Test method for obtaining the required elongation value of self-piercing riveting of body die-cast parts

Abstract

This application relates to the field of vehicle parts processing technology, and in particular to a test method for obtaining the required elongation value of self-piercing riveting in die-cast body parts. The test method includes the following steps: fabricating test samples, including upper and lower test samples; fabricating a sample assembly, and machining multiple riveting points on the sample assembly; determining the target riveting points; locking the critical crack-free position; fabricating a tensile sample; and obtaining the required elongation value of self-piercing riveting in the die-cast part. The test method for obtaining the required elongation value of self-piercing riveting in die-cast body parts provided by this application can be obtained based on riveting processes, quality requirements, and similar test materials under actual production and manufacturing conditions, ensuring high reliability and accuracy of the relevant test results. It fills the technical gap in obtaining the minimum required elongation value of self-piercing riveting during the development of die-cast body parts, effectively solving an industry pain point.

Description

Technical Field

[0001] This application relates to the field of vehicle parts processing technology, and in particular to a test method for obtaining the required elongation value of self-piercing riveting of die-cast body parts. Background Technology

[0002] Currently, in the vehicle manufacturing process, to further improve the lightweight effect of the whole vehicle, the application of large-size, integrated aluminum-magnesium alloy high-vacuum die castings is gradually increasing. Correspondingly, new requirements for joining technologies are also gradually emerging. In terms of the connection between aluminum-magnesium alloy high-vacuum die castings and surrounding steel plate stampings, resistance spot welding is gradually being replaced by self-piercing riveting technology because it cannot achieve high-quality connections between dissimilar materials such as steel-aluminum and steel-magnesium.

[0003] When aluminum-magnesium alloy high-vacuum die-cast parts for vehicle bodies are large in size, the significant differences in elongation at different connection edges, coupled with the high elongation requirements of self-piercing riveting on the underlying material, inevitably lead to defects such as cracks and fissures in the actual connection process, especially with lightweight alloys often used as the underlying material. Currently, there are no technical reports in the industry regarding obtaining the minimum elongation requirement for castings in self-piercing riveting, thus failing to provide effective guidance for the structural design and elongation control of castings. Ultimately, this results in the inability to completely avoid the aforementioned connection defects in production. Accurately obtaining the minimum elongation requirement for the overlapping edges of castings in self-piercing riveting remains a key technical challenge for the industry.

[0004] To address the aforementioned issues, the industry typically employs methods such as optimizing casting processes and increasing product wall thickness to improve the elongation of the connection zone. However, this leads to increased manufacturing costs and a loss of lightweighting effects. Since these measures cannot provide a minimum required elongation value for the connection zone, they merely reduce the probability of crack formation. To overcome these technical challenges and better serve the design, production, and application of integrated die-cast aluminum-magnesium alloy structural components, there is an urgent need to develop a test method for obtaining the minimum required elongation value for self-piercing riveting of vehicle body die-cast parts. Summary of the Invention

[0005] The purpose of this application is to provide a test method for obtaining the required elongation value of self-piercing riveting of vehicle body die castings, so as to solve to some extent the technical problem that vehicle die castings are prone to cracking during the connection process in the prior art.

[0006] This application provides a test method for obtaining the required elongation value of self-piercing riveting of die-cast body parts, including the following steps: S100. Prepare test samples. Prepare an upper test sample and a lower test sample respectively. Both the upper test sample and the lower test sample are in the shape of long strips and flat plates. The lower test sample is a die casting. S200. To make a sample assembly, the upper test sample and the lower test sample are attached to each other and aligned to form a sample assembly. Multiple riveting points are formed by processing the sample assembly, and the multiple riveting points are spaced apart along the length direction of the sample assembly; The multiple riveting points are formed sequentially along the direction from the high elongation region to the low elongation region of the lower test sample. S300. Determine the target riveting point. During the process of riveting the sample assembly to form multiple riveting points, when the first riveting point with a crack appears, the first riveting point with a crack is defined as the first target riveting point. S400, Lock the critical non-crack position, and define the first rivet point that has not produced a crack adjacent to the first target rivet point as the second target rivet point; S500, Further lock the critical non-cracking position, and according to step S400, make multiple sample assemblies, mark a first mark point at the position of the first target rivet point of each sample assembly, and mark a second mark point at the position of the second target rivet point of each sample assembly. Each of the sample assemblies is riveted at different positions between the first mark point and the second mark point to form a locking riveting point. The distance from the locking riveting point to the first mark point is different on different sample assemblies. When the first locking rivet point that develops a crack appears, the first locking rivet point that develops a crack is defined as the first locking rivet point, and the rivet point that does not develop a crack and is adjacent to the first locking rivet point is defined as the second locking rivet point. S600. Make a tensile sample. Prepare multiple identical sample assemblies according to step S500. Mark the position of the second locking rivet point on each sample assembly as the center point. The sample assembly is cut to obtain a tensile specimen, with the center point located at the center of the tensile specimen. S700. Obtain the required elongation value for self-piercing riveting of die-cast parts, and use a tensile testing machine to perform tensile tests on the tensile samples to test the elongation of each tensile sample.

