JP6989818B2 - Manufacturing method of metal tube - Google Patents

Description

The present invention relates to a method for manufacturing a metal tube having an O-shaped cross section from a flat metal plate.

Patent Document 1 describes an example of a method for manufacturing a metal tube having an O-shaped cross section from a flat metal plate. This method includes a U-bending step of press-molding a flat plate-shaped metal plate into a U-shaped cross section, and an O-bending step of press-molding the U-shaped metal plate with a pair of upper and lower split molds to form a tubular shape. ing. This is the so-called UO molding method. The width of the flat metal plate (the length between the two ends abutted by the U-bending step and the O-bending step) is set to be equal to the outer peripheral length of the metal tube obtained by the press molding.

Re-table 2013/111308 Gazette

As shown in FIG. 17, in UO molding, when a tubular metal plate a is formed by a split mold in the O bending process, tensile strain is generated on the outer peripheral side of the metal plate a and tensile stress acts on the inner peripheral side. Compressive strain occurs and compressive stress works. When the binding force due to the split mold is removed, the tubular metal plate a shrinks in the circumferential direction on the outer peripheral side and in the circumferential direction on the inner peripheral side as shown in FIG. 18 due to the stress distribution of tension and compression. It grows to. As a result, a large gap is created on the outer peripheral side of the butt end of the tubular metal plate a. When such a large gap is generated, it becomes difficult to laser weld the butt end of the tubular metal plate c, or even in the case where the tubular metal plate c is used without welding, the gap may become a problem in use.

Therefore, the present invention prevents a large gap from being formed at the butt end portion of the obtained tubular metal plate in UO molding.

In order to solve the above problems, the present invention makes the tensile stress on the outer peripheral side of the tubular metal plate zero or close to zero in the O-bending step.

The method for manufacturing a metal tube disclosed here is a method for manufacturing a metal tube having an O-shaped cross section from a flat metal plate.
The U-bending process of press-molding the flat metal plate into a U-shaped cross section,
It is provided with an O-bending step of press-molding a metal plate formed into a U-shape by the above-mentioned U-bending step so as to form a tubular having an O-shaped cross section.
After the O-bending step, a welding step of laser welding the butt end of the metal plate is provided.
In the O-bending step, a pair of split dies having opposite arc-shaped molded surfaces are used, the curved portion of the U-shaped metal plate is received by one split-shaped arc-shaped molded surface, and the other split die is received. The press molding is performed by combining one of the above split molds.
The other split mold has a recess in a portion corresponding to a position where both ends of the U-shaped metal plate are abutted on the arcuate molded surface.
As the flat metal plate, the length between the ends abutted by the press molding in the O bending step is longer than the peripheral length of the annular molded surface formed by combining the pair of split arc-shaped molding surfaces. Using a metal plate
In the O-bending step, the U-shaped metal plate is restrained so as not to cause movement of the material in the longitudinal direction of the metal plate at the butt end portion, and the plate thickness is the other portion at the butt end portion. Press-molded so that it becomes thicker on the outer peripheral side by the depth of the concave portion of the arc-shaped molded surface.
The compressive stress in the circumferential direction over the entire circumference of the tubular metal plate by the O-bending step from the inner peripheral surface of the metal plate toward the outer peripheral side within a range of at least 90% of the plate thickness of the metal plate. Is characterized by causing.

In this manufacturing method, when the metal plate is bent into an O-shaped cross section in the O-bending process, tensile stress is generated on the outer peripheral side of the metal plate until both ends of the metal plate are in a butt state, and the inner peripheral side. Compressive stress is generated in. However, since the length between both ends of the metal plate is longer than the circumferential length of the annular molded surface consisting of a pair of split molds, when the metal plate is subsequently in a state along the arcuate molded surface of the split mold, the split mold Compressive force is applied to the metal plate. At this time, since the outer peripheral side of the metal plate is restrained by the split mold, the inner peripheral surface of the metal plate moves inward. That is, the metal plate is plastically deformed in the direction in which the plate thickness increases inward. Along with this, the portion where the tensile stress is generated on the outer peripheral side of the metal plate behaves as if it recovers elastically, and the tensile stress is released, and eventually the stress state shifts to the compression side.

