Mold suitable for forming thin-walled carbon fiber rod

Abstract

The application provides a mold suitable for forming a carbon fiber thin-walled rod, and belongs to the technical field of carbon fiber composite material forming molds. The mold comprises an upper mold, a lower mold, a lateral sliding block, a mold core, a first butterfly spring assembly, a second butterfly spring assembly and a connecting rod assembly; the mold core is connected with a winding machine through the connecting rod assembly to perform carbon fiber winding, and the upper mold and the lateral sliding block are respectively subjected to flexible pressure through the two butterfly spring assemblies, balanced mold closing in the up-down direction and the left-right direction of the product is realized, and the mold is placed in a hot press tank for curing after mold closing. The application does not need vacuum-assisted mold closing, has simple structure, uniform pressure and convenient operation, and can reduce processing and production costs.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber composite material molding die technology, specifically, it relates to a die suitable for molding thin-walled carbon fiber rods. Background Technology

[0002] Carbon fiber composites possess advantages such as high specific strength and high specific modulus. Thin-walled rectangular carbon fiber rods can be used in the aerospace field for spacecraft frames and support structures. For thin-walled rectangular carbon fiber rods with a wall thickness of less than 1 mm and a angular shape, the small wall thickness places high demands on the mold structure, pressure application method, and molding precision during the molding process.

[0003] Current methods for molding thin-walled rectangular carbon fiber rods typically involve using metal molds with vacuum bags and sealing strips for external pressure. To meet vacuum pressure requirements, the molds usually need to have a multi-lobed structure and space reserved for suction nozzles, resulting in complex mold structures and high processing costs. Furthermore, each curing cycle requires vacuum bag placement, sealing, and airtightness checks, making the process cumbersome and posing a risk of product spoilage due to leaks.

[0004] In addition, when using vacuum bags for pressurization, it is difficult to accurately control the pressure on the product. For thin-walled rectangular rods, warping and uneven wall thickness are likely to occur during the curing process due to excessive local or unilateral pressure, which affects the molding accuracy of the product.

[0005] Currently, the relevant existing technologies include: A Chinese patent document with publication number CN103434140A discloses a method for forming carbon fiber rods. The method involves winding a portion of the rib thickness onto two steel core molds, sealing them with vacuum bags and sealing strips, and then pre-pressing them in an autoclave. The pre-pressed laminate and mold cores are then assembled and wound together, and finally sealed again with vacuum bags and sealing strips before being cured in an autoclave. This method requires vacuum bag and sealing strip sealing during the forming process, making the procedure relatively complex.

[0006] Therefore, it is necessary to provide a carbon fiber thin-walled rod forming mold and forming method that is relatively simple in structure, has balanced stress, and is easy to operate, in order to solve the above problems. Summary of the Invention

[0007] In view of the deficiencies in the prior art, the purpose of this invention is to provide a mold suitable for forming thin-walled carbon fiber rods.

[0008] The mold for forming carbon fiber thin-walled rods according to the present invention includes: an upper mold, a lower mold, a side slider, a mold core, a first butterfly spring assembly, and a second butterfly spring assembly; The upper mold, lower mold, and lateral slider are arranged around the outside of the mold core, and form a molding space between them for accommodating the carbon fiber preform. The lateral slider is slidably disposed within the positioning groove of the lower mold; The first butterfly spring assembly is disposed above the upper mold and applies elastic pressure toward the lower mold to the upper mold, so that the upper mold and the lower mold press the carbon fiber preform together in the vertical direction; The second butterfly spring assembly is disposed on the side of the lateral slider away from the mold core, and applies an elastic thrust toward the mold core to the lateral slider so that the lateral slider and the lower mold press the carbon fiber preform in the left and right directions.

[0009] Preferably, the carbon fiber thin-walled rod has a rectangular cross-section with a width of A, a height of B, a length of L, and wall thicknesses of t1 and t2, respectively, and both t1 and t2 are less than 1 mm. The upper mold is fitted to the upper side plane of the carbon fiber thin-walled rod. The lower mold fits into the lower plane and one side plane of the carbon fiber thin-walled rod. The lateral slider is used to fit the other side plane of the carbon fiber thin-walled rod, and the mold core has a molding surface that matches the inner cavity contour of the carbon fiber thin-walled rod.

[0010] Preferably, the first butterfly spring assembly includes an internal hexagonal screw, a washer, and a first butterfly spring. The internal hexagonal screw passes through the upper mold in a vertical direction and is connected to the lower mold. The washer and the first butterfly spring are disposed between the head of the internal hexagonal screw and the upper mold. The second butterfly spring assembly includes a set screw, a retaining ring, and a second butterfly spring. The set screw is disposed horizontally on the side of the lower mold. The second butterfly spring and the retaining ring are disposed in the positioning hole of the lateral slider. The retaining ring is located between the set screw and the second butterfly spring. The set screw has a spherical head at one end facing the retaining ring, and the spherical head makes line contact with the inner hole of the retaining ring.

[0011] Preferably, the first and second butterfly springs have the same specifications and combination. Each of the first butterfly spring assemblies includes four sets of first butterfly springs, each set consisting of two butterfly springs joined together; each of the second butterfly spring assemblies includes four sets of second butterfly springs, each set consisting of two butterfly springs joined together. The compression of both the first and second butterfly springs is 80% of the maximum deformation of the corresponding butterfly spring.

[0012] Preferably, the first butterfly spring assembly is disposed on the upper mold and forms two columns along the width direction of the mold, and multiple first butterfly spring assemblies in each column are spaced apart along the length direction of the mold, with the arrangement spacing between adjacent first butterfly spring assemblies being 2C; The second butterfly spring assembly forms a row along one side of the lateral slider and is arranged at intervals of C along the length of the mold, where 2C = 2 × C; Along the length of the mold, the second butterfly spring assembly is positioned at a distance corresponding to the interval between adjacent first butterfly spring assemblies, so that the first and second butterfly spring assemblies are staggered along the length of the mold, and the total number of the first and second butterfly spring assemblies is the same.

