A gradual transition structure between the cone surface and the folded edge vertical surface of a carbon fiber loudspeaker diaphragm and a manufacturing method thereof

Abstract

This invention discloses a gradual transition structure between the conical surface and the folded edge surface of a carbon fiber loudspeaker diaphragm and its manufacturing method, belonging to the field of electroacoustic technology. The structure includes a diaphragm formed by one-time hot pressing of carbon fiber prepreg. The diaphragm has a conical main body and a folded edge surface located at the outer edge of the conical main body. A gradual transition zone is provided between the conical main body and the folded edge surface. The thickness of the gradual transition zone linearly changes from the thickness of the conical main body to the thickness of the folded edge surface, with a transition length ≥30mm. The gradual transition zone achieves continuous thickness variation through ply cutting angle control, and the ply cutting edge is beveled. This invention also discloses a manufacturing method for this gradual transition structure, including ply design, bevel cutting, and hot pressing. By controlling the ply termination position and bevel cutting angle, the interlaminar shear stress is reduced from approximately 38MPa in traditional structures to approximately 15MPa, increasing the fatigue life of the diaphragm bending area by 3-5 times. This invention solves the problem of interlaminar delamination caused by abrupt thickness changes at the bending root of large-diameter loudspeaker diaphragms, significantly improving the structural integrity and long-term reliability of the diaphragm.

Description

Technical Field

[0001] This invention relates to the field of electroacoustic technology, and in particular to a gradual transition structure between the cone surface and the folded edge surface of a carbon fiber loudspeaker diaphragm and its manufacturing method. Background Technology

[0002] The diaphragm of large-diameter subwoofers (15 inches and above, preferably 18–24 inches) is subjected to extreme reciprocating displacement during operation (stroke can reach ±20 mm or even greater). The folded edge of the diaphragm is a critical transition area connecting the conical body and the suspension edge, and it is also the part with the most stress concentration and the most prone to failure. With the increase in speaker diameter and power, interlayer delamination at the bending root has become the main bottleneck restricting the long-term reliability of carbon fiber diaphragms.

[0003] Carbon fiber composites are widely used in high-end loudspeaker diaphragms due to their high specific stiffness, high specific strength, and excellent damping characteristics. Carbon fiber laminates are made by laminating and curing multiple layers of prepreg, with each layer bonded together by a resin matrix. At points of abrupt thickness change (such as a sudden transition from a thicker area in a conical body to a thinner area in a folded edge), the rapid change in interlayer stress easily leads to stress concentration and delamination. Especially under long-term fatigue conditions with large amplitude, the root of the bend becomes the delamination initiation point, severely affecting the reliability and service life of the diaphragm.

[0004] In existing technologies, the following two transition methods are typically used between the conical body of the carbon fiber loudspeaker diaphragm and the folded edge facade: (1) Stepped thickness transition: One or more steps are set between the conical main body and the folded edge facade, with the height of each step usually being 0.1 to 0.3 mm. This method creates stress concentration points at each step, and the peak value of interlayer shear stress can reach 20 to 25 MPa, which is close to the shear strength limit of the epoxy resin matrix (about 25 MPa), resulting in a very high risk of delamination.

[0005] (2) Right-angle bend: The conical body is directly bent at a right angle to form a folded edge facade, and the thickness changes abruptly from 0.8mm to 0.5mm. This method generates the maximum stress concentration at the root of the bend, and the peak value of the interlaminar shear stress can reach 35-40MPa, which far exceeds the shear strength of the resin matrix, making delamination almost inevitable.

[0006] The two traditional structures mentioned above can be maintained under static load or small amplitude conditions, but under the large amplitude reciprocating fatigue load of a large-diameter subwoofer, interlaminar cracks will initiate from the stress concentration point and propagate rapidly, eventually leading to the complete separation of the folded facade from the conical body and the failure of the speaker.

