JP2006272451A - Metal bend having sectional shape for component, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal bend having a sectional shape for components, and its manufacturing method in which the material reduction in the bending is suppressed, a sectional shape deformed in the axial direction is compatibly realized, the cost can be reduced by reducing the man-hour and improving the yield of a stock metal tube, the weight of a pipe after forming the pipe having the sectional shape for components is reduced, the installation space of the pipe can be saved, and an inexpensive stock metal tube such as a ferritic stainless steel tube can be used by suppressing the material reduction. <P>SOLUTION: A metal tube is bent so that the direction X of the axis at one end of the metal tube forms an angle θ of ≥60° with respect to the direction Y of the axis at the other end of the metal tube. The hydraulic pressure is applied in the metal tube, and the hydroforming to apply the pushing force in the axial direction is performed on at least one end of the metal tube so that the metal tube has the sectional shape for components. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a metal bent pipe having a cross-sectional shape for parts used as piping for automobiles, electrical equipment, etc., in addition to air conditioning equipment and various plants, a manufacturing method thereof, and a bending method of a metal pipe in the manufacturing process thereof. .

In addition to air-conditioning equipment and various plants, a bent metal pipe having a cross-sectional shape peculiar to the pipe may be used as a pipe for an automobile or an electric device. An example of a metal curved pipe having such a unique cross-sectional shape is shown in FIG. (A) is a top view, (b) is a side view, (c) is each sectional drawing.
For example, as shown in FIG. 11, two metal bent tubes having such a unique cross-sectional shape are conventionally prepared by press-molding the metal plate 10 and then trimming to form the flange 20 portion. The flange 20 is welded so that the front and back surfaces are opposed to each other so that the whole is substantially tubular. Although not shown in the drawing, there is a case where a portion of the overlap margin 30 formed by welding is trimmed and removed.

However, such a manufacturing method with many man-hours has a problem that it is very time-consuming and the cost is higher than anything.
Furthermore, since it is necessary to perform trimming after press forming, generation of trimming scraps (scrap) is unavoidable, and the yield of the metal sheet is poor, which also increases the cost.

  In addition, since there is a flange 20 for welding and an overlap margin 30, a pipe after being formed into a metal bent pipe having such a unique cross-sectional shape (hereinafter, a metal bent pipe having a cross-sectional shape for parts) In addition to the above-mentioned air conditioning equipment and various plants, the design of automobiles, electrical equipment, etc. may be affected, such as being heavier than necessary or being too large and requiring additional installation space. As described above, trimming and cutting off the flange 20 after welding has a problem that leads to high costs due to an increase in man-hours.

In addition, various characteristics are required for the various pipes described above. That is, in order not to be deformed or broken under the usage environment, in addition to strength, corrosion resistance, heat resistance, wear resistance, and the like may be required.
When designing various types of piping as described above, increase the thickness of the piping so that it can withstand even if there is an effect of thinning due to corrosion or wear, or a decrease in strength due to temperature rise. In order to ensure durability. That is, the material to be used is determined from the characteristics required for the piping, such as corrosion resistance and heat resistance, but once the material is determined, the strength at the highest temperature to be used is also determined, the above-mentioned corrosion and Even if there is an influence of thinning due to wear or an influence of strength reduction due to temperature rise, the lower limit of the plate thickness that can be sufficiently endured is also determined.

Then, it is most important that the various pipes designed as described above are molded so as not to fall below the lower limit of the plate thickness at the manufacturing stage. In other words, when thinning occurs due to molding, it is important to reduce the thinning as much as possible so that it does not fall below the lower limit of the plate thickness.
When manufacturing bent metal pipes with a cross-sectional shape for parts, the use of various metal pipes including steel pipes as the material reduces the number of parts and reduces the need for welding. Since the yield of the metal tube is improved, there is a possibility of cost reduction.

An example of a metal tube in which the axial direction X at one end forms an angle θ of 60 degrees or more with the axial direction Y at the other end is shown in FIG. 12, but a bending process of 60 degrees or more, particularly a 180 degree bending process is performed. In so-called U-shaped bending, thinning occurs along with such bending. And the thinning becomes so remarkable that the curvature radius of bending becomes small.
In addition, if the pipe is expanded by machining in order to obtain a metal bent pipe having a cross-sectional shape for a part, it is necessary to insert a core metal having a complicated shape to build the cross-sectional shape.

