Laser cutting nozzle and method for laser cutting using a laser cutting nozzle

Abstract

The invention relates to a laser cutting nozzle (1) for a 2D laser cutting machine (2), comprising a nozzle channel (7), for a laser beam (8) and a process gas (9), extending between a nozzle inlet (3) and a nozzle mouth (4) along a nozzle longitudinal axis (5) through a nozzle body (6), wherein the nozzle channel (7) continuously converges in the direction of the nozzle mouth (4) in a convergence section (10) up to a narrow point (11) of the nozzle channel (7), and, starting at the narrow point, the nozzle channel (7) continuously diverges in a divergence section (12) up to the nozzle mouth (4), and wherein the convergence section (10) transitions directly into the divergence section (12) at the narrow point (11), wherein the nozzle mouth (4) has a mouth cross section (15) of at least 15.9 mm2, in particular at least 19.6 mm2, and the narrow point (11) has a flow cross section (16), wherein the mouth cross section (15) is at least 1.65 times and max. six times the flow cross section (16) of the narrow point (11).

Description

[0001] Laser cutting nozzle and methods for laser cutting using a laser cutting nozzle

[0002] The present invention relates to a laser cutting nozzle for a 2D laser cutting machine, comprising a nozzle channel for a laser beam and a process gas extending between a nozzle inlet and a nozzle outlet along a nozzle longitudinal axis through a nozzle body, wherein the nozzle channel converges continuously in a convergence section towards the nozzle outlet up to a constriction point of the nozzle channel, and wherein the nozzle channel diverges continuously from the constriction point in a divergence section up to the nozzle outlet, and wherein the convergence section transitions directly and seamlessly into the divergence section at the constriction point. The invention further relates to a method for laser cutting using a laser cutting nozzle.

[0003] A 2D laser cutting machine is a device, known in principle from the prior art, that uses a high-intensity laser beam to cut, mark, or engrave various materials. Such laser cutting machines typically have a laser cutting head responsible for focusing the laser beam, which is movable relative to the workpiece. The laser cutting head usually receives the laser beam from an external radiation source and modifies it so that it is suitable for cutting materials. During operation, the beam passes through at least one focusing optic (lens, lens group, or mirror), usually first a collimation optic (lens, lens group, or mirror) located in the laser cutting head, which parallelizes the beam, and then a focusing optic that focuses the beam onto the workpiece.Typically, at least one nozzle is present, directing a cutting gas onto the cutting point to remove molten or vaporized material and positively influencing the reactions of the workpiece material at the cutting point. Such a laser cutting head often also features a distance sensor that continuously adjusts the distance between the nozzle and the workpiece surface to ensure a constant focus of the laser beam relative to the workpiece surface and optimal gas coupling into the cutting gap. At the exit side of the laser cutting head, facing the workpiece, there is usually at least one protective glass that shields the internal components and optics of the laser cutting head from emissions and spatter during the cutting process.Cooling is also often provided, which ensures that the temperature of the laser cutting head components remains within specified limits to avoid beam distortion or damage to the components.

[0004] In 2D laser cutting processes, especially when processing metals, nozzles with a conical inner contour are commonly used. This nozzle shape has proven effective in many applications, but encounters significant limitations and problems under certain process conditions.

[0005] Cutting processes using nozzles with a conical inner contour and a nozzle-to-workpiece distance of more than 1 mm, especially more than 2 mm, frequently result in quality defects at the cut edge of the components. An increased nozzle distance is often chosen to minimize collisions between the nozzle and tilted workpiece parts.

[0006] However, the increased nozzle distance leads to undesirable effects on the cut edges. The cut edges exhibit more burrs, a more inhomogeneous scoring pattern, and more oxidation in the lower third of the cut edge than is the case with cutting processes using a small nozzle distance (< 1 mm). Furthermore, with large workpiece thicknesses, the large nozzle distances can cause cut-off, which significantly impairs process stability and the quality of the final products.

[0007] The cause of these problems lies in the large nozzle spacing, which can be, for example, 4 mm. At such spacings, it is not possible to couple the cutting gas from conical nozzles into the kerf at a relatively high and consistent pressure level over a sufficiently large surface area. Standard nozzles with a conical inner contour do not achieve a consistent pressure profile of the cutting gas on the workpiece surface, resulting in uneven gas distribution. This, in turn, leads to poorer cutting quality and limits the workpiece thicknesses that can be cut.

[0008] A similar problem occurs with bevel cutting. In laser bevel cutting, which is used to create chamfers or angled cut edges with a laser cutting head that is not perpendicular to the workpiece surface, the increased effective distance between the nozzle and the workpiece during the angled cutting head results in poorer coupling of the cutting gas into the kerf. This distance is limited by the nozzle's obstruction during the angled cutting process. This limitation results in reduced bevel cut quality and a reduction in the maximum material thickness that can be processed.

[0009] It is therefore an object of the invention to avoid or at least reduce the problems known from the prior art and to provide an improved laser cutting nozzle. It is further an object of the invention to realize an optimized method for laser cutting using a laser cutting nozzle.