Then, in the above-mentioned manufacturing method, the circumferential direction is in the range of at least 90% of the plate thickness of the metal plate from the inner peripheral surface of the metal plate toward the outer peripheral side over the entire peripheral length of the tubular metal plate. Causes compressive stress. Therefore, when the binding force due to the split mold is removed from the tubular metal plate, the inner peripheral side extends in the circumferential direction, but the outer peripheral side does not shrink in the circumferential direction.

As mentioned earlier, the thickness of the metal plate increases inward when a compressive force is applied to the metal plate from the split mold, but the increase in the thickness increases the circumference of the inner peripheral surface of the metal plate. Since it is small (less than a comma in%), the increase in compressive stress due to this increase in plate thickness is also small. That is, even if the compressive stress in the circumferential direction is generated in the range of at least 90% of the plate thickness of the metal plate, the compressive stress on the inner peripheral side of the metal plate is only slightly increased. When the force is removed, the elongation in the circumferential direction on the inner peripheral side of the metal plate does not increase so much.

As described above, according to the above manufacturing method, the tubular metal plate extends in the circumferential direction on the inner peripheral side when the binding force due to the split mold is removed, but the amount of elongation is not so large, while the elongation amount is not so large. Since there is almost no shrinkage in the circumferential direction on the outer peripheral side, it is possible to avoid creating a large gap at the butt end of the metal plate.

In a preferred embodiment, the O-bending step causes a circumferential compressive stress over the entire circumference of the tubular metal plate over the entire circumference of the tubular metal plate. As a result, the gap generated at the butt end of the metal plate can be further reduced.

Further, as described above, the manufacturing method includes a welding step of laser welding the butt end portion of the metal plate after the O bending step.
The other split mold has a recess in a portion corresponding to a position where both ends of the U-shaped metal plate are abutted on the arcuate molded surface.
In the O-bending step, the U-shaped metal plate is press-formed so that the plate thickness is thicker on the outer peripheral side by the depth of the concave portion of the arcuate molded surface than the other portions at the butt end portion. ..

A pressing force is applied to the butt end portion of the metal plate in the butt direction by press molding of the metal plate by the split mold. Since the butt end portion is a contact having a small contact area and has a boundary condition in an open state due to the recess, it is easily plastically deformed by the pressurization. The plastically deformed portions at both ends of the metal plate enter the recesses of the arcuate molded surface, so that the thickness of the metal plate becomes thicker at the butt ends.

Therefore, in the laser welding of the butt end portion, the excess wall portion where the plate thickness of the butt end portion is increased is melted by the welding heat to fill the gap. As a result, the joint length of the butt end portion in the plate thickness direction is increased, that is, the joint area is increased, which is advantageous for ensuring the welding strength. In addition, it is advantageous in preventing HAZ (heat-affected zone) cracking that tends to occur in the vicinity of the welded portion.

Further, in the above-mentioned manufacturing method, as described above, in the above- mentioned O-bending step, the above-mentioned metal plate is restrained and press-formed so as not to cause movement of the material in the longitudinal direction of the metal plate at the butt end portion thereof.

By the above restraint, the material is prevented from escaping in the longitudinal direction of the metal plate at the butt end of the metal plate, so that the butt portion is plastically deformed and easily enters the recess of the arcuate molded surface, and the butt end is concerned. It is advantageous for thickening the part.

In the O-bending step of the preferred embodiment,
The first process of receiving the curved portion of the U-shaped metal plate on the arcuate forming surface of one of the pair of split dies.
By bringing the pair of split dies relatively close to each other, the arcuate forming surface of the other split die of the split dies is U-shaped at the ends of the opposing side walls of the metal plate. Second process of contacting,
Due to the further approach of the pair of split molds, the ends of each of the opposing side walls are guided by the arcuate molded surface of the other split mold and abutted over the entire length of the side wall at the innermost portion of the arcuate molded surface. Due to the third process of becoming a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in the same state. It has a fourth process in which the plate becomes tubular,
Since the length between both ends of the flat metal plate is longer than the peripheral length of the annular molded surface formed by combining the pair of split arc-shaped molded surfaces, the tubular metal plate is formed in the fourth process. Generates compressive stress in the circumferential direction.

