Rivets for joining upper high strength material to lower low ductility material and method of installation

Abstract

The present disclosure provides a rivet and installation method for connecting an upper layer of high-strength material with a lower layer of low-ductility material, the rivet comprising: a rivet cap, an annular chip groove being provided outside the lower edge of the rivet cap; a rivet leg extending downward from the rivet cap, a nail cavity being formed inside the rivet leg, a nail tip being provided at the bottom end of the rivet leg inside the nail cavity, and a groove being provided on the outer wall of the rivet leg for accommodating the softened lower layer of low-ductility material during the connection process; wherein the rivet is heat treated to obtain a hardness matching the strength of the upper layer of high-strength material, so that the rivet can pierce the upper layer of high-strength material; the groove is configured as a mechanical interlocking formation area, and the softened lower layer of low-ductility material during the connection process enters the groove and forms a mechanical lock; the mechanical lock is formed by filling the material in the groove, and does not rely on the radial expansion of the rivet leg. The present disclosure can realize a pre-punching hole-free, cracking-free, high-sealing, and high-strength connection.

Description

Technical Field

[0001] This disclosure relates to the field of riveting technology, and in particular to a rivet for connecting an upper high-strength material to a lower low-ductility material, and a method for installing the rivet for connecting an upper high-strength material to a lower low-ductility material. Background Technology

[0002] In the automotive manufacturing sector, the demand for joining large die-cast aluminum alloy parts with high-strength steel is increasing, especially in scenarios where high-strength steel is on top and die-cast aluminum alloy parts are on the bottom. Due to the low ductility of die-cast aluminum alloys and the high strength of high-strength steel, joining these dissimilar materials presents significant challenges. Traditional self-piercing riveting (SPR) relies on plastic deformation to create a mechanical interlock. In scenarios where the bottom layer is a die-cast aluminum alloy part, the lower material needs to undergo significant plastic deformation to form the interlocking structure. However, the poor ductility of die-cast aluminum alloys makes them prone to cracking during deformation, affecting the mechanical properties and service reliability of the joint. To address this issue, a preheating-assisted self-piercing riveting scheme has been proposed. This scheme heats the lower die-cast aluminum alloy part to improve its plasticity, thereby reducing the risk of cracking. However, this scheme adds a heating step, resulting in a longer process flow and reduced production efficiency. Flow drilling and riveting (FDS) technology achieves penetration and connection through frictional heat generated between the high-speed rotating fastener and the materials being joined. However, in scenarios where the upper layer is a high-strength steel plate, the intense friction between the fastener and the high-strength steel plate can easily cause the fastener tip to wear, soften, or even break, making it difficult to directly penetrate the high-strength steel plate. Therefore, it is usually necessary to pre-machine through holes in the high-strength steel plate before connecting, which increases the manufacturing process and production costs.

[0003] Furthermore, in connection methods that rely on rivet expansion to form mechanical interlocks, the rivets need to possess both sufficiently high strength to penetrate high-strength steel plates and good ductility to achieve expansion interlocking, creating a certain contradiction. This contradiction becomes more pronounced as the strength and thickness of the upper steel plate increase.

[0004] Therefore, how to achieve an efficient and reliable connection between high-strength steel and die-cast aluminum alloy parts without the need for pre-drilled holes and external preheating, while taking into account both the penetration capability of high-strength steel and the mechanical interlocking capability, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This disclosure provides a rivet for connecting a high-strength upper material to a low-ductility lower material, and a method for installing the rivet. Self-piercing riveting has the following problems when connecting a high-strength upper material to a low-ductility lower material: on the one hand, the low-ductility lower material is prone to cracking during large deformations; on the other hand, the high-strength upper material is difficult to pierce directly with conventional rivets, usually requiring preheating of the lower material or pre-drilling holes in the upper material, resulting in a complex process and low efficiency. Furthermore, traditional mechanical interlocking relies on the plastic expansion of the rivet legs, while rivet piercing high-strength materials requires high hardness, making it difficult to achieve both simultaneously. This disclosure aims to solve at least one of the above-mentioned technical problems.

[0006] In a first aspect, embodiments of this disclosure provide a rivet for connecting an upper high-strength material and a lower low-ductility material, comprising: a rivet cap, wherein an annular chip groove is provided on the outer side of the lower edge of the rivet cap; a rivet leg extending downward from the rivet cap, wherein a rivet cavity is formed inside the rivet leg, and a rivet tip is provided at the bottom end of the rivet leg located inside the rivet cavity; and a groove is provided on the outer side wall of the rivet leg for accommodating the lower low-ductility material softened during the connection process; wherein the rivet is heat-treated to obtain a hardness matching the strength of the upper high-strength material, so that the rivet can pierce the upper high-strength material; the groove constitutes a mechanical interlocking region, wherein the lower low-ductility material softened during the connection process enters the groove and forms a mechanical lock; wherein the mechanical lock is formed by filling the groove with material, independent of the radial expansion of the rivet leg.

[0007] In some embodiments, the groove is arranged axially along the rivet leg, and after the rivet pierces the upper high-strength material, at least a portion of the groove is located within the thickness region of the upper high-strength material, thereby forming a local gap between the outer wall of the rivet leg and the upper high-strength material at the location of the groove.

[0008] In some embodiments, the volume of the groove satisfy: ;in, The outer diameter of the rivet leg is... The inner diameter of the nail cavity, The length of the rivet leg. A constant related to the rivet tip structure, representing the ratio of the volume of material flowing out of the rivet cavity during the connection process to the volume of the rivet leg, so that the groove can accommodate the material flowing out of the rivet cavity.

[0009] In some embodiments, the cross-sectional profile of the groove is such that the bottom width is smaller than the opening width, and the groove is connected to the outer wall of the rivet leg by an arc transition.

[0010] In some embodiments, the depth of the groove satisfy: ;in, The outer diameter of the rivet leg is... The inner diameter of the rivet leg.

[0011] In some embodiments, the lower edge of the groove and the upper region of the nail tip are connected by an arc transition; The distance between the lower edge of the groove and the nail tip satisfy: ;in The outer diameter of the rivet leg is... The inner diameter of the rivet leg is... The angle of the nail tip.

[0012] In some embodiments, the length of the rivet leg is greater than the thickness of the upper high-strength material and less than the total thickness of the upper high-strength material and the lower low-ductility material minus the reserved remaining thickness of the lower low-ductility material.

[0013] In some embodiments, the rivet cavity is a blind hole structure extending axially from the bottom end of the rivet leg, the depth of the rivet cavity being greater than the length of the rivet leg, so that the rivet cavity extends into the interior of the rivet cover; the rivet cavity has a receiving space for accommodating material that enters the rivet cavity during the connection process.

[0014] Secondly, embodiments of this disclosure provide a method for installing a rivet for connecting an upper high-strength material and a lower low-ductility material, comprising: stacking and clamping workpieces to be connected, including an upper high-strength material and a lower low-ductility material, such that the rivet is located on one side of the upper high-strength material, and the lower low-ductility material is supported by a flat mold, wherein the rivet includes a rivet leg forming a rivet cavity inside and a groove provided on the outer side wall of the rivet leg, and a rivet tip is provided on the inner side of the bottom end of the rivet leg; driving the rivet downward at a first feed speed and a first rotation speed until the rivet pierces the upper high-strength material and the outer side of the rivet leg is... The groove on the side corresponds axially to the cut-off upper high-strength material to reduce the contact area between the outer wall of the rivet leg and the upper high-strength material during rotation. After the groove corresponds axially to the cut-off upper high-strength material, the rivet is driven to feed downwards at a second feed speed and a second rotation speed. The lower low-ductility material is softened by heat generated through rotational friction, and the lower low-ductility material fills the groove to form a mechanical interlock. The second rotation speed is greater than the first rotation speed. Feeding stops when the lower edge of the rivet cap of the rivet compacts the upper high-strength material, thus completing the connection.