[0007] In the above technical solution, further, in step S200, the sample assembly is sequentially riveted along a first direction to form a plurality of riveting points, wherein the first direction is the direction from the high elongation region to the low elongation region of the lower test sample. In any of the above technical solutions, the width of the lower test sample is W2, and the width of the upper test sample is W1, then W2≤W1.

[0008] In any of the above technical solutions, the length of the upper test sample is L1, the length of the lower test sample is L2, the upper test sample and the lower test sample are attached to each other and centered, the distance between one end of the lower test sample and one end of the upper test sample is L3, and the distance between the other end of the lower test sample and the other end of the lower test sample is L4, then L1 = L2 + L3 + L4.

[0009] In any of the above technical solutions, the multiple riveting points are further arranged at equal intervals, and the distance between any two adjacent riveting points is M, where M≤50mm.

[0010] In any of the above technical solutions, further, in step S500, the multiple sample assemblies are numbered one by one from smallest to largest, and the locking rivet points are riveted one by one by increasing the fixed distance of the multiple sample assemblies according to the numbering order.

[0011] In any of the above technical solutions, the fixed distance is further defined as 5mm.

[0012] In any of the above technical solutions, step S001 is further included before step S100: obtaining the actual product self-piercing riveting quality requirements based on the product drawing.

[0013] In any of the above technical solutions, step S001 is further followed by step S002: obtaining qualified riveting process parameters and making a flat plate sample based on the actual riveting points and structure of the actual product; the flat plate sample includes an upper flat plate sample and a lower flat plate sample. With the goal of achieving the actual product self-piercing riveting quality requirements, riveting process tests were conducted along the center line of the assembly composed of the upper and lower plate samples, and qualified process parameters were obtained.

[0014] In any of the above technical solutions, the lower plate sample serves as a reference for the fabrication of the lower test sample; the upper plate sample serves as a reference for the fabrication of the upper test sample. Compared with the prior art, the beneficial effects of this application are as follows: The test method provided in this application for obtaining the required elongation value of self-piercing riveting of body die-casting parts includes the following steps: Includes the following steps: S100. Prepare test samples. Prepare upper test samples and lower test samples respectively. Both upper and lower test samples are long strips and flat plates. The lower test sample is a die casting. S200. To make a sample assembly, the upper test sample and the lower test sample are attached to each other and aligned to form a sample assembly. Multiple riveting points are formed by machining the sample assembly, and these multiple riveting points are spaced apart along the length of the sample assembly; The formation sequence of multiple rivet points is as follows: along the direction from the high elongation area to the low elongation area of ​​the lower test sample; S300. Determine the target riveting point. During the process of riveting the sample assembly to form multiple riveting points, when the first riveting point with a crack appears, the first riveting point with a crack is defined as the first target riveting point. S400, Lock the critical non-crack position, and define the first rivet point that does not produce a crack adjacent to the first rivet point as the second target rivet point; S500, Further lock the critical non-cracking position, according to step S400, make multiple sample assemblies, mark the first mark point at the position of the first target rivet point corresponding to each sample assembly, and mark the second mark point at the position of the second target rivet point corresponding to each sample assembly. Multiple sample assemblies are riveted one by one at different positions between the first and second marking points to form locking riveting points. The distance from the locking riveting points to the first marking point is different on different sample assemblies. When the first locking rivet point that develops a crack appears, the first locking rivet point that develops a crack is defined as the first locking rivet point, and the rivet point that does not develop a crack and is adjacent to the first locking rivet point is defined as the second locking rivet point. 600. Make a tensile sample. Prepare multiple identical sample assemblies according to step S500. Mark the position of the second locking rivet point on each sample assembly as the center point. The tensile specimen is prepared by cutting the sample assembly, so that the center point is located at the center of the tensile specimen. S700. Obtain the required elongation value for self-piercing riveting of die-cast parts, and use a tensile testing machine to perform tensile tests on tensile samples to test the elongation of each tensile specimen.

[0015] The test method provided in this application for obtaining the required elongation value of self-piercing riveting in die-cast body parts can be obtained based on the riveting process, quality requirements and similar test materials under actual production and manufacturing conditions, ensuring the high reliability and accuracy of the relevant test results. It fills the technical gap that the minimum requirement value of self-piercing riveting elongation cannot be obtained in the development process of die-cast body parts, effectively solving the industry pain point. By obtaining the minimum value of self-piercing riveting elongation in advance as a reference value for the production and processing of die-cast body parts, the non-conformity rate in subsequent product manufacturing and connection processes can be effectively reduced. At the same time, because it is directly based on the riveting process and riveting quality requirements under actual production and manufacturing conditions, it ensures the high adaptability and effectiveness of the test results. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the specific embodiments of this application or 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 this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 A schematic diagram of a partial connection structure of a body die-casting part in an actual product in the test method for obtaining the required elongation rate of self-piercing riveting of body die-casting parts provided in the embodiments of this application; Figure 2 A schematic diagram of the flat plate sample used in the test method for obtaining the required elongation value of self-piercing riveting of body die-castings provided in the embodiments of this application; Figure 3 A schematic diagram of the sample assembly in the test method for obtaining the required elongation value of self-piercing riveting of body die-casting parts provided in the embodiments of this application; Figure 4 for Figure 3 A schematic diagram illustrating the selection of each locking riveting point in the provided test method for obtaining the required elongation value of self-piercing riveting of die-cast body parts; Figure 5 A schematic diagram of center point selection in the test method for obtaining the required elongation value of self-piercing riveting of body die-casting parts provided in the embodiments of this application; Figure 6 A schematic diagram of the riveting point cross-section in the test method for obtaining the required elongation value of self-piercing riveting of die-cast body parts provided in the embodiments of this application.

