JP3583850B2 - Laser tack welding method - Google Patents

Description

[0001]
[Industrial application fields]
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]
[Prior 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 subsequent steel slab are joined. These steel pieces have a thickness of about 20 to 80 mm and a width of about 600 to 2000 mm. The temperature of the steel slab is around 1000 ° C. As one method of joining the steel slabs, the rear end of the preceding steel slab and the front end of the succeeding steel slab are abutted together, tack welded along the abutting part, and then the steel slab that has been tack welded is used as a steel slab A method of joining both steel pieces by reducing in the thickness direction is well known.
[0003]
It is also known that laser welding is used for the tack welding. For example, WO. No. 94/6838 discloses a method of performing continuous rolling by abutting the trailing end portion of the preceding rolled material being rolled with the leading end portion of the following rolled material and then welding the butted portion with a laser beam. Yes. The energy density of the laser beam can be increased by condensing the laser beam into a circular shape with a lens or a concave mirror. For this reason, the steel of the condensing irradiation part evaporates instantly and a keyhole is generated on the steel piece surface. In laser welding, the keyhole is moved along the welding line, and the steel pieces are joined and welded. That is, as the keyhole moves, the surrounding steel is melted to form a molten pool, and the molten steel is solidified from the rear of the molten pool to complete the welding.
[0004]
The front end and the rear end of the steel piece are cut with a running shear. The shape of the cut portion does not become a straight line due to the properties of the steel piece, the cutting method, or the like, and it is inevitable that it becomes a curved line. For this reason, as shown in FIG. 1, the butt position is shifted from the welding reference line L by E, and the butt line becomes a curve. Therefore, the laser beam must be moved along the butt line. Even if the laser beam is moved along the butt line in this way, the laser beam may be misaligned from the butt due to gaps, welding head deflection, groove dimensional error, groove position measurement error, etc. It may happen. If this misalignment becomes larger than a certain level, the laser beam irradiation shifts from the abutting portion, resulting in poor welding.
[0005]
As a method for preventing welding defects that occur due to off-axis, there is a method of controlling the focused irradiation position of the laser beam with high accuracy so as not to deviate from the butt portion of the steel piece. However, this method requires a high-accuracy groove position measuring device and a welding head scanning control device, and has the disadvantage that the joining device becomes large and complicated.
[0006]
As another method, there is a method in which the welding speed is made low, the melt width is enlarged, and missing is lost. However, in this method, since the welding speed is lowered, the welding time becomes long and the cost becomes high. Further, when the welding speed cannot follow the rolling line speed, there is a problem that the rolling line speed has to be lowered, resulting in a decrease in production efficiency. Furthermore, there is a problem that the heat-affected layer of the welded portion is widened, the mechanical strength is lowered, and the joint portion is broken in the next rolling process.
[0007]
[Problems to be solved by 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 apparatus and capable of tack welding a billet at a high speed without missing.
[0008]
[Means for Solving the Problems]
The laser tack welding method of this invention is performed when the preceding steel piece and the succeeding steel piece are joined by pressure welding and the rear end portion of the preceding steel piece and the leading end portion of the succeeding steel piece are brought into contact with each other. In the welding method, (2 × maximum misalignment E [mm] −melting width w [mm]) / 2 + margin Y [mm] is defined as amplitude a [mm], and 4a / {(3 to 100) × required welding. The laser beam is vibrated in a direction perpendicular to the welding direction with a speed Vo [m / min]} as a period T [sec].
[0009]
The maximum off-axis amount E is the maximum off-axis value measured from the welding reference line L. The maximum off-axis amount E varies depending on the size of the steel piece, the cutting shape of the front and rear ends, the mechanical setting accuracy of the laser processing head, and is obtained by actual measurement.
[0010]
