An annular hollow defocused laser cladding device

Abstract

The present invention discloses an annular hollow off-axis laser cladding device, which relates to the technical field of laser processing. The device includes a housing, a conical reflector, an annular off-axis parabolic focusing mirror, a nozzle and a powder spraying tube. An incident light port is provided at the top of the housing. The conical reflector is arranged inside the housing and faces the incident light port. The annular off-axis parabolic focusing mirror is opposite to and coaxially arranged with the conical reflector. A nozzle is installed below the conical reflector, and the lower end of the nozzle is connected with the powder spraying tube. The powder spraying tube is coaxial with the annular hollow off-axis light formed after being reflected by the annular off-axis parabolic focusing mirror, and a collimating protective gas sleeve is arranged outside the powder spraying tube. The annular off-axis parabolic focusing mirror is used to horizontally offset the focusing focus of the mother parabola. The present invention realizes the uniformization of the energy density of the annular light spot, improves the coupling effect between the laser beam and the powder, improves the utilization rate of metal powder, and improves the cladding quality and morphology.

Description

Technical Field

[0001] The present invention relates to the technical field of laser processing, and particularly to an annular hollow defocused laser cladding device. Background Art

[0002] Laser cladding technology is an advanced manufacturing technology that combines laser technology and additive manufacturing technology, and has developed rapidly in recent years. As an advanced processing and forming technology, it is widely used in metal 3D printing, surface modification of materials, and repair of failed parts, etc., solving many problems in engineering practice and creating huge economic benefits in engineering applications. Laser cladding equipment mainly includes a laser, a cladding nozzle, a processing platform, and a feeding device. The laser cladding nozzle is the key core component of the laser cladding system, which can realize the transmission, transformation, focusing of the laser beam, and the synchronous delivery of the cladding material, and precisely couple the laser beam, the cladding material, and the molten pool on the surface of the substrate to continuously form a cladding layer. Among them, the shaping transformation and focusing of the laser beam, the transmission, injection, and convergence of the material, and the coupling method of the light and the material are the key technologies of the cladding nozzle. Currently, laser cladding nozzles can generally be divided into two types of powder feeding technologies from the structure:

[0003] One is the method of coaxial inclined powder feeding with multiple powder tubes surrounding a solid light (powder feeding outside the light). In its existing technology, the synchronous powder feeding laser cladding forming of metal materials is completed by a specially designed laser cladding nozzle. The method and structure can refer to European Patent W02005028151, Japanese Patent JP2005219060, etc. Its basic principle is a scheme of centering the light beam and surrounding the metal powder for transportation. The cylindrical laser beam emitted by the laser is focused into a solid conical laser beam, and the processing surface is placed near the focus. Multiple powder nozzles or annular powder feeding nozzles inclined relative to the beam axis are arranged outside the solid conical laser beam. The convergence point of multiple powder beams ejected from multiple nozzles is also placed near the focus. The focused spot and the powder beam both perform two-dimensional or three-dimensional scanning movements relative to the workpiece. The metal powder is continuously and real-time added to the focused spot to achieve cladding and solidify to form a molten channel, and finally gradually stack and form.

[0004] The other is the method of a single powder tube centered vertical powder feeding surrounded by a hollow annular light (powder feeding inside the light). The coaxial powder feeding nozzle inside the light adopts the light-powder coupling mode of "light enclosing powder". The circular solid light beam is converted into an annular conical beam or multiple beams, and the powder feeding tube is vertically placed in the hollow lightless area to achieve a hollow light beam and a centered powder tube for powder feeding inside the light.

[0005] A light, powder and gas coaxial delivery device for laser cladding forming with the application number 201020022781.1, comprising a powder feeding nozzle cylinder body. An optical inlet is provided above the cylinder body, and an optical outlet is provided below it. A conical reflector is provided inside the cylinder body facing the optical inlet, and an annular reflection focusing mirror is provided opposite to and coaxially with the conical reflector. A powder feeding pipe is fixedly provided below the conical reflector, and a nozzle is connected to the lower end of the powder feeding pipe. The nozzle is coaxial with the incident laser beam. It is characterized in that a collimating protective gas sleeve is provided between the periphery of the nozzle and the nozzle outlet between the conical reflector and the nozzle outlet. By providing a collimating protective gas sleeve outside the nozzle in the present invention, the coaxial delivery of light, powder and gas is realized, and the deficiencies in the use of protective gas in the prior art are solved.

