Nozzle for laser processing

Abstract

To provide a nozzle for laser machining that is able to discharge dross satisfactorily even when assist gas pressure is low.SOLUTION: A nozzle for laser machining includes: a tubular inner nozzle (71) having a first through-hole (711); and a tubular outer nozzle (72) having a second through-hole (723) and a mounting portion (727) to be mounted on a housing of a machining head (1). A second air-passage is formed between an outer peripheral surface of the inner nozzle (71) and an inner peripheral surface of the second through-hole (723), and a leading-end surface (714a) of the inner nozzle (71), on a second-end side, is located axially inward of a leading-end surface (72b) of the outer nozzle (72). Assist gas (AG) is blown off from a first air-passage and the second air-passage, a laser beam is emitted from the first air-passage, and a flow rate (fr), a density (ρ), and a pressure (Ps) of the assist gas (AG) can be made equal to or higher than acoustic velocity, equal to or lower than 2.1 kg / m3, and equal to or lower than 0.13 MPa, respectively, at a cutting front lower-end.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a nozzle for laser processing. to the loop

Background Art

[0002] In the laser processing method described in Patent Document 1, while controlling the distance between the workpiece and the nozzle to maintain a predetermined nozzle gap by following control, the workpiece is cut with laser light irradiated from the nozzle. In this laser processing method, the molten metal generated during processing is blown away by the assist gas ejected from the nozzle and discharged from the kerf.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When cutting mild steel with laser light, relatively low-pressure oxygen is used as the assist gas. This is because in thermal cutting with laser light, the oxidation reaction heat between the molten iron and the oxygen supplied as the assist gas further promotes melting. On the other hand, when cutting stainless steel with laser light, instead of oxygen, relatively expensive high-purity nitrogen gas or the like is used as the assist gas. This is because in the case of cutting stainless steel, it is generally desired that no black oxide film adheres to the cut surface, and chromium contained in stainless steel is known to have an unfavorable effect on the viscosity of dross due to its oxide. Also, in the cutting of mild steel with laser light, when it is not desired that an oxide film adheres to the cut surface, an assist gas mainly composed of nitrogen is used. ​Conventionally, in order to suppress dross adhesion and promote the discharge of molten metal as the thickness of the steel material to be cut increases, assist gas has been set to a gas pressure exceeding, for example, 1 MPa since the era when carbon dioxide lasers were mainstream. Therefore, generally in laser processing, it is desired to inject assist gas at a low pressure of, for example, 1 MPa or less to suppress the consumption amount and reduce the cost.

[0005] In addition, in order to efficiently flow the assist gas into the kerf even at a low pressure, it has been considered to reduce the nozzle gap to 0.5 mm or less. However, there is a problem that the clogging of the nozzle due to the splash back of the spatter and the risk of damage due to contact with the pierce mark during piercing increases. From these, when cutting a workpiece with a laser beam, even if the gas pressure of the assist gas is set to a low pressure of, for example, 1 MPa or less, it is desired that the laser processing nozzle can suppress dross adhesion and discharge the molten metal better without causing problems in the laser processing nozzle.

[0006] Therefore, the problem to be solved by the present invention is a laser processing nozzle that can suppress dross adhesion and discharge the abducted metal well without causing problems in the laser processing nozzle even when the gas pressure of the assist gas is low. propose It is to provide this.

Means for Solving the Problem

[0007] In order to solve the above problems, the present invention has the following configuration 1). 1) An inner nozzle having a through hole for injecting a laser beam and an assist gas, and an outer nozzle that forms a ring-shaped opening for injecting the assist gas between the inner nozzle, When the outer diameter of the tip of the inner nozzle is D3, the inner diameter of the through hole is D1, and the inner diameter of the outer nozzle is D2, the inner diameter D2 is in the range of a minimum of 7.0 mm and a maximum of 13.0 mm, When (inner diameter D2, inner diameter D1) is (x, y), Satisfies y = (1 / 3)x - 1 / 3, When (inner diameter D2, outer diameter D3) is (x, y), y = (2 / 3)x + Satisfies 4 / 3, It is a nozzle for laser processing.

Advantages of the Invention

[0008] According to the present invention, even when the gas pressure of the assist gas is low, there is no problem with the nozzle for laser processing, and dross adhesion can be suppressed, and molten metal can be discharged well.

Brief Description of the Drawings

[0009]

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DETAILED DESCRIPTION OF THE INVENTION

[0010] (Example) The laser processing apparatus according to the embodiment of the present invention will be described by the laser processing apparatus 51 of the example.

[0011] FIG. 1 is a diagram showing the overall configuration of the laser processing apparatus 51. The laser processing apparatus 51 includes a laser processing head 1, a laser oscillator 2, an assist gas supply device 3, a drive unit 4, and an NC device 5 as a control unit.

[0012] The laser processing head 1 has a cylindrical housing 11 and a laser processing nozzle 7 attached to the tip of the housing 11. The laser processing nozzle 7 is detachably attached to the housing 11 by a screw-threaded structure or the like. Inside the housing 11, a collimation lens 12, a bend mirror 13, and a focusing lens 14 are arranged.

[0013] The housing 11 has a nozzle gap measurement unit 15 for measuring the nozzle gap Hg. The nozzle gap Hg is the distance between the tip surface 72b of the laser processing nozzle 7 (see FIG. 2) and the upper surface Wa of the workpiece W processed by the laser processing apparatus 51. Hereinafter, the laser processing nozzle 7 is also simply referred to as the nozzle 7.

[0014] The laser oscillator 2 is, for example, a fiber laser, and generates laser light Lsa under the control of the NC device 5. The wavelength of the generated laser light Lsa may be in the so-called 1-μm band (900 nm to 1100 nm band) including the range of 1060 nm to 1080 nm, or a wavelength shorter than the 1-μm band. The laser oscillator 2 is not limited to a fiber laser, and may be, for example, a disk laser or a DDL (direct diode laser). In other words, the laser oscillator 2 may be a short-wavelength laser that is less susceptible to the influence of nitrogen plasma, which is likely to occur in a carbon dioxide laser in the 10-μm band with a relatively long wavelength, and has a high absorption rate of the metal to be processed.

[0015] The laser light Lsa generated by the laser oscillator 2 is supplied into the housing 11 via the process fiber 21 and the coupler 21a. The laser light Lsa supplied into the housing 11 from the coupler 21a is divergent light, and is made into a parallel light beam by a collimation lens and travels toward the bend mirror 13. The laser light Lsa made into a parallel light beam is specularly reflected by the bend mirror 13 and is processed into laser light Ls that is emitted from the nozzle 7 so as to form a focus at a desired position by the focusing lens 14. The laser light Ls is emitted to the outside from the opening 71a of the inner nozzle 71 that opens near the tip of the nozzle 7 (see FIG. 2).

[0016] The laser processing head 1 has a focusing lens drive unit 14a that moves the focusing lens 14 in the optical axis direction. By moving the focusing lens 14 in the optical axis direction, the focus position of the laser light Ls is adjusted. The operation of the focusing lens drive unit 14a is controlled by the NC device 5.

