JPH08290276A - Method and device for laser tack welding in billet joining - Google Patents

Abstract

PURPOSE: To obtain a high joining strength in a short welding time and also to attain simplification and miniaturization of laser tack welding equipment by performing laser tack welding with an abutting part scanned with a laser beam polarized in the direction parallel to the abutting face. CONSTITUTION: In seat bar joining equipment, the tip end and the rear end of seat bars 1, 3 are cut off along the width direction of the bar by a flying shear 11 so that a linear joined face is formed. Then, the rear end face of the preceding seat bar 1 is joined with the front end face of the succeeding seat bar 3, with this linear abutting part 5 tack-welded 7 by laser welding. After that, both seat bars 1, 3 are continuously rolled through a line of rolling mills to complete the joining between the seat bars 1, 3. Accordingly, it is possible to obtain a high joining strength in a short welding time and also to attain the simplification and miniaturization of the laser tack welding equipment. In addition, misalignment is also suppressed at the time of laser tack welding in a line for rolling billets with various thickness.

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 and apparatus used for joining rolled steel pieces such as sheet bars and slabs.

[0002]

2. Description of the Related Art In a hot or cold rolling line, in order to continuously roll a steel slab such as a slab or a sheet bar, the trailing end of the preceding billet being rolled and the leading end of the trailing billet are joined. , There is a method of continuously rolling the joined steel pieces.

WO. In 94/16838, the rear end portion of the preceding steel piece being rolled and the leading end portion of the trailing steel piece are butted and temporarily welded by a laser beam, and the temporarily attached steel piece is rolled and pressure welded, A method of performing continuous rolling is disclosed.

Here, the thickness of the steel pieces to be joined is 20 to 5
It is 0 mm. The rear end of the preceding steel piece and the front end of the rear end are shaped by a running shear or the like and then abutted, but the cutting shape by the running shear has a sag as shown in FIG. 1 (b). Since it occurs, the thickness t that can actually be abutted
e changes depending on the thickness of the billet as shown in FIG. In laser tack welding, the penetration depth basically cannot exceed this te, but the thickness of the steel slab is 20-5.
In the range of 0 mm, it is possible to secure 30% or more of the total thickness.

Next, the relationship between the ratio of the penetration depth of the tack welding to the total thickness and the ratio of no fracture at the joint during rolling after the tack welding is shown in FIG. From this result, in order to perform highly accurate joining by laser tack welding and pressure welding by rolling, the ratio of the penetration depth to the total thickness is 3
It is necessary to realize tack welding of 0% or more.

From the above, the penetration depth by tack welding is
It needs to be as deep as possible. However, the penetration depth in laser welding strongly depends on the focused spot diameter together with the power density of the focused laser beam. Therefore, it is necessary to focus the laser beam on a spot as small as possible. On the other hand, the bead width and the focused spot diameter have a strong positive correlation, and the smaller the spot diameter, the narrower the bead width. For this reason, when performing laser tack welding by focusing the laser beam on a small focused spot diameter, unless the laser irradiation position and the abutting surface are matched with each other with extremely high accuracy, the welding bead causes deviation from the abutting surface, Effective joining cannot be realized. In order to deal with such a problem, conventionally, measures as shown in FIGS. 3 and 4 have been proposed (Japanese Patent Application No. 5-7335).

FIG. 3 shows a method in which a laser beam is obliquely applied to the abutting surface of the steel slab to widen the bead width to prevent eye contact. FIG. 4 shows a method in which the bead width is also widened by vibrating the laser beam in the direction perpendicular to the abutting surface to prevent eye slippage. Although any of the methods widens the margin of deviation, there is a drawback that the energy of the laser beam is wasted and the penetration depth becomes shallow because an unnecessary penetration portion is generated.

There is also a method of lowering the welding speed in order to secure the penetration depth, but it is necessary to make the welding speed as fast as possible when joining the steel pieces on the rolling line. In addition, there is a problem that the rolling equipment becomes huge and the cost is significantly increased.

[0009]

DISCLOSURE OF THE INVENTION The present invention provides a laser tack welding method capable of obtaining a high joining strength in a short welding time and capable of simplifying and miniaturizing a laser tack welding apparatus. is there. Further, the present invention provides a tack welding method capable of obtaining a high joining strength in a short welding time in a rolling line for rolling billets having various thicknesses and capable of suppressing deviation of eyes during laser tack welding.

[0010]

According to a first aspect of the present invention, there is provided a laser tack welding method for joining steel slabs, wherein a trailing end of a preceding steel slab and a leading end of a trailing steel stake are abutted to each other and the abutting portion is welded by laser welding. In the method of temporarily joining and joining the preceding steel piece and the following steel piece by pressure welding, the laser tacky welding is performed by scanning the butted portion with a laser beam polarized in a direction parallel to the butted surface. To do.