[0006] A three-dimensional space arbitrary direction laser cladding device with the application number 201811548923.5, comprising a support frame and a cladding nozzle located above the support frame. A beam splitter and a focusing mirror are provided in the support frame. The beam splitter receives the incident light beam and reflects the incident light beam to form a reflected light beam. The focusing mirror receives the reflected light beam and converts the reflected light beam into a focused light beam. A beam channel through which the focused light beam can pass is provided in the support frame. The cladding nozzle includes a nozzle body and a nozzle orifice formed at the end of the nozzle body. A cladding channel for the cladding material to pass through is provided inside the nozzle body. The cladding channel is communicated with the nozzle orifice to send out the cladding material through the nozzle orifice. The three-dimensional space arbitrary direction laser cladding device further includes a protective gas curtain forming assembly provided between the nozzle orifice and the support frame to form a protective gas curtain above the support frame and blow / disperse the cladding material located above the beam channel through the protective gas curtain. When the three-dimensional space arbitrary direction laser cladding device performs cladding at a large angle of inclination, vertical upward or continuous transformation of the orientation in space, the splashing and dripping of the cladding material will not damage the focusing mirror, realizing all-round cladding in three-dimensional space.

[0007] A focusing device for in-light coaxial powder feeding with the application number 201621159526.5, such as Figure 1As shown in the figure, a collimating mirror 3, a conical reflecting mirror 5, and an annular off-axis focusing parabolic mirror 7 are successively installed behind the laser beam output port. Both reflecting mirrors are rotationally symmetric structures around the central axis, and the reflecting surfaces are arranged oppositely. The divergent laser beam 2 emitted by the laser is collimated into a parallel cylindrical collimated beam 4 by the collimating mirror 3. The cylindrical collimated beam 4 is reflected by the conical reflecting mirror 5 and then reflected to the annular off-axis focusing parabolic mirror 7. The reflected cylindrical collimated beam 4 is divided into a ring-shaped conical focusing beam 8, which is finally focused on the working plane 11, forming a point light spot at the focal position. However, generally during operation, according to requirements, the working plane 11 should be at an out-of-focus position above or below the focusing focus 13, so that a hollow circular light spot with a certain size is formed on the cross-section of the ring-shaped conical focusing beam 8 to form a molten pool with the required size and melt the powder material ejected from the nozzle 9. The hollow annular light spot shifts the central energy peak of the original solid light spot outward, strengthening the energy on the outside of the light spot.

[0008] As Figure 1 described above, when the above-mentioned existing focusing devices perform conventional cladding in a state of no defocus and negative defocus, an annular light spot with the required size can be obtained to form an annular high-temperature molten pool, thereby melting the metal powder beam 10 ejected into the molten pool by the nozzle 9, and at the same time, the light energy distribution on the scanning line can be made uniform. Continuous scanning movement will continuously cladding and solidify to form cladding tracks with different widths. However, in order to efficiently form wide cladding tracks at a large defocus amount, the duty ratio of the annular light spot on its cross-section is too large, resulting in insufficient light energy in the middle of the molten pool, an incomplete morphology of the cladding layer, and even defect problems. Therefore, in view of the above problems, it is necessary to propose a further solution.

[0009] Compared with the traditional external powder feeding laser cladding method, the internal powder feeding laser cladding method has the following characteristics: The divergent laser is converted into parallel light through the collimating mirror system, and the incident parallel light is dispersed into uniform annular light by the beam splitter and irradiated onto the annular focusing reflecting mirror (the principle is as Figure 2 shown, the cross-section of its annular off-axis parabolic focusing mirror can be regarded as a section of the mother parabolic surface. Both have the same focus, but the optical axis is parallel to and deviated from the optical axis of the mother parabolic surface. The beam generated by the focusing of the reflecting mirror forms an off-axis angle with the original incident optical axis. The size of the off-axis angle depends on the selection of the cross-section of the mother parabolic surface and the width of the mother parabolic surface. Selecting a cross-section far from the axis of the parabolic surface will generate a larger off-axis angle, thus generating a larger focusing focal length). The focused beam converges into a hollow annular optical path. The internal space of the hollow annular optical path is large, and a complete set of circulation systems such as powder, gas, and cooling water can be placed. This not only reduces the volume of the entire cladding nozzle, but also when the powder tube is located on the central axis of the nozzle, there is an annular collimating protection gas pipe outside the powder tube, which together form the cladding nozzle. Under the combined action of gravity and powder-carrying gas, the divergence degree of the powder beam is small, and better integration of light, powder, and gas coaxiality is achieved.

