JPH09174257A - Tack welding method by vertical oscillation laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make billet joining equipment miniaturized and simplified and enable billets to be tack-welded at a high speed. SOLUTION: In the method in which the rear end of a preceding billet 1 is abutted on the tip end of a succeeding billet 3, in which the abutting part 5 is tack-welded by laser welding, and in which both of these billets 1, 3 are rolled and joined, laser welding is performed by scanning the irradiation position of the laser beam along the abutting line while the converging position of the laser beam is oscillated vertically against the surface of the billet with an amplitude 0.4-3.0mm and with a frequency 25-100Hz.

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 performed when joining hot rolled steel pieces such as a sheet bar and a slab.

[0002]

2. Description of the Related Art In the hot rolling of steel slabs such as sheet bars and slabs, the rear end of the preceding steel slab and the front end of the following steel slab are joined together. These steel pieces 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 steel slab, the rear end face of the preceding steel slab and the front end face of the trailing steel slab are butted, and temporarily welded along the butt portion,
A method is known in which a steel piece which is subsequently tack welded is pressed down in the thickness direction of the steel piece to join the two steel pieces together.

It is also known that laser welding is used for the tack welding. For example, WO. 94/6838
The publication discloses a method of abutting the trailing end of the preceding rolled material and the leading end of the trailing rolled material during rolling, and then welding the abutting portion with a laser beam to perform continuous rolling. The laser beam can be condensed into a circular shape with a lens or a concave mirror to increase the energy density. For this reason, the steel in the concentrated irradiation portion is instantly evaporated and a keyhole is generated on the surface of the steel slab. In laser welding, this keyhole is moved along a welding line to join and weld steel pieces. That is, as the keyhole moves, the surrounding steel melts to form a molten pool, and the molten steel solidifies from the rear of the molten pool to complete welding.

The front end and the rear end of the steel slab are cut by a running shear or the like. It is inevitable that the shape of the cut portion does not become a straight line and becomes a curved line depending on the properties of the steel slab and the cutting method. Therefore, a gap g occurs between the preceding steel piece and the following steel piece. (Wb-g) / 2 for bead width wb
The beam spot must be moved along the weld line (butt line) of the billet within the following range. Even if the beam spot is moved along the welding line of the steel piece in this way, the beam spot is displaced from the butt portion due to welding head deflection, groove dimensional error, groove position measurement error, etc. May occur. If the margin of deviation becomes larger than a certain level, the melted portion generated in the beam spot will be displaced from the butt portion, and welding failure will occur. In the following, the maximum value of the margin of deviation in which the fusion zone does not shift from the abutting section and welding failure does not occur is referred to as "permissible margin of margin".

As a method for preventing welding failure caused by misalignment, there is a method in which the focused irradiation position of the laser beam is controlled with high accuracy so as not to shift from the butt portion of the steel slab. However, this method requires a highly accurate groove position measuring device and a welding head copying control device, and has a drawback that the joining device becomes large and complicated.

As a method other than this, there is a method in which the welding speed is reduced to increase the melting width to increase the margin of deviation. However, in this method, since the welding speed is slowed, the welding time becomes long and the cost becomes high. Further, there is a drawback that the heat-affected layer becomes wider and the mechanical strength is lowered, which causes a fracture of the joint portion in the next rolling step.

[0007]

SUMMARY OF THE INVENTION The present invention is intended to provide a laser tack welding method capable of reducing the size and simplification of a billet joining device and tack-welding billets at high speed. It is a thing.

[0008]

The laser tack welding method of the present invention is performed when a leading steel piece and a trailing steel piece are pressure-welded and joined to each other. In the method of butt-welding the tips of the lasers and performing laser tack welding, the focus position of the laser beam is amplitude 0.
While vibrating 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 steel piece and the following steel piece. To do.

If the amplitude of the laser focusing position is less than 0.4 mm, the above effect cannot be obtained even if vibrated, and the amplitude is 3.0 mm.
If it exceeds 1.0 mm, the design of the optical system becomes complicated and the size of the apparatus becomes large.

The frequency of the laser focusing position is 25 Hz.
If it is less than 100%, the above effect cannot be obtained even when vibrating, and
Introducing a mechanism that vibrates above Hz will complicate the optical system and increase the size of the device.
It was as follows.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The steel piece to be joined in the present invention is a sheet bar or 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 piece and the front end portion of the following steel piece may be shaped into a shape by a running shear or a laser cutting device, and then abutted to perform laser welding.

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

FIG. 1 (a) shows a cross-sectional shape of a fusion zone at a processing point by laser welding of a conventional method 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 fusion zone has an almost inverted triangular shape, the penetration depth is 18 mm, and the fusion width at a depth of 15 mm from the surface of the workpiece is 1.0 mm.
Met. Thus, a wide melting width is obtained near the surface of the material to be processed, but the melting width is narrow in the deep portion. Therefore, the eye-drop margin is relatively large at the upper part of the abutting portion, but is small at the bottom portion. Therefore, even if the preceding steel piece and the trailing steel piece can be tack-welded at the upper part of the butt portion, the stitching is not possible at the lower part and tack-welding cannot be performed, and as a result, fracture may occur during pressure welding. is there.

