Welding method for hollow member and vent hole formation method

Abstract

Provided is a welding method for a hollow member that can reliably seal a vent hole by welding without burn-through around the vent hole. This welding method for a hollow member includes: a vent hole formation step for forming, in a hollow member (21) made of a metal material and including a hollow structure, a vent hole (23) that penetrates the hollow member (21) to the hollow side, and forming the vent hole such that the periphery of the vent hole is bent and protruded to the hollow side; a welding step for performing a welding process of welding a workpiece (25) to the hollow member provided with the vent hole; and a vent hole sealing step for sealing the vent hole by welding after the welding step.

Description

Welding Method and Vent Hole Forming Method for Hollow Members

[0001] The present disclosure relates to a welding method and a vent hole forming method for hollow members.

[0002] In the sealed welding method for hollow products described in Patent Document 1, a vent hole is provided so that air or gas can escape from the inside of the hollow part. After the hollow part is welded and joined, a metal plugging member is inserted into the vent hole, and the plugging member is welded to the hollow product to seal the hollow part. A welding method is disclosed.

[0003] Japanese Patent Application Laid-Open No. 2005-193289

[0004] In the sealed welding method for hollow products described in Patent Document 1, since a plugging member is inserted into the vent hole and welded after the hollow part is welded and joined, an additional member is required. On the other hand, if arc welding is performed without inserting a plugging member into the vent hole, heat is concentrated around the vent hole, and there is a risk that the periphery of the vent hole will melt and fall off. When the periphery of the vent hole melts and falls off, there is a problem that spatter enters the hollow side and causes abnormal noise.

[0005] An aspect of the present disclosure aims to provide a welding method and a vent hole forming method for hollow members that can reliably seal the vent hole by welding without the periphery of the vent hole melting and falling off.

[0006] In order to solve the above problems, a welding method for a hollow member according to an aspect of the present disclosure includes forming a vent hole penetrating to the hollow side in a hollow member made of a metal material and having a hollow structure, and forming the vent hole so that the periphery of the vent hole bends and protrudes toward the hollow side; a welding step of performing a welding process of welding a workpiece to the hollow member provided with the vent hole; and a vent hole sealing step of sealing the vent hole by welding after the welding step.

[0007] Furthermore, in order to solve the above problems, a ventilation hole forming method according to one aspect of the present disclosure includes a holding step of holding a hollow member between a die and a pad corresponding to the shape of a hollow member made of a metal material and having a hollow structure, and a hole forming step of moving a punch having a tip portion whose cross-sectional area decreases towards the tip and a straight portion with a constant cross-sectional area through a punch-through hole in the pad toward the hollow member, so that the punch reaches a position where at least the tip portion of the punch penetrates the hollow member.

[0008] According to one aspect of this disclosure, a vent can be reliably sealed by welding without the area around the vent melting down.

[0009] This figure shows an example of the schematic configuration of a ventilation hole forming apparatus according to the first embodiment. This is a plan view and a side view showing an example of the tip of a punch. This figure illustrates an example of the process of forming a ventilation hole in a hollow member using a ventilation hole forming apparatus. This is a schematic diagram showing how a workpiece is attached to a hollow member with a ventilation hole formed therein by arc welding. This figure shows an example of sealing a ventilation hole by arc welding. This is an explanatory diagram illustrating an example of providing a ventilation hole in a hollow member according to the second embodiment. This figure shows an example of sealing the ventilation hole shown in Figure 6 by arc welding. This figure illustrates a method for forming a ventilation hole according to modified example 1.

[0010] The first and second embodiments of this disclosure will be described in detail below with reference to the drawings. The same or equivalent components and members shown in each drawing will be denoted by the same reference numerals, and redundant descriptions will be omitted as appropriate.

[0011] [First Embodiment] Hereinafter, a first embodiment embodying the present disclosure will be described with reference to Figures 1 to 5.