[0010] However, the current internal powder feeding laser cladding method also has the following problems:

[0011] Before reaching the substrate, the powder will be irradiated by the laser beam. Since it is in a hollow annular optical path and the spot energy in different regions is different, when the powder passes through the laser beam and falls onto the substrate surface, there will be several different states:

[0012] 1) The powder particles are heated sufficiently and completely melted into a droplet state;

[0013] 2) The powder particles are not heated sufficiently and partially melted, and the other parts absorb heat during the mixing process with the melted liquid and finally melt;

[0014] 3) The powder particles are severely insufficiently heated and even not melted and remain solid particles.

[0015] Generally, when the melted powder particles in a liquid state drop onto the substrate surface, they will adhere to it; the powder particles that are not heated sufficiently will bounce off when hitting the substrate surface, and sparks can be seen flying everywhere. There are also particles that are not heated sufficiently entering the molten pool and continuing to melt when heated. The state of the powder particles when reaching the substrate surface has a great influence on the quality of the finally formed cladding part.

[0016] At the same time, the conventional laser cladding rate is relatively low, generally 0.5 - 3 m / min, the powder utilization rate is low, generally about 60%, and the roughness of the cladding layer is relatively large, resulting in serious material waste. Moreover, the laser energy is focused on the substrate material, and the powder is incorporated and combined by melting the substrate material, which makes the laser energy utilization efficiency and cladding rate low. At a large defocus amount, the energy absorbed by the center of the powder is insufficient, resulting in solid particles when the powder binds to the substrate material, and the surface smoothness of the finished product is poor. In order to improve the cladding efficiency, by increasing the laser power and increasing the spot area, but it will lead to an increase in the deformation amount of the workpiece, and a larger machining allowance needs to be reserved;

[0017] When using a non-defocused internal powder feeding laser cladding nozzle and attempting to perform wide-spot cladding at a large defocus amount, the duty cycle of the annular spot on its working plane becomes larger, resulting in insufficient light energy in the middle of the molten pool. The high-density powder ejected from the powder tube on the central axis falls into the hollow area of the spot and cannot be fully melted. As a result, under-fusion, powder adhesion, holes, etc. are more likely to occur, causing adhesion defects between the cladding layer and the substrate, resulting in an unfilled cladding layer morphology and failure of the cladding deposition. That is, the non-defocused annular hollow laser cannot achieve high-efficiency wide-channel cladding forming by changing the defocus amount.

[0018] Therefore, there is an urgent need to provide a new small-duty-cycle annular hollow laser cladding device to solve the above problems existing in the prior art. Summary of the Invention

[0019] The object of the present invention is to provide an annular hollow defocused laser cladding device to solve the above problems existing in the prior art. By changing the horizontal position of the annular focusing parabolic mirror, that is, changing the defocus amount of the focus of the mother parabola, the energy density of the annular light spot is homogenized, the coupling effect between the laser beam and the powder is improved, the utilization rate of the metal powder is increased, and the cladding quality and morphology are improved.

[0020] To achieve the above object, the present invention provides the following solution: The present invention provides an annular hollow defocused laser cladding device, including a housing, a conical reflector, an annular off-axis parabolic focusing mirror, a nozzle and a powder spraying pipe. An incident light port is provided at the top of the housing. The conical reflector is arranged inside the housing and faces the incident light port. The annular off-axis parabolic focusing mirror is opposite to and coaxially arranged with the conical reflector. The nozzle is installed below the conical reflector, and the lower end of the nozzle is connected with the powder spraying pipe. The powder spraying pipe is coaxial with the annular hollow defocused light formed after being reflected by the annular off-axis parabolic focusing mirror. A collimated protective gas sleeve is arranged outside the powder spraying pipe, and the collimated protective gas sleeve is located between the annular hollow defocused light and the powder spraying pipe. The annular off-axis parabolic focusing mirror is used to horizontally offset the focus of the mother parabola.

