Laser welding apparatus and laser welding method

Abstract

In a laser welding apparatus that welds multiple welds using laser light, the occurrence of welding defects in the first weld is suppressed. [Solution] The laser welding apparatus 20 comprises a laser medium 50, an excitation light source 51, and a control unit 24. The control unit 24 supplies driving power to the excitation light source 51 to inject excitation energy into the laser medium 50. Before welding the first weld to be made, the control unit 24 injects energy for pre-excitation into the laser medium 50 by supplying a pre-excitation power Pw2 of 25W or more to the excitation light source 51 for a pre-supply time T2 of 10ms or more. After the pre-supply time T2 has elapsed and after an interval T3, the driving power Pw1 for welding the first weld is supplied to the excitation light source 51, thereby welding the first weld.

Description

Technical Field

[0001] The present invention relates to a laser welding apparatus for welding a welding portion of a workpiece having a plurality of welding portions, and a laser welding method.

Background Art

[0002] In order to weld a workpiece composed of a plurality of small metal plates such as a suspension for a disk device, laser welding may be used as described in Patent Document 1 or Patent Document 2. For example, a suspension for a disk device includes a base plate, a load beam made of a thin stainless steel plate, and a flexure arranged along the load beam. In order to fix the flexure to the load beam or fix the load beam to the base plate, spot welding using a laser beam (hereinafter referred to as laser welding) is applied.

[0003] When forming a plurality of welding portions on one workpiece, so-called high-speed pulse welding is applied in order to shorten the welding time. In high-speed pulse welding, for example, more than 100 welding portions per second are welded. However, in high-speed pulse welding, the output of the laser beam of the first welding portion to be welded first among the plurality of welding portions may become unstable, and the welding quality may become a problem.

[0004] In order to prevent welding defects from occurring in the first welding portion, so-called discard of the laser beam may be performed. Discarding of the laser beam means irradiating the laser beam to a location other than the workpiece or irradiating the laser beam to a blank portion that is part of the workpiece and has nothing to do with welding immediately before welding the first welding portion.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] In the case of minute workpieces, such as suspensions for disk drives, it may not be possible to secure space on a portion of the workpiece for a test run of the laser beam. If the test run is performed while the workpiece is moving toward the welding stage, it may not be possible to focus the laser beam to the desired position. For this reason, it is desirable to perform the test run when the workpiece is stopped on the welding stage, but this results in extra time being spent before the first weld can be completed, thus reducing productivity.

[0007] Therefore, the object of the present invention is to provide a laser welding apparatus and a laser welding method that can avoid welding defects in the first weld when forming multiple welds on a single workpiece, without performing a test run of laser beam. [Means for solving the problem]

[0008] One embodiment is a laser welding apparatus for welding multiple welds on a workpiece using laser light, comprising: a laser medium that emits the laser light for the welds when excitation energy is injected; an excitation light source that injects the excitation energy into the laser medium when drive power is supplied; and a control unit that supplies the drive power for the excitation energy to the excitation light source.

[0009] The control unit includes means for injecting energy for pre-excitation into the laser medium by supplying pre-excitation power of 25 W or more to the excitation light source for a pre-supply time of 10 ms or more before welding the first of the plurality of welds to be welded; means for allowing a predetermined interval to pass after the pre-excitation but before welding the first weld; and means for welding the first weld by supplying the drive power to the excitation light source after the interval has elapsed.

[0010] In the above embodiment, a scanning mechanism including a galvanometer scanner for scanning the plurality of welds may be provided. The pulsed laser light emitted by the laser medium may be sequentially irradiated onto the plurality of welds via the galvanometer scanner.

[0011] The laser welding apparatus of the above embodiment may further include a workpiece support section for placing a plurality of workpieces and a moving mechanism. The moving mechanism moves the workpieces placed on the workpiece support section toward the welding stage and stops the workpiece to be welded toward the welding stage. The control unit may also have means for supplying the preliminary excitation power to the excitation light source while the workpiece to be welded is moving toward the welding stage.

