JP2017164811A - Laser welding method, welded joint manufacturing method, spark plug electrode manufacturing method, and spark plug manufacturing method - Google Patents

Abstract

[Purpose] Two members are superposed, the edge of the superposed surface is irradiated with a laser beam, and the edge is used as a welding line, and the laser beam is scanned from the welding start position to the end to superimpose the two members. On the surface, when the two members are laser welded, spatter is not generated, the penetration depth on the scanning start position side is not insufficient, and the welding is performed at a desired penetration depth. SOLUTION: At a welding start position S1 of two overlapped members 10 and 20, laser light La irradiation is started at an output that does not generate spatter, and after the start, the laser light is not scanned without scanning the laser light La. The output of La is gradually increased so that the melting depth toward the depths of the overlapping surfaces 10a and 20a of the two members 10 and 20 from the irradiated edge 20e is within a predetermined melting depth range. After the gradual increase, the laser beam La is scanned toward the terminal S2 so as to be kept within the penetration depth range. [Selection diagram] FIG. 6

Description

  The present invention superimposes (butts) two members, irradiates the edge of the overlapping surface with laser light toward the back of the overlapping surface, and a desired penetration depth (penetration) The present invention relates to a method of laser welding the two members on their overlapping surfaces and a method for manufacturing a welded joint and the like.

  For example, one main surface (flat surface) of one member (plate member) is overlapped with one flat surface of the other member, for example, a rectangular parallelepiped, and both members are laser welded (hereinafter simply referred to as “welding surface”) Sometimes referred to as welding). In this case, one side (hereinafter also simply referred to as one side) of the edge (outer edge) on the overlapping surface is irradiated with laser light toward the back of the overlapping surface. As a welding line, laser beam scanning is performed at a constant speed to weld both members (base materials) on their overlapping surfaces. For example, it is at the time of manufacture of the ground side electrode which comprises the spark plug used for a motor vehicle engine (refer patent document 1). In such welding, in order to increase the welding strength (joining strength) while ensuring the accuracy, it is necessary to perform melting and solidification on the widest possible surface of the overlapping surface within a range that does not cause excessive melting. . For this purpose, from one edge of the overlapping surface to one side of the light receiving part (incident side) irradiated with the laser light, one opposite side located at the back of the irradiation (one side where the laser light travels) Select the conditions such as the laser beam output and the scanning speed (irradiation time) so that both metals have the necessary and sufficient penetration depth (melting depth in the irradiation direction) on the overlapping surface. There is a need to.

  FIG. 6 is an enlarged view for explaining an example of such welding. In the production of the ground side electrode (component) 31 constituting the spark plug 100 as shown in FIG. (Only shown) is a partial schematic enlarged view for explanation when the noble metal tip 20 is welded to a portion near the tip of 10. FIG. 8 is a longitudinal cross-sectional half view showing an example of a conventionally known spark plug 100, which has a cylindrical metal shell 40 with a different diameter and a hollow shaft-like shape disposed in the inside thereof. The insulator 50 is welded to the center electrode 60 which is assembled in the center shaft hole of the insulator 50 and exposes its tip at the tip (upper end in the figure) 53 of the insulator 50, and the tip surface 43 of the metal shell 40. The noble metal tip 20 is fixed to the tip of the ground-side electrode body 10 by welding, and the tip of the center electrode 60 is fixed to the tip of the ground-side electrode body 10 by welding. And forms a spark discharge gap. Here, the noble metal tip 20 is for improving the discharge ignitability and the durability with the tip of the center electrode 60 which is the counterpart electrode in the spark plug 100. Hereinafter, in the present application, the ground side electrode and the center electrode are also simply referred to as electrodes, and the ground side electrode body and the center electrode body are also referred to as electrode bodies.

  As shown in FIG. 6, in welding the noble metal tip 20 to a portion near the tip of the ground-side electrode body 10, the tip of the ground-side electrode body (for example, a strip-shaped square bar member made of nickel alloy) 10. 6A (front view) and FIG. 6, a noble metal tip (a fine rectangular parallelepiped made of a noble metal such as platinum or iridium or an alloy containing these as a main component) 20 is formed on a plate surface (plane) 13 near the surface 11. As shown in -B (plan view), it is aligned and overlapped with (or brought close to) the front end surface 11 of the main body 10. And among the edges of the overlapping surfaces 10a, 20a of both the members (welding members) 10, 20, for example, the right edge (edge of the noble metal tip) 20e in FIG. 6B (plan view). The laser beam La is irradiated from one end S1 to the other end S2 along one side (welding line WL) on the front end surface 11 side of the ground-side electrode body 10 so that scanning is performed at a constant speed. Were welded at the overlapping surfaces 10a and 20a. Such a ground-side electrode body 10 is a small square bar member (elongated strip-like member) having a width W1 in the cross section of 2 mm to 3 mm and a thickness H1 of about 1 mm to 1.5 mm. A noble metal tip (hereinafter also referred to as a tip) 20 to be welded to a thin rectangular parallelepiped having a thickness H2 of about 0.4 mm to 1 mm and a plane (see FIG. 6B) of about 1 mm to 1.5 mm square. is there. Therefore, since the length of the welding line WL is also as short as about 1 mm to 1.5 mm, the welding is performed along the welding line WL as described above, and the laser beam La is transmitted from one end (welding start position) S1 to the other. The scanning was performed once at a constant speed so as to pass toward the end (end) S2 (for example, from bottom to top in FIG. 6B).

