An electrode cap for controlling nugget shift in resistance spot welding of aluminum workpieces and a welding method thereof

Abstract

An electrode cap for controlling the nugget shift of aluminum workpiece resistance spot welding and its matching welding method, the electrode cap comprises a first cylinder, a geometric body and a second cylinder, the geometric body is smoothly transitioned to the welding end face through a cambered surface or a conical surface to optimize the current distribution, so as to promote the nugget to shift to the thin plate side during the welding process, and effectively increase the penetration of the thin plate side; during the welding process, the electrode cap is used in cooperation with a conventional spherical electrode cap without special design, and a complete welding solution is formed. The solution covers three key stages of pre-pressing, welding and cooling, and through accurate regulation and control of parameters such as pressure, welding current, welding time and cooling time in each stage, the efficiency and stability of the welding process are ensured. The welding quality of the unequal-thickness aluminum alloy workpiece is improved, the problem of nugget shift is effectively solved, and a more reliable and efficient welding technology selection is provided for the high-end manufacturing fields such as new energy vehicles and aerospace.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of resistance spot welding, and more particularly to an electrode cap for controlling nugget shift in resistance spot welding of aluminum workpieces and a corresponding welding method. BACKGROUND

[0002] In the field of new energy vehicles, lightweight design is of paramount importance. Given the significant advantages of aluminum alloys, such as low density, high strength, and strong corrosion resistance, they have become the preferred material for manufacturing new energy vehicle bodies and panels. However, the welding characteristics of aluminum alloys are relatively complex, placing more stringent requirements on welding technology.

[0003] Traditional resistance spot welding technology faces a series of challenges when applied to aluminum alloy welding, such as uneven welding temperature, insufficient weld strength, and high energy consumption. These problems limit the application of traditional resistance spot welding technology in the field of new energy vehicles.

[0004] At the same time, the thickness of aluminum alloy sheets used in different parts of new energy vehicle bodies also varies greatly. This thickness diversity poses higher challenges to resistance spot welding technology. In particular, when dealing with aluminum alloy sheet welding with large thickness ratios (e.g., 3:1 or 4:1), the nugget often shifts towards the thick sheet side, while almost no nugget forms on the thin sheet side. This uneven distribution of nuggets directly leads to a significant decrease in weld joint strength, which in turn threatens the structural strength and safety of the entire vehicle body.

[0005] To address this challenge, the industry has tried various measures, including optimizing welding parameters, improving electrode design, and introducing preheating or post-heating techniques. However, these measures are often limited by process conditions, equipment performance, and operator level in practical applications, and their effects are not always satisfactory. For example, patent document CN109014535A proposes a spot welding method for unequal thickness aluminum sheets, which adjusts the curvature of the electrode cap end surface to change the effective contact area between the electrode cap and the sheet, thereby controlling the current density and penetration depth. This method to some extent balances the heat distribution of unequal thickness sheets during welding, effectively improving the problem of nugget shift. However, this method also brings new problems: greater current density accelerates electrode wear, leading to premature pitting of the electrode, which in turn requires frequent grinding of the electrode. This not only increases operating costs but also seriously affects the efficiency of resistance spot welding.

[0006] Therefore, how to ensure welding quality while improving welding efficiency and reducing operating costs remains a key problem to be solved in the field of aluminum alloy resistance spot welding technology for new energy vehicles. SUMMARY

[0007] The electrode cap for controlling the nugget deviation of aluminum workpiece resistance spot welding can effectively weld aluminum alloy workpieces with different thicknesses, deviates the nugget to the thin plate side, increases the penetration of the thin plate side, and makes the nugget meet the requirements of the aluminum alloy resistance spot welding standard.

[0008] The first aspect provides an electrode cap for controlling the nugget deviation of aluminum workpiece resistance spot welding, which is characterized by comprising: an electrode cap body, which is divided into three geometric body parts, i.e., a first cylinder, a geometric body and a second cylinder, wherein the geometric body is any one of a cylinder, a rhombic cylinder, a rhombic prism, a cylinder or a circular prism, and is used for connecting the first cylinder and the second cylinder;

[0009] A welding end face is used for contacting the aluminum workpiece.

