A flame-assisted multi-focal laser cutting method and apparatus

Abstract

The present application belongs to the technical field of metal hot cutting, and specifically discloses a flame-assisted multi-focus laser cutting method and device. The method uses multi-focus laser beams, cutting gas, combustion gas and combustion-supporting gas to act on a workpiece to be cut, thereby realizing efficient and high-quality flame-assisted laser cutting of the workpiece. The present application can not only realize positive defocusing cutting, but also negative defocusing cutting, thereby making the energy density of the laser beam at the bottom of the workpiece higher. Compared with single-focus flame-assisted laser cutting technology, the present application has more advantages in cutting thick metal workpieces, higher cutting efficiency and better cutting quality under the same laser power level, and can use lower laser power under the same cutting efficiency, thereby effectively solving the problems of the existing flame-assisted laser cutting technology, such as the need for very high laser power, low cutting efficiency, poor cutting quality and high equipment cost.

Description

Technical Field

[0001] This invention belongs to the field of metal thermal cutting technology, and more specifically, relates to a flame-assisted multi-focus laser cutting method and apparatus. Background Technology

[0002] Metal thermal cutting technologies using lasers, plasma, and flames as heat sources are widely used in the manufacturing of metal parts, with applications in machinery manufacturing, shipbuilding, automotive, aerospace, and railway transportation. Among these, laser cutting, as one type of metal thermal cutting technology, is widely used for cutting various thin metal sheets due to its high cutting speed, high precision, good quality, and small heat-affected zone. In recent years, with the continuous improvement of technological maturity and the continuous decrease in equipment prices, laser cutting technology and equipment have been squeezing the market share of plasma cutting and flame cutting due to their high efficiency and high quality. However, in the cutting of thick metal sheets (thickness greater than 30mm), laser cutting technology is disadvantaged in market competition with plasma cutting and flame cutting due to its high laser power requirements, low cutting efficiency, and high equipment costs, limiting its further application in related industrial fields. Flame cutting technology, with its low cutting cost and particular suitability for cutting thick metal sheets, has always been one of the mainstream methods for cutting thick metal sheets. However, the shortcomings of flame cutting technology are: low cutting efficiency, large heat-affected zone and thermal deformation, long preheating time and weak piercing ability, which make it unable to meet the requirements of high precision and high efficiency cutting of thick metal plates.

[0003] To improve laser cutting efficiency and maximum cutting thickness, patent CN201410160925.2 proposes a laser-flame composite cutting device, and patent CN201410160921.4 proposes a laser-flame composite cutting method. Compared with existing flame cutting technology and traditional laser cutting technology, this laser-flame composite cutting technology significantly improves the maximum thickness of the cut metal material, cutting efficiency, and kerf quality, and retains the advantage of traditional laser cutting that it does not require preheating. However, the above-mentioned existing technologies have the following shortcomings:

[0004] First, the aforementioned existing technology uses a single-focus laser beam to cut thick metal materials. To ensure a certain depth of focus after focusing, a long focal length focusing lens with a focal length of 600mm is used. This design leads to a series of negative chain reactions: on the one hand, the laser beam spot diameter at the focal point is relatively large, resulting in a decrease in the power density of laser cutting, and thus necessitating the use of higher power lasers (such as high-power lasers of 6 kilowatts or even more than 10,000 watts); on the other hand, to ensure that the laser beam passes through the cutting nozzle without energy loss, the inner diameter of the cutting nozzle must be larger, which further leads to a significant increase in the required working gas flow rate, and the cutting cost is also significantly increased.

[0005] Second, because the diameter of the laser spot after being focused by the long focal length focusing lens is larger, the laser energy density is reduced, the actual energy utilization rate of the laser is reduced, and the laser cutting ability is also reduced as a result.

[0006] Third, due to the limitation of the cutting nozzle diameter, the focal point of the laser beam during laser cutting can only be located at a certain distance above the workpiece surface, that is, in a positive defocus state. This results in a low actual laser beam energy density on the workpiece surface and inside the kerf, which is not conducive to improving laser cutting efficiency and kerf quality.

[0007] Therefore, those skilled in the art still need to conduct further research to obtain a flame-assisted laser cutting technology with higher cutting efficiency, better cutting quality, and applicability to thick metal materials. Summary of the Invention

[0008] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a flame-assisted multi-focus laser cutting method and apparatus, which aims to solve the problems of the existing flame-assisted laser cutting technology for cutting thick metal materials, which requires very high laser power and has low cutting efficiency, poor cutting quality and high equipment cost.

[0009] To achieve the above objectives, according to one aspect of the present invention, a flame-assisted multifocal laser cutting method is proposed, which utilizes a multifocal laser beam in conjunction with cutting gas, combustion gas and combustion-supporting gas to achieve high-efficiency and high-quality flame-assisted laser cutting of the workpiece to be cut.

[0010] As a further preferred embodiment, the method includes the following steps:

[0011] S1. Combustion gas and combustion-supporting gas are input into the cutting nozzle and ignited at the outlet below the cutting nozzle to produce a high-temperature flame;

[0012] S2. The multi-focus laser beam and cutting gas are input from above and output from below the cutting nozzle, and work together with the high-temperature flame on the workpiece to be cut, achieving high-efficiency and high-quality flame-assisted laser cutting of the workpiece.

[0013] According to another aspect of the present invention, a flame-assisted multifocal laser cutting device is provided, comprising a laser, an optical system, and a cutting nozzle. The laser is connected to the optical system and is used to provide a laser beam. The optical system is used to convert the laser beam into a multifocal laser beam and guide the multifocal laser beam into the cutting nozzle. The cutting nozzle is located below the optical system and has a main channel and a mixed gas channel. The main channel is used for the multifocal laser beam and cutting gas to pass through, and the mixed gas channel is used for the combustion gas and combustion-supporting gas to pass through. The multifocal laser beam, cutting gas, combustion gas, and combustion-supporting gas, after passing through, act together on the workpiece to be cut to achieve flame-assisted laser cutting of the workpiece.

[0014] As a further preferred embodiment, the optical system includes a beam conversion unit and a multifocal focusing mirror arranged vertically. The beam conversion unit is used to convert the laser beam into a parallel beam and make it perpendicularly incident on the upper surface of the multifocal focusing mirror. The multifocal focusing mirror is used to convert the parallel beam into a multifocal laser beam.

[0015] As a further preferred embodiment, the multifocal focusing lens is a single lens, a combination lens, a diffractive lens, a reflective lens, or a metal lens;

[0016] As a further preferred embodiment, the multifocal focusing lens is a single plano-convex lens, one side of which is a plane and the other side is a convex curved surface. The convex curved surface is composed of multiple focal curved surfaces with different curvatures, and the curvature of each focal curved surface gradually increases from the center of the multifocal focusing lens outwards. Adjacent focal curved surfaces are transitioned by transition surfaces.

[0017] As a further preferred embodiment, the number of focal surfaces is N, the number of transition surfaces is N-1, where N is the number of focal points of the multifocal laser beam, and N≥2.

[0018] As a further optimization, the surface equations y of each surface... i Determine using the following formula:

[0019]

[0020] Where n is the refractive index of the multifocal focusing lens, and f i Let r be the focal length corresponding to surface i. i Let be the distance from the edge of surface i to the optical axis of the multifocal focusing mirror, and H be the thickness of the center of the multifocal focusing mirror. Let i = 1, 2, 3, ..., 2N-1, where the surface located at the center of the multifocal focusing mirror is the focal surface, defined as the first surface, and the surface located at the outermost edge of the multifocal focusing mirror is defined as the 2N-1 surface.

[0021] As a further preferred embodiment, the focal length of the focal surface and the distance from its edge to the optical axis of the multifocal focusing mirror are preset, and the focal length f of the transition surface is... k 'Determined by the following formula:'

[0022]

[0023] Among them, f k-1 Let r be the focal length of surface k-1. k-1 Let be the distance from the edge of surface k-1 to the optical axis of the multifocal focusing mirror, and r be the distance from the edge of the transition surface to the optical axis of the multifocal focusing mirror, r∈[r k-1 r k+1 ], k = 2, 4, 6, ..., 2N-2.

[0024] As a further preferred embodiment, the focal length of the focal surface located at the center of the multifocal focusing lens is 200mm to 600mm, preferably 300mm to 500mm.

[0025] As a further preferred option, the distance between two adjacent focal points is 5mm to 50mm, preferably 10mm to 40mm.

[0026] As a further preferred embodiment, the light-transmitting area of ​​other focal surfaces is 1 to 3 times that of the focal surface located at the center of the multifocal focusing lens.

