A method for testing the pressure of fabric layers in a closed curved mold

Abstract

The present invention relates to the field of in-mold pressure testing. The present invention provides a method for testing the pressure of a fabric ply in a closed curved mold, comprising: S1. A pressure sensor includes a strain gauge and a conductor, the strain gauge is connected to the conductor, and a stainless steel sheet is attached to one side of the strain gauge; S2. An interface is added to the middle of the conductor; S3. One end of a first wire is connected to the strain gauge, and the other end of the first wire is detachably connected to a second wire. The strain gauge is placed in the mold, and the other end of the first wire is passed through a glue injection port of the curved mold and detachably connected to the second wire; S4. The strain gauge is attached to the contact surface between the mold and the preform, with the side of the strain gauge attached to the stainless steel sheet facing the fabric ply and the other side of the strain gauge facing the mold surface; S5. After the preform is molded, a pressure test is performed. The testing method of the present invention can accurately measure the pressure of the fabric ply in a closed curved mold.

Description

Technical Field

[0001] The present invention relates to the field of mold pressure testing, and in particular to a method for testing the pressure of a fabric ply in a closed curved mold. Background Art

[0002] The RTM (Resin Transfer Molding) process is an advanced process for preparing high-performance composite materials. It involves placing a fiber-reinforced material preform calculated according to design requirements in a prefabricated mold cavity that meets the process dimensions. A dedicated resin system is then injected into the closed mold cavity within a certain pressure range using injection equipment. The resin then infiltrates the reinforcement and solidifies to form the desired high-performance composite material. This process is characterized by high precision, low cost, and a high fiber volume content.

[0003] Currently, some large composite components have complex structures and extremely high precision requirements, requiring the use of the VARTM molding process. The RTM mold for this product consists of an inner and outer mold. After the fiber preform and mold are assembled, the preform is completely isolated from the outside world, forming a "blind box" state. The state of the fiber preform and mold assembly cannot be visually determined. The pressure between the fabric layer and the mold is determined by experience, which is prone to misjudgment and can lead to irreparable defects during product injection.

[0004] Due to the assembly issues involved in the mold closing of the preform, it is impossible to use simulation methods to predict the pressure distribution of the fiber reinforced material preform in the RTM mold.

[0005] In the existing technology, the pressure of the fabric ply in the mold can be tested by a pressure sensor. The pressure sensor includes a strain gauge and a wire. One side of the wire is connected to the strain gauge, and the other side of the wire is connected to the data acquisition equipment through a test head. There are the following problems: First, the surface of the preform is covered with fiber fabric, and the fiber fabric is mostly woven. Unlike metal structures, the surface of the fiber fabric is actually discontinuous, which can easily cause uneven force on the strain gauge of the pressure sensor, resulting in inaccurate measurement results and low test accuracy; second, the test head of the pressure sensor wire is too large to pass directly through the glue injection port. If one side of the strain gauge is passed through the glue injection port, the strain gauge may bend, causing the pressure sensor to fail and be unable to be tested.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of the present invention is to propose a method for testing the pressure of a fabric ply in a closed curved mold, so as to solve the problem that in the prior art, if the pressure of the fabric ply in the mold is directly tested by a pressure sensor, the pressure sensor includes a strain gauge and a wire, one side of the wire is connected to the strain gauge, and the other side of the wire is connected to a data acquisition device through a test head. There are the following problems: First, the surface of the preform is covered with fiber fabric, and the fiber fabric is mostly woven. Unlike metal structures, the surface of the fiber fabric is actually in a discontinuous state, which can easily cause uneven force on the strain gauge of the pressure sensor, resulting in inaccurate measurement results and low test accuracy; second, the test head of the wire of the pressure sensor is too large to pass directly through the glue injection port. If one side of the strain gauge is passed through the glue injection port, the strain gauge may be bent, resulting in failure of the pressure sensor and inability to test.

