JP2572072B2 - Pipe bending method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a pipe bending method for bending a pipe at at least two adjacent locations.

[Prior art and its problems] Conventionally, when bending a pipe at two or more locations, the bending is performed in a convenient order in the process regardless of the bending angle of the pipe.

As a result, when the bending of a pipe with a large bending angle and the bending of a pipe with a small bending angle are performed close to each other, the work-hardened region generated during the first bending is removed by the second bending. As a result, a crack is generated at the outer edge of the bent portion of the pipe, and wrinkles are generated at the inner edge.

That is, while bending the pipe two or more times,
In particular, a problem occurs when the bent portions are close to each other.

If the work hardening region generated at the time of the first bending process and the work hardening region of the second and subsequent bending processes are close to each other so as to overlap with each other, work hardening by the first bending process is performed. The stress limit of the pipe material could be exceeded due to the synergistic effect of work hardening by the second bending.

As a result, in the worst case, a crack is generated at the outer edge portion of a bend to which a tensile stress is mainly applied, exceeding the stress limit of the pipe material. Also, wrinkles were generated mainly at the inner edge of the bend to which compressive stress was applied.

[Means for Solving the Problems] and [Operation] In order to solve the problems described above, according to the present invention,
In order to perform pipe bending by the draw bend method, at least the first bending portion having a small bending angle and the second bending portion having a large bending angle are bent while clamping the pipe with a clamp die and rotating the bending die. Pipe bending method for bending pipes, wherein, when the first bent portion and the second bent portion are close to each other, the first bent portion after bending is shaped into the shape of the first bent portion. By bending the second bending portion in a state where the second bending portion is clamped by a clamp die having a shape such that a work hardened region at the time of bending the first bending portion does not reach the second bending portion. Good bending can be performed on bending portions that are close to each other.

Hereinafter, an embodiment according to the present invention will be described in detail with reference to the drawings.

FIG. ₁ shows a work hardening region generated when a pipe 1 is bent by a bending apparatus by the draw bend method from a bending start position 2a indicated by a broken line to a bending end position 3a by an angle of 30 ° indicated by an angle θ1. FIG. 4 is a diagram indicated by oblique lines 4a.

FIG. 2 is similar to the pipe 1 shown in FIG. 1, work hardening region occurs upon only bending angle of 60 ° as shown at the end position 3b through an angle theta ₂ bent from the bending start position 2b Is a diagram indicated by oblique lines 4b.

The hardness of the pipe material before bending is Vitzkars hardness, and the hardness as a measure of work hardening is shown in FIG. 1 and FIG. 2 after bending pipes of H _V = 200 at bending angles of 30 ° and 60 °, respectively. Were measured at points a to e shown in Table 1.
Was obtained.

As a result, it is understood that no work hardening occurs at the points d and e when the bending angle is 30 °. Therefore, by setting the vicinity line 5a where the work hardening region ends near the end position 3a of the first bending work to the bending start position 2b of the second bending work, the work hardening generated in the first bending work is performed. The second bending can be performed without being affected by the area.

 That is, the pipe can be bent in close proximity.

If the process shown in FIG. 2 in which the bending angle of the pipe is larger is performed for the first time, the second bending process must be performed while avoiding the work hardening zone. The indicated neighborhood line 5b must be located at the start of the second bending. As a result, close pipe bending cannot be performed.

Hereinafter, in the drawing of the pipe bending process of the draw bend method as shown in FIGS. 3a, 3b, and 3c of the present embodiment, the bending process having a small angle is performed for the first time, and the second time, FIG. A case of performing a bending process with a large angle shown in FIG. 3c will be described.

In the pipe bending process diagram of FIG. 3a, a mandrel 8 is inserted into the pipe 1 to prevent the cross section of the pipe from becoming elliptical at the bent portion sandwiched between the bending die 6 and the pressure die 9. However, this technique is known in Japanese Patent Application Laid-Open No. 61-180620. First, the pipe 1 is clamped by the clamp mold 7a and the clamp mold 7b attached to the bending mold 6 when the material is straight. Next, the bending die 6 rotates in the direction of the arrow A, and almost in synchronism therewith, the pressure die 9 moves straight in the direction of the arrow B by the action of the hydraulic cylinder 10, and the pipe 1 is bent. In FIG. 3a, the first
This shows a state where the second bending is completed.

In FIG. 3b, the second bending is performed by being clamped between the clamp dies 11a and 11b that match the outer shape of the pipe obtained by the first bending. .

After clamping in this manner, the bending die 6 is rotated in the direction of arrow C shown in FIG. 3c, and the pressure die 9 is moved straight in the direction of arrow D almost in synchronism therewith to perform the second bending process. The pipe was collected using cowpea to such machining processes, and how the work hardening zone 4b when the first time in bending at 60 ° of the angle theta ₂ processed in Figure 4, the angle theta ₁ to the second time of
While showing a state of work hardening zone 4a in the case of bending and at 30 °, when performing processing from Figure 4 bent at the second time 30 ° angle theta ₁ first round of work hardening zone 4b is the second It can be seen that it has greatly entered the second bending area.

On the contrary, the first time to perform a bending at 30 ° of the angle theta _1, when the second time to perform a bending at 60 ° of the angle theta _2, the work hardening zone 4a almost second It can be seen that it did not enter the bending area.

[Effects of the Invention] As described above, according to the present invention, in order to perform the bending process on the pipe by the draw bend method, at least the bending angle is small while holding the pipe by a clamp die and rotating the bending die. When bending a second bending portion having a large bending angle with the first bending portion, particularly when the first bending portion and the second bending portion are close to each other, a work hardening region at the time of bending the first portion. Can be provided so as not to reach the second bent portion, and a good bending process can be performed at the bent portions adjacent to each other.

[Brief description of the drawings]

1 and 2 are views showing a work hardening zone of the pipe, FIGS. 3a to 3c are drawings of a bending process of the pipe of the present embodiment, and FIG. 4 is an external view of the pipe after twice bending. It is. In the drawing, 1... Pipe, 2a, 2b... Pipe bending start position, 3a, 3b... Pipe bending end position, 4a, 4b... Work hardening zone, 5a, 5b. Bending mold, 7a, 7b ... clamp type, 8 ... mandrel, 9 ... pressure type, 10 ... hydraulic cylinder, 11a, 11b ... clamp type.

Claims (1)

(57) [Claims] In order to bend a pipe by a draw bend method, the pipe is clamped by a clamp die.
While rotating the bending mold, at least the first bending angle is small.
A method of bending a pipe for bending a second bent portion having a large bending angle with a bent portion, wherein the first bent portion and the second bent portion are close to each other. The second bending portion is bent in a state where the first bending portion is sandwiched by a clamp having the shape of the first bending portion, thereby forming the first bending portion at the time of bending. A bending method for a pipe, wherein a bending region adjacent to the bending region is bent so that a hardened region does not reach the second bending region.