JPS61283422A - Method and apparatus for bending pipe - Google Patents

Abstract

PURPOSE:To form a bent part having a circular section without a change in the wall thickness of the section in the stage of bending a pipe by inserting a mandrel into the pipe and bending the pipe by means of an upper die and split lower dies while pressurizing the pipe at both ends by cylinders. CONSTITUTION:The pipe 10 to be bent is put on a supporting groove 18 of the lower dies 14 consisting of split dies 14A, 14B. The pressurizing cylinders 22 on both sides are advanced so that the mandrel part 28 is pressurized and inserted into the pipe by a pushing die 26. The upper die 12 having a guide groove 16 is placed thereon and is pressed toward the lower dies. The split dies 14A, 14B of the lower dies 14 are opened toward both sides to bend the pipe 10. Compressive force is exerted to the pipe wall on the side outer than the neutral axis of the pipe 10 to prevent the generation of elongation on the outside of the bent part. The pipe is pressurized by the actuation of the cylinders 22 in synchronization with the bending in the supporting step parts at the pipe end faces which are provided to the die 26 and are oblique with the pipe axial center. The pipe is thereby formed to the circular shape without decreasing the wall thickness on the outside of the bent part and without flattening the section of the bent part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pipe bending method and apparatus suitable for use in press bending, which is a type of pipe bending method.

[Prior art]

Conventionally, in press bending of pipes, the pipe is placed on a lower die that can be opened double-sided, and the upper die, which has an arc-shaped bending guide groove, is pressed from the outside perpendicular to the pipe toward the lower die, and the pipe is pressed into the bending guide groove. The pipes are bent in a similar manner.

[Problem that the invention seeks to solve]

However, according to the conventional bending method, the cross-sectional shape of the bent portion of the pipe after bending tends to become flat, and a perfect circle cannot be maintained. In other words, conventionally, the bending force of the pipe acts on the upper die in a direction perpendicular to the pipe axis, so this external force, which is the bending force, creates bending stress in the pipe, and the inside of the pipe is compressed between the neutral axis of the pipe. The stress is
Tensile stress is generated on the outside. As a result, the wall thickness of the pipe increases on the inside of the neutral axis and decreases on the outside due to elongation. When the pipe is bent to a large extent, the increase or decrease in the inner and outer wall thicknesses of the neutral axis cannot compensate for the difference in the inner and outer bureau lengths, and as a result, the cross section at the center of the pipe bend becomes flat. If this kind of flattening of the bent pipe occurs,
When trying to connect other parts to this bent part by welding, etc., it is necessary to correct the flattened cross section.
There was also the drawback of being forced to undergo difficult correction work.

Even after correction, the wall is still thin, especially on the outer circumferential side, resulting in a structure that cannot maintain sufficient strength.

The present invention has focused on the above-mentioned problems, and aims to provide an improved pipe bending method and apparatus that prevent flattening from occurring during pipe bending.

[Means for solving problems]

The present invention relies only on the elongation of the pipe on the outside of bending during bending to correct the bureau difference, from the viewpoint that the difference between the circumference outside and inside the neutral axis of one bend is the cause of flattening. Without,
By actively feeding the material in a direction that suppresses elongation, the difference in the length of one bending section is reduced and the occurrence of flattened sections is attempted to be prevented.

For this reason, the bending method according to the present invention is
When bending the pipe, the pipe is configured such that the outer end surface of the bent pipe is forcibly pushed inward along the axial direction of the pipe. In addition, the apparatus for carrying out the above method includes disposing a pushing die integrally having a core metal part to be inserted into the pipe on one side of a bending die consisting of an upper bending die and a lower bending die; is provided with a support step on the end surface of the pipe obliquely intersecting the pipe axis, and the pushing amount is determined by applying pressure by bringing the support step into contact with at least the outside end surface of the pipe bending in synchronization with the bending operation. It has a structure in which pressure cylinders are connected in series.

[Effect]

According to the above structure, the outer end surface of the bending neutral shaft is supported by the push-type support stepped portion and pushed in by the pressurizing cylinder at the same time as the bending process, so that the difference in the length between the inside and outside of the neutral shaft becomes small. Since the flattening of the curved portion of the pipe is due to the difference in elongation based on the difference in length, the cause of flattening is eliminated and the roundness of the bent portion is maintained even during press bending.

