Checking the positioning of the fiber preform in the blade

Abstract

The invention relates to a method for checking the positioning of a fiber preform in a blade, the blade having been obtained by injecting resin into a mold having the shape of the blade and in which the preform has been placed, the blade extending in an orthogonal blade reference coordinate system X, Y, Z, the blade comprising a blade root and an airfoil portion, the blade root extending longitudinally along an axis X, the airfoil portion extending from the blade root along an axis Z, the blade having a thickness defined along the axis Y, the preform comprising a glass tracer positioned on a surface of the preform, the center of the tracer defining a neutral axis being positioned along the axis Z in a direction defined by the axis X. At a height, the method comprises the following steps: acquiring (E31) 2D tomographic projections of the blade using an imaging system including an X-ray source, each projection being acquired at a given orientation of the X-ray source relative to the blade; accumulating (E32, E32a, E32b) the 2D projections along the direction of the axis Y to obtain an accumulated 2D image in the directions X and Z; determining (E33) a grayscale profile for each column of pixels defined along the direction of the axis Z; processing (E34) each of the obtained profiles to locate the position of the neutral axis in the direction of the axis X in Z.

Description

Technical Field

[0001] The present invention relates to the general field of turbine blades made of composite materials and to a method for controlling the manufacture of preforms and moulds for such blades. Background Art

[0002] Composite materials can be used to manufacture turbine blades, particularly blades for turbine fans.

[0003] like Figure 1 As shown, the blade generally comprises a body 1 made of composite material from a preform. The preform comprises a braid of a plurality of braided yarns or fibers, including warp and weft yarns. The braid may be a single piece obtained by three-dimensional braiding and may in particular comprise glass, aramid and / or ceramic carbon fibers.

[0004] The composite body includes a root portion 11, a strut portion 12, and an aerodynamically contoured airfoil portion 13. A blade reference coordinate system (X, Y, and Z) is defined as follows: axis X corresponds to the longitudinal direction of the blade root, axis Z corresponds to the longitudinal direction along which airfoil portion 13 extends from root portion 11, and axis Y corresponds to the thickness of the blade. Naturally, axes X, Y, and Z are orthogonal to each other, and the blade reference system is orthogonal.

[0005] The preforms are cut according to the shapes and sizes of the parts that make up the blade and are placed in a mould.

[0006] A binder containing a thermosetting resin is then injected into the mold to impregnate the entire preform. After heating the mold, the molded part is removed from the mold. The molding process can be, for example, a vacuum resin injection molding process such as RTM (Resin Transfer Molding) or even VARR™ (Vacuum Resin Transfer Molding).

[0007] During the manufacturing process of the blade, a thick preform is thus deposited in the cavity of the injection mold. The 3D woven preform is a thick, one-piece fabric. In the case of a turbine fan blade, the thickness of the one-piece preform is variable in order to adapt to the aerodynamic profile of the blade (see Figure 1 ).

[0008] Therefore, when such a variable thickness preform is deposited in a variable thickness injection mold, it is important to ensure that the preform is correctly positioned in order to obtain a part with uniform material integrity. In fact, if the thick areas of the preform are not well positioned and are positioned in the thin areas of the mold, the fiber volume fraction of the part will be greatly affected and may not meet the requirements.

[0009] Thus, of the two sets of yarns provided for the preform, there are structural yarns that ensure the preform's structure, and tracer yarns that are visually distinguishable from the other yarns and are at least uniformly arranged on the preform's surface. These small numbers of glass yarns positioned on the surface are referred to as glass tracers or tracers, and will be described below. These yarns, represented as a visible grid, make it possible to spatially locate the preform and thus assess its correct positioning.

[0010] To verify the integrity of the blade after injection, the positioning of the preform in the blade obtained after injection is controlled. This control consists in measuring the height of the center of a glass tracer (called neutral fiber) along the axis X in the reference coordinate system of the blade.

[0011] To this end, X-ray tomography was performed on the blade to ensure its integrity and to verify the positioning of the neutral fibers relative to their theoretical positions.

[0012] In particular, thanks to tomography, it is possible to reconstruct the neutral fibers in the tomographic volume and verify their correct positioning. However, this method can only capture fragments of the glass tracer, but not the entire glass tracer and thus the fragments of the neutral fibers.

