JP3139953B2 - Vertical vibration laser tack welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser tack welding method for joining hot rolled steel slabs such as sheet bars and slabs.

[0002]

2. Description of the Related Art In hot rolling of billets such as sheet bars and slabs, a rear end of a preceding billet and a front end of a succeeding billet are joined. These billets have a thickness of 20 to
The width is about 50 mm and the width is about 600 to 2000 mm. The temperature of the billet is around 1000 ° C. As one of the joining methods of this billet, the rear end face of the preceding billet and the front end face of the succeeding billet are abutted and temporarily welded along the butt portion,
It is well known that the tack-welded steel slab is successively pressed down in the thickness direction of the slab to join the two slabs.

It is also known that laser welding is used for the tack welding. For example, WO. 94/6838
Japanese Patent Application Laid-Open Publication No. H11-163873 discloses a method in which a rear end portion of a preceding rolled material being rolled is abutted against a tip end of a succeeding rolled material, and then the butt portion is welded with a laser beam to perform continuous rolling. The energy density of the laser beam can be increased by converging the laser beam into a circle with a lens or a concave mirror. For this reason, the steel of the condensing irradiation part evaporates instantaneously, and a keyhole is generated on the surface of the steel piece. In laser welding, the keyhole is moved along a welding line, and the steel slab is joined and welded. That is, with the movement of the keyhole, the surrounding steel melts to form a molten pool, and the molten steel solidifies from behind the molten pool to complete the welding.

[0004] The leading and trailing ends of the billet are cut by a running shear or the like. The shape of the cut portion does not become a straight line due to the properties of the billet, the cutting method, and the like, and it is inevitable that the cut portion becomes a curve. For this reason, a gap g occurs between the preceding billet and the succeeding billet. (Wb-g) / 2 for bead width wb
The beam spot must be moved along the slab welding line (butt line) within the following range. Even if the beam spot is moved along the welding line of the slab, the beam spot deviates from the joint due to runout of the welding head, dimensional error of the groove, measurement error of the groove position, etc. May occur. If the gap increases to a certain degree or more, the melted portion generated in the beam spot shifts from the butt portion, and welding failure occurs. In the following, the maximum value of the gap in which the fusion zone does not deviate from the butted portion and no welding failure occurs is referred to as “missing gap”.

As a method for preventing welding failure caused by misalignment, there is a method of controlling the focused irradiation position of a laser beam with high precision so as not to shift from a butt portion of a billet. However, this method requires a high-precision groove position measuring device and a welding head scanning control device, and has a drawback that the joining device becomes large and complicated.

[0006] As another method, there is a method in which the welding speed is reduced and the melting width is increased to increase the out-of-offset allowable value. However, in this method, the welding time is long because the welding speed is low, and the cost is high. Further, there is a disadvantage that the heat-affected layer is widened, the mechanical strength is reduced, and the joint is broken in the next rolling step.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser tack welding method which can reduce the size and simplification of a billet joining apparatus and can tack-weld a billet at a high speed. Things.

[0008]

SUMMARY OF THE INVENTION A laser tack welding method according to the present invention is performed when a preceding steel slab and a succeeding steel slab are pressed and joined to each other. In this method, the laser beam is focused and the laser beam is condensed at an amplitude of 0.
While oscillating at a frequency of 4 to 3.0 mm and a frequency of 25 to 100 Hz, the irradiation position of the laser beam is scanned along the butt line to perform laser welding of the preceding and succeeding slabs. I do.

If the amplitude of the laser condensing position is less than 0.4 mm, the above effect cannot be obtained even if the laser is vibrated, and the amplitude is 3.0 mm.
Exceeds 0.4 mm, the design of the optical system becomes complicated and the size of the apparatus increases.

The frequency of the laser focus position is 25 Hz
If it is less than 100%, the above-mentioned effect cannot be obtained even if it is vibrated.
Introducing a mechanism to vibrate over Hz complicates the optical system and increases the size of the device.
It was as follows.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The steel slab to be joined in the present invention is a sheet bar or a slab having a thickness of 20 to 50 mm and a temperature of 900 to 1200 ° C. The rear end portion of the preceding steel slab and the front end portion of the following steel slab may be shaped by a running shear or a laser cutting device or the like, and then butted and laser welded.