[0012] One embodiment of the laser welding method is a laser welding method for welding a weld portion of a workpiece with laser light, wherein, before welding the weld portion, energy for pre-excitation of a strength that does not melt the workpiece is injected into the laser medium by supplying a pre-excitation power of 25 W or more to the excitation light source for a pre-supply time of 10 ms or more, after the pre-excitation has been performed and a predetermined interval has elapsed, and after the interval has elapsed, driving power for welding is supplied to the excitation light source to inject excitation energy into the laser medium, and the weld portion is welded by emitting the laser light from the laser medium. [Effects of the Invention]

[0013] According to the present invention, when forming welds on a workpiece having multiple welds, it is possible to avoid welding defects in the first weld without performing a test run with laser light. [Brief explanation of the drawing]

[0014] [Figure 1] Plan view of a workpiece with multiple welded joints. [Figure 2] A schematic perspective view showing a laser welding apparatus according to one embodiment. [Figure 3] A front view of a portion of the laser welding apparatus shown in Figure 2. [Figure 4] A schematic plan view showing the laser oscillator of the laser welding apparatus. [Figure 5] This time chart shows the relationship between the power supplied to the excitation light source of the laser welding apparatus and the time. [Figure 6] A flowchart showing the first part of a laser welding method according to one embodiment. [Figure 7] A flowchart showing the latter part of a laser welding method according to one embodiment. [Figure 8] This figure shows the relationship between the shot number from the first shot and the energy value for the first to fourth embodiments, each with different pre-excitation conditions. [Figure 9] This figure shows the relationship between the shot number from the first shot and the energy value for the fifth to eighth embodiments, in which the number of shots per unit time differs from one another. [Modes for carrying out the invention]

[0015] Below, a laser welding apparatus and laser welding method according to one embodiment will be described with reference to Figures 1 to 9. Figure 1 shows a suspension for a disc drive as an example of a workpiece 1 having multiple welds. Workpiece 1 includes a base plate 10 made of stainless steel, a first plate (load beam) 11, and a second plate (flexure) 12.

[0016] The first plate 11 and the second plate 12 are each made of springy stainless steel. The first plate 11 and the second plate 12 are fixed to each other by a plurality of welding parts 13. These welding parts 13 are formed by the laser welding apparatus 20 and the laser welding method described below.

[0017] The first plate 11 is made of stainless steel with a thickness of 200 μm or less. The thickness of the first plate 11 is greater than the thickness of the second plate 12. The second plate 12 is made of stainless steel with a thickness of 100 μm or less. An example of the thickness of the first plate 11 is 30 μm. An example of the thickness of the second plate 12 is 18 μm. A wiring part 15 is formed along one surface of the second plate 12. The wiring part 15 includes an insulating layer made of an insulating resin such as polyimide and a conductor made of copper.

[0018] The second plate 12 is made of the same metal as the first plate 11 (for example, austenitic stainless steel such as SUS304). The chemical composition of SUS304 is C: 0.08 or less, Si: 1.00 or less, Mn: 2.00 or less, Ni: 8.00 - 10.50, Cr: 18.00 - 20.00, and the balance is Fe.

[0019] FIG. 2 schematically shows the laser welding apparatus 20. The laser welding apparatus 20 has a function of sequentially welding a plurality of welding parts 13 of the workpiece 1 by laser light emitted in a pulsed manner. The laser welding apparatus 20 shown in FIG. 2 includes a workpiece support part 21 that supports a plurality of workpieces 1, a moving mechanism 22 that moves the workpiece support part 21, a laser irradiation apparatus 23, and a control part 24. The control part 24 includes an electrical configuration for controlling the moving mechanism 22 and the laser irradiation apparatus 23, software for control, a memory for storing control data, and the like.

[0020] With the first plate 11 and the second plate 12 of workpiece 1 stacked in the thickness direction, workpiece 1 is fixed to workpiece support 21 by a holding jig. The workpiece support 21 has the function of holding workpiece 1 on a predetermined welding stage 25. The welding stage 25 is located in a position corresponding to the laser irradiation device 23. An example of the workpiece support 21 is made of ceramic. If the workpiece support 21 is made of ceramic, it is possible to avoid the molten metal generated in the weld 13 adhering to the workpiece support 21.

[0021] As shown in Figure 2, multiple workpieces 1 are connected to each other by a frame member 1a at a predetermined pitch P1 in the direction of movement of the workpieces 1 (indicated by arrow M1). The movement mechanism 22 includes a guide member 26 along the direction of movement of the workpieces 1 and an actuator 27. An example of the actuator 27 is a servo motor electrically controlled by a control unit 24. The actuator 27 moves the workpiece support portion 21 in the direction along the guide member 26 via a force transmission mechanism such as a ball screw.

[0022] The moving mechanism 22 intermittently moves the workpiece 1, which is placed on the workpiece support 21, toward the welding stage 25 in the direction indicated by arrow M1 in Figure 2, at a pitch of P1. The workpiece 1 to be welded, which is placed on the workpiece support 21, can be stopped at the welding stage 25.

