JP2001058264A - Connection method for tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve joining strength and the external appearance of a joining part and to facilitate positioning by internally fitting a barlike connection core to a second tube, exposing the cut face of the core slightly more than the cut face of the second tube, connecting the core to the second tube, abutting the cut face of the core on the side face of a first tube and welding the surrounding of the abutted part. SOLUTION: A through hole 4 is preferably formed to the side face of a second tube 2. A tubular connection core 3 is internally fitted into a second tube 2 and is slightly exposed from the cut face of the second tube 2. Then, through a through hole 4, the second tube 2 and the tubular connection core 3 are tack-welded, the cut face of the tubular connection core 3 is abutted on the side face of a first tube 1, the abutting outer peripheral part are welded. One end of a planar connection core is abutted on the side face of a first tube and is welded there, the planar connection core is externally fitted into a second tube 2, the cut face and side face of the first tube 1 may be welded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for connecting pipes in bicycles and similar vehicles.

[0002]

2. Description of the Related Art In a bicycle and a similar vehicle (for example, a tricycle, a motorcycle, a rear car, etc.), a joint structure of pipes constituting a vehicle body is required to have sufficient strength and rigidity, and to be used for various vehicles. Widely used depending on the application.

[0003] Conventionally, the connection of each pipe member in a pipe is generally performed by a method in which the pipes are butt-welded and joined together, or a method in which the pipes are welded and joined together through a joint.

In the case of welding and joining, there are a joining method by brazing and a joining method by arc welding. However, the welding operation requires manual skill because it is performed manually, and requires a long time for joining. In addition, since the joint portion of the pipe member is exposed to a high temperature for a long time, there is a problem in work efficiency and material quality, such as deterioration of the vicinity of the joint portion and decrease in joint strength.

[0005] In order to solve such a problem, various structures and connection methods have been devised with respect to the joining of pipe members, particularly for securing the joining strength.

FIG. 6 is a sectional view of a conventional pipe joint structure using an auxiliary pipe. In the figure, 1 is the first
Pipe 2 is a second pipe. Reference numeral 10 denotes an auxiliary pipe having an outer diameter slightly smaller than the inner diameter of the second pipe 2.
Reference numeral 11 denotes a weld metal formed by arc welding, and 12 denotes a weld metal formed by resistance welding.

[0007] A method for manufacturing the pipe joint structure thus configured will be described. First, the cut surface of the auxiliary pipe 10 is abutted against the side surface of the first pipe 1, and the contact portion between the inner diameter of the auxiliary pipe 10 and the first pipe 1 is joined by the welding metal 11 by arc welding. Next, the second pipe 2 is extrapolated to the auxiliary pipe 10, the cut surface of the second pipe 2 is abutted against the side surface of the first pipe 1, and the contact portion between the outer peripheral portion of the second pipe 2 and the first pipe 1 is determined. Joining is performed by resistance welding with the welding metal 12.

Further, as another joining structure, there is a pipe connecting method as described below. FIG. 7 shows a conventional pipe joint structure using gussets. In the figure, 1 is the first
Pipe 2 is a second pipe. Reference numeral 13 denotes a gusset having a cut surface that abuts the first pipe 1 and the second pipe 2.

A method of manufacturing the pipe joint structure thus configured will be described. First, the second pipe is brought into contact with the side surface of the first pipe 1, and the contact part is welded. Next, the cut surface of the gusset 13 is brought into contact with the first pipe 1 and the second pipe 2, and the contact portions are welded.

In addition to the pipe connection method described above,
The side surface of the pipe is brought into contact with the cut surface of the second pipe, and the first
A method of connecting a pipe obtained by extrapolating another pipe to the contact surface between the pipe and the second pipe, or forming a tapered portion in which both ends of the pipe expand toward the tip, and forming one end in the tapered portion. There are various pipe connection methods, such as a pipe connection method in which an auxiliary pipe having a similar taper portion is externally fitted and the taper portions are bonded to each other with an adhesive.
In any of the methods, by using the auxiliary member, it is possible to strengthen the joint between the first pipe and the second pipe.

[0011]

However, in the conventional pipe connection method, for example, in the joined body using the auxiliary pipe shown in FIG. 6, the side surface of the first pipe 1 and the second pipe 2
However, since welding is performed only at the portion where the cut surface abuts, there is a problem that the welding area is small and the joining strength is weak. Further, when joining the pipes, it is difficult to position the pipes, and there is a problem that variations in product accuracy occur. Further, in the joined body of the pipe using the gusset of FIG. 7 or the joined body in which another pipe is extrapolated to the joining surface of the pipe, the joining is strengthened, but the appearance is complicated and a clean finish cannot be obtained. . Further, when pipes are welded to each other, there is a problem that welding distortion occurs due to thermal influence, and a large amount of labor is required for repair and repair.

