Electrode cap for controlling resistance spot welding nugget deviation of aluminum workpiece and welding method matched with electrode cap

Abstract

The invention discloses an electrode cap for controlling resistance spot welding nugget deviation of an aluminum workpiece and a matched welding method, the electrode cap comprises a first cylinder, a geometry and a second cylinder, the geometry is in smooth transition to a welding end face through a cambered surface or a conical surface to optimize current distribution, so that the nugget is promoted to deviate towards a thin plate side in the welding process, and the welding quality is improved. The fusion depth of the thin plate side is effectively increased; in the welding process, the electrode cap is used in cooperation with a traditional spherical electrode cap without special design, and a set of complete welding solution is formed. According to the scheme, three key stages of pre-pressing, power-on welding and cooling are covered, and high efficiency and stability of the welding process are ensured by accurately regulating and controlling parameters of each stage, such as pressure, welding current, power-on duration and cooling time. According to the method, the welding quality of the aluminum alloy workpieces with different thicknesses is improved, the problem of nugget deviation is effectively solved, and a more reliable and efficient welding technology choice is provided for the high-end manufacturing fields of new energy automobiles, aerospace and the like.

Description

Technical Field

[0001] The invention relates to the field of resistance spot welding, and more specifically to an electrode cap for controlling the deviation of the molten core in resistance spot welding of an aluminum workpiece and a matching welding method thereof. Background Art

[0002] In the field of new energy vehicles, lightweighting is a crucial design consideration. Given the significant advantages of aluminum alloys such as low density, high strength and strong corrosion resistance, it has become the preferred material for the manufacture of new energy vehicle bodies and panels. However, the welding characteristics of aluminum alloys are relatively complex, which puts 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 welding point 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 plates used in different parts of the new energy vehicle body also varies greatly. This thickness diversity poses a higher challenge to resistance spot welding technology. Especially when welding aluminum alloy plates with a large thickness ratio (such as 3:1 or 4:1), the molten core tends to be biased towards the thick plate side, while almost no molten core is formed on the thin plate side. This uneven distribution of molten cores will directly lead to a significant decrease in the strength of the welded joint, which in turn poses a threat to the structural strength and safety of the entire vehicle body.

[0005] In order to meet this challenge, the industry has tried to take a variety of measures, including optimizing welding parameters, improving electrode design, and introducing preheating or post-heating technology. 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 aluminum plates of unequal thickness, which changes the effective contact area between the electrode cap and the plate by adjusting the curvature of the end face of the electrode cap, thereby achieving regulation of current density and penetration depth. This method balances the heat distribution of plates of unequal thickness during welding to a certain extent, and effectively improves the problem of nugget offset. However, this method also brings new problems: a larger current density will accelerate the wear of the electrode, causing premature pitting of the electrode, and then the electrode needs to be frequently ground. This not only increases the operating cost, but also seriously affects the welding efficiency of resistance spot welding.

[0006] Therefore, how to improve welding efficiency and reduce operating costs while ensuring welding quality is still a key issue that needs to be urgently solved in the current aluminum alloy resistance spot welding technology in the field of new energy vehicles. Summary of the invention

[0007] The object of the present invention is to provide an electrode cap for controlling the deviation of the molten core in resistance spot welding of aluminum workpieces, so as to efficiently weld aluminum alloy parts of unequal thickness, make the molten core deviate to the thin plate side, increase the penetration depth on the thin plate side, and make the molten core meet the requirements of aluminum alloy resistance spot welding standards.

[0008] In a first aspect, an electrode cap for controlling the displacement of a molten core in resistance spot welding of an aluminum workpiece is provided, which is characterized in that it comprises: an electrode cap body, which is divided into three geometric body parts, namely, a first cylinder, a geometric body and a second cylinder, wherein the geometric body is any one of a cylinder, a rhombus, a rhombus, a cylinder or a frustum, and is used to connect the first cylinder and the second cylinder;

[0009] Welding end face, used for contact with aluminum workpiece;

[0010] The side surface connects the second cylinder and the welding end surface, and the side surface is an arc surface or a conical surface, which is used to guide the molten core to deviate toward the thin plate side during 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 surface is 6-14 mm.

[0013] In another preferred example, the height of the second cylinder may be 0.

[0014] In another preferred embodiment, the geometric body may be a prism, a pyramid, a cylinder or a frustum.

