Method for predicting air film hole depth on blade based on industrial CT (Computed Tomography)

Abstract

The invention belongs to the technical field of industrial detection, and relates to a method for predicting the air film hole depth on a blade based on industrial CT, which comprises the following steps: 1) acquiring a three-dimensional grid model of a to-be-processed blade based on industrial CT; 2) obtaining all triangular patches on the blade based on the three-dimensional mesh model of the blade to be processed obtained in the step 1); 3) uniformly converting the three-dimensional grid model and the theoretical model of the to-be-processed blade obtained in the step 1) into a machine tool coordinate system; and performing intersection calculation on the theoretical hole position of each film hole of the blade in the theoretical model and all the triangular patches on the blade obtained in the step 2) to obtain an intersection calculation result, and completing simulation measurement of the film holes according to the calculation result. According to the method for predicting the depth of the air film hole in the blade based on the industrial CT, reference is provided for the number of laser machining layers, the blade damage phenomenon can be well eliminated, and the machining yield is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of industrial inspection, and relates to a thickness measurement method, and particularly relates to a method for predicting the depth of film cooling holes on a blade based on industrial CT. Background Art

[0002] As a key structural feature of the blade, the film cooling holes play an important role in heat dissipation and temperature reduction during operation, and to a certain extent, extend the working life of the blade; however, due to their irregular shapes, mostly circular holes are connected with special-shaped holes, so the processing methods mainly rely on special processing, such as laser processing, electric discharge machining, and wire cutting. Among them, femtosecond laser has gradually become the preferred processing method due to its higher processing efficiency and better adaptability to hole shapes.

[0003] However, currently, when using laser to process the film cooling holes of blades (such as Figure 1 a certain engine blade shown), there are problems such as wall damage, sidewall injury, and rib injury; mainly because during the casting process of the blade blank, the wall thickness on the surface is uneven, resulting in obvious differences in the number of laser processing layers; when using a fixed laser processing layer, some blades with relatively thin wall thicknesses still cannot avoid being injured even in the filled state; while for blades with relatively large wall thicknesses, processing cannot be completed (cannot be processed through). As a result, the blade damage is relatively serious, causing a considerable loss of equipment cost and blade blank parts.

[0004] As an industrial imaging device for scanning and modeling, CT can achieve a model reconstruction accuracy of 0.02 mm. However, currently, no method for predicting the depth value of film cooling holes using CT combined with three-dimensional vision before blade processing has been found to guide the number of laser processing layers, thereby effectively preventing damage and improving the processing yield. Summary of the Invention

[0005] In order to solve the above technical problems in the background art, the present invention provides a method for predicting the depth of film cooling holes on a blade based on industrial CT, which can effectively eliminate the blade injury phenomenon and improve the processing quality.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for predicting the depth of film cooling holes on a blade based on industrial CT, characterized in that: the method for predicting the depth of film cooling holes on a blade based on industrial CT includes the following steps:

[0008] 1) Obtain a three-dimensional mesh model (i.e., mesh) of the blade to be processed based on industrial CT;

[0009] 2) Based on the three-dimensional mesh model of the workpiece to be processed obtained in step 1) (at this time, there are no film cooling holes on the blade), obtain all triangular patches on the blade (the model may contain fixtures, standard blocks, etc., and these need to be removed in this step, that is, only the triangular patches of the blade are retained);

[0010] 3) Uniformly transform the three-dimensional mesh model of the workpiece to be processed and the theoretical model (i.e., the design model, which contains the positions of the film cooling holes) obtained in step 1) into the machine tool coordinate system; then perform an intersection calculation between the theoretical hole positions of each film cooling hole on the blade and all the triangular patches on the blade obtained in step 2), and obtain the result of the intersection calculation. Complete the simulation measurement of the film cooling holes according to the calculation result.

[0011] The specific implementation method of the above step 1) is as follows:

[0012] 1.1) Use industrial CT to scan the blade before processing to obtain the CT scan data of the blade before processing;

[0013] 1.2) Construct a three-dimensional mesh model of the blade to be processed according to the CT scan data of the blade before processing obtained in step 1.1).