[0021] Preferably, the annular off-axis parabolic focusing mirror is an annular off-axis parabolic focusing mirror formed by reducing the horizontal cutting depth of the turning tool during machining.

[0022] Preferably, an upper cover plate is provided at the top of the housing, and the incident light port is opened on the upper cover plate.

[0023] Preferably, the annular off-axis parabolic focusing mirror and the conical reflector are coaxially arranged on a composite mirror base bracket. A nozzle adjusting seat is fixedly provided below the composite mirror base bracket. The nozzle adjusting seat is located below the conical reflector, and the nozzle is installed on the nozzle adjusting seat. The nozzle is connected with a powder sprayer for providing powder.

[0024] Preferably, a protective mirror is provided at the bottom of the composite mirror base bracket.

[0025] Preferably, air outlet holes are opened in the circumferential direction of the collimated protective gas sleeve, and a collimated protective gas sleeve nozzle is provided on the collimated protective gas sleeve.

[0026] Preferably, the nozzle includes a nozzle adjusting shaft, a pressure reducing cavity and a powder pipe spring clip. A pressure reducing cavity retaining ring is provided on the pressure reducing cavity, and a spring clip locking nut is provided on the powder pipe spring clip. The collimated protective gas sleeve is connected with the pressure reducing cavity. The powder spraying pipe passes through the powder pipe spring clip and the spring clip locking nut and is coaxially butted with the pressure reducing cavity.

[0027] Preferably, a pressure reducing chamber connecting pipe is further arranged on the pressure reducing chamber, and the pressure reducing chamber connecting pipe is used for communicating with the external atmosphere.

[0028] Preferably, a protective gas hood is further connected to the bottom of the outer shell. The protective gas hood is located outside the nozzle, and the annular hollow defocused light is located between the protective gas hood and the nozzle.

[0029] The present invention has achieved the following beneficial technical effects compared with the prior art:

[0030] When using a non-defocused in-light powder feeding laser cladding nozzle and attempting to perform wide-spot cladding at a large defocus amount, while the laser energy density per unit area is small, the duty ratio of the annular light spot on its working plane becomes larger, resulting in insufficient light energy in the middle of the molten pool. The high-density powder ejected from the middle powder pipe cannot be fully melted, and thus it is relatively easy to occur powder sticking and holes, causing adhesion defects between the cladding layer and the substrate, resulting in an unfull cladding layer morphology and failure of the cladding deposition; that is, the non-defocused annular hollow laser cannot achieve high-efficiency wide-channel cladding forming by changing the defocus amount.

[0031] The present invention can change the horizontal position of the annular focusing parabolic mirror, that is, change the horizontal position of the focus of the mother parabola, so that the annular focusing beam overlaps towards the center, the beam focus is defocused, and after overlapping, it is annularly dispersed and focused to form a focusing ring. On the working plane with a negative defocus amount, an annular light spot or a solid working light spot with a larger diameter and a smaller duty ratio is formed. Since the duty ratio of the light spot near the positive and negative defocus of the laser focus is reduced, the diameter of the solid focusing light spot at the laser focus is enlarged, the upper limit value of the melt width is increased, and the light energy distribution on the working light spot can be adjusted according to the working conditions, realizing the uniformization of the energy density of the annular light spot, increasing the coupling area between the laser beam and the powder, improving the utilization rate of metal powder and the cladding quality and morphology; in addition, by changing the defocus amount of the working plane, the continuous change from a large-size hollow annular light to a large-size solid annular light can be realized.

[0032] When the laser cladding head works within the positive defocus range, the powder ejected from the powder spraying pipe will first pass through the converging focus point, and the purpose of preheating is completed by blocking a part of the laser beam, so that the powder reaching the substrate can be fully melted, reducing the residual stress caused by temperature difference and phase change during the cladding forming process and avoiding defects such as pores and cracks in the cladding layer, realizing that the powder particles are fully heated and melted into a droplet state before reaching the substrate, reducing the rebound of the unmelted powder on the substrate, and improving the powder utilization rate and the cladding efficiency;

[0033] When the laser cladding works within the negative defocus range, since the annular hollow defocused laser can reduce the spot duty ratio near the negative defocus of the laser focus, that is, it enlarges the solid focus spot diameter at the laser focus, namely, there is a maximum solid spot, broadens the powder beam diameter that can be radiated and heated, and increases the upper limit value of the melt width of the melt channel. Due to the characteristics of the in-light powder feeding defocused beam, the highest laser energy density is no longer a small focused spot that converges, but a focused spot with uniform energy density, making the morphology of the cladding layer tend to be flat and full.