[0023] As shown in Figure 2, the laser irradiation device 23 has a laser head 31 equipped with a galvanometer scanner 30. The galvanometer scanner 30, which functions as a scanning mechanism, has the function of moving the focusing position of the laser beam emitted from the laser irradiation device 23 to the weld area 13 of the workpiece 1 that is to be welded while the workpiece is stationary. In other words, the focusing position of the laser optical system of the laser irradiation device 23 can be moved at high speed toward the weld area 13 by the scanning operation of the galvanometer scanner 30.

[0024] Figure 3 schematically shows the workpiece 1 and a part of the laser welding apparatus 20. The laser irradiation apparatus 23 shown in Figure 3 includes a laser oscillator 40, which is the source of the laser light, and an optical lens system 41. The lens system 41 has the function of focusing the laser light 42 output by the laser oscillator 40 and irradiating the welding area 13 of the workpiece 1 with increased energy density. An example of the laser welding apparatus 20 is a solid-state laser using a YAG (Yttrium Aluminum Garnet) rod. However, a gas laser such as a CO2 laser may be used as needed, or a semiconductor laser or fiber laser may be used.

[0025] Figure 4 schematically represents the laser oscillator 40. The laser oscillator 40, which functions as an optical resonator, includes a laser medium 50, an excitation light source 51, a high-reflectivity mirror 55, and a low-reflectivity mirror 56. The excitation light source 51 injects excitation energy into the laser medium 50 according to the supplied drive power. The high-reflectivity mirror 55 and the low-reflectivity mirror 56 are arranged facing each other. The control unit 24 supplies drive power to the excitation light source 51 for injecting excitation energy.

[0026] When power to generate laser light is supplied to the excitation light source 51, the excitation energy 57 emitted by the excitation light source 51 is injected into the laser medium 50. When the excitation energy 57 is injected into the laser medium 50, the light 60 emitted from the laser medium 50 resonates between the high-reflectivity mirror 55 and the low-reflectivity mirror 56 and is amplified.

[0027] When the energy of the amplified light 60 exceeds the energy loss of the laser medium 50, laser oscillation occurs, and laser light 42 is emitted from the low-reflectivity mirror 56. The energy injected into the laser medium 50 can be changed according to the power supplied to the excitation light source 51. An example of the wavelength of the laser oscillator 40 is 1.06 μm.

[0028] The laser welding method of this embodiment will be described below with reference to the time chart shown in Figure 5 and the flowcharts shown in Figures 6 and 7. In this specification, one irradiation of laser light for welding may be referred to as one shot.

[0029] In step ST1 in Figure 6, the workpiece 1 to be welded is moved toward the welding stage 25 by the moving mechanism 22 and stopped on the welding stage 25. While the workpiece 1 is moving in step ST1, or while the workpiece 1 is stopped on the welding stage 25, step ST2 is performed in which energy for pre-excitation is injected into the laser medium 50.

[0030] In step ST2, just before welding the first weld 13 to be welded, energy for pre-excitation is injected. Specifically, in step ST2, power (referred to as pre-excitation power Pw2) that is less than the driving power Pw1 (shown in Figure 5) that generates excitation energy in the laser medium 50 is supplied to the excitation light source 51 for a pre-supply time T2 that is longer than the pulse width T1 of the driving power Pw1. By step ST2, energy (referred to as pre-excitation energy) less than the excitation energy is injected into the laser medium 50.

[0031] Step ST2 may be performed while the workpiece 1 is moving toward the welding stage 25 in step ST1. That is, step ST2 functions as a means of supplying preliminary excitation power Pw2 to the excitation light source 51 while the workpiece 1 is moving toward the welding stage 25. In this way, step ST2 supplies preliminary excitation power Pw2, which is smaller than the drive power Pw1, to the excitation light source 51 for a preliminary supply time T2 that is longer than the pulse width T1, before welding the first weld to be welded.

[0032] In step ST3 shown in Figure 6, the scanning operation of the galvanoscanner 30 is controlled so that the laser beam emitted from the laser irradiation device 23 is focused towards the first (first shot) weld area of ​​the workpiece 1.

[0033] In step ST2, after the pre-supply time T2 (shown in Figure 5) has elapsed, a predetermined interval T3 (shown in Figure 5) is elapsed in step ST4 immediately before welding the first weld. The interval T3 is the same as or longer than the pulse width T1 of the drive power Pw1. Also, the interval T3 is shorter than the pre-supply time T2 and shorter than the pulse interval T4 of the drive power Pw1. Step ST4 functions as a means to allow the predetermined interval T3 to elapse before welding the first weld.