The melt width w can be determined as follows. First, the preceding steel slab and the subsequent steel slab are laser-welded by combining various values of the welding speed V and the laser output P, and the relationship A between the welding cross section S to the welding speed V and the laser output P from the weld cross section. And the relationship B of the melt width w is obtained. Then, the required laser output Po and the required welding speed Vo are obtained from the required melted section sectional area So (2 × maximum amount of extraordinary amount E × required melt depth Do) based on the above relationship A, and the required laser output Po and the required welding speed Vo. From the above relationship B, the melt width w is obtained. The melt width w is a melt width when welding is performed without vibrating the laser beam.
[0011]
The required melting depth Do refers to the melting depth of a laser tack weld that gives strength that does not cause fracture when the preceding steel piece and the subsequent steel piece are joined by pressure welding. The margin Y takes into consideration the drive error of the laser beam vibration device, the variation in the deviation, and the like, and is about 0.1 to 1 mm.
[0012]
If the amplitude a is less than (2 × maximum extraordinary amount E−melting width w) / 2 + margin Y, the extraordinary occurrence occurs. If the amplitude a exceeds the above amplitude, the steel piece is melted more than necessary, which is uneconomical. When the period T exceeds the amplitude a / (3 × required welding speed Vo), a location where a sufficient melting depth cannot be obtained occurs in the weld line direction, that is, a location where the strength of the joint is insufficient. Further, if the period T is less than the amplitude a / (100 × required welding speed Vo), it is difficult to increase the speed of the vibration mechanism, and the equipment becomes expensive.
[0013]
Since the laser beam is oscillated with an amplitude a of (2 × maximum extraordinary amount E−melting width w) / 2 + margin Y, the melting width is expanded and there is no extraordinary loss. Further, since the laser beam is vibrated at a period T of amplitude a / {(3 to 100) × required welding speed Vo}, the melted portion becomes uniform over the entire length of the butt portion, and the strength at which the joint portion does not break during pressure welding is obtained.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
In this invention, the steel pieces to be joined are sheet bars or slabs having a thickness of 20 to 50 mm, and the temperature is 900 to 1200 ° C. It is desirable that the rear end portion of the preceding steel piece and the front end portion of the succeeding steel piece are trimmed with a running shear or a laser cutting device, and then abutted to perform laser tack welding. In laser tack 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 a butt portion of a steel piece running on a rolling line. As a method of vibrating the laser condensing position, a method of vibrating a condensing optical element that condenses the laser at a processing point is suitable.
[0015]
FIG. 2 shows an example of the relationship A between the welding speed V and the laser output P obtained in the experiment and the cross-sectional area of the fusion zone. FIG. 2 shows that the melt area cross-sectional area S = laser power P × (welding speed V) ⁻¹ . FIG. 3 shows the relationship between the welding speed V and the melt width w when the laser output P is 45 kW.
[0016]
In order to obtain the amplitude a, the melt width w is required, and the melt width w can be obtained from FIG. 2 and FIG. That is, the melted section sectional area S is provisionally determined from the required melting depth Do determined from the strength of the joint. The welding speed V is arbitrary as long as it is equal to or higher than the minimum speed required in the rolling line, but is temporarily determined in consideration of the laser output in order to reduce the equipment cost. The laser output P is obtained from FIG. 2 on the basis of these temporarily determined melt cross-sectional area S and welding speed V. Next, based on the laser output P and the welding speed V, the melt width w is obtained from FIG. When the obtained melt width w exceeds 2 × the maximum extraordinary amount E, it is useless to further oscillate the laser beam to widen the melt width. In such a case, the laser condensing optical system is adjusted so that the melt width is equal to or less than 2 × the maximum deviation amount E.
[0017]
【Example】
The embodiment of the present invention will be described with reference to FIGS. 4 and 5 by taking hot-rolled sheet bar joining as an example. FIG. 4 is a side view schematically showing a steel piece joining facility provided in the hot rolling facility, and FIG. 5 is a plan view of the facility.
[0018]
4 and 5, the front and rear ends of the sheet bars 1 and 3 that run in the A direction are cut off along the bar width direction by the running shear 11 to form a linear joint. A surface is formed. Next, the rear end surface of the preceding seat bar 1 and the front end surface of the succeeding seat bar 3 are abutted, and the linear abutting portion 5 is tack welded 7 by laser welding. Subsequent to the tack welding 7, in the continuous hot rolling mill row 16, both the sheet bars 1 and 3 are continuously rolled by the rolling mill 17, and the joining of the sheet bar 1 and the sheet bar 3 is completed.
