Laser deposition repairing method for turbine runner chamber blade

Abstract

The invention provides a water turbine runner chamber blade laser deposition repairing method. The method comprises the following steps that S1, a to-be-repaired part of a blade is pretreated; s2, performing gridding partition planning on the to-be-repaired part to form a plurality of processing units; s3, laser deposition is conducted on the multiple machining units through a random and ordered machining strategy; s4, in the deposition process, based on curvature changes of all the machining units, the temperature of a molten pool in the machining area is monitored in real time, and the laser power is dynamically adjusted so that the temperature of the molten pool can be maintained within a preset threshold value interval; and S5, the deposition process in the step S3 and the step S4 is executed repeatedly, and layer-by-layer accumulation is conducted till the accumulated thickness of the deposition layer meets the repair thickness requirement of the blade. According to the method, a gridding partition strategy is adopted, a real-time closed-loop control method for the temperature of the molten pool based on the curvature characteristics is combined, and an efficient solution is provided for laser deposition repair of large-size and variable-curvature turbine runner chamber blades.

Description

Technical Field

[0001] This invention relates to the field of turbine runner blade repair technology, specifically to a laser deposition repair method for turbine runner blades. Background Technology

[0002] As the core component of hydroelectric power generation, the turbine's runner blades are subjected to the combined effects of high-speed water flow, silt abrasion, cavitation erosion, and alternating loads over long periods. This makes them prone to severe dimensional thinning, pitting, cracking, and even perforation in critical areas such as the inlet and outlet edges of the blades. These damages not only reduce the turbine's energy conversion efficiency but also cause unit vibration, threaten operational safety, and even lead to unplanned shutdowns, resulting in significant economic losses. Therefore, timely and efficient repair of damaged blades is crucial for ensuring the safe and stable operation of the power plant and extending equipment lifespan.

[0003] Traditional blade repair methods primarily employ welding techniques. However, the welding process involves concentrated and high-volume heat input, easily generating significant thermal stress in the repair area, leading to blade deformation and cracking. This is particularly pronounced for large-sized, thin-walled turbine blades with complex three-dimensional curved surfaces, where deformation is especially problematic. Post-repair repairs often require extensive and tedious reshaping and machining, resulting in long repair cycles and high costs. Furthermore, the weld overlay layer exhibits coarse microstructure and uneven composition, leading to unstable metallurgical bonding with the substrate, and its resistance to cavitation erosion and abrasion is insufficient to meet demanding operating conditions.

[0004] In recent years, laser deposition repair technology, as an advanced additive remanufacturing technology, has shown great potential in the field of blade repair due to its advantages such as low heat input, low dilution rate, fine cladding layer structure, and metallurgical bonding with the substrate. This technology simultaneously delivers powder and a high-energy laser beam to form a dense deposition layer on the substrate surface point by point and layer by layer, thereby restoring the geometric dimensions and performance of the part. However, directly applying laser deposition repair technology to large and complex curved surface parts such as turbine runner blades still faces significant challenges: 1. Challenges in Heat Accumulation and Deformation Control: The curved structure of the blade causes the length and direction of the repair path to change continuously, resulting in differences in the residence time and heat conduction conditions of the laser heat source in different curvature regions. Under a continuous and sequential deposition path, heat is prone to excessive accumulation in local areas (especially concave surfaces or areas with small curvature radii), forming an uneven temperature field, which generates large residual stress and ultimately leads to unpredictable warping deformation of the blade, affecting its hydraulic performance.

[0005] 2. Challenges in Consistent Repair Quality: Due to the complex geometry of the blade surface, the stability and morphology of the cladding pool are significantly affected by changes in the curvature of the matrix. In regions with drastic curvature changes, the coupling efficiency between the laser beam and the powder, as well as the flow behavior of the cladding pool, will alter. If fixed process parameters (such as constant laser power) are used for repair, fluctuations in the thickness, dilution rate, and even microstructure of the cladding layer in different areas will occur, making it difficult to guarantee the uniformity and reliability of the performance across the entire repaired area.

[0006] Therefore, there is an urgent need in this field for a laser deposition repair method that can effectively suppress thermal deformation and ensure uniform and stable repair layer quality for large-sized, variable curvature turbine runner blades. Summary of the Invention

[0007] To address the technical problems existing in the background art, this invention proposes a laser deposition repair method for turbine runner blades.

[0008] The present invention proposes a laser deposition repair method for turbine runner blades, comprising the following steps: S1. Pre-treat the parts of the blade to be repaired; S2. The area to be repaired is divided into grid-based partitions, which are then evenly divided into multiple processing units of roughly the same size. S3. Laser deposition is performed on the multiple processing units using a random and ordered processing strategy. S4. During the deposition process, based on the curvature change of each processing unit, the temperature of the molten pool in the processing area is monitored in real time, and the laser power is dynamically adjusted to keep the temperature of the molten pool within the preset threshold range. S5. Repeat the deposition process of steps S3 and S4, layer by layer, until the cumulative thickness of the deposition layer meets the repair thickness requirements of the blade.