[0034] The present invention can adjust the size of the working spot according to the required power and power density. While the diameter of the adjusted spot increases, it is ensured that the working spot is a solid spot or a small-duty-ratio annular spot, and the area of the hollow region relative to the spot is reduced. In summary, the present invention provides a new technical device that can simultaneously perform high-speed cladding under positive defocus and wide-spot cladding under extremely negative defocus. Brief Description of the Drawings

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0036] Figure 1 is the schematic diagram of the in-light coaxial powder feeding device in the prior art;

[0037] Figure 2 is the schematic diagram of the annular off-axis parabolic focusing mirror in the prior art;

[0038] Figure 3 is the powder heating diagram of the in-light defocused laser high-speed cladding of the present invention;

[0039] Figure 4 is the schematic diagram of the annular hollow defocused laser of the present invention;

[0040] Figure 5 is the structural schematic diagram of the annular hollow defocused laser cladding device of the present invention;

[0041] Figure 6 is the working schematic diagram of the annular off-axis parabolic focusing mirror of the present invention;

[0042] In the figure, 1 - fiber optic outlet; 2 - diverging laser beam; 3 - collimating mirror; 4 - collimated beam; 5 - conical reflecting mirror; 6 - optical axis center line; 7 - annular off-axis parabolic focusing mirror; 71 - parent paraboloid; 72 - parabolic optical axis; 8 - conical focusing beam; 9 - nozzle; 10 - powder beam; 11 - working plane; 12 - focal plane; 13 - focusing focus; 14 - annular light energy distribution at large defocus; 15 - annular light energy distribution at small defocus; 16 - upper cover plate; 17 - composite mirror base bracket; 18 - housing; 19 - protective mirror; 20 - nozzle adjustment seat; 21 - nozzle adjustment shaft; 22 - decompression chamber; 23 - decompression chamber retaining ring; 24 - collimated protective gas sleeve; 25 - powder tube spring clamp; 26 - spring clamp locking nut; 27 - powder spraying tube; 28 - protective gas hood; 29 - light inlet; 101 - unheated powder; 102 - heated powder; 103 - molten pool; 104 - wide spot small duty cycle spot position; 105 - maximum solid spot position; 106 - minimum solid spot position; 107 - original paraboloid; 108 - current paraboloid; 109 - focal plane; 110 - focusing ring; 111 - maximum solid spot light energy distribution; 112 - minimum solid spot light energy distribution; 113 - spot light energy distribution under positive defocus; 114 - spot light energy distribution under negative defocus; 115 - parabolic center axis before defocus; 116 - parabolic center axis after defocus; 117 - parent paraboloid before defocus; 118 - parent paraboloid after defocus; 119 - original focusing beam; 120 - defocused beam. Detailed implementation mode

[0043] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

[0044] The purpose of the present invention is to provide an annular hollow defocused laser cladding device to solve the above problems in the prior art. By changing the horizontal dimension of the annular focusing parabolic mirror, that is, changing the defocus amount of the focus of the parent parabola, the uniformization of the energy density of the annular light spot is realized, the coupling effect between the laser beam and the powder is improved, the utilization rate of the metal powder is increased, and the cladding quality and morphology are improved.

[0045] To make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation modes.

[0046] Embodiment 1

[0047] As Figures 3-6As shown in the figure, this embodiment provides an annular hollow off-axis laser cladding device, which includes an upper cover plate 16, a housing 18, a compound mirror base bracket 17, a conical reflector 5, an annular off-axis parabolic focusing mirror 7, a protective mirror 19, a jet base, a protective gas hood 28, etc. An incident light port 29 is provided above the housing 18. Inside the housing 18, facing the incident light port 29, there is a conical reflector 5 (a conical straight surface reflector can be used). Opposite to and coaxial with the conical reflector 5, there is an annular off-axis parabolic focusing mirror 7. The compound mirror base bracket 17 is installed inside the housing 18. The outer ring of the compound mirror base bracket 17 is provided with an installation part for the annular off-axis parabolic focusing mirror 7, and the middle part is provided with an installation part for the conical reflector 5. The two installation parts can be connected by rib plates. The two installation parts are arranged alternately with the annular hollow off-axis light, and there is a space for the annular hollow off-axis light to pass between the two installation parts; the annular off-axis parabolic focusing mirror 7 and the conical reflector 5 are coaxially arranged on the compound mirror base bracket 17.

