U-shaped section composite ring frame forming mold with controllable curing pressure

Abstract

The invention discloses a curing pressure controllable U-shaped section composite material ring frame forming mold, and belongs to the technical field of resin matrix composite material forming. The forming die comprises a bottom die, an inner die, an outer die, a pressing plate, a cover plate and a mixed core die. The bottom mold, the inner mold and the pressing plate are of an annular metal integral structure, the outer mold is of an arc-shaped metal block type structure, and the mixed core mold is composed of a metal core mold with variable section thickness and a silicon rubber soft mold. After prepreg is laid on the forming faces of the bottom die and the inner die, the mixed core die is assembled firstly, then the block type outer die is assembled, then the die is locked through a pressing plate, the metal core die is positioned through a cover plate, and heating curing forming is carried out. By reasonably designing the variable-thickness metal core mold and the silicone rubber soft mold, the curing pressure gradient in the U-shaped groove of the composite ring frame can be effectively controlled, pressure distribution of the ring frame in a gradually decreasing mode from the root to the outside in the curing process is achieved, it is guaranteed that prepreg is fully compacted, and bubbles are fully discharged; and the defects of dense pores, layering and the like caused by internal suffocation at the root are avoided.

Description

Technical Field

[0001] The invention relates to the technical field of resin-based composite material structure molding, in particular to a U-shaped cross-section composite ring frame molding die with controllable curing pressure. Background Art

[0002] U-section composite ring frames and U-section-like composite components are widely used in the load-bearing frames of aerospace structures. Compared with metal end frames, they have the advantages of light weight and high strength. The U-section composite ring frame is located at the end of the load-bearing structure and is directly connected to the external structural parts to transmit the main load. Therefore, the molding quality and dimensional accuracy of the U-section composite ring frame are very important. Existing U-section composite ring frames generally adopt the structure of metal outer mold + metal core mold or metal outer mold + silicone core mold. The mold form of metal outer mold + metal core mold has problems in use, such as difficulty in closing the mold, uneven pressurization, and low pass rate; the mold form of metal outer mold + silicone core mold has problems in use, such as uneven wall thickness caused by slippage, many air holding defects at the root, and difficulty in ensuring molding quality. Summary of the Invention

[0003] The technical problem solved by the present invention is to overcome the shortcomings of the existing technology and provide a U-section composite ring frame forming mold with controllable curing pressure, so as to solve the problems of many internal defects and low product qualification rate in the existing forming mold scheme of U-section composite ring frames.

[0004] The technical solution of the present invention is: a U-shaped cross-section composite ring frame forming mold with controllable curing pressure, wherein the U-shaped cross-section ring frame is formed by laying composite material prepreg on the forming mold at room temperature and curing the resin gel under heating and pressure conditions, and the U-shaped cross-section composite ring frame forming mold includes a bottom mold, an inner mold, an outer mold, a pressure plate, a cover plate and a hybrid core mold;

[0005] The inner mold is an annular metal integral structure, located inside the U-shaped cross-section ring frame and connected to the bottom mold;

[0006] The outer mold is an arc-shaped metal block structure, located outside the U-shaped cross-section ring frame and connected to the bottom mold to ensure synchronous radial movement of each block;

[0007] The pressure plate is an annular metal integral structure, and the connection surface between the pressure plate and the outer mold is a conical surface, ensuring that the outer mold is pressurized evenly and locked synchronously;

[0008] The hybrid core mold is located inside the U-shaped cross-section ring frame. The hybrid core mold consists of a metal core mold with variable cross-sectional thickness and silicone rubber soft molds located on both sides of the metal core mold.

[0009] The inner mold and outer mold are aligned with the open end surface of the U-section ring frame, and the cover plate is connected to the metal core mold and pressed on the open end surface of the hybrid core mold to achieve the positioning connection between the metal core mold and the inner mold and outer mold.

[0010] Preferably, the thermal expansion coefficient of the metal core mold material is greater than the thermal expansion coefficients of the outer mold and the inner mold.

[0011] Preferably, by adjusting the thickness ratio of the metal core mold and the silicone rubber soft mold in the U-shaped groove, it is ensured that the pressure decreases from the root of the ring frame to the outside during the curing process, and the pressure gradient is ≥0.2MPa.