[0015] In some embodiments, during the process of filling the groove with the lower low-ductility material to form a mechanical interlock, the rivet leg does not undergo outward plastic deformation, and the mechanical interlock is formed by filling the groove with material.

[0016] In some embodiments, the first rotational speed is less than 600 rpm, and the second rotational speed ranges from 600 rpm to 3600 rpm; the first feed rate ranges from 1 mm / s to 20 mm / s, and the second feed rate ranges from 0.5 mm / s to 6 mm / s.

[0017] In some embodiments, the feeding is stopped and the connection is completed when the lower edge of the rivet cover compacts the upper high-strength material. This includes: when the lower edge of the rivet cover contacts the surface of the upper high-strength material, the lower edge of the rivet cover and the surface of the upper high-strength material form a solid-state connection under rotational friction, and axial pressure is applied to the upper high-strength material; during continued feeding, the axial pressure reduces the gap between the upper high-strength material and the lower low-ductility material, as well as the gap between the rivet and the upper high-strength material; when the lower edge of the rivet cover has compacted the upper high-strength material and all gaps have closed, the feeding is stopped and the connection is completed.

[0018] This disclosure decouples the rivet piercing function from the mechanical interlocking function. Instead of relying on the plastic expansion of the rivet leg to form the mechanical interlock, this disclosure uses a softened material to fill the groove, making the rivet piercing and interlocking functions independent. The rivet can be made of higher hardness to meet the piercing requirements of the upper high-strength material without needing to consider plastic expansion requirements, thus making it suitable for upper high-strength materials of different strength grades and thicknesses. This disclosure achieves a high-quality connection without pre-drilled holes or cracking. Through a segmented rotary friction process, the first stage achieves direct piercing of the upper high-strength material by the rivet, eliminating the need for pre-drilling holes; the second stage uses rotary friction to generate heat and soften the lower low-ductility material, avoiding cracking of the lower material due to large deformation in traditional connection processes, thus achieving a reliable connection between the upper high-strength material and the lower low-ductility material. This improves the joint strength, sealing performance, and flatness. The lower edge of the rivet cover forms a solid-state connection with the surface of the upper material through rotational friction. Simultaneously, the chip groove accommodates the flash generated during the connection process and closes the joint gap during compaction, thereby improving the joint's sealing performance. The groove volume matches the material flow rate during connection, accommodating the extruded material and reducing gaps between plates and surface bulges, resulting in a smoother joint surface. This disclosed process is simple and efficient, requiring no preheating or pre-drilled holes; connection can be completed in a single clamping operation, effectively shortening the process flow, improving production efficiency, and making it suitable for large-scale industrial applications. Attached Figure Description

[0019] Figure 1 This is a cross-sectional view of a rivet used to connect an upper high-strength material and a lower low-ductility material, according to an embodiment of this disclosure.

[0020] Figure 2 This is a partially enlarged cross-sectional view of the rivet tip according to an embodiment of the present disclosure.

[0021] Figure 3 This is a schematic diagram of a nail tip puncture defect, showing a comparison diagram where the cut steel plate is stuck near the nail tip and cannot fill the nail cavity when the nail tip structure is not set inside the nail leg.

[0022] Figure 4 This is a flowchart illustrating a method for installing rivets to connect a high-strength upper layer material to a low-ductility lower layer material, according to an embodiment of this disclosure.

[0023] Figure 5 This is a schematic diagram of the connection method in Embodiment 1.

[0024] Figure 6 This is a metallographic image showing the effect of Example 1.

[0025] Explanation of reference numerals in the attached figures: 1. Rivet; 2. Drive shaft; 3. Pressure ring; 4. Workpiece to be connected; 5. Support mechanism; 6. Planar structure; 101. Rivet cover; 102. Rivet leg; 103. Groove. Detailed Implementation

[0026] To enable those skilled in the art to better understand the technical solutions of this disclosure, the technical solutions of this disclosure will be described in detail below with reference to the accompanying drawings.

[0027] Exemplary embodiments will be described more fully below with reference to the accompanying drawings; however, these exemplary embodiments may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will enable those skilled in the art to fully understand the scope of this disclosure.

[0028] Where there is no conflict, the various embodiments of this disclosure and the features thereof in the embodiments may be combined with each other.

[0029] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated entries.

[0030] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, the singular forms “a” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It will also be understood that when the terms “comprising” and / or “made of” are used in this specification, the presence of the stated feature, integral, step, operation, element, and / or component is specified, but the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof is not excluded.

[0031] The embodiments described herein can be described with reference to plan views and / or cross-sectional views using the ideal schematic diagrams of this disclosure. Therefore, the example illustrations can be modified according to manufacturing techniques and / or tolerances. Therefore, the embodiments are not limited to those shown in the drawings, but include modifications to configurations formed based on manufacturing processes. Therefore, the areas illustrated in the drawings are schematic in nature, and the shapes of the areas shown in the figures illustrate specific shapes of areas of an element, but are not intended to be limiting.

[0032] Unless otherwise specified, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art. It will also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and this disclosure, and will not be interpreted as having an idealized or overly formal meaning, unless expressly so defined herein.

[0033] This disclosure provides a rivet and its installation method for connecting an upper high-strength material with a lower low-ductility material, which is particularly suitable for connecting high-strength materials such as upper high-strength steel and titanium alloys with lower low-ductility materials such as aluminum alloys and magnesium alloys.

[0034] The rivets are made of high-strength materials and undergo heat treatment to achieve the hardness required to pierce the upper high-strength material. Furthermore, the rivet's hardness, leg length, and the position and size of the groove can be adjusted to suit the connection requirements of different materials being joined, depending on the combination of upper steel plate strength and thickness.

[0035] During installation, a segmented rotary friction connection process is employed, with process parameters designed based on the actual material and plate thickness combinations. The rivet first pierces the upper high-strength material, then uses the heat generated by rotational friction to soften the lower low-ductility material. The softened material fills the groove on the outside of the rivet leg, forming a mechanical interlock. For materials of different strength grades and plate thickness combinations, the coordinated design of the rivet structure and segmented process parameters enables connections without pre-drilled holes. The piercing function of the rivet is separated from the mechanical interlocking function, allowing the rivet to maintain high hardness to pierce the upper high-strength material while forming a reliable mechanical interlock without relying on plastic deformation of the rivet leg, thus achieving a high-strength connection joint.

[0036] Figure 1 This is a cross-sectional view of a rivet used to connect an upper high-strength material and a lower low-ductility material, according to an embodiment of this disclosure.

[0037] Firstly, referring to Figure 1 This disclosure provides a rivet 1 for connecting a high-strength upper material and a low-ductility lower material, comprising: a rivet cover 101, wherein an annular chip groove is provided on the outer side of the lower edge of the rivet cover; a rivet leg 102 extending downward from the rivet cover 101, wherein a rivet cavity is formed inside the rivet leg 102, and a rivet tip is provided at the bottom end of the rivet leg 102 located inside the rivet cavity; and a groove 103 is provided on the outer wall of the rivet leg 102 for accommodating the softened low-ductility lower material during the connection process; wherein the rivet 1 is heat-treated to obtain a strength matching that of the high-strength upper material. The hardness is such that the rivet 1 can pierce the upper high-strength material, and the rivet leg 102 does not undergo plastic deformation to form a mechanical interlock during the connection process; the groove 103 is configured as a mechanical interlock forming area, and the softened lower low-ductility material enters the groove 103 during the connection process and forms a mechanical lock; wherein, the mechanical lock is formed by filling the groove 103 with material, independent of the radial expansion of the rivet leg 102, and the mechanical interlock between the rivet 1 and the lower low-ductility material is formed only by filling the groove 103 with material.

