CN112638558A

CN112638558A - Method for manufacturing steel pipe and press die

Info

Publication number: CN112638558A
Application number: CN201880097036.2A
Authority: CN
Inventors: 堀江正之; 日当洸介; 川野友裕; 田村征哉
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2018-09-14
Filing date: 2018-09-14
Publication date: 2021-04-09
Anticipated expiration: 2038-09-14
Also published as: KR102425607B1; WO2020054051A1; EP3851220A4; BR112021004322A2; RU2769596C1; JP6791397B2; KR20210041032A; CN112638558B; JPWO2020054051A1; EP3851220A1

Abstract

A method for manufacturing a steel pipe, wherein a plate material subjected to end portion bending at both ends in the width direction is subjected to bending in the width direction 3 times or more to form a formed body having a U-shaped cross section, the formed body is subjected to press working to form an open pipe having a bead gap portion in the longitudinal direction, and then the bead gap portion is joined to form the steel pipe, wherein when the width of the plate material before the end portion bending is set to a plate width W, the formed body is subjected to press working so that the open pipe has a light-worked portion or an unprocessed portion from which bending is omitted and to which a curvature smaller than that of other regions is given, with a portion separated from the plate width end portion by W/4 as a center, and the shape of the open pipe is set to: the range of 20 [% ] or more of the plate width W centered on the lowest part of the U-shaped cross section and the range of 10 [% ] or more of the plate width W from the plate width end part are connected to the arc having the same or almost the same diameter as the outer diameter of the steel pipe.

Description

Method for manufacturing steel pipe and press die

Technical Field

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

Background

In the past, UOE forming technology has been widely used as a technology for forming steel pipes. The UOE forming technology comprises the following steps: the steel plate is first press-worked into a U-shape and then press-worked into an O-shape, and a pipe body, i.e., an open pipe, having a weld gap portion between plate-width end portions facing each other in the circumferential direction is formed. However, in the UOE forming technique, in a step of press-working a steel sheet into U-shape or O-shape to form an open pipe, a high press force is required, and therefore, a large press machine is required.

Therefore, in the case of manufacturing a steel pipe, as a technique for reducing a punching force to form an open pipe, for example, a press bending method has been put into practical use in which after bending an end portion in a width direction of a steel plate to impart an end bent portion, 3-point bending punching is performed a plurality of times using a punch and a die supported by a punch support body to form the steel plate into a substantially circular shape to form an open pipe. On the other hand, the open pipe formed by the press bending method has a larger expansion amount of the bead gap portion than the width of the punch support body, but if the expansion amount is too large, a force required to butt the plate width end portions facing each other to close the bead gap portion becomes large to weld the bead gap portion, and the facility for closing the bead gap portion becomes large. In addition, in the welded portion after welding the bead gap portion having an excessively large expansion amount, a force to expand the bead gap portion is applied due to springback, and therefore, a welding defect is likely to occur, and if the force is excessively large, the welded portion is broken.

Therefore, patent documents 1 to 4 disclose techniques for reducing the amount of expansion of the weld gap portion of the open pipe after press bending. Patent document 1 discloses a technique of reducing the width of a punch support body by making a joint portion between a punch tip portion and the punch support body rotatable, thereby reducing the amount of expansion of a weld gap portion of an open pipe. Patent document 2 discloses the following technique: a gap holding mechanism for limiting the movement of the plate material in the direction orthogonal to the moving direction of the punch is provided, and when the wide end of the plate is not in contact with the punch support body, a large pressure is applied in the final bending process to reduce the opening amount of the gap between the open pipes. Patent document 3 discloses a technique of measuring a gap between a sheet width end portion and a punch support body after a final reduction step, and reducing the gap as much as possible to reduce the amount of expansion of a bead gap portion in pipe opening. Further, patent document 4 discloses the following technique: the amount of reduction by the punch in the final step is determined based on the time when the distance between the sheet width ends reaches the predetermined value at the time of reduction in the final bending step, so that the amount of opening of the open seam clearance portion can be reduced regardless of the difference in shape that occurs in the previous press-bending step.

However, in the techniques disclosed in patent documents 1 to 4, the amount of expansion of the bead 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 pipe after the press bending to reduce the amount of opening of the weld gap portion. Patent document 5 discloses a technique of forming a steel pipe after press bending with a small load by hot roll forming. Patent document 6 discloses the following technique: a strain detector capable of detecting the inclination or strain of a pressing member attached to a slider is disposed, the pressing member is disposed so as to be capable of being moved in an inclined manner or in a parallel manner in accordance with the detection of the inclination or strain of the strain detector, and when a molding material is press-molded into a tubular shape, the pressing member is moved in an inclined manner or in a parallel manner so as to reduce the amount of strain in accordance with the amount of inclination or strain of the pressing member, and press-molding is performed. Patent document 7 discloses the following technique: the slit pipe having the non-circular preform is formed by performing slight forming in at least 1 bending step on the inner surface of the plate material in comparison with other bending steps on the left and right sides with respect to the center defined by the longitudinal axis of the upper tool which is inserted into the gradually-formed plate material, and thereafter, pressing forces acting on the pre-slightly-formed regions on both sides of the center are applied to the non-circular preform from the outside as appropriate, thereby forming a complete slit pipe. Further, patent document 8 discloses the following technique: in a molded body having flat portions between portions bent with at least 2 tube curvatures, a tube having a closed slit portion is molded by imparting plastic deformation to only at least 1 flat portion to form a predetermined curvature. Further, patent document 9 discloses the following method: when a molded body provided with a lightly processed portion having a curvature smaller than that of other regions or an unprocessed portion from which bending is omitted is pressed down to open a pipe, a pressing force is applied to the lightly processed portion or the unprocessed portion without constraining the lightly processed portion or the unprocessed portion, and the pipe having a closed slit portion is molded. In addition, at the time of this pressing, it is preferable that the molded body is held in the mold in a U-shaped posture in which the open portion faces upward, and is supported at the lowermost end of the molded body.

Patent documents 10 and 11 disclose a technique for manufacturing a UOE tube having a product diameter in which the diameter of the inner surface of an O-press die is different from the outer diameter of a product tube. The die disclosed in patent document 10 has a shape in which only a part of a horizontally long circular shape is cut out of the inner surface of the upper and lower dies, and in fig. 3(a) and 4(a) illustrating the operation of the die of patent document 10, the entire inner surface of the O-press die is in contact with the O-tube. Further, patent document 11 discloses a method of: a die having an inner surface formed with an arc having a radius larger than the outer diameter of a product and having end faces ground in advance to have a sufficiently large gap is used, the die is filled with a material and compressed at a predetermined rate, and then the pipe obtained by the molding is rotated by substantially 90 DEG to be further O-stamped to be formed into a circular shape. In the 1 st O-press step, the steel pipe is in close contact with the entire surface of the die.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2004-82219