[0012] Preferably, the thickness calculation formula of the metal core mold and the silicone rubber soft mold is as follows:

[0013]

[0014] Where W0, W1, W2, and W3 are the width of the U-shaped ring frame, the thickness of both sides of the U-shaped ring frame, the thickness of the metal core mold, and the thickness of the silicone rubber soft mold respectively; α SR , α AL , α ST are the volume expansion coefficients of the silicone rubber soft mold, metal core mold and bottom mold respectively; K SR is the bulk modulus of the silicone rubber core mold; ΔT is the difference between the prepreg gel temperature and room temperature; f is the compression of the prepreg after curing relative to before curing; P is the design expansion pressure of the silicone rubber during curing.

[0015] Preferably, the design expansion pressure P of the silicone rubber during curing at the root of the U-shaped ring frame is usually 0.8-1.2 MPa.

[0016] Preferably, the edge pressure of the ring frame is smaller than the root pressure, and the difference between the two is not less than 0.2 MPa.

[0017] Preferably, glue overflow grooves are designed at the joints between the inner mold and the bottom mold, and between the outer mold and the bottom mold.

[0018] Preferably, the glue overflow groove is a semicircular glue overflow groove with a diameter of Φ3mm to Φ6mm.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The present invention controls the thickness ratio of the metal core mold and the silicone rubber soft mold in the U-shaped groove by designing a variable thickness metal core mold and a silicone rubber soft mold, thereby forming a pressure distribution of the ring frame that decreases from the root to the outside during the curing process, thereby achieving full compaction of the prepreg and full discharge of bubbles, and avoiding defects such as dense pores and stratification caused by internal air holding at the root.

[0021] (2) The present invention realizes the precise matching of the molding pressure gradient of the mold to the process design, which provides favorable support for achieving precise pressure control during the product curing process and improving the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0023] Figure 1 This is a cross-sectional schematic diagram of a U-shaped composite ring frame forming mold with controllable curing pressure according to an embodiment of the present invention.

[0024] Figure 2 This is an overall schematic diagram of a U-shaped cross-section composite ring frame forming mold with controllable curing pressure according to an embodiment of the present invention.

[0025] In the figure, 101 is a bottom mold, 102 is an inner mold, 103 is an outer mold, 104 is a pressure plate, 105 is a cover plate, 106 is a metal core mold, 107 is a silicone rubber soft mold, and 108 is a U-section ring frame. DETAILED DESCRIPTION

[0026] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several variations and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0027] Example 1

[0028] In response to the current situation where existing U-section composite ring frame forming mold solutions have many internal defects and low product qualification rate, the present invention proposes a U-section composite ring frame forming mold with controllable curing pressure and a design method thereof, which solves the problems of poor forming quality and low qualification rate of U-section composite ring frames and U-section-like composite components.

[0029] The U-shaped cross-section composite material ring frame forming mold with controllable curing pressure has a mold structure as follows: Figure 1 、 2 As shown, it includes a bottom mold 101, an inner mold 102, an outer mold 103, a pressing plate 104, a cover plate 105 and a mixed core mold.

[0030] Specifically, the inner mold is an annular metal integral structure, located inside the U-shaped cross-section ring frame, and connected to the bottom mold through positioning pins and screws to ensure the dimensional accuracy of the U-shaped ring frame 108.

[0031] Specifically, the outer mold is an arc-shaped metal block structure, located outside the U-shaped cross-section ring frame 108, and connected to the bottom plate through guide pins to ensure synchronous radial movement of each block.

[0032] Specifically, the pressing plate is an annular metal integral structure, and the connecting surface between the pressing plate and the outer mold is a conical surface to ensure synchronous pressurization and locking.

[0033] Specifically, the U-shaped cross-section composite material ring frame forming mold with controllable curing pressure realizes the positioning connection between the metal core mold and the inner and outer molds through the cover plate, thereby ensuring the thickness accuracy of the side wall of the U-shaped ring frame after curing.

[0034] Specifically, the hybrid core mold is located inside the U-shaped cross-section ring frame and consists of a metal core mold with variable cross-section thickness and silicone rubber soft molds located on both sides of the metal core mold. The thermal expansion coefficient of the metal core mold is greater than that of the outer mold and the inner mold.

[0035] Specifically, the cross-section of the metal core mold 106 inside the hybrid core mold is wedge-shaped. By adjusting the thickness ratio of the metal core mold 106 embedded in the U-shaped groove and the silicone rubber soft mold 107, the outward pressure at the root of the ring frame is reduced during the curing process, and the pressure gradient is ≥0.2MPa.

