Friction stir welding device and control method

Abstract

The invention relates to a friction stir welding device and a control method, the friction stir welding device is provided with a material placing plane and a welding table of a first mounting groove, a plate can be placed on the material placing plane and fixed by a surrounding clamping mechanism, a first heating unit is placed in the first mounting groove, and the heating surface of the first heating unit can be lifted and attached to the side, facing the material placing plane, of the plate; the distance between the central projection and the weld joint projection is a first target distance, and the controller regulates and controls the temperature to a first target temperature determined according to the plate performance, the thickness and the welding temperature. According to the friction stir welding device, heat input to the bottom of a welding seam is enhanced in the friction stir welding process, the deformation and quality problems caused by insufficient heat are effectively solved, the more uniform temperature gradient is achieved, and the welding stability and the joint quality are remarkably improved.

Description

Technical Field

[0001] The invention relates to a friction stir welding device, and in particular to a friction stir welding device and a control method. Background Art

[0002] Friction stir welding has been widely used in aerospace, rail transportation, automobile manufacturing, electronic equipment and other fields. Compared with traditional melting welding methods, friction stir welding does not require welding materials and does not involve a melting process. Therefore, it can effectively avoid welding defects such as pores and thermal cracks that occur during welding and improve the mechanical properties of welded joints.

[0003] Traditional friction stir welding is a solid-state welding method. During the welding process, the stirring head rotates at high speed and is inserted between the materials to be welded. The friction between the stirring head and the material generates heat, which softens the material and achieves welding under the pressure of the stirring head.

[0004] However, since friction stir welding is achieved by generating heat through friction between the stirring head and the material, its heat input is limited by the efficiency of friction heat generation and the thermal conductivity of the material. When welding some aluminum alloy plates, because there is a temperature gradient along the thickness direction of the plate (the temperature at the bottom of the weld is much lower than the temperature in the middle and upper layers of the weld), the weld at the bottom of the plate will have too much deformation around the weld due to insufficient heat input, thus affecting the welding quality. Therefore, in order to improve the welding quality, a new design needs to be proposed to solve the above problems. Summary of the invention

[0005] The object of the present invention is to provide a friction stir welding device and a control method for reducing the deformation of the bottom of the weld by preheating the area near the weld at the bottom of the plate.

[0006] The technical solution adopted by the present invention to solve the above-mentioned problem is: a stir friction welding device, comprising a welding table, a clamping mechanism, a first heating unit and a controller, wherein the welding table comprises a material placement plane for placing a plate, and a first mounting groove is provided on the material placement plane. The clamping mechanism is arranged around the welding table to fix the plate at the material placement plane during the welding process. The first heating unit is arranged in the first mounting groove, and the first heating unit comprises a first heating surface, and the first heating surface is controlled to rise and fall, and the first heating surface is configured to fit with the side of the plate facing the material placement plane when the plate is placed on the material placement plane; and the distance between the orthographic projection of the center of the first heating surface on the material placement plane and the orthographic projection of the weld of the plate placed on the material placement plane on the material placement plane is defined as a first target distance. The controller is connected to the first heating unit to control the temperature rise and fall of the first heating surface. Wherein, when the stir friction welding device is in working state, the controller controls the working temperature of the first heating surface according to the target parameters of the plate, the first target distance and the welding temperature of the plate, and the working temperature of the first heating surface is defined as the first target temperature.

[0007] Preferably, the orthographic projection of the first heating unit on the loading plane is located on one side of the orthographic projection of the weld of the plate placed on the loading plane on the loading plane.

[0008] The friction stir welding device also includes a second heating unit connected to the welding table, the second heating unit moves in a controlled manner, the second heating unit includes a second heating surface, the temperature of the second heating surface rises and falls in a controlled manner, and the second heating surface is configured to be in contact with the side of the plate facing the loading plane when the plate is placed on the loading plane; and the distance between the orthographic projection of the center of the second heating surface on the loading plane and the orthographic projection of the weld of the plate placed on the loading plane on the loading plane is defined as the second target distance, and the orthographic projection of the second heating unit on the loading plane is located on the other side of the orthographic projection of the weld of the plate placed on the loading plane on the loading plane. Wherein, when the friction stir welding device is in working state, the controller controls the working temperature of the second heating surface according to the target parameters of the plate, the second target distance, the welding temperature of the plate and the first target temperature, and the working temperature of the second heating surface is defined as the second target temperature.

[0009] In particular, a control method for the above-mentioned friction stir welding device includes: obtaining the welding temperature at the weld of the plate when the plate is in a welding state according to the target parameters of the plate to be welded; determining the actual temperature of the weld facing the welding table side when the plate is in a welding state according to the welding temperature and the target parameters; determining the first target temperature according to the actual temperature, the target parameters and the first target distance, and determining the second target temperature according to the actual temperature, the target parameters, the first target temperature and the second target distance; controlling the first heating surface and the second heating surface to operate at the first target temperature and the second target temperature, respectively.

[0010] Preferably, the target parameters of the plate also include the specific heat capacity of the plate and the plastic temperature range of the plate.

[0011] The determining of the first target temperature according to the actual temperature, the target parameter and the first target distance, and the determining of the second target temperature according to the actual temperature, the target parameter, the first target temperature and the second target distance, comprises: determining the deformation sensitive parameter of the bottom of the plate according to the plastic temperature range of the plate, the thickness of the plate, the thermal conductivity of the plate and the specific heat capacity of the plate; determining the first target temperature according to the deformation sensitive parameter of the bottom of the plate, the first target distance and the actual temperature; determining the second target temperature according to the deformation sensitive parameter of the bottom of the plate, the second target distance and the actual temperature. Preferably, the two sides of the plate weld are respectively defined as the forward side and the backward side according to the rotation direction of the stirring member of the stir friction welding device.

[0012] The control method also includes: correcting the first target temperature and the second target temperature according to the temperature difference between the forward side and the backward side of the weld of the plate in the welding state to obtain a third target temperature and a fourth target temperature; controlling the first heating surface and the second heating surface to operate at the third target temperature and the fourth target temperature respectively.

[0013] Beneficial effects of the embodiments of the present invention: By adopting the technical means of enhancing the heat input to the bottom of the weld through a heating unit during the stir friction welding process, the problem of excessive deformation and reduced welding quality caused by insufficient heat input to the bottom of the weld in the prior art is effectively solved, thereby achieving the technical effect of a more uniform weld temperature gradient, significantly improved welding stability and joint quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic structural diagram of a friction stir welding device proposed in one embodiment of the present invention.

[0015] Figure 2It is a schematic top view of a friction stir welding device proposed in one embodiment of the present invention.

[0016] Figure 3 It is a flowchart of a control method of a friction stir welding device proposed in one embodiment of the present invention.

[0017] Figure 4 It is a flowchart of a method for determining the temperature of a plate weld proposed in one embodiment of the present invention.

[0018] Figure 5 It is a flowchart of a method for determining the actual temperature of a weld facing a welding station, proposed in one embodiment of the present invention.

[0019] Figure 6 It is a flowchart of a method for determining a first target heating temperature and a second target heating temperature proposed in one embodiment of the present invention.

[0020] Figure 7 It is a flowchart of a method for determining the target temperatures of the first heating surface and the second heating surface after considering the temperature difference between the advancing side and the retreating side of the weld, proposed in one embodiment of the present invention.

[0021] Among them: 10, welding table; 110, material placement plane; 20, clamping mechanism; 30, first heating unit; 310, first heating surface; 40, carrier; 50, second heating unit; 510, second heating surface; 60, controller; 70, plate. DETAILED DESCRIPTION

[0022] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0023] See also Figure 1 to Figure 2 In a preferred embodiment of the present application, a friction stir welding device is proposed to preheat the weld area of ​​the plate 70 to be welded before friction stir welding, thereby reducing the deformation at the bottom of the weld. In addition, the target object applicable to the friction stir welding device is an aluminum alloy plate 70 with a thickness limited to 2mm to 5mm. This is because it is difficult to use double-sided friction stir welding to fully process the weld of the thin plate 70, so a large range of deformation may occur on the side of the bottom of the weld (away from the stirring piece) due to poor conduction of welding temperature.

