Carbon fiber composite transmission shaft and forming die and forming method thereof

Abstract

The invention discloses a carbon fiber transmission shaft and a forming mold and a forming method thereof, and relates to the field of carbon fiber composite materials. The carbon fiber transmission shaft comprises a transmission shaft body and a shaft head. The transmission shaft body is made of a carbon fiber composite material and is tubular, and shaft heads are arranged in cavities at two ends of the transmission shaft body; the shaft head is made of metal or alloy and is tubular; the shaft head and the transmission shaft body are installed in an inverted fit mode. And the shaft head and the transmission shaft body are co-cured integrally formed parts. The invention further discloses a forming die and a forming method, reverse buckling type connection and co-curing integrated forming of the transmission shaft body and the shaft head can be achieved on the basis of the forming die and the forming method, and the defects caused by the fact that in the prior art, a carbon fiber composite transmission shaft cannot be wound away after connection and after connection are overcome. The connection strength of the carbon fiber composite transmission shaft is improved, the dynamic balance of the transmission shaft is optimized, and the production efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber composite materials, and specifically relates to a carbon fiber composite drive shaft and its preparation method. Background Technology

[0002] Lightweighting is a major trend in the automotive and aerospace industries, and an important means of achieving energy conservation and emission reduction. For example, in automobiles, lightweighting can reduce fuel consumption or increase driving range. Data shows that a 15% reduction in aircraft weight can shorten takeoff distance by 15%, increase range by 20%, and increase payload by 30%. Furthermore, lightweighting can improve handling and comfort. The high specific strength, fatigue resistance, and corrosion resistance of carbon fiber composites have led to their widespread application in structural design in automobiles and aerospace.

[0003] The driveshaft system is one of the heaviest and most critical components in mechanical equipment, and its load-bearing capacity and dynamic mechanical properties directly affect the safety and stability of the entire machine. Currently, in addition to traditional metal driveshafts, the industry has begun research and development of carbon fiber driveshafts. Current research and development of carbon fiber driveshafts primarily involves first preparing a tubular or cylindrical driveshaft body through wet winding, prepreg winding, and pultrusion molding. This tubular or cylindrical driveshaft body is then connected to metal ends. Therefore, all driveshaft bodies produced by any molding method inevitably involve the core issue of "post-connection." The current post-connection methods and their shortcomings are detailed below: (1) Bonding: The metal shaft head is inserted or fitted onto both ends of the carbon fiber drive shaft body and bonded with high-strength structural adhesive. This method will cause the problem of interface stress concentration: Since the adhesive layer is a significant area of ​​abrupt change in mechanical properties, when transmitting torque, the stress will be concentrated at the edge of the bonding area, which is very easy to cause the adhesive layer to crack or the carbon fiber drive shaft body to delaminate. (2) Press fitting: The metal shaft head is pressed into the carbon fiber drive shaft body (inside the carbon fiber tube) with an interference fit. On the one hand, this method has extremely strict tolerance requirements. If the tolerance is too large, the connection strength will be insufficient. If the tolerance is too small, the metal shaft head will not be pressed into the carbon fiber tube. On the other hand, due to the low interlaminar shear strength of carbon fiber composite materials, the huge radial force during the press fitting process can easily cause the ends of the carbon fiber tube to be crushed, delaminated, or the internal fibers to be damaged. (3) Adhesive bonding + keyway / spline: that is, keyways or splines are machined in the metal shaft head and the inner hole of the carbon fiber tube, and then glue is applied to connect them; this method will cut the continuous fiber bearing the core load when machining the keyway or spline, causing serious stress concentration points, which greatly sacrifices the integrity of the structure and fatigue life. (4) Adhesive bonding + mechanical fastening: that is, on the basis of adhesive bonding, radial riveting or screw connection is used; this method will also cut off the fiber continuity during the hole processing, introducing new stress concentration points.

[0004] In addition to the aforementioned drawbacks, all of the above connection methods suffer from long process flows and low production efficiency.

