JP2007090402A - Laser welding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser welding method capable of preventing occurrence of low-temperature cracks in a part of a weld bead or the like even when the laser welding method is applied to a circumferential weld or the like over the whole circumferential contour of a member. <P>SOLUTION: While a boss 20 as a one side member is inserted in an insertion hole part 12C in a web 12 as the other partner member, a laser beam welding machine 21 is arranged at a laser beam irradiation starting point (the position of a point PA). The laser beams 22 for the first round are continuously moved to the position making one turn along the contour of the boss 20 (an irradiation locus 23 of the radius R). Next, in the laser beam irradiation step on the second round, the laser beams are irradiated along the irradiation locus 25 while the power of the laser beams 22 is gradually reduced from the power of the laser beam irradiation on the first round without stopping the irradiation of the laser beams 22 by the laser beam welding machine 21. The irradiation of the laser beams 22 is stopped at the end position on the second round (for example, the position of the point PE). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laser welding method suitably used for laser-welding a member having, for example, a circular, square, or triangular contour to the other member over the entire circumference.

  In general, a laser beam is emitted using a laser oscillator, and the laser beam is focused by a condenser lens or the like, so that a welding bead is formed by irradiating the focused laser beam to a welding target portion, and a welding operation is performed. A laser welding apparatus and a welding method configured as described above are known (for example, see Patent Documents 1 and 2).

  In this type of conventional laser welding, the energy density on the surface of the member to be welded is increased to about 10 to 100 times, for example, compared with arc welding or the like by narrowing the spot diameter of the laser beam. It is possible to obtain a deep penetration by reducing the width of the weld bead.

  And since such laser welding has high energy density, high-speed welding can be realized, and the amount of heat input to the welding target (member to be welded) is extremely small compared to arc welding, enabling low distortion welding. It becomes. Further, since the amount of heat input is small, the weld metal part (weld bead part) is rapidly heated and rapidly cooled to form a martensite structure, which is very hard.

JP 52-103354 A JP 54-71059 A

  By the way, when the above-described laser welding according to the prior art is applied to, for example, a welding operation of a circular member having a circular contour, a problem peculiar to so-called circumferential welding performed along the entire circumference of the circular member is cold cracking or the like. There is a problem that occurs.

  In other words, when laser welding (circumferential welding) is performed on a circular member over the entire circumference of the counterpart member, the circular member is surrounded and completely restrained from the outside by the counterpart member, and thermal deformation due to the thermal influence during welding ( (Expansion or contraction) is regulated, and this causes cold cracking. In particular, the weld metal part (weld bead part) of laser welding has the property that it is rapidly heated and quenched to become a martensite structure and becomes very hard as described above, and therefore there is a crack on the surface side of the weld bead. It is easy to generate.

  Further, when performing laser welding (circumferential welding) as described above, the circular member located on the inside rises in temperature because heat input by welding cannot be diffused outward, and cooling after welding is performed. There is a tendency to slow down. On the other hand, the outer counterpart member surrounding the circular member can diffuse heat input during welding to the outside, so that the cooling rate tends to be relatively high.

  For this reason, the cooling rate after welding becomes uneven between the inner circular member and the outer counterpart member, and a temperature difference is likely to occur, and thermal expansion / contraction is unbalanced. In addition, in the case of laser welding, the weld bead portion is rapidly heated and rapidly cooled to become a martensite structure, and the adverse condition that it becomes very hard overlaps, so that cracks (cracks) are likely to occur in the weld bead portion.

  In the case of circumferential welding, since the welding start position and the end position coincide with each other, the temperature distribution over the contour (the entire circumference) of the circular member becomes non-uniform, and the welding deformation also becomes non-uniform. And even if a crack (crack) etc. generate | occur | produces even a little in the part of a weld bead, there exists a problem that this becomes a starting point and causes the strength of the whole welded structure to fall.

  In particular, the laser welding according to the prior art (Patent Documents 1 and 2) is intended to arrange the bead shape after welding by remelting, and instead of continuously changing the laser power, the laser irradiation is stopped, Re-irradiation is performed intermittently. Moreover, the laser irradiation target position is, for example, the same irradiation position at the first time and the second time, and is remelted without changing the laser irradiation target position.

