Processing head for laser beam cutting of parts and laser beam cutting method

Abstract

In the processing head, a cutting gas as a first gas stream and a laser beam are directed toward the part to be cut through a nozzle arranged in the direction of the part to be cut. The cutting gas supply unit is surrounded, at least in the region of the nozzle of the cutting gas supply unit, by an annular or polygonal slit nozzle or individual nozzles arranged in an annular or polygonal configuration and separated from each other, and the nozzle of the cutting gas supply unit is arranged at the center of a circle or the center of gravity of the polygonal slit nozzle or the polygonal nozzle. A second gas stream is directed toward the surface of the part to be cut through the annular or polygonal slit nozzle or the annular or polygonal nozzle. The pressures of the cutting gas and the second gas stream are independently adjustable, and the pressure of the cutting gas at the outlet opening of the cutting gas nozzle is greater than the pressure of the second gas stream, at least three times greater.

Description

[Technical Field]

[0001] The present disclosure relates to a processing head configured for laser cutting of parts, preferably metal parts, and to a laser cutting method. [Background technology]

[0002] When cutting with laser radiation, a coaxially arranged gas jet is used as the cutting gas to expel the material melted by the laser beam from the cutting gap. Laser cutting, especially of metals, produces nearly vertical grooves at the cutting edge. These significantly determine the roughness of the cutting edge and form typical horizontal zones with characteristic characteristics in terms of wavelength and roughness. Furthermore, the grooves are spatially related to the formation of a burr at the bottom edge of the cut material, thus determining the quality of the cutting result.

[0003] A nozzle, typically positioned coaxially with the laser beam, is used to create the gas jet, and the diameter of the nozzle is generally significantly larger than the resulting cutting gap. In addition to simple, e.g., conical tapered nozzles, there are also nozzle concepts that internally split the gas flow into separate channels within the nozzle, which are then recombined within or below the respective nozzles and above the workpiece. It is also common for the inside and underside of the nozzle to be specially designed to affect the flow characteristics of the cutting gas.

[0004] To reduce gas losses above the part to be cut and improve gas utilization, the concept of an attachment nozzle is also currently used, in which the movable outer ring of the nozzle is guided directly onto the workpiece surface.

[0005] However, none of the nozzle concepts so far has been successful in significantly influencing the structuring of the cutting edge surface, or even in completely preventing groove formation.

[0006] For example, JP 2011-224600 A shows a method of using a laser beam to form a hole in a workpiece.

[0007] WO 2018 / 0084001 relates to the laser processing of plastic parts, in particular those reinforced with carbon fibres.

[0008] A laser welding method and a corresponding device are described in EP 1 153 696 A1.

[0009] Japanese Patent Publication No. 06-304777 shows the possibility of a sealed battery. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-224600 [Patent Document 2] International Publication No. 2018 / 0084001 [Patent Document 3] European Patent Application Publication No. 1153696 [Patent Document 4] Japanese Patent Application Publication No. 06-304777 Summary of the Invention [Problem to be solved by the invention]

[0011] It is therefore an object of the present disclosure to identify ways to improve the surface quality of the cut edge obtained by laser beam cutting, where possible without additional post-processing. [Means for solving the problem]

[0012] The object of the present disclosure is achieved by a processing head having the features of claim 1. Claim 9 relates to a laser beam cutting method. Advantageous embodiments and developments of the present disclosure can be realized by the features of the dependent claims.

[0013] The processing head according to the present disclosure comprises: To form the cutting gap, the cutting gas supply along its central longitudinal axis includes a cutting gas supply section in which a first gas flow and a laser beam are directed toward the part to be cut through a nozzle positioned in the direction of the part to be cut. the cutting gas supply is surrounded, at least in the region of the nozzles of the cutting gas supply, by a ring-shaped or polygonal slit nozzle or by a ring-shaped or polygonal arrangement of individual nozzles arranged separately from one another, The nozzle of the cutting gas supply unit The annular slit nozzle or the polygonal slit nozzle or the polygonal nozzle arrangement is positioned at the center of a circle defined by the annular slit nozzle or the polygonal nozzle arrangement, or at the center of gravity defined by the polygonal slit nozzle or the polygonal nozzle arrangement. A second gas stream is directed toward each surface of the part to be cut through the annular or polygonal slit nozzle or the annular or polygonal nozzle arrangement. The pressure of the cutting gas supplied through the nozzle of the cutting gas supply unit and the pressure of the second gas stream flowing through the annular or polygonal slit nozzle or the annular or polygonal nozzle arrangement are independently adjustable. Furthermore, the pressure of the cutting gas supplied through the nozzle of the cutting gas supply unit at the outlet opening of the nozzle is greater than the pressure of the second gas stream at the outlet opening of the annular or polygonal slit nozzle or the annular or polygonal nozzle arrangement. The pressure in the nozzle of the cutting gas supply unit is up to three times the pressure of the second gas stream at the outlet opening of the annular or polygonal slit nozzle or the annular or polygonal nozzle arrangement. This essentially means the pressure at the outlet opening of the nozzle for cutting gas and of the annular or polygonal slit nozzle or nozzles of the annular or polygonal arrangement. DETAILED DESCRIPTION OF THE INVENTION

