Forming method and device for large-curvature thick-layer composite material hollow structural part

Abstract

The invention belongs to the manufacturing technology of helicopter composite material blades, and relates to a forming method and device for a large-curvature thick-laying-layer composite material hollow structural part. The forming device comprises a forming die upper die and a forming die lower die, the inner side of the forming die upper die is provided with a forming die upper die profile matched with the shape of a hollow spar to be formed, and the inner side of the forming die lower die is provided with a forming die lower die profile matched with the shape of the hollow spar to be formed. The shape of the hollow spar to be formed is jointly defined by the upper mold surface of the forming mold and the lower mold surface of the forming mold; grooves are formed in the positions, corresponding to R corner areas of the front edge and the rear edge of the hollow spar to be formed, of the inner sides of the upper forming die and the lower forming die respectively, and movable blocks are arranged in the grooves. The butt joint position of the movable blocks is further provided with a mold closing seam glue flowing channel, and a certain gap is reserved between the movable blocks; the forming device further comprises a pressurizing assembly, the pressurizing assembly is arranged in an inner cavity of the to-be-formed hollow spar, and pressure is applied to the outer surface from the interior of the to-be-formed hollow spar. And in the pressure forming process, overflowing glue liquid is discharged out of the inner surface of the die cavity from the gap of the movable block and the glue flowing channel of the die closing seam. According to the process method provided by the invention, a spar paving layer structure and a time interval for reducing the viscosity of the resin are fully utilized, a relatively large internal pressure is repeatedly applied to the raw material, and the resin is driven to flow from a high pressure position to a low pressure position and from an inner layer to an outer layer through repeated extrusion, so that the glue solution is accelerated to be discharged together with surplus gas between layers.

Description

Technical Field

[0001] The invention belongs to the manufacturing technology of helicopter composite material blades, and relates to a large curvature area molding method of a hollow spar in a blade and a related device used therein. Background Art

[0002] Composite helicopter blades or other aircraft wings all use composite hollow beam structures as load-bearing components. As the main load-bearing component of the blade, the spar in the helicopter blade needs to have a special structural shape to meet the aerodynamic requirements of the blade, such as a hollow tubular structure, an oblate cross-section, a large slenderness ratio in the span direction, a certain torsion angle, a large size change from the root section to the wing tip section, a wide opening in the root section, and a small opening in the tip section.

[0003] Composite wing beams generally use molded tooling to ensure the outer shape, and use core molds to ensure the inner shape. The outer shape tooling is made of metal materials with high rigidity and expansion coefficient close to that of the composite material. There are many types of core molds to choose from, such as variable structure metal materials, silicone with thermal expansion properties, airbags, soluble core molds, memory materials, etc. When the composite wing beam is formed and cured, the core mold needs to provide a certain internal pressure to the wing beam layer to ensure that the internal pressure is provided to the layer during the softening and flowing process of the resin, and at the same time, the excess adhesive between the layers is discharged.

[0004] For large-sized blades, the geometric features of the wing beam are more prominent, and the layers are thicker. In order to meet the flapping stiffness requirements of the blades, the upper and lower wing surfaces are often thicker, and the leading and trailing edge layers are thinner. There are obvious changes in the layers and curvature in the transition area. This feature causes problems such as insufficient internal pressurization and slow resin flow in locations with thicker layers and greater curvature when the wing beam is formed. During the curing period, the resin and air cannot quickly penetrate into the outer layer of the skin and be exported through the tooling, resulting in resin accumulation on the surface of this area and gap stratification between layers.

[0005] In view of this type of problem, the present invention proposes a method and device for solving the problem of resin accumulation in the large curvature area of ​​the wing spar, including a spar laying method, a pressurized air guide method, a tooling design structure, a guide process, etc. It can effectively solve the problems of resin accumulation in the large curvature area of ​​the wing spar, gap formation between layers, etc. Summary of the invention

[0006] For large-sized blade spar, the R angle area is prone to resin-rich and interlayer gap stratification problems due to factors such as large curvature and large layer thickness. The purpose of the present invention is to reduce the difficulty of spar forming and solve the problems of resin-rich and interlayer gap stratification by adjusting the layer structure, designing the forming tooling structure, and providing a method of air pressure pressurization and negative pressure assisted forming.

