Thin-walled tube internal expansion clamp

Abstract

This utility model discloses an internal expansion clamp for thin-walled tubes, including a mandrel, expansion components, and expansion sleeves disposed on the outside of the mandrel. The expansion sleeves are arc-shaped plate structures, and multiple expansion sleeves are arranged around the circumference of the mandrel. Two expansion components are provided, symmetrically arranged at both ends of the mandrel. When clamping the thin-walled tube, the two ends of the expansion sleeves extend through the inner hole of the thin-walled tube to the outer sides of both ends of the tube, and the two ends of the expansion sleeves respectively abut against the tensioning components at both ends of the mandrel. The expansion components drive the expansion sleeves away from the axial direction of the mandrel to fit and tighten the inner wall of the thin-walled tube through which the expansion sleeves pass. This utility model uses expansion sleeves that pass through the thin-walled tube to tighten and clamp the inner wall of the thin-walled tube, with the expansion sleeves contacting the entire length of the thin-walled tube, thereby increasing the contact area, reducing local stress, and minimizing deformation of the thin-walled tube product.

Description

Technical Field

[0001] This utility model relates to the field of fixture technology for thin-walled tube processing, and specifically to an internal expansion fixture for thin-walled tubes. Background Technology

[0002] Thin-walled tubes are steel pipes with relatively thin walls, typically with an outer diameter to wall thickness ratio greater than 10. Due to their light weight and material savings, thin-walled tubes are widely used in aerospace, automotive manufacturing, and machining, serving as core components for lightweight products. However, their thin walls, poor rigidity, and low strength make them highly susceptible to deformation under external forces during processing. Traditional external clamping fixtures (such as three-jaw chucks) apply external force, easily causing indentations and deformation of the tube wall, failing to meet the demands of high-precision machining.

[0003] To address this issue, internal expansion clamps have emerged. The core principle of internal expansion clamps is to apply radial expansion force from within the thin-walled tube. Through structures such as expansion components, conical mandrels, or fluid pressure, the expansion components are brought into contact with the inner wall of the tube to achieve positioning and clamping. Theoretically, this reduces deformation caused by external extrusion, making it the mainstream clamp type for thin-walled tube processing. For example, Chinese Patent Publication No. CN103223506A discloses a clamp for processing thin-walled steel tubes, which clamps the thin-walled tube by expanding the inner diameter of the tube at both ends of its inner cavity.

[0004] Existing technologies for internal expansion clamps used in thin-walled tubes still have the following main drawbacks:

[0005] 1. Uneven distribution of tension force: In the existing technology, most tensioning components clamp by expanding the blades. The blade contact area is small. Especially when the thin-walled tube is locally tightened at both ends, it is easy to cause local stress concentration, which can lead to deformation or even rupture of the thin-walled tube and reduce the yield.

[0006] 2. Insufficient centering accuracy: After the flaps of the expansion component expand, there is an inclination at the front and rear ends, or the concentricity deviation is difficult to adjust, which affects the perpendicularity and coaxiality of the inner hole and outer circle of the thin-walled tube.

[0007] 3. Narrow range of applicability: Due to structural limitations, the expansion size of the tightening components has a small adjustable range. The adjustable range of some clamps is usually within 1mm, which can only be used to fit thin-walled tubes of a single or small range of sizes, increasing procurement and maintenance costs.

[0008] 4. Poor clamping stability: Some clamps rely on mechanical structure for tightening, and slippage is easy to occur between the workpiece and the tightening surface; although some vacuum adsorption clamps can reduce stress, they have high requirements for the sealing of the contact surface, and it is difficult to adapt to irregular or cylindrical surfaces. In addition, a vacuum must be maintained throughout the process, resulting in high cost and low reliability.

