Patent Description:
For example, in the above steel floor slab, a side edge of the U-rib joined to the surface of the deck plate by fillet welding is obliquely joined to the deck plate. On this occasion, a non-welded portion remains at a root part of a joining portion between the deck plate and the side edge of the U-rib, but the penetration depth of a welded portion meets a prescribed numerical value that is previously determined, so that the strength is secured.

However, it is known that cracks (a deck growth crack that grows in a direction of piercing the deck plate and a bead growth crack that grows in a direction of piercing a welding bead) beginning at the non-welded portion of the root part are generated at the joining portion between the deck pate and the side edge of the U-rib, due to aging deterioration or metallic fatigue.

Conventionally, in the case where the above crack beginning at the non-welded portion of the root part is generated at the joining portion between the deck plate and the side edge of the U-rib in the steel floor slab, a paved portion on the steel floor slab is taken away and then reinforcement by a stiffening plate and repair are performed.

In this conventional repair construction, for taking away the paved portion on the steel floor slab, it is necessary to perform traffic regulation. In recent years, for avoiding the traffic regulation, for example, a welding method described in Patent Document <NUM> has been proposed.

In this welding method, the irradiation direction of a laser beam is set to a growth direction of the crack that is generated in the bead, and thereby the crack is eliminated.

However, the above conventional welding method for crack removal is not intended for the removal of the deck growth crack that grows in the direction of piercing the deck plate, even though the bead growth crack can be eliminated by the irradiation with the laser beam. Accordingly, there is conventionally a problem about how to remove the deck growth crack by the irradiation with the laser beam.

The present invention has been made for solving the above conventional problem, and has an object to provide a repairing laser welding method and a use of a repairing laser welding device that make it possible to remove not only the bead growth crack but also the deck growth crack by the irradiation with the laser beam, without taking away the paved portion on the steel floor slab, in the case where the crack beginning at the non-welded portion of the root part is generated at the joining portion between the deck plate and the side edge of the U-rib in the steel floor slab, for example.

A first aspect of the present invention defines a repairing laser welding method for melting and eliminating a crack by irradiation with a laser beam according to claim <NUM>, the crack being generated beginning at a non-welded portion of a root part between a first welded material and a second welded material obliquely joined to a surface of the first welded material by fillet welding, in which the irradiation with the laser beam is performed along a welding bead at the root part while the laser beam is aimed at a contact point between the first welded material and the second welded material as an irradiation point of the laser beam, from a side of the welding bead, the contact point being contained in the non-welded portion of the root part.

The position of the contact point between the first welded material and the second welded material that is contained in the non-welded portion of the root part is identified by non-destructive inspection.

A second aspect of the present invention defines a use of a repairing laser welding device for melting and eliminating a crack by irradiation with a laser beam according to claim <NUM>.

The repairing laser welding method according to the present invention exerts a very excellent effect of making it possible to remove not only the bead growth crack but also the deck growth crack by the irradiation with the laser beam, without taking away the paved portion on the steel floor slab, in the case where the crack beginning at the non-welded portion of the root part is generated at the joining portion between the deck plate and the side edge of the U-rib in the steel floor slab, for example.

The present disclosure will be explained below based on the drawings.

<FIG> and <FIG> show a steel floor slab in a steel floor slab box girder of a bridge to which a repairing laser welding method according to the present disclosure is applied, and <FIG> and <FIG> show a repairing laser welding device used in a repairing laser welding method according to the present disclosure.

As shown in <FIG>, a steel floor slab <NUM> that constitutes a steel floor slab box girder <NUM> together with a plurality of main girders <NUM> includes a deck plate (a first welded material) <NUM> on which a paved portion H of the bridge is placed, and a plurality of U-ribs (second welded materials) <NUM> that is disposed on a downward-facing surface <NUM> on the opposite side of a paved portion placement surface <NUM> of the deck plate <NUM>.

As also shown in an enlargement circle in <FIG>, single bevel grooves <NUM>, <NUM> are respectively formed at distal ends of a pair of side edges <NUM>, <NUM> of the U-rib <NUM> that obliquely abuts on the downward-facing surface <NUM> of the deck plate <NUM>. The U-rib <NUM> is attached to the deck plate <NUM> by forming welding beads B by fillet arc welding between the single bevel grooves <NUM>, <NUM> and the downward-facing surface <NUM> of the deck plate <NUM> over the entire length, and thereby forming a closed section structure together with the deck plate <NUM>.

