Aluminum resistance spot welding electrode cap

Abstract

The utility model discloses an aluminum workpiece resistance spot welding electrode cap, which is characterized in that a pit is arranged in the center of a welding end face of the electrode, a plurality of raised annular ridges are arranged on a first welding end face outside the pit, and a second welding end face without an annular ridge is arranged on the first welding end face and is connected with the outermost annular ridge. A height difference exists between the second welding end face and the adjacent first welding end face. During welding, in the initial stage of welding, the pits limit current distribution on the annular ridges, the welding stability is improved, the annular ridges can pierce an oxidation film on the surface of an aluminum workpiece, so that the surface contact resistance of the aluminum workpiece is reduced, the service life of an electrode is prolonged, the second welding end face without the annular ridges can participate in welding earlier due to the fact that the second welding end face is lifted by a certain height, and the welding efficiency is improved. And more current distribution is participated, so that the current is uniformly distributed on the welding end face of the electrode cap, and external splashing caused by current concentration is avoided.

Description

Technical Field

[0001] The utility model patent relates to the field of resistance spot welding, and more specifically to an electrode cap used for resistance spot welding of aluminum workpieces. Background Art

[0002] With the development of the automobile industry, fossil fuel consumption has increased dramatically, which has led to an increase in greenhouse gas emissions. Reducing fuel consumption and improving fuel efficiency are one of the effective ways to reduce greenhouse gas emissions. Reducing vehicle weight and improving engine efficiency can effectively reduce fuel consumption.

[0003] Aluminum alloys have become one of the ideal accessories to replace steel due to their low density and high strength and stiffness to weight ratio. In the automotive industry, they can reduce the weight by 50% compared to traditional materials without affecting the strength and safety of the vehicle body. Therefore, they are expected to replace steel as the main material in the automotive industry. However, aluminum alloys have the characteristics of low melting point, low resistivity, high thermal conductivity and expansion coefficient, which brings certain challenges to aluminum alloy resistance spot welding. In addition, there is an insulating oxide film on the surface of aluminum alloys. During the welding process, it is easy to generate large resistance heat between the aluminum workpiece and the copper electrode, causing the electrode to stick and accelerate electrode wear. These challenges and welding characteristics make it easier for aluminum alloy spot welding to produce defects such as spatter, pores, cracks, etc., and affect the surface quality of the weld and the stability of the weld performance.

[0004] Patent CN104043898A discloses a new electrode with multiple raised annular ridges on a spherical electrode, which mainly uses the raised rings to pierce the surface oxide film to improve the electrode life and surface quality. However, since the welding heat is still mainly concentrated in the center of the weld, this method is very likely to cause premature electrode pitting in the center of the weld due to excessive heat input, thereby affecting the welding efficiency.

[0005] Patent CN220112537U discloses a resistance spot welding electrode, which improves the life of the electrode by designing a protruding annular ridge on the welding end face to pierce the aluminum surface oxide film, and the electrode is designed with a pit on the electrode welding end face so that the center of the welding end face does not participate in welding in the initial stage, thereby improving the problem of premature pitting failure in the center of the electrode welding end face caused by heat concentration in the center of the weld spot. However, the presence of the pit also causes the current to be mainly concentrated in the innermost convex ring, causing the heat of the innermost convex ring to be concentrated and pitting to occur prematurely. Utility Model Content

[0006] In the first aspect of the utility model, the purpose of the utility model is to provide an electrode cap for resistance spot welding of aluminum workpieces. The electrode cap of the utility model can effectively weld aluminum alloy parts and make the current evenly distributed on the welding end face of the electrode cap, thereby avoiding heat concentration and effectively slowing down electrode pitting, increasing the service life of the electrode and improving production efficiency.

[0007] The utility model provides an electrode cap for resistance spot welding of aluminum workpieces, the electrode cap comprising: an inwardly recessed pit 5 located at the center of the first welding end face of the electrode cap; 0-5 protruding annular ridges coaxial with the pit 5 are provided on the first welding end face 4 surrounding the outside of the pit 5, and a second welding end face 3 is present in the outermost ring of the annular ridges, and the second welding end face 3 is not adjacent to the first welding end face 4, but is raised by a certain height h1 relative to the first welding end face.

