Laser processing head suitable for long-distance processing

Abstract

The utility model discloses a laser processing head suitable for long-distance processing. The laser processing head comprises a collimating mirror, a beam shaper and a focus lens which are sequentially arranged in the laser transmission direction. Wherein the collimating mirror is used for collimating a laser beam, and the beam shaper is used for expanding the aperture angle of the collimated beam before the collimated beam enters the focusing mirror and increasing the incidence height of the collimated beam; the focus lens is used for converging the annular light with different incident heights in the laser beam to different positions in the optical axis direction to form an axial multi-focus light beam. According to the laser processing head suitable for long-distance processing provided by the utility model, the formation of a main focus near a workpiece is avoided, and enough energy density is formed in an extension area of a light path to support the formation of a laser filament, so that breakdown is not caused, and the laser processing head is suitable for long-distance processing. The problems that in the working process of an existing machining head, generated metal splash and return light return to the interior of the machining head, and a laser beam acts on a nozzle, so that the nozzle is overheated can be solved.

Description

Technical Field

[0001] The utility model relates to the field of laser processing, and particularly relates to a laser processing head suitable for long-distance processing. Background Art

[0002] Laser processing technology is a processing technology that uses the characteristics of the interaction between a laser beam and a substance to cut, weld, surface-treat, drill holes, and micro-machine materials (including metals and non-metals). By converging the laser light at a point and irradiating the surface of the workpiece, the temperature of the workpiece surface rises sharply, causing the irradiated surface of the workpiece to melt or evaporate, and finally cutting or welding the workpiece.

[0003] The vertical distance between the output end of the laser processing head and the surface of the workpiece is usually called the working distance. In order to achieve effective focusing and blowing air at a short distance (protective gas is necessary for cutting and optional for welding), the working distance generally needs to be designed small enough. However, this easily leads to the collision between the nozzle and the workpiece surface (i.e., hitting the plate), and the return light generated during the processing is also likely to enter the inside of the processing head, affecting the optical path therein; at the same time, the short working distance limits the application of the laser processing head in some scenarios, such as remote laser welding.

[0004] It can be understood that raising the design of the nozzle of the processing head is the key to solving the above problems. However, simply raising the nozzle and still using the conventional optical path inside still has the following problems: the divergence angle and spot diameter of the laser beam of the conventional optical path are relatively large. When only the nozzle is raised, some beams with larger apertures will directly act on the nozzle, resulting in too high a temperature of the nozzle. During the actual test process, a 10-minute continuous cutting operation will cause overheating and shutdown.

[0005] Therefore, the utility model aims to provide a non-contact, effectively focusable laser processing head suitable for long-distance processing to prevent metal splash generated during the processing from entering the inside of the nozzle and causing blockage, prevent the return light from entering the inside of the processing head and interfering with the normal operation of the optical path therein, and at the same time solve the overheating problem at the nozzle. Summary of the Utility Model

[0006] In view of the above-mentioned disadvantages of the prior art, the purpose of the utility model is to provide a laser processing head suitable for long-distance processing to prevent metal splash generated during the processing from entering the inside of the nozzle and causing blockage, prevent the return light from entering the inside of the processing head and interfering with the normal operation of the optical path therein, and at the same time solve the overheating problem at the nozzle.

[0007] To achieve the above purpose and other related purposes, the utility model provides a laser processing head suitable for long-distance processing,

[0008] A laser processing head suitable for long-distance processing, the laser processing head includes, arranged in sequence along the laser transmission direction: a collimating mirror, a beam shaper, and a focusing mirror; wherein,

[0009] The collimating mirror is used to collimate the laser beam output by the laser;

[0010] The beam shaper is a conical lens or a spherical mirror, and is used to expand the aperture angle of the collimated beam before it is incident on the focusing mirror and increase the incident height of the collimated beam;

[0011] The focusing mirror is used to converge the annular light with different incident heights in the laser beam to different positions along the optical axis direction respectively, forming an axially multi-focus beam.

[0012] As a preferred solution, the distance between the nozzle of the laser processing head and the workpiece surface is not less than 10 mm.

[0013] As a preferred solution, the conical lens is a plano-concave conical lens, and an inner concave curved surface is formed at the center of the concave surface of the plano-concave conical lens, and the inner concave curved surface is smoothly connected to the concave surface.

[0014] As a preferred solution, the concave surface of the plano-concave conical lens is used as the incident surface.

