A flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts

Abstract

The application relates to the field of aviation engine part clamping, in particular to a flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts, which comprises the following steps: analyzing a part structure to determine a clamping position, designing an inner cavity of a flexible clamp and the size, selecting a flexible surface material, calculating the size of a clamping force, designing an internal flow channel and a fluid medium, and checking the clamping effectiveness through finite element simulation and other means. The application can solve the problem of non-reference clamping caused by near-net forming process, significantly improve clamping consistency and efficiency, and realize stable clamping of the part through the flexible clamp, so that stress concentration and surface damage are avoided, and the application is suitable for efficient and reliable clamping of various SiC fiber reinforced SiC ceramic matrix composite curved surface parts.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of aero-engine part clamping, and particularly relates to a flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts. BACKGROUND

[0002] Ceramic matrix composite has become an ideal material for a new generation of aero-engines due to its small density, high strength, excellent high-temperature resistance and corrosion resistance, etc. In practical applications, ceramic matrix composite curved surface parts are usually prepared by near-net-shape forming process. Although this process can realize efficient manufacturing of complex-shaped parts, it also brings problems such as large part difference, uneven distribution of shape allowance, and lack of clear positioning reference. The traditional clamping method for metal curved surface parts relies on clear geometric reference and regular shape features. However, for ceramic matrix composite curved surface parts, due to their special forming method and material properties, the traditional clamping method cannot meet the positioning and clamping requirements of the parts, which may lead to under-positioning or over-positioning, thereby affecting the subsequent machining precision and making the parts unable to meet the design requirements. In addition, the existing clamping method lacks flexibility when dealing with parts without reference or unclear reference, has low clamping efficiency, and is difficult to ensure the consistency and reliability of clamping. Therefore, in view of the characteristics of ceramic matrix composite curved surface parts, it is urgent to develop a flexible clamping method to solve the technical problems caused by part difference and lack of reference in the clamping process, improve the clamping efficiency and machining precision, and meet the manufacturing requirements of high-performance parts in the field of aero-engines. SUMMARY

[0003] In view of the problems in the prior art, the application provides a flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts, which realizes efficient and reliable clamping of ceramic matrix composite curved surface parts through the design and application of flexible clamps, and solves the problem that the traditional clamping method cannot meet the clamping requirements of parts without reference.

[0004] The technical scheme of the application is as follows:

[0005] The application provides a flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts, which comprises the following steps:

[0006] Analyzing the structure of the ceramic matrix composite curved surface part, determining the minimum allowance position or non-machining area as the clamping position, and clearly defining the size and shape of the position;

[0007] Designing the inner cavity of the flexible clamp according to the size and shape of the clamping position, determining the number and size of the clamps, and ensuring that the length of the inner cavity of the flexible clamp is greater than the length of the clamping position and the width is smaller than the width of the clamping position;

[0008] Selecting flexible fixture surface material and determining clamping method;

[0009] Calculating clamping force according to part size, designing fixture internal flow channel and determining flow channel medium;

[0010] Checking fixture clamping effectiveness;

[0011] Implementing flexible clamping.

[0012] Further, the flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts, the minimum wall thickness of the cavity is determined according to the clamping force, ensuring that the strength of the cavity can withstand the maximum clamping force. When the cavity is circular, the minimum wall thickness of the side wall is calculated by the formula , wherein s is the minimum wall thickness of the side wall, p is the clamping force, H is the height of the cavity, and E is the elastic modulus, δ is the allowable deformation amount; the minimum thickness of the bottom plate is , wherein h is the minimum wall thickness of the bottom plate, r is the radius of the bottom plate. When the cavity shape is rectangular, the minimum wall thickness is , wherein t is the minimum wall thickness of the rectangular cavity, k is the boundary coefficient, l is the side length of the rectangle, [σ] is the material allowable stress.

[0013] Further, the flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts, the flexible fixture surface material is selected from rubber, polyurethane or resin, which has high density, softness, strong elastic deformation ability and wear resistance.

[0014] Further, the flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts, the clamping method includes pneumatic clamping and hydraulic clamping, wherein pneumatic clamping is used for clamping force less than 20N, and hydraulic clamping is used for clamping force greater than 20N.

[0015] Further, the flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts, the method for calculating clamping force is based on the material properties of the part, the processing requirements and the actual measurement data, and the determination of the clamping force is completed by finite element simulation or process test.

[0016] Further, the flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts, the shape of the internal flow channel of the fixture is selected from circular, trapezoidal, semicircular or U-shaped, and the flow channel medium is selected from compressed air, hydraulic oil, water-in-oil emulsion or silicone oil.

[0017] Further, the above-mentioned flexible clamping method for SiCf / SiC ceramic matrix composite curved parts, the clamping effectiveness verification adopts finite element simulation, theoretical calculation or actual measurement method, and a force meter or strain gauge sensor is arranged on the surface of the clamp during actual measurement.

