Deep hole inner-cooling step drill with chip breaker groove

Abstract

The utility model belongs to the technical field of drill bits, particularly relates to a deep hole inner-cooling step drill with a chip breaker groove, and provides the following scheme aiming at the problems that an existing step drill adopts an integrated design, an abraded part cannot be independently replaced, and only the whole drill bit can be discarded or integrally repaired. Comprising a drill rod, a first step drill body and a second step drill body, the second step drill body is connected with the first step drill body through a positioning insertion rod, a threaded rod and a fastening nut, independent disassembly and replacement of the second step drill body can be achieved, when the second step drill body is abraded, only the part needs to be replaced, the whole drill bit does not need to be replaced, and cost is reduced; compared with the prior art, the resource utilization rate is improved, a maintainer can directly detach the worn second step drill and replace or maintain the worn second step drill, complex repair operation on the whole drill bit is not needed, the maintenance time and the labor cost are saved, the maintenance efficiency is improved, equipment can be put into production again more quickly, and the downtime caused by equipment maintenance is shortened.

Description

Technical Field

[0001] This utility model relates to a step drill, specifically a deep hole internal cooling step drill with chip breaking grooves, belonging to the field of drill bit technology. Background Technology

[0002] In the field of machining, deep hole machining is an extremely challenging task, placing stringent requirements on the performance and reliability of drilling tools. Currently, the deep hole internal cooling step drill with chip breaker grooves, which is widely used in deep hole machining, is typically in a pagoda-like structure. In actual drilling operations, this structure relies primarily on the lower drill bit to drill first, followed by the upper drill bit to enlarge the hole.

[0003] Existing stepped drills, such as the one disclosed in patent number CN214815120U, have a transition surface between the steps and the conical surface to form an arc transition. When machining thin plates, as the drill passes through one step to the next, the cutting width gradually increases from the starting point of the arc. This can alleviate impact force and prevent the drill bit from getting stuck due to overcutting. However, in deep hole machining using this type of stepped drill, the lower drill bit, which undertakes the initial drilling task, faces more complex working conditions and greater cutting resistance. Its usage frequency is much higher than that of the upper drill bit, which makes the lower drill bit extremely prone to wear. Once the drill bit wears out, because existing stepped drills are designed as a single unit, the worn part cannot be replaced individually. The entire drill bit must be discarded or repaired. Discarding the entire drill bit not only causes a huge waste of resources and increased costs, but also delays the project schedule for some projects with tight processing cycles due to frequent replacement of new drill bits. Repairing the entire drill bit requires specialized equipment and technology, and the repair process is complex and time-consuming, which also affects processing efficiency and reduces the company's production benefits. Utility Model Content

[0004] This invention addresses the problem that existing step drills, with their integrated design, cannot individually replace worn parts, requiring the entire drill bit to be discarded or repaired. Instead, it provides a deep-hole internally cooled step drill with chip-breaking grooves.

[0005] The present invention achieves the above-mentioned objective through the following technical solution: a deep hole internal cooling step drill with chip breaking groove, comprising a drill rod, a first step drill and a second step drill, characterized in that: the first step drill is fixedly connected to the bottom end of the drill rod, the second step drill is installed on the bottom surface of the first step drill, and the drill rod, the first step drill and the second step drill are coaxially connected.

[0006] The surface of the drill rod is symmetrically provided with mounting holes, which penetrate the interior of the first step drill and extend to the bottom side of the first step drill. The surface of the second step drill is symmetrically fixedly connected with positioning pins, the installation positions of the positioning pins correspond to the mounting holes, and the top of each positioning pin is fixedly connected with a threaded rod. The surface of each threaded rod is threaded with a fastening nut. The second step drill is connected to the first step drill through the cooperation of the positioning pins, threaded rods, and fastening nuts.