  For this reason, when laser welding according to the prior art is applied to, for example, an all-around welding (circumferential welding) operation in which a one-side member having a circular or non-circular contour is welded to the other member over the entire circumference, the above-described operation is performed. Thus, as a problem peculiar to so-called circumferential welding or the like, there is a problem that a crack or the like is likely to occur in the weld bead portion.

  The present invention has been made in view of the above-described problems of the prior art, and the object of the present invention is, for example, in the case of a weld bead portion even when applied to a welding operation over the entire contour of a member such as circumferential welding. An object of the present invention is to provide a laser welding method capable of preventing the occurrence of cracks and improving the reliability.

  In order to solve the above-described problems, the present invention is applied to a laser welding method in which a one-side member having a circular or non-circular contour is laser-welded to a counterpart member over the entire circumference.

  In the welding method according to the first aspect of the present invention, the laser beam is irradiated until it makes one round along the outline of the one side member, and a weld bead is formed over the entire circumference of the outline. Laser irradiation step and second laser irradiation step of irradiating a laser beam along a position outside the position of the weld bead on the first round without stopping the laser beam irradiation performed on the first round. It is in including.

  According to the invention of claim 2, in the laser irradiation process of the second round, laser irradiation is performed along the contour of the weld bead while gradually reducing the power of the laser beam from that of the laser irradiation of the first round. The laser irradiation is stopped when the second round is completed.

  On the other hand, according to the invention of claim 3, in the laser irradiation process of the second round, the laser beam is irradiated along the contour of the weld bead while defocusing the laser beam rather than the laser irradiation of the first round. Laser irradiation is stopped when the round ends.

  According to the invention of claim 4, in the laser irradiation process of the second round, the peak temperature of the portion where the weld bead is formed is set to a temperature lower than the austenitization transformation point (A1). .

  According to the invention of claim 5, in the second laser irradiation step, the peak temperature of the portion where the weld bead is formed is set to a temperature higher than the martensitic transformation start point (Ms). Yes.

  According to the invention of claim 6, in the second laser irradiation step, the peak temperature of the portion where the weld bead is formed is lower than the austenitization transformation point (A1) and the martensitic transformation starts. A peak temperature higher than the point (Ms) is set.

  As described above, according to the first aspect of the present invention, in the laser irradiation process in the first round, the laser beam is irradiated to the position that makes one round along the outline of the one side member. A weld bead that extends over the entire circumference of the contour can be formed with the member, and then, in the second laser irradiation step performed without stopping the laser beam irradiation, the laser beam is applied to the one side member. By irradiating the laser beam along a position outside the position of the weld bead without irradiating, a portion (a counterpart member) located outside the weld bead can be heated and the temperature of the counterpart member can be raised. .

  As a result, the temperature difference between the one side member and the counterpart member can be reduced, the temperature distribution between the inside and outside of the weld bead can be made equal, and the cooling rate of both can be made almost equal, so that cracks etc. occur in the weld bead portion. Can be prevented. That is, in the conventional laser welding method, the weld bead portion is rapidly cooled, and the structure tends to be martensite and easily cracked. However, in the present invention, the temperature distribution between the inside and outside of the weld bead is made equal by slowing the cooling rate of both by reheating the portion located outside the weld bead by the second round of laser irradiation. be able to. For this reason, the weld bead portion is gradually cooled to prevent the structure from becoming martensite, and it is possible to prevent weld cracks and improve reliability.

  Further, according to the invention of claim 2, in the second laser irradiation step, laser irradiation is performed along the contour of the weld bead while gradually reducing the power of the laser beam from that of the first laser irradiation, Since the laser irradiation is stopped when the second round is completed, the temperature distribution can be made substantially equal on the inside and outside of the weld bead, and the temperature can be made uniform in the circumferential direction of the weld bead. Variations can be kept small to prevent cracks and the like from occurring. And since the power of a laser beam is made small gradually, the heat input by the laser irradiation of the 2nd round can be reduced, and welding distortion and a deformation | transformation can be suppressed.

