JP4927659B2 - Laser welding method - Google Patents

Description

  The present invention provides laser welding in which spot welds are sequentially formed along a planned welding region set on a workpiece by irradiating a plurality of workpieces superimposed on each other with a laser beam for a predetermined time. Regarding the method.

As a conventional laser welding method, plasma light generated on a workpiece by laser irradiation during welding is detected by a plasma light sensor, and it is determined whether or not a welding abnormality due to a gap abnormality has occurred at the weld formation position. There is something to do (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2002-210575

  However, when it is determined after forming the welded portion whether or not there is a gap abnormality at the welded portion forming position as in the laser welding method described above, the following problems may occur. That is, when a laser beam is irradiated to a place where a gap abnormality has occurred, it is conceivable that the melted portion of the work piece penetrates into the gap and acts to further widen the gap. If welding is continued with such a phenomenon left unattended, the gap amount may gradually increase as the welding position advances to a new weld formation position. Therefore, it is difficult to ensure the yield of the joined body by the method of performing the gap abnormality determination after welding as in the laser welding method described above.

  The present invention has been made to solve such a problem, and a laser welding method capable of improving the yield of a joined body when spot-like welds are sequentially formed along a planned welding region. The purpose is to provide.

  In order to solve the above-described problem, a laser welding method according to the present invention irradiates a plurality of stacked workpieces with a laser beam for a predetermined time, thereby along a planned welding region set on the workpieces. A laser welding method for sequentially forming spot-like welds, wherein a predetermined determination reference time is set between the irradiation start time and the irradiation end time of the laser beam, and between the irradiation start time and the determination reference time. Irradiating the workpiece with the laser beam, and detecting the vibration propagated in the workpiece by the irradiation of the laser beam with the vibration detecting means, and obtaining the output value output from the vibration detecting means at the determination reference time. A step of determining the presence or absence of a gap abnormality between workpieces by comparing a determination value calculated based on a predetermined threshold value, The Most When determining continues the irradiation of the laser beam to the irradiation end time, when it is determined that the gap abnormality is present, and wherein the interruption in the determination reference time irradiation of the laser beam.

  According to such a laser welding method, whether or not there is a gap abnormality is determined at the determination reference time set between the irradiation start time and the irradiation end time of the laser beam. The laser beam irradiation is interrupted at the determination reference time without performing the irradiation end time. Therefore, even if a gap abnormality occurs at the weld formation position, it is possible to suppress the penetration of the work piece from entering the gap. Accordingly, even when the welded portions are sequentially formed along the planned welding region, it is possible to prevent the gap between the workpieces from expanding and improve the yield of the joined body.

  Moreover, it is preferable that the determination reference time is set to a time after the penetration due to laser beam irradiation at the time of forming the weld reaches the back side of the workpiece on the laser beam irradiation side. The inventors of the present invention have a clear difference in the output value of the vibration detection means between when the gap abnormality is present and when there is no gap, when the penetration due to the laser beam irradiation reaches the back side of the workpiece on the irradiation side. It has been found that this occurs, and by setting the determination reference time after such a time, the accuracy of the determination of the gap abnormality can be improved. Furthermore, even if there is a gap abnormality, it is possible to determine the presence or absence of a gap before the work piece penetrates into the gap and acts to further widen the gap. Even when the welds are sequentially formed along the region, the gap between the workpieces can be prevented from expanding and the yield of the joined body can be improved.

  In addition, when it is determined that there is a gap abnormality, the laser beam irradiation is continued from the determination reference time to the irradiation end time while applying pressure to the work pieces so that the work pieces are pressed against each other by the pressure applying means. It is preferable to do. In this case, for the weld formation position where the gap abnormality has occurred, the laser beam irradiation is temporarily interrupted at the determination reference time without performing the irradiation end time, and the gap abnormality between the workpieces is caused by the pressure applying means. It is possible to irradiate the laser beam again in a state of eliminating the above. As a result, the gap between the workpieces can be prevented from widening, and the yield of the joined body can be improved. Furthermore, since the gap can be quickly narrowed when a gap abnormality is detected, welding work efficiency can be improved.