[0008] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0009] A method for testing the pressure of a fabric layer in a closed curved mold, the method comprising the following steps:

[0010] S1. The pressure sensor includes a strain gauge and a wire. The strain gauge is connected to the wire, and a stainless steel sheet is attached to one side of the strain gauge.

[0011] S2. Add an interface in the middle of the wire to divide the wire into a first wire and a second wire, set a first interface on the first wire, and set a second interface on the second wire, wherein the first interface and the second interface are detachably connected;

[0012] S3. One end of the first wire is connected to the strain gauge, and the other end of the first wire is detachably connected to the second wire. The strain gauge is placed in the mold, and then the other end of the first wire is passed through the glue injection port of the curved mold and detachably connected to the second wire.

[0013] S4. Adhere the strain gauge between the mold and the fabric ply, with the side of the strain gauge bonded to the stainless steel sheet facing the fabric ply and the other side of the strain gauge facing the surface of the mold;

[0014] S5. After the preform is molded, a pressure test is performed;

[0015] In step S4, the distance between the center of the strain gauge and the injection port used for its wire is 100-150 mm;

[0016] In step S1 , the thickness of the stainless steel sheet is 0.2-0.3 mm, and the area of the stainless steel sheet is less than or equal to the area of the strain gauge.

[0017] Furthermore, the strain gauge is square, and the side length of the strain gauge is ≤50 mm; or, the strain gauge is circular, and the diameter of the strain gauge is ≤50 mm.

[0018] Furthermore, the distance between two adjacent pressure sensors is ≤500 mm.

[0019] Furthermore, at least one pressure sensor is provided on each row of injection ports on each mold.

[0020] Furthermore, the diameter of the glue injection port is 7-8 mm.

[0021] Furthermore, in step S1, after the stainless steel sheet is attached to one side of the strain gauge, the total thickness of the strain gauge and the stainless steel sheet is 0.232 mm.

[0022] The present invention provides a method for testing the pressure of a fabric ply in a closed curved surface mold. Compared with the prior art, the method for testing the pressure of a fabric ply in a closed curved surface mold provided by the present invention has the following beneficial effects:

[0023] 1) The method for testing the pressure of a fabric ply in a closed curved mold described in the present invention can accurately measure the pressure of the fabric ply in a closed (after-mold-closing) curved mold, thereby effectively monitoring the clamping pressure between the fiber preform and the mold after mold-closing. The method can also fine-tune the fabric ply based on the actual clamping pressure to ensure uniform pressure distribution in each area, significantly reducing quality risks and process difficulties during the molding process and improving product qualification rates.

[0024] 2) The method for testing the pressure of a fabric ply in a closed-mold curved mold described in the present invention requires only a simple modification of the pressure sensor. It has strong applicability and is suitable for pressure testing of composite materials products formed by various closed-mold processes, with significant economic and military benefits.

[0025] 3) The present invention describes a method for testing the pressure of a fabric ply within a closed curved mold. A stainless steel sheet is attached to one side of the pressure sensor strain gauge, increasing the pressure sensor's accuracy in testing the pressure of a special-shaped mold. Furthermore, the thinner sheet ensures that the actual pressure data and the test value do not cause significant errors, thus maintaining the original functionality of the sensor.

[0026] 4) In the method for testing the pressure of a fabric ply in a closed curved mold described in the present invention, pressure sensors can be arbitrarily arranged according to the mold injection port, with few restrictions on position and number. By adding test points, the pressure distribution in different areas can be intuitively observed. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1A schematic diagram of the structure of a pressure sensor for a method of testing the pressure of a fabric ply in a closed curved mold according to an embodiment of the present invention;

[0028] Figure 2 Schematic diagram of the use of a pressure sensor in a method for testing the pressure of a fabric ply in a closed curved mold according to an embodiment of the present invention.

[0029] Description of reference numerals:

[0030] 10. Pressure sensor; 1. Strain gauge; 2. Wire; 20. Mold; 30. Fabric layup. DETAILED DESCRIPTION

[0031] In order to make the technical means, objectives and effects of the present invention easier to understand, embodiments of the present invention are described in detail below with reference to specific figures.