[0014] The specific implementation method of the above step 2) is as follows:

[0015] 2.1) Preprocess the three-dimensional mesh model of the blade to be processed obtained in step 1);

[0016] 2.2) Use distance-based point cloud clustering to obtain the characteristic point cloud of the blade part on the three-dimensional mesh model after step 2.1);

[0017] 2.3) From the obtained blade point cloud, according to the topological relationship between points and surfaces, obtain all the triangular patches on the blade.

[0018] The preprocessing method in the above step 2.1) is to perform Gaussian smoothing on the model.

[0019] The specific implementation method of the above step 3) is as follows:

[0020] 3.1) Convert the theoretical hole position coordinates of each film cooling hole on the blade and the point cloud coordinates of the three-dimensional mesh model of the blade to be processed obtained in step 1) into the machine tool's spatial coordinate system, and obtain the corresponding machine tool spatial coordinates of the theoretical hole positions and the machine tool spatial coordinates corresponding to the three-dimensional mesh model; if the three-dimensional model can be positioned by a fixture, the theoretical model is realized by six-point positioning.

[0021] 3.2) Through step 3.1), at this time, the machine tool spatial coordinates corresponding to the obtained theoretical hole positions and the machine tool spatial coordinates corresponding to the holes to be processed on the three-dimensional mesh model are aligned;

[0022] 3.3) Obtain the hole axis equation in the machine tool space coordinates corresponding to the theoretical hole positions of the air film holes;

[0023] 3.4) Perform an intersection calculation between the hole axis equation obtained in step 3.3) and all the triangular patches on the blade obtained in step 2) to obtain all the intersection points of the hole axis equation and the three-dimensional mesh model of the blade;

[0024] 3.5) Sort the intersection points obtained in step 3.4) in ascending order of the distance to the theoretical hole positions of the air film holes, calculate the distances between adjacent points, and respectively obtain the hole depth value and the distance to the opposite wall value according to the distances between adjacent points to complete the simulation measurement of the air film hole depth.

[0025] The specific implementation method of the above step 3.3) is as follows:

[0026] 3.3.1) Obtain the hole position information in the machine tool space coordinates corresponding to the theoretical hole positions (for example, through a 6-point positioning method), and the hole position information includes the hole position coordinates (x0, y0, z0) and the axis direction (a, b, c);

[0027] 3.3.2) Construct a hole axis equation according to the hole position information, and the expression of the hole axis equation is:

[0028] (x - x0) / a = (y - y0) / b = (z - z0) / c

[0029] Where:

[0030] x, y, and z are the independent variables in the expression of the space straight line equation respectively.

[0031] The specific implementation method of the above step 3.4) is as follows:

[0032] Traverse all the triangular patches on the blade obtained in step 2) based on the hole axis equation, calculate the intersection points of the plane of each triangular patch and the hole axis equation in turn, and take the intersection points within the triangular patches to obtain all the intersection points of the hole axis equation and the three-dimensional model of the air film holes on the blade.

[0033] The calculation method of the distance between adjacent points in the above step 3.5) is as follows:

[0034] D = √

(x1 - x2)×(x1 - x2) + (y1 - y2)×(y1 - y2) + (z1 - z2)×(z1 - z2)

[0035] Where:

[0036] (x1, y1, z1), (x2, y2, z2), (x3, y3, z3), and (x4, y4, z4) are the coordinates of 4 adjacent points among the intersection points of the hole axis equation and the three-dimensional model of the air film holes on the blade respectively.

