Welding method and welding apparatus

Abstract

To provide a welding method that can ensure adequate welding quality in areas where multiple metal plates are welded together, even when the welding speed in laser welding is increased. [Solution] In the welding method of the embodiment, multiple metal plate portions are laser-welded. In the welding method, an oxide film is formed on the welded portion by injecting an oxygen-containing mixed gas into the welded portion while the oxygen concentration is adjusted to a specified concentration range lower than the concentration in the atmosphere, thereby suppressing the flow of molten metal by the oxide film.

Description

Technical Field

[0001] Embodiments of the present invention relate to a welding method and a welding apparatus.

Background Art

[0002] In the process of manufacturing products, etc., laser welding is performed to weld a plurality of metal plate parts by irradiating a laser. For example, in the manufacture of a battery in which an exterior part is formed from a metal exterior container and a lid plate, the lid plate is welded to the peripheral plate part of the exterior container by laser welding. When welding a plurality of metal plate parts by laser welding, from the viewpoint of improving the productivity of the product, etc., it is required to increase the welding speed, that is, the moving speed (scanning speed) of the laser head that irradiates the laser. Further, even when the welding speed in laser welding is increased, it is required to appropriately ensure the welding quality at the portion where the plurality of metal plate parts are welded. For example, even when the welding speed in laser welding is increased, at the portion where the plurality of metal plate parts are welded, the occurrence of undercut is suppressed, and the unevenness degree at the raised portion (weld bead) caused by humping is reduced.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The problem to be solved by the present invention is to provide a welding method and a welding apparatus capable of appropriately ensuring the welding quality at the portion where the plurality of metal plate parts are welded even when the welding speed in laser welding is increased.

Means for Solving the Problems

[0005] In the welding method of this embodiment, multiple metal plate sections are laser-welded. In the welding method, an oxide film is formed on the welded section by injecting an oxygen-containing mixed gas onto the welded section while the oxygen concentration is adjusted to a specified concentration range lower than the concentration in the atmosphere, thereby suppressing the flow of molten metal. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 is a schematic perspective view showing an example of a battery manufactured through a manufacturing process that includes laser welding, according to the first embodiment. [Figure 2] Figure 2 is a schematic perspective view showing the battery casing and cover plate of Figure 1 separated from each other. [Figure 3] Figure 3 is a schematic diagram showing the state in which the cover plate is welded to the peripheral plate during the battery manufacturing process in the first embodiment. [Figure 4] Figure 4 is a schematic cross-sectional view showing an example of the configuration of the welded portion and the surrounding area in the first comparative example, in a cross-section along the width direction of the welded portion. [Figure 5] Figure 5 is a schematic cross-sectional view showing an example of the configuration of the portion where the peripheral plate and the cover plate are welded, and the vicinity thereof, in the first embodiment, in a cross-section along the width direction of the welded portion. [Figure 6] Figure 6 is a schematic cross-sectional view showing an example of the configuration of the welded portion of the peripheral plate and cover plate in the second comparative example, in a cross-section along the welding direction (direction of movement of the laser head) in laser welding. [Figure 7] Figure 7 is a schematic cross-sectional view showing an example of the configuration of the portion where the peripheral plate and the cover plate are welded together in the first embodiment, in a cross-section along the welding direction (direction of movement of the laser head) in laser welding. [Figure 8] Figure 8 is a schematic diagram showing the welding speed and injected gas for each of the eight conditions under which laser welding was performed in verification related to the embodiment, etc. [Figure 9]Figure 9 is a schematic diagram showing the observation results regarding undercuts under each of the eight conditions under which laser welding was performed in verification related to the embodiment, etc. [Figure 10] Figure 10 is a schematic diagram showing the results of a comparison of the degree of unevenness of the uneven structure formed on the raised portion among eight laser welding conditions in verification related to the embodiment, etc. [Figure 11] Figure 11 is a schematic diagram showing a state in which multiple metal plate portions are welded together in a first modified example of the embodiment. [Figure 12] Figure 12 is a schematic cross-sectional view showing an example of the configuration of a portion where multiple metal plate portions are welded together, and the surrounding area, in the third comparative example, in a cross-section along the width direction of the welded portion. [Figure 13] Figure 13 is a schematic cross-sectional view showing an example of the configuration of a portion where multiple metal plates are welded together, and the vicinity thereof, in the first modified example, in a cross-section along the width direction of the welded portion. [Modes for carrying out the invention]

[0007] Embodiments will be described below with reference to the drawings. In one embodiment, a welding method and welding apparatus are provided for welding a plurality of metal plate portions by laser welding.

[0008] (First embodiment) First, a first embodiment will be described as an example of a welding method and welding apparatus. In the first embodiment, in the manufacturing of the battery product, the lid plate is welded to the peripheral plate portion of the outer casing by laser welding. Figure 1 is a schematic perspective view showing an example of a battery 1 manufactured through a manufacturing process including laser welding in the first embodiment. As shown in Figure 1, the battery 1 comprises an electrode group 2, an outer casing 3, and a lid plate 5. In the battery 1, the outer casing is formed by the outer casing 3 and the lid plate 5. The outer casing 3 and the lid plate 5 are each made of metal. Examples of metals used to form the outer casing 3 and the lid plate 5 include aluminum and aluminum alloys. In one example, the outer casing 3 and the lid plate 5 may each be made of iron or stainless steel, etc.

[0009] Figure 2 is a schematic perspective view showing the outer casing 3 and lid plate 5 of the battery 1 in Figure 1, separated from each other. As shown in Figures 1 and 2, the battery 1 and its outer casing (outer casing 3 and lid plate 5) are defined in the height direction (directions indicated by arrows Z1 and Z2), the circumferential direction (direction indicated by arrow P) that intersects (orthogonal or nearly orthogonal to) the height direction, and the radial direction that intersects (orthogonal or nearly orthogonal to) both the height direction and the circumferential direction. Furthermore, the battery 1 and its outer casing are defined by a virtual central axis C along the height direction. In the battery 1, the direction around the central axis C corresponds to the circumferential direction. Also, in the battery 1, the side approaching the radial central axis C is the inner circumference side, and the side moving away from the radial central axis C is the outer circumference side.