  In addition, when it is determined that there is a gap abnormality, it is preferable that the laser beam irradiation is interrupted at the determination reference time, and the laser beam irradiation position is moved to the next welded portion formation position. In this case, even if a gap abnormality has occurred at the predetermined weld formation position, it is possible to move to the next weld formation position without interrupting the welding operation for the operation to eliminate the gap abnormality. Workability can be improved. Furthermore, about the welding part formation position where the gap abnormality has occurred, the penetration of the laser beam is interrupted at the determination reference time, thereby suppressing the penetration of the work piece into the gap. For this reason, even if the work for eliminating the gap abnormality is not performed, the gap between the workpieces can be prevented from being widened, and thereby the yield of the joined body can be ensured.

  Moreover, it is preferable to further include a step of storing the determination result of the presence / absence of the gap abnormality in the information storage means in association with the weld formation position. In this case, by using the information stored in the information storage means, for example, after the welding operation is completed once, the weld formation position where the gap abnormality has occurred is specified, and only at the weld formation position again. A laser beam can be irradiated. Furthermore, the number of such weld formation positions can be counted, and the laser beam can be irradiated again only when the number exceeds a predetermined value. Furthermore, the traceability of the product using the joined body can be ensured by maintaining the determination result of the presence or absence of a gap abnormality at each weld formation position for the joined body.

  ADVANTAGE OF THE INVENTION According to this invention, when forming a spot-like welding part sequentially along a welding plan area | region, it can prevent that the gap between workpieces expands and can improve the yield of a joined body. .

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, terms such as “upper” and “lower” are based on the state shown in the drawings and are for convenience.

  FIG. 1 is a schematic view showing a laser welding system according to an embodiment of the present invention. As shown in FIG. 1, a laser welding system 1 includes, for example, an outer panel and a bone member (hereinafter referred to as “workpieces (workpieces) 10A and 10B”) used in a railway vehicle structure, which are overlapped by a laser beam. It is constructed as a system for welding (hereinafter simply referred to as “laser welding”). The laser welding system 1 includes a laser welding device 2 that forms a spot-like welded portion on the workpieces 10A and 10B by irradiating a laser beam, and a control device 3 that performs control related to laser welding. In the following description, the case where the welds W1 to Wn are sequentially formed along the planned welding region R set linearly in the substantially central portion viewed from the laser irradiation direction in the workpieces 10A and 10B will be exemplified. Further, in the workpieces 10A and 10B, positions where the welded portions W1 to Wn are formed are referred to as welded portion forming positions N1 to Nn, respectively.

  The laser welding apparatus 2 includes a feeding device 21, a laser beam irradiation device 22, a gas supply device 23, and a guide device (pressure applying means) 24. These devices 21 to 24 are connected to the control device 3 and automatically execute each operation in accordance with the operation instruction information output from the control device 3.

  The feeding device 21 is a device that scans the irradiation positions of the laser beams on the workpieces 10A and 10B, and includes a movable stage 27 on which the workpieces 10A and 10B can be placed. When the feeding device 21 receives the operation instruction information for instructing the start of scanning from the control device 3, the feeding device 21 scans the movable stage 27 along the planned welding region R. Thus, the workpieces 10A and 10B placed on the movable stage 27 move relative to the irradiation position of the laser beam by the laser head 28 along the planned welding region R.

  The laser beam irradiation device 22 is a device that irradiates a laser beam toward the planned welding region R of the workpieces 10A and 10B. The laser beam irradiation device 22 has a laser head 28 disposed above the workpieces 10A and 10B. When receiving the operation instruction information for instructing the start of irradiation from the control device 3, the laser beam irradiation device 22 emits a YAG laser having a wavelength of, for example, 1.06 μm and an output of about 4.0 kW from the tip of the laser head 28.