[0010] This problem is solved by a laser cutting nozzle for a 2D laser cutting machine with a nozzle channel for a laser beam and a process gas extending between a nozzle inlet and a nozzle outlet along a nozzle longitudinal axis through a nozzle body, wherein the nozzle channel converges continuously in a convergence section towards the nozzle outlet up to a constriction point of the nozzle channel, and wherein the nozzle channel diverges continuously from the constriction point in a divergence section up to the nozzle outlet, and wherein the convergence section transitions directly and seamlessly into the divergence section at the constriction point, and wherein the nozzle outlet has an outlet cross-section of at least 15.9 mm². 2 , in particular at least 19.6 mm 2The convergence zone has a flow cross-section where the outlet cross-section is at least 1.65 times and at most six times the flow cross-section of the convergence zone. The fact that the convergence section transitions directly and seamlessly into the divergence section at the convergence zone means that the convergence zone between the convergence section and the divergence section has no transition section, and in particular no cylindrical transition section, with an axial extent.

[0011] This laser cutting nozzle offers the advantage that the continuous convergence and divergence of the nozzle channel ensures a uniform and laminar gas flow both within the nozzle and at the workpiece. This results in optimal distribution of the cutting gas, guaranteeing high cut quality even at greater nozzle distances from the workpiece. In particular, clean cut edges without burrs and with minimal oxidation can be achieved. The specific cross-section of the nozzle orifice and constriction ensures that the gas pressure is transferred to the cutting front constantly and efficiently, enabling continuous cutting even with thicker workpieces. The resulting more precise machining of workpieces at greater distances reduces the risk of the nozzle colliding with tilted workpiece parts.This increases the efficiency of the cutting process and extends the service life of the nozzle, ultimately leading to lower operating costs.

[0012] A further significant advantage of the laser cutting nozzle according to the invention results from the specific ratio of the flow cross-section at the nozzle constriction to the flow cross-section at the nozzle opening. This precise ratio significantly determines the pressure conditions inside and outside the nozzle. Particularly when the distance between the nozzle face and the workpiece is more than 1 mm, the gas pressure remains constant over a sufficiently large area of ​​the workpiece surface due to the selected ratio of the flow cross-sections. Even at greater distances, the cut quality remains consistently high, as the laminar gas flow efficiently expels the melt from the cutting gap. This makes it possible to achieve high-quality cut edges despite the greater distance. The uniform pressure distribution on the workpiece surface prevents the formation of burrs and reduces oxidation, which is particularly advantageous for thicker workpieces.In the laser cutting nozzle according to the invention, the constriction between the convergence section and the divergence section lacks a transition section with an axial extension, and the convergence section transitions directly into the divergence section at the constriction. This direct transition from the convergence section to the divergence section without a transition section improves the flow characteristics of the process gas. This minimizes turbulence in the gas flow, resulting in a more homogeneous gas flow and a uniform pressure profile, which is particularly advantageous at high cutting speeds and larger nozzle distances. The cut quality thus remains consistently high, even under demanding conditions.

[0013] For the purposes of this patent application, a nozzle body is the component of the laser cutting nozzle that encloses the nozzle channel and ensures the structural integrity of the nozzle. The nozzle body extends from the nozzle inlet to the nozzle outlet and forms the physical framework that connects and supports the various sections of the nozzle. The nozzle body is thus the supporting structure of a laser cutting nozzle, containing the essential elements for guiding the laser beam and the process gas. The nozzle body is preferably made of a material that withstands high temperatures and mechanical stresses such as those occurring during the laser cutting process. A coupling section can be provided on the nozzle body of the laser cutting nozzle for connecting the laser cutting nozzle.

[0014] Preferably, the nozzle body is designed to have a smooth inner contour along its nozzle channel, minimizing flow losses and promoting a uniform gas flow. The nozzle body can also comprise various sections, such as the convergence and divergence sections of the nozzle channel, which are specifically coordinated to ensure optimal flow dynamics. Preferably, the nozzle body has a coupling section at its other end. In this coupling section, the nozzle body is configured for coupling with a nozzle holder of a laser cutting head. For this purpose, the nozzle body preferably has a thread in the coupling section, allowing the laser cutting nozzle to be screwed into the nozzle holder. However, other connection methods between the nozzle holder and the coupling section are also conceivable, such as snap-fit ​​or bayonet connections.

[0015] Furthermore, the nozzle body preferably has a first conical contact surface at the transition between the coupling section and a rotating step, which forms a stop surface when the nozzle is screwed into the nozzle holder. Preferably, the conical first stop surface of the nozzle body, or the stop chamfer, is dimensioned such that a gap remains between the laser cutting nozzle and the nozzle holder when the nozzle is screwed into the nozzle holder. This gap serves to prevent stresses caused by differing thermal expansion. The first conical contact surface can also serve to center the nozzle when it is screwed into the nozzle holder of the processing head.

[0016] The nozzle body of the laser cutting nozzle can preferably be made of a material with high thermal conductivity, for example, at least 300 W / mK, preferably at least 350 W / mK, for example, approximately 355 W / mK. This improves heat dissipation from the nozzle. Furthermore, to implement a distance sensor for a laser processing method, the nozzle body can preferably be made of an electrically conductive material. In particular, the nozzle body can be made of copper or a copper alloy. Preferably, the nozzle body is also formed in one piece.

[0017] The nozzle body can have an outer contour that can be subdivided into further sections. In addition to a coupling section, the nozzle body can, for example, also have an engagement section extending from a rotating step towards the outlet opening of the laser cutting nozzle, wherein the nozzle body preferably has its largest outer diameter in the engagement section and / or wherein the nozzle body has a polygonal cross-section or a polygonal outer contour in the engagement section. The engagement section can preferably be designed such that it can be gripped by means of a gripping tool (e.g., an open-end wrench) and the nozzle can thus be inserted, in particular screwed into, the socket of a nozzle holder. This can be done automatically, for example, by means of a nozzle changer, as described by way of example in EP 2 589 458 B1 of the applicant.Preferably, the nozzle body has six flat engagement surfaces along its outer circumference in the engagement section, with two circumferentially adjacent engagement surfaces arranged at an angle of 60° to each other. The distance between two opposing engagement surfaces is preferably between 23 mm and 25 mm, particularly between 23.9 mm and 24 mm.