In the laser tack welding method for joining steel pieces of the second invention, the rear end portion of the preceding steel piece and the tip portion of the trailing steel piece are butted, and the butted portion is temporarily attached by laser welding.
In the method of joining the preceding steel piece and the following steel piece by pressure welding,
Laser butting welding is performed by scanning the abutting portion with a laser beam polarized in a direction perpendicular to the abutting surface.

In the laser tack welding method for joining steel pieces of the third invention, the rear end portion of the preceding steel piece and the tip portion of the trailing steel piece are butted, and the butted portion is temporarily attached by laser welding.
In the method of joining the preceding steel piece and the following steel piece by pressure welding,
If the thickness of the billet is 40 mm or more, the thickness of the billet is 40 mm with a laser beam polarized in the direction parallel to the abutting surface.
If less than the above, the laser welding method is characterized by performing laser tack welding by scanning the abutting portion with a laser beam polarized in a direction perpendicular to the abutting surface.

A laser tack welding apparatus according to a fourth aspect of the present invention is the third aspect.
Which is used for carrying out the laser tack welding method for joining steel slabs according to the invention, wherein the polarization plane of the laser beam is switched between a direction parallel to the butt surface and a direction perpendicular to the butt surface. It is characterized by having a polarization plane switching optical system.

The steel pieces to be joined in the present invention have a thickness of 2
It is a 0-50mm sheet bar or slab. 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.

The laser welding may be carried out by using a continuous wave CO ₂ laser oscillator having an output of 25 to 50 kW and scanning the laser beam irradiation position along the abutting portion of the steel strip running on the rolling line. Good. The moving speed of the laser beam may be 3 to 20 m / min as in the conventional laser welding.

FIG. 5 is a graph showing the correlation between the reflectance r of the laser beam on the surface of the billet and the incident angle θ of the laser beam when the billet is scanned by inclining the laser beam as shown in FIG. 5 (b). Here, at a ratio of (1-r), the energy of the laser beam with which the surface of the steel slab is irradiated is absorbed by the steel slab and contributes to the processing. Here, S-polarized light refers to a linearly polarized laser beam whose plane of polarization is perpendicular to the laser beam scanning direction, and P-polarized light refers to a linearly polarized laser beam whose plane of polarization is parallel to the laser beam scanning direction.

When the laser beam is applied from the direction normal to the surface of the billet, it corresponds to the condition of θ = 0 ° in FIGS. 5 (a) and 5 (b), and is between the S-polarized laser beam and the P-polarized laser. In addition, there is no difference in reflectance on the surface of the billet. However, the actual laser welding process involves the formation of a keyhole, and once the keyhole is formed, the laser beam irradiates the side surface of the keyhole. Therefore, as shown in FIG.
The incident angle θ is significantly increased. Therefore, as shown in FIG. 5B, the P-polarized light has a higher absorptance, and the penetration property is improved.

FIG. 7 shows the result of an experiment conducted to confirm this fact. FIG. 7 summarizes the penetration depth and the bead width when the laser beam scanning direction is sequentially changed with respect to the polarization direction of the linearly polarized laser beam.
In the definition of FIG. 5, β = 0, 180 ° is S-polarized, β = 90,
270 ° corresponds to P-polarized light. From FIG. 7, in welding using P-polarized light, the bead width is narrow, the penetration depth is deep, and S
It can be seen that in welding using polarized light, the bead width is wider and the penetration depth is shallower than in welding using P polarized light.

From the results of this experiment, it is necessary to scan the welding line with a P-polarized laser beam in order to perform tack welding with a deep penetration depth, but in actual laser tack welding, the butt welding is performed. It is necessary to consider the shape of the part. FIG.
(A) is a schematic diagram when an ideal butt surface is obtained, and when it is desired to deepen the penetration depth, a P-polarized laser beam whose polarization surface is perpendicular to the paper surface may be used. On the other hand, FIG.
(B) and (c) show the cross-sectional shape of the steel slab abutting portion whose shape has been adjusted by the running shear. The abutting part mainly consists of a ductile fracture area (el) and a brittle fracture area (p).
l). An effective butt surface is obtained in tack welding in the pl region, and the ratio of this region to the total thickness changes depending on the thickness of the billet as shown in FIG. Therefore, in the case of thick steel slab, a relatively steep el region is obtained as shown in FIG. 8B, and in the case of thin steel slab, as shown in FIG. The shape is close to the surface. Therefore, the penetration depth for the thickness of the billet is 3
In order to achieve 0% or more, the thick steel piece in FIG. 8 (b) requires a deep penetration depth, but the thin steel piece in FIG. 8 (c) requires a deep penetration depth in the thick steel piece. It may be shallower than the depth.

