A method of forming a composite material blade fatigue test retrofit

Abstract

The present application belongs to the field of helicopter blade design, and particularly relates to a forming method of a composite material blade fatigue test modification piece. In the curing process of the blade modification piece, the pressure is large and the metal press mold itself is heavy, which is easy to cause damage to the foam at the edge of the blade modification area, resulting in early failure of the blade during the fatigue test. The metal press mold is changed to a composite material press mold in the present application, and the forming method is redesigned, which greatly reduces the extrusion of the press mold on the foam at the edge of the blade modification area, avoids the problem of early failure of the test piece during the fatigue test caused by the crushing of the foam, makes the pressure distribution more uniform, reduces the phenomenon of internal wrinkles and accumulated glue of the part, and effectively improves the surface quality of the modification piece.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of helicopter blade design, and particularly relates to a forming method of a composite material blade fatigue test modification piece. BACKGROUND

[0002] At present, composite materials are increasingly used to replace metal materials for manufacturing rotor blades of helicopters. As one of important moving parts on helicopters, it is crucial to accurately grasp the service life and fatigue resistance of blades to ensure the safety of blades in flight. Therefore, before being put into mass production, the molded blades are modified into fatigue test pieces and subjected to blade fatigue tests.

[0003] The fatigue test piece is composed of clamped metal plates on the basis of a blade modification piece. The blade modification piece is generally made by directly laying a cloth on the inner surface of a metal mold and assembling the blade with the cloth after curing in one step, and the pressure is large during the curing process of the modification piece, and the metal mold itself is heavy. During the curing process using the metal mold, the foam at the edge of the blade modification area is easily damaged, resulting in premature failure of the blade during the fatigue test. SUMMARY

[0004] The purpose of the present application is to provide a forming method of a composite material blade fatigue test modification piece, which solves the damage to the blade itself during the manufacturing process of the composite material blade modification piece, accurately controls the volume distribution of each part of the modification piece, reduces the occurrence of defects such as surface area glue of the modification piece, and improves the forming quality of the blade modification piece.

[0005] The technical scheme of the present application provides a forming method of a composite material blade fatigue test modification piece, which comprises the following steps:

[0006] S1. Designing a three-dimensional numerical model of an intermediate piece with a certain machining allowance according to the drawing requirements of the test modification piece, the intermediate piece comprising a clamping area and a transition area;

[0007] S2. Processing the foam raw material according to the three-dimensional numerical model to obtain a core mold;

[0008] S3. Manufacturing an upper and lower two-part composite material negative mold based on the core mold;

[0009] S4. Laying a beam tape on the inner surface of the upper and lower two-part composite material negative mold in the length direction, and the number of laid beam tapes is related to the thickness of the area;

[0010] S5. Pre-assembling the composite material negative mold with the laid beam tape on the blade, opening the mold for inspection and supplementing or removing the material;

[0011] S6. Closing the mold again and vacuum curing, and removing the upper and lower two-part composite material negative mold;

[0012] S7, numerical control machining according to the theoretical size of the intermediate piece to obtain the intermediate piece;

[0013] S8, laying cloth on the surface of the intermediate piece along the contour from the leading edge of the lower wing surface to the leading edge of the upper wing surface, and adding a certain amount of process cloth in the clamping area of the upper and lower wing surfaces;

[0014] S9, surface treatment after vacuum curing;

[0015] S10, numerical control machining of the upper and lower surfaces and clamping holes in the clamping area.

[0016] Advantageously, in step S3, a certain thickness of composite fabric is laid on the outer surface of the core mold, and is laid in the order of 0°, ±45°, 90°; after vacuum curing, an upper and lower two-part composite mold is formed which is adapted to the contour of the intermediate piece.

[0017] Advantageously, in step S4, the upper and lower two-part composite mold after laying the girder belt is vacuum compacted.

[0018] Advantageously, in step S6, the vacuum pressure is maintained at -0.08 to -0.098 MPa, the temperature is lowered to below 60°C, and the part surface nodule is cleaned.

[0019] Advantageously, in step S7, a five-axis numerical control machining machine tool is used, the composite material end face of the blade root is taken as the reference, the thickness and twist angle values of the clamping area and the transition area are milled to the required values according to the size of the twist angle and thickness required by the drawing of the modified part.

[0020] Advantageously, in step S10, the midpoint of the two bushing holes of the blade root and the thickness at the blade root are used to determine the position of the two reference holes in the clamping area according to the 25% chord line of the blade.