[0007] As a further embodiment of this utility model: a first internal coolant channel is provided at the central axis position of both the drill rod and the first stepped drill. The first internal coolant channel penetrates the interior of both the drill rod and the first stepped drill. A first branch channel is symmetrically provided on both sides of the first internal coolant channel inside the first stepped drill. The first branch channel penetrates the first stepped drill and extends to the outside of the first stepped drill. The first branch channel is connected to the first internal coolant channel. A second internal coolant channel is provided at the central axis position of the second stepped drill. The second internal coolant channel is connected to the first internal coolant channel. A second branch channel is symmetrically provided on both sides of the second internal coolant channel inside the second stepped drill. The second branch channel penetrates the second stepped drill and extends to the outside of the second stepped drill. The second branch channel is connected to the second internal coolant channel.

[0008] As a further embodiment of this utility model: a first chip removal groove is formed on the surface of the first step drill, and a second chip removal groove is formed on the surface of the second step drill. Both the first chip removal groove and the second chip removal groove are spirally arranged, and the first chip removal groove and the second chip removal groove are connected.

[0009] As a further improvement of this utility model: the surface of the first step drill is provided with a first chip breaking groove, and the surface of the second step drill is provided with a second chip breaking groove.

[0010] As a further embodiment of this utility model: the bottom surface of the first step drill is provided with symmetrical diamond-shaped positioning grooves on both sides of the first internal coolant channel. A spring is fixedly connected in each diamond-shaped positioning groove, and a diamond plate is fixedly connected to the bottom end of the spring. The diamond plate can slide in the diamond-shaped positioning groove. Diamond-shaped positioning blocks are symmetrically fixedly connected on both sides of the surface of the second step drill in the second internal coolant channel. The diamond-shaped positioning blocks and the diamond-shaped positioning grooves are compatible.

[0011] As a further embodiment of this utility model: an annular sealing groove is formed on the bottom surface of the first step drill located on the outer circumference of the first internal coolant channel, and an annular sealing ring is fixedly connected to the bottom surface of the second step drill located on the outer circumference of the second internal coolant channel, with the annular sealing groove and the annular sealing ring being compatible.

[0012] As a further improvement of this utility model, the surface of the fastening nut is provided with multiple insertion holes arranged in a circular array.

[0013] The beneficial effects of this utility model are:

[0014] 1. In this utility model, the second step drill is connected to the first step drill via a positioning rod, a threaded rod, and a fastening nut, enabling the independent disassembly and replacement of the second step drill. When the second step drill is worn, only this part needs to be replaced, without replacing the entire drill bit, thus reducing costs and improving resource utilization. Compared to the integrated drill bit repair, which requires specialized equipment and technology to repair the entire bit, this structure makes maintenance more convenient. Maintenance personnel can directly remove the worn second step drill for replacement or repair without performing complex repair operations on the entire drill bit, saving maintenance time and labor costs, improving maintenance efficiency, and enabling the equipment to be put back into production more quickly, reducing downtime caused by equipment maintenance.

[0015] 2. This utility model, by setting up a first internal coolant channel, a first branch channel, a second internal coolant channel, and a second branch channel, allows the internal coolant to flow sequentially through each channel during use, providing comprehensive cooling for the first and second step drill bits. This reduces the drill bit temperature during drilling, minimizes wear caused by high temperatures, and extends the drill bit's service life. Furthermore, during deep hole machining, the internal coolant flowing out from each channel also flushes the chips, assisting in their removal from the deep hole and preventing chip accumulation. This avoids chip blockage affecting drilling quality and efficiency, reduces the risk of drill bit breakage, and improves cooling and chip removal efficiency. This helps maintain the drill bit's accuracy and stability, preventing problems such as drill bit deformation and annealing caused by high temperatures. It ensures the dimensional accuracy and surface quality of the drilled hole, reduces machining errors, and makes deep hole machining more reliable.

[0016] 3. By setting up a spiral-shaped first and second chip removal groove, this utility model can provide a clear discharge path for chips. Utilizing the guiding effect of the spiral, the chips are discharged in an orderly manner along a specific direction, preventing chips from accumulating randomly during drilling, reducing the possibility of chips clogging the drill hole, and ensuring the smooth progress of the drilling process. At the same time, smooth chip removal can avoid excessive friction and collision between chips and the drill bit and hole wall, reducing the wear effect of chips on the tool, thereby extending the service life of the first and second step drills, reducing the tool replacement frequency, and improving the economy and efficiency of machining.

