JP2001314986A - Laser beam cutting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an absorption coefficient improving effect at a groove by a relatively small output laser power even in the case of a fast cutting speed. SOLUTION: A separate preceding laser beam 2 is arranged in front of a main laser beam 7 for cutting a steel plate 5. The steel plate is cut along a groove by the main laser beam 7 while forming the groove 1 on the surface of the steel plate. The steel plate has a washboard-shape having irregularities crossing across the cutting line in the bottom shape of the groove formed by the preceding laser beam 2. Pitch of the irregularities is made larger than the wave length of the main cutting laser or the pitch of the irreguralities of the groove bottom is controlled by the pulse repetition frequency control while using pulse modulation of a pulse laser or a continuous wave laser as the preceding laser beam, or pulse of an asist gas stream is used when grooving by the preceding laser beam to control the pitch of the irregularities of the groove bottom.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser cutting method for cutting a metal material, such as a thick steel plate, generally having an oxide layer or a foreign matter adhered to the surface thereof by irradiating a laser beam.

[0002]

2. Description of the Related Art Generally, an oxide layer (scale) is formed on the surface of a thick steel plate. This is generated because oxidation of the surface proceeds while being left on the cooling floor after finish rolling at a high temperature. Plates are usually traded with scales, since they serve to block the atmosphere and the steel plate and prevent further oxidation of the plate body.

On the other hand, a thick steel plate is a plate-shaped product, and the producer adjusts to the dimensions required by the customer before shipping. Conventionally, cutting means for dimension adjustment include shear cutting and gas cutting. In recent years, laser cutting, plasma cutting, and the like have attracted attention due to the high cutting speed. Above all, laser cutting has preferable features such as cutting accuracy, narrow cutting margin (kerf width), and dross-free, and has been spreading in the field of thick plates with the increase in laser output.

[0004] Conventionally, laser cutting has been effective in the field of thin sheets having relatively clean surface properties. In particular, it was described that the power saving effect by the automatic operation and the omission of the post-process was great.
However, since the surface properties of a thick plate are not always clean or uniform, poor cutting properties such as scrambled cross-sections and dross adhesion have occurred, and the superiority thereof has been significantly impaired.

[0005] As a method for suppressing such a cutting failure in terms of a device, means as disclosed in Japanese Patent Application Laid-Open No. Hei 10-277773 is disclosed. This is due to the inventors' invention, but in front of the main laser beam for cutting the steel sheet, separately, a small output preceding laser beam is arranged, and while the groove is provided on the steel sheet surface online, First, there is a laser cutting method for cutting along a groove with a succeeding main cutting beam.
An increase in the absorptance due to multiple reflections of the main cutting beam on the inner wall of the groove is a point of improving the cross-sectional quality. The above method
Certainly, it has been found that the sheet has extremely high resistance to cutting defects caused by uneven surface properties of the thick plate.

However, following experiments by the inventors,
An unexpected fact turned out. According to this, the increase in the absorption coefficient is observed from the groove depth of about 100 μm, and considering that the groove width at that time is about 700 μm in practical use,
The cross-sectional shape of the groove is not a V-shape but a very shallow U-shape.
In this case, multiple reflections on the groove side wall cannot occur, and the shape of the groove bottom has to be determined for the cause of increased absorption. This fact was the focus of the present invention.

[0007] The inventors have also studied the speed dependence of groove processing. In a region where the material to be cut is relatively thick and the cutting speed is as low as 1 m / min or less, the average output 2
It is possible to form a groove having a depth of about 100 μm and a width of about 700 μm at which an absorptivity increasing effect is exhibited with a low power laser of about 00 W, but it is good in a medium thickness area of about 20 mm or less. It was also confirmed that it was difficult to obtain a sufficient groove depth with the above small output because the appropriate cutting speed for obtaining the cut surface was faster. Of course, if the output of the groove providing laser is increased, the groove depth can be increased even in such a situation. However, this simply leads to an increase in capital investment, which is not industrially desirable.

[0008]

An object of the present invention is to obtain a sufficient effect of improving the absorptivity even in a shallow groove with a relatively small output laser power even when the cutting speed is high. That is, it is an object of the present invention to form a fine V-groove array with low laser power and good reproducibility with the aim of industrial advantage.