Because of such problems, the various pipes as described above are rarely used for mass production on an industrial scale.
By the way, as a technique of using a steel pipe as a material and performing hydroforming so as to have an irregular cross-sectional shape, a method of devising the shape of a mold as in Patent Document 1, Patent Document 2, and Patent Document 3 Thus, there has been a method for defining the mechanical properties and surface properties of the steel pipe used for hydroforming.

Here, Patent Document 4 and Patent Document 5 are cited as prior arts related to rotational pulling that appear in the best mode for carrying out the invention described later.
JP 2000-343141 A Japanese Patent Laid-Open No. 10-175027 JP 2000-17329 A JP 55-128324 A JP 5-96332 A

However, all assume that hydroforming is performed on a straight pipe. Thus, hydroforming is the object of the present invention, as shown in FIG. 12, the axial direction X at one end of the curved metal tube is 60 degrees with the axial direction Y at the other end of the curved metal tube. It has not yet been applied to the formation of a metal bent tube having an irregular cross-sectional shape having the above angle θ.
In addition, austenitic stainless steel pipes typified by SUS304 are often used for applications that require corrosion resistance or heat resistance as materials for various pipes as described above. Recently, although it is relatively inexpensive, various studies so far have brought corrosion resistance and workability closer to austenitic stainless steel pipes. It has come out.

However, although corrosion resistance and workability have approached SUS304, ferritic stainless steel still requires some improvement in workability such as elongation, and for applications that require high workability, Difficult to use.
The present invention has been made to solve the above-described problems of the prior art, and relates to a metal bent pipe having a cross-sectional shape for a part and a method for advantageously manufacturing the same.

  The present invention also relates to a method of bending a metal tube before hydroforming in the manufacturing process.

The gist of the present invention is as follows.
(1) After bending the metal tube so that the direction of the axis at one end of the metal tube forms an angle of 60 degrees or more with the direction of the axis at the other end of the metal tube, A cross-sectional shape for a component is characterized in that the metal tube has a cross-sectional shape for a component by applying hydroforming that applies a pressure and an axial pushing force to at least one end of the metal tube. Metal bent pipe with.
(2) A bent metal pipe having a cross-sectional shape for a part, wherein the bending process of (1) is performed separately so that one bending angle is 70 degrees or less.
(3) The bent metal pipe having a cross-sectional shape for parts according to (1) or (2), wherein the metal pipe is a ferritic stainless steel pipe.
(4) The metal bent pipe having a cross-sectional shape for a component according to (3), wherein the ferritic stainless steel pipe has an r value of 1.3 or more.
(5) When bending the metal tube so that the direction of the axis at one end of the metal tube forms an angle of 60 degrees or more with the direction of the axis at the other end of the metal tube, two or more times The method of bending a metal tube is characterized in that bending is performed separately.
(6) The method for bending a metal pipe according to (5), wherein the bending is performed so that the bending angle per bending of the plurality of times is 70 degrees or less.
(7) Bending is performed by rotational pulling so that the axial pressing force in the second and subsequent bending processes among the multiple bending processes is not less than the axial pressing force in the first bending process. The method for bending a metal tube according to (5) or (6), wherein:
(8) The metal tube according to any one of (5) to (7), wherein the metal tube before bending used for bending the metal tube has an r value of 1.3 or more. Bending method.
(9) Bending the metal tube so that the direction of the axis at one end of the metal tube forms an angle of 60 degrees or more with the direction of the axis at the other end of the metal tube; A cross-sectional shape for a component, wherein the metal tube has a cross-sectional shape for a component by applying hydroforming that applies a pressure and an axial pressing force to at least one end of the metal tube. A method for manufacturing a metal bent pipe.
(10) A method of manufacturing a metal bent tube having a cross-sectional shape for a part, wherein the bending process of (9) is performed separately so that one bending angle is 70 degrees or less.
(11) The method for producing a bent metal pipe having a cross-sectional shape for parts according to (9) or (10), wherein the metal pipe is a ferritic stainless steel pipe.
(12) The method for producing a bent metal pipe having a cross-sectional shape for parts according to (11), wherein the ferritic stainless steel pipe has an r value of 1.3 or more.

