JP4593458B2 - Welding method of lap joint - Google Patents

Description

  The present invention relates to a lap joint welding method. In particular, the present invention relates to a method for welding a lap joint formed by overlapping a plurality of joints made of a thin metal material.

  Automotive parts such as exhaust manifolds tend to be thinned to reduce vehicle weight. In addition, among exhaust parts for automobiles, exhaust system parts such as exhaust manifolds require the airtightness and joint strength of joints, so that welding is inevitable for joints of thinned parts. There is. Conventionally, arc welding is often used when welding a part of two material steel plates for constituting exhaust system parts, but the material steel plates are thin. There is a drawback that distortion, deformation of the joint, burn-out, perforation, etc. are likely to occur. For this reason, laser welding that can be welded with relatively small heat input has attracted attention as a welding technique suitable for lap welding of thin steel plates.

  However, laser lap welding also has some difficulties. First, since the laser beam diameter is relatively thin, it is necessary to position the thin steel plate to be welded very accurately. Second, at the time of laser beam irradiation, it is necessary to keep the gap (gap) between the steel plates at the welding target portion (that is, the portion constituting the lap joint) in the two thin steel plates very narrow. Specifically, in the case of a lap joint, it is difficult to obtain good welding quality unless the gap between the steel plates is 10% or less of the plate thickness. However, many of the thin-walled steel plates used for exhaust system parts such as exhaust manifolds are sheet metal parts manufactured by plastic processing such as press working. In many cases, the gap between the steel plates is large due to the influence of the spring back or the like. Further, as the weld length becomes longer, there is a problem that the gap is further enlarged due to thermal distortion during welding, and thus a vicious circle is likely to occur.

  In order to obtain a good welding quality by reducing the gap between the steel plates at the time of lap welding by laser, Patent Document 1 discloses a laser welding jig for superposed plates. In Patent Document 1, by providing a pair of pressure rollers on both sides of a laser beam that is scanned along the planned line of overlap welding, pressing the flange portion of the workpiece with these pressure rollers, The gap between the flange portions of the workpiece in the superposed state is eliminated, and reliable and stable laser welding can be performed on the flange portions. However, the method of Patent Document 1 has some problems. When laser welding is performed while pressing the flange portion of the workpiece with a pressure roller, the laser welding speed (laser scanning speed) decreases. Further, not only the productivity is deteriorated due to the decrease in the welding speed, but also the thermal distortion and deformation of the workpiece are increased due to the increase in the heat input amount, and the welding quality may be deteriorated. Furthermore, since a space for running a pair of pressure rollers on both sides of the planned welding line is required, the method of Patent Document 1 is not suitable for welding in a narrow part, and restrictions on the shape and dimensions of the lap joint. Has the disadvantage of being large.

JP 2001-38480 A (summary)

  An object of the present invention is to provide a lap joint welding method that enables high-quality laser welding by eliminating or reducing gaps between a plurality of joints constituting the lap joint as much as possible.

  The present invention relates to a lap joint welding method configured by superimposing a plurality of joints, and superimposing a plurality of joints made of a thin metal material to form a superposed part extending in a strip shape. And a plurality of portions of the band-shaped overlapped portion are pressed in the thickness direction of the joint portion to form a pressure-contact portion extending in the width direction of the band-shaped overlapped portion. A plurality of press contact steps formed at intervals along the longitudinal direction of the laser beam, a laser beam to the belt-like overlapping portion on which the press contact portions are formed, and a scanning line of the beam of the plurality of press contact portions. By irradiating while scanning so as to intersect with each other, a laser welding mark intersects each of the plurality of press contact portions over almost the entire longitudinal direction of the strip-shaped overlapping portion. A welding method of lap joint, characterized in that it comprises a laser welding step of applying over the weld.

  According to this method, a plurality of joining portions made of a thin metal material are overlapped to form an overlapping portion that extends in a band shape, and then pressed (applied) in the thickness direction of the bonding portion at a plurality of locations of the band-like overlapping portion. By applying pressure welding, a plurality of press contact portions are formed while being spaced apart along the longitudinal direction of the belt-like overlapping portion. For this reason, even when there are problems such as molding distortion and springback in the thin metal material when a plurality of joints are overlapped, at the time of completion of pressure welding, the plurality of joints are joined to each other at least in the belt-like overlap part. There is almost no gap in the thickness direction between the joints. Therefore, the quality of laser welding with respect to the belt-shaped overlapping portion after the pressure welding can be made very good.

