Welding method for first cylindrical part and second cylindrical part, manufacturing method for water heater, manufacturing method for compressor, and welding device

Abstract

This welding method for a first cylindrical part and a second cylindrical part comprises a step for forming a molten pool, and a step for rotating at least one among the first cylindrical part and the second cylindrical part. In the step for forming the molten pool, a first cylindrical end of the first cylindrical part of a first member is welded to a second cylindrical end of the second cylindrical part which is included in a second member and fitted to the first cylindrical part, the end face of the second cylindrical end being aligned with the first cylindrical end, and a molten pool straddling the first cylindrical end and the second cylindrical end is formed across the entire circumference. In the step for rotating at least one among the first cylindrical part and the second cylindrical part, said at least one among the first cylindrical part and the second cylindrical part is rotated in the circumferential direction at least in the period from the formation of the molten pool to the solidification of the molten pool.

Description

Method for welding first cylindrical portion and second cylindrical portion, method for manufacturing water heater, method for manufacturing compressor, and welding device

[0001] The present disclosure relates to a method for welding a first cylindrical portion and a second cylindrical portion, a method for manufacturing a water heater, a method for manufacturing a compressor, and a welding device.

[0002] Some methods for welding cylindrical portions together, i.e., welding a first cylindrical portion and a second cylindrical portion, include a step of fitting the second cylindrical portion of one member into the first cylindrical portion of the other member, and then melting both cylindrical ends while aligning the end faces of the cylindrical ends of the first cylindrical portion and the second cylindrical portion, thereby welding the cylindrical ends together.

[0003] In this type of welding method, the two cylindrical ends with aligned end faces are generally annular when viewed from the axial direction of the cylinders. Therefore, the cylindrical ends are melted by moving a welding device in an annular motion along the cylindrical ends. For example, when laser welding is used, the cylindrical ends are melted by scanning a laser beam along the annular surface of the cylindrical ends. However, this type of welding method requires time for the laser beam to scan. As a result, it takes a long time to melt most of the end surface area of ​​the cylindrical ends. Therefore, to shorten the time required for melting, processing devices that can melt the entire annular area simultaneously have been developed.

[0004] For example, Patent Document 1 discloses a laser processing device including a laser oscillator that outputs laser light, a first lens that converts the laser light output by the laser oscillator into parallel light of a fixed diameter, and a second lens that converts the parallel light of a fixed diameter converted by the first lens into annular parallel light. In the laser processing device described in Patent Document 1, the laser light is annular parallel light, so by irradiating the laser light onto the end of the above-mentioned annular cylinder, the entire annular region can be melted simultaneously.

[0005] Japanese Patent Application Laid-Open No. 2005-28428

[0006] However, even if the laser processing device described in Patent Document 1 simultaneously melts the entire end face region of the cylindrical end, the molten material, such as molten metal, may be concentrated in a certain region due to convection after melting. In this case, the molten metal may be insufficient in other regions. As a result, the weld strength is reduced, and sufficient strength cannot be obtained.

[0007] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a welding method for a first cylindrical portion and a second cylindrical portion, a manufacturing method for a water heater, a manufacturing method for a compressor, and a welding device that suppress a decrease in welding strength.

[0008] In order to achieve the above-mentioned object, the welding method of the first cylindrical portion and the second cylindrical portion according to the present disclosure comprises the steps of: melting a first cylindrical end of the first cylindrical portion of the first member and a second cylindrical end of the second member fitted to the first cylindrical portion, the second cylindrical end having an end face aligned with the first cylindrical end, to form a molten pool spanning the first cylindrical end and the second cylindrical end over the entire circumference; and rotating at least one of the first cylindrical portion and the second cylindrical portion in a circumferential direction at least during the period from when the molten pool is formed until it solidifies.

[0009] According to the configuration of the present disclosure, at least one of the first cylindrical portion and the second cylindrical portion is rotated in the circumferential direction at least from the time when the molten pool is formed until the time when the molten pool solidifies, so that the molten material in the molten pool is convected in the circumferential direction by centrifugal force. This prevents the molten material from concentrating in one area and reducing the amount of molten material in other areas. As a result, a decrease in weld strength is suppressed.

[0010] a perspective view of a portion of a hot water storage tank including a cylindrical portion to be welded by the method for welding cylindrical portions according to embodiment 1 of the present disclosure; a perspective view of a nipple including another cylindrical portion to be welded by the method for welding cylindrical portions according to embodiment 1 of the present disclosure; a cross-sectional view of a welded portion when cylindrical portions are welded together by the method for welding cylindrical portions according to embodiment 1 of the present disclosure; a cross-sectional view of a molten pool when cylindrical portions are welded together without using the method for welding cylindrical portions according to embodiment 1 of the present disclosure; a cross-sectional view of a molten pool and a cylindrical portion when the amount of melting at the cylindrical end is small when the cylindrical ends of cylindrical portions are welded together without using the method for welding cylindrical portions according to embodiment 1; a cross-sectional view of a molten pool and a cylindrical portion when the amount of melting at the cylindrical end is large when the cylindrical ends of cylindrical portions are welded together without using the method for welding cylindrical portions according to embodiment 1; a cross-sectional view of a molten pool and a cylindrical portion when the amount of melting at the cylindrical end is small when the cylindrical ends of thick cylindrical portions are welded together without using the method for welding cylindrical portions according to embodiment 1;a cross-sectional view of a molten pool and a cylindrical portion when the amount of melting at the cylindrical end is large; a flowchart of a cylindrical portion welding method according to embodiment 1 of the present disclosure; a cross-sectional view of a welding device for performing the cylindrical portion welding method according to embodiment 1 of the present disclosure; a perspective view of a cylindrical portion rotated in a rotation process provided by the cylindrical portion welding method according to embodiment 1 of the present disclosure and another cylindrical portion into which the cylindrical portion is fitted; an enlarged top view of a cylindrical portion rotated in a rotation process provided by the cylindrical portion welding method according to embodiment 1 of the present disclosure and another cylindrical portion into which the cylindrical portion is fitted; a perspective view of two cylindrical portions rotated in a rotation process provided by a cylindrical portion welding method according to embodiment 2 of the present disclosure; an enlarged top view of a cylindrical portion rotated in a rotation process provided by the cylindrical portion welding method according to embodiment 2 of the present disclosure; a flowchart of a cylindrical portion welding method according to embodiment 2 of the present disclosure; a melting process provided by the cylindrical portion welding method according to embodiment 2 of the present disclosure; a top view of a cylindrical portion onto which a laser irradiator irradiates laser light in a process; a perspective view of two cylindrical portions rotated in a modified rotation process included in the method for welding cylindrical portions according to embodiment 2 of the present disclosure; a cross-sectional view of a welding apparatus used in the method for welding cylindrical portions according to embodiment 3 of the present disclosure; a cross-sectional view of a hot water storage tank including cylindrical portions welded by the method for welding cylindrical portions according to embodiment 4 of the present disclosure; a flowchart of a method for welding cylindrical portions according to embodiment 5 of the present disclosure; a cross-sectional view of a cylindrical portion to which a circular member is attached in a circular member attachment process included in the method for welding cylindrical portions according to embodiment 5 of the present disclosure; a cross-sectional view of a cylindrical portion and a modified circular member used in the method for welding cylindrical portions according to embodiment 5 of the present disclosure;

[0011] Hereinafter, a welding method for a first cylindrical portion and a second cylindrical portion, a manufacturing method for a water heater, a manufacturing method for a compressor, and a welding apparatus according to embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the same or equivalent parts in the drawings are designated by the same reference numerals. In the Cartesian coordinate system XYZ shown in the drawings, when the pipe axis direction of the first cylindrical portion and the second cylindrical portion is oriented vertically, the vertical direction is the Z axis and the horizontal plane is the XY plane. Below, this coordinate system will be referenced as appropriate in the description.

[0012] (Embodiment 1) A method for welding a first cylindrical portion and a second cylindrical portion according to embodiment 1 is a method for welding a first cylindrical portion that surrounds a through hole formed by burring to a second cylindrical portion that forms a circular pipe. Hereinafter, the welding method for the first cylindrical portion and the second cylindrical portion according to embodiment 1 will be described using an example in which a first cylindrical portion formed by burring at a water inlet of a hot water storage tank included in a water heater is welded to a second cylindrical portion that is provided at the tip of a nipple and forms a circular pipe. First, with reference to FIGS. 1 to 3, the first cylindrical portion, the second cylindrical portion, and the welded portion when the first cylindrical portion and the second cylindrical portion are combined and welded will be described.

[0013] In the following description, the first cylindrical portion and the second cylindrical portion will be simply referred to as the cylindrical portion.

[0014] Fig. 1 is a perspective view of a portion of a hot water storage tank 10 including a cylindrical portion 1 to be welded using a welding method for welding cylindrical portions 1 and 2 according to a first embodiment. Fig. 2 is a perspective view of a nipple 20 including another cylindrical portion 2 to be welded using the same welding method. Fig. 3 is a cross-sectional view of a welded portion 5 when cylindrical portions 1 and 2 are welded using the same welding method. Note that, for ease of understanding, Fig. 1 shows only a portion near the water inlet of the hot water storage tank. Also, Fig. 3 shows a cross-section of cylindrical portions 1 and 2 cut along a plane along the cylindrical axis.

[0015] As shown in Figure 1, a hot water storage tank 10 installed in a water heater has a through hole 12 in a wall portion 11 to supply water to the hot water storage tank 10. This forms a water supply port. The through hole 12 is surrounded by a cylindrical portion 1 formed by burring to connect a pipe. A nipple 20 is inserted into this cylindrical portion 1 to facilitate pipe connection.

[0016] In contrast, nipple 20 has a tubular shape with a tapered tip, as shown in Fig. 2. In detail, nipple 20 has a cylindrical main body 21 into which a pipe from an external device is inserted and connected, and a cylindrical portion 2 which is provided closer to the tip of main body 21, i.e., on the +Z side, and has smaller outer and inner diameters than main body 21, so as to be inserted into and joined to cylindrical portion 1 of hot water storage tank 10 described above.

[0017] The cylindrical portion 2 can be fitted into the cylindrical portion 1 of the hot water storage tank 10, and has an outer diameter that allows it to come into close contact with the inner wall of the cylindrical portion 1 when fitted into the cylindrical portion 1. The cylindrical portion 2 is concentrically fitted into the cylindrical portion 1 and joined to the cylindrical portion 1, as shown in FIG.

