Repair method for precise forming of blade tip of ultralow-stress single-crystal turbine blade

Abstract

The invention discloses an ultra-low stress single crystal turbine blade tip accurate forming repairing method which comprises the following steps: obtaining slice data capable of being used for SLM repairing by utilizing a complex profile blade section contour visual detection system; secondly, according to the size data obtained in the first step, a five-axis numerical control machine tool is adopted to carry out precise machining on the damaged part of the damaged blade to remove a damaged plane, machining and ultrasonic cleaning are carried out through a bench worker, and a repaired plane is obtained; a to-be-repaired blade is placed in an SLM equipment forming cylinder, a coordinate system of the repairing model is adjusted to coincide with a coordinate system of the to-be-repaired blade, an SLM high-temperature preheating system is started for preheating, and after preheating is completed, the SLM equipment is started to achieve additive repairing of the damaged blade; secondly, according to the size data obtained in the first step, machining allowance control is conducted on the repaired area of the repaired blade through a self-adaptive machining method till the size and tolerance requirements of the blade profile are met. The problem that an existing single-crystal turbine blade is difficult to repair is solved.

Description

Technical Field

[0001] The present invention relates to an aircraft engine maintenance method and field, and in particular to a repair method for the precise forming of an ultra-low stress single crystal turbine blade tip. Background Art

[0002] With the rapid development of the aviation industry, higher requirements are placed on the performance of aircraft engines. One of the main ways to improve the thrust of aircraft engines is to increase the turbine inlet temperature. In order to meet the stringent performance requirements of aircraft engines, nickel-based high-temperature alloys, as the base material of turbine blades, have undergone generational upgrades from equiaxed crystals, oriented crystals, and single crystals. The current single-crystal turbine blades can meet the turbine inlet temperature requirements of aircraft engines up to 1800 °C. The casting process of single-crystal turbine blades is complex, the yield is low, the cycle is long, and they contain a large amount of precious metals, such as Ru and Re, which makes the cost of single-crystal turbine blades extremely expensive. Since single-crystal turbine blades serve in an extremely high temperature and high pressure environment and are also subjected to extremely high composite forces, they may suffer microscopic damage such as wear, cracks, ablation, and corrosion, resulting in the degradation of blade performance and decommissioning. If new blades are used to replace blades with only microscopic damage, it is difficult to meet the needs of existing aircraft engines, and it will cause a huge waste of materials and is economically unaffordable. Therefore, the development of high-quality single-crystal turbine blade remanufacturing technology enables them to continue to serve, which can greatly reduce the engine operation and maintenance costs and improve the reliability of aviation equipment.

[0003] Single crystal turbine blade damage repair generally adopts selective laser melting (SLM). Through rapid laser scanning, the metal powder is melted and a large temperature gradient is formed, which promotes the directional solidification of the melt and shows an epitaxial growth trend. The core of epitaxial growth is to accurately control the process parameters, form a large temperature gradient, and form favorable solidification conditions. The large cooling rate produces large residual stress, which needs to be removed by reprocessing. The traditional stress relief method adopts heat treatment, which may cause tissue degradation and thermal cracking. Patent CN115700156 A discloses a method for removing residual stress after single crystal turbine blade repair. It is found that the residual stress in the repair area of ​​the single crystal turbine can be removed by hot isostatic pressing. However, the tenon of the single crystal turbine blade may be recrystallized after hot isostatic pressing, which cannot meet the repair requirements.

[0004] Therefore, how to achieve ultra-low residual stress in the repair area during the repair process to achieve the goal of reducing process flow and increasing the qualified rate of repaired turbine blades is an engineering challenge in the repair of single-crystal turbine blades. Summary of the invention

[0005] The purpose of the present invention is to provide a method for repairing the tip of an ultra-low stress single-crystal turbine blade with precise forming, so as to solve the problem of difficulty in repairing existing single-crystal turbine blades.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions: A repair method for the precise forming of the tip of an ultra-low stress single-crystal turbine blade comprises the following steps: Step 1: using a complex profile blade cross-section profile visual detection system to obtain slice data that can be used for SLM repair; Step 2: according to the size data obtained in Step 1, using a five-axis CNC machine tool to accurately machine the damaged part of the damaged blade to remove the damaged plane, and performing bench processing and ultrasonic cleaning to obtain a repair plane; Step 3: placing the blade to be repaired in a forming cylinder of an SLM device, adjusting the coordinate system of the repair model to make it coincide with the coordinate system of the blade to be repaired, turning on the SLM high-temperature preheating system for preheating, and after the preheating is completed, turning on the SLM device to implement additive repair of the damaged blade; Step 4: according to the size data obtained in Step 1, using an adaptive processing method to control the machining allowance of the repair area of ​​the repaired blade until the size and tolerance requirements of the blade profile are met.