  On the other hand, according to the third aspect of the present invention, in the second laser irradiation step, laser irradiation is performed along the contour of the weld bead while the laser beam is defocused rather than the first laser irradiation. In this case, the temperature distribution can be made almost equal between the inside and outside of the weld bead, and the temperature can be made uniform in the circumferential direction of the weld bead. Variation in speed can be reduced. Since irradiation is stopped while the laser beam is defocused, the heat input by the second round of laser irradiation can be reduced, the temperature of the entire material can be made uniform, and the occurrence of weld cracks and the like can be prevented. , Welding distortion and deformation can be suppressed. In addition, the defocusing of the laser beam eliminates the need for crater processing at the welding end position, which is a problem in circumferential welding, for example, and simplifies the welding operation.

  In the invention according to claim 4, the peak temperature of the portion where the weld bead is formed is set to a temperature lower than the austenitization transformation point (A1) in the second laser irradiation step. In the laser irradiation step, heat treatment similar to so-called tempering can be performed, and internal stress can be removed, hardness can be suppressed, cracking can be prevented, and toughness can be imparted to the welded portion.

  Further, the invention according to claim 5 sets the temperature of the portion where the weld bead is formed in the second laser irradiation step to a peak temperature higher than the martensitic transformation start point (Ms). This part can be gradually cooled to prevent the structure from becoming martensite, and weld cracks can be prevented and reliability can be improved.

  Furthermore, in the invention described in claim 6, the peak temperature of the site where the weld bead is formed in the second laser irradiation step is lower than the austenitization transformation point (A1) and the martensitic transformation start point. Since the peak temperature is set higher than (Ms), the weld bead portion can be gradually cooled to prevent the structure from martensite, and weld cracks can be prevented to improve reliability. it can.

  Hereinafter, a laser welding method according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings, taking a construction machine (hydraulic excavator) as an example of application.

  Here, FIG. 1 to FIG. 7 show a first embodiment of the present invention. In the figure, reference numeral 1 denotes a hydraulic excavator as a construction machine. The hydraulic excavator 1 includes a self-propelled track-type lower traveling body 2 and an upper revolving body 3 mounted on the lower traveling body 2 so as to be pivotable. The offset boom type working device 4 provided on the front side of the upper swing body 3 so as to be movable up and down is generally constituted.

  In this case, the working device 4 includes a lower boom 5 attached to the upper swing body 3 so as to be able to move up and down, an upper boom 6 attached to a tip portion of the lower boom 5 so as to be swingable leftward and rightward, and the upper boom 6. The arm stay 7 is attached to the front end of the arm stay 7 so as to be swingable in the left and right directions, the arm 11 described later is attached to the arm stay 7 so as to be able to move up and down, and the arm stay 7 is turnable to the front end of the arm 11 It is roughly constituted by a bucket 8 as an attached work tool. And the lower boom 5, the upper boom 6, and the arm 11 comprise the working arm for construction machines.

  Further, in the offset boom type working device 4, a link rod (not shown) is provided between the tip portion of the lower boom 5 and the arm stay 7 so as to be rotatable in the left and right directions. Yes. The link rod constitutes a parallel link together with the lower boom 5, the upper boom 6, and the arm stay 7, and the arm 11 and the lower boom 5 are always kept parallel by the parallel link.

  Further, a boom cylinder 5 A is provided between the upper swing body 3 and the lower boom 5, an arm cylinder 7 A is provided between the arm stay 7 and the arm 11, and between the arm 11 and the bucket 8. Is provided with a bucket cylinder 8 </ b> A via bucket links 9 and 10.

  Reference numeral 11 denotes an arm of a working device 4 that constitutes a working arm of the hydraulic excavator 1, and this arm 11 includes left and right webs 12 (only one shown) and upper and lower flanges 13 and 14 as shown in FIG. Is formed as a welded structure having a closed cross section with a quadrangular cross section.

  Here, the left and right webs 12 are formed with cut portions 12A that are inclined obliquely on one side (base end side) in the length direction, and a reinforcing plate 17 described later is laser welded to the cut portions 12A. It joins by means, such as. Further, on the other side (front end side) of the web 12, a semicircular cutout portion 12B to which a boss 19 described later is joined, and a circular insertion hole portion 12C to which a boss 20 described later is joined in an inserted state, Is provided.

