JP3436862B2 - Laser cutting method and apparatus for thick steel plate - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for cutting thick steel plates with a laser.

[0002]

2. Description of the Related Art Conventionally, a gas cutting method has been mainly used for cutting thick steel plates having a thickness of 10 to 50 mm. However, in recent years, a laser cutting method in which a thick steel plate is cut by a laser is attracting attention due to the progress of higher output of a laser oscillator and the improvement of a beam mode.

Compared with the gas cutting method, the laser cutting method has the advantages that the cutting surface is excellent in accuracy, the processing speed is high, and the depth of the heat affected zone can be reduced. However, when the laser cutting method is applied to a thick steel plate, the influence of scale, which is an oxide film formed on the surface of the thick steel plate, becomes a problem.

Generally, a thick steel plate is subjected to a cutting process in a state where the scale remains attached to the surface thereof, but the thickness thereof is not uniform unless there is a special manufacturing method, and it is usually varied. When such a steel sheet is irradiated with a laser, the scale causes an exothermic reaction of oxidation, but if the scale thickness is not uniform as described above, the amount of heat generated by the scale becomes uneven. For this reason, when the laser cutting method is applied to thick steel plates, there arises a problem that the progress direction of the cutting process fluctuates.

In the laser cutting of thick plates and the like, oxygen gas of very high purity is used as an assist gas to accelerate the oxidation heat generation of the molten pool and to adjust the components of the thick plates so that the viscosity of the melt becomes low. However, in order to solve the above-mentioned problems, methods such as making the scale thickness of the steel plate surface uniform or limiting the production conditions of the steel plate to reduce the surface roughness ( JP-A-5-112821, JP-A-7-48622, and JP-A-7-1559.
No. 75) is proposed.

[0006]

However, the technique described in the above publication adjusts the composition and manufacturing conditions of steel in order to impart special characteristics for laser cutting to thick steel plates. Steel plate manufacturing costs are inevitable. Therefore, even if the laser cutting method having the above-mentioned advantages is applied to such a thick steel plate, there is little merit as a whole.

In view of the above problems of the prior art, the present invention is a versatile laser cutting method that can be applied as it is to existing thick steel plates without imparting special characteristics to the thick steel plate as a workpiece. The present invention also provides a laser cutting method for a steel sheet which is not adversely affected by scale during processing.

[0008]

The present invention is as follows.

(1) In a method of irradiating a thick steel plate with a laser beam to heat and melt the cut portion to perform laser cutting of the thick steel plate, a cutting laser oscillator for generating a cutting laser and a thick steel plate
A descaling laser that removes the scale layer on the plate surface
Generated by a descaling laser oscillator and transmitted from
Both cutting and descaling lasers into one
When the beam is focused and irradiated with a gap between the cut parts of the thick steel plate,
In both cases, the cutting laser is irradiated at the position where the descaling laser is irradiated.
Laser irradiation position moving direction forward of the laser irradiation position
By first, irradiating the cutting portion of the thick steel plate with a descaling laser to remove the scale layer on the surface of the thick steel plate, and then irradiating the scale removing portion with a cutting laser to cut the thick steel plate. Laser cutting method for thick steel plate.

(2) A pulse laser is used as the descaling laser, the pulse energy is kept constant, and the pulse repetition frequency is controlled in accordance with the cutting speed so that the scale removing portion is continuous along the cutting line. The method for laser cutting a thick steel plate according to (1) above.

(5) A cutting laser oscillator for generating a cutting laser, a descaling laser oscillator for generating a descaling laser for removing a scale layer on the surface of a thick steel plate, and a cutting and descaling laser from the laser oscillator are transmitted. Laser transmitting means, one processing head for converging and irradiating both the cutting and descaling lasers from the laser transmitting means at the cutting portion of the thick steel plate with an interval , and the irradiation position of the cutting and descaling laser is cut. And a driving means for moving the processing head or the thick steel plate so as to move along the line, and the position at which the processing head irradiates the descaling laser is the laser irradiation position moving direction forward of the position at which the cutting laser is irradiated. Laser cutting device for steel sheet.

(4) The thickness according to (3) above, wherein the cutting laser and the descaling laser are focused and irradiated on the surface of the thick steel plate by a single focusing lens provided on the processing head. Laser cutting device for steel sheet.

The steel plate to be cut by the present invention is mainly a thick steel plate, and has a remarkable effect particularly in the cutting work of a thick steel plate having a plate thickness of 10 mm or more. The above-mentioned steel sheet is usually subjected to cutting work in the as-rolled state, but during the cutting work, a scale which is an oxide film having a thickness of 1 to 10 μm is formed on the surface thereof.

