Laser cladding head and laser cladding low porosity forming method

Abstract

This invention provides a laser cladding head and a method for forming low-porosity laser cladding. The laser cladding head includes a nozzle body, an annular air inlet, and a flow equalization assembly. The main protective gas enters through the air inlet and is first circumferentially distributed through the air inlet groove and vent holes of the annular air inlet, then radially evenly distributed through the air guide groove and flow equalization holes of the flow equalization assembly, and finally output to the molten pool area through the central channel. This solves the problems of local flow deviation, vortex, and uneven velocity of the main protective gas. The laser cladding head also includes an annular gas curtain assembly, which generates a high-speed annular auxiliary airflow through the Laval nozzle channel to form an annular barrier gas curtain around the powder flow and the main protective gas, preventing the lateral entrainment of external air; and a micro-negative pressure suction assembly, which suctions the mixed gas outside the annular barrier gas curtain, reducing gas retention and backflow at the edge of the molten pool. This invention can significantly reduce porosity and oxide inclusions in the laser cladding layer, and improve the density and bonding strength of the cladding layer.

Description

Technical Field

[0001] This invention relates to the field of laser cladding technology, and in particular to a laser cladding head and a laser cladding method for forming low porosity. Background Technology

[0002] Laser cladding technology is a surface engineering technology that uses a high-energy laser beam to melt metal powder and deposit it on the surface of a substrate to form a wear-resistant, corrosion-resistant, or high-temperature resistant cladding layer. It is widely used in mold repair, aerospace parts remanufacturing, mining machinery repair, and marine equipment repair.

[0003] Most existing laser cladding heads use a central channel for the laser beam to pass through and for the main protective gas to be output. In this structure, the main protective gas enters the nozzle directly from the side inlet and then flows into the central channel. However, before entering the central channel, the gas is prone to local high speed, flow deviation, vortex, or pressure fluctuations, resulting in uneven output of the main protective gas from the central channel. If the flow rate of the main protective gas is blindly increased, it can easily cause turbulence in the protective gas jet, leading to powder flow deviation, molten pool disturbance, or enhanced air entrainment.

[0004] Furthermore, the main protective gas output from the central channel primarily acts on the central region of the molten pool along the laser beam propagation direction, while its outer boundary remains in contact with the outside air. Under conditions of powder flow disturbance, rising thermal plume, or high-speed scanning, outside air can easily be entrained laterally into the molten pool protection zone from the periphery of the main protective gas jet and powder flow. For materials sensitive to oxygen, hydrogen, or water vapor, such as tin bronze, aluminum alloys, titanium alloys, and nickel-based alloys, if outside air is entrained into the molten pool region, or if metal vapor or oxide fumes remain at the edge of the molten pool and flow back, defects such as pores and oxide inclusions can easily form in the cladding layer, reducing its density and bonding strength. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a laser cladding head and a laser cladding low-porosity forming method to solve the problems in the prior art where the main protective gas directly enters the central channel, which easily causes local flow deviation, vortices and velocity unevenness, resulting in uneven output of the main protective gas; and the outer boundary of the main protective gas output from the central channel is in contact with the outside air, and under the conditions of powder flow disturbance, hot plume rise or high-speed scanning, the outside air is easily laterally entrained into the molten pool protection zone, resulting in defects such as pores and oxide inclusions in the cladding layer.

[0006] To achieve the above and other related objectives, the present invention provides the following technical solutions: In a first aspect, the present invention provides a laser cladding head, comprising a nozzle body, an annular air inlet, and a flow equalization assembly; The nozzle body has a central channel running along its axis inside, which is used for the laser beam to pass through and for the main protective gas to be output along the direction of laser beam propagation. The upper end of the nozzle body is provided with a mounting hole communicating with the central channel, and the outer wall of the nozzle body is provided with an air inlet for introducing the main protective gas. The annular air intake component is disposed in the mounting hole. An air intake groove is formed around the outer wall of the annular air intake component. The air intake groove is connected to the air inlet. Several through vent holes are formed around the air intake groove of the annular air intake component at intervals. The flow equalization component is coaxially disposed on the radial inner side of the annular air intake component. The flow equalization component includes at least one annular flow equalization element. The annular flow equalization element has a central hole that extends along its axis inside. The annular flow equalization element has an air guide groove around its outer wall. The annular flow equalization element has multiple flow equalization holes. The flow equalization holes are used to connect the air guide groove and the central hole. The central channel is connected to the central hole of the innermost annular flow equalization element.

[0007] With the above structure, the main protective gas enters through the air inlet on the outer wall of the nozzle body, first entering the air inlet groove on the outer wall of the annular air inlet and diffusing circumferentially along the air inlet groove. Then, it enters the flow equalization component through the vent holes on the annular air inlet, and is further circumferentially distributed through the air guide groove on the outer wall of the annular flow equalization component. It then enters the central hole from the outside in through multiple flow equalization holes, and finally enters the central channel through the central hole and is output to the molten pool area along the laser beam propagation direction. Because the air inlet groove and vent holes of the annular air inlet achieve circumferential distribution of the main protective gas, and the air guide groove and flow equalization holes of the annular flow equalization component achieve circumferential and radial flow equalization, the problems of local flow deviation, vortex, and velocity unevenness of the main protective gas are solved, improving the stability of the main protective gas output from the central channel.