  A closing plate 15 is provided on the proximal end side (one side in the length direction) of the arm 11 so as to sandwich a reinforcing plate 17 described later between the lower flange 14 and the closing plate 15. In order to close one side of the arm 11, each web 12, the upper flange 13, and the end of the reinforcing plate 17 are joined by welding.

  A cylinder bracket 16 is joined to the outer surface of the upper flange 13 and the closing plate 15 by welding, and the tip of the arm cylinder 7A is pin-coupled to the cylinder bracket 16 as shown in FIG. In addition, the base end portion of the bucket cylinder 8A is pin-coupled.

  Reference numeral 17 denotes a reinforcing plate for attaching the boss 18 to the base end side of the arm 11, and the reinforcing plate 17 is formed using a substantially triangular plate (steel plate) as shown in FIG. 12 cut portions 12A, the lower flange 14, the closing plate 15 and the outer periphery of the boss 18 are joined by welding. 1 is coupled to the boss 18 so as to be pivotable.

  In this case, the reinforcing plate 17 is formed of a thicker plate material than the web 12 and increases the bonding strength of the boss 18 to the web 12, the lower flange 14, and the closing plate 15 of the arm 11, and the lower flange. 14 and the closing plate 15 have a function of reinforcing the boss 18.

  Reference numeral 19 denotes another boss provided at the tip of the arm 11 (the other side in the length direction). The boss 19 is the tip of the notch portion 12B of the left and right webs 12 and the upper and lower flanges 13 and 14. Each of them is fixed by welding. And the bucket 8 shown in FIG. 1 is pin-coupled to the boss 19 so as to be rotatable.

  Reference numeral 20 denotes another boss provided on the distal end side of the arm 11. The boss 20 extends through the arm 11 in the left and right directions, and both end sides thereof are inserted into the insertion holes 12 </ b> C of the left and right webs 12. They are joined by laser welding described later. 1 is coupled to the boss 20 so that one side of the bucket link 9 shown in FIG.

  Here, the boss 20 is formed as a cylindrical tube having an outer diameter of a radius R with respect to the center line OO as shown in FIG. 3, for example, and constitutes one side member having a circular outline. Is. The boss 20 is inserted into the insertion hole 12C of the web 12 serving as a counterpart member as shown in FIG. 3, and circumferential welding using a laser beam 22 described later is performed between the two. . Thereby, the boss | hub 20 is joined to the penetration hole part 12C of the web 12 over a perimeter.

  Reference numeral 21 denotes a laser welding machine used in the present embodiment. This laser welding machine 21 converts laser light emitted from a laser oscillator (not shown) into a condensing device (not shown) such as a condensing lens and a reflecting mirror. 3), the focused laser beam 22 is irradiated toward the welding object (between the web 12 and the boss 20) as shown in FIG.

  Further, the laser welding machine 21 is moved along irradiation tracks 23 and 25 described later on the outer peripheral side of the boss 20 to execute the first and second laser irradiation processes. In addition, it is good also as a structure which supplies filler materials, such as a filler wire, to the laser welding part between the web 12 and the boss | hub 20 as needed.

  The hydraulic excavator 1 to which the laser welding method according to the present embodiment is applied has the above-described configuration. Next, the operation thereof will be described.

  First, for example, when the hydraulic excavator 1 (vehicle) travels on the road at a work site or the like, the vehicle can be moved forward or backward by driving the lower traveling body 2 to travel. In addition, the direction of the working device 4 can be appropriately changed by driving the upper swing body 3 to rotate on the lower traveling body 2.

  When excavation work such as earth and sand is performed by the offset boom type working device 4, the boom cylinder 5A, the arm cylinder 7A and the bucket cylinder 8A are expanded and contracted to operate the lower boom 5, the arm 11 and the bucket 8 of the working device 4. The bucket 8 can perform excavation work.

  Further, the offset boom type working device 4 can turn the upper boom 6 left and right with respect to the lower boom 5 by extending and contracting an offset cylinder (not shown), and the arm 11 with respect to the lower boom 5. For example, a side trenching operation can be easily performed with the left and right translated.

  Further, as shown in FIG. 1, in a state where the lower boom 5 of the working device 4 is largely lifted upward and the arm 11 and the bucket 8 are turned so as to be folded toward the lower boom 5, the entire working device 4 is moved to the upper swing body 3. Therefore, excavation work such as earth and sand can be performed smoothly without contacting with surrounding obstacles even in a narrow work site.