On this occasion, as shown in <FIG>, a non-welded portion S remains at a root part R of a joining portion between the deck plate <NUM> and the side edges <NUM>, <NUM> of the U-rib <NUM> obliquely joined to the downward-facing surface <NUM> of the deck plate, and cracks (a deck growth crack Cd that grows in a direction of piercing the deck plate <NUM> and a bead growth crack Cb that grows in a direction of piercing the welding bead B at the joining portion) beginning at the non-welded portion S can be generated at the joining portion between the deck plate <NUM> and the U-rib <NUM>, due to aging deterioration or metallic fatigue.

A repairing laser welding device <NUM> that removes these cracks Cd, Cb generated at the joining portion between the deck plate <NUM> and the U-rib <NUM> includes a laser oscillator <NUM>, a laser head <NUM> that condenses a laser beam L supplied from the laser oscillator <NUM> through an optical fiber <NUM> and that irradiates a repair location, and a head drive mechanism <NUM> that moves the laser head <NUM> along the welding bead B, as schematically shown in <FIG> and <FIG>.

The head drive mechanism <NUM> includes a rail base <NUM> that is attached and fixed to a bottom <NUM> between the side edges <NUM>, <NUM> of the U-rib <NUM> by a magnet or the like, and a carriage <NUM> that runs with the laser head <NUM> equipped through an arm <NUM>.

In this case, wheels 12a, 12a of the carriage <NUM> are placed on rails 11a, 11a of the rail base <NUM>, and thereby the carriage <NUM> is suspended and supported by the rail base <NUM>. By dynamic power from an unillustrated motor equipped in the carriage <NUM>, the carriage <NUM> runs on the rails 11a, 11a, that is, runs along the welding bead B.

Further, the repairing laser welding device <NUM> includes a copying mechanism <NUM> that causes the irradiation point of the laser beam L that is emitted from the laser head <NUM> that is moved along the welding bead B by the head drive mechanism <NUM>, to copy after the joining portion between the deck plate <NUM> and the U-rib <NUM>.

The copying mechanism <NUM> includes two copying legs 8a, 8b each of which is disposed at the laser head <NUM> and includes a roller 8c at the distal end, a sub-arm 9a provided on the carriage <NUM>, and a tension-spring 9b. In the copying mechanism <NUM>, the tension-spring 9b is disposed between the sub-arm 9a and the arm <NUM>, and presses the two copying legs 8a, 8b against the downward-facing surface <NUM> of the deck plate <NUM> and the side edge <NUM> of the U-rib <NUM> respectively, so that the irradiation point of the laser beam L that is emitted from the laser head <NUM> copies after the joining portion between the deck plate <NUM> and the U-rib <NUM>.

The copying mechanism that causes the irradiation point of the laser beam L to copy after the joining portion between the deck plate <NUM> and the U-rib <NUM> is not limited to the above configuration. For example, a non-contact-type copying mechanism with a sensor may be used.

Furthermore, the repairing laser welding device <NUM> includes a weaving mechanism <NUM> that is incorporated in the laser head <NUM>, and can perform the weaving with the laser beam L in a direction crossing the welding bead B in a range of an arrow in <FIG>.

Moreover, the repairing laser welding device <NUM> includes a shift mechanism. In this configuration the arm <NUM> supporting the laser head <NUM> serves also as the shift mechanism. Specifically, the arm <NUM> is constituted by a support arm 7a that is provided on the carriage <NUM>, an arm body 7c that is linked with the support arm 7a through a pin 7b so as to be capable of pivoting, and a movement arm 7d that is fit to the arm body 7c provided on the laser head <NUM> side so as to be capable of moving in the axial direction (the arrow direction in the figure).

That is, the arm <NUM> that serves also as the shift mechanism moves the movement arm 7d relative to the arm body 7c linked with the support arm 7a so as to be capable of pivoting, and thereby can shift the irradiation point of the laser beam L from the root part R of the joining portion between the deck plate <NUM> and the U-rib <NUM>, to the welding bead B side.

