Method of laser welding

Abstract

To strike a balance between facilitation of laser processing application for a copper-based material and suppression of thermal diffusion by a laser beam.SOLUTION: A method for laser welding of a copper-based material includes the steps of: disposing a copper-based material on a jig of a laser welding system; oscillating a blue laser beam on the basis of pulse drive by one or more power sources constituting the laser welding system; and pulse-irradiating a processing part of the copper-based material with the oscillated blue laser beam via a transmission fiber and a processing head.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to laser welding methods. [Background technology]

[0002] Patent Document 1 discloses a laser processing method in which an inorganic workpiece is irradiated with a pulsed ultraviolet laser beam to perform grooving or cutting. In this laser processing method, the pulse width of the ultraviolet laser beam is set longer as the processing depth of the grooving or cutting is deeper or the scanning speed of the ultraviolet laser beam is faster. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-123004 A Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide a laser welding method that facilitates laser processing of copper-based materials while suppressing thermal diffusion caused by laser light. [Means for solving the problem]

[0005] The present disclosure provides a method for laser welding a copper-based material, the method comprising the steps of: placing the copper-based material on a jig of a laser welding system; oscillating blue laser light based on pulse driving by one or more power sources constituting the laser welding system; and irradiating a processing location of the copper-based material with the oscillated blue laser light in a pulsed manner via a transmission fiber and a processing head. Effect of the Invention

[0006] According to the present disclosure, it is possible to facilitate laser processing of copper-based materials while suppressing thermal diffusion caused by laser light. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing a configuration example of a laser welding system according to an embodiment of the present invention. [Figure 2A] A schematic diagram showing an example of a processing process for copper-based materials using laser irradiation based on CW oscillation. [Figure 2B] A schematic diagram showing an example of a machining process for copper-based materials using pulsed laser irradiation. [Diagram 3] A schematic diagram showing an example of the power characteristics over time for a CW blue laser beam and a blue pulsed laser beam. [Figure 4A] A schematic diagram showing an example of the melt width and melt depth of a melted part generated in a copper-based material by irradiation with a CW blue laser beam. [Figure 4B] FIG. 1 is a schematic diagram showing an example of the molten width and the penetration depth of a molten part formed in a copper-based material by irradiation with a blue pulsed laser beam. [Diagram 5] A diagram showing a comparison of processing parameters for CW blue laser light and blue pulsed laser light. [Figure 6A] FIG. 1 is a schematic diagram showing an example of the fusion width and fusion depth of a fusion part formed in a copper-based material by irradiation with a low-frequency pulsed laser. [Figure 6B] FIG. 1 is a schematic diagram showing an example of the fusion width and fusion depth of a fusion part formed in a copper-based material by irradiation with a high-frequency pulse laser. [Figure 7] FIG. 2 is a diagram showing an example of the relationship between the pulse width and power of a low-frequency pulse laser and a high-frequency pulse laser; [Figure 8] A graph showing a schematic example of the relationship between the molten width of the molten part of a copper-based material with a workpiece thickness of 2 mm and the pulse frequency for each processing speed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] 0. Background to this disclosure Generally, copper-based materials, which are mainly composed of copper, have high reflectivity, high thermal conductivity, and high heat capacity. For this reason, it is known that laser processing (laser welding) of copper-based materials is very difficult. Facilitation of processing of copper-based materials is required, for example, in the manufacture of one or more electrodes installed in a power control unit or battery that is mounted in an electric vehicle (EV) that has become widespread in recent years and handles large currents. This is based on the fact that, for example, if an electrode configuration is used in which a land made of copper-based material and an electrode terminal made of copper-based material are connected by existing solder, the solder melts due to heat generated by the large current, causing the connection between the land and the electrode terminal to become detached, resulting in deterioration of electrical conductivity. In addition, the base plate material such as resin that supports the land is often a low heat-resistant material, and it is expected that the base plate material will deteriorate or be damaged due to thermal diffusion from the land to the base plate material by the laser light, and it is also required to suppress the thermal diffusion by the laser light as much as possible.

[0009] Patent Document 1 discloses a technique for irradiating an inorganic workpiece with a pulsed ultraviolet laser beam. However, the laser processing disclosed in this document is not intended for the above-mentioned copper-based material as the workpiece, and no technical measures for suppressing thermal diffusion caused by the laser beam are disclosed. In other words, it is assumed that a technique for both facilitating laser processing of the above-mentioned copper-based material and suppressing thermal diffusion caused by the laser beam has not yet been established.

[0010] In the following embodiment, an example of a laser welding method that can simultaneously facilitate laser processing of copper-based materials and suppress thermal diffusion caused by laser light will be described.

[0011] Hereinafter, with reference to the drawings as appropriate, an embodiment specifically disclosing the laser welding method according to the present disclosure will be described in detail. However, more detailed explanation than necessary may be omitted. For example, detailed explanation of already well-known matters or duplicate explanation of substantially the same configuration may be omitted. This is to avoid the following explanation becoming unnecessarily redundant and to facilitate understanding by those skilled in the art. Note that the attached drawings and the following explanation are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

[0012] 1. Definitions In the following description, unless expressly stated otherwise, the term "laser welding" is intended to have the broadest possible meaning and includes welding (fabrication), soldering, melting, joining, annealing, softening, tackifying, resurfacing, peening, heat treating, fusing, sealing, and stacking.

