CT Detection and Evaluation Method for a Large-Size Additive Manufacturing Ramjet

Abstract

The present invention relates to a CT detection and evaluation method for a large-sized additive manufacturing ramjet engine, belonging to the technical field of ray non-destructive testing. When performing CT scanning on a large-sized additive manufacturing ramjet engine, first, the turntable is offset a certain distance from the central ray for the first scan, and then the turntable drives the engine to translate to a symmetric position on the other side of the central ray for the second scan. The data of the two scans are logically rearranged, which is equivalent to the CT scan of the flat panel detector translation and splicing; when evaluating the size compliance and contour compliance, first perform the above-mentioned three-dimensional CT scan on the large-sized additive manufacturing ramjet engine, obtain three-dimensional volume data after reconstruction, preprocess the image and perform image segmentation, convert it into point cloud data, and grid-convert it into the STL point cloud model of the engine. After fitting, the wall thickness size and measurement contour deviation of the engine can be measured. The present invention solves the problem that the traditional CT scanning method has a small flat panel detector size and cannot cover the overall large-sized workpiece.

Description

Technical Field

[0001] The present invention belongs to the technical field of ray non-destructive testing, and relates to a CT detection and evaluation method for a large-size additive manufacturing ramjet engine. Background Art

[0002] Currently, large-size additive manufacturing ramjet engines adopt complex integral engines with thin walls, multiple pipelines, and closed inner cavities. There are problems such as the difficulty in comprehensively characterizing the overall quality status by means of conventional metrological detection and two-dimensional CT detection of the wall thickness of the inner cavity wall, the spatial angle of the pipeline, the flow path profile of the engine, and the overall contour dimensions. At the same time, there are also problems such as internal structure deformation and flow path blockage. If the destructive "sectioning and scribing measurement" method is used, it will not only greatly increase the research and development cost, reduce the finished product delivery rate, but also seriously affect the research and development progress.

[0003] For complex integral engines, their overall compliance mainly includes two aspects: dimensional compliance and contour compliance. The wall thickness dimensions and angular element relationships of key parts of the inner cavity are related to the performance, safety, and reliability of the engine. Due to the complexity of the inner cavity and the special shape of the structure, traditional measurement methods are not applicable, and the existing "sectioning and tangent measurement" has disadvantages such as high cost and long cycle. For complex integral casting engines, structural deformation may occur during the forming process, which will cause problems in the overall structure or subsequent processing of the engine. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a CT detection and evaluation method for a large-size additive manufacturing ramjet engine.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A CT detection and evaluation method for a large-size additive manufacturing ramjet engine, the method including an industrial CT scanning detection method for a large-size additive manufacturing ramjet engine, and a dimensional compliance and contour compliance evaluation method.

[0007] Optionally, the industrial CT scanning detection method for the large-size additive manufacturing ramjet engine is as follows:

[0008] Adopt a detector logic stitching scanning method with a rotating table translation, and use a small-size panel with a pixel number of N to achieve scanning of a large-size workpiece with a diameter of D. The scanning detection process is as follows:

[0009] 1) At the first imaging position, that is, the position where the workpiece center is offset by E / 2, the workpiece rotates one week, and M indexing projections are collected to obtain projection data P 1 ,…,P N ;

[0010] 2) The turntable is translated along the negative y-axis by a distance E, and the turntable is rotated counterclockwise by a certain angle so that the projection PN coincides with the line connecting the center of the detector Dp and the focus S, reaching the second imaging position;

[0011] 3) At the second imaging position, that is, the position where the workpiece center is offset by E / 2, the workpiece rotates one week, and M indexing projections are collected at the same indexing positions to obtain the projection data P’ p ,…,P’ N ;

[0012] 4) The data corresponding to the same indexing at the two imaging positions are combined into M indexing projections;

[0013] 5) Reconstruct the three-dimensional image in the large-size panel mode;

[0014] The method of dividing and correcting data is adopted to reduce the difference in image gray levels obtained from the two scans. The formula (1) is used to calculate every 32 rows of the data from the two scans to obtain the correction value and correct the data collected in the second time, effectively removing the stitching rings that appear in the reconstructed image;

[0015]

[0016] where y 1 , y 2 are respectively the average values of the left and right columns at the stitching position, and p 2 [i] and p' 2 [i] are the data before and after correction respectively.

