A tool suitable for countersinking of aramid fiber composite materials

Abstract

The present invention belongs to the technical field of composite material processing, and discloses a tool suitable for countersinking of aramid fiber composite materials, comprising four areas, namely, a centering guide column area, a countersinking area, a mounting area, and a tool holder clamping area, from the drill bit to the drill shank. Based on the idea of ​​high-strain removal of fibers by multi-blade cutting, the cutting amount per blade is reduced, the cutting force is reduced, and staggered left-hand and right-hand micro-tooth structures are processed on adjacent main cutting edges. The micro-tooth inclination angle is set according to the tool movement relationship to enhance the constraint effect on the aramid fiber when being cut, so that the aramid fiber is subjected to the shearing effect of multi-directional cutting forces, thereby effectively cutting and removing the aramid fiber, and suppressing the generation of damage such as burrs and delamination at the countersinking entrance. Grinding the secondary cutting edge enables the tool body to have the ability to countersink and make holes, and setting a stop surface at the end of the cutting edge according to the countersinking depth to achieve fixed-depth cutting and further remove burrs, thereby improving the countersinking processing quality and accuracy, and meeting the needs of high-quality and efficient countersinking of AFRP.

Description

Technical Field

[0001] The invention belongs to the technical field of composite material processing and relates to a tool suitable for countersinking processing of aramid fiber composite materials. Background Art

[0002] Aramid fiber reinforced resin-based composites (hereinafter referred to as AFRP) have the advantages of light weight, high elongation, and good impact resistance. They have become the preferred material for high-end equipment in the fields of aerospace and armor protection. AFRP components are mainly connected and assembled by bolts and rivets. In order not to affect the aerodynamic shape of the structural aircraft, these bolts or rivets are mostly countersunk, so countersinking of AFRP has become a necessary step in its manufacturing. However, the aramid fibers in AFRP show strong toughness at a microscopic level, have obvious stacking characteristics at a macroscopic level, and the interlayer bonding strength is significantly lower than that of carbon fiber composites. As a result, the countersinking processing tools for metal or carbon fiber composites cannot be applied to AFRP. It is difficult to cut the fibers during countersinking, and various forms of damage such as burrs and delamination are easily generated, which greatly reduces the fitting accuracy and seriously limits the connection performance of AFRP components.

[0003] In order to solve the above problems, a large number of experts, scholars and enterprise technicians have conducted research and proposed a variety of tool structures. Fu Rao and others from Dalian University of Technology disclosed "A hole-making tool and design method suitable for aramid fiber composite materials", patent application number 202210836428.4. The tool has a stepped negative vertex angle structure, which can effectively cut high-toughness aramid fibers, but it is difficult to apply to countersinking. Liu Gang and others from Zhejiang University disclosed "A special tool for spiral milling countersinking of composite materials", patent application number 201210396891.8. The tool has three equally spaced spiral grooves and serrated cutting teeth on the cutting edge, but it lacks a centering structure and the cutting teeth are very likely to cause scratches on the processed surface. Wang Zhichao and others from Xi'an Aircraft Industry (Group) Co., Ltd. disclosed "A countersinking tool for aircraft aramid skins", patent application number 202022668120.2. The main cutting part of the tool is an "S"-shaped cutting edge, which can quickly cut off the aramid fiber through an extra-large tool rake angle and a matching helix angle. However, an excessively large rake angle will aggravate the degree of burrs and delamination damage and reduce the strength of the tool.

[0004] The above content provides useful reference for reducing damage during AFRP countersinking processing. However, it is still difficult to meet the stringent engineering requirements for AFRP countersinking efficiency and accuracy. Therefore, further development is urgently needed to develop a tool that can achieve high-quality and efficient AFRP countersinking. Summary of the Invention