[0018] The advantages and beneficial effects of the present application are as follows:

[0019] 1. The present application solves the problems of shape difference and no reference caused by near-net forming process of ceramic matrix composite curved parts through the design of flexible clamp, significantly improving the consistency of clamping. The flexible clamping method can quickly realize the clamping and alignment of no-reference parts, greatly shortening the clamping time and improving the production efficiency. The flexible clamp can be flexibly adjusted according to the shape and size of different parts, and is suitable for the clamping needs of various ceramic matrix composite curved parts. The selection of the surface material of the flexible clamp and the application of the fluid medium ensure the uniform distribution of clamping force and the reliability of multiple clamping, thereby effectively avoiding the under-positioning or over-positioning problems existing in the traditional clamping method.

[0020] 2. The present application ensures the strength and stability of the clamp during clamping through specific measures such as calculation of the minimum wall thickness size of the flexible clamp cavity, size limitation of the inner cavity and flow channel design. The high density and elastic deformation ability of the surface material of the flexible clamp enable it to form good contact with the surface of the part during clamping, thereby improving the clamping effect. The accurate calculation of clamping force and the reasonable selection of fluid medium make the clamping force not only meet the processing requirements, but also avoid damaging the parts.

[0021] 3. The present application ensures the uniform distribution of clamping force and the reliability of clamping through the effectiveness verification of the flexible clamping scheme. The verification method combining finite element simulation, theoretical calculation and actual measurement can comprehensively evaluate the performance of the clamp during clamping, thereby providing a scientific basis for the optimization design of the clamp. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The flowchart of the flexible clamping method for ceramic matrix composite curved parts;

[0023] Figure 2 The schematic diagram of the flexible clamping of the present application;

[0024] In the figure, 1 is the inner cavity of the clamp, 2 is the part, and 3 is the clamping force. DETAILED DESCRIPTION

[0025] The present application provides a flexible clamping method for SiCf / SiC ceramic matrix composite curved parts, which is described in detail in the following specific embodiments in conjunction with the accompanying drawings.

[0026] Example 1

[0027] In the specific embodiment, for SiCf / SiC ceramic matrix composite curved surface parts, the flexible clamping method is as follows Figure 1 as shown in the flowchart.

[0028] First, the machining area and non-machining area of the part are determined, and the area with the smallest or no machining allowance is selected as the clamping position. As shown in Figure 2 , by analyzing the geometric characteristics and machining requirements, the non-machining area of the upper and lower surfaces of the part 2 is determined as the clamping position, the upper and lower surfaces of the part 2 are respectively in contact with the inner cavity of the clamp 1, and the clamping force 3 is transmitted through the fluid medium to realize the fixation of the part. This selection is based on the premise of avoiding affecting the machining accuracy of the part, while ensuring that the clamping process will not cause damage to the surface of the part.

[0029] After selecting the clamping position, the flexible clamp inner cavity needs to be designed according to the specific size and shape of the part. The design of the inner cavity of the flexible clamp needs to meet certain strength requirements, while taking into account the rationality of the inner cavity size. Specifically, according to the machining requirements, the same material as the part is tested for machining, the force during machining is measured to be 10 N, and the weight of the workpiece is 3 N, so the clamping force can be ensured to be not less than 20 N.

[0030] The maximum width of the clamping position of this typical curved surface part is 30 mm, and the length is 50 mm, so the inner cavity width of the flexible clamp can be designed to be 30 mm, and the inner cavity length is designed to be 50 mm. The cavity is rectangular, so the minimum wall thickness under this clamping force is calculated as , where t is the minimum wall thickness of the rectangular cavity, k is the boundary coefficient, l is the length of the rectangle, [σ] is the material allowable stress, here k is 0.028, l is 30 mm and 50 mm respectively, and the clamping force p is 20 N. Assuming that the clamp is made of 304 stainless steel, its allowable stress [σ] is 150 MPa, so the minimum wall thickness is calculated to be 2.4 mm, so the minimum wall thickness of the clamp inner cavity is determined to be 3 mm, ensuring that the strength of the cavity can withstand the maximum clamping force.

[0031] On this basis, the number and size of the flexible clamp are further determined. Considering the overall size of the part and the clamping requirement, two flexible clamps are selected to clamp from the upper and lower surfaces of the workpiece respectively. This design can ensure that the clamping force is evenly distributed, thereby improving the stability and reliability of the clamping.