[0013] Preferably, there is a sliding gap of 0.2 mm between the upper surface of the lateral slider and the corresponding contact surface of the upper mold. The side of the lateral slider away from the mold core has a 2mm pre-tightening gap with the inner wall of the positioning groove of the lower mold. The positioning hole of the lateral slider has a single-sided assembly gap of 0.25mm between itself and the second disc spring, and the positioning hole has a single-sided assembly gap of 0.1mm between itself and the retaining ring. After the upper and lower molds are closed, the corresponding cavity position has a forming gap of 0.05mm on one side.

[0014] Preferably, the lateral slider is provided with overflow grooves on the upper and lower sides near the product molding surface. The overflow groove is spaced 1mm apart from the product molding surface. The overflow groove extends along the length direction of the lateral slider, and each end of the groove retains a solid wall thickness of 2mm between its two ends and the corresponding end face of the lateral slider. The overflow groove has a semi-circular cross-section with a radius of 3mm.

[0015] Preferably, the mold suitable for forming carbon fiber thin-walled rods further includes: connecting rod assemblies respectively disposed at both ends of the mold core. The connecting rod assembly includes: a connecting rod, a connecting rod socket screw, and a nut; The connecting rod is provided with a positioning groove for accommodating the end of the mold core and a positioning hole corresponding to the positioning hole of the mold core. The internal hexagonal screw of the connecting rod passes through the corresponding positioning holes of the connecting rod and the mold core and is connected to the nut; The outer periphery of the connecting rod is provided with a cylindrical clamping part for the three-jaw chuck of the winding machine to hold, so that the winding machine drives the mold core to rotate through the connecting rod.

[0016] A method for forming carbon fiber thin-walled rods, implemented using a mold suitable for forming carbon fiber thin-walled rods provided according to the present invention, includes: Step S1: Install the connecting rod assembly at both ends of the mold core; Step S2: Clamp the mold core onto the winding machine using the connecting rod assembly; Step S3: Drive the mold core to rotate, so that the carbon fiber bundles are wound on the forming surface of the mold core to form a carbon fiber thin-walled rod preform; Step S4: Remove the mold core containing the carbon fiber thin-walled rod preform from the winding machine and position it in the lower mold; Step S5: Install the second disc spring and the retaining ring into the positioning hole of the side slider; Step S6: Insert the lateral slider into the positioning groove of the lower mold; Step S7: Install the upper mold above the lower mold, so that the upper mold, lower mold and side slider surround the outside of the mold core with the carbon fiber thin-walled rod preform; Step S8: Tighten the second butterfly spring assembly to push the lateral slider toward the mold core, and tighten the first butterfly spring assembly to apply elastic pressure toward the lower mold to the upper mold, so as to flexibly pre-tighten the carbon fiber thin-walled rod preform in the left-right and up-down directions respectively. Step S9: Place the mold assembly, after mold closing and flexible pre-tightening, into an autoclave for high-temperature curing.

[0017] Preferably, in step S1, the connecting rod and the mold core have a single-sided assembly gap of 0.15mm at the surface mating position, and the connecting rod internal hexagon screw and the corresponding positioning hole have a single-sided assembly gap of 0.05mm. In step S5, there is a single-sided assembly gap of 0.25mm between the positioning hole of the lateral slider and the second butterfly spring, and a single-sided assembly gap of 0.1mm between the positioning hole and the retaining ring. In step S6, there is a 0.2mm sliding gap between the upper plane of the lateral slider and the corresponding contact surface of the upper mold, and there is a 2mm pre-tightening gap between the lateral slider and the inner wall of the positioning groove of the lower mold. In step S7, after the upper mold and the lower mold are closed, the corresponding cavity position has a molding gap of 0.05mm on one side. In step S8, the compression of the first and second butterfly springs is controlled to be 80% of the maximum deformation of the corresponding butterfly springs.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses a built-in butterfly spring to apply flexible pressure, achieving balanced force on the product in the vertical and horizontal directions. It eliminates the need for vacuum-assisted mold closing, simplifies the mold structure and operation process, reduces processing and production costs, and improves molding efficiency and precision. 2. This invention matches the specifications, quantity, layout and compression of the disc springs to provide stable and controllable pressure during the curing process, and can compensate for dimensional changes caused by thermal expansion and resin flow, reducing molding defects caused by uneven pressure or improper pressure. 3. By setting an intermediate force transmission structure and adopting an automatic centering force transmission method, this invention can reduce eccentric pressure and spring damage, and improve the force transmission effect, pressure stability and spring service life. 4. By setting reasonable sliding, pre-tightening and molding gaps, the present invention provides movement space for lateral pressure and adapts to resin flow and thermal expansion during the curing process, which helps to ensure product dimensional accuracy. 5. By setting up an overflow structure to accommodate excess resin generated during the curing process and retaining a reinforcing area at the end, the present invention can reduce the risk of cracking caused by stress concentration during pressure and high-temperature curing. 6. This invention enables quick connection and disassembly of the mold core and the winding equipment, and limits relative movement during the winding process; at the same time, the mold size and the number of butterfly spring assemblies can be adjusted according to different product sizes, which has good applicability. Attached Figure Description

[0019] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a cross-sectional schematic diagram of a carbon fiber thin-walled rod according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the mold structure applicable to the forming of carbon fiber thin-walled rods according to an embodiment of the present invention; Figure 3 This is a schematic diagram showing the layout of the first and second butterfly spring assemblies according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the first butterfly spring assembly according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the structure of the second butterfly spring assembly according to an embodiment of the present invention; Figure 6 This is a schematic diagram of the connecting rod assembly according to an embodiment of the present invention; Figure 7 This is a schematic diagram of the assembly gap between the connecting rod assembly and the mold core according to an embodiment of the present invention; Figure 8This is a schematic diagram of the assembly clearance between the lateral slider and the lower mold in an embodiment of the present invention; Figure 9 This is a schematic diagram showing the positional relationship between the overflow groove of the lateral slider and the product molding surface in an embodiment of the present invention; Figure 10 This is a schematic diagram of the overflow groove structure of the lateral slider in an embodiment of the present invention; Figure 11 This is a schematic diagram of the assembly clearance between the lateral slider, the second butterfly spring, and the retaining ring in an embodiment of the present invention. Figure 12 This is a schematic diagram of the assembly gap between the upper and lower molds in an embodiment of the present invention.