[0024] The friction stir welding device includes a welding table 10, a clamping mechanism 20, a first heating unit 30 and a controller 60, wherein the welding table 10 includes a placing plane 110 for placing a plate 70, a first mounting groove is opened on the placing plane 110, and the clamping mechanism 20 is arranged around the welding table 10 to fix the plate 70 on the placing plane 110 during the welding process.

[0025] Specifically: The welding table 10 is usually made of metal materials, preferably materials with high rigidity, high temperature resistance and good thermal conductivity (such as cast iron or low thermal expansion alloy) to ensure stability during heating and subsequent stir friction welding. When the welding table 10 is installed on a horizontal plane, the material placement plane 110 is located on the top plane of the welding table 10 for placing the plate 70 to be welded, and the material placement plane 110 can be designed according to the size and shape of the plate 70, usually in a rectangular or square layout to accommodate plates 70 of different thicknesses, lengths and widths. It should be noted that the material placement plane 110 is usually also provided with a positioning component, which is specifically represented by a positioning pin or positioning groove for coarse positioning of the plate 70, so as to simplify the fine-tuning and alignment of the position of the plate 70 before formal clamping.

[0026] The clamping mechanism 20 is arranged around the welding table 10 and can be set according to the surrounding space or peripheral contour of the welding table 10 to ensure that the plate 70 can be clamped from multiple directions during operation. The specific mechanical clamping form can be bolts, knobs, pressure plates, etc., and adjusted manually or with auxiliary tools. Furthermore, if there are higher requirements for clamping efficiency or stability, the clamping mechanism 20 can also use a cylinder or a hydraulic cylinder to achieve automatic or semi-automatic clamping. In the welding state, the clamping mechanism 20 can act downward (or inward) on the plate 70, so that the plate 70 is pressed and fixed on the material plane 110, avoiding displacement or warping due to thermal expansion and contraction, vibration or stirring force during subsequent welding.

[0027] In order to suppress the deformation amount at the bottom of the weld after the plate 70 is welded, the bottom of the weld of the plate 70 needs to be preheated. Therefore, in this embodiment, the friction stir welding device also includes a first heating unit 30 and a controller 60. Among them, the first heating unit 30 is arranged in the first mounting groove, the first heating unit 30 includes a first heating surface 310, the first heating surface 310 is controlled to rise and fall, the first heating surface 310 is configured to be in contact with the side of the plate 70 facing the material plane 110 when the plate 70 is placed on the material plane 110, and the distance between the orthographic projection of the center of the first heating surface 310 on the material plane 110 and the orthographic projection of the weld of the plate 70 placed on the material plane 110 on the material plane 110 is defined as a first target distance, and the controller 60 is connected to the first heating unit 30 to control the temperature rise and fall of the first heating surface 310. Furthermore, when the friction stir welding device is in working state, the controller 60 controls the working temperature of the first heating surface 310 according to the target parameters of the plate 70, the first target distance and the welding temperature of the plate 70, and the working temperature of the first heating surface 310 is defined as the first target temperature.

[0028] Specifically: the first installation groove is usually opened at a position corresponding to the weld preheating area at the material placement plane 110 of the welding table 10. The installation groove is opened or hollowed out according to the actual size of the device and the specifications of the plate 70, and the internal space can accommodate the first heating unit 30. The shape of the installation groove can be rectangular, circular or other regular geometric shapes for easy installation and maintenance.

[0029] The first heating surface 310 is usually planar and made of high temperature resistant and thermally conductive materials (such as high temperature alloys, high temperature resistant ceramic coated metals, etc.). The heating element of the first heating unit 30 can be in the form of resistance wire, electric heating tube or induction coil, etc., which are integrated on the back or inside of the first heating surface 310 to ensure the stability and uniformity of heating. Furthermore, if fast response or precise temperature control is required, zone heating or double-layer structure can be used to make the heating effect more flexible and the control more precise. In addition, in order to control the temperature of the first heating surface 310, the first heating unit 30 also includes a third temperature sensor (not shown in the figure). Specifically, the third temperature sensor can be installed on or near the first heating surface 310 to facilitate the detection of the real-time temperature of the first heating surface 310.

[0030] The first target distance refers to the distance from the center point of the first heating surface 310 to the weld. Since the purpose of the friction stir welding device in the present application is to preheat the weld area near the plate 70, in order to control the temperature of the weld area near the plate 70, it is necessary to determine the first target temperature based on the thermal conductivity of the plate 70 and the first target distance, so as to more accurately control the temperature within a preset range at the bottom of the weld area of ​​the plate 70 (from the center of the first heating surface 310 to the weld of the plate 70).

[0031] The controller 60 monitors the real-time temperature of the first heating surface 310 in real time and adjusts the temperature of the first heating surface 310 by adjusting the heating power or current, so that the real-time temperature of the first heating surface 310 is accurately maintained at the required first target temperature.

[0032] It should be noted that the controller 60 can obtain the first target temperature according to the target parameters of the plate 70, the first target distance, the welding temperature and welding direction of the plate 70, and adjust the working temperature of the first heating surface 310 to the first target temperature. The specific method for obtaining the first target temperature is referred to the control method described later.

[0033] When the aluminum alloy plate 70 is placed on the material plane 110 of the welding table 10, the first heating surface 310 of the first heating unit 30 is docked with the bottom of the plate 70, and then, under the precise control of the controller 60, the first heating surface 310 maintains the first target temperature to provide continuous and stable heat to the preset range at the bottom of the weld of the plate 70. In this way, preheating or auxiliary heat compensation can be provided for the bottom of the plate 70 and the root of the weld before or during the stir friction welding process, so that the plate 70 maintains a more uniform and suitable temperature distribution at the welding position, reducing welding deformation and stress concentration. Taking the aluminum alloy plate 70 as an example, the thick aluminum alloy plate 70 to be welded is placed on the material plane 110, and it is fixed by the surrounding clamping mechanism 20, and the first heating surface 310 is attached to the side of the plate 70 facing the material plane 110. According to the specific position of the weld, the distance between the orthographic projection of the weld on the material plane 110 and the orthographic projection of the center point of the first heating surface 310 on the material plane 110 is determined, and this distance is the first target distance. The controller 60 determines the first target temperature required for the first heating surface 310 according to the target parameters of the plate 70 (such as thickness, thermal conductivity, specific heat capacity, etc.) and the planned friction stir welding temperature. When the first heating unit 30 is started, the third temperature sensor will monitor the temperature of the first heating surface 310 in real time, and the controller 60 will perform closed-loop regulation to ensure that it works stably in the target temperature range. After heating for a preset time, the temperature at the bottom of the weld of the plate 70 will be similar to the temperature of the first heating surface 310. At this time, the friction stir welding device can be started to weld the seam of the plate 70. At this time, the upper side generates heat due to the high-speed rotation and friction of the stirring head, and the lower side is continuously heated by the first heating surface 310, which reduces the temperature gradient difference in the upper and lower directions of the weld area, and reduces the probability and deformation of incomplete fusion caused by too low temperature at the bottom of the weld.

[0034] In this embodiment, by preheating the bottom before and during welding, the deformation can be effectively suppressed and the welding quality can be improved. Specifically, after the bottom temperature is compensated, the thermoplasticized area produced by the stir friction welding head is more uniform, the weld is denser, and the grain refinement effect is better, thereby significantly improving the strength and reliability of the weld. Moreover, compared with the traditional large-area heating method, by heating at a fixed point at the bottom of the weld, energy can be saved, and the temperature of the weld area can be specifically increased, reducing the unnecessary heat impact on the surrounding non-welding parts or equipment.

[0035] It should be noted that the friction stir welding device in this embodiment should also include a controlled welding part (such as a rotating part and a stirring part, etc.), but because the welding part of the friction stir welding device is a prior art, it is not described in detail in this application.