  According to the present invention, by combining bending and hydroforming, it is possible to achieve both the reduction in thickness and the realization of the cross-sectional shape for parts, reduce man-hours, and reduce the cost by improving the yield of the material metal tube. This contributes to reducing the weight of the pipe after molding into a bent metal pipe with a cross-sectional shape for use and saving installation space. In addition, since metal thinning can be suppressed, inexpensive metal pipes such as ferritic stainless steel pipes can be used.

(Metal bent pipe with cross-sectional shape for parts)
FIG. 1 shows one embodiment of a method for producing a metal bent tube having a cross-sectional shape for a component according to the present invention.
In the present invention, “having a cross-sectional shape for a part” means that when a certain point is taken at any part of a bent metal tube, the direction of the central axis at that point is taken as a normal line. This means that the cross section of the bent metal pipe cut by a virtual plane is a non-simple shape designed to satisfy the function as a part. Non-simple means that a metal tube having a cylindrical cross-section is simply bent or is not flattened.

The material used is a ferritic stainless steel pipe made of SUS430, which is a typical ferritic stainless steel. The shape of the cross-section of each part of the ferritic stainless steel pipe after the final processing including hydroforming is the same as that shown in FIG.
First, bend the ferritic stainless steel pipe. In the present embodiment, the bending radius of curvature is 1D (bending radius of curvature = the diameter of the ferritic stainless steel pipe material), and after bending 180 degrees, the transferred inner shape of the outer shape to be processed The ferritic stainless steel pipe is set to a die 40 having a shape, and a hydraulic pressure is applied to the ferritic stainless steel pipe, and at least one end of the ferritic stainless steel pipe is subjected to hydroforming to apply an axial pressing force. Ensure that the stainless steel pipe has a cross-sectional shape for the part.

The series of manufacturing steps will be described in further detail below.
(Metal pipe bending method)
The target of the shape after bending is the shape of the ferritic stainless steel pipe after the final processing including hydroforming, and the axial direction X at one end is 180 degrees with the axial direction Y at the other end. First, bending is performed at 180 degrees. In the present embodiment, the bending process is performed by a method called rotational pulling, which will be described later. The rotary pulling and bending machine used here can bend up to 90 degrees at a time because of its mechanical specifications. Therefore, as shown in Fig. 1 (a), the 180 degree bending process is divided into 90 degrees twice. It takes the least amount of work. However, in theory, bending of a ferritic stainless steel pipe after final processing, including hydroforming, can be performed at a maximum of 180 degrees at a time, as long as the degree of thinning of the portion where bending was performed is allowed. It can also be done.

On the other hand, in FIG. 1 (b), the bending process of 180 degrees is performed in three steps of 60 degrees, but as the number of bending processes is increased in this way, the angle of one bending process becomes smaller. Further, it is possible to suppress the thinning of the portion where the bending of the ferritic stainless steel pipe after the final processing including the hydroforming is performed.
However, as the number of times of bending increases, the man-hour increases and the production efficiency decreases. From the viewpoint of suppressing this, it is preferable that bending of 180 degrees is completed in three times or less, and the angle is not necessarily equal. There is no need to bend each step, for example, 70 degrees, 55 degrees, and 55 degrees may be performed. For this reason, the bending process is preferably performed so that the bending angle at one time is 70 degrees or less.

  Here, the rotational pulling bending described above will be described. FIG. 2 shows an outline of the rotary bending machine used here. In FIG. 2, 1 is a bending die that bends the metal tube 10, 2 is a clamp that rotates the metal tube 10 and rotates together with the bending die 1, and 3 is a mandrel that is inserted into the metal tube 10. It has a plurality of balls 5 at its tip and is inserted by a shaft 6. 7 is a holding die configured to be movable along with the movement of the metal tube 10, 8 is a wiper member for suppressing wrinkles at the inner bent portion of the metal tube 10, and 9 is a back booster that performs axial pushing of the end of the metal tube 10. It is.

