METHOD FOR FLAME CUTTING BY MEANS OF A LASER BEAM

Abstract

A method for flame cutting of a workpiece, in particular a planar workpiece, with a thickness of at least 10 mm is performed by a laser beam with power of more than 10 kW and with oxygen as a cutting gas. Accordingly, a focal position in the beam direction of the laser beam is located within the workpiece at a depth that is greater than half the thickness of the workpiece. The laser beam emerges from a nozzle opening of a cutting gas nozzle together with the cutting gas, wherein a distance of a workpiece-side nozzle end face from the workpiece surface is at least 2 mm, preferably at least 3 mm, particularly preferably at least 5 mm.

Claims

1. A method for flame cutting of a workpiece having a thickness of at least 10 mm by means of a laser beam with a power of at least 10 kW and using oxygen as a cutting gas, which comprises the steps of: directing a focal position in a beam direction of the laser beam within the workpiece at a depth that is greater than half a thickness of the workpiece, the laser beam emerging from a nozzle opening of a cutting gas nozzle together with the cutting gas; and setting a distance of a workpiece-side nozzle end face from a workpiece surface to be at least 2 mm.

2. The method according to claim 1, which further comprises generating the laser beam in a laser beam generator which is connected via an optical fiber to a cutting head where the cutting gas nozzle is attached, the optical fiber being configured as a single core fiber or as a multi-core fiber.

3. The method according to claim 2, which further comprises setting a core diameter of the single-core fiber to be between 50 μm and 150 μm.

4. The method according to claim 1, wherein the laser beam has a Gaussian intensity profile at the workpiece surface.

5. The method according to claim 1, which further comprises setting a focal diameter of the laser beam at the focal position to be between 150 μm and 300 μm.

6. The method according to claim 1, which further comprises generating the laser beam by means of a solid-state laser or by means of a diode laser as the laser beam generator.

7. The method according to claim 1, wherein an overpressure of the cutting gas before an emergence from the cutting gas nozzle is between 0.4 bar and 1 bar.

8. The method according to claim 1, which further comprises: using a planar workpiece as the workpiece; and setting the distance of the workpiece-side nozzle end face from the workpiece surface to be at least 3 mm.

9. The method according to claim 1, which further comprises setting the distance of the workpiece-side nozzle end face from the workpiece surface to be at least 5 mm.

10. The method according to claim 5, which further comprises setting the focal diameter of the laser beam at the focal position to be 200 μm.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0021] FIG. 1 is a diagrammatic, longitudinal sectional view through a cutting gas nozzle and through a planar workpiece in the case of flame cutting by means of a laser beam;

[0022] FIG. 2 is a graph showing a focal position of the laser beam as a function of a workpiece thickness; and

[0023] FIG. 3 is a perspective view of a laser cutting machine for carrying out a method for flame cutting.

DETAILED DESCRIPTION OF THE INVENTION

[0024] In the following description of the figures, identical reference signs are used for identical or functionally identical components.

[0025] Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a cutting gas nozzle 1 for the laser cutting of a planar metallic workpiece 2 (a sheet metal) with a thickness D of at least 10 mm by means of a laser beam 3 and a cutting gas 24 (cf. FIG. 3). The cutting gas 24 and the laser beam 3 both emerge together from a nozzle opening 5 of the cutting gas nozzle 1. The laser beam 3 has a beam direction 6 which runs in the negative Z-direction of an XYZ-coordinate system. The laser cutting process is a flame cutting process, in which oxygen is used as cutting gas 24.

[0026] The cutting gas nozzle 1 is moved over the workpiece 2 in a cutting direction 7, which corresponds to the X-direction of the XYZ-coordinate system, in order to produce a cutting gap in the workpiece 2. A distance A from a workpiece-side nozzle end face 8 to the workpiece surface 9 that faces the cutting gas nozzle 1 is at least 2 mm in the example shown, preferably at least 3 mm, in particular at least 5 mm. A focal position F in a beam direction 6 of the laser beam 3 is situated within the thickness D of the workpiece 2, more precisely in the lower half of the workpiece 2 which is further away from the cutting gas nozzle 1. Expressed differently, the focal position F of the laser beam 3 in the beam direction 6 is located within the workpiece 2 at a depth that is greater than half D/2 the thickness D of the workpiece 2. In this case, a focal diameter d.sub.F at the focal position F in the workpiece 2 is between 150 μm and 300 μm, preferably is approximately 200 μm.

[0027] FIG. 2 shows the focal position in the workpiece 2 (sheet metal) in millimeters against the workpiece thickness (sheet-metal thickness) in millimeters in a graph. It is possible to recognize that the focal position F is ever deeper in the workpiece 2 with increasing thickness of the workpiece 2. The greater the workpiece thickness D, the greater the distance therefore is between the focal position F and the workpiece surface 9.

[0028] FIG. 3 shows a laser cutting machine 20 that is suitable for carrying out the flame cutting method described further above.

[0029] The laser cutting machine 20 contains a solid-state laser or a diode laser as a laser beam generator 21. The laser cutting machine 20 further contains a displaceable (laser) cutting head 22 and a workpiece rest 23, on which the workpiece 2 is arranged. The laser beam 3 which is guided from the laser beam generator 21 to the cutting head 22 by means of an optical fiber (not shown) is generated in the laser beam generator 21. The optical fiber is a single-core fiber in the example shown, that is to say the optical fiber has only a single core in which the laser beam 3 or the laser radiation of the laser beam generator 21 propagates. In the example shown, the single-core fiber has a core diameter which is between 50 μm and 150 μm. Alternatively, a multi-core fiber can also be used to guide the laser beam 3 from the laser beam generator 21 to the cutting head 22.

[0030] The laser beam 3 is directed at the workpiece 2 by a focusing optical unit arranged in the cutting head 22. The laser beam 3 which emerges from the single-core fiber has a Gaussian intensity profile and keeps the latter when being focused on the workpiece 2, that is to say the laser beam 3 likewise has a Gaussian intensity profile at the workpiece surface 9.

[0031] Moreover, the laser cutting machine 20 is supplied with a cutting gas 24, shown here in exemplary fashion as oxygen or nitrogen. To carry out the above-described flame cutting method, oxygen as a cutting gas 24 is supplied to the cutting gas nozzle 1 of the cutting head 22, to be precise at an overpressure of approximately 0.4-1.0 bar before the emergence of the cutting gas 24 from the cutting gas nozzle 1.

[0032] Further, the laser cutting machine 20 contains a machine controller 25 which is programmed to displace the cutting head 22 with its cutting gas nozzle 1 in accordance with a cutting contour relative to the stationary workpiece 2. The machine controller 25 also controls the power of the laser beam generator 21, which is more than 10 kW in the flame cutting process described further above and which may optionally be up to 20 kW or more. In this way it is possible to attain a cutting speed (feed motion) of 3.1 m/min in the case of a workpiece thickness of 15 mm and a cutting speed of 1.75 m/min in the case of a workpiece thickness of 25 mm, with the cutting speed increasing with increasing laser power.

[0033] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: [0034] 1 Cutting gas nozzle [0035] 2 Workpiece [0036] 3 Laser beam [0037] 5 Nozzle opening [0038] 6 Beam direction of the laser beam [0039] 7 Cutting direction [0040] 8 Nozzle end face [0041] 9 Workpiece surface [0042] 20 Laser cutting machine [0043] 21 Laser beam generator [0044] 22 Cutting head [0045] 23 Workpiece rest [0046] 24 Cutting gas [0047] 25 Machine controller [0048] F Focal position [0049] D Workpiece thickness [0050] A Distance [0051] d.sub.F Laser beam diameter