[0017] 4. By setting a first chip-breaking groove and a second chip-breaking groove, this utility model can obstruct and compress the chips during their formation process, changing the flow direction and shape of the chips, causing the chips to break at appropriate positions, avoiding the formation of continuous long chips, preventing long chips from wrapping around the drill bit or blocking the chip removal channel. At the same time, the first and second chip-breaking grooves can enable the chips to break in time, reduce the friction caused by the chips, reduce the wear of the drill bit, extend the service life of the drill bit, reduce the frequency of tool replacement, and improve processing efficiency.

[0018] 5. By setting up a rhombus-shaped positioning groove and a rhombus-shaped positioning block, this utility model can ensure precise positioning between the first step drill and the second step drill during installation, making their central axes more aligned, ensuring uniform force transmission during drilling, preventing drill bit deflection, and improving processing accuracy and stability. Furthermore, by applying elastic force to the rhombus plate through a spring, the rhombus plate is tightly pressed against the rhombus-shaped positioning block, further enhancing the tightness and firmness of the connection. When the drill bit is subjected to large cutting forces, it can effectively prevent the connection from loosening.

[0019] 6. This utility model, by setting an annular sealing groove and an annular sealing ring, enables the annular sealing ring to be embedded in the annular sealing groove, achieving a tight fit between the two. This forms an effective sealing barrier at the connection point of the first and second step drills, preventing coolant leakage. Furthermore, the annular sealing ring has a certain degree of elasticity. When the coolant pressure within the channel changes, the annular sealing ring can compensate through its own elastic deformation. When the pressure increases, the annular sealing ring is pressed more tightly into the annular sealing groove, enhancing the sealing effect; when the pressure decreases, it can partially return to its original shape, maintaining good sealing performance at all times, ensuring effective prevention of coolant leakage under different pressure conditions. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the appearance and structure of this utility model;

[0021] Figure 2 This is a schematic diagram of the disassembly structure of the first and second step drills in this utility model. Figure 1 ;

[0022] Figure 3 This is a schematic diagram of the disassembly structure of the first and second step drills in this utility model. Figure 2 ;

[0023] Figure 4 This is a schematic diagram of the structure of the first step drill in this utility model;

[0024] Figure 5 This is a schematic diagram of the fastening nut in this utility model;

[0025] Figure 6 This is a schematic cross-sectional view of the first-step drill in this utility model. Figure 1 ;

[0026] Figure 7 This is a schematic cross-sectional view of the first-step drill in this utility model. Figure 2 ;

[0027] Figure 8 for Figure 7 Enlarged structural diagram at point A in the middle;

[0028] Figure 9 This is a schematic diagram of the structure of the second-step drill in this utility model;

[0029] Figure 10 This is a cross-sectional structural diagram of the second-step drill in this utility model.

[0030] In the diagram: 1. Drill rod; 2. First step drill; 3. Second step drill; 4. First chip removal groove; 5. First chip breaking groove; 6. First internal coolant channel; 7. First branch channel; 8. Second chip removal groove; 9. Second chip breaking groove; 10. Mounting hole; 11. Diamond positioning groove; 12. Spring; 13. Diamond plate; 14. Annular sealing groove; 15. Diamond positioning block; 16. Positioning rod; 17. Threaded rod; 18. Annular sealing ring; 19. Second internal coolant channel; 20. Second branch channel; 21. Fastening nut; 22. Insertion hole. Detailed Implementation

[0031] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model. Example 1

[0032] like Figures 1 to 10 As shown, a deep hole internal cold step drill with chip breaking groove includes a drill rod 1, a first step drill 2 and a second step drill 3. The first step drill 2 is fixedly connected to the bottom end of the drill rod 1, and the second step drill 3 is installed on the bottom surface of the first step drill 2. The drill rod 1, the first step drill 2 and the second step drill 3 are coaxially connected.

