JP2008093687A - Method and apparatus for bending steel pipe - Google Patents

Abstract

A steel pipe bending method and a bending apparatus capable of forming a steel pipe with high dimensional accuracy by reducing spring back of the steel pipe after bending.
In a stretch bend device 50, a deformed steel pipe P is set beside an inner mold 31 for bending (step S11), and then a portion of the expanded portion P1 formed in a part of the deformed steel pipe P is gripped. In the state of being gripped by the molds 32a and 32b (steps S12 and 13), the inner mold 31 is pressed while pulling the gripping molds 32a and 32b, and a bending bending force is applied to the deformed steel pipe P by bending. Perform (Steps S14 to S16).
[Selection] Figure 10

Description

  The present invention relates to a bending method and a bending apparatus for a steel pipe that grips both ends of the steel pipe and performs tensile bending.

In recent years, a bending method has been used in which a pipe material made of a steel pipe is pressed against a bending die to be processed into a predetermined bending shape.
For example, Patent Literatures 1 to 3 disclose bending methods and apparatuses that perform tensile bending in a state where both ends of a steel pipe are gripped by a chuck or a clamp.
JP 2006-43765 A (published February 16, 2006) Japanese Patent Laid-Open No. 10-71428 (published March 17, 1998) Japanese Patent Laid-Open No. 10-314851 (published on December 2, 1998)

However, the above conventional pipe bending method has the following problems.
That is, in the pipe bending method disclosed in the above publication, the bending process is performed while holding both ends of the steel pipe to be bent so as to be sandwiched between gripping members such as chucks and clamps. Since slip is generated between the steel pipe and the steel pipe, the strain distribution is not uniform and the spring back after processing is large, which may reduce the dimensional accuracy.

  An object of the present invention is to provide a steel pipe bending method and a bending apparatus capable of forming a steel pipe with high dimensional accuracy by reducing spring back of the steel pipe after bending.

  A steel pipe bending method according to a first aspect of the present invention is a steel pipe bending method provided with a pipe expanding portion, and includes first to third steps. The first step is to install the steel pipe along the first mold for bending. In the second step, the expanded portion included in the steel pipe is gripped by the second mold for pulling. In the third step, bending is performed along the first mold while pulling the second mold in the extending direction of the steel pipe.

Here, it is a method for bending a steel pipe partially provided with a pipe expanding portion, and bending is performed using the pipe expanding portion.
Specifically, after the pipe expansion portion is set and held in the second mold for pulling, the steel pipe is bent along the first mold for bending. In addition, the pipe expansion part may be formed in the both ends of a steel pipe, and may be formed inside the end of a steel pipe, or the edge part of a steel pipe. Further, the pipe expansion part may be formed at the time of forming the steel pipe, or may be a part obtained by expanding a part of the steel pipe. Furthermore, the first step and the second step are not necessarily performed in this order, and the order may be reversed.

  Thereby, at the time of tensile bending, since the expanded portion having a larger pipe diameter than the other portion is caught in the second mold, the amount of slip between the grip portion by the second mold and the steel pipe is reduced. Can be reduced. As a result, the spring of the steel pipe after bending is reduced by reducing the amount of slip at the gripping part during bending compared to the conventional method of pulling bending while pressing and holding both ends of the steel pipe with a cylinder. It is possible to manufacture a bent product of a steel pipe with reduced back and improved dimensional accuracy.

The steel pipe bending method according to the second invention is a steel pipe bending method according to the first invention, and in the second step, the expanded portions respectively formed at both ends of the steel pipe are formed by the second mold. Hold it.
Here, the steel pipe is bent in a state in which the expanded portions formed at both ends of the steel pipe are respectively held by the second mold.
Thereby, compared with the time of bending of the steel pipe in which the expanded portion is formed only on one side, it is possible to more effectively reduce the slip amount between the gripping member such as a mold and the steel pipe at the gripping portions at both ends. it can. As a result, the spring back of the steel pipe after bending can be reduced, and a steel pipe with higher dimensional accuracy can be obtained.