[0027] As a further preferred embodiment, the cutting nozzle includes a nozzle body, the main channel is located in the middle of the nozzle body and is coaxially arranged with the nozzle body, and its lower end is designed as a Laval structure, and the mixed gas channel is located on the side of the nozzle body.

[0028] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0029] 1. The flame-assisted multi-focus laser cutting method provided by this invention can obtain a laser beam with a greater depth of focus (30mm~80mm) and a smaller divergence angle, enabling not only positive defocus cutting but also negative defocus cutting during laser cutting. This results in a higher energy density of the laser beam at the bottom of the workpiece, which is more advantageous than single-focus flame-assisted laser cutting for cutting thick metal workpieces. At the same laser power level, it has higher cutting efficiency, better cutting quality, and greater cutting thickness. Under the premise of the same metal plate thickness, cutting efficiency, and cutting quality, a lower laser power (less than 2 kW) can be used. Compared with the existing technology that requires 6 kW or even tens of thousands of watts of laser power, this invention will greatly reduce the laser power without affecting the cutting efficiency and quality, achieving a qualitative breakthrough in this field.

[0030] 2. Because this invention can obtain a laser beam with a greater depth of focus and a smaller divergence angle, even if the Laval structure of the cutting nozzle is very narrow, the laser beam can still pass through the area without loss. At the same time, the narrow Laval structure continuously accelerates the cutting gas, ensuring that the oxygen concentration and flow rate in the area of ​​the workpiece being cut remain at a high level, making the oxygen-iron reaction more complete, releasing more heat energy, and achieving better slag removal, cutting speed, and kerf quality. Furthermore, because the laser beam spot diameter is smaller, the diameter of the Laval structure at the bottom of the cutting nozzle can be correspondingly smaller, resulting in less cutting gas consumption and lower cutting costs under the same conditions.

[0031] 3. This invention combines a multi-focus laser beam with a Laval cutting nozzle, making it possible to cut thicker metal materials with lower laser power. It can cut metal materials of varying thicknesses, thus broadening its applicability. The energy generated by the flame-assisted laser cutting of this invention includes the incident energy of the high-energy-density laser beam, the heat of flame combustion, and the energy generated by the exothermic reaction of oxygen-iron combustion. Through the combined effect of these three factors, flame-assisted laser cutting of thick metal materials has significant advantages. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating the principle of the flame-assisted laser cutting method based on a dual-focus laser beam provided in an embodiment of the present invention.

[0033] Figure 2 This is a schematic diagram of the structure of the plano-convex bifocal focusing lens provided in an embodiment of the present invention;

[0034] Figure 3 This is a side view of the plano-convex bifocal focusing lens provided in an embodiment of the present invention;

[0035] Figure 4 This is a diagram of the internal structure of the cutting nozzle provided in an embodiment of the present invention;

[0036] Figure 5 This is a schematic diagram illustrating the principle of the flame-assisted laser cutting method based on a trifocal laser beam provided in an embodiment of the present invention.

[0037] Figure 6 This is a schematic diagram of the structure of the flame-assisted laser cutting device based on a dual-focus laser beam provided in an embodiment of the present invention;

[0038] Figure 7 This is a schematic diagram of the structure of the cutting nozzle air intake unit provided in an embodiment of the present invention.

[0039] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0040] 1-Laser, 1.1-Laser beam, 1.2-Parallel beam, 1.3-Multifocal laser beam; 2-Beam conversion unit; 2.1-Protective mirror; 2.2-Collimating mirror; 3-Multifocal focusing mirror; 4-Cutting nozzle, 4.1-Main channel, 4.2-Mixed gas channel, 4.3-Laval structure, 4.4-Gas mixing component, 4.5-Inlet component; 5-Cutting gas; 6-Mixed gas; 7-Workpiece to be cut. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0042] In the description of this invention, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0043] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0044] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0045] As described in the background section, current flame-assisted laser cutting technology is a single-focus cutting method, which has several drawbacks: the use of a long focal length focusing lens results in a larger spot diameter, reducing the power density of the laser cutting and lowering the actual energy utilization rate of the laser. This necessitates the use of a higher-power laser (6kW-20kW) and a cutting nozzle with a larger inner diameter. Furthermore, due to the limitation of the cutting nozzle diameter, the focal point of the laser beam can only be located above the workpiece surface (positive defocus), resulting in lower actual laser beam energy density both on the workpiece surface and inside the kerf, which is detrimental to improving laser cutting efficiency and kerf quality.

[0046] Based on the above problems, this invention has conducted research and proposed a method for flame-assisted multifocal laser cutting of metallic materials, especially thick metal plates. The basic principle of this method is to utilize a multifocal laser beam, cutting gas, combustion gas, and combustion-supporting gas to act together on the workpiece to be cut, thereby achieving high-efficiency and high-quality flame-assisted laser cutting. Compared with flame-assisted single-focal laser cutting, the flame-assisted multifocal laser cutting method of this invention has a larger depth of focus and a smaller divergence angle, enabling not only positive defocus cutting but also negative defocus cutting. This results in a higher laser beam energy density at the bottom of the workpiece, giving it a greater advantage in cutting thick metal workpieces. At the same laser power level, it has higher cutting efficiency, better cutting quality, and can cut larger plate thicknesses. Furthermore, at the same cutting efficiency, plate thickness, and cutting quality, a lower power laser can be used.

[0047] Specifically, the flame-assisted multi-focus laser cutting method includes the following steps:

[0048] S1. Combustion gas and combustion-supporting gas are input into the cutting nozzle and ignited at the outlet below the cutting nozzle to form a high-temperature flame;

[0049] S2. The multi-focus laser beam and cutting gas are input from above and output from below the cutting nozzle, and work together with the high-temperature flame on the workpiece to be cut, achieving high-efficiency and high-quality flame-assisted laser cutting of the workpiece.

[0050] Specifically, the high-energy laser beam emitted by the laser is transformed into a multi-focus laser beam after passing through a collimation and beam expansion unit and a multi-focus focusing lens. The multi-focus laser beam, together with the cutting gas and auxiliary gas, acts on the surface of the workpiece to be cut after passing through the cutting nozzle. Under the combined action of the high-power-density multi-focus laser beam and the high-temperature flame, the workpiece melts or even vaporizes rapidly. The molten liquid metal is then blown away by the cutting gas, creating a kerf. This achieves high-efficiency and high-quality flame-assisted laser cutting of the workpiece.

[0051] like Figure 1As shown, the present invention also provides a flame-assisted multifocal laser cutting device, which includes a laser 1, an optical system, and a cutting nozzle 4. The laser 1 is connected to the optical system and is used to provide a laser beam and guide the laser beam into the optical system, for example, by transmitting the laser beam to the optical system through an optical fiber. The optical system is used to convert the laser beam into a multifocal laser beam and guide the multifocal laser beam into the cutting nozzle 4. The cutting nozzle 4 is located below the optical system and has a main channel 4.1 and a mixed gas channel 4.2. The main channel 4.1 is used for the multifocal laser beam and cutting gas to pass through, and the mixed gas channel 4.2 is used for the combustion gas and combustion-supporting gas to pass through. The multifocal laser beam, cutting gas, combustion gas, and combustion-supporting gas act together on the workpiece to be cut to achieve flame-assisted laser cutting of the workpiece.

[0052] like Figure 1 As shown, the optical system includes a beam conversion unit 2 and a multifocal focusing mirror 3 arranged vertically. The beam conversion unit 2 is used to convert the laser beam into a parallel beam, and the multifocal focusing mirror 3 is used to convert the parallel beam into a multifocal laser beam. The beam conversion unit 2 mainly includes optical devices such as a collimating lens or a collimating beam expander group, used to collimate and expand the input laser beam with a certain divergence angle, making it a parallel beam. The laser beam 1.1 output by the laser 1 with a certain divergence angle is converted into a parallel beam 1.2 after passing through the beam conversion unit 2, and is perpendicularly incident on the surface of the multifocal focusing mirror 3, forming a multifocal beam 1.3 with a greater depth of focus and a smaller divergence angle. The optical devices constituting the beam conversion unit 2 are not limited to quartz lenses, nor are they limited to specific collimating beam expander groups or collimating lenses; any optical component that can achieve the above functions is acceptable.

