Laser-resistance seam welding method and system for galvanized sheet for battery trays

Abstract

This invention provides a laser-resistance seam welding composite welding method and system for galvanized steel sheets used in battery trays, relating to the field of welding technology for galvanized ultra-high-strength steel. The laser-resistance seam welding composite welding method for galvanized steel sheets used in battery trays includes the following steps: galvanized steel sheets are roll-formed into a H-shaped cross-section structure using filler wire welding, with the interior of the H-shaped cross-section structure consisting of lap joints connected in an overlapping manner; the lap joints are subjected to laser penetration welding, with the welding spot employing a combination structure of four laser spots and annular laser spots, wherein the diameter of each individual laser spot in the four laser spots is 0.6 mm to 1 mm, and the four laser spots form a circular area with a diameter of 2 mm to 3 mm; the annular spot is used to preheat the surface of the lap joint; and a resistance seam welding machine equipped with a three-phase DC inverter power supply is used to simultaneously roll and heat the weld bead after laser penetration welding, with the surface temperature of the weld bead controlled within the range of 280 ℃ to 300 ℃.

Description

Technical Field

[0001] This invention relates to the field of welding technology for galvanized ultra-high strength steel, and more specifically, to a laser-resistance seam welding composite welding method and system for galvanized sheets used in battery trays. Background Technology

[0002] As a key load-bearing structure for battery packs in new energy vehicles, battery trays are increasingly demanding in terms of lightweighting and high strength. The mainstream technical approach has been to roll-form 1500MPa grade martensitic ultra-high strength steel into H-shaped or rectangular profiles, and then weld them to form the tray frame. However, this material faces significant challenges during welding. The galvanized layer on the material surface vaporizes during laser welding, generating high-pressure zinc vapor, which easily causes spatter and forms micropores. These pores become stress concentration points, significantly reducing the fatigue life of the joint. Simultaneously, the roll-forming process requires welding speeds as high as 5 m / min to 15 m / min, resulting in extremely rapid solidification of the molten pool. 1500MPa grade martensitic steel has a high hardening tendency, and rapid cooling easily forms a hardened martensitic structure. Residual stress cannot be released in time, leading to the formation of microcracks after laser welding. These cracks will propagate delayedly under stress, causing delayed fracture of the welded joint. Summary of the Invention

[0003] The present invention aims to solve the problem that 1500MPa grade martensitic steel is prone to forming hardened martensite structure, which leads to the inability to release residual stress in time, resulting in micro-cracks after laser welding.

[0004] To address the aforementioned problems, this invention provides a laser-resistance seam welding composite welding method and system for galvanized sheets used in battery trays.

[0005] In a first aspect, the present invention provides a laser-resistance seam welding composite welding method for galvanized sheets used in battery trays, comprising the following steps: S1: The galvanized sheet is roll-formed into a H-shaped cross-section structure by welding without filler wire. The inside of the H-shaped cross-section structure is an overlapping joint connected in an overlapping manner. S2: Laser penetration welding is performed on the lap joint. The welding spot adopts a combination structure of four spots and ring spots. The diameter of each laser spot in the four spots is 0.6 mm to 1 mm, and the four laser spots form a circular area with a diameter of 2 mm to 3 mm. The ring spot is used to preheat the surface of the lap joint. S3: Using a resistance seam welding machine equipped with a three-phase DC inverter power supply, the weld bead after laser penetration welding is simultaneously rolled and heated, and the surface temperature of the weld bead is controlled within the range of 280 ℃ to 300 ℃.

[0006] Optionally, in S1, fillerless welding is performed at a speed of 5 m / min to 8 m / min, and the lap gap of the lap joint is ≤0.1 mm.

[0007] Optionally, in S2, the laser welding power for laser penetration welding is 11,500 W to 12,500 W.

[0008] Optionally, in S2, the combined power of the four spots and the ring spot accounts for 20% to 40% of the power of the ring spot.

[0009] Optionally, in S2, the welding speed of laser penetration welding is from 5 m / min to 15 m / min.

[0010] Optionally, in S2, the resistance seam welding machine is located 450 mm to 550 mm behind the laser welding station, the power of the resistance seam welding machine is 460 KVA to 500 KVA, and the heating width of the resistance seam welding machine is 5 mm to 6 mm.

[0011] Optionally, in S3, the weld surface temperature is controlled within the range of 280 ℃ to 300 ℃, specifically including the following steps: S31: Collect the surface temperature signal of the heated area of ​​the weld and transmit the surface temperature signal to the PID controller; S32: The PID controller filters and amplifies the surface temperature signal to calculate the deviation between the actual temperature and the target temperature. S33: The PID controller sends control commands to the resistance seam welding machine equipped with a three-phase DC inverter power supply based on the deviation value, changes the output current frequency of the resistance seam welding machine, realizes the dynamic adjustment of the welding power of the resistance seam welding machine, and controls the surface temperature of the weld bead within the range of 280 ℃ to 300 ℃.

[0012] Optionally, in S31, the sampling frequency for the surface temperature signal of the heated area of ​​the weld bead is 10 Hz.

[0013] In a second aspect, the present invention provides a laser-resistance seam welding composite welding system for galvanized sheets used in battery trays, for operating the laser-resistance seam welding composite welding method for galvanized sheets used in battery trays as described above, comprising: The laser welding device features a composite welding head with four laser spots plus a ring spot, used for wire-free welding and laser-penetrating welding of galvanized sheets; and The resistance seam welding machine is equipped with a three-phase DC inverter power supply, which is used to simultaneously roll and heat the weld after laser penetration welding, so that the surface temperature of the weld is controlled within the range of 280 ℃ to 300 ℃.

[0014] Optionally, it also includes: The temperature detection unit is used to collect the surface temperature signal of the heated area of ​​the weld bead. The PID controller receives the surface temperature signal, filters and amplifies it, calculates the deviation between the actual temperature and the target temperature, and sends a control command to the resistance seam welding machine based on the deviation to change the output current frequency of the resistance seam welding machine.

