JP2002103067A - Method for laser beam cutting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an excellent laser beam cutting of a metallic structural body which is an assembly of thin plates or bars and has gaps between individual elements by optimizing parameters of machining condition and suppressing the generation of a self-burning phenomenon. SOLUTION: In a method for a laser beam cutting, a work 4, which is a metallic structural body which is an assembly of thin plates 4a or bars and has gaps 4b between individual elements, is cut by being irradiated with a laser beam 10 while an assist gas 9 is blown upon the work through a machining torch 3 in which a conversion lens 3a is built up, the cutting is performed by reciprocatively scanning several times the laser beam with respect to the work in the cutting direction. In this case, the focal point O of the conversion lens is set in the inner side of the work, and the parameters are so varied that the input power of the laser beam per a unit length of cutting and the supplying amount of the assist gas is gradually increased in accordance with the progress of the reciprocal scanning.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of cutting a metal structure such as a structural waste of a nuclear reactor facility, which is an assembly of thin plates or rods and has a gap between individual elements. The present invention relates to a laser cutting method applied to the case.

[0002]

2. Description of the Related Art As a processing method of cutting a metal structure (work) such as a steel material using a laser beam, a laser beam output from a laser oscillator is irradiated on a surface of the work through a condenser lens, and is irradiated on a laser irradiation surface. The work is moved in the cutting direction while blowing assist gas (oxygen), and the irradiation point of the work is melted using the energy of the laser beam and the heat of oxidation reaction of the assist gas. A processing method of scattering and cutting is well known.

FIG. 2 shows an outline of a laser processing apparatus used for laser cutting. In FIG. 2, 1 is a laser oscillator, 2 is a mirror, 3 is a processing torch (laser head), 4
Denotes a work table, 5 denotes a moving table on which the work 4 is placed, 6 denotes an assist gas cylinder, 7 denotes a flow control valve, and 8 denotes a control unit. Further, the processing torch 3 has a built-in condenser lens 3a and irradiates the work 4 with the laser beam 9 through the nozzle 3b at the tip. Further, the assist gas 10 supplied from the assist gas cylinder 6 is introduced into the inside of the processing torch 3 from the gas inlet 3c through the flow control valve 7, and is blown to the work through the nozzle 3b at the tip. Then, the output of the laser oscillator 1, the cutting speed of the work 4 set on the moving table 5,
The controller 8 sets and controls the supply amount of the assist gas set by the flow control valve 7 and the like. When the laser oscillator 1 is a YAG laser, it is possible to transmit a laser beam by connecting a flexible optical fiber between the laser oscillator 1 and the processing torch 3 without using the mirror 2. It is.

FIG. 3 shows the relationship between the work and the processing torch when the laser cutting is performed by using the laser processing apparatus shown in FIG. FIG. 4 is a schematic diagram showing parameters, where g is the distance between the nozzle 3b of the processing torch 3 and the work 4, O is the focal position of the condenser lens 3a, f is the focal length, and fd is based on the work surface. Defocus distance.

[0005] Here, when cutting stainless steel (bulk material) having a thickness of 50 mm, the processing conditions include an average output of a laser oscillator (pulsed YAG laser): 2 kW,
Pulse width: 9.5 ms, frequency: 10 Hz, defocus distance fd: ± 3 mm or less, cutting speed: 100 mm / m
In, by using oxygen as an assist gas and performing laser cutting while setting the gas pressure in the processing torch to be 0.3 MPa, the work 4 does not have a self-burning phenomenon, and the workpiece 4 can be cut even at the cut surface. Can be cut to obtain parallel drag lines. In addition, the kerf width of the cut portion is cut at substantially the same width from the front surface to the back surface of the work 4 corresponding to the spot diameter of the laser beam applied to the front surface of the work 4. This is because, after the laser beam converges to the minimum spot diameter at the focal position O, it travels in a zigzag manner while repeatedly reflecting on the cut surface of the work, so that the beam diameter spreads as in the case where the laser goes straight. However, it is considered that as a result, the end of the kerf width at the cutting portion is suppressed.