[0007] Technical solution: To achieve the above-mentioned purpose, the present invention designs a molding device for a hollow structural member of a composite material with a large curvature and thick plies, the molding device comprises an upper molding die and a lower molding die, the inner side of the upper molding die has an upper molding die shape surface matching the outer shape of the hollow spar to be formed, the inner side of the lower molding die has a lower molding die shape surface matching the outer shape of the hollow spar to be formed, after the upper and lower molds are closed, the upper molding die shape surface and the lower molding die shape surface jointly define the outer shape of the hollow spar to be formed;

[0008] Grooves are respectively provided on the inner sides of the upper and lower dies of the forming mold at positions corresponding to the R corner areas of the front and rear edges of the hollow wing beam to be formed, and movable blocks are arranged in the grooves; a mold seam glue flow channel is also provided at the joint position of the movable blocks, and a certain gap is left between the movable blocks; the forming device also includes a pressurizing 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 be formed to the outer surface; during the pressurized forming process, the overflowed glue is discharged from the inner surface of the mold cavity through the gap between the movable blocks and the mold seam glue flow channel.

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

[0010] Furthermore, a sealing channel is added around the parting surface of the upper mold and the lower mold of the molding mold, and a sealing belt is provided, so that a sealed space is formed inside the mold after the upper and lower molds are closed.

[0011] Furthermore, the pressurizing component includes a core mold airbag and an isolation layer. The core mold airbag is arranged in the inner cavity of the hollow wing spar 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 spar to be formed.

[0012] Furthermore, the core mold airbag inflation interface is arranged at the end positions of the upper mold of the forming mold and the lower mold of the forming mold, and a sealing belt is added between the inflation interface and the sealing channel.

[0013] Furthermore, sealing covers are designed at the end positions of the upper mold of the molding mold and the lower mold of the molding mold. The sealing covers are used to seal the sealing belt, and a glue overflow port is also opened in the middle of the sealing cover.

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

[0015] On the other hand, the present invention also proposes a molding method for a hollow structural member of a composite material with a large curvature and thick layers, using the molding device designed as above, and the process is as follows:

[0016] In the first step, the hollow spar to be formed is laid and transferred to the forming device. There is a certain gap between the outer shape of the hollow spar to be formed and the inner surface of the forming mold to meet the requirements of the spar mold assembly. In order to minimize the gap and fully compact the product before the start of curing, the internal pressurization component of the hollow spar to be formed is quickly applied with pressure P3 at room temperature after mold assembly. When the viscosity of the material does not decrease, the overlap area is relaxed and extended outward to approach the mold cavity. Repeat 2-3 times and then return to the high pressure state P1.

[0017] In the second step, as the product temperature rises and enters the first constant temperature platform T1, the viscosity of the raw materials gradually decreases to the lowest. At this time, the pressure will spread between the layers and bring excess gas and resin to a position with lower pressure. The glue has a certain time limit in the low viscosity range, and then the viscosity will gradually increase and enter the rubber state; before this, the inside of the hollow spar to be formed is pulsed pressurized again, and after repeating 2-3 times, it returns to the high pressure state P1. At this time, the excess glue and gas will be gradually taken out of the product due to the pulsed extrusion force and flow out from the overflow area;

[0018] In the third step, the negative pressure P2 is maintained unchanged throughout the entire process until the material is completely solidified; after cooling down, all the pressure P1 is unloaded, and then the mold is opened to complete the wing beam forming.

[0019] Furthermore, when the hollow spar to be formed is laid, the overlap position between the layers needs to be selected at the position with larger curvature of the front and rear edges, that is, the R angle area of ​​the front and rear edges of the spar, and the overlap areas should be spaced as far as possible in the same normal direction.

[0020] Technical effect: During the curing and heating process of the spar in the furnace, the resin attached to the surface of the composite material will gradually turn into a molten state due to the increase in the surrounding temperature, and the viscosity will gradually decrease and the fluidity will reach the maximum, showing a liquid state. As the temperature rises again, the viscosity of the resin will gradually increase, gradually changing from a liquid state to a rubber state, and finally becoming a solid state. The process method provided in the present invention makes full use of the spar ply structure and the time interval for the resin viscosity to decrease, repeatedly applies a large internal pressure to the raw materials, and through repeated extrusion, drives the resin to flow from a high pressure area to a low pressure area, and from the inner layer to the outer layer, thereby accelerating the discharge of the glue together with the excess gas between the layers.

