Resistance spot welding method and system

Abstract

The present application relates to the technical field of welding, and provides a resistance spot welding method and system, which comprises the following steps: selecting at least two plates with thickness difference, and forming a conductive silver-based layer on one side of the plate with the thinnest thickness; moving the plate with the thinnest thickness to a gluing loading area and coating adhesive on the other side of the plate with the thinnest thickness by a preset gluing procedure; moving the plate with the thinnest thickness after gluing to an assembly area and bonding with the remaining plates; selecting a test plate matched with the plates, performing test welding on the test plate, generating welding process parameters for formal welding based on the welding result, performing resistance spot welding on the bonded plates by the welding process, monitoring welding quality in real time during the resistance spot welding, and adjusting the welding process parameters based on the monitored welding quality; and performing surface treatment on the welding points on the surface of the welded plate.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and in particular to a resistance spot welding method and system. Background Technology

[0002] Resistance spot welding is a method with stable welding quality and high production efficiency, and it is widely used in the manufacturing of rail vehicles, automobiles, electronics, and home appliances. However, current resistance spot welding processes still have technical problems such as low penetration on thin plates and insufficient airtightness after welding. Therefore, a novel resistance spot welding method is urgently needed to solve these problems. Summary of the Invention

[0003] This invention provides a resistance spot welding method to solve the technical problems of low melt penetration on the thin plate side and insufficient air tightness after welding in the prior art, so as to achieve uniform melt penetration and good air tightness.

[0004] The present invention also provides a resistance spot welding system.

[0005] This invention provides a resistance spot welding method, comprising the following steps:

[0006] Select at least two plates with a thickness difference, and form a conductive silver base layer on one side of the thinnest plate.

[0007] Move the thinnest sheet to the glue application area and apply adhesive to the other side of the thinnest sheet using a preset glue application program.

[0008] Move the glued boards to the assembly area and bond them with the remaining boards.

[0009] Select a test plate that matches the plate material, perform test welding on the test plate, and generate welding process parameters for formal welding based on the welding results. Use the welding process to perform resistance spot welding on the bonded plate material, and monitor the welding quality in real time during the resistance spot welding process. Adjust the welding process parameters based on the monitored welding quality.

[0010] The weld points on the surface of the welded plates are then subjected to surface treatment.

[0011] According to a resistance spot welding method provided by the present invention, the step of selecting at least two plates with a thickness difference and forming a conductive silver substrate on one side of the thinnest plate includes:

[0012] Two plates with a thickness difference are selected, namely a thin plate and a thick plate. A conductive silver-based material is coated on the outer surface of the thin plate to form a conductive silver base layer with a thickness of 10-20 micrometers. The thick plate is then attached to the side of the thin plate away from the conductive silver base layer.

[0013] Wherein, the thickness of the thin plate is t1, and the thickness of the thick plate is t2;

[0014] Wherein, 2t1 > t2 > t1, and the thickness of the pad is 0.3 mm;

[0015] Alternatively, t2 > 3t1, and the thickness of the pad is 0.5 mm.

[0016] According to a resistance spot welding method provided by the present invention, the step of selecting at least two plates with a thickness difference and forming a conductive silver substrate on one side of the thinnest plate includes:

[0017] Three plates with different thicknesses are selected, namely a thin plate, a relatively thick plate, and a thick plate. A conductive silver-based material is coated on the outer surface of the thin plate to form a conductive silver base layer with a thickness of 10-20 micrometers. The thick plate and the relatively thick plate are attached to the side of the thin plate away from the conductive silver base layer.

[0018] Wherein, the thickness of the thin plate is t3, the thickness of the thicker plate is t4, and the thickness of the thickest plate is t5;

[0019] Where t5 > t4 > t3, and t5 > 3t3, the thickness of the pad is 0.8 mm.

[0020] According to a resistance spot welding method provided by the present invention, the step of moving the thinnest plate to the adhesive loading area and applying adhesive to the other side of the thinnest plate according to a preset adhesive application program includes:

[0021] An adhesive application procedure is established based on the assembly logic between the boards. The thinnest board is picked up and placed in the adhesive loading area. The position of the board in the adhesive loading area is identified and moved to a preset point in the adhesive loading area. The corresponding adhesive application unit is selected based on the adhesive application procedure. The adhesive seam of the board located at the preset point is identified by the identification unit mounted on the adhesive application unit. The adhesive application unit is used to apply adhesive to the other side of the thinnest board along the adhesive seam according to the adhesive application procedure.

[0022] According to a resistance spot welding method provided by the present invention, the step of moving the glued sheet to the assembly area and bonding it with the remaining sheets includes:

[0023] The identification unit identifies the boards coated with adhesive. An assembly robot picks up the boards and moves them to the assembly area. The remaining boards picked up by the assembly robot are then attached to the boards coated with adhesive. A flexible clamping unit is used to clamp at least two boards together. The assembly robot then picks up a scraper and uses the scraper to remove the adhesive that has overflowed from the edges of at least two boards.

[0024] According to a resistance spot welding method provided by the present invention, the steps of selecting a test plate adapted to the plate material, performing test welding on the test plate, and generating welding process parameters for formal welding based on the welding results include:

[0025] Establish a database of the relationship between welding process and welding quality. Use an identification component to identify a test plate that matches the plate material. Use a gripping component to grip the corresponding test plate onto the welding platform. Based on the welding process in the database, perform test welding on the test plate on the welding platform. After the test welding is completed, perform performance testing.

[0026] If the performance test is passed, the current welding process parameters will be used as the welding process parameters for the formal welding.

[0027] If the performance test fails, the current welding process parameters are adjusted and the trial welding is continued until the performance test passes and the welding process parameters for formal welding are output.

[0028] The performance test steps include: spot welding three solder joints consecutively on at least three test plates, tearing the last solder joint on each test plate, and measuring the diameter of the weld nugget after tearing;

[0029] The performance testing steps also include: cutting the solder joint along the X-axis and Y-axis at the solder joint of the test board to obtain the molten core morphology cross-section inside the solder joint of the test board, enlarging the molten core morphology cross-section several times to generate a macroscopic cross-section, and comparing the macroscopic cross-section with the cross-section digital model.

[0030] According to a resistance spot welding method provided by the present invention, the step of resistance spot welding the bonded plates using the welding process includes:

[0031] The pad is attached and fixed to the outer surface of the conductive silver base layer by at least one of the following methods: bonding, tooling, and fastener fixing. A first electrode rod and a second electrode rod with different diameters are selected and placed on the outer side of the pad and the outer side of the remaining plates, respectively. Based on the thickness parameters of the thinner of the two outermost plates, the solder joint spacing, the distance from the solder joint to the edge, the welding current, the welding time, the cooling time, the number of pulses, the holding time, and the electrode pressure are set. At least two plates are welded using the first electrode rod and the second electrode rod with preset welding current, welding time, cooling time, number of pulses, holding time, and electrode pressure.

[0032] The diameter of the first electrode rod is smaller than the diameter of the second electrode rod.

[0033] According to a resistance spot welding method provided by the present invention, the step of real-time monitoring of welding quality during the resistance spot welding process and adjusting welding process parameters based on the monitored welding quality includes:

[0034] Establish a database on the relationship between welding processes and welding quality;

[0035] Obtain the gap parameters between at least two plates before welding, and adjust the pre-pressure value before welding based on the comparison between the gap parameters and the gap threshold in the relational database;

[0036] The expansion volume parameters of the weld nugget at the weld point are obtained during the welding process. Based on the comparison between the expansion volume parameters and the weld nugget expansion threshold in the relational database, the welding parameters during the welding process are adjusted.

