Positioning fixture and machining method for shaft parts with external threads at both ends

Abstract

This invention discloses a positioning fixture and processing method for shaft-like parts with external threads at both ends. Pushing the first handle shaft stretches the tension spring, causing the main clamping component to rotate on the secondary clamping component. The first internal thread groove, driven by the main clamping component, moves away from the second internal thread groove. The external thread at the end of the shaft-like part with the machined notch can pass through the area between the first and second internal thread grooves. Releasing the first handle shaft allows the first and second internal thread grooves to clamp one end of the shaft-like part by engaging with its external thread under the spring's rebound force. The second handle shaft can then be placed on the lever of the CNC thread grinding machine headstock spindle, facilitating the clamping and positioning of the shaft-like part. The rotation of the CNC thread grinding machine headstock spindle drives the lever to rotate, further rotating the positioning fixture. Then, the rotation of the grinding wheel spindle drives the grinding wheel to rotate, facilitating grinding of the notch on the shaft-like part. This effectively shortens the preparation cycle required for the physical and chemical testing of important engine components, and the operation is safe and convenient.

Description

Technical Field

[0001] This invention belongs to the field of shaft parts processing, specifically relating to a positioning fixture and processing method for shaft parts with external threads at both ends. Background Technology

[0002] During the machining of engine parts, certain critical components require testing of their physical and chemical properties. Physical and chemical testing is playing an increasingly important role in the manufacturing of aero-engines. For an increasing number of critical component materials, after sampling according to standard requirements, specimen preparation is carried out according to the corresponding physical and chemical testing items.

[0003] A certain machine's high-temperature combined long-term circular tensile test specimen is as follows: Figure 1 As shown, the outer diameter M1 of the threads at both ends of the specimen is an M12X1.75 external thread. The specimen has a first type A center hole 1 and a second type A center hole 2 machined at both ends. The diameters between the two ends decrease in a stepped manner from right to left, with diameters of D1 and D respectively. There are transition sections between M1, D1, D, and M1. The outer diameter M1 of the threads at both ends of the specimen is required to be concentric with the smallest cylinder diameter D and the largest cylinder diameter D1 in the middle. D is Ф5 and D1 is Ф7. There is a V-shaped notch on the surface of the largest cylinder. The specimen length L = 72. The previous process of machining this specimen has been completed. Except for the 0.25mm grinding allowance on one side of the cylinder diameter D and the notch on the cylinder diameter D1, all other dimensions have been machined to the required size.

[0004] To achieve Figure 1 The finished sample of the high-temperature combined endurance circular tensile specimen shown requires subsequent processing using a CNC thread grinder to machine a V-notch surface. First, a chuck clamp is mounted on the cylinder diameter D. The first A-type center hole 1 is installed in the front center of the CNC thread grinder, and the second A-type center hole 2 is installed in the rear center. The chuck clamp is then fixed to the spindle of the CNC thread grinder. The rotation of the spindle drives the chuck clamp, which in turn rotates the specimen. The grinding wheel spindle then rotates the grinding wheel, and the notch surface is then ground.

[0005] Therefore, when machining the notched surface of a high-temperature composite endurance circular tensile specimen, the CNC thread grinding machine is used to machine the notched surface. The above machining method has the following two problems: (1) Due to the certain diameter difference between the outer diameter M1 and the outer diameter D of the thread (the outer diameter of the thread is M12, and the outer diameter of D is M12), When clamping the outer diameter of D, first pass the left end M12 threaded outer diameter through the chuck, and then clamp it. The outer circle is machined. After the machining is completed, the chicken heart clamp is loosened to a distance greater than M12 on the outer circle, and then the sample is taken out. As it is a batch production, this clamping and machining process seriously affects the sample preparation efficiency and thus the entire sample testing cycle. (2) Because the chicken heart clamp is clamped on the cylinder diameter D, when the grinding wheel is machining the notch surface on the cylinder diameter D1, the distance between the chicken heart clamp and the grinding wheel is too close, which poses a risk of friction and collision, and poses a safety hazard, which is not conducive to safe production. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a positioning fixture and processing method for shaft-type parts with external threads at both ends. This method can greatly improve the clamping and unloading efficiency of high-temperature combined long-term circular tensile specimens on CNC thread grinding machines, eliminate safety hazards, ensure the preparation quality of specimens and human and machine safety, effectively shorten the preparation cycle required for the physical and chemical testing of important engine parts, and is safe and convenient to operate.

