A cooling device and segmented cooling control method for controlling weld joint deformation

Abstract

This invention discloses a cooling device and a segmented cooling control method for controlling the deformation of welded joints, including cooling pipes and cooling plate assemblies; multiple cooling zones are set on the surface of the workpiece to be welded from top to bottom along its longitudinal direction, and two adjacent cooling zones are set as a group of cooling areas from top to bottom. Each cooling area is provided with a cooling plate assembly and a third shut-off valve; the cooling plate assembly includes an upper cooling plate and a lower cooling plate; the upper cooling plate is fixed on the upper cooling zone, and the lower cooling plate is fixed on the lower cooling zone; the third shut-off valve is used to control the cooling pipes to flow through the upper cooling flow path of the upper cooling zone or through the lower cooling flow path of the lower cooling zone; and the first shut-off valve, the second shut-off valve, and the third shut-off valve cooperate to control the segmented cooling of the upper cooling plate / lower cooling plate.

Description

Technical Field

[0001] This invention relates to the field of aerospace tank welding technology, and in particular to a cooling device and segmented cooling control method for controlling joint deformation during friction stir welding of long welds (>3m). Background Technology

[0002] In the field of aerospace tank manufacturing, the longitudinal seam welding of large-size thin-walled cylindrical sections faces the following technical bottlenecks: Due to heat accumulation during welding, the material expands unevenly, and long welds (>3m) make it difficult for heat to dissipate evenly, potentially creating a large temperature gradient, resulting in residual stress and ultimately deformation of the cylindrical section. Traditional methods for controlling section deformation include post-weld straightening or overall cooling. Post-weld straightening refers to adjusting the deformation that has occurred after welding through mechanical or heat treatment methods. This involves the use of additional equipment, such as hydraulic straighteners or heating furnaces, which increases the complexity and cost of the production process. Post-weld straightening relies on accurate measurement and compensation of the completed deformation, but due to factors such as material springback, the actual straightening effect may deviate. Furthermore, the straightening process may generate secondary stress in the material, especially during heat treatment, where temperature changes may cause changes in the microstructure, such as grain growth or phase transformation, thus affecting the material's mechanical properties. The overall cooling method uses single-channel cooling or fixed-position cooling devices to control the stability of the welding temperature field. It is suitable for shorter welding paths but cannot adapt to temperature changes at different welding stages. Especially in long welds (>3m), the problem of uneven cooling will be more obvious. Inconsistent cooling rates may cause some areas to cool too quickly while other areas cool too slowly, increasing the risk of deformation.

[0003] Friction stir welding (FSW) is a novel solid-state welding technology primarily used for joining metallic materials. Its principle involves fixing the workpieces to be welded using a fixture, and then generating heat through friction between a high-speed rotating stirring head and the workpiece surface. This heat causes plastic flow at the interface between the metal materials, achieving welding below the melting point of the metals. Due to its advantages such as high joint strength and the elimination of the need for filler material, friction stir welding has been applied in the manufacture of rocket propellant tanks.

[0004] In friction stir welding, heat is generated by the friction between the stirring head and the workpiece, which is an unavoidable phenomenon. For ultra-large, thin-walled pressure vessel structures such as rocket propellant tanks, the heat input during friction stir welding has a significant impact on the weld quality. The welding heat input directly affects the temperature distribution of the weld joint. Excessive heat input will cause the temperature of the workpiece to rise, resulting in thermal expansion and plastic deformation. Conversely, uneven welding heat input will also cause corresponding thermal stress and thermal deformation in different parts of the workpiece.

[0005] To address this issue, external cooling measures are typically employed, such as water spray cooling and air cooling. Water spray cooling absorbs heat and lowers the workpiece temperature by spraying water mist or streams onto the welding area. This method can reduce heat input and deformation to some extent, but it may exacerbate uneven temperature distribution in the welding area, generating high thermal stress. Furthermore, water spray cooling may affect the cleanliness of the welding environment, placing higher demands on equipment maintenance. Air cooling removes heat from the welding area by blowing air. Compared to water spray cooling, air cooling is less effective and more susceptible to the influence of ambient temperature and humidity. Air cooling may also lead to uneven heat distribution and has limited effectiveness on large workpieces. The limited effectiveness of methods like water spray cooling and air cooling, coupled with the tendency to cause uneven temperature distribution in the welding area, further impacts welding quality.