[0010] A side face is connected to the second cylinder and the welding end face, and the side face is an arc face or a conical face, which is used for guiding the nugget to deviate to the thin plate side in the resistance spot welding process.

[0011] In another preferred embodiment, the geometric body is a cylinder, and the diameter of the cylinder is 4-8 mm, and the height of the cylinder is 0.5-3 mm.

[0012] In another preferred embodiment, the diameter d2 of the welding end face is 6-14 mm.

[0013] In another preferred embodiment, the height of the second cylinder can be 0.

[0014] In another preferred embodiment, the geometric body can be a rhombic cylinder, a rhombic prism, a cylinder or a circular prism.

[0015] In another preferred embodiment, the radius of curvature of the welding end face is 100 mm.

[0016] The second aspect of the present application provides a resistance spot welding method, which comprises:

[0017] (a) providing an electrode cap described above on the thin plate side, and using a conventional spherical electrode cap without the special design on the thick plate side, which has the same curvature as the welding end face;

[0018] (b) pre-pressing stage: placing the electrode cap on both sides of the stacked aluminum workpieces with different thicknesses, without aligning the positive and negative electrodes, performing pre-pressing, and moving the positive electrode towards the aluminum alloy plate until the welding end face is closely attached to the plate, applying a pressure of 2500-6000 N, and the pre-pressing duration is 200-2000 ms;

[0019] (c) current welding stage: passing a welding current, and the effective value of the welding current is 15-60 kA, and the current welding time is 80-200 ms.

[0020] (d) cooling stage: after the welding current is stopped, the electrode cap is kept pressed on both sides of the sheet and lasts for 30-400 ms, the molten metal solidifies to form a welding spot.

[0021] The mechanism of the present application is as follows: taking the welding of two layers of aluminum alloy workpieces with different thicknesses as an example, for the symmetrical electrode without the special design, during the welding process, the electrode at the thin plate has better heat dissipation than the electrode at the thick plate, and the body resistance of the thick plate is much larger than the body resistance of the thin plate, so the thin plate generates resistance heat by the contact resistance between the two plates, and the thick plate generates resistance heat by the body resistance and the contact resistance, in summary, the thick plate generates much more heat than the thin plate, and the heat dissipation is much smaller than that of the thin plate, which leads to the uneven heat on both sides of the thin plate and the thick plate, and the molten core shifts to the thick plate side after the welding is completed. When the electrode with the special design is used on the thin plate side, the contact surface area S of the geometric body and the first cylinder and the second cylinder is much smaller than the end surface area S1 of the electrode body, S1 = (Πd1 2 ) / 4, so the geometric body can prevent most of the heat from flowing back to the cooling water return groove of the second cylinder, reducing the heat dissipation at the thin plate, which makes the molten core shift to the thin plate side by a certain depth.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] 1) The special design of the electrode cap, especially the introduction of the geometric body part (cylinder, rhombic cylinder, rhombic prism, cylinder or circular prism, etc.), effectively changes the contact area of the electrode cap and the plate and the current density distribution. By adjusting the shape and size of the geometric body part, the heat distribution during the resistance spot welding process can be guided, and the molten core can be shifted to the thin plate side, thereby solving the problem of molten core shift during the welding of aluminum workpieces with different thicknesses. By optimizing the structure of the electrode cap, the friction and wear between the electrode and the plate during the welding process can be reduced, and the service life of the electrode can be prolonged.

[0024] 2) Since the contact surface area of the geometric body and the first cylinder and the second cylinder is much smaller than the end surface area S1 of the electrode body, S1 = (Πd1 2 ) / 4, the heat dissipation at the thin plate is reduced by the geometric body, thereby making the molten core extend to the thin plate by a certain depth, and the molten core depth at the thin plate meets the resistance spot welding standard.

[0025] 3) The method of the present application uses an optimized electrode cap structure and precise welding parameter control, so that the welding quality can be ensured while the welding efficiency is improved. By precisely controlling the parameters (such as pressure, welding current, welding time and cooling time, etc.) of the pre-pressing stage, the welding stage and the cooling stage, precise control of the welding process is realized. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only need to be some embodiments of the present application, and other alternative embodiments can be obtained by those skilled in the art without any creative effort on the basis of the accompanying drawings.