[0007] This invention is achieved through the following technical solution:

[0008] A positioning fixture for shaft-type parts with external threads at both ends includes a main clamping component, a secondary clamping component, a first handle shaft, and a second handle shaft.

[0009] The main clamping component and the auxiliary clamping component are elongated. The upper surface of the main clamping component is provided with a first internal thread groove that connects the two ends of its own length direction. The upper surface of the auxiliary clamping component is provided with a second internal thread groove that connects the two ends of its own length direction. Both the first internal thread groove and the second internal thread groove are arc-shaped and cooperate with the external threads at both ends of the shaft-like part.

[0010] The main clamping component is located at the upper end of the auxiliary clamping component. One side of the first internal thread groove is hinged to the corresponding side of the second internal thread groove, and the other side of the first internal thread groove and the corresponding side of the second internal thread groove are left with a gap at the top and bottom.

[0011] The main clamping component and the auxiliary clamping component are respectively equipped with a first handle shaft and a second handle shaft near the gap. A tension spring is installed between the first handle shaft and the second handle shaft. When one end of the shaft part is inserted into the first internal thread groove and the second internal thread groove, the tension spring is in a stretched state.

[0012] Preferably, it also includes a third handle shaft, which is fixed on the secondary clamping component and disposed close to the main clamping component.

[0013] Furthermore, the first handle shaft, the second handle shaft, and the third handle shaft are all made of 40Cr tempered steel.

[0014] Furthermore, the outer ends of the first and third handle shafts are handles with evenly distributed perforated teeth.

[0015] Furthermore, the first handle shaft, the second handle shaft, and the third handle shaft are all cylindrical. The inner end of the first handle shaft is welded to the main clamping component, and the inner ends of the second and third handle shafts are welded to the auxiliary clamping component.

[0016] Furthermore, the main clamping component and the auxiliary clamping component have the same length, and their two ends are flush. The length is 0.85 to 1.15 times the length of the external thread at one end of the shaft-like part to be positioned. The central axes of the first handle shaft, the second handle shaft, and the third handle shaft are located on the same horizontal plane, and the horizontal plane is located at the center of the length direction of the main clamping component.

[0017] Preferably, the cross-section of both the main clamping component and the auxiliary clamping component is a circular ring. The two end faces of the auxiliary clamping component are horizontal and evenly distributed. The end face of the main clamping component that is hinged to the auxiliary clamping component is lower than the other horizontally distributed end face.

[0018] Furthermore, the arc corresponding to the ring of the secondary clamping component is (0.75~0.8)π, and the arc corresponding to the ring of the main clamping component is π.

[0019] Furthermore, it also includes a pin. The cross-section of the end face S of the main clamping component that is hinged to the secondary clamping component is an elliptical arc, forming a protruding section of the main clamping component. The protruding section is located at the center of the main clamping component in the length direction. The length of the protruding section is 0.75 to 0.8 times the length of the main clamping component. The ellipse foci corresponding to the arc are F1 and F2. The straight line passing through F1 and F2 is L. The intersection of L and the lowermost point of the protruding section is distributed near the outer side of the protruding section.

[0020] The upper surface of the end face S' corresponding to the end face S in the auxiliary clamping component is provided with a groove that is inserted into the lower end of the protrusion. The lower end of the protrusion is inserted into the groove. A first through hole is provided in the lower end of the protrusion, which connects the two ends of its own length direction. The center of the first through hole is on L. The lower end of the first through hole is close to the lower end of the protrusion. A second through hole is provided on both sides of the groove, which connects to itself and is located in the length direction of the auxiliary clamping component. The inner diameter of the second through hole is the same as that of the first through hole, and the center of the second through hole coincides with the center of the first through hole.

