JPH11104879A - Laser cutting nozzle and laser cutting method - Google Patents

Abstract

(57) [Problem] To provide a laser cutting nozzle for efficiently cutting a thick steel plate and obtaining good cut surface quality. SOLUTION: This laser cutting nozzle is provided with the following members. (A) a center nozzle that injects both laser light and oxygen gas as a first assist gas, and (b) a ring nozzle that injects oxygen gas as a first assist gas provided around the center nozzle.
(C) an auxiliary nozzle provided behind the center nozzle for injecting a second assist gas along a cutting groove formed by the laser beam. This makes it possible to quickly discharge the burned and melted oxide (dross) from the cut groove, so that the thick steel plate can be easily laser-cut and its cut surface quality can be obtained. When an inert gas or Ar gas is used as the second assist gas, the quality of the cut surface of the thick steel plate can be further improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser cutting nozzle used in a laser cutting apparatus for cutting a workpiece such as a thick steel plate using a laser beam, and a laser cutting method using the nozzle.

[0002]

2. Description of the Related Art A large amount of hot-rolled steel sheets are used for shipbuilding, construction, bridges and the like. In the construction of these steel structures using hot rolled steel sheets, welding and cutting account for much of the cost and man-hours.To streamline these constructions, the automation of not only the welding method but also the cutting method has been remarkably advanced. It is getting.

[0003] In particular, as a method for cutting a steel sheet, a laser cutting method having a very narrow cutting width and a small thermal deformation due to heat input for cutting has a better cut surface quality than other heat cutting methods. Due to the excellent characteristics that fumes are less generated and the working environment is good and the cutting work is completely automatic, it is rapidly spreading, especially for cutting relatively thin steel plates. .

As described above, the laser cutting method is the most effective method for rationalizing the cutting of a steel sheet. However, as the thickness of the steel sheet increases, the range of an appropriate cutting speed for laser cutting is limited. There were limits to the application. In particular, when the cutting speed is increased in order to increase the cutting productivity, the energy input per unit cutting length becomes small, so that it becomes difficult to melt the entire plate thickness.

[0005] It is also difficult to remove molten metal,
An oxide called dross adheres to the cut lower surface. For this reason, there is a problem that not only deteriorates the quality of the cut surface but also requires extra man-hours to remove it,
Laser cutting of a thick steel plate having a thickness of more than 20 mm is difficult, and its application is currently limited.

In laser cutting, a laser beam is emitted from a laser light source, and the laser beam is condensed and irradiated on a workpiece, thereby heating and melting a portion to be cut. At this time, at the same time, an assist gas for supporting the melting and burning of the material is supplied to gouge the cut portion, to eliminate the melted portion, or to melt and cut the remaining plate thickness. As the assist gas, high-purity oxygen gas is usually used to support combustion. Therefore, the role of the laser cutting nozzle for condensing the laser beam and simultaneously supplying the assist gas plays an extremely large role.

Conventionally, nozzles having various structures have been developed and used as laser cutting nozzles. They can be broadly classified into (1) a single-nozzle system in which the laser beam and the assist gas are injected coaxially, and (2) a nozzle system in which the laser beam and the assist gas are injected coaxially and are also injected and supplied from different paths. .

In general, in the laser cutting method, it is important to sufficiently increase the pressure of the assist gas. However, since the pressure resistance of the laser condensing lens is small, the pressure is not sufficiently increased in the single nozzle method (1). Difficult to increase. For this reason, various methods have been devised for the method (2) for injecting the assist gas from a path different from that of the laser light, and there are a side nozzle method, a double nozzle method, a multi-nozzle method and the like.

The side nozzle system is a system in which an assist gas is also supplied from an auxiliary nozzle provided on a side of a center nozzle for condensing a laser beam. Double nozzle method
A ring-shaped opening is provided outside the center nozzle, and assist gas is coaxially ejected from the center nozzle and the ring-shaped opening.
No. 6,086,045.

