Self-piercing riveting method for low-ductility plates

Abstract

The invention provides a self-piercing riveting method for a low-ductility plate, and relates to the technical field of riveting, and the self-piercing riveting method comprises the following steps: aligning, stacking, clamping and fixing the to-be-riveted low-ductility plate with the ductility of 4-8% and a steel plate; a spherical riveting die or an annular riveting die is selected as a bottom die, the depth of a cavity of the riveting die ranges from 0.6 mm to 0.8 mm, and the diameter of the cavity of the riveting die ranges from 11 mm to 12 mm; correspondingly selecting rivets with matched hardness according to the strength grade of the steel plate to be riveted; riveting parameters corresponding to the rivets are synchronously determined, and the riveting parameters comprise riveting force and riveting feeding speed; according to the method, the selected rivet is placed at the preset riveting point position, the technical problems that in the prior art, when the plate with the ductility smaller than 8% is riveted, an aluminum casting is prone to cracking, and a connection structure loses efficacy are solved, and the technical effects that the cracking phenomenon is avoided, the riveting quality is improved, and the connection reliability of a connector is guaranteed are achieved.

Description

Technical Field

[0001] This invention relates to the field of riveting technology, and in particular to a self-piercing riveting method for low-ductility sheet metal. Background Technology

[0002] With the development of electrification and lightweighting in the automotive industry, the application of lightweight materials, represented by cast aluminum parts, in vehicle body structures is increasing. Efficient and reliable connection of dissimilar materials has become a core technological requirement in vehicle body manufacturing. Self-piercing riveting (SPR), as a cold-forming mechanical connection process that does not require pre-drilling, overcomes the shortcomings of traditional riveting processes, such as poor appearance, low production efficiency, and complex processes. It allows for the completion of both punching and riveting in one step, and the connection process does not damage the coating of the sheet metal. It is currently widely used in the mass production of automotive body structural parts and body panels.

[0003] Existing self-piercing riveting processes explicitly require castings to have a ductility greater than 8%. During SPR operations, the riveted plates must undergo controllable plastic deformation due to the punching and pressing of the rivets to form a stable mechanical interlocking structure with the outward turning of the rivet legs. Only when the ductility of the cast aluminum part is greater than 8% can it withstand the plastic deformation during the riveting process without failure. Current industry practices for riveting die selection, rivet parameter matching, and riveting process window settings are all based on this ductility requirement, ensuring a reliable connection between cast aluminum parts and steel plates that meet the ductility standard.

[0004] However, with the integration and increase in size of body castings, the mechanical properties of different parts of the castings are significantly uneven due to differences in the filling and solidification processes during the molding process. The elongation rate differs significantly between the near-gate end and the far end, with the material ductility of some far-gate areas reaching only about 4%, which is lower than the current technical requirement of 8%. This makes SPR unable to meet the riveting requirements of such low-ductility cast aluminum parts. During the riveting process, problems such as cracking of cast aluminum parts, insufficient interlocking of rivet points, and failure of connection structures are very likely to occur, resulting in batch scrapping of castings and a significant increase in production costs. Summary of the Invention

[0005] The purpose of this invention is to provide a self-piercing riveting method for low-ductility sheet metal, so as to alleviate the technical problems existing in the prior art, such as the easy occurrence of cracking of cast aluminum parts and failure of connection structure during the riveting process when dealing with sheet metal with ductility of less than 8%.

[0006] The self-piercing riveting method for low-ductility sheet metal provided by the present invention includes: Step 1: Align and stack the low-ductility sheet metal with an elongation of 4% to 8% to be riveted with the steel plate and clamp it in place; Step 2: Select a spherical riveting die or a ring riveting die as the bottom die. The cavity depth of the riveting die is 0.6mm to 0.8mm, and the cavity diameter of the riveting die is 11mm to 12mm. Step 3: Select a rivet with matching hardness according to the strength grade of the steel plate to be riveted; and simultaneously determine the riveting parameters corresponding to the rivet, including riveting force and riveting feed speed. Step 4: Place the selected rivet at the preset riveting point and complete the self-piercing riveting using a self-piercing riveting machine.

[0007] Furthermore, in step 3, the thickness of the steel plate to be riveted is no more than 2mm, and the strength grades of the steel plate to be riveted are divided into low-strength steel plate with strength ≤ 280MPa, medium-strength steel plate with strength 280MPa < strength < 500MPa, and high-strength steel plate with strength 500MPa ≤ strength < 800MPa.