[0007] Furthermore, while there are reports in existing technologies of using tapered ply drop-off to achieve thickness gradients in aerospace composite materials, this technology is applied to aerospace structural components (such as wing skin) under static or low-frequency aerodynamic loads, which are fundamentally different from the high-frequency (20–100 Hz), large-amplitude (±20 mm) reciprocating fatigue loads of loudspeaker diaphragms. More importantly, the tapered ply drop-off technology for aerospace composite materials does not consider the acoustic-structural coupling requirements unique to loudspeaker diaphragms: the gradient transition zone must simultaneously satisfy structural integrity (no delamination) and acoustic performance (no introduction of additional mass, no change in diaphragm vibration modes). Therefore, the tapered ply drop-off technology in the aerospace field cannot be directly transferred to the field of loudspeaker diaphragms, and there are no reports in existing loudspeaker diaphragm literature of applying tapered ply drop-off to the conical-folded transition region.

[0008] In summary, existing technologies lack a gradient transition structure specifically designed for the root of a loudspeaker diaphragm bend that balances structural reliability and acoustic performance, as well as an industrially feasible manufacturing method for it. Summary of the Invention

[0009] The purpose of this invention is to provide a gradual transition structure between the cone surface and the folded edge surface of a carbon fiber loudspeaker diaphragm and its manufacturing method. By eliminating stress concentration at the abrupt change in thickness through the linear gradual transition zone, the delamination initiation at the bending root under long-term fatigue with large amplitude is prevented, thereby significantly improving the structural integrity and fatigue life of the diaphragm bending area.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a gradual transition structure between a carbon fiber loudspeaker diaphragm cone and a folded edge facade, comprising: a diaphragm, formed by hot pressing carbon fiber prepreg in a mold in one step, having a cone-shaped main body and a folded edge facade located at the outer edge of the cone-shaped main body; a gradual transition zone located between the cone-shaped main body and the folded edge facade, wherein the thickness of the gradual transition zone gradually changes linearly from the thickness of the cone-shaped main body to the thickness of the folded edge facade, and the gradual transition length is ≥30mm; wherein the gradual transition zone achieves continuous thickness variation through ply cutting angle control, rather than a step-like abrupt change; the cutting edge of the ply is beveled; the bevel angle of the bevel is 15°~45°, so that the interlayer stress concentration factor at the cutting point is less than 2.0.

[0011] Secondly, the present invention provides a method for manufacturing a gradual transition structure between the conical surface of a carbon fiber loudspeaker diaphragm and the folded edge surface, comprising the following steps: S1. Layup Design: Based on the target thickness of the conical main body and the target thickness of the folded edge facade, determine the number of carbon fiber prepreg layers and the termination position of each layer; The conical main body is composed of n layers of prepreg, and the folded edge facade is composed of m layers of prepreg, where n > m ≥ 2; The gradient length L of the gradient transition zone is ≥30mm; S2. Beveling: The excess ply of the conical body is gradually cut radially within the gradient transition zone, and the cut edge of each ply is beveled at an angle of 15° to 45°. The outermost layer is the first to terminate, and the termination position is (nm) × ΔL from the inner edge of the folded facade, where ΔL is the distance between the termination positions of two adjacent layers. The innermost layer of the intermediate layer is the last to terminate, and the termination position is 5mm to 10mm away from the inner edge of the folded facade. S3. Laying and positioning: Lay the cut layers of prepreg in the mold cavity in the order of layup, ensuring that the beveled edges of each layer overlap smoothly in the gradient transition zone; S4. Hot pressing: The prepreg is hot pressed in a mold in one step, so that the resin flows to fill the gaps between the layers and cures, forming a continuous gradient transition zone without interfaces. S5. Demolding inspection: After cooling, demold and visually inspect the transition zone and perform ultrasonic non-destructive testing to confirm that there is no delamination or porosity defects.

[0012] Preferably, the thickness of the conical body is 0.6mm to 1.0mm, and the thickness of the folded edge is 0.4mm to 0.6mm; The conical main body is composed of 3 to 5 layers of carbon fiber prepreg, and the folded edge facade is composed of 2 layers of carbon fiber prepreg.

[0013] Preferably, the gradient length of the gradient transition zone is 30mm to 50mm; The multi-layered ply of the conical body is gradually cut and reduced radially within the gradient transition zone, with the outermost ply terminating first, followed by the intermediate layers, and the innermost layer terminating last. This creates a continuous linear transition from the thickness of the conical main body to the thickness of the folded facade.

