Annular coaxial powder feeding head for underwater laser cladding

Abstract

The invention discloses an annular coaxial powder feeding head for underwater laser cladding. The annular coaxial powder feeding head comprises a nozzle top, a nozzle middle part, a nozzle lower part, a drainage upper part, a drainage middle part and a drainage lower part which are sequentially mounted and connected from top to bottom, an upper laser cavity is formed in the middle hollow part of the top of the nozzle; a plurality of powder feeding screw holes are formed in the upper surface of the nozzle top and penetrate through the nozzle top and the nozzle middle to form a powder feeding channel, and a first air curtain / water curtain flow channel is formed in the nozzle top; the nozzle lower part and the nozzle middle part are similar in structure, the middle of the drainage upper part is a laser powder cavity, the upper surface of the drainage upper part is provided with two third air curtain / water curtain flow channels which are connected with the first air curtain / water curtain flow channels in a penetrating manner, and the drainage middle part and the drainage lower part are similar in structure; a water curtain, an air curtain structure and a nozzle are combined, an expanding protection curtain is formed at the bottom, the protection range is larger, and meanwhile the influence on powder feeding airflow and powder flow is smaller.

Description

Technical Field

[0001] The present invention relates to the field of an annular coaxial powder feeding head for underwater laser cladding. More specifically, the present invention relates to an annular coaxial powder feeding head for underwater laser cladding. Background Art

[0002] With the development and increase of marine engineering and submarine industrial facilities, the loss and repair of many underwater metal products have become a problem that cannot be ignored, such as the copper-based propellers of ships in the water, the pipeline steel used for submarine pipelines, and the anti-corrosion and corrosion-resistant coatings used by Chuanshen. These parts face chemical corrosion, electrochemical corrosion, biological corrosion, and tidal corrosion in the harsh environment of the seabed, and the wear of their surfaces and the thinning and fracture of structural parts will cause serious losses. Conventional repair methods, such as dock repair of ships and segmented water repair of submarine pipelines, can achieve better repair effects, but their efficiency is low and costly. Seeking a low-cost process method and device that can directly repair damaged parts underwater with good results is the research goal of many researchers. 3D printing, additive manufacturing is a "bottom-up" manufacturing method that uses powder or wire as raw materials through material accumulation, and can realize the manufacture of complex structural parts with the help of computer control. Laser, as a high-density heat source, can quickly heat up the powder and matrix to accurately prepare components according to the route specified by the computer. However, due to the excessive local heat input of the laser, it will cause warping and deformation of local components. For additive manufacturing, a process that "grows" a large amount of raw materials over a long period of time, the slight deformation of the components will accumulate into deformation that affects the overall structure due to the cumulative effect. At the same time, due to the high local heat input, the laser must be protected by an atmosphere when preparing some materials with an oxidation tendency, which not only increases the cost but also limits the preparation of some large components with complex structures.

[0003] Underwater laser additive manufacturing is a new type of repair and rapid prototyping process. Its principle is to use a high-power laser as a heat source underwater and a synchronous coaxial powder feeding process. The powder melts at or above the deposition point, and the substrate forms a micro-molten pool at the deposition point. After the laser moves, it quickly solidifies locally to form a high-quality cladding layer. In the underwater environment, the protective gas in front of the powder feeding head and the powder feeding airflow are used to drain the water near the deposition point, and the surrounding water environment is used to protect the easily oxidized substrate and powder. At the same time, because the water environment has a large heat capacity, it will have a cooling effect on the overall structure, effectively controlling the deformation of the component. This method has broad application prospects for surface modification and repair of components and overall rapid manufacturing.

[0004] At present, underwater synchronous laser additive manufacturing can be operated by a completely underwater dry method. Although this method can avoid the adverse effects of the water environment and try to create a dry environment that is the same as the atmospheric environment, its disadvantages are relatively obvious. First, it is difficult to create a local dry environment, and the design and production costs of the completely dry pressure chamber are high; second, the additional pressure chamber will increase the load of the load robot, which will affect the cladding accuracy; finally, the local dry method cannot completely eliminate the influence of the water environment and cannot guarantee the relevant performance of the cladding layer. Therefore, it is imperative to use a more integrated coaxial laser method.