[0036] In order to further suppress the deformation of the bottom of the weld of the plate 70, in some embodiments, as Figure 2As shown, the orthographic projection of the first heating unit 30 on the loading plane 110 is located on one side of the orthographic projection of the weld of the plate 70 placed on the loading plane 110 on the loading plane 110 . The friction stir welding device also includes a second heating unit 50, which is connected to the welding table 10. The second heating unit 50 moves in a controlled manner. The second heating unit 50 includes a second heating surface 510. The temperature of the second heating surface 510 rises and falls in a controlled manner. The second heating surface 510 is configured to be in contact with the side of the plate 70 facing the loading plane 110 when the plate 70 is placed on the loading plane 110; and the distance between the orthographic projection of the center of the second heating surface 510 on the loading plane 110 and the orthographic projection of the weld of the plate 70 placed on the loading plane 110 on the loading plane 110 is defined as a second target distance, and the orthographic projection of the second heating unit 50 on the loading plane 110 is located on the other side of the orthographic projection of the weld of the plate 70 placed on the loading plane 110 on the loading plane 110. When the friction stir welding device is in working state, the controller 60 controls the working temperature of the second heating surface 510 according to the target parameters of the plate 70, the second target distance, the welding temperature of the plate 70, the welding direction and the first target temperature, and the working temperature of the second heating surface 510 is defined as the second target temperature.

[0037] Specifically: the first heating unit 30 is installed on one side of the bottom of the weld of the plate 70, and the second heating unit 50 is installed on the other side of the bottom of the weld of the plate 70. The first heating unit 30 cooperates with the second heating unit 50 to heat both sides of the bottom of the weld of the plate 70 at the same time to overcome the limitation of unilateral heating.

[0038] The second heating unit 50 is similar to the aforementioned first heating unit 30, and the second heating surface 510 is similar to the first heating surface 310. The second heating surface 510 is generally made of a material that is resistant to high temperatures and has good thermal conductivity, and can provide controlled heat when it is close to or close to the bottom of the plate 70. In addition, in order to control the temperature of the second heating surface 510, the second heating unit 50 further includes a fourth temperature sensor. Specifically, the fourth temperature sensor can be installed on or near the second heating surface 510 to facilitate real-time monitoring of the temperature of the second heating surface 510.

[0039] It should be noted that the second heating unit 50 is of movable design and is installed on a carrier 40. The carrier 40 can be embodied as a long strip plate in a specific manner, and the long strip plate can be moved according to the specific state of the plate 70 to be welded, so that the weld of the plate 70 is located between the first heating unit 30 and the second heating unit 50 before preheating. The second heating unit 50 moves with the carrier 40, and the carrier 40 can be connected in a specific manner by means of a slide rail, a support arm or an electric push rod, so that it can be controlled to move (or lift) within a certain range.

[0040] When the device is working, the controller 60 will combine the target parameters of the plate 70 (such as the thickness of the plate 70, thermal conductivity, specific heat capacity, etc.), the second target distance (the distance between the orthographic projection of the weld on the material plane 110 and the orthographic projection of the center of the second heating surface 510 on the material plane 110), the welding temperature of the plate 70, the welding direction and the first target temperature to obtain the second target temperature. In addition, the second target temperature can be the same as or different from the first target temperature, depending on the comprehensive requirements for temperature gradient, heat input and required welding quality during welding.

[0041] In this embodiment, the double-sided heat compensation at the bottom of the weld of the plate 70, compared with the traditional single bottom preheating or heating from only one side, can make the entire welding area more evenly heated by controlled heating on both sides of the weld at the bottom of the plate 70, reduce local stress concentration, and thus more effectively suppress the deformation of the weld in the longitudinal or transverse direction. In addition, the first heating surface 310 and the second heating surface 510 can independently set the target temperature (first target temperature, second target temperature), which helps to adopt different thermal management strategies for different positions and different welding stages during the welding process.

[0042] In some embodiments, in order to uniformly heat the entire weld before welding, the number of the first mounting grooves is several, and each of the first mounting grooves is arranged along a first direction, and the first direction is parallel to the weld extension direction of the plate 70 placed on the material placement plane 110. The number of the first heating units 30 is several, and each of the first heating units 30 is installed in each of the first mounting grooves in a one-to-one correspondence. The number of the second heating units 50 is several, and each of the second heating units 50 is configured to be arranged along the first direction when the stir friction welding device is in working state.

[0043] Specifically, there are several first installation grooves, which are arranged in sequence and equidistantly along the first direction (i.e., parallel to the extension direction of the weld). The number and spacing of these installation grooves can be designed according to actual process requirements (such as the length of the plate 70, the length of the weld, the heat distribution requirements, etc.). Several first heating units 30 are respectively installed in the corresponding first installation grooves to ensure that each installation groove accommodates a heating unit. Such an arrangement allows each heating unit to play a preheating or heating role in the corresponding area below the weld, meeting the continuous or segmented heating requirements for the bottom of long welds or multi-segment welds. In addition, each first heating unit 30 has a first heating surface 310, which is usually planar and fits or contacts closely with the bottom of the plate 70. When the plate 70 is placed on the material placement plane 110, the first heating surface 310 can provide contact or proximity heating to keep the area near the weld at an ideal temperature.

[0044] Several second heating units 50 are similar to the first heating unit 30. The second heating units 50 are also arranged in multiple groups and should also be distributed in parallel along the direction of the weld. This multi-point or multi-segment setting can further enhance the temperature control of different positions at the bottom of the weld of the plate 70. Each second heating unit 50 has a second heating surface 510 that fits the bottom of the plate 70, and is usually fitted with the bottom of the plate 70 during welding or preheating. Furthermore, in some cases, by independently regulating the temperature of the second heating surface 510, it can cooperate with the first heating unit 30 to achieve multi-segment and multi-temperature heating management.

[0045] In this embodiment, by arranging a plurality of first mounting grooves and a plurality of first heating units 30 in sequence in the first direction, the weld can be sufficiently supplied with heat through segmented or integrated multi-point heating even if it is long. Furthermore, after the second heating unit 50 is arranged at multiple points, the bottom can be preheated simultaneously or sequentially in multiple sections to achieve full coverage of weld shapes and sizes of different shapes. Moreover, because each heating unit can set its own target temperature and heating sequence, even different sections of the same weld can be heated differentially according to factors such as the thickness difference of the plate 70 and the local stress characteristics. In addition, multi-segment heating can form a more continuous and uniform temperature field at the bottom of the weld, improve the plastic fluidity of the material during stir friction welding, reduce welding defects caused by local cold spots, and enable the plate 70 to be fully preheated and heat compensated in multiple locations, reduce thermal stress concentration and weld deformation, and achieve better forming quality.

[0046] In order to accurately monitor the temperature on both sides of the bottom weld of the plate 70, in some embodiments, the first heating unit 30 further includes a first temperature sensor (not shown in the figure), the first temperature sensor is connected to the controller 60, and the first temperature sensor is configured so that when the plate 70 is placed on the material placement plane 110, the temperature measuring portion of the first temperature sensor contacts the side of the plate 70 facing the material placement plane 110. The second heating unit 50 further includes a second temperature sensor (not shown in the figure), the second temperature sensor is connected to the controller 60, and the second temperature sensor is configured so that when the plate 70 is placed on the material placement plane 110, the temperature measuring portion of the second temperature sensor contacts the side of the plate 70 facing the material placement plane 110.

[0047] Specifically: In this embodiment, on the basis of the original friction stir welding device (including the first heating unit 30, the second heating unit 50, the welding table 10, etc.), a first temperature sensor and a second temperature sensor are added. The first temperature sensor and the second temperature sensor are the same temperature measuring element, which can independently or collaboratively measure the bottom temperature of the welding plate 70. The two sets of temperature sensors are electrically connected to the controller 60 to form a real-time temperature detection and feedback closed loop, providing a basis for the temperature adjustment of the heating unit.

[0048] Since the temperature measuring part of the first temperature sensor and the temperature measuring part of the second temperature sensor are required to contact the side of the plate 70 facing the material plane 110, the sensors are usually arranged at the material plane 110 of the welding table 10 so that they can naturally fit on the lower surface when the plate 70 is placed. The specific installation method can be embedded, that is, a through hole or groove is reserved in the material plane 110, or a convex type, so that the sensor head is slightly higher than the material plane 110, so as to better fit the bottom of the plate 70.

[0049] The controller 60 is connected to both the first temperature sensor and the second temperature sensor, and can use their respective temperature signals for real-time monitoring. When it is sensed that the temperature in the area around the bottom of the weld of the plate 70 fluctuates or does not reach the preset value, the controller 60 can maintain or restore the ideal heating temperature range by adjusting the working parameters (such as heating power) of the first heating unit 30 and / or the second heating unit 50.