[0037] After welding, the quality parameters of the weld nugget at the weld point are obtained. Based on the comparison between the quality parameters and the quality threshold of the weld nugget in the relational database, the post-processing parameters are adjusted.

[0038] According to a resistance spot welding method provided by the present invention, the step of surface treatment of the weld spots on the surface of the welded plate includes:

[0039] Electrolytic removal of solder joints on the surface of the sheet metal;

[0040] Based on the qualified electrolytic descraping of the sheet metal, the surface of the sheet metal is passivated as a whole;

[0041] Clean the surface of the board to remove the electrolytic scratch remover and electrolytic passivation solution adhering to the surface.

[0042] The present invention also provides a resistance spot welding system, comprising:

[0043] Central control unit

[0044] The selection unit, electrically connected to the central control unit, is used to select at least two plates with a thickness difference.

[0045] The coating unit, electrically connected to the central control unit, is used to form a conductive silver base layer on one side of the thinnest sheet material.

[0046] The glue application unit is electrically connected to the central control unit and is used to move the thinnest sheet to the glue application and feeding area and apply adhesive to the other side of the thinnest sheet according to a preset glue application program.

[0047] The assembly unit, which is electrically connected to the central control unit, is used to move the glued board to the assembly area and bond it with the other boards.

[0048] The test welding unit is electrically connected to the central control unit and is used to select a test plate that is compatible with the plate material, perform test welding on the test plate, and generate welding process parameters for formal welding based on the welding results.

[0049] The formal welding unit is electrically connected to the central control unit and is used to perform resistance spot welding on the bonded plates using the welding process.

[0050] The monitoring and adjustment unit is electrically connected to the central control unit and is used to monitor the welding quality in real time during the resistance spot welding process and adjust the welding process parameters based on the monitored welding quality.

[0051] The surface treatment unit, which is electrically connected to the central control unit, is used to perform surface treatment on the weld points on the surface of the welded plate.

[0052] The resistance spot welding method provided in this invention can improve the resistivity of the thin plate side by arranging a conductive silver base layer to enhance the nucleation ability, thereby improving the penetration rate of the thin plate side. The method of bonding first and then spot welding makes the welded plate have good airtightness, which overcomes the engineering limitation of spot welding of rail vehicle bodies that is not sealed. The welding process parameters are adjusted in real time during the welding process to ensure the quality of the weld. After welding, the surface is treated so that the plate can meet the usage requirements.

[0053] The resistance spot welding system provided in this invention can improve the resistivity of the thin plate side by arranging a conductive silver base layer to enhance the nucleation ability, thereby improving the penetration rate of the thin plate side. The method of bonding first and then spot welding makes the welded plate have good airtightness, which overcomes the engineering limitation of spot welding of rail vehicle bodies that is not sealed. The welding process parameters are adjusted in real time during the welding process to ensure the quality of the weld. After welding, the surface is treated so that the plate can meet the usage requirements. Attached Figure Description

[0054] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0055] Figure 1 This is a schematic flowchart of the resistance spot welding method provided by the present invention;

[0056] Figure 2 This is a schematic diagram of the resistance spot welding system provided by the present invention;

[0057] Figure 3 This is a schematic diagram illustrating the principle of using laser to measure the gap between two plates, provided by the present invention.

[0058] Figure 4 This is a schematic diagram of the structure of the photosensitive element provided by the present invention;

[0059] Figure 5 This is a schematic diagram showing the state of the first and second electrode rods welding two plates.

[0060] Figure 6 This is a graph showing the relationship between the weld spot spacing and the weld nugget diameter in the resistance spot welding method provided by this invention and in the traditional welding method.

[0061] Figure 7 This is a graph showing the relationship between the weld spot spacing and the maximum tensile shear force in the resistance spot welding method provided by this invention and the traditional welding method.

[0062] Figure 8 This is a schematic diagram of the electrolytic mark removal path in this invention;

[0063] Figure 9 This is a schematic diagram of the overall passivation path in this invention. Detailed Implementation

[0064] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0065] The following is combined with Figures 1-9 The resistance spot welding method of the present invention includes the following steps:

[0066] S100. Select at least two plates with a thickness difference and form a conductive silver base layer on one side of the thinnest plate.

[0067] S200: Move the thinnest sheet to the glue application area and apply adhesive to the other side of the thinnest sheet using a preset glue application program.

[0068] S300: Move the glued board to the assembly area and bond it with the remaining boards.

[0069] S400. Select a test plate that matches the plate material, perform test welding on the test plate, and generate welding process parameters for formal welding based on the welding results. Perform resistance spot welding on the bonded plates using the welding process, and monitor the welding quality in real time during the resistance spot welding process. Adjust the welding process parameters based on the monitored welding quality.

[0070] S500: Perform surface treatment on the weld points on the surface of the welded plates.

[0071] In this embodiment, the resistivity of the thin plate side can be increased by arranging the conductive silver base layer to improve the nucleation ability, thereby improving the melting penetration rate of the thin plate side. The method of bonding first and then spot welding makes the welded plate have good airtightness, which overcomes the engineering limitation of spot welding of rail vehicle body that is not sealed. The welding process parameters are adjusted in real time during the welding process to ensure the quality after welding. After welding, the surface is treated so that the plate can meet the usage requirements.

[0072] The main component of the conductive silver substrate is silver tin oxide (AgSnO2). Silver tin oxide can increase the contact resistance of the material surface, thereby increasing the resistivity of the thinnest plate side. Under the same spot welding parameters, the greater the contact resistance, the stronger the nucleation ability, thus improving the nucleation ability of the thin plate side and increasing the penetration rate of the thin plate side.

[0073] In this embodiment, the step of selecting at least two plates with a thickness difference and forming a conductive silver base layer on one side of the thinnest plate includes: selecting two plates with a thickness difference, the two plates being a thin plate and a thick plate, coating the outer surface of the thin plate with a conductive silver base material and forming a conductive silver base layer with a thickness of 10-20 micrometers, and attaching the thick plate to the side of the thin plate away from the conductive silver base.

[0074] When welding two plates, the thinner plate can be placed on top of the thicker plate, and a conductive silver-based material can be coated on the upper surface of the thinner plate to form a conductive silver base layer. During the welding process, the conductive silver base layer can increase the contact resistance on the thinner plate side, improve the nucleation ability on the thinner plate side, so that the weld nugget is located at the junction of the thinner and thicker plates, thereby improving the penetration rate on the thinner plate side and improving the weld quality. Combined with a backing plate on the outer surface of the conductive silver base layer and asymmetrically arranged first and second electrode rods, the penetration rate can be increased from the original 20% to 50%.

[0075] The thickness of the thin plate is t1, and the thickness of the thick plate is t2. When 2t1 > t2 > t1, the thickness of the backing plate is 0.3 mm. When t2 > 3t1, the thickness of the backing plate is 0.5 mm. The thickness of the backing plate varies based on the thickness of the thin and thick plates. When the thickness of the thick plate is slightly greater than that of the thin plate (it should be noted that "slightly greater" here also requires that the thickness of the thick plate is at least 3 mm greater than that of the thin plate), the thickness of the backing plate can be set to 0.3 mm. In this case, the backing plate has the best effect on reducing the heat dissipation rate on the thin plate side and meets the welding requirements. When the thickness of the thick plate is much greater than that of the thin plate, the thickness of the backing plate can be set to 0.5 mm. In this case, the backing plate has the best effect on reducing the heat dissipation rate on the thin plate side and meets the welding requirements.