[0038] In the embodiments disclosed herein, such as Figure 1 As shown, a rivet 1 for connecting an upper high-strength material and a lower low-ductility material includes: a rivet cap 101 and a rivet leg 102 extending downward from the rivet cap 101. The lower edge of the rivet cap 101 has an annular chip groove to accommodate protrusions formed by material extrusion during the connection process, thereby improving the surface smoothness of the joint. During rotational friction, the lower edge of the rivet cap 101 contacts the upper surface of the upper high-strength material and forms a solid-phase connection, thereby improving the sealing performance of the joint. Furthermore, the rivet cap is provided with a torque transmission structure and a positioning structure for realizing the rivet's feed and rotational movements.

[0039] The rivet leg 102 has an axially extending rivet cavity inside, and the bottom end of the rivet leg 102 is provided with a rivet tip located inside the rivet cavity.

[0040] Figure 2 This is a partially enlarged cross-sectional view of the rivet tip according to an embodiment of the present disclosure. Figure 3 This is a schematic diagram of nail tip puncture defects in related technologies, showing a comparative diagram of a cut-off steel plate stuck near the nail tip and unable to fill the nail cavity when the nail tip structure is not set inside the nail leg.

[0041] like Figure 2 As shown, the bottom end of the rivet leg and the inner wall of the rivet cavity are connected in an arc shape, forming a sharp blade structure. This rivet tip design serves to pierce the steel plate and needs to be sufficiently sharp. At the same time, the rivet tip angle design ensures that the steel plate is cut flat inside the rivet cavity, reduces the resistance of cutting the steel plate and filling the rivet cavity, and avoids material accumulation or jamming near the rivet tip.

[0042] like Figure 3 As shown, if the spike tip structure is not located on the inside of the spike leg, the cut steel plate will get stuck near the spike tip during piercing, unable to enter the spike cavity smoothly, resulting in insufficient filling of the spike cavity, forming gaps or accumulation, thus affecting the joint quality. In contrast, this disclosure places the spike tip on the inside of the spike leg (e.g., Figures 1 to 2 As shown in the figure, this allows the cut steel plate to enter the nail cavity smoothly, avoiding the aforementioned jamming problem.

[0043] A groove 103 is provided on the outer wall of the rivet leg 102, forming a mechanical interlocking area. During the connection process, the lower low-ductility material deforms under frictional softening and enters the groove 103, thereby forming a mechanical locking structure. The groove 103 has a dual function: during the process, when the rivet 1 pierces the upper high-strength material, the groove 103 corresponds axially with the cut high-strength material, reducing the contact area between the outer wall of the rivet leg 102 and the high-strength material, thus reducing the torque during rotation; simultaneously, this correspondence reduces the radial pressure of the high-strength material on the rivet leg 102, reducing the torque at the moment of starting the second-stage rotation, preventing damage to the main shaft motor due to excessive rotational resistance, and reducing frictional wear between the rivet 1 and the steel plate. In the final joint, the groove 103 is filled with the softened lower low-ductility material, forming a mechanical lock and improving the load-bearing capacity of the joint.

[0044] Rivet 1 is heat-treated to achieve a hardness matching the strength of the upper high-strength material, thus meeting the requirements for piercing the upper high-strength material. In some embodiments, rivet 1 achieves a hardness of 490-550 HV through heat treatment, maintaining structural stability during connection and preventing radial expansion plastic deformation used to form a mechanical lock. In some embodiments, rivet 1 may be made of 35CrMo material and obtained the required hardness range through quenching and tempering. Different hardness ranges of rivets can be selected for upper steel plates of different strength grades to achieve reliable piercing and stable forming. For example, for upper steel plates with a strength lower than DP590, the rivet hardness can be 430 HV to 490 HV; for upper steel plates with a strength higher than DP590, the rivet hardness can be 490 HV to 550 HV; and for upper steel plates with a strength higher than DP1000, the rivet hardness can be above 550 HV.

[0045] In this disclosure, the mechanical locking structure is provided by a lower layer of low-ductility material filling the groove 103, and does not depend on the radial expansion deformation of the rivet leg 102. By decoupling the "piercing function" from the "interlocking function," the rivet 1 can achieve a reliable connection while maintaining high hardness, thereby resolving the technical contradiction in traditional structures where high hardness makes it difficult to form radial expansion interlocking. This technology allows for piercing of steel plates of different strengths / thicknesses by increasing the rivet hardness without compromising the rivet's ability to undergo plastic deformation due to increased rivet strength.

[0046] The rivet leg 102 does not produce radial expansion deformation required to form a mechanical lock; the locking structure required for the mechanical interlock is provided by a lower layer of low-ductility material filled within the groove. Because the rivet tip structure enables a relatively smooth cut, there is no significant gap between the upper and lower plates, and some material enters the groove area to further enhance the joint's load-bearing capacity.

[0047] In some embodiments, the position of the groove 103 in the axial direction of the rivet leg 102 is determined according to the thickness of the upper high-strength material, such that after the rivet 1 pierces the upper high-strength material, at least a portion of the groove 103 is located in the axial region corresponding to the upper high-strength material.

[0048] In this embodiment, the groove 103 is arranged along the axial direction of the rivet leg 102, wherein the axial direction is the length direction along the rivet 1 from the tip to the rivet cap. The axial position of the groove 103 is set according to the thickness of the upper high-strength material, such that after the rivet 1 pierces the upper high-strength material, the axial region where the groove 103 is located corresponds to the upper high-strength material in the thickness direction, thereby forming a local gap between the outer wall of the rivet leg 102 and the upper high-strength material at the position of the groove 103.

[0049] Through the above design, the contact between the outer wall of the rivet leg 102 and the upper high-strength material is changed from continuous contact to intermittent contact at the groove 103 position, thereby reducing the frictional resistance and rotational torque between the rivet and the upper material during rotation.

[0050] In some embodiments, the volume of the groove 103 satisfy: ;in, The outer diameter of rivet leg 102 The inner diameter of the nail cavity. The length of rivet leg 102, A constant related to the rivet tip structure, representing the ratio of the volume of material flowing out of the rivet cavity during the connection process to the volume of the rivet leg, so that the groove 103 can accommodate the material flowing out of the rivet cavity. In this embodiment of the present disclosure, the groove 103 is used to accommodate a portion of the material displaced by the rivet leg 102 material and flowing out of the rivet cavity during the connection process, and the volume of the groove 103 is... The above formula must be satisfied to ensure that the groove 103 has sufficient capacity.

[0051] In one implementation, The value can be obtained through connection tests for specific rivet structures, i.e., by measuring the actual volume of material flowing to the outside of the rivet cavity and entering the groove during the connection process and comparing it with the volume difference of the rivet leg; or by selecting it based on an empirical calibration relationship established in advance for different rivet tip structures.

[0052] The above design ensures that the volume of the groove matches the volume of material flowing out of the nail cavity during the connection process, thereby preventing material from accumulating or overflowing at the workpiece interface, causing gaps or surface bulges, ensuring the flatness of the upper and lower surfaces of the joint after connection, and improving the interface filling quality and connection reliability.

[0053] In some embodiments, the cross-sectional profile of the groove 103 is such that the bottom width is smaller than the opening width, and the groove 103 is connected to the outer wall of the rivet leg 102 by an arc transition.

[0054] In this embodiment, the groove 103 is used to reduce the contact area between the outer wall of the rivet leg 102 and the upper high-strength material after the rivet pierces the upper high-strength material, so as to reduce the frictional resistance during rotation; and after the connection is completed, it serves as a mechanical interlocking area to provide filling space for the softened lower low-ductility material to form a mechanical interlocking structure.