[0037] The advantages of the present invention are as follows:

[0038] The present invention provides a method for predicting the depth of film cooling holes on a blade based on industrial CT, which includes: 1) obtaining a three-dimensional grid model of the blade to be processed based on industrial CT; 2) obtaining all triangular patches on the blade based on the three-dimensional grid model of the blade to be processed obtained in step 1); 3) uniformly transforming the three-dimensional grid model of the blade to be processed obtained in step 1) and the theoretical model into the machine tool coordinate system; performing an intersection calculation between the theoretical hole positions of the film cooling holes on the blade in the theoretical model and all the triangular patches on the blade obtained in step 2), obtaining the result of the intersection calculation, and completing the simulation measurement of the film cooling holes according to the calculation result. Based on the CT scan model, the present invention proposes a simulation measurement scheme for the depth of film cooling holes before blade processing, provides guidance for the number of laser processing layers, and can effectively eliminate the phenomenon of blade damage. The method for predicting the depth of film cooling holes on a blade based on industrial CT proposed by the present invention combines 3D vision and graphics to realize a simulation measurement method for the processing thickness and processing result of film cooling holes. When the wall thickness of the blade (less than 2 mm) is known, the laser processing process can determine the number of processing layers of the film cooling holes, with an error of less than 10 layers, which can effectively prevent wall damage, side wall damage, and rib damage, and is of great significance for improving processing quality and reducing blank cost. Brief Description of the Drawings

[0039] Figure 1 is a cross-sectional view of a certain engine blade;

[0040] Figure 2 is a schematic diagram of the model smoothing process;

[0041] Figure 3 is a schematic diagram of the intersection operation;

[0042] Figure 4 is a flow chart of the method for predicting the depth of film cooling holes on a blade based on industrial CT provided by the present invention. Detailed Embodiments

[0043] See Figure 4 , to solve the problem of blade damage caused by side wall, opposite wall, and rib damage during the processing of film cooling holes, the present invention provides a method for predicting the depth of film cooling holes on a blade based on industrial CT. The method includes: first, scanning the blade before processing through industrial CT to reconstruct the model, and then simulating and predicting the processing result of the film cooling holes on the blade according to the theoretical hole positions; finally, determining the number of processing layers of each film cooling hole according to the calculated hole depth result, so as to prevent blade damage and ensure the delivery yield.

[0044] Specifically, the method for predicting the depth of film cooling holes on a blade based on industrial CT provided by the present invention includes the following steps:

[0045] 1) Obtain a three-dimensional mesh model of the blade to be machined based on industrial CT;

[0046] Specifically:

[0047] 1.1) Use industrial CT to scan the blade before machining to obtain the CT scan data of the blade before machining;

[0048] 1.2) Construct a three-dimensional mesh model of the blade to be machined based on the CT scan data of the blade before machining obtained in step 1.1).

[0049] 2) Obtain all the triangular facets of the blade based on the three-dimensional mesh model of the blade obtained in step 1). Specifically:

[0050] 2.1) Preprocess the three-dimensional mesh model of the blade to be machined obtained in step 1). The preprocessing method is to perform Gaussian smoothing on the model to remove the triangular facets with surface burrs. Generally speaking, there will be many noise points on the mesh model generated after CT scanning the blade. Whether it is a single-layer wall or a double-layer wall blade, the main noise areas are concentrated in the suction side area. At this time, if the thickness is calculated according to the original scan model, the accuracy of repeated measurement will be poor. Therefore, denoising treatment is required. Exemplarily, the present invention can adopt the following denoising scheme: It is verified through the built-in denoising algorithm of CT that direct denoising will cause the loss of point clouds in the areas with more noise points and lose the original shape. Therefore, it is necessary to denoise according to the contour of the original model and perform smoothing treatment to obtain the final model participating in the calculation and registration to improve the measurement repeatability. The model after smoothing treatment is as Figure 2 shown.

[0051] 2.2) Use distance-based point cloud clustering to obtain the characteristic point cloud of the blade part on the three-dimensional mesh model after step 2.1);

[0052] 2.3) From the obtained blade point cloud, according to the topological relationship between points and surfaces, obtain all the triangular facets of the blade.