[0015] As a preferred solution, the conical lens is a plano-convex conical lens, and an outer convex curved surface is formed at the center of the convex surface of the plano-convex conical lens, and the outer convex curved surface is smoothly connected to the convex surface.

[0016] As a preferred solution, the convex surface of the plano-convex conical lens is used as the incident surface.

[0017] As a preferred solution, the focusing mirror is further used to expand the distance between the positions where the laser beams incident from different incident heights are converged on different positions of the optical axis.

[0018] As a preferred solution, the convergence position of the laser beam incident from the far-axis region is closer to the exit surface of the focusing mirror than the convergence position of the laser beam incident from the near-axis region.

[0019] As a preferred solution, the focusing mirror is a double-convex spherical mirror.

[0020] As a preferred solution, the cone angle of the conical lens is between 0.5° - 3°.

[0021] As described above, a laser processing head suitable for long-distance processing provided by the present utility model includes a collimating mirror, a beam shaper, and a focusing mirror in sequence along the laser transmission direction. Among them, the collimating mirror is used to collimate the laser beam output by the laser; the beam shaper is a conical lens or a spherical mirror, and is used to expand the aperture angle of the collimated beam before it is incident on the focusing mirror and increase the incident height of the collimated beam; the focusing mirror is used to converge the annular light with different incident heights in the laser beam to different positions along the optical axis direction respectively, forming a multi-focus beam.

[0022] The utility model raises the incident height of the laser beam through a beam shaper, uses aberration to make the beam focus on different positions on the optical axis, and further sets the focusing lens with reverse curvature, so that the focusing positions of the laser beam on the optical axis are dispersed, and there is a certain distance between each focusing position. The axially multi-focus beam formed thereby can be not affected by the nozzle with the raised design during the processing operation, can meet the defocusing use requirements of the laser processing head, and effectively prevent the metal spatter and the return light generated during the processing from entering the nozzle, causing internal blockage and optical path damage; moreover, the divergence angle of the beam output from the laser processing head of the utility model is extremely small, the change rate of the spot size is low, and the nozzle is less heated; when the lens has a temperature drift, the influence of the beam output from the laser processing head of the utility model on the consistency of the processing section is also small. Description of the Drawings

[0023] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplary illustrations do not limit the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements. Unless otherwise stated, the drawings in the figures do not constitute a proportional limitation.

[0024] Figure 1 is a schematic diagram of the position where the laser converges in the prior art processing;

[0025] Figure 2 is a schematic diagram of the optical path structure in an embodiment of the present application;

[0026] Figure 3 is the effect schematic diagram that can be achieved by adopting the Figure 2 optical path structure;

[0027] Figure 4 is a schematic diagram of the structure of the plano-concave conical lens provided in this embodiment;

[0028] Figure 5 is a schematic diagram of the structure of the plano-convex conical lens provided in this embodiment.

[0029] Figure 6 is a schematic diagram before the improvement of the optical path structure;

[0030] Figure 7 is the effect schematic diagram achieved by adopting the Figure 6 optical path structure;

[0031] Figure 8 is a schematic diagram of the optical path structure in another embodiment of the present application;

[0032] Figure 9 is a schematic diagram of the optical path structure in still another embodiment of the present application;

[0033] Figure 10 This is a schematic diagram of the principle of using a prism to align collimated light to achieve lateral beam narrowing in an embodiment of the present application. Specific implementation manners

[0034] To facilitate the understanding of the present utility model, the present utility model will be described in more detail below with reference to the accompanying drawings and specific embodiments. It should be noted that when an element is expressed as "fixed to" another element, it can be directly on the other element, or there can be one or more intermediate elements therebetween. When an element is expressed as "electrically connected to" another element, it can be directly connected to the other element, or there can be one or more intermediate elements therebetween. The orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "bottom", etc. in this specification is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present utility model and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation to the present utility model. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0035] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the technical field to which the present utility model belongs. The terms used in the specification of the present utility model are only for the purpose of describing specific embodiments and are not used to limit the present utility model. The term "and / or" used in this specification includes any and all combinations of one or more of the related listed items.

[0036] In addition, the technical features involved in different embodiments of the present utility model described below can be combined with each other as long as they do not conflict with each other.

[0037] The spot diameter of the focused beam output by the existing laser processing head is small, and the focal depth is limited. On the one hand, it is easy to cause a relatively thin cut / weld seam when it is applied to process medium-thick metal plates, resulting in low laser energy utilization rate and being unfavorable for slag removal; on the other hand, even if the laser penetrates the plate, the material removal at the bottom of the plate is inconsistent, and a large amount of molten slag adheres, resulting in poor quality of the cut / weld joint.