  By the way, in order to obtain a desired high welding strength without causing a decrease in accuracy in such laser welding, as described above, the precious metal in the overlapping surfaces 10a and 20a (FIG. 6B (plan view)). Corresponding to the side length Lh of the noble metal tip 20 in the laser light irradiation direction (from right to left in FIGS. 6A and 6B) without causing excessive melting of both metals in the same area as the plane of the chip 10). It is necessary to ensure a sufficient penetration depth. The penetration depth is one side (welding line WL) from the start position (hereinafter also referred to as start position) that is one end S1 of irradiation to the end that is the other end S2, which is the scanning direction of the laser beam La. It must be ensured that there is no great variation even if That is, the penetration depth is a sufficient penetration depth corresponding to the side length Lh of the noble metal tip 20, and with respect to the side length Lh so that no large variation occurs along the welding line WL, The penetration depth range (side length Lh ± α) should be within the range of as small an error α as possible. If the spark plug is exposed to harsh conditions such as the grounding electrode of the spark plug and requires ignition performance and durability, the entire overlapping surfaces 10a and 20a (entire surface) can be reliably obtained without degrading accuracy. This is because the required welding is required. For this reason, conventionally, when performing such welding, the laser beam output, scanning speed, etc. are determined based on test welding so that the necessary and sufficient penetration depth can be obtained. I was scanning with. This laser beam scanning can be performed not by the laser side but by the relative movement of the welding member (base material) side or both. Shall be.

  On the other hand, in such laser welding, conventionally, the output of a constant output laser beam used for the irradiation has been set high. The reason is as follows. There is already heat input in the vicinity of the scanning portion of the welding base material (the ground side electrode main body and the noble metal tip forming both members in FIG. 6) in a state where the laser beam is irradiated and melting is started. However, at the start position S1 at the start of laser beam irradiation (at the start of welding), the base material in the cooled and solidified state is irradiated with laser beam and melted. More heat energy is required than the heat energy necessary for melting near the melted part in the welded base material (work after starting irradiation) that has been irradiated with laser light and has already started scanning and melting. . That is, since there is already heat input in the vicinity of the melted portion of the weld base material in a state where scanning and melting have started, a desired penetration depth can be obtained with a relatively small output laser beam. On the other hand, at the starting position S1 where there is no heat input and melting due to irradiation, the desired penetration depth cannot be obtained unless the laser beam output is increased by the amount of such heat input and melting. . This is the reason why the output is set high in the conventional technique of welding by irradiation and scanning with a laser beam having a constant output.

JP 2008-277272 A

  However, when laser welding is performed by irradiating and scanning the laser beam by setting the output of the laser beam high as described above, spatter (slag or metal particles scattered during welding) is performed during the welding process. ) Are likely to occur, and there is a problem to be solved that this easily adheres to the surface of the base material. As described above, at the starting position of the laser beam irradiation (welding), the irradiation is performed on the base material in the cooled and solidified state. Will occur. In addition, as described above, when the irradiation is started with the laser beam output set to a high value and scanning is performed, the heat input to the base material at the welding start position (light receiving part), the temperature The rise is even more rapid. For this reason, at the starting position of the irradiation of the base material, a rapid temperature increase occurs due to rapid heat conduction locally on the surface or in the vicinity of the surface of the base material, and excessive melting tends to occur thereafter. As a result, including the starting position, bumping of the molten metal occurs, which is considered to cause spattering and scattering. Such spatter generation and adhesion due to scattering are not permissible per se, but if such generation and scattering occur, the loss of molten metal will be caused accordingly. In laser welding, which is precision welding of small parts as in the manufacture of the above, and has a fine beat width, there is a big problem that the welding strength (joining strength) is also affected.