[0007] The present invention first uses a complex-surface blade cross-section profile visual detection system to obtain the interface profile point cloud data of the blade to be repaired, and aligns it with the corresponding theoretical point cloud profile data to obtain slice data that can be used for SLM repair. Then, the damaged plane is accurately machined by a five-axis CNC machine tool to obtain a blade surface suitable for SLM repair. Finally, a customized SLM high-temperature preheating system is used to preheat the blade and monitor the blade body temperature in real time. The high-temperature blade is additively repaired according to the set SLM process strategy, and finally the ultra-low stress turbine blade is accurately formed and the performance is restored. The main reason why the final product has low stress after repair by this repair scheme is that, first, a clear contour to be repaired is obtained, and the repair material can be more accurately combined with the surface to be repaired during repair, and the combined surface has been processed and is cleaner. Second, the SLM high-temperature preheating system is used for preheating to reduce the temperature difference between the blade and the cladding layer. In addition, due to the SLM high-temperature preheating system, a slow cooling treatment can be performed after the cladding is completed, thereby effectively reducing the stress of the repaired product and obtaining a repaired single-crystal turbine blade with ultra-low stress.

[0008] As a further preference of the present invention, the specific steps of obtaining the slice data that can be used for SLM repair in step one are: using a complex-surface blade cross-section profile visual detection system to collect data on the blade body contour, preprocessing the collected data and splicing it to generate blade cross-section profile point cloud data, and aligning it with the corresponding theoretical point cloud contour data, and finally obtaining slice data that can be used for SLM equipment repair.

[0009] In addition, a complex blade cross-section profile visual inspection system is used, which can automatically and intelligently process the data obtained by reverse engineering based on the geometric model of the scanned blade, ensuring the precise forming of the blade tip.

[0010] As a further preferred embodiment of the present invention, the complex profile blade cross-section profile visual detection system comprises: a camera, a double telecentric lens and a planar shadowless light source.

[0011] For the specific structure, please refer to the solution disclosed in CN202310042581.4.

[0012] As a further preferred embodiment of the present invention, in the step 2, before using a five-axis CNC machine tool to accurately machine the damaged part of the damaged blade to remove the damaged plane, the blade to be repaired needs to be fixed in a special profiling fixture for turbine blades so that the blade tenon fits tightly with the fixture and the blade tip plane is ensured to be parallel to the horizontal plane.

[0013] Fixed tooling is used throughout the process to ensure accurate testing and repair of the blade tip profile.

[0014] As a further preferred embodiment of the present invention, in step 2, a five-axis CNC machine tool is used to process the blade tip so that the damage depth is 2-3 mm.

[0015] During the service of single crystal blades, a large amount of heat generated by instantaneous scraping produces thermal stress on the local microstructure of the blade tip, and the action depth is generally less than 2 mm. In order to ensure that the thermal stress generated during the blade scraping process is completely removed, the processing depth needs to be set to 2-3 mm during the processing of the damaged area of ​​the blade. By processing the blade tip to a depth of 2-3 mm, the local stress distribution at the blade tip can be changed, the high stress area generated during the service of the blade can be removed, and the cracking caused by thermal stress problems during the repair process can be guaranteed.

[0016] As a further preferred embodiment of the present invention, the temperature for preheating by the SLM high temperature preheating system in step three is 700-1000°C, and the preheating is completed when it is tested that the root temperature of the blade is consistent with the set temperature.

[0017] The preheating temperature is selected to be 700-1000 ℃, mainly because by reducing the temperature distribution gradient in the molten pool, a relatively wider and deeper molten pool is formed during laser scanning, which reduces the cooling rate of the molten pool, thereby significantly reducing the residual stress during the repair process. When the temperature is lower than 700 ℃, the temperature gradient is still large, and the cooling rate of the molten pool is still large, which cannot significantly reduce the residual stress. When the preheating temperature is too high, it may cause recrystallization of the blade body and tenon. The temperature of the substrate is maintained during the repair process, which is equivalent to a stress relief process, which also ensures ultra-low stress in the repair area after repair.