[0032] The selection of the flexible clamp surface material is one of the key steps of the method. According to the characteristics of the ceramic matrix composite material, a material with high density, low hardness and strong elastic deformation ability is selected as the flexible clamp surface material. In this embodiment, polyurethane is selected as the flexible clamp surface material, the friction coefficient between the polyurethane and the SiCf / SiC ceramic matrix composite material is 0.6, the friction force is 12 N, the workpiece to be clamped is a blade type part, the mass is relatively light, which is 0.3 kg, and the gravity is 3 N, which is less than the friction force between the clamp and the workpiece, so that the stability in the clamping process can be ensured. In addition, the polyurethane material has good wear resistance and can maintain stable performance in multiple clamping processes, thereby prolonging the service life of the clamp.

[0033] After the design of the flexible clamp is completed, the clamping force needs to be calculated and the appropriate clamping method needs to be selected. When the SiCf / SiC ceramic matrix composite curved surface part is subjected to trial machining, the measured machining force is 10 N. According to the principle of force synthesis, the friction force should be not less than 12 N, and the clamping force should be not less than 20 N, so as to ensure that the part will not be displaced during machining. On this basis, the clamping method is selected according to the size of the clamping force. For parts with small clamping force, a pneumatic clamping method is adopted, that is, compressed air is filled in the inner cavity of the clamp.

[0034] In this embodiment, for the blade type part with a clamping force of 10 N, the internal flow channel is designed in a circular shape, the flow channel width is 10 mm, and the medium in the flow channel is compressed air. The circular flow channel can ensure the uniform distribution of compressed air in the flow channel, thereby achieving uniform transmission of the clamping force.

[0035] The effectiveness verification of the flexible clamping scheme is a key step to ensure the reliability of clamping. In this embodiment, when the above-mentioned flexible clamp is subjected to finite element simulation, the simulation results show that the maximum clamping force of the clamp is 25 N, which can meet the requirement of 20 N clamping force in the machining process. The theoretical calculation derives the distribution of the clamping force through the mechanical formula, which provides a theoretical basis for the design of the clamp. The actual measurement directly obtains the actual value of the clamping force by arranging sensors such as force sensors or strain gauges on the surface of the clamp. For example, after the strain gauges are installed on the surface of the clamp, the measurement results show that the maximum clamping force is 24.8 N, which is basically consistent with the simulation results. Through the combination of various verification methods, the performance of the clamp in the clamping process can be comprehensively evaluated, and a scientific basis for the optimized design of the clamp is provided.

[0036] Embodiment 2

[0037] In the specific embodiment, the flexible clamping method for the SiCf / SiC ceramic matrix composite curved surface part is as shown in the flowchart. Figure 1

[0038] ​Firstly, the machining area and non-machining area of the part are determined, and the area with the smallest or no machining allowance is selected as the clamping position. Through the analysis of its geometric characteristics and machining requirements, the non-machining area of the upper and lower surfaces of the part is determined as the clamping position, and the upper and lower surfaces of the part are respectively in contact with the inner cavity of the fixture, and the clamping force is transmitted through the fluid medium to realize the fixation of the part. This selection is based on the premise of avoiding affecting the machining accuracy of the part, while ensuring that the clamping process will not damage the surface of the part.

[0039] After selecting the clamping position, the inner cavity of the flexible fixture needs to be designed according to the specific size and shape of the part. The inner cavity of the flexible fixture needs to meet certain strength requirements, while considering the rationality of the inner cavity size. Specifically, according to the machining requirements, the same material as the part is tested for machining, and the force during machining is measured to be 100 N, and the workpiece mass is 5 kg, so the clamping force is guaranteed to be not less than 120 N. The maximum width of the clamping position of the typical curved surface part is 100 mm, and the length is 100 mm, so the inner cavity width of the flexible fixture can be designed as a cylindrical inner cavity with a width of 100 mm to ensure that it will not break when the internal pressure is large. To ensure the space of the inner cavity, the height is designed to be 80 mm. Since the cavity is cylindrical, the minimum wall thickness calculation formula of the side wall is used to calculate the minimum wall thickness under the clamping force, where s is the minimum wall thickness of the side wall, p is the clamping force, H is the cavity height, E is the elastic modulus, δ is the allowable deformation; here p is 120 N, H is 80 mm, the cavity material is selected as 304 stainless steel, the elastic modulus E is 193 GPa, and the maximum allowable deformation δ is 0.1 µm. The calculation shows that the minimum wall thickness of the side wall is 7.3 mm, so the minimum wall thickness of the inner cavity of the fixture is determined to be 8 mm. The minimum thickness of the bottom plate is used to calculate the minimum thickness of the bottom plate, where h is the minimum thickness of the bottom plate, r is the bottom plate radius, r is 50 mm, and the calculation shows that the minimum thickness of the bottom plate is 0.6 mm, so the minimum thickness of the bottom plate of the inner cavity of the fixture is determined to be 1 mm, ensuring that the strength of the cavity can withstand the maximum clamping force.