  In order to prevent the occurrence of such spatter, the output of the laser beam is set to be low, or the output is sufficiently low so as not to cause the occurrence in the initial or first half of the scan where the possibility of occurrence of spatter is high. It is also conceivable that the laser beam is increased to an output capable of obtaining a predetermined penetration depth in the subsequent scanning process. However, in any of these cases, a desired penetration depth cannot be obtained at least in the irradiation start position that is the initial stage of the scanning process and in the vicinity thereof. As a result, in the overlapping surfaces 10a and 20a of both members, as shown by double hatching in FIG. 7, even if a penetration range having a sufficient depth is obtained on the end S2 side of irradiation (welding), the start position The penetration depth in the initial or first half of the scan close to S1 is shallower than that on the end S2 side, and a sufficient welding area on the overlapping surface cannot be obtained. In such welding, not only the welding area is simply reduced, but also the depth of the welding surface along the scanning direction (welding line WL) is the side length Lh direction of the noble metal tip 20 (the horizontal direction in FIG. 7). ), The bonding strength is unbalanced. In this way, even if it is possible to prevent the occurrence of spatter by reducing the output in the initial or first half of welding, it is not possible to obtain a sufficient welding area or unbalance of the welding surface, and Stable welding strength cannot be obtained.

  The present invention has been made in view of the problems in laser welding as described above. Two members are overlapped, the edge of the overlap surface is irradiated with laser light, and a line along the edge is welded. In the laser welding method in which two members are welded on the overlapping surface by scanning the laser beam from the welding start position to the end, spattering is not caused and the start of the welding is performed. The welding depth can be welded at a desired penetration depth from the edge to the back of the overlapping surface in the scanning direction without causing a shortage of the penetration depth at the position and its vicinity. And providing a method for manufacturing a welded assembly including such a welding process, a method for manufacturing an electrode for a spark plug (ground side electrode, center electrode), and the like. For the purpose of.

According to the first aspect of the present invention, two members are overlapped, laser light is irradiated to the edge of the overlapping surface, and a line along the edge is used as a welding line from the welding start position to the end. In a laser welding method of welding two members on the overlapping surface by scanning a laser beam
Laser beam irradiation is started at an output that does not generate spatter at the welding start position of the welding line,
After the start, the laser beam output is gradually increased without scanning the laser beam so that the penetration depth from the edge toward the back of the overlapping surface is within a predetermined penetration depth range. And
After the gradual increase, the laser beam is scanned toward the end so that the penetration depth is maintained within a predetermined penetration depth range.

According to the second aspect of the present invention, two members are overlapped, laser light is irradiated to the edge of the overlapping surface, and a line along the edge is used as a welding line from the welding start position to the end. In a laser welding method of welding two members on the overlapping surface by scanning a laser beam
Laser beam irradiation is started at an output that does not generate spatter at the welding start position of the welding line,
Only within a predetermined time after the start, while scanning the laser beam at a relatively slower speed than the scanning at other times, the output of the laser beam is directed from the edge to the back of the overlapping surface. Gradually increase so that the penetration depth falls within the prescribed penetration depth range,
After the gradual increase, the laser beam is scanned toward the end so that the penetration depth is maintained within a predetermined penetration depth range.

The present invention according to claim 3 is the invention according to claim 1 or 2,
Instead of scanning the laser beam so that the penetration depth is maintained within a predetermined penetration depth range,
Laser welding characterized in that the laser beam is scanned, including scanning while gradually decreasing the output within a predetermined output range, so that the penetration depth is maintained within a predetermined penetration depth range. Is the method.
The present invention according to claim 4 provides the method according to claim 1 or 2,
Instead of scanning the laser beam so that the penetration depth is maintained within a predetermined penetration depth range,
Laser welding characterized in that the laser beam is scanned, including scanning while gradually increasing the speed within a predetermined speed range so that the penetration depth is maintained within a predetermined penetration depth range. Is the method.

The present invention according to claim 5 provides the method according to claim 1 or 2,
Instead of scanning the laser beam so that the penetration depth is maintained within a predetermined penetration depth range,
While gradually decreasing the output of the laser beam within a predetermined output range and gradually increasing the speed within a predetermined speed range so that the penetration depth is maintained within the predetermined penetration depth range. The laser welding method is characterized in that the scanning is performed including the above-described scanning.
According to a sixth aspect of the present invention, one of the two members is an electrode main body constituting a ground side electrode or a center electrode for a spark plug, and the other member is welded to the tip of the electrode main body. The laser welding method according to any one of claims 1 to 5, wherein the laser welding method is a noble metal tip.

A seventh aspect of the present invention is a method of manufacturing a welded joint including a step of welding the two members by the laser welding method according to any one of the first to fifth aspects.
The present invention described in claim 8 is a method for manufacturing an electrode for a spark plug, comprising the step of welding the electrode body and the noble metal tip by the laser welding method according to claim 6.
A ninth aspect of the present invention is a spark plug manufacturing method including the method for manufacturing a spark plug electrode according to the eighth aspect.