A steel pipe bending method according to a third invention is a steel pipe bending method according to the first or second invention, and in the second step, an insertion member is inserted on the inner diameter side of the expanded portion, The expanded portion is held by the second mold.
Here, the expanded portion of the steel pipe gripped by the second mold is gripped by the second mold with an insertion member such as a mandrel inserted on the inner diameter side of the expanded portion.

  As a result, even when the expanded portion is gripped and pulled by the second mold, the expanded portion is crushed by the second mold because the insertion member is placed on the inner diameter side of the expanded portion. This can be prevented. As a result, it is possible to realize a highly accurate steel pipe bending method while minimizing deformation of the expanded portion that is likely to be loaded during tensile bending.

A steel pipe bending method according to a fourth invention is a steel pipe bending method according to any one of the first to third inventions, and in the third step, the second mold is extended to the steel pipe. The first mold is pressed against the steel pipe while pulling in the direction.
Here, the first mold is pressed and pulled and bent while pulling the second mold that holds the expanded portion of the steel pipe in the extending direction of the steel pipe.
Thereby, since the steel pipe can be pulled and bent without changing the pulling direction of the second mold, the configuration of the bending apparatus can be simplified.

  A steel pipe bending apparatus according to a fifth invention is a steel pipe bending apparatus for performing the steel pipe bending method according to any one of the first to fourth inventions, wherein the first mold, A second mold. The first mold is pressed against the steel pipe to become a bending mold. A 2nd metal mold | die hold | maintains the pipe expansion part formed in some steel pipes.

  Thereby, at the time of tensile bending, since the expanded portion having a larger pipe diameter than the other portion is caught in the second mold, the amount of slip between the grip portion by the second mold and the steel pipe is reduced. Can be reduced. As a result, the spring of the steel pipe after bending is reduced by reducing the amount of slip at the gripping part during bending compared to the conventional method of pulling bending while pressing and holding both ends of the steel pipe with a cylinder. The back can be reduced and the dimensional accuracy can be improved.

  According to the apparatus according to the present invention, by reducing the slip amount at the gripping portion during bending, the spring back of the steel pipe after bending can be reduced and the dimensional accuracy can be improved.

A steel pipe stretch bend method (bending method) and a stretch bend device (bending device) according to an embodiment of the present invention will be described below with reference to FIGS.
Here, first, a method and apparatus for forming an expanded portion of a steel pipe, which is a premise of the steel pipe stretch bend method according to the present embodiment, will be described with reference to FIGS.

[Configuration of Tube Expansion Apparatus 10]
The pipe expansion molding apparatus 10 is an apparatus that performs pipe expansion molding by inserting a pipe 12 for pipe expansion molding having a predetermined shape into a deformed steel pipe P. As shown in FIG. 1, a main cylinder 11 and pipe expansion molding are performed. Punch 12, die 13, side pressure device 15 including side mold 21, and control unit 20.

The deformed steel pipe P is a member formed for a frame column constituting a cab mounted on a construction machine such as a hydraulic excavator, and a round steel pipe having a circular cross section is formed into a deformed cross section by roll forming.
The main cylinder 11 applies a pressing force for inserting the punch 12 to the deformed steel pipe P that is fixedly arranged.

  As shown in FIGS. 2A and 2B, the punch 12 is a member that is inserted into the deformed steel pipe P to form the expanded portion P1 in the deformed steel pipe P, and has a first surface. 12a, a second surface 12b and a third surface 12c parallel to the first surface 12a, and a tapered portion 12d. The second surface 12b and the third surface 12c are arranged so that the distances from the first surface 12a are different from l1 and l2 (l1 ≠ l2), respectively, and are connected via a tapered portion 12d. . By performing tube expansion molding using this punch 12, it is possible to perform tube expansion molding of a part of one surface while maintaining the parallel portion of the first surface 12a and the second surface 12b.

