JP3031189B2 - Corrugation processing method for metal pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of corrugating a metal pipe, that is, a method of bulging an outer peripheral local portion of a metal pipe having plasticity into an uneven shape. A metal pipe corrugated by this method is suitable for use in a steering shaft, an oil cooler tube, or the like.

[0002]

2. Description of the Related Art Conventionally, as a method of corrugating a metal pipe, a cold bulge processing method in which a local outer peripheral portion of a pipe is bulged in a convex shape by applying an axial compressive load to the pipe at room temperature is generally used. Is known to. Since this cold bulging method requires a large compression load and is inferior in workability, in recent years, other corrugating methods capable of solving this problem and the like have been developed.

[0003] That is, Japanese Utility Model Application Laid-Open No. 63-85319 discloses a method of forming a flare tube by forming a flare tube by projecting a local portion of an outer periphery of a pipe in a convex manner without using a mold. I have. In this hot dieless corrugating method, first, a heating portion is formed by heating a local portion of an outer periphery of a pipe extending in an axial direction in a circumferential direction by a high-frequency coil. Then, by applying a compressive load in the axial direction to the pipe, the heating portion is bulged in a convex shape. With this method, if the formation and swelling of the heating portion are performed at other positions, the local portion of the outer periphery of the pipe is swelled in an uneven shape.

[0004]

However, it has been clarified that in the above-mentioned hot dieless corrugating method, the limit of the pipe expansion ratio (the ratio of the outer diameter after bulging to the outer diameter of the pipe;%) is low. The cause is considered to be as follows. That is, in the hot dieless corrugating method, as shown in FIG. 17, a tensile stress T is generated in the circumferential direction of the material constituting the pipe W, but a compressive stress C acts in the axial direction, and the axial direction. The material is supplied from and the swelling is performed. Here, in order to raise the limit of the expansion rate,
It is necessary to increase the molding allowance (the amount of displacement of the compressive load in the axial direction), and therefore, it is necessary to increase the axial width of the heating unit. In this case, the variation in the position where local buckling occurs becomes large, and especially when the width of the heating portion is equal to or larger than the outer diameter of the pipe, the formability becomes extremely unstable. For this reason, the expansion ratio becomes insufficient due to the instability of the formability.

[0005] The inadequate pipe expansion ratio is a serious problem in view of the purpose of use of the pipe after corrugation. For example, when a corrugated pipe is used as a displacement or impact absorbing member such as a steering shaft, the amount of displacement absorption or the amount of energy absorbed by impact strongly depends on the expansion ratio. Also, when a corrugated pipe is used as a radiator like an oil cooler tube, the amount of heat radiated per unit length depends on the expansion ratio. For this reason, pipes with an insufficient expansion ratio have inferior characteristics.

An object of the present invention is to make it possible to improve the expansion rate limit in a method of corrugating a metal pipe.

[0007]

According to a first aspect of the present invention, a method for corrugating a metal pipe according to the first aspect includes heating a local portion of an outer circumference of a metal pipe extending in an axial direction in a circumferential direction.
A heating step of forming a heating unit, and a pair of
The abutting jig whose inner end surface is the abutting surface is
And each corresponding contact surface straddles a specific position of the heating section.
The first compression load in the axial direction is applied to the pipe while being in contact with the heating section.
By applying a load, a first swelling of the heating section is performed.
(1) Swelling step and release of contact between each corresponding contact surface and the heating section
And applying a second compressive load in the axial direction to the pipe.
A second swelling step of secondary swelling the heating section .

(2) In the method of corrugating a metal pipe according to claim 2, a first heating portion is formed by heating a local outer peripheral portion of a metal pipe extending in an axial direction in a circumferential direction . A heating step and applying a first compression load in the axial direction to the pipe.
By applying a load, the first heating unit is caused to primary swell.
A first bulging step, the first heating section and the side of the first heating section.
The second heating part is formed by heating the one in the circumferential direction
A second heating step of applying a second compression load to the pipe in the axial direction.
A second bulging step of secondary bulging the second heating section by applying a load .

(3) The method for corrugating a metal pipe according to a third aspect of the present invention is to heat a metal pipe extending in an axial direction to a local portion of an outer periphery in a circumferential direction, so that a maximum temperature is reached at a specific position.
Degree high-temperature heating part, and the two ends of the high-temperature heating part in the axial direction.
A heating step of forming a low-temperature heating section lower in temperature than the high-temperature heating section, and applying a compression compression in the axial direction to the pipe without using a mold.
By applying a load, the specific position is
While buckling, the high-temperature heating unit is
And a swelling step of swelling to a large degree .