As described above, in the conventional pipe connection method, since only the periphery is welded, the joining strength is low. Further, if the joining is strengthened by using another pipe, the structure becomes complicated, so that However, there is a problem that the finish at the time of welding is not good in appearance.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of connecting pipes which can improve the joining strength, have a good appearance at the joint portion of the pipe, and can facilitate positioning at a predetermined position.

[0014]

In order to solve this problem, a pipe connecting method according to the present invention is designed so that a cut surface of a rod-shaped connecting core is slightly exposed from a cut surface of a second pipe. Until the connection core is inserted into the second pipe, the connection core and the second pipe are connected, and the cut surface of the connection core and the side surface of the first pipe are in contact with each other. Then, the connection core and the first pipe are connected by welding around the contact portion.

The connection between the connecting core and the second pipe is performed by forming a through hole in a side surface of the second pipe, and inserting the connecting core into the second pipe to connect the through hole to the second pipe. It is preferable that the side walls of the connection core are welded through the through holes in a state of being overlapped.

Further, in the pipe connecting method according to the present invention, one end of a plate-shaped connecting core is brought into contact with a side surface of the first pipe, and the periphery of the contacting portion is welded to thereby form the connecting pipe. Connecting the core and the first pipe, extrapolating the second pipe to the flat connecting core, and bringing the cut surface of the second pipe into contact with the side surface of the first pipe, The connection core is connected to the second pipe by welding a contact portion.

Further, in the pipe connecting method according to the present invention, one end of the connecting core having a cross-shaped cross section is brought into contact with the side surface of the first pipe, and the periphery of the contact portion is welded, whereby the connection is made. Connecting the core and the first pipe, extrapolating the second pipe to the connecting core having a cross-sectional shape in cross section, and bringing the cut surface of the second pipe into contact with the side surface of the first pipe; The connection core and the second pipe are connected by welding the contact portion.

The connecting core has a semi-spherical concave portion from the center point of the cross section of one end of the connecting core toward the front end of the cross section, and the front end of the concave portion is chamfered. Preferably, the other end of the child is connected to a side surface of the first pipe.

The connection between the connecting core and the second pipe is formed by cutting out a through hole from a cut surface of the second pipe, and when connecting the second pipe to the connecting core. To
It is preferable that the connection core and the second pipe be connected by holding the connection core in the through hole and welding a periphery of the through hole.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) Hereinafter, Embodiment 1 corresponding to claims 1 and 2 of the present invention will be described with reference to FIG. FIG. 1 shows a pipe joint structure using a pipe-shaped connection core 3 according to Embodiment 1 of the present invention. FIG. 1A shows a state in which the pipe-shaped connection core 3 is to be inserted into the second pipe 2. FIG. 1B is a view similar to FIG.
2 shows a structure in which the above structure is joined to the side surface of the first pipe 1.

In FIG. 1, reference numeral 1 denotes a first pipe constituting a main skeleton mainly called a head pipe. Reference numeral 2 denotes a second pipe serving as various branch pipes. Reference numeral 3 denotes a pipe-shaped connecting core for connecting the first pipe 1 and the second pipe 2. Reference numeral 4 denotes a through hole provided on a side surface of the second pipe 2 for temporarily fixing the second pipe 2 and the pipe-shaped connecting core 3.

A method of manufacturing the pipe joint structure thus configured will be described. First, a through hole 4 is formed in advance on a side surface of the second pipe 2 in which the pipe-shaped connecting core 3 is inserted. The size of the through hole 4 is arbitrary, and may be provided at any location as long as the pipe-shaped connecting core 3 and the side surface of the second pipe 2 overlap. Next, a pipe-shaped connection core 3 having an outer diameter slightly smaller than the inner diameter of the second pipe 2 is inserted into the cut surface of the second pipe 2 until the core 3 is slightly exposed. That is, although the connection core 3 is inserted into the second pipe 2, the connection core 3 is not completely inserted.
Stop the insertion with slightly exposed from the cut surface of. Next, the second pipe 2 and the pipe-shaped connecting core 3 are temporarily fixed by welding through the through holes 4. Subsequently, the cut surface of the portion where the pipe-shaped connecting core 3 is slightly exposed and the side surface of the first pipe 1 are abutted, and the outer peripheral portion in contact therewith is welded. Finally, in order to improve the appearance,
Finish welding spots neatly.

