Combined rivet, manufacturing method thereof and dissimilar metal joint welded by adopting combined rivet

Abstract

The invention provides a combined rivet which comprises a cap and a core part, so that when the rivet is manufactured, the cap and the core part are made of different types of metal respectively, a combined rivet connecting part is formed by the top surface of the core part and the center part of the top surface of the cap, and mechanical connection of the core part and the cap is achieved. And the difficulty and the manufacturing cost of combined installation of the cap and the core part are reduced. Meanwhile, metallurgical self-healing of the combined rivet connecting part arranged in the center is achieved in the welding process, and the excellent welding effect of the combined rivet is guaranteed. The invention further provides a manufacturing method of the combined rivet and a joint of dissimilar metal welded by the combined rivet.

Description

Technical Field

[0001] This invention belongs to the field of welding dissimilar alloys, specifically relating to a combination rivet, its manufacturing method, and a dissimilar metal joint welded using the combination rivet. Background Technology

[0002] In recent years, lightweight aluminum and magnesium alloys have been increasingly used in automobile manufacturing to replace some steel components, achieving weight reduction in the vehicle body. Meanwhile, the steel components used in automobiles are also trending towards higher (ultra-high) strength, such as the extensive use of ultra-high strength hot-formed steel (1500–2000 MPa) in critical load-bearing areas. Therefore, the demand for joining dissimilar metals, such as aluminum and steel, in automobiles is very high. However, traditional welding processes, such as resistance spot welding, laser welding, and arc welding, tend to generate brittle intermetallic compounds in the weld, which are easily induced by weld thermal stress and residual stress, leading to joint performance that fails to meet standards.

[0003] Traditional mechanical joining methods, such as self-piercing riveting and flow drill screws, struggle to form reliable joints when joining dissimilar metal materials containing high (or ultra-high) strength steel due to the difficulty in piercing the high-strength steel workpiece. Currently, a welding-riveting hybrid welding method based on resistance spot welding for joining dissimilar metals exists. This method utilizes the pressure and resistance heat softening properties of resistance spot welding to press the rivet into the low-melting-point workpiece (e.g., aluminum alloy) and connect it to the high-melting-point workpiece (e.g., high-strength steel). The rivet is then firmly riveted to the low-melting-point workpiece (e.g., aluminum alloy), achieving both welding and riveting connections between dissimilar metals. To ensure stable and reliable welding of dissimilar metals while maintaining low-cost rivet manufacturing, numerous research efforts have focused on improving the rivet structure.

[0004] For example, patent document CN 118650261 A discloses a fastener (referred to herein as a rivet) with a cap having a thin wall and an end flush with the lower end face of the shaft. The rivet's shaft side arm is designed as a rounded shaft side arm structure with multiple arc transitions. This structural design is beneficial for improving the plastic flow of the material during stamping manufacturing, improving the forming of the thin-walled cap structure, and enhancing the rivet's ability to pierce the workpiece while ensuring the weld point forming effect. However, due to the significant thickness difference between the shaft and cap structures, the thin-walled cap requires multiple stamping thinning processes during production, which leads to higher manufacturing costs.

[0005] Patent CN118595755A proposes a manufacturing method for a split-type stamped rivet. The thin-walled area of ​​the cap is manufactured using a thin blank, while the thicker shaft area is manufactured using a thick blank. This method significantly reduces rivet manufacturing costs. However, the riveting scheme for the cap and shaft of this composite rivet is relatively complex, and there is still considerable room for optimization.

[0006] Therefore, it is necessary to improve the rivet assembly structure to reduce the complexity of the rivet structure, improve the reliability of the rivet assembly and the stability during welding, and reduce the manufacturing cost of the rivets. Summary of the Invention

[0007] To reduce the structural complexity of composite rivets, improve their manufacturing stability, and lower manufacturing costs, a composite rivet is provided according to one aspect of the present invention. The rivet includes a cap and a core. The cap is in the shape of an inverted bowl, and a cap connecting portion is provided at the center of its top surface. The core has a core connecting portion at the center of its top surface that mates with the cap connecting portion. The core is located inside the cap, and its top surface is in contact with the cap top surface, causing the core connecting portion and the cap connecting portion to deform and lock together upon contact, forming a composite rivet connecting portion and achieving mechanical anchoring of the cap and core.

[0008] Optionally, the cap connecting part is a riveting hole penetrating the top surface of the cap, and the core connecting part is an upwardly protruding pin. When the protruding pin is inserted into the riveting hole, its top end is plastically deformed under pressure to form a radially expanding brim structure, so that the protruding pin and the side wall of the riveting hole form an interference fit.

[0009] Optionally, the cap connecting part is a blind riveting hole that does not penetrate the top surface of the cap, and the core connecting part is an upwardly protruding pin with an expansion portion at the top. When the protruding pin is installed in contact with the blind riveting hole, the expansion portion is compressed and expands radially within the blind riveting hole, locking it with the blind riveting hole.

