JP2002137078A - Laser beam cutting method and laser beam cutting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam cutting method for a steel plate and its device which realize laser beam cutting having excellent quality in a cut face by solving problems such as roughness on the cut face, reduction in vertical streak pitch, and adhesion of dross in the laser beam cutting. SOLUTION: In this method wherein a steel plate 1 is heated and melted by irradiating the steel plate 1 with a laser beam 4, and the steel plate 1 is brought into the laser beam cutting by shifting a laser beam irradiation part along a cut line, a plurality of, two or more condensing spots 8 of the laser beam are arranged side by side in a direction perpendicular to a cutting and traveling direction on the steel plate 1, and the steel plate 1 is cut.

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 steel sheet by laser. In particular, it is concerned with thick plate cutting technology.

[0002]

2. Description of the Related Art As one of the methods for fusing a steel sheet, there is a laser cutting method in which a cutting portion is irradiated with a laser beam and is blown with an oxygen gas to be heated and melted for cutting. Compared with other cutting methods, the laser cutting method has advantages in that the dimensional accuracy after cutting is excellent, the processing speed is high, and the depth of the heat-affected zone can be reduced.

The mechanism of laser cutting is described in, for example, (Reference: Miyamoto and Maruo, INDIAN WELDING JOURNA
L, March, 1992). According to this, a vertical streak (hereinafter referred to as striation) is formed on a cut cross section by the relationship between the laser beam diameter d and the reaction speed due to the oxidative heat generation of oxygen gas as an assist gas, and its pitch and roughness are determined. . The smaller the beam diameter d, the smaller the striation pitch of the cut cross section.

On the other hand, when a laser beam having a beam diameter D is condensed by a lens having a focal length f, a relation of d = (M ² × f × λ) / (π × D) is generally applied to the converged spot diameter d. Holds. (M
² : Condensing performance parameter, f: focal length, λ: wavelength, D:
Therefore, in order to improve the quality of the cut cross section, the converging diameter d is reduced.

[0005] Normally, if the focal length f small or condenser before the beam diameter D is large, i.e. F-number adopts a small laser recruitment and M ² value of the small converging optical system by performing smaller diameter I have. FIG. 3 shows the relationship between the F number F = f / D and the cross-sectional roughness of the cut surface. The circle mark in the figure indicates the beam diameter before condensing D = 25 m
The marks m and x indicate that the focal length of the condenser lens was f = 190.5 mm.

Since the spot diameter becomes extremely small in the vicinity of the focal point, the striation pitch and the cross-sectional roughness are reduced, but at the same time, the kerf width (cutting margin) as the cutting margin is also reduced. For this reason, the dross becomes difficult to flow, and stays as it is, leading to a cutting failure (dross adhesion). As described above, the cutting ability is reduced in the region where the cross-sectional roughness is the smallest.

Particularly, when cutting a thick steel plate, the volume to be melted increases according to the thickness of the steel plate, so that a laser beam with a high output density is required. Therefore, since the spot diameter decreases as M ² value is smaller condenses the light collecting highly laser beam to induce burning (gouge in cross-section) with the generation of the output density becomes too high plasma cutting section quality (Cut surface roughness) is rather deteriorated. For this reason, it was difficult to cut a thick steel plate with good cross-sectional quality and dross-free.

[0008]

SUMMARY OF THE INVENTION The present invention has been made based on the above circumstances, and provides a laser cutting method and a laser cutting apparatus capable of easily and stably cutting a high-quality steel sheet. The purpose is to do so.

[0009]

In order to achieve the above object, a laser cutting method according to the present invention comprises irradiating a steel sheet with a laser beam, heating and melting the steel sheet, and moving the laser irradiated portion along the cutting line to cut the steel sheet. The laser cutting method is characterized in that a plurality of laser beam condensed spots are arranged on a steel plate in a direction perpendicular to the cutting direction and cut.