  The gas supply device 23 is a device that supplies assist gas to the planned welding region R of the workpieces 10A and 10B, and has a supply nozzle 29 that is arranged to be inclined at about 45 degrees with respect to the workpieces 10A and 10B. ing. When the gas supply device 23 receives the operation instruction information for instructing the start of supply from the control device 3 during the operation of the laser beam irradiation device 22, the irradiation position of the laser beam on the workpieces 10 </ b> A and 10 </ b> B (hereinafter, “ Assist gas is supplied to the processing point). As the assist gas, helium gas, argon gas, or the like is used for the purpose of preventing oxidation and sputtering of the workpieces 10A and 10B.

  The guide device 24 is a device that applies pressure to the workpiece 10A and presses it against the workpiece 10B. The guide device 24 is attached to the guide roller support portion 31 attached to the side surface of the laser head 28 and the lower end portion of the guide roller support portion 31. The guide roller 32 is provided. When the guide device 24 receives the operation instruction information instructing the start of pressing from the control device 3, the guide device 24 moves the guide roller support portion 31 downward and presses the surface of the workpiece 10 </ b> A with the guide roller 32. Accordingly, the workpiece 10A is pressed against the workpiece 10B in the vicinity of the machining point.

  On the other hand, the control device 3 is physically a computer system including a CPU, a memory, a communication interface, an information storage unit such as a hard disk, a display unit such as a display, and the like. An AE (Acoustic Emission) sensor (vibration detecting means) 26 is connected to the control device 3.

  This AE sensor 26 measures the vibration strength of the elastic wave generated along with the melt solidification phenomenon at the processing points when forming the welded portions W1 to Wn on the workpieces 10A and 10B. In the workpiece 10B, an area that does not overlap the workpiece 10A is formed on one end side in the scanning direction of the movable stage 27, and the AE sensor 26 is disposed on the upper surface side of the area. The AE sensor 26 outputs an output signal corresponding to the vibration intensity of the elastic wave propagated from the workpiece 10 </ b> A into the workpiece 10 </ b> B to the gap abnormality determination unit 37 described later in the control device 3 at the time of laser beam irradiation.

  The control device 3 includes, as functional components, a laser beam irradiation control unit 33, a movement control unit 34, an applied pressure control unit 36, a gap abnormality determination unit 37, and an information storage unit (information storage unit) 38. And have. The laser beam irradiation control unit 33 sends operation instruction information to the laser beam irradiation apparatus 22 at predetermined intervals so that the laser beam is irradiated in pulses from the irradiation start time to the irradiation end time during welding. Output. When the laser beam irradiation control unit 33 receives determination result information indicating that there is a gap abnormality between the workpieces 10A and 10B from the gap abnormality determination unit 37 in the process of irradiating the laser beam for one pulse. When the operation instruction information for interrupting the laser beam irradiation from the laser beam irradiation device 22 is output at that time and the determination result information indicating that there is no gap abnormality is received, the laser beam irradiation is performed until the irradiation end time. The operation instruction information to continue is output.

  The movement control unit 34 moves the movable stage 27 at a constant speed during welding, and welds W1 along the planned welding region R of the workpieces 10A and 10B by a laser beam irradiated with pulses from the laser head 28 at a predetermined interval. The operation command information is output to the feeding device 21 so that .about.Wn is formed at equal intervals.

  When the application pressure control unit 36 receives determination result information indicating that there is a gap abnormality at the weld formation position Ni from the gap abnormality determination unit 37, the application pressure control unit 36 provides operation instruction information for moving the guide roller support unit 31 downward. Output to the guide device 24. When the determination result information indicating that there is no gap abnormality is received, no operation instruction information is output to the guide device 24.

  The gap abnormality determination unit 37 receives an output value (output signal) from the AE sensor 26, and determines whether or not there is a gap abnormality between the workpieces 10A and 10B based on the output value. Specifically, the gap abnormality determination unit 37 is a cumulative sum of squares of output values from the AE sensor 26 from the laser beam irradiation start time to the preset determination reference time for forming one spot weld. Is calculated as a determination value at the determination reference time. Then, at the determination reference time, the gap abnormality determination unit 37 compares the calculated determination value with a preset threshold value, and determines that there is no gap abnormality when the determination value is equal to or greater than the threshold value. If it is lower than that, it is determined that there is a gap abnormality. The gap abnormality determination unit 37 outputs determination result information indicating that there is a gap abnormality or determination result information indicating that there is no gap abnormality to the laser beam irradiation control unit 33 and the applied pressure control unit 36. A detailed description of the determination reference time and the threshold value to be set will be described later.