[0017] The assist gas supply device 3 supplies, for example, nitrogen gas as the assist gas AG to the laser processing head 1. The operation of the assist gas supply device 3 is controlled by the NC device 5. The reason for using nitrogen gas as the assist gas AG is to suppress the oxidation of the cutting site of the workpiece W, which is the material to be processed, in the thermal cutting process by the laser beam Ls. As the nitrogen gas used for the assist gas AG, high-purity nitrogen gas supplied by a cylinder or the like, or nitrogen-rich gas generated from the atmosphere can be used.

[0018] The laser processing head 1 is three-dimensionally moved by the drive unit 4 in either one or both of the horizontal direction and the orthogonal direction with respect to the upper surface Wa of the workpiece W to be processed. The operation of the drive unit 4 is controlled by the NC device 5. During the execution of the laser processing, the NC device 5 operates the drive unit 4 to control the vertical position of the laser processing head 1 so that the nozzle gap Hg measured by the nozzle gap measurement unit 15 becomes a predetermined value.

[0019] Next, the details of the nozzle 7 will be described with reference to FIGS. 2 to 4. FIGS. 2 to 4 are a longitudinal sectional view, a top view, and a bottom view of the nozzle 7, respectively. FIG. 2 is a longitudinal sectional view at the S2 - S2 position in FIG. 3. The nozzle 7 is of a so-called double nozzle type and has an inner nozzle 71 and an outer nozzle 72. For the sake of convenience in explanation, the vertical direction is defined as the direction indicated by the arrow in FIG. 2.

[0020] The inner nozzle 71 has a through hole 711 which is a first through hole having the vertical direction as the axial direction and is formed in a tubular shape. The inner nozzle 71 has, from the upper side, an engaging portion 712, an intermediate portion 713, and a tip portion 714. The engaging portion 712 is in a straight tubular shape and has a male thread portion 712a formed on the outer peripheral surface. In FIG. 2, the thread shape of the male thread portion 712a is omitted.

[0021] The middle part 713 is formed in a straight tubular shape with an outer diameter smaller than the valley diameter of the male thread part 712a. The tip part 714 is formed such that the upper end part is connected to the middle part 713 and the outer diameter becomes concentric and decreases to the outer diameter D3 as it goes downward. The through hole 711 has an upper hole part 711a and a lower hole part 711b. The upper hole part 711a is a tapered hole part whose inner diameter decreases to the inner diameter D1 from the upper end face to the middle of the tip part 714 as it goes downward. The lower hole part 711b has an upper end part connected to the upper hole part 711a and opens at the tip face 714a with a constant inner diameter D1 by the lower hole part 711b.

[0022] The outer nozzle 72 has a through hole 723 which is a second through hole with the vertical direction as the axis and is formed in a tubular shape. The outer nozzle 72 has a mounting part 727, a flange part 721, and an inclined part 722 from the upper end part side which is the first end part side toward the lower end part side which is the second end part side opposite to the first end part.

[0023] The mounting part 727 has a male thread part 727a formed on the outer peripheral surface. The male thread part 727a is screwed into a female thread part 11a (see FIG. 1) formed at the lower end part of the housing 11. By this screwing structure, the nozzle 7 is detachable from the housing 11.

[0024] The through hole 723 has a female thread part 723a, a basic hole part 724, an intermediate hole part 725, and a tip hole part 726 from the upper part. The female thread part 723a has a female thread formed on the inner peripheral surface of the upper part of the through hole 723. The female thread part 723a is screwed into the male thread part 712a of the engaging part 712 of the inner nozzle 71. The basic hole part 724 is formed straight from the lower end part of the female thread part 723a to the middle of the inclined part 722. The intermediate hole part 725 has an upper end connected to the basic hole part 724 and is formed such that the inner diameter decreases to the inner diameter D2 as it goes downward. The tip hole portion 726 has an upper end connected to the intermediate hole portion 725, is formed with a constant inner diameter D2, and opens at the tip surface 72b by the tip hole portion 726.

[0025] When the male screw portion 727a of the mounting portion 727 of the flange portion 721 is screwed into the female screw portion 11a of the housing 11 (rotated in the direction in which the screwed portion increases), it abuts against the lower end surface 11b of the housing 11 (see FIG. 1) at a predetermined position and restricts further screwing.

[0026] The inner nozzle 71 can be integrated with the outer nozzle 72 by inserting the tip portion 714, which is the second end portion, into the through hole 723 of the outer nozzle 72 from above in a posture where the tip portion faces downward, and screwing the male screw portion 712a of the inner nozzle 71 into the female screw portion 723a of the mounting portion 727 of the outer nozzle 72. The vertical position of the inner nozzle 71 mounted on the outer nozzle 72 is regulated to a predetermined position by the lower end portion of the male screw portion 712a abutting against the basic hole portion 724 having a smaller diameter than that.

[0027] When the inner nozzle 71 is inserted into a predetermined position with respect to the outer nozzle 72, the vertical position of the tip surface 714a of the inner nozzle 71 is above the position of the tip surface 72b of the outer nozzle 72. Let the height of the tip surface 714a with respect to the tip surface 72b be the distance H1.

[0028] As shown in FIG. 3, a plurality of cut portions 716, which are cut in a chord shape in a cross-sectional shape, for example, with respect to a circular outer periphery, are formed at equal angular intervals on the outer peripheral surface of the engaging portion 712 of the inner nozzle 71. In a state where the inner nozzle 71 is mounted on the outer nozzle 72 at a predetermined position, a ventilation passage ARa extending in the axial direction (vertical direction) is formed between each cut portion 716 and the through hole 723 of the outer nozzle 72.

[0029] With the nozzle 7 attached to the housing 11, the upper end of the ventilation passage ARa communicates with the space V11 (see FIG. 1) inside the housing 11, and the lower end communicates with the ventilation passage ARb, which is the space between the outer peripheral surface of the middle portion 713 of the inner nozzle 71 and the inner peripheral surface of the through hole 711 of the outer nozzle 72. The lower end of the ventilation passage ARb communicates with the external space Vg, which is the space inside the tip hole portion 726, through a ring-shaped opening 72a. On the other hand, the through hole 711 serves as a ventilation passage ARc whose upper end communicates with the space V11 inside the housing 11 and whose lower end communicates with the external space Vg. Therefore, as shown in FIG. 4, the space V11 inside the housing 11 communicates with the external space Vg below the nozzle 7 through the first ventilation passage AR1 formed by the ventilation passage ARc and the second ventilation passage AR2 formed by the ventilation passages ARa and ARb.

[0030] Due to the above structure, the assist gas AG supplied into the housing 11 branches and enters the first ventilation passage AR1 and the second ventilation passage AR2. Then, the gas flow that enters the first ventilation passage AR1 jets out as the first gas flow AG1 from the opening 71a toward the outside, and the gas flow that enters the second ventilation passage AR2 jets out as the ring-shaped second gas flow AG2 from the opening 72a toward the outside.