[0036] The design expansion pressure P of the silicone rubber during curing at the root of the U-shaped ring frame is usually 0.8-1.2 MPa. The pressure at the edge of the ring frame is lower than that at the root, and the difference between the two is not less than 0.2 MPa.

[0037] Specifically, in the hybrid core mold design method, the cross-sectional dimensions of the metal core mold are designed with linear variable thickness, and the thicknesses of the metal core mold and the silicone rubber soft mold are calculated by formulas (1) and (2).

[0038] The thickness calculation formula of the metal core mold and the silicone rubber soft mold is as follows:

[0039]

[0040] Where W0, W1, W2, and W3 are the width of the U-shaped ring frame, the thickness of both sides of the U-shaped ring frame, the thickness of the metal core mold, and the thickness of the silicone rubber soft mold respectively; α SR , α AL , α ST are the volume expansion coefficients of the silicone rubber soft mold, metal core mold and bottom mold respectively; K SR is the bulk modulus of the silicone rubber core mold; ΔT is the difference between the prepreg gel temperature and room temperature; f is the compression of the prepreg after curing relative to before curing; P is the design expansion pressure of the silicone rubber during curing.

[0041] Specifically, the U-shaped composite ring frame mold with controllable curing pressure features overflow grooves at the joints between the inner and lower molds, and between the outer and lower molds, to ensure the escape of excess resin and the adequate removal of bubbles from the outer prepreg layer. The overflow grooves are semicircular with a diameter of 3 to 6 mm.

[0042] According to the present invention, a U-shaped cross-section composite material ring frame forming mold with controllable curing pressure is provided, which is designed using the above-mentioned U-shaped cross-section composite material ring frame mold design method.

[0043] The present invention provides a U-section composite material ring frame forming die with controllable curing pressure, which is suitable for the design of forming dies for U-section composite material ring frames or components containing U-shaped composite materials, and solves the problems of poor forming quality and low pass rate of composite material ring frames containing U-shaped sections.

[0044] Example 1

[0045] Implementation Example 2 is a preferred example of Implementation Example 1.

[0046] like Figure 1 、 2As shown, this embodiment further illustrates a composite ring frame forming mold with a U-shaped cross-section and its design method; the product has a U-shaped cross-section, a ring frame cross-section width of 40mm, and a carbon fiber composite annular satellite bearing frame with a single-side wall thickness of 4mm. The forming mold structure designed for this product consists of a bottom mold 101, an inner mold 102, an outer mold 103, a pressure plate 104, a mixed core mold, and a cover plate 105. The bottom mold, inner mold, and pressure plate are designed as an annular integral structure. The bottom mold is a Q235 annular metal plate with a thickness of 40mm, and the inner mold is an annular integral machined part of Q235 steel. It is connected to the bottom mold with 2-φ20mm locating pins and 18-M14 screws evenly distributed around the circumference. A Φ5 semicircular glue overflow groove is designed at the joint between the inner mold and the bottom mold. The outer mold is a circular Q235 steel block, evenly divided into six lobes along its circumference. Each block has two 30-20mm diameter waist-shaped holes. It is connected to the base plate via 2 20mm diameter pins to ensure synchronous tightening during mold closing. A Φ5 semicircular overflow groove is designed at the joint between the outer and base molds. The pressure plate is a Q235 steel annular metal monolithic structure, connected to the outer mold with a 70° taper to ensure synchronous pressure and locking. The hybrid core mold consists of a metal core mold 106 with a variable cross-sectional thickness and a silicone rubber soft mold 107. The metal core mold is made of 6063 aluminum alloy, and the silicone rubber material has a bulk expansion coefficient of 4.4E-4 / °C. According to formulas (1) and (2), when the prepreg gel temperature is 125°C and the compression of the prepreg before and after curing is 0.1, the design value of the silicone rubber expansion pressure at the root of the ring frame during curing is P = 1.0 MPa, and the design value of the ring frame edge is P = 0.4 MPa. The calculated cross-sectional thickness of the metal core mold at the root of the U-shaped ring frame is 8.50 mm, and the cross-sectional thickness of the silicone rubber soft mold is 11.30 mm on one side; the cross-sectional thickness of the metal core mold at the edge of the U-shaped ring frame is 9.81 mm, and the cross-sectional thickness of the silicone rubber soft mold is 10.64 mm on one side. The cover plate is a 20 mm thick Q235 annular metal plate. The metal core mold is positioned and connected to the inner and outer molds through φ10 mm positioning pins and holes to ensure the thickness accuracy of the U-shaped ring frame side wall after curing. After the composite ring frame is formed using the forming mold of this structure, the root void ratio is reduced to less than 1%, and the product quality meets the A-level requirements of GJB2895.

