Composite material box body forming mold capable of automatically compensating mold expansion through thermal dissociation in curing process

Abstract

The invention discloses a composite material box body forming mold capable of automatically compensating mold expansion through thermal dissociation in the curing process, and belongs to the technical field of resin-based composite material forming. The forming die comprises a box core die, a flange end frame, a flange limiting frame and an end extension shaft. The box body core mold is of a box-shaped metal structure with metal wall plates and reinforcing ribs. The flange end frame is an integral metal frame ring, is sleeved at the end part of the core mold and can slide along the axial direction when the core mold is heated and expanded so as to compensate the axial thermal deformation of the core mold; the flange limiting frame is of a metal plate-shaped structure and is used for initially limiting the flange end frame in the layering stage. According to the method, the problems that due to the fact that the thermal expansion difference between materials and products of a low-cost die is large, the number of forming defects of the integrally-formed composite material long box body with the flange in the flange root corner area is large, and the product percent of pass is low are solved, and the purposes of low die cost and high product quality are achieved at the same time are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of resin-based composite material structure molding, in particular to a composite box molding mold capable of thermally releasing and automatically compensating for mold expansion during a curing process. Background Art

[0002] Carbon fiber composite enclosures are widely used in aerospace antennas, load-bearing tubes, launch boxes, and other products. Compared to metal structures, they offer advantages such as light weight, high strength, fewer parts, and better dimensional consistency. Composite enclosures often exceed 1000mm in length and feature flanges at the ends. To achieve rapid manufacturing and improve structural strength at the flanges, composite enclosures are currently being molded in a single piece, with the flanges integrated into the enclosure body. Due to the significant difference in thermal expansion coefficients between composite materials and traditional mold materials such as structural steel and aluminum alloys, these long, integrally manufactured enclosures with flanges experience significant delamination and overhang at the flange corners, resulting in poor mold quality and a low yield rate. While Invar has a similar thermal expansion coefficient to the product, its material price is 10 to 20 times that of ordinary steel, making it difficult to use in large quantities in molds. A mold structure that combines low cost with high mold quality would significantly promote the application of carbon fiber composite enclosures. Summary of the Invention

[0003] The technical problem solved by the present invention is: to overcome the defects in the existing technology and provide a composite box forming mold that can be thermally freed and automatically compensate for mold expansion during the curing process, thereby solving the problems of excessive defects in the flange root corner area and low product qualification rate during the overall curing molding of a long composite box with a flange, thereby achieving the goal of low mold cost and high product quality.

[0004] The technical solution of the present invention is: a composite box forming mold that can be thermally freed and automatically compensate for mold expansion during the curing process. The end of the composite box has a flange structure, and the flange and the box are cured and formed as one piece. The composite box forming mold includes a box core mold, a flange end frame, and a flange limit frame.

[0005] The box core mold is a box-shaped structure welded by metal wall panels + web ribs, with steps and extension shafts at the ends; the flange end frame is mounted on the steps of the box core shaft to form an outward-turned structure at the end of the box core mold; the flange limit frame is located at the end of the box core mold, and the flange end frame and the box core mold are connected by screws to determine the initial position of the flange end frame on the core mold; in the initial state, a sliding gap δ is set between the flange end frame and the core shaft limit step along the length direction of the box core mold, and the surface of the composite box core mold is covered with a prepreg made of fiber layer and resin, and the end of the prepreg is turned along the box core mold to the surface of the mold flange end frame; when heated and pressurized for curing, the flange limit frame is removed, and the expansion of the box core mold along the length direction of the box is greater than the expansion of the composite box prepreg. The flange end frame can be thermally freed to offset the length difference between the box core mold and the box, so that the distance between the two flanges of the mold is always consistent with the composite box.

[0006] Preferably, the extension shaft at the end of the box core mold is a metal tube structure that can be connected to the box core mold.

[0007] Preferably, the composite material box is a long box with a length often exceeding 1000 mm.

[0008] Preferably, in the initial state, the sliding gap δ between the flange end frame and the core shaft limiting step is:

[0009] δ=fL(α m -α p )ΔT

[0010] Where, f is the process coefficient, ranging from 0.5 to 1; L is the length of the box; α m , α p are the linear expansion coefficients of the box core mold and the box body respectively; ΔT is the difference between the box resin gel temperature and room temperature.

