JPH10277764A - Method and device for cutting thick steel plate by laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effect highly versatile laser cutting that is applicable to an existing thick steel plate as it is, without imparting a special property to it, by emitting a descaling laser beam to the cutting part of the thick steel plate, removing a scale layer on the plate surface, irradiating the scale-removed part with a cutting laser beam and cutting the thick steel plate. SOLUTION: First, a descaling laser beam 7 is converged on its converging part 13, vaporizing and removing scales 3; then, a cutting laser beam 5 is converged on its converging part 11, performing cutting on a thick steel plate 1. The width of the scale 3 removed by the descaling laser 7 is desirably about 3 times as wide as the cutting width. While an assist gas is supplied using and assist gas nozzle 9, it is desirable that the gas contains O2 gas as the main component. The assist gas is supplied so as to flow from the front to the rear in the machining direction.

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 a thick steel plate by laser.

[0002]

2. Description of the Related Art Conventionally, a gas cutting method has been mainly used for cutting a thick steel plate having a thickness of 10 to 50 mm. However, in recent years, a laser cutting method of cutting a thick steel plate with a laser has attracted attention as the output of a laser oscillator has increased and the beam mode has been improved.

[0003] Compared to the gas cutting method, the laser cutting method has advantages in that the accuracy of the cut surface is excellent, 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 the scale, which is an oxide film formed on the surface of the thick steel plate, becomes a problem.

[0004] In general, a thick steel plate is subjected to cutting while the scale remains adhered to the surface. However, the thickness of the steel plate is non-uniform unless a special manufacturing method is used, and there is usually a variation. Irradiation of laser on such a steel sheet causes the scale to undergo an oxidative heat generation reaction. However, if the scale thickness is not uniform as described above, the heat generated by the scale will be uneven. For this reason, when the laser cutting method is applied to a thick steel plate, problems such as fluctuations in the direction of the cutting process occur.

[0005] In laser cutting of a thick plate or the like, very high-purity oxygen gas is used as an assist gas to promote oxidation heat generation of a molten pool or to adjust the composition of the thick plate so that the viscosity of the molten material becomes low. However, in order to further solve the above-mentioned problems, methods such as equalizing the scale thickness of the surface of the thick steel plate and reducing the surface roughness by limiting the manufacturing conditions of the thick steel plate ( JP-A-5-112821, JP-A-7-48622, JP-A-7-1559
No. 75 publication) has been proposed.

[0006]

However, the technique described in the above publication is to adjust the composition of steel and the manufacturing conditions so as to impart special properties for laser cutting to a thick steel plate. Steel sheet 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.

[0007] In view of the problems of the prior art, the present invention provides a highly versatile laser cutting method that can be applied to existing thick steel plates without imparting special properties to the thick steel plates to be processed. Another object of the present invention is to provide a laser cutting method for a steel sheet which is not adversely affected by scale during processing.

[0008]

SUMMARY OF THE INVENTION 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 and laser-cutting the thick steel plate, first, a descaling laser is applied to a cut portion of the thick steel plate to irradiate the cut surface of the thick steel plate. A laser cutting method for a thick steel plate, comprising removing a scale layer, and then irradiating a cutting laser to the scale removing portion to cut the thick steel plate.

(2) The pulse repetition frequency is controlled in accordance with the cutting speed so that a pulse laser is used as the descaling laser, the pulse energy is kept constant, and the scale removing portion is continuous along the cutting line. The method for laser cutting a thick steel plate according to the above (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 the surface of a thick steel plate, and transmitting the cutting and descaling laser from the laser oscillator. A laser transmission means, a processing head for irradiating both the cutting and descaling laser from the laser transmission means to the cut portion of the thick steel plate, and a processing so that the irradiation position of the cutting and descaling laser moves along the cutting line. A laser cutting device for a thick steel plate, comprising: a driving means for moving a head or a thick steel plate, wherein a position at which the processing head irradiates the descaling laser is ahead of a position at which the cutting laser is radiated, in a laser irradiation position moving direction.

(4) The thickness according to (3), wherein the cutting laser and the descaling laser are respectively condensed and irradiated on the surface of the thick steel plate by a single condensing lens provided on the processing head. Laser cutting equipment for steel plates.

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

In conventional laser cutting applied to a thick steel plate, a laser beam is irradiated while using an O ₂ gas as an assist gas to promote the heating and melting of the steel plate by an oxidation reaction with the O ₂ gas. Here, a scale layer is formed on the surface of the thick steel plate as described above, and this scale layer is also subjected to an oxidation reaction by laser irradiation and 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. For this reason, for example, in a thick portion of the scale layer, the calorific value becomes excessive, which may cause a problem such that the cutting direction fluctuates.

Therefore, in the present invention, at the time of laser cutting, first, the scale layer formed on the surface of the steel sheet is 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 evaporating and removing the scale layer is referred to as a descaling laser.