[0009]

In order to investigate the possibility of using a low power groove forming laser to exert a defect suppressing effect, the inventors of the present invention applied the groove bottom formed under various conditions to the surface. As a result of measurement using a roughness meter, it was found that the bottom of the groove where the increase of the absorption coefficient was well observed was not smooth but had characteristic irregularities. The pitch of the irregularities is larger than 10.6 μm, which is the wavelength of the cutting laser,
It turned out that it has a shape close to a V groove. In other words, in this case, it is considered that the multiple reflection of the beam occurs not in the side wall of the groove but in the row of V-shaped grooves in the form of a small washing plate at the bottom of the groove, thereby increasing the effective absorption coefficient for the cutting laser. As a practical conclusion, the inventors have found that the increase in absorption coefficient does not depend solely on the depth of the groove, but even if the groove is shallow, a washing plate-shaped fine V-groove at the bottom of the groove can be obtained under appropriate conditions. They found that it could happen as long as it was granted.

[0010] Therefore, the above-mentioned problem is solved by the following constitution of the present invention: (1) In cutting a steel material by using a laser, another preceding laser beam is arranged in front of a main laser beam for cutting a steel plate; In a laser cutting method in which a groove is formed on a surface of a steel sheet and a main cutting beam is cut along the groove, a washing method having a concave and convex portion in which a bottom shape of a groove formed by the preceding laser beam crosses in a cutting line direction. A laser cutting method having a plate-like shape. (2) The laser cutting method, wherein the pitch of the concave and convex portions at the groove bottom is larger than the wavelength of the main cutting laser. (3) In the laser cutting method, a pulse modulation of a pulse laser or a continuous wave laser is used as the preceding laser beam, and the pitch of the concave and convex portions at the bottom of the groove is controlled by controlling a pulse repetition frequency. (4) The laser cutting method according to the above, wherein the pitch of the unevenness at the bottom of the groove is controlled by utilizing the pulsation of the assist gas flow when the groove is formed by the preceding beam. Can be solved.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, in order to clarify the gist of the present invention, description will be made with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In this embodiment,
A pulse laser (not shown) can be used as a laser beam source for providing the groove 1. A flash lamp pumped pulse YAG laser can be used. The laser beam 2 is guided to a step index type optical fiber 3 having a core diameter of 800 μm, and a focusing head 4 having a one-to-one image forming optical system is provided at the fiber emitting end. Irradiate. Then, an air jet is blown from the air jet nozzle 6 to the irradiation point in the direction in which the groove processing proceeds, and the molten steel is removed.

The condition setting for providing the groove 1 can be generalized as follows. That is, the laser beam 2 for machining the groove 1 and the steel material 5
Is the relative speed of v (m / s), the wavelength of the main cutting laser beam 7 is λ (m), the pulse repetition frequency of the groove processing laser is f (Hz), and the focused beam diameter of the laser is d (m). When the pitch of the concave and convex portions at the bottom of the groove is p (m), p = v / f and d
This means that the pulse repetition frequency f should be selected so that>p> λ. In other words, the laser beam cannot enter the groove having a width smaller than the wavelength λ of the main cutting laser, and the pulsed groove processing beam needs to overlap the irradiation points with the preceding and succeeding pulses. is there. By rewriting the above equation, v / λ>f> v / d. At this time, when walking while straddling the footprints on the snow, the traces of the heels remain, and like a groove on the washing board, the laser beam for groove processing in a direction perpendicular to the direction of the groove processing by the laser , A fine V-groove pattern follows.

For example, the opening diameter of the air jet nozzle 6 is 2.5 mm, the original pressure is 0.5 MPa, the spray angle is 45 °,
The distance between the irradiation point and the nozzle opening was 10 mm. At this time, the light collecting head 4 was fixed and the steel material 5 was moved. The moving speed of the steel material 5 was 1.0 m / min. The pulse repetition frequency of the YAG laser was 550 Hz. Y on steel 5
The AG laser power was 120W. At this time, the pitch of the unevenness at the bottom of the groove was 33 μm. Wavelength 10.6μ
When the absorption rate was measured with a carbon dioxide laser of m, it was 65% on the scale surface and 98% on the groove.

In this embodiment, a flash lamp excitation pulse YAG laser is used as a laser for forming grooves having irregularities at the bottom, but other methods such as modulating a continuous wave laser may be used. . In practice, there are limitations due to the capabilities of commercially available laser devices. For example, when the converging diameter of a YAG laser for groove processing is 700 μm, the pulse repetition frequency can be 30 Hz. A flashlamp pumped YAG laser corresponds. Therefore, in order to make use of the economics of the present invention, it is more preferable to apply modulation by a continuous wave pump laser that can be repeated relatively quickly. The inventors point out this fact.