[0013] In the following description, the object to be processed by laser welding is referred to as a "workpiece." In the following embodiment, the workpiece is, for example, a plate-shaped copper-based material constituting an electrode in the power control unit or battery described above. However, the copper-based material does not have to be limited to the plate-shaped one described above.

[0014] In the following description, unless expressly stated otherwise, the term "copper-based material" is intended to have the broadest possible meaning and includes copper, copper materials, copper metals, materials electroplated with copper, metallic materials containing at least about 10% to 100% copper by weight, metals and alloys containing at least about 10% to 100% copper by weight, metals and alloys containing at least about 20% to 100% copper by weight, metals and alloys containing at least about 50% to 100% copper by weight, metals and alloys containing at least about 70% to 100% copper by weight, and metals and alloys containing at least about 90% to 100% copper by weight.

[0015] In the following description, the terms "blue laser light" and "blue laser beam" have the broadest possible meaning unless otherwise explicitly stated, and refer to a laser beam or light having a wavelength of about 400 nm to about 500 nm that is provided or propagated. It is known that light having a blue wavelength (e.g., blue laser light) has a high absorption rate (up to about 65%) in copper.

[0016] 2. System Configuration First, referring to FIG. 1, a configuration example of a blue laser welding system 100 according to the present embodiment will be described. FIG. 1 is a schematic diagram showing a configuration example of a blue laser welding system 100 according to the present embodiment. As shown in FIG. 1, when a workpiece Wk is held and placed by a holding jig JG1 on an XY stage 40, a plane that defines a two-dimensional plane of the surface of the workpiece Wk, which is a processing location, is called an XY plane, and a direction in which the blue pulsed laser light BPL is irradiated from above onto this XY plane is called a Z direction. That is, the X direction and the Y direction are mutually orthogonal, and one direction for defining the coordinates of the two-dimensional plane of the surface of the workpiece Wk, which is a processing location, is the X axis, and the other direction for defining the coordinates is the Y axis.

[0017] In the blue laser welding system 100, blue pulsed laser light BPL is generated by oscillation in a laser oscillator 10 based on pulse driving by each of a plurality of pulsed power sources PLW1 to PLW4, and the blue pulsed laser light BPL is pulse-irradiated to a processing location of a workpiece Wk, which is a target processing object, via a transmission fiber 21 and a processing head 30. In addition, in FIG. 1, four laser blades are provided in the laser oscillator 10 so as to match the number of pulsed power sources, and the number of pulsed power sources and laser blades need not be limited to four. In addition, the laser blade may be referred to as a laser module for generating blue laser light.

[0018] Blue laser welding system 100 includes a laser oscillator 10, a processing verification machine housing 20 equipped with a processing environment (see below), a pulse command branch board 60, and a plurality of pulse power sources PLW1 to PLW4.

[0019] The laser oscillator 10 generates blue laser light by oscillating the laser blades 11-14 corresponding to the pulsed power supplies PLW1-PLW4 based on pulse driving by each of the multiple pulsed power supplies PLW1-PLW4. Furthermore, the laser oscillator 10 combines the blue laser light oscillated by each of the laser blades 11-14 in a beam combiner 15, and transmits the high-output blue pulsed laser light BPL obtained by the combination to a transmission fiber 21. The laser oscillator 10 has at least the multiple laser blades 11, 12, 13, 14, the beam combiner 15, and a power supply interface 16, which are housed in the same housing.

[0020] In this embodiment, when laser processing (laser welding) the workpiece Wk, which is the target object to be processed, blue laser light (blue laser beam) having a blue wavelength (i.e., 400 nm to 500 nm) is used. This is because light having a blue wavelength has a characteristic of having a high absorption rate (up to about 65%) in copper (Cu), which is the main component of copper-based materials, and this characteristic is utilized.

[0021] The laser blade 11 has a laser diode configured by, for example, a semiconductor laser array. The laser blade 11 discretely oscillates (generates) blue laser light by the laser diode using a pulse current that repeats a predetermined current value and a zero value flowing out from the pulse power supply PLW1 by pulse driving of the corresponding pulse power supply PLW1 based on a control command from the pulse command branch board 60. The oscillated blue laser light is input to the beam combiner 15.

[0022] The laser blade 12 has a laser diode configured by, for example, a semiconductor laser array. The laser blade 12 may be called a laser module for generating blue laser light. The laser blade 12 discretely oscillates (generates) blue laser light by the laser diode using a pulse current that repeats a predetermined current value and a zero value flowing out from the pulse power supply PLW2 by pulse driving of the corresponding pulse power supply PLW2 based on a control command from the pulse command branch board 60. This oscillated blue laser light is input to the beam combiner 15.

[0023] The laser blade 13 has a laser diode configured by, for example, a semiconductor laser array. The laser blade 13 may be called a laser module for generating blue laser light. The laser blade 13 discretely oscillates (generates) blue laser light by a laser diode using a pulse current that repeats a predetermined current value and a zero value flowing out from the pulse power supply PLW3 by pulse driving of the corresponding pulse power supply PLW3 based on a control command from the pulse command branch board 60. This oscillated blue laser light is input to the beam combiner 15.