[0021] The outer diameter of the pin is the same as the inner diameter of the first through hole, and the pin is inserted into the second through hole and the first through hole.

[0022] A method for machining a shaft-like part with external threads at both ends, wherein the shaft-like part is composed of several cylindrical segments with different diameters, and the diameters of each cylindrical segment are distributed in a stepped manner, wherein the diameters of the cylindrical segments at both ends are the same and the largest, and the cylindrical segment near one end has a notch surface to be machined with a smaller diameter than the cylindrical segment at the corresponding end, and a positioning fixture for the shaft-like part with external threads at both ends based on any one of the above methods includes the following steps:

[0023] S1, push the first handle shaft to stretch the tension spring, the main clamping component rotates on the secondary clamping component, and the first internal thread groove moves away from the second internal thread groove under the drive of the main clamping component;

[0024] S2, pass the external thread of one end of the shaft part through the area between the first internal thread groove and the second internal thread groove, release the first handle shaft, and under the action of the spring force, the first internal thread groove and the second internal thread groove clamp one end of the shaft part by engaging with the external thread.

[0025] S3, A-type center holes are provided on both end faces of the shaft part. The A-type center hole on the left is placed into the front center of the CNC thread grinding machine, and the A-type center hole on the right is placed into the rear center of the CNC thread grinding machine. Then, the second handle shaft is placed on the lever of the headstock spindle of the CNC thread grinding machine to complete the clamping and positioning of the shaft part.

[0026] S4, the rotation of the headstock spindle of the CNC thread grinding machine drives the rotation of the lever, the rotation of the lever drives the rotation of the positioning fixture, and then the rotation of the grinding wheel spindle drives the grinding wheel to rotate, and the grinding wheel grinds the cylindrical section notch surface of the shaft part.

[0027] Compared with the prior art, the present invention has the following beneficial technical effects:

[0028] This invention discloses a positioning fixture for a shaft-like part with external threads at both ends. The elongated main clamping component and auxiliary clamping component facilitate positioning one end of the shaft-like part. The first internal thread groove in the main clamping component and the second internal thread groove in the auxiliary clamping component are arc-shaped, engaging with the external threads at both ends of the shaft-like part. When the first handle shaft is pushed, the tension spring is further stretched, causing one end of the main clamping component to rotate at the corresponding end of the auxiliary clamping component. This increases the gap between the first and second internal thread grooves, allowing the external thread at one end of the shaft-like part to pass through the area between the first and second internal thread grooves. Releasing the first handle shaft, under the rebound force of the tension spring, causes the first and second internal thread grooves to clamp one end of the shaft-like part by engaging with its external thread. This shaft-like part can be the outer diameter of a high-temperature composite endurance circular tensile test specimen, allowing for on-site assembly and disassembly and flexible use. This positioning fixture solves the problems of low clamping efficiency and safety hazards associated with high-temperature composite endurance circular tensile test specimens on CNC thread grinding machines, ensuring the quality of specimen preparation and human and machine safety. The positioning clamp of the present invention has a novel and compact structure, reliable and safe clamping, convenient operation, simple maintenance, and low manufacturing cost.

[0029] This invention discloses a method for machining shaft-like parts with external threads at both ends. Pushing the first handle shaft stretches the tension spring, causing the main clamping component to rotate on the secondary clamping component. Driven by the main clamping component, the first internal thread groove moves away from the second internal thread groove. The external thread at the end of the shaft-like part with the machined notch can pass through the area between the first and second internal thread grooves. Releasing the first handle shaft allows the first and second internal thread grooves to clamp one end of the shaft-like part by engaging with its external thread under the spring's rebound force. The second handle shaft can then be placed on the lever of the CNC thread grinding machine headstock spindle for convenient clamping and positioning of the shaft-like part. Finally, the rotation of the CNC thread grinding machine headstock spindle drives the lever to rotate, further rotating the positioning fixture. Then, the rotation of the grinding wheel spindle drives the grinding wheel to rotate, facilitating grinding of the notch on the shaft-like part. This significantly shortens the preparation cycle for the physical and chemical testing of a crucial engine component. Actual measurements show that the efficiency is increased by an average of 80% compared to previous clamping methods. Safety hazards caused by clamping are completely eliminated, ensuring the quality of sample preparation and shortening the overall preparation cycle time of the physical and chemical testing of parts by 20%. Attached Figure Description

[0030] Figure 1 A schematic diagram of a finished high-temperature composite endurance circular tensile test specimen for a certain machine.