[0010] Optionally, the cap connecting part is a locking part, and the core connecting part is a concave hole. The locking part is formed by plastic deformation caused by mechanical force acting on the central area of ​​the cap, and the locking part is embedded in the concave hole to form a mechanical interlock.

[0011] Preferably, the diameter D1 of the rivet hole is smaller than the diameter D2 of the protruding pin, so that the two form an interference fit when they are in contact and installed.

[0012] Optionally, an annular groove is provided around the root of the protruding pin. When the protruding pin is deformed and locked, some material around the cap connection is squeezed into the annular groove to achieve tolerance compensation and secondary locking.

[0013] Preferably, the cap connecting part is provided with a convex ring structure that conforms to the annular groove around its periphery, thereby improving the locking effect between the cap connecting part and the core connecting part.

[0014] Preferably, the diameter D3 of the top surface of the core is greater than twice the maximum diameter D4 of the combined rivet connection portion, and the diameter D4 ranges from 2 mm to 4 mm.

[0015] Optionally, as the top surface of the cap extends from the outer edge to the center, the wall thickness of the cap gradually increases, with the maximum wall thickness located in the area surrounding the cap connection portion; as the top surface of the core extends from the outer edge to the center, it has a downwardly concave curved structure, forming a conformal fit with the inner top surface of the cap.

[0016] Preferably, the gap formed after the inner top surface of the cap and the top surface of the core are fitted together does not exceed 0.5 mm.

[0017] Optionally, the cap extends from the center of the top surface to the lower end surface of the cap in a bowl-shaped structure, and the wall thickness of the cap first decreases and then increases. The minimum wall thickness T2 of the cap appears in the bending area and is not less than 0.2 mm. The maximum wall thickness T1 of the cap is adjacent to the cap connection part and is less than 1 mm.

[0018] Preferably, the minimum wall thickness T2 of the cap is controlled within the range of 0.3 mm to 0.45 mm, and the maximum wall thickness T1 of the cap is controlled within the range of 0.6 mm to 0.8 mm.

[0019] Optionally, the lower end face of the core does not protrude from the plane containing the lower end face of the cap.

[0020] Optionally, the volume fraction of ferrite in the microstructure of the cap is greater than 90%, and the volume fraction of martensite in the microstructure of the core is greater than 30%.

[0021] According to another aspect of the present invention, a method for manufacturing a composite rivet is provided, wherein a cap and a core are manufactured separately, wherein the cap is manufactured by a first mold in a first press, and the core is manufactured by a second mold in a second press; the core is conveyed from a continuous feeder on the side of the first mold into the first mold, so that the core and the cap in the first mold are aligned and assembled; pressure is applied to plastically deform the cap connecting part and the core connecting part and mechanically anchor and lock them together, thereby realizing the parallel manufacturing of the core and the cap.

[0022] Optionally, the forming process of the combined rivet in the first die includes:

[0023] S1. Multiple drawing: The cap blank is drawn multiple times through the first die core to form the cap shape;

[0024] S2, Shaping: Correcting the shape of areas such as wrinkles and depressions on the surface of the cap to form a cap with the target precision;

[0025] S3. Trimming and punching: Correct the lower end face of the cap to meet the design size requirements, and punch out the cap connection part at the center of the top surface of the cap.

[0026] S4. Connection: The core is conveyed to the first mold by a continuous feeder and assembled with the cap. Pressure is applied by the anchoring mold to achieve a mechanical lock connection between the core and the cap.

[0027] According to another aspect of the present invention, a dissimilar metal joint using the combined rivet welding of the present invention is provided. The dissimilar metals include a first alloy with a melting point below 700°C and a second alloy with a melting point above 1300°C. During welding, the core of the combined rivet penetrates the first alloy, and its bottom surface forms a contact interface with the second alloy, with at least a portion of this contact interface being a welded portion. The contact interface in the combined rivet connection portion, as well as the contact surface between a portion of the inner top surface of the cap and the top surface of the core, constitutes a metallurgical welded interface. The cap of the combined rivet is located on the upper surface of the first alloy, and the top surface of the cap forms a concave shape from the outside in. The annular closed cavity of the cap accommodates the effluent metal discharged during welding, forming a mechanical riveting structure. The gap between the inner top surface of the cap and the top surface of the core is filled with the effluent metal discharged during welding. The sidewalls of the core are surrounded by a first metal melting zone, and the first metal melting zone and a portion of the effluent metal are fused together.

[0028] Optionally, at least a portion of the contact surface between the first alloy melting zone and the core sidewall forms a metallurgical weld, and the discharged metal forms a metallurgical weld with at least a portion of the contact surface between the core and the cap sidewall.

[0029] Optionally, the core of the combined rivet is made of the same type of steel as the second alloy.