  Regarding the output of the laser beam, an approximate boundary value between the output that does not generate spatter and the output that can be generated can be known by performing test welding according to the member (base material) to be welded. Here, the test welding may be performed while changing the output of the laser beam or the like according to the melting point, thermal conductivity, and heat capacity of the base material. For this reason, what is necessary is just to set arbitrarily the output which does not generate | occur | produce a sputter | spatter based on such test welding. That is, the start output at the welding start position may be 0, or may be set with an appropriate safety factor such as 50% of the average output at which spatter generation is started in test welding. .

  In the present invention, the “predetermined penetration depth range” is to be welded out of the overlapping surfaces in accordance with the material and size of the two members to be welded and the size of the overlapping surfaces. What is necessary is just to set based on the area etc. which are set. For example, when the overlapping surfaces of two members are rectangular and one of the long sides is the edge (welding line) on the irradiation side, the entire overlapping surface is melted, solidified, and welded. The depth of insertion is along the short side. The “predetermined penetration depth range” may be set based on the length of the short side. For example, if the length of the short side is 1.5 mm, the welding dimension accuracy, etc., as 1.4 mm to 1.6 mm, 1.3 mm to 1.4 mm, or 1.4 mm to 1.5 mm, etc. Based on the above, an appropriate dimensional tolerance may be given and set. Further, after the gradual increase, the laser beam may be scanned toward the end so that the penetration depth is maintained within a predetermined penetration depth range. It is sufficient to keep it in relation to the speed.

  The gradual increase in the output of the laser beam is not limited as long as the output increases as time elapses, and the increase is performed even if the output is linearly proportional to time. It may be a plurality of linear changes having a plurality of bending points, a curve change, a step change, or a combination of these. In consideration of the difference between the output at the start of irradiation and the output when the specified penetration depth is obtained, welding is performed so that there is no sudden heat input or temperature rise that may cause spattering. Control that gradually increases may be performed according to the conditions of the power member and the like.

  According to the first aspect of the present invention, the gradual increase control of the output until the predetermined penetration depth range is obtained without scanning the laser beam at the welding (irradiation) start position, and after the gradual increase The scanning of the laser beam toward the terminal end is controlled. For this reason, generation | occurrence | production of a spatter can be prevented thru | or suppressed, and welding by the desired penetration depth range can be performed along a welding line. As a result, since welding with a desired welding area can be obtained without causing excessive melting, strong and stable welding can be efficiently obtained.

  According to the first aspect of the present invention, the output is gradually increased without scanning the laser beam until a predetermined penetration depth range is obtained, that is, at the welding start position, in a stopped state. Then, as described in claim 2, the laser beam output is changed while scanning the laser beam at a relatively slower speed than scanning at other times only within a predetermined time after the start. It is good also as gradually increasing so that the penetration depth which goes to the back of the said superimposition surface from an edge may become in the predetermined penetration depth range. Here, the “relatively slow speed” means a speed that is slower than the speed at which the laser beam is scanned toward the end after the gradual increase. In the invention according to claim 2, the relatively slow speed is used. However, until the predetermined penetration depth range is reached, the predetermined penetration depth cannot be obtained in the scanning range of the welding line as much as there is scanning. Therefore, this “relatively slow speed” is preferably set to a speed as close to the low-speed stop state as possible so that the range in which such a predetermined penetration depth cannot be obtained is as short as possible in the welding line. . Further, in the scanning process, it is preferable to control to increase the output increasing speed (gradual increase rate) as much as possible without causing spattering.

  Note that after the output is gradually increased within the predetermined penetration depth range, the laser beam is scanned toward the end so that the penetration depth is maintained within the predetermined penetration depth range. The output in this scanning process may be the same as or different from the output when the predetermined penetration depth range is obtained. Instead of scanning the laser beam so that the penetration depth is maintained within a predetermined penetration depth range, as in the invention described in claim 1 or 2, It is preferable to scan the laser light including scanning while gradually decreasing the output within a predetermined output range so that the penetration depth is maintained within a predetermined penetration depth range. This is because excessive heat input and excessive melting after the gradual increase in output can be prevented, and variations in the penetration depth can be suppressed. Here, including a scan while gradually decreasing the output means that the gradual decrease may or may not be the full scan process after the gradual increase. For example, it may be decreased gradually only in the first half of the second half of the scanning process following the increase. Further, the speed in the scanning after such a gradual increase may be constant or change in consideration of the relationship with the output so that the desired predetermined penetration depth range is maintained.