[0027] Figure 1 An embodiment showing that the geometric body 2 is a cylinder.

[0028] Figure 2 An embodiment showing Figure 1 An embodiment showing a cross-sectional view of A-A in FIG.

[0029] Figure 3 An embodiment showing Figure 1 An embodiment showing a partial front view.

[0030] Figure 4 An embodiment showing that the upper and lower connecting surfaces of the geometric body 2 are asymmetric.

[0031] Figure 5 An embodiment showing the type of the geometric body 2.

[0032] Figure 6 An embodiment showing a partial side view of the resistance spot welding of an aluminum alloy workpiece.

[0033] Figure 7 An embodiment showing a schematic diagram of the actual current output of the resistance spot welding process.

[0034] Figure 8 An embodiment showing a cross-sectional view of the weld nugget when the plate thickness ratio is 3:1 using a traditional symmetric spherical electrode.

[0035] Figure 9 An embodiment showing a cross-sectional view of the weld nugget when the plate thickness ratio is 3:1 using the electrode of the present application on the thin plate side.

[0036] Figure 10 An embodiment showing a cross-sectional view of the weld nugget when the plate thickness ratio is 4:1 using a traditional symmetric spherical electrode.

[0037] Figure 11 An embodiment showing a cross-sectional view of the weld nugget when the plate thickness ratio is 4:1 using the electrode of the present application on the thin plate side.

[0038] In each of the accompanying drawings, each of the following is indicated:

[0039] 1-first cylinder

[0040] 2-geometric body

[0041] 3-second cylinder

[0042] 4-electrode cap side

[0043] 5-Welding end face

[0044] 6-Cooling water return tank

[0045] 7-Small connecting surfaces of geometry 2

[0046] 8-Geometry 2 Large Connecting Surface

[0047] 9, 10 - Welding gun arm

[0048] 11-Melting core offset electrode cap

[0049] 12-Standard Electrode Cap

[0050] 13-Thick plate aluminum workpiece

[0051] 14-Thin sheet aluminum workpiece

[0052] 15-Melting Core Detailed Implementation

[0053] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, the accompanying drawings are schematic diagrams, and therefore the apparatus and device of the present invention are not limited to the size or scale of the schematic diagrams.

[0054] An electrode cap for controlling the offset of the weld nugget during resistance spot welding of aluminum workpieces includes: an electrode cap body divided into three geometric parts: a first cylinder, a geometric body, and a second cylinder, wherein the geometric body is any one of a cylinder, a rhombus, a frustum, a cylinder, or a frustum, used to connect the first cylinder and the second cylinder; a welding end face disposed at one end of the geometric body part for contacting the aluminum workpiece; and a side surface connecting the second cylinder and the welding end face, wherein the side surface is an arc surface or a conical surface, used to guide the weld nugget to offset towards the thin plate side during resistance spot welding.

[0055] Example 1

[0056] like Figure 1 As shown, the electrode cap for controlling the offset of the weld nugget in resistance spot welding of aluminum workpieces in this embodiment includes an electrode cap body, a side surface 4, and a welding end face 5. The electrode cap body can be further divided into a first cylinder 1, a geometric body 2, and a second cylinder 3. The diameters of the first cylinder 1 and the second cylinder 3 are both d1; the diameter of the welding end face is d2; the geometric body 2 can be a cylinder, and its diameter d3 is less than d2. The height of the geometric body 2 is greater than 0, preferably 0.5-2mm.

[0057] In another preferred embodiment, the geometry is a cylinder with a diameter d3 of 6 mm and a height of 1.5 mm.

[0058] Example 2

[0059] The present embodiment discloses a device and a welding process for welding aluminum workpieces using the controlled nugget shift electrode cap of the present invention. Figure 6 b, which comprises a first welding gun arm 9, a second welding gun arm 10, a nugget shift electrode cap 11, a normal electrode cap 12, a thick aluminum workpiece 13 and a thin aluminum workpiece 14. The thin aluminum workpiece 14 is a wrought aluminum alloy with a thickness of 0.5-1.5 mm; the thick aluminum workpiece is made of cast aluminum or wrought aluminum alloy with a thickness of 2.5-4 mm.

