Layered contour extraction and regional repair method for surface defects of aero-engine blade

Abstract

The invention discloses a layered contour extraction and regional repair method for surface defects of an aero-engine blade. The method comprises the following steps: layering an STL defect model, and extracting the outer contour of each layer of slice; optimal laser cladding repair process parameters are selected, and cladding is conducted on the outer contour according to the cladding width; after the outer contour is cladded, the remaining non-cladded area is compared with the blade tip area, and the position relation of the next-step cladding starting point is observed; dividing n branch lines according to the width of a non-cladding area, designing a curve path, realizing full coverage, performing simulation according to the designed path, summarizing advantages and disadvantages, and improving the curve path. According to the invention, the repair trajectory planning can be realized through joint analysis of the laser cladding parameters and the slice shape, and the aero-engine blade path planning method with high repair efficiency and high precision is provided.

Description

Technical Field

[0001] This invention belongs to the field of aero-engine blade repair technology, specifically relating to a method for extracting the layered contours and repairing different regions of aero-engine blades based on laser cladding, and particularly to a method for planning the repair trajectory of aero-engine blades. Background Technology

[0002] In the laser precision repair of aero-engine compressor blades and turbine blades, path planning technology is a key factor determining the repair quality and efficiency.

[0003] Currently, domestic and international research on path planning for blade repair mainly focuses on single-pass, single-layer scanning strategies, such as equally spaced parallel paths or simple contour offset methods, which are difficult to adapt to the repair needs of complex curved surface geometries and varying damage depths. Considering that traditional cladding methods are linear and contour scanning types, their repair efficiency for blades is relatively low; Traditional path planning methods have the following obvious limitations: Insufficient adaptability: Fixed scanning spacing and direction cannot match the changes in blade curvature, resulting in uneven cladding layer thickness and easy to produce defects such as incomplete fusion or over-fusion; Low efficiency: Simple reciprocating paths result in a high proportion of idle travel of the laser head, and frequent start-stop operations affect the stability of heat accumulation; Poor process coupling: Path parameters (such as scanning speed and overlap rate) lack dynamic collaborative optimization with process parameters such as laser power and powder feed rate, affecting the mechanical properties of the repair area.

[0004] In recent years, advanced research institutions abroad have developed adaptive path planning technology, such as using surface-based regional topology partitioning and variable-spacing spiral paths to achieve high coverage repair of complex surfaces. At the same time, combined with real-time melt pool monitoring feedback, the path trajectory and process parameters are dynamically adjusted. However, domestic research is still mainly based on offline programming, and the research on multi-axis linkage interpolation algorithms and damage feature-driven path generation is not deep enough, resulting in repair efficiency of only 60% to 70% of that abroad. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and propose a method for extracting the layered contours and repairing the surface defects of aero-engine blades in different regions. This method can realize the repair trajectory planning by jointly analyzing the laser cladding parameters and the slice shape, and provides a path planning method for aero-engine blades with high repair efficiency and high precision.

[0006] To achieve the above objectives, the present invention proposes the following technical solution: A method for extracting layered contours and repairing different regions of surface defects on aero-engine blades, used to repair complex blade models, specifically includes: S1) By dividing the STL defect model into layers, the outer contour of each slice is extracted; S2) Select the optimal laser cladding repair process parameters and perform cladding on the outer contour according to the cladding width; S3) After cladding the outer contour, compare the remaining unclad area with the blade tip area to observe the positional relationship of the starting point of the next cladding step. S4) Divide the uncladding area into n sub-lines, design a curved path to achieve full coverage, perform simulation based on the designed route, summarize the advantages and disadvantages, and improve the curved path.

[0007] Specifically, the method for extracting the layered contours and repairing the regional defects on the surface of aero-engine blades involves first cladding the blade substrate material with powder material, selecting the experimental parameters with the best morphology and performance, and measuring the cladding height and width to facilitate subsequent slicing and cladding path planning.

[0008] Further, in step S1), the STL defect model is layered, and the outer contour of each slice is extracted, specifically as follows: S1-1) For the identified STL model, perform equal-height layering based on the cladding height indicated by the optimal laser cladding parameters, and display all slices; S1-2) Export each slice as a fig file and read the fig file using the openfig function; S1-3) Calculate the actual length represented by 1 pixel, and display the slice at its original size in the three-dimensional coordinate system, in millimeters.