[0018] As a further preferred embodiment of the present invention, during the repair in step three, the laser power is 125-200 W, the scanning speed is 1000-1200 mm / s, the powder layer thickness is 20 μm, and the focal length is 0.09-0.11 μm; the scanning strategy is from the tip of the back of the blade - the end of the blade - the end of the blade basin.

[0019] Since the blade tip is thin, with a thickness of only 0.5-1.2 mm, and since the substrate preheating temperature is 700-1000°C, the laser power and scanning speed must be matched to reduce the instantaneous heat input of the blade and ensure that the blade tip does not collapse. The scanning path is scanned from the blade back to the blade basin, mainly because the thickness of the blade back is relatively thick, which can reduce the risk of blade tip collapse. In addition, the blade structure itself has structural stress, and the position with the largest structural stress is mainly located in the blade basin. Starting scanning from the blade back can ensure that when scanning to the blade basin, the substrate temperature is higher than the preheating temperature, thereby ensuring that the temperature gradient at the blade basin is small, and the cooling rate is even smaller when scanning the blade back, which can effectively ensure that the thermal stress at the blade basin is extremely low.

[0020] As a further preference of the present invention, the material of the blade is the second-generation nickel-based single crystal high-temperature alloy DD406, and the mass fractions of the alloy elements constituting the second-generation nickel-based single crystal high-temperature alloy DD406 are as follows: Cr: 3.8-4.8 parts, Co: 8.5-9.5 parts, W: 7.0-9.0 parts, Al: 5.2-6.2 parts, Ta: 6.0-8.5 parts, Mo: 1.5-2.5 parts, Re: 1.6-2.4 parts, Nb: 0-1.2 parts, Hf: 0.05-0.15 parts, C: 0.001-0.04 parts, Ni: 55.71-66.349 parts.

[0021] As a further preferred embodiment of the present invention, the repair powder used for repairing the blade made of the second-generation nickel-based single crystal high-temperature alloy DD406 is Rene 142 high-temperature alloy powder, the powder particle size is 15-45μm, and the mass fractions of the alloy elements constituting the Rene 142 high-temperature alloy powder are as follows: Cr: 6.5-7.0 parts, Co: 11.5-12.5 parts, Mo: 1.0-2.0 parts, Re: 2.5-3.2 parts, W: 4.8-5.2 parts, Al: 5.5-6.5 parts, Ta: 6-6.5 parts, Hf: 1.3-1.7 parts, B: 0.01-0.02 parts, Ni: 55.38-60.89 parts. .

[0022] The advantage of choosing Rene 142 high-temperature alloy powder to repair DD6 single crystal high-temperature alloy is that Rene 142 does not contain Ti, which can effectively reduce the risk of liquefaction cracks. In addition, the content of Co and Cr in the alloy composition of Rene 142 is higher than that of DD6, which can ensure that the repair area has good high temperature resistance and heat corrosion resistance.

[0023] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. The present invention first uses a complex-surface blade cross-section profile visual detection system to obtain the interface profile point cloud data of the blade to be repaired, and aligns it with the corresponding theoretical point cloud profile data to obtain slice data that can be used for SLM repair. Then, the damaged plane is accurately machined by a five-axis CNC machine tool to obtain a blade surface suitable for SLM repair. Finally, a customized SLM high-temperature preheating system is used to preheat the blade and monitor the blade body temperature in real time. According to the set SLM process strategy, the high-temperature blade is additively repaired, and finally the ultra-low stress turbine blade is accurately formed and the performance is restored. The main reason why the final product has low stress after repair by this repair scheme is that, first, a clear contour to be repaired is obtained, and the repair material can be more accurately combined with the surface to be repaired during repair, and the combined surface has been processed and is cleaner. Second, the SLM high-temperature preheating system is used for preheating to reduce the temperature difference between the blade and the cladding layer. In addition, due to the SLM high-temperature preheating system, a slow cooling treatment can be performed after the cladding is completed, thereby effectively reducing the stress of the repaired product, and a repaired single-crystal turbine blade with ultra-low stress is obtained.

[0024] 2. In addition, a complex blade cross-section profile visual inspection system is used, which can automatically and intelligently process the data obtained by reverse engineering based on the geometric model of the scanned blade, ensuring the precise forming effect of the blade tip.

