Self-piercing riveting system based on double annular electrodes and reinforcing method

Abstract

A self-piercing riveting joint reinforcing method based on double annular electrodes belongs to the technical field of automobile manufacturing, and comprises an annular upper electrode and an annular lower electrode, and the annular upper electrode, a plate to be welded and the annular lower electrode are sequentially arranged from top to bottom. According to the invention, the method for reinforcing the self-piercing riveting joint by using a resistance spot welding process is realized by adopting the double annular electrodes. According to the self-piercing riveting technology, the thin plates are connected through interlocking of the rivets and the bottom plate, resistance spot welding is introduced to form a layer of brazing between aluminum steel, solid-phase connection can be achieved on the basis of an original mechanical connection joint, and therefore the strength of the riveting joint can be improved to a large extent through the finally formed mechanical-solid-phase double-connection joint. And secondly, the application range of the self-piercing riveting process can be expanded, so that riveting of plates with different thicknesses by the self-piercing riveting process becomes possible, the number of equipment on an automobile body manufacturing production line can be reduced, and the cost is further reduced. In addition, the strength of a single riveting joint is improved, so that the number of rivets used on the automobile body in white is effectively reduced, and the light weight effect of the automobile body is improved.

Description

Technical Field

[0001] The invention relates to the technical field of mechanical engineering, and in particular to a self-piercing riveted joint reinforcement method based on double annular electrodes. Background Art

[0002] In order to cope with the increasingly severe energy and environmental challenges and achieve sustainable development on a global scale, improving the fuel economy of cars has received great attention from countries around the world. Therefore, the use of new lightweight materials such as aluminum and high-strength steel has become one of the important means for automobile manufacturers around the world to improve their competitiveness. Compared with high-strength steel, aluminum has the characteristics of low density, strong corrosion resistance and easy recycling, but the preparation of aluminum is much more difficult than steel. Therefore, in order to reduce costs, some structures in the body manufacturing still use steel as the body material. Therefore, it has become a top priority for major automobile manufacturers to achieve a reliable connection between aluminum and steel dissimilar metals. However, the melting point and thermal expansion coefficient of aluminum and high-strength steel are very different, and hard and brittle intermetallic compounds will be formed during fusion welding, so it is difficult to form a good joint using traditional resistance spot welding methods.

[0003] In response to the above problems, a mechanical cold forming process that forms a firm interlock between rivets and sheet materials has been proposed abroad - semi-hollow rivet self-piercing riveting (SPR) replaces resistance spot welding technology to achieve the connection between aluminum alloy and advanced high-strength steel plates. This method effectively avoids the problems existing in the melting welding of dissimilar materials mentioned above. However, there are still some problems when riveting dissimilar metals using the self-piercing riveting method. First, self-piercing riveting is suitable for riveting material combinations with similar thicknesses, but when riveting aluminum plates and steel plates with a thickness ratio greater than 3:1, the self-locking degree of the joint is low, which greatly affects the quality of the connection. Second, when riveting high-strength steel, due to the high strength and difficulty of deformation of high-strength steel, a larger riveting force is required, and the rivets should be prevented from being roughened and cracked during the riveting process. Therefore, riveting high-strength steel puts higher requirements on the performance indicators of rivets and equipment, thereby increasing production costs. Third, in the body-in-white currently assembled and manufactured using the self-piercing riveting process, the number of semi-hollow rivets reaches thousands, which greatly reduces the lightweight effect achieved by the use of lightweight materials. Summary of the invention

[0004] The present invention aims at the deficiencies of the above two connection methods (resistance spot welding and self-piercing riveting), and proposes a self-piercing riveted joint strengthening method by combining the characteristics of the two methods. The present invention uses a resistance spot welding process to weld the original riveted joint once after the self-piercing riveting process, and strives to form a mechanical-solid phase double connection. This process combining self-piercing riveting and resistance spot welding can effectively improve the strength of the joint, expand the thickness selection range of the riveted sheet in the self-piercing riveting process, and reduce the number of rivets used in actual production, which can reduce production costs on the one hand and increase the lightweight effect on the other.

