Rivet with improved internal structure

Abstract

A rivet with an improved internal structure comprises a rivet cover, a rivet shoulder and a rivet body, and the improved internal structure is arranged in a rivet cavity formed by the rivet cover and the rivet body. The improved internal structure is an annular boss structure and / or a cone-shaped structure. In the using process, the specific size of the internal structure of the rivet can be designed according to actual requirements, so that the rivet with different inner cavity structures is obtained, the improved structure can effectively overcome the matching problem of the rivet and the thickness of a plate, and higher internal solid-phase connection strength is obtained; and meanwhile, in order to obtain internal structures with different sizes, a modular design method is provided, the joint design is simple, and the quality is controllable. And due to the modular design, the cost of rivet design is reduced, the machining difficulty of the rivet is reduced, and the research and development period of the friction rivet welding process is shortened.

Description

Technical Field

[0001] The present invention relates to a technology in the riveting field, in particular to a rivet with an improved internal structure. Background Art

[0002] Existing applications in aerospace, automotive, and shipbuilding often rely on alloy sheet metal for joining. Due to the high thermal conductivity and linear expansion coefficient of 7-series aluminum alloys, cast aluminum, and magnesium alloys, traditional fusion welding techniques can easily produce defects such as pores, cracks, and voids, resulting in lower joint strength. Furthermore, these materials have relatively poor ductility, making them prone to severe cracking when using traditional solid-phase joining techniques. Summary of the Invention

[0003] This invention addresses the problems of existing riveting welding processes when connecting materials, including the poor adaptability of rivet design to changing process conditions and the difficulty in controlling solid-phase joint strength. By doing so, it proposes a rivet with an improved internal structure. During use, the specific dimensions of the rivet's internal structure can be designed according to actual needs, resulting in rivets with different internal cavity structures. This improved structure effectively overcomes the difficulty of matching the rivet with the plate thickness, achieving higher internal solid-phase joint strength. Furthermore, a modular design approach is proposed to achieve internal structures of varying sizes, resulting in simple joint design and controllable quality. This modular design reduces rivet design costs, eases rivet processing difficulty, and shortens the R&D cycle of friction riveting processes.

[0004] The present invention is achieved through the following technical solutions:

[0005] The present invention relates to a rivet with an improved internal structure, comprising a rivet cover, a rivet shoulder and a rivet body, wherein the rivet cavity formed by the rivet cover and the rivet body is provided with the improved internal structure; the improved internal structure is an annular boss structure and / or a conical structure.

[0006] The length L of the rivet body and the thickness of the workpiece to be connected satisfy: Where: t i is the thickness of the i-th layer of workpieces to be connected, n is the number of layers of workpieces to be connected, and n≥1, so that the rivet legs can be interlocked in the bottom layer of workpieces without the rivet penetrating the lower layer of workpieces.

[0007] The rivet cover is provided with a torque transmission structure and a positioning structure for realizing the feeding motion and rotation motion of the rivet; an annular groove is provided on the nail shoulder for accommodating the material extruded by the nail leg and forming a new interlocking structure.

[0008] The volume V of the rivet cavity satisfies: Where: D I 、D Oare the inner diameter and outer diameter of the nail leg respectively, L is the length of the nail leg, a is the opening amount of the nail leg, and by adjusting the volume of the inner cavity, a joint with a specific nail leg opening amount can be obtained, l c is the distance from the top of the improved internal structure to the bottom of the rivet body, l c <t1, where: t1 is the thickness of the uppermost workpiece. To achieve solid-phase connection at the interface of the uppermost workpiece.

[0009] The maximum depth h of the described rivet cavity satisfies: where D I is the inner diameter of the rivet body, D O is the outer diameter of the rivet body. Thus, there is sufficient space inside the rivet body to accommodate the extruded material, and it is ensured that the final modular combined rivet has sufficient adjustment space.

[0010] The inner diameter D of the described annular boss structure Ic satisfies: 0.2D I <D Ic <0.7D I , where: D I is the inner diameter of the rivet body. Technical effects

[0011] Through the rivet with improved internal shape, the present invention can effectively improve the strength of solid-phase connection and obtain a riveted joint with adjustable nail leg opening amount; through the central convex structure, the strength of solid-phase connection can be effectively adjusted and the filling effect of the inner side thread of the rivet body can be improved; by changing the structure of the rivet inner cavity, the material flow during the rivet forming process has changed greatly. For the rivet with annular boss structure, the area of the fine crystal zone inside the joint expands, the shape becomes triangular, the solid-phase connection strength is significantly improved, and the joint strength is significantly improved; for the rivet with central cone structure, the shape of the fine crystal zone inside the joint becomes a shape with a central depression, the solid-phase connection strength is significantly improved, and at the same time, the filling rate of the thread is also significantly improved, and the joint strength is significantly improved. Description of the drawings