[0018] Further towards the outlet opening of the laser cutting nozzle, the nozzle body can preferably have a second conical contact surface in which the outer diameter of the nozzle body preferably tapers continuously. This surface serves as a bearing section, for example, in a correspondingly machined contact surface of a nozzle magazine or nozzle changer. In this bearing section, the nozzle body thus has a conical shape tapering towards the outlet opening. The second conical contact surface can be subdivided into sections with different cone angles, the cone angle preferably decreasing towards the outlet opening relative to the nozzle's longitudinal axis. The tapered circumferential surface in the bearing section of the nozzle body can serve as a contact surface for a nozzle holder, for example, in a nozzle changer.

[0019] Preferably, the nozzle body has its smallest outer diameter at the outlet opening for the laser beam and the cutting gas.

[0020] For the purposes of this patent application, a nozzle inlet is the section of the laser cutting nozzle through which the process gas and the laser beam enter the nozzle channel. The nozzle inlet forms the beginning of the continuous nozzle channel, which extends to the nozzle outlet.

[0021] The nozzle inlet preferably has a cylindrical shape, enabling the process gas to be introduced into the nozzle channel with minimal pressure loss. Advantageously, the nozzle inlet can also have a slightly conical shape to minimize inlet resistance and optimize flow characteristics. Furthermore, it is conceivable to provide a nozzle inlet with integrated flow guides and / or ribs that serve to distribute the process gas evenly and promote laminar flow. Another embodiment could include a nozzle inlet with an extended inlet area that reduces the pressure of the incoming gas and thus increases the flow velocity.

[0022] Nozzle mouth

[0023] For the purposes of this patent application, a nozzle opening is the section of the laser cutting nozzle where the process gas and the laser beam exit the nozzle channel in the direction of the workpiece. The nozzle opening forms the end of the continuous nozzle channel that runs from the nozzle inlet to the nozzle opening.

[0024] A nozzle opening can include flow guides or ribs that serve to stabilize the flow of the process gas and reduce turbulence. This design can increase gas utilization efficiency and further improve cutting quality.

[0025] Mouth cross-section and flow cross-section

[0026] The nozzle cross-section and flow cross-section of the laser cutting nozzle can be designed in various ways, each offering specific advantages for optimizing the efficiency and quality of the cutting process. The nozzle cross-section can be circular. This circular shape allows for a uniform and symmetrical distribution of the process gas around the laser beam, meaning the influence of the process gas on the cutting front is independent of direction, thus eliminating the need to rotate the nozzle when changing direction. Another advantage of the circular cross-section is its ease of manufacture, which reduces production costs.

[0027] Alternatively, the nozzle cross-section can also be elliptical. An elliptical nozzle cross-section can allow for a wider coverage of the process gas along the cutting line. This shape can adapt the flow dynamics to meet specific gas distribution requirements, thus increasing the flexibility of the cutting process.

[0028] Another possible embodiment is a rectangular or square orifice cross-section. A rectangular orifice cross-section allows for a precise and uniform distribution of the process gas along the cutting edge, which improves efficiency when cutting specific geometries.

[0029] The flow cross-section at the constriction of the laser cutting nozzle can also be designed in various ways. A circular flow cross-section ensures uniform acceleration of the process gas through the constriction, promoting laminar flow and stable gas distribution. This shape minimizes flow losses and optimizes pressure conditions, resulting in high cutting quality.

[0030] It is particularly preferred that the entire nozzle channel has circular flow cross-sections.

[0031] nozzle longitudinal axis

[0032] For the purposes of this patent application, a nozzle longitudinal axis is the imaginary line extending from its inlet to its outlet, preferably also forming the axis of symmetry of the laser cutting nozzle. The laser beam preferably runs parallel and particularly preferably concentrically to the nozzle longitudinal axis.

[0033] Nozzle channel

[0034] For the purposes of this patent application, a nozzle channel is the continuous cavity in the nozzle body of the laser cutting nozzle, which extends from the nozzle inlet to the nozzle outlet, so that the process gas and the laser beam can be guided through the nozzle.

[0035] The nozzle channel can be configured with various sections. Advantageously, the nozzle channel begins with a cylindrical inlet section that efficiently receives the process gas and the laser beam. This is followed by a convergence section that continuously narrows the channel to a constriction point. This constriction point is where the gas pressure is maximized. Beyond the constriction point is a divergence section that widens the channel again and directs the gas evenly onto the workpiece.

[0036] Advantageously, the convergence section is designed to accelerate the process gas uniformly and create a laminar flow. At the constriction, the gas reaches its highest velocity, while the divergence section ensures that the gas strikes the workpiece at a constant velocity and uniform pressure.

[0037] Preferably, the nozzle channel is designed such that its inner walls are smooth and free of edges or protrusions in the flow direction. This minimizes flow losses and turbulence, resulting in more efficient gas flow and improved cutting performance. Another conceivable embodiment is a nozzle channel with flow guides or ribs on the inner walls running in the flow direction, which stabilize the process gas flow and further reduce turbulence. Additionally, special coatings can be used in the nozzle channel to further improve the flow characteristics and extend the nozzle's service life. Laser cutting head

[0038] The laser cutting head is a component of a laser cutting machine responsible for focusing and aligning the laser beam onto the workpiece. The laser cutting head consists of several technical components, including, for example, a cutting head housing, collimation optics, focusing optics, and a nozzle.