[0024] The laser blade 14 has a laser diode configured by, for example, a semiconductor laser array. The laser blade 14 may be called a laser module for generating blue laser light. The laser blade 14 discretely oscillates (generates) blue laser light by a laser diode using a pulse current that repeats a predetermined current value and a zero value flowing out from the pulse power supply PLW4 by pulse driving of the corresponding pulse power supply PLW4 based on a control command from the pulse command branch board 60. This oscillated blue laser light is input to the beam combiner 15.

[0025] Inside each of the laser blades 11-14, blue laser light beams with slightly different wavelengths in the range of 400 [nm] to 500 [nm] emitted from multiple semiconductor laser arrays are superimposed on a diffraction grating at angles corresponding to each wavelength, and are combined into one laser beam (laser light) by resonating between a partial transmission mirror common to all the blue laser light beams and the end face of each semiconductor, and then emitted from the laser blade. This combination is already known as Wavelength Beam Combining (WBC) synthesis technology.

[0026] The beam combiner 15 collects the laser beams (laser lights) from each laser blade using polarization combining and spatial combining techniques, and transmits the collected laser beams to the input end of the transmission fiber 21. As a result, the laser beams (laser lights) from all the laser blades 11 to 14 are input to one transmission fiber 21, and the laser oscillator 10 can generate high-power blue pulsed laser light exceeding several kW (kilowatts).

[0027] When the power supply interface 16 receives a pulse control command from the controller 50 (see below), it generates a pulse control command for instructing each of the pulsed power supplies PLW1 to PLW4 to drive them with pulses based on the pulse control command and sends the pulse control command to the pulse command branch board 60. The power supply interface 16 of the laser oscillator 10 and the pulse command branch board 60 are connected by a control signal line, and the pulse control command from the power supply interface 16 is sent to the pulse command branch board 60 via this control signal line.

[0028] The processing verification machine housing 20 has a processing environment, and holds the workpiece Wk, which is an object to be processed by the blue laser welding system 100, in the processing environment. Specifically, the processing environment is composed of a transmission fiber 21, a processing head 30, an XY stage 40, and a controller 50. Note that the processing environment may include the workpiece Wk, which is an object to be processed.

[0029] One end of the transmission fiber 21 is optically connected to the beam combiner 15 of the laser oscillator 10, and the other end opposite to the one end is optically connected to the processing head 30. The transmission fiber 21 transmits the blue pulsed laser light generated by the laser oscillator 10 to the processing head 30.

[0030] The processing head 30 two-dimensionally scans the blue pulsed laser light BPL transmitted through the transmission fiber 21 and irradiates it toward the processing location of the workpiece Wk held by the holding jig JG1 of the XY stage 40. The processing head 30 has optical components (e.g., a collimation lens, a reflection mirror, and a condenser lens) and a laser light scanner. The laser light scanner may have a known configuration, and includes, for example, an X positioning mirror, a Y positioning mirror, an X motor for driving the X positioning mirror, and a Y motor for driving the Y positioning mirror. These optical components are housed in the housing of the processing head 30 while maintaining a predetermined positional relationship (see, for example, FIGS. 1 and 2 of JP 2022-60808 A).

[0031] The collimation lens receives the blue pulsed laser light BPL emitted from the transmission fiber 21, converts it into parallel light, and makes it incident on the reflection mirror. The collimation lens is connected to a drive unit (not shown) and is configured to be displaceable in response to a control signal from the controller 50. By displacing the collimation lens, the focal position of the blue pulsed laser light BPL can be changed, and the blue pulsed laser light BPL can be appropriately irradiated in accordance with the shape of the workpiece Wk. In other words, the collimation lens also functions as a focal position adjustment mechanism for the blue pulsed laser light BPL in combination with the controller 50. The focusing lens may be displaced by the controller 50 to change the focal position of the blue pulsed laser light BPL. The mechanism for adjusting the focal position of the blue pulsed laser light BPL is not limited to the displacement of the collimation lens described above, and may be a method of simply raising and lowering the height position in the Z direction of the processing head 30.

[0032] The reflecting mirror reflects the blue pulsed laser beam BPL that has passed through the collimation lens and makes it enter the laser beam scanner. The surface of the reflecting mirror is arranged to form an angle of about 45 degrees with the optical axis of the blue pulsed laser beam BPL that has passed through the collimation lens.

[0033] The condenser lens condenses the blue pulsed laser light BPL, which is reflected by the reflecting mirror and scanned by the laser light scanner, onto the surface of the workpiece Wk.

[0034] The laser light scanner is a known galvanometer scanner having a first galvanometer mirror and a second galvanometer mirror. The first galvanometer mirror has a first mirror, a first rotation axis, and a first drive unit. The second galvanometer mirror has a second mirror, a second rotation axis, and a second drive unit. The blue pulsed laser light BPL transmitted through the focusing lens is reflected by the first mirror, and is further reflected by the second mirror, and is irradiated onto the surface of the workpiece Wk.