[0053] Specifically, the multifocal focusing lens can be a single lens, a combination of lenses, or even a diffractive, reflective, or metallic lens. Its main function is to transform the collimated parallel beam into a laser beam with multiple focal points distributed along the optical axis. This invention preferably uses a single plano-convex lens, which has the advantages of simple structure, ease of implementation, and low cost. Furthermore, the multifocal laser beam generated by this lens has a more uniform energy distribution, resulting in a smoother cutting surface, better perpendicularity, and faster cutting speed. The multifocal focusing lens 3 focuses the perpendicularly incident parallel beam 1.2 into a beam with multiple focal points (P1, P2, ..., P...) along the optical axis. N The multi-focus laser beam 1.3 can be designed with the spacing and energy of each focus point as needed. Depending on the thickness of the metal sheet being cut, the focus points of the multi-focus laser beam 1.3 can be located on the upper part, surface, and interior of the workpiece 7 to be cut, with the number of focus points N≥2.

[0054] like Figure 2 and Figure 3 As shown, the multifocal focusing mirror 3 is a plano-convex mirror with a flat lower surface and a convex upper surface. The convex surface is composed of multiple focal surfaces with different curvatures, and the curvature of each focal surface gradually increases from the center of the multifocal focusing mirror outwards. Furthermore, adjacent focal surfaces are connected by transition surfaces. Specifically, there are N focal surfaces and N-1 transition surfaces, where N is the number of focal points of the multifocal laser beam, and N≥2. That is, the convex surface of the multifocal focusing mirror is designed to have multiple different surfaces from the center of the lens along the edge direction, i.e., it consists of 2N-1 different surfaces, including N focal surfaces and N-1 transition surfaces connecting the focal surfaces.

[0055] More specifically, the focusing lens has rotational symmetry, allowing the calculation of surface equations for different curved surfaces on the convex surface of the focusing lens in a two-dimensional plane. Taking the center of the focusing lens plane as the origin, let the surface equation be y. i =g(r i ), where y is the thickness from the convex surface of the focusing lens to the plane (g(0) = H), and the surface equations y of each surface (including the focal surface and the transition surface) are... i Determine using the following formula (1):

[0056]

[0057] Among them, y i Let f be the surface equation of surface i, n be the refractive index of the multifocal focusing lens, and f be the surface equation of surface i. i Let r be the focal length corresponding to surface i. i Let be the distance from the edge of surface i to the optical axis of the multifocal focusing mirror (maximum value is D / 2, where D is the diameter of the multifocal focusing mirror), H is the center thickness of the multifocal focusing mirror, i = 1, 2, 3, ..., 2N-1, where the surface located at the center of the multifocal focusing mirror is the focal surface, defined as the first surface, and the surface located at the outermost edge of the multifocal focusing mirror is defined as the second (N-1)th surface. That is, from the center of the multifocal focusing mirror outwards, the surfaces are numbered 1, 2, 3, ..., 2N-1, and the first, third, fifth, ..., 2N-1 are focal surfaces, while the second, fourth, sixth, ..., 2N-2 are transition surfaces.

[0058] Furthermore, the focal length of the focal surface and the distance from the edge of the focal surface to the optical axis of the multifocal focusing mirror can be preset according to actual needs. The focal length of the transition surface is determined by the following formula (2) based on the focal lengths of the focal surfaces before and after the transition and the distance from the edge of the focal surface to the optical axis of the multifocal focusing mirror:

[0059]

[0060] Among them, f k-1Let r be the focal length of surface k-1 (i.e., the focal length corresponding to each focal surface). k-1 Let be the distance from the edge of surface k-1 to the optical axis of the multifocal focusing mirror (i.e., the distance from the edge of each focal surface to the optical axis of the multifocal focusing mirror), and r be the distance from the edge of the transition surface to the optical axis of the multifocal focusing mirror, r∈[r k-1 r k+1 ], that is, r takes values ​​within the range of distances from the edges of the front and rear focal surfaces to the optical axis of the multifocal focusing mirror, k = 2, 4, 6, ..., 2N-2.

[0061] Substituting n, H, and the focal length values ​​corresponding to different surfaces into formula (1), the surface equations y of each surface on the convex surface of the multifocal focusing mirror can be calculated. i =g(r i The collimated parallel beam is transmitted to different curved surfaces on the convex surface of the focusing lens. These surfaces have different f-values, focusing the laser beam to different positions on the optical axis. Surfaces 1, 3, 5, ..., 2N-1 are focal surfaces, forming N focal points. Surfaces 2, 4, 6, ..., 2N-2 are transition surfaces, with their focal lengths gradually changing within the range of adjacent focal surfaces. Changing the focal length of the focal surfaces and the distance from their edges to the optical axis of the multifocal focusing lens alters the relative positions of the focal points and the beam energy at each focal point and in the focal transition zone.

[0062] Specifically, the optical system also includes a protective mirror 2.1, which is positioned above the beam conversion unit 2 (collimating mirror 2.2) and below the multifocal focusing mirror 3 to prevent dust from falling in and damaging the collimating mirror and the multifocal focusing mirror.

[0063] Depending on the thickness of the workpiece 7 to be cut, different refractive indices, radii of curvatures, and the number and area of ​​surfaces can be selected to change the spacing and number of focal points of the multifocal laser beam 1.3, as well as the laser energy at each focal point. Furthermore, to ensure sufficient energy and a suitable distribution within the workpiece 7, the number of focal points N and the spacing S should not be too large. When cutting thick metal materials, the focal points of the laser beam should be located as much as possible within the workpiece 7 to effectively overcome problems such as severe slag buildup caused by insufficient laser energy at the bottom of the material when cutting thick metal materials with a single-focal laser beam. Furthermore, to ensure that the multifocal laser beam passes through the cutting nozzle without energy loss and that the focal point of the laser beam is located inside the workpiece to be cut, while also ensuring that the energy at each focal point of the laser beam is reasonably distributed to adapt to the cutting of metal materials of different thicknesses, the focal length of the focal surface located at the center of the multifocal focusing mirror 3 is 200mm to 600mm, preferably 300mm to 500mm, the number of focal points is 2 to 8, preferably 2 to 4, the distance between two adjacent focal points is 5mm to 50mm, preferably 10mm to 40mm, and the light transmission area of ​​other focal surfaces is 1 to 3 times that of the focal surface located at the center of the multifocal focusing mirror.

[0064] Specifically, the laser can be a fiber laser, a disc laser, a diode-pumped solid-state laser, a high-power gas laser, or a semiconductor laser, with fiber lasers being preferred. Preferably, the fiber core diameter of the fiber laser is 1μm to 100μm, more preferably 10μm to 50μm. Using a small core diameter laser helps to reduce the divergence angle of the laser beam, thereby obtaining a laser beam with a larger depth of focus. By using a fiber laser with the above parameters in conjunction with a multifocal design, a laser beam with a divergence half-angle of 2° to 8° and a depth of focus of 30mm to 80mm can be obtained.

[0065] Furthermore, in this invention, the collimating lens has a diameter of 20mm to 60mm, preferably 30mm to 50mm, a thickness of 2mm to 15mm, preferably 4mm to 10mm, and a focal length of 50mm to 200mm, preferably 70mm to 150mm. The protective lens has a diameter of 20mm to 60mm, preferably 30mm to 50mm, and a thickness of 1mm to 15mm, preferably 3mm to 10mm. The multifocal focusing lens 3 is located 10mm to 300mm below the collimating lens, preferably 50mm to 150mm. The multifocal focusing lens 3 has a diameter of 20mm to 60mm, preferably 30mm to 50mm, and a center thickness H of 2mm to 15mm, preferably 4mm to 10mm. Using these parameters allows the laser beam to pass through the cutting nozzle without energy loss, and the multifocal design ensures that the focal point of the laser beam acts below the workpiece surface.

[0066] Specifically, the protective lens, collimating lens, and multifocal focusing lens have two surfaces coated with an anti-reflection film that is the same as or similar to the wavelength of the laser beam. This increases the transmittance of the laser beam and prevents reflection from optical components, thus avoiding energy loss or even damage to the optical components. Furthermore, the collimating lens, multifocal focusing lens, and protective lens are replaceable. In this invention, the collimating lens, multifocal focusing lens, and protective lens can all be installed on the mounting base via a plug-in method, facilitating inspection of the optical system for damage or contamination and enabling lens replacement. For example, horizontally arranged mounting slots are provided at corresponding positions for the protective lens, collimating lens, and multifocal focusing lens. All components, including the protective lens, collimating lens, and multifocal focusing lens, can be inserted into the mounting slots as a whole, making replacement very convenient.

