Punch forming fastener for dissimilar metal welding

Abstract

A punch forming fastener for dissimilar metal welding comprises a shaft part, a transition part and a cap, the transition part is located on the periphery of the upper end face of the shaft part, the cross section of the transition part and the shaft part form a Y shape, the cap extends out of the transition part and forms a cap-shaped structure distributed in the circumferential direction, and the end of the cap at least extends to the horizontal plane where the lower end face of the shaft part is located. Rib structures distributed around the axis at equal angles are arranged on the side face of the shaft part, extend to the side face of the transition part from the lower end face of the shaft part and are used for forming a concave-convex embedded structure between the side face of the shaft part and a contact workpiece, and the connection strength between the workpiece and the shaft part of the fastener is enhanced. Further, a knurling structure is arranged on the side face of the shaft part between the rib structures. After welding, the rib structure and the knurling structure enhance the mechanical locking strength between the side face of the shaft part and contact metal of the side face of the shaft part, the risk that an interface is rapidly cracked due to stress is reduced, and meanwhile the sealing performance of the connector is improved.

Description

Technical Field

[0001] This utility model belongs to the field of dissimilar metal joining, specifically relating to a stamped fastener for dissimilar metal welding. Background Technology

[0002] To achieve energy conservation, emission reduction, and improve vehicle safety and range, the automotive industry is increasingly adopting multi-material hybrid construction, primarily using steel and aluminum alloys, in vehicle body manufacturing. Especially with the widespread adoption of large-scale integrated cast aluminum technology, integrated cast aluminum is becoming increasingly common in certain areas of the vehicle body, such as the rear floor panel. Meanwhile, high-strength (and ultra-high-strength) steel is extensively used in critical areas such as the passenger compartment, including the A / B pillars and side panels, to ensure vehicle safety. This has created a significant demand for aluminum / steel-based dissimilar metal connections. However, due to the significant differences in thermophysical and electrochemical properties between aluminum and steel, traditional welding processes easily lead to cracks and brittle intermetallic compounds in the weld, making it difficult to meet the joint's mechanical properties and strength requirements of the vehicle body structure. Therefore, mechanical connection technologies, such as self-piercing riveting and blind riveting, are primarily used for joining dissimilar metals in vehicle body manufacturing. However, with the increasing strength of steel used in automobiles, particularly the further increase in the use of steel with a strength greater than 1000 MPa, mechanical connection processes face significant challenges. In addition, when high-strength steel and poorly ductile cast aluminum are mechanically connected, rivets have difficulty piercing the high-strength steel, while cast aluminum is also prone to cracking.

[0003] Patent CN115780980A discloses a welding element (referred to in this utility model as a fastener) and a welding method, enabling the fastener to quickly pierce low-melting-point metals (e.g., aluminum alloys) and weld with high-melting-point metals (e.g., steel). This fastener and welding method are highly effective for welding dissimilar metals with large melting point differences, such as aluminum and steel. However, when welding aluminum / steel dissimilar metals with the fastener described in patent CN115780980A, the aluminum alloy outside the shaft side of the fastener melts during the welding process. The molten aluminum and the shaft side form an intermetallic compound layer through element diffusion, thus forming a metallurgical connection. Because the shaft side is relatively smooth and the formed intermetallic compound layer is relatively fragile, it is prone to cracking between the aluminum alloy and the fastener shaft during service, reducing the mechanical locking effect of the fastener shaft on the aluminum alloy in both the circumferential and axial directions. In particular, when welding magnesium / steel, the fasteners of patent CN115780980A do not have a solid solution between the magnesium alloy and the steel, and do not produce solid solutions or intermetallic compounds in the liquid state. Therefore, no metallurgical connection is formed between the side of the shaft and the magnesium alloy, resulting in relatively weak connection strength and sealing performance. Utility Model Content

[0004] To address the issue of weak connection strength between the side of the shaft and the low-melting-point metal when welding dissimilar metals, this invention proposes a stamped fastener for welding dissimilar metals. By creating raised ridges and knurled structures on the side of the fastener shaft, more mechanical locking structures are formed between the side of the shaft and the contacting metal after welding, thereby enhancing the joint connection strength.

[0005] This utility model is achieved through the following technical methods:

[0006] This utility model provides a stamped fastener for welding dissimilar metals, comprising a shaft portion, a transition portion, and a cap. The shaft portion is a solid shaft. The transition portion is located on the outer periphery of the upper end face of the shaft portion. The cap extends from the transition portion and forms a circumferentially distributed cap-shaped structure, and the end of the cap extends at least to the horizontal plane where the lower end face of the shaft portion is located. The side of the shaft portion is provided with a convex rib structure evenly distributed around the axis. The convex rib structure extends from the lower end face of the shaft portion to the side of the transition portion, which is used to form a concave-convex interlocking structure between the side of the shaft portion and the contacting workpiece, thereby enhancing the connection strength between the workpiece and the shaft portion of the fastener.