[0050] In this embodiment, by attaching the first temperature sensor and the second temperature sensor to both sides of the bottom of the weld of the plate 70, the actual heating conditions on both sides of the bottom of the plate 70 can be captured in time, avoiding deviations caused by relying on indirect ambient temperature or heating surface temperature. In addition, compared with only monitoring the temperature of the heating element itself, directly monitoring the bottom temperature of the plate 70 can better reflect the heat input condition of the weld root. In particular, when the bottom temperature of the plate 70 is lower than or higher than the first target temperature or the second target temperature, the controller 60 can quickly adjust the temperature of the corresponding first heating surface 310 and / or the second heating surface 510 to ensure that the heat supply of the entire welding process is always in the best state. This plays a key role in aluminum alloy plates (especially 2mm to 5mm medium and thin plates) that are sensitive to heat input in stir friction welding, and can effectively reduce thermal stress concentration and welding defects.

[0051] In order to make the weld of the plate 70 better under the action of the above-mentioned stir friction welding device, a control method suitable for the above-mentioned stir friction welding device is proposed. The control method is for the plate 70 in the stir friction welding state. By acquiring the target parameters (including the material, thickness, thermal conductivity, specific heat capacity, etc. of the plate 70) and the ambient temperature, combined with the moving speed and rotation speed of the stirring member or the stirring needle or the stirring head, the temperature distribution of the plate 70 during welding is calculated. Then, according to the actual temperature, plastic temperature range and deformation sensitivity of the bottom of the plate 70, the first target heating temperature and the second target heating temperature are determined respectively to control the first heating surface 310 and the second heating surface 510, so as to provide the optimal heat input at the bottom of the weld. Moreover, because of the temperature difference between the forward side and the backward side of the weld, steps S500 and S600 need to be executed for correction and compensation to balance the temperature on both sides of the weld. Figures 3 to 7 As shown, the control method includes: Step S100: deriving the welding temperature at the weld of the plate 70 when the plate 70 is in a welding state according to the target parameters of the plate 70 to be welded.

[0052] Step S200: determining the actual temperature of the side of the weld facing the welding table 10 when the plate 70 is in a welding state according to the welding temperature and the target parameter; Step S300: determining the first target temperature according to the actual temperature, the target parameter and the first target distance, and determining the second target temperature according to the actual temperature, the target parameter, the first target temperature and the second target distance; Step S400: controlling the first heating surface 310 and the second heating surface 510 to operate at the first target temperature and the second target temperature respectively.

[0053] Among them, see Figure 4The target parameters of the plate 70 include the material of the plate 70 and the thickness of the plate 70. Step S100 obtains the welding temperature at the weld of the plate 70 when the plate 70 is in a welding state according to the target parameters of the plate 70 to be welded, including: Step S110: determining the optimal moving speed and the optimal rotating speed of the stirring member corresponding to when the quality of the weld of the plate 70 is within the optimal range according to the material of the plate 70 and the thickness of the plate 70 .

[0054] Step S120: deriving the welding temperature at the weld of the plate 70 when the plate 70 is in a welding state according to the material of the plate 70, the thickness of the plate 70, the optimal moving speed of the stirring member, and the optimal rotating speed of the stirring member.

[0055] Wherein: Step S110, the material of the plate 70 (such as aluminum alloy or other alloys) will affect the plastic temperature range and optimal welding speed of stir friction welding. The thickness of the plate 70 (for example, 2mm to 5mm) will determine the heat distribution of the stirring member in the weld area, the insertion force of the stirring needle, and the upper limit of the movement and rotation speed. Generally, the optimal process window (including movement speed, rotation speed, temperature, etc.) of stir friction welds of different materials and thicknesses can be obtained based on a large amount of test data or technical manuals. After confirming the optimal forming requirements of the weld, select or calculate the "optimal movement speed of the stirring member" and "optimal rotation speed of the stirring member", which are the basic parameters for subsequent temperature calculations.

[0056] Specifically, the target object of the friction stir welding device proposed in this embodiment is aluminum alloy as a typical example. It is usually determined by material selection during the production process, or given by the supplier / technical specification (for example, 6061 aluminum alloy). In the technical document or material description, its chemical composition, thermophysical properties, etc. will be indicated. The material of the plate 70 directly determines the key thermal and mechanical properties such as the plastic temperature range (see below), thermal conductivity, specific heat capacity, etc., thereby affecting the friction stir welding process window and heating strategy.

[0057] The thickness of the plate 70 refers to the size of the metal plate to be welded perpendicular to its plane, usually in millimeters. It can be measured by a caliper, a micrometer or an automated thickness gauge, and is marked by the raw materials during mass production. It is understandable that the greater the thickness of the plate 70, the longer the heat conduction path, the greater the temperature gradient, and the insertion depth of the stirring needle and the rotation speed of the stirring head also need to be adjusted accordingly. Many calculations in the method (such as thermal conductivity, deformation sensitivity evaluation, etc.) rely on the plate thickness.

[0058] The moving speed of the stirring piece refers to the speed at which the stirring tool (including stirring needle, stirring shoulder, etc.) moves along the direction of the weld, and the unit is usually mm / min or m / min. Specifically, a suitable range can be found in a large number of tests or experience curves. If the moving speed is too high, insufficient heat input will lead to weld defects, and if it is too low, the production efficiency will be low and it is easy to overheat. Through steps S110 and S120, the best value is selected in combination with thickness and material.

[0059] The rotation speed of the stirring element refers to the rotation speed of the stirring tool in the axial direction, and the unit is rpm (revolutions per minute). The specific speed can be obtained through process tests or by referring to the existing mature process window.

[0060] Furthermore, the combination of the rotation speed and the moving speed of the stirring member determines the degree of material plasticization and the quality of the weld, and also affects the formation of the welding temperature. The optimal moving speed and the optimal rotation speed refer to the combination of moving / rotating speeds that can make the weld achieve the best or better balance in terms of quality standards such as strength, density, and surface forming. Specifically, the optimal range can be found through a large number of tests or by consulting industry standards and data documents. After locking these two parameters in step S110 and step S120, the subsequent temperature distribution and heating control are calculated. The weld quality is in the optimal range, which means that the weld metal meets or even exceeds the design or industry standard requirements in terms of appearance, internal defects (such as holes, cracks, etc.) and mechanical properties (tensile strength, fatigue performance, etc.). Specifically, it can be judged whether the weld reaches the "optimal" or close to the optimal quality range by a comprehensive evaluation of indicators such as penetration, stirring sufficiency, metallographic structure or tensile test. In addition, in step S110, the stirring member process parameters (moving speed and rotation speed) are determined together with the thickness and material of the plate 70.

[0061] In terms of specific methods, take 3mm thick 6061 aluminum alloy sheet metal as an example: Before actual production, the process window data corresponding to the best performance of the weld can be obtained through repeated welding tests. The specific steps are as follows: First, determine the experimental parameter range: the stirring piece rotation speed range is 600-1500rpm, and the stirring piece movement speed range is 50-500mm / min. Secondly, implement orthogonal tests or single variable tests. For example, through orthogonal tests, different rotation speeds (for example: 600, 900, 1200, 1500rpm) and different movement speeds (for example: 50, 100, 200, 300, 400, 500mm / min) are combined for welding tests. Then, after welding, the quality of the weld can be evaluated by the following indicators: Appearance quality, the surface flatness and finish of the weld can be visually inspected. Internal defects, non-destructive testing technologies such as X-rays or ultrasound can be used to detect holes and cracks inside the weld. In addition, tensile tests can also be used to detect the tensile strength of the weld. Finally, after the experiment is completed, the test data is recorded and analyzed to find the parameter range that satisfies the strength ≥ 80% to 90% of the parent material strength and the weld has no obvious defects. Based on the data, the optimal rotation speed and optimal movement speed of the 6061 aluminum alloy plate 70 of the corresponding thickness can be determined. In addition, this method can be repeatedly applied to plates 70 of different materials or thicknesses to obtain the optimal process parameter database.