[0008] There are grooves between the annular ridges, and there is a first annular welding end face directly between the pit and the outermost annular ridge.

[0009] In another preferred embodiment, the resistance spot welding electrode cap includes a side surface 2, the electrode cap body 1 and the welding end surface are transitionally connected through the side surface 2, and the side surface 2 is an arc surface or a conical surface.

[0010] In another preferred embodiment, the side surface 2 and the second welding end surface 3 are connected by arc transition or chamfering.

[0011] In another preferred embodiment, the raised second welding end face 3 is connected to the first welding end face 4 through an arc surface transition or a plane.

[0012] In another preferred embodiment, a height h1 of the second welding end face 3 relative to the first welding end face 4 satisfies 0

[0013] In another preferred embodiment, the distance 9 between the second welding end face 3 and the outermost convex ring of the first welding end face is d2, and satisfies 0<d2<2mm.

[0014] In another preferred embodiment, the number of annular ridges on the first welding end face 4 is 0-5.

[0015] When the first welding end face is a curved surface, the curvature radius of the curved surface is 20-100 mm; when the first welding end face is a conical surface, the conical angle of the conical surface is 120°-179°.

[0016] The distance between the second welding end face and the outermost annular ridge on the first welding end face is d2, and satisfies 0<d2≤1.5d1.

[0017] The first welding end surface is composed of an annular ridge, a groove between the annular ridge, a first annular welding end surface and a second annular welding end surface.

[0018] In another preferred embodiment, the distance between two adjacent annular ridges, that is, the width of the groove 10, is 50-1500 μm.

[0019] In another preferred embodiment, there is a first annular welding end face between the innermost annular ridge and the pit, and the first annular welding end face is connected to the pit via an arc or a chamfer.​

[0020] In another preferred embodiment, the shape of the pit is spherical, and the diameter d of the pit is 1-4 mm.

[0021] In a second aspect of the present invention, a resistance spot welding method is provided, the method comprising:

[0022] (a) providing a pair of electrode caps as described above;

[0023] (b) Pre-pressing stage: a pair of electrode caps are placed on both sides of two or more stacked aluminum workpieces, and pre-pressing is performed. The two electrodes are moved closer to the aluminum alloy plate until the innermost annular ridge of the first welding end face of the electrode is tightly fitted to the plate, and a pressure of 2000-8000N is applied. The pre-pressing duration is 200-2000ms;

[0024] (c) Power-on welding stage: one or more welding currents are applied, and the effective value of the welding current is 18-60 kA. In the initial stage of welding, due to the presence of a pit in the middle of the electrode, the innermost ring 8 of the first welding end face is the first to pass the current, which also allows the molten core to be preferentially nucleated at the contact position of the two plates corresponding to the ring 8. As the welding proceeds, the molten core expands inward from the position corresponding to the ring 8 and eventually melts the two plates at the pit to form a molten core. As the molten core is formed, the plate softens accordingly, and the electrode continues to be pressed into the outside of the plate, so that the outer rings 7 and 6 also participate in the diversion, and the molten core also nucleates at the plate contact surface corresponding to the convex ring; then the second welding end face also participates in the diversion and forms a molten core.

[0025] (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.

[0026] In another preferred embodiment, the welding current is composed of more than three pulses, and there is a cooling interval between each pulse current.

[0027] In another preferred embodiment, each pulse current action time t n is 7-25ms, n is the number of pulses, and the cooling interval is t n-1 , and satisfy 0.1t n ≤t n-1 <10ms, where the cooling interval time is counted from the second welding pulse.

[0028] In another preferred embodiment, the value of the pulse welding current may be different, such as the current value increases gradually.

[0029] 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.

[0030] The mechanism of the utility model is as follows: taking welding of two layers of aluminum alloy workpieces as an example, during welding, since the innermost ring near the pit contacts the aluminum alloy workpiece first, the aluminum alloy workpieces at corresponding positions also contact each other, and resistance heat is generated in the contact area to form an annular molten pool. As welding proceeds, the outer annular ridges and pits 5 participate in welding in turn, and after the outermost annular ridge participates in welding, the second welding end face 3 also begins to participate in welding. The molten core also gradually grows as welding proceeds until welding is completed.