[0013] Figure 2a and Figure 2b A tracer 21 partially detected in the blade 1 by X-ray tomography and a 3D reconstruction as well as a theoretical tracer 22 are shown, respectively.

[0014] When the detection of the neutral fiber is inaccurate, the correct positioning of the preform and thus the verification of the integrity of the part is inaccurate. Summary of the Invention

[0015] The present invention makes it possible to overcome the above-mentioned drawbacks.

[0016] To this end, according to a first aspect, the invention proposes a method for verifying the positioning of a fiber preform in a blade, the blade having been obtained by injecting resin into a mold having the shape of a blade and in which a preform has been placed, the blade extending in an orthogonal blade reference coordinate system X, Y, Z, the blade comprising a blade root and an airfoil, the blade root extending longitudinally along an axis X, the airfoil extending from the blade root along an axis Z, the blade having a thickness defined along the axis Y, the preform comprising a glass tracer positioned on a surface of the preform, the center of the tracer defining a neutral fiber being positioned at a height along the axis Z along a direction defined by the axis X, the method comprising the following steps:

[0017] acquiring 2D tomographic projections of the blade by means of an imaging system comprising an X-ray source, each projection being acquired at a given position of the X-ray source relative to the blade;

[0018] Accumulating the 2D projections along the direction of the axis Y to obtain accumulated 2D images along directions X and Z;

[0019] For each pixel column defined along the direction of the axis Z, determining a gray level profile;

[0020] Each of the obtained graphs is processed to locate the position of the neutral fiber in Z along the direction of the axis X.

[0021] According to a first aspect, the present invention is advantageously achieved by any of the following features, alone or in any technically possible combination:

[0022] - the projection comprises: obtaining a 2D image consisting of pixels having a maximum gray level in a stack of pixels of different slices stacked in the direction of the axis Y;

[0023] - the projection comprises: the 2D image is composed of pixels whose gray level is the sum of pixels of different slices stacked along the direction of the axis Y;

[0024] The grayscale curve is a Gaussian distribution, and the location of the neutral fiber is the center of the Gaussian distribution;

[0025] - the grayscale curve is a double Gaussian distribution, and the location of the neutral fiber is the center of the double Gaussian distribution;

[0026] - said method comprising the steps of filtering the positioning of said neutral fibre in said direction Z along said axis X;

[0027] - said method comprises the step of comparing the positioning of said neutral fibres thus obtained with the theoretical positioning of said neutral fibres.

[0028] According to a second aspect, the invention proposes a method for manufacturing a turbine blade made of a composite material, the method comprising the following steps:

[0029] placing the fiber preform in a mold having the shape of a blade;

[0030] injecting resin into said mold comprising said preform under vacuum conditions to obtain said blade, which is called an injection-molded blade;

[0031] The positioning of the fiber preform in the injection-molded blade is checked by the method according to the invention.

[0032] According to a third aspect, the present invention proposes a blade for a turbomachine fan, obtained by the method according to the second aspect of the present invention.

[0033] According to a fourth aspect, the invention proposes an aircraft comprising a fan blade according to the third aspect of the invention.

[0034] From the perspective of time accuracy, repeatability, reproducibility and control time, the advantages of the present invention are multiple.

[0035] Compared to known techniques, the accuracy of the detection is improved, in particular from the point of view of precision, repeatability, reproducibility and control time.

[0036] The processing operations achieved are fast and require few resources, since, unlike conventional tomography, no dimensionality is required to achieve a 3D reconstruction.

[0037] This results in a highly precise measurement of the positioning of the neutral fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Other features, objects and advantages of the present invention will appear from the following description which is intended to be illustrative rather than restrictive and should be read in conjunction with the accompanying drawings in which, in addition to those already discussed, Figure 1 、 Figure 2a and Figure 2b In addition:

[0039] - Figure 3 The steps of the method for manufacturing a turbine blade according to the present invention are shown;

[0040] - Figure 4 An imaging system according to the present invention is shown;

[0041] - Figure 5 The steps of the method according to the invention for verifying the positioning of a preform in a blade are shown;

[0042] - Figure 6 The pixels of an image are schematically shown;

[0043] - Figure 7 and Figure 8 shows a gray level curve diagram obtained by the method according to the present invention;

[0044] - Figure 9 Shown by Figure 5 The 2D image is obtained by the method.