[0006] Water-cooled fixtures offer a more direct and effective cooling method. They absorb heat from the welding area through circulating cooling water, thereby lowering the workpiece temperature and reducing welding deformation. A water-cooled fixture consists of cooling water pipes and a fixture body. The cooling water pipes deliver cooling water to the welding area, while the fixture body secures the workpiece. By adjusting the flow rate and temperature of the cooling water, heat distribution during the welding process can be effectively controlled, thus minimizing welding deformation. Summary of the Invention

[0007] The present invention addresses the deficiencies of the prior art by providing a cooling device and segmented cooling control method for controlling welding deformation of long weld seams (>3m) friction stir joints. The device uses circulating cooling water to absorb heat from the welding area, thereby reducing the workpiece temperature and minimizing welding deformation.

[0008] A cooling device for controlling joint deformation during friction stir welding of long welds, wherein multiple cooling devices are longitudinally arranged on two opposite workpieces to be welded for segmented cooling of the workpieces; multiple cooling zones are arranged on the surface of the workpieces from top to bottom along the longitudinal direction, and two adjacent cooling zones are arranged from top to bottom as a group of cooling areas, and each cooling area is provided with a cooling device, the cooling device including a cooling pressure plate assembly, a cooling pipeline and a third shut-off valve;

[0009] The cooling pipeline is divided into an upper cooling flow path and a lower cooling flow path. The cooling plate assembly includes an upper cooling plate and a lower cooling plate. Two upper cooling plates are fixedly mounted opposite each other on the cooling partition above the workpiece to be welded, and two lower cooling plates are fixedly mounted opposite each other on the cooling partition below the workpiece to be welded. The upper cooling flow path flows through the two upper cooling plates, and the lower cooling flow path flows through the two lower cooling plates. The upper and lower cooling flow paths are connected by a third shut-off valve, which controls the flow of coolant through the upper or lower cooling flow path, thereby achieving segmented cooling of the upper / lower cooling plates.

[0010] The upper cooling zone includes upper cooling plates located on the two workpieces to be welded and an upper cooling flow path; the upper cooling plates have liquid inlets and outlets on their opposite sidewalls along their longitudinal direction, and the liquid inlets and outlets of the two upper cooling plates are in opposite positions; the upper cooling flow path is as follows:

[0011] The coolant flows from the cooling water tank through the cooling water pump, the third branch, the upper cooling pressure plate on one side, the first shut-off valve, the third shut-off valve, another first shut-off valve, and the upper cooling pressure plate on the other side in sequence, and then returns to the cooling water tank through the fourth branch.

[0012] The lower cooling zone includes a lower cooling plate located on two workpieces to be welded and a lower cooling flow path; the lower cooling plate has an inlet and an outlet on its opposite sidewalls along its longitudinal direction, and the inlet and outlet positions of the two lower cooling plates are opposite.

[0013] The lower cooling flow path is as follows:

[0014] The coolant flows from the cooling water tank through the cooling water pump, the first branch, the lower cooling pressure plate on one side, the second shut-off valve, the third shut-off valve, another second shut-off valve, and the lower cooling pressure plate on the other side, before returning to the cooling water tank via the second branch.

[0015] The cooling device for controlling joint deformation during friction stir welding of long welds is particularly suitable for welds longer than 3 meters. When the workpiece is particularly long, multiple cooling zones are arranged longitudinally, each equipped with a cooling pressure plate assembly and a third shut-off valve. Each cooling zone can achieve segmented cooling through the control of cooling pipes and cooling pressure plate assemblies.

[0016] Furthermore, two oppositely arranged workpieces 51 to be welded are respectively placed on the welding platform, and a space for the welding area is reserved between the two workpieces 51; and the workpiece to be welded is a rectangular workpiece with a weld seam longer than 3m.

[0017] Furthermore, the upper cooling plate and the lower cooling plate are fixed to the workpiece to be welded by a clamp, which is set on both sides of the workpiece to constrain the lateral movement of the workpiece.