In the laser welding, for example, a continuous wave CO ₂ laser oscillator having an output of 25 to 50 kW may be used to irradiate a laser beam along a butt portion of a steel slab traveling on a rolling line. In this case, the laser beam irradiation is performed while moving the processing point along the butted portion of the steel slab at about 3 to 20 m / min.

FIG. 1A shows a cross-sectional shape of a melted portion at a processing point by a conventional laser welding using a CO ₂ laser having an output of 45 kW. The welding speed of this laser welding is 5m /
min. As shown in FIG. 1 (a), the cross section of the melted portion has a substantially inverted triangular shape.
Met. As described above, a wide melting width is obtained near the surface of the workpiece, but the melting width is narrow at a deep portion. Therefore, the permissible outlier is relatively large in the upper part of the butted portion, but is smaller in the lower part. Therefore, even if tack welding of the preceding and succeeding slabs is performed at the upper part of the butt joint, misalignment occurs at the lower part and the tack welding cannot be performed. is there.

At the time of pressure welding, 30% of the depth of the butted portion
It has been confirmed that the above-mentioned fracture does not occur if the region is tack-welded. Therefore, to join billets having a thickness of 20 to 50 mm as in the present invention,
It is necessary to perform tack welding over a depth of 15 mm from the billet surface. That is, the permissible offset value in the laser tack welding of the hot-rolled steel slab is not effective unless the maximum value of the offset in which the molten portion does not deviate from the butt portion in the above range. From this, the permissible out-of-offset value in laser welding whose cross section is shown in FIG. 1A is substantially ± 0.5.
mm.

FIG. 1B shows that the position of the focal point of the laser focused at the processing point is vibrated up and down, and the other conditions are as shown in FIG.
2 shows the cross-sectional shape of the melted portion by laser welding performed under the same conditions as the conventional laser welding showing the cross section of the melted portion. FIG.
As shown in (b), the shape of the cross section of the fusion zone was substantially rectangular, the penetration depth was 22 mm, and the fusion width at a depth of 15 mm from the surface of the workpiece was 2.0 mm. Therefore, the actual outlier tolerance is ± 1.0 mm,
This is better than the conventional laser welding used in FIG. The cross-sectional area of the fusion zone is almost the same as when no vibration is applied. This is because there is no change in the amount of energy applied to the workpiece.

Therefore, in the present invention, the laser tack welding is performed while the laser condensing position at the processing point is vibrated up and down. More specifically, the laser focusing position refers to the position of the focal point of the laser focused on the processing point. here,
The oscillation of the laser focus position is performed at an amplitude of 0.4 to 3.0 mm and a frequency of 25 to 100 Hz. Also, the center of the vibration shall be about 0.2 to 1.5 mm below the surface of the steel plate butt.

The laser condensing position is oscillated about 0.2 to 1.5 mm below the surface of the butted portion of the steel plates, and this condition is almost the same as in ordinary laser welding. This is because there is no difference from ordinary laser welding in that a keyhole is formed in the beam spot, a molten pool is formed, and welding is performed.

As a method of vibrating the laser condensing position, the condensing optical element for condensing the laser at the processing point may be vibrated. A parabolic mirror, a lens, or the like is used as the condensing optical element.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to joining of a hot-rolled sheet bar as an example. FIG. 2 is a side view schematically showing the sheet bar joining equipment provided in the hot rolling equipment,
FIG. 3 is a plan view of the facility. In the sheet bar joining equipment shown in FIGS. 2 and 3, the front end and the rear end of the sheet bars 1 and 3 are cut off along the bar width direction by the running shear 11 to form a straight joining surface. . Then
The rear end surface of the preceding sheet bar 1 and the front end surface of the succeeding sheet bar 3 are butted, and this linear butted portion 5 is temporarily welded 7 by laser welding. Following the tack welding 7, both sheet bars 1 and 3 are continuously rolled by the rolling mill train 16 to
The joining of the sheet bar 1 and the sheet bar 3 is completed.