[0010]

[0011]

[0012]

(1) In the processing method according to the first aspect, in the heating step, a heating portion is formed by heating a local outer peripheral portion of a pipe extending in the axial direction in a circumferential direction. And
In the first bulging step, a pair of inner end faces aligned in the axial direction
Place the contact jig with the contact surface on the outer peripheral side of the pipe,
Each contact surface straddles a specific position of the heating section and contacts the heating section.
While applying a first compressive load in the axial direction to the pipe. Like this
Primary swelling of the heating section. During the first swelling step, heating
In the process, make the width of the heating section larger than the outer diameter of the pipe, etc.
Even if it is taken, the buckling position is specified by striking each contact surface
Position and there is almost no variation.

Next, in the second bulging step, each contact surface
Releases contact with the heating section of the pipe, and applies a second compression to the pipe in the axial direction.
Apply the load. Thus, the heating section is secondarily expanded. This
As a result, a large amount of secondary bulge can be secured from a specific position.
Therefore, moldability is stabilized. For this reason, due to the widening of the heating section
Even if the molding allowance is expanded, since the moldability is stable,
The expansion rate limit can be improved. (2) According to the processing method of the second aspect, in the first heating step, the first heating portion is formed by heating the local portion of the outer circumference of the pipe extending in the axial direction in the circumferential direction.

[0014]

[0015]

[0016] In its, in the first bulging step, to grant the first compression load in the axial direction in the pipe, to the primary bulged first heating portion. Thus, the buckling position is specified for the first heating unit.
Next, in the second heating step, the second heating unit is formed by heating the first heating unit and the side of the first heating unit in the circumferential direction.

Thereafter, in a second swelling step, a second compressive load in the axial direction is applied to the pipe to cause the second heating section to swell secondarily. Thus, even if the width of the second heating section is set to be larger than the outer diameter of the pipe in the second heating step, the buckling position is specified by the first heating section, and there is no variation. For this reason, the formability is stabilized, and if the forming margin is increased by widening the second heating section, the limit of the pipe expansion ratio can be improved.

[0018] (3) In the processing method according to claim 3, in first heating step, by heating the outer peripheral part of the pipe extending axially in the circumferential direction, high maximum temperature in a specific position
High- temperature heating at the heating section and at both axial ends of the high-temperature heating section
And a low-temperature heating part lower in temperature than the part . Then, in the swelling step, when an axial compressive load is applied to the pipe without using a mold, and a specific position is buckled by the high-temperature heating unit.
In both cases, the high-temperature heating section bulges to a greater degree than the low-temperature heating section .

[0019] At this time, since the high temperature heating portion of the specific position is the highest temperature, the yield stress of the high temperature heating unit at a specific position is lower than the yield stress of the low-temperature heating section. For this reason, the buckling position becomes the high-temperature heating section at the specific position, and there is no variation. For this reason, the formability is stabilized, and if the forming margin is increased by widening the low-temperature heating section, the limit of the pipe expansion rate can be improved .

[0020]

[0021]

EXAMPLES Hereinafter, the reference example will be described with reference to the drawings and embodying examples invention of each claim 1-3, wherein. ( Reference Example 1)

First, as shown in FIG. 1, an aluminum pipe W extending in the axial direction is prepared. This pipe W has an outer diameter of 12.7 mm, a wall thickness of 1.2 mm, and material JIS-A300.
3H18 drawn tube. This pipe W is attached to a pair of fixed chucks (not shown) of the molding apparatus. In this molding apparatus, a high-frequency coil 1 is provided between both fixed chucks, and a molding die 2 divided into three in a radial direction is provided below the high-frequency coil 1, and an inner surface of the molding die 2 extends in an axial direction. The molding surface 2a has a width of 13 mm. Molding surface 2a
Has the largest hollow at the center, and is formed vertically symmetrically from this center. The pipe W is located in the high-frequency coil 1 and the mold 2.

[Heating Step] The high frequency coil 1 heats a local portion of the outer periphery of the pipe W in the circumferential direction. At this time, the operating frequency is 40 kHz, the heating temperature is about 600 ° C., and the heating time is 1 second. Thus, the pipe W has an axial width l.
₀ heating unit W ₀ of (13 mm) to form. Immediately after completion of "bulging step" heating step, as shown in FIG. 2, to move the pipe W in the axial direction, to position the heating unit W ₀ on the molding plane 2a of the mold 2, for clamping a mold 2 . Then, an axial compressive load F, F ′ (F ′ is a reaction of F) is applied to the pipe W. At this time, the forming allowance (the amount of axial displacement under load) is 7 mm, and the load speed is 200 mm / sec. Thus, as shown in FIG. 3, to bulge the heated portion W ₀ while constrained by the molding surface 2a.