[0067] like Figure 4 As shown, the cutting nozzle 4 has a main channel 4.1 and a mixed gas channel 4.2. The main channel 4.1 is used for the multi-focus laser beam and cutting gas to pass through, and the mixed gas channel 2.41 is used for the combustion gas and combustion-supporting gas to pass through. The multi-focus laser beam, cutting gas, combustion gas and combustion-supporting gas together act on the workpiece to be cut to realize flame-assisted laser cutting of the workpiece.

[0068] Specifically, the cutting nozzle 4 includes a nozzle body, wherein a main channel 4.1 is located in the middle of the nozzle body and is coaxially arranged with the nozzle body. The upper end of the main channel 4.1 serves as the inlet for the cutting gas and the laser beam output from the laser. The laser beam is transformed into a multifocal laser beam after passing through a multifocal lens. The lower end of the main channel 4.1 serves as the outlet for the cutting gas and the multifocal laser beam, and the lower end is designed as a Laval structure 4.3. This Laval structure 4.3 is used to ensure that the flow velocity of the cutting gas reaches a supersonic state when leaving the main channel 4.1, thereby effectively blowing away the liquid metal in the kerf. A mixed gas channel 4.2 is located on the side of the nozzle body and is used to output the mixed gas (combustion gas and combustion-supporting gas) from the lower end of the nozzle body. Preferably, the mixed gas channel 4.2 is arranged around the main channel 4.1. In order to make the outer flame with the highest flame temperature act on the surface of the workpiece to be cut, the distance from the bottom of the cutting nozzle to the workpiece surface is set to 1mm to 10mm, preferably in the range of 3mm to 8mm. The energy generated by the flame-assisted laser cutting of the present invention includes the incident energy of the high-energy-density laser beam, the heat of flame combustion, and the energy generated by the exothermic reaction of oxygen-iron combustion. Through the combined effect of the above three, flame-assisted laser cutting of thick metal materials has outstanding advantages.

[0069] Furthermore, to ensure uniform energy distribution of the high-temperature flame generated by the mixed gas along the outlet direction of the cutting nozzle, the upper end of the mixed gas channel 4.2 is designed as an annular groove, and the lower end is designed as multiple strip-shaped grooves evenly distributed (equally spaced) along the circumference of the nozzle body. These strip-shaped grooves are connected to the annular groove and are arranged vertically. In other words, the lower end of the mixed gas channel 4.2 is configured as an array of gas channels. The fully mixed gas is ignited after passing through each gas channel to form a high-temperature flame. The equally spaced gas channels ensure uniform temperature distribution in all directions of the flame. The cross-section of the strip-shaped grooves can be U-shaped, rectangular, square, or any other feasible shape; this invention is not limited to any particular shape. Additionally, the gas channels are at a certain angle to the axis of the cutting nozzle. The length of the gas channels is 5mm to 30mm, the cone angle is 10° to 30°, and the depth gradually increases along the outlet direction of the cutting nozzle, with a depth of 0.5 to 3mm at the outlet. During cutting, the laser beam and cutting gas pass through the burning flame, making the heated area of ​​the workpiece hotter. The high temperature of the heated area, in turn, makes its energy absorption rate of the laser beam higher. Therefore, the reaction at the metal / laser / oxygen interface is more intense. The viscosity of the metal oxides and liquid metal formed at the cut is lower. Under the action of accelerated high-pressure gas, they can be blown away at a faster speed, thus obtaining a higher cutting speed and a steeper, smoother cut.

[0070] In this invention, the cutting gas is generally oxygen, which can be oxygen of ordinary purity or oxygen in a high-purity, high-pressure state; the combustion gas is generally organic combustion gas such as propane, acetylene, or natural gas; the combustion-supporting gas is low-pressure oxygen with a pressure of 0.1 bar to 2 bar, which acts as a combustion-supporting agent to react with the combustion gas to produce a high-temperature flame.

[0071] Specifically, the Laval structure 4.3 is used to accelerate the cutting gas, bringing its flow rate to supersonic speeds, thereby aiding combustion and blowing the liquid metal away from the kerf. In this invention, the Laval structure 4.3 is integrally formed with the main channel 4.1, meaning the Laval structure 4.3 is directly formed on the inner wall of the main channel 4.1, or the Laval structure 4.3 is an independent structural component embedded in the lower end of the main channel 4.1. The cutting gas is continuously accelerated as it passes through the Laval structure, reaching the workpiece surface and even the bottom of the kerf at supersonic speeds.

[0072] As a preferred embodiment, the Laval structure 4.3 has a structure that first contracts, then straightens, and then expands. Specifically, the Laval structure 4.3 includes a contraction section, a straight section, and an expansion section arranged sequentially from top to bottom. The cutting gas is continuously accelerated as it passes through the Laval structure 4.3, achieving a supersonic velocity at the final exit. This increases the gas stiffness and ensures high oxygen purity throughout the entire workpiece thickness range, leading to a more complete oxygen-iron combustion reaction and better slag removal. Furthermore, the slender Laval structure effectively reduces the nozzle diameter, significantly decreasing the consumption of the main cutting gas, thereby improving cutting quality and efficiency while reducing cutting costs. In addition, the Laval structure design prevents the gas exiting the cutting nozzle from generating shock waves that could affect cutting quality. Simultaneously, it maintains a high velocity and pressure of the cutting gas at the bottom of the workpiece, improving cutting quality and speed and mitigating issues such as bottom slag buildup.

[0073] Preferably, the total length of the cutting nozzle 4 is 30mm to 100mm, more preferably 60mm to 90mm, and the inlet diameter of the main channel 4.1 of the cutting nozzle 4 is 1mm to 20mm. The Laval structure 4.3 is narrow and long, with a total length of 5mm to 50mm, preferably 10mm to 20mm. The cone angle of the contraction section is 10° to 65°, the inner diameter of the narrowest part of the straight section is 0.5mm to 5mm, preferably 1mm to 3mm, and the cone angle of the expansion section is 5° to 15°. The Laval structure designed with these parameters can effectively accelerate the cutting gas, making the flow rate of the cutting gas reach a supersonic state at the outlet of the cutting nozzle. This ensures that the cutting gas at the bottom of the kerf has a high concentration (oxygen content) and stiffness, thereby achieving the simultaneous maintenance of the oxygen-iron combustion reaction at the bottom of the kerf and the removal of molten liquid metal and its oxides, greatly improving cutting efficiency and cutting quality.

[0074] Compared with flame-assisted single-focus laser cutting technology, the flame-assisted multi-focus laser cutting technology provided by this invention utilizes a multi-focus laser beam 1.3 with a large depth of focus and a small spot diameter, and combines it with the Laval structure 4.3 of the cutting nozzle to accelerate the cutting gas. This allows for the use of a lower-power laser to cut thicker metal materials. At the same time, the diameter of the cutting nozzle 4 can be reduced to 1.25 mm or even smaller. Using a small-diameter cutting nozzle 4 during cutting consumes less cutting gas under the same conditions, thereby significantly improving cutting efficiency, improving kerf quality, and reducing cutting costs.

[0075] Furthermore, such as Figure 7As shown, the cutting nozzle also includes an air intake assembly, which includes a gas mixing component 4.4 and an air intake component 4.5 connected to each other. The gas mixing component 4.4 is located between the air intake component 4.5 and the mixed gas passage 4.2. The air intake component 4.5 is used to send the combustion gas and the combustion-supporting gas into the gas mixing component 4.4 through different inlets. The gas mixing component 4.4 is used to mix the combustion gas and the combustion-supporting gas and then send them into the mixed gas passage 4.2.

[0076] As a preferred embodiment, such as Figure 7 As shown, the air intake component 4.5 has an injection-suction structure, including two inlets, both of which are connected to the gas mixing component 4.4. One inlet is located in the middle of the air intake component for inputting combustion-supporting gas, and the other inlet is arranged around the middle inlet for inputting combustion gas. Generally, the pressure of the combustion-supporting gas is higher than that of the combustion gas. In this invention, the pressure of the combustion gas is 0.05 bar to 0.4 bar, and the pressure of the combustion-supporting gas is 0.1 bar to 2 bar. During cutting, the combustion-supporting gas enters the gas mixing component 4.4 through the middle inlet of the air intake component 4.5. Since the higher-pressure combustion-supporting gas enters the gas mixing component 4.4 first, a certain degree of negative pressure is formed at the inlet of the gas mixing component 4.4. Then, the lower-pressure combustion gas is drawn into the gas mixing component 4.4 under the negative pressure environment and mixes with the combustion-supporting gas in the gas mixing component 4.4 to form a mixed gas. The mixed gas then flows into the mixed gas channel 4.2 of the nozzle. The jet-suction structure of the cutting nozzle can not only reduce the pressure of the combustion gas used for cutting, but also the longer gas mixing component can make the mixing path of the combustion gas and the combustion gas longer and more uniform, so that the mixed gas can burn more completely and release more heat energy, thereby effectively improving the speed of flame-assisted laser cutting of metal sheets and the energy utilization rate during the cutting process.