[0009] Preferably, the randomized and ordered processing strategy is set as follows: any two spatially adjacent processing units are processed discontinuously in time; and for any two spatially adjacent processing units, their respective laser scanning paths are symmetrically arranged during laser deposition.

[0010] Preferably, any two spatially adjacent processing units are processed discontinuously in time. Specifically, after the current processing unit is selected, the next processing unit to be processed is randomly selected from other processing units that are not adjacent to the current processing unit and have not yet been processed.

[0011] Preferably, the laser scanning path is symmetrically arranged, specifically: with the common boundary between adjacent processing units as the baseline, the laser scanning path direction within the two processing units is mirror-symmetrical with respect to the baseline.

[0012] Preferably, in step S4, the strategy for dynamically adjusting the laser power is as follows: based on the deviation between the current molten pool temperature and the predetermined range, the laser power is adjusted in real time so that the current molten pool temperature is maintained within the preset threshold range.

[0013] Preferably, in step S4, the relationship between the molten pool temperature and the curvature change is as follows: in, T R The temperature of the molten pool. T 0 The initial temperature of the matrix. ρ The density of the deposited layer material, C p For specific heat capacity, k Where is the thermal diffusivity, a and b Process the length and width of the unit separately. w The width of the molten pool η abs For heat absorption rate, P For laser power, f For the heat source input frequency, r Let be the radius of curvature. s is the length of the surface with constant curvature.

[0014] Preferably, the initial parameters for laser deposition are: defocusing amount of -3 to 5 mm, laser power of 2000 to 2500 W, powder feed rate of 8 to 12 rmp, deposition rate of 20 to 30 mm / s, and protective gas flow rate of 10 to 15 L / min.

[0015] Preferably, in step S1, the pretreatment includes at least one of cleaning the area to be repaired, removing damaged material, and surface roughening treatment.

[0016] Preferably, in step S2, the number of rows and columns of the grid is not less than 3.

[0017] Preferably, in step S2, the length and width of the processing unit are both less than or equal to 500 nm.

[0018] This invention employs a gridded partitioning strategy combined with a real-time closed-loop control method for molten pool temperature based on curvature characteristics, providing an efficient solution for laser deposition repair of large-size and variable-curvature turbine runner blades. This method significantly improves repair efficiency and effectively suppresses deformation, making it particularly suitable for high-quality repair of severe dimensional thinning, pitting, and perforation defects caused by combined damage mechanisms such as cavitation erosion, abrasion, and scouring. Attached Figure Description

[0019] Figure 1This is a schematic diagram of the deposition sequence of the nine processing units in Example 1; Figure 2 This is a schematic diagram showing the scanning path relationship of the nine processing units in Example 1; Figure 3 This is a schematic diagram of the deposition sequence of the 16 processing units in Example 3. Detailed Implementation

[0020] Example 1 The present invention proposes a laser deposition repair method for turbine runner blades, comprising the following steps: S1. Pre-treatment of the blade portion to be repaired: First, the area of ​​the blade to be repaired and its surroundings are thoroughly cleaned using organic solvents such as acetone or ethanol to remove oil, moisture, and other impurities. Then, fatigue damage layers, microcracks, and other defects are removed by mechanical grinding or milling until the intact substrate material is exposed. Finally, the cleaned area is sandblasted to roughen the surface and improve the bonding strength between subsequent deposited layers and the substrate.

[0021] S2. Divide the area to be repaired into grid-based partitions, evenly dividing it into multiple processing units of roughly the same size: Three-dimensional scanning technology was used to acquire the three-dimensional morphological data of the area to be repaired on the blade. Based on the size and shape of the repair area, it was uniformly divided into multiple processing units of basically the same size. Specifically, in this embodiment, the repair area was divided into a 3×3 grid, totaling 9 processing units, each with a length and width of 500 nm.

[0022] S3, Random Ordered Laser Deposition A randomized and ordered processing strategy is used to perform laser deposition on the 16 processing units divided in step S2. The core of the randomized and ordered processing strategy is that any two spatially adjacent processing units are processed discontinuously in time; and, for any two spatially adjacent processing units, their respective laser scanning paths are symmetrically set during laser deposition.