[0021] The advantages of the present invention are concentrated in the following aspects:

[0022] 1) Based on the traditional molding tooling, the present invention innovatively proposes a resin diversion and structural sealing method. According to the structural characteristics of the wing spar, the positions of the tooling blocks are reasonably arranged to ensure the smooth flow of resin, thereby realizing the rapid derivation of resin at the tooling level;

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

[0024] 3) Through the gradual and rapid expansion and pressurization method, the inter-layer compression force is provided, which provides surging power for the flow of inter-layer resin, avoiding the pressure balance after one pressure application and preventing the continuous flow of resin. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0026] In the figure, 1, upper mold of forming mold; 2, lower mold of forming mold; 3, upper mold surface of forming mold; 4, lower mold surface of forming mold; 5, glue flow channel of upper mold R zone; 6, glue flow channel of lower mold R zone; 7, upper mold movable block; 8, lower mold movable block; 9, glue flow channel of mold joint; 10, sealing tape; 11, mold joint; 12, movable block positioning surface; 13, glue flow micro gap; 101, hollow spar; 102, upper wing surface of spar; 103, lower wing surface of spar; 104, leading edge of spar; 105, R zone of spar;

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

[0028] In the figure, 14, inflation interface; 15, overflow cup; 16 overflow port; 17 vacuum interface; 18 sealing cover; 19 locking mechanism;

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

[0030] In the figure, 201 is an isolation layer; 202 is a breathable layer; 203 is a core mold airbag;

[0031] Figure 4 It is a schematic diagram of the pressurization process of the spar in the forming die;

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

[0033] Figure 5 It is the curing pressurization process curve;

[0034] In the figure, T is the temperature axis; t is the time axis; P is the pressure axis; T1 is the constant temperature platform in the first stage; T2 is the constant temperature platform in the second stage; Tt is the curing temperature curve; P1 is the positive pressure curve; P2 is the negative pressure curve. DETAILED DESCRIPTION

[0035] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] For the helicopter blade spar 101, its notable features are that the upper and lower surfaces 102 and 103 are relatively flat, the leading and trailing edges 104 have a certain curvature, the curvature of the leading and trailing edges and the upper and lower surfaces at the bonding position is relatively large, and there is a certain R angle area 105. Another feature is that the upper and lower wing surfaces 102 and 103 have thicker plies, and 104 has a thinner ply.

[0037] The structure of the forming mold is designed according to the actual appearance characteristics of the spar 101. Generally, the forming mold is divided into an upper and lower structure, a parting surface 11 is set at the front and rear edges of the spar, and the mold is divided into an upper mold 1 and a lower mold 2.

[0038] The mold is provided with glue flow blocks 7 and 8 at the typical glue overflow area at the leading edge or trailing edge of the corresponding wing beam. The blocks are generally thin-layer structures to facilitate mold opening and cleaning. A glue flow micro gap is provided at the joint position between the blocks 7 and 8 and the mold surface 3 and 4. The gap is generally 0.2 mm. Glue flow channels 5 and 6 are provided below the gap. A glue flow channel 9 is added at the parting surface at the interface between the blocks 7 and 8 to prevent glue overflow at the parting surface. A sealing belt 10 is added around the parting surface. Figure 1 .

[0039] In order to improve the air guide and glue discharge speed of the wing spar forming tooling, a guide block is added on the basis of the upper and lower mold clamping structure of the tooling. The cross section of the guide block is located in the R corner area of ​​the product and has a micro-slit structure. A guide channel is provided under the block to quickly discharge the overflowed resin from the inner surface of the mold cavity. Figure 1 At the same time, the tooling is sealed as a whole, and the silicone tape set on the outside of the glue flow channel is used to seal the tooling as a whole and connect the negative pressure pipeline. The excess glue is collected by the vacuum cup set at the glue outlet to prevent overflow into the negative pressure system. Figure 2 The molding die needs to be designed with complete sealing belt and glue flow channel. Figure 2 In the figure, a design method of sealing channel and glue flow channel is listed. The sealing belt is generally filled with silicone rubber, and a sealing cover 18 is designed at the end. The sealing cover is connected to the overflow glue cup 15 and connected to the molding mold through the locking mechanism 19. An anti-backflow vacuum interface 17 is set on the upper part of the overflow glue cup, and the glue will stay in the overflow glue cup after overflowing. In the figure, 14 is the core mold / airbag connection port, which can be connected to the positive pressure air source.