As the descaling laser, a pulse laser having a high peak power is preferably used. The reason is,
This is because the scale layer is rapidly heated by the high peak power, and the irradiated portion is efficiently removed by the reaction force of the blast accompanying the evaporation. Specifically, for example, the peak output 30
It is preferable to use a CO ₂ pulse laser or an excimer pulse laser of about 500 kW.

FIG. 1 shows that the scale layer surface has a wavelength of 10.6 μm.
The relationship between the depth of the scale layer evaporated / removed when irradiating the m ₂ CO ₂ pulse laser and the pulse energy density of the laser is shown. In the steel plate to be processed by the present invention,
Since the thickness of the scale is at most about 10 μm, the pulse energy density of the descaling laser is 8 to 12 μm.
J / cm ² may be used.

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 formed again. The regrowth rate of the scale layer is about 5 μm / sec. If the thickness of the scale is 1 μm or less, the effect on the laser cutting can be ignored. Therefore, it is preferable that the time between the irradiation of the descaling laser and the irradiation of the cutting laser be within 0.2 seconds.

When a pulse laser is used as the de-scaling laser in the present invention, the pulse energy is kept constant, and 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 scale may not be able to completely eliminate the adverse effect on the laser cutting.

The laser cutting device of the present invention includes a cutting laser oscillator and a descaling laser oscillator.
The processing head is designed to focus and irradiate both the cutting laser and the descaling laser to the part to be processed on the surface of the steel sheet, and the irradiation position of the descaling laser precedes the irradiation position of the cutting laser, so that the scale The removal of the layer and the laser cutting are continuously performed.

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

According to the apparatus of the present invention, even when laser cutting an existing thick steel plate having a non-uniform scale layer, it is not necessary to provide a descale step separately from the laser cutting step. 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. In addition, since the processing head that irradiates the cutting laser and the processing head that irradiates the descaling laser are integrated, there is no need to increase the complexity and size of the processing head drive mechanism and the like.

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 threading speed of the thick plate production line, and can maximize the production capacity of the line.

Further, it is necessary to eliminate the influence of the scale layer re-formed on the steel sheet surface after the scale layer is removed by the descaling laser on the laser cutting. 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 and irradiation of the cutting laser and the focusing and irradiation of the descaling laser may be performed by using the same focusing lens. In such a case, the laser focusing position can be adjusted by changing the angle at which both lasers enter the focusing lens.

[0026]

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, 1 is a thick steel plate as a workpiece,
Reference numeral 5 denotes a cutting laser, 7 denotes a descaling laser, and 9 denotes an assist gas nozzle. In addition, in FIG.
The cutting laser 5, the descaling laser 7, the gas nozzle 9, and the like move to move the processing head.

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 focused on the descaling laser focusing unit 13 to evaporate and remove the scale layer 3, and then the cutting laser 5 is focused on the cutting laser focusing unit 11 and the steel plate is thickened. 1 is performed.

It is preferable that the width of the scale layer 3 removed by the descaling laser 7 is about three times the cutting width.
That is, the scale layer 3 extends over about three times the width of the thick steel plate evaporated and removed by the irradiation of the cutting laser 5.
Should be evaporated and removed.

FIG. 2 shows a case in which the assist gas is supplied using the assist gas nozzle 9, but it is preferable to use a gas mainly composed of O ₂ gas 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,
When an O ₂ gas is used as the assist gas, an oxide may remain on the cut surface. In order to prevent this, a gas containing no O ₂ may be used as the assist gas. However, in this case, heat generated by oxidization of the molten metal cannot be expected. Therefore, it is necessary to use a higher output cutting laser.

FIG. 3 is a schematic diagram showing an example of a method of synthesizing a cutting laser and a descaling laser and a method of setting a focal position according to the present invention. In FIG. 3, L ₀ is a condenser lens 2
1, the optical axis, L ₁ is the center line of the cutting laser, and L ₂ is the center line 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. By making both lasers incident on the condenser lens 21 at such an angle, and condensing them on the surface of the steel plate 1, as shown in FIG. This can be performed by using two condenser lenses.

FIG. 4 is a schematic view showing an example of a method of making the cutting laser 5 and the descaling laser 7 enter 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 exit side of the beam combiner 23,
The positions of the bending mirrors 25 and 27 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 are axes 31 and 3 in the directions of the arrows by θ ₁ and θ ₂ respectively.
3, the cutting laser 5 and the descaling laser 7 can be incident on the condenser lens 21 at an angle as shown in FIG.

FIGS. 5A to 5E are views showing examples in which the focal positions of the cutting laser and the descaling laser are set by the method shown in FIG. In all cases shown in 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 direction of the arrow in 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, the two laser beams are focused and radiated on the focal position of the focusing lens 21. With this setting, the effect of the present invention cannot be obtained.

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

FIG. 5C shows a 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 opposite side beyond the focal position of the focusing lens 21.

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

FIG. 5E shows a 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 near side of the focal position of the focusing lens 21.