According to another aspect of the present invention, there is provided a laser cutting apparatus including a laser oscillator, a beam transmission optical system, and a cutting torch including a focusing optical system and an assist gas supply device for cutting. A beam splitter for splitting a laser beam input from a cutting torch, a switching mechanism for arranging the split beam at right angles to a cutting progress direction on an irradiation surface, and a condensing lens. It is.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of a torch for laser cutting for carrying out the method of the present invention. As shown in FIG. 1, the cutting torch is configured by arranging a beam splitter 10 and a condenser lens 6 inside the nozzle unit 2. The laser beam 4 guided from the laser oscillator to the cutting torch is
The output is split into two by the beam splitter 10 of the nozzle unit 2, and the light is focused and formed as an image on the upper surface of the steel plate 1 by the condenser lens 6.

FIG. 4 shows an example of a beam splitter usable within the scope of the present invention. In this figure, a) is a chevron beam splitter 15, and b) is a diffractive optical element (Diffractive Optical Element).
s, DOE). In a), the laser beam 4 is split into two in the direction of the arrow by using the difference in the refraction angle by the angled beam splitter 15 having different inclination directions of the left and right slopes.

In b), the laser beam 4 is phase-modulated by a small step of a fine pattern provided on the surface of the beam splitter 16 and output in the direction of the arrow and equally divided into two.

FIG. 2 is a schematic view of a beam arrangement for arranging the converging spot 8 on the steel plate 1. The twin spots are arranged side by side so as to be orthogonal to the cutting direction. At this time, the distance between the centers of the beams is Δy, and the beam diameter is d.

The following describes how to give the twin spot intervals and the output density. In cutting a steel sheet, primary heat energy generated by laser irradiation and oxygen gas
Utilizes heat energy by the subsequent oxidation exothermic reaction.

At this time, since the oxygen gas is supplied coaxially with the optical axis of the laser beam, the oxidative exothermic reaction proceeds at a speed Vo around the focused spot of the laser beam and spreads around. When the cutting speed V is lower than the oxidative heat generation reaction speed Vo, the region having a diameter φ larger than the condensing spot diameter d reaches a temperature higher than the melting point by the oxidative heat generation reaction.

Therefore, when twin spots are arranged in a direction perpendicular to the cutting direction, the interval Δy between the twin spots is considered to be limited to the interval at which the circle region of diameter φ reaching the melting point formed by the respective oxidative exothermic reactions is in contact. Can be
At this time, Δy = φ holds. The region φ that has reached the melting point including the oxidative exothermic reaction is determined by the thickness of the steel sheet, the output density determined by the laser output and the beam diameter, the cutting speed, the oxygen purity of the assist gas, the supply amount, etc., but the phenomenon is extremely complicated. . Hereinafter, the quality of the cut cross section when cutting by the twin spot method will be described with an example.

FIG. 5 is a diagram showing the relationship between the interval between twin beams and the cross-sectional roughness of the cut surface according to the method of the present invention. Focal length
The spot diameter of one beam was condensed to 350 μm with a lens of f = 190 mm, and the center distance between both beams was arranged as Δy. The output of the laser beam was 1000 W, the power per beam was 500 W, and the power density per beam was 5.2 × 10 ⁵ W / cm ² .

The twin beam interval Δy = 0 mm is an undivided beam and corresponds to the conventional method. Cutting section roughness Rz at this time
Is 60 μm. If Δy = 0.1 mm, Rz is significantly reduced,
The cut surface quality is improved. Thereafter, the cut surface roughness gradually decreases and approaches the minimum value when Δy = 0.4 mm. When Δy = 0.8 mm, the thermal energy due to the split beam irradiation does not reach the amount of energy that can melt the thickness of the steel material, and dross adheres, and it becomes impossible to cut.

FIG. 6 shows the relationship between the output density of the laser beam and the cross-sectional roughness Rz of the cut surface according to the method of the present invention. Steel thickness
The beam interval Δy between the twin spots was set to 0.5 mm.
In the conventional method, when the output density is 10 ³ W / cm ² , the heat input by the laser is insufficient, and the sheet thickness cannot be melted. As a result, the molten steel does not flow downward, resulting in poor cutting. Power density
When 10 ⁴ W / cm ² to 10 ⁵ W / cm ² , if the assist gas conditions such as cutting speed and oxygen gas pressure are appropriately set, Rz is 60μ.
Improve to about m. In the ordinary laser cutting, this region where the cut surface quality of the cut material is the best is used.