[0021] Advantageously, a line segment is obtained by connecting the midpoints of the two bushing axis lines, the midpoint of the line segment is selected, and a vertical line is drawn through the point to the plane formed by the two bushing axis lines, which is the 25% chord line.

[0022] Advantageously, according to the angle value between the plane of the blade in the clamping area and the plane of the blade root, the milling cutter is placed at the required angle using a five-axis numerical control machining equipment, and the distance from the reference surface to the 25% chord line is controlled to reach the theoretical value to mill one of the wing surface reference surfaces in the clamping area.

[0023] Advantageously, the reference hole position and the twist angle value of the modified area are measured using a three-coordinate measuring device, and if it exceeds the theoretical range, the processing position is corrected.

[0024] Advantageously, the reference hole is aligned with the lower wing surface reference plane, the gap between the reference plane and the platform plane is less than 0.1mm, the Y-axis direction of the reference hole is consistent with the machine tool direction, and the part is clamped after alignment.

[0025] Advantages of the present application:

[0026] 1. The original metal mold is replaced by a composite material mold, and the vacuum bag is made and vacuumized to raise the temperature for curing, which greatly reduces the extrusion of the mold on the foam at the edge of the blade modification area, avoids the problem of premature failure of the test piece during fatigue test caused by the crushing of the foam, and at the same time, in the process of cloth curing, the vacuum bag is directly made on the surface of the part, so that the pressure distribution is more uniform, the phenomenon of internal wrinkles and glue accumulation of the part is reduced, and the surface quality of the modified part is effectively improved.

[0027] 2. The original modified part is formed by one-time curing, and the modified part girder belt is separately cured, and the 25% chord line position of the blade and the torsion angle value of the modification area are positioned by five-axis numerical control machining, and on this basis, the volume distribution of the modified part girder belt and the plane torsion angle of the modification area and the accurate control of the hole position of the modification area are realized, which effectively improves the forming quality of the modified part and reduces the surface of the modified part.

[0028] 3. The cloth laying of the modified part is changed from the original upper and lower wing surface block laying to the single-layer cloth laying from the front edge to the starting position, which retains the integrity of the cloth fiber at the rear edge of the blade, effectively improves the connection strength of the cloth at the rear edge of the modification area, and solves the problems of cloth debonding and delamination at the rear edge of the modification area during fatigue test. BRIEF DESCRIPTION OF DRAWINGS

[0029] When read in conjunction with the drawings, the exemplary examples and preferred modes of use, other objects and their descriptions will be best understood by referring to the following detailed description of the examples of the present application, in which:

[0030] Figure 1 is a schematic view of the constitution of the blade modification part;

[0031] Figure 2 is a top view of the core mold;

[0032] Figure 3 and Figure 4 is a schematic view of two sides of the core mold.

[0033] 1-blade root, 2-blade, 3-blade modification part girder, 4-inner layer cloth, 5-outer layer cloth, 6-clamping area, 7-transition area DETAILED DESCRIPTION

[0034] The disclosed examples will be described more fully with reference to the accompanying drawings, in which some (but not all) of the disclosed examples are shown. In fact, many different examples may be described, and these examples should not be construed as limited to those set forth herein. Rather, these examples are described so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0035] See the example. Figure 1 The experimental modified part of the present invention is processed based on the existing blade. The blade 2 is cut off in the area near the blade root 1. The blade modification beam 3 is provided on the outer surface of the blade 2. The outer surface of the blade modification beam 3 is provided with composite material, including inner ply 4 and outer ply 5. The clamping part includes clamping area 6 and transition area 7. The clamping area 6 has the largest thickness. It forms an integral structure with other areas through the sloped transition area 7. The clamping area 6 has connecting holes.

[0036] In one embodiment, the specific processing includes the following steps:

[0037] 1. Based on the drawing requirements of the test modification part, modify the three-dimensional digital model of the unprocessed intermediate part, remove the thickness of the cloth covering the surface of the modification part, retain only the shape of the blade body and the main beam of the modification area, and set the process allowance in the clamping area 6 of the upper and lower blade surfaces to finally obtain the three-dimensional digital model of the intermediate part.

[0038] 2. Based on the three-dimensional digital model, a five-axis CNC machine tool and foam raw material were used to process... Figures 2-4 The mandrel shown is covered with a composite material fabric of a certain thickness on its outer surface, which is laid at 0°, ±45° and 90° in sequence to reduce deformation during the curing process. After vacuum curing, a composite material female mold of upper and lower parts that conforms to the shape of the intermediate part is formed for use in the subsequent curing and molding process of the modified part.