The sheet bars 1 and 3 have a length of 20 m, a width of 1100 mm and a thickness of 33 mm. Further, the temperature of the sheet bars 1 and 3 at the time of forming the joining surface is 1000 ° C.
It is. The feed speed of the sheet bars 1 and 3 is 80 m / min. The laser oscillator 13 is a continuous wave CO ₂ laser oscillator, and has a steady output of 45 kW. The laser beam emitted from the laser oscillator 13 is transmitted to the laser processing head 15 via the laser beam transmission optical system 14. Although the laser oscillator 13 is fixed, the laser processing head 15 moves linearly at a speed of 10 m / min along the butting portion 5 while moving in synchronization with the sheet bars 1 and 3.

FIG. 4 shows a schematic side view of the structure of the laser processing head 15. The laser beam transmitted to the processing head is reflected by the reflection mirror 21 in the direction of the converging mirror 23 and condensed on the sheet bar by the converging mirror 23 to form a beam spot. The condenser mirror 23 is a concave reflecting mirror having a focal length of 381 mm, and the reflecting mirror 21 is a plane reflecting mirror. The condensing mirror 23 is oscillated at a frequency of 50 Hz and an amplitude of 3.0 mm in a direction perpendicular to the sheet bar surface by a mirror oscillating device 25.
As a result, the laser beam focus 27 oscillates at a frequency of 50 Hz and an amplitude of 3.0 mm around a point 1.5 mm below the surface of the sheet bar.

With the device having the above configuration,
The permissible tolerance of the melted portion when the butt 5 was irradiated while the laser beam irradiation position was vibrated was ± 1 mm. On the other hand, when the butting portion 5 was scanned with the laser beam under the same conditions except that the laser beam irradiation position was not vibrated, the permissible allowable value of the molten portion generated in the butting portion 5 was ±
0.5 mm. From this result, it can be seen that the outlier tolerance can be increased by the method of the present invention.

[0023]

According to the method of the present invention, by performing the tack welding while oscillating the irradiation position of the laser beam perpendicularly to the steel slab, it is possible to enlarge the allowable tolerance. Therefore, it is possible to reduce the adverse effects of the run-out of the welding head, the dimensional error of the groove, the measurement error of the groove position, and the like on the joining of the billets. Also, there is no need for a high-precision groove position measurement device and a welding head scanning control device,
The joining device can be reduced in size and simplified. further,
Since laser welding can be performed at the same welding speed as in the conventional method, there is no reduction in mechanical strength of the joint caused by reducing the welding speed in the conventional method.

[Brief description of the drawings]

FIG. 1 (a) is a longitudinal sectional view of a molten portion generated when a steel slab is irradiated with a laser beam by a conventional method. (B) It is a longitudinal cross-sectional view of the fusion part which arises when irradiating a steel beam with a laser beam by the method of this invention.

FIG. 2 is a side view schematically showing one example of a billet joining facility for carrying out the method of the present invention.

FIG. 3 is a plan view of the equipment shown in FIG. 2;

FIG. 4 is a schematic diagram showing an example of a laser processing head used for carrying out the method of the present invention, which vertically vibrates a laser beam condensing position.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lead sheet bar 3 Trailing sheet bar 5 Butt joint 7 Temporary welding 11 Running shear 13 Laser oscillator 14 Laser beam transmission optical system 15 Laser processing head 16 Rolling mill train 21 Reflecting mirror 23 Condensing mirror 25 Mirror vibrating device 27 Laser Beam focusing position

──────────────────────────────────────────────────の Continuation of the front page (72) Inventor Moto Kido 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (56) References JP-A-7-290111 (JP, A) 61-111792 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 26/08 WPI / L (QUESTEL)

Claims (1)

(57) [Claims] 1. A method for laser tack welding in which a leading end of a preceding billet and a leading end of a succeeding billet are abutted and joined when a leading billet and a succeeding billet are pressed and joined. The laser beam irradiation position is scanned along the butt line while the laser beam condensing position is vibrated at an amplitude of 0.4 to 3.0 mm and a frequency of 25 to 100 Hz perpendicular to the surface of the steel slab, and the leading position is scanned. A longitudinal vibration laser tack welding method comprising performing laser welding of a billet and a succeeding billet.