[0038] For the problem of poor processing quality in the medium - thick plate scenario, the focusing position of the output laser is usually adjusted so that the processing head can obtain the same processing effect as that in the processing of thin plates in the application of medium - thick plate processing. Specifically, for example, in cutting applications, the height of the processing head is mechanically adjusted to adjust the focusing position of the output beam of the processing head. However, the nozzle height H (the distance between the bottom of the nozzle and the surface to be cut is defined as the nozzle height H in the industry) has a certain adjustment range, which is limited by the parameter limit of the air flow rate output by the nozzle. To ensure the air flow rate, the adjustment range of the relative height H between the nozzle and the workpiece surface is small (its height H is usually between 2 mm and 5 mm). And the thickness of medium - thick plates is usually greater than 4.5 mm. That is to say, in the prior art, by translating the processing head to change its height and further adjusting the focal position, some processing requirements cannot be met. In some other solutions, a beam shaping system can also be designed in the laser processing head. By setting the adjustable distance of the optical axis direction of the internal lens group, the zoom function can be realized, so that the focusing position of the laser can be adjusted axially. Based on the axially adjustable focusing position function, subsequent negative defocus cutting processes for materials such as stainless steel and positive defocus cutting processes for materials such as carbon steel have been derived.

[0039] Exemplarily, such as Figure 1 In (1a) of shows a schematic diagram of the laser convergence position during the negative defocus operation of the laser processing head (only the nozzle part is shown). As Figure 1 In (1b) of shows a schematic diagram of the laser convergence position during the non - defocus operation of the laser processing head (only the nozzle part is shown). As Figure In (1c) of shows a schematic diagram of the laser convergence position during the positive defocus operation of the laser processing head (only the nozzle part is shown).

[0040] Combined with ​ In (1a), (1b), and (1c) of , the nozzle height H of the laser processing head is small. When cutting, a large amount of dust and smoke will be formed, and these impurities will adhere to the protective lens (not shown) of the laser processing head, which easily leads to power attenuation and optical path heat loss. And when the nozzle height H is too small, the probability of these impurities entering the nozzle and the inside of the processing head can be significantly increased. Also, due to the too - small nozzle height, when the nozzle faces a complex surface, limited by the spatial position of the nozzle, it cannot reach the predetermined position for operation, resulting in poor cutting effect; and due to the low flatness of the workpiece, it is easy to hit the plate, which is not conducive to mass production. As ​ As shown in (1c) and (1d) of , by increasing the nozzle height H, the probability of impurity adhesion can be reduced, the reliability of laser processing can be improved, the replacement frequency of consumables can be reduced, and the adaptability to cutting complex surfaces can be improved.

[0041] However, when the nozzle height is raised, as ​As shown in (1a), during negative defocus operation of the laser beam, the waist radius of the laser beam is located below the surface of the material to be processed. Due to the divergence of the laser, when the negative defocus degree of the laser beam focus is too large, the light beam at the edge of the laser beam will be blocked by the nozzle. Although most of the energy of the laser beam is concentrated at the axis of the light beam, the laser for processing medium and thick plates is high-power laser (usually above 5kw), and the edge light beam will still cause the temperature of the nozzle to continue to increase until the temperature is too high, resulting in the shutdown of the laser cutting system, which will affect the stability of the laser processing head and the equipment availability. When the nozzle height is raised, as ​ shown in (1e), in order to prevent the edge of the laser beam from being blocked by the nozzle, the negative defocus action depth of the laser beam will actually be reduced, resulting in poor negative defocus cutting effect of the laser processing head, or even unable to perform negative defocus operation.

[0042] To overcome the defects existing in the above-mentioned prior art, the embodiment of the present utility model provides a beam shaping system for improving the energy utilization rate of the laser beam in laser processing. In one embodiment, the beam shaping system includes, sequentially arranged along the laser transmission direction: a collimating mirror 11, a beam shaper 12, and a focusing mirror 13, as shown in ​ .

[0043] Among them, the collimating mirror 11 is used to collimate the laser beam output by the laser; the beam shaper 12 is a conical lens or a spherical mirror, which is used to expand the aperture angle of the collimated light beam before it is incident on the focusing mirror 13 and increase the incident height of the collimated light beam; the focusing mirror 13 is used to converge each annular light beam with different incident heights in the laser beam to different positions along the optical axis direction, forming an axially multi-focal light beam.