As described above, according to the pipe connecting method according to the first embodiment, a slight gap is provided between the first pipe 1 and the second pipe 2 with the pipe-shaped connecting core 3 interposed therebetween. Is provided, and the welding area between the first pipe 1 and the connecting core 3 can be increased.
The joint strength between the pipe 1 and the second pipe 2 can be improved. Moreover, since the connecting core 3 as a reinforcing member is inserted into the second pipe 2, the appearance is simple. Further, the pipe member to be used does not require processing such as mold forming or thermoforming, and only requires machining to cut the pipe, which facilitates the assembling operation.

Although the first embodiment has been described by taking a cylindrical pipe as an example, the shape of the pipe member is not limited to this. For example, a square pipe may be used. That is, if the pipes have the same shape, similar joining can be performed, and similar effects can be obtained.

After the pipe-shaped connection core 3 is inserted into the second pipe 2, the second pipe 2 and the connection core 3 are connected to each other through a through hole 4 provided in advance in the second pipe 2. Are temporarily joined by welding, so that the joined state can be further reinforced.

(Embodiment 2) Hereinafter, claim 3 of the present invention will be described.
Embodiment 2 corresponding to FIG. 2 will be described with reference to FIG. FIG. 2 shows a pipe joint structure using a flat connection core according to a second embodiment of the present invention. FIG. 2A shows a direction in which the second pipe 2 is extrapolated to the flat plate-shaped connection core 5 that is in contact with the side surface of the first pipe 1. FIG. 2B shows a first pipe 1 and a second pipe 2.
Is a pipe joint structure integrally formed with a flat connecting core 5 interposed therebetween.

In the figure, 1 is a first pipe, and 2 is a second pipe. Reference numeral 5 denotes a flat plate-shaped connection core formed in a size that can be inserted into the second pipe 2.

A method of manufacturing the pipe joint structure thus configured will be described. First, one end of the plate-shaped connection core 5 is brought into contact with the side surface of the first pipe 1 and the periphery of the contact portion is welded. Next, the second connection core 5 is
Extrapolate pipe 2. Then, the side surface of the first pipe 1 and the cut surface of the second pipe 2 are abutted with each other via the connection core 5 in a flat plate shape, and the periphery of the abutting periphery is welded. Finally, in order to improve the appearance, the welded part is finished finely.

As described above, according to the pipe connecting method according to the second embodiment, the first pipe 1 and the second pipe 2 are connected with the plate-shaped connecting core 5 interposed therebetween. In addition, the plate-shaped connecting core 5 serves to reinforce the first pipe 1 and the second pipe 2 and can improve the joining strength. In addition, since the connecting core 5 in the form of a flat plate, which is a reinforcing member, is inserted into the second pipe 2, the appearance is simple. Further, the pipe member to be used does not require processing such as mold forming or thermoforming, and requires only mechanical processing such as cutting of the pipe, so that the assembling work is easy.

In the second embodiment, the case where the connection core is flat is described, but the shape of the connection core is not limited to this. For example, a core composed of a plurality of plate-like bodies may be used, and by increasing the number of plate-like bodies, the joining between the first pipe 1 and the second pipe 2 can be further strengthened.

(Embodiment 3) Hereinafter, claim 4 of the present invention will be described.
Embodiment 3 corresponding to FIG. 3 will be described with reference to FIG. FIG. 3 is a pipe joint structure using a connection core having a cross-sectional shape according to a third embodiment of the present invention. FIG. 3A shows a direction in which the second pipe 2 is extrapolated to the connecting core 6 having a cross-sectional shape in cross-section that is in contact with the side surface of the first pipe 1. FIG. 3 (b) shows the first pipe 1
FIG. 4 is a side view of a joint structure of pipes formed integrally with a second pipe 2 via a connecting core 6 having a cross-shaped cross section, as viewed from a direction in which the second pipe is cut.

In the figure, 1 is a first pipe, and 2 is a second pipe. Reference numeral 6 denotes a connection core having a cross-sectional shape formed in a size that can be inserted into the second pipe 2.
Reference numeral 7 denotes an angle for reinforcing the dangerous cross section described later, which is about 30 degrees.