[0005] The present invention is achieved through the following technical solutions:

[0006] The invention comprises: an annular upper electrode and an annular lower electrode, wherein the double annular electrodes are coaxially arranged, and the annular upper electrode, the thin plate sample to be welded and the annular lower electrode are arranged in sequence from top to bottom.

[0007] The inner diameter of the annular upper electrode is larger than the diameter of the rivet countersunk head, and there is a certain taper between the annular surface and the outer diameter to increase the current density.

[0008] The outer diameter of the annular lower electrode is the same as that of the annular upper electrode. A countersunk hole is provided at the center of the bottom of the cavity of the annular lower electrode. The diameter of the countersunk hole is smaller than the diameter of the bottom of the cavity. The height difference between the end face of the countersunk hole and the upper end face of the annular lower electrode is transitioned through an arc surface, that is, the cavity of the annular lower electrode is surrounded by an arc surface. The function of the countersunk hole is to prevent the bottom end face of the riveted joint from excessively contacting the annular lower electrode.

[0009] The arc surface is completely matched with the bottom side of the riveted joint, and ensures that when the annular lower electrode cavity contacts the bottom of the riveted joint, the upper end surface of the former does not touch the lower plate.

[0010] The annular upper electrode and the annular lower electrode have the same height and are both connected to the welding gun by interference fit.

[0011] When the present invention is implemented, the bottom of the self-piercing riveted joint is first placed in the cavity of the annular lower electrode, and the side surface of the bottom of the riveted joint is tightly attached to the inner side surface of the cavity, and at the same time, it is ensured that the end surface of the annular lower electrode does not contact the lower plate. Afterwards, the two ends of the sample are properly clamped with a clamp. Before clamping, it is necessary to ensure that the centers of the annular upper electrode, the self-piercing riveted joint, and the annular lower electrode are all on the same axis. Set the welding parameters and start welding the riveted joint. During the welding process, the upper and lower electrodes will first press the workpiece, and then maintain the electrode pressure and pass a current of a certain time and magnitude through the riveted joint. The purpose is to form a layer of brazing between the rivet leg and the plate. After welding, the clamping force is maintained for a period of time and the two electrodes are separated again. The sample begins to cool, and the welding condition is completed.

[0012] Compared with the existing technology, the present invention has the following advantages: the present invention performs electric repair welding on the riveted joint, uses the galvanized layer of the steel plate as the brazing material, forms a brazing layer between the aluminum plate and the steel plate through resistance heat, and finally realizes mechanical-solid phase dual connection, greatly improving the static and dynamic mechanical properties of the joint. The present invention can be applied not only to the connection of non-ferrous alloys and high-strength steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the annular upper electrode structure.

[0014] Figure 2 Schematic diagram of the annular lower electrode structure.

[0015] Figure 3 The process flow chart of the embodiment is shown in FIG.

[0016] Figure 4 Schematic diagram of the new annular lower electrode.

[0017] Reference numerals:

[0018] Cone 1, first countersunk hole 2 of upper electrode, inner cavity 3 of upper electrode, first countersunk hole 4 of upper electrode;

[0019] Lower electrode cavity 5, lower electrode countersunk hole 6, plate to be welded 7;

[0020] An annular upper electrode 100 and an annular lower electrode 200;

[0021] The upper end surface 11 of the annular lower electrode, the upper end surface 12 of the countersunk hole, and the fan-shaped notch 13. DETAILED DESCRIPTION

[0022] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented on the premise of the technical solution of the present invention, and provides a detailed implementation method and a specific operation process, but the protection scope of the present invention is not limited to the following embodiment.

[0023] Example 1

[0024] The spot welding electrode head of this embodiment adopts an annular upper electrode and an annular lower electrode. The two electrodes are coaxially arranged.

[0025] like Figure 1 As shown, the annular upper electrode is designed with a 5mm high cone 1, and the cone taper is 27°. The end face of the cone is designed with an upper electrode first countersunk hole 2, the countersunk hole depth is 1.5mm, and the diameter is 8mm. The annular upper electrode has an upper electrode inner cavity 3 with a depth of 12mm, which is used for interference fit with the welding gun, and an upper electrode second countersunk hole 4 with a depth of 1.4mm and a diameter of 5mm is provided on the bottom end face of the upper electrode inner cavity.