[0076] In this embodiment, the step of selecting at least two plates with a thickness difference and forming a conductive silver substrate on one side of the thinnest plate includes:

[0077] Select three plates with different thicknesses: a thin plate, a relatively thick plate, and a thick plate. Coat the outer surface of the thin plate with a conductive silver-based material to form a conductive silver base layer with a thickness of 10-20 micrometers. Attach the thick plate and the relatively thick plate to the side of the thin plate away from the conductive silver base layer.

[0078] When welding three plates, the thinner plate can be placed on top of the thicker plate, and the thicker plate below it, sandwiching the thicker plate between the thinner and thicker plates. A conductive silver-based material is then coated on the upper surface of the thinner plate, forming a conductive silver base layer. During welding, the conductive silver base layer increases the contact resistance on the thinner plate side, enhancing its nucleation ability. This allows the thicker plate to be melted through during nucleation, and also ensures that the thinner and thicker plates can be melted towards the thicker plate, improving the penetration rate on the thinner plate side and enhancing the weld quality. Combined with a backing plate on the outer surface of the conductive silver base layer and asymmetrically positioned first and second electrode rods, the penetration rate can be increased from the original 20% to 50%.

[0079] The thickness of the thin plate is t3, the thickness of the thicker plate is t4, and the thickness of the thickest plate is t5. When t5 > t4 > t3, and t5 > 3t3, the thickness of the backing plate is 0.8 mm. At this thickness, the backing plate best reduces the heat dissipation rate on the thin plate side while still meeting welding requirements.

[0080] In this embodiment, the step of moving the thinnest sheet to the adhesive application area and applying adhesive to the other side of the thinnest sheet using a preset adhesive application program includes:

[0081] A gluing procedure is established based on the assembly logic between the boards. The gluing procedure picks up the thinnest board and places it in the gluing and feeding area. The position of the board in the gluing and feeding area is identified and moved to a preset point in the gluing and feeding area. The corresponding gluing unit is selected based on the gluing procedure. The gluing unit identifies the glue seam of the board located at the preset point through the identification unit. The gluing unit is used to apply glue to the other side of the thinnest board along the glue seam according to the gluing procedure.

[0082] The adhesive application program captures the board material to be used for this adhesive application and transfers it to the adhesive loading area. After identifying the position of the board material in the adhesive loading area, its position is corrected to ensure that the board material is in the preset position, so as to facilitate precise adhesive application in the subsequent process. Then, based on the adhesive application program, the adhesive application unit is selected to apply adhesive to the board material along the adhesive seam, thereby realizing automated adhesive application of the board material to facilitate subsequent processes.

[0083] An RFID chip is embedded in each board. Each RFID chip corresponds to the parameter information of each board. The RFID chip has a radio wave function and can continuously emit signals. In subsequent steps, the signal receiver receives the signals emitted by the RFID chip, and the part information can be converted into electrical signals and transmitted to the gripping unit so that the gripping unit can grip the corresponding board.

[0084] The board material parameters include at least one of the following: material parameters, thickness parameters, and specifications. An RFID chip containing the material, thickness, and specifications is embedded in the board material to convert this information into electrical signals that are transmitted to the part gripping unit. The gripping unit then grips the board material according to a pre-defined program and places it in the adhesive application area.

[0085] The steps of identifying the position of the board in the glue application and feeding area and moving the board to a preset point in the glue application and feeding area include:

[0086] The glue application and feeding area is equipped with a three-dimensional positioning sensing unit and a position adjustment unit. The three-dimensional positioning sensing unit identifies the position of the board in the glue application and feeding area, and the position adjustment unit adjusts the board to the preset point in the glue application and feeding area.

[0087] The three-dimensional positioning sensing unit includes a three-dimensional positioning sensor, and the position adjustment unit includes a three-way adjustment rod. The three-dimensional positioning sensor identifies the position of the board initially placed in the glue application area. Based on the identified position, the positional deviation between the board's position and the reference point is determined. Based on the positional deviation, the three-way adjustment rod is triggered to adjust the position of the board so that it is located at the preset point, so as to facilitate subsequent glue application.

[0088] The steps of selecting the corresponding glue application unit based on the glue application procedure, and identifying the glue joint of the board located at a preset point through the identification unit mounted on the glue application unit, include:

[0089] The glue application process enables the glue application robot's gun-changing disc to pick up the corresponding glue gun. The glue gun is equipped with a vision recognition unit, which identifies the glue joint position and size of the board located at a preset point.

[0090] Due to manufacturing errors in each board, dimensional variations exist between different boards. Therefore, the application location and amount of adhesive will differ for each board. Real-time visual recognition identifies the location and size of the adhesive seams, allowing for adjustment of the nozzle's dispensing speed to ensure adequate adhesive coverage at every seam. In subsequent resistance spot welding, the identified seam locations correspond to the weld locations, and the seam dimensions correspond to the weld seam dimensions.

[0091] The automatic glue application method provided by the present invention includes the step of applying glue to a board material located at a preset point along the glue seam using a glue application unit in a glue application program, comprising:

[0092] A plastic nozzle is fitted onto the glue gun, and the glue-applying robot drives the glue gun to move along the glue seam and apply glue to the board located at a preset point. The glue-applying robot adjusts the glue dispensing speed of the glue gun based on different glue seam sizes.

[0093] Using a plastic nozzle avoids scratching the surface of the sheet material, specifically preventing damage to the car body in the case of rail vehicles. The glue gun moves along the glue seam and applies glue to the sheet material. Furthermore, the real-time recognition unit on the glue gun adjusts the glue dispensing speed based on the detected glue seam size to ensure that each seam is filled with the appropriate amount of adhesive. The glue gun's single-point application amount is 1.0 gram, and the application diameter is 4.5-5.0 mm. Within this range of single-point application amount and diameter, optimal airtightness is ensured after subsequent resistance spot welding, and at least the bonding effect between two sheets is optimal.

[0094] In this embodiment, the adhesive is prepared using compounded rubber, titanium dioxide, and conductive carbon black as the base materials. The resulting adhesive exhibits good spreadability and initial adhesion, and does not flow at any spot welding station. It should be noted that the spot welding stations referred to here include stations in horizontal, vertical, and inverted positions.

[0095] The aforementioned adhesive allows for precise control of the dispensing diameter, enabling subsequent spot welding within three days of application. It withstands the impact and erosion of pretreatment and electrophoretic solutions, ensuring no spillage or contamination. It also exhibits compatibility with arc welding, flame conditioning, and repair processes. The adhesive possesses strong electrical conductivity, ensuring no impact on the quality of subsequent spot welding, and it has a certain tolerance for varying degrees of cleanliness on the sheet surface. Furthermore, it exhibits high flame retardancy, maintaining good stability and sealing even at 1000℃ spot welding temperatures without producing open flames. The adhesive is non-toxic and odorless, posing no health risks to operators. Excess sealant is easily removed. It also boasts excellent storage stability, with a shelf life of up to 180 days.

[0096] In this embodiment, the step of moving the glued board to the assembly area and bonding it with the remaining boards includes:

[0097] The identification unit identifies the boards coated with adhesive. An assembly robot picks up the boards and moves them to the assembly area. The remaining boards picked up by the assembly robot are then attached to the boards coated with adhesive. A flexible clamping unit is used to clamp at least two boards together. The assembly robot then picks up a scraper and uses the scraper to remove the adhesive that has overflowed from the edges of at least two boards.

[0098] The assembly robot grips and bonds the boards together. During bonding, adhesive overflows between the boards. A scraper is used to remove the adhesive to ensure the cleanliness of the board edges.