[0077] Specifically, the gas mixing component 4.4 is provided with a mixing chamber, which includes a contraction section, a straight section, and an expansion section arranged sequentially. The contraction section serves as the input end for the combustion gas and the combustion-supporting gas, the straight section serves as the mixing section for the combustion gas and the combustion-supporting gas, and the expansion section serves as the output end for the combustion gas and the combustion-supporting gas. The combustion-supporting gas and the combustion gas enter the mixing chamber after passing through the jet-type air intake structure, where they are pre-mixed. The pre-mixed gas then enters the mixing gas channel 4.2 for further mixing, ensuring that the gas is fully mixed before the output nozzle. Preferably, the diameter of the straight section of the mixing chamber is 0.5 mm to 5 mm, more preferably 0.8 to 1.8 mm, and the length is 10 mm to 100 mm, more preferably 20 to 40 mm. The mixing chamber designed with these parameters can effectively increase the gas mixing path, making the mixed gas more uniform, the combustion more complete, and releasing more heat energy, thereby improving energy utilization and cutting speed. In addition, the longer gas mixing structure can effectively reduce the length of the mixed gas channel in the nozzle, thereby shortening the overall length of the nozzle and reducing the size of the nozzle, which is more conducive to the laser beam passing through the cutting nozzle without energy loss.

[0078] The following are embodiments of the present invention.

[0079] Example 1

[0080] like Figure 1 As shown, this embodiment of the invention provides a method for flame-assisted laser cutting of metal materials based on dual focus. Specifically, the method involves: a laser beam 1.1 with a certain divergence angle output from laser 1 is transformed into a parallel beam 1.2 by beam conversion unit 2. The parallel beam 1.2 is then converted into a multi-focus laser beam 1.3 with a greater depth of focus, a smaller divergence angle, and a focal point located inside the workpiece after passing through multi-focus focusing lens 3. A mixture 6 of combustion gases such as propane or acetylene and low-pressure oxygen (combustion-supporting gas) is mixed in a mixed gas channel 4.2 and ignited at the nozzle outlet. Simultaneously, the multi-focus laser beam 1.3 and the cutting gas 5 (high-pressure oxygen) act on the workpiece 7 to be cut after passing through the main channel 4.1 with a Laval structure 4.3. Under the combined action of the multi-focus laser beam 1.3 and the high-temperature flame, the workpiece 7 rapidly melts, oxidizes, and even vaporizes. The molten liquid metal and its oxides are blown away by the cutting gas 5. Meanwhile, the cutting nozzle moves along a set cutting path driven by an external robot or machine tool, thereby achieving the cutting of the workpiece.

[0081] Example 2

[0082] This embodiment provides a design description for a bifocal focusing lens. For example... Figure 2As shown, the bifocal focusing lens is a plano-convex lens, and its convex surface has three different curved surfaces S1, S2, and S3 along the edge direction from the center of the lens. The focal lengths of the two focal points (P1, P2) of the bifocal focusing lens are 400mm and 420mm, respectively. Curved surface S1 is the focal surface corresponding to the focal length of 420mm, and curved surface S3 is the focal surface corresponding to the focal length of 400mm. Curved surface S3 is the transition surface connecting the two focal surfaces. The focusing lens diameter is set to 37mm, the center thickness is 8mm, the material refractive index is 1.45, and the radii r1 and r3 of curved surfaces S1 and S3 are 3mm and 7mm, respectively. Substituting the above parameters into formula (1) can calculate the equation y1(r) of curved surface S1 and the equation y3(r) of curved surface S3. In addition, substituting the above parameters into formula (2) can calculate the focal length of the transition surface S2. Where 3≤r≤7, and then substituting the focal length of the transition surface S2 into formula (1), we can obtain the equation y2(r) of the transition surface S2. Using the three surface equations y1(r), y2(r) and y3(r), we can model the F400-F420 bifocal focusing lens, such as Figure 2 As shown, the lens model is imported into optical simulation software (such as Zemax) for optical simulation. If the lens model meets the actual requirements, it can be manufactured according to the engineering drawings of the output lens model.

[0083] Example 3

[0084] like Figure 1 As shown, this embodiment uses a 1kW fiber laser to cut low carbon steel with a thickness of 30mm. The inner diameter of the narrowest part of the Laval structure of the cutting nozzle is 1.1mm and the length is 10mm. The height d of the nozzle from the workpiece surface is 4mm. The laser beam output by the laser becomes a parallel beam after passing through a collimating lens with a focal length of 100mm and is perpendicularly incident on a bifocal focusing lens of F400-F420. The parallel beam is transformed into a bifocal (P1, P2) beam under the action of the bifocal focusing lens. The distance S between the two focal points is 20mm. The distance Δf from the P1 focal point to the surface of the workpiece to be cut is 5mm. Before cutting begins, the low-pressure oxygen output pressure is adjusted to 0.03 MPa and the combustion gas output pressure is adjusted to 0.02 MPa. After the two gases are mixed evenly in the mixed gas channel, they are ignited at the outlet of the cutting nozzle. Then, the main cutting oxygen at a pressure of 0.7 MPa is introduced into the main channel. At the same time, the laser beam is input and transformed into a multi-focus laser beam. The multi-focus laser beam, the cutting gas, and the high-temperature flame act on the same area of ​​the surface of the workpiece to be cut. Under the action of the three energies released by the high-energy laser beam, the high-temperature flame, and the oxygen-iron combustion reaction, the workpiece to be cut melts or even vaporizes rapidly, forming a kerf. The workpiece is cut at a speed of 0.5 m / min. The average roughness of the cut surface of the workpiece is about 20 μm, the perpendicularity is about 88°, and there is basically no slag at the bottom of the kerf.

[0085] Example 4

[0086] In this embodiment, a 1kW fiber laser is used to cut low-carbon steel with a thickness of 30mm. The cutting nozzle is a flame-assisted laser cutting nozzle with a Laval structure. The narrowest inner diameter of the nozzle is 1.1mm and the length is 10mm. The height d of the nozzle from the workpiece surface is 4mm. The laser beam output by the laser is collimated into a parallel beam after passing through a collimating lens with a focal length of 100mm and is perpendicularly incident on a bifocal focusing lens of F400-F420. The parallel beam is transformed into a bifocal (P1, P2) beam under the action of the bifocal focusing lens. The distance S between the two focal points is 20mm. The distance Δf from the P1 focal point to the surface of the workpiece to be cut is 5mm. Before cutting begins, the low-pressure oxygen output pressure is adjusted to 0.1 MPa and the combustion gas output pressure to 0.01 MPa. After the two gases are fully mixed in the mixing chamber of the jet-suction cutting nozzle, they enter the mixed gas channel of the nozzle and are then ignited at the outlet of the cutting nozzle. Subsequently, the main cutting oxygen at a pressure of 0.7 MPa is introduced into the main channel. At the same time, the laser beam is input and transformed into a multi-focus laser beam, so that the multi-focus laser beam, the cutting gas and the high-temperature flame act on the same area of ​​the surface of the workpiece to be cut. Under the action of the three energies released by the high-energy laser beam, the high-temperature flame and the oxygen-iron combustion reaction, the workpiece to be cut melts or even vaporizes rapidly, forming a kerf. The workpiece is cut at a speed of 0.7 m / min. The average roughness of the cut surface of the workpiece is about 18 μm, the perpendicularity is about 88.7°, and there is basically no slag at the bottom of the kerf.