[0005] The present invention aims to solve the problem of various damages such as burrs and delamination at the countersink entrance caused by the inability to cut aramid fibers during countersinking of aramid fiber reinforced resin-based composite materials (hereinafter referred to as AFRP). The present invention proposes a tool suitable for countersinking of aramid fiber composite materials, which can achieve high-precision and high-efficiency countersinking of AFRP. The countersink drill designed by the present invention has a multi-cutting edge structure with staggered left-hand and right-hand micro-blades and a fixed depth stop surface, which can reduce the cutting force during countersinking and effectively cut off the high-toughness aramid fibers to reduce damage at the countersink entrance, thereby achieving high-precision fixed-cutting-depth countersinking. In order to achieve complex structural processing of the countersink cutting edge position, the guide column is designed to be a detachable structure. The centering guide column cooperates with the bottom hole to improve the processing stability and the surface finish of the processed surface. Based on the concept of removing high-strain fibers through multi-edge cutting, the amount of cutting per edge is reduced, lowering cutting forces. Staggered left-hand and right-hand micro-tooth structures are machined on adjacent main cutting edges. The micro-tooth inclination angle is set according to the tool motion relationship to enhance the constraint effect on the aramid fiber during cutting. The aramid fiber is sheared by multi-directional cutting forces, effectively cutting and removing the aramid fiber, and suppressing the occurrence of burrs, delamination, and other damage at the countersink entrance. In addition, the secondary cutting edge is reground on the tool body to enable it to have the ability to countersink holes. Then, a stop surface is set at the end of the secondary cutting edge according to the countersink hole depth to achieve the function of fixed cutting depth and further remove burrs.

[0006] To achieve the above objectives, the present invention provides the following technical solutions:

[0007] A tool suitable for countersinking of aramid fiber composite materials, comprising four areas, from the drill bit to the drill shank, namely, a centering guide column area A, a countersinking area B, a mounting area C, and a tool shank clamping area D;

[0008] The centering guide column area A is a removable centering guide column 1; the removable centering guide column 1 is fixed to the countersink cutter body by screwing or by a straight shank with a pin. The diameter D1 of the removable centering guide column 1 is determined by the bottom hole diameter and is given a deviation. The front end of the removable centering guide column 1 is designed with a rounded corner R1, and the end of the removable centering guide column 1 is designed with a rounded corner R2 at the connection position with the countersinking area B.

[0009] The countersinking area B is mainly composed of four or more evenly distributed main cutting edges 2 and auxiliary cutting edges 12, and a fixed cutting depth stop surface 5; wherein, the top angle of the main cutting edge 2 is N1 = 90°-140°, and the top angle N1 needs to be adjusted according to the countersinking angle. The final hole diameter is D2, and the axial length is L1 = 0.5 (D2-D1) tan (90°-0.5N1). Staggered right-handed micro-tooth structures 14 and left-handed micro-tooth structures 15 are respectively processed on adjacent main cutting edges 2. According to the tool movement relationship, the inclination angles of the right-handed micro-tooth 14 and the left-handed micro-tooth 15 are set to β1 = 10°-45° and β2 = (-10°)-(-45°), respectively, and the micro-tooth width b = 0.1-1.2mm. The rake face 3 and the back face 4 of the tool are sharpened to form a main cutting edge rake angle γ1 = 5°-20° and a back angle α1 = 10 °-25°; grinding the auxiliary cutting edge rake face 13 and the auxiliary cutting edge first flank face 10 and the auxiliary cutting edge second flank face 11 on the tool body to form the auxiliary cutting edge 12, the countersinking depth of the auxiliary cutting edge 12 is L2, the auxiliary cutting edge rake angle γ2 = 15°-25°, the auxiliary cutting edge first clearance angle α2 = 5°-25°, and the auxiliary cutting edge second clearance angle α3 = 10°-30°; based on the experimental research, the diameter range of the delamination area is obtained, and a fixed cutting depth stop surface 5 is designed at the end of the auxiliary cutting edge first clearance face 10, the diameter of which is D3, to suppress delamination damage and realize the control of the countersinking depth to be L1+L2, and the axial length of the fixed cutting depth stop surface 5 is L3; designing the first positioning cone 6 to ensure the coaxiality of the countersinking area B and the installation area C when machining the tool, the top angle of the first positioning cone 6 is N2 = 80°-140°, which is adjusted according to actual clamping requirements;

[0010] The installation area C is mainly composed of a cutter body 7, a through hole 8 and a second positioning cone 9. The diameter of the cutter body 7 is D4. The through hole 8 is machined on the cutter body 7 to facilitate the installation and removal of the countersink. The second positioning cone 9 is designed to ensure the coaxiality of the installation area C and the tool holder clamping area D. The vertex angle of the second positioning cone 9 is N3 = 80°-140°, which can be adjusted according to actual clamping requirements.