[0062] Step S120, the material of the plate 70, the thickness of the plate 70, the optimal moving speed and the optimal rotation speed of the stirring member are brought into the thermal model or empirical formula of the welding process to evaluate the average or peak temperature during the formation of the stir friction weld under the combination of movement and rotation. The calculation result is the welding temperature, which can be regarded as the target temperature range of the center or near-center area of ​​the weld. This is the starting point of the high temperature zone, and the subsequent heat conduction to the bottom of the plate 70 is based on this temperature.

[0063] The welding temperature of the weld seam mainly depends on the heat input generated by the stirring head and the heat dissipation characteristics of the plate 70. Therefore, the following calculation formula for the welding temperature T of the weld seam is proposed: .

[0064] in: : Welding temperature of the weld area of ​​plate 70 (unit: ℃). : Ambient temperature or initial plate temperature at 70°C (unit: °C). : Frictional heat conversion efficiency, dimensionless (usually between 0.8 and 0.95). : The average friction torque (unit: N·m) at the interface between the stirring member and the plate member 70 can be determined through experimental measurement or empirical data. : Rotational speed of the stirring element (rad / s). : Moving speed of stirring element (m / s). : Material density of plate 70 (kg / m³). : Specific heat capacity of the material of the plate 70 (J / (kg·℃)). : The effective cross-sectional area of ​​the friction stir welding weld (m²), which can usually be taken as the weld thickness × the stirring needle diameter. : Thermal conductivity of the plate 70 material (W / (m·°C)). : Plate 70 thickness (m).

[0065] The calculation formula of the weld temperature T covers the main thermodynamic factors in the actual production of stir friction welding. The friction heat efficiency, stirring head torque, rotation speed and moving speed, and plate 70 material properties (density, specific heat capacity, thermal conductivity) are all reflected through real data, and the attenuation factor of heat conduction is taken into account. This formula is essentially a thermal model that combines energy conservation and heat conduction attenuation. It describes how the temperature T of the weld area during stir friction welding is determined by the heat generated by the stirring head and the material properties: Ambient temperature (initial temperature) The formula represents the initial temperature of the plate 70 (Usually ambient temperature.) Because before the actual welding begins, the plate 70 is at ambient temperature, which is the reference point before heat input, and any temperature rise is superimposed on the ambient temperature.

[0066] The heat input is It reflects the contribution of the temperature increase in the weld area after the heat generated by the stir friction welding stirring parts. It is the friction heat conversion efficiency, which is about 0.8 to 0.95. In fact, when the stirring head rubs against the material, not all mechanical energy is converted into heat energy. Some of it is lost in the form of wear, vibration, etc., so an efficiency factor is needed. To express the effective proportion actually used for material heating.

[0067] Friction heat conversion efficiency It indicates the efficiency of converting the mechanical energy input into heat energy during the friction stir welding process, and the value usually ranges from 0.8 to 0.95. The method for determining is as follows: Step 1: Experimental preparation stage. Select the material of the plate 70 to be welded and determine the size of the stirring tool (stirring head diameter, needle length). Set up a certain number of temperature sensors and place them in the weld area (such as the bottom, middle and top of the weld). Equipped with a torque sensor to measure the actual torque value of the stirring tool. Prepare a thermal imager or thermocouple to measure the real-time temperature of the weld area. Step 2: Implement the stir friction welding experiment. Set a specific stirring tool speed (such as 1200rpm) and moving speed (such as 200mm / min). Start welding and record the torque data and temperature data throughout the process. Step 3: Heat calculation (Q value measurement), calculate the actual heat absorbed by the weld area by measuring the temperature rise and material properties: .in, : The actual amount of heat absorbed by the weld area (J). : Weld area volume (m³). : Average temperature of the weld area after welding (°C). In friction stir welding, it is generally defined as: .

[0068] Effective length: The actual length of the weld formed by welding. Effective width: The width of the weld area (usually 1 to 1.2 times the diameter of the stirring needle). Weld thickness: The thickness of the plate 70 (usually equal to the plate thickness ).

[0069] The detailed steps to determine the weld area volume are as follows: First, the effective length of the weld must be determined. The length of the friction stir welding weld can be determined by actual measurement methods. For example, use a tape measure, vernier caliper or laser rangefinder to accurately measure the actual length of the weld. Secondly, the effective width of the weld must be determined. Usually, 1.0 to 1.2 times the diameter of the stirring needle is taken as the weld width W. If the accuracy requirement is high, the actual weld width can be determined by observing the actual weld cross section (measured by metallographic microscope or macroscopic image after slicing). The general engineering method is, .in, : The diameter of the stirring needle is determined by actual measurement. Next, the weld thickness is determined. The weld thickness is usually the thickness of the plate 70, and the plate thickness can be directly measured. For example, use a caliper or micrometer to measure the thickness of the plate. Then, calculate the weld area volume . Substitute the above parameters into the calculation formula: .

[0070] The above is the weld area volume The calculation method will be explained later. method of determination.

[0071] Step 4: Input mechanical energy calculation (W input), calculate the mechanical energy input to the weld area through the experimentally measured torque and stirring head speed: .in, is the average friction torque (N·m) measured experimentally. is the stirring tool speed (rad / s). is the time taken for stirring welding (s). In addition, the average friction torque M reflects the actual friction torque between the stirring head and the plate during the welding process. The method for determining the average friction torque M is as follows: First, during the equipment preparation stage, a high-precision torque sensor (torque meter) is installed on the welding equipment (stirring head spindle), and it is confirmed that the torque meter is accurately calibrated and can record data in real time. Secondly, during the friction torque value measurement stage, the welding process is started, the stirring head rotates and moves, and the sensor records the torque changes during the whole process in real time. In addition, the torque value is continuously recorded in a complete welding test to form a complete torque-time curve. Then, the average torque is calculated, and the torque data recorded during the entire welding process is integrated and averaged: Or a simpler approach is to simply average the consecutive measurements: Usually the experiment is repeated several times to find the average value to obtain a more stable and reliable torque value.

[0072] The above is a specific method for determining the average friction torque M. The following will continue to give the method for determining the efficiency method steps.

[0073] Step 5: Efficiency Calculation, friction heat conversion efficiency That is the ratio of actual absorbed heat to mechanical energy input: , averaging multiple sets of experimental data to obtain a more stable η value, usually between 0.8 and 0.95.

[0074] The above are the specific steps of the method for determining η.

[0075] The friction torque M describes the torque applied by the stirring head on the plate. The greater the torque, the stronger the friction on the material surface and the more heat is generated. Therefore, the torque M directly determines the mechanical energy input to the weld area.

[0076] The faster the angular velocity ω of the stirring head, the more friction times per unit time and the greater the heat input. Therefore, the rotation speed is one of the important variables of heat input.

[0077] The product of the above three items η, M, and ω represents the total heat input power provided by the stirring head per unit time.

[0078] The term V·ρ·Cp·Aeff in the denominator represents the ability of the plate 70 material to absorb and store heat. Specifically: The moving speed V of the stirring head indicates the speed at which heat is transferred into the weld area. The faster the welding speed, the less heat is obtained in the same area per unit time. The larger the material density ρ, the slower the temperature rises after the same volume of material absorbs heat. The specific heat capacity Cp indicates the energy required for the material to increase unit temperature. The higher the specific heat capacity, the slower the temperature rises. The effective cross-sectional area Aeff indicates the size of the area where the weld material effectively absorbs heat. The larger the area, the more dispersed the input heat and the slower the temperature rise. Among them, the effective cross-sectional area refers to the cross-sectional area of ​​the area that actually participates in thermoplasticization and forms the weld, which is usually simplified as: . The determination method is as follows: First, determine the size of the stirring tool and the thickness of the plate 70, and measure or record the diameter of the stirring needle. , determine the thickness of the plate weld area (generally the plate thickness ). Then, the cross-sectional area is calculated, and the effective cross-sectional area is the product of the weld thickness and the stirring needle diameter: This calculation method is practical and simple and is generally widely used in engineering applications.

[0079] The above is the method for determining the effective cross-sectional area Aeff.

