JP2009154186A - Laser welding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser welding method capable of improving the appearance of a workpiece to be welded by suppressing formation of an oxide film on the surface of a weld part. <P>SOLUTION: The laser welding method is used for forming a penetration weld part 32 in a workpiece 23 by radiation of a laser beam L. The workpiece 23 is placed on a stage 24 having a groove 27 formed corresponding to a planned weld region R. The laser welding method includes: a first step S101 of forming a space 28, which is provided with at least one opening 28a, by a workpiece rear side 23b and the groove 27; and a second step S105 of irradiating the planned weld region R with a laser beam L from the side of a workpiece surface side 23a while making an assist gas flow in the space 28 through the opening 28a such that one end part 32b of the penetration weld part is projected into the space 28. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laser welding method.

When laser welding is performed on a workpiece, a convex bead is generated at the welded portion. For this reason, if the workpiece subjected to laser welding is used as it is for the outer plate of a railway vehicle structure or the like, the welded part is conspicuous with respect to other parts, and the appearance of the entire structure may be impaired. Therefore, as a technique for controlling the shape of the bead, for example, in Patent Document 1, the amount of bead protrusion is controlled by blowing gas at an appropriate flow rate from the back bead side of the through-weld portion of the workpiece.
JP-A-6-210479

  By the way, in laser welding, the molten metal reacts with oxygen in the atmosphere to generate an oxide film on the surface of the welded portion, and a temper collar may be generated in the welded portion depending on the thickness of the oxide film. As the thickness of the oxide film increases, the color of the temper color changes to approach black, and the welded portion becomes more conspicuous than the other parts of the workpiece. Therefore, from the viewpoint of improving the aesthetics of the workpiece, it is desirable that generation of an oxide film can be suppressed during welding so that a temper color is not generated.

  The present invention has been made to solve the above problems, and provides a laser welding method capable of improving the aesthetics of a workpiece by suppressing the formation of an oxide film on the surface of a welded portion. Objective.

  In order to solve the above-described problems, a laser welding method according to the present invention is a laser welding method for forming a through-weld portion on a workpiece by irradiation with a laser beam, and is provided corresponding to the formation position of the through-weld portion. A first step of placing a workpiece on a mounting table having a groove portion formed and forming a space having at least one opening portion by one surface of the workpiece and the groove portion; and in the space through the opening portion. And a second step of irradiating the forming position with the laser beam from the other surface side of the workpiece so that one end of the through-welding portion protrudes into the space while circulating the assist gas.

  In this laser welding method, laser welding is performed while assist gas is circulated through a space formed by one surface of the workpiece and the groove. For this reason, in the periphery of the one end part of the penetration welding part protruded in space, oxygen decreases by circulation of assist gas. Thereby, in one end part of a penetration welding part, it becomes difficult to generate an oxidation reaction and it can control the thickness of an oxide film. When the thickness of the oxide film is suppressed, the reflected light of the welded portion and the reflected light of the oxide film interfere with each other, so that the temper color is suppressed, and the color of the welded portion becomes less conspicuous than the color of the other part of the workpiece. . Therefore, it is possible to improve the aesthetic appearance of one surface of the workpiece from which one end of the through-welding portion protrudes.

  In the laser welding method of the present invention, in the first step, it is preferable to form an assist gas supply port and a discharge port in a space formed by one surface of the workpiece and the groove. As a result, the direction in which the assist gas flows in the space is uniquely determined, so that the atmosphere can be expelled from the space more reliably and the assist gas can be quickly circulated in the space.

  In the laser welding method of the present invention, in the second step, it is preferable that the assist gas is circulated in the space from the keyhole generated in the molten pool of the workpiece toward the opening. Accordingly, the assist gas can be circulated in the space without newly providing means for supplying the assist gas to the space formed by the one surface of the workpiece and the groove.

  In the laser welding method of the present invention, it is preferable that the workpiece is an outer plate used for a railway vehicle structure, and one surface of the workpiece is an outer wall surface of the railway vehicle structure. Similarly, in the laser welding method of the present invention, it is preferable that the workpiece is an inner plate used for a railway vehicle structure, and one surface of the workpiece is an inner wall surface of the railway vehicle structure. As a result, one surface of the workpiece having a thin oxide film and a conspicuous welded portion is used as an easily visible outer wall surface or inner wall surface, so that the beauty of the railway vehicle structure can be improved.