  The method of gradually decreasing the output after gradually increasing the output in claim 3 is opposite to the above-described method of gradually increasing the output of the laser beam, but may be a linear change proportional to time. One having a plurality of linear changes having one or more bending points, a curve change, a step change, or a combination of these But you can. What is necessary is just to set so that the desired penetration depth range may be hold | maintained according to the speed of a scan, the magnitude | size of a base material and an overlapping surface, the length of a welding line, etc. In addition, as described above, the start timing of the gradual decrease of the output may be after the predetermined penetration depth is obtained, that is, immediately after the end of the gradual increase or after a lapse of time.

  In claim 3, the output is gradually decreased after the output is gradually increased in order to prevent excessive heat input and excessive melting and to suppress the variation in the penetration depth. However, as in the invention according to claim 4, According to any one of claims 1 and 2, in place of scanning the laser beam so that the penetration depth is maintained within a predetermined penetration depth range, the penetration depth is predetermined. The laser beam may be scanned, including scanning while gradually increasing the speed within a predetermined speed range, so that the laser beam is held within the range of the penetration depth. Thus, since the irradiation time can be shortened by gradually increasing the scanning speed, the same effect can be obtained. It should be noted that the method of gradually increasing the scanning speed in such a case can be of an appropriate pattern, similarly to the method of gradually increasing the output described above.

  As will be understood from claims 3 and 4, in the present invention, as in the invention of claim 5, it is also possible to perform control combining them. In this case, the gradual decrease of the output and the gradual increase of the speed may be combined so that the desired predetermined penetration depth range can be obtained without variation along the welding line.

  In the laser welding method according to the sixth aspect of the present invention, one member is an electrode body constituting a ground side electrode or a center electrode for a spark plug, and the other member is a tip of the electrode body. Extremely when high precision and high welding strength are required for welding, such as electrodes for spark plugs, where the welded joint continues to be exposed to harsh conditions, as in the case of precious metal tips welded to Suitable. However, the object to be welded in the present invention is not limited to this, and even if it is a part for the same spark plug, it can be applied to other than an electrode as long as it is a welded joint, and welded joint used for other than a spark plug. The present invention can also be applied when obtaining a body (two-member welded body). Moreover, according to the manufacturing method of the welding joined body including the process of welding the said 2 member with the laser welding method of any one of Claims 1-5 like this invention of Claim 7, A welded assembly with high accuracy and high welding strength can be obtained.

  In addition, the welded joined body includes constituent parts and constituent members of various parts such as a sensor such as a gas sensor and a car part such as a glow plug (mounted part for automobile), and the present invention according to claim 8. According to the method for manufacturing an electrode for a spark plug, an electrode (a ground side electrode or a center electrode) with high accuracy and high welding strength can be obtained as described above. Therefore, according to the spark plug manufacturing method including the spark plug electrode manufacturing method according to claim 8 as in the present invention according to claim 9, not only the discharge ignition property but also the durability is reliable. A high quality spark plug with high performance can be obtained.

FIG. 1-A shows a case where a noble metal tip (a rectangular parallelepiped) is positioned and superimposed on a ground side electrode body (strip-shaped plate member or square bar member) for a spark plug, and both members are laser-welded on the overlapping surface ( 6) is a diagram for explaining the relationship between the time of the laser beam output and the output of the laser beam, in which the horizontal axis represents time and the vertical axis represents the output change state. FIG. FIG. 6 is an explanatory diagram of the relationship between time and the scanning speed of laser light in a changing state, in which the horizontal axis represents time and the vertical axis represents the changing state of the scanning speed. The schematic diagram for description of the penetration depth (double hatching part) in the overlapping surface when laser welding in FIG. The figure explaining another example (4 patterns of the change state of time and the output of a laser beam) of how to make the output of a laser beam gradually increase. After gradually increasing the laser beam output until a predetermined penetration depth range is obtained, a method of gradually decreasing (time and the change state of the laser beam output) is described to explain an example (4 patterns) in which the output is gradually decreased. Illustration to explain. After gradually increasing the laser beam output until a predetermined penetration depth range is obtained, an example (2 patterns) in which the scanning speed is gradually increased will be described. How to gradually increase (time and scanning speed change state) will be described. To do. Partial enlarged schematic diagram for explanation when a noble metal tip (cuboid) is positioned and superimposed on a ground electrode body (strip-shaped plate member or square bar member) for a spark plug, and both members are laser welded on the overlapping surface. A is a front view, B is a plan view of A, and C is a view of A from the right side (a view of the ground-side electrode body viewed from the front end surface). The typical top view explaining the problem in the laser welding of FIG. The longitudinal section half sectional view which shows an example of a conventionally well-known spark plug.