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

[0016] In a second aspect of the present invention, a resistance spot welding method is provided, the method comprising:

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

[0018] (b) Pre-pressing stage: the electrode caps are placed on both sides of two stacked aluminum workpieces of unequal thickness, without constraining the positive and negative electrodes, and pre-pressing is performed, the positive electrode is moved closer to the aluminum alloy plate until the welding end face is tightly fitted to the plate, and a pressure of 2500-6000N is applied, and the pre-pressing duration is 200-2000ms;

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

[0020] (d) Cooling stage: After the welding current stops, the electrode caps remain pressed against both sides of the plate for 30-400ms, and the molten metal solidifies to form a weld.

[0021] The mechanism of the present invention is as follows: taking welding of two layers of aluminum alloy workpieces of unequal thickness as an example, for symmetrical electrodes without the special design, during welding, due to the smaller thickness of the thin plate, the heat dissipation of the electrode at the thin plate is better than that of the electrode at the thick plate, and the body resistance of the thick plate is much greater than that of the thin plate, so the thin plate generates resistance heat by relying on the contact resistance between the two plates, while the resistance heat of the thick plate is generated by the body resistance and the contact resistance. It can be seen that the heat generated by the thick plate is much greater than that of the thin plate, while the heat dissipation is much less than that of the thin plate, which leads to uneven heat on both sides of the thin plate and the thick plate, and the molten core shifts to the thick plate side after welding. When the specially designed electrode is used on the thin plate side, since the contact surface area S between the geometric body and the first cylinder and the second cylinder is much smaller than the end surface area S1 of the electrode body = (Πd1 2 ) / 4, so the geometry can prevent most of the heat from being lost to the cooling water return groove of the second cylinder, reducing the heat loss 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 invention has the following beneficial effects:

[0023] 1) The special design of the electrode cap, especially the introduction of the geometric body (cylinder, prism, rhombus, cylinder or truncated cone, etc.), effectively changes the contact area and current density distribution between the electrode cap and the plate. By adjusting the shape and size of the geometric body, the heat distribution during resistance spot welding can be guided to shift the molten core to the thin plate side, thereby solving the problem of molten core shifting when welding aluminum workpieces of unequal thickness. By optimizing the structure of the electrode cap, the friction and wear between the electrode and the plate during welding can be reduced, and the service life of the electrode can be extended.

[0024] 2) Since the contact surface area between the geometric body and the first cylinder and the second cylinder is much smaller than the end surface area of ​​the electrode body S1 = (Πd1 2 ) / 4, the heat loss in the thin plate is reduced through the geometry, so that the molten core extends to a certain depth in the thin plate, so that the depth of the molten core in the thin plate meets the resistance spot welding standard.

[0025] 3) The method of the present invention adopts an optimized electrode cap structure and precise welding parameter control, so it can improve welding efficiency while ensuring welding quality. By precisely controlling the parameters of the pre-pressing stage, the power-on welding stage and the cooling stage (such as pressure, welding current, power-on time and cooling time, etc.), precise control of the welding process is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other alternative implementation methods can be obtained based on these drawings without paying creative work.

[0027] Figure 1 An embodiment in which the geometric body 2 is a cylinder is shown.

[0028] Figure 2 express Figure 1 An embodiment of a cross-sectional view of section AA.

[0029] Figure 3 express Figure 1 One embodiment of a partial elevation view.

[0030] Figure 4 Schematic diagram showing the asymmetry of the upper and lower connecting surfaces of geometric body 2.

[0031] Figure 5 A type diagram representing geometry 2.

[0032] Figure 6 A partial side view showing an aluminum alloy workpiece during resistance spot welding.

[0033] Figure 7 A schematic diagram showing actual current output during a resistance spot welding process according to one embodiment.

[0034] Figure 8 Represents the cross-sectional view of the weld nugget with a plate thickness ratio of 3:1 for a conventional symmetrical spherical electrode.

[0035] Fig. 9 This figure shows the cross-sectional view of the weld nugget with a thickness ratio of 3:1 when the electrode of the present invention is used on the thin plate side.

[0036] Fig.10 This is a cross-sectional diagram of a weld nugget with a plate thickness ratio of 4:1 when using a conventional symmetrical spherical electrode.

[0037] Fig.11 This figure shows the cross-sectional view of the weld nugget with a thickness ratio of 4:1 when the electrode of the present invention is used on the thin plate side.

[0038] In the accompanying drawings, the symbols are as follows:

[0039] 1-First cylinder

[0040] 2- Geometry

[0041] 3- Second cylinder

[0042] 4-Electrode cap side

[0043] 5-Welding end face

[0044] 6-Cooling water return tank

[0045] 7-Small connected surface of geometry 2

[0046] 8-Large connecting surface of geometry 2

[0047] 9, 10-Welding gun arm

[0048] 11-Nugget offset electrode cap

[0049] 12-Ordinary electrode cap

[0050] 13-Thick plate aluminum workpiece

[0051] 14- Thin sheet aluminum workpiece

[0052] 15-Nugget DETAILED DESCRIPTION

[0053] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, the accompanying drawings are schematic diagrams, so the device and apparatus of the present invention are not limited by the size or ratio of the schematic diagrams.