[0005] Currently available laser powder feeding heads partially use multi-needle coaxial powder feeding, and partially use lateral powder feeding. The lateral powder feeding method is more suitable for laser cladding for surface repair and modification, but it is difficult to adopt due to the large restrictions on the production conditions of additive manufacturing. The multi-needle coaxial powder feeding head is highly integrated and suitable for additive manufacturing, but because the powder has strict requirements for each outlet position, the processing accuracy is difficult to guarantee, which usually results in poor powder convergence and low powder utilization. There are also coaxial annular powder feeding heads, but the quality of their internal structures is uneven, which can easily cause the powder to heat too fast, or the overall centering is poor and the powder utilization is low. In addition, conventional coaxial annular powder feeding heads cannot work underwater and cannot reflect the advantages of underwater laser additive manufacturing. Summary of the invention

[0006] In order to achieve these purposes and other advantages according to the present invention, a preferred embodiment of the present invention provides an annular coaxial powder feeding head for underwater laser cladding, comprising a nozzle top, a nozzle middle, a nozzle lower, a drainage upper part, a drainage middle, and a drainage lower part which are sequentially installed and connected from top to bottom;

[0007] The top of the nozzle is a circular plate-like structure, and the hollow part in the middle is the upper laser chamber; the upper surface of the top of the nozzle is provided with a plurality of screw holes for powder delivery, which penetrate directly through the top of the nozzle and the middle of the nozzle to form a powder delivery channel for powder to pass through; the upper surface of the top of the nozzle is provided with two connecting screw holes, which penetrate directly through the top of the nozzle and are connected to the upper part of the drainage to form a first air curtain / water curtain flow channel, which is used to provide gas or liquid to form an air curtain / water curtain, and form a local water-free area above the deposition point;

[0008] The middle part of the nozzle includes a circular ring plate located at the upper part and a middle funnel located at the lower part. The middle of the circular ring plate is a middle laser chamber, which is connected to the upper laser chamber. The middle funnel has a powder flow channel inside. The powder enters the powder flow channel in the middle part of the nozzle through the powder feeding channel. The powder is decelerated when it hits the wall for the first time to increase the laser heating time.

[0009] The structure of the lower part of the nozzle is similar to that of the middle part of the nozzle. The lower part of the nozzle has a lower laser chamber, which is connected with the upper laser chamber and the middle laser chamber to form a laser chamber with protective gas. The powder enters the lower part of the nozzle through the powder flow channel and is fully mixed. The lower part of the nozzle has a second air curtain / water curtain flow channel connected to the first air curtain / water curtain flow channel of the nozzle.

[0010] The upper part of the drainage is a circular plate-like structure, and its bottom extends outward to form a connecting part. The middle of the upper part of the drainage is a laser powder chamber. The upper surface of the upper part of the drainage has two third air curtain / water curtain flow channels, which are connected to the first air curtain / water curtain flow channels. The air curtain and the water curtain can pass through the interior to generate a protective curtain and cool down the inside of the nozzle.

[0011] The drainage middle part and the drainage lower part have similar structures, both of which include an upper annular columnar structure and a lower truncated cone-shaped expansion section. The upper part of the drainage lower part is connected to the connecting part of the drainage upper part, and the drainage middle part is sleeved on the upper part of the drainage lower part.

[0012] The first air curtain / water curtain flow channel, the second air curtain / water curtain flow channel and the third air curtain / water curtain flow channel are connected to form a water and air curtain area to exclude the external water environment.

[0013] Preferably, a fixing screw hole is provided on the upper surface of the nozzle top to connect with the laser; a concentric centering groove is provided on the upper part of the lower part of the lower nozzle to be connected with the middle part of the nozzle; an annular sealing groove is provided on the top of the middle part of the drainage to connect with the upper part of the drainage to form a seal, and the laser powder chamber is separated from the third air curtain / water curtain flow channel by an annular partition.

