Welding method and welding equipment

Abstract

To provide a welding method which prevents deterioration in strength of a weld part and can secure a quality of a product.SOLUTION: A welding method for welding a first metal member 21 and a second metal member 22 arranged so as to overlap the first member 21 includes: a first welding step of irradiating a first part 31 along at least a part of an annular welding object region with a laser while gradually increasing energy density and scanning a part where the first member 21 and the second member 22 overlap each other with the laser; a second welding step of irradiating a second part 32 along at least a part of the annular welding object region while scanning the overlapping part with the laser at constant energy density, continuous to the first welding step, and irradiating the second part overlapping the first part 31 with the laser at the time of finish; and a third welding step of irradiating a third part 33 overlapping at least a part of the second part 32 with a laser while gradually decreasing the energy density and scanning the overlapping part with the laser, continuous to the second welding step.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] This disclosure relates to a welding method. and Welding Equipment Place Regarding. [Background technology]

[0002] Laser (LASER: Light Amplification by Stimulated Emission of Radiation) welding excels in obtaining narrow beads and deep penetration shapes due to the steep energy density distribution of the laser, making it possible to perform deep penetration welding with high speed and precise heat input control. In addition, it has the advantage of being efficient because the equipment can be easily automated. As an example, laser welding is used to weld terminals and bus bars equipped in power conversion devices.

[0003] Patent Document 1 discloses a welding method for joining metal members including a first metal member and a second metal member arranged to overlap the first member by laser welding. In this welding, in order to firmly join the overlapped metal members or to ensure airtightness between the joined metal members, the welding start and end points of the weld are overlapped and the laser is scanned in a circular pattern to perform welding. In this welding method, the output of the laser is increased at the start of laser irradiation, and when the temperature of the material is sufficiently increased to make it easy to melt, the laser output is reduced to perform welding. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-143656 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the welding method described in Patent Document 1, since the output is large at the start of laser irradiation, there is a risk of a keyhole being formed in the metal member heated to the evaporation temperature. When metal vapor is generated from the keyhole, a convection current is generated in the molten pool formed around the keyhole by the reaction force of the metal vapor toward the upper side of the keyhole. A part of the molten pool may be detached from the metal member due to the convection current, and spatter may be generated. In particular, at the start of laser irradiation, if a keyhole is formed rapidly, spatter may be generated due to the convection current remaining in the molten pool when the laser irradiation is stopped at the welding end portion. Therefore, there is a problem that the strength of the welded part in the metal member is reduced by the molten metal being detached as spatter. In addition, when the terminal and the bus bar of a product including a power conversion device are welded with this welding method, there is a problem that the quality of the product is reduced by the spatter generated in the welding process being mixed into the product as a conductive foreign matter.

[0006] The present disclosure has been made in consideration of the above-mentioned circumstances, and provides a welding method capable of preventing a decrease in strength of a welded portion and ensuring product quality. and Welding Equipment Place The purpose is to provide. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the welding method of the present disclosure is a method for welding a first metal member and a second metal member placed overlapping the first member, and includes a first welding step in which a laser is irradiated to a first portion along at least a portion of an annular region to be welded while scanning the laser with a gradually increasing energy density at the portion where the first member and the second member overlap, a second welding step continuous with the first welding step in which a laser is irradiated to a second portion along at least a portion of the annular region to be welded while scanning the laser with a constant energy density, and at the end of the step, the laser is irradiated to an area overlapping the first portion, and a third welding step continuous with the second welding step in which a laser is irradiated to a third portion overlapping at least a portion of the second portion while scanning the laser with a gradually decreasing energy density. Effect of the Invention

[0008] According to the present disclosure, it is possible to suppress the generation of spatter that occurs at the start and end of laser irradiation, thereby preventing a decrease in the strength of the welded portion and ensuring product quality. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 shows a welding device according to a first embodiment of the present disclosure. [Diagram 2] FIG. 1 is a block diagram showing a control unit of a welding device according to a first embodiment of the present disclosure. [Diagram 3] FIG. 1 is a block diagram showing a welding device according to a first embodiment of the present disclosure. [Figure 4] FIG. 1 is a diagram illustrating a first welding process according to the first embodiment of the present disclosure. [Diagram 5] 1 is a flowchart showing a first welding process according to a first embodiment of the present disclosure. [Figure 6] FIG. 1 is a diagram showing a metal member according to a first embodiment of the present disclosure. [Figure 7] Cross-sectional view of FIG. 6 taken along the line VII-VII [Figure 8] FIG. 1 is a diagram showing a laser output and a scanning speed according to a first embodiment of the present disclosure. [Figure 9] FIG. 1 shows a power conversion device manufactured by a welding method according to embodiment 1 of the present disclosure. [Figure 10] FIG. 1 is a diagram showing a metal member according to a second embodiment of the present disclosure. [Figure 11] FIG. 13 is a diagram showing a metal member according to a third embodiment of the present disclosure. [Figure 12] Sectional view of XII-XII in Fig. 11 [Figure 13] 11 is a flowchart showing a second welding process according to a fourth embodiment of the present disclosure. [Figure 14] FIG. 13 is a diagram showing a laser output and a scanning speed according to a fourth embodiment of the present disclosure. [Figure 15] FIG. 13 shows a welding method according to a fifth embodiment of the present disclosure. [Figure 16] FIG. 13 is a diagram showing a metal member according to a sixth embodiment of the present disclosure. [Figure 17] FIG. 13 is a cross-sectional view showing a metal member according to a seventh embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, a welding method, a welding apparatus, and a metal member according to embodiments of the present disclosure will be described.