[0008] Furthermore, the vent holes are arranged at uniform intervals or symmetrically along the circumference of the annular air inlet.

[0009] In a preferred embodiment, the flow equalization assembly includes at least two annular flow equalization elements, which are sequentially embedded radially from the outside to the inside. Adjacent annular flow equalization elements are connected by air guide grooves and flow equalization holes, allowing the main protective gas to pass through multiple stages of radial flow equalization from the outside in before entering the central hole of the innermost annular flow equalization element. This multi-stage nested flow equalization structure extends the airflow diffusion path, improves flow equalization damping and flow equalization effect, and makes the main protective gas entering the central channel more uniform and stable.

[0010] Preferably, the flow equalization holes on two adjacent annular flow equalization elements are staggered in the circumferential direction. By staggering them, the main protective gas can be prevented from passing through the multi-stage flow equalization elements along a straight path, thereby extending the airflow diffusion path and further improving the flow equalization effect.

[0011] More preferably, the flow equalization holes on the annular flow equalization element are distributed in a honeycomb pattern, or the flow equalization holes on the annular flow equalization element are distributed in a regular array of micropores, or the annular flow equalization element is a sintered metal porous medium. All of the above structures can subdivide, dampen, and homogenize the main protective gas, reducing airflow pulsation and radial velocity difference.

[0012] Furthermore, the flow equalization hole is obliquely disposed on the annular flow equalization member, and the height of the inlet end of the flow equalization hole is lower than that of its outlet end.

[0013] Furthermore, the central hole of the innermost annular flow equalizer communicates with the central channel to form a tapered hole with a gradually decreasing inner diameter. This allows the main protective gas entering the central hole through the flow equalizer to converge towards the central channel along the tapered hole. This tapered hole reduces the abrupt impact when the main protective gas enters the central channel, reduces airflow backflow and pulsation, and ensures stable airflow output along the laser beam propagation direction.

[0014] Furthermore, the nozzle body also includes a powder feeding channel surrounding the central channel. The powder feeding channel extends to the lower end face of the nozzle body to form a powder outlet, and the outer wall of the nozzle body has a powder feeding port communicating with the powder feeding channel. Powder enters the powder feeding channel through the powder feeding port and is output to the laser beam action area through the powder outlet, achieving coaxial powder feeding.

[0015] Furthermore, the laser cladding head also includes an annular gas curtain assembly, which includes an inner sleeve and an outer sleeve. The inner sleeve is coaxially sleeved on the outside of the nozzle body, and the outer sleeve is coaxially sleeved on the outside of the inner sleeve. An annular cavity surrounding the powder feeding channel is formed between the inner sleeve and the outer sleeve, as well as at least two Laval nozzle channels communicating with the annular cavity. The Laval nozzle channels include a converging section, a throat, and an expanding section connected in sequence, which are used to introduce auxiliary gas and generate a high-speed annular auxiliary airflow surrounding the main protective gas jet and the powder flow.

[0016] The high-speed annular auxiliary airflow is located outside the powder flow and the main protective gas. Its purpose is not to directly impact the center of the molten pool, but rather to form an annular barrier air curtain around the powder flow and the main protective gas, preventing outside air from being laterally entrained into the molten pool area. Through this structure, in addition to the stable output of the main protective gas from the central channel, external air is further isolated, thereby improving the stability of the local inert atmosphere around the molten pool.

[0017] Furthermore, the multiple Laval nozzle channels are arranged at uniform intervals along the circumference of the nozzle body.

[0018] Furthermore, the outlet of the Laval nozzle channel is located on the outer periphery of the powder outlet, causing a high-speed annular auxiliary airflow to form around the powder flow. This maintains a spatial separation between the annular barrier air curtain and the powder flow, reducing the cutting and disturbance of the powder flow by the high-speed auxiliary airflow.

[0019] Furthermore, there is an angle of 40° to 50° between the axis of the Laval nozzle flow channel and the axis of the nozzle body.

[0020] Furthermore, the main protective gas flow rate Q1 is 8 L / min to 25 L / min; The auxiliary gas flow rate Q2 is 5% to 40% of Q1; The auxiliary gas supply pressure is 0.15 MPa to 1.0 MPa.

[0021] Furthermore, a micro-negative pressure suction assembly is provided on the outer side of the annular gas curtain assembly. The micro-negative pressure suction assembly includes a suction chamber, a suction pipe communicating with the suction chamber, and a suction port communicating with the suction pipe. The suction port is located on the outer periphery of the outlet of the Laval nozzle flow channel and is used to suction the mixed gas outside the annular barrier gas curtain. The mixed gas includes at least one of the following: outside air, metal vapor, oxidized dust, water vapor, and a protective gas mixture.