[0033] The surface of the drill rod 1 is symmetrically provided with mounting holes 10, which penetrate the interior of the first step drill 2 and extend to the bottom side of the first step drill 2. The surface of the second step drill 3 is symmetrically fixedly connected with positioning rods 16, the installation positions of which correspond to the mounting holes 10. The top end of each positioning rod 16 is fixedly connected with a threaded rod 17, and the surface of each threaded rod 17 is threaded with a fastening nut 21. The second step drill 3 is connected to the first step drill 2 through the cooperation of the positioning rods 16, the threaded rods 17, and the fastening nuts 21. The connection between the second step drill 3 and the first step drill 2 through the positioning rods 16, the threaded rods 17, and the fastening nuts 21 allows for the individual disassembly and replacement of the second step drill 3. When the second step drill 3 is worn, only this part needs to be replaced, without replacing the entire drill bit, which reduces costs and improves resource utilization.

[0034] The bottom surface of the first step drill 2 is symmetrically provided with rhomboid positioning grooves 11 on both sides of the first internal coolant channel 6. A spring 12 is fixedly connected in each rhomboid positioning groove 11, and a rhomboid plate 13 is fixedly connected to the bottom end of the spring 12. The rhomboid plate 13 can slide in the rhomboid positioning groove 11. The surface of the second step drill 3 is symmetrically fixedly connected with rhomboid positioning blocks 15 on both sides of the second internal coolant channel 19. The rhomboid positioning blocks 15 and the rhomboid positioning grooves 11 are adapted to each other. In use, the rhomboid positioning grooves 11 and the rhomboid positioning blocks 15 are adapted to each other. During installation, it can ensure accurate positioning between the first step drill 2 and the second step drill 3, so that the central axis of the two are more aligned, ensuring uniform force transmission during drilling, preventing drill bit deflection, improving processing accuracy and stability. Furthermore, the spring 12 applies elastic force to the rhomboid plate 13, so that the rhomboid plate 13 tightly abuts against the rhomboid positioning block 15, further enhancing the tightness and firmness of the connection. When the drill bit is subjected to large cutting forces, it can effectively prevent the connection from loosening.

[0035] The fastening nut 21 has multiple insertion holes 22 arranged in a circular array on its surface. When the mounting hole diameter is too small to be used with a conventional wrench, the user can use a tool to insert into the insertion hole 22, so that the fastening nut 21 can be installed and removed smoothly without being limited by the size of the mounting hole, thus increasing the flexibility of operation. Example 2

[0036] In addition to all the technical features included in Embodiment 1, this embodiment also includes:

[0037] Both drill pipe 1 and the first stepped drill 2 have a first internal coolant channel 6 at their central axis positions. The first internal coolant channel 6 penetrates the interior of both drill pipe 1 and the first stepped drill 2. The interior of the first stepped drill 2 has symmetrically arranged first branch channels 7 on both sides of the first internal coolant channel 6. The first branch channels 7 penetrate the first stepped drill 2 and extend to the outside of the first stepped drill 2, and are connected to the first internal coolant channel 6. A second internal coolant channel 19 is provided at the central axis position of the second stepped drill 3. The second internal coolant channel 19 is connected to the first internal coolant channel 6. The interior of the second stepped drill 3 has symmetrically arranged second branch channels 20 on both sides of the second internal coolant channel 19. The second branch channels 20 penetrate the second stepped drill 3 and extend to the first internal coolant channel 6. The outer side of the two-step drill 3 is connected to the second branch channel 20 and the second internal coolant channel 19. During use, the internal coolant can flow from the first internal coolant channel 6 of the drill rod 1 through the first branch channel 7 of the first-step drill 2, and then to the second branch channel 20 of the second-step drill 3, cooling the first-step drill 2 and the second-step drill 3 in all directions, reducing the temperature of the drill bit during drilling, reducing wear caused by high temperature, and extending the service life of the drill bit. At the same time, in deep hole machining, the internal coolant flows out from the first internal coolant channel 6, the first branch channel 7, the second internal coolant channel 19 and the second branch channel 20, which can have a flushing effect on the chips, assisting the chips to be discharged from the deep hole, preventing the chips from accumulating in the hole, avoiding chip blockage that affects the drilling quality and efficiency, and reducing the risk of drill bit breakage.