[0048] At the bottom of the installation part of the conical reflector 5, a nozzle adjustment seat 20 is fixedly provided. The nozzle adjustment seat 20 is located below the conical reflector 5 and is used to install the nozzle 9. The lower end of the nozzle 9 is connected to a powder spraying pipe 27. The powder spraying pipe 27 is coaxially arranged with the annular hollow off-axis light formed after being reflected by the annular off-axis parabolic focusing mirror 7. A collimating protective gas sleeve 24 is arranged outside the powder spraying pipe 27. The collimating protective gas sleeve 24 is located between the annular hollow off-axis light and the powder spraying pipe 27. A protective mirror 19 is also provided at the bottom of the compound mirror base bracket 17.

[0049] When the annular hollow off-axis laser cladding device of this embodiment is in use, the circular fundamental mode laser beam emitted by the laser enters the cavity of the housing 18 along the axis of the annular hollow off-axis laser cladding device through the incident light port 29, and is incident on the conical reflector 5 installed inside the housing 18. The laser beam after being reflected by the conical reflector 5 is incident on the annular off-axis parabolic focusing mirror 7 that is opposite to and coaxially installed with the conical reflector 5, and then an annular hollow off-axis laser is formed. A circular conical hollow lightless area is formed in the middle of this light beam.

[0050] In this embodiment, the annular off-axis parabolic focusing mirror 7 can make the horizontal offset of the focusing focus 13 of the mother parabola compared with the annular off-axis parabolic focusing mirror 7 in the prior art, and finally changes the defocus amount of the focused light beam and the duty ratio of the light spots on different defocus planes; specifically, when machining the annular off-axis parabolic focusing mirror 7 in this embodiment, the horizontal cutting depth of the turning tool is reduced, thereby changing the horizontal position of the reflecting surface of the annular off-axis parabolic focusing mirror 7 (that is, changing the size of the annular through hole in the middle of the annular off-axis parabolic focusing mirror 7), so as to make the horizontal offset of the focusing focus 13 of the mother parabola.

[0051] As Figure 6As shown in the figure, the original horizontal dimension of the annular off-axis parabolic focusing mirror 7 is R1. The horizontal dimension R1 of the annular off-axis parabolic focusing mirror 7 is reduced, and the parabolic mirror is horizontally moved inward by a distance of Δx, so that the horizontal dimension of the annular off-axis parabolic focusing mirror 7 becomes R2, that is, the central axis of the parabola is offset by a distance of Δx. Without changing the off-axis angle α, the focusing focus 13 also has an offset of Δx in the focusing plane 109 to form a hollow focusing ring 110, and finally a defocused beam 120 with a variable duty ratio under different defocus planes is formed.

[0052] In this embodiment, the nozzle 9 is placed in the annular conical hollow lightless area. The nozzle 9 mainly includes a nozzle adjustment shaft 21, a pressure reduction chamber 22, a pressure reduction chamber retaining ring 23, a powder tube spring clip 25, and a spring clip locking nut 26. The nozzle adjustment shaft 21 is arranged in the middle of the nozzle 9. The nozzle 9 is installed on the nozzle adjustment shaft 21. The nozzle adjustment shaft 21 is coaxially installed at the bottom of the installation part of the conical mirror 5. A pressure reduction chamber 22 is arranged on the outer ring of the nozzle 9. The powder spraying tube 27 is installed at the lower end of the nozzle 9 through the powder tube spring clip 25. During operation, the powder provided by an external powder feeder enters the nozzle 9 and then is sent into the powder spraying tube 27 and sprayed out to the center of the beam. A collimation protection gas sleeve 24 is arranged around the powder spraying tube 27. While the powder spraying tube 27 sprays powder, the collimation protection gas sleeve 24 sprays collimation protection gas through the air holes opened in the circumferential direction to form a collimation protection gas curtain. The collimation protection gas moves in one dimension and is laminar flow or close to laminar flow under appropriate pressure, which can collimate the powder beam 10. In this way, the beam is hollow, the powder beam 10 can be centered, and the collimation protection gas curtain surrounds the powder beam 10, realizing the coaxiality of the protection gas, the annular hollow defocused laser, and the powder beam 10 sprayed out by the powder spraying tube 27.