[0032] It should be noted that all terms used in the present invention to indicate direction and position, such as "up", "down", "left", "right", "front", "back", "vertical", "horizontal", "inside", "outside", "top", "low", "lateral", "longitudinal", "center", etc., are only used to explain the relative positional relationship and connection status between the various components in a certain specific state (as shown in the accompanying drawings). They are only for the convenience of describing the present invention, and do not require that the present invention must be constructed and operated in a specific orientation. Therefore, they cannot be understood as limiting the present invention. In addition, the descriptions of "first", "second", etc. in the present invention are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features.

[0033] In the description of the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical connections; direct connections or indirect connections through an intermediary; and internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in the present invention based on the specific circumstances.

[0034] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative uses of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0035] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0036] Example

[0037] In the prior art, if the pressure of the fabric ply in the mold is directly tested by a pressure sensor, the pressure sensor 10 includes a strain gauge 1 and a wire 2, and the strain gauge 1 is connected to the wire 2. There are the following problems: First, the surface of the preform is covered with fiber fabric, and the fiber fabric is mostly woven. Unlike the metal structure, the surface of the fiber fabric is actually in a discontinuous state, which can easily cause the strain gauge 1 of the pressure sensor 10 to be unevenly stressed, resulting in inaccurate measurement structure and low test accuracy; second, the test head of the wire 2 of the pressure sensor 10 is too large to pass directly through the glue injection port. If one side of the strain gauge is passed through the glue injection port, the strain gauge 1 may bend, causing the pressure sensor 10 to fail.

[0038] In order to solve the above problems, Figures 1 and 2 As shown, the applicant proposes a method for testing the pressure of a fabric layer in a closed curved mold, the testing method comprising the following steps:

[0039] S1. The pressure sensor 10 includes a strain gauge 1 and a wire 2. The strain gauge 1 is connected to the wire 2, and a stainless steel sheet is attached to one side of the strain gauge 1.

[0040] S2. Add an interface in the middle of the wire 2 to divide the wire 2 into a first wire and a second wire, set a first interface on the first wire, and set a second interface on the second wire, wherein the first interface and the second interface are matched and detachably connected;

[0041] S3. One end of the first wire is connected to the strain gauge 1, and the other end of the first wire is detachably connected to the second wire. The strain gauge 1 is placed in the mold 20, and then the other end of the first wire is passed through the injection port of the curved mold 20 to be detachably connected to the second wire.

[0042] S4, such as Figure 2 As shown, the pressure sensor 10 is pasted between the mold 20 and the fabric ply 30, and the strain gauge 1 is pasted between the mold 20 and the fabric ply 30, with the side of the strain gauge 1 bonded to the stainless steel sheet facing the fabric ply 30, and the other side of the strain gauge 1 facing the surface of the mold 20;

[0043] S5. After the preform is molded, a pressure test is performed.

[0044] In the testing method of the present invention, steps S1 to S5 are interrelated and inseparable, and play multiple roles:

[0045] 1. Optimizing Force Uniformity: By attaching a stainless steel sheet to one side of strain gauge 1, the continuous, rigid surface of the stainless steel sheet replaces the discontinuous contact surface of the fiber fabric, transforming pressure transmission from discrete point contacts to uniform surface contact. The stainless steel sheet, acting as a pressure transmission intermediary layer, disperses the irregular stress distribution of the fabric ply, significantly improving the strain gauge's force uniformity and fundamentally resolving the existing issues of inaccurate test structures and low test accuracy caused by the discontinuous fabric surface.

[0046] 2. Improved Wire Route Reliability: A segmented, detachable wire design connects the first and second wires via an interface, breaking through the limitations of traditional sensor monolithic wire structures. During testing, the wire connected to the strain gauge (the first wire) can be threaded through the injection port separately before being connected to the external wire (the second wire). This eliminates the problem of traditional large test heads being unable to pass through the narrow injection port without damaging the mold structure, while also preventing the risk of strain gauge 1 bending and failure caused by forced wire routing, thereby ensuring the integrity and test reliability of the pressure sensor 10.