In the multi-nozzle system, a plurality of auxiliary nozzles are provided outside a center nozzle, and an assist gas is also non-coaxially jetted from the auxiliary nozzles. It is disclosed in the gazette.

However, the single nozzle method and the side nozzle method are suitable for cutting thin steel sheets,
When the plate thickness is large, it is difficult to make the assist gas sufficiently reach the cutting groove, and therefore, it is not suitable for cutting a thick steel plate having a plate thickness exceeding 20 mm.

The double nozzle method disclosed in Japanese Patent Application Laid-Open No. 6-7985 is expected to improve the laser cutting properties of a steel sheet. However, the present invention is aimed at improving the bead shape of the welded portion in laser welding, mainly by preventing the adhesion of metal oxides, and does not mention laser cutting of thick steel plates. The effect is not clear.

Further, the multi-nozzle system disclosed in Japanese Patent Application Laid-Open No. 4-200888 can increase the pressure of the assist gas as compared with the single-nozzle system and the side-nozzle system. There is expected. However, it does not disclose an embodiment of cutting a steel plate. In addition, in the study of the present inventors, even if this method is used, a steel plate having a thickness of about 20 mm can be cut off for the reason described below, but the quality of the cut surface is not satisfactory. Further, it was impossible to cut a steel plate having a thickness of 30 mm.

[0014]

As described above, when the laser cutting nozzle disclosed in the prior art or the prior art is used, when the thickness of the steel plate becomes 20 mm or more, the quality of the cut surface is good. Is difficult to obtain. Therefore, an object of the present invention is to provide a laser cutting nozzle for efficiently cutting a thick steel plate and obtaining good cut surface quality.

[0015]

Means for Solving the Problems The inventors of the present invention have studied in detail various factors concerning a laser cutting ability of a thick steel plate for laser cutting, and as a result, have reached the following invention.
A first invention is a laser cutting nozzle comprising the following members. (A) a center nozzle for injecting both laser light and oxygen gas as a first assist gas, (b) a ring nozzle provided on the outer periphery of the center nozzle for injecting oxygen gas as a first assist gas, c) An auxiliary nozzle provided behind the center nozzle, for injecting a second assist gas along a cutting groove formed by the laser light. According to the present invention, the oxide (dross) that has been burned and melted can be quickly discharged from the cut groove, so that the thick steel plate can be easily laser-cut and the good cut surface quality can be obtained.

A second invention is a laser cutting nozzle, wherein the second assist gas is an inert gas. According to the present invention, by injecting the inert gas from the auxiliary nozzle, the quality of the cut surface of a thick steel plate can be further improved.

A third invention is a laser cutting nozzle, wherein the inert gas is an argon gas.
Examples of the inert gas include an argon gas, a nitrogen gas, and a mixed gas thereof, but an argon gas is preferable because a high-purity gas is easily available.

According to a fourth aspect of the present invention, the injection of gas from the center nozzle, the ring nozzle, and the auxiliary nozzle can be controlled independently by adjusting the flow rate and / or pressure. Laser cutting nozzle. According to the present invention, it is possible to eject high-pressure assist gas from the ring nozzle and the auxiliary nozzle without damaging the focusing lens of the center nozzle having a small withstand pressure,
In particular, cutting of a thick steel plate is facilitated, and control of cutting conditions is also simplified.

According to a fifth aspect of the present invention, when cutting a thick steel plate, a laser beam and an oxygen gas as a first assist gas are injected around the laser beam, and the laser beam is further cut along a cutting groove formed by the laser beam. 2 is a laser cutting method characterized by injecting 2 assist gases. By the laser cutting method of injecting an inert gas from the auxiliary nozzle, the laser cutting of a thick steel plate is particularly easy, and the quality of the cut surface can be ensured.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

The inventors of the present invention have studied in detail various factors concerning the laser cutting ability of a thick steel plate with respect to laser cutting properties, and as a result, have found that a thick steel plate having a thickness of more than 20 mm can be cut with a good cut surface. In order to release, the following two points were found to be particularly important.