[0007] Preferably, the width and height of the convex ridge structure gradually increase as it extends from the lower end face of the shaft to the side of the transition portion.

[0008] For example, the cross-sectional shape of the convex ridge structure is an isosceles triangle, an isosceles trapezoid, a semicircle, or a square.

[0009] As an example, the shaft portion is in the shape of a frustum, and the position of the frustum's edge is set as a convex edge structure.

[0010] For example, the number of the convex ridge structures is 4 to 10.

[0011] Furthermore, the shaft side between the convex rib structures is provided with a knurled structure, and the maximum depth t of the knurled structure is 80-200μm.

[0012] Preferably, the knurled structure opening faces the lower end face of the shaft.

[0013] As an example, the knurled structure is regularly distributed on the side of the shaft, and its geometric shape is semi-circular, triangular, square, etc.

[0014] Preferably, the knurled structure includes a knurled bottom surface and a knurled side surface, wherein the knurled bottom surface is parallel to the axis of the shaft, and the knurled side surface forms an angle β with the horizontal plane ranging from 0° to 30°.

[0015] Furthermore, a high-temperature resistant non-metallic gasket is nested at the end of the cap.

[0016] Furthermore, the transition portion extends upward and outward from the outer periphery of the upper surface of the shaft portion, forming a "Y" shape with the shaft portion in cross-section, and the angle α formed between the transition portion and the horizontal plane ranges from 40° to 70°.

[0017] Technical effects of this utility model:

[0018] (1) By setting the transition portion and the shaft portion to a "Y" shape in cross section, the fastener can be smoothly extruded along the transition portion during stamping manufacturing, thus improving the forming effect of the fastener during stamping manufacturing. In addition, the volume of the receiving cavity formed by the cap is increased while effectively controlling the compact size of the shaft portion.

[0019] (2) A raised rib structure is provided on the side of the fastener to increase the connection area between the side of the shaft and the low melting point metal in contact with it, so that the contact surface forms a concave-convex interlocking mechanical structure in the circumferential direction, thereby enhancing the torsional strength between the shaft and the low melting point metal around the shaft of the fastener.

[0020] (3) A knurled structure with an opening facing the lower end face of the shaft is provided on the periphery of the fastener to increase the contact area and axial mechanical locking strength between the side of the shaft and the low melting point metal, thereby avoiding the risk of cracking between the low melting point metal and the side of the shaft.

[0021] (4) A high-temperature resistant non-metallic gasket is provided at the end of the cap. After welding, the end of the cap will firmly press the non-metallic gasket onto the surface of the workpiece, which will enhance the sealing performance between the end of the cap and the surface of the workpiece, prevent water vapor or corrosive media from entering the cap, and reduce the electrochemical corrosion rate of the joint. Attached Figure Description

[0022] Figure 1 A schematic cross-sectional view of a fastener in one embodiment of this utility model;

[0023] Figure 2 A three-dimensional schematic diagram of a fastener in one embodiment of the present invention;

[0024] Figure 3 A schematic diagram of the cross-section of the welded shaft portion in one embodiment of this utility model;

[0025] Figure 4 A three-dimensional schematic diagram of a fastener in another embodiment of the present invention shows that the fastener A1 has a frustum-shaped shaft portion, and the fastener A2 has a convex ridge structure on the ridge line portion of the shaft portion.

[0026] Figure 5 A schematic cross-sectional view of the fastener in another embodiment of this utility model;

[0027] Figure 6 In another embodiment of this utility model, a schematic diagram of different knurling structures on the shaft of the fastener is shown, where B1 is a semicircle and B2 is a triangle.

[0028] Figure 7 A three-dimensional schematic diagram of the fastener in another embodiment of this utility model;

[0029] Figure 8 This utility model provides a schematic diagram of the installation position of the non-metallic washer in the fastener.

[0030] Figure 9 A schematic diagram of the cross-section of the dissimilar metal welded joint in Embodiment 1 of this utility model; Detailed Implementation

[0031] The embodiments of this utility model will be further described in detail below with reference to the accompanying drawings.

[0032] The fastener 100 of this invention is used for welding a laminated structure of a first metal 300 and a second metal 400, wherein the first metal has a melting point of less than 750°C, the second metal has a melting point of greater than 1300°C, and the fastener is made of the same material as the second metal. During welding, the fastener is located on the side of the lower melting point first metal. Current and pressure are applied to the weld joint by a welding electrode. Under the action of heat and force, the axial portion of the fastener 100 pierces the first metal 300 and achieves a firm weld with the second metal 400.