[0014] Preferably, the diaphragm is made of carbon fiber prepreg by autoclaving or compression molding, with a molding temperature of 120±5°C, a molding pressure of 0.4~0.6MPa, and a holding time of 25~35 minutes; The gradient transition zone, the conical main body, and the folded edge facade are made of the same continuous material and have no adhesive interface.

[0015] Preferably, the outer edge of the folded facade also has a rolled edge, which is integrally formed with the folded facade and the gradient transition area; the rolled edge is a semi-rolled edge structure with a width of 8-12mm.

[0016] Preferably, the diaphragm is a 15-inch to 24-inch large-diameter subwoofer diaphragm; The effective vibration zone radius of the conical main body is 180mm to 270mm, and the radial width of the folded edge facade is 12mm to 18mm.

[0017] Preferably, the carbon fiber prepreg is a T300 or T700 grade carbon fiber / epoxy resin prepreg with an areal density of 150-250 g / m², a resin content of 30%-40%, and a single-layer cured thickness of 0.22 mm-0.30 mm.

[0018] Preferably, the interlaminar shear stress in the gradual transition zone is ≤18MPa. Under a ±20mm stroke and a 20Hz sinusoidal fatigue load, the gradual transition zone withstands 10... 6 No layers are visible after the next iteration.

[0019] Preferably, in step S1, n = 3 to 5, m = 2; the gradient length L = 30 mm to 50 mm; and ΔL = 10 mm to 20 mm.

[0020] Preferably, in step S2, the beveling is performed by CNC cutting or laser cutting, with a cutting accuracy of ±0.5mm; the beveling angle is 20° to 30°.

[0021] Preferably, in step S3, the mold cavity includes: a conical forming area, a gradient transition forming area, and a folded edge forming area; The surface of the gradient transition forming zone is a continuous smooth curved surface with a tangent slope change rate ≤ 0.05 / mm.

[0022] Preferably, in step S4, the hot pressing is performed using an autoclave process or a molding process; The autoclave process parameters are as follows: heating rate 1.5~2.5°C / min, molding temperature 120±5°C, molding pressure 0.4~0.6MPa, heat preservation and pressure holding time 25~35 minutes; cooling rate ≤2°C / min to prevent thermal stress concentration.

[0023] Preferably, in step S4, before hot pressing, the prepreg is pre-compacted: the pre-compacting temperature is 80-100°C, the pre-compacting pressure is 0.1-0.2 MPa, and the pre-compacting time is 5-10 minutes; after pre-compacting, a vacuum is drawn to below -0.08 MPa to remove interlayer air bubbles.

[0024] Preferably, in step S5, the ultrasonic non-destructive testing adopts A-scan ultrasonic testing, with a probe frequency of 5-10MHz and a detection sensitivity ≤ Φ1mm flat-bottom hole equivalent; the ultrasonic attenuation coefficient of the gradual transition zone is ≤0.5dB / mm. Beneficial effects

[0025] 1. Elimination of stress concentration: By using linear thickness variation in the gradual transition zone (gradual length ≥ 30mm), abrupt thickness changes between the conical main body and the folded edge facade are avoided, allowing interlayer stress to transition smoothly in the radial direction. Finite element simulation shows that the gradual transition structure of this invention reduces the maximum interlayer shear stress from approximately 38MPa in the traditional right-angle bending scheme to approximately 15MPa, a reduction of over 60%, far below the reference value of the epoxy resin matrix shear strength (approximately 25MPa), fundamentally eliminating the mechanical conditions for delamination initiation.

[0026] 2. Prevention of delamination initiation: Under large-amplitude reciprocating fatigue loads (±20mm stroke, 20Hz), there are no obvious stress peaks in the gradual transition zone, making interlaminar crack initiation difficult. Fatigue simulation predicts that the fatigue life of the structure of this invention can reach 10 years. 6 More than 2 times, while the traditional stepped transition scheme is approximately 2×10 5 Next, the right-angle bending scheme is approximately 5×10. 4 Furthermore, the fatigue life of this invention is increased by 3 to 5 times.

[0027] 3. Structural integration: The gradual transition zone, the conical main body, and the folded edge facade are formed by hot pressing in one step, forming a continuous body of the same material with no adhesive interface, thus avoiding the risk of adhesive failure; at the same time, the continuous gradual transition does not change the vibration mode of the diaphragm and does not introduce additional mass, ensuring that the acoustic performance is not affected.