[0024] Since taking significantly to equal to or greater than the outer diameter of the pipe the width of the heating section W ₀ in the expanded process during the heating step,
As shown in FIG. 3, the buckling position is not constant at the beginning of the bulging. However, as shown in FIG. 4, as the bulging progresses, the buckling position is corrected by the molding surface 2a so that the apex of the enlarged diameter portion becomes the center, and there is no variation. On the other hand, when the same type of pipe W is corrugated by the above-described conventional hot dieless corrugating method, the outer diameter of the bulging portion that can be formed stably is 18.5 mm, and the expansion limit is about 45%. there were.

[0025] In this regard, when the corrugated by working the method of example, even if the expansion of the molding cost by widening of the heating unit W _0, the stable moldability due to correction of the buckling position, in expansion ratio 53% Swelling was possible. Therefore,
If you perform pipe corrugation by this processing method,
It can be seen that the expansion rate limit can be increased.

It is also possible to move the high-frequency coil 1 and the molding die 2 in the axial direction without moving the pipe W in the axial direction. (Embodiment 1) First, as shown in FIG. 5, a pipe W of the same type as that of Reference Example 1 is prepared. This pipe W is attached to a pair of fixed chucks (not shown) of the molding apparatus. In this molding device, the high-frequency coil 1 is provided between the two fixed chucks,
Below the high-frequency coil 1, there is provided a contact jig 3 which is divided into two in the axial direction and divided into three in the radial direction, and a pair of inner end faces aligned in the axial direction of the contact jig 3 are provided. The contact surfaces 3a and 3b are provided. Each contact surface 3a, 3b is formed parallel to the axial direction, and has a curved surface on the side close to each other. Each of these contact surfaces 3a, 3b has a width of 3 mm in the axial direction. The pipe W is composed of a high-frequency coil 1 and a contact jig 3
Is located within.

[Heating Step] As in the reference example , a heating portion W ₀ having an axial width l ₀ (16 mm) is formed in the pipe W by the high-frequency coil 1. Immediately after "first bulging step" heating step, as shown in FIG. 6, the pipe W is relatively moved in the axial direction, the abutment surface 3a of the contact jig 3, the position of the heating unit W ₀ within 3b Then, the contact jig 3 is clamped. In this case, across the center of the heating portion W ₀ each abutment surface 3a, 3b
There so as to contact the heating unit W _0.

Then, first compressive loads F ₁ and F ₁ ′ in the axial direction are applied to the pipe W (F ₁ ′ is a reaction of F ₁ ). At this time, the load speed is 200 mm / sec. Thus,
As shown in FIG. 7, the abutment surface 3a, it is only primary bulging molding allowance 2mm heating section W ₀ and 3b while in contact. This first
During bulging step, also the width of the heating section W ₀ as was taking significantly to equal to or greater than the outer diameter of the pipe W in the heating step, the buckling position becomes the center of the heating portion W _0, there is almost no variation.

"Second swelling step" Immediately after the end of the first swelling step,
As shown in FIG. 8, the contact jig 3 is opened, and each contact surface 3 is opened.
a, to release the contact between the heating portion W ₀ of 3b. Then, second axial compressive loads F ₂ and F ₂ ′ (F ₂ ′ is a reaction of F ₂ ) are applied to the pipe W. At this time, the molding allowance is 6m
m, load speed is 200 mm / sec. Thus, to the heating unit W ₀ is secondary bulge.

[0030] Thus, since the center of the heating portion W ₀ can secure a large secondary bulging formability is stabilized. Therefore, even if the molding allowance is increased by widening the heating unit W ₀ ,
Since the moldability was stable, swelling was possible at a pipe expansion ratio of 60%. (Example 2)

First, as shown in FIG. 9, a pipe W of the same type as in Reference Example 1 is prepared. This pipe W is attached to a pair of fixed chucks (not shown) of the molding apparatus. In this molding apparatus, a high-frequency coil 1 is provided between both fixed chucks. The pipe W is located in the high-frequency coil 1. "First heating step" The high-frequency coil 1 applies an axial width l ₁ (12) to the pipe W.
forming a first heating portion W ₁ of mm). At this time, the operating frequency is 40 kHz, the heating temperature is about 600 ° C., and the heating time is 0.7 seconds.