Patent document 2: japanese patent laid-open publication No. 2011-

Patent document 3: international publication No. 2014/188468

Patent document 4: international publication No. 2014/192043

Patent document 5: japanese patent laid-open publication No. 2005-324255

Patent document 6: japanese patent laid-open publication No. 2005-21907

Patent document 7: japanese laid-open patent publication No. 2012-250285

Patent document 8: specification of U.S. Pat. No. 4149399

Patent document 9: international publication No. 2016/084607

Patent document 10: japanese patent laid-open No. 2003-39115

Patent document 11: japanese laid-open patent publication No. 2002-178026

Disclosure of Invention

Problems to be solved by the invention

However, the technique disclosed in patent document 5 has a problem that the manufacturing cost is significantly increased in consideration of the consumption amount of thermal energy required for heating. In addition, in the case of using a plate material manufactured through a heat treatment process in order to achieve strength, toughness, and weldability, there is a possibility that the characteristics thereof are lost. In the techniques disclosed in patent documents 6 to 8, since the molding material or the non-circular preform is molded independently at the left and right sides, when the deformation amount is different at the left and right sides, a step (difference in appearance) may be formed at a weld gap portion or a slit portion which becomes a welded portion. In addition, in the above technique, when the desired shape is formed 1 time, the deformation may be concentrated locally to deteriorate the roundness of the steel pipe, and therefore, the deformation must be performed a plurality of times, which is a limit in efficient forming. In the technique disclosed in patent document 9, since the radius of the lower die is larger than the outer diameter of the pipe, the bending recovery occurs at the lowermost end of the molded article in the U-shaped posture, and the deformation occurs in which the gap portion opens, so that the gap between the slit portions may not be reduced. In addition, in the techniques disclosed in patent documents 10 and 11, since the O-tube is press-worked in a state of being in close contact with the entire surface of the die, as described above, a large-scale press machine is still required because a high press force is required.

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

Means for solving the problems

In order to solve the above problems and achieve the above object, a method for manufacturing a steel pipe according to the present invention is a method for manufacturing a steel pipe, in which a plate material having end portions bent at both width-directional end portions is bent 3 times or more in a 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 a longitudinal direction thereof, and the bead gap portion is then joined to produce a 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 the other region or an unprocessed portion without bending processing around a portion separated by W/4 from the wide end portion of the plate,

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 20 [% ] or more and the range of the plate width W of 10 [% ] or more from the plate width end with the lowest part of the U-shaped cross section as the center are connected to the arc with the same or almost the same diameter as the outer diameter of the steel pipe.

In the above-described invention, the method for producing a steel pipe of the present invention is characterized in that when a range of 20 [% ] or more of the plate width W centered on the lowermost portion of the U-shaped cross section inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe is denoted by a, and a total range of 10 [% ] or more of the plate width W inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe from both ends of the plate width is denoted by B, expression (1) is satisfied,

2|A-B|/(A+B)＜0.4……(1)

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

In the above-described method for producing a steel pipe of the present invention, in the process of placing one of the pair of dies on the other die so that the one die faces the U-shaped open side of the molded body, sandwiching the molded body between the pair of dies, and press-working the molded body,

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.

In the above invention, the method for manufacturing a steel pipe of the present invention is characterized in that the press working is performed 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.

In the method for producing a steel pipe according to the present invention, in the above invention, a center of a press die used for press working of the formed body is aligned with a center of the formed body in a width direction thereof.

In the method for manufacturing a steel pipe according to the present invention, the molded body is held in a U-shaped posture in which the open side of the U-shape faces upward.

Further, a press die of the present invention is a press die used in the method for producing a steel pipe of the present invention, wherein the press die includes a pair of pressing bodies for sandwiching the molded body, and an arc portion having a radius within a range of ± 3.5 [% ] with respect to a radius corresponding to an outer radius of the steel pipe is formed on a surface of each die contactable with the molded body such that an arc center is positioned at a position corresponding to a machining center of each die,

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

In the press die according to the present invention, the angles of the central angles of the two dies are the same.

In the press mold of the present invention, each of the molds has a straight portion connected to both ends of the arc portion in the arc direction or a small-curvature arc portion having a smaller curvature than the arc portion.

In the method for producing a steel pipe of the present invention, the press die of the present invention is used.

Effects of the invention

The method for manufacturing a steel pipe and the press die according to the present invention have an effect of efficiently forming a steel pipe having a high degree of roundness.

Drawings

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

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

FIG. 3 is a sectional view of a molded article having a U-shaped cross section.

Fig. 4 is a view schematically showing a step of forming an open tube by O-pressing a formed body.

Fig. 5 is an explanatory view of the arc portion, the straight portion, and the center angle of the upper mold and the lower mold.

Fig. 6 is a diagram showing the relationship between the expansion amount of the open seam portion and the restraint range and the press load.

Fig. 7 is a diagram schematically showing a deformation state when the pipe is formed into an open pipe by using an upper die and a lower die having a constraint range of 0 degrees.

Fig. 8 is a diagram showing a relationship between the restraint range and the roundness of the steel pipe before expansion when the open-pipe weld gap portion is closed by welding.

Fig. 9 is a diagram showing a relationship between the restraint range and the press load.

Fig. 10 is a diagram showing the results of the opening amount of the open seam portion in the case where the restriction ranges of the upper die and the lower die are changed.

Fig. 11 is a view showing the result of the roundness of a steel pipe before pipe expansion, which is molded by closing the open weld gap portion by welding, when the restraint ranges of the upper die and the lower die are changed.

Fig. 12 is a diagram showing the result of the press load when the restriction ranges of the upper die and the lower die are changed.

Fig. 13 is a view showing the result of the opening amount of the weld gap portion in the case where the restraining range of the upper die is made the same as the restraining range of the lower die and the length of the lightly processed portion or the unprocessed portion of the press-bent molded body is changed.

Fig. 14 is a view showing the result of roundness of a steel pipe before expansion when the restraint range of the upper die is made equal to the restraint range of the lower die and the length of the worked portion or the non-worked portion of the press-bent formed body is changed.

Fig. 15 is a diagram showing the result of the press load in the case where the restraint range of the upper die is made the same as the restraint range of the lower die and the length of the lightly processed portion or the unprocessed portion of the press-bent molded body is changed.

Fig. 16 is a view showing the results of the opening amount of the open seam space portion in the case where the radii of the arc portions of the upper die and the lower die are changed.

Fig. 17 is a diagram showing the result of the press load when the radius of the arc portion of the upper die and the lower die is changed.

Detailed Description

An embodiment of the method for producing a steel pipe and the press die used in the method for producing a steel pipe according to the present invention will be described below. Fig. 1 is an external perspective view of a die 1, a punch 2, and the like used for forming a formed body having a U-shaped cross section by press bending according to the present embodiment. The die 1 is disposed in a conveying path of the sheet material S formed by a plurality of conveying rollers 3, and is composed of a pair of right and left bar-shaped

members

1a, 1b that support the sheet material S at 2 locations along a sheet material conveying direction. The interval e between the rod-

like members

1a and 1b in the plate material conveying direction can be changed according to the size of the steel pipe to be finally formed.

The punch 2 is movable in a direction approaching or separating from the die 1, and includes a downward projecting punch tip portion 2a that presses the sheet material S, and a punch support body 2b that is connected to a back surface (upper end surface) of the punch tip portion 2a by the same width and supports the punch tip portion 2 a. The upper end portion of the punch support body 2b is coupled to a driving mechanism, not shown, and a pressing force can be applied to the punch tip portion 2a by the driving mechanism.