[0009] 5. Residual stress exists: If the residual stress of the thin-walled tube is not released or offset during clamping, the stress release caused by local clamping after processing can easily lead to secondary deformation of the parts, affecting the accuracy and stability. Utility Model Content

[0010] The purpose of this utility model is to solve the above-mentioned technical problems and provide a thin-walled tube internal expansion clamp.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] A thin-walled tube internal expansion clamp includes a mandrel, an expansion assembly, and an expansion sleeve disposed on the outside of the mandrel. The expansion sleeve has an arc-shaped plate structure, and multiple expansion sleeves are disposed around the mandrel. Two expansion assemblies are disposed symmetrically at both ends of the mandrel. When clamping the thin-walled tube, both ends of the expansion sleeve extend through the inner hole of the thin-walled tube to the outer sides of both ends of the thin-walled tube, and both ends of the expansion sleeve abut against the tensioning assemblies at both ends of the mandrel. The expansion assembly drives the expansion sleeve away from the axial direction of the mandrel to fit and tighten the inner wall of the thin-walled tube through which the expansion sleeve passes.

[0013] Furthermore, the expansion assembly includes a tapered sleeve and a nut. The tapered sleeve is fitted onto the end of the mandrel, and the nut is threaded onto the end of the mandrel. The tapered sleeves in the two expansion assemblies are arranged opposite each other, and the nut is located at the ends of the tapered sleeves that are far apart from each other in the two expansion assemblies. The outer surface of the tapered sleeve is set as a conical surface. The outer diameter of the conical surface in the same expansion assembly at the end away from the nut is smaller than the outer diameter at the end near the nut. The tapered sleeve is inserted into the end of the expansion sleeve near the mandrel. The movement of the nut drives the tapered sleeve to move, causing the conical surface to squeeze the expansion sleeve, which in turn causes the expansion sleeve to move away from the mandrel and expand the thin-walled tube.

[0014] Furthermore, the expansion assembly also includes a sheath that is fitted over the outside of the tapered sleeve. The sheath includes an integrally fixed compression ring and a limiting cylinder. The compression ring is located between the nut and the tapered sleeve, and the limiting cylinder extends to cover the outside of the end of the expansion sleeve.

[0015] Furthermore, a limiting step is provided on the mandrel, the limiting step being located on the side of the tapered sleeve away from the nut, and the diameter of the limiting step being larger than the inner diameter of the tapered sleeve.

[0016] Furthermore, the mandrel has coaxial center holes at both ends.

[0017] Furthermore, the expansion sleeve is made of a material with a surface hardness lower than that of carbon steel, such as nylon, a wear-resistant engineering plastic.

[0018] Furthermore, the two ends of the expansion sleeve are provided with inclined surfaces that match the conical surface near the inner wall of the conical sleeve.

[0019] Furthermore, one end of the mandrel is provided with a smooth stepped shaft, which is coaxial with the mandrel.

[0020] The thin-walled tube internal expansion clamp provided by this utility model has the following beneficial effects:

[0021] 1. Uniform tension and zero deformation clamping. The segmented tensioning structure formed by multiple expansion sleeves has a large contact area with the inner wall of the tube and uniform force distribution, avoiding local stress concentration. Even for extremely thin-walled tubes with a wall thickness of ≤1mm, it can reduce indentation, bulging or cracking. In some embodiments, the form and position tolerance of the workpiece after processing is controlled at the micron level, and the yield rate is significantly improved.

[0022] 2. High centering accuracy and strong machining consistency. The tapered surface on the tapered sleeve compresses the expansion sleeve, forming a self-centering adjustment structure. When the expansion sleeve compresses the thin-walled tube, the expansion surface remains coaxial with the spindle throughout the process, meeting the stringent requirements of high-precision machining for positioning reference and ensuring the consistency of machining accuracy of parts during mass production.

[0023] 3. Wide range of applicability and strong versatility. Breaking through the limitation of traditional clamps that require "one clamp per pipe", in some embodiments, the adjustable range of the expansion diameter is extended to 5-20mm. By quickly adjusting or replacing the modular expansion sleeve, it can adapt to thin-walled pipes of different diameters and lengths; there is no need to frequently change clamps, reducing equipment investment and production changeover time.

[0024] 4. Stable clamping and good vibration resistance. The expansion sleeve is fixed by both radial expansion force and axial positioning, so there is no slippage or movement of the workpiece during processing; it can still maintain stable clamping even in high vibration processing scenarios such as cutting and grinding, reducing tool wear and processing errors.