"First bulging step" Immediately after the end of the first heating step,
As shown in FIG. 10, first compressive loads F ₃ and F ₃ ′ in the axial direction are applied to the pipe W (F ₃ ′ is a reaction of F ₃ ). At this time, the load speed is 200 mm / sec. Thus,
A first heating section W ₁ is only a primary bulge forming allowance 1 mm, buckling location is specified in the first heating portion W _1.

[Second Heating Step] As shown in FIG. 11, a high-frequency coil 1 is used to form a second heating section W ₂ having a width l ₂ (17 mm) in the axial direction on the pipe W at the same position. At this time, the operating frequency is 40 kHz and the heating temperature is about 600
℃, the heating time is 2.0 seconds. "Second bulging process" immediately after the second heating step, the second compression load F ₄ to the pipe W in the axial direction, F ₄ '(F _4' is the reaction of F ₄₎ confer. At this time, the load speed is 200 mm / sec. Thus, as shown in FIG.
₂ bulge.

[0034] Thus, even taking larger second width of the heating section W ₂ to equal to or greater than the outer diameter of the pipe W in the second heating step, the buckling position is identified in the first heating section W _1, no variation. Therefore, moldability is stabilized, the expansion of the molding allowance by the second widening of the heating section W _2, was possible bulging in expansion ratio 64%. In this processing method, the same high-frequency coil 1 was used, and the first and second heating steps were performed by adjusting the output and the heating time. And the like. (Example 3)

First, as shown in FIG. 13, a stainless steel pipe W extending in the axial direction is prepared. This pipe W
Is outer diameter 28.6mm, wall thickness 1.2mm, material JIS-
SUS430. This pipe W is attached to a pair of fixed chucks (not shown) of the molding apparatus. In this molding apparatus, a high-frequency coil 4 is provided between both fixed chucks. In this high-frequency coil 4, the center of the coil has a width of 10
mm, and the temperature at the center of the heating can be made 1000 ° C. The pipe W is located in the high-frequency coil 4.

[Heating Step] The high-frequency coil 4 heats the local portion of the outer periphery of the pipe W in the circumferential direction. At this time, the operating frequency is 40 kHz, the heating temperature is a maximum of about 1000 ° C., and the heating time is 1 second. Thus, a 1000 ° C. high-temperature heating section having an axial width l ₃ (10 mm) at the center of the pipe W and a 950 ° C. low-temperature heating section having an axial width l ₄ (12 mm) around the high- temperature heating section.
Forming a Ranaru heating unit W _0.

[Swelling Step] Immediately after the heating step, an axial compressive load is applied to the pipe W. At this time, the load speed is 200 mm / sec. Thus, as shown in FIG. 12, thereby bulging the heating unit W _2. At this time, since the high temperature heating unit <br/> a central portion of the heating section W ₂ is about 1000 ° C., the yield stress of the high temperature heating portion is decreased remote by low temperature heating portion around. For this reason, the buckling position is a high-temperature heating section , and there is no variation. For this reason, the moldability was stabilized, and swelling was possible at a tube expansion rate of 53% due to an increase in the molding allowance due to the widening of the low-temperature heating section . ( Reference Example 2)

First, as shown in FIG. 14, a pipe W of the same type as in the third embodiment is prepared. This pipe W is attached to a pair of fixed chucks (not shown) of the molding apparatus. In this molding apparatus, a high-frequency coil 1 of the same type as in Reference Example 1 is provided between the two fixed chucks, and a seal base 6 fixed on a substrate 5 is provided below the high-frequency coil 1. A circular hole 6 into which the lower end of the pipe W can be inserted
a is recessed, and a ring groove 6b is formed in the peripheral wall of the circular hole 6a.
Are recessed, and an O-ring 7 is provided in the ring groove 6b. The pipe W is located in the high-frequency coil 1 and the circular hole 6 a of the seal base 6.

[Heating Step] In the same manner as in Reference Example 1 , a heating portion W ₀ having an axial width l ₀ (30 mm) is formed in a pipe W by a high-frequency coil 1. "Swelling process" Immediately after the end of the heating process, 10 kgf / c from the upper end of the pipe W
An axial compression load is applied to the pipe W while supplying compressed air of m ² . At this time, the molding allowance is 9 mm, and the load speed is 200 mm / sec. Thus, as shown in FIG. 12, thereby bulging the heating unit W _2.