[0022] Furthermore, the radial distance between the suction port and the outlet of the Laval nozzle channel is 2 mm to 15 mm.

[0023] Furthermore, the suction chamber is connected to a negative pressure generator, which is used to create a micro negative pressure of -0.2 kPa to -5 kPa at the suction port.

[0024] Furthermore, the laser cladding head also includes a flow field coupling control unit, which includes a pressure sensor, a flow meter, and a controller. The pressure sensor is used to detect at least one of the main protective gas pressure, auxiliary gas pressure, and suction negative pressure; the flow meter is used to detect at least one of the main protective gas flow rate, auxiliary gas flow rate, and suction flow rate; the controller is configured to match the auxiliary gas supply pressure in real time according to the main protective gas flow rate and the nozzle working distance, and to control the suction negative pressure of the micro-negative pressure suction assembly in conjunction.

[0025] A second aspect of the present invention provides a laser cladding method for forming low porosity materials, comprising the following steps: S1. Flow field pre-design: Based on computational fluid dynamics simulation, flow simulation is performed on the system model including the flow equalization component, central channel, powder channel, annular air curtain component and negative pressure suction component. The discrete phase model is coupled to track the trajectory of powder particles and dust particles, optimize structural parameters, predict the initial range of the main protective air flow rate that can output laminar flow field, and preliminarily determine the air curtain supply pressure range and the matching interval of suction air volume. S2. Determining the laminar flow process window: Build a physical system and, based on the prediction in step S1, determine the main protective gas flow window and working distance range that enable the central channel output airflow to maintain a stable laminar flow state and completely cover the molten pool area through experimental observation. This parameter range is defined as the laminar flow process window. S3. Determination of the gas curtain-suction coupling window: Based on the prediction in step S1, the gas curtain supply pressure range that can form a complete supersonic gas curtain barrier without interfering with the stability of the molten pool, and the suction negative pressure range that matches the gas curtain pressure are determined through experimental observation. This combination of parameters is defined as the gas curtain-suction coupling window. S4. Collaborative cladding: The main protective gas flow rate and nozzle working distance are set within the laminar flow process window determined in step S2. At the same time, the air curtain supply pressure and suction negative pressure are set within the air curtain-suction coupling window determined in step S3. Powder is transported through the annular powder channel to perform laser cladding.

[0026] As described above, the laser cladding head and laser cladding low-porosity forming method of the present invention have the following beneficial effects: 1. This invention, by incorporating an annular air inlet, transforms the main protective gas entering from a single or a few inlets into a circumferentially distributed airflow, reducing flow deviation problems caused by unilateral or localized air intake. Furthermore, by using an annular flow equalization component located inside the annular air inlet, the main protective gas undergoes radial and axial flow equalization via a guide groove and multiple flow equalization holes before entering the central channel. This further weakens large-scale vortices, velocity pulsations, and local pressure differences, improving the stability of the main protective gas output from the central channel. When the flow equalization assembly includes at least two annular flow equalization components, the main protective gas can pass through multiple stages of circumferential distribution and radial flow equalization from the outside in, resulting in a more uniform and stable main protective gas entering the central channel, suitable for output to the molten pool region along the laser beam channel.

[0027] 2. This invention, by setting an annular air curtain assembly on the outside of the nozzle body and using the Laval nozzle flow channel to generate a high-speed annular auxiliary airflow surrounding the main protective gas jet and powder flow, can form an annular barrier air curtain around the main protective gas jet and powder flow, preventing external air from being laterally drawn into the molten pool area.

[0028] 3. The present invention uses a micro-negative pressure suction component to draw air, metal vapor, oxidized fumes and mixed gases outside the annular barrier gas curtain, which can reduce the retention and backflow of these gases at the edge of the molten pool, and further reduce the probability of the formation of pores and oxide inclusions.

[0029] 4. The present invention uses a flow field coupling control unit to match the supply pressure of the annular air curtain component in real time according to the main protective gas flow rate and the working distance of the nozzle, and controls the suction negative pressure of the micro negative pressure suction component in conjunction with the flow field coupling control unit. This ensures that the main protective gas, the annular barrier air curtain and the micro negative pressure suction maintain coordinated matching, and avoids the air curtain from interfering with the powder flow or the suction from disturbing the molten pool.

[0030] 5. This invention improves the stability and repeatability of low porosity forming by pre-designing the flow field, determining the laminar flow process window, determining the gas curtain-suction coupling window, and the collaborative cladding process. This is achieved by determining the parameter window based on the airflow state, powder particle trajectory, and dust particle trajectory, rather than relying on experience to adjust the protective gas flow rate during laser cladding. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of the laser cladding head disclosed in Embodiment 1 of the present invention.

[0032] Figure 2 This is a cross-sectional schematic diagram of the laser cladding head disclosed in Embodiment 1 of the present invention.

[0033] Figure 3 This is a disassembly diagram of the laser cladding head disclosed in Embodiment 1 of the present invention.

[0034] Figure 4 This is a cross-sectional schematic diagram of the laser cladding head disclosed in Comparative Example 1.