[0053] 3) In the machine tool coordinate system, perform an intersection calculation between the theoretical hole positions of each film cooling hole of the blade and all the triangular facets on the blade obtained in step 2) to obtain the intersection calculation result, and complete the simulation measurement of the film cooling hole according to the calculation result. Specifically:

[0054] 3.1) Convert the theoretical hole positions of each film cooling hole of the blade and the three-dimensional model of the blade obtained in step 1) to the machine tool coordinate system to obtain the machine tool space coordinates corresponding to the theoretical hole positions and the machine tool space coordinates corresponding to the point cloud on the three-dimensional model. Exemplarily, the present invention realizes the conversion from the CT scan model to the machine tool coordinate system through fixture positioning; and realizes the conversion of the film cooling hole positions of the theoretical model to the machine tool coordinate system through six-point positioning. At this time, the position and axial information of the film cooling hole and its axis, that is, the pose and axial information of the femtosecond laser during the machining process.

[0055] 3.2) Through step 3.1), the machine tool space coordinates corresponding to the theoretical hole positions obtained at this time and the machine tool space coordinates corresponding to the hole positions to be machined on the three-dimensional mesh model have completed spatial alignment;

[0056] 3.3) Obtain the hole axis equation of the machine tool space coordinates corresponding to the theoretical hole positions of the air film holes. Specifically:

[0057] 3.3.1) Obtain the hole position information of the machine tool space coordinates corresponding to the theoretical hole positions. The hole position information includes the hole position coordinates (x0, y0, z0) and the axis direction (a, b, c);

[0058] 3.3.2) Construct the hole axis equation according to the hole position information. The expression of the hole axis equation is:

[0059] (x - x0) / a = (y - y0) / b = (z - z0) / c

[0060] Where:

[0061] x, y, and z are the independent variables in the expression of the space straight line equation respectively.

[0062] 3.4) Perform an intersection calculation between the hole axis equation obtained in step 3.3) and all the triangular patches on the blade obtained in step 2) to obtain all the intersection points of the hole axis equation and the three-dimensional mesh model of the blade to be machined. Exemplarily, this step can be: Traverse all the triangular patches on the blade obtained in step 2) based on the hole axis equation, calculate the intersection points of the plane of each triangular patch and the hole axis equation in turn, and take the intersection points within the triangular patch to obtain all the intersection points of the hole axis equation and the three-dimensional mesh model of the blade to be machined.

[0063] 3.5) Sort the intersection points obtained in step 3.4) in ascending order of the distance to the air film hole position, calculate the distances between adjacent points, obtain the hole depth value and the distance to the wall value respectively according to the distances between adjacent points, and complete the simulation measurement of the air film hole according to the hole depth value and the distance to the wall value. Exemplarily, in this step, the calculation method of the distance between adjacent points is:

[0064] D = √

(x1 - x2)×(x1 - x2) + (y1 - y2)×(y1 - y2) + (z1 - z2)×(z1 - z2)

[0065] Where:

[0066] (x1, y1, z1), (x2, y2, z2), (x3, y3, z3), and (x4, y4, z4) are the coordinates of 4 adjacent points among the intersection points of the hole axis equation and the three-dimensional model of the blade air film hole respectively. Exemplarily, it can also include more intersection points, and more intersection point coordinates can be obtained according to the foregoing method. For example Figure 3As shown, the distance between intersection point 1 and intersection point 2 is the hole depth value, and the distance between intersection point 2 and intersection point 3 is the distance value to the wall. In summary, the simulation measurement of the gas film hole depth is completed based on the CT scan model.

Claims

1. A method for predicting the depth of air film holes on a blade based on industrial CT, characterized in that: The method for predicting the air film hole depth on the blade based on industrial CT comprises the following steps: 1) Obtain the 3D mesh model of the blade to be processed based on industrial CT; 2) based on the three-dimensional mesh model of the blade to be processed obtained in step 1), all triangular facets on the blade are obtained; 3) The three-dimensional mesh model and theoretical model of the blade to be processed obtained in step 1) are uniformly converted to the machine tool coordinate system; the theoretical hole positions of each air film hole on the blade in the theoretical model are intersected with all the triangular facets on the blade obtained in step 2) to obtain the intersection calculation results, and the simulation measurement of the air film holes is completed according to the calculation results.