[0047] 3. Enhanced adaptability of the installation process: The gluing direction of the strain gauge 1 is optimized, with the stainless steel sheet facing the fabric layer. This not only ensures the pressure transmission efficiency, but also protects the strain gauge from direct friction damage of the fabric fibers through the stainless steel sheet. The detachable interface allows the wire threading and sensor layout to be carried out step by step, which is particularly suitable for the narrow operating space of closed curved molds, significantly reducing the difficulty of installation and improving process operability.

[0048] 4. Dual assurance of test accuracy and stability: The stainless steel sheet not only serves as a stress redistribution layer, but its high modulus properties also suppress interference with the sensor caused by local deformation of the fabric layer. Combined with the direct bonding of the strain gauge to the mold surface (the other side faces the mold), a rigid conduction path of "fabric-metal transition layer-strain gauge-mold" is formed, minimizing signal drift during testing and improving long-term stability.

[0049] 5. Modular maintenance and reusability: The segmented wire interface achieves physical isolation between the sensor body and the signal transmission module, making it easy to replace only the vulnerable wire part during multiple injection molding processes while retaining the core strain gauge assembly, reducing usage costs; at the same time, the detachable design supports rapid troubleshooting and improves equipment maintenance efficiency.

[0050] 6. Process compatibility expansion: This solution breaks through the limitation that traditional pressure sensors are only applicable to flat or simple curved surfaces. Through the flexible wire threading solution and rigid transition layer design, it can adapt to various complex curved surface molds (such as double curvature and variable cross-section molds), significantly expanding the application scope of pressure testing technology in the field of composite material molding.

[0051] In summary, the present invention systematically solves the accuracy, reliability and operational difficulties of in-mold pressure testing during the molding of fiber-reinforced composite materials through structural innovation and process optimization, and provides a complete solution for high-precision and high-stability testing of fabric ply pressure in closed-mold curved surface molds.

[0052] The testing method described in the present invention: First, based on the existing RTM mold 20, the pressure sensor 10 is simply modified and installed through the glue injection port of the RTM mold 20. This can accurately measure the pressure of the fabric ply 30 within the closed (after mold clamping) curved surface mold 20, and can obtain the actual contact pressure between the fiber preform and the mold in real time after mold clamping. This allows for effective monitoring of the clamping pressure between the fiber preform and the mold 20 after mold clamping, and allows for fine-tuning of the fabric ply 30 based on the actual clamping pressure, greatly reducing the quality risk and process difficulty during the molding process. Second, the layout of the pressure sensor 10 relies solely on the existing glue injection port, eliminating the need for structural modification of the mold 20 and making it suitable for all types of special-shaped curved surface molds 20. Third, the testing process is fully compatible with the RTM molding process and does not affect subsequent processes such as glue injection and curing.

[0053] The testing method described in the present invention realizes the direct measurement of the pressure of the fabric layer in the curved mold after mold closing for the first time, solving the problem that the pressure distribution cannot be monitored in real time due to mold closing in the traditional RTM process.

[0054] The surface of the preform is covered with fiber fabric. Due to its own characteristics, fiber fabric is mostly woven. Unlike metal structures, its surface is actually discontinuous, which easily causes uneven force on the strain gauge 1. Through step S1, a 0.2~0.3mm stainless steel sheet is pasted on one side of the strain gauge 1, which can convert point contact into surface contact, effectively solving the problem of uneven force caused by the discontinuous surface of the fiber fabric, making the strain gauge 1 area evenly stressed, and increasing the test accuracy of the pressure sensor 10 for the pressure of the special-shaped mold 20, and the test accuracy is improved by more than 30%.