[0030] The beneficial effects of this invention are:

[0031] (1) The cap and core of the rivet can be manufactured independently using different materials, which reduces the manufacturing difficulty and cost of the rivet and ensures the manufacturing precision of the rivet.

[0032] (2) The cap and the core are mechanically connected by a rivet connection in the central part, which greatly reduces the difficulty of assembling the cap and the core.

[0033] (3) The combined rivet connection is set in the center, which improves the deformation ability of the top surface of the cap and the arc area during welding and improves the welding point forming effect.

[0034] (4) The combined rivet connection part is set in the center, avoiding the combination rivet connection part on the outer periphery of the cap, avoiding the connection part on the outer periphery of the cap and reducing the volume of the cap forming the receiving cavity, which is conducive to increasing the volume of the cap forming the receiving cavity and ensuring that the first alloy discharged during the welding process is fully contained.

[0035] (5) The combined rivet connection is set in the center to ensure a uniform transition of wall thickness in the outer area of ​​the cap, which can avoid uneven deformation and cracking of the cap during welding.

[0036] (6) The combination rivet is riveted by interlocking the rivet hole in the center of the cap and the protruding pin in the center of the core. On the one hand, it has a high reliability of connection performance, and on the other hand, the connection structure between the cap and the core is simple, which is conducive to the low cost and high stability of the production of the combination rivet.

[0037] (7) The combined rivet connection part set in the center has a small size and reliable riveting quality. After welding, the mating surface in the combined rivet connection part will form a metallurgical fusion interface, so that the cap and the core have both mechanical and metallurgical connection effects, ensuring that the cap will not fall off during use.

[0038] (8) The small size of the combined rivet connection part located in the center has little impact on welding, thus ensuring the welding effect of the combined rivet. Attached Figure Description

[0039] Figure 1 This is a three-dimensional schematic diagram of the outer surface of the cap in one embodiment;

[0040] Figure 2 This is a cross-sectional schematic diagram of the cap in one embodiment;

[0041] Figure 3 This is a three-dimensional schematic diagram of the core in one embodiment;

[0042] Figure 4 This is a schematic cross-sectional view of the core in one embodiment;

[0043] Figure 5 This is a schematic cross-sectional view of the cap and core assembled in one embodiment;

[0044] Figure 6 This is a cross-sectional schematic diagram of the combined rivet in one embodiment;

[0045] Figure 7 for Figure 6 Enlarged view of the middle combination rivet connection and surrounding area

[0046] Figure 8 This is a three-dimensional schematic diagram of the combined rivets in one embodiment;

[0047] Figure 9Schematic diagram of rivet holes for caps with different structures;

[0048] Figure 10 Schematic diagrams of core cross-sections with different structures;

[0049] Figure 11 A schematic diagram of the combined rivet formed by the core structure and the cap in another embodiment;

[0050] Figure 12 This is a schematic diagram of the combined rivet stamping manufacturing process in one embodiment;

[0051] Figure 13 A schematic diagram of a combined rivet connection part being formed;

[0052] Figure 14 This is a schematic diagram of another type of combined rivet connection.

[0053] Figure 15 A schematic diagram of another type of combined rivet connection;

[0054] Figure 16 This is a schematic diagram of another type of combined rivet connection.

[0055] Figure 17 A schematic diagram of the position configuration and weld preheating process for welding dissimilar metals with composite rivets;

[0056] Figure 18 A schematic diagram of the cross-sectional characteristics of a joint obtained by welding dissimilar metals with combined rivets;

[0057] Figure 19 Optical microscope images of the surface and cross-section of the combined rivet in Example 1;

[0058] Figure 20 This is a surface morphology image taken by an optical microscope after welding the combined rivets in Example 1;

[0059] Figure 21 The image shows a cross-section of the weld point after the combined rivets were welded, as captured by an optical microscope in Example 1.

[0060] Figure 22 for Figure 21 A magnified optical microscope image of a portion of the image.

[0061] The attached table of numbers and names is as follows:

[0062] Detailed Implementation

[0063] The following detailed description of the combined rivet of the present invention, with reference to specific embodiments and accompanying drawings, should be understood. It should be understood that the dimensions mentioned herein are not limited by the dimensions or scale of the schematic diagrams, and the descriptions of the combined rivet, such as the terms "upper," "lower," "left," "right," "inner," and "outer," are merely relative descriptions of the relative positional relationships of the various regions in conjunction with the arrangement of the combined rivet in the accompanying drawings. For some descriptive terms, such as "first…" and "second…," they are only used to distinguish one region (or object) from another, and do not necessarily require or imply any actual progression or ordering relationship between these regions (or objects).