[0028] 4. Industrially Scalable Process: The manufacturing method proposed in this invention (layout design → beveling → layup positioning → hot pressing → demolding inspection) is entirely based on existing carbon fiber composite molding equipment, requiring no additional specialized equipment development. Beveling can be achieved through CNC cutting or laser cutting with an accuracy of ±0.5mm; autoclave or molding processes are mature industry technologies with good mass production consistency.

[0029] 5. Quality control is detectable: The present invention introduces pre-compaction, vacuum defoaming and ultrasonic non-destructive testing steps into the manufacturing method to ensure that there are no pores or delamination inside the gradual transition zone, and the ultrasonic attenuation coefficient is ≤0.5dB / mm, realizing closed-loop quality control from process to testing.

[0030] 6. Wide range of applications: This invention is not only applicable to 21-inch subwoofer diaphragms, but can also be extended to diaphragms of various large-diameter carbon fiber loudspeakers ranging from 15 inches to 24 inches, as well as the transition areas of midrange and tweeter diaphragms, making it versatile. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the overall half-section structure of the diaphragm described in this invention; in the figure: 1-conical main body; 2-folded edge facade; 3-gradient transition zone; 4-rolled edge; 5-suspended edge; Figure 2 for Figure 1 Enlarged view of a section at point A (gradual transition area); 31 - outermost ply; 32 - middle ply; 33 - innermost ply.

[0032] Figure 3 A schematic diagram of the ply cutting process for a gradient transition zone; Figure 4 This is a schematic diagram comparing the stress distribution of a traditional stepped transition with the gradual transition of this invention. Figure 5 This is a flowchart of the manufacturing method of the present invention. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings.

[0034] Example 1: 21-inch subwoofer diaphragm and its manufacturing method like Figures 1 to 3 As shown, this embodiment provides a 21-inch subwoofer diaphragm, including a conical body 1, a folded edge surface 2, a gradient transition area 3, and a rolled edge 4.

[0035] I. Structural Design Parameters The conical body 1 has a conical structure with a thickness of 0.8 mm, and is made of three layers of T300 grade carbon fiber prepreg (area density 200 g / m², resin content 35%, single-layer cured thickness approximately 0.27 mm). The cone angle and radius of curvature of the conical body 1 are determined according to the acoustic design, with an outer diameter of approximately 480 mm (21-inch effective vibration diameter) and an effective vibration area radius of approximately 220 mm (from the center to the outer edge).

[0036] The folded facade 2 is located on the outer edge of the conical main body 1. It is an annular facade used to bond the suspended edge 5. It has a height of 17.5 mm, a radial width of about 15 mm, and a thickness of 0.5 mm. It is made of two layers of T300 grade carbon fiber prepreg (each layer has a cured thickness of about 0.25 mm).

[0037] The gradient transition zone 3 is located between the conical main body 1 and the folded edge facade 2. It is a transition area where the thickness gradually changes from 0.8mm to 0.5mm, with a gradient length of 35mm (≥30mm).

[0038] The starting position of the gradient transition zone 3 is located approximately 20 mm inside the outer edge of the effective vibration area of ​​the conical body 1, and the ending position is located approximately 15 mm inside the outer edge of the folded facade 2, with a total gradient length of 35 mm. This layout ensures that there is sufficient gradient length between the conical body 1 and the folded facade 2 to achieve a smooth transition, while not affecting the bonding area between the folded facade 2 and the overhanging edge 5.

[0039] II. Manufacturing Method S1. Layer design: Based on the target thickness, the conical main body 1 uses 3 layers of prepreg (n=3), the folded facade 2 uses 2 layers of prepreg (m=2), and any extra layer needs to be cut off within the gradient transition zone 3.

[0040] The gradient length is determined to be 35mm, and the distance between the termination positions of two adjacent layers is ΔL=15mm.

[0041] The outermost layer 31 (the 3rd layer) ends 35mm from the inner edge of the folded facade 2; The termination position of the intermediate layer 32 (second layer) is 20mm from the inner edge of the folded facade 2; The innermost layer 33 (layer 1) ends 5mm from the inner edge of the folded facade.