[0055] like Figure 2As shown, in some embodiments, the cross-sectional profile of the groove 103 is generally trapezoidal, and the two side walls are connected to the outer side wall of the rivet leg 102 by a rounded transition. The rounded transition can avoid stress concentration at sharp corners, reduce the risk of cracking of the rivet leg under high hardness conditions, and ensure the structural reliability of the rivet leg.

[0056] In other embodiments, the cross-sectional profile of the groove 103 can also be a composite shape formed by a combination of arc, V, trapezoid and arc, or a rounded rectangle. In the above embodiments, the sidewall and bottom of the groove 103, as well as the groove and the outer sidewall of the rivet leg 102, can be connected by a rounded transition to reduce stress concentration and improve the structural reliability of the rivet leg 102.

[0057] After the rivet pierces the upper high-strength material, the groove 103 reduces the contact area between the outer wall of the rivet leg 102 and the upper high-strength material, thereby reducing the frictional resistance during rotation. After the connection is completed, the softened lower low-ductility material enters the groove 103 and forms a mechanical interlock, improving the load-bearing capacity of the joint.

[0058] Through the aforementioned groove structure, after the rivet penetrates the upper high-strength material, the groove 103 reduces the contact area between the outer wall of the rivet leg 102 and the upper high-strength material, thereby reducing the frictional resistance during rotation; after the connection is completed, the softened lower low-ductility material enters the groove 103 and forms a mechanical interlock, improving the load-bearing capacity of the joint.

[0059] In some embodiments, the depth of the groove 103 satisfy: ;in, The outer diameter of rivet leg 102 This is the inner diameter of rivet leg 102.

[0060] In this embodiment, the depth l of the groove 103 is less than the wall thickness of the rivet leg 102 to ensure that the bottom of the groove 103 has sufficient remaining wall thickness to withstand the load during the connection process without breaking. The above range ensures that the groove 103 has sufficient depth to form a mechanical interlock, and also ensures that the remaining wall thickness at the bottom of the groove 103 meets the strength requirements of the rivet leg.

[0061] In some embodiments, the lower edge of the groove 103 and the upper region of the nail tip are connected by an arc transition; the distance between the lower edge of the groove 103 and the nail tip... satisfy: ;in The outer diameter of rivet leg 102 The inner diameter of the rivet leg is 102. The angle of the nail tip.

[0062] In this embodiment, the starting position of the lower edge of the groove 103 must be equal to the thickness of the outer wall of the rivet. This ensures that when the groove 103 contacts the steel plate, the punch hole pierced by the rivet matches the outer diameter of the rivet, preventing the outer diameter of the upper edge of the groove 103 from being inconsistent with the punch hole in the steel plate, thus increasing process resistance. This design ensures proper fit between the groove 103 and the steel plate while avoiding unnecessary resistance increases.

[0063] In some embodiments, the length of the rivet leg 102 is greater than the thickness of the upper high-strength material and less than the total thickness of the upper high-strength material and the lower low-ductility material minus the reserved remaining thickness of the lower low-ductility material.

[0064] In this embodiment of the disclosure, the length of the rivet leg 102 is... The thickness of the workpiece 4 to be connected satisfies: in, For the first Workpiece thickness, , Reserved thickness for the underlying low-ductility material.

[0065] Through the above design, the length of the rivet leg 102 is greater than the thickness of the upper high-strength material, allowing the rivet to penetrate the upper high-strength material; at the same time, the length of the rivet leg 102 is less than the total thickness of all workpieces minus the reserved remaining thickness, so that the rivet forms a mechanical interlock after entering the lower low-ductility material, without penetrating the lower low-ductility material, thereby ensuring the integrity and reliability of the connection structure.

[0066] In some implementations, a remaining thickness is reserved to prevent penetration or cracking of the underlying low-ductility material. It can be 0.2mm to 1mm.

[0067] In some embodiments, the rivet cavity is a blind hole structure extending axially from the bottom end of the rivet leg 102, and the depth of the rivet cavity is greater than the length of the rivet leg 102, so that the rivet cavity extends into the interior of the rivet cover 101; the rivet cavity has a receiving space for accommodating material that enters the rivet cavity during the connection process.

[0068] In this embodiment, the rivet cavity is a blind hole structure formed by extending axially upward from the bottom opening of the rivet leg 102. The depth of the rivet cavity... Greater than the length of the rivet leg This allows the rivet cavity to pass through the connection area between the rivet leg and the rivet cover and extend into the interior of the rivet cover, thereby forming an axially extending extended receiving space inside the rivet.

[0069] In some embodiments, the rivet cavity has a substantially uniform inner diameter in the rivet leg section and the extension section located inside the rivet cap. This design provides the rivet cavity with a large internal volume, offering ample space to accommodate material entering the cavity during the connection process, preventing material from accumulating or getting stuck near the rivet tip, thus ensuring smooth material entry into the cavity. It also helps reduce gaps at the connection interface, improving the smoothness of the joint interface and the quality of the connection.

[0070] In some embodiments, the maximum depth of the nail cavity satisfy: ;in, The inner diameter of the nail cavity. The outer diameter of the rivet leg. This refers to the rivet leg length. Through the above design, the rivet cavity has sufficient space to receive material entering the cavity during the connection process, thereby preventing the accumulation of cut material near the rivet tip and thus avoiding interference with material flow.

[0071] The groove 103 on the outer wall of the rivet leg 102 is spatially independent of the internal rivet cavity. The rivet cavity is used to accommodate material entering during the connection process, while the groove 103 is used to accommodate material flowing towards the outer side of the rivet leg 102. Together, they constitute a material flow and containment structure to reduce interfacial gaps caused by material accumulation and promote the formation of mechanical interlocking.

[0072] Figure 4 This is a flowchart of an installation method for connecting an upper high-strength material to a lower low-ductility material, according to an embodiment of this disclosure.

[0073] Secondly, referring to Figure 4 This disclosure provides an installation method for connecting an upper high-strength material to a lower low-ductility material, comprising: S11. Stack and clamp the workpieces to be connected, so that the high-strength material is located on one side of the rivet and the low-ductility material is supported by the flat mold. The rivet includes a rivet leg with an internal cavity and a groove on the outer wall of the rivet leg. The bottom inner side of the rivet leg is provided with a rivet tip. S12. Drive the rivet downward at a first feed speed and a first rotation speed until the rivet pierces the high-strength material and the groove on the outer side of the rivet leg corresponds axially with the cut-off high-strength material, so as to reduce the contact area between the outer wall of the rivet leg and the upper high-strength material during rotation. S13. After the groove and the cut high-strength material are axially aligned, the rivet is driven to feed downward at a second feed speed and a second rotation speed. The lower low-ductility material is softened by heat generated by rotational friction and is filled into the groove to form a mechanical interlock. The second rotation speed is greater than the first rotation speed. S14. Stop feeding after the lower edge of the rivet cover has compacted the upper high-strength material, and the connection is completed.

[0074] In this embodiment of the disclosure, the installation method for connecting the upper high-strength material and the lower low-ductility material uses the aforementioned rivets to achieve the connection. For example... Figure 4 and Figure 5 As shown, the installation method specifically includes the following steps: Process preparation and contact stage: The workpieces 4 to be connected are stacked and clamped, with the high-strength material on one side of the rivet and the low-ductility material supported by the flat mold. Specifically, the workpieces 4 to be connected are fixed by the support mechanism 5 and clamped by the pressure ring 3. The rivet 1 is fixed on the drive shaft 2 and contacts the upper steel plate under the action of the drive shaft 2. The workpieces to be connected are stacked, with the steel plate on one side of the rivet, and the die-cast aluminum alloy part is supported by the flat mold below. The rivet includes a rivet leg 102 with an internal cavity and a groove 103 on the outer wall of the rivet leg. The bottom inner side of the rivet leg is provided with a rivet tip.