The first is a state where the laser beam is irradiated,
That is, it is important to increase the oxygen concentration as the first assist gas near the lower end of the cutting groove. For this purpose, it is necessary to increase the pressure of the assist gas and prevent entrainment of air existing around the lower end.

Second, it is important that the burned and melted oxide (dross) generated in the cut groove after the laser beam has passed is discharged from the cut groove as quickly as possible. For this purpose, the pressure of the second assist gas at the lower end of the cut groove must be sufficiently increased, and a gas flow at a sufficient speed must be ensured. The first and second conditions alone are:
Good cut surface quality cannot be ensured, and both of these two conditions must be met.

Therefore, based on the above findings, the present inventors have conducted intensive studies on the structure of a nozzle satisfying the two conditions at the same time. First, in order to increase the oxygen concentration in the vicinity of the lower end of the cutting groove, which is the first problem, a single nozzle system in which laser light and a first assist gas are coaxially injected is used. There is a method of simply increasing the pressure. However, in this method, since the melt combustion by the first assist gas becomes excessive, the width of the cutting groove increases, and a very narrow cutting groove width, which is one of the features of laser cutting, cannot be obtained. In addition, it is difficult to increase the pressure only by the single nozzle method in view of the pressure resistance of the laser condenser lens.

On the other hand, in the multi-nozzle system, even if the gas pressure from the auxiliary nozzle on the outer peripheral portion of the center nozzle is increased, the oxygen concentration is almost the same as the oxygen concentration in the ordinary single nozzle system. The oxygen concentration at the lower end of the groove could not be increased. It is considered that this is because air is drawn in from the gap between the center nozzle and the auxiliary nozzle in the outer peripheral portion.

Therefore, the nozzle according to the present invention is of a double nozzle type, and in addition to the oxygen gas injection as the first assist gas from the center nozzle, the gas pressure from the ring-shaped nozzle around the center nozzle also increases, so that the lower end of the cut groove is formed. Effectively increase the oxygen concentration near the part. This ring-shaped nozzle has a shape in which a continuous concentric slit is provided on the outer periphery of the center nozzle. In this configuration, the flow of the first assist gas from the ring-shaped nozzle surrounds the laser beam, and the surrounding air can be effectively prevented from being entrained by the shielding effect.

Next, a second problem, that is, a measure for increasing the pressure of the second assist gas at the lower end portion of the cutting groove and obtaining a gas flow at a sufficient speed was studied. The side nozzle method or the double nozzle method in which a concentric slit is provided on the outer periphery of the center nozzle increases the pressure of the second assist gas in the cutting groove after the laser beam passes, as compared with the single nozzle method. be able to. However, it has not been possible to obtain a gas flow rate and a gas pressure sufficient to cut a thick steel plate.

As a result, when the thickness of the steel sheet exceeds 20 mm, oxide (dross) is deposited on the portion once melted and burned, and the cut groove is closed, so that the steel sheet cannot be separated.
In order to solve this, it is effective to selectively supply the second assist gas to the cut groove after cutting. Therefore, in the present invention, the second nozzle is provided along the cutting groove behind the center nozzle (backward in the traveling direction of the laser beam).
An auxiliary nozzle for supplying the assist gas is provided.

As described above, when the second assist gas is injected and supplied from the auxiliary nozzle, the burned and melted oxide (dross) can be discharged from the cut groove as quickly as possible. Therefore, the second assist gas ejected from the auxiliary nozzle is not limited to the oxygen gas, and it is also possible to use another gas to remove the oxide. However,
Since the cut surface is still hot, carburize the cut surface,
It can be said that a reactive gas such as nitriding is not preferable.

Based on this finding, the present inventors have studied the gas injected from the auxiliary nozzle, and it is desirable to use an inert gas. However, argon (Ar) gas having a normal purity is somewhat economically disadvantageous. Although disadvantageous, it has been found that the quality of the laser cut surface can be significantly improved.