[0018] Figure label: 1- Actual riveting point; 2- Upper plate; 3- Lower plate; 4- Flat plate sample; 41- Flat plate riveting point; 42- Upper plate sample; 43- Lower plate sample; 5- Sample assembly; 51- Riveting point; 52- Upper test sample; 53- Lower test sample. Detailed Implementation

[0019] The technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0020] The components of the embodiments of this application described and shown in the accompanying drawings can be arranged and designed in a variety of different configurations. Therefore, the following detailed description of the embodiments of this application provided in the drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application.

[0021] Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0022] In the description of this application, 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. They are used only for the convenience of describing this application 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. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0023] In the description of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" 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 between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0024] The following reference Figures 1 to 6 This application describes a test method for obtaining the required elongation value of self-piercing riveting of body die-cast parts, as described in embodiments of the present application.

[0025] See Figures 1 to 6 As shown, embodiments of this application provide a test method for obtaining the required elongation value of self-piercing riveting of die-cast body parts. This test method specifically includes the following steps: S001. Obtain the actual product self-piercing riveting quality requirements. Specifically, based on the product drawings, obtain the actual product self-piercing riveting quality requirements. The specific requirements are: the self-locking value c1 on the left side, the self-locking value c2 on the right side, the head height a, the remaining thickness at the bottom b, and the head gap e should all be within the acceptable range of the design requirements, and there should be no riveting expansion cracks, rivet punctures, rivet breakages, or other quality defects in the joint area.

[0026] It should be noted that the product drawings are known factors, therefore the above-mentioned actual product self-piercing riveting quality requirements can be regarded as known parameters, and the above requirements can be used as a reference for the production of the following samples.

[0027] S002. Obtain qualified riveting process parameters and fabricate a flat plate sample 4 based on the actual riveting point 1 of the actual product and the structure of the actual product; the flat plate sample 4 includes an upper flat plate sample 4 and a lower flat plate sample 4.

[0028] It should be noted that the actual product includes the actual riveting point 1. The actual product requires riveting at the upper plate 2 and the lower plate 3. The riveting overlap between the upper plate 2 and the lower plate 3 is H. Optionally, the upper plate 2 is a steel stamping part, and the lower plate 3 is a die-cast aluminum-magnesium alloy body part. A flat plate sample 4 is made according to the riveting position of the actual product. The flat plate sample 4 includes the stacked flat plate riveting point 51, the upper flat plate sample 4, and the lower flat plate sample 4. The material thickness, type, and surface coating information of the upper flat plate sample 4 are the same as those of the upper plate 2, and the material thickness and type of the lower flat plate sample 4 are the same as those of the lower plate 3.

[0029] With the goal of achieving the actual product self-piercing riveting quality requirements, riveting process experiments were conducted along the centerline of the assembly consisting of upper and lower plate samples 4, and qualified process parameters were obtained. These qualified process parameters included rivet type, hardness, and surface coating condition; upper and lower riveting die type and size; lower riveting die cavity shape; type of structural adhesive used at the connection interface; and riveting pressure, riveting speed, riveting direction, and upper die pressing control method. The riveting direction was from the steel plate stamping part to the aluminum-magnesium alloy die casting part. The upper die pressing control method included two types: constant displacement control and constant pressure control.

[0030] S100. Prepare test samples. Prepare upper test sample 52 and lower test sample 53 respectively. Both upper test sample 52 and lower test sample 53 are long strips and flat plates. The lower test sample is a die casting.

[0031] Specifically, using a casting mold for evaluating the fluidity of castings, a lower test sample 53 with uniform elongation gradient is produced by gravity casting. The lower test sample 53 is in the shape of a long flat plate. An upper test sample 52 is produced by laser cutting or shearing machine cutting. The upper test sample 52 is also in the shape of a long flat plate. Optionally, the upper test sample 52 is a stamped part. The width of the lower test sample 53 is W2, and the width of the upper test sample 52 is W1. The widths of the upper test sample 52 and the lower test sample 53 satisfy W2≤W1. The centerline of the lower test sample 53 along its length coincides with the centerline of the upper test sample 52 along its length. The length of the upper test sample 52 is L1, and the length of the lower test sample 53 is L2. The upper test sample 52 and the lower test sample 53 are closely fitted and centered, such that the distance between one end of the lower test sample 53 and one end of the upper test sample 52 is L3, and the distance between the other ends of the lower test sample 53 and the other ends of the lower test sample 53 is L4. The lengths of the upper test sample 52 and the lower test sample 53 satisfy L1=L2+L3+L4.