[0026] like Figure 2As shown, the annular lower electrode has a lower electrode cavity 5 with a depth of 1.8 mm, and a lower electrode countersunk hole 6 with a depth of 1.5 mm and a diameter of 5 mm is provided at the center of the bottom of the cavity. The function of the countersunk hole is to reduce the contact area between the bottom of the riveted joint and the electrode so as to control the position where the molten core is formed. The arc surface of the inner wall of the cavity is composed of two 1 / 4 arcs with a radius of 0.7 mm and opposite directions. The two arcs are connected by a straight line with an angle of 10° to the vertical direction, and the two ends of the straight line are circumscribed with the two arcs respectively. The distance between the countersunk hole and the inner wall of the arc is 1.2 mm.

[0027] The annular upper electrode and the annular lower electrode are both made of nickel-silicon-copper alloy.

[0028] like Figure 3 In this embodiment, the plate 7 to be welded is: aluminum alloy AA6061-T6 + high-strength steel DP590, that is, the aluminum alloy is on the top and the high-strength steel is on the bottom; the plate thickness is matched: 3mm+1.2mm.

[0029] Process parameters: welding current is 13kA DC, pre-pressing time is 200ms, power-on time is 280ms, holding time is 80ms, welding speed is 25%, electrode pressure is 500kN, sample thickness is set to 4.2mm, and the maximum depth of the electrode allowed to be pressed into the sample is 1.0mm.

[0030] The operation process of this embodiment method is as follows Figure 3 As shown, the thin plate sample 3 to be welded is placed horizontally on a workbench, which consists of two parallel columns. The upper end surfaces of the two columns are in contact with the lower end surface of the sample bottom plate, and ensure that the sample to be welded is horizontal and the workbench does not interfere with the welding gun.

[0031] Manually adjust the position of the welding gun so that the cavity side wall of the annular lower electrode 200 fits tightly with the bottom side of the sample riveted joint, then use the clamp on the workbench to clamp the sample, and perform a "touch up" operation on the welding machine to remember the position of the welding gun at this moment.

[0032] Automatic welding begins. During the welding process, the annular upper electrode 100 and the annular lower electrode 200 will first separate and return to zero position, and then start to move toward each other until the workpiece is clamped. The pressure is maintained for 200ms. The welding machine passes a 13kA DC current through the electrodes. The upper electrode first contacts the aluminum plate. The resistance of aluminum is smaller than that of steel, so the current mainly flows through the aluminum plate. Since the interface resistance between aluminum and steel is very large, heat will be generated at the aluminum-steel interface under the action of the current to form a welded joint. A certain thickness of an intermetallic compound layer will appear in the welding area, and its thickness will increase with the increase of welding current and welding time. The position where the welding area 8 appears is as follows. Figure 3As shown. After the power-on process is completed, the pressure of the upper and lower electrodes on the sample will be maintained for 80ms, and then the annular upper and lower electrodes will separate and return to zero position. After the sample cools down, the clamping device is released and the sample is removed. The entire welding process ends here.

[0033] Example 2

[0034] The spot welding electrode head of this embodiment adopts an annular upper electrode and an annular lower electrode. The two electrodes are coaxially arranged.

[0035] The plate 3 to be welded in this embodiment is: aluminum alloy AA6061-T6+aluminum alloy AA6061-T6; the plate thickness is matched: 3mm+1.6mm.

[0036] Process parameters: welding current is 13kA DC, pre-pressing time is 200ms, power-on time is 480ms, holding time is 80ms, welding speed is 25%, electrode pressure is 500kN, sample thickness is set to 4.6mm, and the maximum depth of the electrode allowed to be pressed into the sample is 1.0mm.

[0037] The other implementations of this embodiment are the same as those of Embodiment 1.

[0038] Example 3

[0039] The spot welding electrode head of this embodiment adopts an annular upper electrode and a novel annular lower electrode. The two electrodes are coaxially arranged.

[0040] The plate 3 to be welded in this embodiment is: magnesium alloy AZ31B+high-strength steel DP590; the plate thickness is matched: 3mm+1.2mm.