When the output density becomes 10 ⁵ W / cm ² to 10 ⁶ W / cm ² , heat is added to the steel material, and the cut surface quality starts to deteriorate. When the output density is higher than that, plasma starts to be generated, causing burning, and the cut surface becomes extremely poor.

On the other hand, according to the method of the present invention, the output density per unit area of the condensed spot obtained by summing the two beams is obtained.
At 10 ³ W / cm ² , as in the conventional method, the amount of heat input is insufficient, resulting in poor cutting. When the power density is 10 ⁴ W / cm ² to 10 ⁶ W / cm ² , by setting the assist gas conditions such as the cutting speed and the oxygen gas pressure set value appropriately, the path of molten steel can be stabilized in the thickness direction. Since the heat source is secured and the heat source is separated, burning is less likely to occur, the cross-sectional quality after cutting is extremely good, and the Rz is improved to about 15 to 50 μm.

In the power density range of 10 ⁶ W / cm ² to 10 ⁷ W / cm ² , the cut surface quality starts to deteriorate due to excessive heat input to the steel material. When the output density becomes 10 ⁷ W / cm ² or more, plasma starts to be generated, causing burning, and the cut surface becomes extremely poor. As described above, according to the method of the present invention, the allowable range of the setting conditions of the laser output density at which the quality of the cut section is the best is wide and stable, and the cut section roughness Rz is reduced to about half or less of the conventional method. I do.

Hereinafter, the method of the present invention will be described in comparison with a conventional method. FIG. 7 is a comparison of a kerf width between a conventional single spot irradiation method and a twin spot irradiation method according to the present invention when a steel material having a thickness of 16 mm is cut with a carbon dioxide gas laser. The horizontal axis is the focal position Δ with respect to the steel surface (the focal position is negative inside the steel), and the vertical axis is the kerf width W. Good cutting area
The mark and the defective cutting area were marked with x.

In the conventional method, when the focal position of the condensing optical system substantially coincides with the vicinity of the surface of the steel material, the kerf width becomes narrower as the beam diameter becomes smaller, and becomes a minimum of 400 μm. When the kerf width is narrow, the molten steel is less likely to flow down in the thickness direction, and dross remains and adheres, leading to poor cutting. When the focal position is -3 mm or less and 3.0 mm or more away from the steel surface, the molten steel flows smoothly and becomes a good cutting area. Further, when the focal position is more than 5 mm away from the surface of the steel material, the beam spot diameter becomes large, the energy density is reduced, and the thickness of the steel material is not melted, resulting in poor cutting. On the other hand, in the method of the present invention, the kerf width is at least 1000 μm, which is wider than that of the conventional method. Therefore, in the range of Δ = −5 to 5 mm, the molten steel flows smoothly and becomes a good cutting area.

FIG. 8 compares the relationship between the focal position Δ with respect to the surface of the steel material and the surface roughness Rz of the cut section under the same conditions as in FIG. A good cutting area is indicated by a circle, and a defective cutting area is indicated by a cross. In the conventional method, Rz is at least about 45 μm,
According to the method of the present invention, Rz is greatly improved to 20 μm.

FIGS. 9 and 10 are schematic views of a cutting torch according to the method of the present invention. The cutting torch shown in FIG.
The beam splitter 10 and the condenser lens 6 are fixed to the nozzle 2.

The rotary beam arrangement switching unit 11 has a mechanism capable of rotating the nozzle unit 2 with respect to the main shaft unit 3. Therefore, the beam splitter 10 installed at right angles to the optical axis also rotates with the nozzle unit 2 around the optical axis, and the arrangement of the twin spots 8 on the upper surface of the steel material 1 can be switched according to the cutting progress direction. . Therefore, it is possible to cope not only with the cutting in the right angle direction but also with the diagonal direction and the cutting of the portion with R at the corner.

The cutting torch shown in FIG. 10 includes a main shaft 3, a sliding beam switching unit 17, and a nozzle 2. Some of the sliding switching units 11 are arranged so as to split the laser beam in a direction perpendicular to each other.
A plurality of beam splitters 10 are provided.