[0031] The nozzle 7 has its inner diameters D1, D2 and outer diameter D3, and the distance H1 set as follows. <Nozzle 7> Inner diameter D1 = 2.0 mm Inner diameter D2 = 7.0 mm Outer diameter D3 = 6.0 mm Distance H1 = 1.0 mm

[0032] Next, a description will be given of an evaluation test in which a hot-rolled steel sheet (SPH material) with a thickness of 6.0 mm is cut with a laser beam using the laser processing method using the nozzle 7, the dross height t generated corresponding to the discharge amount of the molten metal is measured, and the molten metal discharge effect is evaluated in three measurement items. Hereinafter, the SPH material with a thickness of 6.0 mm will be denoted as SPH6.0. The same description will apply to other thicknesses.

[0033] As a test, first, a test nozzle is attached to the laser processing head 1, and while the assist gas AG is ejected at a predetermined gas pressure, the laser beam Ls is irradiated onto a SPH6.0 plate material, and cutting is performed along a predetermined cutting path Q. Then, at a plurality of measurement points set on the cutting path Q, as shown in Fig. 5(a), the protrusion distance of the dross protruding downward with respect to the lower surface Wb of the cut workpiece W is measured as the dross height t. The set conditions for laser processing are as follows. · Processing speed: 10000 mm / min · Laser output: 6000 W · Frequency: 500 Hz · Duty: 100% · Assist gas: N2 · Defocus amount: -0.5 mm

[0034] The three measurement items are the average value and the maximum value of six measurement points set on the straight part in the cutting path Q, and the average value of the corner part in the cutting path Q. Specifically, as shown in Fig. 5(b), the measurement points of the dross height t are a total of 10 points, namely 6 points on the straight part and 4 points on the corner part when the workpiece W is cut along the rectangular cutting path Q. For the 6 points on the straight part, the average value and the maximum value of the 6 points are obtained, and for the corner part, the average value of the 4 points is obtained. The 6 points on the straight part are the measurement points P3, P6 that bisect the short side and the measurement points P1, P2, P4, P6 that trisect the long side in the cutting path Q. The maximum value is the maximum value among the 6 measurement points. Also, the 4 points on the corner part are the measurement points Pe1 to Pe4 at the four corners of the cutting path Q.

[0035] When cutting the SPH6.0 material with the laser beam Ls while setting the gas pressure of the assist gas AG to 1 MPa or less so that the generated dross height t is of a size that does not cause practical problems, conventionally, it was necessary to use a nozzle R1 called a standard nozzle and make the nozzle gap Hg less than 0.5 mm. The main dimensions of the nozzle R1 are as follows. <Nozzle R1> Inner diameter D1 = 3.0 mm Inner diameter D2 = 7.0 mm Outer diameter D3 = 4.0 mm Distance H1 = 5.5 mm Hereinafter, when the gas pressure of the assist gas AG is 1 MPa or less, it is classified as low gas pressure or low pressure, and when the nozzle gap Hg is 0.5 mm or more, it is classified as a large nozzle gap.

[0036] The nozzle 7 has a smaller inner diameter D1, a larger outer diameter D3, and a smaller distance H1 than the nozzle R1. By reducing the inner diameter D1, the opening area S1 shown in FIG. 4 of the nozzle 7 is smaller than that of the nozzle R1. Further, by maintaining the inner diameter D2 and increasing the outer diameter D3, the ring-shaped opening area S2 of the air passage AR2 shown in FIG. 4 of the nozzle 7 is smaller than that of the nozzle R1. Note that in the nozzle 7, the inner diameter D2 of the tip hole 726 of the outer nozzle 72 corresponding to the opening diameter of the nozzle is maintained the same as that of the nozzle R1. On the other hand, the distance H1 that defines the vertical position of the tip surface 714a of the inner nozzle 71 is shortened with respect to the nozzle R1.

[0037] As a comparative example for the nozzle 7, cutting was also performed using nozzles 101 and 102 having the following dimensions, and the dross height t of each was measured. [Nozzle 101] [Nozzle 102] Inner diameter D1 = 3.0 mm Inner diameter D1 = 3.0 mm Inner diameter D2 = 7.0 mm Inner diameter D2 = 7.0 mm Outer diameter D3 = 5.0 mm Outer diameter D3 = 6.0 mm Distance H1 = 1.0 mm Distance H1 = 1.0 mm In the evaluation, for all three measurement items, a nozzle with a lower dross height than the dross height when cutting with the nozzle R1 with a nozzle gap Hg of 0.6 mm was given a good evaluation "○", and a nozzle with a higher dross height in even one item was given an inappropriate evaluation "×".

[0038] The nozzles 101 and 102 of the comparative example are formed by maintaining the opening area S1 of the circular first ventilation passage AR1 with respect to the nozzle R1 and reducing only the opening area S2 of the ring-shaped second ventilation passage AR2. The order of the magnitudes of the opening area S1 of the first ventilation passage AR1 is Nozzle R1 = Nozzle 101 = Nozzle 102 > Nozzle 7 That is. The order of the magnitudes of the opening area S2 of the second ventilation passage AR2 is Nozzle R1 > Nozzle 101 > Nozzle 102 = Nozzle 7 That is.

[0039] Figure 6 shows the measurement results of the dross height t. As shown in Figure 6, when the nozzle gap Hg of the nozzles 101 and 102 of the comparative example is 0.6 mm and the gas pressure is 0.7 MPa, the average dross height at the corners is equal to or higher than the dross height of the reference nozzle R1, resulting in a poor evaluation "×". On the other hand, for nozzle 7, in all three evaluation items, namely the 6-point average and maximum of the straight part, and the average dross height at the corners, the dross height is small, resulting in a good evaluation "○". Therefore, even when the gas pressure of the assist gas AG is low, nozzle 7 can discharge the molten metal better at a nozzle gap Hg of 0.6 mm, which is a large nozzle gap.

[0040] Also, as shown in Figure 6, tests were also conducted on the dross height when each nozzle was used, the nozzle gap Hg was set to the same 0.6 mm, and the gas pressure of the assist gas AG was increased to 0.9 MPa. As a result, the dross height when using nozzle 7 is almost the same as that when using nozzle R1, although it is slightly larger in the 6-point average of the straight part. On the other hand, in the maximum of the straight part and the average of the corners, it is significantly smaller, indicating that the molten metal can be discharged relatively well. Thus, nozzle 7 has an advantage over the reference nozzle R1 and the nozzles 101 and 102 of the comparative example in terms of the molten metal discharge force in cutting with low gas pressure and a large nozzle gap.