  Next, the laser welding method employed in the present embodiment will be described with reference to FIG. 3 to FIG. 7, taking as an example a welded portion (joined part) between the web 12 of the arm 11 and the boss 20.

  First, in a state where the boss 20 that is one side member is inserted into the insertion hole 12C of the web 12 that is the counterpart member as shown in FIG. 3, the laser welding machine 21 is moved to the laser irradiation start point (the point in FIG. 3). PA), and irradiates the laser beam 22 from the laser welding machine 21 directly below the point PA, and continuously moves the laser beam 22 along the contour of the boss 20 to a position that makes one round. (First laser irradiation step).

  In this case, the laser beam 22 of the laser welding machine 21 is moved to the points PA, PB, PC, PD along the irradiation locus 23 with the radius R around the center line OO as shown in FIG. At the stage of returning to the point PA, a weld bead 24 is formed by circumferential welding over the contour (entire circumference) of the boss 20 as shown in FIGS.

  Here, the point PB is at a position separated from the starting point PA by 90 degrees along the irradiation locus 23, and the point PC is located at a position separated from the point PA by 180 degrees along the irradiation locus 23. The point PD is at a position separated by 270 degrees along the irradiation locus 23 from the point PA. The stage where the laser beam 22 makes one round to the point PA again and forms the weld bead 24 over the entire circumference (360 degrees) corresponds to the first laser irradiation step.

  Next, in the laser irradiation process of the second round, without stopping the irradiation of the laser beam 22 by the laser welding machine 21, the power of the laser beam 22 is gradually lowered from the laser irradiation of the first round to the irradiation locus 25. Laser irradiation is performed along this line, and irradiation of the laser beam 22 is stopped at the end position (point PE in FIG. 3) of the second round.

  In this case, the irradiation trajectory 25 of the second round is outside the position of the weld bead 24 along the outline of the weld bead 24 shown in FIG. 4 so as to draw a circular trajectory larger than the irradiation trajectory 23 of the first round. The position is irradiated with a laser beam 22. In the second laser irradiation step, the irradiation of the laser beam 22 is stopped at the point PE that is the end position while gradually decreasing the power of the laser beam 22 along the irradiation locus 25.

  Thus, for example, when the temperature distribution at the point PA, which is the starting point of laser irradiation, is examined, the temperature of the weld bead 24 at the point PA is controlled as indicated by the characteristic line 26 shown in FIG. From the austenite transformation point (A1) while the irradiation position of the weld bead 24 reaches the 90 degree position (for example, the point PB in FIG. 3) from the point PA after starting the laser irradiation of the eyes. Once rises to a higher temperature.

  Then, while the irradiation position of the weld bead 24 reaches a position of 270 degrees (point PD in FIG. 3), the temperature of the weld bead 24 at the position of the point PA approaches the martensitic transformation start point (Ms). descend. However, by performing the second laser irradiation following the first laser irradiation, the temperature of the weld bead 24 (the temperature at the point PA) rises again and gradually reaches the peak temperature T1. Is reduced.

  In this case, in the second laser irradiation, the laser beam 22 is moved to a position outside the position of the weld bead 24 (the irradiation locus shown in FIG. 25), the temperature of the weld bead 24 (peak temperature T1) can be set to a temperature lower than the austenitization transformation point (A1) by the second laser irradiation.

  Further, the temperature of the weld bead 24 (peak temperature T1) can be set to a temperature higher than the martensitic transformation start point (Ms) by the second laser irradiation. For this reason, it can suppress that the structure | tissue of the weld bead 24 formed between the insertion hole part 12C of the web 12 and the boss | hub 20 becomes martensite, and generation | occurrence | production of what is called a cold crack etc. can be prevented.

  Also, the temperature of the weld bead 24 can be controlled as indicated by characteristic lines 27, 28, and 29 shown in FIG. 7 at the positions of points PB, PC, and PD shown in FIG. That is, the temperature of the weld bead 24 is controlled at a point PB as indicated by a characteristic line 27 indicated by a one-dot chain line in FIG. 7, and at a point PC, as indicated by a characteristic line 28 indicated by a two-dot chain line in FIG. Then, the position of the point PD is controlled as shown by a characteristic line 29 shown by a broken line in FIG.