[0099] In this embodiment, the steps of selecting a test plate that matches the plate material, performing test welding on the test plate, and generating welding process parameters for formal welding based on the welding results include:

[0100] A database relating welding processes to welding quality is established. A recognition component identifies test plates that match the sheet metal. A gripping component picks up the corresponding test plates and places them onto the welding platform. Based on the welding processes in the database, trial welding is performed on the test plates on the welding platform. After the trial welding, performance testing is conducted. If the performance test is successful, the current welding process parameters are used as the parameters for the final welding. If the performance test fails, the current welding process parameters are adjusted, and trial welding continues until the performance test is successful, at which point the welding process parameters for the final welding are output. The performance testing steps include: continuously spot welding three weld points on at least three test plates, tearing the last weld point on each test plate, and measuring the diameter of the weld nugget after tearing. If the weld nugget diameter meets the requirements, the performance test is successful. If the weld nugget diameter does not meet the requirements, the performance test is unsuccessful. The performance testing steps also include: cutting the solder joint along the X and Y axes at the solder joint of the test board to obtain the cross-sectional shape of the weld nugget inside the solder joint; magnifying the cross-sectional shape of the weld nugget several times to generate a macroscopic cross-section; and comparing the macroscopic cross-section with the digital model of the cross-section. If the result of the comparison meets the requirements, the performance test is qualified. If the result of the comparison does not meet the requirements, the performance test is unqualified.

[0101] The test plates are matched to the sheet metal, meaning the material of the test plates is the same as the sheet metal. Furthermore, to facilitate experimental welding, all test plates can be the same size. For example, multiple test plates with dimensions of 40mm x 200mm can be selected. Using test plates of the same size also ensures that each spot-welded test plate can be accurately placed by the robot onto the tear testing machine and cross-section cutting test bench for performance testing.

[0102] The cross-sectional section test method can obtain the actual macroscopic morphology at the cross-section. Specifically, the cross-sectional morphology of the melt nugget is magnified under a 60x microscope to obtain the macroscopic cross-section. Based on the comparison between the macroscopic cross-section and the digital model of the cross-section, it is quickly determined whether the morphology of the melt nugget meets the standard requirements. Among them, the main criteria are whether the melt nugget diameter is within the allowable range, whether the melting penetration rate is within the allowable range, and whether the maximum limit of core defects meets the requirements.

[0103] In this embodiment, the test welding steps generally include: identifying the test plate - determining the assembly sequence of the test plates - grabbing the test plate - spot welding the test plate - grabbing the welded test plate - three-point tear test - cross-section section test - outputting results.

[0104] In this embodiment, the step of resistance spot welding the bonded plates using a welding process includes: attaching and fixing a pad to the outer surface of the conductive silver base layer by at least one of the following methods: bonding, tooling, and fastener fixing; selecting a first electrode rod and a second electrode rod with different diameters; placing the first electrode rod and the second electrode rod on the outer side of the pad and the outer side of the remaining plates, respectively; setting the weld point spacing, weld point to edge distance, welding current, welding time, cooling time, number of pulses, holding time, and electrode pressure based on the thickness parameters of the thinner of the two outermost plates; and welding at least two plates using the first electrode rod and the second electrode rod with preset welding current, welding time, cooling time, number of pulses, holding time, and electrode pressure; wherein the diameter of the first electrode rod is smaller than the diameter of the second electrode rod.

[0105] By forming a conductive silver base layer on the outer side of the thinnest sheet, the resistivity of the thin sheet side can be increased to enhance nucleation ability, thereby improving the penetration rate of the thin sheet side. Using adhesives to bond the sheets before subsequent welding ensures excellent airtightness of the welded components, overcoming the engineering limitation of non-sealing spot welding on rail vehicle bodies. Adding backing plates reduces the heat dissipation rate on the thin sheet side during spot welding, further improving its penetration rate. Simultaneously, spot welding using first and second electrode rods of different diameters, with the smaller diameter first electrode rod positioned on the thin sheet side, further reduces heat dissipation, causing the weld nugget to shift towards the thin sheet side, thus improving its penetration rate. Through the synergistic effect of these multiple methods, not only is airtightness improved, but the penetration rate on the thin sheet side is also increased from 20% to 50%, significantly enhancing the penetration rate, resulting in more stable welding between sheets and improved product quality.

[0106] Select an electrode with a diameter of 8 mm and an end spherical radius of 200 mm as the first electrode rod, and select an electrode with a diameter of 16 mm and an end spherical radius of 200 mm as the second electrode rod. Place the first electrode rod and the second electrode rod on the outside of the pad and the outside of the remaining plates, respectively. Weld at least two plates using the first electrode rod and the second electrode rod with a preset current intensity, preset welding time, and preset cooling time.

[0107] Spot welding is performed using an 8mm first electrode rod and a 16mm second electrode rod, with the first electrode rod located on the thin plate side and the second electrode rod located on the thick plate side or a relatively thick plate side. This reduces the heat dissipation rate on the thin plate side, shifts the weld nugget towards the thin plate side, and improves the penetration rate on the thin plate side.

[0108] Based on the thickness of the outermost plate, the parameters for the solder joint spacing and the distance from the solder joint to the edge are set as follows:

[0109]

[0110] like Figure 6 and Figure 7 As shown, when the weld spacing is around 38mm, the diameter of the weld nugget and the maximum tensile shear force after welding are both reduced. Therefore, the spacing value in the range of 36-40mm is discarded when determining the weld spacing.

[0111] The tooling can be fixed by clamping fixtures, which clamp the pad and the plate at their edges to fix the pad in position. Fasteners can be clamping and locking devices, which also clamp the pad and the plate at their edges to fix the pad in position.

[0112] The thickness of the backing plate is 0.3-0.8mm. The specific thickness can be selected according to the aforementioned plate thickness parameters. Furthermore, the shape of the backing plate can be selected based on the shape characteristics of the spot welding area, such as a strip-shaped backing plate or a circular backing plate. The backing plate can be made of stainless steel or copper, and the material can be adjusted to suit the material of the sheet metal.

[0113] In this embodiment, the steps of real-time monitoring of welding quality during resistance spot welding and adjusting welding process parameters based on the monitored welding quality include:

[0114] Obtain the gap parameters between at least two plates before welding, and adjust the pre-pressure value before welding based on the comparison between the gap parameters and the gap threshold in the relational database.

[0115] The expansion volume parameters of the weld nugget at the weld point are obtained during the welding process. Based on the comparison between the expansion volume parameters and the weld nugget expansion threshold in the relational database, the welding parameters during the welding process are adjusted.

[0116] After welding, obtain the weld nugget quality parameters at the weld joint. Based on the comparison between the weld nugget quality parameters and the weld nugget quality threshold in the relational database, adjust the post-weld processing parameters.

[0117] A relational database is established based on welding process and welding quality. Welding process parameters for formal welding are determined based on data in this database and the results of experimental welding. Then, welding process parameters at each stage are adjusted in real-time based on pre-weld, during-weld, and post-weld monitoring data. Specifically, the pre-weld pre-pressure value is adjusted by comparing the gap parameters monitored in real-time before welding with the gap threshold, thereby ensuring that the gap between the plates meets welding quality requirements. During welding, various welding parameters are adjusted by comparing the weld nugget expansion volume monitored in real-time with the weld nugget expansion threshold to ensure that welding quality requirements are met. Finally, post-weld weld nugget quality parameters are compared with the weld nugget quality threshold to determine whether post-treatment parameters need adjustment to ensure that welding quality requirements are met.