[0005] Therefore, the current structural design and connection methods of carbon fiber drive shafts are not conducive to the utilization of the mechanical properties of carbon fiber composite materials. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to provide a carbon fiber composite drive shaft and its preparation method, so as to solve the connection reliability problem of existing carbon fiber composite drive shafts, improve the overall mechanical properties and service life, and improve production efficiency.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A carbon fiber composite drive shaft includes a drive shaft body and shaft heads disposed at both ends of the drive shaft body; the drive shaft body is made of carbon fiber composite material and is tubular; the shaft heads are made of metal or alloy, are tubular, and are internally connected to the cavities at both ends of the drive shaft body; the shaft heads are installed in an inverted fit with the drive shaft body; the shaft heads and the drive shaft body are co-cured integrally molded parts.

[0008] The drive shaft body includes a middle section and shaft head connecting sections at both ends; the outer and inner diameters of the middle section are constant; the outer and inner diameters of the shaft head connecting sections gradually decrease from the end closer to the middle section to the end farther from the middle section; the shaft head includes a first shaft head connecting section and a second shaft head connecting section; the first shaft head connecting section is fitted to the shaft head connecting section, and its outer diameter gradually increases from the end closer to the second shaft head connecting section to the end farther from the second shaft head connecting section, adapting to the inner diameter of the shaft head connecting section, so as to achieve a tight fit between the outer surface of the first shaft head connecting section and the inner wall of the shaft head connecting section; the inner and outer diameters of the second shaft head connecting section are constant; the inner diameters of the first shaft head connecting section and the second shaft head connecting section are equal.

[0009] In another embodiment, the outer surface of the first connecting segment of the shaft head is provided with anchoring protrusions.

[0010] In another embodiment, an R-angle transition zone is provided between the middle section of the drive shaft body and the shaft head connection section.

[0011] In another embodiment, the second connecting section of the shaft head is provided with a connecting structure, the form of which depends primarily on the structure of the mating components.

[0012] In another embodiment, a first slot is provided axially on the inner wall of the shaft head.

[0013] In another embodiment, a locking nut is provided on the shaft head near the shaft head connecting section.

[0014] In another embodiment, the molding die for the aforementioned carbon fiber composite drive shaft includes: a bushing and a mandrel respectively disposed in the cavities at both ends of the bushing; the mandrel includes a first connecting section and a second connecting section; the first connecting section is disposed in the cavity at the end of the bushing, and a shaft head is sleeved on the second connecting section; the mandrel is fixed relative to the bushing, and the shaft head is fixed relative to the mandrel; the outer surface of the bushing and the outer surface of the shaft head near the bushing form a winding molding surface of the drive shaft body; the bushing is composed of a plurality of bushing units joined together in a ring; each bushing unit, with the parting surfaces on both sides as a reference, has an outer arc chord length and an inner arc chord length that are both smaller than the inner diameter of the shaft head of the carbon fiber composite drive shaft, and at least one bushing unit has an outer arc chord length that is less than or equal to the inner arc chord length.

[0015] In another embodiment, a keyway is provided on the first connecting section of the mandrel, and splines that mate with the keyway are provided on the inner walls of both ends of the bushing unit, so that the bushing unit and the mandrel can be snapped together and relatively fixed; a second slot is provided on the outer wall of the second connecting section of the mandrel along the axial direction, which mates with the first slot on the inner wall of the shaft head to form a pin hole for installing a pin, thereby achieving relative fixation between the shaft head and the mandrel.

[0016] In another embodiment, a demolding structure is provided on the end face of the second connecting section of the mandrel, which can be a flange, keyway, thread, etc.