That is, when Ar gas is injected from the auxiliary nozzle into the cut groove, dross does not adhere to the cut surface and the cut surface is smoother than when ordinary oxygen gas is injected. It became clear that the perpendicularity of the cut lower edge was excellent. In addition, when oxygen gas is used, local expansion (notch) of the width of the cut groove occurs, whereas when Ar gas is used, the occurrence of such a notch is suppressed.

This is because when the oxygen gas is injected from the auxiliary nozzle, the molten material such as dross to be generated and discharged becomes a spark and causes excessive combustion, and new dross adheres to the cut surface and the cut surface due to excessive melting. It is presumed that the surface roughness was deteriorated and the corners fell off. Therefore, as the gas injected from the auxiliary nozzle, by using a gas that is more inert to melting and burning the steel sheet than oxygen gas, it is possible to improve the quality of the cut surface while maintaining the elimination of dross. . Here, the quality of the cut surface is based on the Japan Welding Association standard W
The evaluation of the cut surface quality by ES2801 was performed using the items slag (S), roughness (R) and notch (N).

[0033]

Embodiments of the present invention will be described below. Laser cutting uses a 6 kW laser processing machine, laser output 4
The cutting of the thick steel plate was performed at various cutting speeds under the conditions of ６6 kW. In the present example, a thick steel plate having a tensile strength of 400 MPa and a plate thickness of 10 to 60 mm, which is frequently used for a steel structure, was used. Its typical chemical composition is weight% (wt%)
And C: 0.15%, Si: 0.20%, Mn: 0.8
0%, P: 0.018%, S: 0.012%, Al:
0.025%, with the balance being iron and impurities.

Example 1 Oxygen gas was injected as first and second assist gases from a ring nozzle and an auxiliary nozzle to laser cut a thick steel plate. FIG. 1 shows a bottom view and a longitudinal sectional view of the laser cutting nozzle used in Example 1 (Inventive Example) 1.

As shown in FIG. 1, a nozzle hole 1 of a center nozzle 2 having a diameter of 2.5 mmφ and a nozzle hole 4 of a concentric ring nozzle 3 surrounding the nozzle hole 4 (inner diameter 5 mmφ, outer diameter 6 mm)
mm φ, slit width 0.5 mm) and a nozzle hole 6 of a slit-shaped auxiliary nozzle 5 having a length of 5 mm and a width of 1 mm for selectively supplying assist gas to a cutting groove. In such a structure, the assist gas can be independently supplied from the center nozzle 2, the ring nozzle 3, and the auxiliary nozzle 5, and the respective injection pressure and flow rate can be independently adjusted.

The first assist gas is supplied to the gas supply holes 7.
From the gas supply holes 12.
Supplied from The center nozzle 2 is airtightly fixed to the ring nozzle 3 by a flange 10 of the center nozzle 2 via a spacer 9 and a packing 8 disposed around the spacer 9. The laser beam 13 is applied along the center axis of the center nozzle 2.

On the other hand, as a comparative example, the following nozzle was used. Comparative Example 1: A single nozzle including only a center nozzle shown in FIG. Comparative Example 2: A double nozzle having a ring nozzle concentric with the center nozzle shown in FIG. Comparative Example 3: A nozzle shown in FIG. 9 in which auxiliary nozzles are arranged at eight positions in the circumferential direction at regular intervals with the center nozzle.

In this embodiment, the pressure of the injected oxygen gas is
0.01 to 0.05 MPa for the center nozzle, 0 to 0.12 MPa for the ring nozzle, 0 to
Laser cutting was performed in the range of 0.6 MPa. As oxygen, commercially available high-purity oxygen having a purity of 99.8% or more was used.

The laser cutting performance was evaluated by cutting at various cutting speeds and determining an appropriate cutting speed at that time. That is, the upper limit of the cutting speed at which the entire thickness can be melted and dross does not adhere to the cutting lower surface, and
The lower limit cutting speed at which a defective cutting portion called a notch does not occur on the cut surface was determined. The notch is a cut width of 50%
This refers to the enlarged portion.