[0087] Example 5

[0088] In this embodiment, a 2.5kW fiber laser is used to cut 40mm thick low-carbon steel. The inner diameter of the narrowest part of the Laval structure of the cutting nozzle is 1.25mm and the length is 15mm. The height d of the nozzle from the workpiece surface is 4mm. The laser beam output by the laser is transformed into a parallel beam after passing through a collimating lens with a focal length of 100mm and is perpendicularly incident on a bifocal focusing lens of F400-F420. The parallel beam is transformed into a bifocal (P1, P2) beam under the action of the bifocal focusing lens. The distance S between the two focal points is 20mm. The distance Δf from the P1 focal point to the surface of the workpiece to be cut is 10mm. Before cutting begins, the low-pressure oxygen output pressure is adjusted to 0.04 MPa and the combustion gas output pressure to 0.03 MPa. After the two gases are mixed evenly in the mixed gas channel, they are ignited at the outlet of the cutting nozzle. Then, the main cutting oxygen at a pressure of 0.8 MPa is introduced into the main channel, and at the same time, a multi-focus laser beam is input so that the cutting gas and the laser beam act on the same area of ​​the surface of the workpiece to be cut. Under the combined action of the three energies released by the high-energy laser beam, the high-temperature flame and the oxygen-iron combustion reaction, the workpiece to be cut melts or even vaporizes rapidly, forming a kerf. The workpiece is cut at a speed of 0.68 m / min. The average roughness of the cut surface of the workpiece is about 28 μm, the perpendicularity is about 87.2°, and there is basically no slag at the bottom of the kerf.

[0089] Example 6

[0090] In this embodiment, a 3.5kW fiber laser is used to cut 50mm thick low carbon steel. The inner diameter of the narrowest part of the Laval structure of the cutting nozzle is 1.5mm and the length is 20mm. The height d of the nozzle from the workpiece surface is 4mm. The laser beam output by the laser is transformed into a parallel beam after passing through a collimating lens with a focal length of 100mm, and is perpendicularly incident on a bifocal focusing lens of F400-F420. The parallel beam is transformed into a bifocal (P1, P2) beam under the action of the bifocal focusing lens. The distance S between the two focal points is 20mm, and the distance Δf from the P1 focal point to the surface of the workpiece to be cut is 15mm. Before cutting begins, the low-pressure oxygen output pressure is adjusted to 0.05 MPa and the combustion gas output pressure to 0.04 MPa. After the two gases are mixed evenly in the mixed gas channel, they are ignited at the outlet of the cutting nozzle. Then, the main cutting oxygen at a pressure of 0.9 MPa is introduced into the main channel, and at the same time, a multi-focus laser beam is input so that the cutting gas and the laser beam act on the same area of ​​the surface of the workpiece to be cut. Under the action of the three energies released by the high-energy laser beam, the high-temperature flame and the oxygen-iron combustion reaction, the workpiece to be cut is rapidly melted, oxidized and even vaporized to form a kerf. The workpiece is cut at a speed of 0.62 m / min. The average roughness of the cut surface of the workpiece is about 32 μm, the perpendicularity is about 86.6°, and there is basically no slag at the bottom of the kerf.

[0091] Example 7

[0092] In this embodiment, a fiber laser with a maximum power of 4kW is used to cut low carbon steel with a thickness of 30mm. The inner diameter of the narrowest part of the cutting nozzle Laval structure is 1.25mm and the length is 10mm. The height d of the nozzle from the workpiece surface is 4mm. The laser beam output by the laser is transformed into a parallel beam after passing through a collimating lens with a focal length of 100mm, and is perpendicularly incident on a bifocal focusing lens of F400-F420. The parallel beam is transformed into a bifocal (P1, P2) beam under the action of the bifocal focusing lens. The distance S between the two focal points is 10mm, and the distance Δf from the P1 focal point to the surface of the workpiece to be cut is 5mm. Before cutting begins, the output pressure of low-pressure oxygen is adjusted to 0.04 MPa and the output pressure of combustion gas is adjusted to 0.05 MPa. After the two gases are mixed evenly in the mixed gas channel, they are ignited at the outlet of the cutting nozzle to generate a high-temperature flame. Then, the main cutting oxygen at a pressure of 0.7 MPa is introduced into the main channel, and at the same time, a multi-focus laser beam is input so that the cutting gas and the laser beam act on the same area of ​​the surface of the workpiece to be cut. Under the action of the three energies released by the high-energy laser beam, the high-temperature flame and the oxygen-iron combustion reaction, the workpiece to be cut is rapidly melted, oxidized and even vaporized to form a kerf. The workpiece is cut at a speed of 1.3 m / min. The average roughness of the cut surface of the workpiece is about 22 μm, the perpendicularity is about 88.3°, and there is basically no slag at the bottom of the kerf.

[0093] Example 8

[0094] As the workpiece thickness increases, the distance S between the two focal points is increased to ensure a higher melt temperature at the bottom of the kerf. In this embodiment, a fiber laser with a maximum power of 4kW is used to cut 60mm thick low-carbon steel. The inner diameter of the narrowest part of the Laval structure of the cutting nozzle is 1.5mm, and the length is 20mm. The height d of the nozzle from the workpiece surface is 6mm. The laser beam output from the laser becomes a parallel beam after passing through a collimating lens with a focal length of 100mm and is perpendicularly incident on a bifocal focusing lens of F400-F430. Under the action of the bifocal focusing lens, the parallel beam is transformed into a bifocal (P1, P2) beam. The distance S between the two focal points is 30mm, and the distance Δf from the P1 focal point to the surface of the workpiece to be cut is 10mm. Before cutting begins, the output pressure of low-pressure oxygen is adjusted to 0.04 MPa and the output pressure of combustion gas is adjusted to 0.03 MPa. After the two gases are mixed evenly in the mixed gas channel, they are ignited at the outlet of the cutting nozzle to generate a high-temperature flame. Then, the main cutting oxygen at a pressure of 0.8 MPa is introduced into the main channel, and at the same time, the laser beam is input and focused by the multifocal lens to become a multifocal laser beam. The laser beam, the cutting gas and the combustion gas act on the same area of ​​the surface of the workpiece to be cut. Under the action of the three energies released by the high-energy laser beam, the high-temperature flame and the oxygen-iron combustion reaction, the workpiece to be cut melts or even vaporizes rapidly, forming a kerf. The workpiece is cut at a speed of 0.8 m / min. The average roughness of the cut surface of the workpiece is about 35 μm, the perpendicularity is about 86.7°, and there is basically no slag at the bottom of the kerf.

[0095] Example 9

[0096] like Figure 5As shown, a 4kW fiber laser is used to cut 120mm thick low-carbon steel. The laser beam output by the laser is collimated by a collimating lens with a focal length of 100mm and becomes a parallel beam, which is then perpendicularly incident on a trifocal focusing lens with a focal length of F400-F430-F460. The parallel beam is transformed into a trifocal (P1, P2, P3) beam under the action of the trifocal focusing lens. The distances between adjacent focal points S1 and S2 are 30mm, and the distance Δf from focal point P1 to the surface of the workpiece to be cut is 15mm. The inner diameter of the Laval structure of the cutting nozzle is 1.8mm and the length is 20mm. The height of the nozzle from the surface of the workpiece is 6mm. Before cutting begins, the output pressure of low-pressure oxygen is adjusted to 0.05 MPa and the output pressure of combustion gas is adjusted to 0.04 MPa. The two gases are mixed evenly in the mixed gas channel and ignited at the nozzle outlet to generate a high-temperature flame. Then, main cutting oxygen at a pressure of 1 MPa is introduced into the main channel, and a laser beam is simultaneously input. After passing through a multi-focus focusing lens, it is transformed into a multi-focus laser beam, so that the cutting gas, high-temperature flame and laser beam act on the same area of ​​the surface of the workpiece to be cut. Under the action of the three energies released by the high-energy laser beam, high-temperature flame and oxygen-iron combustion reaction, the workpiece to be cut melts or even vaporizes rapidly, forming a kerf. The workpiece is cut at a speed of 0.4 m / min. The average roughness of the cut surface of the workpiece is about 68 μm, the perpendicularity is about 86°, and there is basically no slag at the bottom of the kerf.

[0097] Example 10

[0098] like Figure 6As shown, a 6kW continuous single-mode fiber laser inputs a high-power-density laser beam into the optical system via an optical fiber. The incident beam, with a certain divergence angle, is transformed into a parallel beam after passing through a biconvex aspherical collimating lens with a diameter of 37mm, a thickness of 8mm, and a focal length of 100mm. This parallel beam is then perpendicularly incident on the upper surface of a bifocal focusing lens with a diameter of 37mm, a thickness of 7mm, and a focal length of F400-F420. Under the action of the bifocal focusing lens, the parallel beam becomes a bifocal laser beam with two focal points distributed along the optical axis. Subsequently, it passes through a cutting nozzle and acts on the surface of a 30mm thick low-carbon steel plate. The total length of the cutting nozzle is 90mm, the inlet diameter is 5.5mm, the length of the Laval structure at the bottom of the main channel is 20mm, and the inner diameter at the narrowest point of the straight section is 1.25mm. During cutting, the pressure of low-pressure oxygen is adjusted to 0.04 MPa and the pressure of combustion gas is 0.05 MPa. The mixture of low-pressure oxygen and combustion gas is mixed in the mixing channel of the cutting nozzle and ignited at the nozzle outlet. Then, the main cutting oxygen at a pressure of 0.7 MPa is introduced while a multi-focus laser beam is input. The workpiece to be cut is rapidly melted or even vaporized under the action of the three energies released by the high-energy laser beam, the high-temperature flame and the oxygen-iron combustion reaction to form a kerf. This achieves cutting of the workpiece at a speed of 1.5 m / min. The average roughness of the cut surface of the workpiece is about 18.4 μm, the perpendicularity is about 89°, and there is basically no slag at the bottom of the kerf.