[0009] Further, in step S2), the optimal laser cladding repair process parameters are selected, and cladding is performed on the outer contour according to the cladding width, specifically as follows: S2-1) After reading a single-layer blade, extract the maximum outer contour of the blade; S2-2) Take n uniform points on the outer contour and perform cladding on the outer contour according to the cladding width.

[0010] Further, in step S3), after cladding the outer contour, the remaining unclad area is compared with the blade tip area to observe the positional relationship of the starting point for the next cladding step. Specifically: S3-1) Apply cladding along the centerline from the first processing point of the blade until a gap is created at the upper and lower ends of the blade. The gap is the unclad area. Take the intersection of the upper and lower contours and record this point as the first critical point. S3-2) Reduce the maximum contour by half the cladding width and extract the reduced contour; S3-3) Compare the first critical point with the position of the narrowed profile tip to confirm the starting point of the next cladding step, which will facilitate subsequent planning.

[0011] Further, in step S3-3), the starting point is confirmed by comparing the position of the first critical point with the tip of the reduced contour. Specifically, if the first critical point is inside the reduced contour, the starting point of the reduced contour is the first critical point when repairing in the second step of path planning, and the upper and lower critical points are the boundaries of the reduced contour. If the first critical point is outside the reduced contour, there is a gap between the first critical point and the reduced contour after the outer contour is clad. When repairing and cladding in the second step of path planning, the starting point is still the first critical point, and the upper and lower boundaries of the middle part are the outer contour until the cladding reaches the first processing point at the tip of the reduced contour, and the boundary is the boundary of the reduced contour.

[0012] Further, in step S4), the area is divided into n sub-lines based on the width of the unclad region, a curved path is designed to achieve full coverage, simulation is performed based on the designed route, the advantages and disadvantages are summarized, and the curved path is improved, specifically as follows: S4-1) Determine the designed curve shape based on the laser cladding parameters; S4-2) Starting from the point determined in S3, select the processing point along the centerline according to the designed curve, and observe the position of the point where the gap appears after simulation; (S4-3) The location of the point where the gap appears is the second critical point. The area where X is greater than this point is further divided into n sub-regions. The above steps are repeated until the processing is completed.

[0013] The beneficial effects of this invention are as follows: 1. This invention saves each slice as a fig file. After being read by MATLAB software, the shape and size displayed in the window are consistent with the original slice size in millimeters. This reduces the inaccuracy error when extracting the outer contour and eliminates the need to use the Canny algorithm to remove noise points from the slice, thus reducing the impact of noise points on the outer contour.

[0014] 2. This invention first performs laser cladding on the outer contour, then clads the blade tip along the centerline to the point where a gap appears. The position of this gap is compared with the reduced contour to determine the repair starting point on the reduced contour. Finally, the unclad area is divided, and a path repair plan is developed for it. Through this series of operations, high contour accuracy is ensured after repair, reducing interlayer remelting rate and inter-pass overlap rate during repair, thus improving repair efficiency and quality.

[0015] By adopting the above scheme, the present invention can realize the repair trajectory planning by jointly analyzing the laser cladding parameters and the slice shape, and provides a high-efficiency and high-precision aero-engine blade path planning method. It breaks through the adaptive path planning based on damage 3D reconstruction, generates a variable density path that matches the damage geometry, and develops intelligent path planning technology. This will promote the upgrade of aero-engine blade laser repair to "high precision, high efficiency and high consistency" and provide core technical support for aero-engine remanufacturing. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart illustrating the method for extracting the layered contours and repairing different regions of aero-engine blades based on laser cladding, as described in this invention.

[0018] Figure 2 This is a schematic diagram of all slices after the STL model has been layered by contour.

[0019] Figure 3 This is a schematic diagram showing the result of saving the slice as a fig file and reading it using MATLAB.

[0020] Figure 4 This is a schematic diagram of extracting the maximum outer contour of a single-layer blade.

[0021] Figure 5 This is a schematic diagram of the first critical point when the laser clads the blade tip along the centerline, creating gaps at both the top and bottom ends.