[0018] In detail, the cylindrical portion 2 is inserted into the internal space of the cylindrical portion 1 so as to be concentric therewith, and is positioned with its cylindrical end 23 facing in the same direction as the cylindrical end 13 of the cylindrical portion 1 and with the end faces aligned. That is, the cylindrical portion 2 is positioned in the cylindrical portion 1 with the cylindrical ends 13 and 23 facing in the +Z direction and with the Z positions of the +Z end faces aligned. A weld 5 is provided at the cylindrical end 23 of the cylindrical portion 2 and the cylindrical end 13 of the cylindrical portion 1. As a result, the cylindrical end 23 of the cylindrical portion 2 and the cylindrical end 13 of the cylindrical portion 1 are joined to each other.

[0019] The welded portion 5 is formed by melting and solidifying the material that forms the cylindrical end 13 of the cylindrical portion 1 and the cylindrical end 23 of the cylindrical portion 2. Specifically, the cylindrical portions 1 and 2 are made of a metal material, specifically, a steel material such as ferritic stainless steel or martensitic stainless steel. The welded portion 5 is formed by melting and solidifying the metal material that forms the cylindrical ends 13 and 23.

[0020] When forming the weld 5, the molten metal material may gather in one area, resulting in insufficient weld strength. To solve this problem, the method for welding the cylindrical portions 1 and 2 according to embodiment 1 is carried out in the process of forming the weld 5. Next, the problem of weld strength will be described with reference to Figures 4, 5A, 5B, 6A, and 6B.

[0021] FIG. 4 is a cross-sectional view of a molten pool 60 when the cylindrical portions 1 and 2 are welded together without using the cylindrical portion welding method according to embodiment 1. FIG. 5A is a cross-sectional view of the molten pool 60 and the cylindrical portions 1 and 2 when the cylindrical ends 13 and 23 of the cylindrical portions 1 and 2 are welded together without using the cylindrical portion welding method according to embodiment 1, and the amount of melting at the cylindrical ends 13 and 23 is small. FIG. 5B is a cross-sectional view of the molten pool 60 and the cylindrical portions 1 and 2 when the cylindrical ends 13 and 23 of the cylindrical portions 1 and 2 are welded together without using the cylindrical portion welding method according to embodiment 1, and the amount of melting at the cylindrical ends 13 and 23 is large. Note that, for ease of understanding, arrows A1-A4 in FIG. 4 indicate only representative flows of molten metal. The shapes of the cylindrical portions 1 and 2 are simplified in FIGS. 5A and 5B.

[0022] As described above, the weld 5 joins the cylindrical end 13 of the cylindrical portion 1 and the cylindrical end 23 of the cylindrical portion 2. At this time, to ensure sufficient joint strength and watertightness, the cylindrical ends 13 and 23 must be joined along the entire circumference. For this reason, although not shown in FIG. 3 , the weld 5 is not only provided across the cylindrical ends 13 and 23, but is also formed along the circumferences of the cylindrical ends 13, 23. As a result, the weld 5 is provided along the entire circumference of the cylindrical ends 13, 23. This gives the weld 5 an annular shape when viewed from above, i.e., from the +Z side.

[0023] To form a weld 5 of this shape, it is conceivable to move a heating mechanism that melts the cylindrical ends 13, 23 in the circumferential direction to gradually form a molten pool 60 in the circumferential direction. However, in this case, it takes time to form the weld 5. In addition, a moving mechanism is required to move the heating mechanism in the circumferential direction, which tends to make the device complicated.

[0024] Therefore, in order to shorten the welding time or simplify the device configuration, it is desirable to use a laser irradiation device that can irradiate laser light in an annular manner to melt the entire circumferential direction of the cylindrical ends 13, 23 simultaneously.

[0025] However, when such a laser irradiation device is used, if the entire circumferential direction of the cylindrical ends 13, 23 is simply melted simultaneously, the molten metal concentrates in a certain portion of the circumferential direction of the cylindrical ends 13, 23, resulting in the formation of a pool 61 where more molten metal accumulates than in the surrounding areas, as shown in Figure 4. Experimental results suggest that this is due to (1) the entire circumferential direction of the cylindrical ends 13, 23 being melted simultaneously, forming a molten pool 60 containing a relatively large amount of molten metal that spreads throughout the entire cylindrical ends 13, 23, and (2) the area of ​​the molten pool 60 is large, in other words, the molten pool 60 is long in the circumferential direction, which results in Marangoni convection occurring in the circumferential direction of the cylindrical ends 13, 23, causing the molten metal to concentrate in the low-temperature portions of the circumferential direction.

[0026] 5A, if only a small amount of the end surface portions of the cylindrical ends 13, 23 are melted, the molten metal is subjected to interfacial tension at the end surfaces of the cylindrical ends 13, 23, which makes it difficult for the molten metal to flow within the molten pool 60. As a result, the aforementioned pool 61 does not form. However, in this case, the amount of molten metal is so small that sufficient weld strength cannot be obtained.

[0027] In contrast, if the end surfaces of the cylindrical ends 13 and 23 are sufficiently melted to obtain sufficient weld strength, as shown in FIG. 5B , interfacial tension acts only on the molten metal on the cylindrical ends 13 and 23 side of the weld pool 60, i.e., on the -Z side of the weld pool 60. As a result, the molten metal on the +Z side of the weld pool 60 flows due to Marangoni convection. At this time, as shown by arrows A1-A4 in FIG. 4 , the molten metal on the +Z side flows toward the lower temperature region. This results in the formation of the aforementioned pool 61. When this pool 61 is formed, the amount of molten metal decreases in areas other than the pool 61, resulting in a decrease in weld strength.

[0028] This problem occurs not only in the cylindrical portions 1 and 2 having a small thickness, but also in the cylindrical portions 1 and 2 having a large thickness.

[0029] Fig. 6A is a cross-sectional view of a molten pool 60 and cylindrical portions 1 and 2 when the amount of melting at the cylindrical ends 13 and 23 is small when welding the cylindrical ends 13 and 23 of thick cylindrical portions 1 and 2 together without using the welding method for cylindrical portions according to embodiment 1. Fig. 6B is a cross-sectional view of a molten pool 60 and cylindrical portions 1 and 2 when the amount of melting at the cylindrical ends 13 and 23 is large when welding the cylindrical ends 13 and 23 of thick cylindrical portions 1 and 2 together without using the welding method for cylindrical portions according to embodiment 1. Note that the shapes of cylindrical portions 1 and 2 are simplified in Figs. 6A and 6B to facilitate understanding.

[0030] As shown in Figure 6A, when the thickness of the cylindrical portions 1 and 2 is large, if only a portion near the boundary between the cylindrical portions 1 and 2 in the thickness direction is melted, interfacial tension acts between the surfaces of the cylindrical ends 13 and 23 and the molten metal, making it difficult for the molten metal to flow within the molten pool 60. As a result, the aforementioned pool 61 does not occur. However, because the amount of molten metal is small, sufficient weld strength cannot be obtained, as in the case of Figure 5A.

[0031] In contrast, as shown in Fig. 6B, when the end face portions of the cylindrical ends 13, 23 are sufficiently melted, the molten metal on the +Z side of the molten pool 60 flows due to Marangoni convection, creating the aforementioned pool 61, just as in the case of the thin cylindrical portions 1, 2 in Fig. 5B. As a result, the amount of molten metal decreases in areas other than where the pool 61 is located, resulting in a decrease in the weld strength.

[0032] In this way, if a molten pool 60 is formed that fully covers the end face areas of the cylindrical ends 13, 23, regardless of the thickness of the cylindrical portions 1, 2, a pool 61 as shown in Figure 4 will occur, reducing the weld strength. In order to prevent the formation of this pool 61, the method for welding the cylindrical portions 1 and 2 according to the first embodiment is carried out.

[0033] Next, a method for welding the cylindrical portions 1 and 2 according to the first embodiment will be described with reference to Figures 7 to 10. This welding method uses a dedicated welding device. In the following description, in addition to the method for welding the cylindrical portions 1 and 2 according to the first embodiment, the configuration of the welding device will also be described.

[0034] FIG. 7 is a flowchart of the method for welding the cylindrical portions 1 and 2 according to the first embodiment.

[0035] As shown in FIG. 7 , the method for welding the cylindrical portions 1 and 2 includes a melting step (step S1) for melting the welding points of the cylindrical portions 1 and 2, and a rotation step (step S2) for rotating one of the cylindrical portions 1 and 2 around the cylindrical axis during melting.

[0036] In the method for welding the cylindrical portions 1 and 2, first, as a prerequisite for welding, the hot water storage tank 10 including the cylindrical portion 1 and the nipple 20 including the cylindrical portion 2 are prepared, and the nipple 20 is then assembled to the hot water storage tank 10. Specifically, the cylindrical portion 2 is fitted, starting with the cylindrical end 23, from the end 14 of the cylindrical portion 1 shown in FIG. 3 , which is located on the wall surface 11 side of the hot water storage tank 10. Furthermore, the end faces of the cylindrical end 13 of the cylindrical portion 1 on the side opposite the wall surface 11 and the cylindrical end 23 at the tip side of the cylindrical portion 2 are aligned. For example, the end faces of the cylindrical end 13 of the cylindrical portion 1 and the cylindrical end 23 of the cylindrical portion 2 are aligned perpendicular to the Z axis, and the Z positions of these end faces are aligned. This allows the cylindrical portion 2 to be fitted to the cylindrical portion 1. As a result, the nipple 20 is assembled to the hot water storage tank 10.

[0037] 7, the melting step is carried out next (step S1). In this welding step, the end faces of cylindrical ends 13 and 23 are melted using welding device 4A to weld together the end faces of cylindrical end 13 of cylindrical portion 1 and cylindrical end 23 of cylindrical portion 2.

[0038] Here, the configuration of the welding device 4A used in the melting step will be described with reference to Fig. 8. Fig. 8 is a cross-sectional view of the welding device 4A for carrying out the method for welding the cylindrical portions 1 and 2 according to the first embodiment. Note that, for ease of understanding, Fig. 8 omits the internal structures of the laser irradiator 43 and the motor 44. Also, the shapes of the cylindrical portions 1 and 2 are simplified.

[0039] As shown in Figure 8, the welding device 4A includes a holding mechanism 41 that holds the cylindrical portion 1 to be welded, a holding mechanism 42 that holds the other cylindrical portion 2 to be welded, and a laser irradiator 43 that melts and welds the cylindrical portion 1 held by the holding mechanism 41 and the cylindrical portion 2 held by the holding mechanism 42.