[0031] Technical effect: When the second welding end face is not raised in height, the second welding end face can only participate in welding after the outermost ring participates in welding, and due to the curvature of the welding end face, the welding current distributed on the second welding end face is relatively small, and the current is mainly distributed on the annular ridge, which can easily cause the annular ridge to pit in advance due to high current density and concentrated heat generation; when the second welding end face is raised to a certain height, the second welding end face will participate in welding in advance during the welding process, and participate in more welding current distribution, making the current density distribution of the entire welding end face more uniform, avoiding excessive concentration of current on the annular ridge, excessive heat generation and premature pitting. Therefore, the service life of the electrode can be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the utility model 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 utility model. For ordinary technicians in this field, other alternative implementation methods can be obtained based on these drawings without paying creative work.

[0033] Figure 1 This is an embodiment in which the first welding end face has no ring.

[0034] Figure 2 It is a schematic diagram of an electrode cap with a pit 5 and three annular ridges in the center of the first welding end face, and a second welding end face 3 being raised.

[0035] Figure 3 express Figure 1 An embodiment of a cross-sectional view of section AA.

[0036] Figure 4 express Figure 2 An embodiment of an enlarged view of the welding end surface.

[0037] Figure 5 express Figure 3 An embodiment of the enlarged view of the annular ridge on the right side of the middle.

[0038] Figure 6 A schematic diagram showing the connection type between the first welding end face and the second welding end face.

[0039] Figure 7 Schematic diagram showing the cross-section type of the ring on the first welding end face.

[0040] Figure 8 Schematic diagram showing pit types.

[0041] Fig. 9 A partial side view showing an aluminum alloy workpiece during resistance spot welding.

[0042] Fig.10 A schematic diagram showing a resistance spot welding process of welding an aluminum workpiece with an electrode cap in one embodiment of the utility model.

[0043] Fig.11 A schematic diagram showing the change of current over time during the resistance spot welding process in one embodiment of the utility model.

[0044] Fig.12 The figure shows the surface shape of the plate weld spot after resistance spot welding of two 3.0 mm thick C611 cast aluminum alloy plates using the electrode cap in Example 1 of the utility model.

[0045] Fig.13 It shows the surface shape of the plate weld spot after resistance spot welding two 3.0 mm thick C611 cast aluminum alloy plates using ordinary electrode caps.

[0046] Fig.14 The surface morphology of the positive electrode cap after resistance spot welding of two 3.0 mm thick C611 cast aluminum alloys using the electrode cap in Example 1 of the utility model.

[0047] Fig.15 The surface morphology of the positive electrode cap after resistance spot welding of two 3.0 mm thick C611 cast aluminum alloys using ordinary electrode caps.

[0048] In the accompanying drawings, the symbols are as follows:

[0049] 1-Electrode cap body

[0050] 2-Electrode side

[0051] 3- Second welding end face

[0052] 4-First welding end face

[0053] 5-Pit

[0054] 6-Outermost annular ridge

[0055] 7-Inner annular ridge

[0056] 8-Innermost annular ridge

[0057] 9, 10- Groove

[0058] 11-First annular welding end face

[0059] 12-Second annular welding end face

[0060] 13, 14- welding gun arm

[0061] 15, 16-Electrode cap

[0062] 17, 18-Aluminum workpiece

[0063] 19-Nugget

[0064] 20-Adhesion

[0065] 21-Outer Splash DETAILED DESCRIPTION

[0066] The present invention is 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 used to limit the scope of the present invention. In addition, the accompanying drawings are schematic diagrams, so the device and equipment of the present invention are not limited by the size or proportion of the schematic diagrams.