[0055] like Figure 1As shown, the pressure sensor 10 typically includes a strain gauge 1 and a conductor 2. The strain gauge 1 is connected to a data acquisition device via a long conductor 2. When used in an RTM mold 20, one end must be passed through the mold 20's glue injection port. Because the injection port is small, to prevent significant bending and deformation of the strain gauge 1 during passage, which could lead to damage, a connector is added to the middle of the conductor 2 in step S2. This divides the conductor 2 into a first wire and a second wire. A first connector is provided on the first wire, and a second connector is provided on the second wire. The first and second connectors are detachably connected, replacing the traditional integrated conductor 2 with a detachable connector (first wire + second wire). This innovative step breaks down the pressure sensor 10 installation process into two steps: placing the strain gauge 1 into the mold 20 and passing the conductor connector through the injection port. This avoids the strain gauge bending and damage that can occur when traditional long conductors are passed through holes, increasing the installation success rate by 85%.

[0056] Specifically, in step S4, the distance between the center of the strain gauge 1 and the glue injection port used by its conductor 2 is 100-150 mm. This distance helps optimize the sensor's placement, ensuring that the sensor accurately reflects the pressure distribution of the fabric layer within the mold. It also avoids measurement errors that may be introduced by improper sensor placement.

[0057] Specifically, in step S1, the thickness of the stainless steel sheet is 0.2-0.3 mm, and the area of the stainless steel sheet is ≤ the area of the strain gauge 1. This design allows the stainless steel sheet to be thinner, preventing significant errors between the actual pressure data and the measured values. This improves the accuracy of the pressure sensor 10 in measuring the pressure of the special-shaped mold 20 while maintaining the original functionality of the pressure sensor 10.

[0058] Specifically, the strain gauge 1 is square, and the side length of the strain gauge 1 is ≤50 mm; or, the strain gauge 1 is circular, and the diameter of the strain gauge 1 is ≤50 mm.

[0059] The present invention uses a miniaturized pressure sensor 10, which adopts a square strain gauge with a side length of ≤50 mm or a circular strain gauge with a diameter of ≤50 mm (46 mm square is selected in this embodiment), and a thin design with a total thickness of only 0.232 mm, to minimize interference with the mold cavity 20 and ensure the authenticity of pressure transmission.

[0060] Usually, only one pressure sensor 10 is arranged at one glue injection port.

[0061] Specifically, the distance between two adjacent pressure sensors 10 is ≤500 mm.

[0062] Specifically, at least one pressure sensor 10 is provided on each row of injection ports on each mold 20 .

[0063] In the present invention, the pressure sensors 10 can be arranged arbitrarily according to the injection ports of the mold 20, with little restriction on position and quantity. By adding test points, the pressure distribution in different areas can be intuitively observed.

[0064] Specifically, the diameter of the glue injection port is 7-8 mm.

[0065] The original 7~8mm injection port of the mold is directly used for modification without additional processing, and is suitable for all kinds of special-shaped curved surface molds; it greatly reduces the installation time of a single pressure sensor 10 and greatly reduces the cost of pressure testing.

[0066] Specifically, step S5 also includes subsequent fine-tuning of the fabric according to pressure test data at different positions to ensure uniform pressure distribution in each area.

[0067] More specifically, after the preform is molded together, uneven pressure distribution can occur due to variations in linear precision between the mold 20 and the preform, as well as assembly errors. Post-mold pressure testing provides pressure data, which facilitates subsequent fine-tuning of the fabric layup 30. By establishing a "pressure test-layup adjustment" feedback mechanism, the number of fabric layers can be optimized based on pressure data, significantly improving product qualification rates.

[0068] More specifically, different fabric types and number of layers affect pressure variations in different ways. Through preliminary testing of a small mold 20, a database of relationships between fabric type, number of layers, and pressure was generated. This provided a scientific basis for setting process parameters and reduced the process debugging cycle from the traditional two weeks to three days. In this embodiment, the radius of curvature of the mold 20 surface reached 300mm.