  According to the laser welding method of the present invention, it is possible to improve the aesthetic appearance of one surface of the work piece from which one end portion of the through-welding portion protrudes.

  Hereinafter, preferred embodiments of a laser welding method according to the present invention will be described with reference to the drawings.

  The laser welding method according to the present invention is used for manufacturing a railway vehicle assembly 10 as shown in FIG. More specifically, in this laser welding method, the outer wall portion 11a or the inner wall portion 11b and a bone member (not shown) are disposed between the outer wall portion 11a and the inner wall portion 11b in the side structure body 11 constituting the longitudinal side portion of the railcar structure body 10. To be used in combination.

  FIG. 2 shows a configuration of a laser welding apparatus that realizes a laser welding method according to an embodiment of the present invention. A laser welding apparatus 20 shown in FIG. 2 is an apparatus for lap welding two metal plates 21 and 22 (hereinafter referred to as “workpieces (workpieces) 23”) that are overlapped. In this embodiment, the laser welding apparatus 20 irradiates the workpiece 23 with a laser beam L from the direction of the metal plate 21 in the workpiece 23 to perform through welding on the workpiece 23. Here, the metal plate 21 directly irradiated with the laser beam L of the workpiece 23 is a bone member of the railway vehicle assembly 10 shown in FIG. 1, and the other metal plate 22 is the outer wall portion 11a or the inner wall portion 11b. .

  The laser welding apparatus 20 irradiates the workpiece 23 with a laser beam L and a stage (mounting table) 24 that moves along the planned welding area (formation position of the penetration weld) R of the workpiece 23. A laser irradiation unit 25 and a gas supply unit 26 for supplying an assist gas to the irradiation position of the laser beam L are provided. The stage 24, the laser irradiation unit 25, and the gas supply unit 26 are connected to a host control device (not shown), and automatically execute each operation in accordance with operation instruction information output from the control device.

  The workpiece 23 includes a scheduled welding region R on a surface 23a on the metal plate 21 side (the other surface of the workpiece; hereinafter referred to as “work surface”), and a surface on the metal plate 22 side (one surface of the workpiece. 23 b) is placed on the stage 24 so as to be in contact with the placement surface 24 a of the stage 24.

  The stage 24 has a fixing means (not shown) for fixing the work 23 at a predetermined position on the mounting surface 24a and a moving means (not shown) for moving along the planned welding region R in a state where the work 23 is fixed. )). When the stage 24 receives operation instruction information for instructing the start of scanning from a control device (not shown), the stage 24 moves at a constant speed in the direction (arrow A in FIG. 1) along the planned welding region R of the workpiece surface 23a. Moving. Thereby, the workpiece 23 placed on the stage 24 moves relative to the irradiation position P of the laser beam L by the laser irradiation unit 25 along the planned welding region R. That is, the laser beam L moves on the workpiece surface 23a in the direction opposite to the moving direction of the stage 24 (arrow B in FIG. 1). Alternatively, the stage 24 may be fixed at a predetermined position, and the laser irradiation unit 25 may be moved along the planned welding region R of the work 23.

  The stage 24 is provided with grooves (groove portions) 27 that extend to both ends of the mounting surface 24a on the mounting surface 24a. The groove 27 has a straight body shape having a width of 10 mm and a maximum depth of 10 mm, for example. When the work 23 is fixed to the stage 24, the work back surface 23b and the groove 27 form a space 28 having openings 28a and 28b at both ends.

  The laser irradiation unit 25 irradiates the laser beam L toward the planned welding region R on the workpiece surface 23a. When the laser irradiation unit 25 receives operation instruction information for instructing the start of irradiation from a control device (not shown), the laser beam L is emitted from the laser head L (not shown) with an output that can perform through welding on the workpiece 23. ). As described above, during welding, the stage 24 moves in the direction A along the planned welding region R of the workpiece 23, so that the laser beam L is relatively opposite to the direction A (arrow B in FIG. 1). The irradiation position P on the work surface 23a is scanned. The laser beam L emitted from the laser irradiation unit 25 is, for example, a YAG laser having a wavelength of 1.06 μm and an output of about 4.0 kW.