In the laser cutting which has been conventionally applied to thick steel plates, laser irradiation is carried out while using O ₂ gas as an assist gas, and heating and melting of the steel plates are promoted by an oxidation reaction with O ₂ gas. Here, as described above, the scale layer is formed on the surface of the thick steel plate, and this scale layer is also subjected to the oxidation reaction by the laser irradiation and the supply of O ₂ gas. However, since the thickness of the scale layer is not uniform unless a special manufacturing method is used, the amount of heat generated by the oxidation reaction of the scale layer is not constant. Therefore, for example, in a thick portion of the scale layer, the amount of heat generated becomes excessive, which may cause a problem that the cutting direction fluctuates.

Therefore, in the present invention, at the time of laser cutting, the scale layer formed on the surface of the steel sheet is first evaporated and removed by a laser, and then a cutting laser having a high output and a high energy density is irradiated. In the present invention, the laser for removing the scale layer by evaporation is referred to as a descaling laser.

A pulse laser having a high peak power may be used as the descaling laser. The reason is,
This is because the high peak power rapidly heats the scale layer, and the reaction force of the blast accompanying evaporation causes efficient removal of the irradiated portion. Specifically, for example, the peak output 30
A CO ₂ pulse laser or excimer pulse laser of about 500 kW may be used.

As shown in FIG. 1, the wavelength of 10.6 μ is formed on the surface of the scale layer.
The relationship between the depth of the scale layer vaporized and removed when irradiated with a CO ₂ pulse laser of m and the pulse energy density of the laser is shown. In the thick steel plate to be processed by the present invention,
Since the thickness of the scale is about 10 μm at the maximum, the pulse energy density of the descaling laser is 8 to 12
It should be J / cm ² .

However, even after the scale layer is removed by the descaling laser, the oxidation reaction proceeds on the surface of the steel sheet at a high temperature and the scale layer is reformed. The regrowth rate of this scale layer is about 5 μm / sec, and if the scale thickness is 1 μm or less, the influence on the laser cutting process can be ignored. Therefore, it is preferable that the irradiation between the descaling laser and the cutting laser is within 0.2 seconds.

When a pulse laser is used as the descaling laser in the present invention, the pulse energy is kept constant so that the scale removing portion is continuous along the cutting line.
The pulse repetition frequency may be controlled according to the cutting speed. If the removal of the scale layer is discontinuous, the adverse effect of the scale on the laser cutting process may not be completely eliminated.

The laser cutting apparatus of the present invention comprises a cutting laser oscillator and a descaling laser oscillator,
The processing head is configured to focus and irradiate both the cutting laser and the descaling laser onto the work piece on the surface of the steel sheet, and by setting the irradiation position of the descaling laser ahead of the irradiation position of the cutting laser, the scale The layer removal and the laser cutting process are continuously performed.

The cutting laser oscillator is, for example, 3-5.
A continuous wave CO ₂ laser oscillator with 0 kW output is used. The laser beam generated by such a laser oscillator has a diameter of usually 15 to 75 mm, and by condensing the laser beam to a diameter of 0.2 to 0.6 mm on the surface of the steel sheet by the focusing optical system of the processing head, The power density of the laser beam on the surface is 10-18
It becomes MW / cm ² .

According to the apparatus of the present invention, it is not necessary to provide a descaling process separately from the laser cutting process even when laser cutting an existing thick steel plate having a non-uniform scale layer. Is possible. Moreover, since the laser cutting is performed after the scale is removed by the descaling laser, the scale layer does not affect the laser cutting process. Further, since the processing head that irradiates the cutting laser and the processing head that irradiates the descaling laser are integrated, the processing head drive mechanism and the like are not complicated and large.

The speed at which the processing head drive mechanism moves the processing head is preferably 1 to 100 (m / min). This is comparable to the plate passing speed of the plate manufacturing line, and the production capacity of the line can be maximized.

After removing the scale layer by the descaling laser, it is necessary to eliminate the influence of the scale layer reformed on the surface of the steel sheet on the laser cutting process. In consideration of the processing head moving speed described above, the distance between the irradiation position of the descaling laser and the irradiation position of the cutting laser is 3 to.
It is preferably 333 mm.