At this time, the heating section W is heated by the pressure of the compressed air.
Buckling is likely to occur in the center of ₂ , and there is almost no variation. Therefore, moldability is stabilized and the expansion of the molding cost by widening of the heating section W _2, by the compressed air is stretching the material, it was possible bulging pipe expansion ratio of 55%. In addition,
In the conventional hot dieless corrugating method, the material is supplied from the axial direction by compression, so that a slight increase in wall thickness occurs at the bulging portion. Although this increase in wall thickness depends on the use of the corrugated pipe, the conventional hot dieless corrugating method does not actively control the wall thickness, and the expansion required by the product characteristics is not performed. It is difficult to obtain the ideal thickness of the protrusion.

In this regard, in this working method, the increase in the molding allowance acts in the direction of increasing the wall thickness, and the internal pressure acts in the direction of decreasing the thickness of the molding allowance. Therefore, the thickness of the molding allowance is controlled by controlling the internal pressure. be able to. In the working method of the embodiment, the thickness of the bulging portion could be made substantially constant by controlling the pressure of the compressed air.

As a method for applying the internal pressure, a means for injecting a pressure medium comprising a gas, a liquid, a solid, and a mixture thereof into a pipe can be employed. As a specific example of the pressure medium,
Air, carbon dioxide, nitrogen, oil, water, sand, various powders and the like can be adopted. In addition, as a method for applying the internal pressure, a means for applying a water absorbing resin or the like to the inside of the pipe, performing a heating step in a state in which both end surfaces of the pipe are sealed, and utilizing a vaporization pressure of the water absorbing resin may be employed.

It is also possible to combine the processing methods of claims 1 to 3 . Further, in the processing method according to claims 1 to 3 , if the formation and the bulging of the heating portion are performed at other positions, the local portion of the outer periphery of the pipe can be bulged in an uneven shape. In addition, when this processing method and Example 3 were combined,
The effect of improving the expansion rate limit by several percent was seen. ( Reference Example 3)

In Reference Example 3 , 24 k from the upper end of the pipe W
An axial compression load is applied to the pipe W while supplying pressure sand of gf / cm ² . The other configuration is the same as that of the second embodiment . In this case, the expansion rate is increased by expanding the heating allowance W ₀ , and the pressure sand expands the material.
Swelling was possible at 0%. Also, in this processing method,
By the balance between the internal pressure and the compression load, the thickness of the bulging portion could be controlled in the range of 1.0 to 1.4 mm. (Reference Example 4)

First, as shown in FIG. 15, a pipe W of the same type as in the third embodiment is prepared. This pipe W is attached to a pair of fixed chucks (not shown) of the molding apparatus. In this molding apparatus, a high-frequency coil (not shown) is provided between the two fixed chucks, a molding die 2 is provided below the high-frequency coil 1, and a seal base 6 is provided below the molding die 2. . The pipe W is located in the circular hole 6 a of the high-frequency coil, the molding table 2 and the seal table 6.

[Heating Step] As in Reference Example 1 , a heating portion W ₀ having an axial width l ₀ (34 mm) is formed on a pipe W by a high-frequency coil. “Swelling Step” Immediately after the heating step, the pipe W is moved in the axial direction, and the heating part W ₀ is positioned within the molding surface 2 a of the molding die 2.
Close the mold. Then, 10 kgf from the upper end of the pipe W
/ Cm ² while supplying compressed air at an axial pressure to the pipe W. At this time, the molding allowance is 10 mm, and the load speed is 200 mm / sec. Thus, the molding surface 2a
Thereby bulging the heating unit W ₀ while constrained by.

In this case, the expansion ratio was further improved. Reference example
As in FIGS. 1 and 4 , as shown in FIG. 16, when the molding die 8 having the molding surface 8a having a complicated shape was adopted, the surface area of the pipe W could be improved. Note that Japanese Unexamined Patent Publication No.
Japanese Patent No. 259623 discloses a hot bulging method using a mold. However, this method does not apply an axial compressive load to a pipe, and thus has a drawback that it is difficult to achieve a large expansion ratio. .

Also, Japanese Patent Application Laid-Open No. 2-121828 discloses a hot bulging method using a mold, but this method aims at bulging a resin hose. Since it is easy to move, it is almost unnecessary to specify the buckling position when improving the expansion ratio, and this technique cannot be directly applied to the method of corrugating metal pipes.