[0012] Figure 1 is the metallographic section diagram of the annular boss structure rivet 1 in Example 1;

[0013] In the figure: rivet cap 101, rivet shoulder 102, rivet body 103, annular boss structure 104;

[0014] Figure 2 (a) to (e) are schematic diagrams of the point connection method in Example ①:

[0015] In the figure: a is the process preparation stage, b is the contact stage, c is the softening stage, d is the welding stage, e is the end stage, and the period between d and e is the rapid feed stage; drive shaft 2, blank holder 3, workpiece to be connected 4, support mechanism 5, pressure sensor 6;

[0016] Figure 3 This is the metallographic diagram of the effect of Example 1;

[0017] In the figure: a fine grain zone 7 formed inside the rivet 1;

[0018] Figure 4 This is a cross-sectional metallographic diagram of the center cone structure rivet 8 in Example 2;

[0019] In the figure: rivet cover 801, rivet shoulder 802, rivet body 803, central cone structure 804;

[0020] Figure 5 (a) to (e) are schematic diagrams of the connection method of Example 2:

[0021] In the figure: a is the process preparation stage, b is the contact stage, c is the softening stage, d is the welding stage, e is the end stage, and the period between d and e is the rapid feed stage; drive shaft 2, blank holder 3, workpiece to be connected 4, support mechanism 5, pressure sensor 6;

[0022] Figure 6 This is the metallographic diagram of the effect of Example 2;

[0023] In the figure: a fine grain zone 9 formed inside the rivet 8;

[0024] Figure 7 This is a schematic cross-sectional view of a rivet with an improved internal structure according to Example 3;

[0025] In the figure: a is an annular boss type combination rivet 10, b is a center cone type combination rivet 11; rivet cover 1001, rivet shoulder 1002, rivet body 1003, cylindrical structure 1004, cylindrical structure 1005, rivet cover 1101, rivet shoulder 1102, rivet body 1103, conical and cylindrical combination structure 1104;

[0026] Figure 8 This is a schematic diagram of a 10-point connection method using an annular boss-type combined rivet in Example 3:

[0027] In the figure: a is the process preparation stage, b is the contact stage, c is the softening stage, d is the welding stage, e is the end stage, and the period between d and e is the rapid feed stage; drive shaft 2, blank holder 3, workpiece to be connected 4, support mechanism 5, pressure sensor 6;

[0028] Figure 9 This is a schematic diagram of the 11-point connection method using a center cone combination rivet in Example 3:

[0029] In the figure: a is the process preparation stage, b is the contact stage, c is the softening stage, d is the welding stage, e is the end stage, and the period between d and e is the rapid feed stage; drive shaft 2, blank holder 3, workpiece to be connected 4, support mechanism 5, pressure sensor 6;

[0030] Figure 10 This is a schematic diagram of the effect of Example 3;

[0031] In the figure: a is a fine grain area 12 formed inside the annular boss type combined rivet 10, and b is a fine grain area 13 formed inside the center cone type combined rivet 11; DETAILED DESCRIPTION Example 1

[0032] like Figure 1 As shown, the rivet 1 with an improved internal structure involved in this embodiment includes: a rivet cover 101, a rivet shoulder 102 and a rivet body 103, wherein: an annular boss structure 104 is provided in the rivet cavity formed by the rivet cover 101 and the rivet body 103.

[0033] In this embodiment, the length L of the rivet body 103 is 4.2 mm, the maximum height h of the rivet cavity is 5.2 mm, and the distance l from the top surface of the annular boss structure 104 to the bottom of the rivet leg 103 is c The inner diameter D of the rivet body 103 is 3.5 mm. I 4mm, outer diameter D O The inner diameter D of the annular boss structure 104 is 6 mm. Ir 3mm.

[0034] like Figure 2 As shown, this embodiment relates to a two-stage connection method for forming a connection joint using the rivet with the improved internal structure, for friction welding and riveting 2 mm thick aluminum alloy 7075-T6 and 2 mm thick aluminum alloy 7075-T6, comprising:

[0035] 1) Process preparation: The workpiece 4 to be connected is fixed by the support mechanism 5 and clamped by the blank holder 3, and the rivet 1 with improved internal structure is fixed on the drive shaft 2.

[0036] 2) Contact stage: When the distance between the bottom of the rivet body 103 and the workpiece 4 to be connected is 1 mm, the drive shaft 2 drives the rivet 1 to rotate at a high speed of 3000 rad / min and feeds downward at a speed of 2 mm / s until the rivet contacts the workpiece to be connected, and the data of the pressure sensor starts to rise from zero.

[0037] 3) Softening stage: The frictional heat generated between rivet 2 and workpiece 4 softens the material, reducing the downward pressure resistance of the rivet. The data of the pressure sensor gradually stabilizes and shows a downward trend.