  Further, the gap abnormality determination unit 37 generates a determination result table for the presence or absence of a gap abnormality at the weld formation positions N1 to Nn, and outputs the determination result table to the information storage unit 38. FIG. 2 is a diagram illustrating an example of a determination result table stored in the information storage unit 38. As shown in FIG. 2, the information storage unit 38 includes a determination result table that associates the weld formation position Ni and the determination result of the gap abnormality of the weld Wi formed at the weld formation position Ni. Yes. In the example shown in FIG. 2, the gap abnormality is “present” at the weld formation position “N1”, the gap abnormality is “absent” at the weld formation positions “N2” and “N3”, and the gap is present at the weld formation position “Nn”. Abnormality is “Yes”. In addition, the information storage unit 38 stores a preset reference time and threshold value for each product number of the workpieces 10A and 10B.

  Next, a first operation mode of the laser welding system 1 having the above-described configuration will be described with reference to FIG. FIG. 3 is a flowchart showing a first operation mode of the laser welding system 1.

  In the laser welding system 1, first, laser welding for setting a determination reference time is performed on the workpieces 10A and 10B (hereinafter referred to as “workpieces 10A and 10B for setting a determination reference time”). Is set in advance. Specifically, the following operations are performed.

  First, the workpieces 10A and 10B for setting the reference time are placed on the movable stage 25. Subsequently, the operation instruction information is output from the control device 3 to each of the feeding device 21, the laser beam irradiation device 22, and the gas supply device 23, and workpiece feeding, laser irradiation, and supply of assist gas are started.

  From the laser head 28, the laser beam is irradiated with pulses at a predetermined interval, and at the same time, the movable stage 27 is scanned in the direction of arrow A (see FIG. 1) at a speed of about 10 m / min. As a result, the welded portions W1 to Wn having a substantially circular planar shape are sequentially formed at predetermined intervals at the welded portion forming positions N1 to Nn of the workpieces 10A and 10B for setting the reference time (laser welding for setting the reference time). : S100). Here, it is assumed that the pulse width of the laser beam, that is, the laser beam irradiation time with respect to one weld formation position differs for each weld formation position. For example, the pulse width is 20 ms for the weld formation position N1, the pulse width is 40 ms for the weld formation position N2, the pulse width is 60 ms for the weld formation position N3, and the weld formation position Nn. As the pulse width n (ms), every time the weld formation position advances, the pulse width of the laser beam irradiated thereto is increased by 20 ms. Accordingly, the depths of penetration of the welds W1 to Wn are different.

  While the laser beam is radiated from the laser head 28 to the workpieces 10A and 10B, the AE sensor 26 generates vibrations of the elastic waves generated at and near the machining point in the workpiece 10A and propagated through the workpiece 10B. The intensity is detected, and the voltage is output to the gap abnormality determination unit 37 as an output value. The gap abnormality determination unit 37 calculates a cumulative sum of squares of output values from the laser beam irradiation start time per pulse to a predetermined time, and acquires the value as a determination value at the predetermined time.

  Here, FIG. 4 is a diagram plotting the determination values at a predetermined time when the two types of workpieces 10A and 10B are irradiated with a laser beam having a pulse width of Xms. The horizontal axis of the diagram in FIG. 4 indicates a predetermined time from the laser beam irradiation start time Ts (= 0 ms) to the irradiation end time Te (= Xms), and the vertical axis indicates a determination value at the predetermined time. . As shown in FIG. 4, for one workpiece 10 </ b> A, 10 </ b> B, as shown in graph C, the determination value increased with a substantially constant slope. On the other hand, in the other workpieces 10A and 10B, as shown in the graph G, the gradient of the determination value graph decreases at the time T3, and the determination value at a predetermined time is smaller than the determination value in the graph C. It was.