Here, in the case where temporary welding is performed by irradiating the steel piece abutting portion shown in FIGS. 8B and 8C with a linearly polarized laser beam whose polarization plane is perpendicular to the paper surface of FIG. Think
In this case, since the plane of polarization is parallel to the laser beam scanning direction, it is P-polarized when viewed in the cross section of FIG. 6, but is S-polarized when viewed in the cross section of FIG. Therefore, the penetration depth of tack welding is deeper because it is P-polarized light whose polarization plane is parallel to the welding line direction, but at the same time, the bead width becomes narrower, so that eye spotting easily occurs.

However, when the irradiation position of the laser beam is shifted and the steep el region in FIG. 8B is irradiated, the behavior of the laser beam follows the characteristics of S-polarized light and the incident angle is large. The laser beam is reflected with high reflectance on the billet surface until it reaches the actual butt. Therefore, even if the bead width is narrow, even if the irradiation position of the laser beam deviates, the laser beam reaches the actual abutting portion, so that eye deviation is unlikely to occur. This phenomenon is shown in FIG.
It is schematically shown in (a).

Further, when the light is irradiated to the el region of FIG. 8C, the incident angle is small because the gradient in the el region is not steep, and a bead is formed at the position irradiated with the laser beam. For this reason, even if a deep bead is obtained, the bead width is narrow, and thus eye slippage easily occurs. This phenomenon is schematically shown in FIG.

Next, when the steel piece abutting portion shown in FIGS. 8 (b) and 8 (c) is irradiated with a linearly polarized laser beam whose polarization plane is parallel to the paper surface of FIG. 8, temporary welding is performed. The opposite effect is obtained. That is, in the case of FIG. 8B, since the penetration depth is sacrificed, it is difficult to make the penetration depth 30% or more of the thickness of the steel piece. FIG.
In the case of (c), a shallower penetration depth than in the case of FIG. 8 (b) is sufficient, so there is no problem with the penetration depth, and since the bead width is widened, eye drops are less likely to occur.

As described above, for the thick steel piece having the cross section of the abutting portion as shown in FIG. 8B, the linearly polarized laser beam whose polarization plane is parallel to the abutting surface is used as shown in FIG. 8C. It was clarified that if a linearly polarized laser beam whose polarization plane is perpendicular to the abutting surface is used for a thin steel piece having a partial cross section, sufficient bonding strength can be obtained and eye contact can be prevented.

As described above, it has been shown that it is effective to perform laser tack welding by switching the polarization plane of the linearly polarized laser beam depending on the butt shape and thickness of the steel piece. Here, as a result of evaluating the cross-sectional shapes when the steel plates having various plate thicknesses were cut by the shear during running, as a result, the plate thickness of 40 mm was taken as a boundary.
It was found from FIG. 8B that the cross-sectional shape changed as shown in FIG. Therefore, the thickness of the steel pieces to be joined is 40 mm.
If the above is the case, a linearly polarized laser beam whose polarization plane is parallel to the abutting surface is used, and if the thickness of the billet is less than 40 mm,
It is advisable to use a linearly polarized laser beam whose polarization plane is perpendicular to the butt plane. Further, if the directions of the polarization planes can be switched as needed, it is possible to appropriately temporarily attach steel pieces of various thicknesses with one laser tack welding device.

A specific method of switching the direction of the polarization plane will be shown below. Device for Switching Polarization Plane of Oscillation Beam itself from Laser Oscillator As shown in FIG. 10A, a Brewster plate 29 as a polarization selecting element is provided in a laser oscillator 23 composed of a total reflection mirror 21 and a partial transmission mirror 31. Insert. In the configuration of FIG. 10A, since only the polarized component parallel to the paper surface of FIG. 10 is selectively transmitted through the Brewster plate 29, linearly polarized light polarized in the plane oscillates. In addition, Brewster board 2
The number of 9 is two in order to correct the optical axis shift due to refraction. With this configuration, if two Brewster plates 29 are rotated by 90 ° along the optical axis within the broken line, linearly polarized light having a plane of polarization orthogonal to the plane of FIG. 10 can be obtained. Furthermore, in the case of a high-power laser oscillator used in the present invention, the Brewster plate 2 is used from the viewpoint of light resistance strength.
It may be difficult to insert 9. In this case, for example, the small output linearly polarized light output oscillator 23 shown in FIG.
This output is a large output unstable oscillator 3 like 0 (b).
Introduced as a seed into the output beam 33
It is possible to align the polarization plane of the same with that of the injection seed oscillator 35. Here, if the plane of polarization of the injection seed oscillator 35 is rotated, the plane of polarization of the output beam 33 with a large output also rotates, and the plane of polarization can be switched. The concave mirror 38 and the convex mirror 39 are resonant mirrors of an unstable oscillator configured to obtain a large output laser beam.