[0011] (Embodiment 1) As shown in FIG. 1, the welding device 100 according to the first embodiment includes a laser irradiation unit 10 that irradiates a laser (LASER: Light Amplification by Stimulated Emission of Radiation) L, a robot unit 11 that moves the laser irradiation unit 10, a base plate 12 on which a first member 21 and a second member 22 that are stacked are placed, and a control unit 110 that controls the laser irradiation unit 10 and the robot unit 11. The first member 21 and the second member 22 are formed in a plate shape having a rectangular main surface, and are members to be welded, including terminals in a semiconductor device or terminals or bus bars in a power conversion device. The first member 21 and the second member 22 are not particularly limited as long as they are made of metal, and preferably contain copper (Cu). The second member 22 is arranged to be stacked on the surface of the first member 21, and the back surface of the second member 22 and the surface of the first member 21 are arranged to be in contact with each other. The welding device 100 irradiates a laser L to a first member 21 and a second member 22 to weld them by a lap joint welding method, thereby producing a metal member 20.

[0012] For ease of understanding, mutually orthogonal xyz coordinates are set and referred to as appropriate. The direction in which the first member 21 and the second member 22 extend is set as the x direction, the direction in which the laser irradiation unit 10 irradiates the laser L is set as the z direction, and the direction perpendicular to the x direction and the z direction is set as the y direction. The xy plane is a plane parallel to the surface of the second member 22 that is irradiated with the laser L.

[0013] The laser irradiation unit 10 irradiates the second member 22 with a laser L, and includes a laser oscillator, a mirror or optical fiber that transmits the laser L oscillated by the laser oscillator, an optical system including a condensing lens that condenses the transmitted laser L, and a galvanometer mirror 13 that scans the irradiation position of the laser L when irradiating the surface of the second member 22 with the laser L. The operation of the laser irradiation unit 10 and the galvanometer mirror 13 is controlled by the control unit 110. The galvanometer mirror 13 scans the irradiation position of the laser L in the x direction and the y direction, and can irradiate the laser L at any position. The laser irradiation unit 10 irradiates the laser L by continuous oscillation. The position of the focal point in the z direction is adjusted by the robot unit 11 to a position where it is just focused on the surface of the second member 22 facing the laser irradiation unit 10. The output of the laser L of the laser irradiation unit 10 is controlled by the control unit 110 to an output that does not cause a welding mark on the first member 21. When lap welding a first member 21 and a second member 22 having a thickness of 1.5 mm, the output of the laser L is preferably controlled so that the bead width is 0.5 mm to 1.0 mm and the penetration depth of the first member 21 is 0.1 mm to 0.3 mm. When the thicknesses of the first member 21 and the second member 22 are large, the output of the laser L may be adjusted so that the focused diameter is appropriately increased to increase the bead width and the penetration depth. The output of the laser L is preferably 100 W to 10 kW.

[0014] The robot unit 11 has a first drive unit that drives in the x and y directions and a second drive unit that drives in the z direction, and moves the laser irradiation unit 10 in the x and y directions under the control of the control unit 110. The robot unit 11 also moves the laser irradiation unit 10 in the z direction according to the thickness and shape of the first member 21 and the second member 22, and adjusts the position of the focal point in the z direction to the surface of the second member 22 facing the laser irradiation unit 10.

[0015] The surface plate 12 has a surface parallel to the xy plane, and a first member 21 and a second member 22 are placed thereon.

[0016] 2, control unit 110 has a processor 120 that performs processing for controlling welding device 100, a main memory unit 130 used as a work area for processor 120, an auxiliary memory unit 140 that stores various data and programs used in the processing of processor 120, and a communication unit 150 for communicating with external devices. Main memory unit 130, auxiliary memory unit 140, and communication unit 150 are all connected to processor 120 via bus 160.

[0017] Processor 120 includes a micro processing unit (MPU). Processor 120 executes programs stored in auxiliary storage unit 140 to realize various functions of welding device 100.

[0018] The main memory unit 130 includes a RAM (Random Access Memory). Programs are loaded into the main memory unit 130 from the auxiliary memory unit 140. The main memory unit 130 is used as a working area for the processor 120.