[0064] like Figure 1 The diagram shows the structure of the combined rivet cap, which consists of the following parts: the top surface 104 of the cap expands radially outward and then bends downward to form an arc-shaped area 103, which continues to extend downward to form the side wall 102 of the cap. The lower end surface 101 of the cap is an open end and is located on the same plane, presenting an inverted bowl-shaped structure. A rivet hole 105 is provided at the center of the top surface of the cap.

[0065] Figure 2 The cross-sectional structural features of the cap are shown. The cap features a thin-walled design (thickness < 1 mm) and is integrally extruded from a thin metal blank. Generally, the cap is manufactured using low-carbon steel through stamping to ensure good formability and dimensional accuracy. Preferably, the low-carbon steel used has a ferrite volume fraction > 90% and an elongation > 30%. The wall thickness of the cap first decreases and then increases from the center of the top surface towards the opening end.

[0066] The area surrounding the riveting hole 105 has the maximum wall thickness T1, a design that benefits riveting strength and weldability. Preferably, T1 ranges from 0.6 to 0.8 mm.

[0067] The minimum wall thickness T2 is set at the arc-shaped zone 103 to optimize the adaptability to welding deformation. The preferred range for T2 is 0.3–0.45 mm.

[0068] The wall thickness T3 at the lower end face 101 is greater than T2, and the preferred range is 0.4 to 0.5 mm.

[0069] The top surface 104 of the cap comes into contact with the electrode end face during resistance spot welding. Therefore, the diameter D1 of the riveting hole 105 should be minimized to ensure a larger contact area between the top surface of the cap and the electrode end face, thus reducing the impact of the riveting hole on the welding process. A preferred range for D1 is 2–3 mm.

[0070] Figure 3 and Figure 4The three-dimensional morphology and cross-sectional features of the core 200 of the composite rivet are shown. A raised pin 206 is located at the center of the top surface 205 of the core, with its top plane being the top surface 207 of the raised pin. In design, the outer diameter D3 of the top surface 205 of the core is much larger than the maximum diameter D2 of the raised pin 206, preferably satisfying the relationship D3 ≥ 3 × D2. It is worth noting that the top surface 205 of the core exhibits a downward concave trend as it extends from the periphery towards the raised pin 206. This structural design facilitates the concentration of material in the central area to form the raised pin 206 during the stamping process, and also facilitates contact and mating with the cap top surface 104, whose wall thickness gradually increases from the outside to the inside, ensuring a flat cap top surface without upward protrusion. The flange 202 at the outermost edge of the core provides the support force required for mechanical riveting of the workpiece during the welding of the composite rivet. The shaft portion 201 extends downwards after receding inwards from the flange portion, and its sidewall 204 gradually converges in cross-section, eventually converging at the bottom surface 203 of the core portion. This structure of the shaft portion facilitates piercing the first alloy workpiece during welding. The bottom surface 203 of the core portion is planar. Preferably, the diameter of the bottom surface of the core portion is in the range of 4 to 5.5 mm.

[0071] like Figure 5 As shown, the cross-sectional shape of the core and cap after assembly demonstrates their mating relationship. To achieve a secure riveting connection between the core and cap, the protruding pin 206 will protrude from the area surrounding the top surface 104 of the cap during assembly. Simultaneously, to ensure assembly accuracy, the diameter D1 of the riveting hole 105 is designed to be... Figure 2 ) is set to be less than the maximum diameter D2 of the protruding pin 206. Figure 4 This allows for an interference fit when the two parts are joined. Ultimately, the top surface 205 of the core and the inner top surface 104' of the cap can achieve a tight fit.

[0072] Figure 6 The cross-sectional structure after the core and cap are assembled and riveted is shown. As can be seen from the figure, the protruding pin undergoes plastic deformation under external force, and the resulting deformed protruding pin 206' exerts a compressive effect on the wall of the riveting hole 105, thereby increasing the riveting strength. Meanwhile, as... Figure 7 As shown, the outer periphery of the top surface 207 of the deformed protrusion will expand outward to form the brim structure 208, which further enhances the connection between the cap and the core through mechanical locking.

[0073] Regarding dimensional control, to ensure the flatness of the top surface 104 of the combined rivet cap, the height H1 of the protruding pin top surface 207 protruding from the top surface of the cap around the rivet hole should be controlled within 0.5 mm. Furthermore, as... Figure 6As shown, the top surface 205 of the core and the inner top surface 104' of the cap must fit tightly together, and the gap between the two fitting surfaces should not exceed 0.5 mm. At the same time, it is preferable to set the bottom surface 203 of the core and the lower end surface 101 of the cap on the same plane to ensure that the combined rivet can collect the metal discharged from the weld point in real time during use.

[0074] from Figure 6 It can also be seen that the maximum diameter D4 of the connecting part of the combined rivet of the present invention is much smaller than the end face diameter D5 of the upper welding electrode 300. This design not only reduces the influence of the connecting part of the combined rivet on the contact state between the electrode end face and the combined rivet, but also ensures that the end face of the upper welding electrode 300 can effectively press the top surface 104 of the cap in the circumferential direction, thereby facilitating the metallurgical fusion of the contact surfaces in the connecting part of the combined rivet.