  Further, the laser irradiation unit 25 includes an output switching mechanism (not shown) inside. By this output switching mechanism, the laser irradiation unit 25 can continuously irradiate the workpiece 23 with the laser beam L, or can perform spot welding by irradiating the laser beam L in a pulsed manner.

  The first gas supply unit 26 supplies assist gas to the irradiation position P of the laser beam on the workpiece surface 23a. The first gas supply unit 26 supplies assist gas to the irradiation position P of the laser beam from a direction inclined about 45 degrees with respect to the workpiece surface 23a behind the traveling direction B of the laser irradiation position P. When the first gas supply unit 26 receives operation instruction information for instructing the start of supply from a control device (not shown), the first gas supply unit 26 supplies assist gas to the irradiation position P of the laser beam with a predetermined supply amount. As the assist gas, helium gas, argon gas, or the like is used for the purpose of preventing the work 23 from being oxidized and preventing sputtering.

  When the YAG laser having an output of about 4 kW is used as described above and the welding speed (moving speed of the stage 24) is 3 m / min, the position of the gas supply unit 26 is the position of the laser irradiation position. It is about 20 mm backward.

  The laser welding apparatus 20 further includes a second gas supply unit 29 that supplies assist gas to a space 28 formed by the groove 27 of the stage 24 and the work back surface 23b. The second gas supply unit 29 is also connected to a host control device (not shown), and automatically executes each operation in accordance with operation instruction information output from this control device. When the second gas supply unit 29 receives operation instruction information for instructing the start of supply from a control device (not shown), the second gas supply unit 29 supplies assist gas into the space 28 from one opening 28a of the space 28 with a predetermined supply amount. Supply.

  Next, the laser welding method according to this embodiment will be described. FIG. 3 shows a flowchart of the laser welding method. In this laser welding method, in step S101 (first step) for forming a space 28 having both ends opened by the work 23 and the groove 27, the penetration gas passes through the space 28 from one opening 28a. Steps S102 to S106 (second step) for performing laser welding on the workpiece 23 such that one end 32b (see FIG. 5) of the welded portion 32 protrudes into the space 28 are included.

  First, the work 23 is placed on the stage 24 so that a space 28 having both ends opened is formed by the groove 27 provided on the stage 24 and the work back surface 23b (S101). The workpiece 23 is such that the planned welding region R of the workpiece surface 23a overlaps with the groove 27, and one end portion 32b of the penetration weld portion 32 protruding to the workpiece back surface 23b by penetration welding can contact the space 28 (see FIG. 5). , Fixed on the stage 24.

  Next, the first gas supply unit 26 starts to supply assist gas to the irradiation position P of the laser beam L on the workpiece 23 (S102). Further, the second gas supply unit 29 starts the supply of the assist gas from the one opening 28a of the space 28 into the space 28 (S103). The assist gas supplied to the space 28 is discharged from the other opening 28b, and the assist gas is always circulated in the space 28. Due to the flow of the assist gas, the atmosphere originally in the space 28 is expelled to the outside, and the assist gas always circulates in the space 28 during the following processing.

  Next, the movement of the stage 24 (not shown) starts the movement of the stage 24 at a constant speed in the direction along the planned welding region R of the workpiece 23 (arrow A in FIG. 2) (S104). Further, the laser irradiation unit 25 irradiates the planned welding region R of the workpiece surface 23a with a laser beam (S105). Laser welding is started by executing the processing of steps S102 to S105. Laser welding is continued until it is confirmed in step S106 that laser welding has been completed for the planned welding region R by a control device (not shown).

  When it is confirmed that the laser welding is completed (YES in S106), the control device (not shown) supplies the assist gas by the first gas supply unit 26 and the second gas supply unit 29, and the stage 24 The movement and laser beam irradiation by the laser irradiation unit 25 are stopped (S107), and a series of laser welding processes is completed.