  In addition, each of the plurality of press contact portions formed while being spaced apart along the longitudinal direction of the belt-like overlapping portion by press contact has a shape extending in the width direction of the belt-like overlap portion. For this reason, when irradiating while scanning the laser beam along the longitudinal direction of the belt-shaped overlapping portion, the scanning line of the laser beam is transverse from the originally planned welding line (width direction of the belt-shaped overlapping portion). Even if they are slightly deviated from each other, it is possible to reliably cross the scanning line of the laser beam with each of the plurality of press contact portions. Therefore, even if there is some deviation in the positioning of the belt-shaped overlapped part that is the object of laser welding or the scanning aim at the time of laser beam irradiation, the laser welding is such that the laser welding trace intersects each pressure welding part. Therefore, the quality of laser welding in the lap joint can be maintained.

  The thin metal material is preferably a thin metal material having a thickness of 0.1 to 0.5 mm. Welding of lap joints made by overlapping multiple joints made of thin metal materials with a wall thickness of 0.1 to 0.5 mm has the advantage of laser welding that enables welding with low heat input. Sound welding with no welding defects such as perforation and burn-off can be performed.

  Specific examples of the pressure welding (pressure welding) used in the pressure welding step include cold welding, ultrasonic welding, friction welding, diffusion welding, resistance welding, high frequency welding, gas welding, thermite welding, and the like. it can. Among these pressure welding methods, resistance welding is particularly preferable. In resistance welding, welding is performed by synergistic effects of mechanical pressurization and resistance heat generation by energizing a plurality of joints sandwiched between two opposing electrodes in the thickness direction. For this reason, even if there are problems such as molding distortion and springback in the thin metal material that provides the joint, these gaps can be overcome and the gaps in the thickness direction of the plurality of joints in the belt-like overlapping part are almost eliminated. It is possible to reliably perform the mutual joining in the absence.

  In the laser welding process, the laser beam is irradiated at an incident angle (θ) of 30 to 60 ° with respect to the irradiation target surface of the band-shaped overlapping portion from a lateral direction along the width direction of the band-shaped overlapping portion. It is preferred that As described above, the laser beam is irradiated to the irradiation target surface of the band-shaped overlapping portion from the lateral direction along the width direction of the band-shaped overlapping portion, and is welded to the band-shaped overlapping portion. It is possible to increase the width (w) of the joining interface by laser welding along the width direction of the belt-like overlapping portion while avoiding excessive heat input that causes distortion or the like, and as a result, joining the lap joint The strength can be improved.

  In addition, it is very preferable to apply the welding method of the present invention to welding of a lap joint in an inner pipe for a double pipe structure exhaust manifold. Details thereof will be described in an embodiment of the invention.

  According to the lap joint welding method of the present invention, before laser welding, by applying pressure welding in the thickness direction of the joint portion at a plurality of locations of a strip-like overlapping portion configured by overlapping a plurality of joint portions, Since the gap in the thickness direction between the plurality of joints is eliminated or reduced as much as possible, the welding quality of laser welding can be made very good. In addition, by positioning each of the plurality of pressure contact portions in the belt-like overlapping portion so as to extend in the width direction of the belt-like overlapping portion, positioning of the belt-like overlapping portion after laser welding that is a target of laser welding, or a laser beam Even if there is some deviation in the scanning aim at the time of irradiation, it is possible to reliably carry out laser welding such that the laser welding trace intersects each press contact portion, and it is possible to maintain the quality of laser welding at the lap joint. Furthermore, according to the welding method of the present invention, it is possible to weld a joint constituting a narrow space, and there are few restrictions on the shape and dimensions of the lap joint, and the versatility as a lap joint welding method is excellent.

  Hereinafter, several embodiments in which the welding method of the present invention is applied to welding of a lap joint in an inner pipe for a double pipe structure exhaust manifold will be described with reference to the drawings. The double pipe structure exhaust manifold refers to an exhaust manifold having an inner / outer double pipe structure by disposing an inner pipe inside the outer pipe. In general, the inner pipe that directly defines the exhaust gas passage of the double-pipe structure exhaust manifold is required to have higher airtightness than the outer pipe.