[0010] The outer casing 3 comprises a bottom plate portion 6 and a periphery plate portion 7, and an internal cavity 8 is defined inside the outer casing 3 by the bottom plate portion 6 and the periphery plate portion 7. The electrode group 2 is housed in the internal cavity 8 of the outer casing 3. In the battery 1, the bottom plate portion 6 covers the internal cavity 8 from one side in the height direction. The periphery plate portion 7 covers the internal cavity 8 from the outer circumference, covering the internal cavity 8 around its entire circumference. One end (lower end) of the battery 1 in the height direction is connected to the bottom plate portion 6 of the periphery plate portion 7, and the periphery plate portion 7 extends along the height direction of the battery 1 from the connection point to the bottom plate portion 6. In the outer casing 3, the internal cavity 8 opens on the side opposite to the side where the bottom plate portion 6 is located in the height direction.

[0011] In battery 1, the cover plate 5 is attached to the peripheral plate portion 7 of the outer container 3 at the end opposite to the side where the bottom plate portion 6 is located. The cover plate 5 then closes the opening of the internal cavity 8. In battery 1, the cover plate 5 is attached to the outer container 3 by welding it to the peripheral plate portion 7. Therefore, in battery 1, the peripheral plate portion 7 and the cover plate 5 are welded together as multiple metal plate portions. In battery 1, the side where the internal cavity 8 opens in the height direction is also referred to as the "upper side," and the side opposite to the upper side (arrow Z1 side) in the height direction is also referred to as the "lower side."

[0012] On the cover plate 5, an outer edge E1 is formed around the entire circumference of the battery 1. Also, on the periphery plate portion 7 of the outer casing 3, an opening edge E2 is formed around the entire circumference of the battery 1. In the area where the cover plate 5 and the periphery plate portion 7 are welded, the outer edge E1 and its vicinity of the cover plate 5 are welded to the opening edge E2 and its vicinity of the periphery plate portion 7. Furthermore, in the battery 1, the area where the cover plate 5 and the periphery plate portion 7 are welded is formed around the entire circumference, and the cover plate 5 is welded to the periphery plate portion 7 around the entire circumference of the battery 1.

[0013] In battery 1, the thickness direction of the peripheral plate portion 7 coincides with or approximately coincides with the radial direction of battery 1. The thickness direction of the cover plate 5 coincides with or approximately coincides with the height direction of battery 1. Therefore, the peripheral plate portion 7 and the cover plate 5 are welded together such that the thickness direction of the peripheral plate portion 7 intersects (orthogonal or approximately orthogonal to) the thickness direction of the cover plate 5. In one example, the thickness of the peripheral plate portion 7 at and near the opening edge E2 is 0.4 mm or more and 0.6 mm or less, for example, about 0.5 mm. The thickness of the cover plate 5 at and near the outer edge E1 is 0.4 mm or more and 0.6 mm or less, for example, about 0.5 mm.

[0014] In battery 1, the electrode group 2 includes a positive electrode and a negative electrode. In the electrode group 2, the positive electrode and the negative electrode are electrically insulated from each other. And in the internal cavity 8, an electrolyte such as an electrolytic solution is held by the electrode group 2. Also, in an example of FIGS. 1 and 2, a pair of terminals 11 are attached to the cover plate 5, and each of the terminals 11 is exposed on the outer surface of the cover plate 5. The pair of terminals 11 are arranged apart from each other. In battery 1, one of the pair of terminals 11 serves as the positive electrode terminal, and the other one different from the positive electrode terminal of the pair of terminals 11 serves as the negative electrode terminal.

[0015] The positive electrode of the electrode group 2 is electrically connected to the positive electrode terminal via a conductive member such as a lead, and the negative electrode of the electrode group 2 is electrically connected to the negative electrode terminal via a conductive member such as a lead. Also, each of the terminals 11 is prevented from contacting the cover plate 5 by an insulating member 12 or the like and is electrically insulated from the outer container 3 and the cover plate 5. Also, in the internal cavity 8, the positive electrode and the negative electrode of the electrode group 2 are prevented from contacting the outer container 3 by an insulating member (not shown) and are electrically insulated from the outer container 3 and the cover plate 5.

[0016] In the manufacture of the battery 1 as described above, after attaching the pair of terminals 11 to the cover plate 5, the positive electrode of the electrode group 2 is electrically connected to the positive electrode terminal, and the negative electrode of the electrode group 2 is electrically connected to the negative electrode terminal. Thereby, an electrode group assembly in which the electrode group 2, the cover plate 5, and the pair of terminals 11 are assembled is formed. Then, the electrode group assembly is inserted into the internal cavity 8 of the outer container 3 from the opening with the electrode group 2 at the front, so that the electrode group 2 is housed in the internal cavity 8 and the opening of the internal cavity 8 is closed by the cover plate 5. And in a state where the opening of the internal cavity 8 is closed by the cover plate 5, the cover plate 5 is attached to the peripheral plate portion 7 by welding the cover plate 5 to the peripheral plate portion 7. At this time, the cover plate 5 and the peripheral plate portion 7 which are a plurality of metal plate portions are welded by laser welding for irradiating a laser. And after attaching the cover plate 5 to the peripheral plate portion 7, the battery 1 is manufactured through a predetermined process including injecting an electrolyte such as an electrolytic solution into the internal cavity 8.

[0017] Figure 3 is a schematic diagram showing the state in which the cover plate 5 is welded to the peripheral plate portion 7 during the manufacturing process of the battery 1 in the first embodiment. As shown in Figure 3, in this embodiment, the cover plate 5 is welded to the peripheral plate portion 7 using a welding device 20. The welding device 20 includes a laser head 21, a gas injection nozzle 22, and a moving drive unit 23. The laser head 21 irradiates the parts to be welded, the cover plate 5 and the peripheral plate portion 7, with a laser. In laser welding of the cover plate 5 and the peripheral plate portion 7, the laser head 21 irradiates the laser from above in the height direction, that is, from the side facing the outer surface of the cover plate 5.

[0018] In one example, the laser head 21 emits a laser with a laser output of 4900W or more and 5100W or less, for example, with a laser output of about 5000W. The laser head 21 then emits the laser within a range where the diameter of the irradiation spot at the part to be welded is between 220μm and 240μm, for example, the diameter of the irradiation spot at the part to be welded is about 230μm. The laser head 21 then emits the laser when the peak wavelength of the laser is about 1030nm or 1070nm.