  Regarding the above results, the present inventors have found that the decrease in the slope of the graph G at time T3 is based on the gap amount between the workpieces 10A and 10B in the course of intensive research. FIG. 5 is a cross-sectional view showing how the spot weld is formed when there is no gap abnormality, and FIG. 6 is a cross-sectional view showing how the spot weld is formed when there is a gap abnormality. The relationship between the gap amount and the determination value will be described with reference to FIGS.

  First, the formation of a spot weld when there is no gap abnormality will be described. 5A, 5B, 5C, and 5D are cross-sectional views showing states at times T1, T2, T3, and T4, respectively. As shown in FIGS. 5A and 5B, at times T1 and T2, the penetration portion M does not reach the workpiece 10B and is formed only on the workpiece 10A side. Then, the penetration portion M reaches the back side of the workpiece 10A at time T3 as shown in FIG. 5C, and proceeds to the workpiece 10B side at time T4 as shown in FIG. 5D.

  Next, formation of a spot weld when there is a gap abnormality will be described. 6A, 6B, 6C, and 6D are cross-sectional views showing states at times T1, T2, T3, and T4, respectively. As shown in FIGS. 6A and 6B, at times T1 and T2, the penetration portion M does not reach the workpiece 10B and is formed only on the workpiece 10A side. And the penetration part M reaches | attains the back surface side of the workpiece | work 10A at the time T3, as shown in FIG.6 (c). Here, since a gap is formed between the workpieces 10A and 10B, as shown in FIG. 6 (d), at time T4, before the workpiece 10B starts to melt, the penetration portion M is a gap between the workpieces 10A and 10B. Invade inside.

  The relationship between the gap amount between the workpieces 10A and 10B and the change amount of the determination value can be explained for the following reason. That is, when the penetration portion M is traveling only in the workpiece 10A, there is no difference in the volume of the workpiece newly melted by laser beam irradiation regardless of whether there is a gap abnormality. There is no difference in the vibration intensity of the elastic wave generated in the vicinity, and there is almost no difference in the output value of the AE sensor 26. However, after the penetration part M has advanced to the back side of the workpiece 10A, when there is no gap abnormality, the workpiece 10A and the workpiece 10B are melted together, so the volume of the workpiece to be newly melted Increases at a substantially constant rate, but if there is a gap abnormality, the penetration portion M does not reach the workpiece 10B side only if it penetrates into the gap, or even if it reaches, the amount is small. Therefore, the volume of the newly melted workpiece becomes smaller than that when there is no gap abnormality. Therefore, a difference occurs in the vibration intensity of the elastic wave accompanying the melting and solidification phenomenon due to the difference in the volume of the newly melted workpiece. As a result, a difference occurs in the output value of the AE sensor.

  Considering the above, the time when the judgment value is different due to the influence of the gap abnormality, that is, the time after the time T3 when the penetration portion M reaches the back side of the workpiece 10A after starting the irradiation of the laser beam. If the time T3 ′ is set as the determination reference time, it is considered possible to determine whether there is a gap abnormality between the workpieces 10A and 10B.

  Returning to FIG. 3, when setting the determination reference time, a welding part having a welding bead slightly extending on the back side of the workpiece 10 </ b> A is selected from the welding parts W <b> 1 to Wn, and the pulse width for the selected welding part Wi is selected. refer. Then, the time after the irradiation end time (T3 in FIG. 4) at that time is determined to be the determination reference time Td (T3 ′ in FIG. 4), stored in the information storage unit 38, and set as the determination reference time Td. (S105).