Reference numeral <NUM> in <FIG> denotes a control unit, and the control unit <NUM> controls the spot diameter of the laser beam L that is emitted from the laser head <NUM>, the movement of the laser head <NUM> by the head drive mechanism <NUM>, and the like.

When the deck growth crack Cd generated at the joining portion between the deck plate <NUM> and the U-rib <NUM> in the steel floor slab <NUM> is removed using the repairing laser welding device <NUM> configured in the above way, first, a non-destructive inspection such as an ultrasonic test is performed to the joining portion between the deck plate <NUM> and the U-rib <NUM>, and the position of a contact point P that is the contact point between the downward-facing surface <NUM> of the deck plate <NUM> and the single bevel groove <NUM> at the side edge <NUM> of the U-rib <NUM> and that is contained in the non-welded portion S of the root part R is identified, as shown in <FIG>.

Next, the angle of the arm body 7c of the arm <NUM> (the shift mechanism) supporting the laser head <NUM> is adjusted, and the movement arm 7d is moved relative to the arm body 7c. Thereby, the irradiation point of the laser beam L is determined such that the laser beam L contacts with the above contact point P.

Then, the two copying legs 8a, 8b are set so as to be pressed against the downward-facing surface <NUM> of the deck plate <NUM> and the side edge <NUM> of the U-rib <NUM> by the tension-spring 9b of the copying mechanism <NUM>, respectively.

Thereafter, the carriage <NUM> of the head drive mechanism <NUM> starts to run in response to a command from the control unit <NUM>, and the laser head <NUM> starts to move while irradiating the above contact point P with the laser light L having an appropriate spot diameter. In the configuration, by the movement of the laser head <NUM>, the laser beam L passes (moves) along the welding bead B once.

In the case where the bead growth crack Cb generated at the joining portion between the deck plate <NUM> and the U-rib <NUM> in the steel floor slab <NUM> is removed using the repairing laser welding device <NUM> having the above configuration, the laser head <NUM> is moved while irradiating the welding bead B with the laser beam L.

In the repairing laser welding method, the laser beam L is aimed, as the irradiation point, at the contact point P that is the contact point between the downward-facing surface <NUM> of the deck plate <NUM> and the single bevel groove <NUM> at the side edge <NUM> of the U-rib <NUM> in the steel floor slab <NUM> and that is contained in the non-welded portion S of the root part R, and therefore it is possible to melt the non-welded portion S of the root part R. Then, with the melting of the non-welded portion S, the deck growth crack Cd generated beginning at the non-welded portion S is molten and removed.

<FIG> is a partial enlarged sectional view showing a relation between the laser beam irradiation point and repair condition, and shows the repair condition when the laser beam L passes along the welding bead B once.

When the irradiation point of the laser beam L is set to the inside (less than <NUM> (-)) of the U-rib <NUM> relative to the above contact point P in <FIG>, the molten metal of a welding bead BL due to the irradiation with the laser beam L flows to the inside of the U-rib <NUM>, and a hole is generated in the side edge <NUM> of the U-rib <NUM>, as shown in the partial enlarged sectional view of <FIG>.

On this occasion, even when the focal point of the laser beam L is set so as to coincide with the above contact point P, the outer edge of the spot of the laser beam L actually enters the inside (the region of less than <NUM> (-)) of the U-rib <NUM>.

Accordingly, it is preferable to set the irradiation point of the laser beam L such that at least the outer edge of the spot of the laser beam L contacts with the contact point P, and by setting the irradiation point of the laser beam L in this way, it is possible to surely prevent the flow of the molten metal due to the irradiation with the laser beam L to the inside of the U-rib <NUM>.

On the other hand, when the irradiation point of the laser beam L is set excessively to the welding bead B side (<NUM> +) relative to the above contact point P, the welding bead BL due to the irradiation with the laser beam L does not reach the non-welded portion S, and therefore a remaining non-welded portion is generated, as shown in the partial enlarged sectional view of <FIG>. Accordingly, in the configuration in which the laser beam L passes along the welding bead B once, it is found that it is preferable to set the irradiation point of the laser beam L to the welding bead B side that is about <NUM> away from the above contact point P.