[0041] The superiority of nozzle 7 regarding the molten metal discharge power, which was found in the tests on the above-mentioned SPH6.0 material, was evaluated to see if it could also be obtained with SPH materials of different plate thicknesses. Figure 7(a) shows the respective dross heights t when cutting the SPH material with a plate thickness of 4.5 mm using nozzle R1 and nozzle 7, and (b) shows the dross heights when cutting the SPH material with a plate thickness of 9.0 mm. Since a practical dross height could not be obtained with nozzle R1 at a nozzle gap of 0.6 mm, the dross height at a nozzle gap of 0.3 mm is described for comparison. The setting conditions for laser processing are as follows. · Processing speed: 10000 mm / min · Laser output: 6000 W · Frequency: 500 Hz · Duty: 100% · Assist gas: N2 · Defocus amount: -0.5 mm [SPH4.5] -1.0 mm [SPH9.0]

[0042] As shown in Figure 7(a), in the cutting of the SPH4.5 material, when the nozzle gap Hg of nozzle 7 is 0.6 mm and the gas pressure is 0.7 MPa, the dross height is significantly smaller than the dross height when the nozzle gap Hg of nozzle R1 is 0.3 mm in all evaluation items, and it receives a good evaluation "○". Also, when the nozzle gap Hg is maintained at 0.6 mm and the gas pressure is increased to 0.9 MPa, although the average dross height at the corners of nozzle 7 exceeds that of nozzle R1 by about 39%, the two items at the straight part are lower than those of nozzle R1, resulting in a semi-good evaluation (denoted as "○-"). Therefore, it can be seen that for the SPH4.5 material as well, nozzle 7 has relatively good molten metal discharge in cutting with low gas pressure and a large nozzle gap.

[0043] As shown in Fig. 7(b), in the cutting of the SPH9.0 material, when the nozzle gap Hg of the nozzle 7 is 0.6 mm and the gas pressure is 0.7 MPa, the dross height becomes significantly smaller than the dross height when the nozzle gap Hg of the nozzle R1 is 0.3 mm in all evaluation items, resulting in a good evaluation "○". Also, when the nozzle gap Hg is maintained at 0.6 mm and the gas pressure is increased to 0.9 MPa, in the nozzle 7, although the average dross height at the corner exceeds that of the nozzle R1 by more than about 14%, the two items in the straight part are lower than those of the nozzle R1, resulting in a semi-good evaluation. Therefore, it can be seen that for the SPH9.0 material as well, the nozzle 7 has relatively good discharge of molten metal in cutting with low gas pressure and a large nozzle gap.

[0044] From the above, in the laser cutting of the SPH material, the nozzle 7 can discharge the molten metal relatively well without any problems in the nozzle even when the gas pressure of the assist gas is low and the nozzle gap is large, regardless of the plate thickness. Therefore, it can be effectively used without any practical problems.

[0045] Next, it was evaluated with a stainless steel plate (SUS304) whether the superiority of the discharge of molten metal in the cutting process of the nozzle 7 with low gas pressure and a large nozzle gap, which was observed in the SPH material, is also exhibited in other different steel materials. Hereinafter, the stainless steel plate is referred to as the SUS material. Figs. 8(a) to (c) show the dross height t when cutting the SUS material with a plate thickness of 4.0 mm, 5.0 mm, and 6.0 mm, respectively, in three measurement items. Hereinafter, the SUS material with a plate thickness of 5.0 mm is denoted as SUS5.0. The same applies to other plate thicknesses.

[0046] For the nozzle R1, in the SUS material as well, since a practical dross height could not be obtained with a nozzle gap of 0.6 mm, the dross height with a nozzle gap of 0.3 mm is described for comparison. Also, the cutting of the SUS material was evaluated with the gas pressure of the assist gas AG being 0.6 MPa and 0.8 MPa in the low gas pressure region. The setting conditions for the laser processing are as follows. · Processing speed: 14000 mm / min [SUS4.0] 10000 mm / min [SUS5.0] 8000 mm / min [SUS6.0] · Laser output: 6000 (W) · Frequency: 1000 Hz [SUS4.0] 1500 Hz [SUS5.0] 500 Hz [SUS6.0] · Duty: 100% · Assist gas: N2 · Defocus amount: ±0.0 mm

[0047] As shown in Fig. 8(a), in the cutting of SUS4.0 material, when the nozzle gap Hg of nozzle 7 is 0.6 mm and the gas pressure is 0.6 MPa, although it does not become lower than the dross height at the nozzle gap of 0.3 mm of nozzle R1 in all measurement items, it was confirmed that cutting is possible with a practical dross height. On the other hand, when the nozzle gap Hg was maintained at 0.6 mm and the gas pressure was increased to 0.8 MPa, the dross height could not be suppressed to a practical height (Inappropriate evaluation ×).

[0048] As shown in Fig. 8(b), in the cutting of SUS5.0 material, when the nozzle gap Hg of nozzle 7 is 0.6 mm and the gas pressure is 0.6 MPa and 0.8 MPa, it does not become lower than the dross height at the nozzle gap of 0.3 mm of nozzle R1 in all evaluation items. However, it was confirmed that cutting is possible with a practical dross height.

[0049] As shown in Fig. 8(c), in the cutting of SUS6.0 material, when the nozzle gap Hg of nozzle 7 is 0.6 mm and the gas pressure is 0.6 MPa, the 6-point average dross height of the straight part exceeds that when the nozzle gap Hg of nozzle R1 is 0.3 mm by about 19%. However, other measurement items are lower than the dross height at the nozzle gap of 0.3 mm of nozzle R1, and it can be seen that nozzle 7 can effectively discharge the molten metal to some extent and is practical. On the other hand, when the nozzle gap Hg was maintained at 0.6 mm and the gas pressure was increased to 0.8 MPa, the dross height could not be suppressed to a practical height (inappropriate evaluation ×).

[0050] As described above, even when cutting SUS material, by using the nozzle 7 and appropriately adjusting the gas pressure within the range of low gas pressure, the dross height can be suppressed within a practical height even with a large nozzle gap.

[0051] Fig. 9 is a table showing the main dimensions and preset evaluation values calculated based on the main dimensions of the nozzle R1, the nozzle 7 of the example, and the nozzles 101 and 102 of the comparative example. There are two types of evaluation values. One is the amount based on the opening width of the second ventilation passage AR2. Specifically, it is defined as 2-fold width Δd1, which is twice the value of the average opening width. The other is the distance Δd2, which is half of the difference between the outer diameter D3 indicating the position of the inner wall of the second ventilation passage AR2 and the inner diameter D1 of the first ventilation passage AR1. That is, the distance Δd2 is defined as (inner diameter D3 - inner diameter D1) / 2. The first ventilation passage AR1 and the second ventilation passage AR2 are basically formed concentrically with respect to the optical axis of the laser beam Ls, but they may be intentionally offset slightly if necessary.

[0052] In the two types of evaluation values, the nozzle 7 is defined as a nozzle with a 2-fold width Δd1 of 1.0 mm and a distance Δd2 of 2.0 mm. For the nozzles 101 and 102 of the comparative example, the 2-fold width Δd1 is 2.0 mm and 1.0 mm respectively, and the distance Δd2 is 1.0 mm and 1.5 mm respectively. Therefore, if the 2-fold width Δd1 is 1.0 mm or less and the distance Δd2 is 2.0 mm or more, it can be considered that no problems such as spatter adhering to the nozzle or the nozzle colliding with the pierce mark will occur even when the gas pressure of the assist gas is low. In other words, if the inner diameter D1 of the first ventilation passage AR1 of the nozzle is reduced and the radial distance (inner diameter D3 - inner diameter D1) between the first ventilation passage AR1 and the second ventilation passage AR2 is increased, an effect can be obtained that even when the gas pressure of the assist gas is low, the molten metal can be discharged well without any problems occurring in the nozzle.