  After the determination reference time Td is set, laser welding for threshold setting is performed on workpieces 10A and 10B (hereinafter referred to as “threshold setting workpieces 10A and 10B”) for which there is no gap abnormality. Set. Specifically, the pulse width of the laser beam is set to a predetermined width, and the welded portions W1 to Wn are sequentially formed at the welded portion forming positions N1 to Nn in the same manner as the laser welding for setting the determination reference time (threshold value). Laser welding for setting: S110), the gap abnormality determination unit 37 acquires the determination value at the determination reference time Td for each of the welded portions W1 to Wn. Then, the operator refers to the determination value acquired by the gap abnormality determination unit 37 on a monitor or the like, determines that a determination value equal to or greater than a certain value among these determination values is a threshold value, and stores the determined determination value as information Stored in the unit 38 and set as a threshold (S115).

  In the present embodiment, SUS304 materials having a plate thickness of 0.8 mm and 1.5 mm are used as the workpieces 10A and 10B, respectively, and the output of the laser beam is 4 kW. In such a condition, since the melted portion reaches the back side of the workpiece 10A about 15 ms after the start of laser beam irradiation, the determination reference time Td can be set to 15 ms. Further, the threshold value at this time can be set to 225.

  After setting the threshold, laser welding to be determined is performed on the workpieces 10A and 10B. FIG. 7 is a diagram illustrating an example of a pulse waveform of a laser beam applied to the workpieces 10A and 10B for determination. The laser beam is irradiated in a pulse form from the irradiation start time Ts to the irradiation end time Te, whereby one welded portion Wi is formed on the workpieces 10A and 10B. As shown in FIG. 7, the laser beam irradiation start time Ts is set to 0 ms, and the irradiation end time Te is set to 60 ms. Then, a determination reference time Td, which is a time for determining whether or not there is a gap abnormality, is set to 15 ms that is a value stored in the information storage unit 38.

  First, in the same manner as the laser welding described above, a laser beam is applied to the weld formation position N1 of the determination workpieces 10A and 10B (determination target laser irradiation). While the laser beam is being irradiated, the AE sensor 26 detects the vibration intensity of the elastic wave generated at and near the processing point during welding and propagating through the workpiece 10B, and a gap abnormality of the control device 3 is detected. It outputs to the determination part 37.

  When the irradiation time of the laser beam reaches the determination reference time Td, the gap abnormality determination unit 37 calculates the cumulative sum of squares of output values from the AE sensor 26 from the irradiation start time Ts to the determination reference time Td. A determination value at the determination time Td is acquired (S125).

  Subsequently, the gap abnormality determination unit 37 compares the determination value acquired by calculation with the threshold acquired from the information storage unit 38 to determine whether there is a gap abnormality at the weld formation position N1, and acquires determination result information. . Specifically, the gap abnormality determination unit 37 determines that there is no gap abnormality when the determination value is greater than or equal to the threshold value, and determines that there is a gap abnormality when the determination value is below (S130). And if the gap abnormality determination part 37 acquires the determination result information in the welding part formation position N1, it will be stored in a determination result table whether a gap abnormality exists in the welding part formation position N1 (S135).

  The laser beam irradiation control unit 33 and the applied pressure control unit 36 receive the above determination result information from the gap abnormality determination unit 37 and refer to the contents (S140). If it is determined that there is no gap abnormality, the laser beam irradiation control unit 33 continues the laser beam irradiation from the laser beam irradiation device 22 until the irradiation end time Te (S145). At this time, the applied pressure control unit 36 does not output operation instruction information to the guide device 24 in particular, so that the pressure of pressing the guide roller 32 against the surface of the workpiece 10A is kept constant.

  On the other hand, if it is determined in step S140 that there is a gap abnormality, the laser beam irradiation control unit 33 interrupts the laser beam irradiation from the laser beam irradiation device 22 at the determination reference time Td (S150). Thereafter, the application pressure control unit 36 moves the guide roller support unit 31 downward, thereby pressing the surface of the workpiece 10A with the guide roller 32 to narrow the gap between the workpieces 10A and 10B (S155). The laser beam irradiation control unit 33 continues the irradiation of the laser beam from the laser beam irradiation device 22 until the irradiation end time Te in a state in which the gap abnormality is eliminated by applying such pressure (S145).