FIG. 2 shows a press bending of a shaped body S having a U-shaped cross section₁The step (2). This step specifically shows an example of the following case: the sheet material S on which the end portion bending processing is performed in advance is subjected to the bending processing and the feeding of the sheet material S in the order of top-down in the left row of fig. 2, top-down in the center row of fig. 2, and finally right row of fig. 2. In fig. 2, arrows respectively attached to the punch 2 and the plate material S indicate the moving directions of the punch 2 and the plate material S at the respective stages.

In order to form the sheet S into a tubular shape using the sheet S as a starting material, first, an end portion bending process is performed on the sheet S. In comparison with the case where the plate material S is bent using the die 1 and the punch 2, the end portion bending process is performed on the relatively inflexible plate width end portion, and the end portion bending process portion is provided in advance at the plate width end portion of the plate material S by the end portion bending process, whereby a steel pipe with high roundness can be easily obtained as compared with the case where the end portion bending process portion is not provided. The roundness of a steel pipe is an index indicating how close the cross-sectional shape of the steel pipe is to a circle, and is an index indicating how close the cross-sectional shape of the steel pipe is to a circleA value represented by a ratio obtained by dividing the difference between the maximum and minimum variation amounts from the approximate arc over the entire circumference of the steel pipe by the diameter of the steel pipe. For example, at any pipe length position of a steel pipe having an outer diameter D, the pipe is equally divided in the circumferential direction by 8, 12, 16 or 24, and the outer diameters of the pipe at the opposite positions are measured, and the maximum diameter and the minimum diameter of these are respectively denoted as D_max、D_minIn this case, the degree of roundness [% ]]To be provided with

{(D_max-D_min) and/D }. times.100. The closer the roundness is to 0, the closer the cross-sectional shape of the steel pipe is to a perfect circle.

A sheet material S provided with an end portion bending portion is placed on a die 1 shown in fig. 1, the sheet material S is intermittently fed by a predetermined feed amount, and bending is performed 3 times or more in the width direction of the sheet material S by the step shown in fig. 2, thereby forming a formed body S having a U-shaped cross section as a whole₁。

FIG. 3 shows a molded article S having a U-shaped cross section₁Cross-sectional view of (a). When the width of the sheet material S before the end portion bending is defined as the sheet width W, the sheet material S is formed into a molded body S as shown in FIG. 3₁The blank part P is provided with an unprocessed part P without bending processing, particularly around a W/4 part which is a part separated from the plate width end part by W/4. The unprocessed portion P can be provided by increasing the feeding of the sheet material S to omit the pressing by the punch 2. The molded article S may be₁A part of the first and second sheets, particularly a W/4 part from the widthwise end, is not provided with the unprocessed portion P, but is provided with a lightly processed portion having a smaller curvature (having a very smaller curvature than the other portions) than the other portions. In this case, in the following description, the "unprocessed portion P" may be replaced with the "lightly processed portion" as appropriate. 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.

The shape of the punch 2 shown in fig. 1 and 2 is an I-shape in which the width of the punch tip 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 to this. For example, the punch 2 may have a substantially inverted T-shaped structure in which the width of the punch tip portion 2a in the sheet material conveying direction is larger than the width of the punch support body 2b in the sheet material conveying direction. In the case where the width of the punch support body 2b in the sheet material conveying direction is the same, the use of the punch 2 having a substantially inverted T-shape enables a larger area of the sheet material S to be pressed in 1 press than the use of the punch 2 having an I-shape, and the number of presses can be reduced.

Bending the sheet material S by press bending to form a formed body S having a U-shaped cross section₁Then, the molded body S is formed by using a press mold including an upper mold 4 and a lower mold 5 which are a pair of molds shown in fig. 4₁O-press formed into an O-shape by press working to form an open pipe S as a pipe body having a weld gap G between circumferentially opposed plate-width end portions₂。

Next, the molded article S will be described with reference to FIG. 4₁Performing O-punching to form an open pipe S₂The step (2). First, as shown in fig. 4(a), the mold 4 and the molded body S are used₁In such a manner that the open sides of the U-shape are opposed to each other (as a molded body S)₁In a manner that the open side of the U shape of the sheet faces upward) and a molded body S is formed₁Is arranged on a lower die 5, and a molded body S is formed by an upper die 4 and the lower die 5₁And (4) clamping. In addition, in the molded article S₁In the press working of (3), the press die is set at the working center thereof and the molded body S is formed₁Are aligned with each other in the widthwise center. Thereby, the molded body S can be formed₁The open side of the U-shape presses the wide end of the board evenly in the left and right directions.

As shown in fig. 5, the upper mold 4 and the lower mold 5 can be joined to the molded body S₁The contact surfaces are formed with

arc portions

4a, 5a having the same or substantially the same diameter as the outer diameter of the steel pipe to be formed and a central angle θ, and the range is press-worked into a shape inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe. For example, a central angle θ of 360 degrees corresponds to a plate width of 100 [% ]]And is press-worked into the inscribed shape. Hereinafter, the central angle θ of the

arc portions

4a and 5a is referred to as a constraint range, and the angle is divided by 36The value of 0 degrees is a range to be press-worked so as to be inscribed in an arc having the same diameter or substantially the same diameter as the outer diameter of the steel pipe. The arc center of the arc portion 4a is located at the machining center O of the upper die 4_p4The arc center of the arc portion 5a is located at the same position as the machining center O of the lower die 5_p5A consistent position. The upper die 4 has linear portions 4b connected to both ends of the arc portion 4a in the arc direction, respectively₁、4b₂The lower mold 5 has linear portions 5b connected to both ends of the arc portion 5a in the arc direction, respectively₁、5b₂. In the upper mold 4 and the lower mold 5, the straight portion 4b may be replaced with₁、4b₂、5b₁、5b₂And has a small curvature arc portion having a smaller curvature than the

arc portions

4a, 5 a. In the present invention, the straight portion 4b continuous with the

arc portions

4a and 5a is preferable from the viewpoint of improving the symmetry of the steel pipe to be finally obtained₁、4b₂、5b₁、5b₂Or a small-curvature arc part corresponding to the machining center O_p4、O_p5I.e. the centres of the

circular arc portions

4a, 5a are symmetrical. Preferably, the steel pipe has a radius of. + -. 3.5 [% ] relative to the radius corresponding to the outer radius of the steel pipe]The die for the arc portion in the range of (1) performs press working. The reason for this is described later.