[0053] In this embodiment, the collimation protection gas sleeve 24 is connected to the pressure reduction chamber 22. The powder spraying tube 27 passes through the powder tube spring clip 25 and the spring clip locking nut 26 and is coaxially docked with the pressure reduction chamber 22. A pressure reduction chamber connecting pipe is also arranged on the pressure reduction chamber 22. The pressure reduction chamber connecting pipe is communicated with the external atmosphere to facilitate the powder beam 10 to fall by gravity, so as to achieve a better converging effect and improve the utilization rate of the powder beam 10.

[0054] The working principle in this embodiment is as follows:

[0055] The equipment required in this embodiment includes a laser cladding head developed by the Laser Manufacturing Technology Research Institute of Soochow University and a KUKA robotic arm. In traditional laser cladding, at a large defocus amount, the duty ratio of the laser spot is relatively large, and the powder beam 10 may not be completely melted in the middle, resulting in defects in the middle of the cladding track. In order to make the powder heat evenly in the air and the heating time is lengthened to make the powder melt sufficiently at a large defocus amount, this embodiment adopts a new design of defocus optical path, as Figure 4As shown, the optical path parameters that need attention include the off-axis angle θ, the inner optical path focusing semi-angle α, the defocus amount Δx of the focus of the mother parabola, the upper optical path radius Ri, and the lower optical path radius Ra.

[0056] Among them, the off-axis angle θ depends on the selection of the cross-section of the mother paraboloid 71 and the width of the mother paraboloid 71. Selecting a cross-section closer to the axis of the paraboloid will result in a smaller off-axis angle, and choosing a paraboloid cross-section closer to the focus will make the distance between the center of the mirror and the focus shorter. The width of the mother paraboloid 71 also affects the focal length, that is, the wider the paraboloid, the longer the focal length. Therefore, to control the focal length, it is necessary to reasonably select the position of the cross-section and the width of the mother paraboloid 71.

[0057] In addition, by changing the horizontal dimension of the annular focusing parabolic mirror, that is, changing the defocus amount Δx of the focus of the mother parabola, it will ultimately affect the upper optical path radius Ri and the lower optical path radius Ra of the annular off-axis parabolic focusing mirror 7, resulting in an offset of the focusing focus 13. This makes it possible to form an annular light spot or a solid working light spot with a larger diameter but a smaller duty ratio on the working plane 11 with a positive defocus amount. The size of the working light spot can be adjusted according to the required power and power density. While the diameter of the adjusted light spot increases, it is ensured that the working light spot is an annular light spot or a solid light spot with a small duty ratio, as Figure 3 shown.

[0058] The present invention aims at the problems existing in the "inward powder feeding" nozzle in laser cladding deposition additive manufacturing. By changing the horizontal dimension of the annular focusing parabolic mirror, that is, changing the defocus amount of the focus of the mother parabola, an annular light spot or a solid working light spot with a larger diameter but a smaller duty ratio is formed on the working plane 11 with a positive defocus amount. Since the duty ratio of the light spot near the positive and negative defocus of the laser focus is reduced, the diameter of the solid focusing light spot at the laser focus is enlarged, the upper limit value of the melt width is increased, and the energy distribution on the working light spot can be adjusted according to the working conditions, realizing the uniformization of the energy density of the annular light spot, improving the coupling effect between the laser beam and the powder, increasing the utilization rate of metal powder, and improving the cladding quality and morphology.

[0059] In addition, by changing the defocus amount of the working plane 11, a continuous change from a large-size hollow annular light to a large-size solid annular light can be achieved.