[0039] If the laser cutting head is to be oriented non-perpendicular to the workpiece surface, it can still have a shaft rotating about an A-axis and a shaft rotating about a B-axis. The pivot axis of the laser cutting head then preferably runs approximately centrally through its longitudinal extent. Particularly preferably, the pivot axis runs through the center of gravity of the laser cutting head. Since, in this preferred embodiment, the center of gravity of the laser head is located on the axis of rotation, the inertial forces that arise during movement of the laser cutting head are minimized. This is particularly important when rapid changes in direction of the laser cutting head are required or when high traverse speeds of the laser cutting head are to be achieved.

[0040] The skew cutting angle of the laser cutting head is preferably adjustable between >0° and 50° relative to the surface normal of the workpiece.

[0041] laser cutting machine

[0042] For the purposes of this patent application, a 2D laser cutting machine is a laser processing system designed to cut materials such as metals, plastics, or other materials by applying a focused laser beam. The laser cutting machine comprises at least one laser beam source for generating a processing laser beam. The laser processing method performed by the laser cutting machine can be a fusion cutting process or a flame cutting process, the latter being particularly suitable when the workpiece to be cut is made of structural steel or a similar material. The laser cutting machine further includes at least one laser cutting head equipped with laser processing optics. These optics are responsible for focusing the laser beam onto the workpiece to enable precise cuts.The laser cutting head also includes a nozzle holder and a nozzle, for example, one of the angled cutting nozzles described above, through which the laser beam and a cutting gas are directed onto the workpiece. Preferably, the nozzle holder includes a cooling device, which may, for example, contain a channel system for a cooling fluid. This cooling device can help to effectively dissipate the heat generated during the process and protect the nozzle holder and adjacent components from overheating. A coolant liquid or a cooling gas, which is circulated through the channel system, can serve as the cooling medium.

[0043] The laser cutting machine can be configured to process sheet-shaped workpieces, such as metal sheets, or tubular workpieces.

[0044] Advantageous embodiments of the invention

[0045] According to an advantageous embodiment of the invention, the nozzle opening cross-section can be designed as a circular area with a specific diameter, and / or the flow pattern cross-section of the constriction can be designed as a circular area with a specific flow diameter. Designing the nozzle opening cross-section and / or the flow pattern cross-section as a circular area offers the advantage of optimal flow dynamics. This geometry ensures a uniform distribution of the process gas, resulting in a homogeneous pressure distribution at the workpiece. This improves the cutting quality and reduces gas consumption, as the gas is used more efficiently. Furthermore, the circular cross-sections simplify nozzle manufacturing, thus reducing production costs.

[0046] Preferably, the nozzle orifice diameter is at least 4.5 mm, more preferably at least 5 mm, and at least 1.5 times and at most twice the diameter of the nozzle constriction. The resulting pressure distribution of the cutting gas at the workpiece allows for particularly efficient ejection of the melt, leading to an unexpectedly significant improvement in cut edge quality. The ratio of orifice diameter to flow diameter is particularly preferably between 1.65 and 1.85. This specific ratio ensures an optimal balance between gas pressure and gas flow. This configuration maximizes gas flow efficiency and improves the coupling of the cutting gas into the kerf. This results in more effective ejection of the melt and increased cut edge quality. Furthermore, gas consumption is reduced, which lowers operating costs.

[0047] It has been found that the best results are achieved when the nozzles maintain a nearly constant gas pressure over a region of the workpiece surface with a diameter of at least 4.5 mm, preferably at least 5 mm, and particularly preferably at least 6 mm. This uniform pressure region of at least 4.5 mm, preferably at least 5 mm, and particularly preferably at least 6 mm in diameter should also be maintained at a nozzle distance to the workpiece of >1 mm, preferably >2 mm.

[0048] Ideally, gas consumption when using laser cutting nozzles should not exceed 120m³. 3 The cost per hour should not increase compared to conventional cutting processes. Therefore, the diameter of the constriction should preferably not exceed 3.5 mm.

[0049] According to a further particularly preferred embodiment of the invention, the flow diameter at the constriction can thus be < 3.5 mm, in particular between 2.5 mm and 3.5 mm. Limiting the flow diameter at the constriction to < 3.5 mm significantly reduces gas consumption without impairing cutting performance. This leads to economic advantages through lower operating costs and enables the nozzle to be used in a wider range of laser cutting machines.

[0050] At the same time, the quality of the cut edges remains high, which improves the overall production quality. This also contributes to keeping gas consumption within the typical machine setup conditions of 120 m³. 3 / h remains. Furthermore, the invention can also be further developed such that the nozzle diameter is 5 mm to 6 mm. The nozzle diameter of 5 mm to 6 mm ensures that a sufficiently wide gas flow is generated, which completely covers the cutting front. This enables a uniform gas pressure distribution on the workpiece surface, which improves the cut edge quality and stabilizes the cutting process.

[0051] In a further preferred embodiment of the invention, the constriction may also have a radially inwardly curved inner wall, the radius of which at the constriction has a length of 15 mm to 17 mm. The radially inwardly curved inner wall at the constriction with a radius of 15 mm to 17 mm promotes a laminar flow of the process gas. This reduces turbulence and improves the efficiency of the gas outlet. The uniform gas distribution leads to better cut edge quality and minimizes the formation of burrs and oxidation.