[0042] S2. Bevel cut: A CNC cutting machine is used to precisely cut the three-layer prepreg. The cutting path is a concentric arc, and the cutting accuracy is ±0.5mm.

[0043] Each layer of the ply is cut at a bevel angle of 25° (within the range of 15° to 45°).

[0044] Beveling: Use a special beveling tool or laser cutting head to cut the prepreg at a 25° angle along the cutting path to create a smooth bevel at the cut edge and avoid stress concentration caused by right-angle cuts.

[0045] S3. Lamination Positioning: The cut 3 layers of prepreg are laid in the mold cavity in the order from the inside out (1st layer → 2nd layer → 3rd layer).

[0046] The mold cavity includes: a conical forming area (the cone angle is consistent with the cone angle designed for the diaphragm), a gradual transition forming area (a continuous smooth curved surface with a tangent slope change rate ≤ 0.05 / mm), and a folded edge forming area (vertical surface).

[0047] When laying out layers, ensure that the beveled edges of each layer overlap smoothly within the gradient transition zone 3, without overlapping gaps or step misalignment.

[0048] Positioning pins and vacuum adsorption are used to fix the position of the layers and prevent slippage during hot pressing.

[0049] S4. Hot pressing: The autoclave process is adopted, and the specific parameters are as follows: Pre-compaction: Temperature 90°C, pressure 0.15MPa, time 8 minutes; after pre-compaction, vacuum to -0.09MPa and maintain for 5 minutes to remove interlayer air bubbles.

[0050] Heating: Increase the temperature from room temperature to 120°C at a rate of 2°C / min.

[0051] Insulation and pressure holding: Temperature 120°C, pressure 0.5MPa, insulation and pressure holding time 30 minutes. During this stage, the resin flows fully, filling the gaps between the beveled edges of each layer, forming a continuous, gradual transition without interfaces.

[0052] Cooling: Cool down to below 60°C at a rate of 1.5°C / min to prevent thermal stress concentration from causing warping or microcracks.

[0053] Open the can and retrieve the item.

[0054] S5. Demolding inspection: After cooling, demold and visually inspect the gradient transition zone 3 to confirm that there is no visible delamination, no bubbles, and no fiber wrinkles.

[0055] The gradual transition zone 3 was subjected to non-destructive testing using A-scan ultrasonic testing (probe frequency 7.5MHz, detection sensitivity Φ1mm flat-bottom hole equivalent). The measured ultrasonic attenuation coefficient was 0.35dB / mm (≤0.5dB / mm), which was deemed acceptable.

[0056] III. Structural Features Through the above manufacturing method, the thickness of the gradient transition zone 3 is continuously and linearly reduced from 0.8 mm (3 layers) on the side of the conical main body 1 to 0.5 mm (2 layers) on the side of the folded edge facade 2, without any abrupt change in the middle.

[0057] The three-layer ply is cut at a 25° bevel angle. During hot pressing, the resin flows to fill the bevel gaps and forms a continuous body without interfaces after curing.

[0058] The rolled edge 4 is located at the lower outer edge of the folded edge facade 2, with a width of 10mm. It is formed by hot pressing together with the folded edge facade 2, the gradient transition area 3, and the conical body 1 in one step. The rolled edge 4 is a semi-rolled edge structure, used to fit with the inner edge of the overhanging edge 5.

[0059] IV. Simulation Verification To verify the technical effect of the present invention, the finite element software ANSYS Workbench was used to perform exemplary static and fatigue analysis on the diaphragm of the 21-inch subwoofer in this embodiment.

[0060] Material model: T300 carbon fiber / epoxy resin composite material, layup sequence [0° / 45° / 90°], elastic modulus E1=135GPa, E2=10GPa, shear modulus G12=5GPa, Poisson's ratio ν12=0.3.

[0061] Boundary conditions: The outer edge of the diaphragm is fixed, and a displacement load equivalent to ±20mm of the maximum stroke is applied to the center.

[0062] Mesh type: hexahedral elements, mesh size 2mm, with local mesh refinement to 1mm in the gradient transition area.

[0063] Comparison with Option A (traditional stepped transition): A two-step transition is used between the conical main body and the folded facade. The first step decreases from 0.8mm to 0.6mm (step height 0.2mm), and the second step decreases from 0.6mm to 0.5mm (step height 0.1mm).