[0019]
The sheet bars 1 and 3 have a length of 20 m, a width of 1100 mm, and a thickness of 80 mm. Further, the temperature of the sheet bars 1 and 3 at the time when the bonding surface is formed is 1000 ° C. The feeding 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 at a constant speed of 5 m / min along the butting portion 5 while moving in synchronization with the sheet bars 1 and 3.
[0020]
A schematic side view of the structure of the laser processing head 15 is shown in FIG. The processing head 15 condenses the transmitted laser beam by the parabolic mirror 21, reflects it by the galvanometer mirror 25, and irradiates the surfaces of the sheet bars 1 and 3. The galvanometer mirror 25 is oscillated around the rotation center axis 23 by the mirror vibration device 22, and the laser beam is oscillated across the welding reference line L at the converging position of the surface of the sheet bar 1 and 3.
[0021]
The example which joined the sheet | seat bar with the said apparatus is demonstrated.
[0022]
The seat bar dimensions are as described above. The required melting depth Do is 40 mm (50% of the sheet bar thickness), and the required welding speed Vo is 5 m / min. The melt width w was 1.0 mm and the required laser output Po was 45 kW. Further, the maximum off-axis amount E was 1.1 mm and the margin Y was 0.15 mm. From these values, laser beam welding was performed by vibrating the laser beam with an amplitude a of 0.75 mm and a period of T0.01 sec (frequency f: 100 Hz). As a result, the laser bar tack welded sheet bars 1 and 3 were continuously rolled by the subsequent hot rolling mill row 16 and the sheet bar 1 and the sheet bar 3 were pressed and joined, but breakage occurred. I did not. Meanwhile, laser tack welding was performed under the same conditions as described above except that the period was 0.1 sec. As a result, the joint of the sheet bar was broken by rolling.
[0023]
【The invention's effect】
In laser tack welding according to the method of the present invention, a melted portion having a sufficient width and depth can be formed in the butt portion, and it is possible to prevent breakage of a steel slab that occurs during pressure welding due to defective tack welding. Can do. Further, since the laser beam is merely vibrated, the steel piece joining apparatus can be reduced in size and simplified.
[Brief description of the drawings]
FIG. 1A is a drawing schematically showing a cross section of a melted portion, and FIG. 1B is a drawing showing deviation of a steel piece butt line from a welding reference line.
FIG. 2 is a grab showing the relationship of the weld cross-sectional area to the welding speed and laser output.
FIG. 3 is a graph showing the relationship of the melt width to the welding speed and laser output.
FIG. 4 is a side view schematically showing an example of a steel piece joining facility for carrying out the method of the present invention.
FIG. 5 is a plan view of the facility shown in FIG. 4;
FIG. 6 is a schematic side view showing the structure of a laser processing head.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Leading sheet bar 3 Subsequent sheet bar 5 Butting part 7 Tack welding 11 Running shear 13 Laser oscillator 14 Laser beam transmission optical system 15 Laser processing head 16 Rolling mill row 21 Parabolic mirror 22 Mirror vibration device 23 Rotation center shaft 25 Galvano Mirror 27 Mirror vibration device

Claims (2)

In a method in which the rear end portion of the preceding steel piece and the front end portion of the subsequent steel piece are brought into contact with each other and are joined when the preceding steel piece and the subsequent steel piece are joined by pressure welding, Displacement amount E [mm] −melting width w [mm]) / 2+ margin Y [mm] is amplitude a [mm], and 4a / {(3 to 100) × required welding speed Vo [m / min]} is a period. A laser tack welding method, wherein a laser beam is vibrated in a direction perpendicular to the welding direction as T [sec]. Various combinations of the welding speed V and the laser output P are used to laser weld the preceding steel slab and the subsequent steel slab. From the weld cross section, the welding speed V and the relation A of the melted section cross-sectional area S to the laser output P and the melting The relationship B of the width w is obtained, the necessary laser output Po and the necessary welding speed Vo are obtained based on the relationship A from the necessary melt cross-sectional area So (2 × maximum misalignment E × necessary melt depth Do), and the necessary laser The laser tack welding method according to claim 1, wherein the melt width w is obtained from the output Po and the required welding speed Vo based on the relationship B.

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