[0047] In summary, the metal core mold and silicone rubber soft mold of the present invention are rationally designed with variable cross-sectional thickness, which can effectively control the curing pressure gradient in the U-shaped groove of the composite ring frame, and realize a decreasing pressure distribution of the ring frame from the root to the outside during the curing process, which can ensure that the composite material prepreg is fully compacted and the bubbles are fully discharged, avoiding defects such as dense pores and stratification caused by internal air holding at the root.

[0048] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention. Unless there is a conflict, the embodiments of this application and the features in the embodiments may be combined with each other in any manner.

Claims

1. A U-shaped cross-section composite ring frame forming die with controllable curing pressure, wherein the U-shaped cross-section ring frame is formed by laying composite material prepreg on the forming die at room temperature and curing the resin gel under heating and pressure conditions, characterized in that The U-shaped cross-section composite ring frame forming mold includes a bottom mold, an inner mold, an outer mold, a pressing plate, a cover plate and a mixed core mold; The inner mold is an annular metal integral structure, located inside the U-shaped cross-section ring frame and connected to the bottom mold; The outer mold is an arc-shaped metal block structure, located outside the U-shaped cross-section ring frame and connected to the bottom mold to ensure synchronous radial movement of each block; The pressure plate is an annular metal integral structure, and the connection surface between the pressure plate and the outer mold is a conical surface, ensuring that the outer mold is pressurized evenly and locked synchronously; The hybrid core mold is located inside the U-shaped cross-section ring frame. The hybrid core mold consists of a metal core mold with variable cross-sectional thickness and silicone rubber soft molds located on both sides of the metal core mold. The inner mold and outer mold are aligned with the open end surface of the U-section ring frame, and the cover plate is connected to the metal core mold and pressed on the open end surface of the hybrid core mold to achieve the positioning connection between the metal core mold and the inner mold and outer mold.

2. A U-shaped cross-section composite ring frame forming mold with controllable curing pressure according to claim 1, characterized in that The thermal expansion coefficient of the metal core mold material is greater than the thermal expansion coefficients of the outer mold and the inner mold.

3. The U-shaped cross-section composite ring frame forming mold with controllable curing pressure according to claim 1, characterized in that: By adjusting the thickness ratio of the metal core mold and the silicone rubber soft mold in the U-shaped groove, it is ensured that the pressure at the root of the ring frame decreases outward during the curing process, and the pressure gradient is ≥0.2MPa.

4. The U-shaped cross-section composite ring frame forming mold with controllable curing pressure according to claim 1, characterized in that: The thickness calculation formula of the metal core mold and the silicone rubber soft mold is as follows: Where W0, W1, W2, and W3 are the width of the U-shaped ring frame, the thickness of both sides of the U-shaped ring frame, the thickness of the metal core mold, and the thickness of the silicone rubber soft mold respectively; α SR , α AL , α ST are the volume expansion coefficients of the silicone rubber soft mold, metal core mold and bottom mold respectively; K SR is the bulk modulus of the silicone rubber core mold; ΔT is the difference between the prepreg gel temperature and room temperature; f is the compression of the prepreg after curing relative to before curing; P is the design expansion pressure of the silicone rubber during curing.

5. The U-shaped cross-section composite ring frame forming mold with controllable curing pressure according to claim 1, characterized in that: The design expansion pressure P of the silicone rubber during curing at the root of the U-shaped ring frame is usually 0.8-1.2 MPa.

6. The U-shaped cross-section composite ring frame forming mold with controllable curing pressure according to claim 1, characterized in that: The pressure at the edge of the ring frame is smaller than the pressure at the root, and the difference between the two is not less than 0.2 MPa.

7. The U-shaped cross-section composite ring frame forming mold with controllable curing pressure and the design method thereof according to claim 1, characterized in that: Overflow grooves are designed at the joints between the inner mold and the bottom mold, and between the outer mold and the bottom mold.

8. The U-shaped cross-section composite ring frame forming mold with controllable curing pressure and the design method thereof according to claim 1, characterized in that: The glue overflow groove is a semicircular glue overflow groove with a diameter of Φ3mm to Φ6mm.

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