[0006]

By the way, a metal structure such as a structural waste of a nuclear reactor facility, which is a collection of thin plates or rods and having a gap between individual elements, is referred to as a laser. When cutting, there are the following problems. That is, as shown in FIG. 4, a metal structure in which a plurality of stainless steel thin plates 4a each having a thickness of about 5 to 6 mm are laminated with a gap 4b therebetween (total thickness is substantially the same as the bulk material in FIG. 3) When laser cutting was performed as the work 4 under the same processing conditions as the cutting of the bulk material described in FIG. 3, a self-burning phenomenon occurred, a large explosion hole was formed in the work 4, and the cut surface became irregular. It was found that good cutting could not be performed because the function of the assist gas did not work sufficiently. In addition, it has been confirmed that even when a metal structure that is to be an aggregate of round bars is laser-cut, a self-burning phenomenon occurs similarly to the above, and it cannot be cut properly.

The occurrence of the self-burning phenomenon is considered to be caused by the following points. That is, the individual thin plates 4a or the thin round bars constituting the work 4 have a much smaller heat capacity than the thick bulk material shown in FIG. 3, and a gap 4b exists between them. . For this reason, when a high-power laser beam is irradiated to the surface side of the work 4 under the previously set processing conditions, and oxygen is blown as an assist gas, the total energy of the oxidation reaction heat of the laser beam and the assist gas is reduced. It is presumed that explosive combustion occurs at the cut portions of the thin plates and round bars arranged in excess on the surface of the work, and the combustion spreads to the surroundings. In addition, since the gap exists inside the work, the assist gas blown to the cutting point escapes to the gap, and the function as the assist gas cannot be sufficiently performed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and is intended for use in a case where laser cutting is performed using a metal structure having a gap between individual elements in a set of thin plates or rods as a work. Optimize various parameters as processing conditions,
It is an object of the present invention to provide a laser cutting method capable of satisfactorily cutting by suppressing the occurrence of a self-burning phenomenon.

[0009]

According to the present invention, in order to achieve the above object, according to the present invention, a metal structure work having a gap between individual elements in an aggregate of thin plates or bars is provided. In a laser cutting method for cutting a work by irradiating a laser beam at the same time while blowing an assist gas through a processing torch, the work is repeatedly reciprocally scanned with a laser beam in a cutting direction a plurality of times, and the laser scanning process The input power per unit cutting length of the laser is gradually increased from the initially set lower value in accordance with the progress of the laser scanning (Claim 1). Thus, the cutting speed of the work is gradually reduced (claim 2) or the laser output is gradually increased (claim 3).

When a metal structure composed of an aggregate of thin plates or rods is laser-cut as a work, the parameters of the laser processing conditions are set as described above, so that the self-burning phenomenon occurs from the start to the end of cutting. Stable cutting can be performed without generation of cracks. That is, in the first scanning step, the input power of the laser for irradiating the surface of the work is suppressed to a low level, so that the energy of the laser beam applied to the thin plate having a small heat capacity or the thin round bar does not become excessive. The occurrence of the self-burning phenomenon is suppressed. Further, by gradually increasing the input power of the laser in accordance with the progress of the laser beam scanning process, the individual thin plates or rods constituting the work are compensated for by the loss of the laser beam scattered in the gap inside the work. The material can be cut reliably.

According to the present invention, more stable laser cutting can be performed by using the following method in combination with the above processing conditions. (1) Increasing the supply amount of assist gas gradually with the progress of laser scanning, participating in laser cutting by compensating for the amount of gas escaping into the gap between thin plates or thin rods inside the work The function of the assist gas is ensured (claim 4).

(2) The focal position of the condenser lens incorporated in the processing torch is set by defocusing inside the work, and the spot diameter of the laser beam is made as small as possible within the irradiation range up to the back surface of the work. The kerf width of the cutting portion is prevented from unnecessarily expanding. (Claim 5).