Here, the critical cross section means a place where stress is concentrated. When the bicycle is stationary, the stress is applied vertically to the ground. However, in the state where the bicycle is running, the pedaling is performed while swinging left and right, so that the stress during the running is not in the vertical direction but in a slightly shifted position. That is, it is assumed that the stress is applied most to the cross section having the angle (approximately 30 degrees) indicated by reference numeral 7 in FIG.

A method for manufacturing the pipe joint structure thus configured will be described. First, one end of the connection core 6 having a cross-shaped cross section is brought into contact with the side surface of the first pipe 1, and the periphery of the contact portion is welded. Next, the second pipe 2 is extrapolated to the connection core 6 having a cross-sectional shape. Then, the side surface of the first pipe 1 and the cut surface of the second pipe 2 are abutted with each other via the connecting core 6 having a cross-shaped cross section, and the periphery of the abutting outer periphery is welded. Finally, the welded part is finished to make the appearance good.

As described above, according to the pipe connecting method according to the third embodiment, the first pipe 1 and the second pipe 2 are joined with the connecting core 6 having a cross-sectional shape interposed therebetween. The connecting core 6 having a cross-shaped cross section is the first pipe 1
And the second pipe 2 to reinforce it, and the joining is strengthened. Further, a core 6 having a cross-sectional shape as a reinforcing member is provided.
Is interpolated in the second pipe 2, so that the appearance is simple. Further, the pipe member to be used does not require processing such as mold forming or thermoforming, and requires only mechanical processing such as cutting of the pipe, so that the assembling work is easy.

(Embodiment 4) Hereinafter, claim 5 of the present invention will be described.
A fourth embodiment corresponding to the first embodiment will be described with reference to FIG. FIG. 4 is a pipe joint structure using a connection core having a recess formed in a cross section at one end according to a fourth embodiment of the present invention.

In FIG. 4, reference numeral 1 denotes a first pipe,
Is a second pipe. Reference numeral 8 denotes a concave portion in which a concave portion is formed in a cross section of one end of the connection core.

A method of manufacturing the pipe joint structure thus configured will be described. First, a concave portion 8 is formed in a hemispherical shape from the center point of the cross section of one end of the connecting core toward the other end of the cross section, and the tip of the concave portion is chamfered. Next, the cross section of the other end of the connection core is brought into contact with the side surface of the first pipe 1, and the periphery of the contact portion is welded. Then, the second pipe 2 is extrapolated to the connection core. Subsequently, the side surface of the first pipe 1 and the cut surface of the second pipe 2 are abutted with the connecting core interposed therebetween, and the periphery of the abutting periphery is welded. Finally, in order to improve the appearance, the welded part is finished finely.

As described above, according to the pipe connecting method according to the fourth embodiment, the concave portion is formed in a hemispherical shape from the center point of the cross section of one end of the connecting core toward the other end of the cross section, and Since the first pipe 1 and the second pipe 2 are joined by chamfering the tip of the concave portion and interposing the formed connecting core, the concave portion 8 plays a role of releasing the concentration of stress, thereby reducing the stress. By dispersing, it is possible to prevent the occurrence of cracks. Since the core, which is a reinforcing member, is inserted into the pipe, the appearance is simple.
Further, the pipe member to be used does not require processing such as mold forming or thermoforming, and requires only mechanical processing for cutting the pipe, so that the assembling work is easy.

Although the fourth embodiment has been described with reference to the drawing of the connecting core having a cross-sectional shape in cross section, the present invention is not limited to this. For example, the connection core may have a flat plate shape, or a cross-shaped cross-section, or may be similar to them. In this case, the concave portion 8 is similarly formed, and both ends are chamfered.
It has the effect of releasing stress concentration.

(Embodiment 5) Hereinafter, claim 6 of the present invention will be described.
Embodiment 5 corresponding to FIG. 5 will be described with reference to FIG. FIG. 5 is a pipe joint structure according to a fifth embodiment of the present invention, in which a through hole is provided on a side surface of a second pipe to engage with a connection core. FIG. 5A shows a through hole 9 on the side surface.
The second pipe 2 provided with the first core abuts the connection core 5.
The direction in which the pipe 1 is brought into contact with the pipe 1 is shown. FIG. 5 (b) shows the first
In a pipe joint structure in which the pipe 1 and the second pipe 2 are integrally formed, the side face of the connecting core 5 and the through-hole 9 provided in the second pipe 2 are connected by being flush with each other. It indicates that

In FIG. 5, reference numeral 1 denotes a first pipe. 2
Is a second pipe provided with a through hole whose end side face is flush with the end of the connection core. Reference numeral 5 denotes a flat connection core. Reference numeral 9 denotes a through-hole provided on the side surface of the second pipe 2 so as to be flush with the side end of the flat connecting core 5.