[0017] A method for molding a carbon fiber drive shaft includes using the above-mentioned molding die, specifically comprising the following steps: S1. Connecting and assembling the molding die assembly, including: first connecting and assembling the mandrel and the bushing, then fitting the shaft head onto the second connecting section on the mandrel, and ensuring that the mandrel is fixed relative to the bushing and the shaft head is fixed relative to the mandrel; S2. The blank of the winding drive shaft body: The carbon fiber composite material layer is wound on the winding molding surface of the drive shaft body of the mold assembly according to the tube wall size of the carbon fiber drive shaft body. S3. Heat curing: Transfer the mold assembly with the carbon fiber composite material layer wound onto a heating device for heat curing. S4. Demolding: After the cured mold assembly has cooled, first remove the cylindrical pin between the mandrel and the shaft head, and then pull out the mandrels at both ends respectively; after the mandrels at both ends are pulled out, the bushing loses the support of the mandrel, and the bushing units can be taken out one by one from the cavity of the carbon fiber shaft body.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The metal shaft head and the carbon fiber drive shaft body are connected by an inverted snap and integrally formed, which can ensure the connection strength. The shaft head and the drive shaft body are in surface contact, which can prevent stress concentration. The shaft head and the drive shaft body are integrally cured and formed. During the curing process, the resin of the carbon fiber composite material layer forms a strong mechanical interlock and chemical bond with the metal shaft head. The interface strength is much higher than that of the later adhesive bonding. (2) There are no processes such as post-processing such as drilling and pressing that damage the fiber properties, thus maintaining the fiber continuity of the drive shaft body and maximizing the fiber properties, which greatly improves the torsional strength and fatigue life of the connection. (4) Simplify the production process and improve production efficiency: The traditional discrete processes such as "fiber tube forming → curing → machining → surface treatment → gluing / assembly → secondary curing" are integrated into three core steps: "integrated winding → curing → demolding". This eliminates the most time-consuming and difficult-to-automate post-processing and assembly links, and greatly shortens the production cycle. (5) Optimized dynamic balance: Integrated molding reduces assembly errors and improves initial dynamic balance performance; (6) The transmission shaft body and the shaft head are bonded with resin and the tail end is designed with an inverted buckle and locked with a locking nut to form a double insurance, which improves the safety factor of the transmission shaft. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a carbon fiber composite drive shaft structure. Figure 2 This is a partial enlarged view of a carbon fiber composite drive shaft; Figure 3 This is a schematic diagram of the shaft head structure; Figure 4 This is a schematic diagram of the carbon fiber driveshaft assembly. Figure 5 This is a partial enlarged view of the carbon fiber driveshaft assembly; Figure 6 This is a schematic diagram of the molding die structure; Figure 7 This is a schematic diagram of an exploded mold. Figure 8 This is a schematic diagram of the cross-section of the forming mold; Figure 9 This is a schematic diagram of the first bushing unit structure; Figure 10 This is a schematic diagram of the second bushing unit structure; Figure 11 This is a schematic diagram of the mandrel structure; Figure 12 A schematic diagram of the structure after the carbon fiber composite material layer is wrapped around the molding die; Figure 13 This is a magnified view of a portion of the mold after the carbon fiber composite material layer has been wound around it. Explanation of reference numerals in the attached drawings: 1-Drive shaft body; 11-Shaft head connecting section; 12-Intermediate section; 13-Rounded corner transition area; 2-Shaft head; 21-Shaft head first connecting section; 211-Anchoring protrusion; 22-Shaft head second connecting section; 23-First slot; 3-Universal joint; 4-Locking nut; 5-Mandrel; 51-Mandrel first connecting section; 511-Keyway; 52-Mandrel second connecting section; 521-Second slot; 522-Internal threaded hole; 6-Shaft sleeve; 61-First shaft sleeve unit; 62-Second shaft sleeve unit; 63-Spline. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. The following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0021] In the description of this invention, it should be noted that the terms "upper," "lower," "front," "rear," "left," "right," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing this invention 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, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0022] In the description of this invention, it should also be noted that, unless otherwise explicitly specified or limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0023] See appendix Figure 1 and 2A carbon fiber composite drive shaft includes a drive shaft body 1 and shaft heads 2 disposed at both ends of the drive shaft body 1. The drive shaft body 1 is made of carbon fiber composite material and is tubular. The shaft heads 2 are made of metal or alloy, are tubular, and are internally connected to the cavities at both ends of the drive shaft body 1. The shaft heads 2 are installed in an inverted fit with the drive shaft body 1. The shaft heads 2 and the drive shaft body 1 are co-cured integrally molded parts, that is, the shaft heads 2 are pre-embedded or connected in the drive shaft body blank during the molding of the drive shaft body 1, and then co-cured integrally with the drive shaft body blank to form a carbon fiber composite drive shaft. Because the shaft heads 2 are connected and fixed to the carbon fiber drive shaft body 1 by an inverted fit, the shaft heads 2 are tightly confined in the cavities at both ends of the drive shaft body 1 and are difficult to remove. Compared with the connection structure in the prior art, this inverted fit installation can effectively ensure the connection effectiveness of the carbon fiber composite drive shaft. The shaft head 2 and the drive shaft body 1 are co-cured and integrally formed, avoiding the defects caused by the "post-connection" method in the prior art, such as: insufficient strength due to the destruction of fiber continuity by drilling; insufficient strength and poor durability of the connection due to adhesive bonding; and crushing due to radial pressure during the press-fitting process.

