W/4 part are 59 degrees, and the angle between the tangent at the center of the plate width and the tangent at the W/4 part The angles θ ₁₁ and θ ₁₂ are 61 degrees. The moldings A and B are symmetrical with respect to the straight line connecting the center of the plate width end and the 1/2 plate width, and Table 3 and Table 4 show the values of the 1/2 plate width. In addition, the amount of reduction at the time of O punching was set to be such that the distance between the outer surface side of the W/2 portion and the outer surface side of the plate width end portion became 553 [mm].

_In addition, after measuring the opening amount of the open pipe S2 after the O stamping of the molded bodies _A and B, the weld gap G of the open pipe S2 is welded to form a steel pipe with an outer diameter of 553 [mm], and then, in the circumferential direction The diameter was measured at 8 places at intervals of 22.5 degrees, and the difference between the maximum and minimum of said diameters was obtained. Table 3 and Table 4 collectively show the die shape (constraint range), press load, opening amount, and roundness. The true roundness at this time is the value obtained by dividing the difference between the maximum and minimum by the outer diameter of the steel pipe.

It should be noted that, in the case of the welding machine used in this example, the opening cannot be closed when the opening amount after O punching exceeds 40 [mm]. Both ends and the center of the pipe axial direction are temporarily welded, and then full-length welding of the weld gap G is performed. In addition, the roundness is 1.0 [%] or less by tube expansion and 2.5 [%] before tube expansion as a pass standard.

[table 3]

[Table 4]

In Nos. A1 to A7, A9, and A10 in Table 3 and Nos. B1 to B7, B9, and B10 in Table 4 within the scope of the examples of the present invention, the amount of opening was small and the roundness was also good. In particular, when the constraint range is 90° to 110°, the roundness is 1.0 [%] or less even without pipe expansion. In addition, the smaller the average value of the constraint range, the smaller the punching load.

On the other hand, in No.A8 and A11 in Table 3 and No.B8 and B11 in Table 4 where the constraint ranges of the upper mold 4 and the lower mold 5 are a combination of 60 degrees and 90 degrees, although the amount of opening is small, they are true circles. degree of deterioration. In addition, in No.A12-A16 of Table 3 and No.B12-B16 of Table 4, the average value of the restraint range is 60 degrees or less, the opening amount is large, especially No.A15, A16 of Table 3, and No. In No. B16, the roundness could not be measured because the welded portion after welding the weld gap G was broken.

Also, in the case of using the molded body B whose width of the unprocessed part is larger than that of the molded body A, compared with the case of using the molded body A, the pressing load and the roundness are substantially the same, but the opening amount is smaller.

[Example 3]

Prepare to press after end bending a steel plate with a plate width of 2687 [mm], a length of 1000 [mm], a plate thickness of 50.8 [mm], and a tensile strength of 779 [MPa] using an edge milling machine. The molded body S ₁ obtained by bending. Next, the molded body S1 was O-pressed with _a press machine of 30 [MN] using the upper mold 4 and the lower mold 5 of various constraint ranges, and the molded bodies A and B were molded. Table 5 and Table 6 show the shapes of the moldings A and B. It should be noted that the letters A and B at the beginning of "No." in Table 5 and Table 6 indicate the shape of the molded body (molded body A, B), and the numbers after the letters A and B indicate the upper mold 4 and the lower mold 5 combinations of constraint ranges.

Table 5 shows the following molded body A: As condition A, centering on the W/4 part from the plate width end, an unprocessed part is provided at a width of 224 [mm] (W/12), and the plate width end The angles θ ₂₁ and θ ₂₂ formed by the tangent at the center of the plate width and the tangent at the W/4 portion are 73 degrees, and the angles θ ₁₁ and θ ₁₂ formed between the tangent at the center of the plate width and the tangent at the W/4 portion are 72 degrees. Table 6 shows the following molded body B: as the condition B, centering on W/4 from the end of the sheet width, the width is 448 [mm] (W/6) (twice the width of the condition A) Set the unprocessed part, the angle θ ₂₁ and θ ₂₂ formed by the tangent at the end of the plate width and the tangent at the W/4 part are 58 degrees, and the tangent at the central part of the plate width and the tangent at the W/4 part The angles θ ₁₁ and θ ₁₂ are 59 degrees. The moldings A and B are symmetrical with respect to the straight line connecting the center of the plate width end and the 1/2 plate width, and Table 5 and Table 6 show the values of the 1/2 plate width. In addition, the reduction amount at the time of O punching is set to be such that the distance between the outer surface side of the W/2 portion and the outer surface side of the plate width end portion becomes 905 [mm].