[0014] Preferably, the lower surface of the nozzle top has a laser protection mirror to protect the Aurora lens from water splashing back and powder contamination to the lens when the Aurora lens is working in water;

[0015] A countersunk hole is arranged on the side of the top of the nozzle for connecting the protective gas to prevent water from flowing back into the laser chamber in case of an accident.

[0016] Preferably, the powder flow channel as a whole contracts at a certain angle to ensure that the powder is gathered at the end while the end is minimally affected by the water pressure.

[0017] Preferably, a protruding waterproof sealing groove is provided on the lower surface of the nozzle top for sealing the protective gas and powder feeding gas path from the cooling water, and an annular sealing ring is installed inside the waterproof sealing groove to seal the nozzle top 1 from the external environment by extrusion.

[0018] Preferably, there are three sealing rings in the lower part of the nozzle for isolating the powder mixing chamber from the laser chamber and the external environment.

[0019] Preferably, the outer periphery of the upper drainage part is provided with an annular sealing groove, and the inner part is provided with an annular sealing ring, which is connected to the lower part of the nozzle to seal the nozzle, and the sealing ring groove is connected to the lower part 3 of the nozzle to isolate the water environment.

[0020] Preferably, the upper inner wall of the middle portion of the drainage is provided with threads, which are connected with the threads of the outer wall of the connecting portion of the upper portion of the drainage to form the outer wall of the protective curtain;

[0021] Preferably, an annular sealing groove is provided at the top of the drain lower part, which is connected to the drain upper part to form a seal, and the threads on the upper outer wall of the drain lower part are connected to the threads on the inner wall of the drain upper part to form the inner wall of the protective curtain.

[0022] Preferably, the expansion section in the middle of the drainage and the expansion section in the lower portion of the drainage both expand outward at an angle greater than 60°.

[0023] The present invention has at least the following beneficial effects:

[0024] (1) Powder flow channel inside the coaxial ring laser powder feeding head

[0025] In the present invention, powder enters through a straight pipe at the top of the nozzle. Furthermore, a powder flow channel in the middle of the nozzle is at a certain angle relative to the front viewing surface and the right viewing surface, so as to make the outlet area of ​​the powder entering the powder mixing chamber through the flow channel larger and avoid the collision area, and the particle deceleration effect is more obvious; further, the powder is mixed in the lower part of the nozzle, and the volume of the lower half is expanded, so that the powder mixing volume is larger.

[0026] 2. Integrated expansion type water curtain and air curtain protection device

[0027] The upper, middle and lower drainage parts together form a water curtain and air curtain structure with a local cavity, which is different from the shrinkable protective curtain of the traditional underwater nozzle.

[0028] The present invention combines a water curtain, an air curtain structure with a nozzle to form an expansion type protection curtain at the bottom, which has a larger protection range and less impact on the powder delivery airflow and powder flow.

[0029] 3. Overall structure of coaxial ring laser powder feeding head

[0030] The powder feeding head of the present invention has a layered stacked assembly form. Since the powder in the internal powder flow channel is decelerated by multiple collisions, its speed decreases after leaving the outlet, and the laser action time increases, which is suitable for underwater low-temperature and long-term additive manufacturing; further, the air curtain or water curtain can isolate a water-free area at the deposition point, and the expansion sections in the middle and lower parts of the drainage can prevent the suction of a large amount of ambient water at the same time.

[0031] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the overall structure of an annular coaxial powder feeding head in one embodiment of the present invention.

[0033] Figure 2 Schematic diagram of the structure of the nozzle top in one embodiment of the present invention.

[0034] Figure 3 It is a schematic structural diagram of the middle part of the nozzle in one embodiment of the present invention.

[0035] Figure 4 It is a schematic structural diagram of the lower part of the nozzle in one embodiment of the present invention.

[0036] Figure 5 It is a schematic structural diagram of the upper drainage part in one embodiment of the present invention.

[0037] Figure 6 It is a schematic diagram of the structure of the middle part of the drainage in one embodiment of the present invention.

