Forming method and device for hollow structural parts of composite materials with large curvature and thick layers

Abstract

This invention pertains to helicopter composite material rotor blade manufacturing technology, specifically a molding method and apparatus for hollow structural components made of high-curvature thick-lay composite materials. The molding apparatus includes an upper molding die and a lower molding die. The upper molding die has an inner surface that matches the shape of the hollow spar to be molded. The lower molding die has an inner surface that matches the shape of the hollow spar to be molded. After the upper and lower molds are closed, the upper and lower molding die surfaces together define the shape of the hollow spar to be molded. The molding device includes grooves on the inner sides of the upper and lower molds, corresponding to the R-angle areas of the front and rear edges of the hollow wing beam to be molded. Movable blocks are arranged within these grooves. A glue-flowing channel is also provided at the joint of the movable blocks, and a certain gap is left between the movable blocks. The molding device further includes a pressure-applying component, which is arranged within the cavity of the hollow wing beam to be molded, applying pressure from inside the hollow wing beam to the outer surface. During the pressure molding process, the overflowing glue is discharged from the gap between the movable blocks and the glue-flowing channel through the mold cavity. The process method provided in this invention fully utilizes the wing beam's ply structure and the time interval during which resin viscosity decreases, repeatedly applying a large internal pressure to the raw material. Through repeated extrusion, the resin is driven to flow from high pressure areas to low pressure areas, and from the inner layer to the outer layer, thereby accelerating the discharge of the glue along with excess gas between layers.

Description

Technical Field

[0001] This invention pertains to helicopter composite material rotor blade manufacturing technology, specifically a method for forming the large curvature region of the hollow spar inside the rotor blade and the related apparatus used. Background Technology

[0002] Composite material hollow beam structures are used as load-bearing components in helicopter rotor blades and other aircraft wings. The spar in helicopter rotor blades, as the main load-bearing component, needs to have a special structural shape to meet the aerodynamic requirements of the blade, such as a hollow tubular structure, a flattened round cross-section, a large spanwise slenderness ratio, a certain twist angle, and a large dimensional variation from the root section to the wingtip section, with a wide opening at the root section and a smaller opening at the tip section.

[0003] Composite wing spars typically employ molding fixtures to ensure their external shape and mandrels to ensure their internal shape. The external fixtures are made of metal materials with high rigidity and a coefficient of thermal expansion close to that of the composite material. A variety of mandrel types are available, such as variable-structure metal materials, silicone with thermal expansion properties, air bladders, soluble mandrels, and shape-memory materials. During the molding and curing of the composite wing spars, the mandrel needs to provide a certain internal pressure to the wing spar ply, ensuring internal pressure is maintained during the resin softening and flow process, while simultaneously expelling excess adhesive between layers.

[0004] For large blades, the geometry of the spars is more prominent, with thicker ply thicknesses. To meet the blade's flapping stiffness requirements, the upper and lower surfaces are often thicker with thinner ply thicknesses at the leading and trailing edges, resulting in significant ply and curvature variations in the transition areas. This characteristic makes it easy for insufficient internal pressurization and slow resin flow to occur in areas with thicker ply thicknesses and greater curvature during spar molding. During curing, resin and air cannot quickly penetrate to the outer skin layer and be discharged through the tooling, leading to resin accumulation and interlayer delamination on the surface in these areas.

[0005] To address this type of problem, this invention proposes a method and apparatus for solving resin buildup in the high curvature region of a wing spars, including a wing spars layup method, a pressurized air guiding method, a tooling design structure, and a flow guiding process. This effectively solves problems such as resin accumulation and interlayer delamination that occur in the high curvature region of the wing spars. Summary of the Invention

[0006] For large-sized blade spars, the radius (R-angle) region is prone to resin enrichment and delamination due to factors such as large curvature and thick ply thickness. The purpose of this invention is to reduce the difficulty of spar molding and solve problems such as resin enrichment and delamination by adjusting the ply structure, designing molding tooling, and providing a pneumatic and negative pressure assisted molding method.

[0007] Technical solution: To achieve the above objectives, the present invention provides a molding device for hollow structural components of composite materials with large curvature and thick ply. The molding device includes an upper molding die and a lower molding die. The inner side of the upper molding die has an upper molding die surface that matches the shape of the hollow wing beam to be molded. The inner side of the lower molding die has a lower molding die surface that matches the shape of the hollow wing beam to be molded. After the upper and lower molds are closed, the upper molding die surface and the lower molding die surface together define the shape of the hollow wing beam to be molded.