[0025] 3. Fixed tooling is used throughout the process to ensure accurate testing and repair of the blade tip profile. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Flow chart for high temperature preheating of SLM repair for single crystal turbine blade tips.

[0027] Figure 2 Scanning path for high temperature preheating SLM repair of turbine blade tip. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0030] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0032] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0033] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the invention is usually placed when in use, or the positions or positional relationships commonly understood by those skilled in the art, 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 operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0034] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. Specific embodiment 1: During the development of a new DD406 single-crystal turbine blade, a 0.1 mm crack was found at the blade tip.

[0036] Figure 1 , Figure 2 The process of repairing by the method of the present invention is shown as follows: Step 1: Perform fluorescent flaw detection on the blade, and find a 0.1 mm crack at the tip and base of the blade, and mark it; Step 2: Use the complex blade cross-section profile visual inspection system to scan the blade tip to obtain the blade cross-section profile data, and cut the model to ensure that all cracks are removed; Step 3: Fix the blade in the special profiling fixture for turbine blades, so that the blade tenon fits tightly with the fixture, and at the same time ensure that the blade tip plane is parallel to the horizontal plane. According to the dimensional data obtained in step 2, the damaged surface is removed by precision machining using a five-axis CNC machine tool, and then polished and ultrasonically cleaned by a fitter to obtain a clean repair surface; Step 4: Place the blade to be repaired, which is fixed on the special profiling fixture for turbine blades, in the SLM equipment forming cylinder, and adjust the coordinate system of the repair model to coincide with the coordinate system of the blade to be repaired; use Rene 142 high-temperature alloy powder for repair; turn on the customized SLM high-temperature preheating system, and set the preset temperature to 700°C. When the blade temperature reaches 700°C, turn on the SLM program to extend and repair the blade tip; the repair path is the tip of the blade back-the end of the blade-the end of the blade basin; the repair process parameters are: laser power 150 W, scanning speed 1000 mm / s, powder layer thickness 20 μm, focal length 0.09-0.11 μm; Step 5: After the first layer is extended, wait for 5 seconds and repeat step 4 to extend the blade tip for the second layer; Step 6: Repeat step 4 to repair the third layer of the blade tip; Step 7: Based on the blade tip profile data obtained in step 2, the repaired blade is subjected to machining allowance control in the repaired area using an adaptive machining method until the size and tolerance requirements of the blade profile are met.

[0037] After the repair was completed, non-destructive testing was carried out on the repaired blade and no macro or micro cracks were found.