[0044] When the optical path structure shown in ​ is applied to cutting, the effect is as shown in ​ . The light spot formed at the positive focus position is annular, and the light spot formed at the negative focus position maintains a circular shape. The diameter of the light spot at the waist is larger than that without adding a beam shaper, the light beam divergence angle is reduced, and the change of the light spot size along the optical axis direction is relatively slow, which is beneficial to reducing the sensitivity of the cutting process to the focus.

[0045] Optionally, the beam shaping system further includes a driving unit, which is connected to the collimating mirror 11 and is used to drive the collimating mirror 11 to move along the optical axis direction to adjust the energy distribution of the collimated light beam, so that the energy of the collimated light beam is evenly distributed along the optical axis to improve the axial utilization rate of the collimated light beam. Optionally, the driving unit can adopt a vibration motor. It can be understood that by driving the collimating mirror to move along the optical axis direction, the energy can be evenly distributed on a certain section of the optical axis, realizing the optical energy state with a long depth of field to achieve high-speed cutting.

[0046] In this embodiment, the incident height of the laser beam is raised by the beam shaper 12, and the focusing mirror 13 is further reversely curved to disperse the laser beam at the focal position of the optical axis. That is, the aberration is used to focus the beam at different positions on the optical axis, with a certain distance between each focal position. The axial multi-focus beam thus formed is not affected by the elevated nozzle design during processing, which can meet the defocusing requirements of the laser processing head and effectively prevent metal splashes and return light generated during processing from entering the nozzle, causing internal blockage and damage to the optical path. At the same time, the present application also drives the collimator mirror 11 to vibrate at a predetermined frequency along the optical axis through a driving unit to adjust the energy distribution of the collimated beam so that the energy of the collimated beam is evenly distributed along the optical axis to improve the axial utilization rate of the collimated beam.

[0047] In the prior art, the focused beam spot diameter output by conventional laser processing heads is typically small, with a limited depth of focus. When used to cut medium-thick metal plates, this small spot diameter results in a thin kerf, hindering slag removal. Even if the laser penetrates the plate, material removal at the bottom is inconsistent, resulting in a large amount of slag adhering to the plate and poor cut quality. To address this poor cut quality in medium-thick plate applications, the laser's focus position is typically adjusted to achieve the same results when cutting thin plates. However, the laser head's nozzle height (H) has a limited adjustment range, which can be achieved mechanically by adjusting the focus position. This adjustment range is limited by the nozzle's airflow rate. To ensure adequate airflow, the relative height (H) of the nozzle to the surface being processed is adjusted over a narrow range (typically 2mm-5mm; the industry defines the distance between the nozzle base and the surface being cut as the nozzle height H). This makes it suitable only for welding thin plates with a thickness between 0.5mm and 4mm. However, the thickness of medium and thick plates is usually greater than 4.5 mm. This means that by translating the processing head, the overall height of the processing head changes, and further the focus position changes, which cannot meet actual application needs.

[0048] like ​ As shown, a conventional laser processing head only has a collimator 11 and a focusing lens 13, and the collimator is usually fixed. After exiting the collimator 11, the collimated light beam is incident on the incident surface of the focusing lens 13 at the same incident height and an aperture angle of 0°. To reduce the optical medium surface of the beam shaping system and simplify the system design, the focusing lens 13 is usually a biconvex lens for converging the light beam. When designing the focusing lens 13, the matching method is used to eliminate aberrations in the optical path system as much as possible, so that the laser beam is focused on the same position of the optical axis as much as possible.

[0049] Use ​The laser processing head with the optical path structure shown forms circular spots at both the positive focus and the negative focus. The spot diameter at the beam waist is small, and the optical path for processing is short, as ​ shown.

[0050] In the embodiment of the present utility model, by adding a beam shaper 12 between the collimating mirror 11 and the focusing mirror 13 and cooperating with the collimating mirror that vibrates along the optical axis direction at a predetermined frequency, the direction of the collimated beam is changed. At the same time, after the beam exits from the beam shaper 12, it enters the focusing mirror 13 at a certain aperture angle, and the incident height of the beam is increased, so that the spot area of the collimated beam incident on the focusing mirror 13 is larger. That is, the beam that should originally enter the focusing mirror 13 from the paraxial region is changed to enter the focusing mirror 13 from a relatively off-axis region. The driving unit drives the collimating mirror to vibrate and adjusts the vibration frequency of the collimated beam, so that the energy of the laser can be evenly distributed in a specific area per unit time, thereby realizing uniform heating of the molten pool formed on the surface of the workpiece, which is beneficial to reducing the spatter generated during the processing.