[0039] 3. Lay the beam strip along the length direction on the inner surface of the composite material female mold obtained in the above process. The thickness is the largest in the clamping area 6 and decreases in the transition area 7. The specific thickness is coordinated with the blade airfoil and the mold. The number of bundles to be laid depends on the situation. After laying, vacuum compaction is performed.

[0040] 4. Assemble the composite material female mold on the upper and lower sides of the blade, insert the positioning pin into the reserved positioning hole, vacuum and pressurize for 10 minutes, then open and check whether there are any missing or excess materials in the composite material female mold, and replenish or remove materials for any missing or excess materials until the pre-assembly is qualified.

[0041] 5. Insert the blades into the lower composite material female mold, close the upper composite material female mold, and insert the positioning pin. Make a vacuum bag and compact it. When closing the mold, check and adjust the positions of the upper and lower molds to ensure they are aligned before vacuuming and compacting.

[0042] 6. The part is sent into the curing oven for curing, maintaining vacuum pressure -0.08 to -0.098 MPa, and cooling to below 60°C to discharge the oven, and cleaning the part surface glue tumor;

[0043] 7. Using a five-axis numerical control machining machine tool, taking the composite material end face of the blade root 1 as a reference, and according to the drawing, the thickness and torsion angle values of the clamping area 6 and the transition area 7 are milled to the required values to ensure that the beam profile conforms to the drawing, and the intermediate part profile is obtained.

[0044] 8. The cloth is laid on the surface of the intermediate part from the lower wing surface leading edge to the upper wing surface leading edge along the profile (the cloth is a whole piece, and the rear edge is not divided), and a certain amount of process cloth is added to the clamping area 6 of the upper and lower wing surfaces, after the laying is completed, the vacuum bag is made to wrap the transformation area and vacuumize into the oven for curing, when the part is cooled to below 60°C, the pressure is released to discharge the mold, the part surface is polished, and the glue tumor is cleaned.

[0045] 9. Using the midpoint of the center of the two bushing holes of the blade root 1 and the thickness of the composite material at the blade root, the 25% chord line of the blade is found (a line segment is obtained by connecting the midpoint of the two bushing axis, the midpoint of the line segment is selected, and a straight line perpendicular to the plane formed by the two bushing axis through the point is the 25% chord line), and two reference holes are determined and processed in the clamping area 6 according to the 25% chord line of the blade.

[0046] 10. According to the angle value between the plane of the clamping area 6 of the blade and the plane of the blade root 1 (which can be obtained in the three-dimensional model), the five-axis numerical control machining equipment is used to place the milling cutter to the required angle, the lower wing surface reference surface of the clamping area 6 is milled, and the distance from the reference surface to the 25% chord line is controlled to reach the theoretical value, and then the three-coordinate measuring equipment is used to measure the hole position of the reference hole and the torsion angle value of the transformation area.

[0047] 11. The part is aligned using the reference hole and the lower wing surface reference surface, the gap between the reference surface and the platform plane is less than 0.1 mm, the Y-axis direction of the reference hole is consistent with the direction of the machine tool, and after alignment, the part is clamped using the clamp.

[0048] 12. The upper wing surface reference surface of the clamping area 6 is processed so that the thickness of the clamping area 6 reaches the required value, and according to the three-coordinate measurement results and the reference hole position, the positions of all holes of the transformed part are determined and bored to the final value.

[0049] In order to avoid damage to the blade body caused by metal molds during the curing process, the forming mold is changed from the original metal mold to a composite material mold, and the original hot press bed pressing curing method is cancelled, and a vacuum bag is made on the surface of the composite material mold for curing under vacuum pressure.

[0050] In order to prevent the defects caused by uneven volume distribution of the retrofit part girder belt area, solve the problems of internal glue accumulation and wrinkles of the retrofit part, the original one-time solidification forming method is changed to first make an intermediate part containing only the paddle and the girder part of the retrofit area according to the shape of the paddle and the girder belt area, and then process the thickness and plane of the girder belt area to be qualified by a five-axis numerical control machine tool according to the angle between the paddle retrofit area and the paddle root, and then wrap the retrofit area cloth around the paddle leading edge on the surface of the intermediate part, and make a vacuum bag on the surface of the intermediate part for solidification.