[0038] Comparative Example 1: SLM extension was carried out on the DD406 sample at a preheating temperature of 180 ℃, and stress relief annealing was performed after sample preparation. The results showed that macro thermal cracks appeared at the starting point of the scan after annealing. This was mainly due to the low substrate temperature at the starting point of the scan, the large temperature gradient of the molten pool after powder scanning, and the high cooling rate, which led to high residual thermal stress after the starting point of the scan. During the stress relief annealing process, the release of thermal stress led to the generation of macro cracks. Under the same conditions, SLM extension was carried out on the DD406 sample at a preheating temperature of 700 ℃. No macro cracks were generated after heat treatment, indicating that high-temperature preheating of the substrate can significantly reduce the thermal stress in the repair area, thereby reducing the crack sensitivity and ensuring the quality of the repaired blade. Specific embodiment 2: A repair method for the precise forming of the tip of an ultra-low stress single-crystal turbine blade comprises the following steps: Step 1: using a complex profile blade cross-section profile visual detection system to obtain slice data that can be used for SLM repair; Step 2: according to the size data obtained in Step 1, using a five-axis CNC machine tool to accurately machine the damaged part of the damaged blade to remove the damaged plane, and performing bench processing and ultrasonic cleaning to obtain a repair plane; Step 3: placing the blade to be repaired in a forming cylinder of an SLM device, adjusting the coordinate system of the repair model to make it coincide with the coordinate system of the blade to be repaired, turning on the SLM high-temperature preheating system for preheating, and turning on the SLM device after the preheating is completed to realize additive repair of the damaged blade; Step 4: according to the size data obtained in Step 1, using an adaptive processing method to control the machining allowance of the repair area of ​​the repaired blade until the size and tolerance requirements of the blade profile are met; The specific steps of obtaining the slice data that can be used for SLM repair in the step 1 are: using a complex profile blade cross-section profile visual detection system to collect data on the blade body profile, pre-processing the collected data and splicing them to generate blade cross-section profile point cloud data, and aligning them with the corresponding theoretical point cloud profile data, and finally obtaining slice data that can be used for SLM equipment repair; The complex profile blade cross-section profile visual detection system comprises: a camera, a double telecentric lens and a plane shadowless light source; In the step 2, before the damaged part of the damaged blade is precisely machined by a five-axis CNC machine tool to remove the damaged plane, the blade to be repaired needs to be fixed in a special profiling fixture for turbine blades so that the blade tenon fits tightly with the fixture and the blade tip plane is parallel to the horizontal plane. In the step 2, the blade tip damage depth is 2 mm using a five-axis CNC machine tool; The temperature of preheating by the SLM high temperature preheating system in step 3 is 700°C, and the preheating is completed when the blade root temperature is tested to be consistent with the set temperature; During the repair in step 3, the laser power is 150W, the scanning speed is 1100 mm / s, the powder layer thickness is 20 μm, and the focal length is 0.09 μm; the scanning strategy is from the tip of the back of the blade - the end of the blade - the end of the blade basin; The material of the blade is the second generation nickel-based single crystal high temperature alloy DD406, and the mass fractions of the alloy elements constituting the second generation nickel-based single crystal high temperature alloy DD406 are as follows: Cr: 3.8 parts, Co: 8.5 parts, W: 9.0 parts, Al: 5.5 parts, Ta: 6.0 parts, Mo: 1.5 parts, Re: 2.4 parts, Nb: 1 part, Hf: 0.05 parts, C: 0.001 parts, Ni: 57 parts; The repair powder used to repair the blades made of the second-generation nickel-based single crystal high-temperature alloy DD406 is Rene 142 high-temperature alloy powder with a powder particle size of 15 μm. The mass fractions of alloy elements constituting the Rene 142 high-temperature alloy powder are as follows: Cr: 6.5 parts, Co: 11.5 parts, Mo: 2.0 parts, Re: 2.8 parts, W: 4.8 parts, Al: 6.5 parts, Ta: 6.5 parts, Hf: 1.3 parts, B: 0.015 parts, Ni: 58. Specific embodiment 3: A repair method for the precise forming of the tip of an ultra-low stress single-crystal turbine blade comprises the following steps: Step 1: using a complex profile blade cross-section profile visual detection system to obtain slice data that can be used for SLM repair; Step 2: according to the size data obtained in Step 1, using a five-axis CNC machine tool to accurately machine the damaged part of the damaged blade to remove the damaged plane, and performing bench processing and ultrasonic cleaning to obtain a repair plane; Step 3: placing the blade to be repaired in a forming cylinder of an SLM device, adjusting the coordinate system of the repair model to make it coincide with the coordinate system of the blade to be repaired, turning on the SLM high-temperature preheating system for preheating, and turning on the SLM device after the preheating is completed to realize additive repair of the damaged blade; Step 4: according to the size data obtained in Step 1, using an adaptive processing method to control the machining allowance of the repair area of ​​the repaired blade until the size and tolerance requirements of the blade profile are met; The specific steps of obtaining the slice data that can be used for SLM repair in the step 1 are: using a complex profile blade cross-section profile visual detection system to collect data on the blade body profile, pre-processing the collected data and splicing them to generate blade cross-section profile point cloud data, and aligning them with the corresponding theoretical point cloud profile data, and finally obtaining slice data that can be used for SLM equipment repair; The complex profile blade cross-section profile visual detection system comprises: a camera, a double telecentric lens and a plane shadowless light source; In the step 2, before the damaged part of the damaged blade is precisely machined by a five-axis CNC machine tool to remove the damaged plane, the blade to be repaired needs to be fixed in a special profiling fixture for turbine blades so that the blade tenon fits tightly with the fixture and the blade tip plane is parallel to the horizontal plane. In the step 2, the blade tip damage depth is 2.5 mm using a five-axis CNC machine tool; The temperature of preheating by the SLM high temperature preheating system in step 3 is 1000°C, and the preheating is completed when the blade root temperature is consistent with the set temperature; During the repair in step 3, the laser power is 125W, the scanning speed is 1000mm / s, the powder layer thickness is 20 μm, and the focal length is 0.1 μm; the scanning strategy is from the tip of the back of the blade - the end of the blade - the end of the blade basin; The material of the blade is the second generation nickel-based single crystal high temperature alloy DD406, and the mass fractions of the alloy elements constituting the second generation nickel-based single crystal high temperature alloy DD406 are as follows: Cr: 4.8 parts, Co: 8.8 parts, W: 7.0 parts, Al: 5.2 parts, Ta: 7 parts, Mo: 2.5 parts, Re: 1.8 parts, Nb: 0 parts, Hf: 0.15 parts, C: 0.002 parts, Ni: 55.71 parts; The repair powder used to repair the blades made of the second-generation nickel-based single crystal high-temperature alloy DD406 is Rene 142 high-temperature alloy powder with a powder particle size of 30μm. The mass fractions of alloy elements constituting the Rene 142 high-temperature alloy powder are as follows: Cr: 6.8 parts, Co: 12.5 parts, Mo: 1.8 parts, Re: 3.2 parts, W: 5 parts, Al: 5.5 parts, Ta: 6.2 parts, Hf: 1.7 parts, B: 0.02 parts, Ni: 55.38. Specific embodiment 4: A repair method for the precise forming of the tip of an ultra-low stress single-crystal turbine blade comprises the following steps: Step 1: using a complex profile blade cross-section profile visual detection system to obtain slice data that can be used for SLM repair; Step 2: according to the size data obtained in Step 1, using a five-axis CNC machine tool to accurately machine the damaged part of the damaged blade to remove the damaged plane, and performing bench processing and ultrasonic cleaning to obtain a repair plane; Step 3: placing the blade to be repaired in a forming cylinder of an SLM device, adjusting the coordinate system of the repair model to make it coincide with the coordinate system of the blade to be repaired, turning on the SLM high-temperature preheating system for preheating, and turning on the SLM device after the preheating is completed to realize additive repair of the damaged blade; Step 4: according to the size data obtained in Step 1, using an adaptive processing method to control the machining allowance of the repair area of ​​the repaired blade until the size and tolerance requirements of the blade profile are met; The specific steps of obtaining the slice data that can be used for SLM repair in the step 1 are: using a complex profile blade cross-section profile visual detection system to collect data on the blade body profile, pre-processing the collected data and splicing them to generate blade cross-section profile point cloud data, and aligning them with the corresponding theoretical point cloud profile data, and finally obtaining slice data that can be used for SLM equipment repair; The complex profile blade cross-section profile visual detection system comprises: a camera, a double telecentric lens and a plane shadowless light source; In the step 2, before the damaged part of the damaged blade is precisely machined by a five-axis CNC machine tool to remove the damaged plane, the blade to be repaired needs to be fixed in a special profiling fixture for turbine blades so that the blade tenon fits tightly with the fixture and the blade tip plane is parallel to the horizontal plane. In the step 2, the blade tip damage depth is 3 mm using a five-axis CNC machine tool; The temperature of preheating by the SLM high temperature preheating system in step 3 is 800°C, and the preheating is completed when the blade root temperature is consistent with the set temperature; During the repair in step 3, the laser power is 200 W, the scanning speed is 1200 mm / s, the powder layer thickness is 20 μm, and the focal length is 0.11 μm; the scanning strategy is from the tip of the back of the blade - the end of the blade - the end of the blade basin; The material of the blade is the second generation nickel-based single crystal high temperature alloy DD406, and the mass fractions of the alloy elements constituting the second generation nickel-based single crystal high temperature alloy DD406 are as follows: Cr: 4 parts, Co: 9.5 parts, W: 8 parts, Al: 6.2 parts, Ta: 8.5 parts, Mo: 2.5 parts, Re: 1.6 parts, Nb: 1.2 parts, Hf: 0.10 parts, C: 0.04 parts, Ni: 66.349 parts; The repair powder used to repair the blades made of the second-generation nickel-based single crystal high-temperature alloy DD406 is Rene 142 high-temperature alloy powder with a powder particle size of 45 μm. The mass fractions of alloy elements constituting the Rene 142 high-temperature alloy powder are as follows: Cr: 7.0 parts, Co: 12 parts, Mo: 1.0 parts, Re: 2.5 parts, W: 5.2 parts, Al: 5.9 parts, Ta: 6 parts, Hf: 1.5 parts, B: 0.01 parts, and Ni: 60.89.