[0053] The nozzle 7 of the embodiment is a nozzle that can obtain an effect that even when the pressure of the assist gas AG is in a low gas pressure region of 1 MPa or less and the nozzle gap Hg is set in a large nozzle gap region of 0.5 mm or more, the flow velocity of the assist gas AG in the kerf can be maintained high and the discharge of the molten metal can be promoted. In order to distinguish a nozzle capable of obtaining this effect from a nozzle in which the effect is difficult to obtain, two kinds of evaluation values and the ranges that each should satisfy are set by setting two kinds of evaluation values and the ranges that each should satisfy. For the nozzle 7 of the embodiment, both of the two kinds of evaluation values obtained from the dimensions of the nozzle 7 are within the ranges that each should satisfy.

[0054] Specifically, as described above, for the nozzle 7 of the embodiment, the value of the double width Δd1, which is twice the average value of the opening width of the second ventilation passage AR2, is equal to or less than a first predetermined value, and the distance Δd2 is equal to or greater than a second predetermined value. The first predetermined value is 1.0 mm, and the second predetermined value is 2.0 mm.

[0055] Therefore, for the three types: the nozzle 7 of the embodiment, and the nozzles 101 and 102 of the comparative example, the distributions of the flow velocity fr, density ρ, and pressure Ps of the assist gas AG in the vicinity of the cutting front were evaluated by simulation. Hereinafter, the results of the simulation will be described with reference to FIGS. 10 to 15. FIG. 10 shows the distribution of the flow velocity fr, FIG. 11 shows the distribution of the density ρ, and FIG. 12 shows the distribution of the pressure Ps. Further, FIG. 13 is a graph showing the Mach number of the flow velocity fr at the lower end position of the cutting front in FIG. 10, FIG. 14 is a graph showing the value of the density ρ at the lower end position of the cutting front in FIG. 11, and FIG. 15 is a graph showing the value of the pressure Ps at the lower end position of the cutting front in FIG. 12.

[0056] FIG. 10(a) shows the flow velocity distribution of the assist gas AG in the case of the nozzle 7 of the example, FIG. 10(b) shows the flow velocity distribution of the assist gas AG in the case of the nozzle 101 of the comparative example, and FIG. 10(c) shows the flow velocity distribution of the assist gas AG in the case of the nozzle 102 of the comparative example, together with the shape of each nozzle, the workpiece Ws during cutting, and the cutting front 93. In FIGS. 10(a) to 10(c), the flow velocity fr is divided into three stages in the high-velocity region, and each region is distinguishable by hatching or the like. The first to third regions, which are the three-stage regions, correspond to the following flow velocities. First region fr1: 512 ≦ fr Second region fr2: 448 ≦ fr < 512 Third region fr3: 384 ≦ fr < 448 The unit is m / s. In any of FIGS. 10(a) to 10(c), it was confirmed that the flow velocity of the assist gas AG is 1.5 or more Mach in the range of 5 mm (-5 mm) on the rear side in the processing direction (X-axis direction) from the nozzle center at the lower end position of the cutting front 93.

[0057] FIG. 11(a) shows the density distribution of the assist gas AG in the case of the nozzle 7 of the example, FIG. 11(b) shows the density distribution of the assist gas AG in the case of the nozzle 101 of the comparative example, and FIG. 11(c) shows the density distribution of the assist gas AG in the case of the nozzle 102 of the comparative example, together with the workpiece Ws during cutting and the cutting front 93. In FIGS. 11(a) to 11(c), the density ρ is divided into three stages in the high-density region, and each region is distinguishable by hatching or the like. The first to third regions, which are the three-stage regions, correspond to the following densities. First region ρ1: 4.50 ≦ ρ Second region ρ2: 3.65 ≦ ρ < 4.50 Third region ρ3: 3.20 ≦ ρ < 3.65 The unit is kg / m3.

[0058] Fig. 12(a) shows the pressure distribution of the assist gas AG in the case of the nozzle 7 of the example, Fig. 12(b) shows the pressure distribution of the nozzle 101 of the comparative example, and Fig. 12(c) shows the pressure distribution of the nozzle 102 of the comparative example, together with the workpiece Ws and the cutting front 93 during cutting. In Figs. 12(a) to 12(c), the pressure Ps divides the pressure region into three stages, and each region is distinguishable by hatching or the like. The first to third regions, which are the three-stage regions, correspond to the following pressures. First region Ps1: 0.380 ≤ Ps Second region Ps2: 0.280 ≤ Ps < 0.380 Third region Ps3: 0.240 ≤ Ps < 0.280 The unit is MPa.

[0059] As shown in Fig. 10, in the simulation results of the flow velocity distribution, it is confirmed that in both the nozzle 7 and the nozzles 101 and 102, no separation occurs in the flow of the assist gas within the kerf, which is the region on the left side of the cutting front 93. It is also confirmed that a high flow velocity equal to or higher than the speed of sound is ensured throughout the region including the lower end of the cutting front 93. As a result, the metal melted by the irradiation of the laser beam is discharged well outside the kerf because the flow velocity of the assist gas AG is high and equal to or higher than the speed of sound.

[0060] As shown in Fig. 11, in the simulation results of the density distribution, in the case of the nozzle 7 of the example, in the region on the left side of the cutting front 93 that becomes the kerf, the first region ρ1 to the third region ρ3 are distributed biased only to the upper part on the nozzle 7 side. On the other hand, in the nozzles 101 and 102 of the comparative example, the first region ρ1 to the third region ρ3 extend from the upper part to the central part in the vertical direction, showing a distribution clearly different from that of the example.

[0061] Also, as shown in Fig. 12, in the simulation results of the pressure distribution, in the nozzle 7 of the embodiment, in the kerf, the first region ρ1 to the third region ρ3 are unevenly distributed only in the upper part on the nozzle 7 side. On the other hand, in the nozzle 101 of the comparative example, the first region Ps1 to the third region Ps3 extend from the upper part to the central part in the vertical direction. In the nozzle 102, although the first region Ps1 to the third region Ps3 do not extend to the central part as much as in the case of the nozzle 101, they extend downward and are distributed more than the nozzle 7. That is, also in the pressure distribution, the distribution of the nozzle 7 of the embodiment is clearly different from the distributions of the nozzles 101 and 102 of the comparative example.

[0062] Figs. 13 to 15 are graphs showing the flow velocity fr, density ρ, and pressure Ps in the range from the center of the nozzle at the lower end of the cutting front 93 in Figs. 10 to 12 to the position Pf1 (position at -5 mm in the X-axis direction: refer to Fig. 10(a)) 5 mm behind in the machining direction.