  In this way, in the second round of laser irradiation, the laser beam 22 is moved to a position outside the position of the weld bead 24 (the irradiation shown in FIG. 4) while gradually reducing the power of the laser beam 22 compared to the first round of laser irradiation. In order to irradiate along the locus 25), for example, at the position of point PB, the weld bead 24 has a peak temperature T2 between an angle of 450 degrees and 540 degrees as shown by the characteristic line 27, and this peak temperature T2 is changed to the peak at the point PA. The temperature can be set lower than the temperature T1 (T2 <T1).

  At the point PC, the weld bead 24 reaches a peak temperature T3 when the angle 540 degrees slightly passes as shown by the characteristic line 28, and this peak temperature T3 is lower than the peak temperatures T1 and T2 at the points PA and PB. The temperature can be set (T3 <T2 <T1). Further, the peak temperatures T2 and T3 at the positions of these points PB and PC can be set higher than the martensitic transformation start point (Ms).

  Then, during the second laser irradiation, for example, after the position of the angle 550 degrees and until the position of the angle 720 degrees (point PE in FIG. 4) at which the laser irradiation is stopped, the points PA to PD are covered. The temperature of the weld bead 24 is substantially uniformized and lowered so as to be gradually lower than the martensite transformation start point (Ms) as shown by the characteristic lines 26 to 29, and the weld bead 24 over the entire circumference of the boss 20 is reduced. The part can be gradually cooled (slow cooling).

  Thus, according to the present embodiment, in the first laser irradiation step, the laser beam 22 is irradiated to the position of one round along the outline (irradiation locus 23) of the boss 20 made of the cylindrical member having the radius R. Thus, the weld bead 24 can be formed over the entire circumference between the insertion hole 12 </ b> C of the web 12 and the boss 20.

  In this case, by narrowing the spot diameter of the laser beam 22 by the laser welding machine 21, the energy density can be increased to about 10 to 100 times as compared with arc welding or the like, and the weld bead 24 can be increased. It is possible to obtain a deep penetration by reducing the width of.

  Further, in the second laser irradiation step that is performed without stopping the irradiation of the laser beam 22 thereafter, the irradiation locus 25 that is located outside the position of the weld bead 24 without irradiating the boss 20 with the laser beam 22. By irradiating the laser beam 22 along, the portion located outside the weld bead 24 (around the insertion hole 12A of the web 12) can be heated, and the temperature on the web 12 side can be increased.

  Moreover, in the laser irradiation process for the second round, laser irradiation is performed along the contour of the weld bead 24 while gradually reducing the power of the laser beam 22 as compared with the laser irradiation for the first round, and the end position (point Since the laser irradiation is stopped at the position (PE), the temperature difference between the web 12 and the boss 20 can be reduced, the temperature distribution on the inside and outside of the weld bead 24 can be made equal, and the circumferential direction of the weld bead 24 can also be reduced. As shown by characteristic lines 26, 27, 28 and 29 in FIG.

  That is, in the conventional laser welding method, the weld bead portion is rapidly cooled, and the structure tends to be martensite and easily cracked. However, in the present embodiment, the temperature distribution between the inside and outside of the weld bead 24 is made equal by reheating the periphery of the insertion hole portion 12A located outside the weld bead 24 by laser irradiation of the second round. Thus, the cooling rate of both can be reduced.

  For this reason, the weld bead 24 portion is gradually cooled to prevent the structure from becoming martensite, and the weld bead 24 can be prevented from being cracked. In the second laser irradiation, the power of the laser beam 22 is gradually reduced, so that it is possible to suppress a variation in the cooling rate over the entire circumference of the weld bead 24, and to the second laser irradiation. Heat input can be reduced, welding distortion and deformation can be suppressed, and occurrence of cracks and the like can be prevented.

  Therefore, according to the present embodiment, even in so-called circumferential welding in which the weld bead 24 is formed over the entire circumference between the insertion hole 12C of the web 12 and the boss 20, cracks are generated in the middle portion of the weld bead 24. Generation | occurrence | production can be prevented and the reliability of circumferential welding can be improved.