[0075] Figure 8 The three-dimensional structural details of the composite rivet are shown. The core 200 is installed at the center of the cap 100, forming a semi-open annular cavity structure with the cap.

[0076] like Figure 9 As shown, a riveting hole 105 is provided at the center of the top surface of the cap 100. Its specific outline can be customized according to design requirements to ensure that the combined rivet connection part has good forming performance, a smooth surface effect, and reliable riveting quality. Preferably, the specific shape of the riveting hole can adopt the following design schemes:

[0077] 1) such as Figure 9 The countersunk hole shape shown in B;

[0078] 2) such as Figure 9 The inclined hole wall structure shown in C;

[0079] 3) such as Figure 9 The side wall features a localized downward deformation design, as shown in Figure D.

[0080] These design optimizations all contribute to improving the overall performance of riveted connections.

[0081] Figure 10 Four preferred cross-sectional designs for the rivet core of this assembly are shown. Among them, Figure 10 The structure shown in Figure A has a planar bottom surface 203 for the core, a vertical side wall 204 for the shaft, and a chamfered structure 204' around the bottom surface of the core to improve the effect of the shaft 201 piercing the workpiece. The flange 202 is formed by the shaft side wall 204 tilting upward and extending outward, and the top surface 205 of the core has a planar structure. The central protruding pin 206 can be designed as a regular geometric shape (such as a cylinder or prism).

[0082] Figure 10The core structure shown in Figure B eliminates the flange design, and the top surface 205 of the core extends towards the center in a concave shape. In this structure, the protruding pin 206 adopts a frustum-shaped design to optimize the assembly efficiency of its riveting hole with the cap.

[0083] exist Figure 10 In the core structure of the C-type connector, the bottom surface 203 of the core is spherical, the side wall 204 of the shaft extends upward in an inclined expansion state, and the flange 202 is formed by the horizontal extension of the upper end of the side wall of the shaft. The top surface 205 of the core extends towards the center in a raised shape. In this structure, the protruding pin 206 adopts a conical design, which can directly pierce the center part of the cap during the cap assembly process, simultaneously realizing the formation of the riveting hole and the establishment of the combined rivet connection.

[0084] Figure 10 The structure shown in Figure D eliminates the flange design. The top surface 205 of the core is a flat structure, and the raised pin 206 on it adopts a stepped design that is larger at the top and smaller at the bottom. This structural optimization helps to improve the connection strength with the cap riveting hole. It should be noted that, depending on the differences in the thickness and physical properties of the workpieces being welded in actual working conditions, the above core structure can be adaptively improved and optimized.

[0085] In yet another embodiment, the core structure is as follows: Figure 11 As shown in Figure A: An annular groove 209 is provided around the protruding pin 206, the bottom surface of which is lower than the top surface 205 of the core. When the cap and the core are assembled, the riveting hole 105 on the cap is significantly compressed under the action of the deformed protruding pin 206', causing the material around the riveting hole to be pressed into the annular groove 209. This design not only helps to control the top surface 207 of the protruding pin to be flush with the top surface 104 of the cap, but also helps to ensure that the inner top surface 104' of the cap and the top surface 205 of the core fit tightly, thereby effectively reducing the gap between them. In addition, in this embodiment, the bottom surface 203 of the core can be designed to be slightly higher than the horizontal plane where the lower end surface 101 of the cap is located, and the distance H2 between them is preferably less than 1 mm.

[0086] In one embodiment, the combined rivet of the present invention is manufactured using a stamping process, the specific process of which is as follows: Figure 12 As shown, the cap 100 is continuously stamped on the first press 501 using a first mold 503: the cap blank 502 is continuously fed into the first mold, and pressure is applied sequentially by multiple first mold cores 504 to achieve the integrated forming of the cap. Simultaneously, the core 200 is continuously stamped on the second press 510 using a second mold 512. The core blank 511 is continuously fed into the second mold, and after multiple pressure applications, a core structure conforming to the design requirements is formed.

[0087] To complete the assembly of the core and cap, the core 200 produced by the second press needs to be conveyed to the continuous feeder 506 via the core transfer path 514. A rigorous inspection process (not shown) for the core's dimensions and appearance is also included in this transfer path to ensure core quality. Qualified cores are placed in the continuous feeder 506, automatically oriented and sorted, and fed into the first mold along the feeding track 507. Subsequently, a gripping mechanism installed around the anchoring mold 505 precisely aligns it with the cap, and under the pressure of the anchoring mold, the core 200 and cap 100 are anchored and assembled, thus achieving parallel production of the core and cap.