[0031] Figure 2 A schematic diagram of the main clamping component;

[0032] Figure 3 This is a structural schematic diagram of the secondary clamping component;

[0033] Figure 4This is a front view of the initial state of the high-temperature combined long-lasting circular tensile specimen positioning fixture of the present invention.

[0034] In the figure: 1-First A-type center hole, 2-Second A-type center hole, 3-First internal thread groove, 4-First through hole, 5-Second internal thread groove, 6-Second through hole, 7-Main clamping component, 8-Secondary clamping component, 9-Pin, 10-Tension spring, 11-First handle shaft, 12-Second handle shaft, 13-Third handle shaft. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] This invention provides a positioning fixture for shaft-type parts with external threads at both ends. It employs a combined positioning and clamping method and is suitable for positioning and clamping high-temperature combined endurance circular tensile specimens. The positioning fixture includes, as follows: Figure 2 The main clamping component 7 shown is as follows: Figure 3 The auxiliary clamping component 8, pin 9, first handle shaft 11, second handle shaft 12, third handle shaft 13, and tension spring 10 are shown. The main clamping component 7, auxiliary clamping component 8, pin 9, first handle shaft 11, second handle shaft 12, and third handle shaft 13 are all made of 40Cr tempered steel, and the tension spring 10 is a standard part.

[0037] Figure 2 The main clamping component 7 and Figure 3 The secondary clamping components 8 are all elongated strips of the same length. The upper surface of the main clamping component 7 has a first internal threaded groove 3 connecting both ends along its length, and the upper surface of the secondary clamping component 8 has a second internal threaded groove 5 connecting both ends along its length. Both are arc-shaped and conform to the shape of both ends of the shaft-like part, and engage with the external threads at both ends of the shaft-like part, thus facilitating clamping. Therefore, the lengths of the main clamping component 7 and the secondary clamping component 8 are designed to be 0.85 to 1.15 times the length of the external thread at one end of the shaft-like part to be positioned.

[0038] like Figure 4As shown, the main clamping component 7 is located above the auxiliary clamping component 8. At this time, one side of the first internal thread groove 3 is hinged to the corresponding side of the second internal thread groove 5. The two ends of the main clamping component 7 and the auxiliary clamping component 8 are flush, and there is a gap between the other side of the first internal thread groove 3 and the corresponding side of the second internal thread groove 5. The first handle shaft 11 is welded to the main clamping component 7, and the second handle shaft 12 is welded to the auxiliary clamping component 8. The first handle shaft 11 and the second handle shaft 12 are distributed close to the gap. One end of the tension spring 10 is welded to the second handle shaft 12, and the other end is welded to the first handle shaft 11. When one end of the shaft-like part is inserted into the first internal thread groove 3 and the second internal thread groove 5, the tension spring 10 is in a stretched state because it needs to be clamped by the tension force of the tension spring 10. When clamped, one end of the shaft-like part is located at the center position of the main clamping component 7 and the auxiliary clamping component 8.

[0039] The third handle shaft 13 is welded to the secondary clamping component 8 near the main clamping component 7, allowing the first handle shaft 11 and the third handle shaft 13 to be gripped by hand, facilitating the extension of the tension spring 10. Furthermore, to facilitate gripping and increase friction at the handle, the first handle shaft 11, the second handle shaft 12, and the third handle shaft 13 are all cylindrical, and the first handle shaft 11 and the third handle shaft 13 are each divided into two parts: the outer part is a handle with evenly distributed serrations on the outer cylindrical surface, while the inner part is left untreated.