_In addition, after measuring the opening amount of the open pipe S2 after O stamping of the molded bodies _A and B, the weld gap G of the open pipe S2 is welded to form a steel pipe with an outer diameter of 905 [mm], and then The diameter was measured at 8 places at intervals of 22.5 degrees, and the difference between the maximum and minimum of said diameters was obtained. Table 5 and Table 6 collectively show the die shape (constraint range), press load, opening amount, and roundness. The true roundness at this time is the value obtained by dividing the difference between the maximum and minimum by the outer diameter of the steel pipe.

It should be noted that, with the welding machine used in this example, the opening cannot be closed when the opening amount after O punching exceeds 40 [mm]. Both ends and the center in the axial direction are temporarily welded, and then the full length of the weld gap G is fully welded. In addition, regarding the roundness, it was set to be 1.0 [%] or less by tube expansion and 2.5 [%] before tube expansion as a pass standard.

[table 5]

[Table 6]

In Nos. A1 to A7, A9, and A10 in Table 5 and Nos. B1 to B7, B9, and B10 in Table 6 within the scope of the examples of the present invention, the opening amount was small and the roundness was also good. In particular, when the constraint range is 90° to 110°, the roundness is 1.0 [%] or less even without pipe expansion. In addition, the smaller the average value of the constraint range, the smaller the punching load.

On the other hand, in No.A8 and A11 in Table 5 and No.B8 and B11 in Table 6 where the constraint ranges of the upper mold 4 and the lower mold 5 are a combination of 60 degrees and 90 degrees, although the amount of opening is small, they are true circles. degree of deterioration. In addition, in No.A12 to A16 in Table 5 and No.B12 to B16 in Table 6, where the average value of the constraint range is 60 degrees or less, the amount of opening is large, especially No.A15 and A16 in Table 5, and No. In .B16, the roundness could not be measured because the welded portion after welding the weld gap G was broken.

Also, in the case of using the molded body B whose width of the unprocessed part is larger than that of the molded body A, compared with the case of using the molded body A, the pressing load and the roundness are substantially the same, but the opening amount is smaller.

[Example 4]

In order to manufacture steel pipes with a target outer diameter of 621 [mm] to 687 [mm], it is prepared to use a milling machine to set a bevel to process a plate width of 1826 to 2032 [mm], a length of 1000 [mm], and a plate thickness of 40 [ mm] and a steel plate with a tensile strength of 635 [MPa], which is a formed body S ₁ obtained by bending at the end and then performing press bending. Next, using a variety of upper molds 4 and lower molds 5 with a radius of 327mm of arc portion and a restraining range of 45 degrees, the molded body S1 is O-pressed with _a press machine of 30 [MN] to form molded bodies D1 to D11 . Table 7 shows the molding conditions of the molded bodies D1 to D11. In the moldings D1 to D11, an unprocessed part is provided with a width of W/12 centered on the W/4 part from the end of the sheet width based on the initial sheet width W, and the tangent line at the end of the sheet width and W/4 The angles θ ₂₁ and θ ₂₂ formed by the tangents at the W/4 portion were set to 75 degrees, and the angles θ ₁₁ and θ ₁₂ formed between the tangents at the center of the plate width and the tangents at the W/4 portion were set to 75 degrees. In addition, in the O press, the pressing was carried out so that the distance between the outer surface side of the W/2 portion and the outer surface side of the sheet width end became a value corresponding to the initial sheet width W as shown in Table 7. In addition, Table 7 shows the outer diameter of the steel pipe after the O press reduction.

Then, the opening amount of the open tube S2 after O _punching of these formed bodies D1 to D11 was measured. Table 7 also shows the press load and the opening amount as the results.

[Table 7]

No. D6 in Table 7 whose ratio of the radius of the arc portion to the outer radius of the steel pipe is 1.00 has the smallest opening amount, and the opening amount increases as the outer radius of the steel pipe decreases or increases. In addition, Nos. D2 to D10 in Table 7 are Nos. D2 to D10 in Table 7, which can be closed by the welding machine used in Example 1. The ratio of the radius of the arc to the outer radius of the steel pipe is 0.96 to 1.04. In addition, in Example 1, the opening amount of 50 [mm] without weld fracture is also No. D2 to D10 in Table 7, and the ratio of the radius of the arc portion to the outer radius of the steel pipe is 0.96 to 1.04.

It should be noted that the amount of opening that can weld the gap portion G of the weld seam to close it, and the amount of opening that does not cause fracture of the welded portion are different according to welding equipment and welding methods, but the radius of the arc portion of the upper mold 4 and the lower mold 5 The standard is 0.96 to 1.04 of the outer radius of the steel pipe.

Industrial availability

According to the present invention, it is possible to provide a method for manufacturing a steel pipe and a press die capable of efficiently forming a steel pipe with high roundness.