[0035] For example, the first driving unit and the second driving unit are galvano motors, and the first rotating shaft and the second rotating shaft are output shafts of the motors. Although not shown, the first driving unit is rotated by a driver that operates in response to a control signal from the controller 50, so that the first mirror attached to the first rotating shaft rotates around the axis of the first rotating shaft. Similarly, the second driving unit is rotated by a driver that operates in response to a control signal from the controller 50, so that the second mirror attached to the second rotating shaft rotates around the axis of the second rotating shaft.

[0036] The first mirror rotates around the axis of the first rotation shaft to a predetermined angle, whereby the blue pulsed laser light BPL scans in one direction (e.g., X direction) on the XY plane of the workpiece Wk. The second mirror rotates around the axis of the second rotation shaft to a predetermined angle, whereby the blue pulsed laser light BPL scans in another direction (e.g., Y direction) on the XY plane. In other words, the laser light scanner is configured to two-dimensionally scan the blue pulsed laser light BPL within the XY plane and irradiate it toward the workpiece Wk.

[0037] The holding jig JG1 is fixedly disposed on the mounting table of the XY stage 40, and functions as a clamper that immobilize the workpiece Wk to be irradiated with the blue pulsed laser light BPL.

[0038] The XY stage 40 holds the clamp jig JG1 for holding the workpiece Wk on the mounting table, and displaces the workpiece Wk in both the X and Y directions by a movement amount corresponding to the command based on a command from the controller 50. The XY stage 40 may adopt a known configuration as long as it is configured to drive the placed workpiece Wk in two-dimensional directions. In addition, the XY stage 40 may hold the processing head 30 in a fixed manner, or may move the processing head 30 up and down along the Z direction by a predetermined amount corresponding to the command based on a command from the controller 50.

[0039] The controller 50 controls (1) the laser oscillation of the laser oscillator 10, (2) the movement of the processing head 30 in the Z direction, and (3) the two-dimensional movement along the XY plane of the workpiece Wk held by the clamping jig JG1 placed on the XY stage 40.

[0040] (1) Laser Oscillation of the Laser Oscillator 10 The controller 50 controls the laser oscillation by generating pulse control commands having various parameters including a duty ratio (see FIG. 3) such as output (power) and on-time for the laser oscillator 10 connected to each of the pulsed power sources PLW1 to PLW4 and sending the pulse control commands to the laser oscillator 10. The controller 50 and the laser oscillator 10 are connected by a control signal line, and the pulse control commands from the controller 50 are sent to the laser oscillator 10 via this control signal line.

[0041] (2) Movement of the processing head 30 in the Z direction The controller 50 can move the processing head 30 fixed to the XY stage 40 in the Z direction by issuing a control command to the XY stage 40. This is executed, for example, when adjusting the focal position of the blue pulsed laser light BPL.

[0042] (3) Two-dimensional movement of the workpiece Wk along the XY plane The controller 50 can move the workpiece Wk held by the holding jig JG1 placed on the XY stage 40 two-dimensionally along the XY plane by issuing a control command to the XY stage 40. This is executed, for example, when machining the workpiece Wk by shifting the machining location to be irradiated with the blue pulsed laser light BPL.

[0043] When the pulse command branching board 60 receives a pulse control command from the laser oscillator 10, the pulse command branching board 60 generates a control command for executing pulse driving using various parameters including the output (power) and duty ratio (see FIG. 3) included in the pulse control command based on the pulse control command, and sends the control command to each of the pulse power sources PLW1 to PLW4. The pulse command branching board 60 is arranged, for example, in a rack (not shown) in which each of the pulse power sources PLW1 to PLW4 is arranged, as a separate body from the pulse power sources PLW1 to PLW4. However, the arrangement of the pulse command branching board 60 does not have to be limited to the example described above. The pulse command branching board 60 and each of the pulse power sources PLW1 to PLW4 are connected by a control signal line, and the control command from the pulse command branching board 60 is sent to each of the pulse power sources PLW1 to PLW4 via this control signal line.

[0044] The pulse power supply PLW1 performs pulse driving to generate a pulse current for oscillating blue pulsed laser light in the laser blade 11 of the laser oscillator 10 based on a control command from the pulse command branch board 60. This allows the pulse power supply PLW1 to supply a pulse current for oscillating blue pulsed laser light to the laser blade 11 of the corresponding laser oscillator 10.

[0045] The pulse power supply PLW2 performs pulse driving to generate a pulse current for oscillating blue pulsed laser light in the laser blade 12 of the laser oscillator 10 based on a control command from the pulse command branch board 60. This allows the pulse power supply PLW2 to supply a pulse current for oscillating blue pulsed laser light to the laser blade 12 of the corresponding laser oscillator 10.

[0046] The pulse power supply PLW3 performs pulse driving to generate a pulse current for oscillating a blue pulsed laser beam in the laser blade 13 of the laser oscillator 10 based on a control command from the pulse command branch board 60. This allows the pulse power supply PLW1 to supply a pulse current for oscillating a blue pulsed laser beam to the laser blade 13 of the corresponding laser oscillator 10.

[0047] The pulse power supply PLW4 performs pulse driving to generate a pulse current for oscillating a blue pulsed laser beam in the laser blade 14 of the laser oscillator 10 based on a control command from the pulse command branch board 60. This allows the pulse power supply PLW1 to supply a pulse current for oscillating a blue pulsed laser beam to the laser blade 14 of the corresponding laser oscillator 10.