[0040] In addition, for ease of operation, the central axes of the first handle shaft 11, the second handle shaft 12 and the third handle shaft 13 are located on the same horizontal plane, and this horizontal plane is located at the center of the main clamping component 7 in the length direction.

[0041] To facilitate processing, the cross-sections of both the main clamping component 7 and the auxiliary clamping component 8 are designed as a circular ring. The two end faces of the auxiliary clamping component 8 are horizontal and evenly distributed. Specifically, the arc corresponding to the ring is (0.75~0.8)π. The end face of the main clamping component 7 that is hinged to the auxiliary clamping component 8 is lower than the other horizontally distributed end face, and the arc corresponding to the ring is π. This arc design ensures that the main clamping component 7 can pass through the area between the first internal thread groove 3 and the second internal thread groove 5 by only a small rotation within the auxiliary clamping component 8.

[0042] To facilitate the hinge connection between the main clamping component 7 and the auxiliary clamping component 8 mentioned above, the end face of the main clamping component 7 that is hinged to the auxiliary clamping component 8 is designated as S. The cross-section of S is an elliptical arc, which forms a protruding segment extending downward from the main clamping component 7. This protrusion is located at the center of the length direction of the main clamping component 7. The length of the two ends of the upper surface of the protruding segment is 0.75 to 0.8 of the total length of the main clamping component 7. Let the foci of the ellipse corresponding to the above-mentioned elliptical arc be F1 and F2, and let the straight line passing through F1 and F2 be L. Since the definitions of these symbols are relatively simple and only for the convenience of later description, they are not marked in the figure. The intersection of L and the lowest point of the protruding segment is distributed near the outer side of the protruding segment. This shape design facilitates small-amplitude rotation of the main clamping component 7 in the auxiliary clamping component 8 without causing significant changes in the relative positions of the two. Correspondingly, the end face of the secondary clamping component 8 corresponding to the end face S is designated as S'. A groove is provided on the upper surface of S'. This groove can be inserted into the lower end of the protruding section, and a certain gap is left. Thus, the lower end of the protruding section is inserted into the groove.

[0043] To facilitate the installation of pin 9, a first through hole 4 is opened at the lower end of the protruding section, connecting the two ends of its own length direction. The center of the first through hole 4 is on L, and the lowermost end of the first through hole 4 is close to the lowermost end of the protruding section. A second through hole 6 is opened on both sides of the groove, connecting itself. The second through holes 6 are distributed along the length direction of the secondary clamping component 8. The inner diameter of the second through hole 6 is the same as that of the first through hole 4, and their centers coincide. In this way, as long as the outer diameter of pin 9 is the same as the inner diameter of the first through hole 4, pin 9 can be inserted into the second through hole 6 and the first through hole 4, realizing the hinge connection between the main clamping component 7 and the secondary clamping component 8.

[0044] The machining methods for the main clamping component 7 and the secondary clamping component 8 are as follows:

[0045] First, an M12 internal thread through hole is machined at the center of a cylinder with a length of 0.85 to 1.15 times the length of the external thread at one end of the aforementioned shaft-type part. In this way, the size of the internal thread through hole and the external thread of the shaft-type test piece belong to a helical pair.

[0046] Next, the cylinder is cut along the horizontal plane, thus dividing it into two parts, upper and lower. A notch of size L1 is machined on the left side of the upper part along the horizontal plane to meet the above curvature. The right side is machined into the protruding section described above, and a groove is machined on the right side of the lower part.

[0047] Then, a first through hole 4 is machined at the lower end of the protruding section in the upper part, and a second through hole 6 is machined on both sides of the groove in the lower part.

[0048] Insert the lower end of the protruding section into the groove. The first through hole 4 and the second through hole 6 form a pin hole. Insert the pin 9 into the pin hole and connect the main clamping component 7 and the auxiliary clamping component 8 in a hinged manner.