Further, when the deck growth crack Cd is small, it is possible to remove the deck growth crack Cd, simply by causing the laser beam L to pass along the welding bead B once and forming the welding bead BL due to the irradiation of the laser beam L, as shown in a partial enlarged sectional view of <FIG>. When the deck growth crack Cd is large, it is possible to remove the deck growth crack Cd by performing the passing multiple times while the irradiation point of the laser beam L is shifted from the root part R of the joining portion between the deck plate <NUM> and the U-rib <NUM> to the welding bead B side by the arm <NUM> that serves as the shift mechanism (by forming a plurality of welding beads BL due to the irradiation with the laser beam L), as shown in a partial enlarged sectional view of <FIG>.

On this occasion, it is possible to reduce the risk of hot cracking by causing the weaving mechanism <NUM> to perform the weaving with the laser beam L and forming a wide welding bead BLW due to the irradiation with the laser beam L, as shown in a partial enlarged sectional view of <FIG>.

<FIG> and <FIG> show a repairing laser welding device used in a repairing laser welding method according to the present disclosure.

As schematically shown in <FIG> and <FIG>, a repairing laser welding device 1A includes the laser head <NUM> that condenses the laser beam L supplied from an unillustrated laser oscillator through the optical fiber <NUM> and irradiates a repair location, and a head drive mechanism 10A that moves the laser head <NUM> along the welding bead B.

The head drive mechanism 10A includes a rail 11A and a carriage 12A that runs on the rail 11A, and the laser head <NUM> is equipped in the carriage 12A through an arm 7A.

The repairing laser welding device 1A includes a rail disposition mechanism <NUM>, and the rail disposition mechanism <NUM> includes an L-shaped member <NUM> on which magnets <NUM>, <NUM> are disposed at both ends and a guide <NUM> that is disposed on the rail 11A of the head drive mechanism 10A.

The rail 11A of the head drive mechanism 10A is fixed to the bottom <NUM> of the U-rib <NUM> through one magnet <NUM> of the L-shaped member <NUM> of the rail disposition mechanism <NUM>. On this occasion, the other magnet <NUM> of the L-shaped member <NUM> is attached to the downward-facing surface <NUM> (the surface of the first welded material to which the second welded material is joined) of the deck plate <NUM>, and the guide <NUM> abuts on the side edge <NUM> of the U-rib <NUM>.

That is, the rail 11A of the head drive mechanism 10A is fixed with reference to both the downward-facing surface <NUM> of the deck plate <NUM> and the side edge <NUM> of the U-rib <NUM>, and thereby the irradiation point of the laser beam L to be emitted from the laser head <NUM> that moves along the welding bead B together with the carriage 12A is aimed at the joining portion between the deck plate <NUM> and the U-rib <NUM> (at the contact point P that is the contact point between the downward-facing surface <NUM> of the deck plate <NUM> and the single bevel groove <NUM> at the side edge <NUM> of the U-rib <NUM> and that is contained in the non-welded portion S of the root part R in <FIG>).

When the deck growth crack Cd generated at the joining portion between the deck plate <NUM> and the U-rib <NUM> in the steel floor slab <NUM> is removed using the repairing laser welding device 1A first, the non-destructive inspection such as an ultrasonic test is performed to the joining portion between the deck plate <NUM> and the U-rib <NUM>, and the position of the contact point P that is the contact point between the downward-facing surface <NUM> of the deck plate <NUM> and the single bevel groove <NUM> at the side edge <NUM> of the U-rib <NUM> and that is contained in the non-welded portion S of the root part R is identified, as shown in <FIG>.

Next, by attaching the other magnet <NUM> of the L-shaped member <NUM> of the rail disposition mechanism <NUM> to the downward-facing surface <NUM> of the deck plate <NUM> and causing the guide <NUM> to abut on the side edge <NUM> of the U-rib <NUM>, that is, with reference to both the downward-facing surface <NUM> of the deck plate <NUM> and the side edge <NUM> of the U-rib <NUM>, the rail 11A of the head drive mechanism 10A is fixed to the bottom <NUM> of the U-rib <NUM> through the one magnet <NUM> of the L-shaped member <NUM>.