[0012] [Outline Configuration of the Ventilation Hole Forming Apparatus] First, the outline configuration of the ventilation hole forming apparatus 1 according to the first embodiment will be described based on Figure 1. Figure 1 is a diagram showing an example of the outline configuration of the ventilation hole forming apparatus 1 according to the first embodiment. As shown in Figure 1, the ventilation hole forming apparatus 1 consists of a die 12 mounted on a lower mold 11, and a pad 15, punch 16, retainer 17, pad pressure source 18, etc., mounted on an upper mold 13. The die 12 mounted on the lower mold 11 has a recessed portion 12A with a semicircular cross-section that is recessed downwards, on which a hollow metal member 21 is placed. The hollow member 21 has a hollow structure formed in a cylindrical shape and has a sealed structure in which both ends in the axial direction are sealed.

[0013] The hollow member 21 is not limited to a cylindrical shape; it may be formed as a cylindrical shape with a polygonal cross-section such as a square, pentagon, or hexagon, or as a cylindrical shape with an elliptical cross-section. In this case, the recessed portion 12A of the die 12 may be formed to be recessed downwards in the shape of the lower half of the cross-section of the hollow member 21.

[0014] The upper part of the punch 16 is inserted upward from the lower surface of the retainer 17 and attached to the upper die 13. The punch 16 protrudes downward vertically from the lower surface of the retainer 17. In addition, the upper ends of multiple pad pressure sources 18, which are composed of, for example, coil springs or gas cylinders, are fixed to the lower surface of the retainer 17.

[0015] The lower ends of the multiple pad pressure sources 18 are fixed to the upper end surface of the pad 15. On the lower surface of the pad 15, a recessed portion 15A is formed, which has a semicircular cross-section and is recessed upward, at a position opposite to the recessed portion 12A of the die 12. The recessed portion 15A is formed so that the upper half of the hollow member 21 placed on the recessed portion 12A of the die 12 can be fitted into it, and when the upper die 13 is moved downward, the hollow member 21 can be pressed into the recessed portion 12A via the multiple pad pressure sources 18.

[0016] The pad 15 has a punch relief hole 15B formed at a position opposite to the apex of the hollow member 21 placed on the recess 12A, extending from the upper end surface of the pad 15 to the recess 15A. The punch relief hole 15B functions as an example of a punch passage hole. The lower portion of the punch 16, that is, the tip portion, is inserted through the punch relief hole 15B so as to be movable in the vertical direction. The punch 16 has a tip portion 16A whose cross-sectional area decreases towards the tip, and a cylindrical straight portion 16B with a constant cross-sectional area, and the portion from the straight portion 16B to the retainer 17 side is configured to have a gradually increasing outer diameter. The punch relief hole 15B may also be provided with a guide function to guide the lower portion of the punch 16.

[0017] Then, as shown in Figure 1, when the upper die 13 moves upward and the pad 15 is separated from the die 12, each pad pressure source 18 extends and the tip 16A of the punch 16 is housed at a predetermined height above the lower end of the punch relief hole 15B. On the other hand, when the upper die 13 moves downward and the pad 15 comes into contact with the hollow member 21 and the die 12, and then the upper die 13 moves further downward into a pressed state, each pad pressure source 18 is compressed and presses the pad 15 downward. Also, the tip 16A of the punch 16 moves toward the hollow member 21 through the punch relief hole 15B in accordance with the downward movement of the upper die 13 and protrudes downward from the lower end of the punch relief hole 15B (see Figure 3).

[0018] Here, an example of the shape of the tip portion 16A of the punch 16 will be described based on Figure 2. Figure 2 is a plan view and a side view showing an example of the tip portion 16A of the punch 16. In Figure 2, from left to right, the tip portion 16A1 has two cutting edge surfaces, the tip portion 16A2 has three cutting edge surfaces, and the tip portion 16A3 has four cutting edge surfaces. In detail, the tip portion 16A1 extends in a cutting edge shape from the tip of the cylindrical straight portion 16B and has cutting edge surfaces that face each other in the diametrical direction, and the cross-sectional area decreases towards the tip.

[0019] Furthermore, the tip portion 16A2 extends in a triangular pyramidal shape from the tip of the cylindrical straight portion 16B, with its cross-sectional area decreasing towards the tip. Similarly, the tip portion 16A3 extends in a square pyramidal shape from the tip of the cylindrical straight portion 16B, with its cross-sectional area decreasing towards the tip. However, the shape of the tip portions 16A (16A1 to 16A3) of the punch 16 is not limited to these. For example, the shape of the tip portion 16A of the punch 16 may be configured to extend in a polygonal pyramidal or conical shape, with its cross-sectional area decreasing towards the tip.