As described above in detail, the setting when θ ₁ = 0 and θ ₂ > 0 shown in FIG. 5B is most preferable. In addition to the reasons described above, this setting is also excellent in that irradiation with the descaling laser can be performed while the energy density of the cutting laser to be focused and irradiated is high.

FIG. 6 is a schematic view of a processing head for performing laser cutting according to the present invention. The processing head includes a casing 31 and a gas supply port 33 provided in the casing 31.
And a condenser lens 21 disposed in a casing 31. A laser is incident from the upper part of the casing 31, the laser is focused by the condenser lens 21, and the laser is emitted from the lower side. The light is condensed and irradiated on the surface of No. 1.

[0041]

FIG. 7 is a view showing an embodiment of the composite laser cutting apparatus according to 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 transport device 41.

The cutting laser oscillator 42 has an output of 10 kW,
This is a cwCO ₂ laser in the intensity distribution donut mode, and the beam diameter on the laser output side is 60 mm. The descaling laser oscillator 43 is a Q-switched CO ₂ laser having 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 has a beam diameter of 15 mm at the laser output side.

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

The beam combiner 23 has two mirrors, and reflects and transmits the cutting laser 5 and the descaling laser 7 incident on these mirrors to the condenser lens 21 provided in the processing head 49. . At this time, mirror 2
By adjusting 5, 27, the cutting laser 5 becomes parallel to the optical axis of the condenser lens 21, and the descaling laser 7 makes an angle of θ = 7 ° with respect to the optical axis of the condenser lens 21. To do. Note that θ refers to 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 surface is irradiated.

The condenser lens 21 has a focal length of 127 mm.
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 condenser lens 21, the cutting laser condenser section 11 is located at the focal position of the condenser lens 21 and the diameter of the focused beam is 40.
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 focused on the thick steel plate 1 with a shift 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 role of the assist gas nozzle 9 (see FIG. 2) are unknown.) The processing head 49 is provided with the gas supply port 33. ,
An oxygen gas is supplied from a gas supply device (not shown).

An assist gas nozzle 9 is provided on the front side of the processing head 49 in the processing direction. An assist gas supply device (not shown) is connected to the assist gas nozzle 35, and 99% O ₂ gas, which is an assist gas, can be blown at a 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 transported in the direction of the arrow in FIG. 7 by the steel plate transport 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 Irradiated.
Therefore, laser cutting by the cutting laser 5 can be performed with higher accuracy.

When the steel sheet conveying device 41 cuts a 20 mm-thick ordinary steel sheet at a speed of 5 m / min using the above-configured apparatus, the straightness of the cutting process is 1/1000 mm. Was.

[0050]

As described above in detail, according to the present invention, it is possible to cope with a conventional thick steel plate without performing a special treatment on a workpiece and to obtain advantages of laser processing. A laser cutting process fully utilized can be realized.

[Brief description of the drawings]

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

FIG. 2 is a drawing schematically showing a laser cutting process according to the present invention.

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

FIG. 4 is a schematic diagram showing an example of a method of making a cutting laser 5 and a descaling laser 7 enter a condenser lens 21 at an angle.

5A and 5B are diagrams showing an example in which a focal position is set by the method shown in FIG. 3, wherein FIG. 5A shows θ ₁ = θ ₂ = 0, and FIG.
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.

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

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

[Explanation of symbols]

L ₀ Optical axis of condenser lens L ₁ Center line of cutting laser L ₂ Center line of de-scaling laser 1 Steel plate 3 Scale 5 Cutting laser 7 De-scaling laser 9 Assist gas nozzle 11 Cutting laser condensing unit 13 De-scaling laser condensing Unit 15 scale removing unit 17 cut portion 21 condensing lens 23 beam combiner 24, 25, 26, 27 mirror 31 casing 33 gas supply port 41 steel plate transport device 42 cutting laser oscillator 43 descaling laser oscillator 45 cutting laser transmission optical system 47 Descaling laser transmission optical system 49 Processing head

Claims (4)

[Claims] 1. A method of irradiating a thick steel plate with a laser beam to heat and melt a cut portion, and laser cutting the thick steel plate,
First, a descaling laser is applied to the cut portion of the steel plate to remove the scale layer on the surface of the steel plate, and then the cutting laser is applied to the scale removing portion to cut the steel plate. Cutting method. 2. A pulse laser is used as a de-scaling 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 the surface of a thick steel plate,
A laser transmission means for transmitting a cutting and descaling laser from the laser oscillator, a processing head for irradiating both the cutting and descaling laser from the laser transmission means to the cutting portion of the thick steel plate, and a cutting and descaling laser. Driving means for moving the processing head or the thick steel plate so that the irradiation position moves along the cutting line, and the position at which the processing head irradiates the descaling laser is more in the laser irradiation position moving direction than the position at which the cutting laser irradiates Laser cutting device for thick steel plate at the front. 4. The thick steel plate according to claim 3, wherein a cutting laser and a descaling laser are respectively condensed and irradiated on the surface of the thick steel plate by a single focusing lens provided on the processing head. Laser cutting device.