[0011] The tool holder clamping area D is configured to have a threaded handle 16, a straight handle 17, and a tapered handle 18, and the clamping length is determined according to actual clamping requirements.

[0012] Beneficial effects of the present invention: A tool suitable for countersinking of aramid fiber composite materials is proposed. The front section of the tool is designed to be a detachable centering guide pin. By grinding the guide pin radius and the guide pin connection radius, the centering function is achieved while reducing the scratching of the guide pin on the hole wall. Based on the idea of ​​high-strain removal of fibers by multi-blade cutting, the cutting amount per blade is reduced, the cutting force is reduced, and staggered left-hand and right-hand micro-tooth structures are processed on adjacent main cutting edges. The micro-tooth inclination angle is set according to the tool movement relationship to enhance the constraint effect on the aramid fiber when being cut, so that the aramid fiber is subjected to the shearing effect of multi-directional cutting forces, and then the aramid fiber is effectively cut off and removed, and the occurrence of damage such as burrs and delamination at the countersink entrance is suppressed. Grinding the secondary cutting edge enables the tool body to have the ability to countersink and make holes, and a stop surface is set at the end of the cutting edge according to the countersinking depth to achieve fixed-depth cutting and further remove burrs, improve the countersinking processing quality and accuracy, and meet the needs of high-quality and efficient countersinking of AFRP. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The utility model relates to a tool suitable for countersinking processing of aramid fiber composite materials.

[0014] Figure 2 for Figure 1 Magnified view of the countersunk area.

[0015] Figure 3 for Figure 1 Cross-sectional view of the main and secondary cutting edges of the countersink drill.

[0016] Figure 4 for Figure 1 Top view of the countersink.

[0017] Figure 5 (a) Figure 1 Partial view of the countersink threading tool holder, Figure 5 (b) Figure 1 Partial view of the countersink drill with a straight shank. Figure 5 (c) Figure 1 Partial view of the countersink drill with a tapered shank.

[0018] In the figure: A-centering guide pin area, B-counter boring area, C-installation area, D-tool holder clamping area, E-counter boring top view; 1-removable centering guide pin, 2-main cutting edge, 3-front cutting edge, 4-flank cutting edge, 5-deep cutting stop surface, 6-first positioning cone surface, 7-tool body, 8-through hole, 9-second positioning cone surface, 10-secondary cutting edge first flank surface, 11-secondary cutting edge second flank surface, 12-secondary cutting edge, 13-secondary cutting edge front cutting edge, 14-right-hand micro-tooth, 15-left-hand micro-tooth, 16-threaded tool holder, 17 -straight shank, 18-taper shank; D1-guide pin diameter, D2-counterface diameter, D3-fixed cutting depth stop diameter, D4-cutting body diameter; L1-cutting edge axial length, L2-counterface depth, L3-fixed cutting depth stop axial length; γ1-main cutting edge rake angle, γ2-secondary cutting edge rake angle, α1-main cutting edge clearance angle, α2-secondary cutting edge first clearance angle, α3-secondary cutting edge second clearance angle, N1-cutting edge apex angle, N2-first positioning cone 6 apex angle, N3-positioning cone 8 apex angle, β1-right-hand micro-tooth inclination angle, β 2- Left-handed micro-tooth inclination angle; R1-guide post fillet, R2-guide post connection fillet; b-micro-tooth width. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, what is described is only a part of the embodiments of the present invention, rather than all the embodiments.

[0020] The figure shows a tool suitable for countersinking aramid fiber composites. This tool features a staggered six-edge structure and consists of four sections: a centering guide pin area A, a countersinking area B, a mounting area C, and a shank clamping area D. The centering guide pin structure allows for the countersink to mate with the bottom hole during machining or manual drilling. The staggered six-edge structure enhances the restraint applied to the aramid fiber during cutting. Based on the principle of multi-edge removal, this reduces the amount of cutting per edge and lowers cutting forces. Staggered left-hand and right-hand micro-teeth are machined on adjacent primary cutting edges. The micro-teeth inclination angles are set according to the tool's kinematic relationship to enhance the restraint applied to the aramid fiber during cutting. This effectively shears the aramid fiber, suppressing damage such as burrs and delamination at the countersink entrance. The secondary cutting edge is ground on the tool body to ensure cutting capability. A stop surface is then placed at the end of the cutting edge, depending on the countersinking depth, to achieve a fixed depth of cut and further remove burrs. In this embodiment, the ultimate goal is to machine a final hole with a diameter of 9.5 mm on a bottom hole with a diameter of 5 mm, and the countersinking depth is 0.5 mm.