[0015] The beneficial effects of the laser-resistance seam welding composite welding method and system for galvanized steel sheets used in battery trays of the present invention are as follows: By combining laser welding first with resistance seam welding later, the challenges faced by 1500MPa grade martensitic ultra-high strength galvanized steel sheets in high-speed roll forming welding are effectively solved. Preheating with annular laser spots suppresses spatter and porosity caused by galvanized layer vaporization, reducing porosity by 92%; the circular area of ​​the four laser spots expands the weld width. Controlling the surface heating temperature of the weld bead between 280℃ and 300℃ effectively eliminates residual stress without causing excessive oxidation of the galvanized layer or overheating of the base material, avoiding galvanized layer volatilization and deterioration of sheet performance. Simultaneously, the synchronous rolling action of the resistance seam welding after laser welding eliminates residual stress within a specific temperature range, repairing and eliminating micro-cracks generated by laser welding, reducing the delayed crack incidence rate from 30% to below 0.5%, thus preventing delayed cracks. Due to the significant reduction in crack rework rate, overall energy consumption is reduced by 18%, optimizing energy efficiency. This method ensures that the welding speed matches the roll forming production line, while achieving a tensile strength of over 98% of the base material after composite welding, increasing fatigue life by 4 times, improving the strength and toughness of the welded joint, and maintaining the performance of the galvanized layer and the base material. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of the laser-resistance seam welding composite welding method for galvanized sheet used in battery trays according to the present invention. Figure 2 Metallographic image of the battery tray longitudinal beam product prepared in Example 1; Figure 3 Metallographic image of the battery tray longitudinal beam product prepared for Comparative Example 1; Figure 4 This is an internal view of the product in Example 1; Figure 5 This is a view of the outer side of the product in Example 1; Figure 6 This is a view of the battery tray longitudinal beam product after it has been crushed, as shown in Example 1. Figure 7 This is a view of the battery tray longitudinal beam product after it has been crushed, as shown in Comparative Example 1. Detailed Implementation

[0017] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0018] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this invention's description is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "comprising" and its variations as used herein are open-ended inclusion, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the description below.

[0019] In related technologies, traditional laser welding, even with techniques like four-spot or ring-spot welding, can suppress spatter to some extent, but it cannot solve the problems of hardened structure and residual stress caused by rapid cooling of the molten pool. Single resistance seam welding, on the other hand, cannot match the high-speed requirements of roll forming production lines and struggles to guarantee penetration depth and appearance quality. Existing composite welding processes mostly follow a sequence of resistance welding followed by laser welding to fix the workpiece and eliminate gaps. They do not address the process design of using resistance seam welding after laser welding for roll forming and heating to eliminate cracks, and lack precise control methods for resistance heating temperature. If the heating temperature is too high, it can lead to galvanization, coarse grains in the sheet metal, and reduced material strength; if the temperature is too low, crack repair and weld strengthening cannot be achieved. Therefore, there is an urgent need to develop a composite welding process that is compatible with high-speed roll forming production lines, can effectively eliminate welding cracks and delayed fracture risks, and can precisely control the heating temperature.

[0020] To address the problems existing in the aforementioned related technologies, embodiments of the present invention provide a laser-resistance seam welding composite welding method and system for galvanized sheets used in battery trays.

[0021] like Figure 1 As shown, an embodiment of the present invention provides a laser-resistance seam welding composite welding method for galvanized steel sheets used in battery trays, comprising the following steps: S1: The galvanized sheet is roll-formed into a H-shaped cross-section structure by welding without filler wire. The inside of the H-shaped cross-section structure is an overlapping joint connected in an overlapping manner. S2: Laser penetration welding is performed on the lap joint. The welding spot adopts a combined structure of four spots and a ring spot. Among them, the diameter of a single laser spot of the four spots is 0.6 mm to 1 mm, and the four laser spots of the four spots form a circular area with a diameter of 2 mm to 3 mm; the ring spot is used to preheat the surface of the lap joint. S3: Use a resistance seam welding machine equipped with a three-phase DC inverter power supply to perform synchronous rolling and heating treatment on the weld bead after laser penetration welding. The surface temperature of the weld bead is controlled within the range of 280 °C to 300 °C.

[0022] Specifically, the galvanized sheet refers to a steel profile with a zinc layer on its surface, and its zinc layer is mainly used to provide anti-corrosion protection. During the welding process, the zinc layer may be vaporized due to high temperature.

[0023] Non-fill wire welding is a welding method that does not add additional welding wire, mainly relying on the melting and solidification of the base material itself to form a weld seam.

[0024] The H-shaped cross-section structure is a profile cross-section with a specific geometric shape, and it usually contains multiple connection areas inside.

[0025] A lap joint refers to a joint form formed by partial overlap and connection of two or more sheets, which is a common welding structure.

[0026] Laser penetration welding is a welding technology that uses a high-energy density laser beam to melt and penetrate the workpiece for connection. Its characteristics are fast welding speed and concentrated heat input.

[0027] Four spots refer to a welding spot structure composed of four independent laser spots, usually used to expand the molten pool size or improve the heat distribution.

[0028] The ring spot refers to a laser spot distributed in a ring shape, often used to preheat the welding area or assist in melting.

[0029] A resistance seam welding machine refers to a device that applies pressure to the workpiece through electrode wheels and conducts electricity, and uses the resistance heat effect to locally melt the workpiece and form a continuous weld seam.

[0030] A three-phase DC inverter power supply refers to a power supply device that converts alternating current into direct current and realizes precise control of current and voltage through inverter technology. It is often used in resistance welding equipment to provide stable welding energy.

[0031] A weld bead refers to the fusion area formed on the surface of the workpiece after welding, which is the entity connecting two parts of the workpiece.

[0032] Synchronous rolling and heating treatment refers to a composite process that applies mechanical pressure and conducts heat treatment to the weld bead during or immediately after welding to improve the weld structure and performance.

[0033] In this embodiment, the combined application of laser welding followed by resistance seam welding effectively solves the challenges faced by 1500MPa grade martensitic ultra-high strength galvanized sheets in high-speed roll forming welding. Preheating with a ring-shaped laser spot suppresses spatter and porosity caused by galvanized layer vaporization, reducing porosity by 92%; the circular area of ​​the four laser spots expands the weld width. Controlling the surface heating temperature of the weld bead between 280℃ and 300℃ effectively eliminates residual stress without causing excessive oxidation of the galvanized layer or overheating of the base material, thus preventing galvanized layer volatilization and deterioration of sheet performance. Simultaneously, the simultaneous rolling action of the resistance seam welding after laser welding eliminates residual stress within a specific temperature range, repairing microcracks generated by laser welding. The delayed crack incidence rate is reduced from 30% to below 0.5%, preventing delayed cracking. Due to the significant reduction in crack rework rate, overall energy consumption is reduced by 18%, optimizing energy efficiency. This method ensures that the welding speed matches the roll forming production line, while achieving a tensile strength of over 98% of the base material after composite welding, increasing fatigue life by 4 times, improving the strength and toughness of the welded joint, and maintaining the performance of the galvanized layer and the base material.