[0038] The bottom surface of the first step drill 2 is provided with an annular sealing groove 14 on the outer circumference of the first internal coolant channel 6. The bottom surface of the second step drill 3 is provided with an annular sealing ring 18 fixedly connected to the outer circumference of the second internal coolant channel 19. The annular sealing groove 14 and the annular sealing ring 18 are adapted to each other, so that the annular sealing ring 18 can be embedded in the annular sealing groove 14 to achieve a tight fit between the two. An effective sealing barrier is formed at the connection position of the first step drill 2 and the second step drill 3 to prevent coolant from seeping out from here. Example 3

[0039] In addition to all the technical features included in Embodiment 1, this embodiment also includes:

[0040] The surface of the first step drill 2 is provided with a first chip removal groove 4, and the surface of the second step drill 3 is provided with a second chip removal groove 8. Both the first chip removal groove 4 and the second chip removal groove 8 are spirally arranged and connected to each other. The spiral first chip removal groove 4 and the second chip removal groove 8 can provide a clear discharge path for the chips. By using the guiding effect of the spiral, the chips are discharged in an orderly manner along a specific direction, preventing the chips from accumulating randomly during the drilling process, reducing the possibility of chips clogging the drill hole, and ensuring the smooth progress of the drilling process.

[0041] The surface of the first step drill 2 is provided with a first chip breaking groove 5, and the surface of the second step drill 3 is provided with a second chip breaking groove 9. The first chip breaking groove 5 and the second chip breaking groove 9 can cause the chips to be obstructed and squeezed by the grooves during the chip formation process, change the flow direction and shape of the chips, promote the chips to break at a suitable position, avoid the formation of continuous long chips, and prevent long chips from wrapping around the drill bit or blocking the chip removal channel.

[0042] Working principle: When performing deep hole machining, the second step drill 3 is first installed on the bottom surface of the first step drill 2. During this process, the positioning rod 16 of the second step drill 3 is inserted into the mounting hole 10 of the first step drill 2 symmetrically on the surface of the drill rod 1. Then, the fastening nut 21 is sleeved on the surface of the threaded rod 17, and the tool is inserted into the circular array of insertion holes 22 on the surface of the fastening nut 21. The fastening nut 21 is then rotated to tighten and fix it.

[0043] Meanwhile, the rhomboid positioning block 15 of the second step drill 3 is embedded into the rhomboid positioning groove 11 of the first step drill 2 for precise positioning, ensuring that the central axes of the two coincide, so that the force is transmitted evenly during drilling, preventing the drill bit from deviating, and improving the processing accuracy and stability. During the tightening process, the spring 12 pushes the rhomboid plate 13 to press tightly against the rhomboid positioning block 15, enhancing the connection firmness and preventing the connection from loosening under the action of cutting force. This structural design allows the second step drill 3 to be disassembled and replaced separately. When it wears out, there is no need to replace the entire drill bit, which reduces costs and improves resource utilization.

[0044] During processing, the internal coolant flows in from the first internal coolant channel 6 at the central axis of the drill rod 1, and passes sequentially through the first branch channel 7 of the first stepped drill 2, the second internal coolant channel 19 of the second stepped drill 3, and the second branch channel 20. During this process, the internal coolant cools the drill bit in all directions, reducing wear caused by high temperature and extending the service life of the drill bit; it can also flush away chips, assist in chip removal, prevent chip accumulation and blockage, and reduce the risk of drill bit breakage.

[0045] Next, the chips generated during drilling are discharged through the spiral-shaped and interconnected first chip removal groove 4 and second chip removal groove 8. The spiral structure guides the chips to be discharged in an orderly manner, ensuring smooth drilling. At the same time, the first chip breaking groove 5 and the second chip breaking groove 9 will obstruct and compress the chips, causing them to break and preventing long chips from wrapping around the drill bit or blocking the chip removal channel.

[0046] Throughout the entire processing, the annular sealing groove 14 of the first step drill 2 and the annular sealing ring 18 of the second step drill 3 fit tightly together, effectively preventing coolant leakage, protecting the connecting parts, and reducing corrosion and wear. When subsequent operations are required on the fastening nut 21, if the mounting hole diameter is too small to use a conventional wrench, a tool can be inserted into the circular array of insertion holes 22 on its surface to flexibly complete the installation and disassembly, without being limited by the size of the mounting hole.