[0088] Based on actual production conditions, the preferred combination of rivet forming process in the first die includes the following steps:

[0089] S1. Multiple drawing: The cap blank is drawn multiple times using the first die core to gradually form the predetermined shape of the cap.

[0090] S2. Shaping process: Correcting wrinkles and depressions on the surface of the cap to ensure that the target accuracy requirements are met.

[0091] S3. Trimming and punching: Adjust the dimensions of the lower end face of the cap and punch out the cap connection part at the center of the top face of the cap.

[0092] S4. Assembly and Connection: The core is conveyed to the first mold by a continuous feeder and assembled with the cap. Subsequently, under the pressure applied by the anchoring mold, the connecting parts of the core and the cap come into contact with each other to form a locking structure, completing a reliable connection.

[0093] Figure 13 An anchoring process for a combined rivet connection is demonstrated. In this process, when the cap 100 and the core 200 are assembled, an anchoring mold 505 with a central protrusion structure is used for stamping. This process creates a suitable indentation at the center of the top surface 207 of the protruding pin, pushing the protruding pin material to expand outward as a whole, ultimately forming a deformed protruding pin 206' that firmly locks the sidewall of the rivet hole.

[0094] Figure 14 This demonstrates yet another anchoring and forming process for a combined riveted joint. For example... Figure 14 As shown in Figure A, under this process, a recessed hole 210 is provided at the center of the top surface of the core, while the wall thickness of the cap 100 is appropriately increased and the riveting hole is eliminated at the center. Figure 14 As shown in Figure B, under the extrusion action of the anchoring mold 505, a recessed portion 106 is formed in the center of the cap, and some material is squeezed into the core recessed hole 210, thereby forming a reliable locking portion 107.

[0095] Figure 15This demonstrates another method for anchoring and forming the connection of combined rivets. From Figure 15 As can be seen from Figure A, a blind riveting hole 108 is provided in the center of the cap 100, and an annular recess 209 is provided around the protruding pin 206 of the core 200. This design helps to maintain the integrity of the top surface of the cap. Under the extrusion action of the anchoring mold 505 (such as... Figure 15 As shown in Figure B), the sidewall material of the riveting blind hole 108 is squeezed into the annular recess 209, while the protruding pin 206 undergoes upsetting deformation to form 206', and forms a mechanical lock with the sidewall of the riveting blind hole 108. It is worth noting that in this embodiment, the bottom surface 203 of the core can protrude above the plane of the lower end surface 101 of the cap, and the distance H3 between the two is preferably less than 0.5 mm.

[0096] Figure 16 This demonstrates another method of anchoring and forming the connection of a combined rivet. Figure 15 The structures shown are different (e.g.) Figure 16 As shown in Figure A), this embodiment has a recess at the center of the protruding pin 206, thereby forming an annular extension 211 around it. When the protruding pin is combined with the riveting blind hole 108, under the squeezing action of the anchoring die 505 (as shown in Figure A), the protruding pin is formed into a ring-shaped extension 211 around it. Figure 16 As shown in Figure B), the expansion portion 211 undergoes expansion deformation and forms an interlocking structure with the riveting blind hole 108, thereby achieving a firm connection between the cap and the core.

[0097] like Figure 17 As shown in Figure A, this invention employs a combination rivet to weld dissimilar metals. Specifically, a low-melting-point first alloy 600 is placed on top of a high-melting-point second alloy 700, and the combination rivet is positioned on the surface of the first alloy 600. The upper welding electrode 300 is located above the combination rivet, and the lower welding electrode 400 is located below the second alloy 700.

[0098] Figure 17 Figure B illustrates the structural state during the preheating stage: the upper and lower welding electrodes apply pressure and preheating current to the weld joint, ensuring close contact between the electrodes and the workpiece, thus creating conditions for subsequent welding. During this process, the bottom surface 203 of the core and the lower end surface 101 of the cap are tightly bonded to the surface of the first alloy 600, forming an annular sealed cavity V1. Specifically, the preheating current softens the deformed protruding pin, improving the contact between the upper welding electrode and the top surface 104 of the cap and the top surface of the protruding pin. Furthermore, in the pressing area of ​​the upper welding electrode, the inner top surface 104' of the cap and the top surface 205 of the core are also in close contact; while in the outer peripheral area, the gap between them may increase due to the deformation of the cap under stress.

[0099] like Figure 18 As shown in Figure A, the welding process is divided into two stages:

[0100] 1) Puncture stage: A specific current is input to melt the first alloy 600. The molten metal is discharged into the annular cavity under the extrusion action of the core 200. As the molten material is discharged, the core quickly penetrates the first alloy and comes into contact with the second alloy 700.

[0101] 2) Welding stage: Welding current is then applied to form a weld nugget 701 at the contact surface between the core and the second alloy, thus achieving a metallurgical connection between the two.