[0017] Optionally, the method for evaluating dimensional compliance and profile compliance is as follows: After completing the industrial CT scanning and detection of the additive manufacturing ramjet, immediately reconstruct the CT three-dimensional image from the projection data, then perform image enhancement, filtering, calibration, and segmentation processing, and finally realize image measurement and statistical analysis. The engine wall thickness dimension measurement process is as follows:

[0018] 1) Image preprocessing to reduce noise;

[0019] 2) Image segmentation to extract the workpiece area;

[0020] 3) Convert the segmented image to generate an STL point cloud;

[0021] 4) Based on the point cloud data, form a three-dimensional contour map, import the engine CAD model, and register a certain reference plane of the two;

[0022] 5) Based on the point cloud data, measure the wall thickness dimensions of the parts of interest;

[0023] 6) Based on the point cloud data, automatically measure the deviation of the contour and mark it with different colors.

[0024] The beneficial effects of the present invention are as follows:

[0025] Due to the use of the flat panel detector logical stitching CT scanning method with the turntable translation in the present invention, the problem that the small size of the flat panel detector in the traditional CT scanning method cannot cover the overall large-sized workpiece is solved, and the flat panel detector stitching CT scanning can be realized without additionally increasing hardware facilities such as a flat panel detector translation mechanism.

[0026] Since the present invention converts the three-dimensional CT image into point cloud data and utilizes the CAD model of the engine at the same time, the automatic measurement of the key wall thickness dimensions of the additive manufacturing ramjet engine and the automatic measurement and evaluation of the manufacturing compliance of the overall contour of the additive manufacturing ramjet engine are realized.

[0027] Other advantages, objectives and features of the present invention will be described to some extent in the subsequent description, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the following description. Brief Description of the Drawings

[0028] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, where:

[0029] Figure 1 It is a schematic diagram of the flat panel detector logical stitching CT scanning with the turntable translation;

[0030] Figure 2 It is a flow chart for realizing the engine size measurement and contour comparison from the CT image;

[0031] Figure 3 It is the CT scanning principle diagram of the present invention. Detailed Description of the Preferred Embodiments

[0032] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present invention schematically, and the following embodiments and the features in the embodiments can be combined with each other without conflict.

[0033] Among them, the attached drawings are only for illustrative purposes, showing only schematic diagrams rather than physical drawings, and should not be construed as a limitation to the present invention; in order to better illustrate the embodiments of the present invention, some components in the attached drawings will be omitted, enlarged or reduced, which do not represent the dimensions of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the attached drawings may be omitted.

[0034] In the attached drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the attached drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the attached drawings are only for illustrative purposes and should not be construed as a limitation to the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0035] See Figure 1 , when performing CT scanning on a large-sized additive manufacturing ramjet engine, first offset the turntable a certain distance from the central ray for the first scan, then the turntable drives the engine to translate to the symmetric position on the other side of the central ray for the second scan, and logically rearrange the data of the two scans, which is equivalent to the translational stitching CT scanning of the flat panel detector.

[0036] See Figure 2 , first perform the above-mentioned three-dimensional CT scanning on the large-sized additive manufacturing ramjet engine, obtain three-dimensional volume data after reconstruction, preprocess and segment the image, convert it into point cloud data, further grid it and convert it into the STL point cloud model of the engine. At the same time, import the CAD model of the engine, register the reference planes of the two, and further fit to measure the wall thickness dimension and the measurement profile deviation of the engine.

[0037] A CT detection and evaluation method for a large-sized additive manufacturing ramjet engine includes an industrial CT scanning detection method for a large-sized additive manufacturing ramjet engine, a method for evaluating dimensional compliance and profile compliance.

[0038] As Figure 3 shown, the industrial CT scanning detection method for a large-sized additive manufacturing ramjet engine is as follows:

[0039] Adopt the detector logical stitching scanning method of turntable translation, and use a small-sized panel with a pixel number of N to realize the scanning of a large-sized workpiece with a diameter of D. The scanning detection process is as follows:

[0040] 1) At the first imaging position, i.e., the position where the workpiece center is offset by E / 2, the workpiece rotates one week, and M indexing projections are collected to obtain projection data P 1 ,…,P N ;

[0041] 2) The turntable is translated a distance E along the negative y-axis, and the turntable rotates counterclockwise by a certain angle so that the projection PN coincides with the line connecting the center of the detector Dp and the focus S, reaching the second imaging position;