[0099] Example 11

[0100] A 6kW fiber laser is used to cut 160mm thick low-carbon steel. The laser beam output is collimated by a 100mm focal length lens and becomes a parallel beam, which is then perpendicularly incident on a four-focal focusing lens with F400-F440-F480-F520. The parallel beam is transformed into a four-focal beam under the action of the four-focal focusing lens. The distance between adjacent focal points is 40mm. The distance Δf from the F400 focal point to the surface of the workpiece is 15mm. The Laval structure of the cutting nozzle has an inner diameter of 2mm at its narrowest point and a length of 20mm. The height of the nozzle from the workpiece surface is 6mm. Before cutting begins, the output pressure of low-pressure oxygen is adjusted to 0.05 MPa and the output pressure of combustion gas is adjusted to 0.04 MPa. The two gases are mixed evenly in the mixed gas channel and ignited at the nozzle outlet to generate a high-temperature flame. Then, main cutting oxygen at a pressure of 1 MPa is introduced into the main channel, and a multi-focus laser beam is simultaneously input so that the cutting gas and the laser beam act on the same area of ​​the surface of the workpiece to be cut. Under the action of the three energies released by the high-energy laser beam, the high-temperature flame and the oxygen-iron combustion reaction, the workpiece to be cut rapidly melts or even vaporizes to form a kerf, achieving a cutting speed of 0.4 m / min. The average roughness of the cut surface of the workpiece is about 102 μm, the perpendicularity is about 85.3°, and there is basically no slag at the bottom of the kerf.

[0101] Example 12

[0102] An 8kW fiber laser is used to cut 200mm thick low-carbon steel. The laser beam output is collimated by a 100mm focal length lens and becomes a parallel beam, which is then perpendicularly incident on a five-focal focusing lens with F400-F440-F480-F520-F560. The parallel beam is transformed into a five-focal beam under the action of the five-focal focusing lens. The distance between adjacent focal points is 40mm. The distance Δf from the F400 focal point to the surface of the workpiece is 12mm. The inner diameter of the narrowest part of the Laval structure of the cutting nozzle is 2.5mm, the length is 20mm, and the height of the nozzle from the surface of the workpiece is 6mm. Before cutting begins, the output pressure of low-pressure oxygen is adjusted to 0.1 MPa and the output pressure of combustion gas is adjusted to 0.03 MPa. The two gases are mixed evenly in the mixed gas channel and ignited at the nozzle outlet to generate a high-temperature flame. Then, the main cutting oxygen at a pressure of 0.9 MPa is introduced into the main channel, and a multi-focus laser beam is simultaneously input so that the cutting gas and the laser beam act on the same area of ​​the surface of the workpiece to be cut. Under the action of the three energies released by the high-energy laser beam, the high-temperature flame and the oxygen-iron combustion reaction, the workpiece to be cut is rapidly melted or even vaporized to form a kerf, achieving a cutting speed of 0.3 m / min. The average roughness of the cut surface of the workpiece is about 148 μm, the perpendicularity is about 85°, and there is basically no slag at the bottom of the kerf.

[0103] Example 13

[0104] In this embodiment, a 1kW green or blue laser is used to cut copper or copper alloys and other non-ferrous metals with a thickness of 12mm. The inner diameter of the narrowest part of the Laval structure of the cutting nozzle is 0.9mm and the length is 10mm. The height d of the nozzle from the workpiece surface is 4mm. The laser beam output by the laser is transformed into a parallel beam after passing through a collimating lens with a focal length of 100mm, and is perpendicularly incident on a bifocal focusing lens of F400-F410. The parallel beam is transformed into a bifocal (P1, P2) beam under the action of the bifocal focusing lens. The distance S between the two focal points is 10mm, and the distance Δf from the P1 focal point to the surface of the workpiece to be cut is 1mm. Before cutting begins, the low-pressure oxygen output pressure is adjusted to 0.05 MPa and the combustion gas output pressure is adjusted to 0.04 MPa. After the two gases are mixed evenly in the mixing gas channel, they are ignited at the outlet of the cutting nozzle. Then, the main cutting oxygen at a pressure of 1.0 MPa is introduced into the main channel, and at the same time, a multi-focus laser beam is input so that the cutting gas and the laser beam act on the same area of ​​the surface of the workpiece to be cut. Under the combined action of the high-energy laser beam and the high-temperature flame, the workpiece to be cut melts rapidly to form a kerf, achieving a cutting speed of 0.55 m / min. The average roughness of the cut surface of the workpiece is about 41 μm, the perpendicularity is about 88.2°, and there is basically no slag at the bottom of the kerf.

[0105] Example 14

[0106] In this embodiment, a 1kW green or blue laser is used to cut aluminum or aluminum alloy and other non-ferrous metals with a thickness of 15mm. The inner diameter of the narrowest part of the Laval structure of the cutting nozzle is 1.25mm and the length is 10mm. The height d of the nozzle from the workpiece surface is 4mm. The laser beam output by the laser is transformed into a parallel beam after passing through a collimating lens with a focal length of 100mm, and is perpendicularly incident on a bifocal focusing lens of F400-F410. The parallel beam is transformed into a bifocal (P1, P2) beam under the action of the bifocal focusing lens. The distance S between the two focal points is 10mm, and the distance Δf from the P1 focal point to the surface of the workpiece to be cut is 3mm. Before cutting begins, the low-pressure oxygen output pressure is adjusted to 0.05 MPa and the combustion gas output pressure is adjusted to 0.04 MPa. After the two gases are mixed evenly in the mixing gas channel, they are ignited at the outlet of the cutting nozzle. Then, the main cutting oxygen at a pressure of 0.8 MPa is introduced into the main channel, and at the same time, a multi-focus laser beam is input so that the cutting gas and the laser beam act on the same area of ​​the surface of the workpiece to be cut. Under the combined action of the high-energy laser beam and the high-temperature flame, the workpiece to be cut melts rapidly to form a kerf, achieving a cutting speed of 0.5 m / min. The average roughness of the cut surface of the workpiece is about 56 μm, the perpendicularity is about 87.6°, and there is basically no slag at the bottom of the kerf.

[0107] Comparative Example 1

[0108] Referring to Example 1 of patent CN201410160921.4 (Laser-Flame Composite Cutting Method), the laser-flame composite cutting method and device were used to perform laser-flame composite cutting on a 30mm thick low-carbon steel plate. The laser power was 5.5kW, the propane pressure was 0.05MPa (0.5bar), the main cutting oxygen pressure was 0.25MPa (2.5bar), and the auxiliary combustion oxygen pressure was 0.04MPa (0.4bar). The laser focus was located 15mm above the surface of the steel plate, and the lower edge of the laser nozzle was 5mm away from the surface of the steel plate. Finally, the cutting speed was 1.0m / min until the steel plate was broken. The laser used was a 6kW dish solid-state laser with continuous wave laser output mode. The fiber diameter was 0.2mm, the collimation focal length was 200mm, and the focal length of the focusing lens was 600mm.

[0109] Comparative Example 2

[0110] Referring to Example 2 of patent CN201410160921.4 (Laser-Flame Composite Cutting Method), the laser-flame composite cutting method and device were used to perform laser-flame composite cutting on a 140mm thick low-carbon steel plate. The laser power was 6kW, the propane pressure was 0.05MPa (0.5bar), the main cutting oxygen pressure was 0.35MPa (3.5bar), and the auxiliary combustion oxygen pressure was 0.04MPa (0.4bar). The laser focus was located 15mm above the surface of the steel plate, and the lower edge of the laser nozzle was 5mm away from the surface of the steel plate. Finally, the cutting speed was 0.3m / min until the steel plate was broken. The laser used was a 6kW dish solid-state laser with continuous wave laser output mode, fiber diameter of 0.2mm, collimation focal length of 200mm, and focal length of focusing lens of 600mm.