  1 to 3 show a basic embodiment. As shown in FIGS. 1 (A) to 1 (C), an inner pipe for a double-pipe structure exhaust manifold has two parts (first part 1 and 1) corresponding to a split piece when the inner pipe is divided into monaca. It consists of a second part 2). The first and second parts 1 and 2 are sheet metal parts obtained by pressing a stainless steel plate having a thickness of 0.2 to 0.4 mm. The 1st and 2nd components 1 and 2 have the joining flange parts 1a and 2a as a joining part in each peripheral part, and these joining flange parts 1a and 2a also have board thickness 0.2-. It is comprised by a part of 0.4 mm stainless steel plate. These first and second parts 1 and 2 are assembled in the following procedure and finished into a finished product (inner pipe).

  First, as shown in FIGS. 1A to 1C, the joining flange portion 1a of the first component and the joining flange portion 2a of the second component are overlapped with each other, and an overlapping portion 3 extending in a strip shape is formed. Configure (superposition process). At that time, the joining flange portion 1a of the first component and the joining flange portion 2a of the second component are affected by the molding distortion of the first and second components 1 and 2, respectively. It is not always intimately in contact with the entire width direction, and between the two la and 2a, a gap G1 (see FIG. 1 (B)) on the base end side of each joint flange 1a and 2a, A gap G2 (see FIG. 1C) or the like on the tip end side of each joining flange portion 1a, 2a is likely to occur.

  Then, as shown in FIGS. 2A and 2B, resistance welding (a kind of pressure welding) is performed in the thickness direction of the joining flange portions 1a and 2a at a plurality of locations of the strip-like overlapping portion 3 as shown in FIGS. A plurality of press contact portions 4 are formed while being spaced apart along the longitudinal direction of the strip-shaped overlapping portion 3 (preliminary press contact step). The resistance welding here is performed by energizing the two joining flange portions 1a and 2a in the thickness direction using two electrodes facing each other with the strip-shaped overlapping portion 3 interposed therebetween. In each press-contact part 4, the welding by the synergistic effect of the mechanical pressurization by two electrodes and the resistance heat_generation | fever by energization resistance is given. As a result, the gaps (G1, G2) that existed in various places of the belt-like overlapping portion 3 are almost eliminated, and as shown in FIG. 2B, the joining flange portion 1a of the first component and the second component The joint flange portions 2a are tightly joined to each other with almost no gap over the entire width direction of both joint flange portions.

  In this embodiment, the shape of the electrode used for resistance welding is devised so that each press contact portion 4 (or press contact mark 4) has a substantially rectangular shape extending long in the width direction of the strip-shaped overlapping portion 3. Thus, resistance welding is performed (the same applies to other embodiments described later). For this reason, each of the substantially rectangular pressure contact portions 4 extends so as to cross the width direction of the belt-shaped overlapping portion 3, and the internal pressure contact portion 4a formed based on resistance heat generation (see FIG. 2B). Is also present over the entire width direction of the belt-shaped overlapping portion 3.

  When the press-contact of the belt-like superposed portion 3 is completed, as shown in FIGS. 3A and 3B, a laser beam is applied to the belt-like superposed portion 3, and the laser beam scanning lines have a plurality of press-contact portions 4. Irradiation is performed while scanning so as to intersect each of the laser beams (laser welding process). As a result, laser welding is performed so that the laser welding mark 5 intersects each of the plurality of press contact portions 4 over substantially the entire longitudinal direction of the belt-shaped overlapping portion 3, and the joining flange portion 1 a of the first component The joining by the laser welding with the joining flange part 2a of the second part is completed.

  According to the basic embodiment of FIGS. 1 to 3, it is assumed that the first and second parts 1 and 2 have problems such as molding distortion and spring back when the two joining flange portions 1a and 2a are overlapped. However, when the pressure welding by resistance welding is completed, the two joining flange portions 1a and 2a are joined to each other, and there is almost no gap (G1, G2) between the two joining flange portions 1a and 2a. Therefore, the quality of the laser welding for the band-shaped overlapping portion 3 after the pressure welding can be made very good. In addition, each press-contact portion 4 formed on the belt-shaped overlapping portion 3 has a substantially rectangular shape extending long in the width direction of the belt-shaped overlapping portion 3, so that when the laser beam is irradiated while being scanned, the laser beam Even if the scanning line is slightly deviated in the lateral direction (width direction of the belt-like overlapping portion) from the originally planned welding line, the scanning line of the laser beam can be reliably crossed with each press contact portion 4. Therefore, even if there is a slight deviation in the positioning of the belt-like overlapping portion 3 after the pressure welding to be laser welded or the scanning aim at the time of laser beam irradiation, the laser welding marks 5 intersect with the pressure welding portions 4. Laser welding can be reliably performed, and the quality of laser welding in the lap joint can be maintained. Therefore, according to the present embodiment, it is possible to obtain an inner pipe for an exhaust manifold having a double pipe structure in which a laser welded joint has high airtightness and bonding strength.