[0051] It should be noted that for the focusing mirror 13 (spherical lens) used to achieve the converging effect in the present utility model, the image-side intercept of the beam incident from the off-axis region is smaller than that of the beam incident from the paraxial region. Therefore, the converging point of the beam incident from the off-axis region on the optical axis is closer to the exit surface of the focusing mirror 13 relative to the beam incident from the paraxial region; based on the above principle, by setting the beam shaper 12 to make the spot area of the collimated beam larger, the beam is incident on the focusing mirror at a higher incident height, and finally the focusing position of the laser beam on the optical axis is more dispersed, and there are multiple focusing positions of the beam on the optical axis.

[0052] Among them, to cooperate with the beam shaper 12, the focusing mirror 13 provided in this embodiment adopts a double-convex spherical lens to minimize the cost of the optical path system. And when designing it, the bending method is used in reverse to increase the aberration of the focusing mirror (adjust the curvature ratio of the incident surface and the exit surface of the focusing mirror for the purpose of increasing the aberration), so that the distance between the focusing positions of the beam incident from the off-axis region on the optical axis and the focusing positions of the beam incident from the paraxial region on the optical axis is larger, to further disperse the focusing positions of the laser beam on the optical axis and expand the spacing between the focusing positions; through the cooperation of the cone lens and the focusing mirror, as ​ and ​ shown, D3 > L3, D2 > L2, D1 > L1, the spacing between each focusing position (F0, F1, F2, F3) on the optical axis increases, so that the depth of focus DOF of the formed beam increases, and while meeting the requirements of negative defocus operation, the edge of the beam will not be blocked by the nozzle after being raised.

[0053] Meanwhile, it should be noted that in the scenario of cutting medium and thick plates with high-power lasers, the laser beam formed by a conventional zoom system is a Gaussian beam. The energy density at the focal position of the laser beam is too high, which is prone to hole explosion during operation and is not conducive to slag discharge. Therefore, laser cutting is usually carried out at a position with a slightly larger spot diameter. In actual processing applications, each plate thickness and each material have their own relatively appropriate spot size.

[0054] Using the beam shaping system provided in this embodiment as shown in ​ , the energy of its waist part is moved to the negative defocus direction, which can improve the negative defocus cutting efficiency, and the spot diameters of the beams acting on the material are relatively small, and the change degree of the energy density is small, which can avoid the cut surface being stepped and is conducive to reducing hole explosion. And, compared with ​ and ​ , due to the limitation requirements of the cutting process on the spot size, when the same spot size is used to act on the material surface, ​ the formed cutting beam requires a deeper negative defocus depth than the cutting beam formed by ​ to meet the operation requirements. A relatively deeper defocus depth (the nozzle height remains unchanged) will result in a higher beam energy acting on the nozzle, which not only causes the nozzle to heat up but also reduces the energy utilization rate; ​ the formed cutting beam relative to the cutting beam formed by ​ can meet the spot size requirements only by adjusting the defocus depth of the beam within a small depth range. At the same time, the divergence angle of the beam segment acting on the inside of the material is small, and the change rate of the spot size is low. When the lens has a temperature drift, the consistency of the cutting section will not be affected by the temperature drift.

[0055] As an example, as shown in ​ , the beam shaper 12 uses a plano-concave conical lens, whose concave surface is the incident surface, and the cone angle of the concave surface is between 0.5° and 3°. And, in order to prevent the incident surface from forming a sharp surface, the paraxial region of the plano-concave conical lens is set as a smooth surface, such as a smooth spherical surface that is smoothly connected to the conical surface, to avoid heat concentration; when using a plano-concave conical lens and a focusing lens with a reverse curvature design, the incident beams converge at different positions on the optical axis due to different incident heights.

[0056] As another example, the beam shaper 12 uses the plano-concave conical lens shown in ​ , the cone angle of the concave surface is between 0.5° and 3°, but its plane is the incident surface and the concave surface is the exit surface, and the paraxial region of the plano-concave conical lens is set as a smooth surface, which can also increase the incident height of the collimated beam and cooperate with the focusing lens with a reverse curvature design to form a multi-focus beam.

