A heterogeneous material resistance pre-punch riveting welding composite connection system and method thereof

Abstract

This invention proposes a novel process for joining dissimilar metal materials using solid rivets. In the first stage, under pre-pressure, high current, and short time conditions, the upper lightweight metal plate is softened by the current. A pre-pierced hole is made on the surface of the upper plate using a round boss electrode. Driven by the electrode force, the rivet pierces the lightweight metal plate at the center of the hole and contacts the lower steel plate. The piercing time should be as short as possible to minimize the softening of the lightweight metal plate during the piercing process. In the second stage, a weld nugget is formed between the rivet and the lower steel plate by applying a longer current. Excessive deformation of the rivet head edge and excessive softening or thinning of the aluminum plate are avoided. This invention reduces the piercing resistance of the rivet during riveting and welding by using the resistance of the round boss copper electrode for pre-piercing, thus reducing the rivet upsetting degree. During welding, the rivet legs are used to discharge molten metal into the rivet head, ensuring a neat weld joint. Simultaneously, the solid structure of the rivet legs can squeeze out air, reducing porosity defects in the weld nugget. Meanwhile, the process can be precisely controlled by monitoring the dynamic resistance curve, and the weld nugget size can be predicted online using a neural network model based on the welding process signals, enabling non-destructive, real-time assessment of joint quality. This method combines the advantages of high connection strength, minimal deformation, and controllable quality.

Description

Technical Field

[0001] This invention relates to a technology in the field of metal material processing, specifically a heterogeneous material resistance pre-penetration riveting and welding composite connection system and method. Background Technology

[0002] Lightweight manufacturing of thin-walled structures is one of the effective means to address energy conservation and emission reduction. The connection of dissimilar metal materials effectively reduces structural weight while ensuring structural safety, and is receiving increasing attention in the manufacturing of emerging transportation vehicles such as new energy vehicles and high-speed rail. Resistance spot welding, with its advantages of high joint strength, low energy consumption, and fast cycle time, is widely used in the manufacturing of thin-walled structures. However, the contradiction between the load-bearing capacity of the intermetallic compound layer at the joint surface and the hard and brittle characteristics of the compound limits the improvement of joint performance. Therefore, researchers have proposed a series of thermomechanical composite connection processes based on traditional resistance spot welding, such as resistance unit welding. Resistance unit welding technology combines riveting and spot welding processes, transforming dissimilar metal connection into same-metal welding, enabling reliable connection between lightweight metals and steel. However, this technology requires an additional pre-drilling process, which is cumbersome, leading to increased process costs and reduced production efficiency. To overcome these difficulties, resistance spot riveting and self-piercing resistance unit welding processes have been proposed. These processes utilize rivets to directly pierce through the upper metal plate, eliminating the pre-drilling process, simplifying the production process, and improving production efficiency. However, with the widespread use of cast aluminum sheets thicker than 2.5 mm, during the welding process, due to the high heat dissipation coefficient and low resistance of the aluminum sheet, the heat generated by resistance is concentrated on the steel plate side. The aluminum plate near the steel plate softens sufficiently, while the surface of the aluminum plate on the rivet side softens insufficiently, causing the rivet to be upset rather than pierce the aluminum plate, which seriously affects the success rate of the connection and the joint strength. Summary of the Invention

[0003] To address the aforementioned shortcomings of existing technologies, this invention proposes a heterogeneous material resistance pre-piercing riveting and welding composite connection system and method. The system utilizes a copper electrode with a frustum-shaped end face, applying a large current to pierce an upper metal plate, creating pre-drilled holes or through-holes. Subsequently, rivets with heads matching the frustum-shaped electrode are used to rivet and weld at the holes or through-holes, achieving a reliable connection between the heterogeneous materials. The resistance pre-piercing of the frustum-shaped copper electrode reduces the piercing resistance during the riveting and welding process, lessens the rivet upsetting degree, and results in a high-quality joint.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a heterogeneous material resistance pre-penetration riveting and welding composite connection system, comprising, from top to bottom: an upper round boss copper electrode, a rivet that mates with the electrode round boss, a light metal plate to be connected, a steel plate to be connected, and a lower copper electrode.

[0006] The height of the upper circular boss electrode is 0.5-1.5 times the thickness of the light metal plate to be connected.

[0007] The diameter of the end face of the upper circular boss electrode is 3mm-6mm.

[0008] The upper circular protrusion electrode is designed to facilitate the separation of the electrode from the light metal plate after resistive puncture, and its taper is set to 3°-45°.