[0019] The auxiliary storage unit 140 includes a non-volatile memory such as an EEPROM (Electrically Erasable Programmable Read-Only Memory). In addition to programs, the auxiliary storage unit 140 stores various data used in the processing of the processor 120. The auxiliary storage unit 140 supplies the data used by the processor 120 to the processor 120 in accordance with instructions from the processor 120, and stores the data supplied from the processor 120.

[0020] The communication unit 150 includes a network interface circuit for communicating with an external device. The communication unit 150 receives a signal from the external device and outputs data indicated by the signal to the processor 120. The communication unit 150 also transmits a signal indicating the data output from the processor 120 to the external device.

[0021] The control unit 110 executes the programs stored in the auxiliary storage unit 140, thereby functioning as a laser position control unit 111, a laser output control unit 112, and a laser irradiation position control unit 113, as shown in FIG.

[0022] The laser position control unit 111 controls the robot unit 11 to move the laser irradiation unit 10 in the x and y directions, and moves the laser irradiation unit 10 to above the intended welding position of the second member 22. In addition, the laser position control unit 111 moves the laser irradiation unit 10 in the z direction according to the thickness and shape of the first member 21 and the second member 22, and adjusts the position of the light focusing point in the z direction to the surface of the second member 22 facing the laser irradiation unit 10.

[0023] The laser output control unit 112 controls the laser irradiation unit 10 to adjust the energy density of the laser L irradiated from the laser irradiation unit 10. The energy density of the laser L is obtained by dividing the irradiation energy of the laser L by the length of the weld mark formed by the laser L. In detail, the laser output control unit 112 causes the laser irradiation unit 10 to irradiate the laser L with gradually increasing the energy density by setting the output of the laser L at the start of the first welding process to be smaller than the output of the laser L at the second welding process, and gradually increasing the output of the laser L in the first welding process. The output of the laser L at the start of the first welding process is preferably set to 50% or less of the output of the laser L at the second welding process. In addition, the output of the laser L at the end of the first welding process is set to the same as the output of the laser L at the second welding process, and in the second welding process, which is connected to the first welding process, the output of the laser L is kept constant, and the laser L is irradiated with a constant energy density. In addition, the output of the laser L in the third welding process is set to be the same as the output of the laser L in the second welding process at the start, and in the third welding process, which is connected to the second welding process, the output of the laser L is gradually reduced, so that the energy density of the laser L is gradually reduced when irradiating the laser L.

[0024] The laser irradiation position control unit 113 controls the galvanometer mirror 13 to scan the irradiation position in the x direction and the y direction when irradiating the surface of the second member 22 with the laser L. This allows the laser L to be irradiated to the annular welding target area. Here, the scanning speed of the laser L is constant. In detail, in the first welding process, the laser irradiation position control unit 113 controls the galvanometer mirror 13 to move the irradiation position of the laser L to the 90° arc-shaped welding target area from the start position 311 in the first part 31 to the start position 321 in the second part 32 as shown in FIG. 4. Next, in the second welding process, the laser irradiation position control unit 113 controls the galvanometer mirror 13 to move the irradiation position of the laser L to the circular welding target area from the start position 321 in the second part 32 to the start position 331 in the third part 33. Next, in the third welding process, the laser irradiation position control unit 113 controls the galvanometer mirror 13 to move the irradiation position of the laser L to the 90° arc-shaped welding target area from the start position 331 in the third portion 33 to the end position 332 in the third portion 33.

[0025] Next, a first welding process performed by welding apparatus 100 having the above configuration will be described for an example in which welding apparatus 100 welds first member 21 and second member 22 shown in FIG. 1 to produce metal member 20.

[0026] In response to a user's instruction to start the process, welding apparatus 100 starts a first welding process shown in Fig. 5. Hereinafter, the first welding process executed by control unit 110 of welding apparatus 100 will be described with reference to a flowchart.

[0027] When the first welding process is started, the laser position control unit 111 controls the robot unit 11 to move the laser irradiation unit 10 (step S101). In detail, the laser position control unit 111 moves the laser irradiation unit 10 in the x direction and the y direction to move the laser irradiation unit 10 to above the intended welding position of the second member 22. In addition, the laser position control unit 111 moves the laser irradiation unit 10 in the z direction according to the thickness and shape of the first member 21 and the second member 22, and adjusts the position of the focal point in the z direction to the surface of the second member 22 facing the laser irradiation unit 10.