[0040] The holding mechanism 41 has a large cylindrical portion 411 that holds the cylindrical portion 1 and a flange portion 412 for fixing the large cylindrical portion 411 .

[0041] The large cylindrical portion 411 is a portion that supports the wall surface portion 11 of the hot water storage tank 10 with its own cylindrical end. The large cylindrical portion 411 has a cylindrical end 413 with an end surface perpendicular to the cylindrical axis A, and by orienting the cylindrical axis A in the vertical direction, the end surface of the cylindrical end 413 is horizontal. This allows the wall surface portion 11 of the hot water storage tank 10 to be placed on the cylindrical end 413 of the large cylindrical portion 411.

[0042] Although not shown, the end surface of the cylindrical end 413 is annular. As shown in Fig. 8, an annular magnet 414 having the same shape as the end surface is provided on the end surface of the cylindrical end 413. When the wall surface 11 of the hot water storage tank 10 is placed on the cylindrical end 413, the magnetic force of the magnet 414 holds the wall surface 11 of the hot water storage tank 10 in place. Meanwhile, a flange portion 412 is provided on the cylindrical end portion of the large cylindrical portion 411 opposite the cylindrical end 413.

[0043] Although not shown, the flange portion 412 has a circular ring shape with its circular surface horizontal. The flange portion 412 is disposed coaxially with the large cylindrical portion 411. The inner diameter of the flange portion 412 is smaller than the inner diameter of the large cylindrical portion 411, and as a result, the flange portion 412 protrudes toward the inner space of the large cylindrical portion 411. As shown in FIG. 8 , a bearing portion 441 provided on the motor 44 passes through the inner space of the large cylindrical portion 411. The bearing portion 441 is fitted into the circular flange portion 412. The bearing portion 441 is formed integrally with a case 442 of the motor 44. As a result, the flange portion 412 is fixed to the case 442 of the motor 44.

[0044] On the other hand, flange portion 412 is formed integrally with large cylindrical portion 411. Flange portion 412 is fixed to case 442 of motor 44, thereby keeping large cylindrical portion 411 in a fixed position. As a result, when large cylindrical portion 411 holds wall portion 11 of hot water storage tank 10 by the magnetic force of magnet 414, flange portion 412 keeps wall portion 11 of hot water storage tank 10 in a fixed position.

[0045] In contrast, the holding mechanism 42 has a columnar portion 421 that is inserted into the cylindrical portion 2 and a flange portion 422 that supports the columnar portion 421 .

[0046] The columnar portion 421 has an outer diameter smaller than the inner diameter of the cylindrical portion 2 to the extent that a minute gap is formed between the columnar portion 421 and the cylindrical portion 2, and can be fitted onto the cylindrical portion 2 when the cylindrical portion 2 is placed over the columnar portion 421. The columnar portion 421 is arranged with its column axis B facing vertically. A flange 422 is provided at the lower end of the columnar portion 421 to support the cylindrical portion 2 when the cylindrical portion 2 is placed over the columnar portion 421 and fitted onto the cylindrical portion 2.

[0047] The flange 422 protrudes from the columnar portion 421 by a distance greater than the thickness of the cylindrical portion 2. This prevents the cylindrical portion 2 from slipping out downward when the cylindrical portion 2 is fitted over the columnar portion 421. In addition, an annular magnet 423 is provided on the upper side of the flange 422. The magnet 423 attracts the cylindrical portion 2 by its magnetic force when the cylindrical portion 2 is fitted over the columnar portion 421.

[0048] With this configuration, the holding mechanism 42 holds the cylindrical portion 2. A laser irradiator 43 is disposed on the holding mechanisms 41, 42 in order to weld the cylindrical portions 1, 2 together when the cylindrical portions 1, 2 are held.

[0049] An output shaft 443 of the motor 44 is connected to the lower end of the columnar portion 421, and the columnar portion 421 is thereby supported by the output shaft 443. The relationship with the output shaft 443 will be described in detail later.

[0050] Although not shown, the laser irradiator 43 includes a laser oscillator such as a CO2 laser, a YAG (Yttrium Aluminum Garnet) laser, a fiber laser, or a disk laser, and a lens unit that converts the laser light output by the laser oscillator into a parallel beam of a certain diameter and then converts the parallel beam into an annular parallel beam. The outer diameter of the annular parallel beam L is equal to or larger than the outer diameter of the cylindrical portion 1, as shown in FIG. 8 . The inner diameter of the annular parallel beam L is equal to or smaller than the inner diameter of the cylindrical portion 2. The laser irradiator 43 then irradiates the annular parallel beam L converted by the lens unit toward, i.e., downward from, the holding mechanisms 41 and 42, as shown in FIG. 8 . When the cylindrical portions 1 and 2 are held by the holding mechanisms 41 and 42, the laser irradiator 43 emits the annular parallel beam L as laser light to melt the end surfaces of the cylindrical ends 13 and 23 of the cylindrical portions 1 and 2. At this time, the laser irradiator 43 irradiates the laser beam, which is the annular parallel beam L, so that the entire end face portions of the cylindrical ends 13 and 23 are melted at the same time.

[0051] 8, it is desirable that the laser irradiator 43 irradiates the end surface portions of the cylindrical ends 13, 23 with annular parallel light L from the direction in which the cylindrical axes of the cylindrical portions 1, 2 held by the holding mechanisms 41, 42 extend. In other words, it is desirable that the laser irradiator 43 irradiates the end surface portions of the cylindrical ends 13, 23 with annular parallel light L from a direction perpendicular to the end surface portions. This enables the laser irradiator 43 to apply parallel light L of uniform intensity to the entire end surface portions of the cylindrical ends 13, 23.

[0052] 7 , in the melting process of step S1, the welding device 4A is used to melt the end surface portions of the cylindrical ends 13 and 23 of the cylindrical portions 1 and 2. As described above, the laser irradiator 43 irradiates the annular laser beam, so that the entire end surface portions of the cylindrical ends 13 and 23 are melted. As a result, a molten pool is formed spanning the entire circumference of the cylindrical ends 13 and 23.

[0053] Next, when the laser light irradiation to the end face portions of the cylindrical ends 13 and 23 begins in the melting process, i.e., when the end face portions of the cylindrical ends 13 and 23 begin to melt, a rotation process is carried out in parallel with the melting of the end face portions (step S2).

[0054] In this rotation step, the cylindrical portion 2 is rotated in the circumferential direction while the cylindrical portion 1 is left as it is. That is, the cylindrical portion 2 is rotated around the cylindrical axis A shown in Fig. 8. The motor 44 provided in the welding device 4A described above is used to rotate the cylindrical portion 2.

[0055] 8, the motor 44 has a case 442, a bearing 441 that is provided on the upper side of the case 442 and has an outer diameter smaller than that of the case 442, and an output shaft 443 that is rotatably held by the bearing 441 and protrudes upward from the center of the upper end of the case 442. As described above, the bearing 441 is fitted into the annular flange 412 of the holding mechanism 41, and is thereby fixed to the holding mechanism 41 that holds the cylindrical portion 1.

[0056] On the other hand, the upper end of the output shaft 443 is connected to the holding mechanism 42. More specifically, a mounting hole 424 is formed coaxially with the cylindrical axis B in the lower part of the cylindrical portion 421 of the holding mechanism 42. The upper end of the output shaft 443 is inserted into the mounting hole 424, thereby connecting it to the holding mechanism 42. Furthermore, the output shaft 443 extends along the cylindrical axis B. As a result, the output shaft 443 rotates, thereby rotating the holding mechanism 42. Because the holding mechanism 42 holds the cylindrical portion 2, when the holding mechanism 42 rotates, the cylindrical portion 2 also rotates along with the rotation of the holding mechanism 42.

[0057] In the rotation process, the output shaft 443 of the motor 44 is rotated to rotate the cylindrical portion 2 about the columnar axis B. For example, the welding device 4A includes a controller 45 shown in FIG. 8 that controls the rotation of the motor 44, and the controller 45 controls the power supply to the motor 44 to rotate the output shaft 443 of the motor 44, thereby rotating the cylindrical portion 2.

[0058] In this case, when the controller 45 receives a start signal from the laser irradiator 43 indicating the start of irradiation of laser light, it may start supplying power to the motor 44 to rotate the motor 44 .

[0059] The rotation speed of the output shaft 443 of the motor 44, in other words, the rotation speed of the cylindrical portion 2 during the rotation process, may be, for example, several rotations per second to several tens of rotations per second. Furthermore, the rotation of the cylindrical portion 2 may be constant to facilitate control. Alternatively, the rotation may involve acceleration or deceleration to facilitate the generation of convection, as described below. The state of the cylindrical portions 1 and 2 during this rotation process is shown in FIGS. 9 and 10.

[0060] Fig. 9 is a perspective view of the cylindrical portion 2 rotated in the rotation step included in the welding method for cylindrical portions 1 and 2 according to embodiment 1, and another cylindrical portion 1 into which the cylindrical portion 2 is fitted. Fig. 10 is an enlarged top view of the cylindrical portion 2 rotated in the rotation step included in the welding method, and another cylindrical portion 1 into which the cylindrical portion 2 is fitted. Note that the shapes of the cylindrical portions 1 and 2 are simplified in Figs. 9 and 10 for ease of understanding. The area where the molten pool 6 is formed is shaded.

[0061] As shown in FIG. 9, in the rotation step, the cylindrical portion 1 is not rotated, and only the cylindrical portion 2 is rotated clockwise in top view around the cylindrical axis C, for example, as indicated by arrow A5.

[0062] The movement of the molten metal at this time will be described, focusing on portions P10, P20, and P30, which are portions of the weld pool 6 shown in Figure 10. The shapes of portions P10, P20, and P30 shown in Figure 10 are circular before the cylindrical portion 2 rotates. As the cylindrical portion 2 rotates clockwise in a top view, portions P10, P20, and P30 are pulled clockwise and stretched circumferentially, deforming into elliptical portions P11, P21, and P31. As a result, convection, i.e., forced convection, indicated by arrows A10, A20, and A30 occurs within the weld pool 6. By generating a flow stronger than Marangoni convection, it is difficult for a pool 61, where a large amount of molten metal accumulates locally, to occur within the weld pool 6. As a result, the amount of molten metal decreases in areas other than the pool 61, preventing a decrease in the weld strength due to a decrease in the amount of molten metal. When rotating the cylindrical portion 2, it is desirable to make the end faces of the cylindrical end 13 of the cylindrical portion 1 and the cylindrical end 23 of the cylindrical portion 2 horizontal. This makes it desirable to make the molten pool 6 horizontal, as this arrangement reduces the effect of gravity on the molten pool 6.