According to the present invention, in UO forming, as a flat metal plate, the length between both ends abutted by press forming in the O bending step is annular forming in which a pair of split arc-shaped forming surfaces are combined. By using a metal plate longer than the circumference of the surface, at least 90% of the thickness of the metal plate is formed from the inner peripheral surface to the outer peripheral side of the metal plate over the entire circumference of the tubular metal plate. Since the circumferential compressive stress is generated in the range, a metal tube having a small gap at the butt end can be obtained.

The figure which shows the change of the cross-sectional shape from the flat metal plate to the acquisition of a metal tube. FIG. 3 is a perspective view of a first molding die in an opened state in which a U-shaped metal plate is obtained. The perspective view of the mold open state of the 2nd molding die for premolding. The cross-sectional view which shows the state of the metal plate in the middle of molding by the 2nd molding die. The cross-sectional view which shows the state of the final stage of molding of a metal plate by a 2nd molding die. The perspective view of the shape closed state of the 2nd molding die. A perspective view of a metal tube molding die in an opened state. A perspective view of a metal tube molding die in a closed state. The cross-sectional view which shows the intermediate stage of O bending by a metal tube molding die. A cross-sectional view showing that compressive stress is generated in a metal plate in the O-bending process. A cross-sectional view showing a laser welding process of a metal plate after an O-bending process. Sectional drawing of the main part of the split mold which concerns on another embodiment. An enlarged cross-sectional view showing a split mold and a metal plate in the O-bending step of the same embodiment. The enlarged sectional view which shows the laser welding state of the tubular metal plate obtained by the O bending process of the same embodiment. O Cross-sectional view which shows the metal plate restraint means (state before restraint) of a bending process. O Cross-sectional view which shows the metal plate restraint means (constraint state) of a bending process. The figure which shows the stress distribution of the metal plate O-bent molded by the conventional method. The figure which shows the expansion and contraction of the inner peripheral side and the outer peripheral side of the tubular metal plate obtained by the conventional method.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following description of preferred embodiments is merely exemplary and is not intended to limit the invention, its applications or its uses.

As shown in FIG. 1, in the present embodiment, the metal tube 1 is formed by sequentially performing the U bending step A, the preforming step B, the O bending step C, and the welding step from the flat metal plate 5.

<U bending process>
In the U-bending step A, the metal plate 22 having a U-shaped cross section is formed from the flat metal plate 5 by using the first molding die 21 shown in FIG. In the first molding die 21, 23 is a punch and 24 is a die, which are attached to the punch plate 25 and the die holder 26, respectively. By carrying the metal plate 5 onto the die 24 and lowering the punch 23, the metal plate 5 is bent into a U-shaped cross section, and a U-shaped metal having a curved portion 27 and an opposing side wall 28 following the curved portion 27. Obtain plate 22. The obtained U-shaped metal plate 22 has an expanded shape in which the distance between the facing side walls 28 becomes wider toward the end due to the springback.

<Preliminary molding process>
In the preforming step B, the second molding die 31 shown in FIG. 3 is used to incline the opposing side walls 28, which are in the expanded shape of the U-shaped metal plate 22, inward with each other. In the second molding die 31, 33 is a receiving die having an arc-shaped receiving portion 33a for receiving the U-shaped metal plate 22, 34 is a processing die, and 35 is a die plate to which the processing die 34 is attached.

The shape of the concave machined surface of the processing die 34 is substantially triangular, and in order from the opening end side thereof, the facing attracting portion 36, the facing first inclined portion 37 following the attracting portion 36, and the first inclined portion. It is provided with a second inclined portion 38 that follows 37. The facing second inclined portions 38 are connected at the ends so as to form a V-shaped innermost portion 39.

As shown in FIG. 4, when the U-shaped metal plate 22 is received by the die 33 and the processing die 34 is lowered, the facing side walls 28 of the U-shaped metal plate 22 are inserted into the recesses of the processing die 34 from between the invitation portions 36. come in. As the lowering of the processing die 34 progresses, the ends of the side wall 28 come into contact with the first inclined portion 37, and are guided by the first inclined portion 37 to proceed to the second inclined portion 38. Then, the end portions of the side wall 28 reach the V-shaped innermost portion 39 via the second inclined portion 38, and are in a butt state at the innermost portion.