[0020] The diagram shows: Detailed Implementation

[0021] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0022] like Figures 1 to 12 As shown, this embodiment of the invention provides a mold suitable for forming thin-walled carbon fiber rods, used for pre-winding and subsequent curing of thin-walled carbon fiber rods; it is particularly suitable for rectangular carbon fiber rods with a wall thickness of less than 1 mm, i.e., the thin-walled carbon fiber rod to be formed has a rectangular cross-section with a width of A, a height of B, a length of L, and wall thicknesses of t1 and t2, respectively, where both t1 and t2 are less than 1 mm, and the product has a clear corner shape. The mold includes: an upper mold 1, a lower mold 2, a side slider 3, a mold core 4, a first butterfly spring assembly 5, a second butterfly spring assembly 6, and a connecting rod assembly 7.

[0023] The upper mold 1 is used to conform to the upper plane of the carbon fiber thin-walled rod; the lower mold 2 is used to conform to the lower plane and left plane of the carbon fiber thin-walled rod; the lateral slider 3 is disposed in the positioning groove formed by the lower mold 2, conforming to the right plane of the carbon fiber thin-walled rod; the mold core 4 is disposed in the inner cavity of the carbon fiber thin-walled rod, supporting the inner cavity of the product, and the mold core 4 has a molding surface adapted to the contour of the inner cavity of the product. Thus, the upper mold 1, the lower mold 2, and the lateral slider 3 are disposed outside the mold core 4, and together with the mold core 4, define the molding space for accommodating the carbon fiber preform. The upper mold 1 and the lower mold 2 cooperate to form the product in the vertical direction, the lateral slider 3 and the lower mold 2 cooperate to form the product in the horizontal direction, and the mold core 4 is used to define the inner cavity contour of the product, thereby jointly forming the inner and outer contours of the carbon fiber thin-walled rectangular rod.

[0024] Furthermore, the first butterfly spring assembly 5 is positioned above the upper mold 1. The hexagonal screw 51 of the assembly passes through the upper mold 1 in the vertical direction and connects to the lower mold 2. A washer 52 and the first butterfly spring 53 are positioned between the head of the hexagonal screw 51 and the upper mold 1. When the hexagonal screw 51 is tightened, the washer 52 compresses the first butterfly spring 53, causing it to elastically deform and apply elastic pressure towards the lower mold 2 to the upper mold 1. This, in turn, presses the upper and lower surfaces of the product together through the upper mold 1 and the lower mold 2. The washer 52 serves as an intermediate force transmission component, transferring the locking force of the hexagonal screw 51 to the end face of the first butterfly spring 53 and preventing direct contact between the hexagonal screw 51 and the first butterfly spring 53, thus avoiding scratches or localized indentations on the surface of the first butterfly spring 53.

[0025] Furthermore, the second butterfly spring assembly 6 is disposed on the side of the lateral slider 3 away from the mold core 4, the set screw 61 is disposed horizontally on the side of the lower mold 2, and the second butterfly spring 63 and the retaining ring 62 are disposed in the positioning hole of the lateral slider 3, wherein the retaining ring 62 is located between the set screw 61 and the second butterfly spring 63. When the set screw 61 is tightened, the set screw 61 transmits thrust to the lateral slider 3 through the retaining ring 62 and the second butterfly spring 63 in sequence, causing the second butterfly spring 63 to be elastically compressed and pushing the lateral slider 3 toward the mold core 4, thereby pressing the left and right planes of the product together through the lateral slider 3 and the lower mold 2. Thus, the first butterfly spring assembly 5 applies flexible pressure to the product in the vertical direction through the upper mold 1, and the second butterfly spring assembly 6 applies flexible pressure to the product in the horizontal direction through the side slider 3, so that the carbon fiber thin-walled rod is subjected to corresponding elastic compression in both directions. Thus, the first butterfly spring assembly 5 and the second butterfly spring assembly 6 set inside the mold complete the mold closing pressure, without the need for external vacuum bags to assist in mold closing. After mold closing, the mold can be directly placed into the autoclave for high-temperature curing.

[0026] Both the washer 52 in the first butterfly spring assembly 5 and the retaining ring 62 in the second butterfly spring assembly 6 serve as intermediate force transmission components. However, due to the different orientations and force transmission methods of the first and second butterfly spring assemblies 5 and 6, they employ different force transmission structures. Specifically, the set screw 61 is modified from a hexagonal socket head cap screw. The end of the set screw 61 facing the retaining ring 62 forms a spherical head, which makes line contact with the inner hole of the retaining ring 62. When the set screw 61 is tightened, the horizontal thrust is transmitted through the line contact between the spherical head and the retaining ring 62, thereby achieving automatic centering during the force transmission process and reducing the possibility of eccentric pressure. At the same time, the retaining ring 62 can prevent the set screw 61 from directly contacting the end face of the second butterfly spring 63, thus reducing scratches or indentations on the end face of the second butterfly spring 63.

[0027] Furthermore, the first butterfly spring assembly 5 and the second butterfly spring assembly 6 use the same specifications and the same number of butterfly springs. Each first butterfly spring assembly 5 has four sets of first butterfly springs 53, each set of first butterfly springs 53 is composed of two butterfly springs joined together, therefore, each first butterfly spring assembly 5 includes eight butterfly springs; similarly, each second butterfly spring assembly 6 has four sets of second butterfly springs 63, each set of second butterfly springs 63 is composed of two butterfly springs joined together, therefore, each second butterfly spring assembly 6 also includes eight butterfly springs. The first butterfly springs 53 and the second butterfly springs 63 use butterfly springs of the same specifications and adopt the same combination form, so that the two types of butterfly spring assemblies have the same elastic pressure under the same compression state.