[0018] Furthermore, multiple key-shaped pressure blocks are arranged parallel to each other on the upper and lower cooling plates. The key-shaped pressure blocks are fixed on the fixture, and the upper / lower cooling plates are pressed onto the welding workpiece by screws to fix the position of the upper / lower cooling plates and the welding workpiece.

[0019] In particular, the cooling zones of the two oppositely positioned workpieces to be welded are located in corresponding positions, thereby precisely controlling the segmented cooling.

[0020] The segmented cooling control method using the aforementioned cooling device includes:

[0021] Pre-treatment: Before welding, multiple cooling zones are set on the surface of the workpiece to be welded from top to bottom along the longitudinal direction, and the cooling pressure plate assembly is fixed on its upper surface along the longitudinal direction of the workpiece to be welded; and a position for the welding area is reserved in the middle of the workpieces 51 to be welded that are set opposite to each other.

[0022] Start the cooling water pump to circulate the coolant in the cooling pipes and upper / lower cooling plates of the cooling zone to be welded, thereby pre-cooling the cooling zone to be welded. Pre-cooling is considered complete when the temperature is 2-5 degrees below room temperature.

[0023] Welding and cooling of the upper cooling zone: After pre-cooling, friction stir welding is performed, and an infrared temperature sensor located at the stirring head monitors the temperature at the stirring head;

[0024] When the temperature reaches 250-350 degrees, the first and third shut-off valves of the two oppositely arranged cooling pressure plate assemblies in the welding area open, while the second shut-off valve remains closed, allowing the coolant to flow through the upper cooling flow path. The heat generated during welding is carried away by the coolant flowing inside the upper cooling pressure plate.

[0025] After the upper part of the workpiece is welded, continue to run the cooling water pump to ensure that the welding area gradually cools down to room temperature.

[0026] Welding and cooling of the lower cooling zone: Friction stir welding is performed, and an infrared temperature sensor located at the stirring head monitors the temperature at the stirring head.

[0027] When the temperature reaches 250-350 degrees, the second and third shut-off valves of the two oppositely arranged cooling pressure plate assemblies in the welding area are opened, while the first shut-off valves of the two cooling pressure plate assemblies are kept closed, allowing the coolant to flow through the lower cooling flow path. The heat generated by welding is carried away by the coolant flowing in the lower cooling pressure plate.

[0028] After the welding of the lower half of the workpiece is completed, the cooling water pump continues to run to ensure that the welding area gradually cools down to room temperature.

[0029] The beneficial effects of this invention are as follows: This invention divides a weld seam longer than 3 meters into multiple segments (i.e., multiple cooling zones). Each cooling zone is independently equipped with a cooling device, and two cooling pressure plates symmetrically arranged on two opposite welding workpieces are equipped with independent cooling pipes. The cooling pipes are responsible for delivering cooling water to the welding zone, while the fixture body is used to fix the workpieces. The cooling water is supplied by a unified cooling water tank and cooling water pump, and the circulation channel is controlled by different servo valves. By adjusting the flow rate and temperature of the cooling water, the heat distribution during the welding process can be effectively controlled, absorbing heat from the welding zone, reducing the workpiece temperature, and thus reducing welding deformation. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the cooling device described in this invention. In the diagram, the blue and red pipes are labeled as the cold water side and hot water side of the upper cooling section, respectively.

[0031] Figure 2 This is a schematic diagram of the cooling device described in this invention. The blue and red pipes in the diagram are labeled as the cold water side and hot water side of the lower half of the cooling system, respectively.

[0032] Figure 3 This is a comparative example of friction stir welding using conventional friction stir welding and friction stir welding using the cooling device and segmented control method described in this invention.