  Thereafter, the laser beam irradiation control unit 33 determines whether or not the laser welding is completed in the determination workpieces 10A and 10B, that is, whether or not all of the welded portions W1 to Wn are formed (S160). It is determined that the laser welding has not been completed at the time when the welded portion W1 is formed, and the laser welding system 1 repeatedly performs the processes of steps S120 to S160 for the next welded portion formation position N2. After the same processing is sequentially performed for the weld formation positions N3 to Nn, the laser beam irradiation control unit 33 determines that the laser welding has been completed, and the operation of the laser welding system 1 ends.

  As described above, according to the laser welding method according to the present embodiment, the abnormality of the gap between the workpieces 10A and 10B at the determination reference time Td set between the laser beam irradiation start time Ts and the irradiation end time Te. When it is determined whether there is a gap abnormality, the laser beam irradiation is interrupted at the determination reference time Td without performing the irradiation end time Te. Therefore, even if a gap abnormality occurs at the weld formation position Ni, the presence or absence of the gap is confirmed before the penetration portion by laser beam irradiation penetrates into the gap and acts to further widen the gap. Since it can determine, it can suppress that the penetration part by irradiation of a laser beam protrudes in a gap. Accordingly, even when the welded portions W1 to Wn are sequentially formed along the planned welding region R, it is possible to prevent the gap between the workpieces 10A and 10B from expanding and to improve the yield of the joined body. Can do.

  Further, in this laser welding method, the determination of the gap abnormality is made accurate by setting the determination reference time Td at a time after the penetration portion by laser beam irradiation reaches the back side of the workpiece 10A.

  In this laser welding method, when it is determined that there is a gap abnormality, the pressure is applied to the workpiece 10A so that the workpieces 10A and 10B are pressed against each other by the guide roller 32 of the guide device 24, and from the determination reference time Td. The laser beam irradiation is continued until the irradiation end time Te. In this case, the weld formation position Ni where the gap abnormality has occurred is temporarily interrupted at the determination reference time Td without performing the laser beam irradiation until the irradiation end time Te, and the workpiece is detected by the guide roller 32 of the guide device 24. The laser beam can be irradiated again with the gap abnormality between 10A and 10B eliminated. As a result, the gap between the workpieces 10A and 10B can be prevented from widening, and the yield of the joined body can be improved. Furthermore, since the gap can be quickly narrowed when a gap abnormality is detected, welding work efficiency can be improved.

  Next, a second operation mode by the laser welding system 1 will be described with reference to FIG. FIG. 8 is a flowchart showing a second operation mode of the laser welding system 1. This second operation form is a modification of the first operation form described above. As shown in FIG. 8, the operation form when it is determined in step S140 that there is no gap abnormality is the first operation form. It differs from the form. Note that the second operation mode is the same as the first operation mode with respect to the operation mode from step S100 to step S135 and the operation mode when it is determined in step S140 that there is no gap abnormality.

  That is, if it is determined in step S140 that there is a gap abnormality, the laser beam irradiation control unit 33 interrupts the laser beam irradiation from the laser beam irradiation device 22 at the determination reference time Td (S150). Thereafter, without executing the process of narrowing the gap between the workpieces 10A and 10B (step S155 in FIG. 3) and the process of continuing the irradiation of the laser beam from the laser beam irradiation device 22 until the irradiation end time Te (S145), The laser beam irradiation control unit 33 determines whether or not the laser welding is completed in the determination workpieces 10A and 10B, that is, whether or not all of the welded portions W1 to Wn are formed (S160). For example, when it is determined that laser welding is not completed at the weld formation position Ni, the laser welding system 1 repeats the processes of steps S120 to S160 for the next weld formation position, and laser welding is completed. If it is determined that the laser welding system 1 has been operated, the operation of the laser welding system 1 ends.

  As described above, in the second operation mode, after the laser beam irradiation is interrupted at the determination reference time Td in step 150, the next welding is performed without further laser beam irradiation on the weld formation position Ni. It moves to the part formation position Ni + 1 or the operation is finished.