[0008] Furthermore, when the steel plate to be riveted is a low-strength steel plate, rivets with an H2 hardness grade are selected, the nominal diameter of the rivet is Φ5.3mm, and the formula for calculating the rivet length L1 is: L1 = T1 + 0.5mm ~ 1.2mm (1); Where T1 is the total thickness of the riveting; the corresponding riveting force is 43-47KN, and the riveting feed speed is controlled at 60-160mm / s.

[0009] Furthermore, when the steel plate to be riveted is a medium-strength steel plate, rivets with a hardness grade of H4 are selected, the nominal diameter of the rivets is Φ5.3mm, and the formula for calculating the length L2 of the rivets is: L2=T1+0.5mm~1.5mm(2; The corresponding riveting force is 46-50KN, and the riveting feed speed is controlled at 50-150mm / s.

[0010] Furthermore, when the steel plate to be riveted is a high-strength steel plate, rivets with an H6 hardness grade are selected, the nominal diameter of the rivet is Φ5.3mm, and the formula for calculating the rivet length L3 is: L3 = T1 + 0.4 mm ~ 0.9 mm (3); The corresponding riveting force is 48-55KN, and the riveting feed speed is controlled at 40-140mm / s.

[0011] Furthermore, when the steel plate to be riveted is a high-strength steel plate, the distance between the center of the rivet point and the edge of the workpiece in step 4 is 18mm to 20mm.

[0012] Furthermore, in step 1, the low-ductility sheet material with an elongation of 4% to 8% to be riveted is cast aluminum, wrought aluminum, or aluminum alloy.

[0013] Furthermore, the bottom mold in step 2, while keeping the cavity depth and diameter unchanged, also includes an elliptical riveting mold.

[0014] Beneficial effects: The self-piercing riveting method for low-ductility sheets provided by this invention addresses the self-piercing riveting requirements of low-ductility sheets with an elongation of 4% to 8% and steel plates. By limiting the type and size of the bottom die, it effectively disperses local stress during the riveting process, preventing cracking of low-ductility aluminum alloys due to local stress concentration during riveting. Simultaneously, it ensures the consistency of the riveting formation, improving the appearance and internal quality of the rivets. Furthermore, by matching the steel plate strength grade with rivets of suitable hardness and determining the corresponding riveting force and feed speed, the rivet selection is highly compatible with the riveting parameters and the material characteristics of dissimilar riveting sheets. This ensures sufficient contact and connection strength between the rivets and the aluminum alloy / steel plate, while avoiding unqualified rivets caused by improper riveting parameters, achieving a rivet qualification rate of over 99%.

[0015] The self-piercing riveting method of this invention can be directly used with existing self-piercing riveting machines to complete the operation without the need for new complex special equipment or modification of existing equipment, thus reducing the transformation cost and facilitating rapid implementation in production. At the same time, it is tailored to the differentiated needs of steel plates of different strength grades, and is suitable for the riveting requirements of large integrated low-ductility castings in the automotive manufacturing and other fields. While ensuring the reliability of riveting, it breaks through the technical bottleneck of traditional self-piercing riveting processes in the application of low-ductility plates. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 A flowchart of a self-piercing riveting method for low-ductility sheet metal provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of a ring-shaped riveting die for a low-ductility sheet material provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of a spherical riveting die for low-ductility sheet metal provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of a rivet used in a low-ductility sheet material, provided in an embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0019] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0020] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0021] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0022] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0023] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0025] Example 1 like Figures 1-4 As shown, the self-piercing riveting method for low-ductility sheet metal provided by the present invention includes: Step 1: Align and stack the low-ductility sheet metal with a riveting elongation of 4% to 8% with the steel plate and clamp it in place; Step 2: Select spherical riveting mold or ring riveting mold as the bottom mold. The cavity depth of the riveting mold is 0.6mm to 0.8mm, and the cavity diameter of the riveting mold is 11mm to 12mm. Step 3: Select a rivet with matching hardness according to the strength grade of the steel plate to be riveted; and simultaneously determine the riveting parameters corresponding to the rivet, including riveting force and riveting feed speed. Step 4: Place the selected rivet at the preset riveting point, and then complete the self-piercing riveting using a self-piercing riveting machine.

[0026] In step 3, the thickness of the steel plate to be riveted is no more than 2mm. The strength grades of the steel plate to be riveted are divided into low-strength steel plate with strength ≤ 280MPa, medium-strength steel plate with strength 280MPa < strength < 500MPa, and high-strength steel plate with strength 500MPa ≤ strength < 800MPa.