[0049] This invention discloses a method for machining shaft-type parts with external threads at both ends, specifically including the following steps:

[0050] Step 1: First, grasp the first handle shaft 11 and the second handle shaft 12 with your hand to push the first handle shaft 11. By applying a certain pressure, the tension spring 10 is stretched. The main clamping component 7 rotates on the auxiliary clamping component 8. Under the action of the main clamping component 7, the first internal thread groove 3 moves away from the second internal thread groove 5, causing the L1 notch to open, thus allowing the spring to open. Figure 1 The outer circle M1 of the left end of the shaft specimen shown passes through the area between the first internal thread groove 3 and the second internal thread groove 5. Then, the first handle shaft 11 is released. Under the rebound force of the tension spring 10, the first internal thread groove 3 and the second internal thread groove 5 clamp the left end of the shaft part by engaging with the external thread, making the fit stable.

[0051] Step 2: Place the A-type center hole on the left side of the specimen into the front center of the CNC thread grinder, and the A-type center hole on the right side of the specimen into the rear center of the CNC thread grinder. Then, place the second handle shaft 12 onto the lever of the headstock spindle of the CNC thread grinder and connect it securely to it, thus completing the clamping and positioning of the specimen on the CNC thread grinder.

[0052] Step 3: The rotation of the headstock spindle of the CNC thread grinding machine drives the rotation of the lever, which in turn drives the positioning fixture of the present invention to rotate. Then, the rotation of the grinding wheel spindle of the grinding machine drives the grinding wheel to rotate, and the grinding wheel grinds the notched surface of the shaft test piece.

Claims

1. A positioning fixture for a shaft-like part with external threads at both ends, characterized in that, Includes a main clamping component (7), a secondary clamping component (8), a first handle shaft (11), and a second handle shaft (12): The main clamping component (7) and the auxiliary clamping component (8) are elongated. The upper surface of the main clamping component (7) is provided with a first internal thread groove (3) connecting the two ends of its own length direction. The upper surface of the auxiliary clamping component (8) is provided with a second internal thread groove (5) connecting the two ends of its own length direction. The first internal thread groove (3) and the second internal thread groove (5) are both arc-shaped and cooperate with the external threads at both ends of the shaft part. The main clamping component (7) is located at the upper end of the auxiliary clamping component (8). One side of the first internal thread groove (3) is hinged to the corresponding side of the second internal thread groove (5). The other side of the first internal thread groove (3) and the corresponding side of the second internal thread groove (5) are left with a gap above and below. The main clamping component (7) and the auxiliary clamping component (8) are respectively equipped with a first handle shaft (11) and a second handle shaft (12) near the gap. A tension spring (10) is installed between the first handle shaft (11) and the second handle shaft (12). When one end of the shaft part is inserted into the first internal thread groove (3) and the second internal thread groove (5), the tension spring (10) is in a stretched state.

2. The positioning fixture for shaft-like parts with external threads at both ends as described in claim 1, characterized in that, It also includes a third handle shaft (13), which is fixed on the secondary clamping component (8) and located close to the main clamping component (7).

3. The positioning fixture for shaft-like parts with external threads at both ends according to claim 2, characterized in that, The first handle shaft (11), the second handle shaft (12), and the third handle shaft (13) are all made of 40Cr tempered steel.

4. The positioning fixture for shaft-like parts with external threads at both ends according to claim 2, characterized in that, The outer ends of the first handle shaft (11) and the third handle shaft (13) are handles with evenly distributed serrations.

5. The positioning fixture for shaft-like parts with external threads at both ends according to claim 2, characterized in that, The first handle shaft (11), the second handle shaft (12) and the third handle shaft (13) are all cylindrical. The inner end of the first handle shaft (11) is welded to the main clamping component (7), and the inner ends of the second handle shaft (12) and the third handle shaft (13) are welded to the auxiliary clamping component (8).

6. The positioning fixture for shaft-like parts with external threads at both ends according to claim 5, characterized in that, The main clamping component (7) and the auxiliary clamping component (8) are of the same length, and the two ends of the main clamping component (7) and the auxiliary clamping component (8) are flush. The length is 0.85 to 1.15 times the length of the external thread of one end of the shaft part to be positioned. The central axes of the first handle shaft (11), the second handle shaft (12) and the third handle shaft (13) are located on the same horizontal plane, and the horizontal plane is located at the center of the length direction of the main clamping component (7).