[0054] An electrode cap for controlling the displacement of a molten core in resistance spot welding of an aluminum workpiece comprises: an electrode cap body, which is divided into three geometric body parts, namely a first cylinder, a geometric body and a second cylinder, wherein the geometric body is any one of a cylinder, a rhombus, a rhombus, a cylinder or a frustum, and is used to connect the first cylinder and the second cylinder; a welding end face, which is arranged at one end of the geometric body part and is used to contact the aluminum workpiece; a side face, which connects the second cylinder and the welding end face, and the side face is an arc surface or a conical surface, and is used to guide the molten core to deflect toward the thin plate side during the resistance spot welding process.

[0055] Example 1

[0056] like Figure 1 As shown, the electrode cap for controlling the nugget deviation of the resistance spot welding of aluminum workpieces in this embodiment includes an electrode cap body, a side surface 4 and a welding end surface 5, and the electrode cap body can be 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 surface is d2; the geometric body 2 can be a cylinder, and its diameter d3 is smaller than d2. The height of the geometric body 2 is greater than 0, preferably 0.5-2mm.

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

[0058] Example 2

[0059] This embodiment discloses a device and a welding process for welding an aluminum workpiece by controlling the nugget shift of an aluminum workpiece resistance spot welding electrode cap according to the present invention. Figure 6 As shown in FIG. 2 , the device comprises a first welding gun arm 9, a second welding gun arm 10, a nugget shifting electrode cap 11, a common electrode cap 12, a thick plate aluminum workpiece 13 and a thin plate aluminum workpiece 14. The thin plate aluminum workpiece 14 is a deformed aluminum alloy with a thickness of 0.5-1.5 mm; the thick plate aluminum workpiece is made of cast aluminum or a deformed aluminum alloy with a thickness of 2.5-4 mm.

[0060] The electrode cap 11 for controlling the nugget shift of the aluminum workpiece resistance spot welding as described in Example 1 is installed on the welding gun arm 9 on the side of the thin plate aluminum workpiece 14, and the ordinary electrode cap 12 is installed on the thick plate side. Before welding, the electrode cap does not contact the aluminum workpiece. During welding, the welding gun arm is operated to make the two electrodes closely fit the thin plate and thick plate aluminum workpieces 13 and 14. Pressure is applied to clamp the thin plate and thick plate aluminum workpieces 13 and 14, so that the fitting parts of the two aluminum workpieces are melted to form a nugget 15.

[0061] Example 3

[0062] like Figure 8 The example shows the use of common symmetrical electrodes and the Figure 6 The welding device in a Figure 7 The cross-sectional morphology of the nugget after resistance spot welding of 5754 deformed aluminum alloy with a thickness of 0.95 mm and AlSi10MnMg cast aluminum alloy with a thickness of 4.0 mm with the welding parameters shown. It can be seen from the figure that there is almost no nugget on the thin plate side.

[0063] like Fig. 9 The figure shows that the electrode cap for controlling the nugget deviation in the first embodiment of the present invention is used on the thin plate side and the welding device and the welding apparatus in the second embodiment are used. Figure 7 The cross-sectional morphology of the nugget after resistance spot welding of 5754 deformed aluminum alloy with a thickness of 0.95 mm and C611 cast aluminum alloy with a thickness of 3.0 mm is shown in the figure. It can be seen from the figure that more nuggets melt toward the thin plate side.

[0064] Example 4

[0065] like Fig.10 The example shows the use of common symmetrical electrodes and the Figure 6 The welding device in a Figure 7 The cross-sectional morphology of the nugget after resistance spot welding of 5754 deformed aluminum alloy with a thickness of 0.95 mm and AlSi10MnMg cast aluminum alloy with a thickness of 4.0 mm with the welding parameters shown. It can be seen from the figure that there is almost no nugget on the thin plate side.

[0066] like Fig.11 The figure shows that the electrode cap for controlling the nugget deviation in the first embodiment of the present invention is used on the thin plate side and the welding device and the welding apparatus in the second embodiment are used. Figure 7 The cross-sectional morphology of the nugget after resistance spot welding of 5754 deformed aluminum alloy with a thickness of 0.95 mm and AlSi10MnMg cast aluminum alloy with a thickness of 4.0 mm with the welding parameters shown in the figure. It can be seen from the figure that more nuggets melt toward the thin plate side.