[0034] After the interval T3 has elapsed, in step ST5 shown in Figure 7, pulsed drive power Pw1 is supplied to the excitation light source 51, thereby injecting excitation energy into the laser medium 50. Due to the excitation energy injected into the laser medium 50, in step ST6, laser light for the first weld is emitted from the laser medium 50. In other words, step ST5 functions as a means of supplying drive power Pw1 to the excitation light source 51 while the workpiece 1 is stopped on the welding stage 25.

[0035] In step ST7, it is determined whether welding of all welds on a single workpiece has been completed. If welding of all welds has not been completed ("NO" in step ST7), the process proceeds to step ST8, where preparation for the second and subsequent welds begins.

[0036] In step ST8, the scanning operation of the galvanometer scanner 30 is controlled so that the laser beam output from the laser irradiation device 23 is focused towards the second and subsequent welds. Subsequently, steps ST5 and ST6 form the second and subsequent welds.

[0037] In step ST7, if it is determined that all welds on a single workpiece have been welded ("YES" in step ST7), the process proceeds to step ST9. In step ST9, it is determined whether or not welding of all workpieces has been completed.

[0038] If it is determined in step ST9 that welding of all workpieces is not yet complete ("NO" in step ST9), the process returns to step ST1 in Figure 6, and the next workpiece (the second and subsequent workpieces) moves to welding stage 25. The series of processes from step ST2 to step ST9 are then repeated, and the welding of the second and subsequent workpieces is performed. If the arrangement pitch of each workpiece is small, steps ST5 and ST6 may be repeated for the welding area of ​​the adjacent workpiece without returning to step ST1.

[0039] In this embodiment, a common drive power Pw1 is supplied to the excitation light source 51 for each of the multiple welds. However, the thickness and material of the welds may differ depending on the workpiece. In that case, the output (energy value) of the laser light may be adjusted by changing the magnitude of the drive power Pw1 according to the thickness and material of the workpiece.

[0040] Figure 8 shows the relationship between shot number and energy value for four examples (the first to fourth examples) in which experiments were conducted by varying the pre-excitation power Pw2 and pre-supply time T2. In Figure 8, "1" on the horizontal axis represents the first weld (the first weld). In all examples, the number of shots per second (number of welds) is 200, and the excitation energy (driving power) of each shot is 100W.

[0041] The black circles in Figure 8 represent the first embodiment, where the preliminary excitation power Pw2 is 30W and the preliminary supply time T2 is 10ms. The energy value of the first shot in the first embodiment was 0.0772J, and no decrease in energy was observed compared to the second shot and subsequent shots. As a result, welding defects were avoided in the first weld. In the first embodiment, a slight emission of laser light was observed when the preliminary excitation power Pw2 was applied, but it was not enough energy to melt the workpiece.

[0042] The white circles in Figure 8 represent the second embodiment, where the pre-excitation power Pw2 is 25W and the pre-supply time T2 is 10ms. The energy value of the first shot in the second embodiment was 0.0767J, and there was virtually no decrease in energy compared to the second shot and subsequent shots. As a result, welding defects in the first weld were avoided. In the second embodiment, no laser light emission was observed when the pre-excitation power Pw2 was applied.

[0043] The white triangle in Figure 8 represents the third embodiment, where the preliminary excitation power Pw2 is 20W and the preliminary supply time T2 is 10ms. The energy value of the first shot in the third embodiment was 0.0758J, and the energy drop in the first shot was larger compared to the second shot and subsequent shots. This caused a welding defect in the first weld.

[0044] The black square in Figure 8 represents the fourth embodiment, where the preliminary excitation power Pw2 is 30W and the preliminary supply time T2 is 5ms. The energy value of the first shot in the fourth embodiment was 0.07459J, which was significantly lower than the energy of the second and subsequent shots. This caused a welding defect in the first weld.

[0045] Figure 9 shows the relationship between shot number and energy value for four different examples (Examples 5 to 8) where welding is performed without pre-excitation energy, and the number of shots per unit time differs from one another. In Figure 9, "1" on the horizontal axis represents the first weld (the first weld). "PPS" is an abbreviation for Pulse per Second.

[0046] The black circles in Figure 9 represent the fifth embodiment, with 42 pulses per second. The energy value of the first shot in this fifth embodiment was 0.0600 J, and no decrease in energy was observed compared to the second and subsequent shots. In such low-speed pulse welding, the quality of the first weld is not a problem. However, the welding time per workpiece increases, which leads to a decrease in production efficiency.