[0064] Comparison with Option B (traditional right-angle bend): A right-angle bend is used between the conical main body and the folded edge facade, and the thickness changes abruptly from 0.8mm to 0.5mm.

[0065] Comparative scheme C (gradual transition of the present invention): a 35mm linear gradual transition is adopted between the conical main body and the folded edge facade, the thickness is continuously reduced from 0.8mm to 0.5mm, and the ply bevel angle is 25°.

[0066] Static analysis results: Option A (stepped type): Stress concentration occurs at both steps, with the maximum interlaminar shear stress being approximately 22 MPa, close to the reference value for the shear strength of the resin matrix (approximately 25 MPa), indicating a high risk of delamination.

[0067] Option B (right-angle bend): The stress concentration is most severe at the root of the bend, with a maximum interlaminar shear stress of approximately 38 MPa, which is higher than the reference value for the shear strength of the resin matrix, resulting in an extremely high risk of delamination.

[0068] Option C (gradual transition of the present invention): The stress distribution in the gradual transition zone is uniform, and the maximum interlaminar shear stress is about 15MPa, which is lower than the reference value of the shear strength of the resin matrix, and the risk of delamination is extremely low.

[0069] Fatigue analysis results (based on Goodman-corrected SN curve estimation): Option A: Predicted fatigue life is approximately 2 × 10⁻⁶. 5 The next loop; Option B: Predicted fatigue life is approximately 5 × 10⁻⁶. 4 The next loop; Option C: Predicted fatigue life exceeds 10 years 6 The loop continues.

[0070] The fatigue life of the present invention is about 5 times that of scheme A and about 20 times that of scheme B.

[0071] The simulation data above demonstrates that the gradual transition structure of this invention effectively eliminates stress concentration at abrupt thickness changes, significantly reduces interlaminar shear stress, and substantially improves the structural integrity and fatigue reliability of the diaphragm bending region. It should be noted that the above data are exemplary simulation results, and actual values ​​may vary depending on material batches, process parameters, and load conditions.

[0072] Example 2: 18-inch subwoofer diaphragm (4 layers → 2 layers gradient) The difference between this embodiment and embodiment 1 is that the conical body 1 uses 4 layers of T300 grade carbon fiber prepreg with a thickness of 1.0 mm; the folded edge facade 2 uses 2 layers of prepreg with a thickness of 0.5 mm; the extra 2 layers need to be cut off within the gradient transition zone 3.

[0073] Layer design: n=4, m=2, gradient length L=40mm, ΔL=15mm.

[0074] The outermost layer (4th layer) ends 40mm from the inner edge of the folded facade; The termination position of the middle outer layer (3rd layer) is 25mm from the inner edge of the folded facade; The termination position of the intermediate inner layer (second layer) is 10mm from the inner edge of the folded facade; The innermost layer (layer 1) ends 5mm from the inner edge of the folded facade.

[0075] Beveling: Beveling angle 20°, CNC cutting accuracy ±0.5mm.

[0076] Hot pressing: The molding process is adopted, and the mold is an upper and lower part that fits together. The molding temperature is 118°C, the molding pressure is 0.6MPa, and the holding time is 28 minutes.

[0077] Compression molding is suitable for mass production, with a short molding cycle and high dimensional accuracy.

[0078] Test results: Ultrasonic attenuation coefficient 0.42dB / mm, qualified.

[0079] Example 3: 15-inch mid-bass speaker diaphragm (3 layers → 2 layers gradient, small diameter verification) This embodiment verifies the applicability of the present invention to small-diameter (15-inch) diaphragms.

[0080] Conical main body 1: 3 layers of T700 grade carbon fiber prepreg, 0.75mm thick, with an effective vibration area radius of approximately 165mm.

[0081] Folded-edge facade 2: 2 layers of prepreg, 0.5mm thick, 15mm high.

[0082] Gradual transition zone 3: Gradual length 30mm (≥30mm lower limit), ply bevel angle 30°.

[0083] The manufacturing method is the same as in Example 1, using the autoclave process.

[0084] Simulation results show that the maximum interlaminar shear stress is about 16 MPa, which is lower than the shear strength of the resin matrix, verifying that the present invention can effectively reduce stress concentration even with a small gradient length.