[0034] In some specific embodiments, 1500MPa grade martensitic ultra-high strength galvanized steel sheet is used as raw material. The sheet thickness is 1.6mm, and the galvanized layer specification is Zn 50 / 50 (i.e., the thickness of the galvanized layer on both sides is 50g / m). 2 ).

[0035] In step S1, roll forming can employ a multi-pass cold bending process, gradually bending the flat galvanized material into a pre-set H-shaped cross-section through the continuous action of a series of rollers. Wire-free welding can be performed simultaneously during roll forming, for example, by induction heating or friction stirring to achieve localized material bonding. Lap joints can utilize different lap lengths or lap methods to adapt to varying structural strength requirements.

[0036] In step S2, the laser can output a composite beam, which is shaped into a combination of four-spot and ring-spot beams by an optical system. The four-spot beams provide the main welding energy to achieve material penetration. The ring-spot beams, on the other hand, locally heat the material surface before the main welding area to change the thermal state of the material surface.

[0037] In step S3, the resistance seam welding machine can be equipped with a pair of electrode wheels that roll above and below the weld bead while applying pressure and electricity. As current flows through the weld bead, Joule heating is generated using the material's own resistance, thus heating the weld bead. The rolling action is provided by the mechanical pressure of the electrode wheels. Temperature control can be achieved by adjusting the output current or voltage of the resistance seam welding machine; for example, the operator can manually adjust the power parameters based on experience to bring the weld bead surface to the target temperature range.

[0038] Optionally, in S1, fillerless welding is performed at a speed of 5 m / min to 8 m / min, and the lap gap of the lap joint is ≤0.1 mm.

[0039] Specifically, the welding speed without filler wire is controlled within the range of 5 m / min to 8 m / min to ensure a dynamic balance between stable material transport and welding heat input during roll forming. For example, the linear speed of the roll forming equipment can be precisely controlled and linked to the output parameters of the welding power source (such as current and voltage) to ensure that the heat input during welding matches the material movement speed within the set speed range, thus forming a stable molten pool. Alternatively, advanced sensor technology can be used to monitor the roll forming speed in real time, and a feedback control system can automatically adjust the operating speed of the welding equipment to maintain it within the optimized range of 5 m / min to 8 m / min, adapting to any minor fluctuations that may occur on the production line.

[0040] Meanwhile, the lap gap of the joint is strictly controlled to ≤0.1mm. For example, during roll forming, precise design of the roller mold and accurate control of the roll forming pressure can ensure that the edges of the sheet material in the lap area are tightly fitted after forming, thereby controlling the lap gap to below 0.1mm. Alternatively, an online gap measurement system, such as a laser displacement sensor, can be used to monitor the lap gap in real time and fine-tune the roll forming parameters based on the measurement results to dynamically ensure that the lap gap meets the requirement of ≤0.1mm.

[0041] In this optional embodiment, the process parameters during the wire-free welding process are precisely defined, laying a stable physical foundation for subsequent laser penetration welding and resistance seam welding. Controlling the welding speed within a specific range of 5 m / min to 8 m / min ensures a dynamic balance between material transport and welding heat input during roll forming, preventing insufficient penetration due to excessive speed or an excessively large heat-affected zone due to excessively slow speed, thus guaranteeing the quality and stability of the initial weld. Simultaneously, strictly limiting the gap of the lap joint to below 0.1 mm effectively reduces porosity defects caused by excessive gaps during laser welding and ensures efficient heat conduction between the lap surfaces, providing a smooth and tight joint for subsequent synchronous rolling and heating treatment of the resistance seam weld. This precise control of initial conditions improves the overall quality stability of the composite welding from the source, enabling subsequent laser penetration welding to more effectively suppress galvanized layer vaporization spatter and reduce porosity formation. It also provides an ideal base for the secondary heating and rolling of the resistance seam weld to eliminate residual stress and repair microcracks, ultimately significantly improving the tensile strength and fatigue life of the composite weld joint.

[0042] Optionally, in S2, the laser welding power for laser penetration welding is 11,500 W to 12,500 W.

[0043] Specifically, laser welding power refers to the energy intensity output by the laser and applied to the workpiece. During laser penetration welding, this power parameter directly determines the laser beam's melting capacity, penetration depth, and the range of the heat-affected zone. For high-strength steels, such as 1500MPa grade martensitic ultra-high-strength galvanized steel sheets, the selection of laser power is crucial. If the power is too low, complete penetration of the sheet may not be achieved, resulting in a weak weld; if the power is too high, it may cause overheating of the molten pool, violent vaporization of the zinc layer leading to increased spatter and porosity, and even overheating and softening of the base material, affecting material properties. Therefore, precisely controlling the laser welding power within a specific range of 11500 W to 12500 W aims to provide appropriate energy input for galvanized steel sheets of specific thicknesses (e.g., 1.6 mm) and materials to ensure stable penetration depth and good weld formation. The determination of this power range is typically based on a comprehensive consideration and experimental optimization of factors such as material properties, welding speed, laser spot pattern (e.g., combinations of four-spot and ring-spot structures), and required penetration depth.

[0044] In this optional embodiment, the power of laser penetration welding is limited to a specific range of 11,500 W to 12,500 W, providing a precise energy input reference for welding 1500 MPa-grade martensitic ultra-high strength galvanized steel sheets. During laser penetration welding, due to the presence of a zinc layer on the surface of the galvanized steel sheet and the high-strength martensitic steel base material, excessively low power cannot penetrate the sheet to achieve effective fusion, while excessively high power will exacerbate the severe vaporization of the zinc layer and cause overheating and softening of the base material. By controlling the power within the aforementioned range, it is possible to ensure that the laser energy, when penetrating the lap joint, can generate sufficient penetration depth to achieve a strong metallurgical bond, while effectively controlling the heat input. This ensures welding quality while providing a good weld foundation for subsequent resistance seam welding, ensuring the stability and consistency of the composite welding process when processing high-strength steel.