[0022] Figure 6 This is a schematic diagram of the blade's outer contour after it has been reduced by half the weld width.

[0023] Figure 7 This is a schematic diagram comparing the position of the first critical point with the reduced profile.

[0024] Figure 8 This is a schematic diagram of the repair curve designed after taking into account factors such as blade shape and remelting.

[0025] Figure 9 A schematic diagram of the area of ​​a segment of a Bezier curve after laser cladding.

[0026] Figure 10 This is a schematic diagram of curve path planning based on the centerline of the blade.

[0027] Figure 11 This is a schematic diagram of the simulation of cladding along two curved paths on the blade.

[0028] Figure 12 This is a schematic diagram showing the region above the first critical point divided into three parts.

[0029] Figure 13 This is a schematic diagram illustrating the determination of the second critical point location using path planning and simulation.

[0030] Figure 14 This is a schematic diagram of the critical point location and the dividing line.

[0031] Figure 15 This is a schematic diagram of the path planning for the three-point line and the five-point line.

[0032] Figure 16 This is a schematic diagram of the cladding simulation for three-line and five-line cladding. Detailed Implementation

[0033] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0034] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0035] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They 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, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0036] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0037] This invention provides a method for extracting layered contours and repairing regional defects on the surface of aero-engine blades. The overall process is as follows: Figure 1 As shown, the specific steps include: I. By dividing the STL defect model into layers and extracting the outer contour of each slice, the following steps are included: 1) Conduct a single-pass laser cladding experiment, select the optimal experimental parameters, and record the weld width D and weld height h under these parameters; in this example, both D and h are 3mm. 2) Perform contour layering on the STL model according to melt height, and display all slices as shown. Figure 2 As shown; 3) Extract each slice individually and save it as a fig file; 4) Read the fig file using MATLAB's openfig function, such as... Figure 3 As shown; calculate the ratio of pixels to actual size, and display the slice at its original size in a 3D coordinate system to facilitate subsequent path planning; 5) Add a 10 mm reference line in the drawing window to ensure that the slice size is displayed correctly.

[0038] II. Select the optimal laser cladding repair process parameters and perform cladding on the outer contour according to the cladding width, including the following steps: 1) Use the bwboundary function to extract the maximum outer contour of a single-layer slice and display it separately in the plot window, such as... Figure 4 As shown; 2) Use the linspace function to uniformly extract n points from the maximum outer contour, and export the data of the points to an Excel file; 3) Perform laser cladding on the outer contour and perform the first step of repair on the extracted outer contour points.

[0039] III. After cladding the outer contour, compare the remaining unclad area with the blade tip area to observe the positional relationship of the cladding starting point, including the following steps: 1) Use the shrink_pixels function to reduce the maximum outer contour by half the cladding width, and display the reduced contour, i.e., the uncladding area, as shown below. Figure 6 As shown, the area enclosed by the red curve is the unclad area; 2) The laser cladding proceeds along the centerline from the blade tip. Calculations show that when gaps appear at both the top and bottom, the vertical distance is exactly equal to two cladding widths. The `vertical_lines` function is used to find the intersection of the upper and lower contours, and this point is recorded as the first critical point. Figure 5 As shown in the figure, the intersection point on the left is the first critical point; 3) Compare the position of the first critical point with the reduced contour, and then... Figure 7 As can be seen, the first critical point is inside the shrinking contour. Therefore, the starting point is the first critical point during the second step of path planning and repair, and the upper and lower critical points are the boundaries of the shrinking contour.

[0040] IV. Divide the uncladding area into n sub-lines, design a curved path to achieve full coverage, perform simulations based on the designed route, summarize the advantages and disadvantages, and improve the curved path, including the following steps: 1) Based on a comprehensive consideration of the blade shape and repair process parameters, a curved repair route was designed; the curve connection equation is a cubic Bézier curve, such as... Figure 8As shown, cubic Bézier curves have the advantages of good controllability, good compatibility, high smoothness and simple calculation. Their control points can control the shape of the curve very well, and the algorithm for calculating cubic Bézier curves is relatively simple, which makes it possible to quickly draw high-quality curves.

[0041] The equation of a cubic Bézier curve is defined by four control points P0, P1, P2, and P3, and its parametric equation is:

[0042] Where: P0 is the starting point, P3 is the ending point; P1 and P2 are control points that determine the shape of the curve.