[0008] Grooves are respectively opened on the inner sides of the upper mold and the lower mold, corresponding to the R-angle areas of the front and rear edges of the hollow wing beam to be formed. The grooves are filled with movable blocks. A mold-closing seam glue flow channel is also opened at the joint position of the movable blocks, and a certain gap is left between the movable blocks. The forming device also includes a pressure component, which is arranged in the inner cavity of the hollow wing beam to be formed, and applies pressure from the inside of the hollow wing beam to the outer surface. During the pressure forming process, the overflowing glue is discharged from the inner surface of the mold cavity through the gap between the movable blocks and the mold-closing seam glue flow channel.

[0009] Furthermore, the molding device also includes a vacuum cup, which is connected to the outlet of the glue flow channel in the mold seam and is used to collect the overflowing glue.

[0010] Furthermore, sealing channels are added around the parting surfaces of the upper and lower molds, and in conjunction with sealing strips, a sealed space is formed inside the mold after the upper and lower molds are closed.

[0011] Furthermore, the pressurization component includes a core mold airbag and an isolation layer. The core mold airbag is arranged in the inner cavity of the hollow wing beam to be formed and is used to apply pressure to the outside. An isolation layer is arranged between the core mold airbag and the inner wall of the hollow wing beam to be formed.

[0012] Furthermore, the inflation port of the core mold airbag is located at the end of the upper mold and the lower mold of the molding mold, and a sealing strip is added between the inflation port and the sealing channel.

[0013] Furthermore, the upper mold and the lower mold of the forming mold are designed with sealing caps at their ends. The sealing caps are used to seal the sealing strip, and the sealing caps also have an overflow outlet in the middle.

[0014] Furthermore, an R-zone adhesive flow channel is provided at the end of the movable block arranged inside the upper mold and lower mold of the forming mold, and the R-zone adhesive flow channel merges with the adhesive flow channel of the mold closing seam.

[0015] In another aspect, this invention also proposes a molding method for hollow structural components made of thick-lay composite materials with large curvature, employing the molding apparatus designed above, and the process is as follows:

[0016] The first step involves laying up the hollow wing beam to be molded and transferring it to the molding device. A certain gap exists between the outer shape of the hollow wing beam and the inner surface of the molding mold to allow for mold closing and installation. To minimize the gap and fully compact the product before curing begins, pressure P3 is rapidly applied to the internal pressure components of the hollow wing beam after mold closing at room temperature. Before the material viscosity decreases, the overlapping area is relaxed and extended outwards towards the mold cavity. This process is repeated 2-3 times before returning to the high-pressure state P1.

[0017] The second step involves the raw material viscosity gradually decreasing to its lowest point as the product temperature rises and it enters the first constant temperature platform T1. At this point, the pressure spreads between the layers, carrying excess gas and resin to the lower pressure area. The adhesive has a certain time limit in the low viscosity range, after which the viscosity gradually increases and enters the rubber state. Before this, the hollow wing beam to be molded is subjected to pulsed pressurization again, repeated 2-3 times, and then returned to the high pressure state P1. At this point, excess adhesive and gas are gradually carried out of the product by the pulsed extrusion force and flow out from the overflow area.

[0018] The third step is to maintain the negative pressure P2 throughout the entire process until the material is completely cured; after cooling, unload all pressure P1 and then open the mold to complete the wing beam forming.

[0019] Furthermore, when laying up the hollow wing beam, the interlayer overlap position needs to be selected at the position with larger curvature at the front and rear edges, that is, the R-angle area at the front and rear edges of the wing beam. In the same normal direction, the overlap areas should be spaced apart as much as possible.

[0020] Technical Effects: During the curing and heating process of the wing spars, the resin adhering to the surface of the composite material gradually transforms into a molten state due to the increase in ambient temperature. Its viscosity gradually decreases, reaching maximum fluidity and becoming liquid. As the temperature rises further, the resin viscosity gradually increases, transitioning from a liquid to a rubbery state, and finally becoming solid. The process method provided in this invention fully utilizes the wing spars' ply structure and the time interval during which resin viscosity decreases. A large internal pressure is repeatedly applied to the raw materials. Through repeated compression, the resin is driven to flow from areas of high pressure to areas of low pressure, and from the inner layer to the outer layer, thereby accelerating the discharge of the adhesive along with excess gas between layers.

[0021] The advantages of this invention are mainly reflected in the following aspects:

[0022] 1) Based on traditional molding tooling, this invention innovatively proposes a resin guiding and structural sealing method. According to the characteristics of the wing beam structure, the positions of the tooling blocks are reasonably arranged to ensure the smooth flow of resin and realize the rapid export of resin from the tooling layer.