Bending is performed by rotating the bending die by a desired angle while pushing up the metal tube 10 by the clamp 2. At this time, the back booster 9 pushes the end of the metal tube 10 so that the metal tube 10 is smoothly pulled into the bending die 1 along with the bending process.
When hydroforming is performed after bending as described above, a metal bent tube having a cross-sectional shape for parts, which is another aspect of the present invention, can be manufactured. Prior to hydroforming, Annealing may be performed. This is because the ductility is restored by annealing.
(Manufacturing method of bent metal pipe with cross-sectional shape for parts)
Returning to FIG. 1, FIG. 1 (c) shows the hydroforming. In hydroforming, a ferritic stainless steel pipe after bending at 180 degrees is set in a mold having a transfer inner shape of the outer shape to be processed, and hydraulic pressure is applied to the ferritic stainless steel pipe and the ferrite stainless steel pipe is applied. An axial pushing force is applied to at least one end of the stainless steel pipe. In order to be able to set the ferritic stainless steel pipe, which is the raw material, the mold 40 is divided as shown in the lower figure (side view) of FIG. After the steel pipe is set, it is fastened so that it does not open due to the hydraulic pressure and the axial pressing force acting on it.

By applying hydraulic pressure to the ferritic stainless steel pipe, the ferritic stainless steel pipe swells and comes into contact with the mold that has been pre-processed into the transferred inner shape of the outer shape to be processed. At the same time, axial pressing force is applied to both ends of the ferritic stainless steel pipe.
By applying the axial pushing force, the thinning that occurred during the 180 degree bending process is prevented from further progressing, and the compression by the axial pushing reduces the thinning during the 180 degree bending process. A portion of the ferritic stainless steel pipe that is the material is supplied to the portion where the occurrence of this occurs, whereby the thinning can be suppressed or compensated for the thinning.

  However, excessive axial pushing causes buckling of ferritic stainless steel tubes. It is important to appropriately adjust the relationship between the hydraulic pressure and the axial pushing force.

The case where the method of this invention is applied to manufacture of the U-shaped tube shown in FIG. 10 is demonstrated below. The material is a steel pipe made of ferritic stainless steel SUH409 with a diameter of 50 mm, a wall thickness of 2 mm (precisely 1.963 mm), and a length of 500 mm, a Hi-r material (r value = 1.3) and Lo- Two kinds of r materials (r value = 1.0) were used.
FIG. 3 shows the results of measuring the thickness of the outer periphery of the bend, that is, the degree of thinning, when the number of bendings is variously changed using the Hi-r material. . A is divided into 90 degrees twice, B is divided into 60 degrees three times, and C is divided into 45 degrees four times and 180 degrees each.

In all cases, bending was performed at 180 degrees, but it can be seen that there are minimum portions of the plate thickness corresponding to the number of bending times. And among the minimum plate thickness of each minimum location, C is the thickest, and becomes thin in order of C>B> A. That is, it can be seen that as the number of times of bending increases, the minimum plate thickness increases, and the reduction in thickness due to bending at 180 degrees is suppressed.
Further, FIG. 4 shows the plate thickness distribution of the outer periphery of bending when the bending process of 180 degrees with the Hi-r material and the Lo-r material is performed in three steps of 60 degrees. Hi-r material has a larger minimum thickness. That is, it can be seen that the higher the r value of the material, the smaller the thickness reduction due to the bending process of 180 degrees.

FIG. 5 shows the plate thickness distribution of the outer periphery of the bending when the axial pushing force by the back booster 9 is changed during bending. It can be seen that the greater the axial pushing force, the greater the plate thickness ratio to the metal tube before bending, and the reduction in thickness is suppressed.
Figure 6 shows the first bend (0-60 degrees), the second (60-120 degrees), and the third (120-180 degrees) when 180 degrees are bent three times at 60 degrees. In this bending, the axial pushing force at which the clamp 2 slips and the thickness of the outer periphery of the bending are examined. The measurement point of the plate thickness is <1> at the center Z of the outer periphery of the bend appearing in FIG.

  In the second and third bends, the slip limit is almost the same, but in the first bend, the slip limit is low and the clamp 2 slips even with a relatively small axial force. . The straight pipe is easy to slip at the start of the first bend, whereas the metal pipe 10 is already bent to some extent at the start of the bend in the second and third bends. This is because it is difficult to slip. When the clamp 2 slips, the axial pushing force does not act effectively, and the thinning increases.

  From the above results, it is possible to suppress the thinning as the axial pushing force is large in the range where slip does not occur, and the first bending is more likely to generate slip than the second and subsequent bendings, so it is necessary to set the axial pushing force low. I understand that there is. That is, when the bending process is performed in a plurality of times, the axial pressing force after the second bending process among the bending processes performed in a plurality of times is the axial pressing force in the first bending process. It can be seen that it is effective to suppress the thinning to avoid lowering.