  Next, FIG. 8 shows a second embodiment of the present invention. In this embodiment, the same components as those in the first embodiment described above are denoted by the same reference numerals, and the description thereof is omitted. Shall.

  However, the feature of the present embodiment is that, in the laser irradiation process of the second round, the laser beam 31 is defocused more than the laser irradiation of the first round, along the irradiation locus 32 at a position outside the position of the weld bead 24. The laser irradiation is performed, and the laser irradiation is stopped at the end position of the second round (the position of the point PE in FIG. 8).

  Here, the laser beam 31 used for the second round of laser irradiation is defocused more gradually than the first round of laser irradiation, so that the beam diameter becomes a beam diameter 31A near the point PA, and the point PB The beam diameter is 31B in the vicinity of. The beam diameter is 31C near the point PC, the beam diameter is 31D near the point PD, and the beam diameter is 31E at the point PE that is the end position of the second round.

  As described above, the laser beam 31 used for the second round of laser irradiation is gradually defocused along the irradiation locus 32, so that it gradually increases in the order of the beam diameters 31A, 31B, 31C, 31D, and 31E. Are controlled by

  Thus, in the present embodiment configured as described above, it is possible to obtain substantially the same operation and effect as the first embodiment, and the temperature distribution can be made substantially equal between the inside and the outside of the weld bead 24. In the circumferential direction of the weld bead 24, the temperature can be made uniform, and the variation in the cooling rate can be suppressed small.

  In particular, in the present embodiment, the laser beam 31 used for laser irradiation in the second round is gradually defocused along the irradiation locus 32, and the beam diameters 31A, 31B, 31C, 31D, and 31E are gradually increased. The heat input by laser irradiation in the second round can be reduced, the temperature of the entire material can be made uniform, the occurrence of welding cracks can be prevented, and welding distortion and deformation can be suppressed.

  Moreover, due to the defocusing of the laser beam 31, for example, a crater process for irradiating the laser twice at a welding end position (for example, the position of the points PA and E) which is a problem in the case of circumferential welding is specially performed. Therefore, it is possible to simplify the welding operation.

  Next, FIG. 9 shows a third embodiment of the present invention. In this embodiment, the same components as those in the first embodiment described above are denoted by the same reference numerals, and the description thereof is omitted. Shall.

  However, the present embodiment is characterized in that the reinforcing plate 17 for attaching the boss 18 to the proximal end side of the arm 11 is provided on the outer periphery of the cut portion 12A of the web 12, the lower flange 14, the closing plate 15 and the boss 18. Each of them is configured to be joined by laser welding.

  In this case, the reinforcing plate 17 is a one-side member to be welded, and the counterpart member is constituted by the cut portion 12A of the web 12, the lower flange 14, the closing plate 15 and the boss 18. Then, the reinforcing plate 17 is formed using a substantially triangular plate (steel plate) as shown in FIG. 9, and linear weld beads 41A, 41B, 41D are formed around the reinforcing plate 17 by laser irradiation of the first round. And an arc-shaped weld bead portion 41C are formed.

  That is, the linear weld bead portion 41 </ b> A joins between the cut portion 12 </ b> A of the web 12 and the reinforcing plate 17, and the weld bead portion 41 </ b> B joins between the lower flange 14 and the reinforcing plate 17. It is. The arc-shaped weld bead portion 41C is used to join the boss 18 and the reinforcing plate 17 in an arc shape, and the linear weld bead portion 41D is provided between the closing plate 15 and the reinforcing plate 17. It joins linearly.

  Here, in the first laser irradiation step, as indicated by arrows in FIG. 9, the linear weld bead portions 41A and 41B, the arc-shaped weld bead portion 41C, and the linear weld bead portion 41D are in this order. A laser beam (not shown) is irradiated over the outline (surrounding) of the reinforcing plate 17.

  In the second laser irradiation step, the laser beam is irradiated along the positions outside the weld bead portions 41A, 41B, 41C, and 41D in substantially the same manner as in the first or second embodiment described above. The laser beam irradiation is stopped at the end position of the second round.

  Thus, in the present embodiment configured as described above, it is possible to obtain substantially the same operational effects as those of the first and second embodiments. For example, the web around the reinforcing plate 17 having a substantially triangular shape is provided. The 12 cut portions 12A, the lower flange 14, the boss 18 and the closing plate 15 can be joined over the entire circumference.