[0102] During this process, the top surface 104 of the cap moves downward due to the pressure from the upper welding electrode, and bends upward in the outer peripheral area where the upper welding electrode contacts, separating from the outer periphery of the core top surface. During welding, local areas of the cap undergo plastic deformation, and the cap eventually forms an annular cavity V2 that can still completely contain the discharged metal 602. At the same time, the resistance heat generated by the welding current further expands the melting zone 601 of the first alloy, and fuses it with the discharged metal 602 in the cap to form a whole.

[0103] Figure 18 B represents the final joint cross-section: the core 200 is embedded with the first alloy and firmly connected to the second alloy via the weld nugget 701. The cap forms a closed cavity to collect and discharge metal, while simultaneously creating a mechanical riveting effect on the side of the core. (See enlarged view). Figure 18 As shown in Figure C), the top surface 207 of the protruding pin is smoothly connected to the top surface 104 of the cap, forming a metallurgical fusion interface 212 at the contact surface, ensuring a firm connection between the cap and the core, while also ensuring the sealing performance of the weld.

[0104] Example 1:

[0105] In this embodiment, the cap 100 of the combined rivet is integrally stamped from cold-rolled low-carbon steel DC06 with a thickness of 0.2 mm, while the core 200 is made of 316L austenitic stainless steel.

[0106] In terms of specific structure, a 3 mm diameter riveting hole is provided at the center of the top surface 104 of the cap. Correspondingly, a cylindrical protruding pin with the same 3 mm diameter is designed on the top surface of the core. When the riveting hole of the cap and the protruding pin of the core are matched and installed, pressure is applied to cause the protruding pin to undergo upsetting deformation, thereby forming a combined rivet connection between the riveting hole and the protruding pin, achieving a firm connection between the cap and the core.

[0107] from Figure 19 As can be seen from section A, the surface morphology of the combined rivet connection is good, and both the top surface 207 of the protruding pin and the top surface 104 of the surrounding cap are flat and free of cracks. (See cross-sectional observation...) Figure 19As shown in Figure B), the deformed protruding pin 206' exhibits a structure that is narrower at the bottom and wider at the top, forming an outwardly expanding brim structure 208 around the top surface 207 of the protruding pin, thereby achieving a secure riveting of the cap's rivet hole 105. Measurement results indicate that the height difference between the top surface 207 of the protruding pin and the surrounding top surface 104 of the cap is less than 0.3 mm. Due to the thinness of the cap wall, a certain degree of warping deformation occurs under stress, resulting in a gap of less than 0.3 mm between the inner top surface 104' of the cap and the core top surface 205.

[0108] When using this combination of rivets to weld dissimilar metals, the first alloy 600 is a 3 mm thick cast aluminum alloy, while the second alloy 700 is an ultra-high strength hot-formed steel with a strength level of 1500 MPa and a thickness of 1.6 mm. Figure 20 The surface morphology of the assembled rivet after welding is shown: the outer periphery of the top surface 207 of the protruding pin maintains good contact with the riveting hole 105, and no phenomenon of liquid metal overflowing from the outer periphery of the protruding pin is found.

[0109] Further observation of the weld joint cross-section (e.g.) Figure 21 As shown), the shaft portion 201 of the combined rivet successfully pierces the cast aluminum alloy 600 and forms a firm connection with the hot-formed steel 700 through the molten core 701. The sidewall of the shaft portion gradually expands upwards, and combined with the squeezing action of the flange portion 202, provides a reliable mechanical locking effect to the first alloy. It is noteworthy that after the core penetrates the cast aluminum alloy, the discharged molten metal is forced to be completely captured by the annular cavity formed by the cap 100 (as shown). Figure 21 (The discharged metal 602 is shown in the figure).

[0110] The cap top surface 104 gradually curves downward from the outer periphery and joins the outer periphery of the protruding pin top surface 207, so that the outer periphery of the core top surface 205 and the cap top surface 104 form a "V" shaped structure with openings to both sides (e.g., Figure 22 (As shown). The gap is filled with discharged metal 602. Furthermore, from... Figure 22 It can also be observed that the contact surfaces between the sidewall of the rivet hole 105 and the deformed protruding pin 206', as well as the contact surfaces between the inner top surface 104' of the cap and the top surface 205 of the core, all form metallurgical fusion interfaces 212. This indicates that the combined rivet connection transforms into a metallurgical connection interface after welding. This structure not only enhances the connection strength between the cap and the core but also ensures good sealing performance at the connection point.

[0111] It should be understood that the above embodiments are only intended to illustrate the technical concept of the present invention to facilitate understanding by those skilled in the art, and are not intended to limit the scope of protection of the present invention. Within the scope of the claims of the present invention, any improvements and equivalent substitutions to the parts, structures, or method steps involved in the above embodiments, especially combinations of different embodiments without causing structural or principle conflicts, fall within the scope of protection of the present invention.