Device for Switching the Plane of Polarization in the Beam Transmission Line As shown in FIG. 11 (a), it is possible to change the P-polarized light into the S-polarized light by fold the beam three-dimensionally. By using this phenomenon, the polarization can be switched. In FIG. 11B, the mirrors A1 and B1 are in the same height plane, and the polarization plane is as shown. Figure 11
In (c), after being reflected upward from the A2 mirror to the C mirror, it is transmitted to the D mirror of the same height and reflected downward. In this configuration, the final plane of polarization is orthogonal to that in FIG. 11 (b). Therefore, by setting the mirrors C and D at fixed positions and switching the mirrors of A1 and A2 and the B1 mirror in conjunction with each other to move by a cylinder or the like, the polarization plane can be switched. Further, although the example of the geometrical polarization plane rotation is shown here, a configuration of rotating the polarization plane by 90 ° by a phase delay mirror and a method of switching a normal mirror reflection system may be used.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of a hot rolling steel piece joining facility to which the present invention is applied will be described with reference to the drawings. FIG. 12 is a side view schematically showing the sheet bar joining equipment provided in the continuous hot rolling equipment, and FIG. 13 is a plan view of the equipment.
In the seat bar joining equipment shown in FIG. 12 and FIG. 13, the leading and rear ends 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 following sheet bar 3 are butted, and the linear butted portion 5 is temporarily welded 7 by laser welding. Subsequent to the tack welding 7, the rolling mill train 16 continuously rolls both the sheet bars 1 and 3 to complete the joining of the sheet bar 1 and the sheet bar 3. In this sheet bar joining facility, laser tack welding was performed using the polarization plane switching device of FIG. 11, and tack welding was performed with a linearly polarized laser beam.

[Example 1] Thickness 45 mm, width 1100 m
Laser tack welding of a sheet bar having a length of m 2, a length of 40 m and a temperature of 1000 ° C. was performed. The laser output was 45 kW, the laser scanning speed was 10 m / min, and the plane of polarization of the linearly polarized laser beam was parallel to the abutting surface. The penetration depth obtained by laser tack welding is 15 mm and the bead width is 2 mm.
The penetration depth was 33% of the thickness of the sheet bar. The allowable margin of deviation was 1.3 mm. By rolling the temporary tack welded sheet bar by the first-stage rolling mill 17 of the rolling mill train 16 at a rolling reduction of 40%, the sheet bar was pressure-welded with sufficient joining strength, and no fracture occurred during rolling. When laser tack welding is performed with a conventional non-polarized laser beam, the penetration depth obtained at the butt portion is 1
2.5mm, bead width is 2.4mm, penetration depth is less than 30% of the thickness of the sheet bar, even if the rolling of the first stage rolling mill 17 of the rolling mill row 16 rolling reduction of 40% is sufficient No good joint strength was obtained. The allowable margin of deviation in tack welding was 0.9 mm.

Example 2 Thickness 25 mm, width 1100 m
Laser tack welding of a sheet bar having a length of m 2, a length of 40 m and a temperature of 1000 ° C. was performed. The laser output was 45 kW, the laser scanning speed was 10 m / min, and the plane of polarization of the linearly polarized laser beam was perpendicular to the abutting surface. The penetration depth obtained by laser tack welding is 12 mm and the bead width is 2.
It was 8 mm, and the penetration depth was about 50% of the thickness of the sheet bar. The allowable margin of deviation was 1.2 mm. The first-stage rolling mill 1 of the rolling mill row 16 is attached to the temporarily welded sheet bar.
By rolling with a rolling reduction of 40% in No. 7, the sheet bar was pressed with sufficient joining strength, and fracture did not occur during rolling. When laser tack welding is performed with a conventional non-polarized laser beam, the penetration depth obtained at the butt portion is 1
The penetration depth is 2.5 mm, the bead width is 2.4 mm, and there is no problem with the penetration depth. However, the allowable deviation range is 0.9 mm, which is smaller than the allowable deviation range according to the present invention, and the deviation occurs. Cheap.

[0031]

According to the present invention, a high joining strength can be obtained in a short welding time and the laser tack welding apparatus can be simplified and downsized. Further, in a rolling line for rolling billets having various thicknesses, a high joining strength can be obtained in a short welding time, and further, it is possible to suppress the deviation of the eye during laser tack welding.