[0052] It can also be advantageous to further develop the invention such that the angle of a tangent intersecting the nozzle longitudinal axis at the nozzle opening and touching the constriction in the divergence section is between 8 and 11 degrees. The specific orientation of the tangent at the constriction to the nozzle longitudinal axis optimizes the angle of the gas flow, thereby improving the coupling of the cutting gas into the kerf. This leads to more efficient ejection of the melt and higher cut edge quality. Furthermore, the precise control of the gas flow angle optimizes gas consumption, which reduces operating costs.

[0053] It is further preferred that the distance between the constriction and the nozzle opening be at least 6.5 mm and at most 8.5 mm. This defined distance along the nozzle's longitudinal axis allows for optimal expansion of the process gas downstream of the constriction, contributing to a stable and uniform pressure profile at the nozzle opening and thus ensuring precise and clean cut edges. Furthermore, the controlled expansion of the gas within the specified distance range allows for efficient use of the process gas's energy, reducing gas consumption and thereby increasing the efficiency of the cutting process. The defined distance also helps maintain a consistent pressure at the workpiece surface, enabling higher cutting speeds, as the process gas can remove the molten metal from the kerf more quickly and efficiently.

[0054] It has also proven particularly advantageous if the distance between the inlet end of the convergence section and the constriction is between 5.5 mm and 7.5 mm. This defined distance along the nozzle's longitudinal axis ensures that the process gas is sufficiently accelerated in the convergence section before reaching the constriction. This acceleration is crucial for achieving a high gas velocity with laminar flow, which is necessary to effectively expel the melt from the kerf and produce precise cut edges.

[0055] The invention can also be advantageously implemented such that the wall thickness of the nozzle end face, which runs perpendicular to the nozzle's longitudinal axis, is at least 0.5 mm, preferably at least 1 mm, at the nozzle opening. The wall thickness at the nozzle opening of at least 0.5 mm, preferably at least 1 mm, ensures the necessary stability of the nozzle under mechanical stress and collisions. This robustness extends the nozzle's service life and reduces maintenance costs. Furthermore, the sufficient wall thickness enables precise measurement of the nozzle, which improves quality control and production reliability.

[0056] It can also be provided that the nozzle channel has at least one cylindrical inlet section, which is arranged upstream of the convergence section on the inlet side. The cylindrical inlet section upstream of the convergence section improves the flow characteristics of the incoming process gas. This leads to a uniform acceleration of the gas and a more stable flow in the convergence section. This increases the efficiency of gas utilization and improves the cutting quality. In addition, the cylindrical inlet section simplifies the manufacture of the nozzle, which reduces production costs. The object of the invention can be achieved by a laser cutting method using a laser cutting nozzle according to the invention with the following parameters:

[0057] • Setting a laser power of at least 3 kW, preferably at least 6 kW, particularly preferably at least 12 kW;

[0058] • Setting a cutting gas pressure of at least 15 bar, preferably at least 20 bar, for a process gas;

[0059] • Setting a nozzle distance to a workpiece of at least 2 mm for a laser power < 24 kW and at least 1 mm for a laser power of 24 kW and above;

[0060] • Setting the focus position of the laser beam in the upper half of the workpiece thickness.

[0061] The specific parameters for the laser cutting process enable precise and efficient adjustment of the cutting process. High laser power and optimized cutting gas pressure ensure effective molten material ejection and excellent cut edge quality. The defined nozzle distance guarantees a constant pressure distribution across the workpiece surface, increasing cutting accuracy and production speed. This results in an overall improvement in the efficiency and quality of the cutting process.

[0062] It is particularly preferred if the workpiece thickness is set to at least 4 mm, as the method has proven to be particularly suitable for larger workpiece thicknesses.

[0063] In this context, it can also be advantageous to select the process gas from a group including argon, nitrogen, and process gas mixtures containing nitrogen. Choosing the process gas from this group, including argon, nitrogen, and their mixtures, offers the flexibility to adapt the cutting process to different materials and requirements. This selection enables optimal gas utilization and improves cut edge quality by tailoring the gas composition to the specific properties of the workpiece.

[0064] The laser cutting nozzles preferably operate in a pressure range of 20 bar - 25 bar, with a nozzle distance of 2 mm - 5 mm to the workpiece, which has proven to be particularly effective in terms of expelling the melt from the cutting gap during laser cutting.

[0065] workpiece

[0066] In a laser cutting process, the workpiece is the material or object from which parts are cut or engraved using a laser beam. It thus acts as the substrate for the cutting or engraving operations. The workpiece absorbs the laser radiation emitted by the laser, causing a portion of the material to melt, vaporize, or be removed through a chemical reaction with the cutting gas to achieve the desired cut or engraving.

[0067] In 2D laser cutting systems, workpieces are cut in the form of flat plates. In principle, it is also conceivable that the workpiece has a cylindrical or profiled basic shape, or a three-dimensional form.

[0068] It is further preferred that the workpiece be wholly or partially made of a material selected from a group comprising metal, in particular steel, aluminium, non-ferrous metal or titanium, plastic, wood or a composite material.

[0069] The invention will now be explained in more detail with reference to figures, without limiting the general concept of the invention.

[0070] It shows:

[0071] Figure 1 shows a laser processing head in a perspective view,

[0072] Figure 2 shows a laser cutting nozzle in a longitudinal section view, Figure 3 shows a laser cutting machine in a perspective view.