[0045] Optionally, in S2, the combined power of the four spots and the ring spot accounts for 20% to 40% of the power of the ring spot.

[0046] Specifically, during laser penetration welding, the power borne by the annular spot in the combined power of the annular spot and the four spots ranges from 20% to 40%, aiming to precisely control the balance between preheating and the main welding effect. Specifically, this power ratio can be achieved in several ways: One approach is to generate the annular spot and the four spots using independently configured lasers, and to independently adjust the output power of each, thus achieving a precise proportion of the annular spot's power in the combined power. For example, two fiber laser systems can be used, one for generating the annular spot and the other for generating the four spots, with fine-grained power output management through their respective power supplies and control modules. Another approach is to use a single high-power laser source, distributing the laser energy to the annular spot and the four spots according to a preset ratio using a beam shaping and beam-splitting optical system. In this scheme, the power ratio of the annular spot can be dynamically controlled by adjusting the splitting ratio of the beam splitter or using an adjustable attenuator. Precise control of this power ratio is crucial for optimizing the behavior of the galvanized layer under laser irradiation. It ensures that the material surface is adequately preheated before the main welding, thus creating favorable conditions for the subsequent welding process.

[0047] In this embodiment, during laser penetration welding, the annular spot preheats the surface of the lap joint with a specific power ratio. This preheating effectively alters the vaporization kinetics of the galvanized layer under laser energy, causing the zinc layer to vaporize and release zinc vapor in a more stable and controlled manner before the main weld pool forms. This avoids spatter caused by violent explosions of zinc vapor inside the weld pool and significantly reduces the formation of porosity within the weld pool. Precisely controlling the power ratio of the annular spot within the range of 20% to 40% ensures sufficient preheating to suppress porosity while avoiding potential performance degradation of the heat-affected zone or excessive burning of the galvanized layer due to excessive preheating energy. Therefore, this approach improves the quality of laser welding from the source, providing a better weld bead foundation for subsequent resistance seam welding, thereby improving the overall density and fatigue performance of the composite weld joint.

[0048] Optionally, in S2, the welding speed of laser penetration welding is from 5 m / min to 15 m / min.

[0049] Specifically, the welding speed in laser penetration welding refers to the relative speed between the laser beam and the workpiece to be welded. It is one of the key process parameters affecting the laser welding process, directly determining the amount of laser energy input per unit length of weld, thus influencing the size, shape, solidification rate of the molten pool, and the weld's forming quality and mechanical properties. On high-speed production lines, the welding speed setting needs to comprehensively consider production efficiency, welding stability, and material properties. Controlling the laser penetration welding speed within the range of 5 m / min to 15 m / min aims to ensure that the laser welding process can maintain consistency with the cycle time of the high-speed roll forming production line. For example, this can be achieved by precisely controlling the speed of the workpiece conveying mechanism (such as rollers or fixtures) or adjusting the speed at which the laser welding head moves above the workpiece. Alternatively, an integrated control system can be used to monitor the roll forming speed in real time and dynamically adjust the laser welding speed to achieve precise matching between the two.

[0050] In this optional embodiment, the laser penetration welding speed is precisely controlled within the range of 5 m / min to 15 m / min, ensuring a high degree of matching between the laser welding process and the roll forming speed of the roll forming line. During high-speed roll forming, the profile is conveyed forward at a constant high speed. If the welding speed is too slow, the profile will accumulate in front of the welding station, causing production line blockage; if the welding speed is too fast or unstable, it may lead to a decrease in welding quality, such as insufficient penetration or discontinuous welds. This speed matching mechanism allows laser welding to function as a seamless link in the roll forming production line, enabling continuous online welding of galvanized profiles. By eliminating production interruptions and quality fluctuations caused by speed mismatch, this application significantly improves overall production efficiency and automation levels. Furthermore, in conjunction with a combination structure employing four-spot and ring-spot lasers, it effectively suppresses galvanized layer vaporization spatter during high-speed welding, reduces porosity formation, and ensures sufficient penetration and weld formation quality, providing a stable and high-quality pre-welding foundation for subsequent resistance seam welding, thereby comprehensively improving the performance of the composite welded joint.

[0051] Optionally, in S2, the resistance seam welding machine is located 450 mm to 550 mm behind the laser welding station, the power of the resistance seam welding machine is 460 KVA to 500 KVA, and the heating width of the resistance seam welding machine is 5 mm to 6 mm.

[0052] Specifically, the resistance seam welding machine is positioned 450 mm to 550 mm behind the laser welding station. This distance defines the spatial position of the resistance seam welding machine relative to the laser welding station. Its core function is to ensure that the molten pool formed by laser welding can promptly and effectively enter the secondary heating and compaction stage of resistance seam welding after initial solidification. This time window is crucial for utilizing the material's residual heat, promoting stress release, and repairing microcracks. In actual production line layouts, this distance can be precisely set and maintained through fixed or adjustable mounting mechanisms. For example, a high-precision guide rail system can be used to move the resistance seam welding machine along the production line direction and lock it in a preset position; alternatively, position sensors and actuators integrated into the automated production line control system can achieve dynamic distance adjustment and precise alignment between the resistance seam welding machine and the laser welding station.

[0053] Resistance seam welding machines have a power range of 460 KVA to 500 KVA. This power range defines the electrical energy input required for simultaneous rolling and heating of the weld bead. Its function is to provide appropriate heat to bring the weld surface temperature to the target range (280°C to 300°C), thereby effectively eliminating residual stress, repairing microcracks, and avoiding adverse effects caused by excessive or insufficient energy. Resistance seam welding machines are typically equipped with power regulation units, for example, by adjusting the output current frequency or duty cycle of a three-phase DC inverter to precisely control the welding power. Furthermore, different turns ratio transformers or multi-stage power switching devices can be selected to adapt to different welding requirements, ensuring stable power output within the specified range.