[Brief description of drawings]

FIG. 1 (a) is a graph showing a relationship between a thickness te that can be actually butted and a steel piece thickness to. (B) It is drawing which shows the cutting shape of the steel piece end part by running shear.

FIG. 2 is a graph showing the relationship between the ratio of the penetration depth to the total thickness by tack welding and the ratio at which no fracture occurs at the joint.

FIG. 3 is a drawing showing a method of injecting a laser beam obliquely with respect to a steel piece abutting surface.

FIG. 4 is a diagram showing a method of vibrating a laser beam in a direction perpendicular to a butt surface.

FIG. 5 (a) is a drawing showing the definition of the incident angle and scanning direction of a laser beam on a steel slab. (B) A graph showing the correlation between the reflectance of the laser beam on the surface of the steel slab and the incident angle of the laser beam.

FIG. 6 is a schematic diagram showing the behavior of a cross section in the welding line direction during keyhole welding.

FIG. 7 is a graph showing the relationship between the welding characteristics and the angle of the laser beam scanning direction with respect to the polarization direction of the linearly polarized laser beam.

FIG. 8 (a) is a schematic view of a shape of an abutting surface under virtual conditions. (B) It is a schematic diagram of an actual butt surface shape in the case of a thick steel piece. (C) It is a schematic diagram of an actual butt surface shape in the case of a thin steel piece.

FIG. 9 is a schematic view of a formed bead when a laser beam irradiation position is displaced from a butt portion in tack welding using a linearly polarized laser beam having a polarization plane in the welding line direction.

FIG. 10A is a schematic configuration diagram of an optical system that switches a polarization plane of a laser oscillator output beam in the case of a stable resonator. FIG. 6B is a schematic configuration diagram of an optical system that switches the polarization plane of a laser oscillator output beam in the case of an unstable resonator.

FIG. 11A is an explanatory diagram of the principle of changing the polarization plane of a linearly polarized laser beam during laser beam transmission. (B) A schematic view of an optical device for transmitting a linearly polarized laser beam. (C) is a schematic view of an apparatus for rotating the plane of polarization of a linearly polarized laser beam by 90 ° with respect to (b) during laser beam transmission.

FIG. 12 is a side view schematically showing a sheet bar joining facility to which the present invention is applied, which is provided in a continuous hot rolling facility.

FIG. 13 is a plan view of the equipment shown in FIG.

[Explanation of symbols]

 1 Leading Seat Bar 3 Trailing Seat Bar 5 Butt Section 7 Temporary Welding 11 Running Shear 13 Laser Oscillator 14 Laser Beam Transmission Optical System 15 Laser Processing Head 16 Rolling Mill Row 21 Total Reflector 23 Laser Oscillator 25 Window 29 Brewster Plate 31 Partial Transmission Mirror 33 Laser Beam 35 Oscillator for Injection Seed 37 Unstable Oscillator 38 Concave Mirror 39 Convex Mirror

Claims (4)

[Claims] 1. A rear end portion of a preceding steel piece and a front end portion of a following steel piece are butted, and the butted portion is temporarily attached by laser welding,
In the method of joining the preceding steel piece and the following steel piece by pressure welding,
A laser tack welding method for joining steel slabs, characterized in that laser tack welding is performed by scanning a butt portion with a laser beam polarized in a direction parallel to a butt surface. 2. The rear end portion of the preceding steel piece and the front end portion of the following steel piece are butted, and the butted portion is temporarily attached by laser welding,
In the method of joining the preceding steel piece and the following steel piece by pressure welding,
A laser tack welding method for joining steel slabs, characterized in that laser tack welding is performed by scanning the butted portion with a laser beam polarized in a direction perpendicular to the butted surface. 3. The rear end portion of the preceding steel piece and the leading end portion of the following steel piece are butted, and the butted portion is temporarily attached by laser welding,
In the method of joining the preceding steel piece and the following steel piece by pressure welding,
When the thickness of the steel slab is 40 mm or more, the laser beam polarized in the direction parallel to the abutting surface, and the thickness of the steel slab is 40 m.
A laser tack welding method for joining steel pieces, characterized in that when the length is less than m, laser welding is performed by scanning the butted portion with a laser beam polarized in a direction perpendicular to the butted surface. 4. An apparatus used when carrying out the laser tack welding method according to claim 3, wherein the polarization plane of the laser beam is parallel to the abutting surface and perpendicular to the abutting surface. A laser tack welding apparatus, which is provided with a polarization plane switching optical system for switching between each other.