[0042] 3) At the second imaging position, i.e., the position where the workpiece center is offset by E / 2, the workpiece rotates one week, and M indexing projections are collected at the same indexing positions to obtain projection data P’ p ,…,P’ N ;

[0043] 4) The data corresponding to the same indexing positions at the two imaging positions are combined into M indexing projections;

[0044] 5) Reconstruct the three-dimensional image in the large-size panel mode;

[0045] Adopt the method of block-correcting data to reduce the difference in image gray levels obtained from the two scans. Calculate the correction value for every 32 rows of the two scan data using formula (1), and correct the data collected in the second time, effectively removing the stitching rings that appear in the reconstructed image;

[0046]

[0047] where y 1 、y 2 are respectively the average values of the left and right columns at the stitching position, p 2 [i] and p' 2 [i] are respectively the data before and after correction.

[0048] As Figure 3 shown, the methods for evaluating dimensional compliance and contour compliance are as follows: After completing the industrial CT scan and detection of the additive manufacturing ramjet engine, immediately reconstruct the CT three-dimensional image from the projection data, then perform image enhancement, filtering, calibration, and segmentation processing, and finally realize image measurement and statistical analysis. The engine wall thickness dimension measurement process is as follows:

[0049] 1) Image preprocessing to reduce noise;

[0050] 2) Image segmentation to extract the workpiece area;

[0051] 3) Convert the segmented image to generate an STL point cloud;

[0052] 4) Based on the point cloud data, form a three-dimensional contour map, import the engine CAD model, and register a certain reference plane of the two;

[0053] 5) Measure the wall thickness dimension of the part of interest based on the point cloud data;

[0054] 6) Automatically measure the deviation of the contour based on the point cloud data and identify it with different colors.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the present technical solution, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A CT detection and evaluation method for a large-sized additive manufacturing ramjet engine, characterized in that: This method includes an industrial CT scanning detection method for a large-sized additive manufacturing ramjet engine, a dimensional compliance evaluation method, and a contour compliance evaluation method; The industrial CT scanning detection method for the large-sized additive manufacturing ramjet engine is as follows: Adopting a detector logic stitching scanning method with turntable translation, using a small-sized panel with N pixels to achieve scanning of a large-sized workpiece with a diameter of D. The scanning detection process is as follows: 1) At the first imaging position, that is, the position where the workpiece center is offset by E / 2, the workpiece rotates one week, and M indexing projections are collected to obtain projection data P 1 ,…,P N ; 2) The turntable translates a distance E in the negative y-axis direction, and the turntable rotates counterclockwise by a certain angle so that the projection PN coincides with the line connecting the center of the detector Dp and the focus S, reaching the second imaging position; 3) At the second imaging position, i.e., the position where the workpiece center is offset by E / 2, the workpiece rotates one week, and M indexing projections are collected at the same indexing positions to obtain projection data P’ p ,…,P’ N ; 4) Combine the data corresponding to the two imaging positions at each division into M division projections; 5) Reconstruct the three-dimensional image in the large-sized panel mode; Adopt a method of correcting data in blocks to reduce the difference in image grayscales obtained from the two scans. Use formula (1) to calculate every 32 rows of the two scan data to obtain the correction value and correct the data collected in the second time, effectively removing the stitching rings that appear in the reconstructed image; where y 1 and y 2 are the averages of the left and right columns at the splicing position respectively, p 2 [i] and p' 2 [i] are the data before and after correction respectively.

2. According to the CT detection and evaluation method for a large-sized additive manufacturing ramjet engine described in claim 1, characterized in that: The dimensional compliance and contour compliance evaluation method is as follows: After completing the industrial CT scanning detection of the additive manufacturing ramjet engine, immediately reconstruct the CT three-dimensional image from the projection data, and then perform image enhancement, filtering, calibration, and segmentation processing. Finally, realize image measurement and statistical analysis. The engine wall thickness dimension measurement process is as follows: 1) Image preprocessing to reduce noise; 2) Image segmentation to extract the workpiece area; 3) Convert the segmented image to generate an STL point cloud; 4) Based on the point cloud data, form a three-dimensional contour map, import the engine CAD model, and register a certain reference plane of the two; 5) Based on the point cloud data, measure the wall thickness dimensions of the parts of interest; 6) Based on the point cloud data, automatically measure the deviation of the contour and mark it with different colors.

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