Furthermore, Japanese Patent Application Laid-Open No. Sho 62-142030 discloses a hydraulic bulging method. The hydraulic bulging method is basically a processing in which a material is deformed by applying a tensile stress to the material. For this reason, the processing limit depends on the elongation characteristics of the material. If the limit is exceeded, a crack, a crack, or the like is generated in the swollen portion. Further, in the hydraulic bulging method, since the processing is performed by the pressure from the inside of the pipe, the material is elongated, and the greater the degree of processing, the more the thickness is reduced.

[0050]

As described in detail above, if the metal pipe is corrugated according to the first to third aspects of the present invention, the configuration of each claim can increase the limit of the expansion ratio .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a pipe and the like in a heating step according to Reference Example 1.

FIG. 2 is a cross-sectional view of a pipe and the like during a swelling step according to Reference Example 1.

FIG. 3 is a cross-sectional view of a pipe and the like at an initial stage of a swelling step according to Reference Example 1.

FIG. 4 is a cross-sectional view of a pipe and the like during a bulging step according to Reference Example 1.

FIG. 5 is a cross-sectional view of a pipe and the like during a heating step according to the first embodiment.

[6] relates to Example 1, it is a cross-sectional view of a pipe or the like during the first bulging step.

[7] relates to Example 1, it is a cross-sectional view of a pipe or the like during the first bulging step.

FIG. 8 is a cross-sectional view of a pipe or the like during a second bulging step according to the first embodiment.

FIG. 9 is a sectional view of a pipe and the like in a first heating step according to the second embodiment.

FIG. 10 is a cross-sectional view of a pipe and the like during a first bulging step according to the second embodiment.

[11] relate to Example 2, a cross-sectional view of a pipe or the like during the second heating step.

[12] relate to Example 2, a cross-sectional view of a pipe after the second bulging process.

FIG. 13 is a cross-sectional view of a pipe and the like in a heating step according to the third embodiment.

FIG. 14 is a cross-sectional view of a pipe or the like during a swelling step according to Reference Example 2 .

FIG. 15 is a cross-sectional view of a pipe or the like during a swelling step according to Reference Example 4 .

FIG. 16 is a cross-sectional view of a pipe during a bulging step according to a modification.

FIG. 17 is a schematic diagram showing tensile stress and compressive stress acting on a pipe.

[Explanation of symbols]

W: pipe 1, 4, high frequency coil W ₀ , W ₁ , W ₂ : heating unit (W ₁ : first heating unit, W ₂ ...)
2nd heating part) 2, 8 ... Mold 2a, 8a ... Molding surface 3 ... Contact jig 3a, 3b ... Contact surface

──────────────────────────────────────────────────続 き Continuing on the front page (72) Shoichiro Nitta 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Shinobu Ishida 1 Toyota Town Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Shinji Kawasaki 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (56) References JP-A-63-157724 (JP, A) JP-A-63-203217 (JP, A) JP-A-1-192425 (JP, A) JP-A-4-91824 (JP, A) JP-A-63-85319 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21D 15 / 06,19 / 08 H05B 6/10 371

Claims (3)

(57) [Claims] A heating step of forming a heating portion by circumferentially heating a local outer peripheral portion of a metal pipe extending in an axial direction; and a pair of inner end faces aligned in the axial direction with an abutting surface. The abutting jig is disposed on the outer peripheral side of the pipe, and the corresponding first contact load is applied to the pipe while striking the corresponding contact surface over the specific position of the heating section. A first swelling step of primary swelling of the heating portion, and releasing contact of the respective contact surfaces with the heating portion to apply a second compressive load to the pipe in the axial direction. And a second swelling step of secondary swelling of the heating section. 2. A first heating step of forming a first heating section by circumferentially heating an outer peripheral portion of a metal pipe extending in an axial direction, and applying a first compression in the axial direction to the pipe. A first swelling step of primary swelling of the first heating section by applying a load; and a second swelling step of heating the sides of the first heating section and the first heating section in a circumferential direction, thereby providing a second swelling step. A second heating step of forming a heating section, and a second swelling step of secondary swelling the second heating section by applying a second compressive load to the pipe in the axial direction. A method of corrugating metal pipes. By wherein heating the outer peripheral part of the metal pipe extending axially in the circumferential direction, and the high temperature heating portion of the highest temperature in a specific position, said at axial opposite ends of the high temperature heating unit High
A heating step of forming a low-temperature heating section lower than the warm-heating section ; and applying the axial compressive load to the pipe without using a mold, thereby buckling the specific position with the high-temperature heating section.
And the high-temperature heating section is larger than the low-temperature heating section.
And a swelling step of swelling the metal pipe at an appropriate degree .