The pair of beam splitters 10
The sliding beam switching unit 17 can be moved back and forth by a sliding drive mechanism such as an air cylinder or a motor. Then, in response to a command from the host PC (computer), one of the beam splitters enters the optical axis of the laser beam 4, and the direction of the twin spot 8 on the upper surface of the steel material 1 switches by 90 degrees.

FIG. 11 shows a steel sheet 1 obtained by the cutting method according to the present invention.
FIG. 3 shows a top view of the movement trajectory of the cutting torch when cutting out a square in a counterclockwise direction. The steel plate 1 is cut continuously along the arrow from the cutting start point 13 to the cutting end point 14 in FIG. At this time, the twin beam spot is arranged in a direction orthogonal to the traveling direction.

The cutting torch starts from the cutting start point 13 and proceeds in a straight line. When reaching the first 90-degree left bending point 12, the cutting torch synchronizes the rotation switching mechanism in the cutting direction by a command from the host PC and cuts the sheet on the steel plate. Rotate the direction of the twin spot clockwise 270 degrees. In the case of the sliding switching mechanism, at the bending point 12 at the left 90 °, the laser is temporarily stopped, the beam splitter is switched instantaneously, the direction of the twin spot on the steel plate is rotated 90 °, and the laser is turned ON again. Then, the twin beam spot is arranged again in the direction orthogonal to the cutting progress direction, and cutting is performed in the direction of the arrow. Thereafter, the bending point is cut in the same manner, and stops at the cutting end point 14 to complete the cutting.

FIG. 12 is a layout view of a condensed beam in the multi-spot irradiation method in which a plurality of spots are arranged so as to obtain the same effect as the cutting method using the twin spots. As in the twin spot irradiation method, n condensed spots may be arranged side by side in a direction perpendicular to the cutting direction as shown in FIG. The distance Δy between the spots of each beam at this time
Is Δy when the progress limit region diameter of the oxidation exothermic reaction is φ
≦ φ.

In the multi-spot irradiation method, the plate thickness is increased,
This is effective for condensing a small beam diameter. These have the same effect on the dross discharge and the quality of the cut section.

[0035]

Embodiment 1 As shown in FIG. 11, laser cutting was performed to cut out a steel plate having a thickness of 16 mm into a rectangular shape of 3 mx 5 m.

The apparatus is composed of a carbon dioxide laser cutting machine with an output of 1.5 kW and a wavelength of 10.6 μm, a diffractive beam splitter of type b) in FIG. 4 and a rotary switching device, and a focal length f = 19.
A laser cutting torch including a 0 mm condenser lens was used. On a steel plate, twin spots condensed by a condensing lens after being divided into two by a beam splitter were arranged as shown in FIG. 12A, and the cutting torch was configured as shown in FIG. The assist gas is flowed coaxially with the laser beam using 99.6% pure oxygen gas. The cutting speed is v = 0.8m / min and the steel sheet 1 is cut continuously along the arrow from the cutting start point to the cutting end point. And
It was cut out into a 3m x 5m rectangular shape.

The cutting torch turns on the laser at the cutting start point 13 and stops for about 3 seconds, then starts and proceeds in a straight line on the dotted line in the figure. When approaching the first bending point 12 at 90 degrees to the left, the beam splitter rotation switching mechanism was activated by a command from the host PC and rotated clockwise 270 degrees while synchronizing the direction of the twin spot on the steel sheet with the cutting direction. Let it. Then, the twin beam spot is arranged again in the direction orthogonal to the cutting progress direction, and cutting is performed in the direction of the arrow.

Thereafter, the bending point is also cut in the same manner, and stopped at the cutting end point 14 to complete the cutting. The cut surface of the material to be cut that had been cut through these steps had no cutting defects at any point on the outer periphery without dross adhesion or scouring of the cut surface.

[0039]

Embodiment 2 As shown in FIG. 13, laser cutting was performed to cut out a steel plate having a thickness of 16 mm into a rectangular shape of 3 mx 5 m.