[0011] Preferably, the mounting surfaces of the box core mold and the flange end frame are conical surfaces.

[0012] Preferably, the calculation formula of the cone slope K is as follows:

[0013]

[0014] Where, δ is the sliding gap; b is the step length of the box core mold; α d , α m are the linear expansion coefficients of the flange end frame and the box core mold respectively; ΔT is the difference between the box resin gel temperature and room temperature.

[0015] Preferably, the box core mold material is steel or aluminum alloy.

[0016] Preferably, the pressure-bearing areas of the end faces of the flange end frame at both ends of the flange end frame installed on the box core mold are different, and a pressure difference is generated under the curing pressure to cause sliding.

[0017] Preferably, the material of the flange end frame is a material having a thermal expansion coefficient greater than or equal to the thermal expansion coefficient of the core mold.

[0018] Preferably, avoidance grooves are designed at intervals along the generatrix direction of the cone surface at the matching surface between the flange end frame and the end box core mold, so that the contact area between the flange end frame and the box core mold is less than 50% of the matching surface area.

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

[0020] (1) The present invention designs a flange end frame mold structure that can adaptively slide along the axial direction of the box core mold, thereby realizing that the composite material box with flange automatically compensates for the axial deformation of the mold during heating and curing, and solves the problems of stratification and overhead defects that are easy to occur in the flange corner area during the integral molding of the long composite material box with flange.

[0021] (2) Compared with the existing technology of using low thermal expansion Invar material as the molding mold, the mold cost can be significantly reduced while meeting the requirements of low axial tension of product fibers and high molding quality during the heating and curing process.

[0022] (3) The present invention compensates for the axial thermal expansion difference between the mold and the product when the composite material box is heated and cured by matching the conical surface of the flange end frame with the ordinary steel or aluminum core mold and the preset sliding gap, thereby ensuring the product dimensional accuracy and internal quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] 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:

[0024] Figure 1 This is a cross-sectional schematic diagram of a composite box forming mold that can automatically compensate for mold expansion during thermal isolation during the curing process according to an embodiment of the present invention.

[0025] Figure 2 for Figure 1 A partial enlarged view of .

[0026] Figure 3 This is an overall schematic diagram of a composite box forming mold that can automatically compensate for mold expansion during thermal isolation during the curing process according to an embodiment of the present invention.

[0027] In the figure, 101 is the box core mold, 102 is the flange end frame, 103 is the flange limit frame, and 104 is the end extension shaft. DETAILED DESCRIPTION

[0028] 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.

[0029] Example 1

[0030] In response to the current situation in which existing low-cost molds have many internal defects such as overhead and delamination at the corner areas of the end flanges of integrally formed long boxes due to thermal expansion mismatch during molding heating, and the qualified product rate is low, the present invention proposes a composite box molding mold that can be thermally freed and automatically compensate for mold expansion during the curing process. This solves the problems of poor molding quality and low qualified rate of low-cost molds, and achieves the goal of achieving both low mold cost and high molding quality for such products.

[0031] The present invention provides a composite box forming mold that can be thermally freed and automatically compensate for mold expansion during the curing process. The composite box is a long box with a length often exceeding 1000 mm. The mold structure is as follows: Figure 1 、 2 As shown, it includes a box core mold 101, a flange end frame 102, and a flange limit frame 103. The composite box end has a flange structure, and the flange and the box are solidified and formed integrally. The box core mold has end extension shafts 104 at both ends. These end extension shafts are metal tube structures that can be connected to the box core mold.

[0032] The box core mold is a box-shaped structure welded by metal wall panels + web ribs, with steps and extension shafts at the ends; the flange end frame is mounted on the steps of the box core shaft to form an outward-turned structure at the end of the box core mold; the flange limit frame is located at the end of the box core mold, and the flange end frame and the box core mold are connected by screws to determine the initial position of the flange end frame on the core mold; in the initial state, a sliding gap δ is set between the flange end frame and the core shaft limit step along the length direction of the box core mold, and the surface of the composite box core mold is covered with a prepreg made of fiber layer and resin, and the end of the prepreg is turned along the box core mold to the surface of the mold flange end frame; when heated and pressurized for curing, the flange limit frame is removed, and the expansion of the box core mold along the length direction of the box is greater than the expansion of the composite box prepreg. The flange end frame can be thermally freed to offset the length difference between the box core mold and the box, so that the distance between the two flanges of the mold is always consistent with the composite box.