[0047] It will be apparent to those skilled in the art that this invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of this invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of this invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0048] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A deep-hole internal cooling stepped drill with chip-breaking grooves, comprising a drill rod (1), a first stepped drill (2), and a second stepped drill (3), characterized in that: The first step drill (2) is fixedly connected to the bottom end of the drill rod (1), and the second step drill (3) is installed on the bottom surface of the first step drill (2). The drill rod (1), the first step drill (2) and the second step drill (3) are coaxially connected. The surface of the drill rod (1) is symmetrically provided with mounting holes (10). The mounting holes (10) penetrate the interior of the first step drill (2) and extend to the bottom side of the first step drill (2). The surface of the second step drill (3) is symmetrically fixedly connected with positioning rods (16). The installation position of the positioning rods (16) corresponds to the mounting holes (10). The top end of each positioning rod (16) is fixedly connected with a threaded rod (17). The surface of each threaded rod (17) is threaded with a fastening nut (21). The second step drill (3) is connected to the first step drill (2) through the cooperation of the positioning rods (16), the threaded rods (17) and the fastening nuts (21).

2. The deep-hole internal cooling step drill with chip-breaking groove according to claim 1, characterized in that: A first internal coolant channel (6) is provided at the central axis position of the drill rod (1) and the first stepped drill (2). The first internal coolant channel (6) penetrates the interior of the drill rod (1) and the first stepped drill (2). A first branch channel (7) is symmetrically provided on both sides of the first internal coolant channel (6) inside the first stepped drill (2). The first branch channel (7) penetrates the first stepped drill (2) and extends to the outside of the first stepped drill (2). The first branch channel (7) and the first internal coolant channel (6) are connected. A second internal coolant channel (19) is provided at the central axis position of the second stepped drill (3). The second internal coolant channel (19) and the first internal coolant channel (6) are connected. A second branch channel (20) is symmetrically provided on both sides of the second internal coolant channel (19) inside the second stepped drill (3). The second branch channel (20) penetrates the second stepped drill (3) and extends to the outside of the second stepped drill (3). The second branch channel (20) and the second internal coolant channel (19) are connected.

3. The deep-hole internal cooling step drill with chip-breaking groove according to claim 2, characterized in that: The surface of the first step drill (2) is provided with a first chip removal groove (4), and the surface of the second step drill (3) is provided with a second chip removal groove (8). The first chip removal groove (4) and the second chip removal groove (8) are both spiral-shaped, and the first chip removal groove (4) and the second chip removal groove (8) are connected.

4. The deep-hole internal cooling step drill with chip-breaking groove according to claim 3, characterized in that: The surface of the first step drill (2) is provided with a first chip breaking groove (5), and the surface of the second step drill (3) is provided with a second chip breaking groove (9).

5. The deep-hole internal cooling step drill with chip-breaking groove according to claim 4, characterized in that: The bottom surface of the first step drill (2) is symmetrically provided with rhomboid positioning grooves (11) on both sides of the first internal coolant channel (6). A spring (12) is fixedly connected in each rhomboid positioning groove (11). A rhomboid plate (13) is fixedly connected to the bottom end of the spring (12). The rhomboid plate (13) can slide in the rhomboid positioning groove (11). The surface of the second step drill (3) is symmetrically fixedly connected with rhomboid positioning blocks (15) on both sides of the second internal coolant channel (19). The rhomboid positioning blocks (15) and the rhomboid positioning grooves (11) are compatible.

6. The deep-hole internal cooling step drill with chip-breaking groove according to claim 5, characterized in that: The bottom surface of the first step drill (2) is provided with an annular sealing groove (14) on the outer circumference of the first internal coolant channel (6), and the bottom surface of the second step drill (3) is fixedly connected with an annular sealing ring (18) on the outer circumference of the second internal coolant channel (19). The annular sealing groove (14) and the annular sealing ring (18) are compatible.

7. The deep-hole internal cooling step drill with chip-breaking groove according to claim 1, characterized in that: The surface of the fastening nut (21) is provided with a plurality of insertion holes (22) arranged in a circular array.

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