[0024] See Figure 1 , Figure 2 and Figure 3 The drive shaft body 1 includes a middle section 12 and shaft head connecting sections 11 at both ends. The outer and inner diameters of the middle section 12 are constant, while the outer and inner diameters of the shaft head connecting sections 11 gradually decrease from the end closer to the middle section 12 to the end farther away from the middle section 12. The shaft head 2 includes a first shaft head connecting section 21 and a second shaft head connecting section 22. The first shaft head connecting section 21 is fitted to the shaft head connecting section 11, and its outer diameter gradually increases from the end closer to the second shaft head connecting section 22 to the end farther away from the second shaft head connecting section 22, adapting to the change in the inner diameter of the shaft head connecting section 11, thereby achieving a tight fit between the outer surface of the first shaft head connecting section 21 and the inner wall of the shaft head connecting section 11. The outer and inner diameters of the second shaft head connecting section 22 are constant, and the inner diameters of the first shaft head connecting section 21 and the second shaft head connecting section 22 are equal. The connection between the shaft head 2 and the transmission shaft body 1 is a surface contact, forming a strong mechanical interlock and chemical bond. The interface strength is much higher than that of traditional post-adhesive bonding, and there is no stress concentration problem.

[0025] See Figure 3 The surface of the first connecting section 21 of the shaft head is provided with anchoring protrusions 211, which can ensure the locking of the shaft head 2 and the transmission shaft body 1 and prevent slippage and rotation.

[0026] See Figure 2 A rounded transition area 13 is provided between the shaft head connecting section 11 and the middle section 12 of the drive shaft body 1 to prevent stress concentration in this area.

[0027] The second connecting section 22 of the shaft head serves as a structure for connecting with other components. It can be designed according to the structural form of the mating component, such as featuring threads, flanges, splines, end teeth, or ball cages. In this embodiment, the outer surface of the second connecting section 22 of the shaft head is threaded, thereby connecting with the mating component via threads.

[0028] See Figure 3 The inner wall of the shaft head is also provided with a first slot 23 along the axial direction.

[0029] Applications of carbon fiber composite drive shafts Figure 4 and Figure 5 A carbon fiber drive shaft assembly is shown, including the aforementioned carbon fiber composite drive shaft and a universal joint 3 threadedly connected to the second connecting section 22 of the shaft head; it also includes a locking nut 4 disposed between the universal joint 3 and the connecting section 11 of the shaft head.

[0030] See Figure 6 and Figure 7 A molding die for a carbon fiber drive shaft includes a bushing 6 and a mandrel 5 disposed in cavities at both ends of the bushing 6. The mandrel 5 includes a first connecting section 51 and a second connecting section 52. The first connecting section 51 is disposed in the cavity at one end of the bushing 6, and a shaft head 2 is sleeved on the second connecting section 52. The mandrel 5 is fixed relative to the bushing 6, and the shaft head 2 is fixed relative to the mandrel 5. The outer surface of the bushing 6 and the outer surface of the shaft head 2 near the end of the bushing 6 form the winding molding surface of the drive shaft body 1. The bushing 6 is composed of several bushing units joined together in a ring. For each bushing unit, based on the parting surfaces on both sides, the chord length of its outer arc and the chord length of its inner arc are both less than the inner diameter of the shaft head of the carbon fiber composite drive shaft, and at least one bushing unit has an outer arc chord length less than or equal to the inner arc chord length.

[0031] The bushing 6 includes at least two specifications of bushing units. The types and quantities of bushing units of each specification can be flexibly designed and combined. Considering the manufacturing cost and difficulty of the mold, as well as the convenience of mold assembly, the types and quantities of bushing units are usually designed to be as few as possible. In addition, since this mold is subsequently used for winding molding, the stability during circumferential rotation of the mold must be considered. Bushing units of different specifications should be arranged alternately and symmetrically. See Appendix Figures 8-11The diagram shows that the bushing 6 comprises two first bushing units 61 and two second bushing units 62, which are annularly spaced and spliced ​​together. Taking the parting surfaces on both sides of the first bushing unit 61 as a reference, the chord length L1 corresponding to its outer arc and the chord length L2 corresponding to its inner arc are both less than the inner diameter of the shaft head of the carbon fiber composite drive shaft, and the chord length L1 corresponding to its outer arc is less than or equal to the chord length L2 corresponding to its inner arc. Similarly, taking the parting surfaces on both sides of the second bushing unit 62 as a reference, the chord length L3 corresponding to its outer arc and the chord length L4 corresponding to its inner arc are both less than the inner diameter of the shaft head of the carbon fiber composite drive shaft. The sharp corners formed by the parting surfaces and the inner arcs on both sides of the first bushing unit 61 are chamfered.