[0014] Advantageously, the pressure of the cutting gas at the outlet opening of the nozzle for the cutting gas supplied through the nozzle is set to at least 1.5 times, at most 2 times, in particular at least 1.7 times, at most 1.9 times the pressure of the second gas stream at the outlet opening of the annular or polygonal slit nozzle or nozzle of the annular or polygonal arrangement.

[0015] The nozzle opening through which the cutting gas emerges from the nozzle preferably has an inner diameter that matches the outer diameter of the laser beam used for cutting, which can more reliably avoid the formation of grooves in the cutting edge.

[0016] The annular or polygonal nozzles may be geometrically designed, dimensioned and spaced such that the second gas stream emerging from its outlet opening surrounds the annular or polygonal cutting gas stream, forming a closed ring with at least approximately the same flow velocity and pressure maintained around its circumference.

[0017] In the case of polygons, geometric shapes with at least four corners are preferred.

[0018] The annular or polygonal nozzles may be rotationally symmetrical and / or slot-shaped, at least in the region of the outlet opening, which has a free cross-sectional area through which the second gas stream passes. The slot may be formed in the form of a partial circle recessed toward the cutting gas nozzle. It is possible to select the same design and dimensions of the free cross-sectional area for each annular or polygonal nozzle, but it is also possible, for example, to select different designs and dimensions of the free cross-sectional area for each annular or polygonal nozzle, alternating with each other.

[0019] The pressure of the second gas stream in the region of the nozzle outlet opening may be maintained in the range of 0.05 MPa to 2.5 MPa relative to ambient pressure, thereby achieving a flow velocity of more than 300 m / s for the gas emerging from the nozzle outlet. For laser beam cutting with oxygen, a pressure in the range of 0.05 MPa to 0.1 MPa is preferably used.

[0020] The cutting gas supply nozzle, annular or polygonal slit nozzle, or annular or polygonal nozzle arrangement may be converged toward their outlet opening so that the smallest free cross-sectional area through which the cutting gas or second gas flow passes is located at the outlet opening of the cutting gas supply nozzle, annular or polygonal slit nozzle, or annular or polygonal nozzle arrangement. In particular, each inner side of the outward-facing surface of each nozzle may be formed so as to continuously taper toward the center of the outlet opening of the cutting gas supply nozzle in the direction of the central longitudinal axis of the cutting gas supply, i.e., over a length starting at least 15 mm before reaching the respective outlet opening. At least 40% of the circumferential surface of each inner side may be conically tapered.

[0021] The cone angle may be larger on the inner wall of an annular or polygonal slit nozzle or on an annular or polygonal nozzle than on the nozzle of the cutting gas supply, to ensure that the pressure of the individual gas streams is maintained all the way to the outlet opening and to prevent a reduction in the energy content of the cutting gas that could be converted into processing in the processing head.

[0022] The continuous conical taper influences the pressure and flow velocity distribution within each nozzle and can prevent the cutting gas from accelerating to supersonic speed within each nozzle.

[0023] The laser beam is preferably directed coaxially at the part through the nozzle of the cutting gas supply. The laser beam preferably has a cross-sectional area that fills at least 80% and up to 100% of the free cross section of the nozzle of the cutting gas supply in the region of its exit opening. As a result, a cutting gap formed during laser beam cutting can be realized with a gap width that corresponds to the inner diameter of the exit opening of the nozzle of the cutting gas supply.

[0024] The minimum inner diameter of the nozzle of the cutting gas supply at the outlet opening corresponds to the gap width of the cutting gap to be formed with a maximum deviation of ±20% and may be in the range of 0.5 mm to 2 mm. Preferably, this minimum inner diameter exactly corresponds to the gap width of the cutting gap to be formed.