Next, the molded body S sandwiched by the upper mold 4 and the lower mold 5 is clamped₁As shown in fig. 4 (b), the upper die 4 is pressed down to perform O-press. At this time, the molded body S₁Of the upper mold 4 and the lower mold 5, the portions facing the

arc portions

4a and 5a of the upper mold 4 and the lower mold 5 are restrained by the upper mold 4 and the lower mold 5, and the molded body S is formed₁The unprocessed portion P is not restrained by the upper die 4 and the lower die 5. Therefore, the molded article S can be obtained in a ratio of₁The pressing force required for forming the open pipe S shown in fig. 4 (c) is small when the entire circumference of the open pipe S is restricted by the upper mold 4 and the lower mold 5₂。

In the method for manufacturing a steel pipe according to the present embodiment, a press die including an upper die 4 and a lower die 5 is used to open the pipe S₂The shape of (2) is the following shape₁And (3) carrying out stamping: by U20 [% of plate width W centered at the lowermost part of the cross-section of the letter shape]The range of the above (corresponding to the central angle theta of 70 degrees or more) and 10 [% ] of the plate width W from the plate width end]The range of the central angle θ is 35 degrees or more, and the range is in contact with the shape of the circular arc having the same diameter or substantially the same diameter as the outer diameter of the steel pipe.

In the present embodiment, the open pipe S is preferably formed from the viewpoint of improving the shape of the steel pipe to be finally produced₂The range inscribed in the mold is substantially the same size on the upper mold 4 side and the lower mold 5 side. That is, 20 [% ] of the plate width W centering on the lowest part of the U-shaped cross section of the arc having the same or substantially the same diameter as the outer diameter of the steel pipe]A represents the above range, and 10 [% ] of the plate width W from both ends of the plate width, which is inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe]When the total range is B, the formula (1) is preferably satisfied.

2|A-B|/(A+B)＜0.4……(1)

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

The meaning of formula (1) is described below.

In the method of manufacturing a steel pipe of the present embodiment, the pipe is opened S₂In a predetermined range, the molded body S is preferably formed in a shape that is reliably received in the die and has a good shape before the press working, as shown in FIG. 5₁In the U-shaped cross section, a tangent TL is formed at the center of the width of the plate, i.e., at the W/2 portion₁With the tangent TL at the W/4 portion₂₁、TL₂₂Angle theta₁₁、θ₁₂Is more than 35 degrees and less than 90 degrees. Further, it is preferable that the molded body S before press working is applied₁In other words, the tangent TL at the broad end of the board is made₃₁、TL₃₂With the tangent TL at the W/4 portion₂₁、TL₂₂Angle theta₂₁、θ₂₂Is more than 35 degrees and less than 90 degrees. In order to make the inscribed range of the upper mold 4 side and the lower mold 5 side the same, the tangent line TL is preferably selected₁With tangent line TL₂₁、TL₂₂Angle theta₁₁、θ₁₂Sum and tangent TL₃₁、TL₃₂With tangent line TL₂₁、TL₂₂Angle theta₂₁、θ₂₂Approximately the same.

Regarding the above angle, it is necessary to consider the molded article S bent into the U shape for the following reason₁The apparatus for forming a U-shaped molded body S₁Processed into an open pipe S₂The shape of the mold. When the angle is too large, the distance between the wide ends becomes small. If the distance is less than the bending processing of the U-shaped formed body S₁When the punch support body 2b is wide, a U-shaped molded body S cannot be obtained₁. On the other hand, if the angle is too small, the U-shaped molded body S is formed₁The distance between the wide ends of the U-shaped molded body S is increased₁When the sheet is placed on the die, the sheet width end is larger than the opening of the upper die 4, and no working force is applied. Further, the distance between the left and right unprocessed portions P becomes too large to be accurately placed on the lower die 5.

In addition, the upper mold 4 and the molded body S are formed as one of a pair of molds₁The molded body S is formed so that the open sides of the U-shape are opposed to each other₁Is placed on a lower mold 5 as another mold, and a molded body S is formed by an upper mold 4 and the lower mold 5₁Sandwiched to the molded body S₁In the process of performing the press working, the upper die 4 and the lower die 5 have the following working surfaces. That is, the lower die 5 has the following machined surfaces: in the formation of a molded body S₁In the state of being placed on the lower die 5, except 20 [% ] of the plate width W centering on the lowest part of the U-shaped cross section]Molded article S outside the range of the central angle θ of 70 degrees or more₁In a state of not contacting with the opening pipe S and in which the press working is completed, the opening pipe S is pressed by a part of the lower die 5₂A non-contact processing surface. The upper die 4 is provided on the molded body S₁Molded body S in a state of being placed on a lower mold 5₁Is not contacted with the upper die 4 and the open pipe S in the state of being pressed₂A non-contact processing surface.

In the present embodiment, it is preferable that the molded body S is formed of a resin₁At the time of press working of (2), a molded body S₁The center of the press die used in the press working and the molded body S₁Are aligned with each other in the widthwise center. The reason for this is that a relatively shaped body S is applied₁The force symmetrical with respect to the center in the width direction of (a) contributes to the improvement of the shape accuracy of the finally produced steel pipe.

In the present embodiment, the molded body S is preferably used₁The U-shaped body is held in a U-shaped posture with the open side of the U-shaped body facing upward. One reason is that the press working operation is easy in this posture. In addition, another reason is to avoid the following: if the open side of the U-shape is directed downward, the molded body S may be deformed₁The self-weight of (2) acts on the molded body S₁The end of the board width is scratched to scratch the end of the board width or the die.

Here, in the present embodiment, the upper mold 4 and the lower mold 5 are used to form the molded body S₁Performing O-punching to form an open pipe S₂In the case of the molded body S₁The pressing force is applied to the portion W/4 away from the center of the unprocessed portion P toward the plate width end portion in (1), for the following reason. Namely, the molded body S₁The bending moment when the entire pressing member (2) is circular is such that M is F · r · cos Φ (F: pressing force, r: radius of circle) at a position where the central angle is separated from the pressing portion by an angle Φ, and the deformation is maximized at a position separated from the pressing portion by 90 degrees. Therefore, the unprocessed portion P is effectively deformed by applying a pressing force to a position 1/4 that is 90 degrees away from the center of the unprocessed portion P, i.e., the entire circumference. At this time, the bending moment is maximum at a position 90 degrees away from the position where the pressing force is applied, and decreases as it goes away from the 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 the present embodiment, the center of the unprocessed portion P is provided at a position 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 that the pressing force is applied to a portion separated by W/4 from the center of the unprocessed portion P toward the end of the sheet width, the molded body S is formed₁Is formed as an open pipe S₂In the stage (2), due toShaped body S₁Thereby the upper mold 4 and the molded body S are changed₁The contact position of (2) changes, and the position where the pressing force is applied also changes. The unprocessed portion P is provided on the molded body S₁In the case of a portion including a position W/4 away from the wide end of the sheet, the portion to which the pressing force is applied is always the molded body S₁The unprocessed portion P is deformed most largely at the end portion of the sheet width. In this way, the unprocessed portion P can be deformed by 1 pressing without changing the pressing position. Further, it is preferable that the unprocessed portion P is provided at a position where a pressing force is applied, that is, the molded body S₁Is within a range of W/4 + -0.07W from the plate-wide end portion.

In the initial stage of the pressing as shown in fig. 4(a) and 4 (b), since the sheet-width end portion is in contact with the upper die 4, the unprocessed portion P is preferably provided in the molded body S₁Including a portion separated from the wide end by W/4.