[0027] Specifically, low-ductility sheet metal with an elongation of 4%–8% to be riveted is aligned and stacked with a steel plate with a thickness of no more than 2mm. A clamping structure is then used to fix the stacked sheet metal, effectively ensuring the positioning accuracy of the riveting points and eliminating riveting defects caused by misalignment or displacement of the sheet metal. Next, a spherical or ring-shaped riveting die is selected as the bottom die for self-piercing riveting, and the cavity depth of the die is controlled to be 0.6mm–0.8mm and the cavity diameter to be 11mm–12mm. The parameter range is specifically adapted to the material characteristics of low-ductility plates, which have poor plasticity and are prone to cracking. It effectively disperses local stress during the riveting process and avoids cracking problems of low-ductility plates from the mold structure level. At the same time, it ensures the fit between the riveting die, rivets, and workpiece, ensuring the riveting forming effect. The steel plates to be riveted are divided into three categories according to their strength grades: low-strength steel plates with a strength of ≤280MPa, medium-strength steel plates with a strength of 280MPa < strength < 500MPa, and high-strength steel plates with a strength of 500MPa ≤ strength < 800MPa. The rivets with matching hardness are selected according to the strength grade of the steel plate. At the same time, the riveting parameters adapted to the rivet specifications are determined. The riveting parameters include riveting force and riveting feed speed. The rivet hardness and riveting parameters are matched according to the differences in the strength grade of the steel plate. This allows the rivets to be highly compatible with the material characteristics of dissimilar riveting plates, avoiding problems such as loosening of the rivet points and insufficient strength caused by mismatch between parameters and plates, and ensuring the basic connection performance of the riveting.

[0028] After matching and selecting the above parameters and accessories, the selected rivets are precisely placed at the preset riveting points on the sheet metal. Using an existing self-piercing riveting machine with the selected base mold and riveting parameters, the self-piercing riveting operation can be completed directly. This method's entire process is based on existing self-piercing riveting equipment, eliminating the need for complex new specialized devices or significant modifications to existing equipment. This greatly reduces equipment modification costs and operational barriers, facilitating rapid implementation and promotion in production. Furthermore, targeted designs are implemented for each stage, including clamping and positioning, mold selection, and rivet and parameter matching, avoiding riveting defects in low-ductility sheets. This achieves reliable dissimilar riveting of low-ductility sheets with elongation rates of 4%–8% and steel plates of varying strengths, effectively solving the technical problem of easy cracking when using traditional self-piercing riveting processes on low-ductility sheets. It also significantly improves the quality and pass rate of rivet formation, meeting the riveting needs of large-scale integrated low-ductility castings in the automotive manufacturing industry and other fields.

[0029] Example 2 In Embodiment 2 of the present invention, when the steel plate to be riveted is a low-strength steel plate, an H2 hardness grade rivet is selected, the nominal diameter of the rivet is Φ5.3mm, and the length L1 of the rivet is calculated using the following formula: L1 = T1 + 0.5mm ~ 1.2mm (1); Where T1 is the total thickness of the riveting, the corresponding riveting force is 43-47KN, and the riveting feed speed is controlled at 60-160mm / s.

[0030] Specifically, Embodiment 2 of the present invention is applicable to scenarios where the steel plate to be riveted is a low-strength steel plate with a strength ≤280MPa and a thickness not greater than 2mm, and a low-ductility plate with an elongation of 4% to 8% is used for self-piercing riveting. After completing the alignment and stacking of the plates, the selection of the spherical or annular bottom mold, and the setting of the cavity depth parameters, the following exclusive operation is performed: select a rivet with a hardness grade of H2, the nominal diameter of which is Φ5.3mm, and its length L1 is calculated according to Formula 1 to determine the specific length specification of the rivet suitable for the riveting scenario of this embodiment; at the same time, match the corresponding riveting process parameters, control the riveting force in the riveting process within the range of 43 to 47KN, and control the riveting feed speed within the range of 60 to 160mm / s.

[0031] The length design of this embodiment ensures that the rivet is fully formed after riveting, while avoiding excessive deformation due to excessive length and weak connection due to excessive length. The parameters of this embodiment balance the riveting strength and the bearing capacity of the aluminum alloy, avoiding cracking of the aluminum alloy due to excessive riveting force and loosening of the rivet point due to insufficient riveting force. The H2 hardness grade rivet with the length calculated according to the above formula is accurately placed at the preset riveting point on the plate. Using a self-piercing riveting machine with a spherical or annular bottom die with selected and adjusted parameters, and according to the riveting force and riveting feed speed set in this embodiment, the equipment can be directly started to complete the self-piercing riveting operation of low ductility plate and low strength steel plate in this scenario.