[0073] Figure 1 shows a view of a laser cutting nozzle 1 in a laser cutting head 25 of a 2D laser cutting system 2, as also illustrated in Figure 3. The laser cutting head 25 is rotatably mounted about two axes 26 and 27 that are perpendicular to each other. This arrangement enables precise movement and alignment of the laser cutting head 25 in various directions. These two horizontal axes 26 and 27 allow the laser cutting head 25 to rotate at different angles. The first horizontal axis 27 allows the cutting head to be tilted forwards and backwards (relative to the laser cutting system 2), while the second horizontal axis 26 allows the cutting head to be tilted laterally, thus enabling complex cutting tasks and angled cuts. The laser cutting head 25 is attached to a motion unit 28 of the laser cutting system 2.

[0074] The laser beam 8 exits the laser cutting head 25 through the laser cutting nozzle 1 and is directed at the workpiece 29. Upon impact of the laser beam 8 on the workpiece 29, its material is melted or vaporized, thereby creating a precise cut or engraving in the workpiece 29. This process enables the production of highly precise and clean cut edges or engravings.

[0075] To optimize the cut quality, a process gas 9 is guided through the laser cutting nozzle 1 in addition to the laser beam 8. This process gas 9 flows essentially parallel to and around the laser beam 8. The main function of the process gas 9 is to expel the resulting molten material from the cutting gap and to cool the cut edge. This significantly improves the cut quality, as it reduces the formation of burrs and oxidation on the cut edge. The interaction of the laser beam 8 and the process gas 9 thus ensures high precision and efficiency when cutting and engraving the workpiece 29. The laser cutting nozzle 1 is now explained in more detail below with reference to Figure 2. As can be seen from Figure 2, the laser cutting nozzle 1 comprises a nozzle channel 7 for the laser beam 8 and the process gas 9, which runs between a nozzle inlet 3 and a nozzle outlet 4 along a nozzle longitudinal axis 5 through a nozzle body 6.The nozzle channel 7 converges continuously towards the nozzle outlet 4 in a convergence section 10 up to a constriction 11 of the nozzle channel 7. Starting from the constriction 11, the nozzle channel 7 then diverges continuously in a divergence section 12 up to the nozzle outlet 4.

[0076] It is clearly visible how the convergence zone 10 transitions directly into the divergence zone 12 at the constriction 11. The constriction 11 between the

[0077] The convergence section 10 and the divergence section 12 therefore have no transition section with an axial extension. The course of the inner wall 19 of the nozzle channel 7 is continuous and without edges or protrusions in order to avoid turbulence of the cutting gas 9 and to create a uniform pressure cushion on the workpiece 29.

[0078] The nozzle opening 4 has a nozzle cross-section 15 of at least 15.9 mm. 2 , in particular at least 19.6 mm 2The constriction 11 has a flow cross-section 16, wherein the mouth cross-section 15 is at least 1.65 times and at most six times the flow cross-section 16 of the constriction 11.

[0079] In the embodiment shown in Figure 2, both the nozzle opening 15 of the nozzle 4 are circular with an opening diameter 17, and the flow cross-section 16 of the constriction 11 is circular with a flow diameter 18. The ratio of opening diameter 17 to flow diameter 18 is between 1.65 and 1.85. The flow diameter 18 at the constriction 11 is <3.5 mm, specifically between 2.5 mm and 3.5 mm (including extreme values). This allows the gas consumption when using the laser cutting nozzle 1 to be reduced to less than 120 m³. 3The throughput is limited to / h in order to avoid increasing costs compared to conventional cutting processes. In the illustrated embodiment, the orifice diameter 17 has a value between 5 mm and 6 mm (including edge values).

[0080] In the configuration shown, the wall thickness 23 at the nozzle opening 4 is at least 0.5 mm, preferably at least 1 mm. Here, the wall thickness 23 is the width of the annular nozzle end face perpendicular to the nozzle's longitudinal axis 5. This wall thickness ensures sufficient structural integrity and stability of the laser cutting nozzle 1 in the event of potential collisions. When processing workpieces 29, there is always a risk that the laser cutting nozzle 1 will encounter tilted workpiece parts. Sufficient wall thickness protects the laser cutting nozzle 1 from damage and extends its service life. Additionally, the wall thickness at the nozzle opening 4 enables reliable and precise monitoring of the laser cutting nozzle 1 using an automated camera system. These systems are designed to check the laser cutting nozzle 1 for damage or wear and to ensure that it always functions optimally.A wall thickness of at least 1 mm facilitates the accurate measurement and detection of damage, as the robust structure can provide clear and consistent feedback to the camera system.

[0081] The constriction 11 has a radially inwardly curved inner wall 19, the radius 20 of which has a length of 15 mm to 17 mm at the constriction 11.

[0082] The distance between the constriction 11 and the nozzle opening 4 in the direction of the nozzle longitudinal axis 5 is at least 6.5 mm and at most 8.5 mm. This distance ensures that the process gas 9 has sufficient time and space to expand optimally after the constriction 11 and achieve a uniform pressure profile at the nozzle opening 4. The distance between the inlet-side start of the Laval contour, i.e., the beginning of the convergence section 10, and the constriction 11 in the direction of the nozzle longitudinal axis 5 is between 5.5 and 7.5 mm. This dimensioning of the convergence section 10 allows the process gas 9 to be guided uniformly and at high velocity to the constriction 11. This ensures that the process gas 9 is accelerated to the necessary velocity and achieves laminar flow, which is important for the subsequent expansion and pressure distribution in the divergence section 12.