[0025] The width of the slit of an annular or polygonal slit nozzle or the width or outer diameter of the nozzle in an annular arrangement corresponds at least to the width of the inner diameter of the nozzle of the cutting gas supply at its outlet opening, and preferably is twice this inner diameter.

[0026] The outer diameter in the region of the outlet opening is at least twice the diameter of the nozzle of the cutting gas supply at the outlet opening and may be at most 10.00 mm.

[0027] In the case of a polygonal slit nozzle or a polygonal arrangement of nozzles, the maximum distance between the oppositely arranged outlet openings parallel to the cutting gap is maintained at a distance less than the maximum distance between the axially arranged outlet openings perpendicular to the oppositely arranged openings. For example, with a rectangular slit nozzle or nozzle arrangement, a rectangle approximately 10 mm long can be selected. In this case, the long sides can be parallel to the cutting gap or the direction of the feed movement. The length of the perpendicularly aligned sides can be 2 mm to 5 mm.

[0028] A square shape is advantageous compared to a triangle or a shape with more than four corners. A square shape can be selected. Preferably, the long side of this square is aligned at least approximately parallel to the cutting gap to be formed compared to the width of the side aligned perpendicular thereto. A length-to-width ratio of at least 5:1 is particularly preferred.

[0029] The distances between the nozzle outlet opening of the cutting gas supply, the annular or polygonal slit nozzle or the annular or polygonal nozzle arrangement, and the surface of the part to be cut may differ from each other by a maximum of 1 mm. The distance of the nozzle outlet from the surface of the part, where the laser beam cutting gap is formed, may be maintained in the range of 0.2 mm to 2 mm.

[0030] Thus, the present disclosure may include an annular gap nozzle or annular nozzles arranged concentrically around an inner nozzle opening, wherein the annular gap nozzle or annular nozzles have separate gas supplies with independently adjustable or controllable gas pressures, and the respective gas pressures may be affected by valves located at the respective gas supplies. In the case of a polygonal slit nozzle or polygonal nozzles, the nozzles from which the cutting gas is emitted may be located at the centroid of each of the polygons.

[0031] The outer diameter of the outlet opening through which the cutting gas is emitted from the processing head may correspond approximately to the cutting gap width, and preferably be the same size as the gap width of the kerf. The diameter of the annular slit nozzle or the diameter of the ring in which the annularly arranged nozzles are arranged may be a multiple of the cutting gap width.

[0032] The cutting gas outlet opening may be located at the same height as the annular or polygonal slit nozzle or annular or polygonal nozzle arrangement, above the surface of the part to be cut, or slightly above or below it. The distance of the outlet opening from the surface of the part to be cut used for cutting may be less than the diameter of the outlet opening through which the cutting gas exits the processing head.

[0033] The gas pressure or pressure ratio is the absolute pressure ratio p between the outlet opening of the internally arranged cutting gas and the outlet opening of the annular or polygonal slit nozzle or the outlet opening of the annular or polygonal arranged nozzle. i / p a is preferably set to be less than 2.

[0034] The gas supply for the internal nozzles of cutting gas may be provided via a standard cutting gas supply in the processing head, whereas the gas supply for the annular or polygonal slit nozzles or the annular or polygonal arranged nozzles may be provided via an additional connection to the processing head.

[0035] If the absolute pressure of the cutting gas at the outlet opening of the nozzle is 2.0 MPa, it is particularly advantageous to set the absolute pressure of the second gas stream at the outlet opening of the annular or polygonal slit nozzle or the outlet opening of the annular or polygonal arranged nozzle to 1.1 MPa.

[0036] The interior of the nozzle for the cutting gas may be formed as a convergent nozzle, at least in the region near its outlet opening, with the smallest diameter located at the outlet opening.

[0037] The minimum diameter of the nozzle of the cutting gas supply at the outlet opening should approximately match the gap width of the cutting gap to be formed, with a maximum deviation of the minimum diameter from the gap width being ±20%, preferably ±10%.