[0032] S200. Prepare sample assembly 5 by attaching the upper test sample 52 and the lower test sample 53 together and aligning them to form sample assembly 5. Specifically, as described above, the upper test sample 52 and the lower test sample 53 are aligned and attached to form sample assembly 5, which has a double-layer elongated plate structure.

[0033] According to the process parameters obtained in step S002, multiple riveting points 51 are formed on the sample assembly 5. The multiple riveting points 51 are spaced apart along the length direction of the sample assembly 5. The formation order of the multiple riveting points 51 is sequentially from the high elongation area of ​​the lower test sample to the low elongation area. Specifically, the sample assembly 5 is riveted sequentially along the centerline extending along its length direction in the first direction in an equally spaced riveting manner. The riveting direction is from the upper test sample 52 to the lower test sample 53, so that the sample assembly 5 forms multiple equally spaced riveting points 51.

[0034] Among them, the lower test sample 53 is a die casting. During the manufacturing process, due to the influence of the process, the elongation of the die casting near the gate end is higher than that far from the gate end. The first direction is from the high elongation of the lower test sample 53 to the low elongation. In the process of riveting the sample assembly 5 to form multiple riveting points 51, the formation sequence of the multiple riveting points 51 is from the high elongation area at the gate end to the low elongation area far from the gate end.

[0035] S300. Determine the target riveting point 51. During the riveting process of sample assembly 5 to form multiple riveting points 51, when the first riveting point 51 with a crack appears, the riveting is stopped. The first riveting point 51 with a crack is defined as the first target riveting point B, and the first riveting point 51 without a crack adjacent to the first riveting point 51 is defined as the second target riveting point C. Specifically, when riveting sample assembly 5 to obtain riveting points 51, the first riveting point 51 is formed by riveting near the end of sample assembly 5. This first riveting point 51 is defined as the first riveting point 51. Starting from the first riveting point 51, riveting is carried out sequentially along the first direction and along the center line of sample assembly 5 at equal intervals until the first riveting point 51 with a crack appears. The first riveting point 51 with a crack is defined as the first target riveting point. The distance L5 from the first target riveting point to the riveting start direction end face of the lower test sample 53 (hereinafter referred to as the start end) is recorded.

[0036] Optionally, a spacing M is formed between any two adjacent riveting points 51, where M ≤ 50 mm, and preferably, M = 50 mm.

[0037] S400, Lock the critical non-crack position, and define the first crack-free riveting point 51 adjacent to the first target riveting point as the second target riveting point. Specifically, defining the riveting point 51 adjacent to the first target riveting point as the second target riveting point is meaningless, as the second target riveting point is crack-free. The distance between the second target riveting point and the starting end of the lower test sample 53 is L6, then L6 = L5 - M = L5 - 50 mm.

[0038] It should be noted that the position of the second target rivet point on the sample assembly 5 can reflect the position of the minimum elongation of the sample assembly 5 to a certain extent, but the accuracy is low. In order to improve the accuracy of determining the non-cracking position, the following step S500 can be performed.

[0039] S500, Further lock the critical non-cracking position. According to step S400, make multiple sample assemblies 5. Mark the position of the first target rivet point corresponding to each sample assembly 5 with a first mark point E, and mark the position of the second target rivet point corresponding to each sample assembly 5 with a second mark point F. Specifically, a batch of samples with the same material, size and other physical properties as the above sample assemblies 5 can be prepared. Optionally, the number of sample assemblies 5 in the same batch is 9, numbered A1, A2, A3, A4, A5, A6, A7, A8 and A9 in sequence. In the same way as above, find the rivet points 51 at the same position as the first target rivet point and the second target rivet point in the 9 identical sample assemblies 5 in sequence. Define the point corresponding to the first target rivet point as the first mark point and the point corresponding to the second target rivet point as the second mark point.

[0040] A locking rivet point 51 is formed by riveting between the first and second marking points of each sample assembly 5. Specifically, following the numbering sequence from A1 to A9, another point is riveted between the first and second marking points of each sample assembly 5, and this point is defined as the locking rivet point 51. It should be noted that the position of the locking rivet point 51 formed between the first and second marking points is not always the center position between the two, so that the distance between the locking rivet point 51 on different sample assemblies 5 and the first marking point on its side is not the same.

[0041] Preferably, in step S500, the multiple sample assemblies 5 are numbered from smallest to largest, and locking rivet points 51 are riveted onto each of the multiple sample assemblies 5 one by one according to the numbering order. The riveting is performed by progressively increasing a fixed distance difference Δ, so that the distance between the locking rivet point 51 on each sample assembly 5 and the first mark point increases by Δ progressively according to the numbering order. Preferably, Δ = 5mm. Therefore: the point 5mm away from point E is the location of the locking rivet point 51 in the sample assembly 5; the point 10mm away from point E is the location of the locking rivet point 51 in the sample assembly 5; the point 15mm away from point E... The points are: the locking riveting point 51 in sample assembly 5; the point 20mm away from point E; the point 25mm away from point E; the point 10mm away from point E; the point 15mm away from point E; the point 20mm away from point E; and the point 20mm away from point E.