As shown in FIGS. 3A and 3B, the die 13 is disposed so as to cover the outer periphery of the deformed steel pipe P to be subjected to pipe expansion molding together with the side mold 21 described later. And the moldability of pipe expansion molding can be improved by installing the die | dye 13 along the deformed steel pipe P in which the punch 12 is inserted.
The side pressurization device 15 is a mechanism that applies a pressing force in the same direction as the insertion direction of the punch 12 to one open end of the deformed steel pipe P that is an object of pipe expansion molding. As shown, it has a side mold 21, a mold holding part 22, a shaft 23 and a motor M. The side mold 21 is attached to a mold holding portion 22 attached to the tip portion of the shaft 23, and the mold holding portion 22 is moved together with the shaft 23 in the F direction by the rotational driving force transmitted from the motor M. By moving forward, a pressing force is applied to the opening end of the deformed steel pipe P. The motor M is an AC servo motor, and applies an appropriate pressing force toward the opening end of the deformed steel pipe P based on the stroke and speed when the punch 12 in the main cylinder 11 is advanced. The feed forward control is performed by the control unit 20.

As described above, the control unit 20 receives the stroke and speed at which the punch 12 in the main cylinder 11 is moved forward, and moves the side mold 21 by the side pressurizing device 15 forward with the optimum pressing force. Rotation control is performed.
<Flow of tube expansion forming by the tube expansion forming apparatus 10>
In the present embodiment, in the tube expansion forming apparatus 10 having the above-described configuration, the deformed steel pipe P is expanded according to the following procedure according to the flowchart shown in FIG.

That is, in the pipe expansion forming apparatus 10 of the present embodiment, in step S1, as shown in FIG. 3A, the main body 12 is inserted so that the punch 12 is inserted into the deformed steel pipe P set on the die 13. The cylinder 11 (see FIG. 1) is extended.
Next, in step S2, the side mold 21 is moved to the opening end of the deformed steel pipe P on the punch 12 insertion side by the motor M based on the insertion timing of the punch 12 into the deformed steel pipe P and the insertion stroke of the punch 12. While pushing against, push forward.

At this time, the punch 12 is inserted into the deformed steel pipe P as shown in FIG. And the side metal mold | die 21 presses the part by the side of the pipe expansion molding in the cross section of the deformed steel pipe P. As shown in FIG.
Next, in step S3, in the process of inserting the punch 12 into the deformed steel pipe P, the insertion of the punch 12 and the pressing of the side mold 21 are continued until the deformed steel pipe P is expanded and thinning is started. . At this time, as shown in FIGS. 4 (a) and 4 (b), the deformed steel pipe P is formed by inserting a punch 12 having a taper portion having a taper angle θ into a cross section having a height h and a width b1. It is shaped so as to expand to the width (b1 + b2). And the side metal mold | die 21 gives a pressing force intensively with respect to this expanded part.

In addition, the pipe expansion rate of this deformed steel pipe P is calculated based on the following relational expression (1).
Tube expansion rate = b2 / b1 (1)
And when thinning of the deformed steel pipe P starts, it will progress to step S4 and the control part 20 will raise further the pressing force of the side metal mold | die 21 to which the fixed pressing force was once given by the predetermined value. Take control.

  Here, the start of thinning of the deformed steel pipe P is determined by detecting the timing A when the increase in the pressing force of the punch 12 inserted into the deformed steel pipe P stops. That is, in the process of inserting the punch 12 into the deformed steel pipe P, the punch 12 having an outer diameter larger than the inner diameter of the deformed steel pipe P is maintained at a predetermined insertion stroke until the thinning of the deformed steel pipe P starts. Therefore, it is necessary to insert the punch 12 while increasing the pressing force of the punch 12. On the other hand, when thinning of the deformed steel pipe P starts, the increase in the pressing force of the punch 12 stops and becomes flat near a predetermined value. For this reason, it can set as the timing C which raises the force which presses the side metal mold | die 21 by detecting the timing A when the raise of the pressing force of the punch 12 inserted in the deformed steel pipe P stopped. Thereby, it is possible to prevent the thinning from locally progressing and forming defects by increasing the pressing force for pushing the open end of the deformed steel pipe P almost simultaneously with the start of the thinning. .

Note that the side mold 21 is controlled to be constant when the pressing force described above is increased to reach a predetermined maximum value D.
Next, in step S5, when the pressing of the punch 12 and the pressing of the side mold 21 are continued and the main cylinder 11 advances the punch 12 to a predetermined position, it is determined that the molding is completed, and the process proceeds to step S6.