[0020] [Welding Method for Hollow Members] [Ventilation Hole Formation Process] Next, the welding method for the hollow member 21 will be explained based on Figures 3 to 5. Figure 3 is a diagram illustrating an example of the process of forming ventilation holes 23 in the hollow member 21 using the ventilation hole forming device 1 (ventilation hole formation process). The ventilation hole formation process includes a holding process and a hole formation process. The ventilation hole formation process proceeds sequentially along the direction of the thick-axis arrow shown in Figure 3. As shown in Figure 1, the hollow member 21 is placed in the recess 12A of the die 12.

[0021] [Holding Process] As shown in the upper left of Figure 3, first the upper mold 13 moves downward, and the pad 15 comes into contact with the hollow member 21 and the die 12, closing the mold. Then, the hollow member 21, which is placed in the recess 12A of the die 12, is pressed downward by the recess 15A of the pad 15 and held in place.

[0022] [Hole Forming Process] Next, as shown in the center of the upper part of Figure 3, the upper die 13 moves further downward, compressing each pad pressure source 18 and pressing the pad 15 downward. The punch 16 also moves downward through the punch relief hole 15B. The tip 16A of the punch 16 then comes into contact with the apex (part) of the hollow member 21, pressing the apex (part) of the hollow member 21 further downward. As a result, the apex (part) of the hollow member 21 is bent downward and broken by the tip 16A, and the tip of the tip 16A penetrates the apex (part) of the hollow member 21, forming the initial ventilation hole 23A. The bent end of the initial ventilation hole 23A protrudes toward the hollow side (downward in Figure 3).

[0023] In this explanation, since the hollow member 21 is cylindrical, the tip 16A of the punch 16 contacts the apex (part) of the hollow member 21. However, if the shape of the hollow member 21 is different, it is not necessarily required that the tip 16A of the punch 16 contacts the apex (part) of the hollow member 21. At the very least, it is sufficient that the tip 16A of the punch 16 contacts the hollow member 21 and presses the hollow member 21 further downward from the contact point.

[0024] From this state, as shown in the upper right corner of Figure 3, the upper die 13 moves further downward, compressing each pad pressure source 18 and pressing the pad 15 downward. The punch 16 also moves downward through the punch relief hole 15B. The tip 16A of the punch 16 enters the initial ventilation hole 23A formed in the apex (part) of the hollow member 21, enlarging the initial ventilation hole 23A. Subsequently, the upper die 13 moves further downward, reaching a position where part of the straight portion 16B of the punch 16 enters the hole. This series of downward movements of the punch 16 creates a hole in the hollow member 21.

[0025] In the above series of operations, the punch 16 wraps the area around the initial ventilation hole 23A formed by the tip portion 16A of the punch 16 with the straight portion 16B, forming a burring-shaped ventilation hole 23 that protrudes towards the hollow side. For example, if the thickness of the hollow member 21 is about 1.2 [mm] and the diameter of the straight portion 16B of the punch 16 is about 3 [mm], the ventilation hole 23 can be formed in a burring shape with a height of about 2.7 [mm].

[0026] Subsequently, as shown in the center of the lower section of Figure 3, the upper die 13 moves upward, and the straight portion 16B and tip portion 16A of the punch 16 are pulled upward through the ventilation holes 23 of the hollow member 21. Then, the upper die 13 moves further upward, and each pad pressure source 18 extends to its initial length, the pads 15 are separated upward from the die 12, and the hollow member 21 with the burring-shaped ventilation holes 23 formed therein can be removed from the mold.

[0027] [Welding Process] Next, the welding process for welding the workpiece 25 to the hollow member 21 in which the ventilation holes 23 are formed will be explained with reference to Figure 4. Figure 4 is a schematic diagram showing how the workpiece 25 is attached to the hollow member 21 in which the ventilation holes 23 are formed by arc welding. As shown in Figure 4, after forming burring-shaped ventilation holes 23 in the hollow member 21 having a sealed hollow structure, a welding process is performed to attach the workpiece 25, such as a bracket, by arc welding. The workpiece 25 may also be attached by laser welding or the like.