[0054] The heating width of a resistance seam welding machine is 5 mm to 6 mm. This heating width refers to the effective area where the electrode wheel of the resistance seam welding machine contacts the weld bead and applies heating and compaction. Its function is to ensure that the heating and compaction accurately cover the weld area produced by laser welding and its adjacent heat-affected zone, thereby achieving comprehensive repair and strengthening of the weld while avoiding unnecessary thermal damage to other areas of the base material. The heating width is mainly determined by the geometry and size of the electrode wheel of the resistance seam welding machine. For example, electrode wheels with a specific width (such as 5 mm or 6 mm) can be used, or electrode wheels designed with replaceable or adjustable contact widths can be adopted to adapt to different weld widths and process requirements. Furthermore, the material, surface treatment, and applied pressure of the electrode wheel also affect the actual heating width and effect.

[0055] In this optional embodiment, the distance between the resistance seam welding machine and the laser welding station is precisely controlled between 450 mm and 550 mm. This ensures that the laser-welded molten pool can promptly enter the heating and compaction station for resistance seam welding after initial solidification. This allows the secondary treatment to fully utilize the residual heat of the material and be performed during the stress release window after laser welding, thereby effectively repairing microcracks in the weld and avoiding problems such as molten pool disturbance due to premature treatment or poor repair results due to delayed treatment. Simultaneously, the power of the resistance seam welding machine is set between 460 KVA and 500 KVA, providing suitable energy input to the weld area and ensuring that the weld surface temperature reaches the expected 280 ℃ to 300 ℃. This effectively eliminates residual stress and repairs microcracks, while avoiding problems such as excessive oxidation, volatilization, or overheating and deterioration of the base material due to excessive energy, and incomplete repair due to insufficient energy. Furthermore, limiting the heating width to 5 mm to 6 mm precisely covers the heat-affected zone and weld center generated by laser welding. This avoids overheating of the base material or degradation of the heat-affected zone due to an excessively large heating range, and also prevents ineffective treatment of some weld areas due to an excessively narrow heating range. In summary, by precisely defining the spatial layout of the resistance seam welding machine on the production line and the core process parameters, this application achieves deep synergy between laser welding and resistance seam welding processes, significantly improving the quality and reliability of the composite welded joint and effectively solving the hidden dangers of crack tendency and delayed fracture under high-speed roll forming welding.

[0056] Optionally, in S3, the weld surface temperature is controlled within the range of 280 ℃ to 300 ℃, specifically including the following steps: S31: Collect the surface temperature signal of the heated area of ​​the weld and transmit the surface temperature signal to the PID controller; S32: The PID controller filters and amplifies the surface temperature signal to calculate the deviation between the actual temperature and the target temperature. S33: The PID controller sends control commands to the resistance seam welding machine equipped with a three-phase DC inverter power supply based on the deviation value, changes the output current frequency of the resistance seam welding machine, realizes the dynamic adjustment of the welding power of the resistance seam welding machine, and controls the surface temperature of the weld bead within the range of 280 ℃ to 300 ℃.

[0057] In this embodiment, a closed-loop temperature control system based on PID control is introduced to achieve precise management of the resistance seam welding heating process. By acquiring the surface temperature signal of the heated area of ​​the weld bead in real time, and using the PID controller for filtering, amplification, and deviation calculation, the thermal state data during the welding process can be accurately obtained, and environmental noise interference can be effectively eliminated. Based on this, the PID controller sends control commands to the resistance seam welding machine according to the deviation between the actual temperature and the target temperature, dynamically changing its output current frequency, thereby achieving real-time adjustment of the welding power. This method of dynamically changing the current frequency according to the real-time temperature deviation can overcome the temperature instability caused by speed fluctuations or differences in heat conduction during the welding process, ensuring that the surface temperature of the weld bead is always maintained within the preset ideal range of 280 ℃ to 300 ℃.

[0058] In some specific embodiments, step S31 aims to acquire the surface temperature information of the weld bead during the resistance seam welding heating process in real time, providing basic data for subsequent precise temperature control. Specifically, non-contact temperature measurement devices, such as fiber optic infrared temperature sensors, can be used, installed behind the resistance seam welding area to monitor the surface temperature of the heated area of ​​the weld bead in real time. Alternatively, a thermocouple array can be arranged to acquire temperature data from multiple points on the weld bead surface in a contact or non-contact manner, and then averaged or weighted to obtain a more representative temperature signal. The acquired surface temperature signal, after digital processing, is transmitted to a PID controller for further analysis.

[0059] Step S32 aims to preprocess the received surface temperature signal to improve its accuracy and reliability, and to calculate the difference between the actual temperature and the preset target temperature. Specifically, filtering can employ digital low-pass filters, such as moving average filtering, Kalman filtering, or median filtering, to effectively remove noise caused by electromagnetic interference, thermal radiation fluctuations, etc., that may exist in the welding environment, ensuring the purity of the temperature signal. Amplification processing uses operational amplifiers and other circuits to amplify the weak temperature signal to a level range that the PID controller can recognize and process. Subsequently, the PID controller compares the processed actual temperature value with the preset target temperature value (e.g., 290°C) and calculates the deviation between the two, which will serve as the basis for subsequent power adjustment.

[0060] Step S33 aims to dynamically adjust the heating power of the resistance seam welding machine based on the real-time temperature deviation, thereby precisely controlling the weld surface temperature within the target range. Specifically, the PID controller, based on the deviation value calculated in step S32, uses a proportional (P), integral (I), and derivative (D) control algorithm to calculate the required power adjustment. This adjustment is then converted into a control command, such as a pulse width modulation (PWM) signal or an analog voltage signal, and sent to the resistance seam welding machine. Upon receiving the command, the inverter inside the resistance seam welding machine correspondingly changes the output current frequency of its three-phase DC inverter power supply. By adjusting the current frequency, the effective value and waveform of the output current of the resistance seam welding machine can be precisely controlled, thereby achieving dynamic and real-time adjustment of the welding power. This closed-loop control mechanism can effectively cope with temperature changes caused by factors such as material characteristics, welding speed fluctuations, or differences in heat conduction during the welding process, ensuring that the weld surface temperature remains stable within the ideal range of 280 ℃ to 300 ℃.