7. The positioning fixture for shaft-like parts with external threads at both ends according to claim 1, characterized in that, The cross-section of both the main clamping component (7) and the auxiliary clamping component (8) is a circular ring. The two ends of the circular ring of the auxiliary clamping component (8) are horizontal and evenly distributed. The end face of the circular ring of the main clamping component (7) that is hinged to the auxiliary clamping component (8) is lower than the other horizontally distributed end face.

8. The positioning fixture for shaft-like parts with external threads at both ends according to claim 7, characterized in that, The arc corresponding to the ring of the secondary clamping component (8) is (0.75~0.8)π, and the arc corresponding to the ring of the main clamping component (7) is π.

9. The positioning fixture for shaft-like parts with external threads at both ends according to claim 7, characterized in that, It also includes a pin (9). The cross section of the end face S of the main clamping component (7) that is hinged to the secondary clamping component (8) is an elliptical arc, forming a protruding section of the main clamping component (7). The protruding section is located at the center of the length direction of the main clamping component (7). The length of the protruding section is 0.75 to 0.8 times the length of the main clamping component (7). The elliptical foci corresponding to the arc are F1 and F2. The straight line passing through F1 and F2 is L. The intersection of L and the lowest point of the protruding section is distributed near the outer side of the protruding section. The upper surface of the end face S' corresponding to the end face S in the sub-clamping component (8) is provided with a groove that is inserted into the lower end of the protrusion. The lower end of the protrusion is inserted into the groove. A first through hole (4) connecting the two ends of its own length direction is provided in the lower end of the protrusion. The center of the first through hole (4) is on L. The lower end of the first through hole (4) is close to the lower end of the protrusion. A second through hole (6) connecting itself and located in the length direction of the sub-clamping component (8) is provided on both sides of the groove. The inner diameter of the second through hole (6) is the same as that of the first through hole (4). The center of the second through hole (6) coincides with the center of the first through hole (4). The outer diameter of the pin (9) is the same as the inner diameter of the first through hole (4), and the pin (9) is inserted into the second through hole (6) and the first through hole (4).

10. A method for machining a shaft-type part with external threads at both ends, characterized in that, The shaft-like part is composed of several cylindrical segments with different diameters, and the diameters of each cylindrical segment are distributed in a stepped manner. The cylindrical segments at both ends have the same diameter and are the largest. The cylindrical segment near one end has a notch surface to be machined with a smaller diameter than the cylindrical segment at the corresponding end. The positioning fixture for the shaft-like part with external threads at both ends as described in any one of claims 1 to 9 includes the following steps: S1, push the first handle shaft (11) to stretch the tension spring (10), the main clamping component (7) rotates on the auxiliary clamping component (8), and the first internal thread groove (3) moves away from the second internal thread groove (5) under the drive of the main clamping component (7); S2, pass the external thread of one end of the shaft part through the area between the first internal thread groove (3) and the second internal thread groove (5), release the first handle shaft (11), and under the action of the rebound force of the tension spring (10), the first internal thread groove (3) and the second internal thread groove (5) clamp one end of the shaft part by engaging with the external thread. S3, A-type center holes are provided on both ends of the shaft part. The A-type center hole on the left is placed into the front center of the CNC thread grinding machine, and the A-type center hole on the right is placed into the rear center of the CNC thread grinding machine. Then the second handle shaft (12) is placed on the lever of the headstock spindle of the CNC thread grinding machine to complete the clamping and positioning of the shaft part. S4, the rotation of the headstock spindle of the CNC thread grinding machine drives the rotation of the lever, the rotation of the lever drives the rotation of the positioning fixture, and then the rotation of the grinding wheel spindle drives the grinding wheel to rotate, and the grinding wheel grinds the cylindrical section notch surface of the shaft part.

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