[0060] The nugget shift electrode cap 11 of embodiment 1 is installed on the welding gun arm 9 on the side of the thin aluminum workpiece 14, and the normal electrode cap 12 is installed on the thick side. Before welding, the electrode caps do not contact the aluminum workpieces, and during welding, the welding gun arms are operated to make the two electrodes tightly adhere to the thin and thick aluminum workpieces 13 and 14. Pressure is applied to clamp the thin and thick aluminum workpieces 13 and 14, and the adhesion part of the two aluminum workpieces is melted to form a nugget 15.

[0061] Embodiment 3

[0062] As shown in Figure 8 , the cross-sectional morphology of the nugget after resistance spot welding of 5754 wrought aluminum alloy with a thickness of 0.95 mm and AlSi10MnMg cast aluminum alloy with a thickness of 4.0 mm is shown using the normal symmetrical electrode and the welding device in Figure 6 a and the welding parameters in Figure 7 . As can be seen from the figure, there is almost no nugget on the thin side.

[0063] As shown in Figure 9 , the cross-sectional morphology of the nugget after resistance spot welding of 5754 wrought aluminum alloy with a thickness of 0.95 mm and C611 cast aluminum alloy with a thickness of 3.0 mm is shown using the controlled nugget shift electrode cap in embodiment 1 of the present invention on the thin side and the welding device in embodiment 2 and the welding parameters in Figure 7 . As can be seen from the figure, there are more nuggets melted to the thin side.

[0064] Embodiment 4

[0065] As shown in Figure 10 , the cross-sectional morphology of the nugget after resistance spot welding of 5754 wrought aluminum alloy with a thickness of 0.95 mm and AlSi10MnMg cast aluminum alloy with a thickness of 4.0 mm is shown using the normal symmetrical electrode and the welding device in Figure 6 a and the welding parameters in Figure 7 . As can be seen from the figure, there is almost no nugget on the thin side.

[0066] As shown in Figure 11 , the cross-sectional morphology of the nugget after resistance spot welding of 5754 wrought aluminum alloy with a thickness of 0.95 mm and C611 cast aluminum alloy with a thickness of 3.0 mm is shown using the controlled nugget shift electrode cap in embodiment 1 of the present invention on the thin side and the welding device in embodiment 2 and the welding parameters inFigure 7 The cross-section morphology of the nugget after resistance spot welding of 5754 wrought aluminum alloy with a thickness of 0.95 mm and AlSi10MnMg cast aluminum alloy with a thickness of 4.0 mm using the welding parameters shown in the table. As can be seen from the figure, there are more nuggets melted to the side of the thin plate.

[0067] The application also provides a resistance spot welding method, comprising the following steps:

[0068] (a) providing an electrode cap on the side of the thin plate, and using a conventional spherical electrode cap without the special design on the side of the thick plate with the same welding end face curvature;

[0069] (b) pre-pressing stage: placing the electrode cap on the two sides of the stacked aluminum workpieces with different thicknesses, without aligning the positive and negative electrodes, performing pre-pressing, the positive electrode approaching the aluminum alloy plate, until the welding end face is closely attached to the plate, applying a pressure of 2500-6000 N, and the pre-pressing duration is 200-2000 ms;

[0070] (c) welding stage: passing a welding current, the effective value of the welding current is 15-60 kA, and the welding time is 80-200 ms.

[0071] (d) cooling stage: after the welding current is stopped, the electrode cap is kept pressed on the two sides of the plate for 30-400 ms, and the molten metal solidifies to form a welding spot.

[0072] It is understood that the above technical features of the application and the technical features described in detail below (such as the examples) can be combined with each other to form new or preferred technical solutions within the scope of the application. Due to the limited space, they will not be listed one by one here.

[0073] It should be understood that although the embodiments of the application have been shown and described above, it is understood that the above embodiments are exemplary and cannot be construed as limiting the application, and within the scope of the claims of the application, the different embodiments can be adjusted without conflict, and all fall within the protection scope of the application.