[0028] Next, the laser output control unit 112 executes the first welding process (step S102). In the first welding process, the laser output control unit 112 controls the laser irradiation unit 10 to gradually increase the output of the laser L, thereby irradiating the laser L while gradually increasing the energy density. In detail, the laser output control unit 112 sets the output of the laser L at the start of the first welding process to be smaller than the output of the laser L in the second welding process, and gradually increases the output of the laser L to irradiate the laser L while gradually increasing the energy density. In addition, the output of the laser L at the end of the first welding process is set to be the same as the output of the laser L in the second welding process. At this time, the laser irradiation position control unit 113 controls the galvanometer mirror 13 to scan the irradiation position in the x and y directions when irradiating the surface of the second member 22 with the laser L, and moves the irradiation position to a 90° arc-shaped welding target area from the start position 311 in the first portion 31 shown in Figure 4 to the start position 321 in the second portion 32.

[0029] Next, the laser output control unit 112 changes the output condition of the laser L from the condition in which the laser L is irradiated while gradually increasing the output of the laser L to the condition in which the laser L is irradiated at a constant energy density (step S103).

[0030] Next, the laser output control unit 112 executes the second welding process (step S104). In the second welding process, the laser output control unit 112 is connected to the laser irradiation unit 10 in the first welding process, and irradiates the laser L at a constant energy density by keeping the output of the laser L constant. At this time, the output of the laser L in the second welding process is set to be the same as the output of the laser L at the end of the first welding process. In addition, the laser irradiation position control unit 113 controls the galvanometer mirror 13 to scan the irradiation position when irradiating the surface of the second member 22 with the laser L in the x direction and y direction, and moves the irradiation position in the circular welding target area from the start position 321 in the second portion 32 to the start position 331 in the third portion 33 shown in FIG. 4. The start position 331 in the third portion 33 is the same position as the start position 321 in the second portion 32.

[0031] Next, the laser output control unit 112 changes the laser L output condition from one in which the laser L is irradiated with a constant laser L output to one in which the laser L is irradiated while gradually increasing the laser L output (step S105).

[0032] Next, the laser output control unit 112 executes the third welding process (step S106). In the third welding process, the laser output control unit 112 controls the laser irradiation unit 10 to gradually reduce the output of the laser L, thereby irradiating the laser L while gradually decreasing the energy density. In detail, the laser output control unit 112 sets the output of the laser L at the start of the third welding process to the same as the output of the laser L in the second welding process, and causes the laser irradiation unit 10 to gradually reduce the output of the laser L, thereby irradiating the laser L while gradually decreasing the energy density. In addition, it is preferable that the output of the laser L at the end of the third welding process is set to the same as the output of the laser L at the start of the first welding process. At this time, the laser irradiation position control unit 113 controls the galvanometer mirror 13 to scan the irradiation position in the x direction and y direction when irradiating the surface of the second member 22 with the laser L, and moves the irradiation position to a 90° arc-shaped welding target area from a start position 331 in the third portion 33 to an end position 332 in the third portion 33, as shown in Figure 4.

[0033] Next, the laser position control unit 111 judges whether or not an end instruction has been input (step S107). If it is judged that an end instruction has not been input (step S107; No), the process returns to step S101, and steps S101 to S107 are repeated. If it is judged that an end instruction has been input (step S107; Yes), the first welding process is ended.

[0034] When the first welding process is completed, as shown in FIG. 6, a circular weld 30 is formed on the surface of the second member 22. As a result, the first member 21 and the second member 22 are welded to obtain a metal member 20 in which a circular weld 30 is formed on the surface of the second member 22. Returning to FIG. 4, a keyhole type weld mark 35 is formed in the second portion 32. The 90° section of the end portion of the second portion 32 overlaps with an overlap portion 341 between the first portion 31 and a part of the second portion 32. The 90° section of the start portion of the second portion 32 overlaps with an overlap portion 342 between a part of the second portion and the third portion. In the third portion 33, the output of the laser L is gradually reduced to switch from the keyhole type weld mark 35 to a heat conduction type weld mark 36, so that at least a part of the third portion 33 has a heat conduction type weld mark 36, i.e., a glossy surface. In the metal member 20, the first member 21 and the second member 22 are joined at the entire circumference of a circular weld 30. In this example, the weld 30 is joined to the second member 22 without penetrating the first member 21, as shown in Fig. 7. In order to join more firmly or to increase the conductive area, the weld 30 may penetrate the first member 21.

[0035] Next, the output of the laser L in the first welding process will be described. In the first embodiment, the output of the laser L is preferably set to 50% or less of the output of the laser L in the second welding process at the start of the first welding process, as shown in FIG. 8. In this example, it is set to 30% of the output of the laser L in the second welding process. Also, the output of the laser L at the end of the first welding process is set to the same as the output of the laser L in the second welding process. In the first welding process, welding is performed while the output of the laser L is gradually increased in the section from the start position 311 of the first part 31 to the start position 321 of the second part 32. In the second welding process, the output of the laser L is constant. At the start of the third welding process, the output of the laser L is set to the same as the output of the laser L in the second welding process, and in the third welding process, the output of the laser L is gradually decreased, and at the end of the third welding process, it is preferably set to the same as the output of the laser L at the start of the first welding process. Welding is performed while gradually decreasing the output of the laser L in the section from start position 331 of the third portion 33 to end position 332 of the third portion 33. After the third welding step is completed, irradiation of the laser L is stopped. Note that in the first welding step, the output of the laser L may be gradually increased from zero. Note that in the third welding step, the output of the laser L may be gradually decreased to zero.