[0118] Before welding, the gap between the plates can be adjusted according to the preload value. The gap between the plates has a crucial impact on the external spatter and internal weld nugget quality of spot welding. An excessively large gap can lead to surface defects such as spatter and deformation, as well as internal defects such as substandard or excessive weld nugget diameter. Adjusting the gap between the plates improves spot welding quality. Increasing the preload value can decrease the gap between at least two plates; conversely, decreasing the preload value can increase the gap between at least two plates.

[0119] During welding, welding parameters affect the quality of the weld nucleus, especially the expansion volume of the weld nucleus. The need for adjustment of welding parameters is determined based on this expansion volume. Specifically, the adjusted welding parameters include welding current, welding pressure, electrode pressure, welding time, cooling time, holding time, and pulse count.

[0120] After welding, the shape of the weld will be used to determine whether post-processing is needed and the specific method of post-processing.

[0121] In this embodiment, the step of establishing a database relating welding process and welding quality specifically includes:

[0122] Establish a database relating pre-welding pressure, gap threshold, and welding quality; establish a database relating welding parameters, weld nugget expansion threshold, and welding quality during welding; and establish a database relating post-welding processing parameters, weld nugget quality threshold, and welding quality after welding.

[0123] It is understandable that the relational database includes a pre-weld relational database formed by pre-pressure, gap threshold, and welding quality; an in-weld relational database formed by welding parameters, weld nugget expansion threshold, and welding quality; and a post-weld relational database formed by post-processing parameters, weld nugget quality threshold, and welding quality.

[0124] The preload value and the gap value are interrelated. When the preload value increases, the gap between at least two plates decreases; conversely, when the preload value decreases, the gap between at least two plates increases. For example, if the real-time monitored gap parameter is 50 mm and the gap threshold is within 30 mm, it indicates that the gap between the plates is too large, and the gap needs to be adjusted promptly to ensure subsequent welding quality. In this case, the preload is increased before welding to create greater pressure between at least two plates, compressing the gap and reducing it. Once the real-time monitored gap parameter is less than or equal to 30 mm, subsequent steps are performed while maintaining the current preload value.

[0125] The steps of obtaining the gap parameters between at least two plates before welding, and adjusting the pre-welding pressure value based on the comparison of the gap parameters with gap thresholds in a relational database, specifically include:

[0126] A laser is emitted from a first position towards at least two plates. The laser beams are reflected from the surfaces of the two plates, forming at least two reflected beams. At a second position, a photosensitive element receives each of the two reflected beams, which correspond to at least two photosensitive positions on the element. The gap between the two plates is calculated based on the distance between these photosensitive positions. If the gap value is less than or equal to a gap threshold in a relational database, no adjustment to the pre-welding pressure is required. If the gap value is greater than the gap threshold in the database, the pre-welding pressure is increased.

[0127] Taking two boards as an example, such as Figure 3 and Figure 4 As shown, the first plate 310 is first placed on the workbench, and then a laser is emitted by the laser emitting unit 330. After the laser is reflected from the surface of the first plate 310, the reflected light is received at the first photosensitive position 350 of the photosensitive element 340. At this time, the position of the first photosensitive position 350 is marked. Then, the second plate 320 is placed on the surface of the first plate 310, and the second plate 320 and the first plate 310 are brought into contact with a set pre-pressure value. The laser emitting unit 330 emits a laser again, and after the laser is reflected from the surface of the second plate 320, the reflected light is received at the second photosensitive position 360 of the photosensitive element 340. At this time, the position of the second photosensitive position 360 is marked. Based on the distance between the first photosensitive position 350 and the second photosensitive position 360, and after calculating the light reflection angle, the gap value between the first plate 310 and the second plate 320 is calculated. If the gap value is greater than the gap threshold, the pre-pressure value is increased and the above measurement is performed again until the gap value meets the gap threshold.

[0128] If the two plates are transparent welded components, the laser can pass through them. In this case, after placing the first plate 310 on the workbench, the second plate 320 is placed directly on top of the first plate 310, and a set pre-pressure value is applied to bring the second plate 320 and the first plate 310 into contact. A laser can be emitted through the laser emitting unit 330. After the laser is reflected from the surface of the first plate 310, the reflected light is received at the first photosensitive position 350 of the photosensitive element 340. The laser passes through the first plate 310 and is reflected at the position of the second plate 320. After being reflected from the surface of the second plate 320, the reflected light is received at the second photosensitive position 360 of the photosensitive element 340. The positions of the first photosensitive position 350 and the second photosensitive position 360 are recorded. Based on the distance between the first photosensitive position 350 and the second photosensitive position 360, and using the light reflection angle, the gap value between the first plate 310 and the second plate 320 is calculated. If the gap value is greater than the gap threshold, the pre-pressure value is increased, and the above measurement is performed again until the gap value meets the gap threshold.

[0129] The pre-pressure value before welding is adjusted based on the value of the gap parameter. When the pre-pressure value increases, the gap between at least two plates can be reduced; when the pre-pressure value decreases, the gap between at least two plates can be increased.

[0130] In one embodiment, when the real-time monitored gap parameter is 80mm and the gap threshold is within 40mm, it indicates that the gap between the plates is too large and needs to be adjusted promptly to ensure the subsequent welding quality. In this case, the pre-welding pressure is increased to compress the gap between at least two plates, thereby reducing the gap. Once the real-time monitored gap parameter is less than or equal to 40mm, subsequent steps are performed while maintaining the current pre-pressure value.

[0131] The process involves welding at least two plates using welding process parameters and adjusted preload values. During welding, the expansion volume parameters of the weld nugget at the weld joint are acquired. Based on a comparison of these expansion volume parameters with weld nugget expansion thresholds in a relational database, the welding process parameters are adjusted in real-time. This process specifically includes:

[0132] Welding is performed on at least two plates using welding process parameters and adjusted pre-pressure values. An expansion displacement sensor is added to the welding end of the welding mechanism to acquire the expansion volume parameter of the weld nugget at the weld joint in real time. Based on the comparison of the expansion volume parameter with the weld nugget expansion threshold in a relational database, it is determined whether to adjust the welding process parameters. If the expansion volume parameter is within the range of the weld nugget expansion threshold in the relational database, no adjustment of the welding parameters is required. If the expansion volume parameter is outside the range of the weld nugget expansion threshold in the relational database, at least one of the following parameters is adjusted based on the relational database: welding current, welding pressure, electrode pressure, welding time, cooling time, holding time, and pulse number.

[0133] Specifically, an expansion displacement sensor is added to the welding clamp to monitor the fusion expansion volume in real time. The detected expansion volume directly reflects the fusion expansion volume parameters. Based on real-time monitoring, the data monitored by the expansion displacement sensor is fed back to the terminal in real time. The terminal compares the fed-back expansion volume value with the fusion nugget expansion threshold in the terminal's relational database. After comparison and judgment, the result is fed back synchronously to issue an instruction on whether the welding parameters need to be adjusted.

[0134] It is understood that welding parameters include at least one of the following: welding current, welding pressure, electrode pressure, welding time, cooling time, holding time, and pulse number. During the welding process, the need to adjust the welding current, welding pressure, electrode pressure, welding time, cooling time, holding time, and pulse number is determined based on the real-time detected expansion volume parameter. For example, based on changes in the expansion volume parameter, the welding current, welding pressure, electrode pressure, welding time, cooling time, holding time, and pulse number can be increased.

[0135] In one embodiment, the pre-pressure can be set to 3 kN, the spot welding current can be set to 9 kA, the welding time can be set to 180 ms, the cooling time can be set to 30 ms, the number of pulses can be set to 2, the holding time can be set to 600 ms, and the electrode pressure can be set to 5.6 kN.

[0136] The steps for obtaining the weld nugget quality parameters at the weld joint after welding, and adjusting the post-processing parameters based on a comparison of these parameters with weld nugget quality thresholds in a relational database, specifically include:

[0137] A laser rangefinder scans each weld joint along the X and Y axes to form a rectangular scanning area. Height measurements are taken for all detection points within this area, and the X and Y axis values ​​are used to generate a 3D contour. Based on this contour, at least one parameter—the pit depth or the contour diameter—is calculated at the weld nugget. If the pit depth and contour diameter fall within the threshold ranges specified in the relational database, no post-processing is required. If they fall outside these threshold ranges, post-processing is performed on the weld.

[0138] After scanning each weld point along the X and Y axes, a rectangular scanning area of ​​the weld point on the horizontal plane is generated. Height measurement is then performed within this rectangular scanning area, i.e., scanning along the Z axis, thus generating a 3D contour of the weld point based on the coordinates of the X, Y, and Z axes. Based on the obtained 3D contour, at least one parameter, either the pit depth or the contour diameter, at the weld nugget can be directly calculated. The quality of the weld nugget is then judged based on at least one of these parameters.

[0139] The X-axis can be the length of the welding platform, the Y-axis can be the width of the welding platform, and the Z-axis can be the height of the welding platform.

[0140] The steps of obtaining the weld nugget quality parameters at the weld joint after welding, and adjusting the post-weld processing parameters based on the comparison of the weld nugget quality parameters with the weld nugget quality threshold in the relational database, specifically include:

[0141] An ultrasonic scanning device is used to perform ultrasonic scanning along the weld area. Based on the results of the ultrasonic scanning, at least one parameter, either the weld nugget diameter or a quality defect, is calculated. If the weld nugget diameter or quality defect falls within the range of the weld nugget diameter threshold and quality defect threshold in the relational database, no post-processing is required. If the weld nugget diameter or quality defect falls outside the range of the weld nugget diameter threshold and quality defect threshold in the relational database, post-processing is performed on the weld.

[0142] The location of the weld nugget is directly displayed by ultrasonic scanning, thereby calculating at least one parameter, such as the weld nugget diameter or quality defect, to determine the quality of the weld nugget.

[0143] Ultrasonic scanning uses a robot to hold an ultrasonic C-scan probe to scan each weld point. The scanning trajectory is spirally distributed along the weld point area. Based on the results of the ultrasonic scanning, internal quality information such as weld nugget diameter and quality defects is extracted, and the internal quality of the weld point is judged to be qualified based on comparison.

[0144] The steps of obtaining the weld nugget quality parameters at the weld joint after welding, and adjusting the post-weld processing parameters based on the comparison of the weld nugget quality parameters with the weld nugget quality threshold in the relational database, specifically include:

[0145] A gantry crane is positioned along the welding platform. A light pen measuring instrument and a laser tracker (specifically a Leica laser tracker) are mounted on the gantry crane. A dimensional coordinate system is constructed based on the sheet metal. The movement of the gantry crane drives the light pen measuring instrument and laser tracker to measure each weld point. The measurement results, combined with the dimensional coordinate system, can generate at least one parameter from the large span dimension and geometrical tolerance (GMP) for each weld point. If the large span dimension and GMP are within the range of the large span dimension threshold and GMP threshold in the relational database, no post-processing is required. If the large span dimension and GMP are outside the range of the large span dimension threshold and GMP threshold in the relational database, post-processing is performed on the weld.

[0146] A gantry crane, also known as a portal crane, has its guide rails arranged along the length of the welding platform, ensuring that the guide rails are aligned with the welding direction. The gantry crane spans the width of the welding platform, and as it slides along the guide rails, it drives a light pen measuring instrument and a laser tracker to sequentially monitor each weld point in real time along the welding direction. By combining this with the sheet metal component's dimensional coordinate system, all the large dimensions of the sheet metal are unified into a single coordinate system. Based on the characteristics of the detection results for different weld points, large-span dimensions and geometric tolerances such as length, width, height, deflection, diagonal, and flatness are generated. By comparing these large-span dimensions and geometric tolerances with their respective threshold values, it is determined whether post-processing is required.

[0147] Using laser measurement can achieve a measurement accuracy of 0.15mm, shorten the inspection time for a single vehicle body to 1.5 hours, and improve inspection efficiency by more than 30%.

[0148] In this embodiment, the quality of the melt core is reflected based on the generated three-dimensional contour, the results of ultrasonic scanning, and laser measurement. The quality of the melt core is reflected from three aspects to facilitate comprehensive judgment.

[0149] In this embodiment, the step of surface treatment of the weld joints on the surface of the welded board includes: electrolytically removing marks from the weld joints on the board surface; performing overall passivation on the board surface based on the board that passes the electrolytic mark removal; and cleaning the board surface to remove the electrolytic mark removal solution and electrolytic passivation solution adhering to the board surface.

[0150] In this embodiment, electrolytic de-marking eliminates the surface oxidation color of the weld points on the sheet metal surface after resistance spot welding. A passivation step eliminates the color difference between the de-marked weld points and the sheet metal surface, improving the corrosion resistance of the sheet metal in the weld area and maintaining the uniformity and consistency of the sheet metal, ensuring commercial viability. A cleaning step removes residual electrolytic de-marking and passivation solutions from the sheet metal surface, ensuring its cleanliness. This method allows for the rapid and convenient elimination of oxidation color and color difference, as well as improved corrosion resistance, after spot welding of the sheet metal. It not only ensures the quality of surface treatment but also enhances its efficiency.

[0151] Electrolytic demarking and overall passivation are both based on electrochemical principles. A drive unit assembles demarking brush heads and passivation brush heads to form the electrolytic devices for the demarking stage and the overall passivation stage, respectively. After eliminating the oxidation color on the weld surface following resistance spot welding, the demarking process eliminates the color difference between the weld and the sidewall base material surface, and improves the corrosion resistance of the sidewall weld area. This ensures a uniform and consistent commercial appearance for exposed parts of unpainted stainless steel vehicles. Vehicles are delivered in the correct condition after cleaning.

[0152] The steps for electrolytically removing weld marks from the surface of the sheet metal include:

[0153] The descratching program is selected based on the degree of oxidation at the solder joints on the board surface. The drive unit grasps the descratching brush head and introduces electrolytic descratching liquid into the brush head. Based on the descratching program, the drive unit drives the descratching brush head to grind the solder joints and surrounding areas on the board surface until the board surface produces a metallic luster.

[0154] Understandably, the electrolytic resurfacing process is considered successful once a metallic luster is achieved on the board surface. Electrolytic resurfacing should be stopped once this luster is achieved to avoid prolonged grinding, which could lead to white spots on the solder joints and negatively impact the resurfacing effect.

[0155] The steps for selecting a descaling procedure based on the degree of oxidation at the solder joints on the board surface include:

[0156] The oxidation level of the solder joints on the board surface is divided into three categories: light oxidation around the solder joint, moderate oxidation around the solder joint, and heavy oxidation of the entire solder joint. Based on the light oxidation around the solder joint, the scratch-removing brush head grinds the solder joint and surrounding area on the board surface at a first grinding power. Based on the moderate oxidation around the solder joint, the scratch-removing brush head grinds the solder joint and surrounding area on the board surface at a second grinding power. Based on the heavy oxidation of the entire solder joint, the scratch-removing brush head grinds the solder joint and surrounding area on the board surface at a third grinding power. The first grinding power is lower than the second grinding power, and the second grinding power is lower than the third grinding power. The first grinding power is 220 watts (W), the second grinding power is 500 watts, and the third grinding power is 750 watts. The electrolytic scratch-removing solution includes a 10% sodium gluconate solution, making the surface treatment process environmentally friendly and eliminating the need for waste liquid recycling.