[0033] One embodiment of this utility model provides a stamped fastener 100 for welding dissimilar metals. The fastener has a rotationally symmetric structure about axis 100A, and its cross-sectional structural features are as follows: Figure 1 As shown, the device includes a shaft portion 101, a transition portion 102, and a cap 103. The shaft portion 101 is a solid shaft that gradually narrows as it extends from the upper end face 106 to the lower end face 107, allowing the shaft portion to better lock the workpiece after it pierces it. The transition portion 102 is located on the outer periphery of the upper end face of the shaft portion. The transition portion extends upward and outward from the outer periphery of the upper end face 106 of the shaft portion, forming a "Y" shape with the shaft portion 101 in cross-section. The angle α formed between the transition portion and the horizontal plane ranges from 40° to 70°. Since the transition portion 102 is distributed around the outer periphery of the upper end face 106 of the shaft portion, it forms a groove with the upper end face of the shaft portion to accommodate the welding electrode, improving the alignment and matching degree between the welding electrode and the fastener 100. The minimum diameter D1 of the groove is not less than the welding end face of the welding electrode, preferably 5 to 7 mm, and the height H ranges from 0.5 to 2.5 mm. The cap 103 of the fastener extends from the transition portion 102 and forms a circumferentially distributed cap-shaped structure, and the end of the cap extends at least to the horizontal plane where the lower end face 107 of the shaft portion is located. The cap 103 is used to collect liquid metal discharged from the weld point. In order to improve the plastic deformation capacity of the cap 103 during welding, its wall thickness does not exceed 0.65 mm.

[0034] like Figure 2As shown, the fastener's shaft side is also provided with convex rib structures 105 distributed at equal angles around the axis. The convex rib structures 105 extend from the lower end face 107 of the shaft to the side of the transition portion 102. The height of the convex rib structure 105 is 0.3 to 0.7 mm, the width does not exceed 1 mm, and the number of convex rib structures is 4 to 10. According to the actual fastener stamping and welding requirements, the width and height of the convex rib structure can be designed to gradually increase as it extends from the lower end face of the shaft to the transition portion, and the cross-section of the convex rib structure can be an isosceles triangle, an isosceles trapezoid, a semicircle, or a square.

[0035] After welding dissimilar metals, the shaft portion of fastener 100 will pierce the first metal. The shaft portion of the fastener, when viewed in cross-section, appears as follows: Figure 3 As shown, the convex ridge structure 105 is embedded in the first metal 300 in the radial direction, which reduces the continuity of the contact between the shaft side 104 and the first metal 300, thereby further improving the mechanical locking strength between the shaft and the first metal.

[0036] To further enhance the mechanical locking strength of the shaft to the first metal in the circumferential direction after the shaft pierces the first metal, in another embodiment, the shaft is configured as a frustum structure, such as... Figure 4 As shown in A1. The number of frustum-shaped shaft side faces 104” is 4 to 10. Since there is a certain angle between every two adjacent side faces 104”, after the shaft penetrates the first metal, the shaft side faces 104” can further restrict the first metal from rotating circumferentially relative to the shaft, thereby improving the mechanical locking strength between the shaft side faces and the first metal in the circumferential direction. Furthermore, the side edges 105” are set as convex edge structures 105, such as... Figure 4 As shown in A2, the mechanical connection strength between the shaft and the first metal is further improved.

[0037] When welding aluminum alloy and steel together, after the fastener shaft pierces the aluminum alloy, at least a portion of its side surface forms an intermetallic compound layer with the aluminum alloy. This intermetallic compound layer is prone to cracking after the weld joint is subjected to external forces such as impact, resulting in a poor connection between the aluminum alloy and the fastener shaft side surface and the first metal. In another embodiment, a fastener 100 is provided with a knurled structure 108 on the shaft side surface 104 of the fastener, such as... Figure 5 As shown. The knurled structure 108 has various geometric shapes, such as semicircles, triangles, and squares, and the opening faces the lower end face 107 of the shaft, as shown. Figure 6 As shown. The knurled structure 108 includes a knurled bottom surface 1081 and a knurled side surface 1082. The knurled bottom surface 1081 is parallel to the axis of the shaft, and the knurled side surface 1082 forms an angle β with the horizontal plane ranging from 0° to 30°. The maximum depth t of this structure is 80 to 200 μm. Furthermore, the knurled structure 108 is regularly arranged on the side surface of the shaft, such as... Figure 7 As shown.