[0033] in,

[0034] 10: Cooling water tank; 20: Cooling water pump; 31: First branch; 32: Second branch; 33: Third branch; 34: Fourth branch; 40: Fixture; 50: Upper cooling plate; 53: Lower cooling plate; 60: Key block; 41: Socket head cap screw; 42: Welding platform; 51: Welded workpiece; 52: Stirring head; 61: External hexagon head cap screw; 70: First shut-off valve; 71: Second shut-off valve; 72: Third shut-off valve; 80: Infrared temperature sensor. Detailed Implementation

[0035] To make the objectives, technical solutions, beneficial effects, and significant advancements of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings provided in the examples of the present invention. Obviously, all the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In the description of this application, unless otherwise expressly specified and limited, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; the term "multiple" refers to two or more; unless otherwise specified or explained, the terms "connected," "fixed," etc., should be interpreted broadly. For example, "connected" can be a fixed connection, a detachable connection, an integral connection, or an electrical connection; "connected" can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0037] like Figure 1-2 As shown, two welding workpieces 51 are placed side-by-side on the upper surface of a welding platform 42, with a pre-reserved welding area between them to ensure sufficient working space for the stirring head. A cooling device for controlling joint deformation during friction stir welding of long welds is arranged on the welding platform 42, including a cooling water tank 10, a cooling water pump 20, cooling pipes, a clamp 40, a cooling pressure plate assembly, a key-shaped pressure block 60, a first shut-off valve 70, a second shut-off valve 71, and a third shut-off valve 72. The cooling water tank 10, cooling water pump 20, and cooling pressure plate assembly are connected sequentially via cooling pipes. The stirring head 52 can weld the two welding workpieces 51 together using solid-state welding technology through high-speed rotation and forward motion. When the stirring head 52 of the friction stir welding equipment works on the welding workpieces 51, a large amount of heat is generated due to the friction stir and is conducted to the surrounding area. At this time, the cooling pressure plate assembly, under the action of cooling water circulation inside the cooling pipes, effectively diffuses and carries away the heat, avoiding stress deformation caused by heat accumulation. The cooling water tank 10 is used to store coolant and includes an inlet and an outlet. The outlet of the cooling water tank 10 is connected to a cooling water pump 20. The other end of the cooling water pump 20 divides the cooling pipeline into an upper cooling flow path and a lower cooling flow path, which respectively deliver coolant to the upper and lower cooling plates of the cooling plate assembly. The upper cooling plate 50 and the lower cooling plate 53 are both hollow structures and are placed longitudinally along the welded workpiece.

[0038] Two cooling zones are formed on the surfaces of the two workpieces to be welded, arranged longitudinally from top to bottom. The upper cooling zone includes two side-by-side upper cooling plates 50 and an upper cooling flow path; the lower cooling zone includes two side-by-side lower cooling plates 53 and a lower cooling flow path. The upper and lower cooling flow paths are connected by a third shut-off valve 72. The first shut-off valve 70, the second shut-off valve 71, and the third shut-off valve 72 cooperate to control the opening and closing of the upper and lower cooling flow paths, thereby controlling the segmented cooling of the upper cooling plates 50 and the lower cooling plates 53.

[0039] In the upper cooling zone, upper cooling plates 50 are placed side-by-side and correspondingly positioned on the upper surface of the cooling zone above each of the welded workpieces 51. Each upper cooling plate 50 has an inlet and an outlet on its opposite sidewalls along its longitudinal direction, and the inlet and outlet positions of the two upper cooling plates 50 are opposite. Two first shut-off valves 70 are provided in the upper cooling flow path. The upper cooling flow path is as follows:

[0040] The coolant in the cooling water tank 10 flows out of the cooling water tank, flows through the cooling water pump 20 and the third branch 33 (blue flow path) in sequence, and then flows into the upper cooling pressure plate 50 from the top inlet on the left side. After flowing out from the bottom outlet, it flows through the first shut-off valve 70, the third shut-off valve 72, and another first shut-off valve 70 before flowing into the bottom inlet of the upper cooling pressure plate 50 on the right side. Then it flows out from the top outlet and is returned to the cooling water tank 10 through the fourth branch 34 (red flow path). The heat generated by welding is quickly carried away by the coolant flowing in the upper cooling pressure plate 50.