[0048] Each of the pulsed power supplies PLW1 to PLW4 is connected to each of the laser blades 11 to 14 by a power line in a one-to-one correspondence, and a pulsed current from each of the pulsed power supplies PLW1 to PLW4 is supplied to each of the laser blades 11 to 14 via this power line.

[0049] 3. Comparison between CW and pulsed oscillation Next, referring to Fig. 2A, Fig. 2B and Fig. 3, an example of a processing process when a copper-based material is irradiated with a laser by each of CW oscillation and pulse oscillation will be described. Fig. 2A is a diagram showing an example of a processing process by irradiating a copper-based material with a laser based on CW oscillation. Fig. 2B is a diagram showing an example of a processing process by irradiating a copper-based material with a laser based on pulse oscillation. Fig. 3 is a diagram showing an example of the time characteristics of the power of the CW blue laser light CLB and the blue pulsed laser light BPL. The horizontal axis of Fig. 3 indicates time (i.e., processing time), and the vertical axis of Fig. 3 indicates output (power).

[0050] The processing process shown in Figures 2A and 2B shows the bonding of a pad PD1 such as a land, which is a workpiece Wk, and a device terminal DV1, which is a workpiece Wk, to form an electrode formed on a substrate of a power control unit mounted in an electric vehicle. Both the pad and the device terminal are made of copper-based materials. The pad PD1 is supported on a resist RG1, which is a resin material.

[0051] As a comparative example, as shown in FIG. 2A, the pad PD1 and the device terminal DV1 are used as the workpiece Wk, and the CW blue laser light CLB generated by CW oscillation (i.e., continuous oscillation) is irradiated one-dimensionally or two-dimensionally along the scanning direction shown in the figure. This irradiation melts a part or all of the processed part of the workpiece Wk to form a molten part WD1. However, the CW blue laser light CLB based on the CW oscillation is irradiated continuously in time. For this reason, the region RNG1 (in other words, the propagation region of the thermal energy) in the molten part WD1 where the thermal energy is propagated by the irradiation of the CW blue laser light CLB spreads too much, and the thermal diffusion occurs not only in the device terminal DV1 and the pad PD1 which are the workpiece Wk, but also in the resist RG1 which is a low heat-resistant material supporting the pad PD1. This influence causes a problem that a part BR1 of the resist RG1 is damaged, such as cracked.

[0052] Here, a brief description will be given of the steps of laser welding carried out in blue laser welding system 100 according to the present embodiment.

[0053] (Laser welding process) (Step 1) A workpiece Wk made of a copper-based material is held and placed by a holding jig JG1 on the XY stage 40 of the blue laser welding system 100. (Step 2) Based on a pulse control command from controller 50, a pulse current generated by pulse driving of one or more power supplies (e.g., four pulse power supplies PLW1 to PLW4) constituting blue laser welding system 100 is supplied to laser oscillator 10. As a result, blue pulsed laser light BPL is oscillated and generated in laser oscillator 10. (Step 3) The oscillated blue pulsed laser light BPL is irradiated in pulses to a processing location of the workpiece Wk via the transmission fiber 21 and the processing head 30.

[0054] In this embodiment, similarly to FIG. 2A, the pad PD1 and the device terminal DV1 are treated as the workpiece Wk, and the blue pulsed laser light BPL generated by pulse oscillation (i.e., time-discrete oscillation) is irradiated one-dimensionally or two-dimensionally along the scanning direction shown in the figure. This irradiation melts a part or all of the processed portion of the workpiece Wk to form a molten portion WD2. However, unlike FIG. 2A, the blue pulsed laser light BPL based on pulse oscillation has a pulse width (in other words, irradiation time). For this reason, unlike the CW blue laser light CLB, it is not irradiated continuously in time, and there are an on time Ton during which it is irradiated and an off time Toff during which it is not irradiated in the period T (see FIG. 3).

[0055] Here, the ratio of the on-time Ton to the period T is called the duty ratio. This duty ratio is one of the parameters that determine the pulse width of the blue pulsed laser light BPL, and is specified by the controller 50 to determine the pulse drive method of the pulsed power supplies PLW1-PLW4. The reciprocal of the period T is called the pulse frequency. Like the duty ratio, this pulse frequency is also one of the parameters that determine the pulse width of the blue pulsed laser light BPL, and is specified by the controller 50 to determine the pulse drive method of the pulsed power supplies PLW1-PLW4.

[0056] During the off time Toff, the blue pulsed laser light BPL is not irradiated to the melted portion WD2, so that the melted portion WD2 is temporarily cooled during the off time Toff. Then, during the next cycle T, the blue pulsed laser light BPL is irradiated during the on time Ton, and is cooled during the off time Toff. In other words, by repeating this irradiation and cooling, the diffusion of the region RNG2 (in other words, the propagation region of the thermal energy) in the melted portion WD2 where the thermal energy is propagated by the irradiation of the blue pulsed laser light BPL is suppressed compared to the region RNG1 in FIG. 2A. In other words, even if the output (power) is increased by pulse oscillation (i.e., pulsating the blue laser light) compared to CW oscillation, the thermal energy equivalent to the area for the processing time of the blue pulsed laser light BPL in FIG. 3 is equivalent to the thermal energy equivalent to the area for the processing time of the CW blue laser light CLB in FIG. 3.