FIG. 6 shows the pipe to be opened S₂The relationship between the expansion amount of the bead gap portion G and the restraint range and the press load are shown together. The relationship between the amount of expansion and the restraint range and the press load shown in fig. 6 are applied to the pipe S to be opened₂After welding of both end portions of (2), the pipe expansion ratio is 1 [% ]]The shape of the expanded pipe is corrected to be formed into a tensile strength of 630MPa]Outer diameter 660.4[ mm ]]The thickness of the tube is 40.0[ mm ]]The steel pipe of (3).

Molded body S after press bending₁Formed in the following shape: at the portions of both sides of the plate width end portion, which are W/4, an unprocessed portion P having a length of W/12 is provided, and an angle theta formed by a tangent line at the central portion of the plate width and a tangent line at the W/4 portion, which is a portion separated from the plate width end portion by W/4, is formed₁₁、θ₁₂An angle theta of 75 degrees formed by a tangent at the wide end of the plate and a tangent at the W/4 portion₂₁、θ₂₂Is 75 degrees. Is obtained by molding the molded article S₁The shape in the case of being sandwiched by the upper mold 4 and the lower mold 5 having the same restriction range. The pressing amount is set so as to connect the opening pipes S₂The distance of W/2 is equal to the diameter before tube expansion (the amount of reduction in O-press is such that the longitudinal diameter coincides with the diameter before tube expansion). As can be seen from fig. 6, the larger the constraint range isPipe S₂The smaller the opening amount of the bead gap portion G becomes.

FIG. 7 is a view schematically showing the use of the upper and lower dies 4 and 5 having a restriction range of 0 degrees to mold the open pipe S₂And (3) a diagram of the deformation state of the steel sheet. When the restriction range of the upper mold 4 and the lower mold 5 is 0 degree, the upper mold 4 and the molded body S are only used₁Both end portions of (A) are in contact with each other, and the lower mold 5 is in contact with only the molded body S₁The

arc portions

4a and 5a are formed as arcs having a diameter 1.16 times the outer diameter of the steel pipe. As shown in fig. 7 (a), the diameter of the arc portion 5a of the lower die 5 is larger than the diameter of the steel pipe so that the molded body S is formed₁Only the 6 o' clock portion is in contact with the lower mold 5 when viewed as a clock. Therefore, as shown in fig. 7 (b), in the O-press, the molded body S is formed₁The 6 o' clock portion and the vicinity thereof cause the bending recovery in contact with the arc portion 5a of the lower die 5, and the curvature radius becomes larger than the steel pipe diameter. Therefore, after the O-press, the pipe S shown in FIG. 7 (c) is opened₂The opening amount of the weld gap portion G of (2) corresponds to the molded body S₁The 3 o 'clock portion and the 9 o' clock portion of the frame.

FIG. 8 is a diagram showing the restriction range and the pipe to be opened S₂The weld gap portion G in (b) is a graph showing a relationship between the roundness of the steel pipe before expansion when closed by welding. As can be seen from fig. 8, when the constraint range is 60 degrees, the roundness is worse than when the constraint range is 0 degrees, when the constraint range is large, the roundness is better, and when the constraint range is 70 degrees or more, the roundness is better than when the constraint range is 0 degrees. Further, it is found that the roundness is best when the constraint range is 100 degrees to 110 degrees.

Fig. 9 is a diagram showing a relationship between the restraint range and the press load. As can be seen from fig. 9, the press load increases as the restraint range increases. Therefore, when the restriction range is increased, the pipe S is opened₂The opening amount of the bead gap portion G is reduced, but the press equipment is increased in size according to the increase in press load, and therefore it is desirable to reduce the restraint range within a range in which a desired opening amount is obtained. For example, the mold 4 and the lower mold 5 restrain the molded body S so that the press load becomes the above₁90 [% of the entire circumference of the upper die 4 and the lower die 5 within the constraint range of 180 DEG]Hereinafter, the constraint range may be set to 150 degrees or less.

FIG. 10 is a view showing the pipe opening S in the case where the restriction ranges of the upper die 4 and the lower die 5 are changed₂The opening amount of the bead gap portion G of (1). FIG. 11 shows the state where the restriction ranges of the upper die 4 and the lower die 5 are changed, and the pipe is opened S₂The weld gap portion G of (a) is a diagram of a result of closing the roundness of the formed steel pipe before pipe expansion by welding. Fig. 12 is a diagram showing the result of the press load when the restraint ranges of the upper die 4 and the lower die 5 are changed. In fig. 10 to 12, the tensile strength 630[ MPa ] is the same as that in fig. 6, 8 and 9]Outer diameter 660.4[ mm ]]The thickness of the tube is 40.0[ mm ]]The horizontal axis represents the average value of the restraint ranges of the upper die 4 and the lower die 5, and the graph in the drawing is changed in accordance with each restraint range of the lower die 5. In the figure, for example, "lower 60 degrees" indicates that the constraint range of the lower mold 5 is 60 degrees.

As can be seen from fig. 10, regardless of the respective restraint ranges of the upper die 4 and the lower die 5, if the average value of the restraint ranges of the upper die 4 and the lower die 5 is increased, the pipe S is opened₂The opening amount of the bead gap portion G is reduced. As is clear from fig. 11, when the restraint range of either the upper die 4 or the lower die 5 is less than 60 degrees, the roundness of the steel pipe is deteriorated. Therefore, although the restriction ranges of the upper die 4 and the lower die 5 are not necessarily equal to each other for the upper die 4 and the lower die 5, it is desirable that the restriction ranges of the upper die 4 and the lower die 5 are both set to a restriction range exceeding 60 degrees in order to obtain a shape with good roundness of the steel pipe. As can be seen from fig. 12, the larger the average value of the restraint ranges of the upper die 4 and the lower die 5 is, the larger the press load is. Therefore, when the upper limit value of the allowable press load is set, the range of the average value of the restraint ranges of the upper die 4 and the lower die 5 that can be applied is determined in accordance with the upper limit value of the press load.

In fig. 11, when the difference between the upper and lower constraint ranges is 30 degrees and the difference is 29 [% ] of the average values of the upper and lower constraint ranges, i.e., upper 90 degrees/lower 90 degrees, upper 90 degrees/lower 120 degrees, and upper 120 degrees/lower 90 degrees, the roundness after welding and before tube expansion is 1.5 [% ] or less, which is very excellent. On the other hand, when the difference between the upper and lower restraint ranges is 30 degrees, but the difference is large and 40 [% ] to the upper 90 degrees/lower 60 degrees, which is the average value of the upper and lower restraint ranges, the roundness after welding and before tube expansion is 2.0 [% ], and is slightly deteriorated. As described above, by reducing the difference between the upper and lower constraint ranges, a favorable shape can be obtained. That is, in the present invention, the difference between the upper and lower constraint ranges is preferably less than 40 [% ] and more preferably 30 [% ] or less of the average value of the upper and lower constraint ranges. Further, the difference between the upper and lower constraint ranges is preferably less than 30 degrees. In other words, when a range of 20 [% ] or more of the plate width W centered on the lowermost portion of the U-shaped cross section inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe is denoted by a, and a total range of 10 [% ] or more of the plate widths W from both ends of the plate width inscribed in an arc having the same or substantially the same diameter as the outer diameter of the steel pipe is denoted by B, it is preferable that expression (1) is satisfied.