[0080] In summary, the entire heat input term actually reflects: the temperature increase per unit volume of material ≈ friction heat input power / (welding speed × material heat capacity × weld effective cross-sectional area). It can be seen that the higher the friction heat input power, the faster the material heats up. The stronger the heat absorption capacity of the material (the greater the density and specific heat capacity), the slower the temperature rise. The faster the stirring head moves, the shorter the time each area of ​​the material stays heated, and the less the temperature rises. Heat conduction attenuation term It reflects the heat loss caused by the thermal conduction effect of the material. The higher the thermal conductivity λ of the material, the faster the heat conduction loss in the welding area (especially the conduction to the depth of the lower plate 70 and the direction of the welding table 10), and the worse the effect of heat accumulation in the weld area. Therefore, the larger the λ, the smaller the value of the exponential term, and the more obvious the temperature reduction in the weld area. The larger the thickness δ of the plate 70, the longer the distance the heat needs to penetrate, and the more serious the overall heat decay in the weld area. The denominator (V·ρ·Cp) represents the speed of heat input and the heat capacity of the material. If the heat input is fast enough or the heat capacity of the material is large enough, the material heats up quickly, and sufficient heat accumulation can be formed in the weld area to effectively offset the influence of heat conduction loss; on the contrary, the temperature rises slowly and the heat is easily dissipated, and the temperature of the welding area cannot be significantly increased. Therefore, the overall physical meaning of the exponential term is that after considering the thermal conductivity and thickness of the material, the temperature of the weld area caused by the heat input will have an exponential decay trend.

[0081] The fundamental reason why the formula is designed in this way is that the actual welding process is a process in which heat input (frictional heat generation) and heat output (material heat loss) compete with each other. The determinant of heat input (η·M·ω) must be included in the formula, the heat absorption capacity of the material (ρ·Cp·V·Aeff) must be clearly reflected because it affects the amplitude and rate of temperature rise, and the heat conduction loss mechanism (λ·δ) must be reflected in the form of exponential decay, which is a real phenomenon in actual welding. Therefore, through the reasonable combination of the above three core factors, the actual temperature of the weld area during stir friction welding can be estimated more realistically and accurately. This design makes the formula highly consistent with the actual physical process and is more suitable for guiding the formulation and optimization of production processes.

[0082] See also Figure 5 The friction stir welding device further includes a thermometer to obtain the ambient temperature. The target parameter of the plate 70 also includes the thermal conductivity of the plate 70. Step S200 determines the actual temperature of the side of the weld facing the welding table 10 when the plate 70 is in the welding state according to the welding temperature and the target parameter, including: Step S210: determining the conduction temperature of the weld toward the welding platform 10 when the plate 70 is in a welding state according to the thickness of the plate 70, the thermal conductivity of the plate 70 and the welding temperature.

[0083] Step S220: determining the actual temperature of the side of the weld facing the welding station 10 after heat dissipation correction according to the ambient temperature and the conduction temperature.

[0084] Wherein: Step S210, when the temperature of the stirring zone (i.e., the "welding temperature" in S120) is conducted to the bottom of the plate 70 or the root of the weld, a certain temperature gradient will be caused due to the thickness and thermal conductivity of the plate 70. The "conduction temperature" at the bottom of the weld can be obtained through a thermal conduction model or empirical formula, that is, the temperature theoretically transferred from the center of the weld to the lower surface of the plate 70 (before ignoring or simplifying the ambient heat dissipation). The specific method for determining the conduction temperature is as follows: During the friction stir welding process, the temperature at the center (upper part) of the weld is relatively high, which is transferred to the bottom of the weld (i.e., the side in contact with the welding table 10) through the thickness direction of the plate 70. Due to the influence of the thermal conductivity of the material and the thickness of the plate, the bottom temperature must be lower than the center temperature of the weld. The Fourier heat conduction law (simplified model) under the stable heat conduction state can be used: In the formula, is the heat flux (W), which represents the amount of heat transferred per unit time. is the heat conduction cross-sectional area (m²), i.e. the effective cross-sectional area of ​​the weld. is the center temperature of the weld (derived from S120). is the conduction temperature at the bottom of the weld (to be determined). The specific calculation steps for the conduction temperature are as follows: First, determine the heat flux in the weld area The heat input to the stirring zone mainly comes from the friction heat of the stirring head: ;Welding time Next, determine the conduction cross-sectional area , the conduction cross-sectional area is the effective cross-sectional area of ​​the weld. The specific calculation method can be found in the previous text. Then, according to Fourier's law, the bottom conduction temperature is calculated. Specifically, , , , , Substituting into Fourier's formula, we can find : .

[0085] The above formula clearly reflects the influence of material thickness δ and thermal conductivity λ on the temperature gradient: the greater the thickness δ, the greater the temperature difference, making the bottom temperature of the weld of the plate 70 lower. The smaller the thermal conductivity λ, the greater the temperature difference, making the bottom temperature lower. The smaller the thermal conductivity λ, the greater the temperature difference, making the bottom temperature lower.

[0086] Step S220 In the actual friction stir welding process, the lower surface of the weld will be in contact with the welding table 10 or the air, and the ambient temperature will cause heat loss. If a cooling airflow is used or the ambient temperature is low, the impact will be more significant. Therefore, the ambient temperature (the value given by the thermometer) is combined with the conduction temperature of the previous step to obtain an "actual temperature" that is closer to the actual welding environment. This actual temperature is usually lower than the theoretical conduction temperature of S210, and this value needs to be substituted into subsequent calculations to reasonably plan the bottom heating power. In addition, the conduction temperature obtained in step S210 is a theoretical value. The actual bottom of the weld will be cooled by the surrounding environment (such as the welding table 10 and the air), and the temperature will be lower. Therefore, corrections are required: First, the influence of environmental heat dissipation needs to be analyzed. When the bottom temperature of the plate 70 is higher than the ambient temperature, heat will be dissipated from the bottom of the plate to the environment. Specifically, Newton's cooling law can be used to estimate and correct the environmental heat dissipation. Newton's cooling law: .in, is the convection heat transfer coefficient (W / (m²·℃)), which is about 10-25 in air environment and about 100-500 in contact with the welding table 10. is the heat dissipation contact area (m²), i.e. the bottom area of ​​the weld. is the theoretical conduction temperature. is the ambient temperature measured by the thermometer. Secondly, the correction formula for the actual temperature at the bottom of the weld is: ) Considering the influence of conduction temperature and heat dissipation, the following method can be used for approximate calculation: Method 1 is a steady-state approximation. Assuming that the bottom of the plate 70 is in a near-steady-state heat conduction condition, the actual bottom temperature is: .

[0087] This formula takes into account the actual temperature after the balance of heat dissipation by conduction and convection, and is applicable to steady-state conditions.

[0088] Method 2 is the empirical correction method. If the heat dissipation coefficient cannot be accurately obtained , then the empirical correction factor can be used in engineering : .

[0089] It is generally between 0.75 and 0.95, depending on the cooling conditions.

[0090] Among them, the empirical correction coefficient essentially reflects a reduction ratio of the actual temperature at the bottom of the weld to the theoretical conduction temperature during the friction stir welding process, reflecting the degree of influence of the actual environmental cooling conditions on the temperature at the bottom of the weld. When the heat dissipation at the bottom is severe, it is relatively small (such as 0.75-0.85), and when the heat dissipation at the bottom is weak, it is relatively large (such as 0.85-0.95). The following is a specific method for how to obtain the empirical correction coefficient in actual engineering: First, it is the experimental preparation stage. Select the material to be welded (such as 6061 aluminum alloy), determine the thickness of the plate (for example, 3mm), and clarify the parameters of stir friction welding (such as welding speed, stirring head speed). Equip a temperature measuring device (thermocouple, infrared thermometer or thermal imager), and install temperature sensors on the upper surface (center area of ​​the weld) and the lower surface (contact surface with the welding table 10) to actually measure the temperature at the bottom of the weld. At the same time, the ambient temperature must also be measured. Secondly, it is the experimental test (temperature measurement) stage. Start stir friction welding under specific welding parameters. Continuously record and obtain the real-time temperature of the upper surface (center of the weld) of the weld. At the same time, record the actual temperature of the lower surface of the weld. Synchronously record the experimental ambient temperature. In addition, perform at least 3 to 5 welding experiments to obtain reliable temperature data. Then, calculate the theoretical conduction temperature. Calculate according to the thermal conductivity model given in step S210: Next, we need to find the corresponding . Substitute the temperature data measured in each experiment into the following formula to calculate : In this way, a corresponding correction coefficient value can be obtained for each test. Finally, the final empirical correction coefficient is determined. , for all the experimental results Take the arithmetic mean as the final empirical correction factor: Among them, if individual experimental data deviate significantly (such as measurement errors are too large), they can be eliminated first and then averaged.