[0033] Specifically, a limiting step is provided at the end of the long box core mold, and the flange limiting block positions the initial position of the flange end frame. In the initial state, a sliding gap δ is provided between the flange end frame and the core shaft limiting step, which is calculated by formula (1).

[0034] δ=fL(α m -αp )ΔT(1)

[0035] Where, f is the process coefficient, ranging from 0.5 to 1; L is the length of the box; α m , α p are the linear expansion coefficients of the box core mold and the box body respectively; ΔT is the difference between the box resin gel temperature and room temperature.

[0036] Specifically, the core mold end of the long box body and the mounting surface of the flange end frame are matched with each other in a conical surface, and the slope K of the conical surface is calculated by formula (2).

[0037]

[0038] Where, δ is the sliding gap; b is the step length at the end of the box core mold; α d , α m are the linear expansion coefficients of the flange end frame and the box core mold respectively; ΔT is the difference between the box resin gel temperature and room temperature.

[0039] Specifically, the long box core mold material is a cheap mold material such as steel, aluminum alloy, etc., which has a thermal expansion coefficient greater than that of carbon fiber composite materials.

[0040] Specifically, after the flange end frame is installed on the box core mold, the pressure area close to the extended axis side is larger than the pressure area close to the core mold. Under the molding pressure condition, the pressure areas of the end faces of the flange end frame installed on the box core mold are different, and a pressure difference is generated on both sides of the flange end frame along the axial sliding. When the box is cured and heated, the flange end frame slides along the axial direction, and can adaptively slide to offset the length difference between the box core mold and the box.

[0041] Specifically, the flange end frame is made of a material whose thermal expansion coefficient is greater than or equal to the thermal expansion coefficient of the box core mold.

[0042] Specifically, avoidance grooves are designed at intervals along the generatrix direction of the cone surface at the matching surface between the flange end frame and the end box core mold, so that the contact area between the flange end frame and the box core mold is less than 50% of the matching surface area.

[0043] The present invention provides a composite box forming mold and a design method thereof that can be thermally freed and automatically compensate for mold expansion during the curing process. The mold is suitable for the design of forming molds for long composite boxes with end flanges or rods and cylinders with similar structures. It solves the problem of many forming defects in the corner area of the integrated box flange and low box qualification rate caused by the large difference in thermal expansion between the mold and the product.

[0044] Example 2

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

[0046] like Figure 1 、2 、 Figure 3 As shown, this embodiment further describes a composite box forming mold that can automatically compensate for mold expansion during the curing process. The product is a T700 carbon fiber composite rectangular box with flanges at both ends. The box wall thickness is 3mm and the box dimensions are 400mm×400mm×4000mm. The forming mold structure designed for this product includes a box core mold 101, a flange end frame 102, a flange limit frame 103, and an end extension shaft 104. The box core mold is a box-shaped structure welded with a 15mm thick Q235 steel plate + web plate. A step is set at the end, and the flange end frame is mounted on the step of the core shaft. The flange limit frame connects the flange end frame and the end box core mold with screws to determine the initial position of the flange end frame on the core mold. The limit step set at the end of the box core mold and the slope of the flange end frame installation slope are 1:10, and the thermal expansion slip gap between the flange end frame and the core shaft is 3mm. The flange end frame is a square-hole rectangular aluminum alloy plate with a thickness of 30mm. The clearance between it and the mandrel step is 0.05mm. The flange limit frame is an 8mm thick square-hole rectangular steel plate connected to the mandrel end face. It is used when the box body and flange are laid together and is removed after laying and before bag making. The end extension shaft is a steel pipe with a wall thickness of 20mm and a diameter of Φ200mm, which is connected to the mandrel end face via a flange. The rectangular box formed using this mold meets the design length requirements, and there are no defects such as delamination and bridging in the corner area of the end flange. The product molding quality meets the A-level requirements of GJB2895, and the qualified rate has increased from 50% to 95%.