[0057] As shown in Fig. 3, the output (power) of the blue pulsed laser light BPL based on pulsed oscillation is higher (e.g., 1600 W [watts]) than the output (power) of the CW blue laser light CLB based on CW oscillation (e.g., 800 W [watts]). This is achieved by adjusting the amount of pulse current from each of the pulsed power sources PLW1 to PLW4. This pulsation makes it possible to achieve a high output with the same amount of energy, and improves processing performance while suppressing thermal effects.

[0058] Next, a comparison between the melted portion WD1 based on the irradiation of the CW blue laser light and the melted portion WD2 based on the irradiation of the blue pulsed laser light BPL will be described with reference to Fig. 4A, Fig. 4B, and Fig. 5. Fig. 4A is a diagram showing an example of the melt width w1 and the penetration depth d1 of the melted portion WD1 generated in the copper-based material by the irradiation of the CW blue laser light CLB. Fig. 4B is a diagram showing an example of the melt width w2 and the penetration depth d2 of the melted portion WD2 generated in the copper-based material by the irradiation of the blue pulsed laser light BPL. Fig. 5 is a diagram showing a comparative example of processing parameters in the CW blue laser light CLB and the blue pulsed laser light BPL.

[0059] As shown in FIG. 4A, by continuously irradiating the work Wk with the CW blue laser beam CLB, the melted portion WD1 (for example, the pad PD1) has a volume with a melting width w1 and a penetration depth d1. In the irradiation with the CW blue laser beam CLB, the spread of heat is large, and both the penetration depth and the melting width increase.

[0060] On the other hand, as shown in FIG. 4B, by pulse-irradiating the work Wk with the blue pulsed laser beam BPL, the melted portion WD2 (for example, the pad PD1) has a volume with a melting width w2 and a penetration depth d2. In the irradiation with the blue pulsed laser beam BPL, since the energy density of the blue pulsed laser beam BPL is high, it is possible to extend the melting in the depth direction while suppressing the spread of heat.

[0061] Specifically, the relationship of the melting widths is w1 > w2, and the relationship of the penetration depths is d1 < d2. This indicates that when performing laser welding on the work Wk using the blue pulsed laser beam BPL, compared with the case of performing laser welding on the work Wk using the CW blue laser beam CLB, the melting width w2 of the melted portion WD2 can be made narrower, and it is possible to further suppress the influence of heat diffusion to the work Wk.

[0062] FIG. 5 comparatively shows various parameter comparison examples when performing laser welding by continuously irradiating the work Wk with the CW blue laser beam CLB and laser welding by pulse-irradiating the work Wk with the blue pulsed laser beam BPL, respectively. The duty ratio of the pulse irradiation is 50%, that is, the ratio of the on-time Ton in the period T is exemplified as 50%.

[0063] A cross section SEC1 of the melted part (referred to as the "second melted part" in the explanation of FIG. 5) caused by continuous irradiation of the CW blue laser light CLB is compared with a cross section SEC2 of the melted part (referred to as the "first melted part" in the explanation of FIG. 5) caused by pulse irradiation of the blue pulsed laser light BPL. As shown in the cross-sectional image of FIG. 5, although the thermal energy given to the workpiece Wk by the irradiation of the laser light is the same at 80 J [Joules] for both, the melt width wb of the first melted part is smaller than the melt width wa of the second melted part (wa>wb), and the penetration depth db of the first melted part is larger than the penetration depth da of the second melted part (db>da).

[0064] 4. Comparison of pulse widths of blue pulsed laser light Next, a comparison of various characteristics depending on the pulse width of the blue pulsed laser light will be described with reference to Fig. 6A, Fig. 6B, Fig. 7, and Fig. 8. Fig. 6A is a diagram showing an example of the melt width w2a and the penetration depth d2a of the melted part WD2a generated in the copper-based material by irradiation with the low-frequency pulsed laser light BPLa. Fig. 6B is a diagram showing an example of the melt width w2b and the penetration depth d2b of the melted part WD2b generated in the copper-based material by irradiation with the high-frequency pulsed laser light BPLb. Fig. 7 is a diagram showing an example of the relationship between the pulse width and the power of the low-frequency pulsed laser light BPLa and the high-frequency pulsed laser light BPLb. Fig. 8 is a graph showing an example of the relationship between the melt width and the pulse frequency in the melted part of the copper-based material having a workpiece thickness of 2 mm for each processing speed.

[0065] As shown in FIG. 6A, when a low-frequency pulsed laser light BPLa, which is a blue pulsed laser light having a low pulse frequency fa (e.g., 1.0 kHz), is pulse-irradiated onto a workpiece Wk such as a pad PD1, a molten portion WD2a having a molten width w2a and a penetration depth d2a is formed in the workpiece Wk.

[0066] Similarly, as shown in FIG. 6B, when high-frequency pulsed laser light BPLb, which is blue pulsed laser light having a pulse frequency fb (e.g., 3.0 kHz) higher than the pulse frequency fa, is irradiated onto a workpiece Wk such as a pad PD1, a molten portion WD2b having a molten width w2b and a penetration depth d2b is formed in the workpiece Wk.