[0063] This rotation process is continued until the molten metal solidifies. For example, the output shaft 443 of the motor 44 may be kept rotating from the start of rotation until the molten metal solidifies and the output shaft 443 stops rotating. This eliminates the need for a mechanism to detect the solidification of the molten metal, thereby simplifying the device. In this case, the time required for the molten metal to solidify may be determined in advance by experiment, and the controller 45 may drive the motor 44 for a fixed time longer than that time.

[0064] When the molten metal solidifies, a weld 5 shown in Figure 3 is formed. As a result, the cylindrical portions 1 and 2 are welded together. This completes the method for welding the cylindrical portions 1 and 2.

[0065] The hot water storage tank 10 and nipple 20 described in embodiment 1 are an example of the first member and second member defined in the present disclosure. The cylindrical portion 1 of the hot water storage tank 10 and the cylindrical portion 2 of the nipple 20 are an example of the first cylindrical portion and second cylindrical portion defined in the present disclosure. The cylindrical end 13 of the cylindrical portion 1 and the cylindrical end 23 of the cylindrical portion 2 are an example of the first cylindrical end and second cylindrical end defined in the present disclosure. The melting process is an example of a process for forming a molten pool spanning the first cylindrical end and the second cylindrical end over the entire circumference defined in the present disclosure. The rotation process is an example of a process for rotating at least one of the first cylindrical portion and the second cylindrical portion in the circumferential direction defined in the present disclosure.

[0066] Furthermore, the through hole 12 formed in the wall surface portion 11 of the hot water storage tank 10 is an example of a through hole formed in a plate-like portion as defined in the present disclosure. The cylindrical portion 1 formed by burring is an example of a burred portion as defined in the present disclosure. The through hole 12 surrounded by the cylindrical portion 1 is an example of an inlet / outlet for hot water or water of the hot water tank as defined in the present disclosure. The nipple 20 is an example of a pipe as defined in the present disclosure. Furthermore, the holding mechanisms 41, 42 and the laser irradiator 43 provided in the welding device 4A are examples of a first holding mechanism, a second holding mechanism, and a heating mechanism as defined in the present disclosure.

[0067] As described above, in the method for welding the cylindrical portions 1 and 2 according to the first embodiment, the cylindrical portion 2 is rotated in the circumferential direction while the end surface portions of the cylindrical ends 13 and 23 of the cylindrical portions 1 and 2 are melted. As a result, centrifugal force acts on the molten metal due to the rotation of the cylindrical portion 2, causing the molten metal to convect in the circumferential direction. This prevents the molten metal from concentrating in one area and becoming insufficient in other areas. As a result, a decrease in the weld strength of the cylindrical portions 1 and 2 is prevented. According to this welding method, the cylindrical portions 1 and 2 can be welded with sufficient weld strength.

[0068] Furthermore, in the method for welding the cylindrical portions 1 and 2 according to the first embodiment, the rotation of the cylindrical portion 2 begins when the laser beam irradiation is initiated and continues until the molten metal solidifies. This allows the molten metal generated by the laser beam irradiation to be rapidly convected and to continue to convect as long as the molten metal exists. As a result, it is possible to more effectively prevent the molten metal from concentrating in one area and becoming insufficient in other areas.

[0069] (Modification) In the method for welding the cylindrical portions 1 and 2 according to the first embodiment, the cylindrical portion 2 is rotated in the rotation step, but the method for welding the cylindrical portions 1 and 2 is not limited to this. In the method for welding the cylindrical portions 1 and 2, it is sufficient that at least one of the cylindrical portions 1 and 2 is rotated in the circumferential direction in the rotation step. Therefore, in the rotation step, the cylindrical portion 1 may be rotated instead of the rotation of the cylindrical portion 2 described in the first embodiment. This is because even in such a configuration, the molten metal can be convected to prevent the molten metal from concentrating in a certain area.

[0070] (Embodiment 2) As described above, in the method for welding cylindrical portions 1 and 2, it is sufficient that at least one of cylindrical portions 1 and 2 is rotated in the circumferential direction in the rotation step. Therefore, in a method for welding cylindrical portions 1 and 2 according to embodiment 2, both cylindrical portions 1 and 2 are rotated in the rotation step. Hereinafter, a method for welding cylindrical portions 1 and 2 according to embodiment 2 will be described with reference to Figures 11 to 14. In embodiment 2, the configuration different from embodiment 1 will be mainly described.

[0071] FIG. 11 is a perspective view of two cylindrical portions 1 and 2 rotated in a rotation process included in a welding method for cylindrical portions 1 and 2 according to embodiment 2. FIG. 12 is an enlarged top view of the cylindrical portions 1 and 2 rotated in a rotation process included in the welding method. FIG. 13 is a flowchart of the welding method for cylindrical portions 1 and 2 according to embodiment 2. FIG. 14 is a top view of the cylindrical portions 1 and 2 irradiated with laser light by a laser irradiator 43 in a melting process included in the welding method. Note that, as with FIGS. 9 and 10, the shapes of the cylindrical portions 1 and 2 are simplified in FIGS. 11 and 12 for ease of understanding. The area where the molten pool 6 is formed is shaded. Meanwhile, in FIG. 14, the irradiation area IR is hatched to indicate the area irradiated with the laser light.

[0072] As shown in FIG. 11 , in the method for welding cylindrical portions 1 and 2 according to the second embodiment, in the rotation process, both cylindrical portions 1 and 2 are rotated around a cylindrical axis C, which is the central axis of the cylindrical portions 1 and 2.

[0073] Specifically, in the rotation step, the cylindrical portion 1 is rotated counterclockwise in top view as indicated by arrow A6. The cylindrical portion 2 is rotated clockwise in top view as indicated by arrow A5. The rotation speeds of the cylindrical portions 1 and 2 are set to be different. For example, the rotation speed of the cylindrical portion 1 is set to be higher than the rotation speed of the cylindrical portion 2.

[0074] The movement of the molten metal at this time will be described by focusing on portions P10, P20, and P30, which are portions of the molten pool 6 shown in Figure 12. The shapes of portions P10, P20, and P30 shown in Figure 12 are circular, representing the shapes before the cylindrical portions 1 and 2 rotate. As the cylindrical portions 1 and 2 rotate in the directions described above during the rotation process, portions P10, P20, and P30 are pulled in clockwise and counterclockwise directions in a top view. As a result, portions P10, P20, and P30 deform into elliptical shapes, representing portions P12, P22, and P32. Because the rotational speed of either cylindrical portion 1 or 2 is higher, forced convection occurs in the molten pool 6 in the direction of rotation of that portion. For example, if the rotational speed of cylindrical portion 1 is faster than that of cylindrical portion 2, forced convection occurs in the direction of rotation of cylindrical portion 1, as indicated by arrows A11, A21, and A31. If the forced convection is stronger than the Marangoni convection, it becomes difficult for the reservoir 61 to occur in the molten pool 6. As a result, the method for welding the cylindrical portions 1 and 2 according to the second embodiment, like the first embodiment, prevents the amount of molten metal from becoming small in areas other than the reservoir 61, thereby suppressing a decrease in the weld strength.

[0075] In the method for welding the cylindrical portions 1 and 2 according to the second embodiment, the rotation step is started before the melting step (step S21), as shown in Fig. 13. This is to ensure that the laser light emitted by the laser irradiator 43 is uniformly applied to the cylindrical ends 13 and 23 of the cylindrical portions 1 and 2 in the melting step.

[0076] More specifically, in the melting process, for example, the optical axis of the laser beam may be tilted relative to the cylindrical ends 13, 23 of the cylindrical portions 1, 2, resulting in the annular irradiation region of the laser beam not being a uniform ring shape with a uniform width over the entire circumference. Specifically, as shown in FIG. 14 , the annular irradiation region IR of the laser beam may be a ring shape with a narrow width in one portion in the circumferential direction and a wide width in other portions in the circumferential direction. When the laser beam is irradiated in such an irradiation region, melting progresses in one portion of the cylindrical ends 13, 23 of the cylindrical portions 1, 2, generating a large amount of molten metal, while generating less molten metal in other portions. Furthermore, the molten metal is likely to be at a high temperature in one portion of the cylindrical ends 13, 23 and at a low temperature in other portions, which makes it more likely that the accumulation portion 61 due to the Marangoni convection described above will occur.

[0077] To solve this problem, in the method for welding the cylindrical portions 1 and 2 according to the second embodiment, the rotation process is started before the melting process, as shown in FIG. 13 . Because the cylindrical portions 1 and 2 rotate during the rotation process, the amount of laser light irradiated onto each circumferential portion of the cylindrical ends 13 and 23 of the cylindrical portions 1 and 2 during the melting process is uniform. As a result, the amount of melting at each circumferential portion of the cylindrical ends 13 and 23 is uniform, making it less likely that the pool 61 described above will occur. Furthermore, the temperature at each circumferential portion of the cylindrical ends 13 and 23 is also uniform. As a result, the pool 61 due to Marangoni convection is less likely to occur. This prevents the amount of molten metal from becoming small at a portion of the circumferential portion of the cylindrical ends 13 and 23, thereby suppressing a decrease in weld strength.

[0078] The rotation speed of the cylindrical portions 1, 2 is preferably a speed at which the cylindrical portions 1, 2 rotate one or more times during the melting process. This is because such a speed can uniformize the amount of laser light irradiated onto each circumferential portion of the cylindrical ends 13, 23 of the cylindrical portions 1, 2. Furthermore, the cylindrical portions 1, 2 may be rotated relative to the laser irradiator 43, more specifically, relative to the optical axis of the laser light. This is because such rotation uniformizes the amount of laser light irradiated.

[0079] This rotation process is terminated after the melting process (step S22) in order to force convection of the molten metal as much as possible during melting. For example, the rotation process is continued until the molten metal solidifies after the melting process, and then terminated. This prevents the amount of molten metal from becoming small in a portion of the circumferential direction of the cylindrical ends 13, 23 as much as possible, thereby preventing a decrease in weld strength.

[0080] The cylindrical portions 1 and 2 described in the second embodiment are an example of the first cylindrical portion and the second cylindrical portion defined in the present disclosure. The counterclockwise direction in which the cylindrical portion 1 rotates as viewed from above is an example of one circumferential direction defined in the present disclosure. The clockwise direction in which the cylindrical portion 2 rotates as viewed from above is an example of the other circumferential direction defined in the present disclosure.