[0028] At this time, the air inside the sealed hollow member 21 expands due to the heat generated during arc welding, causing the internal pressure to increase. However, even if the internal pressure of the hollow member 21 increases, the pressure inside the hollow member 21 can be reduced through the ventilation holes 23, thereby suppressing deformation (denting) of the molten metal and the generation of minute bubbles in the molten metal, and improving the quality of the product.

[0029] [Ventilation Hole Sealing Process] Next, the ventilation hole sealing process, which is performed after the above welding process is completed, will be explained with reference to Figure 5. Figure 5 shows an example of sealing the ventilation holes 23 by arc welding. As shown in Figure 5, in the ventilation hole sealing process, the ventilation holes 23 of the hollow member 21 are sealed by arc welding.

[0030] The ventilation holes 23 provided in the hollow member 21 are formed in a burring shape that bends and protrudes toward the hollow side from the periphery of the ventilation holes 23, thereby increasing the contact area with the molten metal generated by arc welding. This prevents heat from concentrating around the ventilation holes 23, and allows the area around the holes to be sealed by arc welding without melting into the interior of the hollow member 21.

[0031] As described in detail above, in the welding method for the hollow member 21 according to the first embodiment, the ventilation holes 23 provided in the hollow member 21 are formed so that the area around the ventilation holes 23 bends and protrudes toward the hollow side. Therefore, in the ventilation hole sealing process, the area around the ventilation holes 23 does not melt down, and the ventilation holes 23 can be reliably sealed by arc welding. Because the area around the ventilation holes 23 is formed to protrude toward the hollow side, even when the thickness of the hollow member 21 is thin, the concentration of heat around the ventilation holes 23 can be avoided, and the ventilation holes 23 can be reliably sealed by arc welding.

[0032] Furthermore, when drilling the ventilation holes 23 in the hollow member 21, the tip portion 16A of the punch 16 breaks the hollow member 21 to form the initial ventilation holes 23A. Subsequently, the area around the initial ventilation holes 23A is wrapped around the straight portion 16B of the punch 16 to form a burring-shaped ventilation hole 23 that protrudes towards the hollow side.

[0033] In the ventilation hole sealing process, the diameter of the hole sealed by arc welding the ventilation hole 23 of the hollow member 21 is approximately 6 mm to 7 mm at its maximum. This allows for sealing without spatter intrusion and without melting around the ventilation hole. Therefore, the usable punch diameter in the ventilation hole formation process is the punch 16, which is designed with a diameter less than or equal to the maximum diameter of the hole to be sealed. In other words, since the maximum diameter of the punch 16 is fixed, the above configuration is adopted to maximize the protrusion height toward the hollow side relative to the hole diameter of the ventilation hole 23 under these conditions.

[0034] In other words, by tapering the tip 16A of the punch 16, the height of the protrusion toward the hollow side relative to the diameter of the ventilation hole 23 can be set to half the length of the diameter of the ventilation hole 23, and this can be set to the maximum height. As a result, when sealing the ventilation hole 23 with arc welding, the contact area with the molten metal generated by the arc welding can be increased, preventing heat from concentrating around the ventilation hole 23, and allowing for more reliable sealing by arc welding without the area around the hole melting through.

[0035] Furthermore, since the ventilation holes 23 can be sealed by arc welding, the ventilation holes 23 can be sealed without requiring any additional components.

[0036] [Second Embodiment] Next, a second embodiment embodying the present disclosure will be described with reference to Figures 6 and 7. Figure 6 is an explanatory diagram illustrating an example in which a ventilation hole 23 is provided in the second hollow member 31 according to the second embodiment. Figure 7 is a diagram illustrating an example in which the ventilation hole 23 is sealed by arc welding. For the sake of convenience of explanation, the same reference numerals are used for members having the same function as those described in the first embodiment, and their descriptions will not be repeated.