[0035] Figure 5-1 The CFD internal flow field simulation diagram of the single-sided air-inlet cladding head in Comparative Example 1 is shown. Figure 5-2 This is a CFD simulation diagram of the internal flow field of the laser cladding head in Embodiment 1 of the present invention.

[0036] Figure 6-1 Metallographic image of the cross-section of CuSn12Ni2 cladding layer obtained from the single-sided gas inlet cladding head in Comparative Example 1; Figure 6-2 This is a metallographic image of the cross-section of the CuSn12Ni2 cladding layer obtained by the laser cladding head in Embodiment 1 of the present invention.

[0037] Figure 7 This is a cross-sectional schematic diagram of the laser cladding head disclosed in Embodiment 5 of the present invention.

[0038] Component designation explanation 1. Nozzle body; 2. Central channel; 3. Mounting hole; 4. Air inlet; 5. Annular air inlet; 6. Air inlet groove; 7. Vent hole; 8. Annular flow equalization component; 9. Central hole; 10. Air guide groove; 11. Flow equalization hole; 12. Powder delivery channel; 13. Powder delivery port; 14. Annular air curtain assembly; 15. Inner sleeve; 16. Outer sleeve; 17. Annular cavity; 18. Laval nozzle flow channel. Detailed Implementation

[0039] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. It should be noted that, unless otherwise specified, the following embodiments and features described herein can be combined with each other.

[0040] Example 1 Please see Figures 1-3 This embodiment provides a laser cladding head, including a nozzle body 1, an annular air inlet 5, and a flow equalization component.

[0041] The nozzle body has a central channel 2 running along its axis inside. The central channel 2 is used for the laser beam to pass through and for the main protective gas to be output along the direction of laser beam propagation. The upper end of the nozzle body 1 has a mounting hole 3 that communicates with the central channel 2. The outer wall of the nozzle body 1 has an air inlet 4 that communicates with the mounting hole 3 and is used to introduce the main protective gas.

[0042] An annular air inlet 5 is disposed within the mounting hole 3. The annular air inlet 5 is a cylindrical structure with openings at the top and bottom. An air inlet groove 6 is formed around the outer wall of the annular air inlet 5, which communicates with the air inlet 4. Several through vent holes 7 are formed at intervals around the air inlet groove 6. After the main protective gas enters through the air inlet 4, it first enters the air inlet groove 6 and diffuses circumferentially along the air inlet groove 6, and then enters the flow equalization component through the vent holes 7. In this embodiment, four vent holes 7 are formed at intervals on the annular air inlet 5, and the four vent holes 7 are evenly spaced along the circumference of the annular air inlet 5.

[0043] The flow equalization assembly is disposed inside the annular air intake 5. In this embodiment, the flow equalization assembly includes an annular flow equalization component 8. The annular flow equalization component 8 has a central hole 9 that extends along its axis inside. The annular flow equalization component 8 has an air guide groove 10 around its outer wall. The annular flow equalization component 8 has a plurality of flow equalization holes 11, which are used to connect the air guide groove 10 and the central hole 9. The central channel 2 is connected to the central hole 9 of the annular flow equalization component 8.

[0044] In this embodiment, the flow equalization holes 11 on the annular flow equalization component 8 are distributed in a honeycomb pattern, causing the flow equalization holes 11 to be misaligned in both the circumferential and axial directions, thereby further achieving flow equalization in both the axial and circumferential directions. The flow equalization holes 11 are obliquely arranged on the annular flow equalization component 8, and the height of the inlet end of the flow equalization hole 11 is lower than its outlet end; this oblique arrangement allows for further axial flow equalization of the main protective gas, and the equalized main protective gas more easily enters the central channel 2.

[0045] In this embodiment, the central hole 9 of the annular flow equalizer 8 is connected to the central channel 2 to form a tapered hole with a gradually decreasing inner diameter. After the main protective gas enters the central hole 9 through the flow equalizer 11, it converges towards the central channel 2 along the tapered hole. The tapered hole can reduce the sudden impact when the main protective gas enters the central channel 2, reduce airflow backflow and pulsation, and ensure stable airflow output along the laser beam propagation direction.

[0046] After the main protective gas enters the flow equalization assembly through the vent 7 of the annular air inlet 5, it first enters the air guide groove 10 and is distributed circumferentially along the air guide groove 10. Then, it enters the central hole 9 from the outside to the inside through multiple flow equalization holes 11, and finally enters the central channel 2 through the central hole 9 and is output to the molten pool area along the laser beam propagation direction. Since the air inlet groove 6 and vent 7 of the annular air inlet 5 realize the circumferential distribution of the main protective gas, and together with the air guide groove 10 and flow equalization holes 11 of the annular flow equalization component 8, the circumferential, axial and radial flow equalization is realized, which solves the problems of local flow deviation, vortex and velocity unevenness of the main protective gas, and improves the stability of the main protective gas output from the central channel 2.