[0075] The steel plate piercing stage (first stage): The driving rivet is fed downwards at a first feed speed and a first rotation speed until the rivet pierces the high-strength material and the groove on the outer side of the rivet leg corresponds axially with the cut-off high-strength material. The rivet generates preload under the drive of the drive shaft 2 and feeds downwards at the first feed speed and the first rotation speed, thereby achieving the cutting and piercing of the upper high-strength material.

[0076] In this process, after the rivet pierces through the high-strength material, the groove on the outer side of the rivet leg corresponds axially with the cut high-strength material, so that the groove area corresponds to the thickness range of the steel plate, reducing the contact coverage area in the subsequent rotation process, thereby reducing the rotation resistance and output torque requirements.

[0077] In the first stage, in order to achieve the cutting and piercing of the upper high-strength steel plate by the rivet, the feed speed must meet v>1mm / s while the equipment can provide the maximum axial riveting force.

[0078] The switch between the first and second stages is based on the following condition: the second stage begins when the groove on the outer side of the rivet leg corresponds axially with the cut high-strength material.

[0079] In some implementations, the feed depth when the high-strength upper layer material is pierced and the groove corresponds to the material being cut can be determined through pre-testing, and the axial pressure corresponding to this depth can be used as the basis for stage switching, thereby realizing automatic switching control based on axial pressure.

[0080] Friction softening stage (second stage): After the groove and the cut high-strength material are axially aligned, the rivet is driven to feed downward at a second feed speed and a second rotation speed. The lower low-ductility material is softened by heat generated by rotational friction and is filled into the groove to form a mechanical interlock. The second rotation speed is greater than the first rotation speed.

[0081] During this stage, the frictional heat generated by the rotation of the rivets raises the temperature of the underlying low-ductility material and causes it to soften locally, thereby reducing the downward pressure resistance and preventing material cracking. At the same time, it facilitates the flow of the softened material into the groove area and forms a stable interlocking structure.

[0082] In the second stage, the heat generated by the rotation of the rivets causes the temperature of the lower die-cast aluminum alloy parts to rise, increasing their ductility. In order to generate enough heat in the process to prevent the die-cast aluminum alloy parts from cracking, ω > 600 rpm must be satisfied.

[0083] Compaction and Forming Stage: During the second stage of continuous feeding, as the rivet further penetrates the lower layer of low-ductility material, the softened material continues to flow and fill the groove, forming a mechanical interlock. Once the lower edge of the rivet cap contacts the surface of the upper high-strength material, axial pressure continues to be applied, causing the lower edge of the rivet cap to compact the upper high-strength material and close any remaining gaps between the workpieces. Feeding is then stopped, completing the connection.

[0084] During this process, the extruded material enters the annular chip groove on the outer side of the lower edge of the rivet cover, thereby reducing surface bulge on the workpiece and improving the surface quality of the joint. After the connection is completed, the pressure ring is released, and the drive shaft returns to its original position.

[0085] Throughout the process, segmented process parameter control ensures minimal deformation of the rivet when penetrating the steel plate. Simultaneously, groove filling and interlocking are achieved on the lower plate side, improving joint quality. Frictional heat generation also addresses the deformation and cracking issues of the lower, low-ductility plate. In the joint obtained through this process, the rivet legs do not undergo outward plastic deformation, and the rivet can be considered to be without plastic deformation. The steel plate cut inside the rivet cavity has no significant gap between the upper and lower plates due to the near-flat rivet tip structure. Partial metal from both the upper steel plate and the lower aluminum plate enters the groove at the rivet leg, achieving interlocking and increasing joint strength. The rivet can be considered to be without plastic deformation, with mechanical interlocking achieved solely through aluminum alloy filling in the groove. This process can be used to obtain high-strength joints by designing segmented process parameters for upper steel plates of different strengths and plate thicknesses.

[0086] In some embodiments, during the process of filling the groove with the lower low-ductility material to form a mechanical interlock, the rivet leg does not undergo outward plastic deformation, and the mechanical interlock is formed by filling the groove with material.

[0087] In this embodiment, during the process of filling the groove with the lower low-ductility material to form a mechanical interlock, the rivet leg does not undergo outward expansion plastic deformation to form the mechanical interlock; that is, the rivet leg does not participate in the formation of the mechanical interlock through radial expansion. Unlike traditional self-piercing riveting, which relies on the radial expansion of the rivet leg to form a mechanical interlock, the mechanical interlock of this disclosure is formed by filling the groove with material. Since the rivet does not need to achieve locking through plastic expansion, a high-hardness design that meets the piercing requirements can be adopted to satisfy the requirement of piercing the upper high-strength material.

[0088] This disclosure decouples the piercing function of the rivet from its mechanical interlocking function, implementing them through different structures. The high hardness of the rivet enables the cutting and piercing of the upper high-strength material, while the groove serves as the mechanical interlocking area, filled by a lower low-ductility material to form a mechanical lock. This avoids the performance contradiction in traditional solutions where the rivet needs both high strength to pierce the upper high-strength material and sufficient plasticity to achieve expansion locking. Based on this design, the rivet hardness can be independently selected according to the strength of the upper high-strength material to ensure piercing capability without considering the rivet's plastic deformation capacity. Therefore, this disclosure can achieve piercing of upper high-strength materials of different strengths and thicknesses by increasing the rivet hardness, while ensuring the mechanical interlocking strength of the joint, significantly expanding the applicability of riveting technology in scenarios involving the connection of high-strength and low-ductility materials.

[0089] In some embodiments, the first rotational speed is less than 600 rpm, and the second rotational speed ranges from 600 rpm to 3600 rpm.

[0090] The first feed rate ranges from 1 mm / s to 20 mm / s, and the second feed rate ranges from 0.5 mm / s to 6 mm / s.

[0091] In this embodiment, in the first stage, a lower rotational speed combined with a higher feed rate enables the rivet to quickly cut and pierce the upper high-strength material. If the rotational speed is too high, excessive frictional heat may be generated before piercing is complete, causing localized material softening, thereby reducing cutting efficiency and affecting penetration stability. To achieve rivet cutting and piercing of the upper high-strength steel plate, the feed rate must satisfy v > 1 mm / s while the equipment can provide the maximum axial riveting force.

[0092] In the second stage, increasing the rotational speed enhances frictional heat generation, causing localized softening and improved flowability of the lower-layer low-ductility material. This facilitates material filling into the rivet groove and forming a mechanical interlock. However, excessively high feed rates can lead to excessive axial loads, causing localized deformation of the rivet legs, which is detrimental to subsequent material filling and structural stability. To generate sufficient heat during the process and prevent cracking of the die-cast aluminum alloy parts, ω > 600 rpm is required.

[0093] In the first and second stages, the values ​​of rotational speed and feed rate can be selected based on factors such as the strength and thickness of the upper steel plate.

[0094] In some embodiments, the feeding is stopped until the lower edge of the rivet cap compacts the upper high-strength material, thus completing the connection. This includes: when the lower edge of the rivet cap contacts the surface of the upper high-strength material, the lower edge of the rivet cap and the surface of the upper high-strength material form a solid-state connection under rotational friction, and axial pressure is applied to the upper high-strength material; during continued feeding, the axial pressure reduces the gap between the upper high-strength material and the lower low-ductility material, as well as the gap between the rivet and the upper high-strength material; when the lower edge of the rivet cap has compacted the upper high-strength material and all gaps have closed, the feeding is stopped, thus completing the connection.