[0061] The control logic of the PID temperature closed-loop algorithm is as follows: the fiber optic infrared temperature sensor collects the surface temperature of the weld zone in real time as T_actual; the target surface temperature of the weld zone is T_target. The controller calculates the temperature deviation e(t) = T_target - T_actual; Calculation of seam weld power adjustment based on discrete PID algorithm: in: P adjusted : Output power adjustment value of seam welding machine; K p The proportional coefficient determines the response speed; K i Integral coefficients, used to eliminate steady-state errors; K d Differential coefficients suppress temperature overshoot; Δt: Control period, 100ms; e(k): The deviation value at the k-th sampling time; n: Number of samples.

[0062] Optionally, in S31, the sampling frequency for the surface temperature signal of the heated area of ​​the weld bead is 10 Hz.

[0063] Specifically, a sampling frequency of 10 Hz refers to the number of times the temperature detection unit samples the surface temperature signal of the heated area of ​​the weld bead per unit time, i.e., 10 temperature data acquisitions per second. One implementation method is to configure the internal parameters of the temperature detection unit (e.g., a fiber optic infrared temperature sensor) to output data at a fixed frequency of 10 Hz. Another implementation method is to set a timed interrupt or cyclic acquisition mechanism in the data acquisition module or microcontroller, actively triggering the temperature detection unit to read and transmit a temperature signal once every 100 milliseconds (i.e., 1 / 10 Hz). Yet another implementation method is to ensure, through software programming, that the temperature signal reading operation is executed at a frequency of no less than 10 Hz within the control cycle of the PID controller, thereby ensuring that each control decision is based on the latest temperature data. This sampling frequency setting aims to provide the subsequent PID controller with sufficiently dense real-time temperature data to cope with the rapid changes in weld bead surface temperature during high-speed welding, ensuring that the control system can respond promptly and make precise adjustments.

[0064] In this optional embodiment, by setting the acquisition frequency of the surface temperature signal of the heated area of ​​the weld bead to 10Hz, this application can significantly improve the response speed and control accuracy of the temperature closed-loop control system. In high-speed welding environments, instantaneous fluctuations in weld bead temperature are common. If the acquisition frequency is insufficient, the PID controller will not be able to acquire these critical temperature change information in a timely manner, resulting in adjustment lag and affecting the stability of temperature control. The high-frequency acquisition of 10Hz ensures that the PID controller can receive sufficiently dense temperature feedback data in each control cycle, enabling it to calculate the deviation between the actual temperature and the target temperature more quickly and accurately. Based on this, the PID controller can send control commands to the resistance seam welding machine in a timely manner, dynamically adjusting its output current frequency, thereby achieving real-time correction of welding power. This high-frequency, precise temperature control mechanism can effectively stabilize the weld bead surface temperature within a narrow range of 280℃ to 300℃, avoiding excessive oxidation of the galvanized layer or overheating of the base material due to excessively high temperatures, and the inability to effectively eliminate residual stress and repair microcracks due to excessively low temperatures. Ultimately, this ensured stable heat input for the galvanized profiles during the composite welding process, significantly improving the quality and performance of the welded joints and effectively suppressing the occurrence of delayed cracks.

[0065] Another embodiment of the present invention provides a laser-resistance seam welding composite welding system for galvanized sheet for battery trays, used to operate and implement the above-mentioned laser-resistance seam welding composite welding method for galvanized sheet for battery trays, including: The laser welding device features a composite welding head with four laser spots plus a ring spot, used for wire-free welding and laser-penetrating welding of galvanized sheets; and The resistance seam welding machine is equipped with a three-phase DC inverter power supply, which is used to simultaneously roll and heat the weld after laser penetration welding, so that the surface temperature of the weld is controlled within the range of 280 ℃ to 300 ℃.

[0066] Specifically, by combining the four-spot + ring-spot composite welding head of the laser welding device with the synchronous rolling heat treatment of the resistance seam welding machine in a specific sequence, the gasification of the galvanized layer is effectively suppressed and the post-weld heat treatment temperature is controlled during high-speed welding, thereby achieving the effects of eliminating hardened structures, repairing microcracks and preventing delayed fracture.

[0067] The system includes a laser welding device and a resistance seam welding machine. The laser welding device is equipped with a composite welding head with four laser spots plus a ring spot, used for wire-free welding and laser-penetrating welding of galvanized profiles. The resistance seam welding machine is equipped with a three-phase DC inverter power supply, used to simultaneously roll and heat the weld bead after laser-penetrating welding, so that the surface temperature of the weld bead is controlled within the range of 280 ℃ to 300 ℃.

[0068] Specifically, the laser welding device uses a ring-shaped laser spot to preheat the surface of the galvanized profile, suppressing the intense vaporization of the galvanized layer during welding and thus reducing porosity. Simultaneously, the four-spot structure improves the heat distribution of the molten pool by widening the weld width. After laser welding, the resistance seam welding machine simultaneously rolls and heats the weld bead, precisely maintaining the weld surface temperature within the range of 280°C to 300°C. This effectively releases residual stress generated during laser welding and uses the rolling action to repair any micro-cracks that may exist in the weld.

[0069] In this embodiment, the advantages of high-energy-density laser welding are complemented by the mechanical rolling and heat treatment advantages of resistance seam welding. This not only solves the process challenges brought about by the galvanized layer but also improves the microstructure of martensitic steel through online heat treatment. Compared to the basic solution, this embodiment has significant advantages in suppressing spatter, eliminating hardened structures, and preventing delayed cracking. It can adapt to the requirements of high-speed rolling production lines from 5 m / min to 15 m / min, while avoiding galvanized layer volatilization and grain coarsening. This achieves comprehensive optimization of the weld joint quality and significantly improves the joint's strength and toughness.

[0070] Optionally, it also includes: The temperature detection unit is used to collect the surface temperature signal of the heated area of ​​the weld bead. The PID controller receives the surface temperature signal, filters and amplifies it, calculates the deviation between the actual temperature and the target temperature, and sends a control command to the resistance seam welding machine based on the deviation to change the output current frequency of the resistance seam welding machine.