[0038] Figure 7 It is a schematic structural diagram of the lower part of the drainage in one embodiment of the present invention.

[0039] Figure 8 It is a flow field velocity cloud diagram of an annular coaxial powder feeding head in one embodiment of the present invention.

[0040] Fig. 9 This is a diagram showing the effect of the high-pressure nozzle air curtain of an annular coaxial powder feeding head in one embodiment of the present invention.

[0041] Fig.10 The figure shows the distribution of gas and liquid phases outside the nozzle at 400ms, 1000ms, 1600ms and 2400ms for a nozzle with or without an air curtain in one embodiment of the present invention.

[0042] Fig.11 The cross-sectional SEM images of Ni60A alloy coatings sprayed with the powder feeding head of the present invention under different parameters are shown.

[0043] Fig.12 The macroscopic photograph and cross-sectional SEM image of a single-layer SULC iron-based coating sprayed by the powder delivery head of the present invention are shown. DETAILED DESCRIPTION

[0044] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0045] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are only examples, and those skilled in the art can think of other obvious variations. The basic principles of the present invention defined in the following description can be applied to other embodiments, variations, improvements, equivalents, and other technical solutions that do not deviate from the spirit and scope of the present invention.

[0046] Those skilled in the art should understand that, in the disclosure of the present invention, the orientation or position relationship indicated by the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. are based on the orientation or position relationship shown in the drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the above terms should not be understood as limiting the present invention.

[0047] It is to be understood that the term "one" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element may be one, while in another embodiment, the number of the element may be multiple, and the term "one" should not be understood as a limitation on the quantity.

[0048] like Figure 1-12 As shown, a preferred embodiment of the present invention provides an annular coaxial powder feeding head for underwater laser cladding, comprising a nozzle top 1, a nozzle middle 2, a nozzle lower 3, a drainage upper part 4, a drainage middle 5, and a drainage lower 6 which are sequentially installed and connected from top to bottom;

[0049] The nozzle top 1 is a circular plate-like structure, the middle hollow part of which is the upper laser chamber 11, and the upper laser chamber 11 extends upward to form an annular protrusion 12; the upper surface of the nozzle top 1 is provided with 4 screw holes 15 for powder feeding, which pass through the nozzle top 1 and the nozzle middle part 2 to form a powder feeding channel for powder to pass through, so as to ensure that the powder has a uniform path inside the powder feeding head and after leaving the powder feeding head; the upper surface of the nozzle top 1 is provided with two connecting screw holes 14, which pass through the nozzle top 1 and are connected to the drainage upper part 4 to form a first air curtain / water curtain flow channel 23, which is used to provide gas or liquid to form an air curtain / water curtain, and form a local water-free area above the deposition point; the side of the nozzle top 1 is provided with a countersunk hole 16 for connecting the protective gas to prevent water from flowing back into the laser chamber in case of an accident;

[0050] The top of the nozzle (1) is connected to a coaxial laser, and a centering seal ring 2 and an airtight ring 13 are coaxially arranged on the top of the nozzle to connect with the laser and maintain centering, and to ensure local sealing between the laser and the powder feeding head when working in deep water. The sealing of the centering seal ring 2 and the airtight ring 13 adopts a rigid fixed flexible extrusion seal, so that the pressure resistance range of the invention is 0 to 15 MPa.

[0051] A laser protection mirror is provided on the lower surface of the nozzle top 1 to protect the Aurora lens from water splashing back and powder contamination to the lens when the Aurora lens is working in water.

[0052] The countersunk hole 16 is opened at the top of the nozzle top 1 to ensure that the top of the nozzle top 1 is flat, so that the nozzle and the upper component are more closely combined to ensure sealing;

[0053] The middle part 2 of the nozzle includes a circular ring plate at the upper part and a middle funnel at the lower part. The middle of the circular ring plate is a middle laser chamber 21, which is connected to the upper laser chamber 11. The middle funnel has a powder flow channel 26 inside. The powder enters the powder flow channel 26 of the middle part 2 of the nozzle through the powder feeding channel. The powder is decelerated by the first collision with the wall to increase the laser heating time. The outside of the powder flow channel 26 is conical.