[0047] It is understandable that the flow equalization holes 11 on the annular flow equalization element 8 can be distributed in a honeycomb pattern; they can also be distributed in a regular array of micropores; or the annular flow equalization element 8 can be made into a sintered metal porous medium, thereby naturally forming multiple irregularly distributed flow equalization holes 11. All three structures can subdivide, dampen, and homogenize the main protective gas, reducing airflow pulsation and radial velocity difference.

[0048] Example 2 This embodiment provides a laser cladding method for forming low porosity laser cladding based on the laser cladding head in Embodiment 1, including the following steps: S1. Flow field pre-design: Based on computational fluid dynamics (CFD) simulation, flow simulation is performed on the system model containing the laser cladding head in Example 1, structural parameters are optimized, and the initial range of the main protective gas flow rate that can output laminar flow field is predicted. S2. Determination of laminar flow process window: Build a physical system and, based on the prediction in step S1, determine the main protective gas flow window and working distance range that can keep the central channel output airflow in a stable laminar flow state and completely cover the molten pool area through experimental observation. This parameter range is defined as the laminar flow process window. S3, Laminar Flow Cladding: The main protective gas flow rate and nozzle working distance in the laser cladding process are set within the laminar flow process window to perform laser cladding on the workpiece.

[0049] In this embodiment, the experimental observation method in step S2 is either smoke visualization or particle image velocimetry.

[0050] In this embodiment, the material laser cladding in step S3 is CuSn12Ni2 tin bronze.

[0051] Comparative Example 1 Comparative Example 1 provides a laser cladding head, which differs from Example 1 in that: this cladding head does not include an annular air inlet and a flow equalization assembly. (Refer to...) Figure 4 A conical hole is directly formed through the center of the nozzle body, and an air inlet communicating with the conical hole is formed on the outer wall of the nozzle body. The laser cladding head of Comparative Example 1 is laser claddinged using the method in Example 2.

[0052] Among them, the CFD internal flow field simulation diagram of the single-sided air-inlet cladding head in Comparative Example 1 is as follows: Figure 5-1 As shown; the CFD internal flow field simulation diagram in step S1 of Example 1 is as follows. Figure 5-2 As shown.

[0053] Metallographic image of the cross-section of CuSn12Ni2 cladding layer obtained from the single-sided gas inlet cladding head in Comparative Example 1 is shown below. Figure 6-1 As shown; the cross-sectional metallographic image of the CuSn12Ni2 cladding layer obtained by the laser cladding head in Example 1 is shown below. Figure 6-2 As shown.

[0054] Example 3 Based on Embodiment 1, this embodiment includes at least two annular flow equalization components 8, which are sequentially embedded radially from the outside to the inside. Adjacent annular flow equalization components 8 are connected by air guide grooves 10 and flow equalization holes 11, allowing the main protective gas to pass through multiple stages of radial flow equalization from the outside to the inside before entering the central hole 9 of the innermost annular flow equalization component 8, and then exiting from the central channel 2. This multi-stage nested flow equalization structure extends the airflow diffusion path, improves flow equalization damping and flow equalization effect, and makes the main protective gas entering the central channel 2 more uniform and stable.

[0055] In this embodiment, the flow equalization holes 11 on two adjacent annular flow equalization components 8 are staggered in the circumferential direction. By staggering them, the main protective gas can be prevented from passing through the multi-stage flow equalization components along a straight path, thereby extending the airflow diffusion path and further improving the flow equalization effect.

[0056] In this embodiment, the central hole 9 of the innermost annular flow equalizer 8 is connected to the central channel 2 to form a tapered hole with a gradually decreasing inner diameter; this allows the main protective gas entering the central hole 9 through the flow equalizer 11 to converge towards the central channel 2 along the tapered hole. This tapered hole can reduce the sudden impact when the main protective gas enters the central channel 2, reduce airflow backflow and pulsation, and ensure stable airflow output along the laser beam propagation direction.

[0057] Example 4 Based on Embodiment 1 or Embodiment 3, this embodiment further includes a powder feeding channel 12 surrounding the central channel 2 within the nozzle body. The powder feeding channel 12 extends to the lower end face of the nozzle body to form a powder outlet, and a powder feeding port 13 communicating with the powder feeding channel 12 is provided on the outer wall of the nozzle body. Powder enters the powder feeding channel 12 through the powder feeding port 13 and is output to the laser beam action area through the powder outlet, achieving coaxial powder feeding.

[0058] Example 5 Based on Example 4, this embodiment further includes an annular air curtain assembly 14 in the laser cladding head.

[0059] refer to Figure 7 The annular air curtain assembly 14 includes an inner sleeve 15 and an outer sleeve 16. The inner sleeve 15 is coaxially sleeved on the outside of the nozzle body 1, and the outer sleeve 16 is coaxially sleeved on the outside of the inner sleeve 15. An annular cavity 17 surrounding the nozzle body 1 and at least two Laval nozzle channels 18 communicating with the annular cavity 17 are formed between the inner sleeve 15 and the outer sleeve 16.