[0023] 2) Isomorphically adjust the layup structure and the product dimensions during layup to provide space for resin flow between product layers and overall pre-compaction;

[0024] 3) By gradually increasing the pressure, interlayer clamping force is provided, which provides surging power for the flow of interlayer resin and avoids the continuous flow of resin being stopped due to pressure balance after one pressurization. Attached Figure Description

[0025] Figure 1 This is a partial schematic diagram of the wing beam tooling structure;

[0026] In the diagram, 1. Upper mold; 2. Lower mold; 3. Upper mold surface; 4. Lower mold surface; 5. Glue flow channel in the upper mold's R-zone; 6. Glue flow channel in the lower mold's R-zone; 7. Upper mold movable block; 8. Lower mold movable block; 9. Glue flow channel in the mold closing seam; 10. Sealing strip; 11. Mold closing seam; 12. Movable block positioning surface; 13. Glue flow micro-slit; 101. Hollow spar; 102. Upper spar surface; 103. Lower spar surface; 104. Leading edge of the spar; 105. R-zone of the spar.

[0027] Figure 2 This is a partial schematic diagram of the wing beam tooling structure;

[0028] In the diagram, 14 is the inflation port; 15 is the overflow cup; 16 is the overflow outlet; 17 is the vacuum port; 18 is the sealing cap; and 19 is the locking mechanism.

[0029] Figure 3 This is a schematic diagram of the internal core mold of the wing spars;

[0030] In the diagram, 201 is the isolation layer; 202 is the breathable layer; and 203 is the core mold airbag.

[0031] Figure 4 This is a schematic diagram of the pressurization process of the wing spars within the forming mold;

[0032] In the figure, 107 is the spire assembly overlap position; 108 is the spire assembly interface; 109 is the interlayer resin and gas flow during pressurization; 110 is the overflow of excess resin; 111 is the outer surface of the spire before pressurization; 204 is the internal pressurization direction.

[0033] Figure 5 Curing and pressurization process curve;

[0034] In the figure, T represents the temperature axis; t represents the time axis; P represents the pressure axis; T1 represents the first stage constant temperature platform; T2 represents the second stage constant temperature platform; Tt represents the curing temperature curve; P1 represents the positive pressure curve; and P2 represents the negative pressure curve. Detailed Implementation

[0035] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] For the hollow wing spars 101 of the helicopter, its significant features are that the upper and lower wing surfaces 102 and 103 of the wing spars are relatively flat, the leading edge 104 of the wing spars has a certain curvature, and the curvature of the bonding position between the leading and trailing edges and the upper and lower surfaces is relatively large, with a certain R-angle area 105. Another feature is that the upper and lower wing surfaces 102 and 103 of the wing spars are relatively thick, while the leading edge 104 of the wing spars is relatively thin.

[0037] Based on the actual shape characteristics of the hollow wing spar 101, the structure of the forming mold is designed. Generally, the forming mold is divided into upper and lower structures, with a mold closing seam 11 set at the front and rear edges of the wing spar. The mold is divided into an upper forming mold 1 and a lower forming mold 2.

[0038] The mold features an upper mold block 7 and a lower mold block 8 in the typical overflow area at the leading or trailing edge of the corresponding wing beam. These blocks are typically thin-layered for easy mold opening and cleaning. Micro-gaps, typically 0.2mm in size, are provided at the mating points of the upper mold block 7, lower mold block 8, and the upper mold surface 3 and lower mold surface 4 of the forming mold, respectively. Below these micro-gaps are flow channels 5 (upper mold R-zone) and 6 (lower mold R-zone), respectively. A mold-closing seam flow channel 9 is provided at the parting surface of the upper mold block 7 and lower mold block 8 to prevent overflow at the parting surface. A sealing strip 10 is added around the parting surface of the mold. Figure 1 .

[0039] To improve the air guiding and glue discharge speed of the wing spar molding fixture, a flow guide block is added to the upper and lower mold closing structure of the fixture. The cross-section of the flow guide block is located in the R-corner area of ​​the product and has a micro-slit structure. A flow channel is provided below the block to quickly discharge overflowing resin from the inner surface of the mold cavity. (Refer to...) Figure 1 Simultaneously, the entire tooling is sealed by a silicone strip placed on the outside of the adhesive flow channel, connecting the tooling to a negative pressure pipeline. Excess adhesive is collected by a vacuum cup located at the adhesive outlet to prevent overflow into the negative pressure system. (Refer to...) Figure 2 The molding die needs to be designed with complete sealing strips and glue flow channels. Figure 2 The diagram illustrates a design for a sealing channel and a glue flow channel. The sealing strip is typically filled with silicone rubber and has a sealing cap 18 at one end. The sealing cap communicates with the overflow cup 15 and is connected to the molding die via a locking mechanism 19. An anti-backflow vacuum port 17 is located at the top of the overflow cup, ensuring that the glue remains inside after overflow. In the diagram, 14 is the core mold / airbag inflation port, which allows for the connection of a positive pressure air source.