[0063] As shown in Fig. 13, it is confirmed that the flow velocity fr is at least 1.5 or more in terms of Mach number at the center of the nozzle (0 mm) at the lower end position of the cutting front 93 in any of the nozzles 7, 101, and 102. As shown in Fig. 14, it is confirmed that the density ρ is minimum at 2.1 kg / m3 for the nozzle 7 and 2.2 kg / m3 for the second nozzle 101 at the center of the nozzle (0 mm) at the lower end position of the cutting front 93. As shown in Fig. 15, the pressure Ps is minimum at 0.130 MPa for the nozzle 7 and 0.134 MPa for the second nozzle 102 at the center of the nozzle (0 mm) at the lower end position of the cutting front 93.

[0064] From these results, the nozzle 7 satisfies the ranges where the flow velocity fr is 1.5 or more in terms of Mach number, the density ρ is 2.1 kg / m3 or less, and the pressure Ps is 0.130 or less at the center of the nozzle (0 mm) at the lower end position of the cutting front 93.

[0065] Thus, when using nozzle 7, it is confirmed that the density ρ and pressure Ps of the assist gas AG in the kerf are lower than when using nozzles 101 and 102. As a result, the generation of plasma caused by the irradiation of the laser beam is suppressed, and the energy of the laser beam irradiated to the cutting site is efficiently absorbed by the metal at the cutting site, and the viscosity of the molten metal is kept low. This facilitates the discharge of the molten metal and reduces the dross height.

[0066] When using nozzle 7, the following factors can be considered as the reasons for being able to lower the density and pressure of the assist gas AG in the kerf compared to when using nozzles 101 and 102. That is, the inner diameter D2 indicating the position of the outer wall forming the second ventilation passage AR2 of nozzle 7 is the same value as that of nozzles 101 and 102. Furthermore, for nozzle 7, the total flow area of the first ventilation passage AR1 and the second ventilation passage AR2 is smaller than that of nozzles 101 and 102.

[0067] In laser cutting, it is desired that the injection range of the assist gas AG is as large as that of the standard nozzle R1 so that good cutting can be achieved even when the thickness of the cutting material is thick. On the other hand, as described above, it is also desired to lower the density and pressure of the assist gas AG in the kerf, suppress plasma generation, and improve the energy absorption efficiency of the metal at the cutting site.

[0068] Therefore, for nozzle 7, compared to the standard nozzle R1, the inner diameter D2 of the outer wall of the second ventilation passage AR2 is the same, and the outer diameter D3 of the inner wall of the second ventilation passage AR2 is increased. This maintains a large injection range of the assist gas AG and promotes the suppression of the pressure Ps and density ρ of the assist gas AG in the kerf. In addition, for nozzle 7, compared to the standard nozzle R1, the inner diameter D1 of the first ventilation passage AR1 is decreased. This directly suppresses the pressure Ps and density ρ of the assist gas AG in the kerf, particularly in the space along the cutting front 93.

[0069] In this way, at the lower end position of the cutting front during laser cutting, the nozzle 7 can simultaneously make the flow velocity, density, and pressure of the ejected assist gas be respectively not less than the speed of sound, not more than 2.1 kg / m3, and not more than 0.13 MPa. Thereby, the nozzle 7 can cut thick plates well, and even when the gas pressure of the assist gas is low, it can discharge the molten metal well without any problems occurring in the laser processing nozzle.

[0070] Generally, the larger the thickness of the workpiece W to be cut, the larger the nozzle diameter is used for cutting. Here, the nozzle diameter means the maximum inner diameter of the hole through which the laser beam or the assist gas is ejected. In the case of a double nozzle type nozzle, the nozzle diameter corresponds to the inner diameter D2 of the outer nozzle 72. Therefore, in the case of a nozzle with an inner diameter D2 larger than that of the above-described nozzle 7 (inner diameter D2 = 7.0 mm) that can be applied when the thickness of the workpiece W is large, it was confirmed by a cutting experiment whether a combination of an inner diameter D1 and an outer diameter D3 that gives a good evaluation of the dross height can be obtained. As a result, it was clarified that even in the case of a nozzle with an inner diameter D2 larger than 7.0 mm, a combination of an inner diameter D1 and an outer diameter D3 that gives a good evaluation of the dross height can be obtained under certain specific conditions, which will be described next.

[0071] FIG. 16 is a table showing the representative dimensions of 17 types of nozzles of test numbers 1 to 17 used in the cutting experiment. The breakdown of the 17 types is 4 types, 4 types, and 9 types with inner diameters D2 of 7.0 mm, 10.0 mm, and 13.0 mm, respectively, and different combinations of inner diameters D1 and outer diameters D3. As an example of a nozzle having a larger inner diameter D2 than that of the nozzle 7 and obtaining a good evaluation in terms of the dross height, the nozzle 7A of test number 7 and the nozzle 7B of test number 15 will be described. The above-described nozzle 7 is test number 1. On the other hand, as comparative examples that did not obtain a good evaluation, the nozzle 771 of test number 13 and the nozzle 772 of test number 14 will be described.

[0072] FIG. 17 is a table showing the main dimensions of nozzles 7, 7A, and 7B as examples and nozzles 771 and 772 as comparative examples, and the evaluation results for each (good evaluation "〇", inappropriate evaluation "×"). FIG. 17 shows, in addition to the inner diameter D1, inner diameter D2, outer diameter D3, and distance H1, the distance Δd2 described with reference to FIG. 9 and the width Δd3 that is half of the double width Δd1.

[0073] In the cutting experiment, the nozzles with test numbers 1 to 17 are successively attached to the laser processing head 1, and for each nozzle, while ejecting the assist gas AG at a predetermined gas pressure, the laser beam Ls is irradiated onto a plate material of SPH6.0 to perform cutting along a predetermined cutting path Q. Then, at a plurality of measurement points set on the cutting path Q, as shown in FIG. 5(a), the protrusion distance of the dross protruding downward with respect to the lower surface Wb of the cut workpiece W is measured as the dross height t. The set conditions for the laser processing are as follows. · Processing speed: 10000 mm / min · Laser output: 6000 W · Frequency: 500 Hz · Duty: 100% · Assist gas: N2 · Defocus amount: -0.5 mm

[0074] FIG. 18 is a graph showing the relationship between the inner diameter D2 and the inner diameter D1 and outer diameter D3 for each test nozzle shown in FIG. 17. Specifically, in FIG. 18, the horizontal axis of the graph is set as the linear axis of the inner diameter D2, and the vertical axis is set as the linear axis of the dimension (mm), and the values of the inner diameter D1 and outer diameter D3 are plotted. Also, for the nozzles 771 and 772 which are comparative examples, since the inner diameter D2 is the same as that of nozzle 7B, which is 13.0 (mm), although it should be described at the same position as nozzle 7B, which is originally 3 (mm), in order to avoid overlapping in the drawing, it is separately described independently to the right of nozzle 7B.

[0075] As is clear from FIG. 18, for the inner diameters D1, D2 and outer diameter D3 of the nozzles 7, 7A and 7B which received favorable evaluations “◯”, when (inner diameter D2, inner diameter D1) = (x, y), y = (1 / 3)x - 1 / 3 (Equation 1) is satisfied, and when (inner diameter D2, outer diameter D3) = (x, y), y = (2 / 3)x + 4 / 3 (Equation 2) is satisfied. That is, when the combinations of (inner diameter D2, inner diameter D1) and (inner diameter D2, outer diameter D3) are (x, y) respectively, in either of the combinations of (inner diameter D2, inner diameter D1) and (inner diameter D2, outer diameter D3), y is a linear function of x.