[0047] The white triangle in Figure 9 represents the sixth embodiment, where the pulse rate is 100 pulses per second. The energy value of the first shot in this sixth embodiment was 0.0599 J, showing a decrease in energy compared to the second and subsequent shots. Therefore, the quality of the first weld may be problematic.

[0048] The white square in Figure 9 represents the seventh embodiment, with a pulse rate of 200 pulses per second. The energy value of the first shot in this seventh embodiment was 0.0598 J, showing a decrease in energy compared to the second and subsequent shots. Therefore, the quality of the first weld may be problematic.

[0049] The white circle in Figure 9 represents the eighth embodiment, with a pulse rate of 500 pulses per second. The energy value of the first shot in this eighth embodiment was 0.0582 J, which is a significant decrease in energy compared to the second and subsequent shots. As a result, the quality of the first weld in the eighth embodiment deteriorated.

[0050] As described above, in the case of high-speed pulse welding with more than 100 shots per second, the decrease in the energy value of the first shot becomes a problem. High-speed pulse welding has the advantage of being able to weld many parts in a relatively short time and having high productivity, but on the other hand, the quality of the first weld becomes a problem.

[0051] From the above, it was found that in high-speed pulse welding with 100 or more shots per second, supplying a pre-excitation power Pw2 of 25W or more to the excitation light source 51 with a pre-supply time T2 of 10ms or more is effective in preventing welding defects in the first weld without reducing the efficiency of laser welding.

[0052] It goes without saying that when implementing the present invention, the specific configurations of the laser irradiation device, control unit, workpiece support unit, etc., can be modified in various ways. Furthermore, the present invention can also be applied to welding workpieces other than suspensions for disk devices. [Explanation of symbols]

[0053] 1...Workpiece, 11...First plate, 12...Second plate, 13...Welding area, 20...Laser welding device, 21...Workpiece support, 22...Moving mechanism, 23...Laser irradiation device, 24...Control unit, 25...Welding stage, 30...Galvanometer scanner, 31...Laser head, 40...Laser oscillator, 42...Laser light, 50...Laser medium, 51...Excitation light source, Pw1...Drive power, Pw2...Pre-excitation power, T1...Pulse width, T2...Pre-supply time, T3...Interval, T4...Pulse interval.

Claims

1. A laser welding apparatus that welds multiple weld points on a workpiece using laser light, A laser medium that emits the laser light for the weld when excitation energy is injected, An excitation light source that injects the excitation energy into the laser medium while driving power is supplied, The system includes a control unit that supplies the driving power for the excitation energy to the excitation light source, The control unit, Before welding the first of the multiple welds to be welded, Means for injecting energy for pre-excitation into the laser medium by supplying pre-excitation power of 25 W or more to the excitation light source for a pre-supply time of 10 ms or more, Means for allowing a predetermined interval to elapse after the pre-excitation and before welding the first weld portion, A means for welding the first weld by supplying the driving power to the excitation light source after the interval has elapsed, A laser welding apparatus characterized by being equipped with the following.

2. In the laser welding apparatus according to claim 1, A laser welding apparatus having a pre-excitation power of 30 W or more.

3. In the laser welding apparatus according to claim 1, A laser welding apparatus in which the interval is greater than or equal to the pulse width of the drive power, and the interval is shorter than the pre-supply time.

4. In the laser welding apparatus according to claim 1, The control unit performs high-speed pulse welding with a shot count of 100 or more per second.

5. A laser welding method that welds the welded part of a workpiece using laser light, Before welding the aforementioned weld, a pre-excitation power of 25 W or more is supplied to the excitation light source for a pre-excitation period of 10 ms or more, thereby injecting energy into the laser medium that is strong enough to pre-excite the workpiece without melting it. After the preliminary excitation is performed, a predetermined interval is allowed to pass. A laser welding method characterized by supplying driving power for welding to the excitation light source after the interval has elapsed, thereby injecting excitation energy into the laser medium, and welding the welded portion by emitting the laser light from the laser medium.

6. In the laser welding method according to claim 5, A laser welding method in which the aforementioned pre-excitation power is 30 W or more.

7. In the laser welding method according to claim 5, A laser welding method wherein the interval is greater than or equal to the pulse width of the drive power, and the interval is shorter than the pre-supply time.

8. In the laser welding method according to claim 5, A laser welding method that performs high-speed pulse welding with a number of shots per second of 100 or more after the aforementioned interval has elapsed.

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