[0037] As shown in Figure 6, the second hollow metal member 31 has a cylindrical hollow structure, with one end in the axial direction open and having a circular opening 31A. The other end in the axial direction of the second hollow metal member 31 is closed. The metal plate 33 is formed in a circular shape that can be fitted into the opening 31A of the second hollow metal member 31, and has a burring-shaped ventilation hole 23 in its center.

[0038] Next, a welding method for attaching the plate material 33 to the opening 31A of the second hollow member 31 will be described with reference to Figures 6 and 7. As shown in Figure 6, first, a robot hand (not shown) inserts the pin 35A of a pink lamp 35 attached to the tip of the robot hand into the ventilation hole 23 of the plate material 33 from the opposite side of the burring portion 23B of the ventilation hole 23. The robot hand then expands the diameter of each gripper 35B of the pink lamp 35 to hold the plate material 33. Subsequently, while holding the plate material 33, the robot hand coaxially fits the plate material 33 into the opening 31A of the second hollow member 31 and pushes the outer circumference of the plate material 33 to a position where it can be welded to the inner circumferential surface of the opening 31A.

[0039] Then, a welding device (not shown) temporarily fixes multiple points on the peripheral edge of the plate material 33 to the inner surface of the opening 31A by arc welding. Subsequently, as shown in Figure 7, a robot hand (not shown) reduces the diameter of each gripper 35B of the pink lamp 35 to remove the pins 35A from the ventilation holes 23 of the plate material 33. Then, the welding device (not shown) performs a welding process to fix the peripheral edge of the plate material 33, which is temporarily fixed to the opening 31A, to the inner surface of the opening 31A by arc welding around its entire circumference. At this time, even if the air inside the second hollow member 31, which has a sealed hollow structure, expands due to the heat during arc welding and the internal pressure increases, it can be reduced through the ventilation holes 23. This suppresses "deformation (denting)" of the molten metal and the generation of "tiny bubbles" in the molten metal, thereby improving the quality of the product.

[0040] Subsequently, the ventilation holes 23 in the plate material 33 are sealed by arc welding. The ventilation holes 23 provided in the plate material 33 are formed in a burring shape that bends and protrudes from the periphery of the ventilation holes 23 toward the hollow side. This prevents heat from concentrating around the ventilation holes 23, allowing them to be sealed by arc welding without the area around the holes melting down.

[0041] As described in detail above, in the welding method for the second hollow member 31 according to the second embodiment, the plate material 33 is fitted into the opening 31A, and the peripheral edge of the plate material 33 is welded and fixed to the inner surface of the opening 31A over its entire circumference. As a result, a ventilation hole 23 in which the burring portion 23B protrudes toward the hollow side can be formed in the second hollow member 31. This prevents heat from concentrating around the ventilation hole 23 when sealing the ventilation hole 23 with arc welding, and allows the hole to be sealed by welding without melting through.

[0042] [Modifications] Modifications of the first and second embodiments described above will now be explained. For the convenience of explanation, in the following explanation, components having the same function as those described in the first and second embodiments will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0043] [Modification Example 1] For example, another method of forming the vent hole 23 of the hollow member 21 will be described based on FIG. 8. FIG. 8 is a diagram for explaining the method of forming the vent hole 23 according to Modification Example 1. As shown at the left end of FIG. 8 and the second from the left in FIG. 8, first, a third hollow member 41 having a greater plate thickness than the hollow member 21 is held between a die 12 and a pad 15 corresponding to the shape of the third hollow member 41. The plate thickness of the third hollow member 41 is, for example, about 2.7 [mm]. Then, a die 42 is arranged inside the apex of the third hollow member 41 coaxially with the punch escape hole 15B.

[0044] Also, instead of the punch 16, a thin cylindrical, for example, a cylindrical first punch 43 with a diameter of about 3 [mm] is arranged. Then, the upper die 13 is moved downward to move the first punch 43 through the punch escape hole 15B toward the third hollow member 41 and reach the first punch 43 to a position penetrating the third hollow member 41 to form a lower hole 45 (lower hole forming step).