When the plate thickness is constant, a laser beam with a wide range of the upper and lower cutting speeds has a good laser cutting property. Further, when the plate thickness is increased, the width between the upper limit cutting speed and the lower limit cutting speed becomes narrow, and it becomes difficult to perform a good cutting at a certain thickness.
In the experiment, this critical thickness was determined.

Table 1 shown in FIG. 5 shows the results of a laser cutting test at a plate thickness of 20 mm. When the nozzle of Invention Example 1 was used, the upper limit cutting speed at which dross did not adhere was 750.
mm / min, and at the same time, the lower limit cutting speed at which no notch occurs is 600 mm / min, and good cutting quality is obtained in a high-speed and wide range of laser cutting speed. Furthermore, the cut surface quality after cutting has passed the first class in each of slag (S), roughness (R), and notch (N) of WES2801, which is a standard of cut surface quality specified by the Japan Welding Association.

On the other hand, in Comparative Examples 1 to 3, separation and cutting can be performed by lowering the cutting speed, but the quality of the cut surface is inferior to that of the present invention, and the slag (S) and roughness ( R), notch (N) did not clear the first grade. When the center nozzle and the ring nozzle of Comparative Example 2 are provided, and when the center nozzle and the plurality of auxiliary nozzles of Comparative Example 3 are provided in the circumferential direction, high-pressure oxygen gas is injected from the ring nozzle or the auxiliary nozzle, respectively. The cuttability of the thick steel plate is not improved compared to the case where only the center nozzle of Comparative Example 1 is used.

On the other hand, Table 2 shown in FIG. 6 shows the results of comparing the maximum cuttable thickness having good cut surface quality between the inventive example 1 and the comparative example. Under the conditions of Inventive Example 1, cutting can be performed while maintaining good cut surface quality up to a plate thickness of 40 mm, which is clearly larger than the comparative example.

Embodiment 2 Oxygen gas is injected as a first assist gas from a center nozzle and a ring nozzle, and Ar gas, which is an inert gas, is injected as a second assist gas from an auxiliary nozzle. Was laser cut. At this time, the laser cutting nozzle used in Inventive Example 2 had a center nozzle hole having a diameter of 2.5 mmφ and a concentric ring nozzle hole surrounding the center nozzle hole (inner diameter 5 mmφ, outer diameter 6 mm).
mmφ, slit width 0.5 mm) and an auxiliary nozzle composed of two 2 mmφ circular holes for selectively supplying an inert gas to the cutting groove. FIG. 2 shows a bottom view and a longitudinal sectional view of the nozzle.

As in the first embodiment, the gas can be independently supplied from the center nozzle, the ring nozzle, and the auxiliary nozzle, and the respective injection pressures and flow rates can be independently adjusted. In the present embodiment, the pressure of the oxygen gas as the first assist gas from the center nozzle and the ring nozzle is 0.03
The cutting was performed at an MPa gas of 0.12 MPa and an Ar gas pressure of 0.6 MPa as a second assist gas from the auxiliary nozzle. The evaluation of the laser cutting property is the same as in Example 1.
The results are shown in Table 1.

As Comparative Example 4, a nozzle (FIG. 9) in which auxiliary nozzles were arranged at eight circumferential positions at equal intervals from the center nozzle used in Comparative Example 3 in Example 1 was used.
Oxygen gas was injected from the center nozzle at 0.04 MPa, and Ar gas was injected from the auxiliary nozzle at 0.6 MPa, and laser cutting was attempted. However, in this case, the oxygen concentration in the cutting groove could not be increased, and cutting was impossible.

The upper limit cutting speed when the nozzle of Inventive Example 2 is used at a plate thickness of 20 mm is the same as that of Inventive Example 1 shown in Embodiment 1.
And the lower limit cutting speed is the same as that of Inventive Example 1, and the range of the appropriate cutting speed is sufficiently wide. Invention Example 2
The feature of the present invention is that the same plate thickness 20
mm, the range of the appropriate cutting speed is wide, in other words, there is a margin in cutting a thick steel plate, and the quality of the cut surface is excellent. As shown in Table 2, when the nozzle of Example 2 (FIG. 2) was used, it was possible to cut a thick steel plate up to 54 mm.