[0032] See Figures 9-11 The first connecting section 51 of the mandrel is provided with a keyway 511, and the inner walls of both ends of the first bushing unit 61 and the second bushing unit 62 are provided with splines 63 that cooperate with the keyway 511, so that the mandrel 5 and the bushing 6 are engaged, limiting the maximum engagement length between the mandrel 5 and the bushing 6 and limiting the circumferential rotation of the mandrel 5 within the bushing 6, thereby achieving relative fixation; the second connecting section 52 of the mandrel is provided with a second slot 521, which cooperates with the first slot 23 on the inner wall of the shaft head 2 to form a pin hole for installing a pin, thereby achieving relative fixation between the shaft head 2 and the mandrel 5 and preventing the shaft head 2 from rotating relative to the mandrel 5.

[0033] Furthermore, the diameter of the mandrel 5 is smaller than the inner diameter of the bushing 6 and the inner diameter of the shaft head 2, thereby reducing the contact area between the mandrel 5 and the bushing 6 and the shaft head 2, which facilitates demolding.

[0034] A demolding structure is provided on the end face of the second connecting section 52 of the mandrel. Specifically, in this embodiment, the demolding structure is an internal threaded hole 522, which is axially arranged from the end face. This internal threaded hole 522 can be threadedly connected to an external rotary demolding machine for rotary demolding, thereby removing the mandrel from the bushing. The demolding structure can also be a keyway, flange, etc.; or the length of the mandrel 5 can be designed to be long enough so that the second connecting section 52 of the mandrel extends from the shaft head 2, and an external thread is provided on the extension section, thereby connecting to an external demolding machine for rotary demolding.

[0035] A method for manufacturing a carbon fiber drive shaft includes using the above-mentioned molding die, comprising the following steps: S1. Connecting and assembling the molding die assembly, including: connecting and assembling the mandrel 5 and the bushing 6 to fix the mandrel and the bushing relative to each other; then fitting the shaft head 2 onto the second connecting section 52 of the mandrel to fix the shaft head relative to the mandrel. S2. The preform of the drive shaft body includes: winding a carbon fiber composite material layer in the winding molding area of ​​the drive shaft body of the mold assembly to form the preform of the drive shaft body. S3. Heat curing: Transfer the mold assembly and the entire drive shaft body blank to a heating device for heat curing; S4. Demolding: After the mold assembly has cooled, release the relative fixation between the mandrel and the shaft head, and then use a demolding machine to remove the mandrels at both ends; after the mandrels at both ends are removed, the bushing loses the support of the mandrel, and after the first bushing unit is removed, the remaining bushing units can be removed in sequence.

[0036] In step S1, the relative fixation of the mandrel and the bushing is achieved by the keyway on the mandrel and the spline on the bushing. The relative fixation of the shaft head and the mandrel is achieved by installing a pin in the pin hole formed by the first slot and the second slot. A locking nut is also installed on the shaft head as a clamping end when the molding mold rotates and is demolded, so as to avoid directly clamping the drive shaft and causing deformation or damage to the drive shaft.

[0037] In step S2, carbon fiber prepreg can be wound or continuous carbon fiber can be wound using a wet method. When wound using a wet method, the winding angle includes ±15°, ±45°, and ±89°.

[0038] In step S4, the temperature difference demolding method is used to cool the mold. After the mold cools down, it will shrink and create a gap between the mold and the product, thereby reducing the demolding force and facilitating demolding.

[0039] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions 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 carbon fiber composite material drive shaft, comprising a drive shaft body and shaft ends disposed at both ends of the drive shaft body, characterized in that, The drive shaft body is made of carbon fiber composite material and is tubular; the shaft head is made of metal or alloy, is tubular, and is connected to the cavities at both ends of the drive shaft body; the shaft head and the drive shaft body are installed with an inverted fit; the shaft head and the drive shaft body are co-cured integral molded parts.