  In the first embodiment, the case where the cylindrical boss 20 is circumferentially welded into the insertion hole 12C of the web 12 has been described as an example. However, the present invention is not limited to this, and may be applied to the case where the circular one-side member 51 is laser-welded to the counterpart member 52 as in the first modification shown in FIG.

  Further, for example, as in the second modification shown in FIG. 11, the present invention may be applied to the case where the one-side member 61 having a square shape is laser-welded to the counterpart member 62. Further, the one-side member may be a member having a non-circular shape such as a triangle, a pentagon, a hexagon, or an ellipse.

  In the first embodiment, the case where laser irradiation for the second round is stopped at the position of point PE (for example, a position of 720 degrees) has been described as an example. However, the present invention is not limited to this. For example, the laser irradiation in the second round is shifted before and after the position of the point PE, and the position is about 700 to 750 degrees from the position of the point A as the starting point. Thus, even if laser irradiation for the second round is stopped, the effect of slow cooling on the weld bead can be exhibited. This also applies to the second and third embodiments (modifications 1 and 2).

1 is a front view showing a hydraulic excavator to which a laser welding method according to a first embodiment of the present invention is applied. It is a front view which expands and shows the arm in FIG. It is a perspective view which shows the state which carries out the laser welding of the boss | hub to the web in FIG. It is a front view which expands and shows the welding part of the boss | hub and web in FIG. It is sectional drawing which looked at the welding part of a boss | hub and a web from the arrow VV direction in FIG. It is a characteristic diagram which shows the temperature distribution of the welding bead by circumferential welding. It is a characteristic diagram which shows the temperature distribution of the weld bead by circumferential welding at each of a plurality of locations in the circumferential direction. It is a front view in the same position as FIG. 4 which shows the laser beam etc. by 2nd Embodiment. It is a principal part enlarged view in FIG. 2 which shows the weld bead part etc. of the reinforcement board by 3rd Embodiment. It is a front view in the position corresponding to FIG. 4 which shows a 1st modification. It is a front view in the position corresponding to FIG. 4 which shows a 2nd modification.

Explanation of symbols

1 Excavator (construction machine)
4 Working device 11 Arm 12 Web (counter member)
12C Insertion hole 13 Upper flange 14 Lower flange 15 Blocking plate 17 Reinforcement plate (one side member)
18 Boss 20 Boss (one side member)
21 Laser welding machine 22, 31 Laser beam 23, 25, 32 Irradiation locus 24 Weld bead 31A, 31B, 31C, 31D, 31E Beam diameter 41A, 41B, 41C, 41D Weld bead 51, 61 One side member 52, 62 Element

Claims (6)

In a laser welding method for laser welding a one-side member having a circular or non-circular contour to the other member over the entire circumference,
Irradiating a laser beam along the contour of the one side member until it makes one round, and forming a weld bead over the entire circumference of the contour;
And a second laser irradiation step of irradiating the laser beam along a position outside the position of the weld bead in the first cycle without stopping the laser beam irradiation performed in the first cycle. A characteristic laser welding method.   In the second laser irradiation step, laser irradiation is performed along the contour of the weld bead while gradually reducing the power of the laser beam from that of the first laser irradiation. The laser welding method according to claim 1, wherein the laser welding is stopped.   In the second laser irradiation step, laser irradiation is performed along the outline of the weld bead while the laser beam is defocused more than the first laser irradiation, and the laser irradiation is stopped when the second round is completed. The laser welding method according to claim 1.   4. The laser welding according to claim 1, wherein in the second laser irradiation step, the peak temperature of the site where the weld bead is formed is set to a temperature lower than the austenitization transformation point (A1). Method.   4. The laser according to claim 1, wherein in the laser irradiation process in the second round, the peak temperature of the portion where the weld bead is formed is set to a temperature higher than the martensitic transformation start point (Ms). Welding method.   In the second laser irradiation step, the peak temperature of the portion where the weld bead is formed is set to a temperature lower than the austenitization transformation point (A1) and higher than the martensitic transformation start point (Ms). The laser welding method according to claim 1, 2 or 3 which is set.

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