[0045] Similar elements have the same reference numerals throughout the drawings. DETAILED DESCRIPTION

[0046] General introduction to the method

[0047] about Figure 3 The method for manufacturing a turbine blade made of a composite material comprises the following general steps. These steps can be implemented in various ways known to those skilled in the art and will not be described in detail below, but will only be presented in a general manner (see also the introduction to this application).

[0048] The fiber preform 2 is placed in a mold 3 having the shape of a blade (step E1 ), and under vacuum conditions, resin is injected (step E2 ) into the mold including the preform to obtain the blade.

[0049] The method then comprises the step of inspecting (step E3 ) the blade using an imaging system, in particular capable of obtaining 2D projections or 2D images. This inspection is performed by processing these 2D projections.

[0050] Tomography system

[0051] Figure 4 An imaging system 10 is shown that can acquire 2D projections of a blade 1. X-rays and R-rays from a source S are emitted at different angles (1, ..., i, ..., n) toward the blade 1. After passing through the blade 1, the rays pass through a detector D. et Detection is performed to form a 2D projection set I1,…,I i ,…,I N It should be noted that the number of 2D projections obtained is as many as the number of angles considered. The set of angles covers a semicircle around the blade 1. Thus, by placing the detector D above the blade 1 et For example, the detector is a digital camera.

[0052] The 2D projections are then processed by a processing unit connected to or forming part of the imaging system. The processing unit is, for example, a processor. In the case where the processing unit is remote from the imaging system, the processing unit is connected to the imaging system in a wired or wireless manner. The processing unit enables the implementation of a method for processing the obtained 2D images.

[0053] Verification of the positioning of the fiber preform in the blade

[0054] The positioning of the fiber preform in the blade 1 is checked by the processing unit of the imaging system 10. In particular, the checking includes the following steps: Figure 5 Related steps.

[0055] A plurality of 2D tomographic projections of the blade 1 are acquired (step E31) by the imaging system 10. Each projection corresponds to a given orientation of the X-ray source relative to the blade. Thus, there are N 2D images, namely I1, ..., I N Each projection consists of multiple grayscale pixels.

[0056] These 2D images are then accumulated along axis Y (step E32) in order to obtain an accumulated 2D image (denoted I) along the directions of axes X and Z. In each image, each pixel has a grayscale value. Each pixel (P to P) of the accumulated image I m ) is obtained by averaging the grayscale levels of corresponding pixels along the Y axis. These accumulated pixels have identical coordinates in X and Z. This accumulation eliminates the need for a dimension, here the Y dimension, in the present invention. Indeed, to assess the positioning of the preform, only two coordinates are sufficient, and positional information along the Y axis (in the thickness of the blade 1 ) proves to be less important for assessing the integrity of the blade 1 .

[0057] The accumulation is equivalent to accumulating stereo pixel information along a direction.

[0058] According to one embodiment, the accumulation (step E32a) mentioned above consists in that the accumulated 2D image obtained is composed of the pixels having the maximum gray level in the stack of pixels of different slices (coupes) stacked along the axis Y. According to this embodiment, only glass fibers (the material used for the neutral fibers) are taken into account to the greatest extent possible, but some parts may be omitted if the signal is too weak.

[0059] According to one embodiment, the above-mentioned accumulation (step E32b) comprises: the accumulated 2D image obtained is composed of pixels whose gray level is the sum of the pixels of the different 2D projections stacked along the direction of the axis Y. According to this embodiment, the amount of information considered is maximized, but parasitic signals can be detected.

[0060] Then, for each column of pixels defined along the axis Z, a grayscale profile is determined (step E33 ). The levels are advantageously unsigned 16-bit levels, so that there are 65536 grayscale levels from black at 0 to white (65535). Thus, the number of columns along the axis Z is the same as the number of profiles.

[0061] Figure 6 The image is schematically shown as comprising pixels (one square is one pixel). For each column c1, c2, c3, c4, ..., cM, the graph comprises the variation of the grey level.

[0062] Figure 7 and Figure 8Two graphs are shown, which depend on the glass tracer including a line ( Figure 7 ) or two wires ( Figure 8 ). The graph includes grayscale on the ordinate and distance on the abscissa. Figure 7 The curve in is a simple but broad Gaussian distribution, Figure 8 The graph in Figure 1 shows a double Gaussian distribution consisting of two narrow Gaussian distributions. These two characteristic possible scenarios are characteristic of glass fibers and are the only two scenarios that can be encountered. Glass fibers are essentially a twisted set of glass and carbon strands that appear as two white lines in an X-ray tomography image when the glass strands lie on either side of a neutral fiber, or as a single, thick white line when the strands intersect at the neutral fiber.