[0023] The specific strategy is as follows: After selecting the current processing unit, the next processing unit to be processed is randomly selected from other processing units that are not adjacent to the current processing unit and have not yet been processed. For example, first, unit (2,2) is randomly selected to begin processing; after completion, the next processing unit cannot be (1,2), (2,1), (2,3), (3,2), etc., which are adjacent to (2,2), but should be randomly selected from the remaining units that are not adjacent to (2,2), such as (1,4), (4,1), etc. This process continues until all units have been processed. Figure 1As shown, the nine processing units are deposited in the order of 1→2→3→4→5→6→7→8→9, and any two spatially adjacent processing units are processed discontinuously in time. This "skipping processing" method can effectively disperse heat input, avoid excessive heat accumulation in local areas, and reduce thermal stress and deformation.

[0024] Simultaneously, for any two spatially adjacent processing units, their laser scanning paths are symmetrically arranged. Specifically, taking the common boundary between adjacent units as a baseline, the laser scanning path directions within the two units are mirror-symmetrical with respect to this baseline. That is, if the laser scanning direction of the first processing unit forms a first angle with a preset reference direction, and the laser scanning direction in other processing units adjacent to this unit forms a second angle with the preset reference direction, then the first angle and the second angle are symmetrical with respect to the boundary between the adjacent areas. For example, if the laser scanning direction in the first processing unit (e.g., unit (2,2)) forms a +45° angle (first angle) with the preset reference direction, then when laser deposition is subsequently performed in other processing units adjacent to this unit (e.g., unit (2,3)), its laser scanning direction should form a -45° angle (second angle) with the preset reference direction. In this way, the scanning path of unit (2,2) and the scanning path of unit (2,3) are mirror-symmetrical with respect to their common boundary. Figure 2 As shown, the deposition sequence of the nine processing units is 1→2→3→4→5→6→7→8→9, and the scanning paths of adjacent units are mirror-symmetric. This symmetrical scanning strategy helps to balance the heat distribution and material accumulation between adjacent regions, improving the microstructure uniformity of the repair layer.

[0025] S4, Dynamic Thermal Control During the deposition process, the molten pool temperature in the processing area is monitored in real time based on the curvature changes of each processing unit, and the laser power is dynamically adjusted to maintain the molten pool temperature within a preset threshold range (e.g., 1400℃~1600℃). The relationship between the molten pool temperature and the curvature change is described by the following model: in, T R The temperature of the molten pool. T 0 The initial temperature of the matrix. ρ The density of the deposited layer material, C p For specific heat capacity, k Where is the thermal diffusivity, a and b Process the length and width of the unit separately. w The width of the molten pool η abs For heat absorption rate,P For laser power, f For the heat source input frequency, r Let be the radius of curvature. s is the length of the surface with constant curvature.

[0026] The strategy for dynamically adjusting laser power is as follows: based on the deviation between the current molten pool temperature and the predetermined range, the laser power is adjusted in real time through a PID controller: if the molten pool temperature is higher than the upper threshold, the laser power is reduced; if it is lower than the lower threshold, the laser power is increased to ensure temperature stability.

[0027] This in-situ thermal control based on the curvature feedback of each processing unit can effectively compensate for the heat dissipation differences caused by the geometric changes of the surface, reduce the unevenness of heat accumulation between different regions, and thus obtain a repair layer with more consistent tissue properties.

[0028] S5, Layer-by-layer deposition Repeat steps S3 and S4 to deposit the material layer by layer until the cumulative thickness of the deposited layer meets the repair thickness requirements of the blade (e.g., 3-5 mm).

[0029] Process parameters In this embodiment, the initial parameters for laser deposition are: The defocusing amount is -3 to 5 mm; The laser power is 2000~2500 W; The powder feeding rate is 8~12 rpm; The deposition rate is 20~30 mm / s; The protective gas flow rate is 10~15 L / min.

[0030] Example 2 The difference between this embodiment and Embodiment 1 is that: In step S2, the repair area is divided into a 5×5 grid, with a total of 25 processing units, each with a length and width of 300nm.

[0031] In step S4, the molten pool temperature threshold range is adjusted to 1450℃~1550℃, and the molten pool temperature is monitored in real time using an infrared thermal imager.

[0032] Example 3 The difference between this embodiment and Embodiment 1 is that: In step S2, the repair area is planned as 4 rows × 4 columns, totaling 16 processing units. The length 'a' and width 'b' of each processing unit are both designed to be 400 nm. For example... Figure 3 As shown, the 16 processing units were deposited in the following order: 1→2→3→4→5→6→7→8→9→10→11→12→13→14→15→16.

[0033] The turbine runner blades repaired using the above method were tested and found to be: 1. The deposited layer is well bonded to the substrate and free from defects such as cracks and pores; 2. The repaired area has uniform hardness, and its mechanical properties meet the usage requirements; 3. The heat-affected zone is small, and the deformation is controlled within the allowable range.