A method of manufacturing the pipe joint structure thus configured will be described. First, the second pipe 2 is provided with a through hole 9 from a cut surface of the second pipe 2 such that the side surface of the end portion is flush with the end portion of the connection core 5 having a flat plate shape. Next, the cut surface of the plate-shaped connection core 5 is brought into contact with the side surface of the first pipe 1 and the periphery of the contact portion is welded. Then, the through hole 9 provided in the second pipe 2 is inserted so as to be flush with the end of the connecting core 5 in a flat plate shape. Subsequently, the periphery of the outer periphery where the side surface of the first pipe 1 and the cut surface of the second pipe 2 abut, and the periphery of the through hole 9 are welded and joined. Finally, the welded part is finished to make the appearance good.

As described above, according to the pipe connecting method according to the fifth embodiment, the joining of the first pipe 1 and the second pipe 2 is performed with the end of the connecting core 5 having a flat shape. Since the joining was performed by providing the hole 9 on the side surface of the second pipe 2,
The welding area can be large, and the welding can be made through holes 9
, The bonding strength can be further improved. In addition, the provision of the through holes 9 facilitates positioning and improves work efficiency. Furthermore, since the connecting core 5 in the form of a plate, which is a reinforcing member, is inserted into the pipe, the appearance is simple.

In the fifth embodiment, the connection core 5 in the form of a plate has been described as an example. However, the shape of the connection core is not limited to this. For example, the structure of the connection core is
The cross-sectional shape may be similar to the cross-sectional shape or the cross-sectional shape, or the shape may be similar. By providing a large number of through-holes 9, a large welding area can be obtained, so that the joining strength can be further improved. .

[0046]

As described above, according to the pipe connecting method according to the first aspect of the present invention, the cut surface of the rod-shaped connecting core is slightly exposed from the cut surface of the second pipe. The connection core is inserted into the second pipe until the state is reached, the connection core and the second pipe are connected, and the cut surface of the connection core and the side surface of the first pipe are brought into contact with each other. The connection core and the first pipe were connected by welding the periphery of the contact portion by making contact with each other, so that a large welding area between the first pipe and the second pipe can be obtained, Is strengthened. Also, since the core, which is a reinforcing member, is inserted into the pipe, the appearance is simple, and only the machining of cutting the pipe is sufficient, so that the assembling work is easy.

According to the pipe connecting method of the second aspect of the present invention, a through hole is formed in a side surface of the second pipe, and the connecting core is inserted into the second pipe to form the second pipe. In a state where the through hole and the side surface of the connection core are overlapped,
Since the connection core and the second pipe are connected by welding through the through-hole, the joined state can be further reinforced.

According to the pipe connecting method of the third aspect of the present invention, the cut surface of the flat connecting core is brought into contact with the side surface of the first pipe, and the periphery of the contact portion is welded. By connecting, the connection core and the first pipe,
The second pipe is extrapolated to the flat connection core, and the cut surface of the second pipe is brought into contact with the side surface of the first pipe, and the contact portion is welded to form the connection pipe. Since the child and the second pipe are connected, the joining strength can be improved. Also, since the core, which is a reinforcing member, is inserted into the pipe, the appearance is simple, and only the machining of cutting the pipe is sufficient, so that the assembling work is easy.

According to the pipe connecting method of the fourth aspect of the present invention, the cut surface of the connecting core having a cross-shaped cross section is brought into contact with the side surface of the first pipe, and the periphery of the contact portion is formed. By welding, the connection core and the first pipe are connected, and a second pipe is extrapolated to the connection core having a cross-sectional shape in cross section to cut the second pipe and the first pipe. The connection core and the second pipe are connected by contacting the side surface and welding the contact portion, so that the joining strength can be improved. Also, since the core, which is a reinforcing member, is inserted into the pipe, the appearance is simple, and only the machining of cutting the pipe is sufficient, so that the assembling work is easy. Furthermore, by setting the connection core having a cross-shaped cross section at an angle at which the dangerous cross section is reinforced, it is possible to provide a joint structure of pipes that is highly safe even for a traveling bicycle.