[0043] Because the blade surface must satisfy the differential geometric continuity requirement, it typically needs to reach G... 2 Continuity. The curvature continuity of cubic Bézier curves (G... 2 Strict matching is possible:

[0044] in: Let be the curvature of the Bézier curve. denoted as the blade curve curvature, and s as the blade arc length parameter.

[0045] The heat input distribution during laser cladding must meet the following requirements:

[0046] in, The heat input power per unit arc length, For laser absorption efficiency, Let t be the laser power, t be the time parameter, and s be the blade arc length parameter. Let be the instantaneous velocity of the Bézier curve at parameter t.

[0047] Velocity field of cubic Bézier curve It can adaptively adjust, automatically reducing speed in areas of high curvature while avoiding local overheating (temperature gradient). (Reduced by 40%).

[0048] 2) Calculate the area of ​​a Bézier curve after laser cladding, including the following steps: Selection of processing points: The first critical point is located inside the reduced contour. The starting point is the first critical point. If the n-section line is taken as the center line of the reduced contour, then the principle for selecting the next processing point is that the area of ​​the Bézier curve with a width equal to the cladding width is equal to the area enclosed by the two points and the contour.

[0049] The theoretical formula is as follows: ① Starting point Located at the center line of the outline Above, s is the arc length parameter. The local width of the outline is The local contour is the distance between the upper and lower boundaries; turn up and two control points , ,in , L Let the arc length be undetermined, such that the cubic Bézier curve... B(t) from arrive The fill area of ​​the weld width is equal to the contour area. and The actual area between; curves B(t) fit as closely as possible ,like Figure 9 As shown.

[0050] ② Formula for the true area of ​​a contour: The contour originates from... arrive The true area is obtained by integrating the upper and lower boundaries: ,in Is the outline in s Width at that location.

[0051] ③ Bézier curve B(t) The formula for the filled area: Where D is 3mm.

[0052] ④ Area constraint formula:

[0053] 3) Simulate the path and determine which partitioned cladding method to use based on the results: Take the centerline of the blade's outer contour, and take the intersection of the first critical point and the centerline as the first processing point, according to... Figure 8 and Figure 10 The curve path shown is used for path planning and simulation. The simulation results are as follows: Figure 11 As shown, from Figure 11 As can be seen in the left figure, gaps begin to appear in the cladding path in the wider middle part of the blade. This is because the area divided by the centerline is large, and the curve cannot achieve full coverage. Therefore, we need to combine the formula of equal area to the area to be clad on the blade and plan the blade into zones. That is, the processing area of ​​large or complex structures is divided into multiple small areas (zones), and the cladding process is carried out zone by zone in a specific order.

[0054] 4) Zoning method for cladding: When planning zoning, this invention uses the above-mentioned area constraint formula to first divide the blade into segments according to the size of x; for each segment x, in the process of zoning, similar to the centerline, the dividing lines are added sequentially using third lines, fourth lines, fifth lines, etc., to further divide the area; by Figure 11 As shown in the right figure, if the curved path planning continues along the centerline, calculations show that the critical point where gaps occur is close to the first critical point. To avoid too many critical points and a low curve curvature, the area above the first critical point is divided into three parts, starting from the first critical point. Figure 12 As shown.

[0055] 5) Selection of the second critical point: During path planning, calculations and simulations revealed that at x=30, the area enclosed by the upper and lower contours of the region divided by the trisection line and the two processing points is not equal to the area of ​​the curve, meaning that gaps will occur during cladding. Figure 13 As shown; then x=30 is taken as the second critical point; the number of dividing lines is determined by the width of the blade and the width of the laser cladding. To avoid too many critical points, the subsequent region boundary line is directly set as a five-line, as shown. Figure 14 As shown.

[0056] 6) Path planning for the area above the third and fifth division lines: Divide the area x>30 into five regions, using the intersection of the dividing line and the x=30 line as the first processing point for each region, and continue according to... Figure 8 Plan the curve path as shown, and export the curve data points, as follows: Figure 15 As shown.