[0060] Each Laval nozzle channel 18 includes a converging section, a throat, and an expanding section connected in sequence, used to introduce auxiliary gas and generate a high-speed annular auxiliary airflow surrounding the main protective gas jet and the powder flow.

[0061] The number of Laval nozzle channels 18 is preferably four or more, and these multiple Laval nozzle channels 18 are arranged at uniform intervals along the circumference of the nozzle body 1 to ensure that the annular auxiliary airflow is evenly distributed in the circumferential direction. The outlet of the Laval nozzle channel 18 is located on the outer periphery of the powder outlet, so that the high-speed annular auxiliary airflow is formed around the powder flow. Thus, the annular barrier air curtain maintains a spatial separation from the powder flow, which can reduce the cutting and disturbance of the powder flow by the high-speed auxiliary airflow. Furthermore, there is an angle of 40° to 50° between the axis of the Laval nozzle channel 18 and the axis of the nozzle body 1.

[0062] A high-speed annular auxiliary airflow is located around the powder flow and the main protective gas, forming an annular barrier gas curtain to prevent outside air from being laterally entrained into the molten pool area. This structure, based on the stable output of the main protective gas from the central channel 2, further isolates the external air, thereby improving the stability of the local inert atmosphere around the molten pool.

[0063] In this embodiment, the auxiliary gas flow rate is 5% to 40% of the main protective gas flow rate, and the auxiliary gas supply pressure is 0.15 MPa to 1.0 MPa. For example, when the main protective gas flow rate is 15 L / min, the auxiliary gas flow rate can be set to 0.75 L / min to 6 L / min, and the auxiliary gas supply pressure can be set to 0.3 MPa to 0.8 MPa.

[0064] In this embodiment, the main protective gas and the auxiliary gas are selected from at least one of argon and nitrogen.

[0065] Example 6 Based on Example 5, this embodiment also includes a micro-negative pressure suction component on the outside of the annular air curtain assembly 14.

[0066] The micro-negative pressure suction assembly includes a suction chamber, a suction pipe communicating with the suction chamber, and a suction port communicating with the suction pipe. The suction port is located on the outer periphery of the outlet of the Laval nozzle flow channel 18 and is used to suction the mixed gas outside the annular barrier gas curtain. The mixed gas includes at least one of the following: outside air, metal vapor, oxidized dust, water vapor, and a protective gas mixture.

[0067] The radial distance between the suction port and the outlet of the Laval nozzle flow channel 18 is 2 mm to 15 mm. For example, in practical applications, this radial distance can be set to 5 mm, 8 mm, or 12 mm. A suction chamber is connected to a negative pressure generator, which is used to create a micro-negative pressure of -0.2 kPa to -5 kPa at the suction port. For example, when a larger volume of mixed gas needs to be suctioned, the micro-negative pressure can be set to -3 kPa to -5 kPa; when it is necessary to avoid excessive suction disturbing the molten pool, the micro-negative pressure can be set to -0.2 kPa to -1 kPa.

[0068] By using a micro-negative pressure suction component to draw in air, metal vapor, oxidized fumes, and mixed gases outside the annular barrier gas curtain, the retention and backflow of these gases at the edge of the molten pool can be reduced, further decreasing the probability of porosity and oxide inclusions.

[0069] Example 7 Based on Example 6, this embodiment also includes a flow field coupling control unit.

[0070] The flow field coupling control unit includes a pressure sensor, a flow meter, and a controller. The pressure sensor is used to detect at least one of the main protective gas pressure, auxiliary gas pressure, and suction negative pressure; the flow meter is used to detect at least one of the main protective gas flow rate, auxiliary gas flow rate, and suction flow rate; the controller is configured to match the auxiliary gas supply pressure in real time according to the main protective gas flow rate and the nozzle working distance, and to control the suction negative pressure of the micro negative pressure suction component in conjunction with the flow.

[0071] For example, when the main protective gas flow rate increases or the nozzle working distance increases, the controller automatically increases the auxiliary gas supply pressure to ensure that the annular barrier gas curtain can completely cover the periphery of the powder flow; at the same time, the controller also increases the suction negative pressure to enhance the suction effect on the mixed gas. Conversely, when the main protective gas flow rate decreases or the nozzle working distance decreases, the controller automatically reduces the auxiliary gas supply pressure and suction negative pressure to prevent the gas curtain from interfering with the powder flow or the suction from disturbing the molten pool.

[0072] By using a flow field coupling control unit, the main protective gas, the annular barrier gas curtain, and the micro-negative pressure suction are kept in synergy to ensure stable protection of the molten pool during laser cladding.

[0073] In this embodiment, the main protective gas flow rate is 8 L / min to 25 L / min. For example, for the repair of small-sized parts, the main protective gas flow rate can be set to 8 L / min to 12 L / min; for the additive manufacturing of large-sized parts, the main protective gas flow rate can be set to 18 L / min to 25 L / min.