[0041] In the lower cooling zone, lower cooling plates 53 are placed side-by-side and correspondingly positioned on the upper surface of the lower cooling zone of each welded workpiece 51. Each lower cooling plate 53 has an inlet and an outlet on its opposite sidewalls along its longitudinal direction, and the inlet and outlet positions of the two lower cooling plates 53 are opposite. Two second shut-off valves 71 are provided in the lower cooling flow path. The lower cooling flow path is as follows:

[0042] The coolant in the cooling water tank 10 flows out of the cooling water tank, flows through the cooling water pump 20 and the first branch 31 (blue flow path) in sequence, and then flows into the lower cooling plate 53 from the bottom inlet on the left side. After flowing out from the top outlet, it flows through the second shut-off valve 71, the third shut-off valve 72, and another second shut-off valve 71 before flowing into the top inlet of the lower cooling plate 53 on the right side. Then it flows out from the bottom outlet and is returned to the cooling water tank 10 through the second branch 32 (red flow path). The heat generated by welding is quickly carried away by the coolant flowing in the lower cooling plate 53.

[0043] The upper cooling plate 50 and the lower cooling plate 53 arranged longitudinally are spaced apart to accommodate the first shut-off valve 70, the second shut-off valve 71, the third shut-off valve 72 and part of the cooling flow path.

[0044] In this embodiment, the welding workpiece 51 is a long rectangular 2219 aluminum alloy test plate. Fixtures 40 are positioned on both sides of the welding workpiece 51 to fix its lateral movement, simulating lateral constraints during cylinder welding. Multiple key-shaped pressure blocks 60 are arranged parallel to each other on the upper / lower cooling plates. The key-shaped pressure blocks 60 are fixed to the fixtures 40 using internal hexagonal screws 41, and external hexagonal screws 61 are used to press the upper / lower cooling plates firmly onto the welding workpiece 51, thus fixing the positions of the upper / lower cooling plates and the welding workpiece 51.

[0045] A segmented cooling method for long weld seam friction stir welding using the aforementioned cooling device includes:

[0046] Pretreatment: Before welding, multiple cooling zones are set on the surface of the workpiece to be welded from top to bottom along the longitudinal direction, ensuring that the cooling zones of the two oppositely set welding workpieces 51 are the same size and corresponding in position;

[0047] Place the workpiece 51 on the welding platform 42, place the upper cooling plate 50 on the upper half of the workpiece 51, place the lower cooling plate 53 on the lower half of the workpiece 51, and then use the clamp 40, the key block 60, screws and other fasteners to fix it, ensuring that the workpiece is in close contact with the upper / lower cooling plates.

[0048] According to the welding process parameters, adjust the flow rate and temperature of the coolant, start the cooling water pump 20, and make the coolant circulate in the cooling pipes and upper / lower cooling plates to pre-cool the welding area. Pre-cooling is considered complete when the infrared temperature sensor 80 located at the stirring head detects that the temperature of the welding area is 2-5℃ lower than the room temperature.

[0049] like Figure 1 The upper half welding process shown is as follows: After pre-cooling, friction stir welding is performed; when welding the upper half of the workpiece 51 (i.e., as shown) Figure 1 (As shown in the diagram, the location of the upper cooling plate 50) is monitored by an infrared temperature sensor 80 located at the stirring head, which monitors the temperature at the stirring head.

[0050] Upper cooling process: When the temperature reaches 300 degrees, open the first shut-off valve 70 and the third shut-off valve 72 of the two cooling pressure plate assemblies, keep the second shut-off valve 71 of the two cooling pressure plate assemblies closed, and keep the cooling water pump 20 running.

[0051] The coolant flows through the cooling water tank 10, cooling water pump 20, third branch 33 (blue flow path), upper cooling plate 50, first shut-off valve 70, third shut-off valve 72, and another first shut-off valve 70 before flowing into another upper cooling plate 50. After flowing through the two upper cooling plates 50, the cooling water is returned to the cooling water tank 10 via the fourth branch 34 (red flow path). The heat generated during welding is quickly carried away by the coolant flowing in the upper cooling plate 50.

[0052] After the upper half of the workpiece is welded, the cooling water pump 20 continues to run, so that the coolant continues to circulate in the upper cooling flow path, ensuring that the welding area gradually cools down to room temperature before starting the lower half of the welding.