[0042] When the first locking rivet point 51 that develops a crack appears, the first locking rivet point 51 that develops a crack is defined as the first locking rivet point G, and the locking rivet point 51 that does not develop a crack and is adjacent to the first locking rivet point is defined as the second locking rivet point H. Specifically, in the process of riveting the locking rivet points 51 one by one in the order from A1 to A2, the process stops when the first locking rivet point 51 that develops a crack appears. The first locking rivet point 51 that develops a crack is defined as the first locking rivet point, and the locking rivet point 51 that is adjacent to the first locking rivet point is defined as the second locking rivet point. It can be known without any reason that the second locking rivet point does not have a crack. For example, assuming that the first locking rivet point obtained by riveting number A6 cracks, the second locking rivet point at this time is the first mark point of A6.

[0043] Record the distance between the first locking rivet point and the first mark point as L7, and the distance between the second locking rivet point and the first mark point as L8. Then, L8 = L7 - 5mm. The distance between the second locking rivet point and the starting end of the sample assembly 5 is L9. Then, L9 = L6 + L8 = L5 + L7 - 55mm. This allows us to determine the specific position of the second locking rivet point on the sample assembly 5.

[0044] 600. Prepare tensile samples. According to step S500, prepare multiple identical sample assemblies 5 and mark the position of the second locking rivet point on each sample assembly 5 as the center point N. Specifically, according to the same position, material, size and other conditions as the first locking rivet point 51 where the first crack occurs (i.e., the first locking rivet point) in step S500, multiple sample assemblies 5 are prepared. That is to say, on multiple sample assemblies 5, the distance between the second locking rivet point and the first or second marking point is the same.

[0045] Tensile specimens are prepared by cutting sample assembly 5, with the center point located at the center of the tensile specimen. Specifically, the portion of sample assembly 5 including the center point is cut by wire cutting to obtain the tensile specimen. Optionally, the tensile specimen is dumbbell-shaped and the center point is located at the center of the tensile specimen. Optionally, at least three tensile specimens are prepared. Taking three tensile specimens as an example, they are designated as S1, S2, and S3.

[0046] S700. Obtain the required elongation value for self-piercing riveting of die-cast parts, and use a tensile testing machine to perform tensile tests on tensile samples to test the minimum elongation of each tensile specimen.

[0047] Specifically, the elongation of three tensile specimens, S1, S2 and S3, is tested using a tensile testing machine. The minimum elongation of the three tensile specimens is δ1, which is the minimum elongation of the casting under this material combination.

[0048] It should be noted that if the product involves only a single material combination, the minimum requirement for the elongation of the self-piercing riveting of the body die-casting parts is ≥δ1.

[0049] If the product involves multiple material combinations, the minimum requirement value δi for the self-piercing riveting elongation of the die-cast body parts for each material combination should be obtained first according to the above method, and the maximum value δmax of δi should be taken as the minimum baseline requirement value, that is, the minimum requirement value for the self-piercing riveting elongation of the die-cast body parts is ≥δmax.

[0050] The following are several experimental groups for the practical application of this test method for obtaining the required elongation value of self-piercing riveting of die-cast body parts: (i) Determine the minimum required elongation of the self-piercing riveting connection between the die-cast aluminum shock absorber tower and the surrounding steel plate stamping parts of a certain vehicle body. The material of the cast aluminum shock absorber tower is AlSi10MnMg-T7, and the thickness of the riveting edge is 3.0mm. The surrounding steel plate stamping parts involve only one material, specifically 1.5mm thick DP590D+Z. 1840C structural adhesive is used between the connecting surfaces of the two parts to prevent electrochemical corrosion.

[0051] Based on the product drawings, obtain the actual product's self-piercing riveting quality requirements. Specific requirements are: left-side self-locking value c1 ≥ 0.25mm, right-side self-locking value c2 ≥ 0.25mm, head height -0.5mm ≤ a ≤ 0.3mm, bottom remaining thickness b ≥ 0.10mm, and head gap e ≥ 0.4mm. Furthermore, the joint area must be free of riveting expansion cracks, rivet punctures, rivet breakage, and other quality defects.

[0052] In the actual riveting point 1 of the actual product, the upper plate 2 is 1.5mm thick DP590D+Z, and the lower plate 3 is 3.0mm thick AlSi10MnMg-T7. The flat plate riveting sample consists of flat plate riveting point 51, upper flat plate sample 4, and lower flat plate sample 4. The upper flat plate sample 4 is made of 1.5mm thick DP590D+Z material, and the lower flat plate sample 4 is made of 3.0mm thick AlSi10MnMg-T7 material. To achieve the self-piercing riveting quality requirements of the actual product, riveting process tests were conducted along the centerline of the assembly composed of upper and lower flat plate samples 4, and qualified process parameters were obtained. These qualified process parameters include rivet type, hardness, and surface coating condition; upper and lower riveting die type and size; lower riveting die cavity shape; use of 1840C structural adhesive at the connection interface; and riveting pressure, riveting speed, riveting direction, and upper die pressing control method. The riveting direction is from the steel plate stamping part to the aluminum-magnesium alloy die casting part. The upper die pressing control method is constant displacement control.