[0067] The present invention also provides a resistance spot welding method, which comprises the following steps:

[0068] (a) providing an electrode cap as described above and placing it on the thin plate side, and using a conventional spherical electrode cap without the special design and having the same curvature of the welding end surface on the thick plate side;

[0069] (b) Pre-pressing stage: the electrode caps are placed on both sides of two stacked aluminum workpieces of unequal thickness, without constraining the positive and negative electrodes, and pre-pressing is performed, the positive electrode is moved closer to the aluminum alloy plate until the welding end face is tightly fitted to the plate, and a pressure of 2500-6000N is applied, and the pre-pressing duration is 200-2000ms;

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

[0071] (d) Cooling stage: After the welding current stops, the electrode caps remain pressed against both sides of the plate for 30-400ms, and the molten metal solidifies to form a weld.

[0072] It should be understood that within the scope of the present invention, the above-mentioned technical features of the present invention and the technical features specifically described below (such as embodiments) can be combined with each other to form a new or preferred technical solution. Due to space limitations, they will not be described one by one here.

[0073] It should be understood that although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present invention. Within the scope of the claims of the present invention, adjustments to different implementation methods without conflicting adjustments shall all fall within the scope of protection of the present invention.

Claims

1. An electrode cap for controlling the nugget deviation of resistance spot welding of aluminum workpieces, characterized in that: include: The electrode cap body is divided into three geometric body parts, namely, a first cylinder, a geometric body and a second cylinder, wherein the geometric body is any one of a cylinder, a rhombus, a rhombus, a cylinder or a frustum, and is used to connect the first cylinder and the second cylinder; A welding end face, arranged at one end of the geometric body, for contacting with the aluminum workpiece; The side surface connects the second cylinder and the welding end surface, and the side surface is an arc surface or a conical surface, which is used to guide the molten core to deviate to the thin plate side during the resistance spot welding process.

2. The electrode cap for controlling the nugget deviation of resistance spot welding of aluminum workpiece according to claim 1, characterized in that: The geometric body 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 nugget deviation of resistance spot welding of aluminum workpiece according to claim 1, characterized in that: The diameter of the welding end face is d2, and 6mm≤d2≤14mm.

4. The electrode cap for controlling the nugget deviation of resistance spot welding of aluminum workpiece 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 nugget deviation of resistance spot welding of aluminum workpiece 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 connecting the first cylinder and the second cylinder are different, the area S of the minimum surface is satisfied. min ≤(Πd2 2 ) / 4, the area of ​​the largest face is S max ≤(Πd1 2 ) / 4.

6. The electrode cap for controlling the nugget deviation of resistance spot welding of aluminum workpieces as claimed in claim 5, characterized in that: When the connection surface areas are the same, the connection surface area S≤(Πd2 2 ) / 4.

7. The electrode cap for controlling the nugget deviation of resistance spot welding of aluminum workpieces according to claim 1, characterized in that: When the geometric body is a cylinder, the diameter of the cylinder is d3, and satisfies 4mm≤d3<d2.

8. The electrode cap for controlling the nugget deviation of resistance spot welding of aluminum workpieces according to claim 1, characterized in that: The first cylinder is provided with a cooling water reflux groove, and there is a certain distance h1 between the cooling water reflux groove and the geometric body, and h1>h2 is satisfied. The height of the second cylinder is h2, and h2>0 is satisfied.

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

10. A method for resistance spot welding of an aluminum workpiece, characterized in that: The following steps are involved: (a) Preparation stage: placing the electrode cap as claimed in any one of claims 1 to 9 on the thin plate side, and using a conventional spherical electrode cap with the same curvature of the welding end surface on the thick plate side; (b) Pre-pressing stage: The electrode caps are placed on both sides of two stacked aluminum workpieces of unequal thickness, and a pre-pressing operation is performed to bring the positive electrode closer to the aluminum alloy sheet until the welding end face is tightly fitted to the sheet, and a pressure of 2500-6000N is applied. The pre-pressing duration is 200-2000ms; (c) Power-on welding stage: a welding current is applied, the effective value of the welding current is 15-60 kA, and the power-on time is 80-200 ms, so as to form a molten core between the aluminum workpieces, and the molten core is deflected to the thin plate side through the side of the electrode cap, thereby increasing the penetration depth on the thin plate side; (d) Cooling stage: After the welding current stops, the electrode caps are kept pressed against both sides of the plate for 30-400 ms to allow the molten metal to solidify and form welds.

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