[0042] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for repairing the tip of an ultra-low stress single crystal turbine blade with precise forming, characterized in that: The method comprises the following steps: step 1: using a complex-surface blade cross-section profile visual detection system to obtain slice data that can be used for SLM repair; step 2: according to the size data obtained in step 1, using a five-axis CNC machine tool to accurately machine the damaged part of the damaged blade to remove the damaged plane, and performing bench processing and ultrasonic cleaning to obtain a repair plane; step 3: placing the blade to be repaired in the forming cylinder of the SLM equipment, adjusting the coordinate system of the repair model to make it coincide with the coordinate system of the blade to be repaired, turning on the SLM high-temperature preheating system for preheating, and turning on the SLM equipment after the preheating is completed to realize additive repair of the damaged blade; step 4: according to the size data obtained in step 1, using an adaptive processing method to control the machining allowance of the repair area of ​​the repaired blade until the size and tolerance requirements of the blade profile are met.

2. The method for repairing the ultra-low stress single crystal turbine blade tip precision molding according to claim 1, characterized in that: The specific steps for obtaining the slice data that can be used for SLM repair in step one are: using a complex-surface blade cross-section profile visual detection system to collect data on the blade body contour, preprocessing the collected data and splicing it to generate blade cross-section profile point cloud data, and aligning it with the corresponding theoretical point cloud profile data, and finally obtaining slice data that can be used for SLM equipment repair.

3. The method for repairing the ultra-low stress single crystal turbine blade tip precision molding according to claim 2, characterized in that: The complex profile blade cross-section profile visual detection system comprises: a camera, a double telecentric lens and a planar shadowless light source.

4. The method for repairing the ultra-low stress single crystal turbine blade tip precision molding according to claim 1, characterized in that: In the step 2, before using a five-axis CNC machine tool to accurately machine the damaged part of the damaged blade to remove the damaged plane, the blade to be repaired needs to be fixed in a special profiling fixture for turbine blades so that the blade tenon fits tightly with the fixture and the blade tip plane is parallel to the horizontal plane.

5. The method for repairing the ultra-low stress single crystal turbine blade tip precision molding according to claim 1, characterized in that: In the step 2, the blade tip damage depth is 2-3 mm when processed by a five-axis CNC machine tool.

6. The method for repairing the ultra-low stress single crystal turbine blade tip precision molding according to claim 1, characterized in that: In the step three, the preheating temperature using the SLM high temperature preheating system is 700-1000° C. The preheating is completed when the blade root temperature is tested to be consistent with the set temperature.

7. The method for repairing the ultra-low stress single crystal turbine blade tip precision molding according to claim 1, characterized in that: During the repair in step three, the laser power is 125-200 W, the scanning speed is 1000-1200 mm / s, the powder layer thickness is 20 μm, and the focal length is 0.09-0.11 μm; the scanning strategy is from the tip of the back of the leaf - the end of the blade - the end of the leaf basin.

8. The method for repairing the ultra-low stress single crystal turbine blade tip precision molding according to claim 1, characterized in that: The material of the blade is the second-generation nickel-based single crystal high-temperature alloy DD406, and the mass fractions of the alloy elements constituting the second-generation nickel-based single crystal high-temperature alloy DD406 are as follows: Cr: 3.8-4.8 parts, Co: 8.5-9.5 parts, W: 7.0-9.0 parts, Al: 5.2-6.2 parts, Ta: 6.0-8.5 parts, Mo: 1.5-2.5 parts, Re: 1.6-2.4 parts, Nb: 0-1.2 parts, Hf: 0.05-0.15 parts, C: 0.001-0.04 parts, Ni: parts.

9. The method for repairing the ultra-low stress single crystal turbine blade tip precision molding according to claim 8, characterized in that: The repair powder used to repair the blades made of the second-generation nickel-based single crystal high-temperature alloy DD406 is Rene 142 high-temperature alloy powder with a powder particle size of 15-45 μm. The mass fractions of the alloy elements constituting the Rene 142 high-temperature alloy powder are as follows: Cr: 6.5-7.0 parts, Co: 11.5-12.5 parts, Mo: 1.0-2.0 parts, Re: 2.5-3.2 parts, W: 4.8-5.2 parts, Al: 5.5-6.5 parts, Ta: 6-6.5 parts, Hf: 1.3-1.7 parts, B: 0.01-0.02 parts, and Ni: the rest.

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