〔Example〕

Embodiments of the pipe bending method and apparatus according to the present invention will be explained in detail below with reference to the drawings. 3. Figures 1 and 2 show cross-sectional views of the pipe bending apparatus according to the embodiment before and after bending. . This device is an upper mold 1 for bending a pipe 10.
2 and a lower mold 14. Upper mold 12
is for regulating the bending shape of the pipe 10, and the pipe 10
The guide groove 16 to be fitted into the upper half is curved into an arc shape, and the upper mold 12 is pressed from the outside perpendicular to the central axis of the pipe 10 to form a shape that resembles the guide groove 16. The pipe 10 is bent.

On the other hand, the lower die 14 supports the pipe 10 during bending, and supports the pipe 10 in a straight pipe state before bending, and operates in double-opening mode to allow the upper die 12 to advance during bending. can be split down the middle. Each of the split molds 14A and 14B has a support groove 18 that is fitted into the lower half of the pipe 10 on the surface facing the upper mold 12, and during bending, the pipe 10 is formed at the contact area between the support groove 18 and the guide groove 16. I try to cover the entire circumference. Further, each of the split molds 14A and 14B is attached to a support plate 20, and this plate 20 is configured to be double-opened by a mechanism not shown. Known means may be used for this double door structure and driving means for machining operation of the upper board 12.

Here, the support plate 2 to which the lower mold 14 is attached
0, there is a pressurizing cylinder 2 located on the axis of the pipe 10.
2 is installed. This pressurizing cylinder 22 has a piston rod 24 protruding toward the end opening of the pipe 10, and each split mold 14A, 14B is provided at the tip of the rod 24.
A push-in die 26 that can slide in the support groove 18 is connected thereto.

The push die 26 is a small cylindrical body with approximately the same diameter as the pipe 10 to be processed, and is capable of coming into contact with the open end surface of the pipe 10, and has a core metal portion 28 inserted into the pipe 10 on its tip surface. It is installed in one piece. The structure of the push-in mold 26 having this core metal part 28 is shown in FIGS. 6 and 7. This push die 26 has an outer diameter equal to the outer diameter dimension of the pipe 10, but in particular, only the sliding surface portion with the support groove 18 of the lower die 14,
That is, only the lower half is made equal to the diameter of the pipe 10.

The upper half has the same diameter as the core bar 28. Since there is a diameter difference between the push-in die 26 and the core metal part 2B, a step corresponding to the diameter difference is formed on the tip surface of the push-in die 26, and this step is brought into contact with the pipe end surface. The support step portion 30 is brought into contact with the support step portion 30. This supporting stepped portion 30 is an inclined surface obliquely intersecting the axis of the pipe 10. , pipe 1
During the bending process, the compression of the pressurizing cylinder 22 causes the end surface of the pipe outside the neutral axis to be inclined so as to be pushed inward toward the neutral axis, that is, toward the point of application of the bending force. Further, the core metal part 28 is connected to the pipe 1.
A guide surface 32 is formed on the lower surface of the tip of the pipe 10 to regulate the bending shape of the inner surface outside the neutral axis when the bending process of the pipe 10 is completed. Therefore, the guide surface 32 is formed into an arcuate surface centered on the pipe bending center in the bending completed state shown in FIG.

The bending method using the apparatus configured as described above is performed as follows. First, the divided lower die 14 is arranged in a straight line as shown in FIG. 1, and the pipe 10 to be processed is placed in the support groove 18. Then, both measuring section pressure cylinders 22
is moved forward, the pushing die 26 connected thereto is pushed back into the end surface of the pipe 10, and the core metal part 28 is inserted into the pipe 10. At this time, the push die 26 is in contact with the pipe 10 at one point at the tip of the inclined support step 30.

From this state, press the upper mold 12 toward the lower mold 14,
The pipe 10 is fitted into the guide groove 16 and bent into a shape along the guide groove 16. At this time, there were 14 people in each division type.

