Manufacturing method of prefabricated body with uniform microstructure and prefabricated body

Abstract

The invention relates to a manufacturing method of a prefabricated body with a uniform microstructure and the prefabricated body. The manufacturing method comprises the following steps: cutting a carbon fiber bundle into a chopped tow with a set length; scattering the carbon fibers of the chopped tows by a cotton fluffer to form chopped carbon fiber clusters which are disordered in orientation and fluffy and mainly comprise single fibers; uniformly stuffing the chopped fiber agglomerates from the opening part of the cavity of the shaping mold, and pressing the chopped fiber agglomerates into a prefabricated body with a set axial length by using a pressing head; compared with a prefabricated body obtained by needling, weaving and sewing traditional felts, lines and belts, the prefabricated body is uniform in microstructure and consistent in anisotropic performance, is particularly suitable for being used as a part with a variable stress direction, can replace high-strength metal to manufacture gear parts, and enables the weight of the parts to be lighter.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite materials, and particularly relates to a manufacturing method and a preform of a preform with a uniform mesostructure. Background Art

[0002] In order to reduce the weight of mechanical equipment, especially for the joint reducers of humanoid robots, people have unanimously turned their attention to carbon fiber reinforced composite materials. However, due to the significant non-uniformity and anisotropy of traditional composite materials at the mesoscopic scale of millimeters, its application in small and micro precision mechanical parts is limited. Although the diameter of carbon fiber is only 5-7 μm, in order to meet different requirements and production efficiency, usually carbon fiber tows are assembled by thousands to tens of thousands of carbon fibers. In theory, single carbon fibers can also be provided, but they are not used in actual production because of their extremely high cost and difficult operation. Since the actual cross-sectional area of carbon fiber tows is relatively large, usually greater than 0.5 mm 2 , resulting in the obvious non-uniformity of the composite material reinforced with carbon fiber at the mesoscopic scale visible to the naked eye. Therefore, composite materials with excellent macroscopic properties are not suitable when used for fine parts with small sizes or parts with high requirements for surface properties. For example, carbon / carbon throat lining materials made by needle punching, piercing soft braiding or hard-soft mixed braiding with shaft rods are very excellent for medium and long-range missiles, but are not suitable for the solid rocket engines of tactical weapons with very small throat diameters due to their rough structures. Therefore, the throat lining materials of small solid rocket engines with a throat diameter of less than 15 mm are mainly made of high-temperature resistant metals and tungsten infiltrated copper sweating materials. In addition, for small module gears without high-temperature resistance requirements, it is not ideal to use resin-based composite materials to make gears. Even with lubrication, the serious non-uniformity at the mesoscopic scale will still exacerbate the tooth surface wear. In addition, the serious anisotropy at the mesoscopic scale also makes the composite material perform poorly at the tooth part where the force direction changes complexly. Although carbon fiber felt is very close to isotropic, the carbon fibers used in the existing carbon fiber felt manufacturing technology are all straight long filaments. After unidirectional compression, the anisotropy is obvious and because the short-cut fibers are straight, the composite material made is prone to fiber shedding in some directions during use, resulting in high wear rate or uneven ablation. Summary of the Invention

[0003] The purpose of the present invention is to provide a manufacturing method and a preform of a preform with a uniform mesostructure to solve the above problems.

[0004] To achieve the above purpose, the present invention adopts the following technical solutions: A manufacturing method of a preform with a uniform mesostructure, comprising the following steps: Cut the carbon fiber tow into short cut tows with a set length; Use a carding machine to disperse the short-cut carbon fiber bundles into a short-cut carbon fiber mass that is disordered in orientation and fluffy, mainly composed of single fibers. Then evenly insert the short-cut fiber mass into the mouth of the shaping die cavity, and use a press head to press the short-cut fiber mass into a preform with a set axial length.

[0005] Further, the cutting of the carbon fiber bundle into short-cut fiber bundles of a set length includes: First, use a knitting machine to weave the pre-oxidized fiber into a knitted fabric, then carbonize the pre-oxidized fiber knitted fabric to convert it into a carbon fiber knitted fabric, and then remove the yarn on the knitted fabric and cut it into three-dimensional curved short-cut fibers of a set straightening length.

[0006] Further, the shaping die is evacuated by a vacuum pump. Start the vacuum pump to pump air, and continuously and evenly put the disordered and fluffy short-cut fiber mass at the mouth of the cavity of the tubular part die until the short-cut fibers sucked into the cavity reach the set height. Then cover a plastic film on the mouth of the cavity of the shaping die, and use atmospheric pressure to compact the felt tube. A preform is obtained based on the manufacturing method of the above-mentioned meso-structurally uniform preform.