Next, in step S6, the punch 12 inserted into the deformed steel pipe P is taken out, and in step S7, the pressing of the side mold 21 is also released and retracted from the side of the deformed steel pipe P.
In the tube forming apparatus 10 for the deformed steel pipe P of the present embodiment, as described above, the punch 12 for expanding the tube is inserted into the deformed steel pipe P, and at the same time, the side mold 21 is used to open the deformed steel pipe P. Press a part of the edge.

Thereby, the deformed steel pipe P which is formed by pipe thinning by inserting the punch 12 for pipe expansion molding is locally thinned to avoid forming defects, and the formability in pipe expansion molding is improved. Can be improved.
<Configuration of Stretch Bend Device 50>
In this embodiment, after forming the pipe expansion part P1 at the both ends of the deformed steel pipe P by the above-described pipe expansion forming method, first, a small bending radius R part (R = 204 mm (FIG. 9 ( a)))) is bent.

Here, a stretch bend that performs a tensile bending process that grips a portion of the expanded pipe portion P1 in the deformed steel pipe P that is performed thereafter to form a predetermined large bending radius R shape (R = 6500 mm (see FIG. 9D)). The apparatus and stretch bend method will be described below with reference to FIGS.
Specifically, by using the stretch bend device 50 shown in FIG. 6, the expanded pipe portions P1 at both ends of the deformed steel pipe P are gripped by the gripping molds (second molds) 32a and 32b, and bent. A desired large R shape is formed on the deformed steel pipe P by bending along the inner die (first die) 31 having an R shape.

As shown in FIG. 6, the stretch bend device 50 includes pulling portions 30 a and 30 b in which both ends of the deformed steel pipe P are set, an inner mold 31, and a pressing portion 34.
The pulling portions 30a and 30b have gripping molds 32a and 32b and pressure cylinders 33a and 33b, respectively. The holding molds 32a and 32b are members that hold the expanded pipe P1 of the deformed steel pipe P, and are configured by combining two molds that can be divided vertically. These two molds are fixed by four bolts 41a to 41d shown in FIGS. 11 (a) and 11 (b). The pressurizing cylinders 33a and 33b are connected to the gripping dies 32a and 32b, and as shown in FIGS. 7B and 8B, the gripping dies 32a are extended in the direction in which the deformed steel pipe P is extended. , 32b are moved.

The inner mold 31 is a mold for forming the large R portion of the deformed steel pipe P, and includes a small R portion already formed near the center of the deformed steel pipe P and the large R portion. The deformed steel pipe P is set along the inner mold 31.
The pressing part 34 is a device for pressing the inner mold 31 against the deformed steel pipe P, and applies a pressing force by a hydraulic cylinder.

<Flow of stretch bend process>
Here, with respect to each process when the stretch bend method is performed by the stretch bend apparatus 50 having the above-described configuration, FIGS. 7A to 8B, each process diagram shown in FIG. 9, and FIG. This will be described below using the flowchart shown in FIG.
That is, in step S <b> 11, as shown in FIG. 9A, the deformed steel pipe P formed with a small R of R = 204 mm is arranged along the inner mold 31.

Next, in step S12, as shown to Fig.7 (a), the holding metal mold | dies 32a and 32b contained in the tension | pulling parts 30a and 30b are set to the part of the pipe expansion part P1 formed in the both ends of the deformed steel pipe P. .
Next, in step S13, as shown in FIGS. 11 (a) and 11 (b), a mandrel (insertion member) 36 is inserted on the inner diameter side of the expanded pipe portion P1, and then the holding molds 32a and 32b are configured. The upper and lower mold members are fastened and fixed by the four bolts 41a to 41d. Here, the mandrel 36 inserted into the inner diameter side of the pipe expansion part P1 has a similar shape whose cross section is slightly smaller than the cross-sectional shape of the pipe expansion part P1, and is a portion of the pipe expansion part P1 gripped by the gripping molds 32a and 32b. However, it is inserted in order to suppress deformation during the tensile bending process described later.