2|A-B|/(A+B)＜0.4……(1)

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

FIG. 13 shows a press-bent molded article S obtained by setting the upper mold 4 and the lower mold 5 to have the same range of restraint₁The results of the opening amount of the bead gap portion G when the length L of the unprocessed portion P is changed. FIG. 14 shows a press-bent molded article S obtained by setting the upper mold 4 and the lower mold 5 to have the same range of restraint₁The length L of the unprocessed portion P of (1) is changed, and the result of the roundness of the steel pipe before pipe expansion is shown. FIG. 15 shows a press-bent molded article S obtained by setting the upper mold 4 and the lower mold 5 to have the same range of restraint₁Is obtained by the press load when the length L of the unprocessed portion P is changed. In fig. 13 to 15, an angle formed by a tangent line at the center of the plate width and a tangent line at a W/4 portion, which is a portion separated from the plate width by W/4, is defined as an angleθ₁₁、θ₁₂Let the angle formed by the tangent at the end of the sheet width and the tangent at the W/4 part be theta₂₁、θ₂₂The angles are all set to equal values, and are changed according to the width of the unprocessed portion P. The horizontal axis represents an average value of the restraint range of the upper mold 4 and the restraint range of the lower mold 5.

As can be seen from FIG. 13, all the molded articles S₁The length L of the unprocessed portion P and the angle theta formed by the tangent₁₁、θ₁₂、θ₂₁、θ₂₂In the case of the angle (c), the larger the average value of the restraint range of the upper die 4 and the restraint range of the lower die 5 is, the smaller the opening amount of the weld gap portion G is, and in the case where the restraint range of the upper die 4 is the same as the average value of the restraint range of the lower die 5, the longer the length L is, and the larger the angle θ formed by the tangent lines is₁₁、θ₁₂、θ₂₁、θ₂₂The smaller the angle of (a), the smaller the opening amount. As is clear from fig. 14 and 15, when the restraint range of the upper die 4 is the same as the average value of the restraint range of the lower die 5, the molded body S is hardly found to be a factor of the roundness of the steel pipe and the press load₁The length L of the unprocessed portion P and the angle theta formed by the tangent₁₁、θ₁₂、θ₂₁、θ₂₂The difference caused by the angle of (c). As described above, when the restriction range of the upper mold 4 is the same as the average value of the restriction ranges of the lower mold 5, the molded body S is formed by₁The length L of the unprocessed portion P of (A) is increased to make the angle theta formed by the tangent line₁₁、θ₁₂、θ₂₁、θ₂₂The angle of (2) is reduced, and the pipe opening S can be reduced while avoiding variations in the roundness of the steel pipe and the press load due to the length L₂The opening amount of the bead gap portion G.

FIG. 16 shows the pipe opening S in the case where the radius of the arc portion of the upper die 4 and the lower die 5 is changed₂The opening amount of the bead gap portion G of (1). Fig. 17 is a graph showing the result of the press load when the radius of the arc portion of the upper die 4 and the lower die 5 is changed. In fig. 16 and 17, the upper die 4 and the lower die are illustratedThe center angle of the

arc portions

4a and 5a of the lower mold 5 was set to 45 degrees, and the radius of the

arc portions

4a and 5a was changed to a tensile strength of 630MPa and an outer diameter of 660.4[ mm ]]The thickness of the tube is 40.0[ mm ]]The steel pipe (2) is pressed down by O-press so that the longitudinal diameter thereof coincides with the diameter before expansion. The horizontal axes in fig. 16 and 17 represent the ratio of the radius of the arc portion to the outer radius of the steel pipe (radius corresponding to the outer diameter of the steel pipe), and the ratio is greater than 1.0 when the radius of the arc portion is greater than the outer radius of the steel pipe, and less than 1.0 when the radius of the arc portion is smaller than the outer radius of the steel pipe.

As shown in fig. 16, when the radius of the arc portion of the upper die 4 and the lower die 5 is equal to the outer radius of the steel pipe (the horizontal axis in fig. 16 is 1.0), the opening amount of the bead gap portion G is the smallest. On the other hand, if the radius of the arc portion of the upper die 4 and the lower die 5 is larger than the outer radius of the steel pipe, the molded body S is formed as shown in fig. 7₁The 6 o' clock portion and the vicinity thereof are bent and deformed, and therefore, the opening amount of the bead gap portion G increases as the radius of the arc portion of the upper die 4 and the lower die 5 increases. Further, if the radius of the arc portion of the upper die 4 and the lower die 5 is smaller than the outer radius of the steel pipe, the bend recovery deformation occurs at the portion where the

arc portions

4a and 5a of the upper die 4 and the lower die 5 end, and therefore the opening amount of the bead gap portion G increases as the radius of the arc portion decreases. As described above, although it is most preferable that the radius of the arc portion of the upper die 4 and the lower die 5 is equal to the outer radius of the steel pipe, the radius of the arc portion of the upper die 4 and the lower die 5 is + -3.5 [% ] which is a radius corresponding to the outer radius of the steel pipe]At this time, the amount of expansion of the weld gap portion G was suppressed to 40[ mm ]]The following.

However, as is clear from fig. 17, the press load increases as the radius of the circular arc portion decreases, and particularly when the radius of the circular arc portion is small, the radius thereof needs to be determined in consideration of the load of the press machine.

[ example 1]

The plate width W was prepared by providing a bevel to the edge milling machine to be 1928[ mm ]]And a length of 1000[ mm ]]Thickness of the board 40[ mm ]]Tensile strength of 635 MPa]The steel sheet of (2) is bent at its end portion and then press-bent to obtain a molded body S₁. Next, the molded body S was subjected to₁Using a plurality of constraint rangesMold 4 and lower mold 5 use 30[ MN ]]The punch press of (1) performs O-punching, thereby molding the molded body A, B. The shape of the molded article A, B is shown in tables 1 and 2. In table 1 and table 2, "No.", the first letter A, B indicates the shape of the molded article (molded article A, B), and the numerals after the letter A, B indicate the combination of the ranges of constraint of the upper mold 4 and the lower mold 5.

Table 1 shows the following molded articles a: as condition A, the thickness of the steel sheet was 160[ mm ] from the W/4 portion of the wide end portion of the steel sheet](W/12) width of the blank, and an angle theta formed by a tangent at the end of the sheet width and a tangent at the W/4 portion₂₁、θ₂₂An angle theta of 65 degrees formed by a tangent at the central part of the plate width and a tangent at the W/4 part₁₁、θ₁₂At 73 degrees. Table 2 shows the following molded bodies B: as condition B, 321[ mm ] was used as the center of the W/4 portion from the end of the plate width](W/6) width (width 2 times of condition A) of the unprocessed portion, and angle theta formed by a tangent at the end of the plate width and a tangent at the W/4 portion₂₁、θ₂₂An angle theta of 59 degrees formed by a tangent at the central part of the plate width and a tangent at the W/4 part₁₁、θ₁₂Is 61 degrees. The molded body A, B is symmetrical with respect to a straight line between the center of the wide end of the web and the web width 1/2, and the values of the web width 1/2 are shown in tables 1 and 2. The reduction amount in O-press is such that the distance between the outer surface side of the W/2 portion and the outer surface side of the wide end portion of the sheet is 654[ mm ]]The rolling reduction of (2).