[0057] As another example, as shown in ​As shown, the beam shaper 12 uses a plano-convex conical lens, with its planar surface as the incident surface and its convex surface as the exit surface. The cone angle of the convex surface is between 0.5° and 3°, and the paraxial region of the plano-convex conical lens is set as a smooth surface, which can also raise the incident height of the collimated beam and cooperate with the focusing lens with a reverse curvature design to form a multi-focus beam. When using a plano-convex conical lens, sufficient space needs to be reserved between the conical lens and the focusing lens, and its length is longer than that of the beam shaping system using a plano-concave conical lens.

[0058] As another example, as ​ shown, the beam shaper 12 uses a plano-convex conical lens, with its convex surface as the incident surface and its planar surface as the exit surface. The cone angle of the convex surface is between 0.5° and 3°, and the paraxial region of the plano-convex conical lens is set as a smooth surface, which can also raise the incident height of the collimated beam and cooperate with the focusing lens with a reverse curvature design to form a multi-focus beam.

[0059] As another embodiment of the present application, please refer to ​ and ​ , and its optical path structure includes: a beam shaper 12 and a focusing lens 13; wherein, the beam shaper 12 is used to receive the divergent laser and convert the divergent laser into a collimated light that exits parallelly, that is, the laser exiting from the collimating mirror can be approximated as a collimated beam, and furthermore, it is also used to expand the spherical aberration of the optical path system; the focusing lens 13 is used to converge the collimated beam onto the optical axis to form a focused beam, and furthermore, it is also used to increase the aperture of the optical path system to form an axial multi-focus beam.

[0060] As an example, as ​ shown, the beam shaper 12 uses a double convex lens, and the focusing lens 13 also uses a double convex lens. Moreover, the surface with a smaller radius of curvature in the beam shaper 12 faces the collimated beam, and the surface with a larger radius of curvature faces the divergent beam. The surface with a smaller radius of curvature in the focusing lens 13 faces the collimated beam, and the surface with a larger radius of curvature faces the converging beam to minimize the spherical aberration; the curvature radius ratio of each lens adopts the ​ shown structural relationship, which can make the formed focused beam converge as much as possible at the same position on the optical axis. However, due to the use of spherical lenses, the spherical aberration of the system can only be corrected and reduced as much as possible and cannot be completely eliminated. As ​ shown, the beams in different annuli (different incident heights) are focused at different axial focusing positions on the optical axis (the focusing position is the intersection of the converged beams of different annuli and the optical axis).

[0061] As an example, as ​As shown, the beam shaper 12 uses a bi-convex lens. The surface with a smaller radius of curvature of the bi-convex lens faces the divergent beam, and the surface with a larger radius of curvature faces the collimated beam. That is, the beam shaper 12 uses reverse curvature matching, such that the radius of curvature of the incident surface is greater than that of the exit surface, increasing the spherical aberration while satisfying the collimation function. The focusing lens 13 uses a spherical meniscus lens, and the surface with a smaller radius of curvature faces the collimated beam, and the surface with a larger radius of curvature faces the converging beam. That is, a positive meniscus lens is used. A positive meniscus lens can increase the system NA of the optical path structure. The larger the NA, the larger the spherical aberration, and the distance between the axial focusing positions of different annuli focused on the optical axis can be increased. It should be noted that the collimated beam formed by the collimating lens 11 provided in this embodiment is a weakly collimated beam, which is not a strictly parallel beam. While satisfying the magnification design requirements, since it also undertakes the design function of increasing the spherical aberration, in the beam output by it, the beam of the edge annulus (far axis) forms a certain angle with the optical axis relative to the beam of the near-axis annulus, such that the beam emerging from the collimating lens 11 at a more edge position enters the focusing lens 13 with a higher incident height. As the incident height increases, the distance between the axial focusing positions can be increased.

[0062] Through the cooperation of the collimating lens 11 and the focusing lens 13, as ​ and ​ shown, D3 > L3, D2 > L2, D1 > L1. The spacing limit between each focusing position (F0, F1, F2, F3) on the optical axis increases, increasing the depth of focus DOF of the formed beam. While satisfying the requirements of negative defocus operation, the edge of the beam can be prevented from being blocked by the nozzle after being lifted. At the same time, it should be additionally noted that in the medium-thick plate cutting scenario of high-power lasers, the laser beam formed by a conventional zoom system is a Gaussian beam. The energy density at the focal position of the laser beam is too large, and it is easy to form holes and is not conducive to slag removal during operation. Therefore, laser cutting is usually performed at a position with a slightly larger spot diameter. In actual processing applications, each plate thickness and each material have their own relatively appropriate spot size.