  Next, in step S14, as shown in FIG. 7 (b), the holding dies 32a and 32b that hold the expanded portions P1 at both ends of the deformed steel pipe P are moved in the extending direction of the deformed steel pipe P by the pressurizing cylinders 33a and 33b. Move (first stage pull). At this time, as shown in FIG. 9 (b) and FIG. 11 (a), the expanded pipe portion P1 formed at both ends of the deformed steel pipe P has a larger pipe diameter than the portion of the deformed steel pipe P inside thereof. It is caught in the gripping molds 32a and 32b. For this reason, the slip amount between the holding molds 32a and 32b and the expanded pipe portion P1 when a tensile force is applied to the deformed steel pipe P can be reduced as compared with the conventional case.

  Next, in step S15, as shown to Fig.8 (a), the inner metal mold | die 31 arrange | positioned along the deformed steel pipe P is moved so that it may press toward the deformed steel pipe P1 side by the press part 34. FIG. At this time, as shown in FIG. 9C, the deformed steel pipe P is given a bending force along the large R shape of the inner die 31, and a large R shape with R = 6500 mm is formed on a part of the deformed steel pipe P. A portion along the line can be formed.

  Next, in step S16, as shown in FIG. 8 (b), the holding molds 32a and 32b for holding the expanded portions P1 at both ends of the deformed steel pipe P are again attached to the deformed steel pipe P by the pressurizing cylinders 33a and 33b. Move in the stretching direction (second stage pulling). Here too, as in the case of applying the first stage pulling force, the expanded pipe portion P1 having a large pipe diameter is pulled in the state of being caught by the holding dies 32a and 32b, so the holding dies 32a and 32b and the expanded pipe portion P1 The amount of slipping between the two can be reduced as compared with the prior art. At this time, the deformed steel pipe P is given a bending force by pressing the inner mold 31 and a tensile force by the gripping molds 32a and 32b, and the desired shape of the deformed steel pipe P is shown in FIG. A large R shape with R = 6500 mm can be formed at the position.

Next, in step S17, the pulling portions 30a and 30b (gripping dies 32a and 32b) set at both ends of the deformed steel pipe P are removed, and the deformed steel pipe P having a desired large R shape is taken out.
In the stretch bend method by the stretch bend device 50 of the present embodiment, as described above, the bending process is performed in a state where the expanded portions P1 formed at both ends of the deformed steel pipe P are gripped by the gripping dies 32a and 32b.

As a result, the amount of slippage of the deformed steel pipe P in the gripping portion during processing (during application of tensile force and bending force) can be reduced, so that the amount of springback of the deformed steel pipe P after bending is reduced and dimensioned. A highly accurate bent product can be manufactured.
[Features of the present stretch bend method and apparatus]
(1)
In the stretch bend method of this embodiment, in the stretch bend apparatus 50, as shown in FIG. 10, after setting the deformed steel pipe P near the inner mold 31 for bending (step S11), In a state where the portion of the expanded pipe portion P1 formed in the portion is gripped by the gripping dies 32a and 32b (steps S12 and S13), the inner die 31 is pressed while pulling the gripping dies 32a and 32b, and the deformed steel pipe P is pressed. On the other hand, a bending process is performed by applying a tensile bending force (steps S14 to S16).

  Thus, the amount of slip between the gripping molds 32a and 32b and the pipe expansion part P1 during the tension bending process is performed by performing the tension bending process in a state where the pipe expansion part P1 is caught in the gripping molds 32a and 32b. Can be reduced. Therefore, at the time of tensile bending, a tensile force and a bending force can be applied to the deformed steel pipe P without loss. As a result, the amount of springback of the deformed steel pipe P after bending is reduced, and the dimensional accuracy of the deformed steel pipe P after bending can be improved. Further, by using the pipe expansion portion P1 during the pull bending process, a conventional large-scale device such as sandwiching the pipe end portion from above and below by the cylinder becomes unnecessary, so that the cost of the bending apparatus can be reduced. Furthermore, since the deformation of the pipe end after bending can be minimized as compared with the conventional method in which the pipe end is sandwiched between cylinders and bent, the end of the deformed steel pipe P is bent. It is not necessary to cut after processing, and the product yield can be improved.