[0045] Subsequently, as shown in the third from the left in FIG. 8, instead of the first punch 43, a second punch 47 having a larger cross-sectional area than the first punch 43, for example, a diameter of about 6 [mm], is arranged coaxially with the lower hole 45. Then, the upper die 13 is moved downward again to move the second punch 47 through the punch escape hole 15B toward the third hollow member 41 and reach the second punch 47 to a position penetrating the third hollow member 41 to form a burring (burring forming step).

[0046] As a result, as shown in the fourth from the left in FIG. 8, that is, at the right end of FIG. 8, a burring-shaped vent hole 23 having a burring portion 23B protruding toward the hollow side can be formed in the third hollow member 41. The vent hole 23 can be formed, for example, in a burring shape with a height of about 4.2 [mm]. As a result, when sealing the vent hole 23 by arc welding, heat concentration around the vent hole 23 can be prevented, and it can be sealed by welding without melting around the hole.

[0047] [Modification Example 2] Also, for example, at the tip 16A of the punch 16, the hollow member 21 is broken, the periphery of the perforation is involved at least in the tip 16A of the punch 16, and after forming the initial vent hole 23A that protrudes to the hollow side, the upper die 13 may be moved upward. That is, the vent hole forming device 1 may form the initial vent hole 23A in the hollow member 21 instead of the vent hole 23. The bent end of the initial vent hole 23A protrudes toward the hollow side (lower side in FIG. 3). Thereby, when sealing the initial vent hole 23A by arc welding, heat is prevented from concentrating around the initial vent hole 23A, and it can be sealed by welding without melting around the hole.

[0048] [Summary] The welding method for a hollow member according to Embodiment 1 of the present disclosure forms a vent hole penetrating to the hollow side in a hollow member made of a metal material and having a hollow structure, and the vent hole is formed such that the periphery of the vent hole bends and protrudes toward the hollow side. A vent hole forming step, a welding step of performing a welding process on the workpiece with respect to the hollow member provided with the vent hole, and after the welding step, a vent hole sealing step of sealing the vent hole by welding.

[0049] According to the welding method of the hollow member, since the vent hole provided in the hollow member is formed such that the periphery of the vent hole bends and protrudes toward the hollow side, in the vent hole sealing step, the vent hole can be reliably sealed by welding without the periphery of the vent hole melting away. Since the periphery of the vent hole is formed so as to protrude toward the hollow side, even when the plate thickness of the hollow member is thin, concentration of heat around the vent hole can be avoided, and the vent hole can be reliably sealed by welding.

[0050] The welding method for a hollow member according to Embodiment 2 of the present disclosure, in the above Embodiment 1, the vent hole forming step includes a step of forming the vent hole such that a bent end formed by bending a part of the hollow member toward the hollow side penetrates a part of the hollow member and protrudes toward the hollow side.

[0051] According to the above-described welding method for hollow members, when a ventilation hole is formed by bending a part of the hollow member toward the hollow side and penetrating a part of the hollow member, the bent end protrudes toward the hollow side. This prevents heat from concentrating around the ventilation hole when sealing the hole by welding, allowing the hole to be sealed by welding without melting or dripping around it.

[0052] A welding method for a hollow member according to Embodiment 3 of the present disclosure, in Embodiment 2, the ventilation hole forming step includes a holding step of holding the hollow member between a die and a pad corresponding to the shape of the hollow member, and a hole forming step of moving a punch having a tip portion whose cross-sectional area decreases towards the tip and a straight portion with a constant cross-sectional area through a punch-through hole in the pad toward the hollow member, so that at least the tip portion of the punch reaches a position where it penetrates the hollow member.

[0053] According to the above-described welding method for hollow members, when drilling a ventilation hole in the hollow member, the tip of the punch breaks the hollow member, and the area around the drilled hole is wrapped around at least the tip of the punch, forming a ventilation hole that protrudes into the hollow side. This prevents heat from concentrating around the ventilation hole when sealing the hole by welding, allowing for more reliable sealing by welding without the area around the hole melting through. The punch passage hole may be a relief hole for the punch to pass through, or a guide hole for guiding the punch.

[0054] A welding method for a hollow member according to aspect 4 of the present disclosure, in aspect 3 above, the hole forming step includes a step of moving the punch to a position where the portion of the punch from the tip to a part of the straight portion penetrates the hollow member.