[0095] In this embodiment of the present disclosure, when the second stage feed depth reaches a predetermined value, the lower edge of the rivet cap contacts the upper surface of the workpiece to be joined, and at the same time, the upper layer material cut inside the rivet cavity contacts the upper region inside the rivet cavity. At this time, the rivet continues to feed, and relative rotational friction occurs between the lower edge of the rivet cap and the surface of the upper high-strength material, forming a solid-state connection in the contact area.

[0096] The lower edge of the rivet cap applies axial pressure to the upper high-strength material. Under this axial pressure, the interfacial gap between the lower edge of the rivet cap and the surface of the upper high-strength material, as well as the interfacial gap between the upper high-strength material and the lower low-ductility material, decreases and closes. At the same time, the lower low-ductility material flows into the groove on the outside of the rivet leg under the downward pressure of the rivet, and forms a mechanical locking structure in the groove.

[0097] Once the lower edge of the rivet cap has compacted the upper high-strength material and the gaps between the interfaces have closed, the feeding stops, completing the connection. During this process, the annular chip groove on the outer side of the lower edge of the rivet cap is used to accommodate excess material that has been extruded, preventing it from accumulating at the joint edge and thus improving the joint forming quality.

[0098] This disclosure achieves at least the following beneficial effects through the above technical solution: 1. It enables the connection of dissimilar materials without pre-drilled holes or cracks.

[0099] This disclosure employs a segmented rotary friction connection process. In the first stage, a high-hardness rivet is used to directly pierce the upper high-strength material without pre-drilling holes in the upper material. In the second stage, the heat generated by rotary friction softens the lower low-ductility material, allowing it to complete the connection under relatively small deformation conditions. This avoids the problem of cracking caused by large plastic deformation of the lower low-ductility material in the traditional self-piercing riveting process, and achieves a high-quality connection between the upper high-strength material and the lower low-ductility material.

[0100] 2. The technical contradiction between rivet piercing capability and mechanical interlocking has been overcome.

[0101] This disclosure changes the formation mechanism of mechanical interlocking from the traditional radial expansion locking of the rivet legs to groove filling locking, making the piercing function of the rivet and the interlocking function independent. The rivet can be made with higher hardness to meet the requirements of piercing the upper high-strength material, while the mechanical interlocking is formed by filling the groove on the outside of the rivet leg with softened lower material, without relying on the plastic expansion deformation of the rivet leg, thereby expanding the applicability of the process to high-strength materials of different strength grades and thicknesses.

[0102] 3. Improved the load-bearing capacity and connection reliability of the joint.

[0103] In this disclosure, the lower layer of low-ductility material fills the groove on the outside of the rivet leg to form a mechanical interlock. Both the upper and lower layers of material can participate in the locking action in the groove area, thereby enhancing the mechanical bonding capability of the joint and improving its load-bearing capacity and service reliability.

[0104] 4. Improved the sealing performance of the joint.

[0105] During the connection process, the lower edge of the rivet cap forms a solid-phase connection with the surface of the upper material through rotational friction. At the same time, the rivet cap compacts the upper material, effectively closing the gaps between the rivet and the upper material, as well as between the upper and lower materials. In addition, the annular chip groove can accommodate the flash material generated during the connection process, thereby further improving the surface condition of the joint and enhancing the airtightness and sealing performance of the joint.

[0106] 5. Improved the quality of the joint interface.

[0107] In this disclosure, the rivet tip is located inside the rivet leg, allowing the cut upper material to smoothly enter the rivet cavity, reducing material accumulation and jamming. At the same time, the groove is used to accommodate the material expelled during the connection process, reducing the gap between plates and the bulge on the workpiece surface, thereby improving the joint interface quality and enhancing the connection stability.

[0108] 6. The process is simple and the connection efficiency is high.

[0109] This disclosure eliminates the need for pre-drilling holes in the workpiece and preheating of the underlying low-ductility material. The joint can be manufactured through a single clamping and connection process, offering advantages such as a short process flow, high production efficiency, and ease of automation. It is suitable for large-scale industrial production.

[0110] To enable those skilled in the art to more clearly understand the technical solutions provided by the embodiments of this disclosure, the technical solutions provided by the embodiments of this disclosure will be described in detail below through specific embodiments: Example 1 This embodiment provides a novel self-piercing friction riveting process based on a steel upper layer and an aluminum lower layer, which employs the following... Figure 1 The rivet shown enables connection. The rivet includes: a rivet cap 101, a rivet leg 102 extending downward from the rivet cap 101, and a groove 103 provided on the outer wall of the rivet leg 102. In this embodiment, the length L of the rivet leg 102 is 3.5 mm, the maximum depth h of the rivet cavity is 4.3 mm, and the inner diameter of the rivet leg is... It is 4mm in diameter. The diameter of the rivet cap 101 is 6mm, the outer diameter of the rivet cap 101 is 10mm, and the depth of the groove 103 is 0.3mm.

[0111] This embodiment describes the connection between a 0.8mm thick HC260YD+Z high-strength steel plate and a 3mm thick cast aluminum alloy.

[0112] Figure 5 (a)-(e) in the figure are schematic diagrams of the connection method in Example 1; where a is the process preparation and contact stage, b is the steel plate piercing stage, c is the friction softening stage, d is the welding stage, and e is the end stage.

[0113] like Figure 5 As shown, the installation method in this embodiment specifically includes the following stages: a) Process preparation and contact stage The workpieces 4 to be connected are stacked, with the high-strength steel plate on one side of the rivet and the cast aluminum alloy on the lower layer, supported by the support mechanism 5. The pressure ring 3 clamps the workpieces 4 to be connected. The rivet 1 is fixed on the drive shaft 2 and moves downward under the drive of the drive shaft 2 until the bottom end of the rivet leg 102 contacts the upper surface of the upper steel plate.

[0114] b) Steel plate piercing stage When the bottom end of the rivet leg 102 contacts the workpiece 4 to be connected and generates a preload of 5kN under the drive of the drive shaft 2, the drive shaft 2 drives the rivet 1 to feed downwards at a feed speed of 2mm / s and a rotation speed of 600rpm. Under the action of high-speed feeding, the rivet pierces through the upper high-strength steel plate. Due to the downward bending deformation of the steel plate during the rivet piercing process, the piercing depth is greater than the actual thickness of the steel plate (0.8mm). When the rivet 1 has fed downwards by 2mm, the groove 103 on the outer side of the rivet leg 102 corresponds axially with the cut-off steel plate (i.e., the groove is flush with the cut-off steel plate on the outer side of the rivet), and the piercing stage ends.

[0115] During the piercing process, rivet 1 rotates at 600 rpm to preheat the contact area between the rivet and the workpiece. The main purpose of the first stage is to pierce the upper high-strength steel plate, so the rotation speed is controlled within a low range to avoid softening of the rivet and affecting the piercing ability. After rivet 1 feeds downward 2 mm, the groove 103 corresponds axially with the cut steel plate, creating conditions for reducing rotational resistance in the subsequent friction softening stage.

[0116] c) Friction softening stage After rivet 1 has been fed downwards by 2mm (i.e., the groove 103 corresponds axially to the cut steel plate), drive shaft 2 switches process parameters, driving rivet 1 to continue feeding downwards at a speed of 3000rpm and a feed rate of 0.5mm / s. Intense rotational friction is generated between rivet 1 and the workpiece 4 to be joined. The heat generated by this friction raises the temperature of the lower layer of cast aluminum alloy, increases its ductility, and reduces its flow resistance, thereby preventing cracking of the lower layer of low-ductility material during large deformation.