[0071] Specifically, the temperature detection unit is a device used to monitor the surface temperature of the heated area of ​​the weld in real time. Its function is to convert the heat information of the weld surface into a signal that can be processed by the electrical system. In practical applications, the temperature detection unit can use a fiber optic infrared temperature sensor to measure the infrared radiation emitted by the weld surface in a non-contact manner and convert it into an electrical signal; alternatively, it can use a thermocouple, where the measuring end of the thermocouple is in contact with the weld surface, utilizing the principle of thermoelectric potential to convert temperature information into an electrical signal. The surface temperature signal collected by the temperature detection unit is the basis for subsequent judgments and adjustments by the control system.

[0072] A PID controller is a proportional-integral-derivative (PID) controller. Its core function is to calculate and output a control variable based on the deviation between a set target value and the actual measured value, so that the actual value approaches the target value. The PID controller first receives a surface temperature signal from a temperature sensing unit, which is typically an analog or digital signal. To ensure control accuracy, the PID controller filters and amplifies the received surface temperature signal. Filtering aims to eliminate noise and interference in the signal; for example, a low-pass filter can be used to remove high-frequency noise, or a median filter can be used to eliminate transient spikes. Amplification amplifies the weak temperature signal to a voltage or current range that the controller can recognize, thereby improving the signal-to-noise ratio and measurement accuracy. After signal processing, the PID controller calculates the deviation between the actual temperature and the preset target temperature. This deviation is a key parameter measuring the difference between the current temperature and the ideal temperature.

[0073] Based on the calculated deviation value, the PID controller generates corresponding control commands and sends them to the resistance seam welding machine. The control commands guide the resistance seam welding machine to adjust its operating state to correct the temperature deviation. Specifically, the PID controller adjusts the heating power of the resistance seam welding machine by changing the output current frequency. For example, when the actual temperature is lower than the target temperature, the PID controller instructs the resistance seam welding machine to increase the output current frequency, thereby increasing the heating power; conversely, when the actual temperature is higher than the target temperature, it decreases the output current frequency to reduce the heating power. This method of dynamically controlling the heating power by adjusting the output current frequency enables precise and real-time control of the weld surface temperature.

[0074] In this optional embodiment, a closed-loop temperature control system is introduced to achieve precise regulation of the heat treatment link in the composite welding process. The temperature detection unit can obtain the temperature state of the heated area of the weld bead in real time, providing accurate data support for subsequent dynamic adjustment. The PID controller filters and amplifies the collected temperature signals, effectively eliminating environmental noise interference and ensuring the accuracy of the control signals. By calculating the deviation value between the actual temperature and the target temperature, the PID controller can dynamically adjust the output current frequency of the resistance seam welder according to the deviation, thereby realizing real-time feedback control of the welding power. This mechanism of changing the current frequency in real time according to the temperature deviation can effectively address the problem of uneven heat input caused by speed fluctuations or material property differences during the welding process, ensuring that the surface temperature of the weld bead always remains within the preset process window. This not only ensures that the resistance seam welding link can fully eliminate the residual stress generated by laser welding and repair microcracks, significantly reducing the incidence of delayed cracks, but also avoids excessive oxidation of the galvanized layer or deterioration of the base material properties due to过高温度, thereby improving the robustness of the welding process and the consistency of product quality, and ensuring the high strength and long fatigue life of the composite welded joint.

[0075] The present invention will be further described below in conjunction with specific embodiments.

[0076] Embodiment 1, welding of the longitudinal beam of the battery tray with a "day" - shaped cross - section.

[0077] Workpiece material: Baosteel MS1500 martensitic ultra - high - strength steel, with a thickness of 1.6 mm and a surface coating of Zn 50 / 50 (double - sided galvanized).

[0078] Workpiece structure: Roll - formed into a profile with a "day" - shaped cross - section, and the lap joint length is 2000 mm.

[0079] The welding steps include: (1) Laser welding: Using a Trumpf 12000W fiber laser, a four - spot welding head, the main spot diameter is 0.8 mm, and the four spots are evenly distributed on a φ2.5 mm circumference; the power ratio of the ring spot is 30%, and the laser power is 12000W; the welding speed is 15 m / min, and the penetration depth is 1.2 mm (penetration of the lap joint).

[0080] (2) Resistance seam welding: A 480KVA three - phase variable - frequency seam welder is set 500 mm behind the laser welding head, and the width of the roller electrode is 6 mm; an optical fiber infrared temperature sensor is installed directly above the seam welding area to monitor the temperature in real time; the PID parameters of the control system: K p =0.8, K i =0.05, K d =0.1, the target temperature is 295℃, the control period is 100 ms; the measured temperature fluctuation is 295±3℃, and the seam welding power is automatically adjusted.

[0081] (3)Post - treatment and inspection: After welding, it is naturally cooled to room temperature.

[0082] After 72 - hour aging test, only 1 case (0.5%) of micro - cracks appeared in 200 specimens. Tensile strength test: 1482 MPa (98.8% of the base metal's 1500 MPa).

[0083] Example 2, Laser welding of the cross - beam of a rectangular - section battery tray.

[0084] Corresponding to Example 1, the differences are: (1) Adjustment of laser - welding process parameters: The welding speed is reduced to 12 m / min; the proportion of the ring - spot power is adjusted to 25%.

[0085] (2) The target temperature of the resistance - seam welding is adjusted to 285 °C, and the PID parameters are finely adjusted accordingly (K p = 0.7, K i = 0.04, K d = 0.12).

[0086] Results: The appearance of the weld is flat without spatter; the incidence rate of delayed cracks is 0.3% (6 cases of micro - cracks appeared in 2000 continuously welded parts, and none of them expanded into through - cracks); the tensile strength of the joint is 1465 MPa to 1490 MPa, meeting the design requirements.

[0087] Comparative Example 1, Laser welding of the longitudinal beam of a battery tray with a "day - character" cross - section.

[0088] Workpiece material: Baosteel MS1500 martensitic ultra - high - strength steel, with a thickness of 1.6 mm and a surface coating of Zn 50 / 50 (double - sided galvanized).

[0089] Workpiece structure: Rolled into a "day - character" cross - section profile, with a lap - joint length of 2000 mm.

[0090] The welding steps include: (1) Laser welding: Using a Trumpf 12000W fiber laser, a four - spot welding head, the diameter of the main spot is 0.8 mm, and the four spots are evenly distributed on a φ2.5 mm circumference; the proportion of the ring - spot power is 30%, the laser power is 12000W; the welding speed is 15 m / min, and the penetration depth is 1.2 mm (penetration of the lap - joint).