Further, the open pipe S after O-pressing of the molded product A, B was measured₂After the opening amount of (2), the pipe is split into two₂The gap portion G of the weld joint is welded to be formed into an outer diameter of 654 mm]The diameter of the steel pipe (2) was measured at 8 points at intervals of 22.5 degrees in the circumferential direction, and the difference between the maximum and minimum diameters was determined. Table 1 and table 2 show the die shape (restraint range), press load, opening amount, and roundness. The roundness at this time is a value obtained by dividing the difference between the maximum and minimum values by the outer diameter of the steel pipe (the average value of all the measured values of the diameter).

In the welding machine used in this embodiment, when the opening amount after O-punching exceeds 40[ mm ], the opening cannot be closed, and both ends and the center in the axial direction of the pipe are temporarily welded in the opened and closed state by using another press machine, and then the full length of the weld gap G is finally welded. The roundness was defined as 2.5 [% ] before pipe expansion. The reason for this is that if the roundness before expansion is 2.5 [% ] or less, the roundness after expansion can be made a good value of 1.0 [% ] or less.

[ Table 1]

[ Table 2]

In nos. a1 to a7, a9, and a10 of table 1 and nos. B1 to B7, B9, and B10 of table 2 within the range of the present invention example, the stretching amount was small and the roundness was good. In particular, when the restraint range is 90 to 110 degrees, the roundness is 1.0 [% ] or less even without pipe expansion. In addition, the smaller the average value of the restraint range, the smaller the press load.

On the other hand, in nos. A8 and a11 in table 1 and nos. B8 and B11 in table 2, in which the restraint ranges of the upper die 4 and the lower die 5 are a combination of 60 degrees and 90 degrees, the roundness is deteriorated although the opening amount is small. In addition, in nos. 12 a12 to a16 of table 1 and nos. B12 to B16 of table 2, in which the average value of the restraint range is 60 degrees or less, the expansion amount is large, and in particular, in nos. 15 and a16 of table 1 and No. B16 of table 2, the welded portion after welding the bead gap portion G is broken, and hence the roundness cannot be measured.

In the case of using the molded article B having an unprocessed portion wider than the molded article a, the press load and the roundness are substantially the same as those in the case of using the molded article a, but the opening amount is small.

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

[ example 2]

Prepare to set groove to 1639[ mm ] plate width by using edge milling machine]And a length of 1000[ mm ]]The thickness of the plate is 31.8[ mm ]]And tensile strength of 779 MPa]The steel sheet of (2) is bent at its end portion and then press-bent to obtain a molded body S₁. Next, 30[ MN ] is used using the upper mold 4 and the lower mold 5 having a plurality of constraint ranges]The press of (3) for the molded body S₁O-stamping is performed, thereby molding the molded body A, B. The shape of the molded article A, B is shown in tables 3 and 4. In table 3 and table 4, "No.", the first letter A, B indicates the shape of the molded article (molded article A, B), and the numerals after the letter A, B indicate the combination of the restraint ranges of the upper mold 4 and the lower mold 5.

Table 3 shows the following molded articles a: as condition A, 137[ mm ] was set at the center of the W/4 portion from the end of the plate width](W/12) width of the blank, and an angle theta formed by a tangent at the end of the sheet width and a tangent at the W/4 portion₂₁、θ₂₂An angle theta of 65 degrees formed by a tangent at the central part of the plate width and a tangent at the W/4 part₁₁、θ₁₂Is 72 degrees. Table 4 shows the following molded articles B: as condition B, 273[ mm ] is defined from W/4 from the end of the plate width](W/6) width (width 2 times of condition A) of the unprocessed portion, and angle theta formed by a tangent at the end of the plate width and a tangent at the W/4 portion₂₁、θ₂₂An angle theta of 59 degrees formed by a tangent at the center of the plate width and a tangent at the W/4 portion₁₁、θ₁₂Is 61 degrees. The molded body A, B is symmetrical with respect to a straight line between the center of the wide end of the web and the web width 1/2, and the values of the web width 1/2 are shown in tables 3 and 4. The reduction amount in O-press was set so that the distance between the outer surface side of the W/2 portion and the outer surface side of the wide end portion became 553[ mm ]]The rolling reduction of (2).

Further, the open pipe S after O-pressing of the molded product A, B was measured₂Will open the pipe S after the opening amount₂The gap portion G of the weld joint is welded to be formed as an outer portionDiameter 553 mm]The diameter of the steel pipe (2) was measured at 8 points at intervals of 22.5 degrees in the circumferential direction, and the difference between the maximum and minimum diameters was determined. Table 3 and table 4 show the die shape (restraint range), press load, opening amount, and roundness. The roundness at this time is a value obtained by dividing the difference between the maximum and minimum values by the outer diameter of the steel pipe.

In the welding machine used in this embodiment, when the opening amount after O-punching exceeds 40[ mm ], the opening cannot be closed, and both ends and the center in the axial direction of the pipe are temporarily welded in the opened and closed state by using another press machine, and then the full length of the weld gap G is finally welded. The roundness was determined to be 1.0 [% ] or less by the tube expansion and to be 2.5 [% ] before the tube expansion.

[ 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 range of the invention example, the stretching amount was small and the roundness was good. In particular, when the restraint range is 90 to 110 degrees, the roundness is 1.0 [% ] or less even without pipe expansion. In addition, the smaller the average value of the restraint range, the smaller the press load.

On the other hand, in nos. A8 and a11 in table 3 and nos. B8 and B11 in table 4 in which the restraint ranges of the upper die 4 and the lower die 5 are a combination of 60 degrees and 90 degrees, the roundness is deteriorated although the opening amount is small. In addition, in nos. 12 to a16 of table 3 and nos. B12 to B16 of table 4, in which the average value of the restraint range is 60 degrees or less, the expansion amount is large, and in particular, in nos. 15 and a16 of table 3 and No. B16 of table 4, the welded portion after welding the bead gap portion G is broken, and the roundness cannot be measured.

[ example 3]

Preparation for processing into sheet width 2687[ mm ] by providing groove on edge milling machine]And a length of 1000[ mm ]]Thickness of 50.8[ mm ]]And tensile strength of 779 MPa]The steel sheet of (2) is bent at its end portion and then press-bent to obtain a molded body S₁. Next, the upper mold 4 and the lower mold 5 using the various constraint ranges are set to 30[ MN]The press of (3) for the molded body S₁O-stamping is performed, thereby molding the molded body A, B. The shape of the molded article A, B is shown in tables 5 and 6. In table 5 and table 6, "No.", the first letter A, B indicates the shape of the molded article (molded article A, B), and the numerals after the letter A, B indicate the combination of the ranges of constraint of the upper mold 4 and the lower mold 5.