Claims

1. A combination rivet, characterized in that: It includes a cap (100) and a core (200). The cap is in the shape of an inverted bowl, and a cap connecting part is provided at the center of the top surface (104) of the cap. A core connecting part is provided at the center of the top surface (205) of the core, which cooperates with the cap connecting part. The core is located inside the cap, and the top surface (205) of the core is in contact with the top surface (104) of the cap, so that the core connecting part and the cap connecting part deform and lock together after contact, forming a combined rivet connecting part, thereby realizing the mechanical anchoring of the cap and the core.

2. The combined rivet according to claim 1, characterized in that, The cap connecting part is a riveting hole (105) that penetrates the top surface (104) of the cap, and the core connecting part is an upward protruding pin (206). When the protruding pin is inserted into the riveting hole, its top end is plastically deformed under pressure to form a radially expanding brim structure (208), so that the protruding pin (206) and the side wall of the riveting hole (105) form an interference fit.

3. The combined rivet according to claim 1, characterized in that, The cap connecting part is a blind riveting hole (108) that does not penetrate the top surface (104) of the cap. The core connecting part is an upwardly protruding pin (206), and the top of the protruding pin (206) is provided with an expansion part (211). When the protruding pin is installed in contact with the blind riveting hole, the expansion part (211) is pressed and expands radially in the blind riveting hole (108) to lock with the blind riveting hole.

4. The combined rivet according to claim 1, characterized in that, The cap connecting part is a locking part (107), and the core connecting part is a concave hole (210). The locking part is formed by plastic deformation caused by mechanical force acting on the central area of ​​the cap, and the locking part is embedded in the concave hole to form a mechanical interlock.

5. The combined rivet according to claims 2 and 3, characterized in that, An annular groove (209) is provided around the root of the protruding pin (206). When the protruding pin (206) is deformed and locked, some material around the cap connection part is squeezed into the annular groove (209) to achieve tolerance compensation and secondary locking.

6. The combined rivet according to any one of claims 1 to 4, characterized in that, As the top surface (104) of the cap extends from the outer edge to the center, the wall thickness of the cap gradually increases, with the maximum wall thickness located in the area surrounding the cap connection part; as the top surface (205) of the core extends from the outer edge to the center, it has a downwardly concave curved structure, forming a conformal fit with the inner top surface (104') of the cap.

7. The combined rivet according to any one of claims 1 to 4, characterized in that, The lower end face of the core does not protrude from the plane containing the lower end face of the cap.

8. The combined rivet according to claim 1, characterized in that, The volume fraction of ferrite in the microstructure of the cap is greater than 90%, and the volume fraction of martensite in the microstructure of the core is greater than 30%.

9. A method for manufacturing any combination rivet according to claims 1 to 8, characterized in that: The cap and the core are manufactured separately, wherein the cap is manufactured by a first mold in a first press, and the core is manufactured by a second mold in a second press; The core is conveyed from the side of the first mold by a continuous feeder into the first mold, so that the core and the cap in the first mold are aligned and assembled. Pressure is applied to cause the cap connection part and the core connection part to be plastically deformed and mechanically anchored and locked, so as to realize the parallel manufacturing of the core and the cap.

10. The method for manufacturing a combined rivet according to claim 9, characterized in that, The forming process of the combined rivet in the first die includes: S1. Multiple drawing: The cap blank is drawn multiple times through the first die core to form the cap shape; S2, Shaping: Correcting the shape of areas such as wrinkles and depressions on the surface of the cap to form a cap with the target precision; S3. Trimming and punching: Correct the lower end face of the cap to meet the design size requirements, and punch out the cap connection part at the center of the top surface of the cap. S4. Connection: The core is conveyed to the first mold by a continuous feeder and assembled with the cap. Pressure is applied by the anchoring mold to achieve a mechanical lock connection between the core and the cap.

11. A dissimilar metal joint welded using any combination of rivets according to claims 1 to 8, wherein the dissimilar metal comprises a first alloy with a melting point below 700°C and a second alloy with a melting point above 1300°C, characterized in that: During welding, the core of the combined rivet penetrates into the first alloy, and the bottom surface of the core forms a contact interface with the second alloy, and at least a portion of the contact interface is a welded part. The contact interface in the combined rivet connection part, as well as the contact surfaces of the inner top surface of the cap and part of the top surface of the core, are metallurgical welding interfaces. The cap of the combined rivet is located on the upper surface of the first alloy, and the top surface of the cap forms a concave shape from the outside to the inside. The annular closed cavity of the cap accommodates the metal (602) discharged during welding, forming a mechanical riveting structure. The gap between the inner top surface of the cap and the top surface of the core is filled with metal discharged during welding. The side of the core is surrounded by a first metal melting zone, and the first metal melting zone is fused with the local area of ​​the discharged metal.

Images