  DESCRIPTION OF EMBODIMENTS Embodiments embodying a laser welding method and a welded joint manufacturing method according to the present invention will be described in detail with reference to the drawings. However, in this embodiment, the noble metal tip (cuboid) 20 is positioned and overlapped with the spark plug ground electrode body 10 shown in FIG. 6 as described above, and the edges of the overlapping surfaces 10a and 20a are overlapped. Among them, one side (straight line) which is the end edge (end edge of the tip) 20e on the front end surface 11 (right side of FIGS. A and B) of the electrode main body 10 is defined as a welding line WL. This is a case where both the members 10 and 20 are laser-welded, and a ground side electrode is manufactured as a welded joint. Also, in the welding line WL, the lower end of FIG. 6B (plan view) is the start position S1 of laser beam La irradiation (welding), and the other end, which is the upper end of the figure, is the welding end (end position) S2. Assuming that the laser beam La is controlled to be scanned. The material and size of each member are as described above. Further, the penetration depth range in this example corresponds to the side length Lh (for example, 1.5 mm) of the noble metal tip (cuboid) 20 in a plan view (FIG. 6B), and the direction along the welding line WL. In this case, it should be held within a range of Lh ± α (for example, 1.4 mm to 1.6 mm).

  In this example, a laser welding machine (not shown) is used, and at the start of irradiation at the start position S1 of welding (irradiation of laser light La) in the welding line WL shown in FIG. Irradiation is started with a low (weak) output laser beam La that is not generated. Then, without scanning the laser beam La, the output of the laser beam La is gradually increased at the irradiation start position S1. The gradual increase is performed until the penetration depth from the edge 20e to the back of the overlapping surfaces 10a and 20a is within a predetermined penetration depth range (Lh ± α). Then, after the penetration depth is obtained, the laser beam La having the gradually increased output is scanned toward the end S2 at an appropriate constant speed, for example. This speed is set in a range in which the penetration depth is maintained within a predetermined penetration depth range.

  In such welding, the relationship between the gradual increase in the output of the laser beam La and the time is as shown in FIG. 1A, for example. That is, the output P is set to 0 at the start of the irradiation, and the output is proportional until the output P1 at which a desired predetermined penetration depth is obtained by taking time T1 so as not to cause spattering. The output P1 is maintained after the increase, and the laser beam La is scanned from the start position S1 toward the end S2 at a constant moderate speed V1. That is, in this example, as shown in FIG. 1-B, the laser beam La is stopped at the welding start position S1 until the time T1 when reaching the output P1, and the time T1 when reaching the output P1. Simultaneously, the laser beam (irradiation spot) La having the output P1 is scanned at the constant speed V1 toward the terminal S2. In this example, the output P1 after the gradual increase of the laser light La is set in the range of 250 to 500 W, for example, and the scanning speed V1 is set in the range of 50 to 200 mm / second, for example.

  Thus, according to the laser welding method of the present example, spattering is not caused, and as shown by double hatching in FIG. 20a is welded along a welding line WL within a desired predetermined penetration depth range (Lh ± α). Thus, according to the welding method of the present example, as in the prior art, the irradiation with the output set higher from the irradiation start position S1 of the laser beam La is started, and the output is not scanned as it is, Irradiation is started with a laser beam with an output that does not generate spatter, and the output is gradually increased, so that spatter does not occur. Further, since the laser beam is not irradiated at a low output to scan to the end S2, it is not possible to obtain a desired penetration depth at the irradiation start position S1 and in the vicinity thereof. Thus, according to the present welding method, both members are welded in the entire region of the overlapping surfaces 10a and 20a from the scanning start position S1 to the terminal end S2 without any lack of fusion depth or imbalance. be able to. As a result, since a ground side electrode with a noble metal tip is obtained by strong and stable welding, a spark plug excellent in ignition performance and durability can be obtained.

  That is, the ground-side electrode (component) obtained by the electrode manufacturing method embodying the laser welding method of this example described above is used for manufacturing a spark plug, and is conventionally known as shown in FIG. The spark plug 100 is configured. In addition, since the manufacturing process of such a spark plug 100 is conventionally well-known, it is stopped with simple description, but is as follows, for example (see FIG. 8). The ground-side electrode (component) is connected to the end surface 43 of the metal shell (manufactured product) 40 as described above, as shown by a two-dot chain line in FIG. Resistance welding is performed so that the rear end face is vertically butted. Thereafter, a finishing process such as forming a screw 46 on the outer peripheral surface of the metal shell 40 is performed, and the metal shell with the ground-side electrode thus finished is sent to the subsequent assembly process. In the assembling process, the insulator 50 including the center electrode 60 and its terminal 65 as described above is assembled in the metal shell, the rear end 47 of the metal shell 40 is bent inward, and the tip (FIG. 8), the ground side electrode 31 is bent inward in the ground side electrode body 10 so that a predetermined discharge spark gap is obtained. Through these steps, the spark plug 100 as shown in FIG. 8 is obtained.