Due to the further lowering of the processing die 34 after the butting, as shown in FIGS. 5 and 6, the U-shaped metal plate 22 has both side walls 28 so as to come into contact with the first inclined portion 37 and the second inclined portion 38. It bulges and deforms to both sides. As a result, the U-shaped metal plate 22 basically has a shape in which the opposing side walls 28 are inclined inward with each other even if there is a springback after the demolding.

<O bending process>
In the O-bending step C, the preformed U-shaped metal plate 22 is formed into a tubular shape having an O-shaped cross section by using the metal tube forming die 41 having a pair of split dies shown in FIG. In the metal tube forming mold 41, 42 is a 10% mold that receives the U-shaped metal plate 22. Reference numeral 43 denotes a 20% mold that press-molds the U-shaped metal plate 22 into a tubular shape in combination with the 10% mold 42 by approaching the 10% mold 42. The split molds 42 and 43 have arcuate molded surfaces 44 and 45 for making the metal plate 22 tubular. The 20% mold 43 is attached to the die plate 46.

When the curved portion 27 of the U-shaped metal plate 22 is received by the arcuate molded surface 44 of the 10% mold 42 and the 20% mold 43 is lowered, the arcuate molded surface 44 of the 20% mold 43 becomes a U-shaped metal. It abuts on the end of the opposite side wall 28 of the plate 22. Then, due to the further descent of the 20% mold 43, the opposite side wall 28s bulge and deform to both outer sides, and as shown in FIG. 8, the double split molds 42 and 43 are combined to form a tubular metal plate (metal). Tube) 40 is formed.

Hereinafter, a specific description will be given with reference to FIG. When the 20% mold 43 descends, its arcuate molded surface 45 comes into contact with the end portions of the opposite side walls 28 of the U-shaped metal plate 22. With the further descent of the 20% mold 43, the end portions of the opposing side wall 28s are guided by the arcuate molding surface 45 of the 20% mold 43 and move toward the innermost part of the molding surface 45, and this movement. It bends inward with it. Then, after the ends of the facing side walls 28 are in a butt state at the innermost part of the molded surface 45 over the entire length of the side wall, the 20% mold 43 further descends, whereby the U-shaped metal plate 22 In, the facing side walls 28 bulge and deform to both outer sides.

<Gap at the butt end>
Here, the flat plate-shaped metal plate 5 shown in FIG. 1 has a width W (the length between both end ends that are in a butt state at the innermost portion of the arcuate molded surface 45 of the 20% mold 43 in the O bending step C). The one that is longer than the peripheral length of the annular molded surface formed by combining the arc-shaped molded surfaces 44 and 45 of the split molds 42 and 43 is used.

Therefore, when the metal plate 22 that has undergone the U bending step A and the preforming step B is bent into an O-shaped cross section in the O bending step, the outer periphery of the metal plate 22 is formed until both ends of the metal plate 22 are in a butt state. Tensile stress is generated on the side, and compressive stress is generated on the inner peripheral side. However, after that, as shown in FIG. 10, when the metal plate 22 is in a state along the arcuate forming surfaces 44 and 45 of the split molds 42 and 43 (note that in FIG. 10, only a part of the split mold 43 side is formed. As shown), since the width W (length between both ends) of the metal plate 22 is longer than the circumferential length of the annular molded surface, the compressive force F in the circumferential direction is applied to the metal plate 22 from the split molds 42 and 43. Join.

Since the outer peripheral side of the metal plate 22 is restrained by the split molds 42 and 43, the inner peripheral surface of the metal plate 22 moves inward. That is, the metal plate 22 is plastically deformed in the direction in which the plate thickness increases inward. Along with this, the portion where the tensile stress is generated on the outer peripheral side of the metal plate behaves as if it recovers elastically, and the tensile stress is released, and eventually the stress state shifts to the compression side.