[0036] Next, the scanning speed of the laser L will be described. Before the first welding process, the galvanometer mirror 13 is driven to accelerate the scanning speed of the laser L to a set speed. From the first welding process to the third welding process, the scanning speed of the laser L is kept constant, and the laser L is irradiated onto the second member 22. After the third welding process is completed, the scanning speed of the laser L is decelerated, and the driving of the galvanometer mirror 13 is stopped.

[0037] As described above, according to the welding apparatus 100 and the welding method of the present embodiment, in the first welding step, the laser L is irradiated to the second member 22 while gradually increasing the output of the laser L. As a result, the temperature of the second member 22 gradually increases, so that the depth of the keyhole formed in the second member 22 heated to the evaporation temperature by the irradiation of the laser L can be gradually deepened. Therefore, compared with the case of irradiation without gradually increasing the output of the laser L, the upward convection generated in the molten pool formed around the keyhole can be made gentle, so that the separation of a part of the molten pool as spatter due to the convection can be reduced. Furthermore, in the second welding step, the laser L is irradiated to the second member 22 while keeping the output and the scanning speed of the laser L constant. As a result, welding can be performed without fluctuating the convection generated in the molten pool formed around the keyhole, so that the separation of a part of the molten pool as spatter due to the convection can be reduced. Furthermore, in the third welding step, the laser L is irradiated to the second member 22 while gradually decreasing the output of the laser L. As a result, the depth of the keyhole can be gradually shallowed. Therefore, in the third welding step, keyhole welding is switched to heat conduction welding, and convection remaining in the molten pool can be suppressed, so that the detachment of a part of the molten pool as spatter can be reduced. As a result, the generation of spatter generated during welding can be reduced in the first to third welding steps, so that the strength of the welded part 30 can be reduced and short circuits in the product due to the inclusion of conductive foreign matter can be prevented, and the effect of improving the quality of the product can be achieved. In addition, near the start position 311 of the first portion 31 and the end position 332 of the third portion 33, the output of the laser L is low, so that the joining between the first member 21 and the second member 22 is shallow, but the overlapping portion 341 between the first portion 31 and a part of the second portion 32 and the overlapping portion 342 between a part of the second portion 32 and the third portion 33 overlap, so that the first member 21 and the second member 22 can be joined all around the scanning path of the laser L. Therefore, compared to when there is no overlap, it is possible to eliminate the welded portion 30 that does not contribute to the joining of the first member 21 and the second member 22, so that the welded portion 30 can be set smaller and the length or width of the first member 21 and the second member 22 can be shortened, thereby achieving the effects of making the product smaller, lighter, and less expensive.Furthermore, by forming the welded portion 30 in a circular shape, an external force acting on the welded portion 30 can be dispersed in multiple directions, thereby achieving the effect of preventing the welded portion 30 from being destroyed by an external force.

[0038] Furthermore, the welding method according to the first embodiment may be applied to a power conversion device 40 used in equipment including an automobile, as shown in Fig. 9. The power conversion device 40 includes an inverter 41 that converts DC power into AC power. The inverter 41 includes a plurality of bus bars 42 and a plurality of semiconductor devices 50. The semiconductor device 50 includes a plurality of terminals 51. The plurality of bus bars 42 and the plurality of terminals 51 are arranged side by side. Each bus bar 42 and each terminal 51 of each semiconductor device 50 are joined by the above-mentioned welding method. In this case, the terminal 51 corresponds to the first member 21, and the bus bar 42 corresponds to the second member 22.

[0039] (Embodiment 2) The welding apparatus 100 according to the second embodiment has a similar configuration to the welding apparatus 100 according to the first embodiment. In the second welding step, the welding apparatus 100 according to the first embodiment moves a scanning section of 360° in a circular shape from the start position 321 in the second portion 32 shown in Fig. 4 to the start position 331 in the third portion 33, which is the same position as the start position 321 in the second portion 32, to perform welding. In contrast, the welding apparatus 100 according to the second embodiment moves an irradiation position in an arc shape from the start position 321 in the second portion 32 to the start position 331 in the third portion 33 in a scanning section of less than 360° to perform welding, as shown in Fig. 10.