[0054] The powder flow channel 26 as a whole contracts at a certain angle to ensure that the powder converges at the end and the end is least affected by the water pressure. The powder delivery channel enters the powder flow channel 26 in the middle part 2 of the nozzle and is injected into the powder mixing chamber at a certain angle. The lateral injection increases the outlet area of ​​the powder when it reaches the powder mixing chamber, making the powder more uniform. At the same time, the area where the powder hits the wall of the powder mixing chamber increases, and the powder deceleration effect is more obvious.

[0055] The lower surface of the nozzle top 1 has a protruding waterproof sealing groove 18 for sealing the protective gas and powder feeding gas path with the cooling water. The waterproof sealing groove 18 is equipped with an annular sealing ring to seal the nozzle top 1 with the external environment through extrusion. The top and bottom ends of the nozzle middle part 2 are respectively provided with sealing rings 22 and sealing rings to match the nozzle top 1 and the nozzle bottom 3 respectively;

[0056] There are a plurality of through positioning holes 24 around the middle portion 2 of the nozzle for positioning and connecting with subsequent components.

[0057] The nozzle lower part 3 and the nozzle middle part 2 have similar structures. The nozzle lower part 3 has a lower laser chamber 34, which is connected with the upper laser chamber 11 and the middle laser chamber 21 to form a laser chamber with protective gas. The powder enters the lower part 3 of the nozzle through the powder flow channel 26 and is fully mixed. The nozzle lower part 3 has a second air curtain / water curtain flow channel 35 connected with the first air curtain / water curtain flow channel 23 of the nozzle.

[0058] There are four positioning holes 36 around the nozzle lower part 3, which are used for positioning and connecting with the nozzle middle part 2 and the drainage upper part 4;

[0059] There are three sealing rings 31, 32, 33 in the lower part 3 of the nozzle, which are used to isolate the powder mixing chamber from the laser chamber and the external environment.

[0060] In the present application, an air curtain / water curtain flow channel 14 is added inside, so that the nozzle does not need an internal water cooling structure, which reduces the size and facilitates the heat dissipation inside the laser chamber (21).

[0061] The drainage upper part 4 is a circular plate-like structure, and its bottom extends outward to form a connecting part. The middle of the drainage upper part 4 is a laser powder chamber 43. The upper surface of the drainage upper part 4 has two third air curtain / water curtain flow channels 45, which are connected to the first air curtain / water curtain flow channel 23. The air curtain and the water curtain can pass through the interior to generate a protective curtain and cool the inside of the nozzle.

[0062] The upper surface of the drainage upper part 4 has four mounting holes 42 connected to the nozzle top 1, the nozzle middle 2, and the nozzle bottom 3.

[0063] The outer periphery of the drainage upper part 4 is provided with an annular sealing groove 41 and the inner part is provided with an annular sealing ring, which is connected with the nozzle lower part 3 to seal the nozzle. The sealing ring groove 41 is connected with the nozzle lower part 3 to isolate the water environment.

[0064] The drainage middle part 5 and the drainage lower part 6 have similar structures, both of which include an upper annular columnar structure and a lower truncated cone-shaped expansion section. The upper part of the drainage lower part 6 is connected to the connecting part of the drainage upper part 4, and the drainage middle part 5 is sleeved on the upper part of the drainage lower part 6.

[0065] The first air curtain / water curtain flow channel 23, the second air curtain / water curtain flow channel 35 and the third air curtain / water curtain flow channel 45 are connected to form a water and air curtain area to exclude the external water environment.

[0066] In another technical solution, the upper surface of the nozzle top 1 has a fixing screw hole 17 connected to the laser; the upper part of the lower nozzle lower part 3 has a concentric centering groove 32 for centering connection with the nozzle middle part 2; the top of the drainage middle part 5 is provided with an annular sealing groove 51 to form a seal with the drainage upper part 4. The laser powder chamber 43 is separated from the third air curtain / water curtain flow channel 45 by an annular partition 44.