[0111] A comparison of Comparative Example 1 and Embodiment 7 of the present invention shows that the flame-assisted multi-focus laser cutting technology provided by the present invention, under the premise of the same workpiece thickness, can achieve the cutting of thick plates using lower laser power (4kW vs 5.5kW) and faster cutting speed (1.3m / min vs 1.0m / min). A comparison of Comparative Example 2 and Embodiment 11 of the present invention shows that, under the same laser power, the flame-assisted multi-focus laser cutting technology provided by the present invention can cut thicker workpieces (160mm vs 140mm) at a faster cutting speed (0.4m / min vs 0.3m / min).

[0112] The multi-focal laser beam of this invention has a greater depth of focus, a smaller divergence angle, and a smaller spot diameter within the depth of focus range (0.5mm to 1.5mm). Therefore, during the cutting process, the laser beam maintains a high energy density over a large range (10mm to 200mm) along the workpiece thickness direction, ensuring that the laser beam's focus can penetrate a considerable distance below the workpiece surface (negative defocus), thus achieving higher laser cutting efficiency and kerf quality. This invention utilizes a multi-focal laser beam with a large depth of focus (30mm to 80mm) and a small spot diameter (0.5mm to 1.5mm), combined with high-pressure oxygen acceleration via a cutting nozzle, allowing the use of a lower-power (below 2kW) laser to cut thicker metal materials, thereby significantly improving cutting efficiency, kerf quality, and reducing cutting costs. This invention employs multifocal flame-assisted cutting technology, which allows for a sufficiently small focused spot diameter (0.5mm–1.5mm) and a sufficiently long focal depth (30mm–80mm) for the laser beam. Therefore, even with a smaller diameter nozzle, the multifocal laser beam can pass through the cutting nozzle without energy loss, and the focal point of the multifocal laser beam can penetrate deep into the workpiece, achieving negative defocus cutting. Furthermore, the greater focal depth of the multifocal beam provides a wider focus adjustment range, allowing the laser beam's focus to be adjusted to different positions above, on the surface, or inside the workpiece according to different cutting process requirements, thus meeting the cutting needs of different thicknesses and types of metal materials. In addition, the cutting nozzle continuously accelerates high-pressure oxygen, ensuring that the oxygen concentration, flow rate, and stiffness in the area being cut remain at a high level, resulting in a more complete oxygen-iron reaction, releasing more heat energy, better slag removal, and improved cutting speed and kerf quality. Simultaneously, the smaller nozzle diameter reduces the consumption of cutting gas, lowering cutting costs. The cutting technology provided by this invention is particularly suitable for laser cutting of thick metal materials (over 50mm), and can also cut thin metal materials. Furthermore, the pressure and purity of the cutting gas have a significant impact on cutting quality. Taking Lasox cutting as an example, a 3% decrease in oxygen purity can reduce the cutting speed by 50% or more. Simultaneously, low oxygen flow rate and pressure can lead to insufficient oxygen concentration at the bottom of the material, terminating the exothermic oxygen-iron combustion reaction, and making it difficult to blow away the molten workpiece. This invention, through the design of a Laval structure nozzle, can accelerate the cutting gas, thereby increasing the cutting gas concentration at the bottom of the kerf. This maintains a high level of cutting gas flow rate and pressure at the bottom of the workpiece, thus improving cutting quality and speed, and mitigating problems such as slag buildup.

[0113] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A flame-assisted multi-focus laser cutting method for metallic materials, characterized in that, This method utilizes a multifocal laser beam, cutting gas, combustion gas, and combustion-supporting gas to act on the metal workpiece to be cut, thereby achieving flame-assisted laser cutting of the metal workpiece. The multifocal laser beam is realized by a single multifocal focusing lens, which is a monolithic plano-convex lens with one side being a flat surface and the other side being a convex curved surface. The convex curved surface is composed of multiple focal curved surfaces with different curvatures, and the curvature of each focal curved surface gradually increases from the center of the multifocal focusing lens outwards, with a transition surface between adjacent focal curved surfaces. The surface equations of each surface in the monolithic plano-convex lens Determine using the following formula: in, Let be the refractive index of a single plano-convex lens. Let i be the focal length corresponding to surface i. Let be the distance from the edge of surface i to the optical axis of the monolithic plano-convex lens. The thickness at the center of a single plano-convex lens. The surface located at the center of the monolithic plano-convex lens is the focal surface, defined as the first surface, and the surface located at the outermost edge of the monolithic plano-convex lens is defined as the second surface. The surface is curved, and N is the number of focal points of a single plano-convex lens, where N≥2; The focal length of the transition surface Determine using the following formula: in, Let k-1 be the focal length of the surface. Let be the distance from the edge of the curved surface k-1 to the optical axis of the monolithic plano-convex lens. The distance from the edge of the transition surface to the optical axis of the monolithic plano-convex lens is denoted as . , .

2. The flame-assisted multi-focus laser cutting method as described in claim 1, characterized in that, Includes the following steps: S1. Combustion gas and combustion-supporting gas are input into the cutting nozzle and ignited at the outlet below the cutting nozzle to produce a high-temperature flame; S2. The multi-focus laser beam and cutting gas are input from above and output from below the cutting nozzle, and together with the high-temperature flame, they act on the metal workpiece to be cut, realizing flame-assisted laser cutting of the metal workpiece.

3. A flame-assisted multi-focus laser cutting device for metallic materials, characterized in that, The device includes a laser (1), an optical system, and a cutting nozzle (4). The laser (1) is connected to the optical system and is used to provide a laser beam. The optical system is used to convert the laser beam into a multifocal laser beam and guide the multifocal laser beam into the cutting nozzle (4). The cutting nozzle (4) is located below the optical system and has a main channel (4.1) and a mixed gas channel (4.2). The main channel (4.1) is used for the passage of the multifocal laser beam and cutting gas, and the mixed gas channel (4.2) is used for... The multifocal laser beam, cutting gas, combustion gas and combustion gas together act on the metal workpiece to be cut to achieve flame-assisted laser cutting of the metal workpiece; the optical system includes a multifocal focusing lens (3), which is a single plano-convex lens with one side being a plane and the other side being a convex curved surface. The convex curved surface is composed of multiple focal curved surfaces with different curvatures, and the curvature of each focal curved surface gradually increases from the center of the multifocal focusing lens outwards, and the adjacent two focal curved surfaces are transitioned by a transition surface; The surface equations of each surface in the monolithic plano-convex lens Determine using the following formula: in, Let be the refractive index of a single plano-convex lens. Let i be the focal length corresponding to surface i. Let be the distance from the edge of surface i to the optical axis of the monolithic plano-convex lens. The thickness at the center of a single plano-convex lens. The surface located at the center of the monolithic plano-convex lens is the focal surface, defined as the first surface, and the surface located at the outermost edge of the monolithic plano-convex lens is defined as the second surface. The surface is curved, and N is the number of focal points of a single plano-convex lens, where N≥2; The focal length of the transition surface Determine using the following formula: in, Let k-1 be the focal length of the surface. Let be the distance from the edge of the curved surface k-1 to the optical axis of the monolithic plano-convex lens. This is the distance from the edge of the transition surface to the optical axis of the monolithic plano-convex lens. , .

4. The flame-assisted multi-focus laser cutting device as described in claim 3, characterized in that, The optical system further includes a beam conversion unit (2), which is located between the laser (1) and the multifocal focusing mirror (3) and is used to convert the laser beam into a parallel beam and make it perpendicularly incident on the upper surface of the multifocal focusing mirror (3).

5. The flame-assisted multi-focus laser cutting device as described in claim 3, characterized in that, The focal length of the focal surface located at the center of the multifocal focusing lens (3) is 200mm~600mm, the distance between two adjacent focal points is 5mm~50mm, and the light transmission area of ​​other focal surfaces is 1~3 times that of the focal surface located at the center of the multifocal focusing lens.

6. The flame-assisted multi-focus laser cutting device as described in claim 4, characterized in that, The focal length of the focal surface located at the center of the multifocal focusing lens (3) is 300mm~500mm, and the distance between two adjacent focal points is 10mm~40mm.

7. The flame-assisted multi-focus laser cutting apparatus as described in any one of claims 3-6, characterized in that, The cutting nozzle (4) includes a nozzle body, the main channel (4.1) is located in the middle of the nozzle body and is coaxial with the nozzle body, and its lower end is designed as a Laval structure, and the mixed gas channel (4.2) is located on the side of the nozzle body.

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