[0019] The movable drive unit 23 is composed of a drive member such as an electric motor. When the movable drive unit 23 is driven, the laser head 21 moves. When the peripheral plate portion 7 and the cover plate 5 are being welded by the laser from the laser head 21, the laser head 21 moves along the circumferential direction of the battery 1 and along the opening edge E2 of the opening of the internal cavity 8 and the outer edge E1 of the cover plate 5. As a result, the part irradiated by the laser from the laser head 21 moves along the opening edge E2 of the opening of the internal cavity 8 and the outer edge E1 of the cover plate 5. By performing laser welding while moving the part irradiated by the laser in the circumferential direction of the battery 1, the cover plate 5 and the peripheral plate portion 7 are welded over the entire circumference of the battery 1.

[0020] Here, the movement speed (scanning speed) of the laser head 21 while laser welding is being performed is also referred to as the "welding speed," and the direction of movement of the laser head 21 is also referred to as the "welding direction." In the welding of the lid plate 5 and the peripheral plate portion 7, the welding direction is along the circumferential direction of the battery 1. In this embodiment, laser welding of the lid plate 5 and the peripheral plate portion 7 is performed while the laser head 21 is moved at a relatively high welding speed. In one example, the outer container 3 and the lid plate 5 are formed from aluminum or an aluminum alloy. While laser welding of the lid plate 5 and the peripheral plate portion 7 is being performed, the laser head 21 moves along the circumferential direction of the battery 1 at a welding speed of 500 mm / s or more. At this time, the laser head 21 moves at a welding speed of, for example, about 550 mm / s.

[0021] The gas injection nozzle 22 injects an oxygen-containing mixed gas onto the welded portion of the cover plate 5 and the peripheral plate portion 7 while the battery is being laser-welded. The gas injection nozzle 22 injects the mixed gas from the outer circumference of the battery 1 toward the welded portion. In the example battery 1 shown in Figures 1 to 3, the outer edge E1 of the cover plate 5 has a pair of long edges and a pair of short edges, and when viewed from the plate thickness direction (height direction of the battery 1), the cover plate 5 is rectangular or substantially rectangular. In the example shown in Figure 3, a pair of gas injection nozzles 22A and 22B are provided as the gas injection nozzle 22.

[0022] In the example shown in Figure 3, during laser welding of the cover plate 5 and the peripheral plate portion 7, the portion to be welded is positioned between the gas injection nozzles 22A and 22B. Therefore, laser welding is performed with the cover plate 5 positioned between the gas injection nozzles 22A and 22B. In this case, gas injection nozzle 22A injects a mixed gas onto the welded portion from the side where one of the pair of long edges of the cover plate 5 is located. Gas injection nozzle 22B injects a mixed gas onto the welded portion from the opposite side of gas injection nozzle 22A. In the example shown in Figure 3, multiple injection ports 25 are formed on each of the gas injection nozzles 22A and 22B. Each of the gas injection nozzles 22A and 22B injects a mixed gas from each of the injection ports 25.

[0023] In this embodiment, the gas injection nozzle 22 injects a mixed gas onto the welded area, with the oxygen concentration in the mixed gas adjusted to a specified concentration range. The specified concentration range is set to a range lower than the oxygen concentration in the atmosphere (approximately 20.9%). Therefore, the upper limit of the specified concentration range is lower than the oxygen concentration in the atmosphere. The gas injection nozzle 22 injects, for example, a mixed gas of oxygen and nitrogen. In this case, the nitrogen concentration in the mixed gas injected from the gas injection nozzle 22 is adjusted to be higher than the nitrogen concentration in the atmosphere (approximately 78.1%), and the oxygen concentration is adjusted to be lower than the concentration in the atmosphere. Furthermore, the injected mixed gas does not contain helium, argon, or the like.

[0024] In one example, the outer container 3 and lid plate 5 are made of aluminum or an aluminum alloy. The specified concentration range is between 5% and 12%, and a mixed gas with an oxygen concentration adjusted to within this range is injected from the gas injection nozzle 22. In this case, for example, a mixed gas of nitrogen and oxygen is injected, and the nitrogen concentration in the mixed gas is adjusted to be higher than the nitrogen concentration in the atmosphere.

[0025] Here, we define the width direction that intersects (is perpendicular or approximately perpendicular to) the welding direction, which is the direction of movement of the laser head 21, and the height direction that intersects (is perpendicular or approximately perpendicular to) both the welding direction and the width direction in the portion welded by laser welding and its vicinity. The width direction of the welded portion coincides with or approximately coincides with the radial direction of the battery 1, and the height direction of the welded portion coincides with or approximately coincides with the height direction of the battery 1.

[0026] Furthermore, in the welded portion, the side facing the outer surface of the cover plate 5 is the upper side in the height direction, and the side where the bottom plate portion 6 is located is the lower side in the height direction. Therefore, the upper side in the height direction of the welded portion coincides with or approximately coincides with the upper side in the height direction of the battery 1, and the lower side in the height direction of the welded portion coincides with or approximately coincides with the lower side in the height direction of the battery 1. In addition, in the portion of the manufactured battery 1 where the peripheral plate portion 7 and the cover plate 5 are welded, the welding direction, width direction and height direction are defined in the laser welding, as are the parts welded in the laser welding, and the upper and lower sides in the height direction are defined.

[0027] Here, the first comparative example is an example in which, instead of a mixed gas with an oxygen concentration adjusted to a specified concentration range, either a gas with an oxygen concentration lower than the lower limit of the specified concentration range, or a gas without oxygen, is injected into the area being welded. In the first comparative example, other conditions, including the type of metal material forming the periphery plate 7 and the cover plate 5, the welding speed, the laser output, and the laser irradiation spot diameter, are the same as in the embodiment, except that the injected gas is different. Therefore, in the first comparative example as well, the periphery plate 7 and the cover plate 5 are laser welded at a relatively high welding speed, such as a welding speed of 500 mm / s or more.