[0040] In this example, the welding device 100 according to the second embodiment sets the scanning section of the laser L in the second portion 32 to 330°, and executes the second welding process by the laser L in that section. The section of the end portion of the first portion 31 and the start portion of the third portion 33 overlaps due to the overlapping portion 343 between a part of the first portion 31 and a part of the third portion 33. The output of the laser L is higher in the latter portion of the first portion 31 and the former portion of the third portion 33 than in the former portion of the first portion 31 and the latter portion of the third portion 33, and the first member 21 and the second member 22 can be joined. Therefore, the same effect as that of the first embodiment can be obtained in the second embodiment. Furthermore, since the scanning section of the laser L in the second portion 32 can be shortened compared to the first embodiment, the irradiation time of the laser L can be shortened, and the effect of improving productivity can be achieved.

[0041] (Embodiment 3) Welding apparatus 100 according to embodiment 3 has a similar configuration to welding apparatus 100 according to embodiments 1 and 2. As shown in Fig. 11, in the second welding step, welding apparatus 100 according to embodiment 3 moves the irradiation position in an arc shape over a scanning section greater than 360° from start position 321 in second portion 32 to start position 331 in third portion 33 to perform welding.

[0042] In this example, the welding device 100 according to the third embodiment has the scanning section of the laser L of the second portion 32 set to 390°, and performs the second welding process by the laser L in that section. The overlapping section 344 is an overlapping section between the start portion of the second portion 32 and the end portion of the second portion 32. In this way, as shown in FIG. 12, the welded portion 30 has a weld mark 301 that is thicker than the width of the other weld marks in at least a part of the weld marks in the overlapping section 344 between the start portion of the second portion 32 and the end portion of the second portion 32. Therefore, the third embodiment has the same effect as the first embodiment. Furthermore, the first member 21 and the second member 22 can be more firmly joined in the overlapping section 344 between the start portion of the second portion 32 and the end portion of the second portion 32. Therefore, by making the joining width of the welded portion 30 wider in a direction to which external force is likely to be applied and making the joining area larger than other weld marks, the first member 21 and the second member 22 can be joined more firmly, and the effect of preventing destruction of the welded portion 30 can be achieved.

[0043] (Embodiment 4) The welding apparatus 100 according to the fourth embodiment has a similar configuration to the welding apparatus 100 according to the first to third embodiments. In the welding apparatus 100 according to the first to third embodiments, in the first welding step, the output of the laser L is gradually increased to gradually increase the energy density, and in the third welding step, the output of the laser L is gradually decreased to gradually decrease the energy density, and the laser L is irradiated. In contrast, the welding apparatus 100 according to the fourth embodiment gradually increases or decreases the energy density by decelerating or accelerating the scanning speed of the laser L.

[0044] In response to a user's instruction to start the process, welding apparatus 100 starts the second welding process shown in Fig. 13. The second welding process executed by control unit 110 of welding apparatus 100 will be described below with reference to a flowchart.

[0045] When the second welding process is started, the laser position control unit 111 controls the robot unit 11 to move the laser irradiation unit 10 (step S201). Next, the laser output control unit 112 executes the first welding process (step S202). In the first welding process, the laser output control unit 112 controls the laser irradiation unit 10 to keep the output of the laser L constant. In addition, the laser irradiation position control unit 113 moves the irradiation position in a 90° arc shape from the start position 311 in the first portion 31 to the start position 321 in the second portion 32 shown in FIG. 4. At this time, the laser L is irradiated while gradually increasing the energy density by decelerating the scanning speed of the laser L.

[0046] Next, the laser irradiation position control unit 113 changes the scanning condition of the laser L, in which the laser L is irradiated while decelerating the scanning speed of the laser L, to the scanning condition of the laser L, in which the laser L is irradiated at a constant scanning speed (step S203).

[0047] Next, the laser output control unit 112 executes the second welding process (step S204). In the second welding process, the laser output control unit 112 is connected to the laser irradiation unit 10 in the first welding process, and irradiates the laser L at a constant energy density by keeping the output of the laser L constant. At this time, the output of the laser L in the second welding process is set to be the same as the output of the laser L in the first welding process. In addition, the laser irradiation position control unit 113 controls the galvanometer mirror 13 to move the irradiation position in a circle from the start position 321 in the second portion 32 to the start position 331 in the third portion 33 shown in FIG. 4. At this time, the scanning speed of the laser L is constant, and the laser L is irradiated while keeping the energy density constant.

[0048] Next, the laser irradiation position control unit 113 changes the scanning condition of the laser L from the scanning condition of irradiating the laser L at a constant scanning speed to the scanning condition of irradiating the laser L while accelerating the scanning speed of the laser L (step S205).

[0049] Next, the laser output control unit 112 executes a third welding process (step S206). In the third welding process, the laser output control unit 112 controls the laser irradiation unit 10 to keep the output of the laser L constant. At this time, the laser irradiation position control unit 113 moves the irradiation position in a 90° arc shape from a start position 331 in the third portion 33 to an end position 332 in the third portion 33, as shown in FIG. 4. At this time, the scanning speed of the laser L is accelerated to irradiate the laser L while gradually decreasing the energy density.