[0091] In summary, the recommended range of empirical correction coefficients under different working conditions is 0.70-0.80 for contact with a high thermal conductivity metal welding table 10 and extremely strong heat dissipation (such as a copper table); 0.75-0.85 for contact with a high thermal conductivity metal welding table 10 and extremely strong heat dissipation (such as a copper table); 0.85-0.90 for contact with a low thermal conductivity welding table 10 or an insulation pad and weak heat dissipation; 0.90-0.95 for a case where the bottom is suspended and only air convection is used.

[0092] Through the above detailed steps, we can obtain the empirical correction coefficient that is true and accurate and suitable for actual production use. .

[0093] For further information, see Figure 6 , determining the first target temperature according to the actual temperature, the target parameter, the welding direction and the first target distance, and determining the second target temperature according to the actual temperature, the target parameter, the first target temperature, the welding direction and the second target distance, including: Step S310 : determining the deformation sensitive parameters of the bottom of the plate 70 according to the plastic temperature range of the plate 70 , the thickness of the plate 70 , the thermal conductivity of the plate 70 , and the specific heat capacity of the plate 70 .

[0094] Step S320: determining a first target temperature according to the deformation sensitive parameter of the bottom of the plate 70, the first target distance and the actual temperature.

[0095] Step S330: determining a second target temperature according to the deformation sensitive parameter of the bottom of the plate 70, the second target distance and the actual temperature.

[0096] Wherein: the deformation sensitivity parameter of the bottom of the plate 70 is determined in step S310. The deformation sensitivity parameter characterizes the sensitivity of the material to temperature changes under welding thermal cycle conditions, and is directly related to the tendency of the material to undergo plastic deformation under specific heat input. The general expression of the deformation sensitivity parameter (DSP, DeformationSensitivityParameter) is: .in: It is the deformation sensitive parameter (m²·s / ℃). is the specific heat capacity (J / (kg·℃)). is the upper limit of the material's plastic temperature (°C). is the lower limit of the plastic temperature of the material (℃). , and It reflects the heat storage capacity of the plate, that is, the larger the heat capacity, the slower the plate 70 heats up, and the more difficult it is to quickly enter the plastic state. It reflects the thermal conductivity of the material, that is, the stronger the thermal conductivity, the easier it is for heat to diffuse and the less likely it is to form local high temperatures. It reflects the plastic temperature range. The wider the range, the wider the plastic area of ​​the material, and the easier it is to deform. The core idea of ​​the design of this formula is to clarify the relationship between the plastic deformation trend of the material and the heat input and heat diffusion. During the friction stir welding process, whether the material is prone to obvious deformation (such as warping and twisting) depends on the temperature rise rate caused by the welding heat input and the speed of heat diffusion to the surrounding. Therefore, the design idea of ​​this formula is divided into two parts: First, the molecular part (Heat capacity effect). Specific heat capacity It indicates the amount of heat that needs to be absorbed by a unit mass of material to raise its temperature by 1°C. The larger the value, the slower the heating, and the more difficult it is for the material to quickly reach a high-temperature plastic state. The larger it is, the more mass it contains per unit volume. The larger the value, the more heat is needed, making the heating process slower and more stable. The larger it is, the longer the heat conduction path is, and more heat is required per unit thickness to achieve overall temperature rise. The larger the value, the more obvious the temperature gradient is, making it difficult for the bottom temperature of the material to quickly reach the plastic state.

[0097] In summary, the molecular part ( ) reflects the overall heat capacity of the material and represents the material's ability to resist rapid temperature rise and slow down the trend of plastic deformation.

[0098] Secondly, the denominator (Thermal diffusion and plastic temperature zone effect). Thermal conductivity It reflects the ability of the material to diffuse heat outward. The higher the value, the faster the heat diffuses, making the temperature field around the weld more uniform, making it difficult to form local high temperature, and weakening the tendency of plastic deformation. The lower the temperature, the more obvious the local heat accumulation will be, resulting in a rapid local temperature rise and easy to cause obvious deformation. middle is the upper limit of plastic temperature, is the lower limit of the plastic temperature, and the difference between the two is the temperature range in which the material undergoes plastic deformation. If the plastic temperature range is wide (large), the material may undergo plastic deformation in a wide temperature range, is insensitive to temperature changes, and deformation is easy to occur, but not violent. If the plastic temperature range is narrow (small), a slight change in temperature may cause violent deformation. Therefore, the denominator ( ) comprehensively reflects the inhibitory effect of thermal diffusion on the sensitivity of plastic deformation. The faster the thermal diffusion or the wider the plastic range, the lower the local deformation tendency of the material.

[0099] In summary, the larger the DSP value, the more sensitive the plate 70 material is to temperature changes and the more likely it is to undergo plastic deformation, whereas the smaller the DSP value, the more stable it is. This parameter can be used to reasonably optimize the heating conditions during welding so that the deformation of the weld is within a controllable range. It can be obtained through material manuals and thermal conductivity test experiments, and the plastic temperature zone , It can be determined through material manuals, welding material data or high temperature mechanical experiments. In addition, the design of this formula conforms to the basic laws of thermal physics and material deformation, and can more realistically reflect the influence of the actual working conditions of stir friction welding on the material deformation trend, which is suitable for welding process optimization. The parameters can be obtained from conventional tests and material databases, and have strong ease of use in actual production. This formula has a clear physical basis and clear practical use, which can effectively guide the optimization design of bottom heating conditions in actual welding processes.

[0100] The method for determining the first target temperature in step S320 is specifically as follows: The first target temperature (close to the advancing side of the weld) and the second target temperature (close to the retreating side of the weld) can be expressed as: ; .

[0101] in: is the first target temperature (°C). is the second target temperature (°C). is the actual temperature of the weld bottom (obtained from S220) (℃). is a deformation sensitive parameter. is the first target distance (m) (the distance from the center of the weld to the first heating surface). is the second target distance (m) (the distance from the center of the weld to the second heating surface 510 ). is the correction coefficient, which can be initially taken as 1.0 and gradually corrected and determined through experiments (see below).

[0102] Among them, the correction factor The method for determining is as follows: In order to obtain more accurate temperature compensation, it is necessary to determine the correction factor through actual experiments. .

[0103] Step 1: During the initial welding test, take Step 2: Conduct the initial welding test. Calculate the target temperature according to the above formula , , and conduct welding tests. Measure the weld quality and the actual deformation at the bottom of the weld. Step 3: Evaluate the initial test results. If the plasticity at the bottom of the weld is obviously insufficient (excessive deformation, poor quality), it means that the compensation temperature is too low and should be appropriately increased. Values, such as If the temperature at the bottom of the weld is too high, the deformation will increase, indicating that the compensation is excessive and the ,like Step 4: Repeat the test. Use the adjusted new k value to conduct the welding test again, and then repeat the above second step several times until the deformation of the weld bottom and the weld quality reach the ideal state.

[0104] The above target formula is designed in this way to ensure that the temperature of the weld bottom area reaches a reasonable plastic deformation range, so as to reduce the welding deformation at the bottom of the weld and improve the weld quality. The following points are specifically considered: First, the actual temperature at the bottom of the weld Usually too low to effectively enter the ideal plastic temperature range of the material, so additional compensation heating is required. The compensation temperature depends on the material's sensitivity to changes in heat input (DSP) and the distance from the heating position to the weld. , so the compensation part of the formula is designed as: Secondly, the higher the deformation sensitivity of the material, the more easily the material is deformed by the temperature gradient and heat input, and a greater compensation temperature rise is required. Therefore, the compensation temperature is designed to be The effect of material sensitivity on the temperature compensation is directly proportional to the distance. Then, as the heating position moves away from the weld center, the efficiency of heat transfer to the weld center decreases. Therefore, the farther away from the weld center, the weaker the required temperature compensation effect. Therefore, the compensation temperature is designed to be proportional to the distance. Inversely proportional, it reasonably reflects the effect of heating distance on heat input efficiency. Finally, different welding conditions, environments, and equipment efficiency will produce certain differences, and fixed theoretical values ​​may not be suitable for all actual situations. The purpose is to adjust the actual compensation amount through experiments, reflect the flexibility and adjustability of the formula, and make it more accurately applicable to specific welding conditions.