(2)
In the stretch bend method of the present embodiment, as shown in FIG. 7 and the like, the tensile bending process is performed in a state where the expanded portions P1 formed at both ends of the deformed steel pipe P are gripped by the gripping dies 32a and 32b, respectively.
Thereby, the sliding amount of the deformed steel pipe P in the holding molds 32a and 32b when a tensile bending force is applied to the deformed steel pipe P is compared with the case where the expanded portion P1 is formed only at one end of the deformed steel pipe P. Further, it can be effectively reduced. As a result, it is possible to efficiently apply a tensile force and a bending force to the deformed steel pipe P and form a bent product with less spring back.

(3)
In the stretch bend method of the present embodiment, as shown in FIG. 11 (b), the mandrel 36 is inserted into the inner diameter side of the expanded portion P1 gripped by the gripping molds 32a and 32b, and the bending is performed.
Thereby, even when the tensile bending process is performed in a state where the pipe expansion part P1 is held by the holding molds 32a and 32b, the deformation of the pipe expansion part P1 in the holding molds 32a and 32b can be suppressed to the minimum. As a result, it is possible to reduce the amount of the end portion of the deformed steel pipe P that is cut after the bending process, so that the product yield of the bent product can be improved.

(4)
In the stretch bend method of the present embodiment, as shown in FIG. 10, the deformed steel pipe P is pulled in the extending direction by the holding molds 32 a and 32 b that grip the expanded portions P <b> 1 formed at both ends of the deformed steel pipe P. The inner die 31 is pressed against P to perform bending (steps S14 to S16).

Thereby, in the holding dies 32a and 32b, it is only necessary to apply a tensile force to the deformed steel pipe P, so that the configuration of the stretch bend device 50 can be avoided from becoming complicated.
(5)
In the stretch bend device 50 of the present embodiment, the above-described stretch bend method is performed in a state where the expanded pipe portion P1 is gripped by the gripping dies 32a and 32b.

As a result, as described above, the tensile force and bending force can be imparted to the deformed steel pipe P without loss by reducing the amount of sliding of the expanded pipe portion P1 in the holding dies 32a and 32b during the tensile bending process. be able to. As a result, the amount of spring back of the deformed steel pipe P after bending can be reduced, and the dimensional accuracy of the product after bending can be improved.
[Other Embodiments]
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the summary of invention.

(A)
In the said embodiment, the pipe expansion part 10 WHEREIN: The example which shape | molds the pipe expansion part P1 in the both ends of the deformed steel pipe P using the side pressurization apparatus 15 etc. which contain the punch 12, the die | dye 13, and the side metal mold 21 for pipe expansion molding. And explained. However, the present invention is not limited to this.
For example, the apparatus and method for forming the pipe expansion part are not limited to the above-described embodiments, and the pipe expansion part may be formed by another apparatus or method. Further, the tube expansion part may be formed simultaneously with the formation of the steel pipe, or as described above, the tube expansion part may be separately formed after the steel pipe is formed.

(B)
In the said embodiment, after forming the pipe expansion part P1 in the both ends of the deformed steel pipe P, respectively, it demonstrated and demonstrated the example which hold | grips the pipe expansion part P1 of this both ends with the holding metal mold | dies 32a and 32b, and performs a bending process. However, the present invention is not limited to this.
For example, the pipe expanding part formed at one end of the steel pipe may be gripped and the other end may be gripped by a gripping member such as a cylinder for bending.

Even in this case, since the amount of slip can be reduced on the side where the expanded portion is gripped, the amount of spring back after processing is reduced by forming a uniform strain distribution, and bending processing with higher dimensional accuracy than before is possible. It can be performed.
However, in this case, since the slip of the gripping member with the steel pipe occurs at the other end, the amount of the spring back may not be sufficiently reduced as in the above embodiment. Furthermore, it is more preferable to provide a pipe expanding part at both ends of the steel pipe and to perform bending by gripping these.