[0117] In this stage, since the groove 103 corresponds to the cut steel plate in the axial direction, the contact area between the outer wall of the rivet leg 102 and the upper steel plate is reduced, thereby reducing the torque requirement during the rotational friction process and alleviating the frictional wear between the outer wall of the rivet and the steel plate.

[0118] d) Welding stage When the second feed depth reaches 1mm (i.e., the lower edge of the rivet cover 101 contacts the upper surface of the workpiece 4 to be connected, and the material inside the rivet cavity contacts the upper surface inside the rivet cavity), the pressure continues until the lower edge of the rivet cover 101 compacts the upper steel plate, and the gaps between the rivet and the upper plate, and between the upper plate and the lower plate, are closed. During this process, the softened cast aluminum alloy material in the lower layer flows into the groove 103 on the outside of the rivet leg 102 and forms a mechanical interlock. Throughout the connection process, the rivet leg 102 does not undergo radial expansion plastic deformation to form the mechanical interlock; the mechanical interlock is formed by the material filling the groove 103. At the same time, the extruded flash fills the annular chip groove on the outside of the lower edge of the rivet cover 101, and the lower edge of the rivet cover 101 and the upper surface of the steel plate form a solid-phase weld through rotational friction, ensuring the sealing of the joint.

[0119] e) End Phase The pressure ring 3 is released, and the drive shaft 2 drives the rivet drive mechanism back to the initial position, completing the connection.

[0120] Figure 6 The image shown is a metallographic image of the effect of Example 1, in which the steel plate inside the rivet is cut to form a planar structure 6.

[0121] like Figure 6As shown, in the joint obtained through the above process, the lower part of the rivet leg 102 does not open, and the rivet leg 102 does not undergo plastic deformation to form a mechanical interlock. The rivet cavity contains a planar structure 6 formed by the cut steel plate, and the planar structure 6 can smoothly enter the rivet cavity due to the cutting structure formed by the rivet tip, without forming a significant gap between the upper and lower plates. Part of the material from both the upper steel plate and the lower cast aluminum alloy enters the groove 103 on the outside of the rivet leg 102 to form a mechanical interlock. In this embodiment, the mechanical interlock relies on the material filling in the groove 103, rather than on the radial expansion deformation of the rivet leg, thereby decoupling the rivet piercing function from the mechanical interlocking function. As a result, the rivet hardness can be independently selected according to the strength of the upper high-strength material, ensuring piercing capability while still forming a reliable mechanical interlock, thus improving the applicability of the process to upper high-strength materials of different strength grades and thicknesses.

[0122] In this embodiment, the first stage mainly achieves the cutting and piercing of the upper high-strength steel plate, and the second stage mainly softens the lower cast aluminum alloy by generating heat through rotational friction and forms a groove filling interlock. The two stages respectively undertake the piercing function and the interlocking function, thereby avoiding the design contradiction in traditional self-piercing riveting where the rivet needs to maintain high strength and also needs to undergo expansion deformation.

[0123] Tests showed that the maximum tensile and shear force of the joint obtained in this embodiment was 7186N, which is 122% higher than the maximum tensile and shear force of 3233.3N obtained by the traditional self-piercing riveting process for the same plate combination, significantly improving the joint strength.

[0124] Example 2 This embodiment provides another novel self-piercing friction riveting process based on a steel upper layer and an aluminum lower layer, which employs, as follows: Figure 1 The rivet shown enables connection. The rivet includes: a rivet cap 101, a rivet leg 102 extending downward from the rivet cap 101, and a groove 103 provided on the outer wall of the rivet leg 102. In this embodiment, the length L of the rivet leg 102 is 3.5 mm, the maximum depth h of the rivet cavity is 4.3 mm, and the inner diameter of the rivet leg is... It is 4mm in diameter. The diameter of the rivet cap 101 is 6mm, the outer diameter of the rivet cap 101 is 10mm, and the depth of the groove 103 is 0.3mm.

[0125] This embodiment involves connecting a 0.8mm thick HC340 / DP590 high-strength steel plate to a 3mm thick cast aluminum alloy. Compared to Embodiment 1, the upper steel plate in this embodiment has higher strength, therefore the process parameters were adjusted accordingly to accommodate the higher strength of the joined materials.

[0126] like Figure 5 As shown, the installation method in this embodiment specifically includes the following stages: a) Process preparation and contact stage The workpieces 4 to be connected are stacked, with the high-strength steel plate on one side of the rivet and the cast aluminum alloy on the lower layer, supported by the support mechanism 5. The pressure ring 3 clamps the workpieces 4 to be connected. The rivet is fixed on the drive shaft 2 and moves downward under the drive of the drive shaft 2 until the bottom end of the rivet leg 102 contacts the upper surface of the upper steel plate.

[0127] b) Steel plate piercing stage When the bottom end of the rivet leg 102 contacts the workpiece 4 to be connected and generates a preload of 5kN under the drive of the drive shaft 2, the drive shaft 2 drives the rivet to feed downwards at a feed speed of 1mm / s and a rotation speed of 300rpm. Under the action of high-speed feeding, the rivet pierces through the upper high-strength steel plate. Due to the downward bending deformation of the steel plate during the rivet piercing process, the piercing depth is greater than the actual thickness of the steel plate. When the rivet has fed downwards by 2mm, the groove 103 on the outer side of the rivet leg 102 corresponds axially with the cut-off steel plate (i.e., the groove is flush with the cut-off steel plate on the outer side of the rivet), and the piercing stage ends.

[0128] Compared to Example 1, the upper steel plate in this example is an HC340 / DP590 dual-phase high-strength steel plate, which has a higher strength than the HC260YD+Z steel plate. To reduce the frictional heat between the rivet and the high-strength steel plate during the first-stage piercing process, prevent the rivet tip from softening prematurely, and ensure stable completion of cutting and piercing the upper steel plate, this example uses a rotation speed of 300 rpm and a feed rate of 1 mm / s in the first stage.

[0129] c) Friction softening stage After the rivet has been fed downwards by 2mm (i.e., the groove 103 corresponds axially to the cut steel plate), the drive shaft 2 switches the process parameters, driving the rivet to continue feeding downwards at a speed of 1800rpm and a feed rate of 1mm / s. Intense rotational friction is generated between the rivet and the workpiece 4 to be joined. The heat generated by this friction raises the temperature of the lower layer of cast aluminum alloy, increases its ductility, and reduces its flow resistance, thereby preventing cracking of the lower layer of low-ductility material during large deformation.

[0130] After piercing the steel plate, the process is switched to the second stage based on the heat input requirements and forming requirements of the material combination. This stage employs a friction softening connection at a rotation speed of 1800 rpm and a feed rate of 1 mm / s. In this second stage, the frictional heat generated between the rivet and the lower die-cast aluminum alloy causes localized softening of the die-cast aluminum alloy, which then flows into the groove, thus forming a mechanically interlocked structure. All the above process parameters are within the range specified in this disclosure and can be adjusted according to the strength of the upper high-strength material, the plate thickness combination, and the heat input requirements.

[0131] In this stage, the groove 103 reduces the contact area between the outer wall of the rivet leg and the upper steel plate, reduces the torque requirement during rotation, and alleviates the friction and wear between the outer wall of the rivet and the steel plate.

[0132] d) Welding stage When the second feed depth reaches 1.3mm, the lower edge of the rivet cover 101 contacts the upper surface of the workpiece 4 to be connected, and the material inside the rivet cavity contacts the upper surface inside the rivet cavity. At this point, the pressure continues until the lower edge of the rivet cover 101 compacts the upper steel plate, closing the gaps between the rivet and the upper plate, and between the upper and lower plates. During this process, the softened cast aluminum alloy material flows into the groove 103 on the outside of the rivet leg 102 and forms a mechanical interlock. Throughout the connection process, the rivet leg 102 does not undergo radial expansion plastic deformation to form the mechanical interlock. Simultaneously, the extruded flash fills the annular chip groove on the outside of the lower edge of the rivet cover 101, and the lower edge of the rivet cover 101 and the upper surface of the steel plate form a solid-phase weld through rotational friction, ensuring the sealing of the joint.