  Incidentally, FIG. 4 shows a comparative example. In the comparative example of FIG. 4, spot resistance welding is performed in the thickness direction of the joining flange portions 1 a and 2 a at a plurality of positions of the belt-like overlapping portion 3 in the preliminary pressure welding process of the embodiment of FIGS. 1 to 3. Thus, as shown in FIG. 4 (A), only the point where a plurality of spot-like press contact portions 6 (or press contact marks 6) are formed while being spaced apart by a predetermined distance along the longitudinal direction of the strip-shaped overlapping portion 3 It differs from the embodiment of FIGS. Even when the laser beam is applied to the belt-like superposed portion 3 that has been welded by spot-like resistance welding in this way, the aim is set so that the scanning line of the laser beam can pass through each spot-like welded portion 6 sequentially. A laser beam is irradiated. However, since the spot-like pressure contact portion 6 has a very narrow width, even if laser welding is performed along the belt-like overlapping portion 3, the scanning line of the laser beam tends to deviate from the original planned welding line. For this reason, as shown in FIG. 4 (B), a situation often occurs in which the laser welding mark 5 passes through a position shifted from a part of the spot-like pressure contact portion 6. In such a case, there is a high possibility that the laser beam is irradiated to a portion where a large gap exists between the joint flange portion 1a of the first component and the joint flange portion 2a of the second component. There is a high possibility that a good welding quality is not obtained. In this respect, in the embodiment shown in FIGS. 1 to 3, each press contact portion 4 formed in the band-shaped overlapping portion 3 has a substantially rectangular shape extending long in the width direction of the band-shaped overlapping portion 3. 4 (B) is unlikely to occur.

  Hereinafter, other embodiments will be described.

  FIG. 5 shows an embodiment in which the incident angle θ of the laser beam applied to the band-shaped superposed portion 3 after pressure welding is inclined obliquely in the laser welding process of the basic embodiment. In other words, the laser beam is irradiated from the lateral direction along the width direction of the band-shaped overlapping portion 3 to the irradiation target surface of the band-shaped overlapping portion 3 at an incident angle θ of θ = 30 to 60 °. According to such oblique irradiation of the laser beam, laser welding in the width direction of the belt-like overlapping portion 3 while avoiding excessive heat input that causes welding distortion or the like in the relatively thin belt-like overlapping portion 3. The width w of the bonding interface can be increased. As a result, the joint strength of the lap joint in the belt-like overlapping portion 3 can be improved. When the incident angle θ is less than 30 °, it is difficult to aim the laser beam only at the belt-shaped overlapping portion 3. On the other hand, when the incident angle θ exceeds 60 °, the effect of increasing the width w of the bonding interface is reduced.

  6 and 7, an additional material 7 (for example, a stainless steel plate having a thickness of 0.3 mm) is added as a third joint, and a joint flange 1a of the first part and a joint flange of the second part. The embodiment which carried out resistance welding similarly to the said basic embodiment in the state which overlap | superposed the three of the part 2a and the additional material 7 is shown. In FIG. 6, the additional material 7 is superimposed on the joining flange part 1a of the first component. In FIG. 7, the additional material 7 is overlapped between the two joining flange portions 1a and 2a. The gap between the joints (1a, 2a, 7) is almost eliminated by pressure welding by resistance welding. After the pressure welding, the welding of the three-lap joint is completed by performing laser welding in the same manner as in the basic embodiment. According to the embodiment of FIG. 6 and FIG. 7, the heat capacity is increased by increasing the thickness of the band-shaped overlapping portion 3 by stacking the three joint portions (1a, 2a, 7), and the laser beam enters. Even if the heat increases a little, it becomes difficult to cause problems such as melting and perforation. Moreover, the joint strength of a joint improves by setting it as a 3 sheet | seat joint.