(C)
In the above-described embodiment, in the stretch bend device 50, while bending both ends of the deformed steel pipe P with the gripping molds 32a and 32b, the bending mold inner mold 31 is pressed against the deformed steel pipe P to bend and bend. An example of performing processing has been described. However, the present invention is not limited to this.

For example, instead of pressing the inner mold, bending may be performed by moving the gripping mold in the bending direction.
However, in this case, the gripping mold needs to apply a pulling force and a bending force to the steel pipe, so that the movement becomes complicated, as in the above embodiment, More preferably, the tensile force and bending force of the steel pipe are applied by separate members.

(D)
In the said embodiment, the example which performs the bending process of the large R shape of bending radius R = 6500mm with the stretch bend apparatus 50 was given and demonstrated. However, the present invention is not limited to this.
For example, the size of the bending radius R is not limited to the bending radius R = 6500 mm, but may be a bending process with a bending radius R smaller than 6500 mm, or conversely, the bending radius R larger than 6500 mm. Bending may be used.

(E)
In the above embodiment, as shown in FIG. 9A and the like, an example in which bending with a small bending radius R of bending radius R = 204 mm is performed before bending with a large bending radius R has been described. However, the present invention is not limited to this.
For example, the bending process may be performed by suddenly performing the stretch bend method using the stretch bend apparatus according to the present invention.

(F)
In the said embodiment, the example which performs the bending process of the deformed steel pipe P which has the deformed cross-section shape | molded by roll forming the round steel pipe of circular section was demonstrated and demonstrated. However, the present invention is not limited to this.
For example, the present invention can be applied to bending of a round steel pipe having a circular cross section instead of a deformed steel pipe.

(G)
In the said embodiment, the deformed steel pipe P after pipe expansion forming was bent and processed in the stretch bend apparatus 50, and the example used as a frame support | pillar (A pillar) which comprises the cab mounted in a hydraulic shovel etc. was given and demonstrated. However, the present invention is not limited to this.
For example, the present invention is naturally applicable not only to the cab frame column mounted on a construction machine such as a hydraulic excavator, but also to the expansion of a steel pipe used for other purposes.

Here, with respect to the deformed steel pipe P bent by the stretch bend method and the stretch bend device according to the above-described embodiment, and the deformed steel pipe Pa having no expanded portion processed by the conventional bending method, the spring after bending is processed. The experimental results verified for the back amount and the dimensional accuracy will be described.
Note that the conventional deformed steel pipe Pa used in the experiment has a material, a length, a cross-sectional shape, a bending, except that the expanded portion is not formed, and the both ends are gripped and bent so as to be sandwiched between cylinders. The size, shape, and the like of the inner mold used for processing are assumed to be the same conditions as those of the deformed steel pipe P according to the above-described embodiment.

First, in the deformed steel pipe P having the pipe expansion part P1 according to the above-described embodiment at both ends, as shown in FIG. 12A, the diagonal distance connecting the pipe expansion parts P1 after bending was 2259 mm. On the other hand, as shown in FIG. 12B, the diagonal distance of the deformed steel pipe P after the occurrence of springback after a lapse of a predetermined time was 2291 mm.
On the other hand, in the conventional deformed steel pipe Pa having no expanded portion, as shown in FIG. 13A, the diagonal distance connecting both ends after bending was 2251 mm. On the other hand, as shown in FIG. 13B, the diagonal distance of the deformed steel pipe Pa after the occurrence of the spring back after a predetermined time was 2306 mm.

As a result, as shown in FIG. 14, the springback amount of the deformed steel pipe P according to the present embodiment is 32 mm, whereas the springback amount of the conventional deformed steel pipe Pa is 55 mm, and the springback amount Was reduced by about 42%.
As described above, the deformed steel pipe P processed by the stretch bend method according to the present embodiment has the effect of greatly reducing the amount of spring back after bending and manufacturing a bent product with high dimensional accuracy. Has been demonstrated.

The main factor of the preferable result as described above is that the expanded portion P1 is formed at the end of the deformed steel pipe P, and the tensile bending process is performed while being gripped by the gripping dies 32a and 32b. As shown in FIG. 4, it is mentioned that the amount of slipping in the grip portion is greatly reduced.
Specifically, as shown in FIG. 15, the conventional deformed steel pipe Pa has a maximum slip of about 11 mm, whereas the deformed steel pipe P according to the present embodiment has a maximum slip of about 8 mm. there were.