[0067] The horizontal axis of FIG. 7 indicates the pulse width, and the vertical axis of FIG. 7 indicates the output (power). The pulse width indicates the time width occupied by the on-time during which the blue pulsed laser light is oscillated (generated) in the blue pulsed laser light oscillated (generated) periodically. As shown in FIG. 7, the low-frequency pulsed laser light BPLa and the high-frequency pulsed laser light BPLb have the same peak output (power) and thermal energy at the time of incidence on the workpiece Wk. The pulse width fwa of the low-frequency pulsed laser light BPLa is larger than the pulse width fwb of the high-frequency pulsed laser light BPLb. On the other hand, the pulse frequency fa corresponding to the pulse width fwa of the low-frequency pulsed laser light BPLa is smaller than the pulse frequency corresponding to the pulse width fwb of the high-frequency pulsed laser light BPLb. Since both are pulsed laser lights, it is possible to suppress the thermal effect on the workpiece Wk compared to the irradiation of the CW blue laser light CLB shown in FIG. 4A.

[0068] The melt width w2a of the melted portion WD2a is wider than the melt width w2b of the melted portion WD2b. That is, the melt width w2b of the melted portion WD2b is narrower than the melt width w2a of the melted portion WD2a. The penetration depth d2a of the melted portion WD2a is shorter than the penetration depth d2b of the melted portion WD2b. That is, the penetration depth d2b of the melted portion WD2b is longer than the penetration depth d2a of the melted portion WD2a. Therefore, if the pulse frequency (in other words, the pulse width) is long and the thermal energy per pulse is large, the thermal effect will be expanded by one pulse. For this reason, by increasing the pulse frequency of the blue pulse laser light and increasing the frequency of occurrence of the cooling time due to the off time Toff, the thermal effect per pulse (that is, the area of ​​thermal diffusion) can be reduced.

[0069] The horizontal axis of FIG. 8 indicates the pulse frequency [kHz], and the vertical axis of FIG. 8 indicates the fusion width [μm]. The relationship between the pulse frequency of the blue pulse laser light BPL and the fusion width is shown for each of the welding speeds of 10 [mm / sec], 25 [mm / sec], 50 [mm / sec], 100 [mm / sec], 200 [mm / sec], and 400 [mm / sec] for the irradiation of the blue pulse laser light BPL. As shown in FIG. 8, it is presumed that the relationship between the pulse frequency and the fusion width can be approximated by the characteristic FT1. In other words, when the pulse frequency is 2 [kHz] or more, the fusion width converges to about 300 to 350 [μm] on average at any welding speed, and it can be seen that the fusion width converges to about 300 to 350 [μm] even at 2 [kHz] or more.

[0070] On the other hand, when the pulse frequency is less than 2 [kHz] (for example, about 1 [kHz]), the fusion width does not converge and varies depending on the welding speed. For example, the higher the welding speed, the smaller the fusion width tends to be, but the lower the welding speed, the larger the fusion width tends to be. For example, when the pulse frequency is 0.5 [kHz], if the welding speed is 200 [mm / sec], the fusion width is about 310 [μm], but if the welding speed is 10 [mm / sec], the fusion width is about 550 [μm]. Even with the same pulse frequency, the fusion width varies greatly depending on the welding speed. This is presumably because, for example, when the welding speed is low, the irradiation time of the blue pulsed laser light BPL irradiated to the processing point of the workpiece Wk becomes relatively long, making it more susceptible to the effects of thermal diffusion.

[0071] <About the technology disclosed herein> As described above, the present disclosure discloses the following technical ideas.

[0072] <Technology 1> A laser welding method for a copper-based material (workpiece Wk), comprising: A step of placing the copper-based material on a jig (pressing jig JG1) of a laser welding system (blue laser welding system 100); a step of oscillating blue laser light (blue pulsed laser light BPL) based on pulse driving by one or more power sources (pulse power sources PLW1 to PLW4) constituting the laser welding system; and irradiating the oscillated blue laser light in a pulse form onto a processing location of the copper-based material via a transmission fiber (21) and a processing head (30). Laser welding method. As a result, according to the laser welding method, even if the workpiece is a copper-based material, which is difficult to laser process, by using blue pulsed laser light BPL, which has a high absorption rate for copper, it is possible to easily perform laser processing intended for copper-based materials (e.g., the workpiece Wk) and suppress thermal diffusion caused by the blue pulsed laser light BPL.

[0073] <Technology 2> A first melt width (melt width w2) indicating the melt width of a first melt portion (melt portion WD2, see FIG. 4B) formed at the processed portion based on pulse irradiation of the blue laser light (blue pulsed laser light BPL) is smaller than a second melt width (melt width w1) indicating the melt width of a second melt portion (melt portion WD1, see FIG. 4A) formed at the processed portion when the blue laser light is continuously irradiated. The laser welding method according to claim 1. As a result, according to the laser method, a period during which the melted part of the workpiece Wk is cooled is provided by the off-time when the blue pulsed laser light BPL based on pulsed oscillation is irradiated to the workpiece Wk in pulses, compared to the case of continuously irradiating the workpiece Wk with the CW blue laser light CLB based on CW oscillation. Therefore, it is possible to further suppress the diffusion of thermal energy to the workpiece Wk, and as a result, the melt width of the melted part WD2 formed in the workpiece Wk can be narrowed.