[0028] Furthermore, such as Figure 3 As shown, the first butterfly spring assembly 5 and the second butterfly spring assembly 6 adopt different spatial layouts according to their respective pressure application positions, and are spaced apart and staggered along the length of the mold. The first butterfly spring assembly 5 is located above the upper mold 1 and forms two rows spaced apart along the width of the mold. Multiple first butterfly spring assemblies 5 in each row are spaced apart along the length of the mold, and the arrangement spacing between adjacent first butterfly spring assemblies 5 is 2C. The second butterfly spring assembly 6 is located on one side of the side slider 3 and forms a row. Multiple second butterfly spring assemblies 6 in this row are spaced apart along the length of the mold, and the arrangement spacing between adjacent second butterfly spring assemblies 6 is C, where 2C = 2 × C. Along the length of the mold, the second butterfly spring assembly 6 is located between adjacent first butterfly spring assemblies 5, and the second butterfly spring assembly 6 is not limited to being located in the middle position between adjacent first butterfly spring assemblies 5, so that the first butterfly spring assembly 5 and the second butterfly spring assembly 6 are uniformly and staggered along the length of the mold, and avoid mutual interference. Two rows of first butterfly spring assemblies 5 are arranged along the width of the mold, and one row of second butterfly spring assemblies 6 is arranged along the side. The arrangement spacing of the first butterfly spring assemblies 5 along the length of the mold is twice the arrangement spacing of the second butterfly spring assemblies 6, so that the overall configuration quantity of the first butterfly spring assemblies 5 and the second butterfly spring assemblies 6 is consistent. At the same time, by combining butterfly springs of the same specification, the same quantity and the same compression state in the two types of butterfly spring assemblies, the upper mold 1 and the side slider 3 apply balanced and flexible pressure to the product in the vertical and horizontal directions, respectively.

[0029] Furthermore, when tightening the hexagonal socket screw 51 and the set screw 61, the compression of the first butterfly spring 53 and the second butterfly spring 63 is controlled to be 80% of the maximum deformation of the corresponding butterfly spring. This compression is controlled by adjusting the screw-in depth of the hexagonal socket screw 51 and the set screw 61. By controlling the compression of the butterfly springs within the aforementioned range, the first butterfly spring 53 and the second butterfly spring 63 maintain their respective elastic deformation states during the autoclave curing process. This provides stable pressure while reserving a certain elastic deformation margin to compensate for dimensional changes caused by thermal expansion and resin flow during curing.

[0030] Furthermore, the lateral slider 3 is slidably disposed within the positioning groove formed by the lower mold 2. For example... Figure 8 As shown, after the lateral slider 3 is inserted into the positioning groove of the lower mold 2, a sliding gap is reserved between the upper surface of the lateral slider 3 and the corresponding contact surface of the upper mold 1, so that the lateral slider 3 can move horizontally relative to the lower mold 2 under the action of the second butterfly spring assembly 6, avoiding interference between the lateral slider 3 and the upper mold 1 during the movement. At the same time, a butterfly spring preload gap is reserved between the side of the lateral slider 3 away from the product and the inner wall of the positioning groove of the lower mold 2, to provide space for the lateral movement of the lateral slider 3 and the preload of the second butterfly spring assembly 6.

[0031] Furthermore, such as Figure 11 As shown, the lateral slider 3 forms a positioning hole corresponding to the second butterfly spring assembly 6, and the second butterfly spring 63 and the retaining ring 62 are installed into the positioning hole. An assembly gap is provided between the positioning hole and the second butterfly spring 63, and an assembly gap is also provided between the positioning hole and the retaining ring 62, so as to facilitate the assembly of the second butterfly spring 63 and the retaining ring 62, and ensure that the second butterfly spring assembly 6 can normally generate elastic compression and transmit force.

[0032] Furthermore, such as Figure 12 As shown, after the upper mold 1 and lower mold 2 are closed in place, a molding gap is reserved at the corresponding cavity position. The above molding gap is used to accommodate the resin flow and thermal expansion of the carbon fiber preform formed by winding during the curing process, so that the carbon fiber thin-walled rod can be cured and formed within the space jointly defined by the upper mold 1, lower mold 2, side slider 3 and mold core 4.

[0033] Furthermore, such as Figure 9 and Figure 10As shown, the lateral slider 3 is provided with an overflow groove. This overflow groove is located on the upper and lower sides of the lateral slider 3 near the product molding surface, and is spaced apart from the product molding area. It is used to accommodate excess resin generated during the compaction and curing process of the carbon fiber preform. The overflow groove extends along the length of the lateral slider 3, and neither end of the overflow groove penetrates the end face of the lateral slider 3. Instead, a solid wall thickness is maintained between the two ends of the overflow groove and the end face of the lateral slider 3. This solid portion forms a structural reinforcement area at the end of the lateral slider 3, reducing the possibility of cracking at the end of the lateral slider 3 due to stress concentration during the pressure applied by the second butterfly spring assembly 6 and the high-temperature curing process in the autoclave.

[0034] Furthermore, the connecting rod assembly 7 is disposed at the end of the mold core 4 for connecting the mold core 4 to the winding machine. The connecting rod assembly 7 includes a connecting rod 71, a connecting rod socket head cap screw 72, and a nut 73. Positioning holes are provided at both ends of the mold core 4. The connecting rod 71 has a positioning groove for accommodating the end of the mold core 4 and a positioning hole corresponding to the positioning hole of the mold core 4. During assembly, the end of the mold core 4 is inserted into the positioning groove of the connecting rod 71, so that the positioning hole of the connecting rod 71 corresponds to the positioning hole of the mold core 4. The connecting rod socket head cap screw 72 passes through the corresponding positioning holes of the connecting rod 71 and the mold core 4, and is locked by the nut 73, thereby fixing the connecting rod 71 to the end of the mold core 4.

[0035] The outer periphery of the connecting rod 71 forms a cylindrical clamping part for the three-jaw chuck of the winding machine to hold. The outer diameter of the connecting rod 71 is adapted to the clamping range of the three-jaw chuck of the winding machine. During carbon fiber winding, the three-jaw chuck clamps the outer periphery of the connecting rod 71 and drives the connecting rod 71 to rotate. The connecting rod 71 drives the mold core 4 to rotate synchronously, so that the carbon fiber tow can be wound on the outer surface of the mold core 4 to form a carbon fiber thin-walled rod preform.

[0036] Furthermore, an assembly gap is provided between the connecting rod 71 and the corresponding surface of the mold core 4 to facilitate the installation and disassembly of the connecting rod 71 and the mold core 4; a clearance fit is also provided between the connecting rod internal hexagon screw 72 and the corresponding positioning holes of the connecting rod 71 and the mold core 4, which not only facilitates assembly but also restricts the circumferential position of the connecting rod 71 relative to the mold core 4, so as to reduce the possibility of relative movement between the connecting rod 71 and the mold core 4 during the winding process.