[0028] Figure 4 is a schematic cross-sectional view showing an example of the configuration of the welded portion of the peripheral plate 7 and the cover plate 5, and its vicinity, in the first comparative example, in a cross-section along the width direction of the welded portion. In Figure 4, the directions indicated by arrows W1 and W2 correspond to the width direction of the welded portion, and the directions indicated by arrows H1 and H2 correspond to the height direction of the welded portion. Furthermore, the side of arrow W1 corresponds to the inner circumference of the battery 1, and the side of arrow W2 corresponds to the outer circumference of the battery 1. The side of arrow H1 corresponds to the upper side in the height direction, and the side of arrow H2 corresponds to the lower side in the height direction. In Figure 4, the welded portion is shown in a cross-section perpendicular or approximately perpendicular to the welding direction in laser welding (the direction of movement of the laser head 21).

[0029] In laser welding, the metal forming the peripheral plate 7 and the cover plate 5 melts at the welding point, and a molten pool is formed, which is a reservoir of molten metal. In the molten pool, surface tension acts to deform the molten metal into a spherical shape, and a force acts to reduce the bending radius of the molten metal. As the molten metal flows due to the forces acting on it, a raised portion is formed in the molten pool on the upper side in the height direction. In the first comparative example in Figure 4, the raised portion is formed in the molten pool as the molten metal moves toward the outer circumference of the battery 1.

[0030] As shown in Figure 4, etc., when the molten metal solidifies in the raised portion of the molten pool, a raised portion 31 is formed in the area where the peripheral plate 7 and the cover plate 5 are welded, rising upward in the height direction. In addition, on the cover plate 5, a flat surface 32 is formed on the inner circumference side of the battery 1 relative to the welded portion. The flat surface 32 is formed to be flat or nearly flat by the outer surface of the cover plate 5, and no upwardly protruding portions or downwardly recessed portions are formed, or are hardly formed, on the flat surface 32.

[0031] The raised portion 31 is formed on the outer circumference side of the battery 1 relative to the flat surface 32 and rises upward in the height direction relative to the flat surface 32. Furthermore, as described above, the portion where the cover plate 5 and the peripheral plate portion 7 are welded is formed over the entire circumference of the battery 1. Therefore, the raised portion 31 surrounds the flat surface 32 from the outer circumference over the entire circumference of the battery 1. The raised portion 31 in the welded portion is also referred to as a "weld bead".

[0032] Furthermore, in the first comparative example, laser welding is performed at a relatively high welding speed, so the dimensions of the molten pool along the welding direction become larger in the area welded by laser welding. Also, in the first comparative example, the gas injected into the area being welded does not contain oxygen, or the oxygen concentration is lower than the specified concentration range. As a result, an oxide film is not formed in the area being welded, and the molten metal flows more easily in the molten pool. Consequently, in the first comparative example, the area where the metal has melted is more prone to deformation, resulting in a smaller bending radius. As mentioned above, because the area where the metal has melted is easily deformed, in the first comparative example, a recessed area is formed on the lower side in the height direction between the raised part of the molten pool and the flat surface 32.

[0033] As shown in Figure 4, when the molten metal solidifies with a recessed portion formed in the molten pool, an undercut 33 is formed as a groove that recesses downward in the height direction at the welded portion of the peripheral plate 7 and the cover plate 5. The undercut 33 is formed between the raised portion 31 and the flat surface 32 and is recessed downward in the height direction relative to the flat surface 32. The undercut 33 is adjacent to the raised portion 31 from one side in the width direction of the welded portion, and in the first comparative example in Figure 4, the undercut 33 is adjacent to the raised portion 31 from the inner circumference side of the battery 1. In one example of the first comparative example, the undercut 33 is formed between the raised portion 31 and the flat surface 32, extending over the entire circumference of the battery 1 in the circumferential direction. Here, when the undercut 33 is formed as in the first comparative example, the distance from the flat surface 32 to the bottom of the undercut 33 is defined as the amount of recess Da of the undercut 33.

[0034] Figure 5 is a schematic cross-sectional view showing an example of the configuration of the portion where the peripheral plate portion 7 and the cover plate 5 are welded, and the vicinity thereof, in the first embodiment, in a cross-section along the width direction of the welded portion. In Figure 5, the direction and other elements are defined in the same way as in Figure 4. Also in Figure 5, the welded portion is shown in a cross-section perpendicular or approximately perpendicular to the welding direction in laser welding (the direction of movement of the laser head 21).

[0035] In this embodiment as well, a molten pool is formed in the welded portion, and in the molten pool, surface tension acts to reduce the bending radius of the molten metal portion. As a result, a portion is formed in the molten pool that rises upward in the height direction (towards arrow H1). Therefore, as shown in Figure 5, etc., in this embodiment as well, similar to the first comparative example, a raised portion 31 that rises upward in the height direction is formed in the portion where the peripheral plate portion 7 and the cover plate 5 are welded. The raised portion 31, which is a weld bead, is formed on the outer circumference side of the battery 1 relative to the flat surface 32 and rises upward in the height direction relative to the flat surface 32.

[0036] In this embodiment as well, since laser welding is performed at a relatively high welding speed, the dimensions of the molten pool along the welding direction become larger in the area being welded by laser welding. However, in this embodiment, unlike the first comparative example, the oxygen concentration in the gas injected into the area being welded is adjusted to a specified concentration range. As a result, an oxide film is formed in the area being welded, and the flow of molten metal in the molten pool is suppressed by the oxide film. Therefore, in this embodiment, by injecting a mixed gas with an oxygen concentration adjusted to a specified concentration range into the area being welded, an oxide film is formed in the area being welded in such a state that the flow of molten metal is suppressed by the oxide film.

[0037] In this embodiment, the flow of molten metal in the welded portion is suppressed by the oxide film, so the molten metal portion is less likely to deform to a state where the bending radius is smaller compared to the first comparative example. Therefore, no recessed portion is formed between the raised portion of the molten pool and the flat surface 32. As shown in Figure 5, etc., in the portion where the peripheral plate portion 7 and the cover plate 5 are welded, the aforementioned undercut 33 is not formed, and the flat surface 32 is adjacent to the raised portion 31 from one side in the width direction of the welded portion. In the example battery 1 in Figure 5, etc., the flat surface 32 is adjacent to the raised portion 31 from the inner circumference side of the battery 1. In this embodiment, since the undercut 33 is not formed, the aforementioned recess amount Da in the welded portion is zero or nearly zero.