[0032] Example 3 In Embodiment 3 of the present invention, when the steel plate to be riveted is a medium-strength steel plate, an H4 hardness grade rivet is selected, the nominal diameter of the rivet is Φ5.3mm, and the formula for calculating the rivet length L2 is: L2=T1+0.5mm~1.5mm(2; The corresponding riveting force is 46-50KN, and the riveting feed speed is controlled at 50-150mm / s.

[0033] Specifically, Embodiment 3 of the present invention is applicable to the scenario of self-piercing riveting of medium-strength steel plates with a strength of 280MPa < strength < 500MPa and a thickness of no more than 2mm and low-ductility plates with an elongation of 4% to 8%. After completing the alignment and stacking of the plates and setting the parameters of the spherical or annular bottom mold, rivets with a hardness of H4 are selected. The nominal diameter of the rivet is Φ5.3mm, and its length L2 is calculated according to Formula 2 to determine the specific length specification of the rivet suitable for the riveting scenario of this embodiment. At the same time, the corresponding riveting process parameters are matched to control the riveting force in the riveting process within the range of 46 to 50KN and the riveting feed speed within the range of 50 to 150mm / s.

[0034] This embodiment appropriately increases the rivet length allowance to meet the riveting requirements of higher strength steel plates; this embodiment ensures the connection strength between the rivet and the high strength steel plate by increasing the riveting force, while avoiding excessive fluctuations in riveting speed that could affect the riveting quality.

[0035] Example 4 In Embodiment 4 of the present invention, when the steel plate to be riveted is a high-strength steel plate, an H6 hardness grade rivet is selected, the nominal diameter of the rivet is Φ5.3mm, and the length L3 of the rivet is calculated using the following formula: L3 = T1 + 0.4 mm ~ 0.9 mm (3); The corresponding riveting force is 48-55KN, and the riveting feed speed is controlled at 40-140mm / s.

[0036] In step 4, the distance between the center of the rivet point and the edge of the workpiece is 18mm to 20mm.

[0037] Specifically, Embodiment 4 of the present invention is applicable to the scenario of self-piercing riveting of high-strength steel plates with a strength of 500MPa ≤ 800MPa and a thickness of no more than 2mm and low-ductility plates with an elongation of 4% to 8%. After completing the parameter setting of the plate alignment and stacking clamping and the spherical or annular bottom mold, an H6 hardness grade rivet is selected. The nominal diameter of the rivet is Φ5.3mm, and its length L3 is calculated according to Formula 3 to determine the specific length specification of the rivet suitable for the riveting scenario of this embodiment. At the same time, the corresponding riveting process parameters are matched to control the riveting force in the riveting process within the range of 48 to 55KN, the riveting feed speed within the range of 40 to 140mm / s, and to ensure that the distance between the center of the rivet point and the edge of the workpiece is 18mm to 20mm.

[0038] In this embodiment, due to the high hardness of the steel plate of this strength grade, the rivet length allowance is appropriately reduced to avoid stress concentration caused by an excessively large rivet head after riveting. Simultaneously, the distance between the rivet point and the center edge of the workpiece is limited to 18-20mm. This distance effectively disperses riveting stress, preventing deformation or cracking of the workpiece edge due to stress concentration, further ensuring the rivet point's quality. The H6 hardness grade rivet, with its length calculated according to the above formula, is precisely placed at the preset riveting point that meets the spacing requirements. Following the riveting force and feed speed set in this embodiment, the equipment is directly started to complete the self-piercing riveting operation between the low-ductility plate and the high-strength steel plate in this scenario.

[0039] It should be noted that the H2, H4, and H6 rivets in Embodiments 2-4 of this invention can be replaced with other rivets of the same strength grade and diameter (Φ5.3mm) (such as H1, H3, H5, and H7 models). As long as their hardness and strength are compatible with the strength of the corresponding steel plate, and the parameters such as rivet length and riveting force are adjusted according to the formula and range of this invention, the same riveting effect can be achieved.

[0040] Based on the above embodiments 2-4, the self-piercing riveting method for low-ductility plates provided by the present invention, taking the SPR riveting process of the rear floor of an automobile as an example, is used to rivet cast aluminum material with ductility of 4%-8% and steel plates of different specifications. The specific parameters are shown in Table 1. Table 1

[0041] According to the data in Table 1, when the riveting method of the present invention is used for the SPR riveting operation of the rear floor, no cracks are generated in any of the riveting combinations. The interlocking, head height, and undercut indicators after the riveting points are cut all meet the quality requirements of the industry and actual production, further verifying the feasibility, reliability and practicality of the technical solution of the present invention.