[0037] Furthermore, the upper mold 1, lower mold 2, side slider 3, mold core 4, washer 52, retaining ring 62, and connecting rod 71 are all made of 45# steel and heat-treated to achieve a material hardness of HRC28~32, in order to meet the requirements of the mold in the high-temperature curing process of carbon fiber thin-walled rods. The component hexagon socket head cap screw 51 and the corresponding hexagon socket head cap screw are hexagon socket head cap screws conforming to GB / T70.1-2000 standard, with a strength grade of 12.9; the set screw 61 is modified from a hexagon socket head cap screw conforming to GB / T70.1-2000 standard, with a strength grade of 12.9; the nut 73 is a hexagonal nut conforming to GB / T6170-2000 standard; the first butterfly spring 53 and the second butterfly spring 63 are butterfly springs conforming to GB / T1972-1992 standard.

[0038] Example 1 In a more specific embodiment, such as Figures 1 to 12 As shown, the width A of the carbon fiber thin-walled rod is 18.7mm, the height B is 10mm, the length L is 1600mm, the wall thickness t1 and t2 are both 0.4mm, and the product shape is a clear angle.

[0039] Corresponding to the above product dimensions, the molding surface dimensions of the mold core 4 are 17.9mm × 9.2mm, and the length of the mold core 4 is 1600mm, so that the mold core 4 can be adapted to the dimensions of the product cavity.

[0040] In this embodiment, the upper mold 1, lower mold 2, side slider 3, mold core 4, washer 52, retaining ring 62 and connecting rod 71 are all made of No. 45 steel and have undergone heat treatment, with a hardness of HRC28~32.

[0041] The socket head cap screw 51 in the first butterfly spring assembly 5 is an M12×90 socket head cap screw, conforming to GB / T70.1-2000 standard, with a strength grade of 12.9. The washer 52 has an outer diameter of φ28mm, an inner diameter of φ14mm, and a height of 8mm.

[0042] Each first butterfly spring assembly 5 includes four sets of first butterfly springs 53. Each set of first butterfly springs 53 is composed of two butterfly springs joined together, that is, each first butterfly spring assembly 5 is provided with a total of eight butterfly springs. The first butterfly springs 53 adopt A25-1 specification butterfly springs conforming to GB / T1972-1992 standard.

[0043] The set screw 61 in the second butterfly spring assembly 6 is modified from a semi-finished M12×40 socket head cap screw with a strength grade of 12.9. The machined set screw 61 is 39mm long, and its end facing the retaining ring 62 is machined into an SR5 spherical head. The retaining ring 62 has an outer diameter of φ25.3mm, an inner diameter of φ8mm, and a height of 6mm. The SR5 spherical head of the set screw 61 forms line contact with the inner hole of the retaining ring 62.

[0044] Each second butterfly spring assembly 6 includes four sets of second butterfly springs 63. Each set of second butterfly springs 63 is composed of two butterfly springs joined together, meaning that each second butterfly spring assembly 6 also has eight butterfly springs. The second butterfly springs 63 also adopt A25-1 specification butterfly springs conforming to GB / T1972-1992 standard.

[0045] like Figure 3 As shown, in this embodiment, the first butterfly spring assembly 5 is arranged in two rows along the width direction of the upper mold 1, and the first butterfly spring assemblies 5 in each row are arranged at intervals along the length direction of the mold, with the arrangement spacing 2C between adjacent first butterfly spring assemblies 5 being 100mm; the second butterfly spring assembly 6 forms a row on one side of the lateral slider 3 and is arranged at intervals along the length direction of the mold, with the arrangement spacing C between adjacent second butterfly spring assemblies 6 being 50mm, that is, 2C=2×C.

[0046] By arranging the first two rows of butterfly spring assemblies 5 and the second row of butterfly spring assemblies 6 as described above, the total number of the first butterfly spring assemblies 5 and the second butterfly spring assemblies 6 on the mold is kept consistent. Combined with the same specifications, combination method and compression amount of the first butterfly spring 53 and the second butterfly spring 63, the product is subjected to corresponding balanced pressure in the vertical and horizontal directions.

[0047] When tightening the internal hexagonal screw 51 and the set screw 61 of the assembly, the compression of the first butterfly spring 53 and the second butterfly spring 63 is controlled to 80% of the maximum deformation of the corresponding butterfly spring, so that the two types of butterfly springs can continuously provide elastic pressure during the curing process in the autoclave.

[0048] Furthermore, in this embodiment, after the lateral slider 3 is installed into the positioning groove of the lower mold 2, a sliding gap of 0.2mm is reserved between the upper plane of the lateral slider 3 and the corresponding contact surface of the upper mold 1, and a 2mm butterfly spring pre-tightening gap is reserved between the side of the lateral slider 3 away from the product and the corresponding inner wall of the positioning groove of the lower mold 2.

[0049] The aforementioned 0.2mm sliding gap allows the lateral slider 3 to move horizontally without interfering with the upper mold 1 under the action of the second butterfly spring assembly 6; the aforementioned 2mm butterfly spring preload gap provides the corresponding space for the preload of the second butterfly spring assembly 6 and the movement of the lateral slider 3 toward the product direction.

[0050] A second butterfly spring 63 and a retaining ring 62 are installed in the positioning hole of the side slider 3. There is a single-sided assembly gap of 0.25mm between the positioning hole and the second butterfly spring 63, and a single-sided assembly gap of 0.1mm between the positioning hole and the retaining ring 62.

[0051] Furthermore, after the upper mold 1 and the lower mold 2 are closed in place, the corresponding cavity position has a gap of 0.05mm on one side. This gap is used to accommodate the resin flow and corresponding dimensional changes that occur during the curing process of the carbon fiber preform.

[0052] like Figure 9 and Figure 10 As shown, in this embodiment, the side slider 3 has an overflow groove at a position 1mm away from the product molding surface, one above and one below. The cross-section of the overflow groove is preferably an R3 semi-circle. The overflow groove extends along the length of the side slider 3, and a solid wall thickness of 2mm is maintained between the two ends of the overflow groove and the corresponding end face of the side slider 3.