[0038] Furthermore, a second comparative example is provided in which a mixed gas with an oxygen concentration higher than the upper limit of the specified concentration range, such as a mixed gas with an oxygen concentration similar to that of the atmosphere, is injected into the area being welded. In the second comparative example, other conditions, including the type of metal material forming the periphery plate 7 and the cover plate 5, the welding speed, the laser output, and the laser irradiation spot diameter, are the same as in the embodiment, except that the injected gas is different. Therefore, in the second comparative example as well, the periphery plate 7 and the cover plate 5 are laser-welded at a relatively high welding speed, such as a welding speed of 500 mm / s or more.

[0039] In the second comparative example, similar to the embodiment, the aforementioned raised portion 31 is formed in the area where the peripheral plate portion 7 and the cover plate 5 are welded. Also in the second comparative example, since a mixed gas containing oxygen is injected during laser welding, an oxide film is formed in the welded area. Therefore, similar to the embodiment, the flow of molten metal is suppressed by the oxide film. Consequently, in the second comparative example, no undercut 33 is formed in the area where the peripheral plate portion 7 and the cover plate 5 are welded.

[0040] Figure 6 is a schematic cross-sectional view showing an example of the configuration of the welded portion of the peripheral plate 7 and cover plate 5 in the second comparative example, along the welding direction (movement direction of the laser head 21) in laser welding. In Figure 6, the welded portion is shown in a cross-section passing through the raised portion 31 along the welding direction, and is shown in a cross-section perpendicular or approximately perpendicular to the width direction of the welded portion. In Figure 6, the direction indicated by arrow X1 corresponds to the welding direction, and the side indicated by arrow X2 corresponds to the opposite side from the welding direction. The directions indicated by arrows H1 and H2 correspond to the height direction of the welded portion. The side indicated by arrow H1 corresponds to the upper side in the height direction, and the side indicated by arrow H2 corresponds to the lower side in the height direction.

[0041] As in the second comparative example, when the oxygen concentration in the injected mixed gas is higher than the specified concentration range and laser welding is performed at a relatively high welding speed, the balance of surface tension in the molten pool is easily disrupted. This makes it easier for humping, in which the molten metal vibrates in the height direction, to occur in the molten pool. As shown in Figure 6, when the molten metal solidifies while vibrations due to humping are occurring in the molten pool, an uneven structure 35 is formed on the raised portion 31 in the welded area of ​​the peripheral plate 7 and the cover plate 5. In the raised portion 31, the uneven structure 35 is composed of multiple convex portions that protrude upward in the height direction and multiple concave portions that recess downward in the height direction, and is formed in an uneven manner along the welding direction. Therefore, the uneven structure 35 of the raised portion 31 is uneven in cross-section along the welding direction.

[0042] Furthermore, in the second comparative example, humping is more likely to occur, and the molten metal solidifies with a large amplitude of vibration caused by humping. As a result, the degree of unevenness of the uneven structure 35 formed on the raised portion 31 increases. For example, the maximum displacement Db in the height direction between the most protruding position and the most recessed position in the uneven structure 35 is defined. In the second comparative example, the maximum displacement Db in the uneven structure 35 is large, and in the example in Figure 6, the maximum displacement Db is value Db1. The aforementioned maximum displacement Db in the uneven structure 35 is also referred to as the "peak-to-peak value" of the uneven structure 35.

[0043] Figure 7 is a schematic cross-sectional view showing an example of the configuration of the portion where the peripheral plate portion 7 and the cover plate 5 are welded together in the first embodiment, in a cross-section along the welding direction (the direction of movement of the laser head 21) in laser welding. In Figure 7, as in Figure 6, the welded portion is shown in a cross-section passing through the raised portion 31 along the welding direction, and is shown in a cross-section perpendicular or approximately perpendicular to the width direction of the welded portion. Also in Figure 7, the direction and other parameters are defined in the same way as in Figure 6.

[0044] As described above, in this embodiment, a mixed gas in which the oxygen concentration is adjusted to a specified concentration range lower than the oxygen concentration in the atmosphere is injected during laser welding. Therefore, even when laser welding is performed at a relatively high welding speed, the balance of surface tension in the molten pool is less likely to be disturbed, and humping is less likely to occur. As a result, in this embodiment, the amplitude of vibrations caused by humping is suppressed to a smaller degree compared to the second comparative example, and the molten metal is solidified. Consequently, in this embodiment, the degree of unevenness of the uneven structure 35 formed on the raised portion 31 is smaller than that of the second comparative example. In the example in Figure 7, the maximum displacement amount Db in the uneven structure 35 is Db2, which is smaller than the value Db1 in the example in Figure 6 shown as the second comparative example.

[0045] As described above, in this embodiment, a mixed gas with an oxygen concentration adjusted to a specified concentration range is injected into the welded area, thereby suppressing the flow of molten metal by forming an oxide film in the welded area. As a result, even if the welding speed in laser welding is increased, the occurrence of undercuts 33 is suppressed in the area where the multiple metal plate portions, namely the cover plate 5 and the peripheral plate portion 7, are welded together.

[0046] Furthermore, in this embodiment, the oxygen concentration in the mixed gas injected into the area being welded by laser welding is adjusted to a specified concentration range lower than the oxygen concentration in the atmosphere. As a result, even when laser welding is performed at a relatively high welding speed, the amplitude of vibrations caused by humping in the molten pool is kept small. Therefore, even if the welding speed in laser welding is increased, the degree of unevenness in the raised portion (weld bead) 31 caused by humping in the area where the cover plate 5 and the peripheral plate portion 7 are welded is reduced.

[0047] In this embodiment, even when the welding speed in laser welding is increased, the occurrence of undercuts 33 is suppressed, and the degree of unevenness in the raised portion 31 caused by humping is reduced. Therefore, even when the welding speed in laser welding is increased, the quality of the welding in the portion where the multiple metal plate portions, namely the cover plate 5 and the peripheral plate portion 7, are welded together is appropriately ensured. Furthermore, by achieving a high welding speed in laser welding, it becomes possible to improve the productivity of the battery 1 product and shorten the time required to manufacture the battery 1.