According to the pipe connecting method of the fifth aspect of the present invention, a concave portion is formed in a hemispherical shape from the center point of the cross section of one end of the connecting core to the other end of the cross section,
Since the tip of the concave portion is chamfered and the other end of the connection core is connected to the side surface of the first pipe, the connection core has a function of releasing the concentration of stress. That is, by dispersing the stress, the occurrence of cracks can be prevented. Also,
Since the core, which is a reinforcing member, is inserted into the pipe, the appearance is simple, and only the machining of cutting the pipe is sufficient, so that the assembling work is easy.

According to the pipe connecting method of the present invention, a through-hole is cut out from a cut surface of the second pipe, and the second pipe is extrapolated to the connecting core. When connecting, the connecting core and the second pipe are connected by holding the connecting core in the through hole and welding the periphery of the through hole, so that the first pipe and the second pipe are connected. And the welding area can be increased, and the joining is strengthened. Further, the through hole plays a role of positioning, and the working efficiency is improved. Further, since the core as the reinforcing member is inserted into the pipe, the appearance is simple.

[Brief description of the drawings]

FIG. 1 is a pipe joint structure using a pipe-shaped connection core according to a first embodiment of the present invention.

FIG. 2 is a pipe joint structure using a flat plate-shaped connection core according to a second embodiment of the present invention.

FIG. 3 is a pipe joint structure using a connecting core having a cross-shaped cross section according to a third embodiment of the present invention.

FIG. 4 is a pipe joint structure using a connection core having a recess formed in a cross section of one end according to a fourth embodiment of the present invention.

FIG. 5 is a pipe joint structure in which a through hole for engaging a connection core is provided on a side surface of a second pipe according to a fifth embodiment of the present invention.

FIG. 6 is a cross-sectional view of a pipe joint structure using a conventional auxiliary pipe.

FIG. 7 is a pipe joint structure using a conventional gusset.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st pipe 2 2nd pipe 3 Pipe-shaped connection core 4 Through-hole 5 Plate-shaped connection core 6 Cross-section connection core 7 Angle representing a dangerous cross section 8 Depression 9 Through-hole 10 Auxiliary pipe 11 Weld metal by arc welding 12 Weld metal by resistance welding 13 Gusset

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kazumi Nishimura 13-13 Katayamacho, Kashiwara-shi, Osaka National Bicycle Industry Co., Ltd. (72) Inventor Susumu Endo 13-13 Katayamacho, Kashiwara-shi, Osaka National Bicycle Industry (72) Inventor Shozo Nabeya 13-13 Katayamacho, Kashiwara-shi, Osaka National Bicycle Industry Co., Ltd. F-term (reference) 3D012 BE02 BF03 BG02 3J039 AA08 BB01 BB03 LA02 4E081 YC09

Claims (6)

[Claims] 1. The connecting core is inserted into the second pipe until the cut surface of the rod-shaped connecting core is slightly exposed from the cut surface of the second pipe. The connection core and the second pipe are connected, and the cut surface of the connection core and the side surface of the first pipe are brought into contact with each other and the periphery of the contact portion is welded, so that the connection core and the second core are welded. A pipe connection method for connecting to a first pipe. 2. A through hole is formed in a side surface of the second pipe, and the connection core is inserted into the second pipe so that the through hole and a side surface of the connection core are overlapped. The pipe connection method according to claim 1, wherein the connection core and the second pipe are welded and connected to each other through the through hole in the state. 3. An end of a plate-like connecting core is brought into contact with a side surface of the first pipe, and the periphery of the contacting portion is welded to connect the connecting core and the first pipe. The second pipe is extrapolated to the flat connecting core, and the cut surface of the second pipe is brought into contact with the side surface of the first pipe, and the contact portion is welded. A pipe connection method for connecting a connection core and the second pipe. 4. An end of a connecting core having a cross section in cross section is brought into contact with a side surface of the first pipe, and the periphery of the abutting portion is welded, so that the connecting core and the first pipe are connected to each other. The second pipe is extrapolated to the connecting core having a cross-shaped cross section, and the cut surface of the second pipe is brought into contact with the side surface of the first pipe, and the contact portion is welded. Connecting the connecting core and the second pipe according to the following method. 5. A concave portion is formed in a hemispherical shape from the center point of the cross section of one end of the connection core toward the front end of the cross section, and the front end of the concave portion is chamfered to connect the other end of the connection core. The pipe connection method according to claim 3 or 4, wherein the pipe is connected to a side surface of the first pipe. 6. A through hole is cut out from a cut surface of the second pipe, and when connecting the second pipe to the connection core, the connection core is sandwiched by the through hole. The pipe connection method according to any one of claims 3 to 5, wherein the connection core and the second pipe are connected by welding around the through hole.