[0074] Example 8 This embodiment provides a laser cladding low-porosity forming method based on the laser cladding head in Embodiment 6 or 7, including the following steps: S1. Flow field pre-design: Based on computational fluid dynamics simulation, the system model of the laser cladding head, which includes flow equalization components, central channel, powder channel, annular air curtain components and negative pressure suction components, is simulated. The discrete phase model is coupled to track the trajectory of powder particles and dust particles, optimize structural parameters, predict the initial range of the main protective gas flow rate that can output laminar flow field, and preliminarily determine the air curtain supply pressure range and the matching interval of suction air volume.

[0075] Specifically, a three-dimensional fluid computational domain was established, comprising the nozzle body, annular air inlet, flow equalization assembly, central channel, powder delivery channel, annular air curtain assembly, and micro-negative pressure suction assembly. Boundary conditions for the main protective gas, auxiliary gas, and suction flow rates were set. A turbulence model was used to solve the flow field distribution, and a coupled discrete phase model was used to track the trajectories of powder and dust particles. Through simulation analysis, the initial range of the main protective gas flow rate capable of forming a stable laminar flow field at the central channel outlet was determined; simultaneously, the air curtain supply pressure range capable of forming a complete annular barrier air curtain around the powder flow was determined; and the suction air volume range matching this air curtain pressure was determined.

[0076] S2. Determining the laminar flow process window: Build a physical system and, based on the prediction in step S1, determine the main protective gas flow window and working distance range that can keep the central channel output airflow in a stable laminar flow state and completely cover the molten pool area through experimental observation. This parameter range is defined as the laminar flow process window.

[0077] Specifically, a physical system including a laser cladding head, laser, powder feeder, and worktable was constructed. Under different main protective gas flow rates and nozzle working distances, experimental observation methods such as high-speed photography, schlieren, or laser-induced fluorescence were used to observe the flow state of the airflow at the outlet of the central channel. The experiments determined that when the main protective gas flow rate and nozzle working distance are within the simulated range in step S1, the airflow output from the central channel maintains a stable laminar flow state and can completely cover the molten pool area. This parameter range is defined as the laminar flow process window.

[0078] S3. Determination of the gas curtain-suction coupling window: Based on the prediction in step S1, the gas supply pressure range that can form a complete supersonic gas curtain barrier without interfering with the stability of the molten pool, and the suction negative pressure range that matches the gas curtain pressure are determined through experimental observation. This combination of parameters is defined as the gas curtain-suction coupling window.

[0079] Specifically, within the laminar flow process window determined in step 2, the main protective gas flow rate and nozzle working distance are fixed, while the auxiliary gas supply pressure and suction negative pressure are adjusted. The formation effect of the annular barrier gas curtain and the stability of the molten pool are observed experimentally. Experiments show that when the auxiliary gas supply pressure and suction negative pressure are within the simulated range of step S1, a complete supersonic gas curtain can be formed without interfering with the stability of the molten pool. This combination of parameters is defined as the gas curtain-suction coupling window.

[0080] S4. Collaborative cladding: Set the main protective gas flow rate and nozzle working distance within the laminar flow process window determined in step S2, and set the air curtain supply pressure and suction negative pressure within the air curtain-suction coupling window determined in step S3. Powder is transported through the annular powder channel to perform laser cladding.

[0081] During the cladding process, the flow field coupling control unit monitors the main protective gas flow rate, auxiliary gas pressure, and suction negative pressure in real time, and automatically adjusts the auxiliary gas supply pressure and suction negative pressure according to the change in working distance to ensure coordinated matching between the main protective gas, the annular barrier gas curtain, and the micro-negative pressure suction.

[0082] Using the above method, the laser cladding process no longer relies on empirical adjustment of the protective gas flow rate. Instead, the parameter window is determined based on the airflow state, powder particle trajectory, and dust particle trajectory, thereby improving the stability and repeatability of low-porosity forming. Experimental results show that the porosity of the laser cladding layer prepared by the method of this invention is reduced from 0.5% to 2% in traditional methods to 0.1% to 0.3%, the oxide inclusion content is significantly reduced, and the density and bonding strength of the cladding layer are significantly improved.

[0083] In summary, the main protective gas enters through the inlet and is first circumferentially distributed via the inlet groove and vent of the annular inlet component, then radially evenly distributed via the guide groove and flow equalization hole of the flow equalization component, and finally output to the molten pool area through the central channel. This solves the problems of localized flow deviation, vortices, and uneven velocity of the main protective gas. The laser cladding head also includes an annular gas curtain component, which generates a high-speed annular auxiliary airflow through the Laval nozzle channel to form an annular barrier gas curtain around the powder flow and the main protective gas, preventing the lateral entrainment of external air; and a micro-negative pressure suction component, which suctions the mixed gas outside the annular barrier gas curtain, reducing gas retention and backflow at the edge of the molten pool. This invention can significantly reduce porosity and oxide inclusions in the laser cladding layer, and improve the density and bonding strength of the cladding layer. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0084] The terms used in this specification, such as "upper," "lower," "left," "right," "front," "back," "middle," and "one," are merely for clarity of description and are not intended to limit the scope of the invention. Any changes or adjustments to their relative relationships, without substantially altering the technical content, shall also be considered within the scope of the invention.