[0063] Each of these graphs is then processed (step E34) to locate the neutral fibers. Figure 5 , it is understood that the gray levels of each column make it possible to obtain the height along the axis Z at which the neutral fibers are located.

[0064] In particular, Figure 7 In the case of a graph of the type shown, the above processing involves detecting the center of the Gaussian distribution and Figure 8 In the case of a graph of the type shown, the above processing involves detecting the centers of the two Gaussian distributions. The detected values are shown by the thick dashed curve.

[0065] Thus, at the end of the processing step (step E34 ), the height along the axis X at which the neutral fiber 22 is located is obtained.

[0066] In a complementary manner, the set of heights thus obtained can be filtered (step E35 ) to smooth out the different values and thus filter out outliers. Advantageously, a regression filtering can be performed. Figure 9 The accumulated 2D image of the filtered neutral fibers is shown. Figure 5 Compared with image I, it is observed that the curve representing the neutral fiber has less noise.

[0067] Regardless of whether filtering is used, the images I( Figure 5 ) or imageIf( Figure 9 ) are better than the existing methods (see Figure 2a ) to obtain better image quality.

[0068] Finally, the nominal dimensions and predetermined tolerances of the position of the neutral fiber thus obtained are compared with the nominal dimensions and predetermined tolerances of the theoretical position of the neutral fiber (step E36 ) to enable the integrity of the blade 1 to be assessed.

Claims

1. A method for verifying the positioning of a fiber preform in a blade, the blade having been obtained by injecting resin into a mold having the shape of the blade and in which the fiber preform has been placed, the blade extending in an orthogonal blade reference coordinate system X, Y, Z, the blade comprising a blade root and an airfoil portion, the blade root extending longitudinally along an axis X, the airfoil portion extending from the blade root along an axis Z, the blade having a thickness defined along the axis Y, the fiber preform comprising a glass tracer positioned on a surface of the fiber preform, the center of the glass tracer defining a neutral fiber being positioned at a height along the axis Z along a direction defined by the axis X, the method comprising the following steps: Step (E31): acquiring 2D tomographic projections of the blade by means of an imaging system comprising an X-ray source, the X-ray source emitting X-rays at different angles, each 2D tomographic projection being acquired at a given position of the X-ray source relative to the blade; Steps (E32, E32a, E32b): accumulating the 2D tomographic projections along the direction of the axis Y to obtain accumulated 2D images along the directions of the axes X and Z; Step (E33): determining a graph of gray levels for each column of pixels defined along the direction of the axis Z; Step (E34): Processing each of the obtained graphs to locate the position of the neutral fiber along the direction of the axis X in the direction of the axis Z.

2. The method according to claim 1, wherein The accumulation includes obtaining an accumulated 2D image composed of pixels having a maximum grayscale level in a stack of pixels of different slices stacked along the direction of the Y axis.

3. The method according to claim 1, wherein The accumulation includes: the accumulated 2D image is composed of pixels whose gray level is the sum of pixels of different slices stacked along the direction of the axis Y.

4. The method according to any one of claims 1 to 3, wherein The grayscale graph (G1) is a Gaussian distribution, and the location of the neutral fiber is the center (X1) of the Gaussian distribution.

5. The method according to any one of claims 1 to 3, wherein The grayscale graph (G2) is a double Gaussian distribution, and the location of the neutral fiber is the center (X2) of the double Gaussian distribution.

6. Method according to any one of claims 1 to 3, comprising a step (E35) of filtering the positioning of the neutral fibers along the direction of the axis X in the direction of the axis Z.

7. The method according to any one of claims 1 to 3, comprising a step (E36) of comparing the positioning of the neutral fibers thus obtained with a theoretical positioning of the neutral fibers.

8. A method for manufacturing a turbine blade made of a composite material, the method comprising the steps of: placing the fiber preform in a mold having the shape of a blade; injecting resin into said mold comprising said fiber preform under vacuum conditions to obtain said blade, which is called an injection-molded blade; The positioning of the fiber preform in the injection-molded blade is checked by the method according to any one of claims 1 to 7 .

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