[0051] After the wrapping and solidification are completed, the five-axis numerical control machine tool is used to find the 25% chord line of the paddle (the axis line at the connection between the paddle and the hub), and the surface holes of the retrofit part are positioned according to the distance to the 25% chord line, and the retrofit area plane twist angle value and the retrofit area through hole are milled to obtain the paddle retrofit part.

[0052] Different examples of the systems, devices, and methods disclosed herein include various components, features, and functionalities. It should be understood that various examples of the systems, devices, and methods disclosed herein can include any of the components, features, and functionalities of any of the other examples of the systems, devices, and methods disclosed herein in any combination or sub-combination, and all such possibilities are intended to fall within the scope of the present disclosure.

[0053] Descriptions of different advantageous arrangements have been presented for illustrative and descriptive purposes, but are not intended to be exclusive or limiting to the examples disclosed. Numerous modifications and adaptations will be apparent to those skilled in the art. Additionally, different advantageous examples can provide different advantages as compared to other advantageous examples. One example or more examples are chosen and described so that best illustrates the principles of the examples, the practical application, and to enable others skilled in the art to best utilize the disclosure in various embodiments and with various modifications as are suited to the particular use contemplated.

Claims

1. A method of forming a composite material blade fatigue test retrofit, characterized by, The method comprises the following steps: S1, designing a three-dimensional model of the intermediate part with a certain machining allowance according to the drawing of the test modification part, the intermediate part comprising a clamping area (6) and a transition area (7); S2, processing the foam raw material according to the three-dimensional model to obtain a core mold; S3, manufacturing an upper and lower two-part composite negative mold based on the core mold; Pasting a certain thickness of composite fabric on the outer surface of the core mold, and pasting in the order of 0°, ±45° and 90°; S4, pasting a girder belt on the inner surface of the upper and lower two-part composite negative mold along the length direction, and the number of pasted bundles is related to the thickness of the area; S5, pre-assembling the composite negative mold pasted with the girder belt on the blade, checking and supplementing or removing the material; S6, reassembling and vacuum curing, and removing the upper and lower two-part composite negative mold; S7, numerically controlling the processing to obtain the intermediate part according to the theoretical size of the intermediate part; S8, pasting a cloth on the surface of the intermediate part from the leading edge of the lower surface to the leading edge of the upper surface along the contour, and adding a certain amount of process cloth in the clamping area (6) of the upper and lower surfaces; S9, performing surface treatment after vacuum curing; S10, numerically controlling the processing of the upper and lower surfaces and the clamping hole in the clamping area (6).

2. The molding method according to claim 1, characterized by: In step S4, the upper and lower two-part composite negative mold pasted with the girder belt is vacuum compacted.

3. The molding method according to claim 1, characterized by: In step S6, the vacuum pressure is kept at -0.08 to -0.098 MPa, and the temperature is lowered to below 60°C before being discharged.

4. The molding method according to claim 1, characterized by: In step S7, using a five-axis numerical control machining machine tool, taking the composite material end face of the blade root (1) as the reference, and according to the size requirements of the twist angle value and the thickness in the drawing of the test modification part, the girder thickness and the twist angle value of the clamping area (6) and the transition area (7) are milled to the required value.

5. The molding method according to claim 4, characterized by: In step S10, the midpoint of the two bushing holes of the blade root (1) and the thickness at the blade root are used to find the 25% chord line, and the positions of the two reference holes in the clamping area (6) are determined and processed according to the 25% chord line.

6. The molding method according to claim 5, characterized by: A line segment is obtained by connecting the midpoints of the two bushing axis lines, the midpoint of the line segment is selected, and a vertical line is drawn through the midpoint of the plane formed by the two bushing axis lines, which is the 25% chord line.

7. The molding method according to claim 6, characterized by: According to the angle value between the plane of the blade in the clamping area (6) and the plane of the blade root (1), the milling cutter is placed at the required angle using a five-axis numerical control machining equipment, and one of the wing surface reference surfaces of the clamping area (6) is milled, and the distance between the wing surface reference surface and the 25% chord line is controlled to reach the theoretical value.

8. The molding method according to claim 7, characterized by: The reference hole position and the twist angle value of the modification area are measured by using a three-coordinate measuring device, and if they exceed the theoretical range, the processing position is corrected.

9. The molding method according to claim 8, characterized by: Another wing surface reference surface of the clamping area (6) is processed.

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