Further, in the laser cutting nozzle of the present invention, an auxiliary nozzle for selectively supplying an oxygen gas or an Ar gas as a second assist gas to the cutting groove has the following configuration.
The same effect can be obtained even if the shape is changed to another shape. That is, as shown in FIG. 3, one end of the slit is not in contact with the ring nozzle shown in FIG. 1, or a circular nozzle having a large number of circular holes as shown in FIG.
The effect as an auxiliary nozzle can be achieved.

However, when an inert gas is used as the second assist gas, it is desirable that the ring nozzle hole and the auxiliary nozzle hole be shut off in order to effectively exhibit the characteristics.

Further, as a method of always supplying gas to the cutting groove even when the traveling direction of laser cutting changes, a method of making the nozzle of the present invention rotatable so that the auxiliary nozzle always follows the cutting groove, or A method is also conceivable in which a plurality of auxiliary nozzles are provided and one of the auxiliary nozzles always covers the cutting groove. Further, the steel plate subjected to laser cutting according to the present invention is a general thick steel plate, and it is not particularly necessary to limit the chemical components.

[0051]

As described above, according to the nozzle and the cutting method according to the present invention, a steel plate having a thickness of 20 mm or more, which has been difficult with conventional laser cutting, has excellent cut surface quality and Laser cutting can be efficiently performed. For this reason, it greatly contributes to a reduction in construction cost when constructing a steel structure.

[Brief description of the drawings]

FIG. 1 is a bottom view and a longitudinal sectional view of an example of a laser cutting nozzle of the present invention.

FIG. 2 is a bottom view and a longitudinal sectional view of an example of a laser cutting nozzle of the present invention.

FIG. 3 is a bottom view and a longitudinal sectional view of an example of the laser cutting nozzle of the present invention.

FIG. 4 is a bottom view and a longitudinal sectional view of an example of a laser cutting nozzle of the present invention.

FIG. 5 is a table showing the results of comparison of appropriate upper and lower cutting speeds at which good cutting is possible when cutting a thick steel plate having a thickness of 20 mm.

FIG. 6 is a diagram showing, as Table 2, a result of comparing maximum sheet thicknesses of steel sheets that can be cut satisfactorily.

FIG. 7 is a bottom view and a longitudinal sectional view of a conventional single nozzle used in a comparative example.

FIG. 8 is a bottom view and a longitudinal sectional view of a conventional double nozzle used in a comparative example.

FIG. 9 is a bottom view and a longitudinal sectional view of a nozzle having a conventional multi-nozzle type auxiliary nozzle used in a comparative example.

[Explanation of symbols]

 Reference Signs List 1 center nozzle hole 2 center nozzle 3 ring nozzle 4 ring nozzle hole 5 auxiliary nozzle 6 auxiliary nozzle hole 7 first assist gas supply port to ring nozzle 8 packing 9 spacer 10 center nozzle flange 12 second assist to auxiliary nozzle Gas supply port 13 Laser light

Claims (5)

[Claims] 1. A laser cutting nozzle comprising the following members. (A) a center nozzle for injecting both laser light and oxygen gas as a first assist gas, (b) a ring nozzle provided on the outer periphery of the center nozzle for injecting oxygen gas as a first assist gas, c) An auxiliary nozzle provided behind the center nozzle, for injecting a second assist gas along a cutting groove formed by the laser light. 2. The laser cutting nozzle according to claim 1, wherein said second assist gas is an inert gas. 3. The laser cutting nozzle according to claim 2, wherein said inert gas is argon gas. 4. The gas injection from the center nozzle, the ring nozzle, and the auxiliary nozzle can be independently controlled by adjusting a flow rate and / or a pressure. Item 3. A laser cutting nozzle according to item 1 or 2. 5. When cutting a thick steel plate, a laser beam and a first assist gas are injected around the laser beam, and a second assist gas is injected along a cutting groove formed by the laser beam. A laser cutting method, characterized in that: