A method of spot welding a three-layer sheet metal panel

Abstract

The application discloses a three-layer plate resistance spot welding method, which comprises the following steps: taking a first plate material as a first plate layer, taking a second plate material and a third plate material as a second plate layer, setting a first welding pressure and a first welding current according to the first plate layer and the second plate layer, and spot welding a first welding core on a contact surface of the first plate material and the second plate material; taking the first plate material and the second plate material as a third plate layer and taking the third plate material as a fourth plate layer, setting a second welding pressure and a second welding current according to the third plate layer and the fourth plate layer, and spot welding a second welding core on a contact surface of the second plate material and the third plate material, wherein the second welding core overlaps the first welding core. The three-layer plate spot welding is divided into two steps, the first welding core is first spot welded between the first plate material and the second plate material, then the second welding core is spot welded between the second plate material and the third plate material, and the first welding core and the second welding core overlap to form a welding core, so that stable welding can be realized between the two adjacent plate materials of the three-layer plate, and problems such as false welding and overburning do not occur.

Description

Technical Field

[0001] This application relates to the field of electric welding technology, and in particular to a method for resistance spot welding of three-layer plates. Background Technology

[0002] In existing technologies for resistance spot welding of three-layer plates, the thickness and strength of the three plates differ, resulting in different areas of the two bonding surfaces between the plates. The thinner the plate, the larger the bonding surface. Figure 1 A schematic diagram of the pressing surfaces during the welding of three-layer plates is shown. The pressing surface 12 between the first thick plate 101 and the second thick plate 102 is smaller than the pressing surface 23 between the second thick plate 102 and the thin plate 103. During welding, Joule heat is concentrated on the smaller pressing surface 12, while the temperature of the larger pressing surface 23 is insufficient to form a stable weld nugget. Therefore, during resistance spot welding of the three-layer plates, false welds are easily formed between the second thick plate 102 and the thin plate 103. If the pressure is reduced to prevent false welds between the second thick plate 102 and the thin plate 103, the pressing surface 12 will become too small, leading to false welds or overheating between the first thick plate 101 and the second thick plate 102. Summary of the Invention

[0003] The purpose of this application is to overcome the shortcomings of the prior art in resistance spot welding of three-layer boards, which may result in false welding or overheating, and to provide a resistance spot welding method for three-layer boards that can achieve effective spot welding of three-layer boards.

[0004] This application provides a method for resistance spot welding of three-layer plates, wherein the three-layer plates, from bottom to top, comprise a first plate, a second plate, and a third plate of the same material; the method includes...

[0005] Using the first plate as the first plate layer, and the second plate and the third plate as the second plate layer, a first welding pressure and a first welding current are set according to the first plate layer and the second plate layer, and a first weld nugget is spot welded on the contact surface of the first plate and the second plate.

[0006] Using the first plate and the second plate as the third plate layer, and the third plate as the fourth plate layer, a second welding pressure and a second welding current are set according to the third plate layer and the fourth plate layer. A second weld nugget is spot welded on the contact surface of the second plate and the third plate, and the second weld nugget overlaps with the first weld.

[0007] Further, the step of setting the first welding pressure and the first welding current based on the first plate layer and the second plate layer specifically includes:

[0008] The thinner plate layer between the first plate layer and the second plate layer is used as the first reference plate layer. The first welding pressure and the first welding current are set according to the thickness and strength of the first reference plate layer. If the first reference plate includes two plates, the higher plate strength is taken as the strength of the first reference plate.

[0009] Furthermore, the step of spot welding the first weld nugget on the contact surface between the first plate and the second plate specifically includes:

[0010] First, apply a first welding pressure to the first plate layer and the second plate layer. After maintaining the first pressure for a certain time, apply the first welding current to the first plate layer and the second plate layer. After maintaining the first current for a certain time, stop applying the first welding current. After a first interval, stop applying the first welding pressure.

[0011] Furthermore, the first current holding time includes the current ramp-up time and the current stabilization time;

[0012] The process of applying the first welding current to the first plate layer and the second plate layer, and maintaining the first current for a specified time, specifically includes:

[0013] During the current ramp-up time, the current is controlled to ramp up from zero to the first welding current, and during the current stabilization time, the current is maintained at the first welding current.