[0053] The overflow groove can accommodate excess resin generated during the compaction and curing process of the carbon fiber preform; by retaining a solid wall thickness of 2mm at both ends of the overflow groove, the structural integrity of the end area of ​​the lateral slider 3 can be maintained, thereby reducing the possibility of cracking at the end of the lateral slider 3 due to stress concentration during the pressure application of the second butterfly spring assembly 6 and the curing process in the autoclave.

[0054] like Figure 6 and Figure 7 As shown, in this embodiment, the connecting rod 71 is provided with a positioning groove with a width of 9.5mm and a positioning hole with a diameter of 8.1mm; the forming surface size of the mold core 4 is 17.9mm×9.2mm×1600mm, and φ8mm positioning holes are provided at both ends of the 17.9mm surface.

[0055] When assembling the connecting rod assembly 7, insert the corresponding 9.2mm profiles at both ends of the mold core 4 into the 9.5mm positioning grooves of the connecting rod 71, so that a single-sided assembly gap of 0.15mm is formed at the mating position of the connecting rod 71 and the mold core 4 profiles. Then, pass the M8×50 connecting rod hexagonal screw 72 through the φ8.1mm positioning hole of the connecting rod 71 and the φ8mm positioning hole of the mold core 4, and use the M8 nut 73 to lock and fix it.

[0056] A 0.05mm clearance is formed between the connecting rod's hexagonal screw 72 and the corresponding positioning hole. The 0.15mm clearance between the connecting rod 71 and the mold core 4 facilitates the quick installation and removal of the connecting rod 71; the 0.05mm clearance between the connecting rod's hexagonal screw 72 and the positioning hole restricts the circumferential freedom of the connecting rod 71 relative to the mold core 4 while meeting assembly requirements.

[0057] In this embodiment, the outer diameter of the connecting rod 71 is φ35mm, which is adapted to the clamping range of the three-jaw chuck of the winding machine. After the three-jaw chuck of the winding machine clamps the outer circumferential surface of the connecting rod 71, it drives the mold core 4 to rotate synchronously by driving the connecting rod 71 to rotate, thereby completing the winding of carbon fiber tow on the surface of the mold core 4.

[0058] This invention also provides a method for forming carbon fiber thin-walled rods using the above-mentioned mold, comprising: Step S1: Install the connecting rod assembly 7 at both ends of the mold core 4; specifically, insert both ends of the mold core 4 into the positioning grooves of the corresponding connecting rod 71 respectively, so that a predetermined assembly gap is formed between the connecting rod 71 and the corresponding surface of the mold core 4, pass the connecting rod internal hexagon screw 72 through the corresponding positioning holes of the connecting rod 71 and the mold core 4, and lock and fix it with nut 73.

[0059] In this embodiment, the single-sided clearance between the connecting rod 71 and the mold core 4 is 0.15mm, and the single-sided clearance between the connecting rod hexagonal screw 72 and the corresponding positioning hole is 0.05mm.

[0060] Step S2: The mold core 4 with the connecting rod assembly 7 installed is clamped in the winding machine; specifically, the three-jaw chuck of the winding machine clamps the outer circumferential surface of the connecting rod 71, and a rotational transmission connection between the winding machine and the mold core 4 is established through the connecting rod 71.

[0061] Step S3: Perform carbon fiber winding; start the winding machine, drive the connecting rod 71 to rotate by the three-jaw chuck, and drive the mold core 4 to rotate synchronously through the connecting rod 71, so that the carbon fiber bundle is wound on the forming surface of the mold core 4, thereby forming a carbon fiber thin-walled rod preform with a wall thickness of less than 1mm on the outside of the mold core 4.

[0062] Step S4: Transfer the completed winding core 4 to the lower mold 2; after completing the carbon fiber winding, remove the core 4 with the carbon fiber thin-walled rod preform and the connecting rod assembly 7 from the winding machine, and position the core 4 at the corresponding forming position of the lower mold 2 so that the preform is located on the corresponding forming surface of the lower mold 2.

[0063] Step S5: Install the second butterfly spring assembly 6; install the four sets of second butterfly springs 63 and the retaining rings 62 into the corresponding positioning holes of the side slider 3, so that a predetermined assembly gap is formed between the positioning holes and the second butterfly springs 63, and a predetermined assembly gap is formed between the positioning holes and the retaining rings 62.

[0064] In this embodiment, there is a single-sided assembly gap of 0.25mm between the positioning hole of the lateral slider 3 and the second butterfly spring 63, and a single-sided assembly gap of 0.1mm between the positioning hole of the lateral slider 3 and the retaining ring 62.

[0065] Step S6: Insert the side slider 3 into the lower mold 2; install the side slider 3 equipped with the second butterfly spring 63 and the retaining ring 62 into the corresponding positioning groove of the lower mold 2, so that the side slider 3 facing the product is set opposite to the corresponding side wall of the carbon fiber thin-walled rod preform.

[0066] After assembly, a 0.2mm sliding gap is reserved between the upper surface of the side slider 3 and the corresponding contact surface of the upper mold 1, and a 2mm butterfly spring preload gap is reserved between the side of the side slider 3 away from the product and the inner wall of the positioning groove of the lower mold 2, so that the side slider 3 can move towards the product under the action of the second butterfly spring assembly 6.

[0067] Step S7: Install the upper mold 1 and complete the cavity mold closing; install the upper mold 1 above the lower mold 2, so that the upper mold 1, lower mold 2 and side slider 3 surround the mold core 4 with the preformed body, and together form the molding space of the carbon fiber thin-walled rod.

[0068] In this embodiment, after the upper mold 1 and the lower mold 2 are closed, the corresponding cavity position has a gap of 0.05mm on one side.

[0069] Step S8: Perform bidirectional flexible pre-tightening on the mold; first, tighten the set screw 61 in the second butterfly spring assembly 6, so that the spherical head of the set screw 61 transmits horizontal thrust to the second butterfly spring 63 through the retaining ring 62. The second butterfly spring 63 generates elastic compression and pushes the side slider 3 to move toward the product. The side slider 3 and the lower mold 2 press the left and right planes of the product together; then tighten the internal hexagonal screw 51 of the first butterfly spring assembly 5, so that the first butterfly spring 53 is compressed through the washer 52. The first butterfly spring 53 generates elastic deformation and applies vertical downward pressure to the upper mold 1. The upper mold 1 and the lower mold 2 press the upper and lower planes of the product together.