[0025] 5. Relative stress relief ensures long-term stable accuracy. The large contact area between the expansion sleeve and the inner wall of the thin-walled tube reduces the residual stress on the tube itself during clamping, preventing secondary deformation caused by stress release after processing. Reducing residual stress allows the machined thin-walled tube parts to maintain stable dimensional accuracy for a long period of use after leaving the factory, eliminating the need for subsequent straightening processes. Attached Figure Description

[0026] The specific embodiments of this utility model will be described in further detail below with reference to the accompanying drawings:

[0027] Figure 1 A schematic diagram of the structure of a thin-walled tube internal expansion clamp provided by this utility model;

[0028] Figure 2 A schematic diagram of the structure of a thin-walled tube internal expansion clamp and a thin-walled tube in the cooperation state provided by this utility model;

[0029] Figure 3A cross-sectional structural diagram of a thin-walled tube internal expansion clamp in the engagement state with a thin-walled tube provided by this utility model;

[0030] Figure 4 for Figure 3 Schematic diagram of a partial structure at part A in the middle;

[0031] Figure 5 for Figure 3 Schematic diagram of a partial structure in part B;

[0032] Figure 6 for Figure 3 Schematic diagram of the lateral cross-section structure.

[0033] The following are the labels in the diagram: 1. Mandrel; 11. Limiting step; 12. Center hole; 13. Stepped shaft; 2. Expansion assembly; 21. Tapered sleeve; 211. Tapered surface; 22. Nut; 23. Protective sleeve; 231. Extrusion ring; 232. Limiting cylinder; 3. Expansion sleeve; 31. Inclined surface; 9. Thin-walled tube. Detailed Implementation

[0034] It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0035] The technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this utility model, and not all of them. Based on the embodiments of this utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this utility model.

[0036] It should be noted that all directional indications (such as up-down-left-right-forward-backward...) in the embodiments of this utility model are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly. The connection can be a direct connection or an indirect connection.

[0037] like Figures 1-6As shown, a thin-walled tube internal expansion clamp includes a mandrel 1, an expansion assembly 2, and expansion sleeves 3 disposed on the outside of the mandrel 1. The expansion sleeves 3 are arc-shaped plate structures, and multiple expansion sleeves 3 are arranged around the circumference of the mandrel 1. Two expansion assemblies 2 are provided, and the two expansion assemblies 2 are symmetrically arranged at both ends of the mandrel 1. When clamping the thin-walled tube 9, both ends of the expansion sleeves 3 extend through the inner hole of the thin-walled tube 9 to the outer sides of both ends of the thin-walled tube 9, and both ends of the expansion sleeves 3 abut against the tensioning assemblies at both ends of the mandrel 1. The expansion assembly 2 drives the expansion sleeves 3 away from the axial direction of the mandrel 1 to fit and tighten the inner wall of the thin-walled tube 9 through which the expansion sleeves 3 pass. Specifically, in this embodiment, four expansion sleeves 3 are provided.

[0038] By adopting the above technical solution, the inner wall of the thin-walled tube 9 is tightened and clamped by setting an expansion sleeve 3 that passes through the thin-walled tube 9. The expansion sleeve 3 is in contact with the entire length of the thin-walled tube 9, thereby increasing the contact area, reducing local stress, reducing the deformation of the thin-walled tube 9, and improving the processing accuracy.

[0039] Specifically, the tightening assembly 2 includes a conical sleeve 21 and a nut 22. The conical sleeve 21 is fitted onto the end of the mandrel 1, and the nut 22 is threaded onto the end of the mandrel 1. The conical sleeves 21 in the two tightening assemblies 2 are arranged opposite each other, and the nut 22 is located at the ends of the two tightening assemblies 21 that are far from each other. The outer surface of the conical sleeve 21 is set as a conical surface 211. The outer diameter of the end of the conical surface 211 in the same tightening assembly 2 that is far from the nut 22 is smaller than the outer diameter of the end that is close to the nut 22. The conical sleeve 21 is inserted into the end of the expansion sleeve 3 on the side close to the mandrel 1. The movement of the nut 22 drives the conical sleeve 21 to move, so that the conical surface 211 of the conical sleeve 21 presses against the expansion sleeve 3, causing the expansion sleeve 3 to move away from the mandrel 1 and tighten the thin-walled tube 9. By rotating the nut 22 on the mandrel 1, the conical sleeve 21 is driven to move, so that the conical surface 211 of the conical sleeve 21 presses against the expansion sleeve 3, causing the expansion sleeve 3 to move away from the mandrel 1 and tighten the thin-walled tube 9, making the operation convenient and the clamping more stable.