[0034] As can be seen from the above, compared with the prior art, the beneficial effects of the present invention are specifically reflected in the following three aspects: I. In terms of thermal stress and deformation control: By forcing spatially adjacent processing units to be processed discontinuously in time, and supplementing it with symmetrical laser scanning paths, the heat accumulation chain caused by sequential scanning or adjacent continuous processing is completely broken, and the concentrated heat source is transformed into a discrete distribution, thereby significantly reducing the residual stress of the workpiece and the risk of thermal deformation during the repair process from the source.

[0035] II. Regarding the consistency of repair quality: By employing a closed-loop system that adjusts laser power in real time based on curvature, the temperature fluctuations in the molten pool caused by differences in heat dissipation conditions in different regions (convex and concave) of complex curved surfaces are overcome. This ensures that the entire repair area, regardless of curvature variations, achieves a uniform molten pool morphology and cooling conditions, thereby guaranteeing the uniformity of repair layer thickness, hardness, and microstructure, and eliminating localized weak points.

[0036] Third, in terms of overall performance and reliability: the synergistic innovation of thermal management and path planning methods not only obtained a metallurgically bonded repair layer without defects (such as cracks and pores), but also ensured that the repaired blades could restore their original aerodynamic shape and mechanical properties, significantly extending their service life and improving the operating efficiency and safety margin of the turbine.

[0037] In summary, this invention employs a gridded partitioning strategy combined with a real-time closed-loop control method for molten pool temperature based on curvature characteristics, providing an efficient solution for laser deposition repair of large-size and variable-curvature turbine runner blades. This method significantly improves repair efficiency and effectively suppresses deformation, making it particularly suitable for high-quality repair of severe dimensional thinning, pitting, and perforation defects caused by combined damage mechanisms such as cavitation erosion, abrasion, and scouring.

[0038] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for laser deposition repair of turbine runner blades, characterized in that, Includes the following steps: S1. Pre-treat the parts of the blade to be repaired; S2. The area to be repaired is divided into grid-based partitions, which are then evenly divided into multiple processing units of roughly the same size. S3. Laser deposition is performed on the multiple processing units using a random and ordered processing strategy. S4. During the deposition process, based on the curvature change of each processing unit, the temperature of the molten pool in the processing area is monitored in real time, and the laser power is dynamically adjusted to keep the temperature of the molten pool within the preset threshold range. S5. Repeat the deposition process of steps S3 and S4, layer by layer, until the cumulative thickness of the deposition layer meets the repair thickness requirements of the blade.

2. The laser deposition repair method for turbine runner blades according to claim 1, characterized in that, The randomized and ordered processing strategy is set as follows: any two spatially adjacent processing units are processed discontinuously in time; and for any two spatially adjacent processing units, their respective laser scanning paths are symmetrically set during laser deposition.

3. The laser deposition repair method for turbine runner blades according to claim 2, characterized in that, Any two spatially adjacent processing units are processed discontinuously in time. Specifically, after the current processing unit is selected, the next processing unit to be processed is randomly selected from other processing units that are not adjacent to the current processing unit and have not yet been processed.

4. The laser deposition repair method for turbine runner blades according to claim 2, characterized in that, The laser scanning path is symmetrically set, specifically: with the common boundary between adjacent processing units as the baseline, the laser scanning path direction within the two processing units is mirror-symmetrical with respect to the baseline.

5. The laser deposition repair method for turbine runner blades according to claim 1, characterized in that, In step S4, the strategy for dynamically adjusting the laser power is as follows: based on the deviation between the current molten pool temperature and the predetermined range, the laser power is adjusted in real time so that the current molten pool temperature is maintained within the preset threshold range.

6. The laser deposition repair method for turbine runner blades according to claim 1, characterized in that, In step S4, the relationship between the molten pool temperature and the curvature change is as follows: in, T R The temperature of the molten pool. T 0 The initial temperature of the matrix. ρ Density of the deposited layer material C p For specific heat capacity, k Where is the thermal diffusivity, a and b Process the length and width of the unit separately. w The width of the molten pool η abs For heat absorption rate, P For laser power, f For the heat source input frequency, r Let be the radius of curvature. s is the length of the surface with constant curvature.

7. The laser deposition repair method for turbine runner blades according to claim 1, characterized in that, The initial parameters for laser deposition are: defocusing amount of -3 to 5 mm, laser power of 2000 to 2500 W, powder feed rate of 8 to 12 rmp, deposition rate of 20 to 30 mm / s, and protective gas flow rate of 10 to 15 L / min.

8. The laser deposition repair method for turbine runner blades according to claim 1, characterized in that, In step S1, the pretreatment includes at least one of cleaning the area to be repaired, removing damaged material, and surface roughening treatment.

9. The laser deposition repair method for turbine runner blades according to claim 1, characterized in that, In step S2, the number of rows and columns of the grid is not less than 3.

10. The laser deposition repair method for turbine runner blades according to claim 1, characterized in that, In step S2, the length and width of the processing unit are both less than or equal to 500 nm.

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