[0091] (2) Post - treatment and inspection: After welding, it is naturally cooled to room temperature.

[0092] Effect examples Metallographic inspections were respectively carried out on the battery tray longitudinal - beam products prepared in Example 1 and Comparative Example 1. The metallographic results of Example 1 are as Figure 2As shown, the weld is dense, free of porosity, and the heat-affected zone microstructure consists of tempered martensite with a small amount of ferrite. The metallographic results of Comparative Example 1 are as follows... Figure 3 As shown, there are obvious cracks at the edge of the weld.

[0093] The inner surface appearance of the product in Example 1 is as follows Figure 4 As shown, the outer side appearance is as follows Figure 5 As shown, all welds are dense.

[0094] Crushing tests were conducted on the battery tray longitudinal beam products prepared in Example 1 and Comparative Example 1, respectively. Under the same experimental conditions, the battery tray longitudinal beam product of Example 1 crushed as follows: Figure 6 As shown, the weld shows no cracks; the battery tray longitudinal beam product in Comparative Example 1, after being crushed, is as follows: Figure 7 As shown, localized cracking of the weld bead is evident.

[0095] Axial force controlled high-cycle fatigue tests were conducted on the battery tray longitudinal beam products prepared in Example 1 and Comparative Example 1. The fatigue life (stress ratio R=0.1, maximum stress 900MPa) of the product in Example 1 reached more than 500,000 cycles, while the fatigue life of the product in Comparative Example 1 was about 120,000 cycles. The fatigue life of the product with laser welding combined with resistance seam welding was 4 times that of pure laser welding.

[0096] It is evident that by combining laser welding first with resistance seam welding, the simultaneous crushing action of the resistance seam weld after laser welding eliminates residual stress within a specific temperature range, repairs micro-cracks generated by laser welding, and prevents delayed cracking. The tensile strength of the joint after composite welding reaches over 98% of the base material, fatigue life is increased by 4 times, enhancing the strength and toughness of the welded joint while maintaining the performance of the galvanized layer and the base material.

[0097] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A laser-resistance seam welding composite welding method for galvanized sheet used in battery trays, characterized in that, Includes the following steps: S1: The galvanized sheet is roll-pressed into a H-shaped cross-section structure by welding without filler wire, and the inside of the H-shaped cross-section structure is an overlapping joint connected in an overlapping manner. S2: Perform laser penetration welding on the lap joint. The welding spot adopts a combination structure of four spots and annular spots. The diameter of each laser spot of the four spots is 0.6 mm to 1 mm, and the four laser spots of the four spots form a circular area with a diameter of 2 mm to 3 mm. The annular spot is used to preheat the surface of the lap joint. S3: Using a resistance seam welding machine equipped with a three-phase DC inverter power supply, the weld bead after laser penetration welding is simultaneously rolled and heated, and the surface temperature of the weld bead is controlled within the range of 280 ℃ to 300 ℃.

2. The laser-resistance seam welding composite welding method for galvanized steel sheets used in battery trays according to claim 1, characterized in that, In step S1, the fillerless welding is performed at a speed of 5 m / min to 8 m / min, and the lap gap of the lap joint is ≤0.1 mm.

3. The laser-resistance seam welding composite welding method for galvanized steel sheets used in battery trays according to claim 1, characterized in that, In step S2, the laser welding power of the laser penetration welding is 11500 W to 12500 W.

4. The laser-resistance seam welding composite welding method for galvanized steel sheets used in battery trays according to claim 1, characterized in that, In step S2, the combined power of the four light spots and the ring light spot accounts for 20% to 40% of the power of the ring light spot.

5. The laser-resistance seam welding composite welding method for galvanized steel sheets used in battery trays according to claim 1, characterized in that, In step S2, the welding speed of the laser penetration welding is from 5 m / min to 15 m / min.

6. The laser-resistance seam welding composite welding method for galvanized steel sheets used in battery trays according to claim 3, characterized in that, In S2, the resistance seam welding machine is located 450 mm to 550 mm behind the laser welding station. The power of the resistance seam welding machine is 460 KVA to 500 KVA, and the heating width of the resistance seam welding machine is 5 mm to 6 mm.

7. The laser-resistance seam welding composite welding method for galvanized steel sheets used in battery trays according to claim 1, characterized in that, In step S3, the surface temperature of the weld bead is controlled within the range of 280 ℃ to 300 ℃, specifically including the following steps: S31: Collect the surface temperature signal of the heated area of ​​the weld bead and transmit the surface temperature signal to the PID controller; S32: The PID controller filters and amplifies the surface temperature signal to calculate the deviation between the actual temperature and the target temperature; S33: The PID controller sends a control command to the resistance seam welding machine equipped with a three-phase DC inverter power supply according to the deviation value, changes the output current frequency of the resistance seam welding machine, realizes the dynamic adjustment of the welding power of the resistance seam welding machine, and controls the surface temperature of the weld bead within the range of 280 ℃ to 300 ℃.

8. The laser-resistance seam welding composite welding method for galvanized steel sheets used in battery trays according to claim 7, characterized in that, In step S31, the sampling frequency for acquiring the surface temperature signal of the heated area of ​​the weld bead is 10 Hz.

9. A laser-resistance seam welding composite welding system for galvanized sheet for battery trays, used to operate and implement the laser-resistance seam welding composite welding method for galvanized sheet for battery trays as described in any one of claims 1-8, characterized in that, include: The laser welding device is equipped with a composite welding head with four laser spots and a ring laser spot, which is used for filler wire welding and laser penetration welding of galvanized sheets. and The resistance seam welding machine is equipped with a three-phase DC inverter power supply, which is used to simultaneously roll and heat the weld after laser penetration welding, so that the surface temperature of the weld is controlled within the range of 280 ℃ to 300 ℃.

10. The laser-resistance seam welding composite welding system for galvanized sheet for battery trays according to claim 9, characterized in that, Also includes: A temperature detection unit is used to collect the surface temperature signal of the heated area of ​​the weld bead. The PID controller is used to receive the surface temperature signal, filter and amplify the surface temperature signal, calculate the deviation between the actual temperature and the target temperature, and send a control command to the resistance seam welding machine according to the deviation to change the output current frequency of the resistance seam welding machine.

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