[0014] Furthermore, the step of setting the second welding pressure and the second welding current based on the third and fourth plate layers specifically includes:

[0015] The thinner plate layer between the third and fourth plates is used as the second reference plate layer. The second welding pressure and the second welding current are set according to the thickness and strength of the second reference plate layer. If the second reference plate includes two plates, the higher plate strength is taken as the strength of the second reference plate.

[0016] Furthermore, the step of spot welding a second weld nugget on the contact surface between the second plate and the third plate specifically includes:

[0017] First, apply a second welding pressure to the third and fourth plates. After maintaining the second pressure for a certain time, apply a second welding current to the third and fourth plates. After maintaining the second current for a certain time, remove the second welding current. After a second interval, remove the second welding pressure.

[0018] Furthermore, before applying the second welding pressure to the third and fourth layers, the process also includes...

[0019] Within a first preset time period, the welding pressure is switched from the first welding pressure to the second welding pressure;

[0020] Before applying the second welding current to the third and fourth plates, the process also includes...

[0021] During the second preset time period, the welding current is switched from the first welding current to the second welding current.

[0022] Furthermore, the first plate, the second plate, and the third plate are single-layer plates or multi-layer plates welded together from at least two single-layer plates.

[0023] Furthermore, the first plate, the second plate, and the third plate are all steel plates.

[0024] Furthermore, the thickness of the first plate and the thickness of the second plate are both greater than the thickness of the third plate.

[0025] The above technical solution has the following beneficial effects:

[0026] This application divides the spot welding of the three-layer board into two steps. First, the second and third plates are treated as a single layer, and a first weld nugget is spot welded between the first and second plates. Then, the first and second plates are treated as a single layer, and a second weld nugget is spot welded between the second and third plates. The first and second weld nuggets overlap to form a single weld nugget, which enables stable welding between adjacent plates of the three-layer board and prevents problems such as false welding and overheating. Attached Figure Description

[0027] The disclosure of this application will become more readily understood with reference to the accompanying drawings. It should be understood that these drawings are for illustrative purposes only and are not intended to limit the scope of protection of this application. In the drawings:

[0028] Figure 1 This is a cross-sectional schematic diagram of spot welding of three-layer plates in the prior art;

[0029] Figure 2 This is a cross-sectional schematic diagram of the three-layer plate spot welding in one embodiment of this application;

[0030] Figure 3 This is a flowchart of a three-layer plate resistance spot welding method in one embodiment of this application;

[0031] Figure 4 This is the current and pressure curve during resistance spot welding of a three-layer plate in one embodiment of this application;

[0032] Figure 5 This is a flowchart of a three-layer plate resistance spot welding method in a preferred embodiment of this application;

[0033] Figure 6 This is a flowchart of a three-layer plate resistance spot welding method in another preferred embodiment of this application;

[0034] Figure 7 This is the current and pressure curve during resistance spot welding of a three-layer plate in another preferred embodiment of this application. Detailed Implementation

[0035] The specific embodiments of this application will be further described below with reference to the accompanying drawings.

[0036] It is readily understood that, based on the technical solution of this application, various structural and implementation methods can be interchanged by those skilled in the art without altering the essential spirit of this application. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this application and should not be considered as the entirety of this application or as limitations or restrictions on the technical solution of the application.

[0037] The directional terms such as up, down, left, right, front, back, front, back, top, and bottom mentioned or possibly used in this specification are defined relative to the structures shown in the accompanying drawings. These are relative concepts and may therefore vary depending on their location and usage. Therefore, these or other directional terms should not be interpreted as restrictive. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meanings of the above in this application according to the specific circumstances.

[0039] The three-layer plate resistance spot welding method in the embodiments of this application, such as Figure 2 As shown, the three-layer plate, from bottom to top, comprises a first plate 201, a second plate 202, and a third plate 203, all made of the same material. Specifically, the first plate 201, the second plate 202, and the third plate 203 are made of the same material; generally, all three plates are steel plates. However, the thickness, strength, and other physical properties of the first plate 201, the second plate 202, and the third plate 203 may differ.

[0040] In this embodiment, taking as an example that the thickness of the first plate 201 and the thickness of the second plate 202 are both greater than the thickness of the third plate 203, and the strength of the first plate 201 and the strength of the second plate 202 are both greater than the strength of the third plate 203, for instance... Figure 3 As shown, the resistance spot welding method for three-layer boards includes

[0041] Step S301: Using the first plate as the first layer and the second and third plates as the second layer, set the first welding pressure and the first welding current according to the first and second plates, and spot weld the first weld nugget on the contact surface of the first and second plates.

[0042] Step S302: Using the first plate and the second plate as the third plate layer and the third plate as the fourth plate layer, set the second welding pressure and the second welding current according to the third plate layer and the fourth plate layer, spot weld the second weld nugget on the contact surface of the second plate and the third plate layer, and the second weld nugget overlaps with the first weld.

[0043] Specifically, the first plate 201 is used as the first layer, and the second plate 202 and the third plate 203 are used as the second layers. A first weld nugget 204 is spot-welded between the first and second layers, forming the first weld nugget 204 between the first plate 201 and the second plate 202, thus stably welding the first plate 201 and the second plate 202. When the first weld nugget 204 is formed, unstable false weld points may also appear between the second plate 202 and the third plate 203, with small weld point diameters.

[0044] Next, the already welded first plate 201 and second plate 202 are used as the third plate layer, and the third plate 203 is used as the fourth plate layer. A second weld nugget 205 is spot welded between the third and fourth plate layers. After the first weld nugget 204 is formed, the thickness of the three-layer plate will be reduced by at least 7%, and the resistance will be significantly reduced, allowing the temperature to concentrate near the bonding surface of the second plate 202 and the third plate 203. The second weld nugget 205 is formed between the second plate 202 and the third plate 203, stably welding the second plate 202 and the third plate 203.

[0045] The spot welding positions remain unchanged for the two spot welds, allowing the first weld nugget 204 and the second weld nugget 205 to overlap. Furthermore, based on the thickness and strength of the three-layer sheet, the first welding pressure and first welding current for the first spot weld, and the second welding pressure and second welding current for the second spot weld, can be determined first. The two spot welds are then performed consecutively, with the time interval between the two welds minimized to improve the stability of the two weld nuggets and ensure the welding strength of the three-layer sheet.

[0046] In this embodiment, the spot welding of the three-layer plate is divided into two spot welding operations. The welding pressure and welding current can be determined by the existing double-layer plate spot welding method. The welding method is simple and can ensure that the two adjacent layers of the three-layer plate can be stably welded without the problems of false welding and overheating.

[0047] In one embodiment, a first welding pressure and a first welding current are set according to the first plate layer and the second plate layer, specifically including:

[0048] The thinner plate layer in the first and second plates is used as the first reference plate layer. The first welding pressure and the first welding current are set according to the thickness and strength of the first reference plate layer. If the first reference plate includes two plates, the higher plate strength is taken as the strength of the first reference plate.

[0049] by Figure 2 Taking the three-layer board as an example, the first board 201 serves as the first layer, and the second board 202 and the third board 203 serve as the second layers.

[0050] If the thickness of the first plate layer is relatively thin, then the first plate layer is used as the first reference plate layer. The thickness and strength of the first plate 201 are the thickness and strength of the first reference plate layer, thereby setting the first welding pressure and the first welding current.

[0051] If the thickness of the second plate is relatively thin, then the second plate is used as the first reference plate. The sum of the thicknesses of the second plate 202 and the third plate 203 is the thickness of the first reference plate. The higher of the strengths of the second plate 202 and the third plate 203 is used as the strength of the first reference plate. The first welding pressure and the first welding current are set according to the thickness and strength of the first reference plate.

[0052] The specific method for setting the welding pressure and welding current based on the thickness and strength of the reference plate can be the method in the existing technology, and will not be elaborated here.

[0053] In this embodiment, a thinner plate layer is used as the first reference plate layer to set the first welding pressure and the first welding current. When the first reference plate layer includes two plates, the plate with higher strength is selected as the strength of the first reference plate layer, which can ensure that the first weld nugget 204 is formed between the first plate layer and the second plate layer.

[0054] In one embodiment, a first weld nugget is spot-welded onto the contact surface of the first and second plates, specifically including...

[0055] First, apply a first welding pressure to the first and second plates. After maintaining the first pressure for a certain time, apply a first welding current to the first and second plates. After maintaining the first current for a certain time, stop applying the first welding current. After a first interval, stop applying the first welding pressure.

[0056] Figure 4 The diagram illustrates the current and pressure curves during resistance spot welding of a three-layer plate in one embodiment of this application. Specifically, during welding, the positive and negative terminals of the spot welding head clamp the three-layer plate, and pressure and current are applied to the three-layer plate through the spot welding head.

[0057] First, a first welding pressure N1 is applied to the three-layer plate. After a first pressure holding time t1, a first welding current I1 is applied to the three-layer plate. After holding the first current for a first current holding time t2+t3, the application of the first welding current I1 is stopped. After a first interval time t4, the application of the first welding pressure is stopped again. The first pressure holding time t1 and the first interval time t4 are preferably set to 0.1s, while the first current holding time t2+t3 can be set according to actual welding requirements.

[0058] In this embodiment of the application, when welding the first weld nugget, pressure is applied first to clamp the three-layer plate together to form a circuit before the current is turned on to ensure the smooth execution of the welding. After the welding is completed, the current is removed before the pressure is removed, so that the weld nugget can cool down before the pressure is removed, avoiding the weld nugget from separating after the pressure is removed, and ensuring the welding effect of the first weld nugget.

[0059] In one embodiment, such as Figure 4 As shown, the first current holding time includes the current ramp-up time t2 and the current settling time t3;

[0060] Applying a first welding current to the first and second plates, and maintaining the first current for a specified time, specifically including...

[0061] During the current ramp-up time t2, the control current ramps up from zero to the first welding current I1. During the current stabilization time t3, the current is maintained at the first welding current I1.

[0062] When welding the first weld nugget, because the temperature of the previous three layers of plates is low and the bonding surface between the plates is unstable, directly applying a large current will cause the metal to melt rapidly, resulting in molten metal splashing. In this embodiment, when applying the first welding current, the current is gradually increased from zero to the first welding current I1 by setting a current ramp-up time t2, so that the temperature gradually rises, thereby reducing the occurrence of splashing.

[0063] In one embodiment, a second welding pressure and a second welding current are set according to the third and fourth plates, specifically including...

[0064] The thinner plate layer between the third and fourth plates is used as the second reference plate layer. The second welding pressure and the second welding current are set according to the thickness and strength of the second reference plate layer. If the second reference plate includes two plates, the higher plate strength is taken as the strength of the second reference plate.

[0065] by Figure 2 Taking the three-layer board shown as an example, the first board 201 and the second board 202 serve as the third layer, and the third board 203 serves as the fourth layer.

[0066] If the thickness of the third plate layer is relatively thin, then the third plate layer is used as the second reference plate layer. The sum of the thicknesses of the first plate 201 and the second plate 202 is the thickness of the second reference plate layer. The higher strength value between the strength of the first plate 201 and the strength of the second plate 202 is used as the strength of the second reference plate layer. The second welding pressure and the second welding current are set according to the thickness and strength of the second reference plate layer.

[0067] If the fourth plate layer is thinner, then the fourth plate layer is used as the second reference plate layer, and the thickness and strength of the third plate 203 are the same as the thickness and strength of the second reference plate layer, thereby setting the second welding pressure and the second welding current.

[0068] In this embodiment, a thinner plate layer is used as the second reference plate layer to set the second welding pressure and the second welding current. When the second reference plate layer includes two plates, the plate strength with higher strength is selected as the strength of the second reference plate layer, which can ensure that the second weld nugget 205 is formed between the third plate layer and the fourth plate layer.

[0069] In one embodiment, a second weld nugget is spot-welded onto the contact surface between the second and third plates, specifically including...

[0070] First, apply a second welding pressure to the third and fourth plates. After maintaining the second pressure for a certain period of time, apply a second welding current to the third and fourth plates. After maintaining the second current for a certain period of time, remove the second welding current. After a second interval, remove the second welding pressure.

[0071] like Figure 4 As shown, when welding the second weld nugget 205, a second welding pressure N2 is first applied to the three-layer plate. After a second pressure holding time t5, a second welding current I2 is applied to the three-layer plate. After a second current holding time t6, the second welding current I2 is removed. After a second interval time t6, the second welding pressure is removed again. The second pressure holding time t5 and the second interval time t7 can both be set to 0.1s, and the second current holding time t6 can be set according to actual welding requirements.

[0072] Furthermore, when welding the first weld nugget 204, the bonding surfaces between the three layers are already basically stable. Therefore, in this embodiment, when welding the second weld nugget 205, there is no need to set a current ramp-up time. Instead, the current can be controlled to rise to the second welding current I2 in the shortest possible time according to the equipment's load capacity, so as to quickly complete the welding of the second weld nugget 205. Because the current ramp-up time is extremely short, Figure 4 This is not reflected in the text.

[0073] In this embodiment of the application, when welding the second weld nugget, pressure is first applied to clamp the third and fourth plates together to form a circuit before the current is turned on to ensure the smooth execution of the welding. After the welding is completed, the current is removed before the pressure, which allows the weld nugget to cool down before the pressure is removed, thus avoiding the weld nugget from separating after the pressure is removed and ensuring the welding effect of the second weld nugget. Figure 5 A flowchart of a three-layer plate resistance spot welding method according to a preferred embodiment of this application is shown, specifically including:

[0074] Step S501: Use the first board material as the first layer, and the second and third boards material as the second layer;

[0075] Step S502: Using the thinner plate layer in the first plate layer and the second plate layer as the first reference plate layer, set the first welding pressure and the first welding current according to the plate thickness and strength of the first reference plate layer. If the first reference plate includes two plates, the higher plate strength is taken as the strength of the first reference plate.

[0076] Step S503: First, apply a first welding pressure to the first plate layer and the second plate layer. After maintaining the first pressure for a certain period of time, apply current. During the current ramp-up time, control the current to ramp up from zero to the first welding current. During the current stabilization time, maintain the current at the first welding current. Then, remove the first welding current. After a first interval time, remove the first welding pressure and spot weld the first weld nugget on the contact surface of the first plate and the second plate.

[0077] Step S504: Use the first board and the second board as the third board layer, and the third board as the fourth board layer;

[0078] Step S505: The thinner plate layer between the third and fourth plates is used as the second reference plate layer. The second welding pressure and the second welding current are set according to the thickness and strength of the second reference plate layer. If the second reference plate includes two plates, the higher plate strength is taken as the strength of the second reference plate.

[0079] Step S506: First, apply a second welding pressure to the third and fourth plates. After maintaining the second pressure for a certain time, apply a second welding current to the third and fourth plates. After maintaining the second current for a certain time, remove the second welding current. After a second interval, remove the second welding pressure. Spot weld a second weld nugget on the contact surface between the second and third plates, and the second weld nugget overlaps with the first weld.

[0080] Figure 6 A flowchart of a three-layer plate resistance spot welding method according to another preferred embodiment of this application is shown. The current and pressure curves during resistance spot welding of the three-layer plate in this embodiment are as follows: Figure 7 As shown, the method specifically includes:

[0081] Step S601: Use the first board material as the first layer, and the second and third boards material as the second layer;

[0082] Step S602: Take the thinner plate layer of the first plate layer and the second plate layer as the first reference plate layer, and set the first welding pressure and the first welding current according to the plate thickness and strength of the first reference plate layer. If the first reference plate includes two plates, the higher plate strength is taken as the strength of the first reference plate.

[0083] Step S603: Use the first board and the second board as the third board layer, and the third board as the fourth board layer;

[0084] Step S604: Take the thinner plate layer between the third and fourth plate layers as the second reference plate layer, and set the second welding pressure and the second welding current according to the plate thickness and strength of the second reference plate layer. If the second reference plate includes two plates, the higher plate strength is taken as the strength of the second reference plate.

[0085] Step S605: First, apply a first welding pressure to the first plate layer and the second plate layer. After maintaining the first pressure for a certain period of time, apply current. During the current ramp-up time, control the current to ramp up from zero to the first welding current. During the current stabilization time, maintain the current at the first welding current. Then, stop applying the first welding current. After a first interval time, stop applying the first welding pressure. Spot weld the first weld nugget on the contact surface of the first plate and the second plate.

[0086] Step S606: After stopping the application of the first welding current, switch the welding current from the first welding current to the second welding current within a first preset time period; after stopping the application of the first welding pressure, switch the welding pressure from the first welding pressure to the second welding pressure within a second preset time period.

[0087] Step S607: First, apply a second welding pressure to the third and fourth plates. After maintaining the second pressure for a certain time, apply a second welding current to the third and fourth plates. After maintaining the second current for a certain time, remove the second welding current. After a second interval, remove the second welding pressure. Spot weld a second weld nugget on the contact surface between the second and third plates, and the second weld nugget overlaps with the first weld.

[0088] Wherein, the sum of the second preset time period t8, the first interval time t4, and the second pressure holding time t5 is equal to the first preset time period t9. In this embodiment, the welding pressure and welding current for the two welding operations are determined first, the two welding operations are performed continuously, and the welding current and welding pressure do not need to be removed during the interval between the two welding operations, which can effectively reduce the time interval between the two welding operations and improve the welding effect.