[0081] As described above, in the method for welding cylindrical portions 1 and 2 according to the second embodiment, during the rotation process, cylindrical portion 1 is rotated counterclockwise as viewed from above, and cylindrical portion 2 is rotated clockwise as viewed from above. This causes forced convection of molten metal at cylindrical ends 13 and 23 of cylindrical portions 1 and 2, respectively. As a result, the method for welding cylindrical portions 1 and 2 according to the second embodiment prevents the molten metal from concentrating in some areas of cylindrical ends 13 and 23, resulting in a shortage of molten metal in other areas. Furthermore, a decrease in the weld strength of cylindrical portions 1 and 2 can be suppressed.

[0082] During the rotation process, the rotation speeds of cylindrical portion 1 and cylindrical portion 2 are different, so the molten metal in molten pool 6 is forced to circulate toward the portion with the faster rotation speed overall. As a result, the molten metal is less likely to be concentrated in certain regions of cylindrical ends 13, 23. The method for welding cylindrical portions 1 and 2 according to embodiment 2 can suppress a decrease in the weld strength of cylindrical portions 1 and 2.

[0083] Furthermore, since the rotating step is performed before the melting step, it is possible to uniform the amount of laser light irradiated onto each of the cylindrical ends 13, 23 of the cylindrical portions 1, 2. As a result, in the rotating step, it is possible to uniform the amount of melting and the temperature of each portion in the circumferential direction of the cylindrical ends 13, 23, thereby suppressing uneven distribution of the molten metal. As a result, the rotating step can suppress a decrease in the welding strength of the cylindrical portions 1 and 2.

[0084] (Modification) In the method for welding the cylindrical portions 1 and 2 according to the second embodiment, the cylindrical portions 1 and 2 are rotated in opposite directions in the rotation step, but the method for welding the cylindrical portions 1 and 2 is not limited to this. In the method for welding the cylindrical portions 1 and 2, as described in the first embodiment, it is sufficient that at least one of the cylindrical portions 1 and 2 is rotated in the circumferential direction in the rotation step. Therefore, as long as this is satisfied, the direction of rotation is not limited. For example, the cylindrical portions 1 and 2 may be rotated in the same direction in the rotation step.

[0085] FIG. 15 is a perspective view of the two cylindrical portions 1 and 2 rotated in a modified example of the rotating step included in the welding method for the cylindrical portions 1 and 2 according to the second embodiment.

[0086] In the rotation process, both cylindrical portions 1 and 2 may be rotated clockwise in a top view, as shown in Fig. 15. In this case, as shown by arrows A5 and A7, the rotation speed of cylindrical portion 1 may be faster than that of cylindrical portion 2. Alternatively, although not shown, the rotation speed of cylindrical portion 1 may be slower than that of cylindrical portion 2. In other words, the rotation speeds of cylindrical portions 1 and 2 may be different. This configuration allows the laser beam to be uniformly applied to the cylindrical ends 13 and 23 of cylindrical portions 1 and 2, respectively, in the melting process, and also allows forced convection of the molten metal in the molten pool 6 in the rotation process.

[0087] Naturally, both the cylindrical portions 1 and 2 may be rotated counterclockwise when viewed from above.

[0088] Furthermore, when both cylindrical portions 1 and 2 are rotated clockwise or counterclockwise in a top view, i.e., when cylindrical portions 1 and 2 are rotated in the same direction, cylindrical portions 1 and 2 may rotate at the same speed. Even with this type of rotation, forced convection of the molten metal in the molten pool 6 can be achieved by accelerating or decelerating. Furthermore, when acceleration or deceleration is not performed, forced convection of the molten metal cannot be achieved, but the laser beam can be uniformly applied to the cylindrical ends 13 and 23 of cylindrical portions 1 and 2, respectively.

[0089] (Embodiment 3) Welding device 4A used in the method for welding cylindrical portions 1 and 2 according to embodiment 1 includes holding mechanisms 41 and 42, which hold cylindrical portion 1 of hot water storage tank 10 and cylindrical portion 2 of nipple 20 by the magnetic force of magnets 414 and 423. However, holding mechanisms 41 and 42 are not limited to this. In welding device 4A, holding mechanism 41 may be any mechanism that holds cylindrical portion 1, and in this case, holding mechanism 42 may be any mechanism that holds cylindrical portion 2 fitted into cylindrical portion 1 in a state where the end faces of cylindrical end 13 of cylindrical portion 1 and cylindrical end 23 of cylindrical portion 2 are aligned.

[0090] Here, aligning the end faces of the cylindrical end 13 and the cylindrical end 23 means that the positions of these end faces are aligned to the extent that there is only a step between them that is large enough to form a molten pool across these end faces during the melting process.

[0091] In a welding device 4B used in a method for welding cylindrical portions 1 and 2 according to embodiment 3, holding mechanisms 41 and 42 hold cylindrical portions 1 and 2 by the biasing force of springs. The method for welding cylindrical portions 1 and 2 according to embodiment 3 will be described below with reference to Fig. 16. The description of embodiment 3 will focus on configurations that differ from embodiments 1 and 2.

[0092] FIG. 16 is a cross-sectional view of a welding device 4B used in a method for welding cylindrical portions 1 and 2 according to the third embodiment.

[0093] As shown in FIG. 16 , the large cylindrical portion 411 included in the holding mechanism 41 has a rib 415 that extends along the outer circumferential surface of the large cylindrical portion 411 above the upper end surface of the large cylindrical portion 411. A spring 416 is provided at the upper end of the rib 415 to bias the clamping portion 417 toward the cylindrical end 413 of the large cylindrical portion 411. As described in the first embodiment, the holding mechanism 41 allows the wall portion 11 of the hot water storage tank 10 to be placed on the cylindrical end 413 of the large cylindrical portion 411. When the wall portion 11 of the hot water storage tank 10 is placed on the cylindrical end 413 of the large cylindrical portion 411, the spring 416 presses the clamping portion 417 against the wall portion 11. As a result, the wall portion 11 is sandwiched between the clamping portion 417 and the cylindrical end 413 of the large cylindrical portion 411. As a result, the holding mechanism 41 holds the wall portion 11 of the hot water storage tank 10.

[0094] In contrast, a through-hole 425 is formed in the columnar portion 421 of the holding mechanism 42, penetrating the columnar portion 421 in the horizontal direction. Inside the through-hole 425, a pressing member 426 is provided on one opening side, and a pressing member 427 is provided on the other opening side. A spring 428 is provided between the pressing members 426 and 427 to urge the pressing members 426, 427 toward the openings where they are located. As described in the first embodiment, in the holding mechanism 42, the columnar portion 421 can be fitted into the cylindrical portion 2 of the nipple 20 when the cylindrical portion 2 of the nipple 20 is placed over the columnar portion 421. When the cylindrical portion 2 of the nipple 20 is fitted over the columnar portion 421, the spring 428 urges the pressing members 426 and 427 toward the inner wall surface of the cylindrical portion 2. This causes the pressing members 426 and 427 to be pressed against the inner wall surface of the cylindrical portion 2. As a result, the holding mechanism 42 holds the cylindrical portion 2 of the nipple 20.

[0095] As described above, in welding device 4B used in the method for welding cylindrical portions 1 and 2 according to embodiment 3, holding mechanism 41 includes spring 416 that presses clamping portion 417 against wall portion 11 of hot water storage tank 10. Also, holding mechanism 42 includes spring 428 that presses pressing members 426 and 427 against the inner wall surface of cylindrical portion 2 of nipple 20. As a result, even if wall portion 11 of hot water storage tank 10 and cylindrical portion 2 of nipple 20 are made of a material that is not magnetic and does not attract magnets 414 and 423, such as austenitic stainless steel or aluminum alloy, welding device 4B can hold wall portion 11 of hot water storage tank 10 and cylindrical portion 2 of nipple 20.

[0096] (Embodiment 4) In embodiments 1-3, the configuration of the welding method for cylindrical portions 1 and 2 is described using as an example a case where cylindrical portion 1, which is provided at the water supply port of hot water storage tank 10 provided in a water heater and formed by burring, is welded to cylindrical portion 2, which is provided at the tip of nipple 20 and forms a circular pipe. However, the welding method for cylindrical portions 1 and 2 is not limited to this. The welding method for cylindrical portions 1 and 2 only needs to weld cylindrical portions 1 and 2, and other cylindrical portions may also be welded in addition to these.

[0097] The welding method for cylindrical portions 1 and 2 according to embodiment 4 is a method for welding cylindrical portion 3 to cylindrical portions 1 and 2. Hereinafter, the welding method for cylindrical portions 1-3 according to embodiment 4 will be described with reference to Fig. 17. In embodiment 4, the configuration different from embodiments 1-3 will be mainly described.

[0098] FIG. 17 is a cross-sectional view of a hot water storage tank 30 having a cylindrical portion 1-3 welded by a welding method for a cylindrical portion 1-3 according to the fourth embodiment.

[0099] In the hot water storage tank 30 shown in FIG. 17 , a cylindrical portion 2, which is a circular pipe and can be fitted into the cylindrical portion 1, is inserted into the cylindrical portion 1 provided at the water supply port. The end face of the cylindrical end 23 of the cylindrical portion 2 is aligned with the end face of the cylindrical end 13 of the cylindrical portion 1 in the direction of the cylindrical axis C. Furthermore, in the hot water storage tank 30, a cylindrical portion 3, which is provided at the joint 31 and can be fitted into the cylindrical portion 2, is inserted into the cylindrical portion 2. The end face of the cylindrical end 33 of the cylindrical portion 3 is aligned with the end face of the cylindrical end 23 of the cylindrical portion 2 or the end face of the cylindrical end 13 of the cylindrical portion 1 in the direction of the cylindrical axis C. The cylindrical portions 1-3 arranged in this manner are joined to each other by welds 5 formed at the cylindrical ends 13, 23, and 33.

[0100] Such welding of the cylindrical portions 1-3 is achieved by applying the welding method for the cylindrical portions 1 and 2 described in embodiment 1-3. To explain the welding method for the cylindrical portions 1-3 in detail, first, the cylindrical portions 1-3 are assembled in the above-described arrangement. Then, the melting process described in embodiment 1-3 is applied to the assembled cylindrical portions 1-3 to melt the cylindrical ends 13, 23, and 33 of the cylindrical portions 1-3. Specifically, a laser beam is irradiated onto the cylindrical ends 13, 23, and 33 using a laser irradiator 43, melting the end face portions of the cylindrical ends 13, 23, and 33. This forms a molten pool 6 at the cylindrical ends 13, 23, and 33.