Explanation of reference signs

1 die

1a Rod member

1b Rod member

2 punches

2a Front end of punch

2b Punch support body

3 transport roller

4 upper mold

4a arc part

4b ₁ Straight line or arc with small curvature

4b ₂ Straight lines or small curvature arcs

5 lower mold

5a arc part

5b ₁ Straight line or arc with small curvature

5b ₂ Straight lines or small curvature arcs.

Claims (7)

1. A method for manufacturing a steel pipe, wherein a plate material having both width-direction end portions subjected to end portion bending is bent 3 times or more in the width direction of the plate material to form a formed body having a U-shaped cross section, the formed body is then subjected to press working to produce an open pipe which is a pipe body having a bead gap portion in the longitudinal direction thereof, and the bead gap portion is joined to produce the steel pipe,

when the width of the plate material before the end portion bending is set to the plate width W,

the molded body has a light-processed portion with a curvature smaller than that of other regions or an unprocessed portion without bending processing, with a portion separated from the plate-width end by W/4 as a center,

in the manufacturing method, the open pipe is pressed so that the shape of the open pipe is as follows: the range of the plate width W of more than 20[% ] and the range of the plate width W of more than 10[% ] from the plate width end part, which are centered on the lowest part of the U-shaped cross section, are connected to the circular arc with the same or almost the same diameter as the outer diameter of the steel pipe,

performing press working using a die having an arc portion with a radius within a range of + -3.5 [% ] with respect to a radius corresponding to an outer radius of the steel pipe,

for the formed body before press workingIn other words, a tangent TL at the W/2 portion, which is the central portion of the plate width, in the U-shaped cross section ₁ With the tangent TL at the W/4 portion ₂₁ 、TL ₂₂ Angle theta formed by ₁₁ 、θ ₁₂ A tangent TL at the wide end of the board being more than 35 degrees and less than 90 degrees ₃₁ 、TL ₃₂ With the tangent TL at the W/4 portion ₂₁ 、TL ₂₂ Angle theta ₂₁ 、θ ₂₂ Is more than 35 degrees and less than 90 degrees, and tangent TL ₁ With tangent line TL ₂₁ 、TL ₂₂ Angle theta ₁₁ 、θ ₁₂ Sum is the same as tangent TL ₃₁ 、TL ₃₂ With tangent line TL ₂₁ 、TL ₂₂ Angle theta ₂₁ 、θ ₂₂ The sum is the same.

2. The method of manufacturing a steel pipe according to claim 1, wherein formula (1) is satisfied where A is a range of 20[% ] or more of the plate width W centered on the lowermost portion of the U-shaped cross section and inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe, and B is a total range of 10[% ] or more of the plate width W from both ends of the plate width and inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe,

2|A-B|/(A+B)＜0.4……(1)

wherein, | A-B | represents the absolute value of A-B.

3. The method of manufacturing a steel pipe as claimed in claim 1 wherein, in the step of pressing the molded article by placing the molded article on one of a pair of dies so that the one of the pair of dies faces the open side of the U-shape of the molded article and sandwiching the molded article between the pair of dies,

the other mold has: in a state where the molded body is placed on the other mold, the molded body does not contact with the other mold except for a range of a shape which is inscribed in an arc having the same diameter or substantially the same diameter as the outer diameter of the steel pipe with the lowermost portion of the U-shaped cross section as the center

A processing surface on which a part of the other die does not contact the open pipe in a state where the press processing is completed;

the one mold has: the molded body is not in contact with the other mold in a state where the molded body is placed on the other mold

And a processing surface on which a part of the die does not contact the open pipe in a state where the press processing is completed.

4. The method of manufacturing a steel pipe as claimed in claim 2 wherein, in the step of pressing the molded article by placing the molded article on one of a pair of dies so that the one of the pair of dies faces the open side of the U-shape of the molded article and sandwiching the molded article between the pair of dies,

the other mold has: in a state where the molded body is placed on the other mold, the molded body does not contact with the other mold except for a range of a shape which is inscribed in an arc having the same diameter or substantially the same diameter as the outer diameter of the steel pipe with the lowermost portion of the U-shaped cross section as the center

A machining surface on which a part of the other die does not contact the open pipe in a state where the press working is completed;

the one mold has: in a state where the molded body is placed on the other mold, the molded body does not come into contact with the other mold, and

and a processing surface on which a part of the die does not contact the open pipe in a state where the press processing is completed.

5. The method of manufacturing a steel pipe according to any one of claims 1 to 4, wherein a center of a press die used in the press working of the formed body coincides with a center of the formed body in a width direction at the time of the press working of the formed body.

6. The method of manufacturing a steel pipe as claimed in any one of claims 1 to 4 wherein the molded body is held in a U-shaped posture with the U-shaped open side facing upward.

7. The method of manufacturing a steel pipe as claimed in claim 5 wherein the molded body is held in a U-shaped posture with the U-shaped open side facing upward.

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