[0157] The process of using a descratching procedure to drive a descratching brush head to grind the solder joints and surrounding areas on the board surface until a metallic luster is achieved includes:

[0158] Based on the descratching process, the drive unit drives the descratching brush head to grind the solder joints on the board surface and the area surrounding the solder joints within a 6 mm radius of the solder joint edge. After the electrolytic descratching solution in the descratching brush head reacts with the solder joint surface, the drive unit drives the descratching brush head to grind the solder joints on the board surface. After the solder joints produce a metallic luster, the drive unit drives the descratching brush head to perform multi-stage circular motions around the solder joint as the center and grind the area surrounding the solder joint on the board surface. In the direction from the solder joint to the area surrounding the solder joint, the radius of each stage of circular motion gradually increases, and the rotation direction of each stage of circular motion is the same.

[0159] like Figure 8 The diagram shows the path of the multi-stage circular motion. The solder joint and the 6m annular area around the edge of the solder joint are all subjected to de-marking grinding to ensure the thoroughness of electrolytic de-marking and to completely remove the oxide color from the solder joint and the surrounding area.

[0160] The de-marking brush head first moves to the solder joint to perform electrolytic de-marking. After the electrolytic de-marking at the solder joint is satisfactory, the brush head is driven to make a circular motion with a radius of R1 around the solder joint. When the electrolytic de-marking at the corresponding position in this area is satisfactory, the brush head is driven to make a circular motion with a radius of R2 around the solder joint, where R2 is greater than R1. This gradually increases the radius of the circular motion, gradually completing the electrolytic de-marking of the solder joint and a 6 mm annular area around its edge. Each level of circular motion corresponds to a specific radius value. For example, a circular motion with a radius of R1 can be defined as the first level, a circular motion with a radius of R2 as the second level, a circular motion with a radius of R3 as the third level, and so on. The drive unit drives the brush head to perform multiple levels of circular motions and uses the brush head to grind the area around the solder joint on the surface of the board. The same direction of rotation in each stage of the circular motion ensures that the shape of the exposed substrate after the oxide layer at each location is roughly the same, thus ensuring aesthetics.

[0161] The steps for passivating the entire surface of the sheet metal include:

[0162] The passivation path is set based on the shape of the plate and the position of the solder joints. The drive unit grabs the passivation brush head and introduces the electrolytic passivation solution into the passivation brush head. After the electrolytic passivation solution of the passivation brush head reacts with the plate surface, the passivation brush head performs overall passivation on the plate surface along the passivation path at a preset passivation speed and preset passivation power. The passivation brush head stays at each solder joint for a preset passivation time.

[0163] In this embodiment, the preset passivation speed is 1 meter per minute (m / min), the preset passivation power is 500 watts, and the preset passivation time is 30 seconds (s). The electrolytic passivation solution includes an 8% citric acid solution. The drive unit drives the passivation brush head to move along the passivation path at a speed of 1 meter per minute, stopping at each solder joint for 30 seconds. After passivation along the passivation path is completed, the drive unit drives the passivation brush head to automatically return to its original position at an idle speed. Using an 8% citric acid solution as the electrolytic passivation solution makes the surface treatment process green and environmentally friendly, eliminating the need for waste liquid recycling.

[0164] like Figure 9 As shown, the passivation path consists of multiple sequentially connected U-shaped paths, and the passivation path passes through every solder joint on the surface of the board. The lines and arrows indicate the passivation path and direction. The drive unit drives the passivation brush head along this path to passivate the entire surface of the board, ensuring that every location can be passivated by the electrolytic passivation solution.

[0165] The steps of cleaning the surface of the board to remove the electrolytic trace removal solution and electrolytic passivation solution adhering to the surface of the board include: cleaning the surface of the board by spraying to rinse away the electrolytic trace removal solution and electrolytic passivation solution adhering to the surface of the board.

[0166] Taking the side wall of a rail vehicle as an example, the entire vehicle can be sprayed and cleaned after the side wall is assembled, so that the aforementioned electrolytic demarking and overall passivation can share a single cleaning system and process. This not only reduces the number of cleaning units but also shortens the cleaning process and reduces the time required for surface treatment.

[0167] On the other hand, such as Figure 2 As shown, the present invention also provides a resistance spot welding system, including a central control unit, a selection unit, a coating unit, an adhesive application unit, an assembly unit, a test welding unit, a formal welding unit, a monitoring and adjustment unit, and a surface treatment unit. The selection unit is electrically connected to the central control unit and is used to select at least two plates with a thickness difference. The coating unit is electrically connected to the central control unit and is used to form a conductive silver base layer on one side of the thinnest plate. The adhesive application unit is electrically connected to the central control unit and is used to move the thinnest plate to the adhesive application area and apply adhesive to the other side of the thinnest plate according to a preset adhesive application program. The assembly unit is electrically connected to the central control unit and is used to move the adhesive-coated plate to the assembly area and bond it to the remaining plates. The test welding unit is electrically connected to the central control unit and is used to select a test plate compatible with the plates, perform test welding on the test plate, and generate welding process parameters for formal welding based on the welding results. The formal welding unit is electrically connected to the central control unit and is used to perform resistance spot welding on the bonded plates using a welding process. The monitoring and adjustment unit is electrically connected to the central control unit and is used to monitor the welding quality in real time during resistance spot welding, and adjust the welding process parameters based on the monitored welding quality. The surface treatment unit is electrically connected to the central control unit and is used to perform surface treatment on the weld points on the surface of the welded plate.

[0168] In this embodiment, the resistivity of the thin plate side can be increased by arranging the conductive silver base layer to improve the nucleation ability, thereby improving the melting penetration rate of the thin plate side. The method of bonding first and then spot welding makes the welded plate have good airtightness, which overcomes the engineering limitation of spot welding of rail vehicle body that is not sealed. The welding process parameters are adjusted in real time during the welding process to ensure the quality after welding. After welding, the surface is treated so that the plate can meet the usage requirements.

[0169] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A resistance spot welding method, characterized in that, Includes the following steps: Select at least two plates with a thickness difference, and form a conductive silver base layer on one side of the thinnest plate. Move the thinnest sheet to the glue application area and apply adhesive to the other side of the thinnest sheet using a preset glue application program. Move the glued boards to the assembly area and bond them with the remaining boards. Select a test plate that matches the plate material, perform test welding on the test plate, and generate welding process parameters for formal welding based on the welding results. Use the welding process to perform resistance spot welding on the bonded plate material, and monitor the welding quality in real time during the resistance spot welding process. Adjust the welding process parameters based on the monitored welding quality. Perform surface treatment on the weld points on the surface of the welded plates; The steps of selecting a test plate suitable for the plate material, performing test welding on the test plate, and generating welding process parameters for formal welding based on the welding results include: Establish a database of the relationship between welding process and welding quality. Use an identification component to identify a test plate that matches the plate material. Use a gripping component to grip the corresponding test plate onto the welding platform. Based on the welding process in the database, perform test welding on the test plate on the welding platform. After the test welding is completed, perform performance testing. If the performance test is passed, the current welding process parameters will be used as the welding process parameters for the formal welding. If the performance test fails, the current welding process parameters are adjusted and the trial welding is continued until the performance test passes and the welding process parameters for formal welding are output. The performance test steps include: spot welding three solder joints consecutively on at least three test plates, tearing the last solder joint on each test plate, and measuring the diameter of the weld nugget after tearing; The performance testing steps also include: cutting the solder joint along the X-axis and Y-axis at the solder joint of the test board to obtain the molten core morphology cross-section inside the solder joint of the test board, enlarging the molten core morphology cross-section several times to generate a macroscopic cross-section, and comparing the macroscopic cross-section with the cross-section digital model.