Thereby, the irradiation point of the laser beam L to be emitted from the laser head <NUM> that moves along the welding bead B together with the carriage 12A is set to the contact point P that is contained in the non-welded portion S of the root part R of the joining portion between the deck plate <NUM> and the U-rib <NUM>.

Thereafter, the carriage 12A of the head drive mechanism 10A starts to run, and the laser head <NUM> starts to move while irradiating the above contact point P with the laser light L having an appropriate spot diameter. In this configuration also, by the movement of the laser head <NUM>, the laser beam L passes (moves) along the welding bead B once.

On the other hand, in the case where the bead growth crack Cb generated at the joining portion between the deck plate <NUM> and the U-rib <NUM> in the steel floor slab <NUM> is removed using the repairing laser welding device 1A having the above configuration, the laser head <NUM> is moved while the welding bead B is irradiated with the laser beam L.

In the repairing laser welding method also, the laser beam L is aimed, as the irradiation point, at the contact point P that is the contact point between the downward-facing surface <NUM> of the deck plate <NUM> and the single bevel groove <NUM> at the side edge <NUM> of the U-rib <NUM> in the steel floor slab <NUM> and that is contained in the non-welded portion S of the root part R, and therefore it is possible to melt the non-welded portion S of the root part R. Then, with the melting of the non-welded portion S, the deck growth crack Cd generated beginning at the non-welded portion S is molten and removed.

<FIG> and <FIG> show a repairing laser welding device that is used in a repairing laser welding method according to still another embodiment of the present disclosure.

As schematically shown in <FIG> and <FIG>, a repairing laser welding device 1B according to the embodiment includes the laser head <NUM> that condenses the laser beam L supplied from an unillustrated laser oscillator through the optical fiber <NUM> and irradiates a repair location, and a head drive mechanism 10B that moves the laser head <NUM> along the welding bead B.

The head drive mechanism 10B includes a rail 20B and a carriage 22B that is equipped with the laser head <NUM>. In this case, the rail 20B has an angle steel shape, and includes a vertical plate material 22Y and a horizontal plate material 22X that are coupled so as to be capable of being separated from each other.

The vertical plate material 22Y of the rail 20B includes a magnet <NUM> on each upper end at both end parts in the longitudinal direction (the right-left direction in <FIG>), and the vertical plate material 22Y is fixed to the downward-facing surface <NUM> (the surface of the first welded material to which the second welded material is joined) of the deck plate <NUM> through the magnet <NUM>.

Further, a groove 22Ya along the top-bottom direction is formed on each lower end part at both end parts in the longitudinal direction of the vertical plate material 22Y.

When the vertical plate material 22Y is fixed, as shown in <FIG>, a guide 23B is interposed between the vertical plate material 22Y and the side edge <NUM> of the U-rib <NUM>, and thereby the positioning relative to the U-rib <NUM> is performed.

The guide 23B is interposed at an appropriate position in the longitudinal direction of the vertical plate material 22Y, for example, at both end parts, and is removed after the fixation of the vertical plate material 22Y.

On the other hand, the horizontal plate material 22X of the rail 20B includes a groove insertion protrusion 22Xa that is inserted into the groove 22Ya of the vertical plate material 22Y, at a base end part (at a left end part in <FIG>), and includes a magnet <NUM> at each distal end (at a right end in <FIG>) at both end parts in the longitudinal direction (the right-left direction in <FIG>).

The horizontal plate material 22X is fixed to the bottom <NUM> of the U-rib <NUM> through the magnet <NUM> in a state where the groove insertion protrusion 22Xa is inserted into the groove 22Ya of the vertical plate material 22Y. On this occasion, the vertical position of the groove insertion protrusion 22Xa relative to the groove 22Ya of the vertical plate material 22Y is adjusted, and thereby the positioning is performed with reference to the downward-facing surface <NUM> (the surface of the first welded material to which the second welded material is joined) of the deck plate <NUM>.

A long member 22Yb is disposed on the horizontal plate material 22X, parallel to the vertical plate material 22Y, and forms a running path between the vertical plate material 22Y and the long member 22Yb on the horizontal plate material 22X. As shown in <FIG>, the carriage 22B of the head drive mechanism 10B runs along the running path on the horizontal plate material 22X to which the positioning has been performed, while being guided by the vertical plate material 22Y to which the positioning has been similarly performed and the long member 22Yb.