According to the experiment, when the diameter of the annular molded surface composed of the split molds 42 and 43 is D and the plate thickness of the metal plate 5 is t, the width W of the flat metal plate 5 is the peripheral length (π ×) of the annular molded surface. It was found that when the plate thickness ratio (t / D) to the diameter was longer than D), the circumferential compressive stress Cs was generated in the entire thickness direction of the metal plate 22 as shown in FIG. .. For example, in the case where the diameter D of the annular molded surface is 100 mm and the plate thickness is 2.3 mm, the width W of the flat metal plate 5 is set as follows. That is, the width W is made longer by the dimension of π × t than the peripheral length of the annular molded surface.

W = π × D × (1 + t / D) = π × (D + t) = 102.3 × π
If the width W is excessively increased, buckling occurs in the metal plate 22 in the O bending step. Therefore, it is preferable to set π × D <W ≦ π × (D + 2t).

In this way, if the compressive stress Cs in the circumferential direction is generated in the entire range of the plate thickness of the metal plate 22, the binding force of the split molds 42 and 43 is removed from the tubular metal plate obtained in the O-bending step. At this time, the inner peripheral side extends in the circumferential direction, but the contraction in the circumferential direction on the outer peripheral side is almost eliminated.

Here, when a compressive force is applied to the metal plate 22 from the split molds 42 and 43, the plate thickness of the metal plate 22 increases inward, but the peripheral length of the inner peripheral surface of the metal plate 22 due to the increase in the plate thickness increases. The increase is modest. For example, in the case where the diameter D of the annular molded surface is 100 mm and the plate thickness is 2.3 mm, when the width W is longer than the peripheral length of the annular molded surface by a dimension of π × t, it is roughly estimated that the metal. The plate thickness of the plate 22 increases inward by about 2.3%, but the decrease in the peripheral length of the inner peripheral surface of the metal plate 22 due to the increase is about 0.4% (0.5% or less). be. Therefore, the increase in the compressive stress on the inner peripheral side of the metal plate 22 due to the increase in the plate thickness is also slight. That is, when the binding force of the split dies 42 and 43 is removed, the elongation in the circumferential direction of the inner peripheral side of the metal plate 22 does not become so large.

As described above, when the binding force of the split dies 42 and 43 is removed, the elongation in the circumferential direction of the inner peripheral side of the metal plate 22 is not so large, while the shrinkage in the circumferential direction on the outer peripheral side is almost eliminated. As shown in FIG. 11, the gap 47 generated at the butt end of the obtained tubular metal plate 40 is surely 10% or less of the plate thickness t. That is, it is possible to avoid creating a large gap.

<Welding process>
As shown in FIG. 11, laser L is irradiated toward the butt end portion of the tubular metal plate 40 demolded from the split molds 42 and 43 for welding. Since the gap 47 at the butt end is 10% or less of the plate thickness t, the butt end can be reliably joined by laser welding.

<Another embodiment (thickening of the butt end of the metal plate)>
For this embodiment, only the main parts thereof are shown in FIGS. 12 to 14. As shown in FIG. 12, in the present embodiment, in the O-bending step, a split mold 43 having a recess 48 provided in the innermost portion of the arcuate molded surface 45 on which both side ends of the metal plate 22 are abutted is used. The point is different from the previous embodiment, and the other steps are the same as the previous embodiment. The recess 48 is provided so as to straddle both abutting ends of the metal plate 22.

In the present embodiment, as shown in FIG. 13, in the O-bending step, the ends of the side walls 28 facing each other of the metal plate 22 are in a butt state at the innermost part of the molded surface 45, and the metal plate 22 is further formed by the molded surface. When the state is along the 45, the compressive force F in the circumferential direction is applied to the metal plate 22 as described above. That is, a pressing force is applied to the abutting portions at both ends of the metal plate 22 in the abutting direction. Since the butt end portion is a contact having a small contact area and has an open boundary condition due to the recess 48, it is plastically deformed by the pressurization, and the plastically deformed portion enters the recess 48 of the molding surface 45. .. As a result, the plate thickness of the metal plate 22 is locally increased at the butt end portion. That is, a convex portion 49 corresponding to the concave portion 48 is formed at the abutting end portion of the metal plate 22.