[0009] The rivet that mates with the electrode frustum refers to a rivet head with a groove at the center that mates with the electrode boss.

[0010] The rivet head groove that mates with the electrode frustum has a clearance of 0.05mm-0.5mm with the round boss.

[0011] The rivet leg that mates with the electrode frustum can be a cylinder or a frustum with the same shape and size as the electrode boss.

[0012] The rivet head groove that mates with the electrode frustum may be threaded.

[0013] The rivet legs that mate with the electrode frustum are designed to make full contact with the steel plate to be connected, and the tips of the rivet legs are provided with a cone angle or boss with an angle of 45°-145°.

[0014] The light metal plate to be connected is at least one layer, adjacent to the circular boss electrode.

[0015] The steel plates to be connected shall be at least one layer, and if multiple layers are used, they shall be arranged adjacent to each other;

[0016] The steel plate to be connected can also be a metal plate such as titanium alloy or nickel alloy plate;

[0017] This invention relates to a method for resistive pre-penetration riveting composite connection of the above-mentioned system. It includes the following steps:

[0018] Step 1) Resistance pre-puncture stage: A suitable current is applied to the round boss electrode to soften the upper light metal plate under the action of resistance heat, and the round boss makes resistance pre-puncture holes or through holes on the surface of the light metal plate.

[0019] Step 2) Rivet feeding stage: The electrode round boss and the rivet head are matched by manual rivet placement or automatic rivet feeding.

[0020] Step 3) Rivet piercing stage: The electrode, which is supplied with a suitable current, drives the rivet to pierce the light metal plate in the center of the hole or through hole and make close contact with the underlying steel plate.

[0021] Step 4) Welding stage: Apply a suitable current to the rivet and continue for a period of time to melt it with the steel plate.

[0022] Step 5) Cooling stage: Apply holding pressure, and the molten nugget solidifies under the action of water-cooled copper electrode to form a welded joint.

[0023] Preferably, the current flowing through the circular boss electrode in step 1) is 5kA-15kA.

[0024] Preferably, in step 1), the diameter of the resistor pre-piercing hole or through hole is 3-6 mm, and the shape can be cylindrical or frustum.

[0025] Preferably, the lower steel plate is optional in the resistance pre-puncture process of step 1).

[0026] Preferably, in step 2), the electrode round boss and the rivet head are fitted with a clearance fit.

[0027] Preferably, the holes or through holes in step 3) have the effect of reducing puncture resistance.

[0028] Preferably, the duration of step 4) is 200-500ms. Technical effect

[0029] Compared with the prior art, the resistance pre-penetration riveting and welding composite connection system and method of the present invention can achieve pre-drilled holes and welding by using two spot welding processes of resistance pre-penetration and resistance welding on the same set of equipment, so as to achieve a reliable connection of light metal plates and steel plates with high strength, low deformation and online quality monitoring capability. It is especially suitable for solving the connection problem of light metal plates and steel plates with a thickness greater than 2.5mm. Attached Figure Description

[0030] Figure 1 This is a three-dimensional structural diagram of the rivet used in Embodiment 1 of the present invention;

[0031] Figure 2 This is a cross-sectional schematic diagram of the rivet used in Embodiment 1 of the present invention;

[0032] Figure 3 This is a three-dimensional structural diagram of the rivet used in Embodiment 2 of the present invention;

[0033] Figure 4 This is a cross-sectional schematic diagram of the rivet used in Embodiment 2 of the present invention;

[0034] Figure 5 (a)-(e) are schematic diagrams of the welding process flow of the present invention;

[0035] Figure 6 This is a schematic diagram of the melting core in Example 1;

[0036] Figure 7 This is a schematic diagram of the melting core in Example 2. Detailed Implementation Example 1

[0037] like Figure 1 As shown, this embodiment relates to a steel rivet for joining dissimilar materials, including a countersunk head 101, a rivet head 102, a rivet leg 103, and a rivet leg taper angle 104.

[0038] The countersunk hole 101 of the nail head is frustum-shaped with a depth of 3mm, a diameter of 4.06mm on the top of the frustum, a diameter of 2.13mm at the bottom of the frustum, and a chamfer radius of 0.2mm.

[0039] The nail head 102 has a diameter of 11.89 mm and a height of 2 mm, with a chamfer radius of 0.2 mm.

[0040] The nail leg 103 is cylindrical. The cylinder has a diameter of 5.51 mm and a height of 3.99 mm.