[0063] In contrast, when using the Y1 segment shown in ​ to act on the material for cutting, since the thickness of the plate is greater than the depth of focus, the spot diameter in the Y1 segment increases synchronously in a certain proportion with the divergence angle of the laser beam. The change rate of the spot size is large, the change degree of the energy density is large, the cut seam is in a stepped shape, most of the cutting waste residues accumulate and cannot be discharged downward, normal perforation cannot be performed, and even holes may be formed to return the waste residues to the original optical path, piercing the protective mirror and damaging the processing head. When using the laser processing head with the optical path structure shown in ​ provided in this embodiment, the energy of the waist part of the beam is shifted to the negative defocus direction, which can improve the negative defocus cutting efficiency, and the spot diameters of the beams acting on the material are relatively close, and the change degree of the energy density is small, which can avoid the stepped shape of the cut surface and is beneficial to reducing the formation of holes. And, in comparison​ and ​ , due to the limitation requirements of the cutting process on the spot size, when the same spot size is applied to the material surface, ​ the formed cutting beam relative to ​ the formed cutting beam requires a deeper negative defocus depth to meet the operation requirements. A relatively deeper defocus depth (with the nozzle height unchanged) will result in a higher beam energy acting on the nozzle, which not only causes the nozzle to get hot but also reduces the energy utilization rate;

[0064] It can be understood that ​ the formed cutting beam relative to ​ the formed cutting beam can meet the spot size requirements by adjusting the defocus depth of the beam only within a small depth range. At the same time, the divergence angle of the beam segment acting on the interior of the material is small, and the change rate of the spot size is low. When the lens has a temperature drift, it will not affect the consistency of the cutting section due to the temperature drift.

[0065] Optionally, ​ the waist diameter of the formed focused beam is greater than 0.5 mm, while ​ the waist diameter of the formed focused beam is usually less than 0.1 mm. Although a larger waist diameter is not suitable for the fine cutting of thin plates, it can be adapted to the cutting of medium and thick plates, and due to the low change rate of the spot size, the cutting section has better consistency.

[0066] In this application, a prism pair 10 can also be used to refract and linearly scale the collimated beam at least once to achieve the lateral beam reduction of the laser beam. The principle of using a prism pair 11 to achieve the lateral beam reduction of the collimated light is as ​ shown. This principle has been shown in "Design of Shaping Prisms for Semiconductor Laser Systems" (Zhang Ping, 1990 note), so it will not be elaborated in this application.

[0067] Arrange the first right-angle prism 101 and the second right-angle prism 102 at predetermined spatial positions in the optical path. The collimated beam emitted from the collimator 11 enters from a right-angle surface of the first right-angle prism and exits from the inclined surface of the second right-angle prism, which is beneficial to reducing the spot diameter at the beam waist, achieving a higher energy density and a better focusing effect, and ensuring the clear edge shape of the processing beam.

[0068] It should be noted that the collimator mentioned in this embodiment should be understood as a lens group for realizing the collimation function. Its collimation function can be realized by a single lens or by multiple lenses in cooperation; in the optical path structure of the laser output head, multiple protective lenses can be added to achieve the sealing protection of the collimator and the focusing lens, and a beam splitter can be added to achieve the process monitoring of laser processing. To avoid redundancy, it is not shown in the laser processing head structure as ​ shown, and these optical lenses can be selected in actual applications.

[0069] In addition, to improve the focusing effect of the beam output by the beam shaping system, the beam shaping system further includes at least one pair of right-angle prisms, which are arranged between the beam shaper and the focusing mirror and are optically connected in series. The pair of right-angle prisms is used to perform beam reduction and shaping on the beam output from the beam shaper.

[0070] As ​ shown, the first right-angle prism 101 and the second right-angle prism 102 are arranged at predetermined spatial positions in the optical path. The collimated beam emitted from the collimator 11 enters through a right-angle surface of the first right-angle prism and exits through an inclined surface of the second right-angle prism, which is beneficial to reducing the spot diameter at the beam waist, achieving a higher energy density and a better focusing effect, and ensuring a clear edge shape of the processing beam.

[0071] It can be understood that when the pair of right-angle prisms is configured as one, after the first collimated beam with a circular cross-sectional shape exits from the pair of right-angle prisms, a second collimated beam with an elliptical cross-section is formed (i.e., the beam is compressed in one direction and remains unchanged in the other direction). By utilizing the refraction effect of the prism and the linear scaling effect on the laser collimated beam, the shaping and reduction of the collimated light are achieved.