[0038] A laser beam with a beam cross-sectional area of ​​80% or more and a free cross-sectional area of ​​100% or less at the exit opening region of the cutting gas supply nozzle section generates a cutting gap approximately the same width as the cutting gas exit opening. This ensures that the cutting gas flow enters the generated cutting gap directly and linearly. Compared to the prior art, the upper end of the cutting gap does not act as a flow obstacle in the form of a forward-facing step, allowing the cutting gas flow to enter the cutting gap unimpeded. The present disclosure can prevent separation of the cutting gas flowing from the upper end of the cutting gap and the formation of a recirculation region at the upper end of the cutting gap during laser beam cutting. Compared to the prior art, this prevents or significantly reduces the accumulation of spatial and temporal disturbances in the boundary layer of the cutting gas flow on the cutting edge, allowing the cutting gas flow to uniformly expel the melt formed by the laser beam energy from the kerf.

[0039] An outer annular or polygonal slit nozzle or annular or polygonal nozzle arrangement can be used to prevent contamination of the cutting gas with gases from the surrounding environment and shield the resulting melt. This prevents oxidation in the process zone during melt cutting with an inert process gas, preferably nitrogen, and an annular gap flow or a second annular or polygonal gas flow of an equally inert process gas. On the other hand, in laser cutting, where oxygen is used as the cutting gas and provides energy for the material melting process through oxidation, and the melt is then expelled from the kerf, an inert process gas, such as oxygen or nitrogen, can also flow through the annular or polygonal slit nozzle or annular or polygonal nozzle arrangement toward the surface of the workpiece being cut, thereby affecting the oxygen content of the cutting gas reaching the melt.

[0040] An outer annular or polygonal slit nozzle or annular or polygonal arranged nozzles can be used to increase the effective range of cutting gas for melt distribution within the slit and therefore increase the cuttable material thickness.

[0041] By ensuring that the pressure ratio at the outlet opening of the cutting gas and the annular or polygonal slit nozzle or annular or polygonal nozzle is less than 2, the pressure distribution between the nozzle outlet opening and the surface of the workpiece being cut can be adjusted, preventing the cutting gas from reaching sonic speeds. This means that no shocks are formed in the exiting cutting gas flow and the flow within the cutting gap, increasing the gas energy that can be converted into processing compared to prior art, and suppressing gas boundary layer disturbances in the process zone due to shock boundary layer interactions. When the pressure ratio between the absolute pressures at the outlet openings of the cutting gas nozzle and the slit nozzle or annular or polygonal nozzle is between 2 and 3, the cutting gas flow reaches sonic speeds. Compared to prior art, the slower velocity, higher pressure, and weaker shocks increase the gas energy that can be converted into processing compared to prior art, avoiding losses due to strong shocks. However, when the pressure ratio is less than 2, i.e., the absolute pressure at the outlet opening of the cutting gas nozzle is less than twice the absolute pressure at the outlet opening of the annular or polygonal slit nozzle or nozzle, the cutting gas flow does not reach sonic speeds.

Claims

1. A processing head for laser beam cutting of parts, comprising: A cutting gas supply section is provided along its central longitudinal direction, in which a cutting gas as a first gas flow and a laser beam are directed toward the part to be cut through a nozzle arranged in the direction of the part to be cut, to form a cutting gap; The cutting gas supply unit is surrounded by a circular or polygonal slit nozzle or individual nozzles arranged in a circular or polygonal shape at least in the region of the nozzle of the cutting gas supply unit, and the nozzle of the cutting gas supply unit is arranged at the center of a circle or the center of gravity of the polygonal slit nozzle or the polygonal arrangement of nozzles; A second gas flow is directed toward the surface of the workpiece through the annular or polygonal slit nozzle or the annular or polygonal nozzle arrangement, and the pressure of the cutting gas supplied from the nozzle of the cutting gas supply unit and the pressure of the second gas flow flowing through the annular or polygonal slit nozzle or the annular or polygonal nozzle are independently adjustable; The pressure of the cutting gas supplied from the nozzle of the cutting gas supply unit is greater than the pressure of the second gas flow at the outlet opening of the annular or polygonal slit nozzle or the annular or polygonal arranged nozzle, and is at least three times greater than the pressure of the second gas flow; In the case of the polygonal slit nozzle or the nozzles arranged in the polygonal shape, the maximum distance between the oppositely arranged outlet openings parallel to the cutting gap to be formed is kept smaller than the maximum distance between the outlet openings arranged in the axial direction perpendicular thereto; Or, The distance between the nozzle outlet opening of the cutting gas supply unit and the surface of the workpiece to be cut of the annular or polygonal slit nozzle or the annular or polygonal nozzle differs by a maximum of 1 mm, and the distance is maintained at 0.2 mm or more and 2 mm or less during the laser cutting process. Processing head.