Therefore, as shown in FIG. 14, even if a gap 47 is formed in the butt end portion of the metal plate 22 removed from the split molds 42 and 43, the plate thickness of the butt end portion is formed in the laser welding of the butt end portion. The convex portion 49, which is a surplus portion, is melted by the welding heat to fill the gap 47. As a result, the joint length of the butt end portion in the plate thickness direction is increased, that is, the joint area is increased, which is advantageous for securing the welding strength and also advantageous for preventing HAZ cracking.

Here, the width W1 and the depth d of the recess 48 can be set according to the plate thickness t of the metal plate 22, the size G of the gap 47, and the welding width W2 by the laser.

To explain this point roughly, the size S of the cross-sectional area of the gap 47 can be S = G × t. Considering that the metal having the welding width W2 is melted and solidified by the welding heat, the increase in the plate thickness due to the recess 48 corresponds to the depth d of the recess 48. Therefore, when G × t = W1 × d is established, the gap is established. 47 can be filled with the penetration of the metal plate 22.

Therefore, a recess 48 having a width W1 = W2-G and a depth d = G × t / W1 may be provided on the molding surface 45 of the split die 43.

For example, when the plate thickness of the metal plate 22 is t = 2.3 mm, the size of the gap 47 is G = 0.2 mm, and the welding width is W2 = 1.5 to 2.0 mm, the width W1 = W2-0.2 and depth d = 0.2 × 2.3 ÷ W1 calculation, a recess with a width W of about 1.3 to 1.8 mm and a depth d of about 0.25 to 0.36 mm. 48 will be provided with a molding surface 45.

Here, in the thickening of the butt end portion of the metal plate 22, as shown in FIGS. 15 and 16, the longitudinal direction of the metal plate 22 during press molding (when the metal plate 22 is formed into a tubular shape). It is preferable to provide a restraining means for preventing the material from escaping in the (pipe length direction) direction.

In FIGS. 15 and 16, 51 is a cam slider as a restraining means, and 52 is a cam driver for driving the cam slider 51. Although FIGS. 15 and 16 show one end of the metal tube forming die 41, the cam slider 51 and the cam driver 52 are symmetrically provided at both ends of the metal tube forming die 41.

The cam slider 51 is arranged on both outer sides of the arcuate molded surface 44 in the longitudinal direction of the 10% mold 42. The cam slider 51 is movably supported by the 10% mold 42 in the longitudinal direction, and is springs (in a direction away from the portion where the arcuate molded surface 44 of the 10% mold 42 is formed) outward in the longitudinal direction. It is urged by (not shown).

The cam slider 51 includes a restraint surface 51a that abuts on the end surface of the metal plate 22 received by the arcuate molded surface 44. A cam surface 51b that receives a driving force from the cam driver 52 is provided on the back side of the restraint surface 51a of the cam slider 51.

The cam driver 52 is fixed to the 20% type 43 and protrudes downward. A cam surface 52a that abuts on the cam surface 51b of the cam slider 51 is provided below the cam driver 52. The cam driver 52 descends together with the 20% mold 43, and the cam surface 52a abuts on the cam surface 51b of the cam slider 51 and slides, so that the cam slider 51 slides in contact with the arc-shaped molded surface 44 of the 10% mold 42. Will move toward the formed portion, and the restraint surface 51a will come into contact with the end surface of the metal plate 22.

Hereinafter, a specific description will be given. As shown by arrows in FIG. 15, in the O-bending step, the cam driver 52 moves the cam slider 51 toward the metal plate 22 by lowering the 20% mold 43. As shown in FIG. 9, at the latest, the restraining surface 51a of the cam slider 51 becomes the end surface of the metal plate 22 until the ends of the side walls 28 facing each other of the metal plate 22 are in a butt state at the innermost portion of the molding surface 45. It is in a state of contact (a state shown by a two-dot chain line in FIG. 15).