[0048] Furthermore, when the periphery plate 7 and the cover plate 5 are made of aluminum or an aluminum alloy, the oxygen concentration in the mixed gas is adjusted to a specified concentration range of 5% or more and 12% or less. This suppresses the occurrence of undercuts 33 even when the welding speed in laser welding is increased, and reduces the degree of unevenness in the raised portion 31 caused by humping. Therefore, when the periphery plate 7 and the cover plate 5 are made of aluminum or an aluminum alloy, adjusting the oxygen concentration in the mixed gas to a range of 5% or more and 12% or less ensures that the welding quality in the area where the multiple metal plate portions, the cover plate 5 and the periphery plate 7, are welded together is appropriately ensured, even when the welding speed in laser welding is increased.

[0049] (Verification related to the embodiment, etc.) Here, as verification related to the embodiments described above, the following verification was performed. In the verification, the lid plate 5 was welded to the peripheral plate portion 7 of the outer container 3 by laser welding under eight different conditions α0, α1, α2, α3, α4, α5, α6, and α7. For conditions α0 to α7, the outer container 3 and the lid plate 5 were made using components of the same type of battery 1, specifically components of a battery cell with a rated capacity of 20Ah. Also, for conditions α0 to α7, the outer container 3 and the lid plate 5 were made from the same material, specifically aluminum alloy. Furthermore, for all conditions α0 to α7, the outer container 3 had a peripheral plate portion 7 thickness of 0.5 mm, and the lid plate 5 also had a thickness of 0.5 mm. In addition, for all conditions α0 to α7, a double-core laser head 21 was used, and laser welding was performed with a laser output of 5000W from the laser head 21.

[0050] In the verification, laser welding was performed under condition α0 at a different welding speed than the other conditions α1 to α7. In addition, in the verification, gas was injected from the gas injection nozzle 22 into the area being welded by laser welding under all of conditions α0 to α7. However, the components contained in the injected gas and the ratios of each component in the gas were different under conditions α0 to α7. Figure 8 is a schematic diagram showing the welding speed and injected gas for each of the eight conditions α0 to α7 under which laser welding was performed in the verification related to the embodiment.

[0051] In the verification, under condition α0, the laser head 21 was moved at a welding speed of 320 mm / s, and laser welding was performed at a relatively low welding speed. On the other hand, under conditions α1 to α7, the laser head was moved at a welding speed of 550 mm / s. Therefore, under conditions α1 to α7, the laser head 21 was moved at a faster welding speed than under condition α0, and laser welding was performed at a relatively high welding speed.

[0052] Furthermore, under condition α0, a gas containing only nitrogen was injected during laser welding. Under conditions α1 to α7, a mixed gas containing nitrogen and oxygen was injected during laser welding. The oxygen concentrations in the mixed gases were designated as conditions α1, α2, α3, α4, α5, α6, and α7, in descending order of concentration. Under condition α7, where the oxygen concentration in the mixed gas was highest, the oxygen concentration was made to be approximately the same as the oxygen concentration in the atmosphere.

[0053] In the verification, under each of the conditions α0 to α7, gas was injected from the gas injection nozzle 22 before laser welding. Then, before laser welding, the oxygen concentration in the environment where laser welding was to be performed, i.e., the oxygen concentration in the area where the gas was injected, was measured using a gas sensor. Under conditions α1, α2, α3, α4, α5, α6, and α7, the oxygen concentrations in the gas-injected area were 1.7%, 5.3%, 10.1%, 12.0%, 14.6%, 18.4%, and 21.0%, respectively. In condition α0, only nitrogen was injected, but a small amount of oxygen from the atmosphere mixed with the injected nitrogen, resulting in a concentration equivalent to about 1%.

[0054] In the verification, for each of the conditions α0 to α7, we observed whether or not the aforementioned undercut 33 occurred in the area where the peripheral plate 7 and the cover plate 5 were welded. If an undercut 33 occurred, the amount of indentation Da of the undercut 33 was measured. In addition, the verification compared the degree of unevenness of the aforementioned uneven structure 35 formed in the raised portion 31 in the area where the peripheral plate 7 and the cover plate 5 were welded, between the conditions α0 to α7. In this process, for each of the conditions α0 to α7, we measured the maximum displacement amount Db of the uneven structure 35 and compared the degree of unevenness of the uneven structure 35 by comparing the maximum displacement amount Db between the conditions α0 to α7.

[0055] Figure 9 is a schematic diagram showing the observation results regarding the undercut 33 under each of the eight laser welding conditions α0 to α7 in verifications related to the embodiment, etc. Figure 10 is a schematic diagram showing the comparison results of the degree of unevenness of the uneven structure 35 formed on the raised portion 31 among the eight laser welding conditions α0 to α7 in verifications related to the embodiment, etc. Figure 9 shows a graph with the oxygen concentration in the gas-injected region on the horizontal axis and the amount of indentation Da of the undercut 33 on the vertical axis, and Figure 10 shows a graph with the oxygen concentration in the gas-injected region on the horizontal axis and the maximum displacement (peak-peak value) Db of the uneven structure 35 on the vertical axis. In both Figure 9 and Figure 10, the oxygen concentration is shown as a percentage. In addition, the amount of indentation Da in Figure 9 and the maximum displacement Db in Figure 10 are shown in units of μm.

[0056] As shown in Figure 9, the verification showed that the undercut 33 was formed only under condition α1, and not under conditions α0, α2 to α7. Under condition α0, as mentioned above, laser welding was performed at a relatively low welding speed, so the dimensions of the molten pool along the welding direction in the welded area were smaller compared to the other conditions α1 to α7. Therefore, it is thought that the reason why the undercut 33 was not formed is that the molten portion of the metal did not deform to the extent that the undercut 33 would form.

[0057] Furthermore, in each of the conditions α2 to α7, the suppression of the flow of molten metal by the oxide film is considered to be the reason why the undercut 33 was not formed. Therefore, under the aforementioned conditions, such as when the peripheral plate portion 7 and the cover plate 5 are formed from an aluminum alloy, it has been demonstrated that by increasing the oxygen concentration in the injected mixed gas to 5% or more, the flow of molten metal is suppressed by the oxide film to such an extent that the undercut 33 is not formed, even when laser welding is performed at a relatively high welding speed.