[0070] In this embodiment, the compression of the first butterfly spring 53 and the second butterfly spring 63 is controlled to be 80% of the maximum deformation of the corresponding butterfly spring, so that the first butterfly spring assembly 5 and the second butterfly spring assembly 6 apply corresponding flexible pre-tightening pressure to the carbon fiber thin-walled rod preform from the up and down direction and the left and right direction, respectively.

[0071] Step S9: Perform autoclave curing; After completing the mold closing and bidirectional flexible pre-tightening of the upper mold 1, lower mold 2 and side slider 3, place the entire mold in an autoclave for high-temperature curing, so that the carbon fiber thin-walled rod preform is cured and formed in the forming space jointly defined by the mold core 4, upper mold 1, lower mold 2 and side slider 3.

[0072] During the curing process, the first butterfly spring assembly 5 continuously applies elastic pressure to the product in the vertical direction through the upper mold 1, and the second butterfly spring assembly 6 continuously applies elastic pressure to the product in the horizontal direction through the side slider 3; the first butterfly spring 53 and the second butterfly spring 63 compensate for the corresponding dimensional changes caused by thermal expansion and resin flow during the curing process through their own elastic deformation, thereby maintaining the pressing effect on the carbon fiber thin-walled rod preform.

[0073] Meanwhile, the excess resin generated during the compaction and curing process can enter the overflow grooves set on the upper and lower sides of the side slider 3. The solid wall thickness retained at both ends of the overflow groove is used to improve the structural integrity of the end area of ​​the side slider 3.

[0074] Furthermore, the mold provided by this invention is not limited to the carbon fiber thin-walled rectangular rod of the specific dimensions described above. Based on the cross-sectional length, width, wall thickness, and overall length of the carbon fiber thin-walled rod to be formed, the relevant dimensions of the upper mold 1, lower mold 2, side slider 3, mold core 4, and connecting rod 71 can be adjusted accordingly, and the first butterfly spring assembly 5 and the second butterfly spring assembly 6 can be configured accordingly based on the product length.

[0075] When adjusting the configuration quantity of the first butterfly spring assembly 5 and the second butterfly spring assembly 6, the total quantity of the first butterfly spring assembly 5 and the second butterfly spring assembly 6 should be kept the same, and the corresponding arrangement relationship should be maintained according to the setting position of the two types of butterfly spring assemblies, so as to ensure that the product cavity is subjected to corresponding balanced pressure.

[0076] In summary, this invention defines the inner and outer forming contours of the carbon fiber thin-walled rod through the upper mold 1, lower mold 2, side slider 3, and mold core 4. The upper mold 1 is subjected to vertical flexible pressure by the first butterfly spring assembly 5, and the side slider 3 is subjected to lateral flexible pressure by the second butterfly spring assembly 6. The first butterfly spring assembly 5 forms two rows on the upper mold 1 and is arranged at a spacing of 2C along the mold length direction. The second butterfly spring assembly 6 forms one row on the side and is arranged at a spacing of C along the mold length direction, ensuring that the overall configuration quantity of the two types of butterfly spring assemblies remains consistent. Combined with butterfly springs of the same specifications, the same combination method, and corresponding compression, balanced flexible pressure is achieved in both the vertical and horizontal directions of the product. Simultaneously, the connecting rod assembly 7 enables clamping and rotational transmission between the mold core 4 and the winding machine. The sliding assembly structure of the side slider 3 achieves lateral pressure, and the overflow groove on the side slider 3 accommodates excess resin generated during the curing process. This process enables the pre-forming of the carbon fiber thin-walled rectangular rod through winding, mold closing, and autoclave curing.

[0077] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0078] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A mold suitable for forming thin-walled carbon fiber rods, characterized in that, include: Upper mold (1), lower mold (2), side slider (3), mold core (4), first butterfly spring assembly (5), and second butterfly spring assembly (6); The upper mold (1), lower mold (2) and side slider (3) surround the outside of the mold core (4) and form a molding space between them for accommodating the carbon fiber preform. The lateral slider (3) is slidably disposed in the positioning groove of the lower mold (2); The first butterfly spring assembly (5) is disposed above the upper mold (1) and applies elastic pressure toward the lower mold (2) to the upper mold (1) so that the upper mold (1) and the lower mold (2) press the carbon fiber preform in the vertical direction; The second butterfly spring assembly (6) is disposed on the side of the lateral slider (3) away from the mold core (4), and applies an elastic thrust toward the mold core (4) to the lateral slider (3) so that the lateral slider (3) and the lower mold (2) press the carbon fiber preform in the left and right directions.

2. The mold for forming thin-walled carbon fiber rods according to claim 1, characterized in that, The carbon fiber thin-walled rod has a rectangular cross-section with a width of A, a height of B, a length of L, and wall thicknesses of t1 and t2, respectively, and both t1 and t2 are less than 1 mm. The upper mold (1) is fitted to the upper side plane of the carbon fiber thin-walled rod. The lower mold (2) fits into the lower plane and one side plane of the carbon fiber thin-walled rod. The lateral slider (3) is used to fit the other side plane of the carbon fiber thin-walled rod, and the mold core (4) has a molding surface that is adapted to the inner cavity contour of the carbon fiber thin-walled rod.

3. The mold for forming thin-walled carbon fiber rods according to claim 1, characterized in that, The first butterfly spring assembly (5) includes an internal hexagonal screw (51), a washer (52) and a first butterfly spring (53). The internal hexagonal screw (51) passes through the upper mold (1) in the vertical direction and is connected to the lower mold (2). The washer (52) and the first butterfly spring (53) are disposed between the head of the internal hexagonal screw (51) and the upper mold (1). The second butterfly spring assembly (6) includes a set screw (61), a retaining ring (62), and a second butterfly spring (63). The set screw (61) is disposed horizontally on the side of the lower mold (2). The second butterfly spring (63) and the retaining ring (62) are disposed in the positioning hole of the side slider (3). The retaining ring (62) is located between the set screw (61) and the second butterfly spring (63). The set screw (61) has a spherical head at one end facing the retaining ring (62), and the spherical head forms line contact with the inner hole of the retaining ring (62).