[0069] In this embodiment, if Figure 1 As shown, the strain gauge 1 is square, and the side length of the strain gauge 1 is 46 mm. Therefore, the pressure sensor 10 is selected with a measuring range of 0 to 300 N, that is, a force value of 30 kg.

[0070] In this embodiment, the material of the stainless steel sheet is 316L.

[0071] In this embodiment, in step S1 , after the stainless steel sheet is attached to one side of the strain gauge 1 , the total thickness of the strain gauge 1 and the stainless steel sheet is 0.232 mm.

[0072] In this embodiment, the diameter of the glue injection port is 7.5 mm.

[0073] The number of pressure sensors 10 to be arranged is determined by the number of injection ports of the mold 20. The minimum number of pressure sensors 10 to be arranged takes into account the pressure distribution in different areas. In this embodiment, according to the diagonal principle, the pressure sensors 10 are arranged diagonally on the mold 20. On average, at least one pressure sensor 10 is set for each row of injection ports on each mold 20, and the pressure monitoring blind area is reduced by 90%.

[0074] Effect of the embodiment:

[0075] During the pre-clamping pressure test, the clamping status of the core mold in different areas can be visually determined through pressure testing, which is then verified by the apparent state of the fabric after demolding. The fabric layup 30 is then finely adjusted to achieve uniform pressure distribution in each area. During subsequent RTM injection, the injection pressure in each area is essentially consistent. There are no phenomena such as excessive resin injection pressure due to a large number of fabric layers, or the formation of runners due to a small number of fabric layers. This demonstrates the effectiveness of the pressure test.

[0076] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A method for testing the pressure of a fabric layer in a closed curved mold, characterized in that: The test method comprises the following steps: S1, a pressure sensor (10) comprising a strain gauge (1) and a wire (2), wherein the strain gauge (1) is connected to the wire (2), and a stainless steel sheet is attached to one side of the strain gauge (1); S2, adding an interface in the middle of the wire (2), dividing the wire (2) into a first wire and a second wire, setting a first interface on the first wire, and setting a second interface on the second wire, wherein the first interface and the second interface are matched and detachably connected; S3, one end of the first wire is connected to the strain gauge (1), and the other end of the first wire is detachably connected to the second wire, the strain gauge (1) is placed in the mold (20), and then the other end of the first wire is passed through the injection port of the curved mold (20) and detachably connected to the second wire; S4, pasting the strain gauge (1) between the mold (20) and the fabric ply (30), with the side of the strain gauge (1) adhering to the stainless steel sheet facing the fabric ply (30), and the other side of the strain gauge (1) facing the surface of the mold (20); S5. After the preform is molded, a pressure test is performed; In step S4, the distance between the center of the strain gauge (1) and the injection port used by the wire (2) is 100-150 mm; In step S1, the thickness of the stainless steel sheet is 0.2-0.3 mm, and the area of the stainless steel sheet is ≤ the area of the strain gauge (1).

2. The method for testing the pressure of a fabric layer in a closed curved mold according to claim 1, characterized in that: The strain gauge (1) is square, and the side length of the strain gauge (1) is ≤50 mm; or, the strain gauge (1) is circular, and the diameter of the strain gauge (1) is ≤50 mm.

3. The method for testing the pressure of fabric plies in a closed curved mold according to claim 1, wherein: The distance between two adjacent pressure sensors (10) is ≤500 mm.

4. The method for testing the pressure of a fabric layer in a closed curved mold according to claim 1, wherein: At least one pressure sensor (10) is provided on average for each row of glue injection ports on each mold (20).

5. The method for testing the pressure of fabric plies in a closed curved mold according to claim 1, wherein: The diameter of the glue injection port is 7-8 mm.

6. The method for testing the pressure of fabric layers in a closed curved mold according to claim 1, characterized in that: In step S1, after the stainless steel sheet is attached to one side of the strain gauge (1), the total thickness of the strain gauge (1) and the stainless steel sheet is 0.232 mm.

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