[0040] Specifically, the expansion assembly 2 further includes a sheath 23, which is fitted over the outside of the tapered sleeve 21. The sheath 23 includes an integrally fixed compression ring 231 and a limiting cylinder 232. The compression ring 231 is located between the nut 22 and the tapered sleeve 21, and the limiting cylinder 232 extends to cover the outer side of the end of the expansion sleeve 3. Both ends of the expansion sleeve 3 extend into the limiting cylinder 232, which limits the end of the expansion sleeve 3 to prevent it from falling off. Furthermore, through the contact between the compression ring 231 and the end of the tapered sleeve 21, as the nut 22 rotates with the mandrel 1 via its threads, the nut 22 pushes the compression ring 231 toward the tapered sleeve 21, causing the compression ring 231 to push the tapered sleeve 21 to move. This, in turn, causes the tapered sleeve 21 to compress the expansion sleeve 3, causing it to move away from the mandrel 1 and thus expanding the thin-walled tube 9 product.

[0041] Specifically, a limiting step 11 is provided on the mandrel 1. The limiting step 11 is located on the side of the tapered sleeve 21 away from the nut 22, and the diameter of the limiting step 11 is larger than the inner diameter of the tapered sleeve 21. Thus, the limiting step 11 can block the axial movement of the tapered sleeve 21 and limit the tapered sleeve 21 when the thin-walled tube 9 is not clamped.

[0042] Specifically, the mandrel 1 has coaxial center holes 12 at both ends. This allows cutting equipment, such as a center pin on a lathe, to press against the center holes 12 and support the mandrel 1.

[0043] Specifically, the expansion sleeve 3 is made of a material with a surface hardness lower than that of carbon steel, such as copper or nylon. This causes the expansion sleeve 3 on the contact surface to undergo a certain deformation, thereby increasing the contact area and reducing stress concentration.

[0044] Specifically, the two ends of the expansion sleeve 3 are provided with inclined surfaces 31 that match the conical surface 211 near the inner wall of the tapered sleeve 21. Through the contact and compression of the mutually inclined inclined surfaces 31, the expansion sleeve 3 mandrel 1 is easily compressed outward during the movement of the tapered sleeve 21, so that the expansion sleeve 3 is pressed tightly against the inner wall of the thin-walled tube 9, and the contact area between the expansion sleeve 3 and the tapered sleeve 21 is increased, so as to maintain a stable clamping state during the workpiece cutting process.

[0045] Specifically, one end of the mandrel 1 is provided with a smooth stepped shaft 13, which is coaxial with the mandrel 1. This facilitates the machine tool chuck to clamp onto the stepped shaft 13, making it easy to clamp one end of the mandrel 1 while the other end of the mandrel 1 rests against the machine tool's ejector pin. The smooth stepped shaft 13 ensures a higher degree of coaxiality between the thin-walled tube 9 and the machine tool spindle during clamping.

[0046] In use, install the expansion assembly 2 at the left end of the mandrel 1 onto the mandrel 1, rotate the nut 22 to push the protective sleeve 23 and adjust the tapered sleeve 22 to the appropriate position. The nut 22 locks the protective sleeve 23 and the tapered sleeve 22 to achieve axial positioning of the thin-walled tube 9 workpiece. Insert the expansion sleeve 3 into the protective sleeve 23 at the left end, and put the thin-walled tube 9 product on the outside of the expansion sleeve 3. Install the tapered sleeve 22, protective sleeve 23, and nut 21 at the right end of the mandrel 1 onto the mandrel 1 in sequence, and rotate the nut 21 at the left end of the mandrel 1 to push the protective sleeve 23 and adjust the tapered sleeve 22 to the appropriate position. Insert 22 into the expansion sleeve 3 and continue to rotate the nut 21 so that the outer diameter of the expansion sleeve 3 is in complete contact with the inner diameter of the thin-walled tube 9, achieving the effect of internal expansion and tightening; clamp the stepped shaft 13 at the left end of the mandrel 1 on the chuck of the machine tool, and use the ejector pin of the tailstock of the machine tool to abut against the center hole at the right end of the mandrel 1, using a clamping and ejecting method to clamp the entire fixture, and use the equipment to cut and process the thin-walled tube 9; after processing, remove the nut 21 at the right end, the expansion sleeve 3 retracts, and the thin-walled tube 9 product is taken out, completing the workpiece clamping and processing.