[0133] Compared to Example 1, in this example, the rivet cap contacts the upper surface of the workpiece to be joined when the second-stage feed depth reaches 1.3 mm. This feed depth differs from that of Example 1, mainly due to differences in material composition, sheet metal deformation behavior, and material flow state during the joining process. In practical applications, the feed depth corresponding to the contact between the rivet cap and the workpiece surface can be determined based on the strength and thickness of the upper high-strength material and the forming state during the joining process.

[0134] e) End Phase The pressure ring 3 is released, and the drive shaft 2 drives the rivet drive mechanism back to the initial position, completing the connection.

[0135] In the joint obtained through the above process, the lower part of the rivet leg 102 does not open, and the rivet leg 102 does not undergo plastic deformation to form a mechanical interlock. The rivet cavity contains the cut steel plate, and the cutting structure formed by the rivet tip allows the cut steel plate to smoothly enter the rivet cavity, with no obvious gap between the upper and lower plates. Part of the material from both the upper steel plate and the lower cast aluminum alloy enters the groove 103 on the outside of the rivet leg 102 to form a mechanical interlock. In this embodiment, the mechanical interlock relies on the material filling the groove 103, rather than on the radial expansion deformation of the rivet leg, thus decoupling the rivet piercing function from the mechanical interlocking function. Therefore, the rivet hardness can be independently selected based on the strength of the upper high-strength material, ensuring piercing capability while still forming a reliable mechanical interlock.

[0136] This embodiment demonstrates that when the upper layer material is upgraded from HC260YD+Z steel plate to HC340 / DP590 dual-phase high-strength steel plate, by adjusting the two-stage process parameters, direct piercing of the upper high-strength steel plate without pre-drilled holes can still be achieved, and mechanical interlocking is formed by filling the groove with the lower layer of cast aluminum alloy material. The results show that the non-expansion interlocking connection mechanism proposed in this disclosure does not rely on the plastic deformation of the rivet legs and can be applied to upper high-strength materials of different strength grades. By further adjusting the process parameters and rivet dimensions, this invention can also be applied to connection scenarios with different plate thicknesses and different material combinations.

[0137] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in connection with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in connection with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of this disclosure as set forth by the appended claims.

Claims

1. A rivet for connecting an upper high-strength material to a lower low-ductility material, characterized in that, include: A rivet cover, wherein an annular chip groove is provided on the outer side of the lower edge of the rivet cover; A rivet leg extends downward from the rivet cover, with a rivet cavity formed inside the rivet leg. The bottom end of the rivet leg is provided with a rivet tip located inside the rivet cavity. The outer wall of the rivet leg is provided with a groove for accommodating the lower low-ductility material softened during the connection process. The rivet is heat-treated to obtain a hardness that matches the strength of the upper high-strength material, so that the rivet can pierce the upper high-strength material. The groove forms a mechanical interlocking area, and the softened lower low-ductility material enters the groove and forms a mechanical lock during the connection process; The mechanical locking is formed by filling the groove with material, and does not depend on the radial expansion of the rivet leg.

2. The rivet according to claim 1, characterized in that, The groove is arranged along the axial direction of the rivet leg, and after the rivet pierces the upper high-strength material, at least a portion of the groove is located within the thickness region of the upper high-strength material, so that a local gap is formed between the outer wall of the rivet leg and the upper high-strength material at the location of the groove.

3. The rivet according to claim 1 or 2, characterized in that, The volume of the groove satisfy: ;in, The outer diameter of the rivet leg is... The inner diameter of the nail cavity, The length of the rivet leg. A constant related to the rivet tip structure, representing the ratio of the volume of material flowing out of the rivet cavity during the connection process to the volume of the rivet leg, so that the groove can accommodate the material flowing out of the rivet cavity.

4. The rivet according to claim 1 or 2, characterized in that, The groove has a cross-sectional profile where the bottom width is smaller than the opening width, and the groove is connected to the outer wall of the rivet leg by a rounded transition.

5. The rivet according to claim 1 or 2, characterized in that, The depth of the groove satisfy: ； in, The outer diameter of the rivet leg is... The inner diameter of the rivet leg.

6. The rivet according to claim 1 or 2, characterized in that, The lower edge of the groove and the upper part of the nail tip are connected by an arc transition; The distance between the lower edge of the groove and the nail tip satisfy: ； in The outer diameter of the rivet leg is... The inner diameter of the rivet leg is... The angle of the nail tip.

7. The rivet according to claim 1 or 2, characterized in that, The length of the rivet leg is greater than the thickness of the upper high-strength material and less than the total thickness of the upper high-strength material and the lower low-ductility material minus the reserved remaining thickness of the lower low-ductility material.

8. The rivet according to claim 1 or 2, characterized in that, The rivet cavity is a blind hole structure extending axially from the bottom end of the rivet leg, and the depth of the rivet cavity is greater than the length of the rivet leg, so that the rivet cavity extends into the interior of the rivet cover; The nail cavity has a receiving space for accommodating material that enters the nail cavity during the connection process.

9. A method for installing rivets for connecting an upper high-strength material and a lower low-ductility material, characterized in that, include: The workpieces to be connected, including an upper high-strength material and a lower low-ductility material, are stacked and clamped, with the rivet located on the side of the upper high-strength material. The lower low-ductility material is supported by a flat mold. The rivet includes a rivet leg with an internal cavity and a groove on the outer wall of the rivet leg. The bottom inner side of the rivet leg is provided with a rivet tip. The rivet is driven to feed downward at a first feed speed and a first rotation speed until the rivet pierces the upper high-strength material and the groove on the outer side of the rivet leg corresponds axially with the cut-off upper high-strength material, so as to reduce the contact area between the outer wall of the rivet leg and the upper high-strength material during rotation. After the groove aligns axially with the cut-off upper high-strength material, the rivet is driven to feed downwards at a second feed speed and a second rotation speed. The lower low-ductility material is softened by heat generated through rotational friction, and the lower low-ductility material is filled into the groove to form a mechanical interlock. The second rotation speed is greater than the first rotation speed. Feeding stops once the lower edge of the rivet cap of the rivet has compacted the upper high-strength material, thus completing the connection.

10. The installation method according to claim 9, characterized in that, During the process of filling the groove with the lower low-ductility material to form a mechanical interlock, the rivet leg does not undergo outward plastic deformation, and the mechanical interlock is formed by filling the groove with material.

11. The installation method according to claim 9, characterized in that, The first rotational speed is less than 600 rpm, and the second rotational speed ranges from 600 rpm to 3600 rpm. The first feed rate ranges from 1 mm / s to 20 mm / s, and the second feed rate ranges from 0.5 mm / s to 6 mm / s.

12. The installation method according to any one of claims 9 to 11, characterized in that, Feeding stops once the lower edge of the rivet cap has compacted the upper high-strength material, completing the connection, including: When the lower edge of the rivet cover contacts the surface of the upper high-strength material, the lower edge of the rivet cover and the surface of the upper high-strength material form a solid-phase connection under the action of rotational friction, and apply axial pressure to the upper high-strength material. During the continued feeding process, the axial pressure reduces the gap between the upper high-strength material and the lower low-ductility material, as well as the gap between the rivet and the upper high-strength material. When the lower edge of the rivet cover has compacted the upper high-strength material and all gaps have closed, the feeding stops and the connection is completed.

Images