[0053] Using a casting mold for evaluating casting fluidity, a lower test sample 53 with uniform elongation gradient and equal width was fabricated by gravity casting. The material used was AlSi10MnMg, and the sample thickness was 3.0 mm. Simultaneously, an upper test sample 52 was fabricated using laser cutting or a shearing machine, with a material of 1.5 mm thick DP590D+Z. The width of the lower test sample 53 was W2 = 60 mm, and the width of the upper test sample 52 was W1 = 80 mm. The lower test sample 53 was placed in the exact center of the upper test sample 52, ensuring that the centerlines in the length direction coincided. The lengths L1 of the upper test sample 52 and L2 of the lower test sample 53 satisfied L1 = L2 + L3 + L4, where L1 = 1200 mm, L2 = 750 mm, L3 = 100 mm, and L4 = 150 mm.

[0054] Using the riveting process parameters obtained above, riveting is performed along the center line of the assembly formed by the lower test sample 53 and the upper test sample 52 to create sample assembly 5, forming a series of riveting points 51. The riveting direction is from the upper test sample 52 to the lower test sample 53. The riveting sequence of the riveting points 51 is as follows: starting from the high elongation zone at the gate end, gradually moving to the low elongation zone away from the gate end, that is, starting from point A along the center line of the long strip riveted sample 5, until the first riveting point 51 with a crack appears. The distance between two adjacent riveting points 51 is M, where M = 50 mm.

[0055] When the first cracked riveting point 51 appears in the sample assembly 5, record the distance L5 from the riveting starting direction end face of the lower test sample 53. L5 = 564 mm. Then, the distance L6 from the first adjacent riveting point 51 without cracks to the riveting starting direction end face satisfies: L6 = 514 mm.

[0056] Prepare a batch of 9 samples with identical material, dimensions, and other physical properties to sample assembly 5, numbered A1-A9. Find points on these samples that correspond to points C and B, and number them E and F respectively. Rivet one point between points E and F on each sample. The distance from riveting point 51 of sample A1 to point E is 5mm, and the distance from riveting point 51 of sample A2 to point E is 10mm. Subsequent samples are riveted with a distance increasing by 5mm each time, until the first cracked riveting point 51 appears on sample A4. Record the distance L7 = 20mm from the cracked point G to point E. Then, the distance L8 from the first adjacent non-cracked riveting point 51 to point E is L8, which satisfies L8 = 15mm. In the lower test sample 53, the distance L9 from riveting point 51 to the end face in the riveting starting direction is L6 + L8 = L5 + L7 - 55 = 529mm.

[0057] Prepare three lower-layer test specimens 53 prepared under identical conditions. Locate point N on these specimens, which is at the same position as point H. Ensure that point N is located at the center of the dumbbell-shaped standard tensile specimen. Number these specimens as S1, S2, and S3. Prepare the relevant tensile specimens using wire cutting.

[0058] Using a tensile testing machine, the elongation of three tensile specimens, S1, S2, and S3, was tested. The minimum elongation of the six tensile specimens was measured to be δ1 = 8.3%. Therefore, δ1 is the minimum elongation of all castings under this material combination.

[0059] The minimum requirement for the self-piercing riveting elongation rate of the die-cast aluminum shock absorber tower and the surrounding stamped steel parts of this vehicle body is ≥8.3%.

[0060] (II) Determine the minimum required riveting elongation for the self-piercing riveting of the floor and surrounding steel plate stampings after die casting of a certain vehicle body. The material used is heat-free die-cast aluminum alloy C611 with an overlap thickness of 3.0 mm. The surrounding steel plate stampings involve five materials: 1.2 mm thick St280D+Z, 1.5 mm thick DP590D+Z, 1.0 mm thick DP980D+Z, 0.8 mm thick St16D+Z, and 1.25 mm thick DH780D+Z. 2098G structural adhesive is used between each steel plate part and the cast aluminum part to prevent electrochemical corrosion.

[0061] Based on the product drawings, obtain the actual product's self-piercing riveting quality requirements. Specific requirements are: left-side self-locking value c1 ≥ 0.25mm, right-side self-locking value c2 ≥ 0.25mm, head height -0.5mm ≤ a ≤ 0.3mm, bottom remaining thickness b ≥ 0.10mm, and head gap e ≥ 0.4mm. Furthermore, the joint area must be free of riveting expansion cracks, rivet punctures, rivet breakage, and other quality defects.