[0047] The parts not covered in this technical solution can be implemented using existing technologies.

[0048] The foregoing has shown and described the basic principles, main features, and characteristics of this utility model. Those skilled in the art should understand that this utility model is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this utility model. Various changes and modifications can be made to this utility model without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed utility model. The scope of protection of this utility model includes the appended claims and their equivalents.

Claims

1. A thin-walled tube internal expansion clamp, characterized in that: The device includes a mandrel (1), a tensioning assembly (2), and a tension sleeve (3) disposed on the outside of the mandrel (1). The tension sleeve (3) is an arc-shaped plate structure. Multiple tension sleeves (3) are disposed around the mandrel (1). Two tensioning assemblies (2) are disposed, and the two tensioning assemblies (2) are symmetrically disposed at both ends of the mandrel (1). When clamping the thin-walled tube (9), both ends of the tension sleeve (3) extend through the inner hole of the thin-walled tube (9) to the outside of both ends of the thin-walled tube (9). The two ends of the tension sleeve (3) abut against the tensioning assemblies at both ends of the mandrel (1). The tensioning assembly (2) drives the tension sleeve (3) away from the axial direction of the mandrel (1) to fit and tighten the inner wall of the thin-walled tube (9) through which the tension sleeve (3) is inserted.

2. The thin-walled tube internal expansion clamp according to claim 1, characterized in that: The expansion assembly (2) includes a tapered sleeve (21) and a nut (22). The tapered sleeve (21) is fitted onto the end of the mandrel (1), and the nut (22) is threaded onto the end of the mandrel (1). The tapered sleeves (21) in the two expansion assemblies (2) are arranged opposite to each other. The nut (22) is located at the end of the tapered sleeves (21) in the two expansion assemblies (2) that are far away from each other. The outer surface of the tapered sleeve (21) is set as a tapered surface (211). The outer diameter of the tapered surface (211) in the same expansion assembly (2) that is far away from the nut (22) is smaller than the outer diameter of the end that is close to the nut (22). The tapered sleeve (21) is inserted into the end of the expansion sleeve (3) on the side close to the mandrel (1). The movement of the nut (22) drives the tapered sleeve (21) to move, so that the tapered surface (211) squeezes the expansion sleeve (3), so that the expansion sleeve (3) moves away from the mandrel (1) and expands the thin-walled tube (9).

3. The thin-walled tube internal expansion clamp according to claim 2, characterized in that: The expansion assembly (2) also includes a sleeve (23), which is fitted over the outside of the tapered sleeve (21). The sleeve (23) includes an integrally fixed compression ring (231) and a limiting cylinder (232). The compression ring (231) is located between the nut (22) and the tapered sleeve (21), and the limiting cylinder (232) extends to cover the outside of the end of the expansion sleeve (3).

4. The thin-walled tube internal expansion clamp according to claim 3, characterized in that: The mandrel (1) is provided with a limiting step (11), which is located on the side of the tapered sleeve (21) away from the nut (22) and the diameter of the limiting step (11) is greater than the inner diameter of the tapered sleeve (21).

5. A thin-walled tube internal expansion clamp according to claim 3, characterized in that: The mandrel (1) has coaxial center holes (12) at both ends.

6. The thin-walled tube internal expansion clamp according to claim 3, characterized in that: The two ends of the expansion sleeve (3) are provided with inclined surfaces (31) that match the conical surface (211) near the inner wall of the conical sleeve (21).

7. A thin-walled tube internal expansion clamp according to claim 3, characterized in that: One end of the mandrel (1) is provided with a smooth stepped shaft (13), and the stepped shaft (13) is coaxial with the mandrel (1).

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