[0085] Comparative example: Traditional right-angle bend structure (21 inches) The same materials (3 layers of T300 prepreg) and dimensions as in Example 1 are used, but the conical body 1 and the folded facade 2 are bent at right angles without a gradual transition zone.

[0086] Simulation results: The maximum interlaminar shear stress at the bending root is approximately 38 MPa, exceeding the reference value for the shear strength of the resin matrix (approximately 25 MPa). Fatigue analysis predicts a lifespan of approximately 5 × 10⁻⁶. 4 The cycle is only about 1 / 20 of that in Example 1 (the present invention).

[0087] This comparative example demonstrates that, under the same material and size conditions, the lack of a gradual transition zone will lead to severe stress concentration and early delamination failure.

[0088] Technical boundary declaration of prior patent This invention (gradual transition structure) has a clear technical boundary with the applicant's "circumferential reinforcement structure of carbon fiber loudspeaker diaphragm edge facade" (second patent) filed on the same day / earlier: 1. The problems they solve are different: This invention solves the problem of delamination at the bend caused by the "radial" thickness change between the conical body and the folded facade; the prior patent solved the problem of peeling caused by the "circumferential" interlayer shear of the folded facade.

[0089] 2. Different technical solutions: This invention adopts "radial gradual transition + ply beveling", the core of which is the continuous linear change in the thickness direction; the prior patent adopts "circumferential ply + axial narrow strip", the core of which is the circumferential reinforcement of the folded edge facade.

[0090] 3. Different areas of action: The area of ​​action of this invention is the "gradual transition zone" from the outer edge of the conical main body to the inner edge of the folded facade; the area of ​​action of the prior patent is the "circumferential reinforcement zone" of the folded facade itself.

[0091] 4. Different technical effects: This invention reduces interlaminar shear stress from 38MPa to 15MPa, preventing delamination at the bending root; the prior patent improves the circumferential stiffness of the folded edge facade, preventing circumferential interlaminar shear peeling under large amplitude.

[0092] Both can be implemented independently or used in combination, and do not constitute duplicate licensing.

Claims

1. A gradual transition structure between the conical surface of a carbon fiber loudspeaker diaphragm and the folded edge surface, characterized in that, include: The diaphragm is formed by hot pressing carbon fiber prepreg in one mold, and has a conical main body and a folded edge facade located on the outer edge of the conical main body; A gradient transition zone is located between the conical main body and the folded edge facade. The thickness of the gradient transition zone changes linearly from the thickness of the conical main body to the thickness of the folded edge facade, with a gradient length ≥ 30 mm. The gradient transition zone achieves continuous thickness variation through ply cutting angle control, rather than abrupt step change. The cutting edge of the ply is beveled. The bevel angle of the bevel is 15° to 45°, so that the interlayer stress concentration factor at the cutting point is less than 2.

0.

2. The gradient transition structure according to claim 1, characterized in that, The thickness of the conical body is 0.6mm to 1.0mm, and the thickness of the folded edge facade is 0.4mm to 0.6mm; the conical body is composed of 3 to 5 layers of carbon fiber prepreg, and the folded edge facade is composed of 2 layers of carbon fiber prepreg.

3. The gradual transition structure according to claim 1, characterized in that, The gradient length of the gradient transition zone is 30mm to 50mm; the multi-layer ply of the conical body is gradually cut and reduced in the radial direction within the gradient transition zone, with the outermost ply terminating first, followed by the middle layers, and the innermost layer terminating last, forming a continuous linear transition from the thickness of the conical body to the thickness of the folded edge facade.

4. The gradual transition structure according to claim 1, characterized in that, The diaphragm is made of carbon fiber prepreg by autoclaving or compression molding at a molding temperature of 120±5°C and a molding pressure of 0.4~0.6MPa, with a holding time of 25~35 minutes. The gradient transition zone, the conical body and the folded edge are made of the same material as the continuous body, with no adhesive interface.

5. The gradient transition structure according to claim 1, characterized in that, The outer edge of the folded facade also has a rolled edge, which is integrally formed with the folded facade and the gradient transition area; the rolled edge is a semi-rolled edge structure with a width of 8-12mm.