[0060] As Figure 3 shown, when the laser cladding head works within the positive defocus range, the powder ejected from the powder spraying tube 27 will first pass through the converging focus, and the purpose of preheating is completed by blocking a part of the laser beam, so that the powder reaching the substrate can be fully melted, reducing the residual stress caused by temperature difference and phase change during the cladding forming process and avoiding defects such as pores and cracks in the cladding layer, realizing that the powder particles are fully heated and melted into a droplet state before reaching the substrate, reducing the rebound of the unmelted powder on the substrate, and improving the powder utilization rate and cladding efficiency;

[0061] When the laser cladding works within the negative defocus range, since the annular hollow defocused laser can reduce the spot duty cycle near the negative defocus of the laser focus, that is, it enlarges the diameter of the solid focused spot at the laser focus, namely, there is a maximum solid spot, broadens the diameter of the powder beam 10 that can be radiated and heated, and increases the upper limit value of the melt width of the melt channel. Due to the characteristics of the in-light powder feeding defocused beam 120, the highest laser energy density is no longer a small focused spot where it converges, but a focused spot with uniform energy density, making the morphology of the cladding layer tend to be flat and full.

[0062] In summary, the present invention provides a new technical device that can simultaneously perform high-speed preheating cladding under positive defocus and wide-spot cladding under extremely negative defocus.

[0063] It should be noted that for those skilled in the art, obviously the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention, and any reference signs in the claims should not be regarded as limiting the claimed rights.

[0064] Specific examples are used in the present invention to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A ring-shaped hollow off-axis focused laser cladding device, characterized in that: it includes a housing, a conical reflector, a ring-shaped off-axis parabolic focusing mirror, a nozzle and a powder spraying pipe. An incident light port is provided at the top of the housing. The conical reflector is arranged inside the housing and faces the incident light port. The ring-shaped off-axis parabolic focusing mirror is opposite to and coaxially arranged with the conical reflector. The nozzle is installed below the conical reflector, and the lower end of the nozzle is connected with the powder spraying pipe. The powder spraying pipe is coaxial with the ring-shaped hollow off-axis focused light formed after being reflected by the ring-shaped off-axis parabolic focusing mirror. A collimating protective gas sleeve is arranged outside the powder spraying pipe and is located between the ring-shaped hollow off-axis focused light and the powder spraying pipe. The ring-shaped off-axis parabolic focusing mirror is used to horizontally offset the focusing focus of the parent parabola; the ring-shaped off-axis parabolic focusing mirror is a ring-shaped off-axis parabolic focusing mirror made by reducing the horizontal cutting depth of the turning tool during machining; the ring-shaped off-axis parabolic focusing mirror and the conical reflector are coaxially arranged on a composite mirror base bracket. A nozzle adjusting seat is fixedly provided at the bottom of the composite mirror base bracket. The nozzle adjusting seat is located below the conical reflector, and the nozzle is installed on the nozzle adjusting seat. The nozzle is connected with a powder sprayer for providing powder; the nozzle includes a nozzle adjusting shaft, a pressure reducing cavity and a powder pipe spring clip. A pressure reducing cavity retaining ring is arranged on the pressure reducing cavity, and a spring clip locking nut is arranged on the powder pipe spring clip; the collimating protective gas sleeve is connected with the pressure reducing cavity. The powder spraying pipe passes through the powder pipe spring clip and the spring clip locking nut and is coaxially docked with the pressure reducing cavity.

2. The ring-shaped hollow off-axis focused laser cladding device according to claim 1, characterized in that: a top cover plate is provided at the top of the housing, and the incident light port is opened on the top cover plate.

3. The ring-shaped hollow off-axis focused laser cladding device according to claim 1, characterized in that: a protective mirror is provided at the bottom of the composite mirror base bracket.

4. The ring-shaped hollow off-axis focused laser cladding device according to claim 1, characterized in that: air outlet holes are opened in the circumferential direction of the collimating protective gas sleeve, and a collimating protective gas sleeve nozzle is arranged on the collimating protective gas sleeve.

5. The ring-shaped hollow off-axis focused laser cladding device according to claim 1, characterized in that: a pressure reducing cavity connecting pipe is further arranged on the pressure reducing cavity, and the pressure reducing cavity connecting pipe is used to communicate with the external atmosphere.

6. The ring-shaped hollow off-axis focused laser cladding device according to claim 1, characterized in that: a protective gas hood is further connected to the bottom of the housing. The protective gas hood is located outside the nozzle, and the ring-shaped hollow off-axis focused light is located between the protective gas hood and the nozzle.

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