FIG. 2 is a diagram showing another embodiment of the present invention. In this embodiment, as a beam source for providing the groove 1,
A continuous wave laser (not shown) can be used. More specifically, a so-called arc lamp pumped continuous wave YAG laser can be used. The laser beam 2 is guided to a step index type optical fiber 3 having a core diameter of 800 μm, and a focusing head 4 having a one-to-one image forming optical system is provided at the fiber emitting end. Irradiate. The YAG laser power on the steel 5 is about 120 W. Then, an air jet is blown from the air jet nozzle 6 to the irradiation point in the direction in which the groove processing proceeds, and the molten steel is removed.

The opening diameter of the air jet nozzle 6 is 2.5 m.
m, the original pressure was 0.5 MPa, the spray angle was 45 °, and the distance between the irradiation point and the nozzle opening was 10 mm. At this time, the light collecting head 4 was fixed and the steel material 5 was moved. The moving speed of the steel material 5 was 1.0 m / min. An electromagnetic valve 9 was provided in the air supply pipe 8, and the valve 9 was opened and closed periodically to generate a temporal pulsation in the air jet. In this embodiment, the frequency is set to 550 Hz. At this time, the pitch of the unevenness at the groove bottom was about 30 μm. When the absorptance was measured by a carbon dioxide gas laser having a wavelength of 10.6 μm, it was 65% on the scale surface and 98% on the groove.

The condition setting for providing the groove 1 can be generalized as follows. That is, the relative speed between the light collecting head 4 and the steel material 5
(M / s), the wavelength of the laser is λ (m), the pulsation frequency of the air jet is f (Hz), and the uneven pitch at the groove bottom is p (m).
Then, the pulsation frequency f of the air jet should be selected so that p = v / f> λ. When the diameter of the influence of the wind pressure is d (m) and the pitch of the grooves at the bottom of the groove is p (m), the pulse repetition frequency f should be selected so that d> p = v / f. In summary, v / λ>f> v /
d. In the present embodiment, the electromagnetic valve is used as a method for generating the pulsation of the air jet. However, other methods such as deflecting the air jet nozzle itself may be used.

In the laser cutting method as described above, there is no need to increase the depth of the groove itself in order to obtain the multiple reflection effect on the side wall of the groove, and a shallow groove is sufficient. Therefore, it is possible to cope with a case where the cutting speed is high. That is, the same as the above 120
When groove processing is performed with a constant laser output and a constant air jet at W, the groove depth is only about 50 μm at a speed of 1.0 m / min, and absorption increases due to multiple reflection on the groove side wall. No effect. In order to secure a depth of 100 μm in a groove having no bottom irregularity, which is a groove depth of achieving the same effect in the conventional cited example (Japanese Patent Application Laid-Open No. 10-277663), it is necessary to reduce the speed to about 0.6 m / min. is there.

[0019]

As described above, in the laser cutting method according to the present invention, by effectively controlling the shape of the groove bottom, a sufficient absorptance improvement effect on the main cutting laser can be obtained even in a shallow groove with a small leading laser power. And a higher cutting speed can be accommodated as a result.

[Brief description of the drawings]

FIG. 1 is a view showing the concept of a first embodiment of the present invention.

FIG. 2 is a view showing the concept of a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Groove formed in steel plate surface 2 Laser beam for groove formation 3 Optical fiber 4 Condensing head 5 Steel plate 6 Air jet nozzle 7 Main cutting beam 8 Air piping 9 Electromagnetic valve 10 Dross 11 Air cylinder

Continuation of the front page (72) Inventor Hiroyuki Yamamoto 20-1 Shintomi, Futtsu-shi, Chiba F-term in the Technology Development Division of Nippon Steel Corporation (reference) 4E068 AA05 AD01 AE01 AJ01 CA03 CA08 CD02 CH01 CH08 CJ01 DA14 DB01

Claims (4)

[Claims] In cutting a steel material using a laser, another preceding laser beam is arranged in front of a main laser beam for cutting a steel sheet, and a groove is formed on the surface of the steel sheet along the groove. A laser cutting method for cutting with a main cutting beam, wherein the shape of the bottom of the groove formed by the preceding laser beam is a washing plate-like shape having irregularities crossing the cutting line direction. . 2. The laser cutting method according to claim 1, wherein the pitch of the unevenness at the bottom of the groove is larger than the wavelength of the main cutting laser. 3. The laser according to claim 1, wherein a pulse modulation of a pulse laser or a continuous wave laser is used as the preceding laser beam, and the pitch of the unevenness at the bottom of the groove is controlled by controlling a pulse repetition frequency. Cutting method. 4. The laser cutting method according to claim 1, wherein the pitch of the unevenness at the bottom of the groove is controlled by using the pulsation of the assist gas flow when the groove is formed by the preceding beam.