[0040] The wing spar needs to be laid from the inside to the outside on the surface of the core mold with a certain rigidity. The raw materials can also be laid in groups on other pre-formed tooling surfaces for pre-compaction and then transferred to the surface of the core mold. A thinner air permeable layer can be added to the surface of the core mold to increase the flow of the inner layer of gas. Figure 3 .

[0041] In order to meet the requirements of rapid flow guidance of the wing spar, when laying the wing spar, the overlap position between the layers needs to be selected at the position with larger curvature of the leading and trailing edges, that is, the R angle area of ​​the leading and trailing edges of the wing spar. In the same normal direction, the overlap areas should be spaced as far as possible to avoid thicker layers at the same position and difficulty in mold closing. The size of the wing spar after the layer is laid should be smaller than the inner size of the forming tooling. Figure 4 .

[0042] The wing beam is generally made of a mixed paving of strip composite materials and fabric composite materials, which can be transferred to the surface of the core mold airbag 203 after other tooling completes the laying, or can be laid on the surface of 203. Other laying tooling is not shown in the present invention.

[0043] Before the composite material is laid and closed, the surface of the core mold / airbag needs to be ventilated. Generally, a breathable felt / peelable cloth 202 is used in conjunction with an isolation mold 201, which is evenly wrapped on the surface of the core mold and compacted with vacuum. Figure 3 Since the prepreg is thick before curing, in order to meet the mold requirements, the airbag generally needs to be reduced in size by a certain proportion. The reduction in size is related to the thickness of the layer.

[0044] exist Figure 4 In the figure, an example is given to illustrate the intuitive connection between the overlap position of the spar 101 and the overflow port. The overlap position 107 is not at the leading edge of the spar, and each set of overlaps is staggered as much as possible to avoid excessive thickness of the layer and facilitate overflow of glue.

[0045] When the airbag 203 is pressurized, the pressure is evenly distributed on the outer surface of the airbag. As the pressure is transmitted, the squeezed glue 110 and other gases 109 such as air will gradually be transmitted from the inside to the outside, which will generate a certain pressure gradient. The mixture of resin and air will gradually overflow from the tooling to the outer surface of the product 101. At the same time, due to the impact of air pressure, the spar-shaped surface 101 is more tightly fitted on the surface of the mold cavity 3 and 4. The excess resin and air overflow from the glue flow channels 5, 6, and 9 to the glue overflow cup 15 under the action of negative pressure.

[0046] like Figure 5. The present invention provides a temperature-pressure curve that combines the characteristics of the product. After the spar 101 is laid and transferred to the forming mold, there is a certain gap between the outer shape of the spar and the inner surface of the forming mold to meet the requirements of the spar mold installation. In order to minimize the gap and fully compact the product before the start of curing, the core mold / airbag is quickly rushed with air pressure P3 at room temperature after mold closing, and when the viscosity of the material does not decrease, the overlap area is relaxed and extended outward, close to the mold cavity. Generally, it is repeated 2-3 times and then returns to the high pressure state P1.

[0047] As the product temperature rises and enters the first constant temperature platform T1, the viscosity of the raw materials gradually decreases to the minimum. At this time, the pressure will spread between the layers and bring excess gas and resin to the position with lower pressure, such as the R angle area 105 with larger curvature of the front and rear edges. However, the glue has a certain time limit in the low viscosity range, and then the viscosity will gradually increase and enter the rubber state. Before this, the wing beam needs to be pulse-pressurized again, with a pressure of P1. Generally, it is repeated 2-3 times and then restored to the high pressure state P1. At this time, the excess glue and gas will be gradually taken out of the product due to the pulsed extrusion force and flow out from the overflow area.

[0048] The negative pressure P2 is kept constant during the whole process until the material is completely solidified. After the temperature drops, all the pressure P1 can be unloaded, and the mold can be opened to complete the product molding.