  As described above, according to the stretch bend method of the present embodiment, the slip amount at the gripped portions at both ends when performing the pull bending can be reduced by about 27%. It becomes possible to manufacture a bent product with high dimensional accuracy by reducing the amount.

  The stretch bend method and apparatus of the present invention have the effect of reducing the spring back of the steel pipe after bending and improving the dimensional accuracy by reducing the amount of slip at the gripping portion during bending. Therefore, the present invention is not limited to steel pipes and can be widely applied to bending of members formed of other materials.

The side view which shows the structure of the apparatus which shape | molds the pipe expansion forming part of the steel pipe used as the premise of the stretch bend method and apparatus which concerns on one Embodiment of this invention. (A), (b) is a side view which shows the process at the time of inserting a punch in a deformed steel pipe. (A) is a front view which shows the positional relationship of the side metal mold | die, punch, a deformed steel pipe, and die | dye at the time of inserting a punch in a deformed steel pipe. (B) is sectional drawing which looked at (a) from the side. (A), (b) is the front view and sectional drawing which show the deformed steel pipe pipe-expanded as a result of having inserted the punch. The flowchart which shows the flow of the pipe expansion molding method by the pipe expansion molding apparatus of FIG. Explanatory drawing which shows the structure of the stretch bend apparatus which enforces the stretch bend method which concerns on one Embodiment of this invention. (A), (b) is explanatory drawing which shows each process contained in the stretch bend method using the stretch bend apparatus of FIG. (A), (b) is explanatory drawing which shows each process performed following the process of FIG.7 (b). The figure in the stretch bend apparatus of FIG. The flowchart which shows the flow of the stretch bend method by the stretch bend apparatus of FIG. (A), (b) is an enlarged view which shows the structure of the holding die contained in the stretch bend apparatus of FIG. (A), (b) is the Example figure which investigated the springback amount of the deformed steel pipe processed by the stretch bend method implemented with the stretch bend apparatus shown in FIG. (A), (b) is the comparative example figure which investigated the springback amount of the deformed steel pipe processed by the stretch bend method implemented with the conventional stretch bend apparatus. The graph which compared the springback amount of the steel pipe in a holding part about a present Example and the conventional comparative example. The graph which compared the sliding amount of the steel pipe in a holding part about a present Example and the conventional comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Pipe expansion molding apparatus 11 Main cylinder 12 Punch 13 Die 15 Side pressurization apparatus 20 Control part 21 Side mold 22 Mold holding part 23 Shaft 30a, 30b Pull part 31 Inner mold (1st mold)
32a, 32b Holding mold (second mold)
33a, 33b Pressurizing cylinder 34 Pressing part 36 Mandrel (insertion member)
41a-41d bolt 50 stretch bend device (steel pipe bending device)
M motor P deformed steel pipe (steel pipe)
P1 expansion section

Claims (5)

A method of bending a steel pipe having an expanded portion,
A first step of installing the steel pipe along a first mold for tensile bending;
A second step of gripping the expanded portion included in the steel pipe with a second mold for pulling;
A third step of bending along the first mold while pulling the second mold in the extending direction of the steel pipe;
A method for bending a steel pipe. In the second step, the expanded pipe portions respectively formed at both ends of the steel pipe are gripped by the second mold.
The method for bending a steel pipe according to claim 1. In the second step, an insertion member is inserted into the inner diameter side of the tube expansion portion, and the tube expansion portion is gripped by the second mold.
The method for bending a steel pipe according to claim 1 or 2. In the third step, the first mold is pressed against the steel pipe while pulling the second mold in the extending direction of the steel pipe.
The method for bending a steel pipe according to any one of claims 1 to 3. A steel pipe bending apparatus for executing the steel pipe bending method according to any one of claims 1 to 4,
A first mold that is pressed against the steel pipe to serve as the bending mold;
A second mold for holding the expanded portion formed in a part of the steel pipe;
Steel pipe bending machine equipped with.

Images