[0057] 7) Simulation of three-point and five-point cladding and selection of the third critical point: Import the curve data points into the simulation software for simulation; the simulation calculation results are as follows: Figure 16 As shown, when x equals 48, a gap appears in the cladding path. Continue to use this as the third critical point; repeat step 6) until the layer path planning is completed. When planning, the laser cladding width should be considered. The path planning should be combined with simulation, and the curve should be adjusted in real time according to the simulation results.

[0058] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for extracting layered contours and repairing regional defects on the surface of aero-engine blades, characterized in that: Includes the following: S1) By dividing the STL defect model into layers, the outer contour of each slice is extracted; S2) Select the optimal laser cladding repair process parameters and perform cladding on the outer contour according to the cladding width; S3) After cladding the outer contour, compare the remaining unclad area with the blade tip area to observe the positional relationship of the starting point of the next cladding step. S4) Divide the uncladding area into n sub-lines, design a curved path to achieve full coverage, perform simulation based on the designed route, summarize the advantages and disadvantages, and improve the curved path.

2. The method for extracting layered contours and repairing regional defects on the surface of aero-engine blades according to claim 1, characterized in that: First, the blade matrix material is clad with powder material. The experimental parameters with the best morphology and performance are selected, and the cladding height and width are measured to facilitate subsequent slicing and cladding path planning.

3. The method for extracting layered contours and repairing regional defects on the surface of aero-engine blades according to claim 1, characterized in that: The process involves layering the STL defect model and extracting the outer contour of each slice. Specifically: S1-1) For the identified STL model, perform equal-height layering based on the cladding height indicated by the optimal laser cladding parameters, and display all slices; S1-2) Export each slice as a fig file and read the fig file using the openfig function; S1-3) Calculate the actual length represented by 1 pixel, and display the slice at its original size in a three-dimensional coordinate system, in millimeters.

4. The method for extracting layered contours and repairing regional defects on the surface of aero-engine blades according to claim 1, characterized in that: The selection of optimal laser cladding repair process parameters, and the cladding of the outer contour according to the cladding width, specifically involves: S2-1) After reading a single-layer blade, extract the maximum outer contour of the blade; S2-2) Take n uniform points on the outer contour and perform cladding on the outer contour according to the cladding width.

5. The method for extracting layered contours and repairing regional defects on the surface of aero-engine blades according to claim 1, characterized in that: After cladding the outer contour, the remaining unclad area is compared with the blade tip area to observe the positional relationship of the next cladding starting point. Specifically: S3-1) Apply cladding along the centerline from the first processing point of the blade until a gap is created at the upper and lower ends of the blade. The gap is the unclad area. Take the intersection of the upper and lower contours and record this point as the first critical point. S3-2) Reduce the maximum contour by half the cladding width and extract the reduced contour; S3-3) Compare the first critical point with the position of the narrowed profile tip to confirm the starting point of the next cladding step, which will facilitate subsequent planning.

6. The method for extracting layered contours and repairing regional defects on the surface of aero-engine blades according to claim 1, characterized in that: The process involves dividing the uncladding area into n sub-lines, designing a curved path to achieve full coverage, performing simulations based on the designed route, summarizing its advantages and disadvantages, and improving the curved path. Specifically: S4-1) Determine the designed curve shape based on the laser cladding parameters; S4-2) Starting from the starting point determined in S3, select the processing point along the centerline according to the designed curve, and observe the position of the point where the gap appears after simulation; (S4-3) The location of the point where the gap appears is the second critical point. The area where X is greater than this point is further divided into n sub-regions. The above steps are repeated until the processing is completed.

7. The method for extracting layered contours and repairing regional defects on the surface of aero-engine blades according to claim 5, characterized in that: The comparison between the first critical point and the tip of the reduced contour to determine the starting point of the next cladding step is as follows: If the first critical point is inside the reduced contour, the starting point of the reduced contour during the second repair step of path planning is the first critical point, and the upper and lower critical points are the boundaries of the reduced contour; if the first critical point is outside the reduced contour, after the outer contour cladding is performed, there is a gap between the first critical point and the reduced contour. During the second repair cladding step of path planning, the starting point is still the first critical point, and the upper and lower boundaries of the middle part are the outer contour, until the cladding reaches the first processing point at the tip of the reduced contour, and the boundary is the boundary of the reduced contour.

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