  According to this mode of operation, even if a gap abnormality has occurred in the weld formation position Ni, the operation moves to the next weld formation position Ni + 1 without interrupting the welding operation to eliminate the gap abnormality. Therefore, workability can be improved. Further, for the weld formation position Ni where the gap abnormality has occurred, the laser beam irradiation is interrupted at the judgment reference time Td, thereby preventing the penetration due to the laser beam irradiation from escaping into the gap. Therefore, even if the work for eliminating the gap abnormality is not performed, the expansion of the gap between the workpieces 10A and 10B can be suppressed, and thereby the yield of the joined body can be ensured.

  Further, in this laser welding method, by using the determination result table stored in the information storage unit 38, for example, after the welding operation is once completed, the weld formation position Ni where the gap abnormality has occurred is specified. The laser beam can be irradiated again only on the weld formation position Ni. Furthermore, the number of such weld formation positions Ni is counted, and the laser beam can be irradiated again only when it exceeds a predetermined numerical value. Furthermore, the traceability of the product using the joined body can be ensured by holding the judgment result table on whether or not there is a gap abnormality at each welded portion forming position N1 to Nn for the joined body.

  The present invention is not limited to the above embodiment. For example, in setting the determination reference time, the welded portions W1 to Wn that have slightly welded beads on the back side of the workpiece 10A are selected, but immediately before the weld beads reach the backside of the workpiece 10A. You may choose one.

It is the schematic which shows the laser welding system which concerns on one Embodiment of this invention. It is a figure which shows an example of the determination result table memorize | stored in an information storage part. It is a flowchart which shows the 1st operation | movement form of a laser welding system. It is the diagram which plotted the judgment value in the predetermined time when irradiating the laser beam of the pulse width Xms with respect to two types of workpiece | work. It is sectional drawing which shows the mode of formation of the spot weld part when there is no gap abnormality. It is sectional drawing which shows the mode of formation of the spot welding part when there exists gap abnormality. It is a diagram which shows an example of the pulse waveform of the laser beam irradiated to the workpiece | work for determination. 4 is a flowchart showing a second operation mode of the laser welding system 1.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10A, 10B ... Workpiece | work (workpiece), 24 ... Guide apparatus (pressure provision means), 26 ... AE sensor (vibration detection means), 38 ... Information storage part (information storage means), Ts ... Irradiation start time, Td ... Judgment reference time, Te ... irradiation end time, R ... welding planned area, N1 to Nn ... welding part forming position, W1 to Wn ... welding part.

Claims (5)

A laser welding method in which spot welds are sequentially formed along a planned welding area set on a workpiece by irradiating a plurality of workpieces superimposed on each other with a laser beam for a predetermined time. There,
A predetermined determination reference time is set between the irradiation start time and the irradiation end time of the laser beam,
Between the irradiation start time and the determination reference time, the workpiece is irradiated with the laser beam, and vibrations propagated in the workpiece by the irradiation of the laser beam are detected by a vibration detection means. ,
At the determination reference time, the determination value calculated based on the output value output from the vibration detection means is compared with a predetermined threshold value to determine whether there is a gap abnormality between the workpieces. A step of judging,
When it is determined that there is no gap abnormality, the laser beam irradiation is continued until the irradiation end time, and when it is determined that there is a gap abnormality, the laser beam irradiation is interrupted at the determination reference time. A laser welding method characterized by the above.   The determination reference time is set to a time after the time when the penetration due to the laser beam irradiation when forming the weld reaches the back side of the workpiece on the laser beam irradiation side. The laser welding method according to claim 1.   When it is determined that there is a gap abnormality, the laser beam from the determination reference time to the irradiation end time while applying pressure to the workpiece so that the workpieces are pressed against each other by pressure applying means The laser welding method according to claim 1, wherein the irradiation is continued.   2. The laser beam irradiation is interrupted at the determination reference time when it is determined that the gap abnormality is present, and the laser beam irradiation position is moved to the next weld formation position. Or the laser welding method of 2.   5. The laser welding method according to claim 1, further comprising a step of storing the determination result of the presence or absence of the abnormality of the gap in an information storage unit in association with a weld formation position.

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