  Here, a phenomenon that occurs in the welded part while the laser beam L is applied to the work 23 in steps S <b> 105 to S <b> 106 and the penetration weld 32 is formed on the work 23 will be described. 4 and 5 schematically show the welded portion of the work 23 when the laser welding according to the present embodiment is performed. FIG. 4 is a schematic view showing the welded portion in a cross section along the traveling direction B of the laser beam. In FIG. 5, welding is performed by scanning the laser beam L in the left direction as indicated by an arrow B. FIG. 5 is a cross-sectional view of the welded portion of FIG. 4 taken along line VII-VII.

  As shown in FIG. 4, when the laser beam L is irradiated to the irradiation position P of the workpiece surface 23a, the metal plates 21 and 22 constituting the workpiece 23 are melted and mixed to form the molten pool 31, and eventually penetrate. It becomes the welding part 32. In this process, the molten pool 31 undergoes an oxidation reaction with oxygen in the atmosphere, and as shown in FIG. 7, the end weld portion 32a protruding from the workpiece surface 23a and the penetration weld portion 32 protruding from the workpiece back surface 23b. An oxide film 33 is formed on the surface of the end portion 32b.

  Here, attention is paid to the end portion 32b of the through-welding portion 32 protruding from the workpiece back surface 23b. The surface of the end portion 32 b protrudes into a space 28 formed by the work back surface 23 b and the groove 27. During the welding, the space 28 is always supplied with the assist gas by the second gas supply unit 29 and is circulated in one direction, for example, as indicated by an arrow C in FIG. Due to the flow of the assist gas, the atmosphere originally in the space 28 is expelled to the outside, and the space 28 is always filled with the assist gas during welding. That is, since the amount of oxygen in the space 28 is reduced during welding, the oxidation reaction is slowed around the end portion 32b. Thereby, in the workpiece | work back surface 23b, the thickness of the oxide film 33 adhering to the surface of the penetration welding part 32 is suppressed.

  In the present embodiment, the work 23 is the side structure 11 of the railcar structure 10, and the work back surface 23b is the outer wall portion 11a or the inner wall portion 11b of the side structure 11, as shown in FIG. That is, in the laser welding method according to the present embodiment, penetration welding is performed between the outer wall portion 11a or the inner wall portion 11b of the railway vehicle structure 10 and the bone member (not shown), and the outer wall portion 11a or the inner wall portion 11b. Then, laser welding is performed while assist gas is circulated in the space 28 formed by the groove 27. For this reason, at the time of welding, oxygen decreases in the vicinity of the one end portion 32b of the through-welding portion 32 protruding into the space 28 due to the circulation of the assist gas. Thereby, in the one end part 32b of the penetration welding part 32, an oxidation reaction becomes difficult to generate | occur | produce and the thickness of the oxide film 33 can be suppressed. That is, the oxide film 33 adhering to the surface of the penetration weld 32 can be thinned in the outer wall 11a or the inner wall 11b of the railway vehicle structure 10.

  Specifically, according to this embodiment, the thickness of the oxide film 33 can be reduced to 100 nm or less, and thereby, the reflected light of the penetration weld 32 and the reflected light of the oxide film 33 interfere to suppress the temper color. Is done. When the temper color is suppressed, the color of the through-welded portion 32 approaches the color of the outer wall portion 11a or the other portion of the inner wall portion 11b, and the through-welded portion 32 becomes inconspicuous. Therefore, the beauty of the railway vehicle structure 10 can be improved.

  Further, in the laser welding method of the present invention, in step S101, the space 28 formed by the work back surface 23b and the groove 27 includes two openings 28a and 28b that serve as an assist gas supply port and an exhaust port. Is preferred. As a result, the direction in which the assist gas flows in the space 28 is uniquely determined, so that the atmosphere can be expelled from the space 28 more reliably and the assist gas can be quickly circulated in the space 28.

  Conventionally, in order to suppress the temper color, there is a method of treating an oxidized portion (temper color portion) with an electrolytic etching solution after welding. However, this method requires a separate process after welding, or a complicated process such as adjusting the amount of electrolytic etching solution to change the temper color portion to a desired color. On the other hand, the laser welding method of the present invention does not require such a separate process or a complicated process, and suppresses the temper color of the through-welded portion 32 if the groove 27 is provided in the stage 24 and laser welding is performed. Can do.