Claims

1. An electrode cap for controlling the offset of the weld nugget in resistance spot welding of aluminum workpieces, characterized in that, include: The electrode cap body is divided into three geometric parts: a first cylinder, a geometric body, and a second cylinder. The geometric body is any one of a cylinder, a rhombus, a frustum, a cylinder, or a frustum, and is used to connect the first cylinder and the second cylinder. A welding end face is provided at one end of the geometric part and is used to contact the aluminum workpiece. The side surface connects the second cylinder to the welding end face, and the side surface is an arc or cone surface that tapers toward the welding end face, which is used to guide the weld nugget to shift toward the thin plate side during resistance spot welding. The contact area S between the geometric body and the first and second cylinders is much smaller than the end face area S1 of the electrode body, which is equal to (πd1). 2 ) / 4, where d1 is the diameter of the electrode cap body.

2. The electrode cap for controlling the offset of the weld nugget in resistance spot welding of aluminum workpieces according to claim 1, characterized in that, The geometric part is a cylinder with a diameter of 4-8 mm and a height of 0.5-3 mm.

3. The electrode cap for controlling the offset of the weld nugget in resistance spot welding of aluminum workpieces according to claim 1, characterized in that, The diameter of the welded end face is d2, and 6mm≤d2≤14mm.

4. The electrode cap for controlling the offset of the weld nugget in resistance spot welding of aluminum workpieces according to claim 1, characterized in that, The electrode cap body has a diameter of d1, and the diameters of the first cylinder and the second cylinder are the same as the diameter of the electrode cap body.

5. The electrode cap for controlling the offset of the weld nugget in resistance spot welding of aluminum workpieces according to claim 1, characterized in that, The first cylinder and the second cylinder are connected by a geometric body, and when the areas of the two connecting surfaces of the first cylinder and the second cylinder are different, the area S of the minimum surface is satisfied. min ≤(πd2 2 ) / 4, the area S of the largest face max ≤(πd1 2 ) / 4.

6. The electrode cap for controlling the offset of the weld nugget in resistance spot welding of aluminum workpieces as described in claim 5, characterized in that, When the areas of the connecting surfaces are the same, the area of ​​the connecting surfaces S ≤ (πd2) 2 ) / 4.

7. The electrode cap for controlling the offset of the weld nugget in resistance spot welding of aluminum workpieces as described in claim 1, characterized in that, When the geometry is a cylinder, the cylinder diameter is d3, and 4mm ≤ d3 < d2 is satisfied.

8. The electrode cap for controlling the offset of the weld nugget in resistance spot welding of aluminum workpieces as described in claim 1, characterized in that, The first cylinder is provided with a cooling water return channel, and the cooling water return channel is at a certain distance h1 from the geometry, and h1 > h2. The height of the second cylinder is h2, and h2 > 0.

9. The electrode cap for controlling the offset of the weld nugget in resistance spot welding of aluminum workpieces as described in claim 1, characterized in that, The welding end face is a curved surface with a radius of curvature R, and satisfies 30mm≤R≤100mm.

10. A method for resistance spot welding of aluminum workpieces, characterized in that, Includes the following steps: (a) Preparation stage: Place the electrode cap as described in any one of claims 1 to 9 on the thin plate side, and use a conventional spherical electrode cap with the same curvature of the welding end face on the thick plate side; (b) Pre-pressing stage: Place the electrode caps on both sides of the stacked aluminum workpieces of different thicknesses respectively, and perform the pre-pressing operation to bring the positive electrode closer to the aluminum alloy plate until the welding end face is tightly attached to the plate. Apply a pressure of 2500-6000N and the pre-pressing duration is 200-2000ms. (c) Welding stage: A welding current is applied, the effective value of which is 15-60kA and the energizing time is 80-200ms, so as to form a weld nugget between the aluminum workpieces and, through the side of the electrode cap, to shift the weld nugget toward the thin plate side, thereby increasing the weld depth on the thin plate side. (d) Cooling stage: After the welding current stops, the electrode cap is pressed against both sides of the plate for 30-400ms to allow the molten metal to solidify and form a weld point.

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