  FIG. 8 shows an embodiment in which laser trimming is simultaneously performed in the laser welding process of the basic embodiment. That is, the laser beam for welding and the laser beam for trim are simultaneously irradiated onto the band-shaped overlapped portion 3 after the press contact while simultaneously scanning along the longitudinal direction of the band-shaped overlapped portion 3. According to the embodiment of FIG. 8, laser welding and laser trimming are performed while holding the first and second parts 1 and 2, which are workpieces (workpieces), in the same clamp sail (a kind of jig). Can be performed simultaneously. For this reason, the number of operations for attaching and detaching the workpiece can be reduced, and the machining efficiency can be improved and the running cost can be reduced.

  In the basic embodiment of FIGS. 1 to 3, the joining flange portion 1 a of the first component 1 and the joining flange portion 2 a of the second component 2 are overlapped to perform pressure welding and laser welding. On the other hand, FIGS. 9 to 11 show a narrow joint portion 1b provided at the corner or the peripheral edge of the first component 1 and a narrow joint portion provided at the corner or the peripheral edge of the second component 2. FIG. An embodiment in which 2b is superposed and pressure welding and laser welding are applied thereto is shown. This is an example showing that the present invention can be applied even when a lap joint is formed by superimposing joint portions using the end portions of each component other than the flange-shaped joint portion.

  Specifically, first, as shown in FIGS. 9A and 9B, the joint 1b at the corner or the periphery of the first component 1 and the joint 2b at the corner or the periphery of the second component 2 are mutually connected. To form a belt-like overlapping portion 3 (superimposing step). At that time, as shown in FIG. 9C, for example, the corners or the periphery of the first component 1 may be folded back to form a double hooked joint 1b to form a three-layered belt-like overlapping portion 3. . Next, as shown in FIG. 10, by performing resistance welding in the thickness direction of the joint portions 1 b and 2 b at a plurality of locations on the strip-shaped overlapping portion 3, a predetermined interval is provided along the longitudinal direction of the strip-shaped overlapping portion 3. A plurality of press contact portions 4 are formed while being spaced apart (preliminary press contact step). Each pressure contact portion 4 (or pressure contact mark 4) has a substantially rectangular shape extending long in the width direction of the belt-shaped overlapping portion 3. When the press-contact of the belt-like overlapping portion 3 is completed, as shown in FIGS. 11A and 11B, the laser beam is applied to the belt-like overlapping portion 3, and the laser beam scanning lines have a plurality of pressure-contacting portions 4 as shown in FIGS. Irradiation is performed while scanning so as to intersect each of the laser beams (laser welding process). In this way, the joining of the joining part 1b of the first component 1 and the joining part 2b of the second component 2 is completed based on the laser welding in which the laser welding mark 5 intersects each of the plurality of press contact parts 4. . FIG. 11C shows a case where laser welding is performed on the three-layered belt-like overlapping portion 3 of FIG. 9C. It goes without saying that the embodiment of FIGS. 9 to 11 also has the same operational effects as those of the basic embodiment of FIGS.

  You may change the said basic embodiment and / or other embodiment as follows.

  [Modification] In the basic and other embodiments described above, the constituent material of the first and second parts 1 and 2 is stainless steel, but is not limited to this. For example, an aluminum alloy or a titanium alloy is used. It may be used as a constituent material.

  [Modification] In the above basic and other embodiments, the thickness (plate thickness) of the thin metal material (thin metal plate) constituting the first and second parts 1 and 2 is set to 0.2 to 0.4 mm. Although set, it may be set to 0.1 to 0.5 mm. However, the thickness of the thin metal material is not limited to the range of 0.1 to 0.5 mm, and the upper limit of the thickness can be, for example, 1.0 mm. About the thickness of a thin metal material, it can set variously, such as 0.1-1.0 mm, 0.2-1.0 mm, 0.1-0.8 mm, 0.2-0.8 mm.

  [Modification] In FIGS. 9C and 11C, the corners or peripheral edges of the first component 1 are folded back to form a double hook joint 1b, which is superimposed on the single joint 2b. In the above, an example in which the three-layered belt-like overlapping portion 3 is configured has been shown, but a similar three-layer overlapping configuration may be constructed between the two joining flange portions 1a and 2a. That is, either one of the joining flange portion 1a of the first component 1 or the joining flange portion 2a of the second component 2 is formed wider than the other, and the wide joining flange portion 1a or 2a is folded back. By forming a double flange joint flange portion and superposing it on the remaining single joint flange portion, a three-layer belt-like overlap portion 3 may be formed. The folded portion of the wide joint flange portion 1a or 2a corresponds to the additional material 7 in FIG. 6 or 7, and the arrangement of the folded portion can be the same as the arrangement of the additional material 7. The same effect as in the case of FIG. 6 and FIG. 7 can be obtained by press-welding the three-layer overlapping strip-shaped overlapping portion 3 and laser welding to form a three-layer overlap joint.