  In this example, the case where the present invention is embodied in welding and manufacturing of the ground side electrode 31 is described. However, in the case of manufacturing a center electrode with a noble metal tip formed by welding a noble metal tip to the tip of the center electrode 60. It can also be embodied in the same way. And, at least by making a spark plug using an electrode embodying the present invention in one of the electrodes, it is possible to improve ignition performance and durability compared to a spark plug that does not use such an electrode. it can. As for the process of welding the noble metal tip to the tip of the center electrode (manufacturing process of the center electrode with the noble metal tip), since the noble metal tip usually becomes a cylindrical body (or a disc), the overlapping surface is circular. Therefore, in such a case, the point that the welding line becomes a circumference is different from the case in the above example. However, except for this difference, the welding line can be embodied in the same manner as described above. Details thereof will be described later.

  In the above example (laser welding method example), the case where the output of the laser beam La until the predetermined penetration depth range (Lh ± α) is obtained is gradually increased from 0 at the start of irradiation. However, this gradual increase may be stepwise as shown in FIG. 3-A2, or may be gradually increased (curved downward) as shown in FIG. 3-A3. As shown in FIG. 3-A4, it may be gradually increased by an upwardly convex curve. Further, such a gradual increase in the output is not from 0, but as shown in FIG. 3A5, irradiation may be started with an appropriate low output within a range not causing the occurrence of sputtering. As described above, the method of gradually increasing the output of the laser light La until the predetermined penetration depth range (Lh ± α) is obtained can be embodied as appropriate.

  In the above example, the laser beam La is not scanned at the welding start position S1 and irradiation is started and the output is gradually increased. However, it is assumed that there is scanning of the laser beam La from the start of irradiation. However, if the speed is such a low speed as to be close to the stop position and a predetermined penetration depth range (Lh ± α) is obtained near the start position S1, the predetermined penetration depth range ( During a predetermined time from the start until Lh ± α) is obtained, the laser beam La may be scanned in the process of gradually increasing the output of the laser beam La. However, in this case, there is a portion where the penetration depth is shallower at the portion closer to the start position S1 as much as the laser beam La is scanned (moved) until a predetermined penetration depth is obtained although it is small. Arise. Therefore, in such a case, it is preferable to perform scanning at the lowest possible speed as described above.

  In the above example, the output is gradually increased, and after a predetermined penetration depth range (Lh ± α) is obtained, the laser beam La with a constant output holding the output at the time of the increase is directed toward the terminal S2. Although the case where scanning is performed at a constant speed V1 has been described, after the gradual increase, a predetermined penetration depth range (Lh ± α) can be obtained even if the output of the laser beam La to be scanned is reduced by the heat input so far. ) May be obtained as described above. Therefore, in such a case, in the first half of the scanning process after the predetermined penetration depth range (Lh ± α) is obtained, for example, in the first half, they are shown as A6, A7, A8, and A9 in FIG. In such a change state, the output P1 after the gradual increase may be gradually decreased and then held constant until the end of scanning. Note that such a method of gradually decreasing the output may be set and controlled in consideration of the relationship with the scanning speed so as to obtain a predetermined penetration depth range (Lh ± α).

  Furthermore, in the above example, it has been described that the output is gradually increased and the laser beam La is scanned at a constant speed. However, after the output is gradually increased (after the time T1 has elapsed), the heat input up to that time causes a predetermined amount of heat. After the penetration depth range (Lh ± α) is obtained, the predetermined penetration depth range (Lh ± α) is obtained even if the scanning speed of the laser beam La is gradually increased (even if the irradiation time is shortened). ) Is secured, the speed is not constant (constant speed), but can be gradually increased as shown in FIGS. That is, the speed after time T1 may be proportionally increased as shown in FIG. 5-B2, or gradually increased (increased speed) as shown in FIG. 5-B3. ). In any case, it may be set appropriately in relation to the output so as to obtain a desired predetermined penetration depth range (Lh ± α) along the welding line WL. As is clear from the above, as long as the desired predetermined penetration depth range (Lh ± α) is obtained along the welding line WL after the output is gradually increased (after time T1), the output is gradually decreased. Further, the gradual increase in scanning speed may be combined.