That is, the irradiation point of the laser beam L to be emitted from the laser head <NUM> that moves along the welding bead B together with the carriage 22B is aimed at the joining portion between the deck plate <NUM> and the U-rib <NUM> (at the contact point P that is the contact point between the downward-facing surface <NUM> of the deck plate <NUM> and the single bevel groove <NUM> at the side edge <NUM> of the U-rib <NUM> and that is contained in the non-welded portion S of the root part R in <FIG>).

When the deck growth crack Cd generated at the joining portion between the deck plate <NUM> and the U-rib <NUM> in the steel floor slab <NUM> is removed using the repairing laser welding device 1B, first, the non-destructive inspection such as an ultrasonic test is performed to the joining portion between the deck plate <NUM> and the U-rib <NUM>, and the position of the contact point P that is the contact point between the downward-facing surface <NUM> of the deck plate <NUM> and the single bevel groove <NUM> at the side edge <NUM> of the U-rib <NUM> and that is contained in the non-welded portion S of the root part R is identified, as shown in <FIG>.

Next, the vertical plate material 22Y of the rail 20B is fixed to the downward-facing surface <NUM> (the surface of the first welded material to which the second welded material is joined) of the deck plate <NUM> through the magnet <NUM>, in a state where the guide 23B is interposed between the vertical plate material 22Y of the rail 20B and the side edge <NUM> of the U-rib <NUM>. That is, the vertical plate material 22Y of the rail 20B is fixed to the downward-facing surface <NUM> of the deck plate <NUM> in a state where the positioning relative to the U-rib <NUM> has been performed.

Subsequently, the horizontal plate material 22X is fixed to the bottom <NUM> of the U-rib <NUM> through the magnet <NUM>, in the state where the groove insertion protrusion 22Xa of the horizontal plate material 22X is inserted into the groove 22Ya of the vertical plate material 22Y. On this occasion, the vertical position of the groove insertion protrusion 22Xa relative to the groove 22Ya of the vertical plate material 22Y is adjusted, and the positioning is performed with reference to the downward-facing surface <NUM> (the surface of the first welded material to which the second welded material is joined) of the deck plate <NUM>.

Thereby, the running path for the carriage 22B that runs while being guided by the vertical plate material 22Y and the long member 22Yb (along the welding bead B) is set to the horizontal plate material 22X, and the irradiation point of the laser beam L to be emitted from the laser head <NUM> on the carriage 22B is set to the contact point P that is contained in the non-welded portion S of the root part R of the joining portion between the deck plate <NUM> and the U-rib <NUM>.

Next, the guide 23B is removed from between the vertical plate material 22Y of the rail 20B and the side edge <NUM> of the U-rib <NUM>. Thereafter, the carriage 22B of the head drive mechanism 10B starts to run, and the laser head <NUM> starts to move while irradiating the above contact point P with the laser light L having an appropriate spot diameter. In this configuration also, by the movement of the laser head <NUM>, the laser beam L passes (moves) along the welding bead B once.

On the other hand, in the case where the bead growth crack Cb generated at the joining portion between the deck plate <NUM> and the U-rib <NUM> in the steel floor slab <NUM> is removed using the repairing laser welding device 1B having the above configuration, the laser head <NUM> is moved while the welding bead B is irradiated with the laser beam L.

Further, in the repairing laser welding device the rail 20B is constituted by the vertical plate material 22Y and the horizontal plate material 22X that are coupled so as to be capable of being separated from each other, and therefore at the time of the installation of the rail 20B, the rail 20B is installed while the positioning of the vertical plate material 22Y and the horizontal plate material 22X is performed relative to the downward-facing surface <NUM> of the deck plate <NUM> and the U-rib <NUM> one by one.

That is, it is possible to perform individual works without feeling very heavy, and as a result, the workability is improved since the positioning and installation of the rail 20B are facilitated.