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In FIG. 1, members corresponding to those in FIG. 3 are denoted by the same reference numerals, and detailed description thereof will be omitted. FIG. 1 is a schematic diagram showing a state in which a laser cutting process is performed as a work 4 using an aggregate having a total thickness of 60 mm in which a stainless steel thin plate 4 a having a thickness of 6.5 mm is stacked with a gap 4 b therebetween. In the embodiment, various parameters are set as processing conditions as follows.

That is, assuming that the average output of the laser oscillator (pulse YAG laser) 1 is 2 kW, the focal position O of the laser beam 9 irradiating the work 4 through the condenser lens 3 a of the processing torch 3 is moved inward from the surface of the work 4. It is set by defocusing to a position where it enters about 11 mm. Also,
The laser irradiation on the workpiece 4 is repeated reciprocally scanning in eight times, and the cutting speed is started from 2,000 mm / min in accordance with the progress of the reciprocating scanning, and is reduced to 500 mm / min in the final scanning stroke. In this way, the input power per unit cutting length is increased stepwise. Furthermore, for assist gas (oxygen),
Initially, the internal pressure of the processing torch 3 is set to 0.05 MPa, and is gradually increased in accordance with the progress of the reciprocating scanning. The flow control valve 7 (FIG.
Control).

By the above-described cutting method, it was confirmed that the work 4 as the laminated aggregate of the thin plates 4a shown in FIG. 1 can be cut from the front surface to the back surface with no self-burning and with a uniform kerf width. ing. Note that the set values of the above parameters are only examples,
It should be adjusted to the optimum value according to the conditions such as the material and plate thickness of the work to be applied.

As means for increasing the input power per unit cutting length of the work in a stepwise manner, the cutting speed is gradually reduced in the above-described embodiment. The input may be gradually increased to increase the laser output stepwise. Further, although the pulse YAG laser is used as the laser in the above-described embodiment, it goes without saying that the present invention can be similarly implemented by using a CW laser or a CO ₂ laser.

[0017]

As described above, by adopting the laser cutting method of the present invention, a thin plate which cannot be cut well due to self-burning in the conventional method.
In addition, a metal structure having a gap between individual element bodies in an aggregate of bar materials can be cut stably without generating self-burning.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a state of laser cutting processing using a metal structure of a thin plate laminate according to an embodiment of the present invention as a work.

FIG. 2 is a schematic diagram of a laser processing apparatus used for laser cutting in FIG. 1;

FIG. 3 is a schematic diagram showing parameters of cutting conditions corresponding to cutting of a thick plate by a conventional laser cutting method.

FIG. 4 is a schematic diagram showing a cutting state using a metal structure of a thin plate laminate as a work by a conventional laser cutting method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser oscillator 3 Processing torch 3a Condensing lens 4 Work 4a Thin plate 4b Air gap 9 Laser beam 10 Assist gas

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G21F 9/30 531 G21F 9/30 531D H01S 3/00 H01S 3/00 B // B23K 103: 04 B23K 103 : 04

Claims (5)

[Claims] 1. A metal structure having a gap between individual element bodies, which is an aggregate of thin plates or rods, is used as a workpiece, and is cut by irradiating the workpiece with a laser beam while blowing an assist gas through a processing torch. In the laser cutting method, a workpiece is repeatedly reciprocatedly scanned with a laser beam in a cutting direction a plurality of times, and the input power per unit cutting length of the laser is gradually increased in accordance with the progress of the scanning process. A laser cutting method, comprising: 2. The laser cutting machine according to claim 1, wherein the means for increasing the input power of the laser is such that the cutting speed of the workpiece is gradually reduced in accordance with the progress of the laser scanning process. Processing method. 3. The laser cutting method according to claim 1, wherein the laser output is gradually increased in accordance with the progress of the laser scanning process as means for increasing the input power of the laser. . 4. A laser cutting method according to claim 1, wherein the supply amount of the assist gas is gradually increased in accordance with the progress of the laser scanning. 5. A laser cutting method according to claim 1, wherein the focal position of the condenser lens incorporated in the processing torch is set by defocusing the inside of the work.