[0049] The above specific implementation methods or cases are only used to explain the technical solutions of the present invention, and are not intended to limit the present invention. Any parts not described in detail are regarded as conventional technical means in the art. A person of ordinary skill in the art should understand that based on the design concept of the present application, the technical solutions described in the aforementioned implementation methods should be adaptively modified, or some or all of the technical features therein should be replaced by equivalents. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A forming device for hollow structural parts of composite materials with large curvature and thick layers, characterized in that: The molding device comprises an upper molding die and a lower molding die, wherein the inner side of the upper molding die has an upper molding die surface matching the outer shape of the hollow spar to be molded, and the inner side of the lower molding die has a lower molding die surface matching the outer shape of the hollow spar to be molded, and after the upper and lower molds are closed, the upper molding die surface and the lower molding die surface jointly define the outer shape of the hollow spar to be molded; Grooves are respectively provided on the inner sides of the upper and lower dies of the forming mold at positions corresponding to the R corner areas of the front and rear edges of the hollow wing beam to be formed, and movable blocks are arranged in the grooves; a mold seam glue flow channel is also provided at the joint position of the movable blocks, and a certain gap is left between the movable blocks; the forming device also includes a pressurizing 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 be formed to the outer surface; during the pressurized forming process, the overflowed glue is discharged from the inner surface of the mold cavity through the gap between the movable blocks and the mold seam glue flow channel.

2. A forming device for a hollow structural member of a composite material with a large curvature and thick layers as claimed in claim 1, characterized in that: The molding device also includes a vacuum cup, which is connected to the outlet of the mold seam glue flow channel and is used to collect overflowed glue.

3. The forming device for hollow structural parts of composite materials with large curvature and thick layers as claimed in claim 1, characterized in that: A sealing channel is added around the parting surface of the upper mold and the lower mold of the molding mold, and a sealing belt is used. After the upper and lower molds are closed, a sealed space is formed inside the mold.

4. The forming device for hollow structural parts of composite materials with large curvature and thick layers as claimed in claim 1, characterized in that: The pressurizing component includes a core mold airbag and an isolation layer. The core mold airbag is arranged in the inner cavity of the hollow wing spar 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 spar to be formed.

5. The forming device for a hollow structural member of a composite material with a large curvature and thick layers as claimed in claim 4, characterized in that: The core mold airbag inflation interface is arranged at the end positions of the upper mold of the forming mold and the lower mold of the forming mold, and a sealing belt is added between the inflation interface and the sealing channel.

6. The forming device for a hollow structural member of a composite material with a large curvature and thick layers as claimed in claim 5, characterized in that: Sealing covers are designed at the end positions of the upper die of the forming die and the lower die of the forming die. The sealing covers are used to seal the sealing belts, and a glue overflow port is also opened in the middle of the sealing covers.

7. A forming device for a hollow structural member of a composite material with a large curvature and thick layers as claimed in claim 6, characterized in that: An R-zone glue flow channel is provided at the end of the movable block arranged inside the upper mold and the lower mold of the forming mold, and the R-zone glue flow channel merges with the mold seam glue flow channel.

8. A molding method for a hollow structural member of a composite material with a large curvature and thick layers, using a molding device as claimed in any one of claims 1 to 7, characterized in that: The molding method comprises the following steps: In the first step, the hollow spar to be formed is laid and transferred to the forming device. There is a certain gap between the outer shape of the hollow spar to be formed and the inner surface of the forming mold to meet the requirements of the spar mold assembly. In order to minimize the gap and fully compact the product before the start of curing, the internal pressurization component of the hollow spar to be formed is quickly applied with pressure P3 at room temperature after mold assembly. When the viscosity of the material does not decrease, the overlap area is relaxed and extended outward to approach the mold cavity. Repeat 2-3 times and then return to the high pressure state P1. In the second step, as the product temperature rises and enters the first constant temperature platform T1, the viscosity of the raw materials gradually decreases to the lowest. At this time, the pressure will spread between the layers and bring excess gas and resin to a position with lower pressure. The glue has a certain time limit in the low viscosity range, and then the viscosity will gradually increase and enter the rubber state; before this, the inside of the hollow spar to be formed is pulsed pressurized again, and after repeating 2-3 times, it returns to the high pressure state P1. At this time, the excess glue and gas will be gradually taken out of the product due to the pulsed extrusion force and flow out from the overflow area; In the third step, the negative pressure P2 is maintained unchanged throughout the entire process until the material is completely solidified; after cooling down, all the pressure P1 is unloaded, and then the mold is opened to complete the wing beam forming.

9. A molding method for a hollow structural member of a composite material with a large curvature and thick layers as claimed in claim 8, characterized in that: When laying out the hollow spar to be formed, the overlap position between the layers needs to be selected at the position with larger curvature of the front and rear edges, that is, the R angle area of ​​the front and rear edges of the spar, in the same normal direction, and the overlap areas should be spaced as far as possible.

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