30% of the depth of the abutting portion during pressure welding
It has been confirmed that the above-mentioned breakage does not occur if the region is tack welded. Therefore, in order to join steel pieces having a thickness of 20 to 50 mm as in the present invention,
It is necessary to perform tack welding from the surface of the billet to a depth of 15 mm. That is, the allowable deviation value in the laser tack welding of the hot-rolled steel slab is not effective unless it is the maximum deviation value in which the melted portion does not deviate from the butt portion in the above range. From this, the allowable margin of deviation in laser welding, whose cross section of the fused portion is shown in FIG. 1 (a), is substantially ± 0.5.
It turns out to be mm.

In FIG. 1B, the position of the focal point of the laser focused at the processing point is vertically vibrated, and other conditions are shown in FIG.
The cross-sectional shape of the melted portion by laser welding performed under the same conditions as the conventional laser welding in which the cross-section of the melted portion is shown in FIG. FIG.
As shown in (b), the shape of the cross section of the fusion zone was almost 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 effective margin of deviation is ± 1.0 mm,
This is an improvement over the conventional laser welding used in FIG. The cross-sectional area of the fusion zone is almost the same as that when no vibration is applied. This is because there is no change in the amount of energy applied to the work material itself.

Therefore, in the present invention, laser tack welding is performed while vertically oscillating the focus position of the laser at the processing point. More specifically, the laser focus position refers to the focus position of the laser focused on the processing point. here,
The vibration of the laser condensing position is performed at an amplitude of 0.4 to 3.0 mm and a vibration frequency of 25 to 100 Hz. Further, the center of vibration is about 0.2 to 1.5 mm below the surface of the butted portions of the steel plates.

The laser converging position is oscillated about 0.2 to 1.5 mm below the surface of the butted portion of the steel sheet as a center, 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 to form a molten pool and welding is performed.

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

[0019]

EXAMPLES Examples of the present invention will be described by taking the joining of hot rolled sheet bars 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 equipment. In the sheet bar joining equipment shown in FIGS. 2 and 3, the front and rear ends of the sheet bars 1 and 3 are cut off by the running shear 11 along the bar width direction to form a straight joining surface. . Then
The rear end surface of the preceding sheet bar 1 and the front end surface of the following sheet bar 3 are butted, and this linear butted portion 5 is temporarily welded 7 by laser welding. Following the tack welding 7, the rolling mill train 16 continuously rolls both the sheet bars 1 and 3.
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. The temperature of the sheet bars 1 and 3 at the time of forming the joint 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 the steady output is 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 10 m / min along the abutting portion 5 while moving in synchronization with the sheet bars 1 and 3.

A schematic side view of the structure of the laser processing head 15 is shown in FIG. The laser beam transmitted to the processing head is reflected by the reflection mirror 21 in the direction of the condenser mirror 23, and condensed by the condenser mirror 23 on the sheet bar 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 vibrated at a frequency of 50 Hz and an amplitude of 3.0 mm in a direction perpendicular to the surface of the seat bar by a mirror vibrating device 25.
As a result, the laser beam focus 27 oscillates at a frequency of 50 Hz and an amplitude of 3.0 mm with a point 1.5 mm below the surface of the sheet bar as the center.

With the device having the above-mentioned configuration,
The permissible deviation value of the melted portion generated when the butt portion 5 was irradiated while vibrating the laser beam irradiation position was ± 1 mm. On the other hand, when the abutting portion 5 was scanned with a laser beam under the same conditions as the other conditions without oscillating the laser beam irradiation position, the allowable deviation value of the melted portion generated in the abutting portion 5 was ±.
It was 0.5 mm. From this result, it can be seen that the method of the present invention can increase the margin of deviation value.

[0023]

According to the method of the present invention, by performing the tack welding while vibrating the irradiation position of the laser beam perpendicularly to the steel slab, it is possible to expand the margin of deviation. Therefore, it is possible to reduce the adverse effects that the deflection of the welding head, the groove dimension error, the groove position measurement error, and the like have on the joining of the steel pieces. Further, without requiring a highly accurate groove position measuring device and a welding head copying control device,
The joining device can be made compact and simple. further,
Since the laser welding can be performed at the same welding speed as in the conventional method, there is no reduction in the mechanical strength of the joint portion caused by slowing the welding speed in the conventional method.

[Brief description of the drawings]

FIG. 1 (a) is a vertical cross-sectional view of a molten portion generated when a steel beam is irradiated with a laser beam by a conventional method. (B) It is a longitudinal cross-sectional view of a fusion zone produced when a steel beam is irradiated with a laser beam by the method of the present invention.

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

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

FIG. 4 is a schematic view showing an example of a laser processing head used for carrying out the method of the present invention to vertically vibrate a laser beam focusing position.

[Explanation of symbols]

 1 Leading Seat Bar 3 Trailing Seat Bar 5 Butt Section 7 Temporary Welding 11 Trapping Shear 13 Laser Oscillator 14 Laser Beam Transmission Optical System 15 Laser Processing Head 16 Rolling Machine Row 21 Reflecting Mirror 23 Condensing Mirror 25 Mirror Vibration Device 27 Laser Beam focus position

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B23K 26/08 B23K 26/08 B (72) Inventor Moto Kido 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Stock Company Technology Development Division

Claims (1)

[Claims] 1. A method for laser tack welding, in which a trailing end portion of a preceding steel piece and a leading end portion of a following steel piece are butted against each other, which is performed when the leading steel piece and the trailing steel piece are joined by pressure welding. While oscillating the focus position of the laser beam perpendicularly to the surface of the steel slab with an amplitude of 0.4 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 and preceded. A longitudinal vibration laser tack welding method, which comprises performing laser welding of a billet and a trailing billet.