  [Modification] The application object of the present invention is not limited to the inner pipe for the double-pipe structure exhaust manifold, but the outer pipe for the double-pipe structure exhaust manifold, the single-pipe structure (single pipe structure) exhaust manifold Or the welding method of this invention is applicable also to the welding of the joint in metal parts or products, such as a fuel tank.

1A and 1B show a basic embodiment, and FIG. 3A is a plan view of a belt-shaped overlapping portion, and FIGS. 2B and 2C are partial cross-sectional views taken along line A1-A1. A basic embodiment is shown, (A) is a top view at the time of press-contact of a strip | belt-shaped overlapping part, (B) is a partial cross-sectional view in the A2-A2 line. A basic embodiment is shown, (A) is a top view at the time of the laser welding of a strip | belt-shaped overlapping part, (B) is a partial cross-sectional view in the A3-A3 line. A comparative example is shown, (A) is a top view at the time of pressure welding of a strip | belt-shaped overlapping part, (B) is a top view at the time of laser welding of a strip | belt-shaped overlapping part. The partial cross-sectional view of other embodiment. The partial cross-sectional view of other embodiment. The partial cross-sectional view of other embodiment. The partial cross-sectional view of other embodiment. 4A is a plan view of a belt-shaped overlapping portion, FIG. 4B is a partial cross-sectional view taken along line A4-A4, and FIG. 4C is a partial cross-sectional view of a modified example. The top view at the time of the pressure contact of the strip | belt shaped overlap part in other embodiment. 4A and 4B show another embodiment, in which FIG. 5A is a plan view during laser welding of a belt-shaped overlapping portion, FIG. 5B is a partial cross-sectional view taken along line A5-A5, and FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... 1st component, 1a ... Joining flange part (1st joining part), 1b ... Joining part, 2 ... 2nd component, 2a ... Joining flange part (2nd joining part), 2b ... Joining part, DESCRIPTION OF SYMBOLS 3 ... Band-shaped overlapping part, 4 ... Substantially rectangular press-contact part, 5 ... Laser welding trace, 7 ... Additional material (3rd junction part).

Claims (5)

A lap joint welding method configured by overlapping a plurality of joints,
A superposition step of superposing a plurality of joints made of thin metal materials to form a superposition part extending in a strip shape,
By applying pressure contact in the thickness direction of the joining portion at a plurality of locations of the belt-shaped overlapping portion, a pressure contact portion that has a shape extending in the width direction of the belt-shaped overlapping portion is formed as a longitudinal length of the belt-shaped overlapping portion. A press-contacting process for forming a plurality of the wafers at intervals along the direction;
By irradiating a laser beam onto the belt-shaped overlapping portion on which the pressure contact portion is formed while scanning so that a scanning line of the beam intersects each of the plurality of pressure contact portions, the belt-shaped overlapping portion A lap joint welding method, comprising: a laser welding process in which laser welding is performed so that a laser welding mark intersects each of the plurality of press contact portions over substantially the entire longitudinal direction of the mating portion.   The lap joint welding method according to claim 1, wherein the thin metal material is a thin metal material having a thickness of 0.1 to 0.5 mm.   The lap joint welding method according to claim 1 or 2, wherein the pressure welding used in the pressure welding step is pressure welding by resistance welding.   In the laser welding process, the laser beam is irradiated at an incident angle (θ) of 30 to 60 ° with respect to the irradiation target surface of the band-shaped overlapping portion from a lateral direction along the width direction of the band-shaped overlapping portion. The lap joint welding method according to claim 1, wherein the lap joint is welded. A welding method for a lap joint formed by superimposing joints of the first and second parts between first and second parts constituting an inner pipe for a double-pipe structure exhaust manifold. ,
A welding method for a lap joint in an inner pipe for a double-pipe structure exhaust manifold, characterized by using the welding method according to any one of claims 1 to 4.

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