[0062] Based on the actual product, C611 and St280D+Z heat-free die-cast aluminum alloys were first selected for parameter exploration. In the actual product's actual riveting point 1, the upper plate 2 was 1.2mm thick St280D+Z, and the lower plate 3 was 3.0mm thick C611. The flat plate sample 4 consisted of flat plate riveting point 51, upper flat plate sample 4, and lower flat plate sample 4. The upper flat plate sample 4 was made of 1.2mm thick St280D+Z, and the lower flat plate sample 4 was made of 3.0mm thick C611. With the goal of achieving the self-piercing riveting quality requirements of the actual product, riveting process experiments were conducted along the centerline of the assembly composed of upper and lower flat plate samples 4, and qualified process parameters were obtained. The qualified process parameters included rivet type, hardness and surface coating condition, upper and lower riveting die type and size, lower riveting die cavity shape, use of 2098G structural adhesive at the connection interface, and riveting pressure, riveting speed, riveting direction and upper die pressing control method. The riveting direction is from the steel plate stamping part to the aluminum-magnesium alloy die casting part. The upper die pressing control method is constant pressure control.

[0063] Using a casting mold for evaluating casting fluidity, a lower test sample 53 with uniform elongation gradient and equal width was fabricated by gravity casting. The material selected was C611, and the sample thickness was 3.0 mm. Simultaneously, an upper test sample 52 was fabricated using laser cutting or a shearing machine, with a material of 1.2 mm thick St280D+Z. The width W2 of the lower test sample 53 was equal to the width W1 of the upper test sample 52, both being 65 mm. The length L1 of the upper test sample 52 and the length L2 of the lower test sample 53 satisfied the condition L1 = L2 + L3 + L4, where L1 = 1100 mm, L2 = 700 mm, L3 = 200 mm, and L4 = 200 mm.

[0064] Using the riveting process parameters obtained above, riveting is performed along the center line of the assembly formed by the lower test sample 53 and the upper test sample 52 to create sample assembly 5, forming a series of riveting points 51. The riveting direction is from the upper test sample 52 to the lower test sample 53. The riveting sequence of the riveting points 51 is as follows: starting from the high elongation zone at the gate end, gradually moving to the low elongation zone away from the gate end, that is, starting from point A along the center line of the long strip riveted sample 5, until the first riveting point 51 with a crack appears. The distance between two adjacent riveting points 51 is M, where M = 50 mm.

[0065] When the first cracked riveting point 51 appears in the sample assembly 5, record the distance L5 from the riveting starting direction end face of the lower test sample 53. L5 = 626 mm. Then, the distance L6 from the first crackless riveting point 51 adjacent to it to the riveting starting direction end face satisfies: L6 = 576 mm.

[0066] Prepare a batch of 9 samples with identical material, dimensions, and other physical properties to sample assembly 5, numbered A1-A9. Find points on these samples that correspond to points C and B, and number them E and F respectively. Rivet one point between points E and F on each sample. The distance from riveting point 51 of sample A1 to point E is 5mm, and the distance from riveting point 51 of sample A2 to point E is 10mm. Subsequent samples are riveted with a distance increasing by 5mm each time, until the first cracked riveting point 51 appears on sample A6. Record the distance L7 = 30mm from the cracked point G to point E. Then, the distance L8 from the first adjacent non-cracked riveting point 51 to point E is L8, which satisfies L8 = 25mm. In the lower test sample 53, the distance L9 from riveting point 51 to the end face in the riveting starting direction is L9 = L6 + L8 = L5 + L7 - 55 = 701mm.

[0067] Prepare three lower-layer test specimens 53 prepared under identical conditions. Locate point N on these specimens, which is at the same position as point H. Ensure that point N is located at the center of the dumbbell-shaped standard tensile specimen. Number these specimens as S1, S2, and S3. Prepare the relevant tensile specimens using wire cutting.

[0068] Using a tensile testing machine, the elongation of three tensile specimens, S1, S2, and S3, was tested. The minimum elongation of the six tensile specimens was measured to be δ1 = 7.8%. Therefore, δ1 is the minimum elongation of all castings under this material combination.

[0069] The minimum required elongation rate for self-piercing riveting between the unibody die-cast rear floor and the surrounding 1.2mm thick St280D+Z stamped parts of this vehicle model is ≥7.8%. Using the same method, the minimum required elongation rates for self-piercing riveting between the unibody die-cast rear floor and four types of steel plates—1.5mm thick DP590D+Z, 1.0mm thick DP980D+Z, 0.8mm thick St16D+Z, and 1.25mm thick DH780D+Z—were obtained as follows: ≥8.1%, ≥10.3%, ≥6.9%, and ≥9.2%, respectively. In summary, the minimum required elongation rate for self-piercing riveting between the unibody die-cast rear floor and the surrounding 1.2mm thick St280D+Z stamped parts of this vehicle model is ≥10.3%.