[0076] On the other hand, among the nozzles 771 and 772 of the comparative examples which received unfavorable evaluations “×”, for nozzle 771, (inner diameter D2, inner diameter D1) is (13.0, 3.0) and does not satisfy (Equation 1), and (inner diameter D2, outer diameter D3) is (13.0, 11.0) and does not satisfy (Equation 2). Also, for nozzle 772, (inner diameter D2, inner diameter D1) is (13.0, 3.0) and does not satisfy (Equation 1), and (inner diameter D2, outer diameter D3) is (13.0, 12.0) and does not satisfy (Equation 2).

[0077] The nozzles of test numbers 2 to 6, 8 to 12, 16, and 17 shown in FIG. 16, other than nozzles 771 and 772, which received unfavorable evaluations “×”, also do not satisfy both (Equation 1) and (Equation 2). That is, for the nozzles with unfavorable evaluations “×”, at least one of the pairs of (inner diameter D2, inner diameter D1) and (inner diameter D2, outer diameter D3) does not satisfy one of (Equation 1) and (Equation 2) corresponding to that one.

[0078] For five types of nozzles 7, 7A, 7B and the nozzles 771 and 772 of the comparative examples, by simulation, the distributions of the flow velocity fr, density ρ, temperature tm, and pressure Ps of the assist gas AG in the vicinity of the cutting front 93 were obtained and evaluated. Hereinafter, the results of the simulation will be described with reference to FIGS. 19 to 26.

[0079] Figures 19 and 20 show the distribution of the flow velocity fr, Figures 21 and 22 show the distribution of the density ρ, Figures 23 and 24 show the distribution of the temperature tm, and Figures 25 and 26 show the distribution of the pressure Ps. Among them, in Figures 19, 21, 23, and 25, (a) shows the results of nozzle 7, (b) shows the results of nozzle 7A, and (c) shows the results of nozzle 7B. Also, in Figures 20, 22, 24, and 26, (a) shows the results of nozzle 771 and (b) shows the results of nozzle 772.

[0080] (Regarding the flow velocity fr) In the evaluation of the simulation results of the flow velocity fr, among the three-stage classification of the high-speed region, the boundary value between the first region fr1 and the second region fr2 has been changed with respect to the value explained in Figure 10.

[0081] In nozzles 7, 7A, and 7B with good evaluations shown in Figures 19(a) to (c), most of the vicinity of the cutting front 93 has a flow velocity in the third region fr3 or lower. On the contrary, in nozzles 771 and 772 of the comparative examples with inappropriate evaluations shown in Figures 20(a) and (b), the second region fr2 appears extensively in the vicinity of the cutting front 93, indicating that the flow of the assist gas AG has been accelerated.

[0082] (Regarding the density ρ) In the evaluation of the simulation results of the density ρ, the density region is divided into four stages, the first region ρ11 to the fourth region ρ14, and each of Figures 21(a) to (c) and Figures 22(a) and (b) shows the region discriminable by hatching or the like. The first region ρ11 to the fourth region ρ14 correspond to the following densities. First region ρ11: 4.5 ≤ ρ Second region ρ12: 3.5 ≤ ρ < 4.5 Third region ρ13: 2.0 ≤ ρ < 3.5 Fourth region ρ14: ρ < 2.0 The unit is kg / m3. In Figure 21, the first ρ11 to the third region ρ13 are shown, and in Figure 22, the first region ρ11 to the fourth region ρ14 are shown.

[0083] In the well - evaluated nozzles 7, 7A, and 7B shown in FIGS. 21(a) to (c), most of the vicinity of the cutting front 93 has a density of ρ13 or more in the third region. On the other hand, in the nozzles 771 and 772 of the comparative examples shown in FIGS. 22(a) and (b) which received an inappropriate evaluation, a fourth region ρ14 with a lower density than the second region appears in the vicinity of the cutting front 93, indicating that the flow of the assist gas AG is becoming less dense.

[0084] (Regarding the temperature tm) In the evaluation of the simulation results of the temperature tm, the temperature region is divided into three stages: the first region tm1 to the third region tm3, and is shown discriminable by hatching etc. in FIGS. 23(a) to (c) and FIGS. 24(a) and (b) respectively. The first region tm1 to the third region tm3 correspond to the following temperatures. First region tm1: 20.5 ≤ tm Second region tm2: - 55.5 ≤ ρ < 20.5 Third region tm3: - 84.0 ≤ ρ < - 55.5 The unit is °C.

[0085] The vicinity of the cutting front 93 in the well - evaluated nozzles 7, 7A, and 7B shown in FIGS. 23(a) to (c) is mainly occupied by the second region tm2 and the third region tm3. Also, in the nozzles 771 and 772 of the comparative examples shown in FIGS. 24(a) and (b) which received an inappropriate evaluation, the vicinity of the cutting front 93 is also mainly occupied by the second region tm2 and the third region tm3. Here, paying attention to the difference in the range between the second region tm2 and the third region tm3 in the vicinity of each cutting front 93, the nozzles 771 and 772 of the comparative examples shown in FIGS. 24(a) and (b) which received an inappropriate evaluation have a wider range occupied by the third region tm3 in the vicinity of the cutting front 93 than the nozzles 7, 7A, and 7B. That is, it can be seen that the flow of the assist gas AG in the vicinity of the cutting front 93 is lower in temperature for the nozzles 771 and 772 than for the nozzles 7, 7A, and 7B.

[0086] (Regarding pressure Ps) In the evaluation of the simulation results of pressure Ps, the pressure region is divided into four stages, the first region Ps11 to the fourth region Ps14, and in FIGS. 25(a) to (c) and FIGS. 26(a) and (b), the regions are distinguishable by hatching or the like, respectively. The first region Ps11 to the third region Ps13, which are three-stage regions, correspond to the following pressures. First region Ps11: 0.25 ≤ Ps Second region Ps12: 0.15 ≤ Ps < 0.25 Third region Ps13: 0.09 ≤ Ps < 0.15 Fourth region Ps14: Ps < 0.09 The unit is MPa.

[0087] In the vicinity of the cutting front 93 in the nozzles 7, 7A, and 7B shown in FIGS. 25(a) to (c) that received good evaluations, the fourth region Ps4 appears in the range of half or less in FIGS. 25(b) and (c) of the nozzles 7A and 7B. On the other hand, in the nozzles 771 and 772 of the comparative examples shown in FIGS. 26(a) and (b) that received unfavorable evaluations, the range of the fourth region Ps14 in the vicinity of the cutting front 93 is significantly larger than that of the nozzles 7A and 7B in FIGS. 25(b) and (c), and appears in most of the range in the vicinity of the cutting front 93, indicating that the pressure is reduced.