[0050] Next, the laser position control unit 111 judges whether or not an end instruction has been input (step S207). If it is judged that an end instruction has not been input (step S207; No), the process returns to step S201, and steps S201 to S207 are repeated. If it is judged that an end instruction has been input (step S207; Yes), the second welding process is terminated.

[0051] Next, the output of the laser L in the second welding process will be described. In the fourth embodiment, the output of the laser L is constant from the start of the first welding process to the end of the third welding process, as shown in FIG. 14. Next, the scanning speed of the laser L will be described. Before irradiating the first portion 31 with the laser L, the galvanometer mirror 13 is driven to accelerate the scanning speed of the laser L to the start speed. From the start position 311 of the first portion 31 to the start position 321 of the second portion 32, the laser L is irradiated while decelerating the scanning speed of the laser L to the scanning speed of the second portion 32. In the second portion 32, the laser L is irradiated while keeping the scanning speed of the laser L constant. From the start position 331 of the third portion 33 to the end position 332 of the third portion, the laser L is irradiated while accelerating the scanning speed of the laser L, and the laser irradiation in the third portion 33 is ended. After the laser irradiation of the third portion 33 is completed, the galvanometer mirror 13 is decelerated and stopped. The scanning speed of the laser L at the start position 311 of the first portion 31 and the end position 332 of the third portion 33 may be different from each other. In the acceleration and deceleration of the scanning speed of the laser L in the fourth embodiment, similarly to the gradual decrease or increase of the output of the laser L in the first to third embodiments, the occurrence of sputtering can be suppressed and the effect of improving the quality of the product can be achieved. Moreover, since the scanning speed of the laser L can be improved, the irradiation time of the laser L can be shortened and the effect of improving productivity can be achieved.

[0052] (Modification of the fourth embodiment) In the first welding process and the second welding process, as described above, the second welding step has been described as an example in which the scanning speed and output of the laser L are constant and the laser L is irradiated at a constant energy density. In the second welding step, the scanning speed and output of the laser L may be changed and the laser L may be irradiated at a constant energy density. In particular, the laser L may be irradiated while accelerating the scanning speed of the laser L and gradually increasing the output of the laser L, or the laser L may be irradiated while decelerating the scanning speed of the laser L and gradually decreasing the output of the laser L.

[0053] (Embodiment 5) 15, the welding apparatus 100 according to the fifth embodiment includes a laser irradiation unit 10 that irradiates a laser L having a center beam L1 with a high energy density and a ring beam L2 with a lower energy density than the center beam L1. This allows the welding apparatus 100 to irradiate a laser L with a higher energy density at the center than at the outer periphery. The remaining configuration of the welding apparatus 100 according to the fifth embodiment is similar to that of the welding apparatus 100 according to the first to fourth embodiments.

[0054] The welding apparatus 100 according to the fifth embodiment also has the same effects as those of the first to fourth embodiments. Furthermore, by irradiating the ring beam L2 formed in a ring shape around the keyhole formed by the center beam L1, a wide keyhole opening can be formed, and the convection current toward the keyhole opening that occurs in the molten pool near the keyhole can be made gentler by the downward convection current that occurs near the keyhole opening, thereby preventing a part of the molten pool from detaching as spatter.

[0055] (Embodiment 6) In the first to fifth embodiments, the welding device 100 irradiates the laser L onto a circular region to be welded to form a circular weld 30 on the surface of the second member 22. The welding device 100 according to the sixth embodiment irradiates the laser L onto an elliptical region to be welded to form an elliptical weld 30 on the surface of the second member 22 as shown in FIG. 16. The sixth embodiment also has the same effects as the first to fifth embodiments. Furthermore, since the weld 30 is set short in the longitudinal direction of the first member 21 and the second member 22, the surface where the first member 21 and the second member 22 overlap can be reduced, and the effect of reducing the size, weight, and cost of the product can be achieved. Moreover, the welding device 100 only needs to irradiate the laser L onto the annular region to be welded, and the shape of the region to be welded is not limited as long as it is annular, and may be oval or polygonal.

[0056] (Embodiment 7) In the welding method according to the seventh embodiment, as shown in FIG. 17, the first member 21 and the second member 22 have a plating layer on their surfaces to prevent oxidation of the surfaces. The plating layer is formed by surface treatment with electroless Ni plating 60. In the seventh embodiment, the same effects as those of the first to seventh embodiments can be obtained. Furthermore, the oxidation of the first member 21 or the second member 22 increases the absorption rate of the laser L on the member surfaces, which speeds up convection around the keyhole and causes spatter to occur from the molten pool. However, the plating layer on the member surfaces prevents oxidation of the member surfaces and suppresses the occurrence of spatter, thereby achieving the effect of improving product quality.