[0058] Furthermore, as shown in Figure 10, the verification showed that the degree of unevenness in the raised portion 31 caused by humping was reduced in each of the conditions α2, α3, and α4. That is, in each of the conditions α2, α3, and α4, the degree of unevenness in the raised portion 31 was the same as or reduced compared to the atmosphere in which only nitrogen was injected. Also, in each of the conditions α5 to α7, which includes condition α7 in which the oxygen concentration in the mixed gas is the same as that of the atmosphere, the degree of unevenness in the raised portion 31 caused by humping increased.Therefore, under the aforementioned conditions, such as when the peripheral plate portion 7 and cover plate 5 are formed from an aluminum alloy, it was demonstrated that by setting the oxygen concentration in the injected mixed gas to a range of 5% or more and 12% or less, the degree of unevenness in the raised portion 31 caused by humping can be reduced even when laser welding is performed at a relatively high welding speed.

[0059] From the above verification, it was demonstrated that when the peripheral plate portion 7 and cover plate 5 are formed from an aluminum alloy, adjusting the oxygen concentration in the injected mixed gas to a range of 5% or more and 12% or less suppresses the occurrence of undercuts 33 even when laser welding is performed at a relatively high welding speed, and also reduces the degree of unevenness in the raised portion (weld bead) 31 caused by humping. It was also demonstrated that when the peripheral plate portion 7 and cover plate 5 are formed from an aluminum alloy, adjusting the oxygen concentration in the injected mixed gas to a range of 5% or more and 12% or less ensures that the welding quality in the welded portion is adequately ensured even when the welding speed in laser welding is increased.

[0060] (modified version) In the embodiments described above, the welding of the cover plate 5 to the peripheral plate portion 7 in the manufacturing of the battery 1 was explained. However, injecting a mixed gas containing oxygen into the area being welded by laser welding, while the oxygen concentration is adjusted to a specified concentration range lower than the concentration in the atmosphere, can be applied to laser welding of multiple metal plate portions other than the welding of the cover plate 5 to the peripheral plate portion 7.

[0061] Figure 11 is a schematic diagram showing a state in which multiple metal plate portions 41 and 42 are welded in a first modified example of the embodiment. As shown in Figure 11, in this modified example as well, the metal plate portions 41 and 42 are laser-welded using a welding apparatus 20 equipped with a laser head 21, a gas injection nozzle 22, and a moving drive unit 23. In this modified example as well, while the metal plate portions 41 and 42 are being welded by the laser irradiated from the laser head 21, the gas injection nozzle 22 injects a mixed gas containing oxygen into the area being welded by laser welding, with the oxygen concentration adjusted to a specified concentration range lower than the concentration in the atmosphere. In this modified example as well, the metal plate portions 41 and 42 are laser-welded at a relatively high welding speed, such as a welding speed of 500 mm / s or more. In the example shown in Figure 11, a pipe-shaped gas injection nozzle 22 is used.

[0062] In this modified example, the metal plate portion 41 is stacked on top of a part of the metal plate portion 42, with the thickness direction of the metal plate portion 41 coinciding with or substantially coinciding with the thickness direction of the metal plate portion 42. Then, the portion where the metal plate portions 41 and 42 are stacked is welded by irradiating it with a laser. In the example shown in Figure 11, the laser is irradiated from the side where the metal plate portion 41 is located.

[0063] In this modified example, as in the embodiments described above, the welding direction (direction indicated by arrow X1), which is the direction of movement (scanning direction) of the laser head 21, the width direction (directions indicated by arrows W1 and W2) that intersects (is perpendicular or nearly perpendicular) the welding direction, and the height direction (directions indicated by arrows H1 and H2) that intersects (is perpendicular or nearly perpendicular) both the welding direction and the width direction are defined in the portion welded by laser welding and its vicinity. In this modified example, the welding direction is along the width direction of the respective metal plate portions 41 and 42. Also, in Figure 11, the side indicated by arrow X2 corresponds to the opposite side from the welding direction.

[0064] In this modified example, the height direction of the welded portion coincides with or approximately coincides with the thickness direction of the respective metal plate portions 41 and 42. In the welded portion, the side irradiated with the laser in the height direction is the upper side, and in the example in Figure 11, the side where the metal plate portion 41 is located in the height direction is the upper side (arrow H1 side). In the welded portion, the side opposite to the side irradiated with the laser in the height direction is the lower side, and in the example in Figure 11, the side where the metal plate portion 42 is located in the height direction is the lower side (arrow H2 side). Furthermore, in the portion where the metal plate portions 41 and 42 are welded, the welding direction, width direction, and height direction in laser welding are defined in the same way as in the portion welded in laser welding, and the upper and lower sides in the height direction are defined.

[0065] Here, a third comparative example is provided in which, instead of a mixed gas with an oxygen concentration adjusted to a specified concentration range, either a gas with an oxygen concentration lower than the lower limit of the specified concentration range, or a gas without oxygen, is injected into the area being welded. In the third comparative example, other conditions, including the type of metal material forming the metal plate portions 41 and 42, welding speed, laser output, and laser irradiation spot diameter, are the same as in the embodiment, except that the injected gas is different. Therefore, in the third comparative example as well, the metal plate portions 41 and 42 are laser welded at a relatively high welding speed.

[0066] Figure 12 is a schematic cross-sectional view showing an example of the configuration of a portion where multiple metal plate portions 41 and 42 are welded together, and the surrounding area, in the third comparative example, in a cross-section along the width direction of the welded portion. In Figure 12, the welded portion is shown in a cross-section perpendicular or approximately perpendicular to the welding direction in laser welding (the direction of movement of the laser head 21). In the welding of the metal plate portions 41 and 42, similar to the welding of the peripheral plate portion 7 and cover plate 5 described above, a raised portion (weld bead) 31 is formed in the portion where the metal plate portions 41 and 42 are welded together, rising upward in the height direction (towards arrow H1).

[0067] Furthermore, a flat surface 32 is formed by the upper surface of the metal plate portion 41 at a position offset in the width direction from the welded portion. In the welding of the metal plate portions 41 and 42, flat surfaces 32 are formed by the metal plate portion 41 on both sides in the width direction of the welded portion. In the example shown in Figure 12, a flat surface 32A is formed on one side in the width direction of the welded portion including the raised portion 31, and a flat surface 32B is formed on the opposite side of the flat surface 32A in the width direction, both by the metal plate portion 41.