[0067] In another technical solution, the upper inner wall of the drainage middle part 5 is provided with a thread 52, which is connected with the thread 46 of the outer wall of the connecting part of the drainage upper part 4 to form the outer wall of the protective curtain;

[0068] In another technical solution, an annular sealing groove 62 is provided at the top of the drainage lower part 6, which is connected to the drainage upper part 4 to form a seal, and the thread 61 on the upper outer wall of the drainage lower part 6 is connected to the thread 44 on the inner wall of the drainage upper part 4 to form the inner wall of the protective curtain.

[0069] In another technical solution, the expansion section 54 of the drainage middle part 5 and the expansion section 64 of the drainage lower part 6 both expand outward at an angle greater than 60°.

[0070] Figure 8 The velocity cloud diagram of the flow field of the annular coaxial powder feeding head. When the inlet and outlet airflows are stable and the residual converges, it can be found from the steady-state flow field that the velocity at the gas inlet pipe is relatively large. This is caused by the narrow pipe diameter. After the gas enters the chamber, the velocity decreases and fills the entire chamber. The gas velocity gradually decreases when it is ejected from the nozzle and part of the gas diverges ( Figure 8 (b)), but by adjusting the shielding gas flow rate in the central chamber, the divergence trend of the powder delivery airflow is reduced, making the overall airflow more uniform, reducing the powder divergence and facilitating the powder to converge at the laser focus position. When the shielding gas flow rate is too large, it will cause the airflow to diverge and increase the powder speed, which is not conducive to powder melting. In the SULC process, the unmelted powder is difficult to deposit in the molten pool, which increases the difficulty of underwater coating deposition. Figure 8 It can be seen that the gas velocity in the flow field can reach 70m / s, but the velocity at the outlet position is reduced to below 30m / s. Reducing the gas velocity can increase the particle laser heating time and improve the powder melting rate, but too low a gas velocity will lead to a decrease in the powder flow stiffness and cause the powder to diverge. The powder flow convergence point is difficult to ensure on the laser focal plane, which is not conducive to coating deposition in SULC.

[0071] Since the deposition point needs to be blocked by an air curtain to prevent the external water environment from continuously filling the deposition position, the gas flow rate of the air curtain needs to be greater than the powder delivery gas flow rate. According to preliminary calculations, when the air curtain expansion angle is less than 45°, the gas entrainment volume reaches 1:3, which will cause instability in the powder delivery flow field. When the expansion angle is 60°, the entrainment volume ratio is 1:7. By adjusting the powder delivery gas + protective gas flow rate and the air curtain flow rate, a suitable flow ratio can be obtained. In the simulation, 1:1, 3:1, and 5:1 were selected for calculation. When the air curtain gas flow rate is not higher than 3 times the powder delivery gas flow rate, it can be achieved that no gas entrainment will occur in the local area and the air curtain can form an annular protective cover outward.

[0072] Fig. 9 (a) is the gas distribution around a substrate with a diameter of 100 mm. The airflow will not be sucked inward within the range of 100 mm. Fig. 9(b) is an enlarged view of the inside of the air curtain. It can be found that when the powder delivery airflow and the air curtain flow rate are not greater than 1:3, the airflow backflow entrainment at the deposition point can be controlled, and the air curtain airflow expands outward to form a drainage effect. The drainage capacity of the high-pressure SULC nozzle with air curtain is further verified by the VOF multiphase model, and the effect of the air curtain on the water environment at different times is analyzed by the transient VOF model, and the water entrainment of the nozzle with the same structure without the air curtain is compared.