[0041] The cross section of the spike leg cone angle 104 is an isosceles triangle.

[0042] like Figure 5 (c) shows the welding structure used in this embodiment, wherein the upper electrode cap is 105, the lower electrode cap is 106, the rivet is 107, the upper light metal plate 108 is Shuaiyichi C611 cast aluminum plate, and the lower steel plate 109 is PHS ultra-high strength steel plate, with plate thicknesses of 3mm and 1.55mm respectively.

[0043] like Figure 5 As shown in (a)-(e), the present invention relates to the manufacturing process of the above-mentioned rivets;

[0044] The specific work steps are as follows:

[0045] Step 1: Use a round boss electrode to pre-pierce holes or through holes on the surface of the upper light metal plate, such as... Figure 5 As shown in (a)-(b);

[0046] Step 2: Use manual or automatic rivet feeding to mate the electrode round boss with the rivet head;

[0047] Step 3: The electrode drives the rivet to pierce the light metal plate at the center of the hole or through hole and make close contact with the underlying steel plate.

[0048] Step 4: Apply a suitable current and continue for a period of time to allow the rivet to fuse with the steel plate. During this stage, the system collects dynamic resistance and power signals in real time.

[0049] Step 5: Apply holding pressure, and the molten nugget solidifies under the action of water-cooled copper electrodes to form a welded joint.

[0050] Step 6, Quality Judgment: The system automatically processes the acquired signals, extracts feature values ​​(such as peak resistance, energy, etc.), and inputs them into a pre-trained ELMAN neural network model. The model outputs a predicted value for the weld nugget diameter. If the predicted value is ≥3.0 mm, the system indicates that the weld joint is qualified; otherwise, it indicates an abnormality.

[0051] In this embodiment, the rivet and weld nugget formed as an aluminum-steel mixture have a total intermetallic compound layer thickness of less than 10 μm, an ultimate tensile shear load of not less than 8.0 kN, and exhibit a pull-out fracture failure mode. Figure 6 As shown. Example 2

[0052] like Figure 3 The schematic diagram of the steel rivet used in this embodiment for connecting dissimilar metal materials shows a rivet head 201, a rivet leg 202, and a rivet leg cone angle 203.

[0053] The nail head has a diameter of 11.4 mm, a height of 2 mm, and a chamfer radius of 0.2 mm.

[0054] The nail leg is a solid cylinder with a diameter of 4.5 mm and a height of 2.8 mm.

[0055] The cone angle of the nail leg is similar to an isosceles triangle.

[0056] The welding structure used in this embodiment is the same as that in Embodiment 1.

[0057] This invention relates to the manufacturing process of the aforementioned rivets;

[0058] The specific work steps are as follows:

[0059] Step 1: Use a round boss electrode to pre-puncture holes or through holes on the surface of the upper plate.

[0060] Step 2: Replace the upper electrode with a flat electrode;

[0061] Step 3: Use manual or automatic rivet feeding to ensure good alignment between the flat electrode and the rivet;

[0062] Step 4: The electrode drives the rivet to pierce the light metal plate at the center of the hole or through hole and make close contact with the underlying steel plate.

[0063] Step 5: Apply a suitable current and continue for a period of time to allow the rivet to fuse with the steel plate.

[0064] Step 6: Apply holding pressure, and the molten nugget solidifies under the action of the water-cooled copper electrode to form a welded joint.

[0065] In this embodiment, the rivet and the weld nugget formed after welding are used to create an aluminum-steel mixture, such as Figure 7 As shown. Welding quality monitoring and judgment methods

[0066] To ensure the stability of the pre-piercing resistance riveting process and the reliability of the joints in this invention, the following multi-dimensional criteria are used for quality assessment:

[0067] Method 1: Process stability assessment based on dynamic resistance curves. The dynamic resistance curve during the welding process is monitored in real time, and its characteristics are analyzed to determine process stability. A qualified welding process corresponds to a continuous and smooth dynamic resistance curve, with a characteristic of first decreasing, then rising to a peak, and then steadily decreasing, indicating normal weld nugget formation and growth. If the curve shows an abnormal, sudden drop, it is determined to be a spatter defect.

[0068] Method 2, geometric dimension determination based on macroscopic morphology. Determination is made by macroscopic observation and dimensional measurement of the joint cross-section. A qualified joint should have a continuous and dense weld nugget, free of visible cracks and large pores; key dimensions should meet preset thresholds, including a weld nugget width of not less than 3.0 mm and a weld nugget height of not less than 0.8 mm.