Here, the story changes, but in FIG. 7, when the bending process of 180 degrees is performed in three steps of 60 degrees, hydroforming is performed and the U-shaped tube shown in FIG. 10 is manufactured. The results of the hydraulic pressure and axial pressing conditions and the success or failure of molding are shown.
The diagram of FIG. 7 is broadly divided into a formable region and other unsuitable regions, and the unsuitable regions are further divided into a forming force insufficient region, a rupture region, and a buckling region, respectively. If the amount of axial push is increased too much, buckling will occur, particularly when the hydraulic pressure is low. When the axial push amount is relatively small, it can be seen that if the hydraulic pressure is low, the outer shape to be machined cannot be obtained due to insufficient molding force, and conversely, if the hydraulic pressure is too high, rupture occurs. Therefore, the optimum hydroforming can be performed by adjusting both the hydraulic pressure and the shaft push.

  In the case where hydroforming is performed under the conditions of hydraulic pressure and axial pressing corresponding to the points a to p in the formable region in FIG. 7, the plate thicknesses at the center of the bending outer periphery and the center of the bending side line (see FIG. Thickness measurement points are shown) after 180 degree bending and after hydroforming. The results are shown in Table 1.

  From Table 1, it can be seen that at the measurement point <1>: the center of the outer periphery of bending, the thinning by hydroforming is smaller than the thinning by bending at 180 degrees. This is due to the reason described below. The bending outer peripheral part is the most likely to be thinned by 180 degree bending, but this bending outer peripheral part is restrained by pressing the Z part in FIG. Thinning is suppressed. In hydroforming, conversely, thinning tends to occur at the side line W where the force does not work in the direction pressed against the mold. That is, in the manufacturing method of the present invention, the most prone portion of the thinning does not coincide between bending and hydroforming, when the final shape of the ferritic stainless steel pipe after the end of processing is reached. This makes it possible to suppress thinning.

As described above, the embodiments of the present invention are not limited to those described above.
For example, a metal bent tube having a cross-sectional shape for a component of the present invention is intended for a tube in which the direction of the axis at one end of the metal tube forms an angle of 60 degrees or more with the direction of the axis at the other end of the metal tube. However, if the direction of the axis at one end of the metal tube forms an angle of 60 degrees or more with the direction of the axis at the other end of the metal tube, two-dimensional processing is performed. The present invention is not limited to the case where the axial direction is in the same virtual plane as the axial direction at the other end of the metal tube. Hydroforming is performed after two-dimensional bending, and then three-dimensional processing is performed, or hydroforming is performed after three-dimensional bending. As a result, as shown in FIG. 9, when the direction of the axis at one end of the metal tube is not in the same virtual plane as the direction of the axis at the other end of the metal tube, The angle formed by the direction and the direction of the axis at the other end of the metal tube refers to an angle θ formed by both axes when one of the axes is virtually translated and intersected. .

  In addition, as a method of bending, rotary pull bending, which has been widely used as a method that is relatively excellent in mass productivity, has been taken as an example, but press bending (also referred to as pressing bending), tensile bending (also referred to as pressing bending), roll Any known bending method such as bending or high-frequency local heating bending can be used, and an optimal bending method may be selected and used as appropriate according to the material, product dimensions, and shape.

  Furthermore, the shape of the cross section of each part of the metal curved pipe having a cross section shape for parts is not limited to that shown in FIG. 10, and the cross sectional dimension of the corresponding part of the mold is larger than the diameter of the raw pipe. If the bent metal tube cannot be set in the mold as it is, such as where there is a small part, either after crushing the bent metal tube appropriately, set it in the die, or It is also possible to set while crushing with the fastening force.

Furthermore, in the above-described embodiment, the axial pushing force is applied to both ends of the ferritic stainless steel pipe. However, depending on the outer shape, it is not always necessary to apply the axial pushing force to both ends. It is sufficient to apply an axial pushing force to the surface.
Finally, the present invention can be applied not only to ferritic stainless steel pipes but also to carbon steel and all metal pipes other than steel.