[0038] like Figure 8 As shown, in order to further improve the sealing performance of the joint after fastener welding, a high-temperature resistant non-metallic washer 200 is nested at the end of the cap. The non-metallic washer has a "U" shaped cross section. After welding, the non-metallic washer is squeezed between the end of the cap and the first metal surface, which effectively prevents corrosive media such as water vapor from entering the joint and improves the joint's resistance to electrochemical corrosion.

[0039] Example 1:

[0040] In this embodiment, fastener 100 is made of low-carbon steel by stamping. A raised rib structure with a width of 0.8 mm and a height of 0.6 mm is provided on the side of the fastener shaft portion, and a knurled structure with a depth of 150 μm is provided between the raised rib structures. This fastener is used for welding dissimilar metals, where the first metal 300 is a 2.5 mm thick AA6061 aluminum alloy and the second metal 400 is a 1.8 mm thick hot-formed steel, using multi-stage current welding. During the stage where fastener 100 pierces the first metal 300, three pulse currents are used, each with a current intensity of 16.5 kA and a duration of 52 mm, causing the aluminum alloy to melt rapidly and be sprayed at high speed into the receiving cavity formed by the fastener cap 103. The shaft portion 101 rapidly pierces the first metal under an electrode pressure of 5500 N. Subsequently, a final current is applied to the weld joint, with a current intensity of 12.8 kA and a duration of 250 ms. Figure 9 As shown, a subsequent current causes a steel melt nugget 401 to form between the fastener shaft 101 and the second metal 400, achieving a strong connection between the two. The aluminum alloy on the side of the fastener shaft and part of the discharged metal 302 in the cap 103 further melt under resistance heating, and the aluminum alloy in contact with the shaft side fully fills the knurled structure 108, forming a mechanical locking structure between the aluminum alloy and the knurled structure. Furthermore, due to the knurled structure, the intermetallic compound layer 500 formed at the interface becomes more tortuous, effectively suppressing the rapid propagation of cracks in the intermetallic compound layer 500 and improving the connection strength between the shaft side and the aluminum alloy.

[0041] 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 this utility model. The scope of protection of this utility model is determined by the claims and is not limited to the above-described specific implementations. All implementation schemes within its scope are bound by this utility model.

Claims

1. A stamping fastener for welding dissimilar metals, comprising a shaft, a transition portion and a cap, wherein the shaft is a solid shaft, the transition portion is located at the periphery of the upper end surface of the shaft, the cap extends from the transition portion to form a circumferentially distributed cap-shaped structure, and the end of the cap extends at least to the horizontal plane where the lower end surface of the shaft is located, characterized in that: The side of the shaft is provided with ridge structures distributed at equal angles around the axis, and the ridge structures extend from the lower end surface of the shaft to the side of the transition portion, which are used to form a concave-convex interlocking structure between the side of the shaft and the contact workpiece, thereby enhancing the connection strength between the workpiece and the shaft of the fastener.

2. The fastener according to claim 1, characterized in that When the convex ridge structure extends from the lower end surface side of the shaft portion to the side surface of the transition portion, its width and height gradually increase.

3. The fastener according to claim 1, characterized in that The cross-sectional shape of the convex ridge structure is an isosceles triangle, an isosceles trapezoid, a semicircle or a square.

4. The fastener according to claim 1, characterized in that The shaft portion is in the shape of a prism, and the position where the ridge line of the prism is located is arranged as a convex ridge structure.

5. The fastener according to claim 1, characterized in that The number of the ridge structures is 4 to 10.

6. The fastener according to claim 1, characterized in that A knurling structure is provided on the side surface of the shaft portion between the convex ridge structures, and the maximum depth t of the knurling structure is 80 to 200 μm.

7. The fastener according to claim 6, characterized in that The knurled structure opens toward the lower end surface of the shaft; the knurled structure includes a knurled structure bottom surface and a knurled structure side surface, the knurled structure bottom surface is parallel to the axis of the shaft, and the knurled structure side surface forms an angle β with the horizontal plane in the range of 0° to 30°.

8. The fastener according to claim 6, characterized in that The knurled structures are regularly distributed on the side surface of the shaft, and their geometric shapes are semicircular, triangular or square.

9. The fastener according to claim 1, characterized in that A high temperature resistant non-metallic gasket is embedded at the end of the cap.

10. The fastener according to any one of claims 1 to 9, characterized in that: The transition portion extends upward and outward from the outer periphery of the upper surface of the shaft portion, forming a "Y" shape with the shaft portion in cross section, and the transition portion forms an angle α with the horizontal plane in the range of 40° to 70°.

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