The focusing / irradiation of the cutting laser and the focusing / irradiation of the descaling laser may be performed using the same focusing lens. In such a case, the condensing position of the lasers can be adjusted by changing the angles at which the two lasers are incident on the condensing lens.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 2 is a schematic perspective view of a laser cutting process according to the present invention. In FIG. 2, reference numeral 1 denotes a thick steel plate which is a workpiece,
Reference numeral 5 is a cutting laser, 7 is a descaling laser, and 9 is an assist gas nozzle. In FIG. 2, the thick steel plate 1
Although the case where the cutting process is advanced by moving is shown, when the processing head is moved, the cutting laser 5, the descaling laser 7, the gas nozzle 9 and the like move.

Since the surface of the thick steel plate 1 is covered with the scale layer 3, if the laser cutting is performed as it is, the cutting process is affected by the scale layer. Therefore, in the present invention, first, the descaling laser 7 is condensed on the descaling laser condensing unit 13 to evaporate and remove the scale layer 3, and then the cutting laser 5 is condensed on the cutting laser condensing unit 11 to make the thick steel plate. The cutting process of 1 is performed.

The width of the scale layer 3 removed by the descaling laser 7 is preferably about 3 times the cutting width.
That is, the scale layer 3 is spread over the width of about 3 times the width of the thick steel plate evaporated and removed by the irradiation of the cutting laser 5.
May be evaporated / removed.

Although FIG. 2 illustrates the case where the assist gas is supplied using the assist gas nozzle 9, it is preferable to use a gas containing O ₂ gas as a main component as the assist gas. The assist gas is supplied from the front to the rear in the processing direction as shown in FIG. In addition,
If O ₂ gas is used as the assist gas, the oxide may remain on the cut surface. To prevent this, a gas that does not contain O ₂ may be used as the assist gas. However, in this case, the heat of oxidation of the molten metal cannot be expected, so that a cutting laser with a higher output must be used.

FIG. 3 is a schematic view showing an example of a method of synthesizing a cutting laser and a descaling laser and a method of setting a focus position according to the present invention. In FIG. 3, L ₀ is the condenser lens 2
1 is the optical axis, L ₁ is the centerline of the cutting laser, and L ₂ is the centerline of the descaling laser. As shown in FIG. 3, L ₁ has an angle of θ ₁ and L ₂ has an angle of θ _{2 with} respect to the optical axis L ₀ of the lens. Both lasers are made incident on the condenser lens 21 at such an angle and condensed on the surface of the steel plate 1, so that the cutting laser and the descaling laser are condensed as shown in FIG. This can be done with a single condenser lens.

FIG. 4 is a schematic diagram showing an example of a method of making the cutting laser 5 and the descaling laser 7 incident on the condenser lens 21 at an angle in the method shown in FIG. In FIG. 4, 23 is a beam combiner, and 25 and 27 are mirrors. Here, the cutting laser 5 incident on the mirror 25 is reflected and transmitted to the beam combiner 25, and the descaling laser 7 is similarly transmitted to the beam combiner 25.

At this time, on the output side of the beam combiner 23,
The positions of the bending mirrors 25 and 27, which are set so that the center line L ₁ of the cutting laser and the center line L _{2 of the} descaling laser are parallel to the optical axis L ₀ of the condenser lens 21, are used as reference positions. From bending mirror 25,
27 in the directions of arrows by θ ₁ and θ ₂ respectively
By rotating the laser beam 3 around the center, as shown in FIG. 3, the cutting laser 5 and the descaling laser 7 can be incident on the condenser lens 21 at different angles.

FIGS. 5A to 5E are diagrams showing an example in which the focal positions of the cutting laser and the descaling laser are set by the method shown in FIG. In all the cases of FIG. 5, the distance between the condenser lens 21 and the surface of the steel plate 1 is the focal length of the condenser lens 21, and θ ₁ and θ ₂ are positive in the arrow directions of FIG.

FIG. 5A shows a case where θ ₁ = θ ₂ = 0 and both laser beams are parallel to the optical axis of the condenser lens. In this case, both laser beams are focused and irradiated at the focal position of the focusing lens 21. With this setting, the effect of the present invention cannot be obtained.

FIG. 5B shows the case where θ ₁ = 0 and θ ₂ > 0. In this case, the cutting laser 5 is focused on the focal position of the condenser lens 21, and the descaling laser 7
Is condensed on the opposite side beyond the focal position of the condenser lens 21. With this setting, since the nozzle diameter of the processing head can be minimized, it is advantageous in that the processing head can be reduced in weight and traveling inertia can be reduced when the processing head is moved to perform cutting.