[0083] A laser cutting nozzle 1 can be designed as either a bevel-cut nozzle or a straight-cut nozzle, with significant similarities and specific adaptations to be observed in each case. In both nozzle types, the constriction 11 is located at the same point, relative to the beginning and end of the Laval contour. The path of the Laval contour, consisting of a convergence section 10 leading to the constriction 11 and a divergence section 12 leading from the constriction 11 to the nozzle opening 4, is identical for both nozzle types.

[0084] However, in the angle-cutting nozzles, the length of the cylindrical inlet section 24 is longer than in the laser cutting nozzles 1 for straight cutting. This is because the cutting nozzles are longer overall to reduce the interference contour when the laser cutting head 25 is swiveled. The extended cylindrical inlet section 24 ensures that the process gas 9 enters the convergence section 10 uniformly and stably, which is important for the efficient acceleration and subsequent expansion of the gas in the Laval contour. This adjustment of the length of the cylindrical inlet section 24 in the angle-cutting nozzles allows the cutting head 25 to be swiveled to various angles without collisions or impairment of the flow dynamics.

[0085] The described laser cutting nozzle 1 operates most efficiently in the pressure range of 20 bar to 25 bar. In this pressure range, the process gas 9 is forced through the nozzle channel 7 with sufficient force to effectively expel the molten metal from the cutting gap. However, the decisive factor is not the maximum pressure achieved, but rather that the widest possible area of ​​uniform pressure, referred to as the "effective pressure," is created on the workpiece 29 above the cutting gap due to the selected geometry of the nozzle channel 7. This effective pressure ensures a uniform distribution of the process gas 9 on the surface of the workpiece 29, which significantly improves the stability of the cutting process and the quality of the cuts. The resulting effective pressure on the workpiece 29 correlates directly with the achievable feed rate in the respective process regime.This means that with optimal effective pressure, higher cutting speeds can be achieved without compromising the quality of the cut edges. This leads to more efficient use of the laser cutting system 2 and increases productivity.

[0086] The angle 21 of a tangent 22 intersecting the nozzle longitudinal axis 5 in the nozzle opening 4 and touching the constriction 11 in the divergence section 12 is between 8 and 11 degrees.

[0087] By widening the laser cutting nozzle 1 at the nozzle opening 4, better coverage of the cutting gas 9 across the cutting front can be achieved, since the laser cutting nozzle 1 has the "lavender-shaped" inner contour shown, with a convergent-divergent nozzle channel 7. This shape shapes the gas jet in such a way that a uniform, "top-hat" pressure profile is achieved on the workpiece 29. This makes it possible to couple the process gas 9 more effectively into the kerf, even with a larger nozzle distance, for example, due to an angled cut, in order to expel the molten material.

[0088] When using the laser cutting nozzle 1 for both perpendicular and angled cutting with a nozzle distance to the workpiece 29 of more than 1 mm, the nozzle's inner wall is smooth and free of protrusions or edges. The transition from the convergence to the divergence section is continuous, and the ratio of the narrowest diameter of the Laval contour to the nozzle opening diameter 17 4 is very well matched within a narrow range. This ensures laminar gas flow in the laser cutting nozzle 1 and at the nozzle opening 4, as well as a uniform pressure cushion on the workpiece with a gas pressure distribution exhibiting a high and broad pressure plateau. This specific geometry of the nozzle channel 7 of the laser cutting nozzle 1 thus ensures that the process gas 9 achieves a uniform, nearly constant gas pressure over a portion of the workpiece surface with a diameter of at least 5 mm, preferably 6 mm.It has been shown that the best results are achieved when this uniform pressure range is maintained even with a nozzle distance to the workpiece 29 of more than 1 mm, especially more than 2 mm. This enables effective coupling of the process gas 9 into the cutting gap, thereby...

[0089] The melt is efficiently expelled and a high cutting quality is ensured.

[0090] The nozzle channel 7 also has a cylindrical inlet section 24, which is located on the inlet side in front of the convergence section 10.

[0091] Using the laser cutting nozzle 1, a laser cutting process can now be carried out with the following parameters.

[0092] • Setting a laser power of at least 3 kW, preferably at least 6 kW, particularly preferably at least 12 kW;

[0093] • Setting a cutting gas pressure of at least 15 bar, preferably at least 20 bar, for a process gas 9;

[0094] • Setting a nozzle distance to a workpiece 29 of at least 2 mm for a laser power < 24 kW and at least 1 mm for a laser power of 24 kW and above;

[0095] • Adjusting the focus position of the laser beam 8 in the upper half of the workpiece thickness.

[0096] Process gas 9 is selected from a group of process gases including Ar, N2 and process gas mixtures containing N2.

[0097] Figure 3 shows a laser cutting system 2 with a beam source 38 configured as an example of a solid-state laser (disk laser or fiber laser). Alternatively, the beam source 38 can also be, for example, a CO2 laser or a diode laser. The laser cutting system 2 further comprises a movable laser cutting head 25 and a (stationary) workpiece support 39 on which a workpiece 29 is arranged. A laser beam 8 is generated in the beam source 38 and guided from the beam source 38 to the laser cutting head 25 by means of mirrors or via an optical fiber.

[0098] The laser beam 8 is directed onto the workpiece 29 by means of a focusing optic arranged in the laser cutting head 25. The laser cutting system 2 is connected to a gas supply unit 41. The gas supply unit 41 provides, in particular, the process gas.