[0053] like Figure 2 As shown, the lower half of the welding process: when welding the lower half of the workpiece 51 (i.e., as shown) Figure 2 (As shown in the diagram, the lower cooling plate 53 is located at the position of the lower cooling plate 53). The infrared temperature sensor 80 located at the stirring head monitors the temperature at the stirring head. When the temperature reaches 300 degrees, the lower cooling flow path is activated.

[0054] The second half of the cooling process: the first shut-off valve 70 is closed, the second shut-off valve 71 of the two cooling pressure plate assemblies is opened, and the third shut-off valve 72 is opened. The coolant flows through the cooling water tank 10, the cooling water pump 20, the first branch 31 (blue flow path), the lower cooling pressure plate 53 on the left, the second shut-off valve 71, the third shut-off valve 72, and another second shut-off valve 71 before flowing into the lower cooling pressure plate 53 on the right. The cooling water flows through the two lower cooling pressure plates 53 and then returns to the cooling water tank 10 through the second branch 32 (red flow path), so that the heat generated by welding is quickly carried away by the coolant flowing in the lower cooling pressure plate 53.

[0055] After welding is completed, continue running the cooling water pump 20 to ensure that the welding area in the lower cooling flow path gradually cools to room temperature; then turn off the cooling water pump, remove the clamping device, and take off the welded workpiece.

[0056] During friction stir welding, a large amount of heat is generated in the welding area, causing the workpiece temperature to rise. The cooling device described in this invention absorbs the heat from the welding area through circulating cooling water, thereby reducing the workpiece temperature and minimizing welding deformation. The flow rate and temperature of the cooling water can be adjusted according to the welding process parameters to achieve the best welding results.

[0057] Figure 3 The figures show a comparative example of friction stir welding using conventional methods and friction stir welding using the cooling device and segmented control method described in this invention. It is clearly visible from the figures that the deformation deviation is reduced from over 0.2 mm in the conventional method to less than 0.1 mm, significantly improving manufacturing accuracy and process economy.

[0058] In addition, during the experiment conducted according to this embodiment, the cooling time was more than 30 minutes without the cooling device described in this invention, but it could be cooled to room temperature within 10 minutes after the cooling device described in this invention was installed, which can effectively shorten the process time by 30%.

[0059] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is merely for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A cooling device for controlling the deformation of a welded joint, characterized in that, Multiple cooling devices are longitudinally arranged on two opposite workpieces to be welded (51) for segmented cooling of the workpieces to be welded; multiple cooling zones are arranged on the surface of the workpieces to be welded from top to bottom along the longitudinal direction, and two adjacent cooling zones are arranged from top to bottom as a group of cooling areas. Each cooling area is provided with a cooling device, and the cooling device includes a cooling pressure plate assembly, a cooling pipe and a third shut-off valve (72). The cooling pipeline is divided into an upper cooling flow path and a lower cooling flow path. The cooling plate assembly includes an upper cooling plate (50) and a lower cooling plate (53). The two upper cooling plates (50) are fixedly mounted on the upper cooling partition of the workpiece (51) to be welded, and the two lower cooling plates (53) are fixedly mounted on the lower cooling partition of the workpiece (51) to be welded. The upper cooling flow path flows through the two upper cooling plates (50), and the lower cooling flow path flows through the two lower cooling plates (53). The upper cooling flow path and the lower cooling flow path are connected by a third shut-off valve (72). The third shut-off valve (72) is used to control the flow of coolant through the upper cooling flow path or the lower cooling flow path, thereby realizing segmented cooling of the upper cooling plate (50) / lower cooling plate (53). The upper cooling zone includes upper cooling plates (50) located on the two workpieces to be welded and an upper cooling flow path; the upper cooling plates (50) have liquid inlets and outlets on their opposite sidewalls along their longitudinal direction, and the liquid inlets and outlets of the two upper cooling plates (50) are in opposite positions; the upper cooling flow path is as follows: The coolant flows from the cooling water tank (10) through the cooling water pump (20), the third branch (33), the upper cooling plate (50) on one side, the first shut-off valve (70), the third shut-off valve (72), the other first shut-off valve (70), and the upper cooling plate (50) on the other side, and then returns to the cooling water tank (10) through the fourth branch (34). The lower cooling zone includes a lower cooling plate (53) located on two workpieces to be welded and a lower cooling flow path; the lower cooling plate (53) has an inlet and an outlet on its opposite sidewalls along its longitudinal direction, and the inlet and outlet of the two lower cooling plates (53) are in opposite positions. The lower cooling flow path is as follows: The coolant flows from the cooling water tank (10) through the cooling water pump (20), the first branch (31), the lower cooling plate (53) on one side, the second shut-off valve (71), the third shut-off valve (72), another second shut-off valve (71), and the lower cooling plate (53) on the other side, and then returns to the cooling water tank (10) through the second branch (32). Multiple cooling zones are arranged along the longitudinal direction of the welded workpiece (51), and each cooling zone is equipped with a cooling pressure plate assembly and a third shut-off valve (72); each cooling zone can achieve segmented cooling through the control of the cooling pipeline and the cooling pressure plate assembly; Two workpieces (51) to be welded are respectively set on the welding platform (42), and a welding area is reserved between the two workpieces (51); the workpiece (51) to be welded is a rectangular workpiece with a weld seam longer than 3m. The cooling zones of the two oppositely positioned workpieces (51) to be welded are located in the same position.