[0042] Example 5 In Embodiment 5 of the present invention, the low-ductility sheet material with an elongation of 4% to 8% to be riveted in step 1 is cast aluminum, wrought aluminum, or aluminum alloy.

[0043] The bottom mold in step 2, while keeping the cavity depth and diameter unchanged, also includes an elliptical riveting mold.

[0044] It should be noted that this invention is mainly aimed at the riveting of cast aluminum and steel plate in the rear floor, but it can be extended to other riveting scenarios of aluminum alloys (wrought aluminum, aluminum alloy castings) with ductility <8% and steel plates. As long as the riveting die, rivet selection and parameter matching logic of this invention are used, it can be achieved.

[0045] It should be noted that spherical and ring-shaped riveting dies can be replaced with elliptical riveting dies, as long as their depth is controlled at 0.6-0.8mm and their diameter at 11-12mm, the effect of dispersing riveting stress and preventing aluminum alloy from cracking can still be achieved.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A self-piercing riveting method for low-ductility sheet metal, characterized in that, include: Step 1: Align and stack the low-ductility sheet metal with an elongation of 4% to 8% to be riveted with the steel plate and clamp it in place; Step 2: Select a spherical riveting die or a ring riveting die as the bottom die. The cavity depth of the riveting die is 0.6mm to 0.8mm, and the cavity diameter of the riveting die is 11mm to 12mm. Step 3: Select a rivet with matching hardness according to the strength grade of the steel plate to be riveted; and simultaneously determine the riveting parameters corresponding to the rivet, including riveting force and riveting feed speed. Step 4: Place the selected rivet at the preset riveting point and complete the self-piercing riveting using a self-piercing riveting machine.

2. The self-piercing riveting method for low-ductility sheet metal according to claim 1, characterized in that, In step 3, the thickness of the steel plate to be riveted is no more than 2mm. The strength grades of the steel plate to be riveted are divided into low-strength steel plate with strength ≤ 280MPa, medium-strength steel plate with strength 280MPa < strength < 500MPa, and high-strength steel plate with strength 500MPa ≤ strength < 800MPa.

3. The self-piercing riveting method for low-ductility sheet metal according to claim 2, characterized in that, When the steel plate to be riveted is a low-strength steel plate, rivets with an H2 hardness grade are selected, the nominal diameter of the rivets is Φ5.3mm, and the formula for calculating the length L1 of the rivets is: L1 = T1 + 0.5mm ~ 1.2mm (1); Where T1 is the total thickness of the riveting; the corresponding riveting force is 43-47KN, and the riveting feed speed is controlled at 60-160mm / s.

4. The self-piercing riveting method for low-ductility sheet metal according to claim 2, characterized in that, When the steel plate to be riveted is a medium-strength steel plate, rivets with a hardness grade of H4 are selected, the nominal diameter of the rivets is Φ5.3mm, and the formula for calculating the length L2 of the rivets is: L2=T1+0.5mm~1.5mm(2; The corresponding riveting force is 46-50KN, and the riveting feed speed is controlled at 50-150mm / s.

5. The self-piercing riveting method for low-ductility sheet metal according to claim 2, characterized in that, When the steel plate to be riveted is a high-strength steel plate, rivets with an H6 hardness grade are selected, the nominal diameter of the rivets is Φ5.3mm, and the formula for calculating the rivet length L3 is: L3 = T1 + 0.4 mm ~ 0.9 mm (3); The corresponding riveting force is 48-55KN, and the riveting feed speed is controlled at 40-140mm / s.

6. The self-piercing riveting method for low-ductility sheet metal according to claim 5, characterized in that, When the steel plate to be riveted is a high-strength steel plate, the distance between the center of the rivet point and the edge of the workpiece in step 4 is 18mm to 20mm.

7. The self-piercing riveting method for low-ductility sheet metal according to claim 1, characterized in that, The low-ductility sheet material with an elongation of 4% to 8% to be riveted in step 1 is cast aluminum, wrought aluminum, or aluminum alloy.

8. The self-piercing riveting method for low-ductility sheet metal according to claim 1, characterized in that, The bottom mold in step 2, while keeping the cavity depth and diameter unchanged, also includes an elliptical riveting mold.

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