2. The resistance spot welding method according to claim 1, characterized in that, The step of selecting at least two plates with a thickness difference and forming a conductive silver substrate on one side of the thinnest plate includes: Two plates with a thickness difference are selected, namely a thin plate and a thick plate. A conductive silver-based material is coated on the outer surface of the thin plate to form a conductive silver base layer with a thickness of 10-20 micrometers. The thick plate is then attached to the side of the thin plate away from the conductive silver base layer. Wherein, the thickness of the thin plate is t1, and the thickness of the thick plate is t2; Among them, 2t1>t2>t1, and the thickness of the pad on the outer surface of the conductive silver base layer is 0.3 mm; Alternatively, t2 > 3t1, and the thickness of the pad is 0.5 mm.

3. The resistance spot welding method according to claim 1, characterized in that, The step of selecting at least two plates with a thickness difference and forming a conductive silver substrate on one side of the thinnest plate includes: Three plates with different thicknesses are selected, namely a thin plate, a relatively thick plate, and a thick plate. A conductive silver-based material is coated on the outer surface of the thin plate to form a conductive silver base layer with a thickness of 10-20 micrometers. The thick plate and the relatively thick plate are attached to the side of the thin plate away from the conductive silver base layer. Wherein, the thickness of the thin plate is t3, the thickness of the thicker plate is t4, and the thickness of the thickest plate is t5; Among them, t5 > t4 > t3, and t5 > 3t3, and the thickness of the pad on the outer surface of the conductive silver base layer is 0.8 mm.

4. The resistance spot welding method according to claim 1, characterized in that, The step of moving the thinnest sheet to the adhesive application area and applying adhesive to the other side of the thinnest sheet using a preset adhesive application program includes: An adhesive application procedure is established based on the assembly logic between the boards. The thinnest board is picked up and placed in the adhesive loading area. The position of the board in the adhesive loading area is identified and moved to a preset point in the adhesive loading area. The corresponding adhesive application unit is selected based on the adhesive application procedure. The adhesive seam of the board located at the preset point is identified by the identification unit mounted on the adhesive application unit. The adhesive application unit is used to apply adhesive to the other side of the thinnest board along the adhesive seam according to the adhesive application procedure.

5. The resistance spot welding method according to claim 1, characterized in that, The step of moving the glued board to the assembly area and bonding it with the remaining boards includes: The identification unit identifies the boards coated with adhesive. An assembly robot picks up the boards and moves them to the assembly area. The remaining boards picked up by the assembly robot are then attached to the boards coated with adhesive. A flexible clamping unit is used to clamp at least two boards together. The assembly robot then picks up a scraper and uses the scraper to remove the adhesive that has overflowed from the edges of at least two boards.

6. The resistance spot welding method according to claim 1, characterized in that, The step of resistance spot welding the bonded plates using the aforementioned welding process includes: A pad is attached and fixed to the outer surface of the conductive silver base layer by at least one of the following methods: bonding, tooling, and fastener fixing. A first electrode rod and a second electrode rod with different diameters are selected and placed on the outer side of the pad and the outer side of the remaining plates, respectively. Based on the thickness parameters of the thinner of the two outermost plates, the solder joint spacing, the distance from the solder joint to the edge, the welding current, the welding time, the cooling time, the number of pulses, the holding time, and the electrode pressure are set. At least two plates are welded using the first electrode rod and the second electrode rod with the preset welding current, welding time, cooling time, number of pulses, holding time, and electrode pressure. The diameter of the first electrode rod is smaller than the diameter of the second electrode rod.

7. The resistance spot welding method according to claim 1, characterized in that, The steps of real-time monitoring of welding quality during resistance spot welding and adjusting welding process parameters based on the monitored welding quality include: Establish a database on the relationship between welding processes and welding quality; Obtain the gap parameters between at least two plates before welding, and adjust the pre-pressure value before welding based on the comparison between the gap parameters and the gap threshold in the relational database; The expansion volume parameters of the weld nugget at the weld point are obtained during the welding process. Based on the comparison between the expansion volume parameters and the weld nugget expansion threshold in the relational database, the welding parameters during the welding process are adjusted. After welding, the quality parameters of the weld nugget at the weld point are obtained. Based on the comparison between the quality parameters and the quality threshold of the weld nugget in the relational database, the post-processing parameters are adjusted.

8. The resistance spot welding method according to any one of claims 1-7, characterized in that, The step of surface treatment of the weld points on the surface of the welded plate includes: Electrolytic removal of solder joints on the surface of the sheet metal; Based on the qualified electrolytic descraping of the sheet metal, the surface of the sheet metal is passivated as a whole; Clean the surface of the board to remove the electrolytic scratch remover and electrolytic passivation solution adhering to the surface.

9. A resistance spot welding system, characterized in that, include: Central control unit The selection unit, electrically connected to the central control unit, is used to select at least two plates with a thickness difference. The coating unit, electrically connected to the central control unit, is used to form a conductive silver base layer on one side of the thinnest sheet material. The glue application unit is electrically connected to the central control unit and is used to move the thinnest sheet to the glue application and feeding area and apply adhesive to the other side of the thinnest sheet according to a preset glue application program. The assembly unit, which is electrically connected to the central control unit, is used to move the glued board to the assembly area and bond it with the other boards. The test welding unit is electrically connected to the central control unit and is used to select a test plate that is compatible with the plate material, perform test welding on the test plate, and generate welding process parameters for formal welding based on the welding results. The formal welding unit is electrically connected to the central control unit and is used to perform resistance spot welding on the bonded plates using the welding process. The monitoring and adjustment unit is electrically connected to the central control unit and is used to monitor the welding quality in real time during the resistance spot welding process and adjust the welding process parameters based on the monitored welding quality. A surface treatment unit, electrically connected to the central control unit, is used to perform surface treatment on the weld points on the surface of the welded plate. The steps of selecting a test plate suitable for the plate material, performing test welding on the test plate, and generating welding process parameters for formal welding based on the welding results include: Establish a database of the relationship between welding process and welding quality. Use an identification component to identify a test plate that matches the plate material. Use a gripping component to grip the corresponding test plate onto the welding platform. Based on the welding process in the database, perform test welding on the test plate on the welding platform. After the test welding is completed, perform performance testing. If the performance test is passed, the current welding process parameters will be used as the welding process parameters for the formal welding. If the performance test fails, the current welding process parameters are adjusted and the trial welding is continued until the performance test passes and the welding process parameters for formal welding are output. The performance test steps include: spot welding three solder joints consecutively on at least three test plates, tearing the last solder joint on each test plate, and measuring the diameter of the weld nugget after tearing; The performance testing steps also include: cutting the solder joint along the X-axis and Y-axis at the solder joint of the test board to obtain the molten core morphology cross-section inside the solder joint of the test board, enlarging the molten core morphology cross-section several times to generate a macroscopic cross-section, and comparing the macroscopic cross-section with the cross-section digital model.

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