FIG. 5C shows the case where θ ₁ <0 and θ ₂ <0. In this case, both the cutting laser 5 and the descaling laser 7 are condensed on the opposite side beyond the focal position of the condenser lens 21.

FIG. 5D shows the case where θ ₁ = 0 and θ ₂ <0. In this case, the cutting laser 5 is focused on the focal position of the condenser lens 21, and the descaling laser 7
Is condensed before the focus position of the condenser lens 21.

FIG. 5E shows the case where θ ₁ > 0 and θ ₂ > 0. In this case, both the cutting laser 5 and the descaling laser 7 are focused on the front side of the focus position of the condenser lens 21.

As described above in detail, the setting is most preferable when θ ₁ = 0 and θ ₂ > 0 shown in FIG. 5 (B). In addition to the reasons described above, this setting is also advantageous in that the irradiation of the descaling laser can be performed while the energy density of the cutting laser for focusing and irradiating is kept high.

FIG. 6 is a schematic view of a processing head for carrying out the laser cutting processing of the present invention. This processing head includes a casing 31 and a gas supply port 33 provided in the casing 31.
And a condenser lens 21 arranged in the casing 31, a laser is made incident from the upper part of the caging 31, the condenser lens 21 condenses the laser, and the laser is emitted from the lower side. The light is focused and irradiated on the surface of 1.

[0041]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 7 is a drawing showing an embodiment of the composite laser cutting apparatus of the present invention. This composite laser cutting device mainly includes a cutting laser oscillator 42, a descaling laser oscillator 43, a cutting laser transmission optical system 45, a descaling laser transmission optical system 47, a processing head 49, and a steel plate conveying device 41.

The cutting laser oscillator 42 has an output of 10 kW,
This is a cwCO ₂ laser with an intensity distribution donut mode, and the beam diameter on the laser output side is 60 mm. The descaling laser oscillator 43 is a Q-switch CO ₂ laser with an average output of 1 kW, a pulse energy of 100 mJ, a repetition frequency of 10 kHz, and an intensity distribution donut mode, and the beam diameter on the laser output side is 15 mm.

The cutting laser 5 emitted from the cutting laser oscillator 42 is transmitted to the beam combiner 23 by the cutting laser transmission optical system 45 including the mirrors 24 and 25.
The descaling laser 5 emitted from the descaling laser oscillator 42 is also transmitted to the beam combiner 23 by the descaling laser transmission optical system 47 including mirrors 24 and 25.

The beam combiner 23 is provided with two mirrors, and the cutting laser 5 and the descaling laser 7 incident on these mirrors are reflected and transmitted toward the condenser lens 21 provided in the processing head 49. . At this time, the mirror 2
5, 27 are adjusted so that the cutting laser 5 is parallel to the optical axis of the condenser lens 21, and the descaling laser 7 has an angle of θ = 7 ° with respect to the optical axis of the condenser lens 21. To do so. Note that θ means the angle defined as θ ₂ in FIG. The cutting laser 5 and the descaling laser 7 emitted from the beam combiner 23 enter the condenser lens 21 provided on the processing head 49, and the thick steel plate 1
Is irradiated on the surface of.

The condenser lens 21 has a focal length of 127 mm in Z
It is an nSe lens, and the distance from the condenser lens 21 to the surface of the thick steel plate 1 is 127 mm. Since the cutting laser 5 is parallel to the optical axis of the condensing lens 21, the cutting laser condensing unit 11 is the focal position of the condensing lens 21 and the condensing beam diameter is 40.
It is 0 μm. On the other hand, since the descaling laser 7 is inclined by θ ₁ = 7 ° with respect to the optical axis of the condenser lens 21, it is condensed on the thick steel plate 1 with a deviation of 16 mm from the focal position, and its beam diameter is 100 × 1200 μm. .

(The role of the gas supply port 33 [see FIG. 6] provided in the processing head and the assist gas nozzle 9 [see FIG. 2] is unknown.) The processing head 49 is provided with the gas supply port 33. ,
Oxygen gas is supplied from a gas supply device (not shown).

An assist gas nozzle 9 is provided on the front side of the machining head 49 in the machining direction. An assist gas supply device (not shown) is connected to the assist gas nozzle 35, and 99% O ₂ gas, which is the assist gas, can be sprayed onto the laser irradiation position at an angle of 50 °.