[0057] Various embodiments and modifications of the present disclosure are possible without departing from the broad spirit and scope of the present disclosure. The above-described embodiments are for explaining the present disclosure and do not limit the scope of the present disclosure. That is, the scope of the present disclosure is indicated by the claims, not the embodiments. Various modifications made within the scope of the claims and the scope of the disclosure equivalent thereto are considered to be within the scope of the present disclosure. [Explanation of symbols]

[0058] 10 laser irradiation unit, 11 robot unit, 12 surface plate, 13 galvanometer mirror, 20 metal member, 21: first member, 22 second member, 30 welded portion, 301: thick weld mark, 31 first portion, 311 start position, 32 second portion, 321 start position, 33 third portion, 331 start position, 332 end position, 341-344 overlap portion, 35 keyhole type weld mark, 36 heat conduction type weld mark, 40 power conversion device, 41 inverter, 42 bus bar, 50 semiconductor device, 51 terminal, 60 electroless Ni plating, 100 welding device, 110 control unit, 111 laser position control unit, 112 laser output control unit, 113 laser irradiation position control unit, L laser, L1 center beam, L2 ring beam

Claims

1. A method for welding a first metal member and a second metal member disposed over the first member, comprising the steps of: a first welding step of irradiating a laser beam to a first portion along at least a portion of an annular welding target region while scanning the laser beam at an overlapping portion between the first member and the second member with a gradually increasing energy density; a second welding step in which a laser is irradiated to a second portion along at least a part of the annular welding target region while scanning the second portion with a laser at a constant energy density, and at the end of the second welding step, the laser is irradiated to overlap the first portion; a third welding step in which a laser is irradiated onto a third portion overlapping at least a part of the second portion while scanning the laser with a gradually decreasing energy density, which is continuous with the second welding step; A welding method comprising:

2. In the first welding step to the third welding step, a laser is irradiated onto an overlapping portion between the first member and the second member while scanning the laser, thereby forming an annular welded portion. The welding method according to claim 1.

3. In the first welding step, a heat conduction type welding mark is formed in at least a part of the welding mark, In the second welding step, a keyhole-shaped welding mark is formed in at least a part of the welding mark, In the third welding step, a heat conduction type welding mark is formed in at least a part of the welding mark. The welding method according to claim 1 or 2.

4. A laser output at the start of laser irradiation in the first welding step is set to be smaller than a laser output in the second welding step, and the laser output is gradually increased in the first welding step; a laser output at the end of the laser irradiation in the first welding step is set to be equal to a laser output in the second welding step; A laser output in the third welding step is set to be the same as a laser output at the start of laser irradiation as a laser output at the end of laser irradiation in the second welding step, and the laser output is gradually reduced in the third welding step. The welding method according to any one of claims 1 to 3.

5. A laser scanning speed at the start of laser irradiation in the first welding step is set to be higher than a laser scanning speed in the second welding step, and the laser scanning speed is gradually decreased in the first welding step; a laser scanning speed at the end of the laser irradiation in the first welding step is set to be equal to a laser scanning speed in the second welding step; The scanning speed of the laser in the third welding step is set to be the same as the scanning speed of the laser at the start of the laser irradiation in the second welding step, and the scanning speed of the laser is gradually increased in the third welding step. The welding method according to any one of claims 1 to 4.

6. In the first welding step, the second welding step, and the third welding step, a laser scanning speed is constant. The welding method according to any one of claims 1 to 4.

7. In the third welding step, a laser is irradiated so as to overlap a part of the first portion. The welding method according to any one of claims 1 to 6.

8. At the end of the second welding step, a laser is irradiated to overlap a start portion of the second portion. The welding method according to any one of claims 1 to 7.

9. In the first welding step to the third welding step, a welded portion including at least one thickened portion is formed. The welding method according to any one of claims 1 to 8.

10. In the first welding step to the third welding step, the laser is irradiated by scanning in an elliptical shape. The welding method according to any one of claims 1 to 9.

11. A plating layer is provided on at least one surface of the first member or the second member. The welding method according to any one of claims 1 to 10.

12. In the first welding step, the second welding step, and the third welding step, a laser is irradiated so that the energy density of a central portion is higher than the energy density of an outer periphery. A welding method according to any one of claims 1 to 11.

13. A welding device for welding a first metal member and a second metal member disposed over the first member, comprising: A laser irradiation unit that irradiates a laser, the laser irradiation unit irradiates a first portion along at least a portion of the annular welding target region with a laser while scanning a laser with a gradually increasing energy density at a portion where the first member and the second member overlap, irradiates a second portion adjacent to the first portion along at least a portion of the annular welding target region with a laser while scanning the second portion with a constant energy density, and irradiates the first portion with a laser while overlapping the first portion at the end, and irradiates a third portion adjacent to the second portion with a laser while scanning the third portion with a gradually decreasing energy density. Welding equipment.

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