[0073] Fig.10 The distribution of gas and liquid phases outside the nozzle at 400ms, 1000ms, 1600ms, and 2400ms for nozzle structures with and without air curtains in transient calculations. Since a simplified two-dimensional rotational grid is used for calculations, a rebounding liquid phase will appear at the position of the rotational symmetry axis, which will not appear in a three-dimensional grid. It can be seen from the figure that the nozzle without an outer air curtain structure displaces the water environment by gradually expanding the gas at the deposition point. This expansion is accompanied by the collision of the liquid phase on the substrate surface, which will cause uneven water entrainment. Although the nozzle without an outer air curtain can also displace water after a sufficiently long calculation time (the nozzle used for low-pressure SULC), this time is longer than that of the nozzle with an air curtain structure. In a high-pressure environment, the pressure difference between the nozzle gas and the external pressure is kept the same as that of the normal-pressure SULC, but the high-pressure liquid phase reflux speed is faster. The air curtain makes the displacement speed faster and more conducive to the deposition of high-pressure coatings. The faster displacement speed can further increase the cladding speed of high-pressure SULC. The nozzle with air curtain is different from the structure without air curtain. The process of gas expansion to expel the water environment occurs outside the air curtain annular area, far away from the SULC deposition point. The water environment inside the air curtain is low in content and is emptied by powder delivery gas. At the same time, as the nozzle moves during the cladding process, the air curtain is located before the moving position of the middle part of the nozzle, which can effectively expel the water in advance. There is a high turbulence intensity area on the wall at the nozzle outlet. The velocity difference at the outlet position is large. The direction and speed change strongly in a small space, which is easy to cause the external water environment to be sucked in. The expansion angle of the annular air curtain reduces the turbulence development trend at the original position.

[0074] Fig.11The following is the cross-sectional SEM image of the Ni60A alloy coating using this nozzle under different parameters. It can be seen from the figure that when the laser power is 1200W, only a small amount of molten powder is deposited on the substrate, and there are cracks that penetrate the cladding layer. When the laser power is 1650W, the cross-sectional morphology of the coating is improved, but tiny cracks still appear. When the laser power is 2000W, the molten powder becomes significantly more, and the cladding layer morphology is better. When the laser power is low, the laser beam has less heat input to the substrate and powder, the substrate absorbs less heat, and the molten pool is shallow. The powder absorbs less heat, the amount of molten powder is small, so the cladding layer prepared when the laser power is too small is of poor quality, and even cracks appear. It can be seen from the cross-sectional diagram that when the laser power is constant, the powder feeding flow rate is increased, the coating thickness increases, and the cladding angle increases. When the laser heat input is constant, the powder feeding rate increases, the amount of molten powder per unit time increases, and the amount of deposited powder increases. The amount of powder increases, the drainage force increases, and a better cladding environment is created.

[0075] Fig.12 The macroscopic photo and cross-sectional SEM image of a single SULC iron-based coating. The nozzle uses Ar as the protective gas to form an air curtain and powder supply gas, which effectively prevents the oxidation of powder and substrate at high temperature. The protective gas flow rate is 1.3m 3 / h, the powder feeding gas pressure is 0.4MPa, and the powder feeding nozzle moving speed is 20mm / s.

[0076] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A ring-shaped coaxial powder feeding head for underwater laser cladding, characterized in that: It includes a nozzle top, a nozzle middle, a nozzle bottom, a drainage top, a drainage middle, and a drainage bottom which are sequentially installed and connected from top to bottom; The top of the nozzle is a circular plate-like structure, and the hollow part in the middle is the upper laser chamber; the upper surface of the top of the nozzle is provided with a plurality of screw holes for powder delivery, which penetrate directly through the top of the nozzle and the middle of the nozzle to form a powder delivery channel for powder to pass through; the upper surface of the top of the nozzle is provided with two connecting screw holes, which penetrate directly through the top of the nozzle and are connected to the upper part of the drainage to form a first air curtain / water curtain flow channel, which is used to provide gas or liquid to form an air curtain / water curtain, and form a local water-free area above the deposition point; The middle part of the nozzle includes a circular ring plate located at the upper part and a middle funnel located at the lower part. The middle of the circular ring plate is a middle laser chamber, which is connected to the upper laser chamber. The middle funnel has a powder flow channel inside. The powder enters the powder flow channel in the middle part of the nozzle through the powder feeding channel. The powder is decelerated when it hits the wall for the first time to increase the laser heating time. The structure of the lower part of the nozzle is similar to that of the middle part of the nozzle. The lower part of the nozzle has a lower laser chamber, which is connected with the upper laser chamber and the middle laser chamber to form a laser chamber with protective gas. The powder enters the lower part of the nozzle through the powder flow channel and is fully mixed. The lower part of the nozzle has a second air curtain / water curtain flow channel connected to the first air curtain / water curtain flow channel of the nozzle. The upper part of the drainage is a circular plate-like structure, and its bottom extends outward to form a connecting part. The middle of the upper part of the drainage is a laser powder chamber. The upper surface of the upper part of the drainage has two third air curtain / water curtain flow channels, which are connected to the first air curtain / water curtain flow channels. The air curtain and the water curtain can pass through the interior to generate a protective curtain and cool down the inside of the nozzle. The drainage middle part and the drainage lower part have similar structures, both of which include an upper annular columnar structure and a lower truncated cone-shaped expansion section. The upper part of the drainage lower part is connected to the connecting part of the drainage upper part, and the drainage middle part is sleeved on the upper part of the drainage lower part. The first air curtain / water curtain flow channel, the second air curtain / water curtain flow channel and the third air curtain / water curtain flow channel are connected to form a water and air curtain area to exclude the external water environment.