[0040] The wing spars require layering from the inside out on a mandrel surface with a certain rigidity. Alternatively, raw materials can be grouped, pre-compacted on other pre-forming tooling surfaces, and then transferred to the mandrel surface. A thinner permeable layer can be added to the mandrel surface to increase the flow of gas within the inner layers. (Reference) Figure 3 .

[0041] To meet the rapid flow guidance requirements of the wing spars, the overlap positions during wing spar layup should be selected at locations with greater curvature at the front and rear edges, i.e., the R-angle areas at the front and rear edges of the wing spars. In the same normal direction, the overlap areas should be spaced as far apart as possible. This avoids excessively thick layups at the same location, which would make mold closing difficult. The dimensions of the completed wing spars should be smaller than the internal dimensions of the forming tooling. (Refer to...) Figure 4 .

[0042] The wing spars are generally made of a mixture of directional composite materials and fabric composite materials. They can be transferred to the surface of the mandrel airbag 203 after the layup is completed by other tooling, or they can be laid on the surface of the mandrel airbag 203. Other layup tooling is not shown in this invention.

[0043] Before the composite material layup and assembly, the core mold / airbag needs to undergo a breathable treatment. This is typically done using a breathable felt / peelable fabric breathable layer 202 in conjunction with an isolation mold 201. This layer is then smoothly wrapped around the core mold surface and compacted using vacuum. For example... Figure 3 Because the prepreg is quite thick before curing, the airbag generally needs to be reduced in size by a certain proportion to meet the mold closing requirements. The reduction size is related to the layup thickness.

[0044] exist Figure 4 The example illustrates the intuitive connection between the overlap position of the hollow wing beam 101 and the overflow port. The overlap positions 107 of the wing beam assembly are evenly distributed on the leading edge of the wing beam, and each group of overlaps is staggered as much as possible in the normal phase to avoid excessively thick layers and facilitate overflow.

[0045] When the core mold airbag 203 is pressurized, the pressure is evenly distributed on the outer surface of the airbag. As the pressure is transmitted, the excess resin 110 that is squeezed out and other gases such as air will gradually be transmitted from the inside to the outside, creating a certain pressure gradient. The mixture of resin and air gradually overflows from the tooling to the outer surface of the hollow wing beam 101. At the same time, due to the impact of air pressure, the hollow wing beam 101 is more tightly sealed to the surfaces of the upper and lower mold surfaces 3 and 4. Under the action of negative pressure, excess resin and air overflow from the upper mold R-zone flow channel 5, the lower mold R-zone flow channel 6, and the mold closing seam flow channel 9 to the overflow cup 15.

[0046] like Figure 5This invention provides a temperature-pressure curve that incorporates product characteristics. After the hollow wing spar 101 is laid up and transferred to the molding die, a certain gap exists between the wing spar's outer shape and the inner surface of the molding die to allow for wing spar assembly. To minimize the gap and fully compact the product before curing begins, at room temperature after mold closing, a rapid injection of air pressure P3 is applied to the core mold / airbag. Before the material viscosity decreases, the overlapping area is relaxed and extended outwards towards the mold cavity. This process is typically repeated 2-3 times before returning to the high-pressure state P1.

[0047] As the product temperature rises and it enters the first isothermal platform T1, the viscosity of the raw materials gradually decreases to its lowest point. At this time, the pressure will spread between layers, carrying excess gas and resin to areas with lower pressure, such as the R zone 105 of the spar with larger curvature at the leading and trailing edges. However, the adhesive has a certain time limit in the low viscosity range, after which the viscosity will gradually increase and enter a rubbery state. Before this, the spar needs to be pulsed and pressurized again, with a pressure of P1. This is generally repeated 2-3 times before returning to the high pressure state P1. At this time, excess adhesive and gas will be gradually carried out of the product by the pulsed extrusion force and flow out from the overflow area.

[0048] The negative pressure P2 is maintained throughout the process until the material is completely cured. After cooling, all pressure P1 can be released before demolding to complete product molding.