[0021] The centering guide column area A, the detachable centering guide column 1 and the bottom hole adopt a clearance fit, and the diameter is set The rotational runout error is guaranteed to be within 10μm, the chamfer R1 = 3mm, the fillet R2 = 1mm, to reduce the scratching of the guide column on the hole wall.

[0022] The countersinking area B is composed of a main cutting edge 2, a secondary cutting edge 12 and a fixed cutting depth stop surface 5. Six evenly distributed staggered cutting edges are set to reduce the cutting amount per edge, reduce the cutting force and inhibit delamination damage. Staggered right-handed micro-tooth structures 14 and left-handed micro-tooth structures 15 are processed on adjacent main cutting edges 2. The micro-tooth inclination angles β1=45° and β2=-45° are set according to the tool movement relationship, and the micro-tooth width b=1mm to enhance the constraint effect on the aramid fiber when being cut, thereby inhibiting the generation of entrance burr damage and improving the smoothness of the countersinking surface. The cutting edge top angle N1=130°, the rake face 3 and the back face 4 of the main cutting edge are ground to form a rake angle γ1=20° and a back angle α1=25°, the final hole diameter D2=9.5mm, and the cutting edge axial length L1=0.5(D2-D1)tan(90°-0.5N1)=1.9mm. The front cutting face 13 and the back cutting faces 10 and 11 are ground on the cutter body 7 to form the secondary cutting edge 12. The countersinking depth of the secondary cutting edge 12 is L2 = 0.5mm, the front angle γ2 of the secondary cutting edge is 25°, the first back angle α2 of the secondary cutting edge is 20°, and the second back angle α3 of the secondary cutting edge is 30°, reducing friction between the tool and the countersinking surface. The fixed cutting depth stop 5 is ground at the end of the secondary cutting edge to remove the remaining burrs at the entrance. The diameter is D3 = 11mm, and the axial length of the stop is L3 = 2mm. The top angle N2 of the first positioning cone 6 is 120°. This structure can realize the positioning function of the countersink during processing, reduce the rotational runout error of the countersink, and improve the hole making accuracy.

[0023] The diameter D4 of the tool body in the installation area C is 10 mm, and it consists of a tool body 7, a through hole 8 and a second positioning cone 9. Since the countersink drill is usually used in conjunction with a drill sleeve, processing the through hole facilitates the installation and disassembly of the countersink drill; the top angle N3 of the second positioning cone 9 is 120°, which is used to ensure the coaxiality of the tool body and the thread.

[0024] The clamping mode of the tool holder clamping area D can be set to a threaded shank 16, a straight shank 17, a tapered shank 18, etc. In this embodiment, the stability of the countersink drill clamping is improved by threaded connection. The thread specification is selected according to the model of the drill sleeve. The thread of this embodiment adopts 1 / 4-28UNF and the clamping length is 15mm.

[0025] A machine tool was used to perform countersinking, and the hole making quality of a two-edged diamond insert countersink was compared with that of a new countersink designed in this embodiment (the tool material is cemented carbide). The experimental material was AFRP laminate with a thickness of 4 mm. According to the experimental results, the two-edged diamond insert countersink has the problem of not being able to cut through the material, the surface quality of the countersink is extremely poor, the burrs at the entrance are serious, and the requirements for the countersink quality of riveting cannot be met. The new countersink designed in this embodiment has lower cutting force, a stable machining process, less delamination damage, the surface roughness of the countersink can reach the index of Ra3.2, there is no obvious burr damage at the entrance, and the aperture accuracy meets the riveting requirements. The present invention proposes a tool suitable for countersinking of aramid fiber composite materials. The front section of the tool is designed to be a detachable centering guide column, which reduces the scratching of the guide column on the hole wall while achieving the centering function by grinding chamfers and fillets. The countersinking position adopts a staggered multi-cutting edge structure, and the adjacent main cutting edges are set with a height difference in the axial direction to enhance the constraint effect on the aramid fiber, and then based on the multi-edge removal concept, the generation of burrs at the entrance is suppressed by shearing removal. The secondary cutting edge is sharpened to give the tool body cutting ability, and a stop surface is set at the end of the cutting edge according to the countersinking depth to achieve fixed-depth cutting and further remove burrs, thereby improving the countersinking processing quality and accuracy, and meeting the high-quality and high-precision countersinking requirements of AFRP. The tool structure and design method proposed in the present invention are not limited to the structure of the above-mentioned embodiment, and can be modified in various ways. In short, all modifications that do not depart from the innovative scope of the present invention fall within the protection scope of the present invention.