It is a figure which shows one Embodiment of the manufacturing method of the metal curved pipe with the cross-sectional shape for components of this invention. It is a figure which shows the outline | summary of the rotary draw bending machine used for the bending process of a metal pipe before performing hydroforming in the manufacture process of the metal bent pipe with the cross-sectional shape for components of this invention. It is a figure which shows how the grade of the thinning of a bending outer peripheral part changed when the frequency | count of bending was changed variously by the manufacturing method of the metal curved pipe with the cross-sectional shape for components of this invention. It is a figure which compares and shows the plate | board thickness distribution of a bending outer peripheral part at the time of carrying out 180 degree | times bending process by 60 degree | times 3 times by Hi-r material and Lo-r material. It is a figure which shows the plate | board thickness distribution of a bending outer peripheral part at the time of changing axial pushing force. Clamp in the first (0-60 degrees), second (60-120 degrees), and third (120-180 degrees) bends when bending 180 degrees by 60 degrees 3 times It is a figure which shows the axial pushing force of the limit which slips, and the plate | board thickness of a bending outer peripheral part. Shows the results of hydraulic pressure and axial pushing conditions, and the success or failure of molding when hydroforming and U-shaped tube manufacturing after performing 180 degree bending in 3 steps of 60 degrees FIG. It is a figure which shows the position of the measurement point of the board thickness of a bending outer peripheral part center and a bending side line part center. It is a figure which shows another example of the metal curved pipe with the cross-sectional shape for components of this invention. It is a figure which shows the example of the metal bending pipe which has the cross-sectional shape for components. It is a figure which shows the manufacturing method of the conventional metal curved pipe with the cross-sectional shape for components. It is a figure which shows an example of the metal tube which makes the direction of the axis | shaft in one end the angle of the axis | shaft in the other end, and 60 degrees or more.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bending die 2 Clamp 3 Mandrel 4 Mandrel main body 5 Ball 6 Shaft 7 Holding die 8 Wiper member 9 Back booster 10 Metal plate, metal pipe 20 Flange 30 Overlay 40 Mold x Axial direction X Direction of axis at one end Y Other end Axial direction at
Z part pressed against the mold W side line part θ The angle formed by the direction of the axis at one end of the metal tube and the direction of the axis at the other end of the metal tube

Claims (12)

After bending the metal tube so that the axis direction at one end of the metal tube forms an angle of 60 degrees or more with the axis direction at the other end of the metal tube, hydraulic pressure is applied to the metal tube. And a metal curve having a cross-sectional shape for a component, wherein the metal tube has a cross-sectional shape for a component by performing hydroforming to apply an axial pushing force to at least one end of the metal tube. tube. The metal bending tube having a cross-sectional shape for a part, wherein the bending process according to claim 1 is performed separately so that a single bending angle is 70 degrees or less. 3. The bent metal pipe having a cross-sectional shape for parts according to claim 1, wherein the metal pipe is a ferritic stainless steel pipe. 4. The bent metal pipe having a cross-sectional shape for parts according to claim 3, wherein the ferritic stainless steel pipe has an r value of 1.3 or more. When bending the metal tube so that the axis direction at one end of the metal tube forms an angle of 60 degrees or more with the axis direction at the other end of the metal tube, it is divided into two or more times. A method of bending a metal tube, characterized by bending. 6. The method of bending a metal tube according to claim 5, wherein the bending is performed so that the bending angle per bending of the plurality of bendings is 70 degrees or less. The bending process shall be based on rotational pulling, and the axial pressing force in the second and subsequent bending processes should not be less than the axial pressing force in the first bending process. The method for bending a metal tube according to claim 5 or 6, wherein the metal tube is bent. 8. The metal pipe bending method according to claim 5, wherein the metal pipe before bending used for bending the metal pipe has an r value of 1.3 or more. After bending the metal tube so that the axis direction at one end of the metal tube forms an angle of 60 degrees or more with the axis direction at the other end of the metal tube, hydraulic pressure is applied to the metal tube. And a metal curve having a cross-sectional shape for a component, wherein the metal tube has a cross-sectional shape for the component by performing hydroforming to apply an axial pushing force to at least one end of the metal tube. A method of manufacturing a tube. 10. A method for producing a metal bent tube having a cross-sectional shape for a part, wherein the bending process according to claim 9 is performed separately so that a single bending angle is 70 degrees or less. The method for producing a bent metal pipe having a cross-sectional shape for parts according to claim 9 or 10, wherein the metal pipe is a ferritic stainless steel pipe. 12. The method for producing a bent metal pipe having a cross-sectional shape for parts according to claim 11, wherein the ferritic stainless steel pipe has an r value of 1.3 or more.

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