[0070] In summary, the test method for obtaining the required elongation value of self-piercing riveting in body die-castings provided in this application can be obtained based on the riveting process, quality requirements, and similar test materials under actual production and manufacturing conditions, ensuring the high reliability and accuracy of the relevant test results. It fills the technical gap in obtaining the minimum required elongation value of self-piercing riveting in the development of body die-castings, effectively solving industry pain points. By obtaining the minimum value of self-piercing riveting elongation in advance as a reference value for the production and processing of body die-castings, the non-conformity rate in subsequent product manufacturing and connection processes can be significantly reduced. At the same time, because it is directly based on the riveting process and riveting quality requirements under actual production and manufacturing conditions, it ensures the high adaptability and effectiveness of the test results.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 this application.

Claims

1. A test method for obtaining the required elongation value of self-piercing riveting of die-cast body parts, characterized in that, Includes the following steps: S100. Prepare test samples. Prepare an upper test sample and a lower test sample respectively. Both the upper test sample and the lower test sample are in the shape of long strips and flat plates. The lower test sample is a die casting. S200. To make a sample assembly, the upper test sample and the lower test sample are attached to each other and aligned to form a sample assembly. Multiple riveting points are formed by processing the sample assembly, and the multiple riveting points are spaced apart along the length direction of the sample assembly; The multiple riveting points are formed sequentially along the direction from the high elongation region to the low elongation region of the lower test sample. S300. Determine the target riveting point. During the process of riveting the sample assembly to form multiple riveting points, when the first riveting point with a crack appears, the first riveting point with a crack is defined as the first target riveting point. S400, Lock the critical non-crack position, and define the first rivet point that has not produced a crack adjacent to the first target rivet point as the second target rivet point; S500, Further lock the critical non-cracking position, and according to step S400, make multiple sample assemblies, mark a first mark point at the position of the first target rivet point of each sample assembly, and mark a second mark point at the position of the second target rivet point of each sample assembly. Each of the sample assemblies is riveted at different positions between the first mark point and the second mark point to form a locking riveting point. The distance from the locking riveting point to the first mark point is different on different sample assemblies. When the first locking rivet point that develops a crack appears, the first locking rivet point that develops a crack is defined as the first locking rivet point, and the rivet point that does not develop a crack and is adjacent to the first locking rivet point is defined as the second locking rivet point. S600. Make a tensile sample. Prepare multiple identical sample assemblies according to step S500. Mark the position of the second locking rivet point on each sample assembly as the center point. The sample assembly is cut to obtain a tensile specimen, with the center point located at the center of the tensile specimen. S700. Obtain the required elongation value for self-piercing riveting of die-cast parts, and use a tensile testing machine to perform tensile tests on the tensile samples to test the elongation of each tensile sample.

2. The test method for obtaining the required elongation value of self-piercing riveting of die-cast body parts according to claim 1, characterized in that, In step S200, the sample assembly is sequentially riveted along a first direction to form a plurality of riveting points, wherein the first direction is the direction from the high elongation region to the low elongation region of the lower test sample.

3. The test method for obtaining the required elongation value of self-piercing riveting of die-cast body parts according to claim 1, characterized in that, If the width of the lower test sample is W2 and the width of the upper test sample is W1, then W2 ≤ W1.

4. The test method for obtaining the required elongation value of self-piercing riveting of die-cast body parts according to claim 1, characterized in that, The upper test sample has a length of L1, the lower test sample has a length of L2, the upper test sample and the lower test sample are attached to each other and centered, the distance between one end of the lower test sample and one end of the upper test sample is L3, and the distance between the other end of the lower test sample and the other end of the lower test sample is L4. Then L1 = L2 + L3 + L4.

5. The test method for obtaining the required elongation value of self-piercing riveting of vehicle body die-casting parts according to claim 1, characterized in that, The multiple riveting points are equally spaced, and the distance between any two adjacent riveting points is M, where M≤50mm.

6. The test method for obtaining the required elongation value of self-piercing riveting of die-cast body parts according to claim 1, characterized in that, In step S500, the multiple sample assemblies are numbered one by one from smallest to largest, and the locking rivet points are riveted one by one by increasing the fixed distance according to the numbering order.

7. The test method for obtaining the required elongation value of self-piercing riveting of die-cast body parts according to claim 6, characterized in that, The fixed distance is 5mm.

8. The test method for obtaining the required elongation value of self-piercing riveting of die-cast body parts according to claim 1, characterized in that, Before step S100, there is also step S001, which involves obtaining the actual product self-piercing riveting quality requirements based on the product drawing.

9. The test method for obtaining the required elongation value of self-piercing riveting of vehicle body die-casting parts according to claim 8, characterized in that, Step S001 is followed by step S002, which involves obtaining qualified riveting process parameters and fabricating a flat plate sample based on the actual riveting points and structure of the actual product. The flat plate sample includes an upper flat plate sample and a lower flat plate sample. With the goal of achieving the actual product self-piercing riveting quality requirements, riveting process tests were conducted along the center line of the assembly composed of the upper and lower plate samples, and qualified process parameters were obtained.

10. The test method for obtaining the required elongation value of self-piercing riveting of vehicle body die-casting parts according to claim 9, characterized in that, The lower plate sample serves as a reference for the preparation of the lower test sample; the upper plate sample serves as a reference for the preparation of the upper test sample.

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