[0085] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. All equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this invention should still be covered by the claims of this invention.

Claims

1. A laser cladding head, characterized in that, Includes the nozzle body, annular air intake component, and flow equalization assembly; The nozzle body has a central channel running along its axis inside, which is used for the laser beam to pass through and for the main protective gas to be output along the direction of laser beam propagation. The upper end of the nozzle body is provided with a mounting hole communicating with the central channel, and the outer wall of the nozzle body is provided with an air inlet for introducing the main protective gas. The annular air intake component is disposed in the mounting hole. An air intake groove is formed around the outer wall of the annular air intake component. The air intake groove is connected to the air inlet. Several through vent holes are formed around the air intake groove of the annular air intake component at intervals. The flow equalization component is disposed inside the annular air intake component. The flow equalization component includes at least one annular flow equalization element. The annular flow equalization element has a central hole that extends along its axis inside. The annular flow equalization element has an air guide groove around its outer wall. The annular flow equalization element has a plurality of flow equalization holes, which are used to connect the air guide groove and the central hole.

2. The laser cladding head according to claim 1, characterized in that, The vent holes are arranged at uniform intervals or symmetrically along the axial direction of the annular air inlet.

3. The laser cladding head according to claim 1, characterized in that, The flow equalization assembly includes at least two annular flow equalization elements, which are sequentially embedded radially from the outside to the inside.

4. The laser cladding head according to claim 1 or 3, characterized in that, The flow equalization holes on the annular flow equalization element are distributed in a honeycomb pattern; or the flow equalization holes on the annular flow equalization element are micropores distributed in a regular array; or the annular flow equalization element is a sintered metal porous medium.

5. The laser cladding head according to any one of claims 1 to 4, characterized in that, The flow equalization hole is obliquely disposed on the annular flow equalization component, and the height of the inlet end of the flow equalization hole is lower than that of its outlet end.

6. The laser cladding head according to any one of claims 1 to 5, characterized in that, The nozzle body is also provided with a powder feeding channel surrounding the central channel. The powder feeding channel extends to the lower end face of the nozzle body to form a powder outlet. The outer wall of the nozzle body is provided with a powder feeding port that communicates with the powder feeding channel.

7. The laser cladding head according to any one of claims 1 to 6, characterized in that, The laser cladding head also includes an annular gas curtain assembly; the annular gas curtain assembly includes an inner sleeve and an outer sleeve, the inner sleeve is fitted outside the nozzle body, and the outer sleeve is fitted outside the inner sleeve, forming an annular cavity surrounding the nozzle body and at least two Laval nozzle channels communicating with the annular cavity; the Laval nozzle channels include a converging section, a throat, and an expanding section connected in sequence, used to introduce auxiliary gas and generate a high-speed annular auxiliary airflow surrounding the main protective gas jet and the powder flow.

8. The laser cladding head according to claim 7, characterized in that, The auxiliary gas flow rate is 5% to 40% of the main protective gas flow rate; the auxiliary gas supply pressure is 0.15 MPa to 1.0 MPa.

9. The laser cladding head according to claim 7, characterized in that, The outer side of the annular air curtain assembly is also provided with a micro negative pressure suction assembly. The micro negative pressure suction assembly includes a suction chamber, a suction pipe connected to the suction chamber, and a suction port connected to the suction pipe. The suction port is located on the outer periphery of the outlet of the Laval nozzle flow channel and is used to suction the mixed gas outside the annular barrier air curtain.

10. A laser cladding method for forming low-porosity materials, characterized in that, Includes the following steps: S1. Flow field pre-design: Based on computational fluid dynamics simulation, the system model of the laser cladding head, which includes flow equalization components, central channel, powder channel, annular air curtain components and negative pressure suction components, is simulated. The discrete phase model is coupled to track the trajectory of powder particles and dust particles, optimize structural parameters, predict the initial range of the main protective gas flow rate that can output laminar flow field, and preliminarily determine the air curtain supply pressure range and the matching interval of suction air volume. S2. Determining the laminar flow process window: Build a physical system and, based on the prediction in step S1, determine the main protective gas flow window and working distance range that enable the central channel output airflow to maintain a stable laminar flow state and completely cover the molten pool area through experimental observation. This parameter range is defined as the laminar flow process window. S3. Determination of the gas curtain-suction coupling window: Based on the prediction in step S1, the gas curtain supply pressure range that can form a complete supersonic gas curtain barrier without interfering with the stability of the molten pool, and the suction negative pressure range that matches the gas curtain pressure are determined through experimental observation. This combination of parameters is defined as the gas curtain-suction coupling window. S4. Collaborative cladding: The main protective gas flow rate and nozzle working distance are set within the laminar flow process window determined in step S2. At the same time, the air curtain supply pressure and suction negative pressure are set within the air curtain-suction coupling window determined in step S3. Powder is transported through the annular powder channel to perform laser cladding.

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