6. The gradient transition structure according to claim 1, characterized in that, The diaphragm is a 15-inch to 24-inch large-diameter subwoofer diaphragm; the effective vibration area radius of the conical body is 180mm to 270mm, and the radial width of the folded edge is 12mm to 18mm.

7. The gradient transition structure according to claim 1, characterized in that, The carbon fiber prepreg is a T300 or T700 grade carbon fiber / epoxy resin prepreg with a surface density of 150-250 g / m², a resin content of 30%-40%, and a single-layer cured thickness of 0.22 mm-0.30 mm.

8. The gradient transition structure according to claim 1, characterized in that, The interlaminar shear stress in the gradual transition zone is ≤18MPa. Under a ±20mm stroke and a 20Hz sinusoidal fatigue load, the gradual transition zone undergoes 10... 6 No layers are visible after the next iteration.

9. A method for manufacturing a gradual transition structure between the conical surface of a carbon fiber loudspeaker diaphragm and the folded edge surface, characterized in that, Includes the following steps: S1. Layup Design: Based on the target thickness of the conical main body and the target thickness of the folded edge facade, determine the number of carbon fiber prepreg layers and the termination position of each layer; the conical main body consists of n layers of prepreg, and the folded edge facade consists of m layers of prepreg, where n > m ≥ 2; the gradient length L of the gradient transition zone ≥ 30 mm; S2. Cutting and Beveling: The excess layup of the conical main body is gradually cut radially within the gradient transition zone, and the cut edge of each layup is beveled at an angle of 15° to 45°; the outermost layup terminates first, with the termination position at a distance of (nm) × ΔL from the inner edge of the folded edge facade, where ΔL is the distance between the termination positions of two adjacent layers; the middle layers and the innermost layer terminate last, with the termination position at a distance of 5 mm to 10 mm from the inner edge of the folded edge facade; S3. Layup Positioning: The cut layers of prepreg are sequentially laid into the mold cavity according to the layup sequence, ensuring that the beveled edges of each layer overlap smoothly within the gradient transition zone; S4. Hot pressing: The prepreg is hot-pressed in a mold in one step, so that the resin flows to fill the gaps between the layers and cures, forming a continuous gradient transition zone without interfaces; S5. Demolding inspection: After cooling, the prepreg is demolded, and the gradient transition zone is visually inspected and ultrasonically tested to confirm that there is no delamination or porosity defects.

10. The manufacturing method according to claim 9, characterized in that, In step S1, n = 3 to 5, m = 2; the gradient length L = 30 mm to 50 mm; and ΔL = 10 mm to 20 mm.

11. The manufacturing method according to claim 9, characterized in that, In step S2, the beveling is performed by CNC cutting or laser cutting, with a cutting accuracy of ±0.5mm; the beveling angle is 20°~30°.

12. The manufacturing method according to claim 9, characterized in that, In step S3, the mold cavity includes: a conical forming area, a gradient transition forming area, and a folded edge forming area; the surface of the gradient transition forming area is a continuous smooth curved surface, and the rate of change of the slope of the tangent line of the curved surface is ≤0.05 / mm.

13. The manufacturing method according to claim 9, characterized in that, In step S4, the hot pressing molding adopts an autoclave process or a molding process; the autoclave process parameters are: heating rate 1.5~2.5°C / min, molding temperature 120±5°C, molding pressure 0.4~0.6MPa, heat preservation and pressure holding time 25~35 minutes; cooling rate ≤2°C / min to prevent thermal stress concentration.

14. The manufacturing method according to claim 9, characterized in that, In step S4, before hot pressing, the prepreg is pre-compacted: the pre-compacting temperature is 80-100°C, the pre-compacting pressure is 0.1-0.2MPa, and the pre-compacting time is 5-10 minutes; after pre-compacting, the vacuum is drawn to below -0.08MPa to remove interlayer air bubbles.

15. The manufacturing method according to claim 9, characterized in that, In step S5, the ultrasonic non-destructive testing adopts A-scan ultrasonic testing, with a probe frequency of 5-10MHz and a detection sensitivity ≤ Φ1mm flat-bottom hole equivalent; the ultrasonic attenuation coefficient of the gradual transition zone is ≤0.5dB / mm.

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