[0101] Next, the rotation process described in Embodiments 1-3 is applied to rotate at least one of the cylindrical portions 1-3 around the cylindrical axis C. For example, as described in Embodiment 1, when the laser light irradiation to the end face portions of the cylindrical ends 13, 23, and 33 begins in the melting process, in parallel with the laser light irradiation, only the cylindrical portion 2 is rotated clockwise in a top view around the cylindrical axis C, leaving the cylindrical portions 1 and 3 as they are. The rotation of the cylindrical portion 2 is then continued until the laser light irradiation ends and the molten metal in the molten pool 6 solidifies.

[0102] As the molten metal solidifies, a weld 5 is formed on the cylindrical portion 1-3. As a result, the cylindrical portion 1-3 is welded. Once the cylindrical portion 1-3 is welded, it becomes impossible to rotate the cylindrical portion 2 alone, and as a result, the rotation of the cylindrical portion 2 stops. This completes the welding method for the cylindrical portion 1-3.

[0103] As described above, in the welding method for the cylindrical portions 1-3 according to the fourth embodiment, at least one of the cylindrical portions 1-3 is rotated around the cylindrical axis C during the melting process, from the time when the cylindrical ends 13, 23, and 33 of the cylindrical portions 1-3 are melted to form the molten pool 6 until the molten metal in the molten pool 6 solidifies. Therefore, as in the first and second embodiments, the molten metal is forced to convect in the direction of rotation of at least one of the cylindrical portions 1-3. As a result, the welding method for the cylindrical portions 1-3 according to the fourth embodiment prevents the molten metal from concentrating in certain regions of the cylindrical ends 13, 23, and 33, resulting in a shortage of molten metal in other regions. Furthermore, this welding direction can prevent a decrease in the weld strength of the cylindrical portions 1 and 2.

[0104] In the welding method for cylindrical portions 1-3 according to embodiment 4, an example is shown in which only cylindrical portion 2 is rotated while cylindrical portions 1 and 3 remain in place during the rotation step, but cylindrical portions 2 and 3 may be rotated while cylindrical portion 1 remains in place, or each of cylindrical portions 1-3 may be rotated. In short, in the welding method for cylindrical portions 1-3 according to embodiment 4, it is sufficient to rotate at least one of cylindrical portions 1-3 around cylindrical axis C. In this case, the rotation direction may be either clockwise or counterclockwise when viewed from above.

[0105] (Modification) Furthermore, the welding method for the cylindrical portions 1-3 according to the fourth embodiment is applied to a method for manufacturing a water heater in which the cylindrical portion 2, which is a circular pipe, and the cylindrical portion 3, which is provided at the joint 31, are assembled to the cylindrical portion 1 provided at the water supply port of the hot water storage tank 30. However, the welding method for the cylindrical portions 1-3 according to the fourth embodiment is not limited to this. The welding method for the cylindrical portions 1-3 according to the fourth embodiment may also be applied to a method for manufacturing a compressor in which the cylindrical portion 2, which is a pipe, and the cylindrical portion 3, which is provided at the joint 31, are assembled to the cylindrical portion 1 provided at the housing of the compressor. Naturally, the welding method for the cylindrical portions 1-3 according to the first to third embodiments may also be applied to a method for manufacturing a compressor. For example, the welding method for the cylindrical portions 1-3 according to the first to third embodiments may also be applied to a method for manufacturing a compressor in which the cylindrical portion 2, which is a pipe, is assembled to the cylindrical portion 1 provided at the housing of the compressor.

[0106] (Embodiment 5) In the welding methods for cylindrical portions 1 and 2 according to embodiments 1-3, cylindrical portions 1 and 2 are welded by directly melting the end surface portions of cylindrical end 13 of cylindrical portion 1 and cylindrical end 23 of cylindrical portion 2. In addition, in the welding method for cylindrical portions 1-3 according to embodiment 4, cylindrical portions 1-3 are welded by directly melting the end surface portions of cylindrical ends 13 and 23 and the end surface portion of cylindrical end 33 of cylindrical portion 3. However, the welding methods for cylindrical portions 1 and 2 and the welding methods for cylindrical portions 1-3 are not limited to these. The welding method for cylindrical portions 1 and 2 may involve melting a circular member abutting the end surface portions of cylindrical ends 13 and 23, and melting cylindrical ends 13 and 23 with the heat from melting the circular member. Alternatively, the welding method for the cylindrical portions 1-3 may be such that a ring member is brought into contact with the end face of the cylindrical ends 13, 23, 33 and melted, and the cylindrical ends 13, 23, 33 are melted by the heat of melting the ring member.

[0107] The method for welding cylindrical portions 1 and 2 according to embodiment 5 is a method for welding cylindrical portions 1 and 2 by melting annular members that are in contact with the end surface portions of cylindrical ends 13 and 23 of cylindrical portions 1 and 2, thereby melting the end surface portions of cylindrical ends 13 and 23. Hereinafter, the welding method for cylindrical portions 1 and 2 according to embodiment 5 will be described with reference to Figures 18 to 20. In embodiment 5, the following description will focus on the configuration that differs from embodiments 1 to 4.

[0108] Fig. 18 is a flowchart of a method for welding cylindrical portions 1 and 2 according to embodiment 5. Fig. 19 is a cross-sectional view of cylindrical portions 1 and 2 to which a circular member 7 has been attached in a circular member attaching step included in the method for welding cylindrical portions 1 and 2. Fig. 20 is a cross-sectional view of cylindrical portions 1 and 2 to which a molten pool 6 has been formed in a welding step included in the method for welding cylindrical portions 1 and 2.

[0109] As shown in FIG. 18, in the method for welding the cylindrical portions 1 and 2 according to the fifth embodiment, first, an attachment step of attaching the circular ring member 7 is performed (step S50).

[0110] Specifically, a circular ring member 7 is prepared, the outer diameter and inner diameter of which are the same as those of the circular end surface portion formed by combining the cylindrical end 13 of the cylindrical portion 1 and the cylindrical end 23 of the cylindrical portion 2. This is because a circular ring member 7 having such a shape can cover the above-mentioned circular end surface portion. In addition, a member made of the same material as the metallic material forming the cylindrical portions 1 and 2 is prepared for the circular ring member 7. This is because if such a material is used, the material melted in the melting step can be used as a welding material to weld the cylindrical portions 1 and 2 together.

[0111] 19, the prepared circular member 7 is placed over the end face portions of the cylindrical ends 13, 23. At this time, the central axis AL of the circular member 7 and the cylindrical axis C of the cylindrical ends 13, 23 should be aligned, and the annular surface of the circular member 7 should be brought into contact with the end face portions of the cylindrical ends 13, 23, thereby placing the circular member 7 over the end face portions of the cylindrical ends 13, 23. In this way, the circular member 7 is attached to the cylindrical portions 1, 2.

[0112] In this state, a melting step is carried out to melt the welded portions of the circular ring member 7 and the cylindrical portions 1 and 2 shown in FIG. 18 (step S51).

[0113] More specifically, in step S50, the annular member 7 covering the end surface portions of the cylindrical ends 13, 23 is melted. In this melting process, for example, a welding device 4A equipped with the laser irradiator 43 described in embodiment 1 is used. The annular member 7 is heated by the welding device 4A, and the heat of the molten metal formed by the heating melts the end surface portions of the cylindrical ends 13, 23. As a result, a molten pool 6 is formed spanning the cylindrical ends 13, 23, as shown in FIG. 20 . The molten pool 6 is formed around the entire circumference of the cylindrical ends 13, 23.

[0114] 20, the ring-shaped member 7 may be completely melted, or only a portion of the ring-shaped member 7 may be melted. The molten pool 6 may also include a portion of the ring-shaped member 7 that remains unmelted.

[0115] Returning to FIG. 18, when the end surface portions of the ring member 7 and the cylindrical ends 13, 23 start to melt, a rotation process is carried out in parallel with the melting process (step S52).

[0116] In this rotation step, at least one of the annular member 7 and the cylindrical portions 1, 2 is rotated in the circumferential direction. For example, when the welding device 4A described in the first embodiment is used, when laser irradiation by the laser irradiator 43 begins, the annular member 7 and the cylindrical portion 1 are left as they are, and the output shaft 443 of the motor 44 of the holding mechanism 42 is rotated to rotate the cylindrical portion 2 about the cylindrical axis C. In other words, the cylindrical portion 2 is rotated in the circumferential direction.

[0117] The rotation of the cylindrical portion 2 continues until the laser irradiation by the laser irradiator 43 ends and the molten metal forming the molten pool 6 solidifies. For example, the rotation of the cylindrical portion 2 continues for a while after the laser irradiation by the laser irradiator 43 by rotating the output shaft 443 of the motor 44 of the holding mechanism 42. The rotation of the cylindrical portion 2 continues until the molten metal solidifies, welding the annular member 7 and the cylindrical portions 1 and 2 together, and the output shaft 443 of the motor 44 can no longer rotate.

[0118] When the molten metal forming the molten pool 6 solidifies, a weld is formed at the cylindrical ends 13, 23, although this is not shown in Figure 20. As a result, the cylindrical portions 1 and 2 are welded together, or the cylindrical portions 1, 2 are welded to the unmelted annular member 7. This completes the welding method for the cylindrical portions 1, 2.

[0119] The weld formed by the welding method for the cylindrical portions 1 and 2 is also formed between the cylindrical portions 1 and 2. Alternatively, the weld is also formed between the annular member 7 and the cylindrical portion 1, between the annular member 7 and the cylindrical portion 2, and between the cylindrical portions 1 and 2. Therefore, even if a gap occurs between the cylindrical portions 1 and 2 due to variations in assembly or manufacturing, the weld fills into the gap, allowing the cylindrical portions 1 and 2 to be welded with high strength. Alternatively, even if a step occurs between the cylindrical end 13 of the cylindrical portion 1 and the cylindrical end 23 of the cylindrical portion 2, the weld covers the step and closes the gap with the annular member 7 caused by the step. As a result, the annular member 7 and the cylindrical portions 1 and 2 can be welded with high strength.

[0120] As described above, in the method for welding the cylindrical portions 1 and 2 according to the fifth embodiment, the circular member 7 is brought into contact with the end surfaces of the cylindrical ends 13 and 23 of the cylindrical portions 1 and 2, and these end surfaces are covered with the circular member 7. The circular member 7 is then melted, and the heat from the melting of the circular member 7 melts the cylindrical ends 13 and 23. As a result, a sufficient amount of molten metal is supplied. This allows for high-strength welding even when there is a gap between the cylindrical portions 1 and 2.