[0068] Furthermore, in the third comparative example, similar to the first comparative example described above, an undercut 33 is formed in the portion where the metal plate portions 41 and 42 are welded, recessing downward in the height direction. In the welding of the metal plate portions 41 and 42, undercuts 33 are formed on both sides in the width direction relative to the raised portion 31. In the example shown in Figure 12, an undercut 33A is formed between the raised portion 31 and the flat surface 32A, and an undercut 33B is formed between the raised portion 31 and the flat surface 32B.

[0069] Figure 13 is a schematic cross-sectional view showing an example of the configuration of a portion where multiple metal plate portions 41 and 42 are welded together, and the surrounding area, in the first modified example, in a cross-section along the width direction of the welded portion. In Figure 13 as well, the welded portion is shown in a cross-section perpendicular or approximately perpendicular to the welding direction in laser welding (the direction of movement of the laser head 21). As shown in Figure 13, in this modified example as well, a raised portion 31 is formed in the portion where the metal plate portions 41 and 42 are welded together, rising upward in the height direction. In addition, flat surfaces 32 (32A, 32B) are formed on both sides in the width direction of the portion where the metal plate portions 41 and 42 are welded together by the upper surfaces of the metal plate portions 41.

[0070] In this modified example, unlike the third comparative example, the oxygen concentration in the gas injected into the welded portion is adjusted to a specified concentration range. As a result, similar to the embodiments described above, an oxide film is formed on the welded portion, and the flow of molten metal in the molten pool is suppressed by the oxide film. Therefore, in this modified example, the aforementioned undercut 33 is not formed on the portion where the metal plate portions 41 and 42 are welded. Furthermore, in this modified example, the flat surface 32A is adjacent to the raised portion 31 from one side in the width direction of the welded portion, and the flat surface 32B is adjacent to the raised portion 31 from the opposite side of the flat surface 32A in the width direction of the welded portion.

[0071] Furthermore, in this modified example, a mixed gas with an oxygen concentration adjusted to a specified concentration range lower than the oxygen concentration in the atmosphere is injected during laser welding. Therefore, even when laser welding is performed at a relatively high welding speed, humping is less likely to occur in the molten pool where the metal plate portions 41 and 42 are welded. For this reason, in this modified example, as with the welding of the peripheral plate portion 7 and cover plate 5 in the above-described embodiments, even if the welding speed is increased, the degree of unevenness of the uneven structure 35 formed on the raised portion 31 in the area where the metal plate portions 41 and 42 are welded is reduced.

[0072] As described above, even in the modified example in which the metal plate portions 41 and 42 are laser-welded, by injecting a mixed gas in which the oxygen concentration is adjusted to a specified concentration range lower than the oxygen concentration in the atmosphere during laser welding, the same effects and advantages as in the embodiments described above are achieved. That is, in this modified example as well, even if the welding speed in laser welding is increased, the occurrence of undercuts 33 is suppressed, and the degree of unevenness in the raised portion 31 caused by humping is reduced. Therefore, even if the welding speed in laser welding is increased, the quality of the welding in the portion where multiple metal plate portions 41 and 42 are welded is appropriately ensured.

[0073] Furthermore, in this modified example, if the metal plate portions 41 and 42 are formed from aluminum or an aluminum alloy, the oxygen concentration in the mixed gas is adjusted to a range of 5% or more and 12% or less, which is within the specified concentration range. As a result, even if the welding speed in laser welding is increased, the occurrence of undercuts 33 is suppressed, and the degree of unevenness in the raised portion 31 caused by humping is reduced.

[0074] According to at least one embodiment or example, a mixed gas containing oxygen is injected into the area being welded by laser welding, with the oxygen concentration adjusted to a specified concentration range lower than the concentration in the atmosphere. This makes it possible to provide a welding method and welding apparatus that can appropriately ensure the quality of the weld in the area where multiple metal plates are welded together, even when the welding speed in laser welding is increased.

[0075] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0076] 1...Battery, 3...Outer container, 5...Lid plate, 7...Peripheral plate section, 20...Welding device, 21...Laser head, 22 (22A, 22B)...Gas injection nozzle, 31...Raised section, 32 (32A, 32B)...Flat surface, 33 (33A, 33B)...Undercut, 41, 42...Metal plate section, Da...Amount of indentation, Db...Maximum displacement (peak-peak value).

Claims

1. Laser welding of multiple metal plate sections, By injecting a mixed gas containing oxygen into the area being welded by laser welding, while the oxygen concentration is adjusted to a specified concentration range lower than the concentration in the atmosphere, an oxide film is formed on the welded area in such a state that the flow of molten metal is suppressed by the oxide film. A welding method comprising the following:

2. In the laser welding of the plurality of metal plate portions, the plurality of metal plate portions formed from aluminum or an aluminum alloy are welded together. In the injection of the mixed gas containing the oxygen, the concentration of the oxygen in the mixed gas is adjusted to a range of 5% or more and 12% or less, which is the specified concentration range. The welding method according to claim 1.

3. In the manufacture of a battery in which the outer casing is formed from a metal outer container in which an internal cavity is defined by a bottom plate and a peripheral plate, and a metal lid plate that closes the opening of the internal cavity of the outer container, The peripheral plate portion and the lid plate of the outer container are welded together as the plurality of metal plate portions by laser welding. The mixed gas, in which the oxygen concentration has been adjusted to the specified concentration range, is injected into the portion where the periphery plate and the cover plate are welded together. The welding method according to claim 1.

4. In the laser welding of the periphery plate and the lid plate, the lid plate, which is made of aluminum or an aluminum alloy, is welded to the periphery plate of the outer container, which is made of aluminum or an aluminum alloy. In the injection of the mixed gas containing the oxygen, the concentration of the oxygen in the mixed gas is adjusted to a range of 5% or more and 12% or less, which is the specified concentration range. In the laser welding of the periphery plate and the cover plate, the periphery plate and the cover plate are welded at a welding speed of 500 mm / s or more. The welding method according to claim 3.

5. A laser head that laser-welds multiple metal plate sections by irradiating them with a laser, A gas injection nozzle that forms an oxide film on the welded portion by laser welding, in which a mixed gas containing oxygen is injected into the welded portion while the oxygen concentration is adjusted to a specified concentration range lower than the concentration in the atmosphere, thereby suppressing the flow of molten metal by the oxide film. A welding apparatus equipped with the following:

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