2. The carbon fiber composite material drive shaft according to claim 1, characterized in that, The drive shaft body includes a middle section and shaft head connecting sections at both ends; the outer and inner diameters of the middle section are constant; the outer and inner diameters of the shaft head connecting sections gradually decrease from the end closer to the middle section to the end farther from the middle section; the shaft head includes a first shaft head connecting section and a second shaft head connecting section; the first shaft head connecting section is fitted to the shaft head connecting section, and its outer diameter gradually increases from the end closer to the second shaft head connecting section to the end farther from the second shaft head connecting section, adapting to the inner diameter of the shaft head connecting section, so as to achieve a tight fit between the outer surface of the first shaft head connecting section and the inner wall of the shaft head connecting section; the outer and inner diameters of the second shaft head connecting section are constant; the inner diameters of the first shaft head connecting section and the second shaft head connecting section are equal.

3. The carbon fiber composite material drive shaft according to claim 2, characterized in that, Anchoring protrusions are provided on the first connecting section of the shaft head.

4. A carbon fiber composite material drive shaft according to claim 2, characterized in that, An R-angle transition zone is provided between the middle section of the drive shaft body and the shaft head connection section.

5. A carbon fiber composite material drive shaft according to claim 2, characterized in that, A connecting structure is provided on the second connecting section of the shaft head.

6. A carbon fiber composite material drive shaft according to claim 1, characterized in that, The inner wall of the shaft head is provided with a first slot along the axial direction.

7. A molding die for a carbon fiber composite drive shaft, characterized in that, A method for molding a carbon fiber composite drive shaft according to any one of claims 1-6 includes: a bushing and a mandrel respectively disposed in cavities at two ends of the bushing; the mandrel includes a first connecting section and a second connecting section; the first connecting section is disposed in a cavity at the end of the bushing, and a shaft head is sleeved on the second connecting section; the mandrel is fixed relative to the bushing, and the shaft head is fixed relative to the mandrel; the outer surface of the bushing and the outer surface of the shaft head near the bushing form a winding molding surface of the drive shaft body; the bushing is composed of a plurality of bushing units joined together in a ring, wherein for each bushing unit, based on the parting surfaces on both sides, the chord length corresponding to the outer arc and the chord length corresponding to the inner arc are both smaller than the inner diameter of the shaft head of the carbon fiber composite drive shaft, and at least one bushing unit has an outer arc chord length less than or equal to the inner arc chord length.

8. The molding die for a carbon fiber composite drive shaft according to claim 7, characterized in that, The first connecting section of the mandrel is provided with a keyway, and the inner walls at both ends of the bushing unit are provided with splines that cooperate with the keyway, so that the bushing unit and the mandrel can be snapped together and relatively fixed; the outer wall of the second connecting section of the mandrel is provided with a second slot along the axial direction, which cooperates with the first slot on the inner wall of the shaft head to form a pin hole for installing a pin, thereby achieving relative fixation between the shaft head and the mandrel.

9. The molding die for a carbon fiber composite drive shaft according to claim 7, characterized in that, A demolding structure is provided on the end face of the second connecting section of the mandrel.

10. A method for molding a carbon fiber composite drive shaft, characterized in that, Using the molding die according to any one of claims 7 to 9, the specific steps include: S1. Connecting and assembling the molding die assembly, including: first connecting and assembling the mandrel and the bushing, then fitting the shaft head onto the second connecting section of the mandrel, and ensuring that the mandrel is fixed relative to the bushing and the shaft head is fixed relative to the mandrel; S2. The blank of the winding drive shaft body: The carbon fiber composite material layer is wound on the winding molding surface of the drive shaft body of the mold assembly according to the tube wall size of the carbon fiber drive shaft body. S3. Heating and curing: After the blank of the drive shaft body is wound, it is transferred as a whole with the mold assembly to the heating equipment for heating and curing. S4. Demolding: After curing and cooling, first remove the mandrels at both ends; after the mandrels at both ends are removed, the bushings lose the support of the mandrels, and the bushing units can be taken out one by one from the cavity of the carbon fiber shaft body to obtain the carbon fiber composite material drive shaft.

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