[0121] (Modification) The circular member 7 described in the fifth embodiment has the shape of a thin circular plate, but the shape of the circular member 7 is not limited to this.

[0122] Fig. 21 is a cross-sectional view of a modified example of the circular ring member 7 used in the welding method for cylindrical portions according to embodiment 5, and the cylindrical portions 1 and 2. Fig. 22 is a cross-sectional view of another modified example of the circular ring member 7 and the cylindrical portions 1 and 2.

[0123] 21 , the circular ring member 7 may have an outer peripheral wall portion 71 that protrudes downward along the outer periphery. When the circular ring member 7 is placed over the cylindrical ends 13, 23 of the cylindrical portions 1, 2, the outer peripheral wall portion 71 may cover the outer peripheral wall of the cylindrical portion 1 and engage with the cylindrical portion 1. In short, it is preferable that the cylindrical portion 1 fits into the outer peripheral wall portion 71.

[0124] 22 , the annular member 7 may have an inner peripheral wall portion 72 that protrudes downward along the outer periphery. The inner peripheral wall portion 72 may fit into the internal space of the cylindrical portion 2 when the annular member 7 is placed over the cylindrical ends 13, 23 of the cylindrical portions 1, 2.

[0125] In this way, the shape of the annular member 7 is not limited to a thin annular plate, but may be any shape that covers at least the boundary between the cylindrical ends 13 and 23.

[0126] The above describes the welding method for the cylindrical portion 1-3, the manufacturing method for the water heater, the manufacturing method for the compressor, and the welding devices 4A and 4B relating to embodiments 1-5 of the present disclosure, but the welding method for the cylindrical portion 1-3, the manufacturing method for the water heater, the manufacturing method for the compressor, and the welding devices 4A and 4B are not limited to these.

[0127] For example, in the first embodiment, the rotation step is performed after the start of irradiation of the laser beam to the cylindrical ends 13, 23 of the cylindrical portions 1, 2. In the second embodiment, the rotation step is performed before the start of irradiation of the laser beam. However, the welding method for the cylindrical portions 1-3 is not limited to these. In the welding method for the cylindrical portions 1-3, the rotation step may be a step of rotating at least one of the cylindrical portions 1-3 in the circumferential direction at least during the period from when the molten pool 6 is formed until when it solidifies.

[0128] Here, the cylindrical portion 1-3 refers to a hollow circular cylinder. In this specification, the cylindrical portion 1-3 may include a circular cylinder whose length in the direction of the cylindrical axis C is smaller than its outer diameter, in other words, a circular ring. The cylindrical portion 1-3 may also include a conical cylinder whose thickness tapers toward the tip or base end.

[0129] As described above, the timing of the rotation step is arbitrary as long as it satisfies this condition, since it is sufficient that the rotation step is a step of rotating at least one of the cylindrical portions 1-3 in the circumferential direction at least during the period from the formation of the molten pool 6 to the solidification thereof. For example, the rotation step may be performed simultaneously with the start of irradiation of the cylindrical ends 13, 23, and 33 of the cylindrical portions 1-3 with laser light.

[0130] When the rotation process is performed after the start of laser irradiation of the cylindrical ends 13, 23, and 33 of the cylindrical portion 1-3, it is preferable to start the rotation process after the start of laser irradiation and before the molten metal is generated. Starting the rotation process at such a timing ensures that the rotation is performed during the required period and also shortens the rotation time.

[0131] Furthermore, in embodiment 1-5, the rotation process is performed until the molten metal solidifies. However, the welding method for the cylindrical portion 1-3 is not limited to this. In the welding method for the cylindrical portion 1-3, as described above, the rotation process may be a process of rotating at least one of the cylindrical portions 1-3 in the circumferential direction at least between the formation of the molten pool 6 and solidification. Therefore, the rotation process may be terminated before the molten metal solidifies. For example, when at least one of the cylindrical portions 1-3 is rotated in the circumferential direction during the rotation process, the rotation may be performed by a servo motor, and the servo motor may be controlled to stop the rotation at a predetermined stop position before the molten metal solidifies. In this configuration, if at least one of the rotating cylindrical portions 1-3 has a structure, such as a screw hole, in the circumferential direction, the structure can be welded while being positioned in a fixed position.

[0132] In embodiment 1-5, the rotation process ends when the molten metal solidifies, making it impossible to rotate. In this case, however, since the stopping position cannot be controlled, it is desirable to apply this to the rotationally symmetric cylindrical portion 1-3.

[0133] Furthermore, in embodiment 1-5, the melting of the cylindrical ends 13, 23, and 33 of the cylindrical portion 1-3 in the melting step is achieved by irradiating them with laser light. However, the welding method for the cylindrical portion 1-3 is not limited to this. The welding method for the cylindrical portion 1-3 may be any process that melts the cylindrical ends 13, 23, and 33 of the cylindrical portion 1-3 and forms a molten pool 6 spanning the entire circumference of the cylindrical ends 13, 23, and 33. Therefore, any method can be used to melt the cylindrical ends 13, 23, and 33 as long as this condition is met. For example, the cylindrical ends 13, 23, and 33 may be melted using an electron beam.

[0134] Furthermore, in the first and second embodiments, the cylindrical portions 1 and 2 are formed of a steel material. However, the cylindrical portions 1 and 2 are not limited to this. The cylindrical portions 1 and 2 may be formed of any material as long as the cylindrical end 13 of the cylindrical portion 1 and the cylindrical end 23 of the cylindrical portion 2 fitted into the cylindrical portion 1 are fused together, with the end surface of the cylindrical end 13 being flush with the cylindrical end 23. Therefore, as long as this condition is met, the material of the cylindrical portions 1 and 2 is arbitrary. For example, the cylindrical portions 1 and 2 may be formed of pure aluminum or an aluminum alloy. Furthermore, the cylindrical portion 3 described in the fourth embodiment may also be formed of a material that satisfies the same conditions as the cylindrical portions 1 and 2, and may be formed of steel, pure aluminum, or an aluminum alloy.

[0135] In embodiment 1-5, the cylindrical axis C of the cylindrical portion 1-3 is oriented vertically, and the end faces of the cylindrical ends 13, 23, and 33 are oriented horizontally. However, the orientation of the end faces of the cylindrical portion 1-3 and the cylindrical ends 13, 23, and 33 in embodiment 1-5 is not limited to this. The end faces of the cylindrical portion 1-3 and the cylindrical ends 13, 23, and 33 may be oriented in any direction as long as their relative positions are maintained. The Marangoni convection that generates the reservoir 61 may flow in a direction against gravity if there is a temperature distribution in the molten metal within the molten pool 6. Therefore, the welding method for the cylindrical portion 1-3 can also be applied to configurations in which the end faces of the cylindrical ends 13, 23, and 33 are oriented in a direction other than horizontal. For example, the welding method for the cylindrical portion 1-3 can also be applied to configurations in which the end faces of the cylindrical ends 13, 23, and 33 are oriented vertically, and the cylindrical axis C of the cylindrical portion 1-3 is oriented horizontally.

[0136] In embodiments 1-3 and 5, the welding method for cylindrical portions 1 and 2 is applied to the assembly of hot water storage tank 10 and nipple 20 of a water heater. In a modified example of embodiment 4, the welding method for cylindrical portions 1-3 is applied to the assembly of a compressor housing and piping, or the assembly of a housing, piping, and joint 31. In this way, the welding method for cylindrical portions 1-3 is applicable to the general welding of cylindrical portions 1-3, which aligns and joins the end faces of cylindrical ends 13, 23, and 33.

[0137] In the first to fifth embodiments, the cylindrical portion 1 to be welded surrounds the water supply port of the hot water storage tank 10, but the cylindrical portion 1 is not limited to this, and when the cylindrical portion 1 is provided in the hot water storage tank 10, it may be provided at the hot water or cold water inlet / outlet. For example, the cylindrical portion 1 may be provided at the drain port, hot water supply port, or hot water return port of the hot water storage tank.

[0138] As described above, the welding method for the cylindrical portions 1-3, the manufacturing method for the water heater, the manufacturing method for the compressor, and the welding devices 4A and 4B are not limited to the above-described embodiments, and various modifications and substitutions can be made. Various embodiments of the present disclosure are described below as appendices.