  The laser welding method according to the present invention has been described with reference to a preferred embodiment, but the present invention is not limited to the above embodiment. For example, although the above embodiment has been described for lap welding, the present invention is also applicable to butt welding. In the above embodiment, the groove 27 is provided in the stage 24. However, a jig including the groove 27 may be sandwiched between the work 23 and the stage 24.

  Moreover, in the said embodiment, the groove | channel 27 was provided to the edge part of the stage 24, and the space 28 formed with the groove | channel 27 and the workpiece | work back surface 23b was opened by opening part 28a, 28b at both ends. On the other hand, for example, as shown in FIG. 6, a groove 40 formed in a concave shape inside the mounting surface 24 a of the stage 24, and two passages 41 a that penetrate from the lower part of the stage 24 to the groove part 40, 41b, and the second gas supply unit 29 may supply the assist gas from one passage 41a and be discharged from the other passage 41b.

  In the above embodiment, the assist gas is supplied from the one opening 28 a of the space 28 by the second gas supply unit 29, but the assist gas is supplied by the first gas supply unit 26. The amount may be increased so that the assist gas is supplied from the work surface 23 a to the back surface 23 b through the keyhole 42. In this case, for example, as shown in FIG. 7A, the assist gas supplied by the first gas supply unit 26 through the keyhole 42 is discharged from the openings 43 a and 43 b of the space 43. Further, as shown in FIG. 7B, a groove 44 formed in a concave shape inside the mounting surface 24a of the stage 24 and a passage 45 penetrating from the lower part of the stage 24 to the groove 27 are provided. The assist gas supplied from the first gas supply unit 26 through the hole 42 may be discharged from the passage 45. Thereby, the assist gas can be circulated in the space 28 without providing a new means for supplying the assist gas into the space 28 like the second gas supply unit 29.

It is a figure which shows the structure of the railway vehicle structure using the laser welding method which concerns on one Embodiment of this invention. It is a figure which shows the structure of the laser welding apparatus which implement | achieves the laser welding method which concerns on one Embodiment of this invention. It is a figure which shows the flowchart of the laser welding method which concerns on this embodiment. It is a figure which shows the outline of the welding part of the workpiece | work when the laser welding by this embodiment is implemented. It is sectional drawing when the welding part shown in FIG. 4 is cut | disconnected by the VII-VII line. It is a figure which shows the modification of the groove | channel provided in a stage. It is a figure which shows the modification of the method of distribute | circulating assist gas to the space of the workpiece | work back surface side.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Rail vehicle structure, 11 ... Side structure, 11a ... Outer wall part, 11b ... Inner wall part, 20 ... Laser welding apparatus, 21,22 ... Metal plate, 23 ... Workpiece (workpiece) , 23a... Workpiece surface (other surface of workpiece), 23b... Workpiece back surface (one surface of workpiece), 24... Stage (mounting table), 25... Laser irradiation unit, 26. Supply part, 27 ... groove (groove part), 28 ... space, 28a, 28b ... opening, 29 ... second gas supply part, 31 ... molten pool, 32 ... penetration weld part 32a, 32b ... one end of the penetration weld, 33 ... oxide film, 42 ... keyhole, L ... laser beam, R ... planned welding area (position where the penetration weld is formed) , S101: first step, S102 to S106: second step.

Claims (5)

A laser welding method for forming a through-weld portion in a workpiece by laser beam irradiation,
The work piece is placed on a placing table having a groove portion corresponding to the formation position of the through-welding portion, and a space provided with at least one opening portion by one surface of the work piece and the groove portion. A first step of forming;
While circulating the assist gas in the space through the opening, the laser beam is emitted from the other surface side of the workpiece to the formation position so that one end of the through welded portion protrudes into the space. A second step of irradiating;
A laser welding method comprising:   The laser welding method according to claim 1, wherein in the first step, a supply port and a discharge port for the assist gas are formed in the space.   The laser welding method according to claim 1, wherein in the second step, the assist gas is circulated in the space from a keyhole generated in a molten pool of the workpiece toward the opening. The workpiece is an outer plate used for a railway vehicle structure,
The laser welding method according to claim 1, wherein the one surface of the workpiece is an outer wall surface of the railway vehicle structure. The workpiece is an inner plate used for a railway vehicle structure,
The laser welding method according to claim 1, wherein the one surface of the workpiece is an inner wall surface of the railway vehicle structure.

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