[0049] The above specific embodiments or examples are only used to explain the technical solutions of the present invention and are not intended to limit the present invention. Parts not described in detail are considered as conventional technical means in the art. Those skilled in the art should understand that, based on the design concept of this application, it is possible to make adaptive modifications to the technical solutions described in the foregoing embodiments or to make equivalent substitutions for some or all of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A molding apparatus for hollow structural components of high-curvature thick-lay composite materials, characterized in that, The molding device includes an upper molding die and a lower molding die. The inner side of the upper molding die has an upper molding die surface that matches the shape of the hollow wing beam to be molded. The inner side of the lower molding die has a lower molding die surface that matches the shape of the hollow wing beam to be molded. After the upper and lower molds are closed, the upper molding die surface and the lower molding die surface together define the shape of the hollow wing beam to be molded. Grooves are respectively opened on the inner sides of the upper and lower molds of the molding die, corresponding to the R-angle areas of the front and rear edges of the hollow wing beam to be molded. Movable blocks are arranged in the grooves. Micro-slits for glue flow are respectively set at the contact positions between the upper and lower mold movable blocks and the upper and lower mold surfaces of the molding die. Glue flow channels for the upper and lower mold R-areas are respectively set below the micro-slits, and these channels merge with the mold closing seam glue flow channel. A mold closing seam glue flow channel is set at the parting surface of the upper and lower mold movable blocks. The molding device also includes a pressure assembly, which is arranged inside the hollow wing beam to be molded, applying pressure from inside the hollow wing beam to the outer surface. During the pressure molding process, overflowing glue is discharged from the gap between the movable blocks and the mold closing seam glue flow channel to the inner surface of the mold cavity.

2. The molding apparatus for hollow structural components of large-curvature thick-lay composite materials as described in claim 1, characterized in that, The molding device also includes a vacuum cup, which is connected to the outlet of the glue flow channel in the mold seam and is used to collect the overflowing glue.

3. The molding apparatus for hollow structural components of large-curvature thick-lay composite materials as described in claim 1, characterized in that, A sealing channel is added around the parting surface of the upper and lower molds, and a sealing strip is used to form a sealed space inside the mold after the upper and lower molds are closed.

4. The molding apparatus for hollow structural components of large-curvature thick-lay composite materials as described in claim 1, characterized in that, The pressurization assembly includes a core mold airbag and an isolation layer. The core mold airbag is arranged in the inner cavity of the hollow wing beam to be formed and is used to apply pressure to the outside. An isolation layer is arranged between the core mold airbag and the inner wall of the hollow wing beam to be formed.

5. The molding apparatus for hollow structural components of large-curvature thick-lay composite materials as described in claim 4, characterized in that, The inflation port of the core mold airbag is located at the end of the upper mold and the lower mold of the molding mold, and a sealing strip is added between the inflation port and the sealing channel.

6. The molding apparatus for hollow structural components of large-curvature thick-lay composite materials as described in claim 5, characterized in that, The upper mold and the lower mold of the forming mold are designed with sealing caps at their ends. The sealing caps are used to seal the sealing strip, and there is also an overflow outlet in the middle of the sealing cap.

7. A molding method for hollow structural components of composite materials with large curvature thick lay-up, employing the molding apparatus as described in any one of claims 1 to 6, characterized in that, The molding method includes the following steps: The first step involves laying up the hollow wing beam to be molded and transferring it to the molding device. A certain gap exists between the outer shape of the hollow wing beam and the inner surface of the molding mold to allow for mold closing and installation. To minimize the gap and fully compact the product before curing begins, pressure P3 is rapidly applied to the internal pressure components of the hollow wing beam after mold closing at room temperature. Before the material viscosity decreases, the overlapping area is relaxed and extended outwards towards the mold cavity. This process is repeated 2-3 times before returning to the high-pressure state P1. The second step involves the raw material viscosity gradually decreasing to its lowest point as the product temperature rises and it enters the first constant temperature platform T1. At this point, the pressure spreads between the layers, carrying excess gas and resin to the lower pressure area. The adhesive has a certain time limit in the low viscosity range, after which the viscosity gradually increases and enters the rubber state. Before this, the hollow wing beam to be molded is subjected to pulsed pressurization again, repeated 2-3 times, and then returned to the high pressure state P1. At this point, excess adhesive and gas are gradually carried out of the product by the pulsed extrusion force and flow out from the overflow area. The third step is to maintain the negative pressure P2 throughout the entire process until the material is completely cured; after cooling, unload all pressure P1 and then open the mold to complete the wing beam forming.

8. A molding method for hollow structural components of large-curvature thick-lay composite materials as described in claim 7, characterized in that, When laying up the hollow wing beam, the interlayer overlap position needs to be selected at the position with larger curvature at the front and rear edges, that is, the R-angle area of ​​the front and rear edges of the wing beam. In the same normal direction, the overlap areas should be spaced apart as much as possible.

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