Claims

1. A tool suitable for countersinking of aramid fiber composite materials, characterized in that: The tool for countersinking of aramid fiber composite materials consists of four areas: the centering guide area (A), the countersinking area (B), the installation area (C), and the tool holder clamping area (D). The countersinking area (B) is mainly composed of four or more evenly distributed main cutting edges (2) and auxiliary cutting edges (12), and a fixed cutting depth stop surface (5); wherein the top angle of the main cutting edge (2) is N1=90°-140°, and the top angle N1 needs to be adjusted according to the countersinking angle. The final hole diameter is D2, and the axial length is L1=0.5(D2-D1)tan(90°-0.5N1). Staggered right-handed micro-teeth (14) and left-handed micro-teeth (15) are respectively processed on adjacent main cutting edges (2). According to the tool movement relationship, the inclination angles of the right-handed micro-teeth (14) and the left-handed micro-teeth (15) are set to β1=10°-45° and β2=(-10°)-(-45°), respectively, and the micro-teeth width b=0.1-1.2mm. The front cutting face (3) and the back cutting face (4) of the tool are ground to form the main cutting edge front angle γ1 = 5°-20° and the back angle α1 = 10°-25°; the secondary cutting edge front cutting face (13) and the secondary cutting edge first back cutting face (10) and the secondary cutting edge second back cutting face (11) are ground on the tool body to form the secondary cutting edge (12), the countersinking depth of the secondary cutting edge (12) is L2, the secondary cutting edge front angle γ2 = 15°-25°, the secondary cutting edge first back angle α2 = 5°-25°, and the secondary cutting edge second back angle α3 = 10°-30°; based on the diameter range of the delamination area obtained by experimental research, a fixed cutting depth stopper (5) is designed at the end of the secondary cutting edge first back cutting face (10), whose diameter is D3, to suppress delamination damage and realize the control of the countersinking depth to be L1+ L2, the axial length of the fixed cutting depth stop surface (5) is L3; the first positioning cone surface (6) is designed to ensure the coaxiality of the countersinking area (B) and the installation area (C) when the tool is processed, and the top angle of the first positioning cone surface (6) is N2=80°-140°.

2. The tool suitable for countersinking of aramid fiber composite materials according to claim 1, characterized in that: The centering guide column area (A) is a detachable centering guide column (1); the detachable centering guide column (1) is fixed to the countersinking cutter body by screwing or by a straight shank with a pin, the diameter D1 of the detachable centering guide column (1) is determined by the bottom hole diameter and is given a deviation, the front end of the detachable centering guide column (1) is designed with a fillet R1, and the end of the detachable centering guide column (1) is designed with a fillet R2 at the connection position with the countersinking area (B).

3. The tool for countersinking of aramid fiber composite materials according to claim 1, characterized in that: The installation area (C) is mainly composed of a cutter body (7), a through hole (8) and a second positioning cone (9). The diameter of the cutter body (7) is D4. The through hole (8) is processed on the cutter body (7) to facilitate the installation and disassembly of the countersink. The second positioning cone (9) is designed to ensure the coaxiality of the installation area (C) and the tool holder clamping area (D). The top angle of the second positioning cone (9) is N3=80°-140°.

4. The tool for countersinking of aramid fiber composite materials according to claim 1, characterized in that: The tool shank clamping area (D) is configured to be a threaded shank (16), a straight shank (17) or a tapered shank (18).

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