[0055] According to the above welding method for hollow members, when drilling a ventilation hole in the hollow member, the tip of the punch breaks the hollow member, and the area around the hole is wrapped around the straight part of the punch, forming a burring-shaped ventilation hole that protrudes into the hollow side. As a result, since the minimum usable punch diameter is fixed, the height of the protrusion into the hollow side relative to the hole diameter can be maximized by tapering the tip of the punch. Consequently, when sealing the ventilation hole by welding, it is possible to prevent heat from concentrating around the ventilation hole, and to seal the hole more reliably by welding without melting through the surrounding area.

[0056] The welding method for a hollow member according to Embodiment 5 of the present disclosure is characterized in that, in any one embodiment of Embodiments 1 to 4, the hollow member comprises a sealed hollow structure.

[0057] According to the above-described welding method for hollow members, when welding a workpiece using arc welding, even if the air inside the sealed hollow member expands due to the heat during welding and the internal pressure increases, the pressure can be reduced through the ventilation holes. This suppresses the "deformation (indentation)" of the molten metal and the generation of "tiny bubbles" in the molten metal, thereby improving product quality.

[0058] A welding method for a hollow member according to embodiment 6 of the present disclosure, in any one embodiment of embodiments 1 to 5, the ventilation hole sealing step includes a step of sealing the ventilation hole by arc welding.

[0059] According to the welding method for the hollow member described above, the ventilation holes can be sealed by arc welding, thus enabling the sealing of the ventilation holes without the need for additional members.

[0060] A welding method for a hollow member according to aspect 7 of the present disclosure, in aspect 1 or 2 above, the ventilation hole forming step includes: a holding step of holding the hollow member between a die and a pad corresponding to the shape of the hollow member; a pilot hole forming step of moving a first punch toward the hollow member through a punch-through hole in the pad and reaching the first punch to a position where it penetrates the hollow member to form a pilot hole; and a burring forming step of arranging a second punch having a larger cross-sectional area than the first punch coaxially with the pilot hole and moving it toward the hollow member through the punch-through hole in the pad and reaching the second punch to a position where it penetrates the hollow member to form a burring.

[0061] According to the above-described welding method for hollow members, when the thickness of the hollow member is large, a pilot hole can be formed in the hollow member with a first punch, and the area around the pilot hole can be wrapped around the second punch to form a burring-shaped ventilation hole that protrudes into the hollow side. This prevents heat from concentrating around the ventilation hole when sealing the ventilation hole by welding, allowing for more reliable sealing by welding without the area around the hole melting through.

[0062] A welding method for a hollow member according to embodiment 8 of the present disclosure, in embodiment 1 or 2 above, the ventilation hole forming step includes a second holding step of fitting and holding a metal plate material having the ventilation hole pre-formed and capable of closing the opening into an opening formed on one end of the hollow member such that the burring portion of the ventilation hole protrudes toward the hollow side, and a temporary fixing step of temporarily fixing the peripheral edge of the plate material into the opening by welding.

[0063] According to the above welding method for hollow members, by fitting a plate into the opening and welding the entire circumference of the plate to the inner surface of the opening, a ventilation hole can be formed in the hollow member in which the burring portion protrudes toward the hollow side. This prevents heat from concentrating around the ventilation hole when sealing it by welding, allowing for more reliable welding without melting around the hole.

[0064] A welding method for a hollow member according to aspect 9 of the present disclosure, in aspect 8, the welding step includes a welding process in which the entire circumference of the plate material temporarily fixed in the opening is welded to the inner surface of the opening.

[0065] According to the above-described welding method for hollow members, when the entire circumference of a plate material is welded and fixed to the opening of the hollow member by arc welding, even if the air inside the hollow member expands due to the heat during welding and the internal pressure increases, the pressure can be reduced through the ventilation holes. This suppresses the "deformation (indentation)" of the molten metal and the generation of "tiny bubbles" in the molten metal, thereby improving the quality of the product.