Pressure 7 cylinder 22 on the side of 14B is applied by upper mold 12)
A pressurizing operation is performed in synchronization with the normal operation, and a compressive force of 5 Kf is applied to the pipe wall outside the neutral axis of the pipe 10 so that no elongation occurs in the pipe wall on the outside of the bending process. pipe 1
The support step 30 of the push-in mold 26, which the end surface of the 0. When the machining is completed, the state shown in FIG. 2 is reached, in which the entire inclined support step 30 is in contact with no difference in circumferential length between the inside and outside of the neutral axis. The pressing force from the pressurizing cylinder 22 of this head is the pressure on the pipe 1.
The force is about 1 Torr, although it depends on the force. Then, the pipe 10 is bent, and the core metal part 2 inserted inside the pipe 10 is bent.
8 is provided with a guide surface 32, which prevents the pipe 100 from buckling when pressed by the push die 26, prevents it from deforming into an irregular shape, and maintains the roundness of the bent portion. The cross sections of each part of the pipe 10 at this time are as shown in FIGS. 3 to 5.

According to such a method and apparatus for bending the pipe 10,
During bending, the pushing die 26 applies a pushing force to the outside of the bending of the pipe 10, which prevents a reduction in the wall thickness of the pipe wall on the outside of the bending, and prevents the generation of a difference in the length between the outside and outside of the neutral axis. can be prevented. The flattening of the bent portion that occurs during bending of the pipe 10 is due to the difference in the length between the inside and outside of the neutral axis, so as in the example, the tube wall on the side where the elongation occurs is actively pushed in the direction of suppressing elongation, so that eventually Flattening of the bent portion of the pipe 10 can be prevented.

8-9 and 10-11 show modified examples of the push-in type. In the case shown in FIGS. 8 and 9, an inclined support step 30 is formed over the entire circumference, and this mainly facilitates the manufacture of the push die 26. Also, the 10th
In the example shown in FIGS. 1 to 11, the core metal portion 28 is particularly shortened and the portion where the guide surface 32 is formed is deleted. Push type 2
If there is no possibility that the pipe 100 will buckle due to the pushing force of 6, it is not necessarily necessary to provide the guide surface 32.

Further, the push-in mold 26 and the core metal part 2B do not have to be integrally molded, but the core metal part 28 is formed as an extension, and a sleeve body that can form the support step part 30 is fitted thereto, and then the core metal part 28 is formed by welding or the like. They may be integrated.

〔Effect of the invention〕

As explained above, according to the present invention, when bending a pipe, the material is actively pushed in so as not to reduce the wall thickness on the outside of the bend, thereby eliminating the difference in bureau length between the outside and outside of the neutral axis. This has the excellent effect of preventing deformation such as flattening of the bent portion and maintaining roundness.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the bending device of the embodiment before processing, Fig. 2 is a cross-sectional view after the same processing, Fig. 3 is a cross-sectional view taken along the line I-I in Fig. 2, and Fig. 4 is a cross-sectional view taken along the line tV - + V of Fig. 2. 5 is a sectional view taken along the line v-v, FIG. 6 is a front view of the push-in mold, FIG. 7 is a side view of the same, FIG. 8 is a front view of a modification of the push-in mold, and FIG. 9 is a front view of a modified example of the push-in mold. FIG. 10 is a front view of still another modification, and FIG. 11 is a side view of the same. 10...Pipe, 12...Upper mold. 14... Lower die, 16... Guide groove. 18... Support groove, 22... Pressure 7 cylinder,
26... Push-in mold, 28... Core metal part, 30.
...Support step.

Claims (3)

[Claims] (1) A pipe bending method characterized in that, when bending a pipe, the outer end surface of the bent pipe is forcibly pushed inward along the axial direction of the pipe. (2) A pushing die that has an integral core bar to be inserted into the pipe is placed on one side of the bending die consisting of an upper bending die and a lower bending die. A supporting stepped portion of the pipe end faces that intersects is provided, and a pressurizing cylinder is connected for the pushing amount to bring the supporting stepped portion into contact with at least the outer end surface of the bent pipe and apply pushing pressure in synchronization with the bending operation of the bending die. A pipe bending device characterized by a pipe bending device. (3) The pipe bending device according to claim 2, wherein the core metal is formed with an arcuate surface that follows the pipe bending shape.