[0074] <Technology 3> A first depth (penetration depth d2, see FIG. 4B ) indicating the penetration depth of the first fusion portion (fusion portion WD2) is greater than a second depth (penetration depth d1, see FIG. 4A ) indicating the penetration depth of the second fusion portion (fusion portion WD1); The laser welding method according to Technology 1 or Technology 2. As a result, according to the laser welding method, the melting depth of the workpiece Wk along the irradiation direction of the blue pulsed laser light BPL based on pulsed oscillation can be further extended when the workpiece Wk is pulsed irradiated with blue pulsed laser light BPL based on pulsed oscillation compared to when the workpiece Wk is continuously irradiated with CW blue laser light CLB based on CW oscillation.

[0075] <Technology 4> The pulse width of the blue laser light (blue pulsed laser light BPL) when irradiated in pulses is equal to or less than a predetermined value. The laser welding method according to any one of Techniques 1 to 3. As a result, according to the laser welding method, the pulse width when the blue pulsed laser light BPL is irradiated (e.g., see the pulse widths fwa and fwb in FIG. 7) is set to a predetermined value or less (e.g., the pulse width corresponding to the pulse frequency of characteristic FT1 in FIG. 8 being 2 [kHz]), thereby making it possible to form a narrow molten width of the molten portion formed in the workpiece Wk.

[0076] <Technology 5> The pulse width is adjustable based on a duty ratio (see FIG. 3) when the blue laser light (blue pulsed laser light BPL) is pulse-irradiated. The laser welding method according to claim 4. As a result, according to the laser welding method, the pulse width of the blue pulsed laser light BPL can be easily adjusted using the duty ratio, which is one of the parameters for controlling the pulsed power sources PLW1 to PLW4.

[0077] <Technology 6> The pulse width is adjustable based on the pulse frequency when the blue laser light (blue pulsed laser light BPL) is pulse-irradiated. The laser welding method according to claim 4. As a result, according to the laser welding method, the pulse width of the blue pulsed laser light BPL can be easily adjusted using the pulse frequency, which is one of the parameters for controlling the pulsed power sources PLW1 to PLW4. The pulse width of the blue pulsed laser light BPL may be adjusted using both the pulse frequency and the duty ratio.

[0078] <Technology 7> The pulse frequency is greater than 2 kHz. The laser welding method described in technique 6. As a result, according to the laser welding method, the high-frequency pulsed laser light BPLb can reduce the molten width of the molten part formed in the workpiece Wk more than the low-frequency pulsed laser light BPLa, and can converge it within a certain range (see characteristic FT1 in FIG. 8). Therefore, by employing such a laser welding method, it is possible to form a molten width of a copper-based material that is desirable for an electrode disposed on a board of a power control unit mounted on an electric vehicle, for example.

[0079] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present disclosure is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications, corrections, substitutions, additions, deletions, and equivalents within the scope of the claims, and it is understood that these also naturally belong to the technical scope of the present disclosure. In addition, the components in the various embodiments described above may be arbitrarily combined within the scope of the invention. [Industrial Applicability]

[0080] INDUSTRIAL APPLICABILITY The present disclosure is useful as a laser welding method that achieves both facilitation of laser processing intended for copper-based materials and suppression of thermal diffusion caused by laser light. [Explanation of symbols]

[0081] 10 Laser Oscillator 11, 12, 13, 14 Laser Blade 15 Beam combiner 16 Power Interface 20 Processing verification machine housing 21 Transmission Fiber 30 Processing head 40 XY Stage 50 Controller 60 Pulse command branch board 100 Blue laser welding system JG1 holding jig PLW1, PLW2, PLW3, PLW4 Pulse power supplies Wk Work

Claims

1. 1. A method for laser welding copper-based materials, comprising the steps of: placing the copper-based material on a fixture of a laser welding system; a step of emitting blue laser light based on pulse driving by one or more power sources constituting the laser welding system; and irradiating the oscillated blue laser light to a processing location of the copper-based material through a transmission fiber and a processing head. Laser welding method.

2. A first melt width indicating a melt width of a first melt portion formed at the processing location based on the pulsed irradiation of the blue laser light is smaller than a second melt width indicating a melt width of a second melt portion formed at the processing location when the blue laser light is continuously irradiated. The laser welding method according to claim 1 .

3. A first depth indicating a penetration depth of the first molten portion is greater than a second depth indicating a penetration depth of the second molten portion; The laser welding method according to claim 2 .

4. The pulse width of the blue laser light is equal to or less than a predetermined value. The laser welding method according to claim 1 .

5. The pulse width is adjustable based on a duty ratio when the blue laser light is pulse-irradiated. The laser welding method according to claim 4.

6. The pulse width is adjustable based on a pulse frequency at the time of pulse irradiation of the blue laser light. The laser welding method according to claim 4.

7. The pulse frequency is greater than 2 kHz. The laser welding method according to claim 6.

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