As described above, the surface of the thick steel plate 1 is irradiated with the cutting laser 5 and the descaling laser 7 at intervals of 16 mm. Here, since the thick steel plate 1 is conveyed in the arrow direction of FIG. 7 by the steel plate conveying device 41, the scale layer 3 is first evaporated and removed by the descaling laser 7 on the surface of the thick steel plate 1, and then the cutting laser 5 is used. Is irradiated.
Therefore, the laser cutting by the cutting laser 5 can be performed with higher accuracy.

When a steel sheet conveying speed of the steel sheet conveying device 41 was 5 m / min and ordinary steel having a thickness of 20 mm was cut by the apparatus configured as described above, the straightness of cutting was 1/1000 mm. It was

[0050]

As described in detail above, according to the present invention, the conventional thick steel plate can be dealt with without subjecting the work material to special treatment, and the advantages of the laser processing can be achieved. It is possible to realize fully utilized laser cutting processing.

[Brief description of drawings]

FIG. 1 is a chart showing a correlation between a scale removal depth and a pulse energy density.

FIG. 2 is a diagram showing an outline of laser cutting processing according to the present invention.

FIG. 3 is a schematic view showing an example of a method of combining a cutting laser and a descaling laser and a method of setting a focus position.

FIG. 4 is a schematic view showing an example of a method of making the cutting laser 5 and the descaling laser 7 incident on the condenser lens 21 at an angle.

5 is a drawing showing an example in which the focus position is set by the method shown in FIG. 3, in which (A) is θ ₁ = θ ₂ = 0, (B)
Is θ ₁ = 0, θ ₂ > 0, (C) is θ ₁ <0, θ ₂ <0,
(D) is θ ₁ = 0, θ ₂ <0, and (E) is θ ₁ > 0, θ ₂
> 0 is shown respectively.

FIG. 6 is a schematic view of a processing head that performs laser cutting processing according to the present invention.

FIG. 7 is a drawing showing an embodiment of the composite laser cutting device of the present invention.

[Explanation of symbols]

Optical axis of L ₀ condensing lens L ₁ Cutting laser center line L ₂ Descaling laser center line 1 Thick steel plate 3 Scale 5 Cutting laser 7 Descaling laser 9 Assist gas nozzle 11 Cutting laser condensing unit 13 Descaling laser condensing Part 15 Scale removing part 17 Cut part 21 Condenser lens 23 Beam combiner 24, 25, 26, 27 Mirror 31 Casing 33 Gas supply port 41 Steel plate conveying device 42 Cutting laser oscillator 43 Descaling laser oscillator 45 Cutting laser transmission optical system 47 Descaling Laser Transmission Optical System 49 Processing Head

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B23K 26/00-26/42

Claims (4)

(57) [Claims] 1. A method of irradiating a thick steel plate with a laser beam to heat and melt a cut portion to laser-cut the thick steel plate,
Cutting laser oscillator that generates a cutting laser and thick steel plate
Generates a descaling laser that removes the scale layer on the surface
Descaling laser oscillator
One cutting head for both cutting and descaling lasers
Therefore, it is possible to irradiate condensed light with a gap in the cut part of thick steel plate.
The cutting laser is located at the position where the descaling laser is applied.
The laser irradiation position in the moving direction from the irradiation position.
Thus, first, the cutting portion of the thick steel plate is irradiated with the descaling laser to remove the scale layer on the surface of the thick steel plate, and then the cutting laser is irradiated to the scale removing portion to cut the thick steel plate. Laser cutting method for thick steel plate. 2. A pulse laser is used as the descaling laser, the pulse energy is kept constant, and the pulse repetition frequency is controlled in accordance with the cutting speed so that the scale removing portion is continuous along the cutting line. The method for laser cutting a thick steel plate according to claim 1. 3. A cutting laser oscillator for generating a cutting laser, a descaling laser oscillator for generating a descaling laser for removing a scale layer on a surface of a thick steel plate,
A laser transmission means for transmitting the cutting and descaling laser from the laser oscillator, and one processing for converging and irradiating both the cutting and descaling laser from the laser transmission means at a cut portion of a thick steel plate with a space. Head and
A cutting head and a driving means for moving the thick steel plate so that the irradiation position of the descaling laser moves along the cutting line, and the position where the processing head irradiates the descaling laser is more than the position where the cutting laser is irradiated. Is a laser cutting device for thick steel plates that is forward in the laser irradiation position moving direction. 4. The thick steel sheet according to claim 3, wherein the cutting laser and the descaling laser are focused and irradiated on the surface of the thick steel sheet by a single condenser lens provided on the processing head. Laser cutting device.