Furthermore, in the repairing laser welding device 1B, the running path for the carriage 22B is set to the horizontal plate material 22X of the rail 20B, and therefore a targeting work for the laser beam L to be emitted from the laser head <NUM> is readily performed.

In the repairing laser welding method, in the case where the bead growth crack generated at the joining portion between the deck plate <NUM> and the U-rib <NUM> is removed by the irradiation with the laser beam L, the laser welding is performed while a tab plate T having a rectangular parallelepiped shape shown in <FIG> is disposed at two locations of a starting end and a terminating end of the repair welding location in the welding bead B, as shown in <FIG>, and the tab plates T, T are removed after the finish of the laser welding for repair.

By performing the laser welding while the tab plates T, T are disposed at the starting end and terminating end of the repair welding location in the welding bead B in this way, it is possible to secure the normality of the starting end and the terminating end of the repair welding location in the welding bead B that have high defect generation rate.

In the configuration, as the tab plate that is disposed at the starting end and the terminating end of the repair welding location in the welding bead B, a tab plate T1 having a wedge shape shown in <FIG> and a tab plate T2 having a trapezoidal shape in lateral view shown in <FIG> can be used in place of the tab plate T having a rectangular parallelepiped shape.

For example, in the case where the repairing laser welding is performed using the tab plate T2 having a trapezoidal shape in lateral view, two tab plates T2, T2 are disposed on the surface of a steel material W so as to sandwich a crack Wa, as shown in <FIG>. Then, one side surfaces of the tab plates T2, T2 that are obliquely cut are caused to contact with a surface Wp of the steel material W, the other side surfaces are inclined so as to be away from each other, and joining is performed by spot welding, for example.

Next, the irradiation with the laser beam L is started such that heat is input from the side surface (so-called edge surface) of the tab plate T2 on one side (left side in the figure) that is held so as to contact with the surface Wp of the steel material W with an inclination.

In this case, the laser beam L is set such that the laser beam L is nearly perpendicular to the surface Wp of the steel material W and the distance is constant, and therefore the vicinity of each edge surface of the tab plates T2, T2 has a low energy density and does not melt.

Hence, it is preferable to prevent a temperature difference from being generated in the thickness direction of the steel material W, by employing a tab plate T3 having a groove T3a along the welding direction as shown in <FIG>, employing a tab plate T4 having a cutout T4a on the edge surface as shown in <FIG>, or employing a tab plate T5 having a step T5a on the edge surface as shown in <FIG>, instead of the tab plate T2 having a trapezoidal shape in lateral view.

In the case where the tab plates T3 to T5 having the above groove T3a, cutout T4a and step T5a are used in the repairing laser welding, it is preferable to put a stiffening plate U composed of a steel material or ceramic on the edge surface of the tab plate T3 (T4, T5) as shown in <FIG>, or fit the stiffening plate U into a cutout Ta formed on the tab plate T3 (T4, T5) as shown in <FIG>, for avoiding a base material from melting at each time point of the laser beam irradiation start and laser beam irradiation finish, and in the case where the tab T2 having a trapezoidal shape in lateral view is used, it is preferable to put the stiffening plate U under the tab plate T2 as shown in <FIG>.

<FIG> show a case where a portion positioned at a scallop part <NUM> of a horizontal rib <NUM> disposed over the U-rib is irradiated with the laser beam L when the repairing laser welding is performed to the joining portion between the deck plate <NUM> and the U-rib by the repairing laser welding method.

In the case where the portion positioned at the scallop part <NUM> of the horizontal rib <NUM> is irradiated with the laser beam L in this way, first, the laser head (not illustrated in <FIG>) that moves from the left side to the right side in the figure is stopped temporarily before the horizontal rib <NUM>, and in this state, the portion positioned at the scallop part <NUM> of the horizontal rib <NUM> is irradiated with the laser beam L through a mirror 4a, as shown in <FIG>.

Thereafter, as shown in <FIG>, the laser head is positioned at the right side in the figure of the horizontal rib <NUM>, and the portion positioned at the scallop part <NUM> is irradiated with the laser beam L from the right side in the figure of the horizontal rib <NUM> through the mirror 4a, that is, the portion positioned at the scallop part <NUM> is welded so as to be wrapped.