With the further descent of the 20% mold 43, the facing side walls 28 of the metal plate 22 bulge and deform to both outer sides to be in a state along the arcuate forming surface 45 of the 20% mold 43, and the metal plate 22 A pressing force in the butt direction is applied to both ends of the. In the process of applying this pressing force, as shown in FIG. 16, the cam driver 52 descends from the state of the two-dot chain line so as to be in contact with the back surface of the cam slider 51 (the state shown by the solid line), and the cam slider The restraining surface 51a of the 51 is kept in contact with the end surface of the metal plate 22.

Since the cam slider 51 is provided on both outer sides of the metal plate 22 in the longitudinal direction, the material moves in the longitudinal direction at the butt end when the pressing force in the butt direction is applied to both ends of the metal plate 22. (Escape) is prevented by the restraint surface 51a of the cam slider 51.

Therefore, the butt end portion of the metal plate 22 is plastically deformed by the pressing force so as to fill the recess 48 of the arcuate molded surface 45 of the 20% mold 43. That is, since the restraining means prevents the material from moving in the longitudinal direction of the butt end portion, plastic deformation that fills the recess 48 is likely to occur. Therefore, the convex portion 49 corresponding to the concave portion 48 can be reliably formed at the butt end portion of the metal plate 22.

1 Metal pipe 5 Flat metal plate 21 1st molding mold 22 U-shaped metal plate 27 Curved part 28 Side wall 31 2nd molding mold 41 Metal pipe molding mold 42 10th mold 43 20th split mold 44 Arc-shaped molding surface 45 Arc-shaped molded surface 51 Cam slider (restraint means)
51a Restraint surface

Claims (3)

It is a method of manufacturing a metal tube having an O-shaped cross section from a flat metal plate.
The U-bending process of press-molding the flat metal plate into a U-shaped cross section,
It is provided with an O-bending step of press-molding a metal plate formed into a U-shape by the above-mentioned U-bending step so as to form a tubular having an O-shaped cross section.
After the O-bending step, a welding step of laser welding the butt end of the metal plate is provided.
In the O-bending step, a pair of split dies having opposite arc-shaped molded surfaces are used, the curved portion of the U-shaped metal plate is received by one split-shaped arc-shaped molded surface, and the other split die is received. The press molding is performed by combining one of the above split molds.
The other split mold has a recess in a portion corresponding to a position where both ends of the U-shaped metal plate are abutted on the arcuate molded surface.
As the flat metal plate, the length between the ends abutted by the press molding in the O bending step is longer than the peripheral length of the annular molded surface formed by combining the pair of split arc-shaped molding surfaces. Using a metal plate
In the O-bending step, the U-shaped metal plate is restrained so as not to cause movement of the material in the longitudinal direction of the metal plate at the butt end portion, and the plate thickness is the other portion at the butt end portion. Press-molded so that it becomes thicker on the outer peripheral side by the depth of the concave portion of the arc-shaped molded surface.
The compressive stress in the circumferential direction over the entire circumference of the tubular metal plate by the O-bending step from the inner peripheral surface of the metal plate toward the outer peripheral side within a range of at least 90% of the plate thickness of the metal plate. A method for manufacturing a metal tube, which comprises producing a metal tube. In claim 1,
A method for manufacturing a metal tube, characterized in that a compressive stress in the circumferential direction is generated in the entire range of the plate thickness over the entire circumference of the tubular metal plate by the O-bending step. In claim 1 or 2 ,
In the above O bending process,
The first process of receiving the curved portion of the U-shaped metal plate on the arcuate forming surface of one of the pair of split dies.
By bringing the pair of split dies relatively close to each other, the arcuate forming surface of the other split die of the split dies is U-shaped at the ends of the opposing side walls of the metal plate. Second process of contacting,
Due to the further approach of the pair of split molds, the ends of each of the opposing side walls are guided by the arcuate molded surface of the other split mold and abutted over the entire length of the side wall at the innermost portion of the arcuate molded surface. Due to the third process of becoming a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in a state of being in the same state. It has a fourth process in which the plate becomes tubular,
Since the length between both ends of the flat metal plate is longer than the peripheral length of the annular molded surface formed by combining the pair of split arc-shaped molded surfaces, the tubular metal plate is formed in the fourth process. A method for manufacturing a metal tube, which is characterized in that a compressive stress is generated in the circumferential direction.

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