[0072] In some embodiments, when the pair of right-angle prisms is configured as two (adding another prism group on the basis of the above-mentioned pair of right-angle prisms) and arranged at a certain spatial position, a third collimated beam with a smaller cross-sectional area than that of the first collimated beam can be formed (achieving the compression of the beam in two mutually perpendicular directions), and the cross-section of the third collimated beam is also circular. In this embodiment, the first pair of right-angle prisms causes the beam to change in the XY direction, and the second pair of right-angle prisms causes the beam to change in the XZ direction. It should be noted that the principle of using the prism pair 11 to achieve lateral beam reduction for the collimated light has been shown in "Design of Shaping Prisms for Semiconductor Laser Systems" (Zhang Ping, 1990 Note), so it will not be elaborated in this application.

[0073] In summary, a laser processing head provided by the present utility model suitable for long-distance processing includes a collimating mirror, a beam shaper, and a focusing mirror in sequence along the laser transmission direction. Among them, the collimating mirror is used to collimate the laser beam output by the laser; the beam shaper is a conical lens or a spherical mirror, which is used to expand the aperture angle of the collimated beam before it enters the focusing mirror and increase the incident height of the collimated beam; the focusing mirror is used to converge each annular zone light with different incident heights in the laser beam to different positions along the optical axis direction to form a multi-focus beam. The present utility model raises the incident height of the laser beam through the beam shaper, makes the beam focus on different positions on the optical axis by using aberration, and further sets the focusing mirror with reverse curvature, so that the focusing positions of the laser beam on the optical axis are dispersed, and there is a certain distance between each focusing position. The axial multi-focus beam formed thereby can be not affected by the nozzle with an elevated design during the processing operation, can meet the defocusing use requirements of the laser processing head, and effectively prevent the metal spatter and the return light generated during the processing from entering the nozzle interior, causing internal blockage and optical path damage; moreover, the divergence angle of the beam output from the laser processing head of the present utility model is extremely small, the change rate of the spot size is low, and the nozzle is less heated; when the lens has a temperature drift, the influence of the beam output from the laser processing head of the present utility model on the consistency of the processing section is also small. Therefore, the present utility model effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0074] The above embodiments are only illustrative of the principles and effects of the present utility model, and are not used to limit the present utility model. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present utility model. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present utility model should still be covered by the claims of the present utility model.

Claims

1. A laser processing head suitable for long-distance processing, characterized in that, The laser processing head includes, arranged in sequence along the laser transmission direction: a collimating mirror, a beam shaper, and a focusing mirror; wherein, the collimating mirror is used for collimating the laser beam output by the laser; the beam shaper is a conical lens or a spherical mirror, and is used for expanding the aperture angle of the collimated beam before it is incident on the focusing mirror and increasing the incident height of the collimated beam; the focusing mirror is used for converging the annular lights with different incident heights in the laser beam to different positions along the optical axis direction respectively, so as to form an axially multi-focal beam.

2. The laser processing head according to claim 1, characterized in that, The distance between the nozzle of the laser processing head and the workpiece surface is not less than 10 mm.

3. The laser processing head according to claim 1, characterized in that, The conical lens is a plano-concave conical lens, and an inner concave curved surface is formed at the center of the concave surface of the plano-concave conical lens, and the inner concave curved surface is smoothly connected to the concave surface.

4. The laser processing head according to claim 3, wherein, The concave surface of the plano-concave conical lens serves as the incident surface.

5. The laser processing head according to claim 1, characterized in that, The conical lens is a plano-convex conical lens, and an outer convex curved surface is formed at the center of the convex surface of the plano-convex conical lens, and the outer convex curved surface is smoothly connected to the convex surface.

6. The laser processing head according to claim 5, wherein, The convex surface of the plano-convex conical lens serves as the incident surface.

7. The laser processing head according to claim 1, wherein The focusing mirror is further used for expanding the distance between the positions where the laser beams incident from different incident heights are converged at different positions on the optical axis.

8. The laser processing head according to claim 7, characterized in that, The convergence position of the laser beam incident from the far-axis region is closer to the exit surface of the focusing mirror than the convergence position of the laser beam incident from the near-axis region.

9. The laser processing head according to claim 1, wherein, The focusing mirror adopts a double-convex spherical mirror.

10. The laser processing head according to claim 1, wherein, The cone angle of the conical lens is between 0.5° and 3°.

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