[0088] From the above, in the laser cutting process using the nozzles 771 and 772, the flow of the assist gas AG in the vicinity of the cutting front 93 is faster, lower density, lower temperature, and lower pressure than when using the nozzles 7, 7A, and 7B. In the main dimensions, the nozzles 771 and 772 have the same inner diameter D2 of the first air passage AR1 as that of the nozzle 7B, but the width Δd3, which is the radial gap distance of the second air passage AR2, is smaller than that of the nozzle 7B. In other words, the distance Δd2, which is the radial distance between the second air passage AR2 and the first air passage AR1, of the nozzles 771 and 772 is larger than that of the nozzle 7B.

[0089] When comparing this dimensional aspect with the simulation results, in the nozzles 771 and 772, due to the small width Δd3, the flow velocity of the second gas flow AG2 ejected from the second ventilation passage AR2 of the assist gas AG supplied from the assist gas supply device 3 to the laser processing head 1 under the same conditions as in the case of the nozzle 7B increases. As a result, at the cutting front 93, the amount of heat taken away by the assist gas AG from the metal melted by the irradiation of the laser beam increases, and the temperature of the molten metal becomes lower than that in the case of the nozzle 7B. As a result, it is speculated that the increase in the viscosity of the molten metal due to the decrease in temperature of the molten metal outweighs the effect of promoting the discharge of the molten metal due to the increase in the flow velocity of the assist gas AG, and the discharge of the molten metal is delayed. Therefore, it is considered that it becomes difficult to suppress the height of the dross.

[0090] From the above-mentioned cutting experiments, as well as the results and evaluations of the simulations, it has been clarified that for a double nozzle type nozzle that can satisfactorily suppress the height of the dross in cutting, the following relationships hold.

[0091] Conventionally, it has been understood that it is preferable to perform cutting using a nozzle in which the inner diameter D2 of the outer nozzle 72, so-called nozzle diameter, also varies according to the thickness of the workpiece to be processed. Therefore, a laser processing nozzle group composed of a plurality of nozzles with different inner diameters D2 is prepared in advance, and a nozzle that can satisfactorily suppress the height of the dross according to the thickness of the workpiece to be processed is selected and the processing is executed. However, conventionally, no law has been found in the dimensional relationship of the nozzle group, so the nozzle group has been constructed by setting the combination of the inner diameter D1, the inner diameter D2, and the outer diameter D3 based on experience and the like.

[0092] In contrast, the following has been clarified by the above cutting experiment and simulation. That is, for a plurality of nozzles with different inner diameters D2 that make up the nozzle group, the inner diameter D1 and outer diameter D3 of the nozzle with a larger inner diameter D2 than the other nozzles are larger than the inner diameter D1 and outer diameter D3 of the other nozzles. The inner diameter D1, inner diameter D2, and outer diameter D3 are preferably a combination that satisfies both of the following relationships (1) and (2). (1) When (inner diameter D2, inner diameter D1) = (x, y), y should be a linear function of x. For the numerical values shown in Fig. 17, it is (Equation 1). (2) When (inner diameter D2, outer diameter D3) = (x, y), y should be a linear function of x. For the numerical values shown in Fig. 17, it is (Equation 2).

[0093] Also, based on these relationships, the following (3) and (4) are derived. (3) Regarding the width Δd3, which is the radial gap distance of the second ventilation passage AR2 shown in Fig. 17, when (inner diameter D2, width Δd3) = (x, y), y is a linear function of x. For the specific numerical values shown in Fig. 17, as shown in Fig. 18, y = (1 / 6)x - 2 / 3 (Equation 3) is satisfied.

[0094] (4) Regarding the distance Δd2, which is the radial distance between the second ventilation passage AR2 and the first ventilation passage AR1 shown in Fig. 17, when (inner diameter D2, distance Δd2) = (x, y), y is a linear function of x. For the specific numerical values shown in Fig. 17, as shown in Fig. 18, y = (1 / 6)x + 5 / 6 (Equation 4) is satisfied.

[0095] That is, when the combinations of (inner diameter D2, width Δd3) and (inner diameter D2, distance Δd2) are respectively (x, y), in any of the combinations of (inner diameter D2, width Δd3) and (inner diameter D2, distance Δd2), y should be a linear function of x. (3) and (4) are substantially equivalent because they are naturally derived by subtracting variables from the relationships of (1) and (2). Therefore, the plurality of nozzles constituting the nozzle group may be manufactured so as to satisfy the above (1) and (2), or so as to satisfy the above (3) and (4).

[0096] The embodiments of the present invention are not limited to the above-described configurations and procedures, and may be modified within the scope not departing from the gist of the present invention. In FIG. 17, the distance H1 that forms a step between the inner nozzle 71 and the outer nozzle 72 is set to be constant at 1.0 (mm), but this is not limiting. On the upper surface Wa of the workpiece W, it is only necessary that the first gas flow AG1 ejected from the first ventilation passage AR1 and the second gas flow AG2 ejected from the second ventilation passage AR2 be mixed.

Explanation of Reference Numerals

[0097] 1 Laser processing head 11 Housing 11a Female threaded portion 11b Lower end surface 12 Collimation lens 13 Bend mirror 14 Focusing lens 14a Focusing lens drive unit 15 Nozzle gap measurement unit 2 Laser oscillator 21 Process fiber 21a Coupler 3 Assist gas supply device 4 Drive unit 5 NC device 51 Laser processing device 7, 7A, 7B Nozzles (nozzles for laser processing) 71 Inner nozzle 71a Opening 711 Through hole 711a Upper hole portion 711b Lower hole portion 712 Engagement portion 712a Male threaded portion 713 Intermediate portion 714 Tip portion 714a front end face 716 cut-in part 72 outer nozzle 72a opening 72b front end face 721 flange part 722 inclined part 723 through hole 723a female thread part 724 basic hole part 725 intermediate hole part 726 tip hole part 727 mounting part 727a male thread part 101, 102 nozzles AG assist gas AG1 first gas flow AG2 second gas flow ARa, ARb, ARc ventilation paths AR1 first ventilation path AR2 second ventilation path D1, D2 inner diameters D3 outer diameter fr flow rate Hg nozzle gap H1 distance Lsa, Ls laser light Ps pressure P1~P6, Pe1~Pe4 measurement points Pf1 position Q cutting path R1 nozzle Rt1 ejection area ratio Rt2 second ejection width ratio S1, S2 opening areas t dross height tm temperature Vg external space V11 space W workpiece Wa upper surface Wb lower surface Δd1 double width Δd2 distance Δd3 width ρ density

Claims

Claim 1 An inner nozzle having a through-hole for injecting a laser beam and an assist gas, and an outer nozzle forming a ring-shaped opening for injecting the assist gas between the inner nozzle, when an outer diameter of a tip portion of the inner nozzle is D3, an inner diameter of the through-hole is D1, and an inner diameter of the outer nozzle is D2, the inner diameter D2 is in a range of at least 7.0 mm and at most 13.0 mm, when (inner diameter D2, inner diameter D1) is (x, y), it satisfies y = (1 / 3)x - 1 / 3, when (inner diameter D2, outer diameter D3) is (x, y), it satisfies y = (2 / 3)x + 4 / 3, a nozzle for laser processing.

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