On this occasion, when the thickness of the horizontal rib <NUM> is represented as t and the distance from the deck plate <NUM> to the scallop part <NUM> is represented as R, it is preferable that the irradiation angle θ of the laser beam L with respect to the horizontal rib <NUM> be at least equal to or more than <NUM>/<NUM> of the tangent angle α of tanα expressed as t/R, for preventing a non-welded location from being generated at the portion positioned at the scallop part <NUM>.

Each of the above embodiments has been explained about an example of the case where the repairing laser welding method according to the present disclosure is used for repairing the crack generated at the joining portion between the deck plate constituting the steel floor slab of the bridge and the U-rib joined to the surface of the deck plate by fillet welding, but the present disclosure is not limited to this.

Further, in each of the above embodiments, the crack is removed by only the irradiation with the laser beam L, but the present disclosure is not limited to this. As another configuration, for example, the irradiation with the laser beam L may be performed while a welding material is supplied, and in the case where the irradiation with the laser beam L is performed while the welding material is supplied in this way, it is possible to surely remove the crack.

Furthermore, in each of the above embodiments, the crack is removed by only the irradiation with the laser beam L, but another welding, for example, an arc welding may be concurrently used.

The configurations of the repairing laser welding method and use of a laser welding device according to the present invention are not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention as defined in the appended claims.

The first aspect of the present invention defines a repairing laser welding method for melting and eliminating a crack by irradiation with a laser beam according to claim <NUM>.

Further, in the first aspect of the present invention, optionally, the laser beam is caused to pass along the welding bead multiple times while the irradiation point of the laser beam is shifted from the contact point to the side of the welding bead.

On this occasion, the one-time shift amount at the irradiation point of the laser beam is determined based on the spot diameter of the laser beam.

Furthermore, in the first aspect of the present invention, optionally, the irradiation with the laser beam is performed along the welding bead while weaving with the laser beam is performed in a direction crossing the welding bead.

Moreover, in the first aspect of the present invention, optionally, when the laser beam is aimed at the contact point between the first welded material and the second welded material as the irradiation point of the laser beam, the contact point being contained in the non-welded portion of the root part, the irradiation point is set such that at least an outer edge of a spot of the laser beam contacts with the contact point.

Moreover, in the first aspect of the present invention, optionally, the irradiation with the laser beam is performed while a welding material is supplied.

The second aspect of the present invention defines a use of a repairing laser welding device for melting and eliminating a crack by irradiation with a laser beam according to claim <NUM>.

Furthermore, in the second aspect of the present invention, optionally, the rail of the head drive mechanism has an angle steel shape including a vertical plate material and a horizontal plate material that are coupled so as to be capable of being separated from each other, positioning and fixing of the vertical plate material of the rail are performed with reference to the second welded material, positioning and fixing of the horizontal plate material of the rail are performed with reference to the surface of the first welded material to which the second welded material is joined, with respect to the vertical plate material fixed with reference to the second welded material, and the horizontal plate material of the rail is formed as a running path on which the carriage of the head drive mechanism runs while being guided by the vertical plate material, the carriage being placed on the horizontal plate material.

Moreover, in the second aspect of the present invention, optionally, the repairing laser welding device is configured to include a weaving mechanism that performs weaving with the laser beam in a direction crossing the welding bead.

Moreover, in the second aspect of the present invention, optionally, the irradiation point of the laser beam is set such that at least an outer edge of a spot of the laser beam contacts with the contact point between the first welded material and the second welded material, the contact point being contained in the non-welded portion of the root part.

Claim 1:
A repairing laser welding method for melting and eliminating a crack (Cb, Cd) by irradiation with a laser beam (L), the crack (Cb, Cd) being generated beginning at a non-welded portion (S) of a root part (R) between a first welded material (<NUM>) and a second welded material (<NUM>) obliquely joined to a surface of the first welded material (<NUM>) by fillet welding, wherein
the irradiation with the laser beam (L) is performed along a welding bead (B) at the root part (R) while the laser beam (L) is aimed at a contact point (P) between the first welded material (<NUM>) and the second welded material (<NUM>) as an irradiation point of the laser beam (L), from a side of the welding bead (B), the contact point (P) being contained in the non-welded portion (S) of the root part (R).