[0007] Compared with the prior art, the present invention has the following technical effects: In the present invention, numerous bent carbon fibers that are dispersed into single carbon fibers are stacked to form a felt block or felt tube with a relatively high carbon fiber volume content, which is used for the preform of a composite material with relatively high requirements for meso-uniformity. When axially compressed, the circumferential and radial strengths of the finished product after impregnation and curing are slightly higher than the axial strength, and it is suitable to be used as the preform of composite material gears and spline parts; when radially compressed, the circumferential and axial strengths of the finished product after impregnation and curing are slightly higher than the radial strength, and it is suitable to be used as the preform of composite material pressure-bearing pipes, torque-transmitting pipe fittings and throat liner parts. The preform of the present invention has a more uniform meso-structure and consistent anisotropic properties compared with the preforms obtained by needling, weaving and stitching of traditional felts, wires and tapes. It is particularly suitable for use as parts with changing stress directions, and can replace high-strength metals to make gear parts and make the parts lighter. Using the preform of the present invention as the reinforcing material for the carbon / carbon throat liner of a solid rocket engine, the obtained carbon / carbon throat liner has a uniform meso-structure, the carbon fibers are not easily detached during the ablation process, the ablation surface is flat and smooth, and the ablation rate is relatively low. It can replace expensive tungsten infiltrated copper and other high-temperature resistant metal materials and be used for the throat liner of small throat diameter tactical missile rocket engines. Description of the Drawings

[0008] Figure 1 It is a flow chart of the present invention. Detailed Embodiments

[0009] The present invention will be further described below with reference to the accompanying drawings: A preform with a uniform microstructure is manufactured by first cutting carbon fiber bundles into short cut fiber bundles of a certain length, then using a carding machine to disperse the carbon fibers in the short cut fiber bundles to form a short cut carbon fiber mass that is randomly oriented and fluffy and mainly consists of single fibers. Next, the disordered and fluffy short cut fiber mass is evenly stuffed into the mouth of the mold cavity, and then a pressing head is used to press the fibers into a preform with a certain axial length.

[0010] The short cut carbon fibers are three-dimensionally curved. The manufacturing method is to first use a knitting machine to knit the pre-oxidized fibers into a knitted fabric, then carbonize the pre-oxidized fiber knitted fabric to convert it into a carbon fiber knitted fabric, and then cut the yarns on the knitted fabric into a certain length.

[0011] A set of air extraction holes is provided at the blind end of the cavity of the shaping mold. A layer of micron-level filter cloth is laid on the air extraction holes. The outside of the blind section is connected to a vacuum pump through a pipe. The vacuum pump is started to extract air, and then the disordered and fluffy short cut fiber mass is continuously and evenly placed at the mouth of the cavity of the tubular part mold until the short cut fibers sucked into the cavity reach a certain height. Then, a plastic film is covered on the mouth of the cavity of the tubular part mold, and the felt tube is compacted by using atmospheric pressure.

[0012] Before compacting the felt tube by using atmospheric pressure, an impregnating tube is buried inside the plastic film covered at the mouth of the cavity of the mold, and vacuum infusion impregnation of the tubular carbon felt in the mold cavity is carried out. After heating and curing, the mold is removed to obtain a near-isotropic composite blank.

[0013] Example 1 Please refer to Figure 1 , a preform with a uniform microstructure for a carbon fiber composite gear. The manufacturing method is to first cut the T700-48k carbon fiber bundle into short cut fiber bundles 15 mm long, then use a carding machine to disperse the carbon fibers in the short cut fiber bundles to form a short cut carbon fiber mass that is randomly oriented and fluffy and mainly consists of single fibers. Next, the disordered and fluffy short cut fiber mass is evenly stacked and laid at the mouth of the cavity of a tubular or cylindrical cavity mold, and a pressing head is used to press the fibers into a preform with a certain axial length. Then, vacuum infusion impregnation of the thermosetting resin is carried out on the tubular preform, and it is placed in an autoclave for heating and curing, and the gear blank of the carbon fiber composite is made. The composite material obtained by this method has a uniform microstructure, and the mechanical properties in all directions have small differences. The tooth part of the gear made can better resist the change of the force direction. Using curved short cut carbon fibers can improve the tensile strength of the material and effectively prevent the shedding of surface fibers.