[0089] In one embodiment, the first plate 201, the second plate 202, and the third plate 203 can be configured as single-layer plates or as multi-layer plates welded together from at least two single-layer plates. When at least one of the first plate 201, the second plate 202, and the third plate 203 is configured as a multi-layer plate, the three-layer plate resistance spot welding method of this application can be used to spot weld four or more layers of multi-layer plates.

[0090] The above description is merely the principle and preferred embodiment of this application. It should be noted that for those skilled in the art, implementation methods obtained by appropriately combining the technical solutions disclosed in different embodiments are also included within the technical scope of this invention. Based on the principle of this application, several other modifications can also be made, which should also be considered within the protection scope of this application.

Claims

1. A method for resistance spot welding of three-layer plates, characterized in that, The three-layer board, from bottom to top, comprises a first layer, a second layer, and a third layer of the same material; the method includes... Using the first plate as the first layer, and the second and third plates as the second layer, a first welding pressure and a first welding current are set according to the first and second plates, and a first weld nugget is spot-welded onto the contact surface of the first and second plates; specifically including... First, apply a first welding pressure to the first plate layer and the second plate layer, maintain the first pressure for a certain time, then apply the first welding current to the first plate layer and the second plate layer, maintain the first current for a certain time, then stop applying the first welding current, and after a first interval time, stop applying the first welding pressure. The setting of the welding current specifically includes: The thinner plate layer in the first plate layer and the second plate layer is used as the first reference plate layer. The first welding pressure and the first welding current are set according to the plate thickness and strength of the first reference plate layer. If the first reference plate includes two plates, the higher plate strength is taken as the strength of the first reference plate. Using the first and second plates as the third layer and the third plate as the fourth layer, a second welding pressure and a second welding current are set according to the third and fourth plates. A second weld nugget is spot-welded onto the contact surface of the second and third plates. Specifically, this includes... First, apply a second welding pressure to the third and fourth plates, maintain the second pressure for a specified time, then apply a second welding current to the third and fourth plates, maintain the second current for a specified time, then remove the second welding current, and after a second interval, remove the second welding pressure. Before applying the second welding pressure to the third and fourth plates, the process also includes... Within a first preset time period, the welding pressure is switched from the first welding pressure to the second welding pressure; Before applying the second welding current to the third and fourth plates, the process also includes... During a second preset time period, the welding current is switched from the first welding current to the second welding current; The sum of the second preset time period, the first interval time, and the second pressure holding time is equal to the first preset time period. The welding pressure and welding current for the two welding operations are determined first. The two welding operations are performed continuously, and the welding current and welding pressure do not need to be removed during the interval between the two welding operations. This can effectively reduce the time interval between the two welding operations and improve the welding effect. Furthermore, the second weld nugget overlaps with the first weld nugget; specifically including The thinner plate layer between the third and fourth plate layers is used as the second reference plate layer. The second welding pressure and the second welding current are set according to the thickness and strength of the second reference plate layer. If the second reference plate includes two plates, the higher plate strength is taken as the strength of the second reference plate. The three-layer board is spot welded twice. After the first weld nugget is formed, the thickness of the three-layer board is reduced, which reduces the resistance and concentrates the temperature near the bonding surface of the second and third plates. The welding positions of the two spot welds are the same, so that the first weld nugget and the second weld nugget are overlapped.

2. The resistance spot welding method for three-layer plates according to claim 1, characterized in that, The first current holding time includes the current ramp-up time and the current stabilization time; The process of applying the first welding current to the first plate layer and the second plate layer, and maintaining the first current for a specified time, specifically includes: During the current ramp-up time, the current is controlled to ramp up from zero to the first welding current, and during the current stabilization time, the current is maintained at the first welding current.

3. The resistance spot welding method for three-layer plates according to any one of claims 1-2, characterized in that, The first board, the second board, and the third board are single-layer boards or multi-layer boards welded together from at least two single-layer boards.

4. The resistance spot welding method for three-layer plates according to any one of claims 1-2, characterized in that, The first plate, the second plate, and the third plate are all steel plates.

5. The resistance spot welding method for three-layer plates according to any one of claims 1-2, characterized in that, The thickness of the first plate and the thickness of the second plate are both greater than the thickness of the third plate.

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