[0067] Example 1

[0068] like Figure 1-2 As shown, the resistance spot welding electrode cap of this embodiment includes a cylindrical electrode cap body 1, a side surface 2 and a welding end surface. The welding end surface can be divided into a first welding end surface 4, a second welding end surface 3 and a pit 5 in the center of the first welding end surface. The first welding end surface 4 has an annular ridge 8 close to the pit 5 and an outermost annular ridge 6 close to the second welding end surface, as well as an annular ridge 7 distributed between the two annular ridges. There are also grooves 9 and 10 between the annular ridges. There is a first annular welding end surface 11 between the pit 5 and the annular ridge, and there is also a second annular welding end surface 12 between the second welding end surface 3 and the annular ridge 6. There is a height difference h1 between the second annular welding end surface 12 and the second welding end surface 3. It should be noted that the number of the annular ridges is not limited to 3, and can be 0 or more as needed.

[0069] like Figure 3The pit 5 can be understood as a hole of a certain size dug on the first welding end face 4. The shape of the pit 5 is a curved surface or a boss concave toward the electrode. The pit depth is 0.1-1mm, preferably 0.1-0.5mm. The depth of the pit 5 referred to here is the vertical distance from the first annular welding end face where the edge of the pit 5 is located to the bottom of the pit 5.

[0070] In another preferred embodiment, the pit 5 is spherical in shape, and its outer diameter d is 1-4 mm.

[0071] like Figure 4-5 The height of the annular ridges can be the same or different. The height of the annular ridges can be understood as the vertical distance h2 from the highest point of the annular ridges to the groove contact point between the annular ridges. The groove width is the horizontal distance d1 between the contact points of two adjacent annular ridges and the grooves. The width of the second annular welding end face 12 is d2. The height difference h1 is the vertical distance from the highest point of the second welding end face 3 to the lowest point of the second annular welding end face 12.

[0072] Example 2

[0073] This embodiment discloses a device and a welding process for welding aluminum workpieces using the electrode cap of the utility model. Figure 8 As shown, the device includes a first aluminum alloy workpiece 17 and a second aluminum alloy workpiece 18, and a welding gun at a weld nugget 19, the welding gun includes a first welding gun arm 13, a second welding gun arm 14, a first electrode cap 15 and a second electrode cap 16. The first and second aluminum alloy workpieces 17 and 18 are made of deformed aluminum alloy or cast aluminum alloy, and the thickness of the aluminum alloy workpiece is 0.5-3.5 mm. During welding, the aluminum alloy workpieces can be two or more than two, and the thickness of each aluminum alloy workpiece can be the same or different.

[0074] The first and second welding gun arms 13 and 14 are equipped with the first and second electrode caps 15 and 16 as described in Example 1. Before welding, the welding gun arms and the electrode caps are not in contact with the aluminum alloy workpiece. During welding, the welding gun arms are operated to make the first and second electrode caps close to the aluminum alloy workpieces 17 and 18, and continuously apply pressure to clamp the aluminum alloy workpieces 17 and 18, and transmit current through the welding gun arms and the electrode caps to melt the contacting parts of the aluminum alloy workpieces 17 and 18 to form a molten core 19. The two electrode caps 15 and 16 can be various structures as described in Example 1, and the structures of the two electrode caps 15 and 16 can be the same or different.

[0075] Example 3

[0076] like Fig. 9 and Fig.11The figure shows the morphology of the positive electrode plate welding spot and the surface morphology of the positive electrode cap after resistance spot welding of two pieces of 3.0 mm thick C611 cast aluminum alloy using the electrode cap in Example 1 of the utility model and the welding device and welding principle in Example 2. It can be seen from the figure that only the morphology left by the electrode on the plate surface is not abnormally adhered, and only a small part of the electrode surface is adhered 20.

[0077] Example 4

[0078] like Fig.10 and 12 The figure shows the morphology of the positive electrode plate weld spot and the positive electrode cap surface after resistance spot welding of two 3.0 mm thick C611 cast aluminum alloys using a common electrode cap and the welding device and welding principle in Example 2. As can be seen from the figure, adhesion 20 and external splash 21 occur on the plate surface, and severe adhesion also occurs on the electrode.