[0069] Method 3: Interface quality assessment based on joint microstructure and composition. Joint quality is determined through microscopic analysis of the weld interface. In a qualified joint, the total thickness of the intermetallic compound layer formed at the rivet / aluminum and steel / aluminum interfaces should be less than 10 μm; in the aluminum remelting zone, the morphology of eutectic silicon should change from the plate-like structure of the base material to a fibrous structure.

[0070] Method 4: Online prediction of weld nugget size based on process signals and a neural network model. A set of feature values ​​is extracted from the dynamic resistance and power signals of the welding process and input into a trained ELMAN neural network model for regression prediction. The prediction accuracy of this model must meet the following requirements: correlation coefficient R > 0.95, mean absolute error (MAE) < 0.4 mm. When the predicted weld nugget diameter output by the model is not less than 3.0 mm, the weld joint can be directly judged as qualified online.

[0071] Method 5, based on final mechanical property verification using tensile shear tests. A qualified welded joint should have an ultimate peak load of not less than 8.0 kN, and the failure mode should exhibit "pull-out fracture." If "interfacial fracture" occurs or the load is too low, it indicates insufficient interfacial bonding strength.

[0072] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A rivet for joining dissimilar metal materials, characterized in that, include: The nail head, countersunk hole in the nail head, solid nail leg, and nail leg taper. The countersunk hole in the nail head is located at the center of the top surface of the nail head, the solid nail leg is connected to the nail head, and the nail leg taper is located at the lower end of the nail leg.

2. The rivet for joining dissimilar metal materials according to claim 1, characterized in that, The top surface of the nail head is a circular plane, with a countersunk hole in the center of the top surface and an inclination angle of 3°-45° on the bottom surface of the center to allow air and molten metal to escape during the welding process.

3. The rivet for joining dissimilar metal materials according to claim 1, characterized in that, The solid nail leg has a triangular cross-section at the bottom cone angle with a vertex angle of 45°-145°, and is used to pierce through the upper plate during the welding process.

4. The rivet for joining dissimilar metal materials according to claim 1, characterized in that, The solid nail leg can be cylindrical or frustum-shaped with the same shape and size as the circular boss of the upper circular boss electrode.

5. The rivet for joining dissimilar metal materials according to claim 1, characterized in that, The aforementioned spiked cone angle can melt under the action of electric current and connect with the ultra-high strength steel plate.

6. The rivet for joining dissimilar metal materials according to claim 1, characterized in that, The length and cone angle of the rivet leg are configured such that, after piercing, its end can form a contact area with the lower steel plate that meets the preset current density requirements, so as to facilitate the subsequent formation of a metal mixture weld nugget.

7. The rivet for joining dissimilar metal materials according to claim 1, characterized in that, The rivet has sufficient strength and rigidity to prevent deformation during the piercing of the light metal plate, and the length of the rivet leg after upsetting during high-temperature welding is not less than the thickness of the light metal plate. At the same time, the rivet material has good weldability.

8. A process for joining dissimilar metal materials, characterized in that, This process enables pre-drilling and welding using two spot welding processes—resistance pre-piercing and resistance welding—on the same equipment. In the first stage, under high current, short duration, and significant pre-pressure, the light metal plate is softened by the current. A round boss electrode is used to pre-pierce holes or through-holes on the surface of the upper light metal plate. Manual or automatic rivet feeding is used to ensure the round boss electrode and rivet head mate, guaranteeing good alignment between the round boss electrode, rivet, and hole. The electrode drives the rivet to pierce the light metal plate at the center of the hole or through-hole and make tight contact with the lower steel plate. In the second stage, a prolonged current is applied to achieve welding between the rivet and the lower steel plate. The welding force during both stages can be adjusted appropriately according to the welding materials.

9. The process according to claim 8, characterized in that, The first stage aims to form pre-drilled holes. In the first stage, the completion of pre-puncture is determined by monitoring the dynamic resistance curve. When the curve shows a sudden increase in resistance caused by the electrode puncturing the plate and contacting the lower layer, the pre-puncture is determined to be complete.

10. The process according to claim 8, characterized in that, The second stage aims to form a metallurgical weld; it also includes the step of online quality prediction of the weld joint: collecting dynamic resistance and power signals of the welding process in the second stage, extracting feature values, and inputting them into a trained prediction model to obtain the predicted value of the weld nugget diameter; when the predicted value is not less than 3.0 mm, the weld joint is judged to be qualified.

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