The apparatus is composed of a carbon dioxide laser cutting machine with an output of 1.5 kW and a wavelength of 10.6 μm, a diffraction type beam splitter of type b) in FIG.
A laser cutting torch including a 190 mm condenser lens was used. On a steel plate, twin spots condensed by a condenser lens after being divided into two by a beam splitter were arranged as shown in FIG. 12A, and the cutting torch was configured as shown in FIG. The assist gas is flowed coaxially with the laser beam using 99.6% pure oxygen gas. The cutting speed is v = 0.8m / min and the steel sheet 1 is cut continuously along the arrow from the cutting start point to the cutting end point. did. Laser on cutting torch at cutting start point 13
After stopping for about 3 seconds, start and go straight on the dotted line in the figure.

At the first bending point 12 at 90 degrees to the left, the laser beam is once turned off, and at the same time, the direction of the twin spot on the steel plate is changed by operating the forward / backward sliding switching mechanism of the beam splitter according to a command from the host PC. Rotate 90 degrees. The cutting direction is also switched to the 90-degree bending direction, the laser is turned on again, stopped for 2 seconds, and cut again along the dotted line along the arrow.

Thereafter, the bending point was cut in the same manner, and stopped at the cutting end point 14 to complete the cutting. The cut surface of the material to be cut that had been cut through these steps had no cutting defects at any point on the outer periphery without dross adhesion or scouring of the cut surface.

[0043]

As described above, according to the present invention, the kerf width (cut margin) is increased by using a laser beam having two or more condensed spots as compared with the case of cutting with one beam. By arranging and cutting the focusing spot on the
Cross-sectional quality such as cut cross-sectional roughness is greatly improved compared to conventional cutting methods, and stable cut surface quality without molten steel residue or dross adhesion can be obtained, which is a significant effect on suppression of cutting defects. Can be seen. This eliminates the need for post-processing such as dropping dross after cutting, which is effective in reducing the number of personnel at the manufacturing site and reducing costs.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a laser cutting torch for performing the method of the present invention.

FIG. 2 Layout of twin spot beams on steel plate

FIG. 3 is a diagram showing a relationship between an F number and cut surface roughness.

FIG. 4 is a diagram showing an example of a beam splitter used in the method of the present invention.

FIG. 5 is a diagram showing a relationship between a twin beam interval and a cut surface roughness.

FIG. 6 is a diagram showing a relationship between laser output density and cut surface roughness.

FIG. 7 is a comparison diagram of the cut portion kerf width according to the conventional method and the present invention method.

FIG. 8 is a comparison diagram of cut surface roughness between the conventional method and the method of the present invention.

FIG. 9 is a schematic view of a cutting torch according to the method of the present invention.

FIG. 10 is a schematic view of a cutting torch according to the method of the present invention.

FIG. 11 is a top view of the arrangement and the movement locus of the cutting beam spot according to the method of the present invention.

FIG. 12 is a schematic view of a multi-spot arrangement on a steel plate.

FIG. 13 is a top view of the arrangement and the movement locus of the cutting beam spot according to the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel plate 2 Nozzle part 3 Torch main shaft part 4 Laser beam 5 Uncut part 6 Condensing lens 7 Rotating axis 8 Laser condensing part 9 Cutting part 10 Beam splitter 11 Rotary beam arrangement switching part 12 Twin spot beam arrangement switching point 13 Cutting start point 14 Cutting end point 15 Yamagata beam splitter 16 Diffraction type beam splitter 17 Sliding beam arrangement switching unit

Continued on the front page (72) Inventor Hiroyuki Yamamoto 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Katsuhiro Minata 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation F-term in the Technology Development Division (reference) 4E068 AE00 CD04 CD08 DA14 DB01

Claims (2)

[Claims] A method of cutting a steel sheet by irradiating a laser beam to a steel sheet by heating and melting and moving a laser irradiation part along a cutting line, wherein a plurality of focused spots of the laser beam are cut on the steel sheet. A laser cutting method characterized by arranging and cutting in a direction perpendicular to a traveling direction. 2. A laser cutting apparatus comprising a laser oscillator, a beam transmission optical system, a condensing optical system, and a cutting torch including a cutting assist gas supply device, wherein a beam splitter for splitting a laser beam input from the cutting torch is provided. A laser cutting device, comprising: a switching mechanism for arranging the obtained beam on the irradiation surface at right angles to a cutting progress direction; and a condenser lens.