  In the above example, in the manufacture of the ground side electrode for the spark plug, the case where the noble metal tip is welded to the ground side electrode body has been described. However, the laser welding method of the present invention (the manufacturing method of the welded joint) is as described above. The present invention is not limited to such a member, and can be widely applied when two members are overlapped and welded as described above. That is, as described above, the welding method can be applied regardless of the use, type, etc. of the welded joint (two-member welded body), and the welded joint to be manufactured is a ground electrode for the spark plug, the center In addition to the electrodes, the present invention can be widely applied to constituent parts and constituent members of various parts such as sensors such as gas sensors and automotive parts such as glow plugs (mounted parts for automobiles). Further, the present invention is not limited to welding between different kinds of metals and the same kind of metal, and can be widely applied to laser welding and manufacturing welded joints thereby. Furthermore, in the laser welding method of the present invention, the welding surface (penetration depth) is wide when welding is performed to obtain a desired predetermined penetration depth range even if the welding surface (penetration depth) is not the entire overlapping surface. Applicable.

Further, in the above example, the present invention is embodied in the manufacture of the ground electrode for the spark plug. However, the present invention can be similarly applied to the manufacture of the center electrode for the spark plug as described above. That is, the present invention can also be applied to the case where a noble metal tip is welded to the tip of the center electrode main body (the end that forms the spark gap for discharge) that should form the center electrode. As described above, since such a noble metal tip is usually a cylindrical body (or a disk), the overlapping surface is circular, and thus the welding line WL is circumferential. Irradiates the circumference of the overlapping surface with laser light while rotating the welded member around the center of the circle, for example, one rotation, so that the edge (circumference) is irradiated with laser light. Can be scanned. Thereby, the welding of the predetermined penetration depth range which makes the predetermined width in the radial direction the penetration depth along the circumference is obtained. That is, the welding line in the present invention is not limited to a straight line. Laser welding can be applied to various known types such as YAG laser welding and CO ₂ laser welding.

10 members (ground side electrode body)
10a, 20a Overlapping surface 20 Member (noble metal tip)
20e Edge 31 Ground side electrode for spark plug (welded joint)
60 Spark plug center electrode 100 Spark plug La Laser beam WL Welding line S1 Welding (irradiation) start position S2 End

Claims (9)

Two members are overlapped, laser light is irradiated to the edge of the overlapping surface, and a laser beam is scanned from the start position to the end of welding with the line along the edge as a welding line. In a laser welding method for welding a member on the overlapping surface,
Laser beam irradiation is started at an output that does not generate spatter at the welding start position of the welding line,
After the start, the laser beam output is gradually increased without scanning the laser beam so that the penetration depth from the edge toward the back of the overlapping surface is within a predetermined penetration depth range. And
After the gradual increase, the laser welding method is characterized in that the laser beam is scanned toward the end so that the penetration depth is maintained within a predetermined penetration depth range. Two members are overlapped, laser light is irradiated to the edge of the overlapping surface, and a laser beam is scanned from the start position to the end of welding with the line along the edge as a welding line. In a laser welding method for welding a member on the overlapping surface,
Laser beam irradiation is started at an output that does not generate spatter at the welding start position of the welding line,
Only within a predetermined time after the start, while scanning the laser beam at a relatively slower speed than the scanning at other times, the output of the laser beam is directed from the edge to the back of the overlapping surface. Gradually increase so that the penetration depth falls within the prescribed penetration depth range,
After the gradual increase, the laser welding method is characterized in that the laser beam is scanned toward the end so that the penetration depth is maintained within a predetermined penetration depth range. In either claim 1 or 2,
Instead of scanning the laser beam so that the penetration depth is maintained within a predetermined penetration depth range,
Laser welding characterized in that the laser beam is scanned, including scanning while gradually decreasing the output within a predetermined output range, so that the penetration depth is maintained within a predetermined penetration depth range. Method. In either claim 1 or 2,
Instead of scanning the laser beam so that the penetration depth is maintained within a predetermined penetration depth range,
Laser welding characterized in that the laser beam is scanned, including scanning while gradually increasing the speed within a predetermined speed range so that the penetration depth is maintained within a predetermined penetration depth range. Method. In either claim 1 or 2,
Instead of scanning the laser beam so that the penetration depth is maintained within a predetermined penetration depth range,
While gradually decreasing the output of the laser beam within a predetermined output range and gradually increasing the speed within a predetermined speed range so that the penetration depth is maintained within the predetermined penetration depth range. A laser welding method characterized by performing scanning, including scanning of   One of the two members is an electrode body constituting a ground side electrode or a center electrode for a spark plug, and the other member is a noble metal tip welded to the tip of the electrode body. The laser welding method according to any one of claims 1 to 5.   A method for manufacturing a welded joint, comprising a step of welding the two members by the laser welding method according to claim 1.   The manufacturing method of the electrode for spark plugs including the process of welding the said electrode main body and the said noble metal tip by the laser welding method of Claim 6.   A method for producing a spark plug, comprising the method for producing an electrode for a spark plug according to claim 8.

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