[0066] A ventilation hole forming method according to embodiment 10 of the present disclosure includes a holding step of holding a hollow member between a die and a pad corresponding to the shape of a hollow member made of a metal material and having a hollow structure, and a hole forming step of moving a punch having a tip portion whose cross-sectional area decreases towards the tip and a straight portion with a constant cross-sectional area through a punch-through hole in the pad toward the hollow member, so that the punch reaches a position in which at least the tip portion of the punch penetrates the hollow member.

[0067] According to the above-described welding method for hollow members, when drilling a ventilation hole in the hollow member, the tip of the punch breaks the hollow member, and the area around the hole is wrapped around at least the tip of the punch, forming a burring-shaped ventilation hole that protrudes into the hollow side.

[0068] [Additional Notes] This disclosure is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of this disclosure.

[0069] 1: Ventilation hole forming device 12: Die 15: Pad 15B: Punch relief hole 16: Punch 16A, 16A1, 16A2, 16A3: Tip section 16B: Straight section 21: Hollow member 23: Ventilation hole 25: Workpiece 43: First punch 45: Pilot hole 47: Second punch

Claims

1. A welding method for a hollow member, comprising: a ventilation hole forming step of forming a ventilation hole that penetrates to the hollow side of a hollow member made of a metal material and having a hollow structure, and forming the ventilation hole such that the area around the ventilation hole bends and protrudes toward the hollow side; a welding step of welding a workpiece to the hollow member provided with the ventilation hole; and a ventilation hole sealing step of sealing the ventilation hole by welding after the welding step.

2. The method for welding a hollow member according to claim 1, wherein the ventilation hole forming step includes a step of forming the ventilation hole by bending a part of the hollow member toward the hollow side, such that the bent end formed by penetrating a part of the hollow member protrudes toward the hollow side.

3. The method for welding a hollow member according to claim 2, wherein the ventilation hole forming step includes: a holding step of holding the hollow member between a die and a pad corresponding to the shape of the hollow member; and a hole forming step of moving a punch having a tip portion whose cross-sectional area decreases towards the tip and a straight portion with a constant cross-sectional area through a punch-through hole in the pad toward the hollow member, so that the punch reaches a position where at least the tip portion of the punch penetrates the hollow member.

4. The method for welding a hollow member according to claim 3, wherein the hole forming step includes a step of moving the punch to a position where the portion of the punch from the tip to a portion of the straight portion penetrates the hollow member.

5. The method for welding a hollow member according to claim 1, wherein the hollow member has a sealed hollow structure.

6. The method for welding a hollow member according to claim 1, wherein the ventilation hole sealing step includes sealing the ventilation hole by arc welding.

7. The method for welding a hollow member according to claim 1, wherein the ventilation hole forming step includes: a holding step of holding the hollow member between a die and a pad corresponding to the shape of the hollow member; a pilot hole forming step of moving a first punch toward the hollow member through a punch-through hole in the pad, and reaching the first punch to a position where it penetrates the hollow member to form a pilot hole; and a burring forming step of arranging a second punch having a larger cross-sectional area than the first punch coaxially with the pilot hole, moving it toward the hollow member through the punch-through hole in the pad, and reaching the second punch to a position where it penetrates the hollow member to form a burring.

8. The method for welding a hollow member according to claim 1, wherein the ventilation hole forming step includes: a second holding step of fitting and holding a metal plate material having the ventilation holes pre-formed and capable of closing the opening into an opening formed on one end of the hollow member such that the burring portion of the ventilation holes protrudes toward the hollow side; and a temporary fixing step of temporarily fixing the peripheral edge of the plate material into the opening by welding.

9. The welding method for a hollow member according to claim 8, wherein the welding step includes a welding process to weld the entire circumference of the plate material temporarily fixed in the opening to the inner surface of the opening.

10. A method for forming a ventilation hole, comprising: a holding step of holding a hollow member between a die and a pad corresponding to the shape of a hollow member made of a metal material and having a hollow structure; and a hole forming step of moving a punch having a tip portion whose cross-sectional area decreases towards the tip and a straight portion with a constant cross-sectional area through a punch-through hole in the pad toward the hollow member, so that the punch reaches a position where at least the tip portion of the punch penetrates the hollow member.

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