2. The nozzle of the cutting gas supply unit, the annular or polygonal slit nozzle, or the nozzle arranged in the annular or polygonal shape converges in the direction of the outlet opening of the nozzle of the cutting gas supply unit, the annular or polygonal slit nozzle, or the nozzle arranged in the annular or polygonal shape, The smallest free cross section through which the cutting gas or the second gas flows is arranged at the nozzle of the cutting gas supply, the outlet opening of the annular or polygonal slit nozzle, or the outlet opening of the annular or polygonal arranged nozzle. The machining head according to claim 1 .

3. The laser beam is preferably directed coaxially through the nozzle of the cutting gas supply unit onto the part to be cut and has a beam cross-sectional area that fills at least 80% to 100% of the free cross-section of the nozzle of the cutting gas supply unit in the region of the outlet opening of the nozzle of the cutting gas supply unit. The machining head according to claim 1 or 2.

4. The minimum inner diameter of the nozzle outlet opening of the cutting gas supply unit corresponds to the gap width of each cutting gap to be formed with a deviation of ±20% or less, and preferably corresponds exactly to the gap width of each cutting gap to be formed, and is in the range of 0.5 mm to 2 mm. The machining head according to any one of claims 1 to 3.

5. The width of the slit of the annular or polygonal slit nozzle or the width or outer diameter of the annular or polygonal nozzle is at least equal to the width of the inner diameter of the nozzle of the cutting gas supply part in the area of ​​the outlet opening, and is at least twice the inner diameter. The machining head according to any one of claims 1 to 4.

6. The outer diameter of the outlet opening of the annular slit nozzle or the diameter of the annularly arranged nozzles is at least twice the diameter of the nozzle of the cutting gas supply unit at the outlet opening and is 10.00 mm or less. The machining head according to any one of claims 1 to 5.

7. The nozzle of the cutting gas supply unit, the annular or polygonal slit nozzle, and / or the nozzles arranged in an annular or polygonal shape have an inner side surface facing the outside, which is conically inclined toward the center of the outlet opening of the nozzle of the cutting gas supply unit at least 15 mm before reaching each outlet opening. The machining head according to any one of claims 1 to 6.

8. The pressure of the cutting gas supplied from the nozzle of the cutting gas supply unit to the outlet opening of the cutting gas nozzle is at most twice the pressure of the second gas flow at the outlet opening of the annular or polygonal slit nozzle or the outlet opening of the annular or polygonal arranged nozzle. The machining head according to any one of claims 1 to 7.

9. A method for laser cutting a part using a processing head that supplies cutting gas through a ring-shaped or polygonal nozzle or a ring-shaped or polygonal slit nozzle, directing cutting gas toward a part to be cut through a nozzle and a laser beam as a first gas flow to form a cutting gap in each part, The polygonal slit nozzle or the polygonally arranged nozzle maintains a maximum distance parallel to the cutting gap between the outlet openings arranged opposite each other that is smaller than a maximum distance between the outlet openings arranged perpendicular to the axial direction of the polygonal slit nozzle or the annular or polygonally arranged nozzle; or The distance between the nozzle outlet opening of the cutting gas supply unit and the annular or polygonal slit nozzle or the annular or polygonal nozzle to the surface of the workpiece to be cut is at most 1 mm different, and the distance is maintained at 0.2 mm or more and 2 mm or less during the laser cutting process; Directing a second gas stream toward the surface of the workpiece, and independently setting the pressure of the cutting gas supplied from the first nozzle and the pressure of the second gas stream supplied through the annular or polygonal slit nozzle or the annular or polygonal nozzle, and setting the pressure of the cutting gas supplied from the nozzle at the outlet opening of the nozzle of the cutting gas supply unit to at least three times the pressure of the second gas stream at the outlet opening of the annular or polygonal slit nozzle or the annular or polygonal nozzle. How to laser beam cut parts.

10. The minimum inner diameter of the nozzle of the cutting gas supply unit at the outlet opening is selected to have a deviation of ±20% or less from the gap width of each cutting gap to be formed, preferably to exactly match the gap width of each cutting gap to be formed. The laser beam cutting method according to claim 9.

11. The pressure of the cutting gas supplied through the nozzle is set at an outlet opening of the cutting gas nozzle to be at least 1.5 times and 2 times, in particular 1.7 times and 1.9 times, higher than the pressure of the second gas flow at the outlet opening of the annular or polygonal slit nozzle or the annular or polygonal nozzle. The laser beam cutting method according to claim 9.

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