2. The cooling device for controlling the deformation of welded joints according to claim 1, characterized in that, The upper cooling plate (50) and the lower cooling plate (53) are fixed on the workpiece (51) to be welded by a clamp (40). The clamp (40) is set on both sides of the workpiece (51) to constrain the lateral movement of the workpiece (51).

3. The cooling device for controlling the deformation of welded joints according to claim 2, characterized in that, Multiple key blocks (60) are arranged parallel to each other on the upper surface of the upper cooling plate (50) and the lower cooling plate (53). The key blocks (60) are fixed on the fixture (40) and the upper / lower cooling plates are pressed onto the welding workpiece (51) by screws to fix the position of the upper / lower cooling plates and the welding workpiece (51).

4. The segmented cooling control method for the cooling device according to claim 1, comprising: Pre-treatment: Before welding, multiple cooling zones are set on the surface of the workpiece to be welded from top to bottom along the longitudinal direction, and the cooling pressure plate assembly is fixed on its upper surface along the longitudinal direction of the workpiece (51); and a position for the welding area is reserved in the middle of the workpiece (51) to be welded, which are arranged opposite to each other. Start the cooling water pump (20) to circulate the coolant in the cooling pipes and upper / lower cooling plates of the cooling zone to be welded, thereby pre-cooling the cooling zone to be welded. When the temperature is 2-5 degrees below room temperature, the pre-cooling is considered complete. Welding and cooling of the upper cooling zone: After pre-cooling, friction stir welding is performed, and the infrared temperature sensor (80) located at the stirring head monitors the temperature at the stirring head; When the temperature reaches 250-350 degrees, the first shut-off valve (70) and the third shut-off valve (72) of the two oppositely arranged cooling pressure plate assemblies in the welding area are opened, while the second shut-off valve (71) of the two cooling pressure plate assemblies is kept closed, so that the coolant flows through the upper cooling flow path and the heat generated by welding is carried away by the coolant flowing in the upper cooling pressure plate (50). After the upper half of the workpiece is welded, continue to run the cooling water pump (20) to ensure that the welding area gradually cools down to room temperature; Welding and cooling in the lower cooling zone: Friction stir welding is performed, and an infrared temperature sensor (80) at the stirring head monitors the temperature at the stirring head; When the temperature reaches 250-350 degrees, the second shut-off valve (71) and the third shut-off valve (72) of the two oppositely arranged cooling pressure plate assemblies in the welding area are opened, while the first shut-off valve (70) of the two cooling pressure plate assemblies is kept closed, so that the coolant flows through the lower cooling flow path and the heat generated by welding is carried away by the coolant flowing in the lower cooling pressure plate (53). After the welding of the lower half of the workpiece is completed, continue to run the cooling water pump 20 to ensure that the welding area gradually cools down to room temperature, and then turn off the cooling water pump (20).

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