[0038] 4) Welding stage: When the feed depth is 2.7 mm, the material in the rivet cavity contacts the upper surface of the cylindrical structure 104, and a stirring zone 7 appears inside the rivet. The upper and lower workpieces 4 are welded under the action of the stirring zone, and the data of the pressure sensor shows an upward trend.

[0039] 5) Rapid Feed Stage: Drive shaft 2 drives rivet 1 at a high speed of 3000 rad / min and rapidly feeds it downward at a speed of 4 mm / s until the set feed displacement is reached. The lower end of the rivet body opens to form a mechanical lock.

[0040] 6) Clamping Phase: The rivet's final feed displacement is 4.2 mm, with the rivet shoulder 102 contacting the upper workpiece 4. The blank holder 3 is released. The drive shaft 2 maintains pressure for 1 second before reversing and returning to its original position.

[0041] like Figure 3 As shown in the figure, in the joint obtained by the above process, the lower part of the rivet body is opened, the material in the center of the rivet is solid-phase welded, a triangular fine-grained area appears in the cavity, and the flow of the material is effectively controlled.

[0042] In this embodiment, the maximum riveting force during the riveting process of 2mm aluminum alloy 7075-T6 and 2mm thick aluminum alloy 7075-T6 is 13.2KN, which is 68.9% lower than the riveting force of 42.5KN in the traditional self-piercing riveting method, effectively reducing the process's demand for equipment. The maximum tensile shear force of the joint is 9.2KN, which is 63% higher than the existing self-piercing riveting process and 11.5% higher than the friction riveting process using traditional structural rivets, significantly improving the strength of the joint. Compared with the friction riveting process using traditional rivets, the failure mode of the joint changes from the central aluminum column failure mode to the parent material failure, and the solid-phase connection strength at the center of the joint is improved. Example 2

[0043] like Figure 4 As shown, compared with Example 1, a conical structure 804 is provided in the rivet cavity formed by the rivet cover 801 and the rivet body 803 in this embodiment.

[0044] In this embodiment, the length L of the rivet leg 803 is 4.2 mm, the maximum height h of the rivet cavity is 4.7 mm, and the distance l between the top of the cone-shaped structure 804 and the bottom of the rivet body 803 is c The inner diameter D of the rivet body 803 is 3.7 mm. I 4mm, outer diameter D O 6mm.

[0045] like Figure 5As shown, this embodiment relates to a two-stage connection method for forming a connecting joint using the rivet with the improved internal structure mentioned above, for aluminum alloy 7075-T6 with a thickness of 2 mm and aluminum alloy 7075-T6 with a thickness of 2 mm, compared with Example 1: the rotation speed of the first stage is 2000 rad / min, and the feed speed is 2 mm / s; the rotation speed of the second stage is 1200 rad / min, and the feed speed is 4 mm / s; the feed depth corresponding to the rapid feed stage is 3.5 mm, and the final feed depth is set to 4.2 mm.

[0046] like Figure 6 As shown, in the joint obtained by the above process, the lower part of the rivet body is opened, the center material of the rivet is solid-phase welded, and a fine-grained area 9 with a central depression appears in the cavity. The material flow during the joint forming process is effectively controlled.

[0047] In this embodiment, the maximum riveting force during the riveting process of aluminum alloy 7075-T6 with a thickness of 2mm and aluminum alloy 7075-T6 with a thickness of 2mm is 12.5KN, which is 64.5% lower than the riveting force of the traditional self-piercing riveting method of 35.2KN, effectively reducing the process's demand for equipment; the maximum tensile shear force of the joint is 8.3KN, which is 55% higher than the existing self-piercing riveting process and 10.9% higher than the friction riveting process using only traditional structural rivets, significantly improving the strength of the joint. Compared with the friction riveting process using traditional rivets, the failure mode of the joint changes from the central aluminum column failure mode to the parent material failure, and the solid-phase connection strength of the joint center is improved. At the same time, the thread filling rate is increased from 80% to 100%, and the integrity of the joint is improved.

[0048] like Figure 7 As shown in (a), the annular boss structure can also be realized by arranging a combined structure of a cylindrical structure 1004 and a cylindrical structure 1005 in a rivet body 1003 of a fully hollow structure.

[0049] like Figure 7 As shown in (b), the conical structure can also be realized by setting a conical-cylindrical combined structure 1104 in a semi-hollow rivet body 1103.

[0050] like Figure 8 and Figure 9 As shown in the figure, it is the two-stage connection process of the above-mentioned structural rivets. Figure 10 As shown, the joint obtained by this process is shown. The lower part of the rivet body is opened, and the center material of the rivet is solid-phase welded. A triangular fine-grained area 12 and a central concave fine-grained area 13 appear in the cavity.