4. The mold for forming thin-walled carbon fiber rods according to claim 3, characterized in that, The first butterfly spring (53) and the second butterfly spring (63) have the same specifications and combination form; Each of the first butterfly spring assemblies (5) includes four sets of first butterfly springs (53), each set consisting of two butterfly springs joined together; each of the second butterfly spring assemblies (6) includes four sets of second butterfly springs (63), each set consisting of two butterfly springs joined together; The compression of the first butterfly spring (53) and the second butterfly spring (63) is 80% of the maximum deformation of the corresponding butterfly spring.

5. The mold for forming thin-walled carbon fiber rods according to claim 1, characterized in that, The first butterfly spring assembly (5) is disposed on the upper mold (1) and forms two columns along the width direction of the mold. Multiple first butterfly spring assemblies (5) in each column are spaced apart along the length direction of the mold, and the arrangement spacing between adjacent first butterfly spring assemblies (5) is 2C. The second butterfly spring assembly (6) forms a row along one side of the lateral slider (3) and is arranged at intervals of C along the length of the mold, where 2C = 2 × C; Along the length of the mold, the second butterfly spring assembly (6) is positioned to correspond to the interval between adjacent first butterfly spring assemblies (5), so that the first butterfly spring assembly (5) and the second butterfly spring assembly (6) are staggered along the length of the mold, and the total number of the first butterfly spring assembly (5) and the second butterfly spring assembly (6) is the same.

6. The mold for forming thin-walled carbon fiber rods according to claim 3, characterized in that, The upper surface of the lateral slider (3) has a sliding gap of 0.2 mm with the corresponding contact surface of the upper mold (1). The side slider (3) facing away from the mold core (4) has a 2mm pre-tightening gap with the inner wall of the positioning groove of the lower mold (2); The positioning hole of the lateral slider (3) has a single-sided assembly gap of 0.25 mm between it and the second butterfly spring (63), and the positioning hole has a single-sided assembly gap of 0.1 mm between it and the retaining ring (62). After the upper mold (1) and the lower mold (2) are closed, the corresponding cavity position has a molding gap of 0.05mm on one side.

7. The mold for forming thin-walled carbon fiber rods according to claim 1, characterized in that, The side slider (3) is provided with overflow grooves on the upper and lower sides near the product molding surface. The overflow groove is set 1mm apart from the product molding surface. The overflow groove extends along the length direction of the side slider (3), and its two ends are respectively kept with a solid wall thickness of 2mm between the corresponding end faces of the side slider (3). The overflow groove has a semi-circular cross-section with a radius of 3mm.

8. The mold for forming thin-walled carbon fiber rods according to claim 1, characterized in that, Also includes: Connecting rod assemblies (7) are respectively set at both ends of the mold core (4). The connecting rod assembly (7) includes: a connecting rod (71), a connecting rod socket screw (72), and a nut (73); The connecting rod (71) is provided with a positioning groove for accommodating the end of the mold core (4) and a positioning hole corresponding to the positioning hole of the mold core (4). The internal hexagonal screw (72) of the connecting rod passes through the corresponding positioning holes of the connecting rod (71) and the mold core (4) and is connected to the nut (73); The outer periphery of the connecting rod (71) is provided with a cylindrical clamping part for the three-jaw chuck of the winding machine to hold, so that the winding machine drives the mold core (4) to rotate through the connecting rod (71).

9. A method for forming carbon fiber thin-walled rods, comprising using the mold described in any one of claims 1 to 8 suitable for forming carbon fiber thin-walled rods, characterized in that, include: Step S1: Install the connecting rod assembly (7) at both ends of the mold core (4); Step S2: Clamp the mold core (4) onto the winding machine using the connecting rod assembly (7); Step S3: Drive the mold core (4) to rotate, so that the carbon fiber bundles are wound on the molding surface of the mold core (4) to form a carbon fiber thin-walled rod preform; Step S4: Remove the mold core (4) with the carbon fiber thin-walled rod preform from the winding machine and position it in the lower mold (2); Step S5: Insert the second butterfly spring (63) and the retaining ring (62) into the positioning hole of the side slider (3); Step S6: Insert the lateral slider (3) into the positioning groove of the lower mold (2); Step S7: Install the upper mold (1) above the lower mold (2), so that the upper mold (1), the lower mold (2) and the side slider (3) surround the outside of the mold core (4) with the carbon fiber thin-walled rod preform; Step S8: Tighten the second butterfly spring assembly (6) so that the second butterfly spring (63) pushes the lateral slider (3) toward the mold core (4) and tighten the first butterfly spring assembly (5) so that the first butterfly spring (53) applies elastic pressure toward the lower mold (2) to the upper mold (1) to flexibly pre-tighten the carbon fiber thin-walled rod preform in the left-right and up-down directions respectively; Step S9: Place the mold assembly, after mold closing and flexible pre-tightening, into an autoclave for high-temperature curing.

10. The method for forming carbon fiber thin-walled rods according to claim 9, characterized in that, In step S1, the connecting rod (71) and the mold core (4) have a single-sided assembly gap of 0.15mm at the surface mating position, and the connecting rod internal hexagonal screw (72) and the corresponding positioning hole have a single-sided assembly gap of 0.05mm. In step S5, the positioning hole of the lateral slider (3) and the second butterfly spring (63) have a single-sided assembly gap of 0.25mm, and the positioning hole and the retaining ring (62) have a single-sided assembly gap of 0.1mm. In step S6, there is a sliding gap of 0.2mm between the upper plane of the side slider (3) and the corresponding contact surface of the upper mold (1), and there is a pre-tightening gap of 2mm between the side slider (3) and the inner wall of the positioning groove of the lower mold (2). In step S7, after the upper mold (1) and the lower mold (2) are closed, the corresponding cavity position has a molding gap of 0.05mm on one side; In step S8, the compression of the first butterfly spring (53) and the second butterfly spring (63) is controlled to be 80% of the maximum deformation of the corresponding butterfly spring.

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