Table 5 shows the following molded articles a: as condition A, 224[ mm ] was defined from the W/4 portion of the plate width end as the center](W/12) width of the blank, and an angle theta formed by a tangent at the end of the sheet width and a tangent at the W/4 portion₂₁、θ₂₂An angle theta of 73 degrees formed by a tangent at the central portion of the plate width and a tangent at the W/4 portion₁₁、θ₁₂Is 72 degrees. Table 6 shows the following molded articles B: as condition B, 448[ mm ] was set at W/4 from the end of the plate width](W/6) width (width 2 times of condition A) of the unprocessed portion, and angle theta formed by a tangent at the end of the plate width and a tangent at the W/4 portion₂₁、θ₂₂An angle theta of 58 degrees formed by a tangent at the central portion of the plate width and a tangent at the W/4 portion₁₁、θ₁₂Is 59 degrees. The molded body A, B is symmetrical with respect to a straight line between the center of the wide end of the web and the web width 1/2, and the values of the web width 1/2 are shown in tables 5 and 6. The press-down amount in O-press is set such that the distance between the outer surface side of the W/2 part and the outer surface side of the wide end part of the plate is 905 mm]The rolling reduction of (2).

Further, the open pipe S after O-pressing of the molded product A, B was measured₂After the opening amount of (D), the pipe (S) is opened₂The gap portion G of the weld line is welded to form an outer diameter of 905[ mm ]]Then in the circumferential directionThe diameters were measured at 8 at 22.5 degree intervals and the difference between the maximum and minimum of the diameters was determined. Table 5 and table 6 show the die shape (restraint range), press load, opening amount, and roundness. The roundness at this time is a value obtained by dividing the difference between the maximum and minimum values by the outer diameter of the steel pipe.

In the welding machine used in this example, when the opening amount after O-punching exceeds 40[ mm ], the opening cannot be closed, and both ends and the center in the axial direction of the pipe are temporarily welded in the opened and closed state by using another press machine, and then the full length of the weld gap G is finally welded. The roundness was determined to be 1.0 [% ] or less by pipe expansion and to be 2.5 [% ] before pipe expansion.

[ Table 5 ]]

[ Table 6]

In nos. a1 to a7, a9, and a10 of table 5 and nos. B1 to B7, B9, and B10 of table 6 within the range of the present invention example, the stretching amount was small and the roundness was good. In particular, when the restraint range is 90 to 110 degrees, the roundness is 1.0 [% ] or less even without pipe expansion. In addition, the smaller the average value of the restraint range, the smaller the press load.

On the other hand, in nos. A8 and a11 in table 5 and nos. B8 and B11 in table 6 in which the restraint ranges of the upper die 4 and the lower die 5 are a combination of 60 degrees and 90 degrees, the roundness is deteriorated although the opening amount is small. In addition, in nos. 12 to a16 of table 5 and nos. B12 to B16 of table 6, in which the average value of the restraint range is 60 degrees or less, the expansion amount is large, and in particular, in nos. 15 and a16 of table 5 and No. B16 of table 6, the welded portion after welding the bead gap portion G is broken, and hence the roundness cannot be measured.

[ example 4]

To manufacture a target outer diameter 621 mm]～687[mm]The steel pipe (2) is prepared by providing a groove on an edge milling machine to be processed into a plate width of 1826-2032 [ mm ]]And a length of 1000[ mm ]]Thickness of the board 40[ mm ]]Tensile strength of 635 MPa]The steel sheet of (2) is bent at its end portion and then press-bent to obtain a molded body S₁. Next, 30[ MN ] was used using a plurality of types of upper molds 4 and lower molds 5 having an arc radius of 327mm and a constraint range of 45 degrees]The press of (3) for the molded body S₁O-pressing was performed to mold molded bodies D1 to D11. The molding conditions for the molded articles D1 to D11 are shown in Table 7. In the molded articles D1-D11, the blank part was provided in the width of W/12 with respect to the W/4 part from the end of the initial sheet width W, and the angle θ formed by the tangent at the end of the sheet width and the tangent at the W/4 part was set₂₁、θ₂₂An angle theta formed by a tangent at the center of the sheet width and a tangent at the W/4 portion was set to 75 DEG₁₁、θ₁₂Set to 75 degrees. In the O-press, the pressing was performed so that the distance between the outer surface side of the W/2 portion and the outer surface side of the sheet width end portion became a value corresponding to the initial sheet width W as shown in table 7. Table 7 shows the outer diameters of the steel pipes after the O-press rolling.

Then, the O-stamped open tubes S of the molded articles D1 to D11 were measured₂The amount of flare of (a). Table 7 also shows the press load and the opening amount as the results.

[ Table 7]

No. d6 in table 7, in which the ratio of the radius of the circular arc portion to the outer radius of the steel pipe is 1.00, is the smallest, and the opening amount increases as the outer radius of the steel pipe decreases or increases. Further, the opening amount of closing by the welding machine used in example 1 is 40[ mm ] or less, and Nos. 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. In example 1, the steel pipes were also No. D2 to D10 of Table 7, in which the expansion of the steel pipes, in which no weld breakage occurred, was 50[ mm ], and the ratio of the radius of the arc portion to the outer radius of the steel pipe was 0.96 to 1.04.

The opening amount by which the weld gap G can be welded and closed and the opening amount by which the welded portion is not broken differ depending on the welding equipment and the welding method, but the standard of the radius of the arc portion of the upper die 4 and the lower die 5 is 0.96 to 1.04 of the outer radius of the steel pipe.

Industrial applicability

According to the present invention, a method for manufacturing a steel pipe and a press die capable of efficiently forming a steel pipe having high roundness can be provided.

Description of the reference numerals

1 die

1a Bar-shaped Member

1b Bar-shaped Member

2 punch

2a front end of punch

2b punch support

3 conveying roller

4 go up mould

4a arc part

4b₁Straight line portion or small-curvature arc portion

4b₂Straight line portion or small-curvature arc portion

5 lower die

5a arc part

5b₁Straight line portion or small-curvature arc portion

5b₂Straight line portion or small-curvature arc portion

Claims

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,

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 according to claim 1 or 2, wherein in the step of placing one of a pair of dies on the other die so that the one die faces the open side of the U-shape of the molded body, sandwiching the molded body between the pair of dies, and pressing the molded body,

4. A method of manufacturing a steel pipe as defined in any of claims 1 to 3 wherein the press working is performed 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.

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 steel pipe manufacturing method according to any one of claims 1 to 5, wherein the molded body is held in a U-shaped posture with a U-shaped open side facing upward.

7. A press die used in the method for manufacturing a steel pipe according to any one of claims 1 to 6, characterized in that,

the press die includes a pair of pressing bodies for sandwiching the molded body, and an arc portion having a radius within a range of + -3.5 [% ] with respect to a radius corresponding to an outer radius of the steel pipe is formed on a surface of each die which can be brought into contact with the molded body such that an arc center is positioned at a position corresponding to a machining center of each die,

8. The stamping die of claim 7, wherein the central angles of the two dies are the same angle.

9. The press die according to claim 7 or 8, wherein each die has a straight line portion or a small-curvature arc portion having a smaller curvature than the arc portion, which is connected to both ends of the arc portion in the arc direction, respectively.

10. The method of manufacturing a steel pipe according to any one of claims 1 to 6, wherein the press die according to any one of claims 7 to 9 is used.