[0079] The utility model also provides a resistance spot welding method, which comprises the following steps:

[0080] (a) providing a pair of electrode caps 15 and 16 as described above;

[0081] (b) Pre-pressing stage: a pair of electrode caps are placed on both sides of two or more stacked aluminum workpieces, and pre-pressing is performed. The two electrodes are moved closer to the aluminum alloy plate until the innermost annular ridge of the first welding end face of the electrode is tightly fitted to the plate, and a pressure of 2000-8000N is applied. The pre-pressing duration is 200-2000ms;

[0082] (c) Power-on welding stage: one or more welding currents are applied, and the effective value of the welding current is 18-60 kA. In the initial stage of welding, due to the presence of a pit in the middle of the electrode, the innermost ring 8 of the first welding end face is the first to pass the current, which also causes the molten core to be preferentially nucleated at the contact position of the two plates corresponding to the ring 8. As the welding proceeds, the molten core 19 expands inward from the position corresponding to the ring 8 and eventually melts the two plates at the pit to form the molten core 19. As the molten core is formed, the plate softens accordingly, and the electrode continues to be pressed into the outside of the plate, so that the outer rings 7 and 6 also participate in the diversion, and the molten core also nucleates at the plate contact surface corresponding to the convex ring; then the second welding end face also participates in the diversion to form the molten core 19.

[0083] (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 complete weld nugget19.

[0084] The welding pulses are more than 3 pulses, there is a cooling interval between each welding pulse, and the duration of each welding pulse is t n , n is the number of pulses, and satisfies 7ms≤tn <25ms, the cooling interval between each welding pulse is t n-1 , and satisfies 0.1tn≤tn-1<10ms.

[0085] Among them, when the welding pulse current value increases gradually, the increase of each welding pulse current value does not exceed 15kA.

[0086] 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 aluminum resistance spot welding electrode cap, comprising an electrode cap body, a side surface and a welding end surface, characterized in that: The welding end face is divided into a first welding end face and a second welding end face with a height difference. The second welding end face is located outside the first welding end face. The second welding end face is raised relative to the first welding end face by a certain height h1. There is an inwardly concave pit at the center of the first welding end face.

2. The aluminum resistance spot welding electrode cap according to claim 1, characterized in that: The first welding end surface has a plurality of protruding concentric annular ridges surrounding the recess.

3. The aluminum resistance spot welding electrode cap according to claim 2, characterized in that: There are also grooves between the annular ridges, and there is a first annular welding end face directly between the pit and the outermost annular ridge; there is a second annular welding end face between the second welding end face and the annular ridge, and there is a height difference h1 between the second annular welding end face and the second welding end face, that is, the lifting height of the second welding end face.

4. The aluminum resistance spot welding electrode cap according to claim 1, characterized in that: The pit depth h is 0.01-1 mm, and the pit diameter is 1.0-4.0 mm.

5. The aluminum resistance spot welding electrode cap according to claim 2, characterized in that: The height h2 of the annular ridge is 50-220 μm.

6. The aluminum resistance spot welding electrode cap according to claim 3, characterized in that: The width of the grooves between the annular ridges is d1, and satisfies 0<d1≤1.5mm.

7. The aluminum resistance spot welding electrode cap according to claim 2, characterized in that: The number of the annular ridges is 0-5.

8. The aluminum resistance spot welding electrode cap according to claim 1, characterized in that: When the first welding end face is a curved surface, the curvature radius of the curved surface is 20-100 mm; when the first welding end face is a conical surface, the conical angle of the conical surface is 120°-179°.

9. The aluminum resistance spot welding electrode cap according to claim 1, characterized in that: The lifting height of the second welding end face is h1, and satisfies 0<h1≤1.5h2.

10. The aluminum resistance spot welding electrode cap according to claim 1, characterized in that: The distance between the second welding end face and the outermost annular ridge on the first welding end face is d2, and satisfies 0<d2≤1.5d1.

11. The aluminum resistance spot welding electrode cap according to claim 1, characterized in that: The second welding end surface is connected to the outermost annular ridge on the first welding end surface via an arc surface or a plane.

12. The aluminum resistance spot welding electrode cap according to claim 1, characterized in that: The second welding end surface surrounds the first welding end surface.

13. The aluminum resistance spot welding electrode cap according to claim 1, characterized in that: The first welding end surface is composed of an annular ridge, a groove between the annular ridge, a first annular welding end surface and a second annular welding end surface.

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