[0014] Example 2 Please refer to Figure 1, A preform with a uniform microstructure for a carbon / carbon throat liner. The manufacturing method is as follows: First, 6k PAN-based pre-oxidized fibers are knitted into 1×1 rib knitted fabric using a knitting machine, and then placed in a carbonization furnace for carbonization in an inert gas atmosphere, converting the pre-oxidized fiber knitted fabric into a carbon fiber knitted fabric. Then, the yarns on the knitted fabric are removed, wound up, and cut into short cut fibers with a straightening length of 5-10 mm. The short cut fiber bundles are dispersed by a carding machine to form a fluffy short cut carbon fiber mass mainly composed of single fibers. The short cut fiber mass is evenly stacked and laid in the cavity of a thick plate-shaped mold cavity, and the fibers are pressed into a preform of a certain thickness with a pressing head. The preform is impregnated with phenolic resin by vacuum infusion and then placed in an autoclave for heating and curing. The cured phenolic resin-based carbon fiber composite is placed in a carbonization furnace for carbonization at 700 °C, peeled after being taken out of the furnace, and repeatedly vacuum impregnated with ketone resin or pitch and carbonized until the density of the manufactured carbon / carbon composite meets the design requirements. Finally, a high-temperature graphitization treatment is carried out once to make as much as possible the carbon fibers in the final carbon / carbon material and the free carbon generated by the pyrolysis of the precursor resin transform into a graphite structure and produce more bonding between the two, so that the final obtained carbon / carbon throat liner material has better mechanical properties and stronger erosion resistance. In this example, unidirectional compression is used for the short cut fiber mass. Compression will change the orientation degree of the fibers to a certain extent, but since the fluffy and bent fibers in the compressed preform will still produce a large amount of interlocking and entanglement between the fibers, the anisotropy of each direction is much smaller than that of ordinary short and straight short cut fibers, but its transverse tensile strength will be slightly higher than the longitudinal direction (compression direction). For most throat liner preforms, due to the stress characteristics of the throat liner during operation, it is actually very beneficial for the preform to have moderate anisotropy. For composite materials with higher requirements for material isotropy, spherical compression or three-axis step-by-step compression technology can be used to obtain an isotropic preform.

[0015] Example 3 Please refer to Figure 1 , A carbon fiber preform for a lightweight RV reducer internal gear ring. The forming mold consists of an outer mold and a mandrel, with one end made into a blind hole and the other end having a large opening. The outer mold is composed of multiple mold cavities assembled together. First, the split outer mold and the mandrel are assembled, and then the bent and fluffy short cut carbon fiber mass is continuously stuffed into the cavity from the mouth of the mold and tamped down and compacted with a barbed pressing head until the axial length meets the requirements. Then, the outer mold is removed, an exhaust pipe and an impregnation pipe are laid outside the carbon fiber mass and covered with a vacuum film, and impregnation is carried out by vacuum infusion and then placed in an autoclave for curing.

[0016] As described above, this is only the most typical specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. The listed data are only for describing the working principle of the present invention and do not represent necessary values. Any equivalent changes that can be easily conceived by those skilled in the art of composite material manufacturing and related fields within the technical scope disclosed by the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for manufacturing a preform having a uniform microstructure, characterized in that: The following steps are involved: cutting the carbon fiber bundle into chopped strands of a set length; The carbon fibers of the chopped strands are broken up by a cotton slinger to form a chopped carbon fiber mass with disordered orientation and fluffy and mainly composed of single fibers; Then, the chopped fiber mass is evenly stuffed into the opening of the shaping mold cavity, and then the chopped fiber mass is pressed into a preform with a set axial length by a pressing head.

2. The method for manufacturing a preform having a uniform microstructure according to claim 1, characterized in that: The method of cutting the carbon fiber bundle into chopped strands of a set length comprises: First, the preoxidized silk is woven into a knitted fabric using a knitting machine, and then the preoxidized silk knitted fabric is carbonized to be converted into a carbon fiber knitted fabric, and then the yarn on the knitted fabric is removed and cut into a set length.

3. The method for manufacturing a preform having a uniform microstructure according to claim 2, characterized in that: The chopped strands are three-dimensionally curved.

4. The method for manufacturing a preform having a uniform microstructure according to claim 2, characterized in that: The yarn on the knitted fabric is removed and wound up and then cut into short chopped yarns with a straight length of 5 to 10 mm.

5. The method for manufacturing a preform having a uniform microstructure according to claim 1, characterized in that: The shaping mold is evacuated by a vacuum pump, and the vacuum pump is turned on to draw air, and chaotic and fluffy chopped fiber clusters are continuously and evenly placed at the cavity mouth of the tubular mold until the chopped fibers sucked into the cavity reach a set height, and then a piece of plastic film is covered on the cavity mouth of the shaping mold, and the felt tube is compacted by atmospheric pressure.

6. The method for manufacturing a preform having a uniform microstructure according to claim 5, characterized in that: A group of air extraction holes are arranged at the blind end of the cavity of the shaping mold, and a layer of micron-grade filter cloth is laid on the air extraction holes.

7. The method for manufacturing a preform having a uniform microstructure according to claim 5, characterized in that: The suction hole is connected to a vacuum pump through a tube.

8. The method for manufacturing a preform having a uniform microstructure according to claim 5, characterized in that: Before the felt tube is compacted by atmospheric pressure, a glue-impregnating tube is buried in the plastic film covering the cavity opening of the mold, and the tubular carbon felt in the mold cavity is vacuum-impregnated with glue. After heating and curing, the nearly isotropic composite material blank is demoulded and taken out.

9. The method for manufacturing a preform having a uniform microstructure according to claim 6, characterized in that: The solidified composite material blank is placed in a carbonization furnace for carbonization. After being taken out of the furnace and peeled, it is repeatedly vacuum impregnated with contone resin or asphalt and carbonized until the density of the manufactured carbon / carbon composite meets the design requirements.

10. A preform, characterized in that: The method for manufacturing a preform with uniform microstructure is based on any one of claims 1 to 9.

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