2. The method for predicting the depth of air film holes on a blade based on industrial CT according to claim 1 is characterized in that: The specific implementation method of step 1) is: 1.1) Using industrial CT to scan the blade before processing, and obtaining CT scanning data of the blade before processing; 1.2) Constructing a three-dimensional mesh model of the blade to be processed based on the CT scanning data of the blade before processing obtained in step 1.1).

3. The method for predicting the depth of air film holes on a blade based on industrial CT according to claim 2 is characterized in that: The specific implementation method of step 2) is: 2.1) preprocessing the three-dimensional mesh model of the blade to be processed obtained in step 1); 2.2) using distance-based point cloud clustering to obtain feature point clouds of the blade part on the three-dimensional mesh model after step 2.1); 2.3) Based on the obtained blade point cloud and the topological relationship between points and surfaces, all triangular facets on the blade are obtained.

4. The method for predicting the depth of air film holes on a blade based on industrial CT according to claim 3 is characterized in that: The preprocessing method in step 2.1) is to perform Gaussian smoothing on the model.

5. The method for predicting the depth of air film holes on a blade based on industrial CT according to claim 4 is characterized in that: The specific implementation method of step 3) is: 3.1) The theoretical hole positions of each air film hole of the blade and the three-dimensional mesh model of the blade to be processed obtained in step 1) are converted to the machine tool coordinate system to obtain the machine tool space coordinates corresponding to the theoretical hole positions and the machine tool space coordinates corresponding to the point cloud on the three-dimensional mesh model; 3.2) spatially aligning the machine tool space coordinates corresponding to the theoretical hole positions obtained in step 3.1) with the machine tool space coordinates corresponding to the hole positions to be processed on the three-dimensional grid model; 3.3) Obtain the hole axis equation in the machine tool space coordinates corresponding to the theoretical hole position of the air film hole; 3.4) performing intersection calculation on the hole axis equation obtained in step 3.3) and all triangular facets on the blade obtained in step 2) to obtain all intersection points of the hole axis equation and the three-dimensional mesh model of the blade; 3.5) Sort the intersection points obtained in step 3.4) in order according to the distance to the theoretical hole of the air film hole position to calculate the distance between adjacent points, obtain the hole depth value and the wall distance value according to the distance between adjacent points, and complete the simulation measurement of the air film hole depth according to the hole depth value and the wall distance value.

6. The method for predicting the depth of air film holes on a blade based on industrial CT according to claim 5 is characterized in that: The specific implementation method of step 3.3) is: 3.3.1) Obtaining hole position information of the machine tool space coordinates corresponding to the theoretical hole position, wherein the hole position information includes the hole position coordinates (x0, y0, z0) and the axis direction (a, b, c); 3.3.2) Construct the hole axis equation according to the hole position information. The expression of the hole axis equation is: (x-x0) / a=(y-y0) / b=(z-z0) / c in: xyz are the independent variables in the expression of the space line equation.

7. The method for predicting the depth of air film holes on a blade based on industrial CT according to claim 6 is characterized in that: The specific implementation method of step 3.4) is: Based on the hole axis equation, all the triangular facets on the blade obtained in step 2) are traversed, and the intersection points of the plane of each triangular facet and the hole axis equation are calculated in turn. The intersection points within the triangular facets are taken to obtain all the intersection points of the hole axis equation and the three-dimensional mesh model of the blade to be processed.

8. The method for predicting the depth of air film holes on a blade based on industrial CT according to claim 7 is characterized in that: The distance between adjacent points in step 3.5) is calculated as follows: D=√【(x1-x2)×(x1-x2)+(y1-y2)×(y1-y2)+(z1-z2)×(z1-z2)】 in: (x1, y1, z1), (x2, y2, z2), (x3, y3, z3) and (x4, y4, z4) are the coordinates of the four adjacent points at the intersection of the hole axis equation and the three-dimensional mesh model of the blade to be processed.

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