[0099] The laser cutting system 2 further comprises a machine control 30, which is programmed to move the laser cutting head 25 according to a cutting contour relative to the workpiece 29, which is stationary here by way of example. The machine control 30 also controls the power of the beam source 38 during the execution of the cutting process. The invention is not limited to the embodiments shown in the figures. The foregoing description is therefore not to be considered limiting, but rather explanatory. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not preclude the presence of further features. Insofar as the claims and the foregoing description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing a hierarchy.

[0100] List of reference signs

[0101] 1 laser cutting nozzle

[0102] 2 2D laser cutting machines

[0103] 3 nozzle inlets

[0104] 4 nozzle openings

[0105] 5 nozzle longitudinal axis

[0106] 6 nozzle bodies

[0107] 7 nozzle channel

[0108] 8 Laser beam

[0109] 9 Process gas

[0110] 10 Convergence section

[0111] 11. Narrow point

[0112] 12 Divergence section

[0113] 15 Mouth cross-section

[0114] 16 Flow cross-section

[0115] 17 Mouth diameter

[0116] 18 flow diameters

[0117] 19 Interior wall

[0118] 20 radius

[0119] 21 angles

[0120] 22 Tangent

[0121] 23 wall thickness

[0122] 24 Inlet section

[0123] 25 Laser cutting head

[0124] 26 axle

[0125] 27 axle

[0126] 28 movement units

[0127] 29 workpiece

[0128] 30 Machine control

[0129] 38 Beam source

[0130] 39 Workpiece support 41 Gas supply unit

Claims

Claims 1. Laser cutting nozzle (1) for a 2D laser cutting machine (2) with a nozzle channel (7) extending between a nozzle inlet (3) and a nozzle outlet (4) along a nozzle longitudinal axis (5) through a nozzle body (6) for a laser beam (8) and a process gas (9), wherein the nozzle channel (7) converges continuously in the direction of the nozzle outlet (4) in a convergence section (10) up to a constriction (11) of the nozzle channel (7), and the nozzle channel (7) diverges continuously from the constriction (11) in a divergence section (12) up to the nozzle outlet (4), and wherein the convergence section (10) transitions directly and seamlessly into the divergence section (12) at the constriction (11), and characterized in that the nozzle outlet (4) has an outlet cross-section (15) of at least 15.9 mm 2 , in particular at least 19.6 mm 2exhibits and the constriction (11) has a flow cross-section (16), wherein the mouth cross-section (15) is at least 1.65 times and at most six times the flow cross-section (16) of the constriction (11).

2. Laser cutting nozzle (1) according to claim 1, characterized in that the nozzle opening cross-section (15) of the nozzle opening (4) is a circular area with an opening diameter (17) and / or the flow cross-section (16) of the The constriction (11) is designed as a circular area with a flow diameter (18).

3. Laser cutting nozzle (1 ) according to claim 2, characterized in that the orifice diameter (17) of the nozzle orifice (4) is at least 4.5 mm, preferably at least 5 mm and at least 1.5 times and at most twice the flow diameter (18) of the constriction (11 ).

4. Laser cutting nozzle (1 ) according to claim 2 or 3, characterized in that the ratio of orifice diameter (17) to flow diameter (18) is from 1.65 to 1.

85.

5. Laser cutting nozzle (1 ) according to one of claims 2 to 4, characterized in that the flow diameter (18) at the constriction (11 ) is <3.5 mm, in particular from 2.5 mm to 3.5 mm.

6. Laser cutting nozzle (1 ) according to one of claims 2 to 5, characterized in that the orifice diameter (17) is from 5 mm to 6 mm.

7. Laser cutting nozzle (1 ) according to one of the preceding claims, characterized in that the constriction (11 ) has a radially inwardly curved inner wall (19) whose radius (20) at the constriction (11 ) has a length of 15 mm to 17 mm.

8. Laser cutting nozzle (1 ) according to one of the preceding claims, characterized in that the angle (21 ) of a tangent (22) intersecting the nozzle longitudinal axis (5) in the nozzle opening (4) and touching the constriction (11 ) in the divergence section (12) is between 8 and 11 degrees.

9. Laser cutting nozzle (1 ) according to one of the preceding claims, characterized in that the distance between the constriction (11 ) and the nozzle opening (4) is at least 6.5 mm and at most 8.5 mm.

10. Laser cutting nozzle (1 ) according to one of the preceding claims, characterized in that the distance between the inlet-side beginning of the convergence section (10) and the constriction (11 ) is between 5.5 and 7.5 mm.

11. Laser cutting nozzle (1) according to one of the preceding claims, characterized in that the wall thickness (23) at the nozzle opening (4) is at least 0.5 mm, preferably at least 1 mm.

12. Laser cutting nozzle (1 ) according to one of the preceding claims, characterized in that the nozzle channel (7) has at least one cylindrical inlet section (24) which is arranged on the inlet side upstream of the convergence section (10).

13. Method for laser cutting using a laser cutting nozzle (1) according to one of the preceding claims, with the following parameters: • Setting a laser power of at least 3 kW, preferably at least 6 kW, particularly preferably at least 12 kW; • Setting a cutting gas pressure of at least 15 bar, preferably at least 20 bar, for a process gas (9); • Setting a nozzle distance to a workpiece (29) of at least 2 mm for a laser power < 24 kW and at least 1 mm for a laser power of 24 kW or more; • Adjusting the focus position of the laser beam (8) in the upper half of the workpiece thickness.

14. Method according to claim 13, characterized in that the process gas (9) is selected from a group of process gases comprising Ar, N2 and process gas mixtures with an N2 component.

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