[0040] On this basis, the number and size of the flexible fixture are further determined. Considering the overall size of the part and the clamping requirement, five flexible fixtures are selected to clamp the workpiece from the four corners and the center. This design can ensure that the clamping force is evenly distributed, thereby improving the stability and reliability of the clamping.

[0041] The selection of the flexible clamp surface material is one of the key steps of the method. According to the characteristics of the ceramic matrix composite material, a material with high density, low hardness and strong elastic deformation ability is selected as the flexible clamp surface material. In this embodiment, rubber is selected as the flexible clamp surface material, the friction coefficient between the rubber and the SiCf / SiC ceramic matrix composite material is 0.7, the friction force is 84 N, the workpiece clamped is a large structural part, the mass is 6.5 kg, and the gravity is 65 N, which is less than the friction force between the clamp and the workpiece, so that the stability in the clamping process can be ensured. In addition, the rubber material has good wear resistance and can maintain stable performance during multiple clamping processes, prolonging the service life of the clamp.

[0042] After the design of the flexible clamp is completed, the clamping force is calculated and the appropriate clamping method is selected. When the SiCf / SiC ceramic matrix composite curved surface part is trial machined, the measured machining force is 50 N. According to the principle of force synthesis, the friction force should be not less than 84 N, and the clamping force should be not less than 120 N to ensure that the part does not displace during machining. On this basis, the clamping method is selected according to the size of the clamping force. Since the clamping force in this embodiment is large, a liquid medium is used to transmit pressure through the internal flow channel to make the flexible material deform more to meet the clamping requirement. The liquid medium used in this embodiment is silicone oil, and the design of the internal flow channel of the clamp needs to be optimized according to the size and distribution requirement of the clamping force. In this embodiment, for large structural parts with a clamping force of 120 N, the internal flow channel is designed in a U shape, the flow channel width is 90 mm, and the medium in the flow channel is silicone oil. The U-shaped flow channel can ensure that the silicone oil in the flow channel has enough support on the clamping surface, thereby achieving stable clamping.

[0043] The effectiveness verification of the flexible clamping scheme is a key step to ensure the reliability of clamping. In this embodiment, when the above flexible clamp is theoretically calculated, the calculation result shows that the clamping force of the clamp is 150 N, which can meet the requirement of 120 N clamping force in the machining process. Theoretical calculation deduces the distribution of clamping force through mechanics formula, which provides a theoretical basis for clamp design. Actual measurement directly obtains the actual value of clamping force by arranging force sensors or strain gauges on the surface of the clamp. For example, after installing strain gauges on the surface of the clamp, the measurement result shows that the clamping force is 148.9 N, which is basically consistent with the simulation result. Through the combination of various verification methods, the performance of the clamp in the clamping process can be evaluated comprehensively, which provides a scientific basis for the optimization design of the clamp.

Claims

1. A flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts, characterized in that: The following steps are involved: Analyze the structure of ceramic matrix composite curved surface parts, determine the minimum allowance position or non-machining area as the clamping position, and clarify the size and shape of the position; Design the inner cavity of the flexible fixture according to the size and shape of the clamping position, ensuring that the length of the inner cavity of the flexible fixture is greater than the length of the clamping position and the width is smaller than the width of the clamping position. On this basis, further determine the number and size of the flexible fixtures; Select the flexible fixture surface material; Calculate the clamping force based on the part size, determine the clamping method based on the clamping force, design the flow channel inside the fixture, and determine the flow channel medium; Check the effectiveness of fixture clamping; Implement flexible clamping.

2. The flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts according to claim 1, characterized in that: The minimum wall thickness of the cavity is determined based on the clamping force calculation to ensure that the strength of the cavity can withstand the maximum clamping force.

3. The flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts according to claim 1, characterized in that: The surface material of the flexible clamp is selected from rubber, polyurethane or resin, and has high density, soft hardness, strong elastic deformation ability and wear resistance.

4. The flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts according to claim 1, characterized in that: The clamping methods include pneumatic clamping and hydraulic clamping, wherein pneumatic clamping is used when the clamping force is less than 20N, and hydraulic clamping is used when the clamping force is greater than 20N.

5. The flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts according to claim 1, characterized in that: The method for calculating the clamping force is based on the material properties of the parts, processing requirements and actual measurement data, and the clamping force is determined through finite element simulation or process testing.

6. The flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts according to claim 1, characterized in that: The shape of the flow channel inside the fixture is selected from circular, trapezoidal, semicircular or U-shaped, and the flow channel medium is selected from compressed air, hydraulic oil, water-in-oil emulsion or silicone oil.

7. The flexible clamping method for SiCf / SiC ceramic matrix composite curved surface parts according to claim 1, characterized in that: The clamping effectiveness check adopts finite element simulation, theoretical calculation or actual measurement, and during actual measurement, a force gauge or strain gauge sensor is set on the surface of the fixture.

Images