[0047] In summary, the present invention realizes the ability of automatic compensation of mold expansion during the curing process by designing a thermally free flange end frame structure that can slide along the axial direction of the mold, avoiding the delamination and overhead problems in the flange corner area at the end of the box caused by the thermal expansion of the mold stretching the fiber layer during the molding of the long composite material box, and achieving the goal of low mold cost and high molding quality for this type of product.

[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 composite box forming mold capable of thermally dissociating and automatically compensating for mold expansion during the curing process, wherein the composite box end has a flange structure, and the flange is integrally cured and formed with the box. The composite box forming mold comprises a box core mold, a flange end frame, and a flange limit frame; The box core mold is a box-shaped structure welded by metal wall panels + web ribs, with steps and extension shafts at the ends; the flange end frame is mounted on the steps of the box core shaft to form an outward-turned structure at the end of the box core mold; the flange limit frame is located at the end of the box core mold, and the flange end frame and the box core mold are connected by screws to determine the initial position of the flange end frame on the core mold; in the initial state, a sliding gap δ is set between the flange end frame and the core shaft limit step along the length direction of the box core mold, and the surface of the composite box core mold is covered with a prepreg made of fiber layer and resin, and the end of the prepreg is turned along the box core mold to the surface of the mold flange end frame; when heated and pressurized for curing, the flange limit frame is removed, and the expansion of the box core mold along the length direction of the box is greater than the expansion of the composite box prepreg. The flange end frame can be thermally freed to offset the length difference between the box core mold and the box, so that the distance between the two flanges of the mold is always consistent with the composite box.

2. The composite box forming mold capable of thermally releasing and automatically compensating for mold expansion during the curing process according to claim 1, characterized in that: End extension shafts are provided at both ends of the box core mold, and the end extension shafts are metal tube structures that can be connected to the box core mold.

3. The composite box forming mold capable of thermally releasing and automatically compensating for mold expansion during the curing process according to claim 1, characterized in that: The composite material box is a long box with a length often exceeding 1000 mm.

4. The composite box forming mold capable of thermally releasing and automatically compensating for mold expansion during the curing process according to claim 1, characterized in that: In the initial state, the sliding gap δ between the flange end frame and the core shaft limit step is: δ=fL(α m -a p )ΔT Where, f is the process coefficient, ranging from 0.5 to 1; L is the length of the box; α m , α p are the linear expansion coefficients of the box core mold and the box body respectively; ΔT is the difference between the box resin gel temperature and room temperature.

5. The composite box forming mold capable of thermally releasing and automatically compensating for mold expansion during the curing process according to claim 1, characterized in that: The mounting surfaces of the box core mold and the flange end frame are conical surfaces.

6. The composite box forming mold capable of thermally releasing and automatically compensating for mold expansion during the curing process according to claim 5, characterized in that: The calculation formula of the cone slope K is as follows: Where, δ is the sliding gap; b is the step length at the end of the box core mold; α d , α m are the linear expansion coefficients of the flange end frame and the box core mold respectively; ΔT is the difference between the box resin gel temperature and room temperature.

7. The composite box forming mold capable of thermally releasing and automatically compensating for mold expansion during the curing process according to claim 1, characterized in that: The box core mold material is steel or aluminum alloy.

8. The composite box forming mold capable of thermally releasing and automatically compensating for mold expansion during the curing process according to claim 1, characterized in that: The pressure areas of the end faces of the flange end frame installed on the box core mold are different. Under the solidification pressure, the flange end frame slides in the axial direction.

9. The composite box forming mold capable of thermally releasing and automatically compensating for mold expansion during the curing process according to claim 6, characterized in that: The material of the flange end frame is a material whose thermal expansion coefficient is greater than or equal to the thermal expansion coefficient of the core mold.

10. The composite box forming mold capable of thermally releasing and automatically compensating for mold expansion during the curing process according to claim 1, characterized in that: Avoidance grooves are designed at intervals along the generatrix direction of the cone surface at the matching surface of the flange end frame and the end box core mold, so that the contact area between the flange end frame and the box core mold is less than 50% of the matching surface area.

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