[0041] like Figure 4 As shown, the novel annular lower electrode is processed on the basis of the original annular lower electrode. A 60° fan-shaped notch 13 is cut out every 60° from the upper end face 11 of the original annular lower electrode to the upper end face 12 of the countersunk hole. The contact area between the novel annular lower electrode and the bottom of the riveted joint is reduced by half, which greatly improves the current density and reduces the difficulty of welding aluminum alloy materials by this method.

[0042] Process parameters: welding current is 13kA DC, pre-pressing time is 200ms, power-on time is 200ms, holding time is 80ms, welding speed is 25%, electrode pressure is 500kN, sample thickness is set to 4.2mm, and the maximum depth of the electrode allowed to be pressed into the sample is 1.0mm.

[0043] The other implementations of this embodiment are the same as those of Embodiment 1.

[0044] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A self-piercing riveting system based on double ring electrodes, characterized in that: The system is used for riveting a thin plate sample to be welded, and comprises: an annular upper electrode and an annular lower electrode. The annular upper electrode, the thin plate sample to be welded and the annular lower electrode are arranged in sequence from top to bottom; A lower electrode cavity is arranged on the top of the annular lower electrode, and a lower electrode countersunk hole is arranged at the center of the bottom of the lower electrode cavity.

2. A self-piercing riveting system based on double annular electrodes according to claim 1, characterized in that: The annular upper electrode comprises a cone, the end face of which is designed with an upper electrode first countersunk hole, the annular upper electrode is provided with an upper electrode inner cavity for interference fit with the welding gun, and an upper electrode second countersunk hole is provided at the bottom end face of the upper electrode inner cavity.

3. A self-piercing riveting system based on double annular electrodes according to claim 1, characterized in that: The arc-shaped surface of the inner wall of the lower electrode cavity is composed of two opposite 1 / 4 arcs, the two arcs are connected by a straight line that forms an angle of 10° with the vertical direction, and the two ends of the straight line are circumscribed with the two arcs respectively.

4. The self-piercing riveting system based on double annular electrodes according to claim 1, characterized in that: The annular upper electrode and the annular lower electrode are assembled on the welding gun through interference fit.

5. The method for strengthening a self-piercing riveted joint based on double annular electrodes according to claim 1 is characterized in that: When the annular electrodes are subjected to interference fit, the pressure used to press the annular upper electrode and the annular lower electrode must be greater than the pressure used to press the thin plate sample during welding.

6. The method for strengthening a self-piercing riveted joint based on double annular electrodes according to claim 1 is characterized in that: The annular upper electrode and the annular lower electrode ensure the horizontality of the end faces of the two electrodes after assembly.

7. The method for strengthening a self-piercing riveted joint based on double annular electrodes according to claim 1 is characterized in that: The annular upper electrode and the annular lower electrode are both made of copper and its alloy.

8. The method for strengthening a self-piercing riveted joint based on double annular electrodes according to claim 1 is characterized in that: A plurality of fan-shaped notches are cut out in the portion between the upper end surface 11 of the annular lower electrode and the upper end surface 12 of the countersunk hole.

9. The method for strengthening a self-piercing riveted joint based on double annular electrodes according to claims 1-8, characterized in that The specific implementation steps are as follows: first place the bottom of the self-piercing riveted joint in the cavity of the annular lower electrode, and the bottom side of the riveted joint is tightly attached to the inner side of the cavity, and at the same time ensure that the end face of the annular lower electrode does not contact the lower plate. After that, use a clamp to properly clamp both ends of the sample. Before clamping, it is necessary to make sure that the centers of the annular upper electrode, the self-piercing riveted joint, and the annular lower electrode are on the same axis. Set the welding parameters and start welding the riveted joint. During the welding process, the upper and lower electrodes will first press the workpiece, then maintain the electrode pressure and pass a certain amount of current through the riveted joint for a certain time and size. The purpose is to form a layer of brazing between the rivet leg and the plate. After welding, the two electrodes are separated after the clamping force is maintained for a period of time, and the sample begins to cool, and the welding condition is completed.

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