[0139] (Supplementary Note 1) A method for welding a first cylindrical portion and a second cylindrical portion, comprising: a step of melting a first cylindrical end of a first cylindrical portion provided on a first member and a second cylindrical end of a second cylindrical portion provided on a second member and fitted to the first cylindrical portion, the second cylindrical end having an end face aligned with the first cylindrical end, to form a molten pool spanning the first cylindrical end and the second cylindrical end over the entire circumference; and a step of rotating at least one of the first cylindrical portion and the second cylindrical portion in a circumferential direction at least during the period from when the molten pool is formed until when it solidifies. (Supplementary Note 2) A method for welding a first cylindrical portion and a second cylindrical portion, comprising: a step of bringing a circular member into contact with a first cylindrical end of a first cylindrical portion included in a first member and a second cylindrical end of a second cylindrical portion included in a second member and fitted to the first cylindrical portion, the second cylindrical portion having an end face aligned with the first cylindrical end, and covering the first cylindrical end and the second cylindrical end with the circular member; a step of melting the circular member and melting the first cylindrical end and the second cylindrical end with the heat from melting the circular member, thereby forming a molten pool spanning the first cylindrical end and the second cylindrical end over the entire circumference; and a step of rotating at least one of the first cylindrical portion, the second cylindrical portion, and the circular member in a circumferential direction at least during the period from when the molten pool is formed to when it solidifies. (Supplementary Note 3) The method for welding a first cylindrical portion and a second cylindrical portion according to Supplementary Note 1 or 2, wherein, in the step of forming a molten pool, a laser beam is annularly irradiated onto an annular surface formed by an end face of the first cylindrical end and an end face of the second cylindrical end, thereby melting the first cylindrical end and the second cylindrical end. (Supplementary Note 4) The method for welding a first cylindrical portion and a second cylindrical portion according to Supplementary Note 3, wherein the laser beam is annular parallel beam, and, in the step of forming a molten pool, the laser beam is irradiated onto the annular surface from a direction in which a cylindrical axis of the first cylindrical portion or the second cylindrical portion extends. (Supplementary Note 5) The method for welding a first cylindrical portion and a second cylindrical portion according to Supplementary Note 3 or 4, wherein the step of rotating at least one of the first cylindrical portion and the second cylindrical portion in the circumferential direction is performed at least after the start of irradiation of the laser beam. (Supplementary Note 6) The method for welding a first cylindrical portion and a second cylindrical portion according to Supplementary Note 3 or 4, wherein the step of rotating at least one of the first cylindrical portion and the second cylindrical portion in the circumferential direction is performed before the start of irradiation with the laser light.(Supplementary Note 7) The method for welding a first cylindrical portion and a second cylindrical portion according to any one of Supplementary Notes 1 to 6, wherein, in the step of rotating at least one of the first cylindrical portion and the second cylindrical portion in the circumferential direction, the first cylindrical portion is rotated in one circumferential direction, and the second cylindrical portion is rotated in the other circumferential direction. (Supplementary Note 8) The method for welding a first cylindrical portion and a second cylindrical portion according to any one of Supplementary Notes 1 to 6, wherein, in the step of rotating at least one of the first cylindrical portion and the second cylindrical portion in the circumferential direction, the first cylindrical portion is rotated in one circumferential direction, and the second cylindrical portion is rotated in the one circumferential direction at a different speed than the first cylindrical portion. (Supplementary Note 9) The method for welding a first cylindrical portion and a second cylindrical portion according to any one of Supplementary Notes 1 to 8, wherein at least one of the first cylindrical portion and the second cylindrical portion is a burring portion surrounding a through hole formed in a plate-like portion. (Supplementary Note 10) A method for welding a first cylindrical portion and a second cylindrical portion according to any one of Supplements 1 to 8, wherein at least one of the first cylindrical portion and the second cylindrical portion is a circular pipe. (Supplementary Note 11) A method for manufacturing a water heater, using the welding method according to any one of Supplements 1 to 10 to weld the first cylindrical portion provided at a hot water or cold water inlet / outlet of a hot water tank to the second cylindrical portion of a piping. (Supplementary Note 12) A method for manufacturing a compressor, using the welding method according to any one of Supplements 1 to 10 to weld the first cylindrical portion provided on a housing of a compressor to the second cylindrical portion of a piping. (Supplementary Note 13) A welding device comprising: a first holding mechanism that holds a first cylindrical portion of a first member; a second holding mechanism that holds a second cylindrical portion of a second member, fitted onto the first cylindrical portion, with end faces of a first cylindrical end of the first cylindrical portion and a second cylindrical end of the second cylindrical portion aligned; and a heating mechanism that melts the first cylindrical end of the first cylindrical portion held by the first holding mechanism and the second cylindrical end of the second cylindrical portion held by the second holding mechanism, to form a molten pool spanning the first cylindrical end and the second cylindrical end over the entire circumference, wherein at least one of the first holding mechanism and the second holding mechanism rotates at least one of the first cylindrical portion and the second cylindrical portion in a circumferential direction at least during the period from when the molten pool is formed by the heating mechanism to when the molten pool solidifies.(Supplementary Note 14) The welding device according to Supplementary Note 13, wherein the heating mechanism is a laser irradiator that annularly irradiates a laser beam onto an annular surface formed by an end face of the first cylindrical end and an end face of the second cylindrical end. (Supplementary Note 15) The welding device according to Supplementary Note 14, wherein the laser irradiator is arranged in a direction in which a cylindrical axis of the first cylindrical portion or the second cylindrical portion extends, and irradiates the laser beam, which is annular parallel light, onto the annular surface. (Supplementary Note 16) The welding device according to any one of Supplementary Notes 13 to 15, wherein at least one of the first holding mechanism and the second holding mechanism rotates at least one of the first cylindrical portion and the second cylindrical portion relative to the heating mechanism.

[0140] The present disclosure allows various embodiments and modifications without departing from the broad spirit and scope of the present disclosure. Furthermore, the above-described embodiments are intended to explain the present disclosure and do not limit the scope of the present disclosure. That is, the scope of the present disclosure is defined by the claims, not the embodiments. Various modifications made within the scope of the claims and within the meaning of the disclosure equivalent thereto are considered to be within the scope of the present disclosure.

[0141] This application is based on Japanese Patent Application No. 2022-146737 filed on September 15, 2022. The entire specification, claims, and drawings of Japanese Patent Application No. 2022-146737 are incorporated herein by reference.

[0142] 1-3 Cylindrical portion, 4A, 4B Welding device, 5 Welding portion, 6 Molten pool, 7 Annular member, 10 Hot water storage tank, 11 Wall portion, 12 Through hole, 13 Cylinder end, 14 End portion, 20 Nipple, 21 Main body, 23 Cylinder end, 30 Hot water storage tank, 31 Joint, 33 Cylinder end, 41 Holding mechanism, 42 Holding mechanism, 43 Laser irradiator, 44 Motor, 45 Controller, 60 Molten pool, 61 Reservoir portion, 71 Outer peripheral wall portion, 72 Inner peripheral wall portion, 411 Large cylindrical portion, 412 Flange portion, 413 Cylinder end, 414 Magnet, 415 Rib, 416 Spring, 417 Clamping portion, 421 Cylindrical portion, 422 Flange portion, 423 Magnet, 424 Mounting hole, 425 Through hole, 426, 427 pressing member, 428 spring, 441 bearing portion, 442 case, 443 output shaft, A cylinder shaft, A1-A6, A10, A11, A20, A21, A30, A31 arrows, AL central axis, B cylinder axis, C cylinder axis, IR irradiation area, L parallel light, P10, P11, P12, P20, P21, P22, P30, P31, P32 portions.

Claims

1. a step of melting a first cylindrical end of a first cylindrical portion of a first member and a second cylindrical end of a second cylindrical portion of a second member fitted to the first cylindrical portion, the second cylindrical end having an end surface aligned with the first cylindrical end, to form a molten pool spanning the first cylindrical end and the second cylindrical end over the entire circumference; rotating at least one of the first cylindrical portion and the second cylindrical portion in a circumferential direction at least during a period from when the molten pool is formed to when the molten pool is solidified; Equipped with A method for welding a first cylindrical portion and a second cylindrical portion.

2. a step of bringing a circular member into contact with a first cylindrical end of a first cylindrical portion of a first member and a second cylindrical end of a second cylindrical portion of a second member, the second cylindrical portion being fitted to the first cylindrical portion and having an end surface aligned with the first cylindrical end, and covering the first cylindrical end and the second cylindrical end with the circular member; a step of melting the annular member and melting the first cylindrical end and the second cylindrical end with heat of the melting of the annular member to form a molten pool spanning the first cylindrical end and the second cylindrical end over the entire circumference; rotating at least one of the first cylindrical portion, the second cylindrical portion, and the annular member in a circumferential direction at least during a period from when the molten pool is formed to when the molten pool is solidified; Equipped with A method for welding a first cylindrical portion and a second cylindrical portion.

3. In the step of forming the molten pool, a laser beam is irradiated in an annular shape onto a surface formed by an end face of the first cylindrical end and an end face of the second cylindrical end, thereby melting the first cylindrical end and the second cylindrical end.

3. The method for welding the first cylindrical portion and the second cylindrical portion according to claim 1 or 2.

4. the laser light is a circular parallel light, In the step of forming the molten pool, the laser light is irradiated onto the annular surface from a direction in which a cylindrical axis of the first cylindrical portion or the second cylindrical portion extends. The method for welding the first cylindrical portion and the second cylindrical portion according to claim 3.

5. The step of rotating at least one of the first cylindrical portion and the second cylindrical portion in the circumferential direction is performed at least after the start of the irradiation of the laser light. The method for welding the first cylindrical portion and the second cylindrical portion according to claim 3.

6. The step of rotating at least one of the first cylindrical portion and the second cylindrical portion in the circumferential direction is performed before starting the irradiation of the laser light. The method for welding the first cylindrical portion and the second cylindrical portion according to claim 3.

7. In the step of rotating at least one of the first cylindrical portion and the second cylindrical portion in the circumferential direction, the first cylindrical portion is rotated in one direction in the circumferential direction, and the second cylindrical portion is rotated in the other direction in the circumferential direction.

3. The method for welding the first cylindrical portion and the second cylindrical portion according to claim 1 or 2.

8. In the step of rotating at least one of the first cylindrical portion and the second cylindrical portion in the circumferential direction, the first cylindrical portion is rotated in one direction in the circumferential direction, and the second cylindrical portion is rotated in the one direction in the circumferential direction at a speed different from that of the first cylindrical portion.

3. The method for welding the first cylindrical portion and the second cylindrical portion according to claim 1 or 2.

9. At least one of the first cylindrical portion and the second cylindrical portion is a burring portion surrounding a through hole formed in the plate-like portion.

3. The method for welding the first cylindrical portion and the second cylindrical portion according to claim 1 or 2.

10. At least one of the first cylindrical portion and the second cylindrical portion is a circular tube.

3. The method for welding the first cylindrical portion and the second cylindrical portion according to claim 1 or 2.

11. The welding method according to claim 1 or 2 is used to weld the first cylindrical portion provided at a hot water or cold water inlet / outlet of a hot water tank to the second cylindrical portion of a piping. How water heaters are manufactured.

12. The welding method according to claim 1 or 2 is used to weld the first cylindrical portion provided in a housing of a compressor to the second cylindrical portion of a pipe. A method for manufacturing a compressor.

13. A first holding mechanism that holds a first cylindrical portion of the first member; a second holding mechanism provided in the second member, which holds the second cylindrical portion fitted to the first cylindrical portion in a state in which an end surface of a first cylindrical end of the first cylindrical portion and an end surface of a second cylindrical end of the second cylindrical portion are aligned; a heating mechanism that melts the first cylindrical end of the first cylindrical portion held by the first holding mechanism and the second cylindrical end of the second cylindrical portion held by the second holding mechanism to form a molten pool spanning the first cylindrical end and the second cylindrical end over the entire circumference; Equipped with At least one of the first holding mechanism and the second holding mechanism rotates at least one of the first cylindrical portion and the second cylindrical portion in a circumferential direction at least during a period from when the molten pool is formed by the heating mechanism to when the molten pool is solidified. Welding equipment.

14. The heating mechanism is a laser irradiator that irradiates a laser beam in an annular shape onto a circular surface formed by an end surface of the first cylindrical end and an end surface of the second cylindrical end. The welding apparatus of claim 13.

15. The laser irradiator is disposed in a direction in which a cylindrical axis of the first cylindrical portion or the second cylindrical portion extends, and irradiates the laser light, which is an annular parallel light, onto the annular surface. The welding apparatus of claim 14.

16. At least one of the first holding mechanism and the second holding mechanism rotates at least one of the first cylindrical portion and the second cylindrical portion relative to the heating mechanism.

15. A welding device according to claim 13 or 14.