2. The annular coaxial powder feeding head for underwater laser cladding according to claim 1, characterized in that: A fixing screw hole is provided on the upper surface of the nozzle top for connection with the laser; a concentric centering groove is provided on the upper part of the lower nozzle bottom for connection with the middle part of the nozzle; an annular sealing groove is provided on the top of the middle part of the drainage for connection with the upper part of the drainage to form a seal, and the laser powder chamber is separated from the third air curtain / water curtain flow channel by an annular partition.

3. The annular coaxial powder feeding head for underwater laser cladding according to claim 1, characterized in that: The lower surface of the nozzle top has a laser protection mirror to protect the Aurora lens from water splashback and powder contamination when working in water; A countersunk hole is arranged on the side of the top of the nozzle for connecting the protective gas to prevent water from flowing back into the laser chamber in case of an accident.

4. The annular coaxial powder feeding head for underwater laser cladding according to claim 1, characterized in that: The powder flow channel as a whole contracts at a certain angle to ensure that the powder is gathered at the end while the end is minimally affected by the water pressure.

5. The annular coaxial powder feeding head for underwater laser cladding according to claim 1, characterized in that: A protruding waterproof sealing groove is provided on the lower surface of the nozzle top for sealing the protective gas and powder feeding gas path with the cooling water. An annular sealing ring is installed inside the waterproof sealing groove to seal the nozzle top 1 with the external environment through extrusion.

6. The annular coaxial powder feeding head for underwater laser cladding according to claim 1, characterized in that: There are three sealing rings in the lower part of the nozzle to isolate the powder mixing chamber from the laser chamber and the external environment.

7. The annular coaxial powder feeding head for underwater laser cladding according to claim 1, characterized in that: The outer periphery of the upper drainage part is provided with an annular sealing groove, and the inner part is provided with an annular sealing ring, which is connected with the lower part of the nozzle to seal the nozzle, and the sealing ring groove is connected with the lower part 3 of the nozzle to isolate the water environment.

8. The annular coaxial powder feeding head for underwater laser cladding according to claim 1, characterized in that: The upper inner wall of the middle part of the drainage is provided with a thread, which is connected with the thread of the outer wall of the connecting part of the upper part of the drainage to form the outer wall of the protective curtain.

9. The annular coaxial powder feeding head for underwater laser cladding according to claim 1, characterized in that: An annular sealing groove is arranged at the top of the drainage lower part, which is connected with the drainage upper part to form a seal, and the threads on the upper outer wall of the drainage lower part are connected with the threads on the inner wall of the drainage upper part to form the inner wall of the protective curtain.

10. The annular coaxial powder feeding head for underwater laser cladding according to claim 1, characterized in that: The expansion section in the middle of the drainage and the expansion section in the lower part of the drainage both expand outward at an angle greater than 60°.

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