[0051] The present invention successfully achieves solid-phase welding within the rivet by using a rivet with an improved internal structure. When only the rivet base is used to connect the aforementioned plate combinations, effective solid-phase welding is not achieved within the rivet body. The rivet with this improved structure successfully improves the connection state of the joint. By adjusting the height of the cylindrical structure, the rivet's adaptability to different plate thickness combinations can be increased. At the same time, compared to rivets with the same non-improved internal structure, the joints using the rivet with the improved internal structure exhibit the same solid-phase welding effect. This combined approach effectively shortens the time and cost of rivet design and processing in the laboratory.

[0052] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principles and purpose of the present invention. The scope of protection of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. All implementation schemes within its scope shall be subject to the constraints of the present invention.

Claims

1. A rivet with an improved internal structure, characterized in that: include: A rivet cover, a rivet shoulder and a rivet body, wherein: the rivet cavity formed by the rivet cover and the rivet body is provided with an improved internal structure; The improved internal structure is an annular boss structure and / or a conical structure.

2. The rivet with improved internal structure according to claim 1, characterized in that: The annular boss structure is realized by arranging a combined structure of a cylindrical structure and a cylindrical structure in a rivet body of a fully hollow structure.

3. The rivet with improved internal structure according to claim 1, characterized in that: The conical structure is realized by arranging a conical-cylindrical combined structure in a semi-hollow rivet body.

4. The rivet with improved internal structure according to claim 1, characterized in that: The length L of the rivet body and the thickness of the workpiece to be connected satisfy: Where: t i is the thickness of the i-th layer of workpieces to be connected, n is the number of layers of workpieces to be connected, and n≥1, so that the rivet legs can be interlocked in the bottom layer of workpieces without the rivet penetrating the lower layer of workpieces.

5. The rivet with improved internal structure according to claim 1, characterized in that: The rivet cover is provided with a torque transmission structure and a positioning structure for realizing the feeding motion and rotation motion of the rivet; an annular groove is provided on the nail shoulder for accommodating the material extruded by the nail leg and forming a new interlocking structure.

6. The rivet with improved internal structure according to claim 1, 2 or 3, characterized in that: The volume V of the rivet cavity satisfies: Where: D I , D O are the inner diameter and outer diameter of the nail leg respectively, L is the length of the nail leg, a is the opening amount of the nail leg, and a joint with a specific nail leg opening amount can be obtained by adjusting the volume of the inner cavity. l c is the distance from the top of the improved internal structure to the bottom of the rivet body, l c < t1, where: t1 is the thickness of the uppermost workpiece, so as to achieve solid-phase connection at the interface of the uppermost workpiece.

7. The rivet with improved internal structure according to claim 1, characterized in that: The maximum depth h of the rivet cavity satisfies: Among them D I D is the inner diameter of the rivet body, O The outer diameter of the rivet ensures that there is sufficient space inside the rivet to accommodate the material to be squeezed in, and ensures that the final internal structure design of the rivet has sufficient adjustment space.

8. The rivet with improved internal structure according to claim 1 or 2, characterized in that: The inner diameter D of the annular boss structure Ic Satisfied: 0.2D I <D Ic <0.7D I , where: D I is the inner diameter of the rivet body.

9. A two-stage connection method for forming a connection joint based on a rivet with an improved internal structure as claimed in any one of claims 1 to 8, characterized in that: include: 1) Process preparation: Fix and clamp the two workpieces to be connected through the support mechanism and the blank holder, and fix the rivet that improves the internal structure through the drive shaft; 2) Contact stage: When the distance between the bottom of the rivet body and the upper workpiece to be connected is 1 mm, the drive shaft drives the rivet to rotate at a high speed of 3000 rad / min and feeds downward at a speed of 2 mm / s until the rivet contacts the workpiece to be connected and the pressure sensor data starts to rise from zero; 3) Softening stage: The frictional heat generated between the rivet and the workpiece softens the material and reduces the downward pressure resistance of the rivet. The data of the pressure sensor gradually stabilizes and shows a downward trend. 4) Welding stage: When the feed depth is 2.7 mm, the material in the rivet cavity contacts the upper surface of the rivet cavity, and a stirring zone appears inside the rivet. The upper and lower workpieces are welded together under the action of the stirring zone, and the pressure sensor data increases; 5) Rapid feed stage: The drive shaft drives the rivet to rotate at a high speed of 3000 rad / min and feeds it downward at a speed of 4 mm / s until the set feed displacement is reached and the lower end of the rivet body opens to form a mechanical lock; 6) Clamping stage: The final feed displacement of the rivet is 4.2 mm. The rivet shoulder contacts the upper workpiece to be connected. The blank holder is released and the drive shaft maintains the pressure unchanged. After holding the pressure for 1 second, the reverse feed is completed.

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