[0105] In step S400, the controller 60 is used to execute control. The controller 60 sends temperature settings or power instructions to the first heating surface 310 and the second heating surface 510 respectively. In addition, the controller 60 can form a closed-loop control through the third temperature sensor and the fourth temperature sensor to continuously maintain the target temperature.

[0106] Specifically, the first target temperature / second target temperature refers to the set temperature values ​​of the first heating surface 310 and the second heating surface 510 obtained in step S320, which are used to achieve local preheating / insulation at the bottom of the plate 70 or different sides of the weld, so as to adjust the "actual temperature" to the ideal range. Specifically, the temperature can be calculated by combining the deformation sensitive parameter, the actual temperature, and the first target distance, the second target distance and other parameters, and the temperature will be converted into a heating power or current parameter in the controller 60.

[0107] See also Figure 7 The two sides of the weld of the plate 70 are defined as the forward side and the backward side respectively according to the rotation direction of the stirring member of the friction stir welding device. In order to balance the influence of the temperature difference between the forward side of the weld and the backward side of the weld on the two sides of the weld at the bottom of the plate 70, the control method further includes: Step S500: Correcting the first target temperature and the second target temperature according to the temperature difference between the advancing side and the retreating side of the weld of the plate 70 in the welding state to obtain the third target temperature and the fourth target temperature.

[0108] Step S600: controlling the first heating surface 310 and the second heating surface 510 to operate at the third target temperature and the fourth target temperature respectively.

[0109] During the friction stir welding process, there is often a temperature difference between the forward side AS and the backward side RS of the weld. This is because the rotation direction of the stirring head on the forward side is consistent with the welding movement direction, resulting in more friction heat input and higher temperature; while the rotation direction of the stirring head on the backward side is opposite to the welding movement direction, resulting in less friction heat input and lower temperature. Therefore, in order to ensure the temperature balance on both sides of the weld, it is necessary to adjust the heating temperature on both sides of the weld bottom separately, that is, to correct the first target temperature and the second target temperature determined previously, and obtain the third target temperature and the fourth target temperature that are closer to the actual needs.

[0110] The method for determining the third target temperature and the fourth target temperature in step S500 is specifically as follows: Step 1: Identify the temperature difference. During the welding process, the actual temperature difference between the forward and backward sides of the weld can be obtained through actual measurement or thermal simulation: Among them: If , indicating that the temperature on the forward side is higher than that on the backward side; if , indicating that the temperature on the retreat side is higher than that on the forward side (with a very small probability). It should be noted that: in general, the forward side temperature is higher. is a positive value, and this article also uses this as an example. Step 2: In order to facilitate calculation, a temperature difference correction factor is introduced .in: is the temperature of the center area of ​​the weld (obtained from the previous steps); the corresponding factor for the forward side (higher temperature) is Cooling; the corresponding factor for the retreat side (lower temperature) is Step 3: Formulas for the third target temperature and the fourth target temperature. Among them, the third target temperature corresponding to the forward side is (Original first target temperature The fourth target temperature corresponding to the retreat side (Original second target temperature of corrections). . .in: , It is an empirical correction coefficient (generally between 0.3 and 0.8), and its function is to control the compensation or reduction range to avoid excessive adjustment. , The first target temperature and the second target temperature (bottom compensation temperature) are respectively obtained in steps S330 and S340. It is the actual temperature difference between the advancing side and the retreating side, which can be obtained by thermocouple measurement or simulation during welding. is the welding temperature at the center of the weld, which can be obtained through the previous steps.

[0111] During the friction stir welding process, the temperature difference between the forward side and the backward side is an important reason for the unstable welding quality. The forward side AS has a higher temperature due to the local heat accumulation caused by the rotation direction of the stirring head and the welding direction. The backward side RS has a relatively insufficient heat input and a lower temperature due to the rotation direction opposite to the welding direction. If not handled, the microstructure and properties on both sides of the weld will be inconsistent, resulting in welding defects (such as deformation, cracks, etc.). Therefore, it is necessary to make a certain degree of cooling correction on the forward side temperature, and a certain degree of heating correction on the backward side temperature. This design is based on the physical mechanism and actual process requirements, and is more in line with the actual welding production requirements. The correction formula can effectively reduce or eliminate the temperature difference on both sides of the weld in actual engineering, making the thermal field in the weld area more uniform. It can also improve the uniformity of plastic flow of the weld and significantly reduce the welding deformation. Furthermore, it can also improve the microstructure of the weld, enhance the mechanical properties and reliability of the welded joint, thereby improving the stability and consistency of production, and making it easier to standardize and control quality.

[0112] The basic target temperature in the above formula is the ideal compensation temperature preliminarily calculated based on the actual bottom temperature and material sensitivity, which can provide a reasonable temperature benchmark. On this basis, adjustments are made considering the difference between the forward side and the backward side to ensure the rationality of the initial temperature setting.

[0113] The temperature difference directly reflects the actual heat input difference between the forward and backward sides of the weld. It can be used as the basis for core adjustment. The larger the temperature difference, the larger the adjustment required. It directly determines the size and direction of the compensation amplitude (heating or cooling). It can be obtained by measuring the actual temperature difference on both sides of the welding process through actual experiments. Welding center temperature Provides a reasonable temperature reference benchmark, reflecting the temperature difference The relative proportional relationship within the overall welding temperature range. Thus, the absolute temperature difference is converted into a relative temperature difference ratio. , ensuring that adjustments can be made with a uniform scale under different welding conditions and materials, making it easier to promote and use. and It is used to control the actual compensation amplitude and flexibility, provide flexible adjustment function, optimize according to the experimental results, and prevent over- or under-compensation. It can adapt to different welding conditions, material types, and plate thickness changes. It can be repeatedly adjusted and determined through actual welding tests during the experimental measurement of welding quality.

[0114] , It is the adjustment range control factor. The specific determination method is as follows: Step 1: Preliminary determination of the range. Usually, the values ​​taken in the first test are ,Right now , Step 2: Conduct the initial welding test. The initial third and fourth target temperatures can be calculated using the above formula , , and conduct welding experiments. Real-time measurement of the bottom temperature of the weld on the forward and backward sides, and record the actual weld quality and deformation. The third step is to evaluate the initial welding results and adjust , If the adjusted temperature difference is significantly reduced and the weld quality is significantly improved, it means that the selected , If the forward side cools down too much or too little, or the backward side heats up too much or too little, make appropriate adjustments. If the forward side temperature does not drop significantly, increase , the temperature on the retreat side does not increase significantly, so it can be increased The experiment was then repeated until the temperature difference was significantly reduced and the weld quality was significantly improved.

[0115] Step S600 determines the third target temperature and the fourth target temperature. , After that, the actual control process is as follows: First, the first heating unit 30 (below the forward side) is controlled to operate at the third target temperature. Secondly, control the second heating unit 50 (below the back side) to operate at the fourth target temperature .

[0116] In this way, by applying differentiated target heating temperatures to the forward side and the backward side of the bottom of the weld respectively, the temperature difference naturally formed between the forward side and the backward side during the welding process is effectively offset, so that the temperature on both sides of the bottom of the weld tends to be balanced, and finally the overall quality and deformation of the weld are effectively controlled. It should be noted that in the field of stir friction welding, general technicians usually pay attention to the compensation of the overall heat in the weld area, and believe that only setting the first heating unit 30 on one side of the bottom of the weld can meet the heating requirements of the bottom of the weld and reduce deformation, and usually do not consider the temperature difference between the forward side and the backward side of the weld. Because, for conventional technical solutions, only the bottom heating unit needs to be used to ensure uniform heat input during welding, so as to avoid defects (such as cracks, deformation, etc.) caused by local overheating or overcooling. However, the difficulty of this conventional solution is that, when further considering the temperature difference problem, the existing heating strategy is difficult to deal with the temperature difference between the forward and backward sides of the weld due to the inconsistency between the rotation direction of the stirring head and the welding direction. This temperature difference leads to uneven temperature distribution on both sides, which directly affects the welding quality, weld formation and deformation, etc. However, in the existing technology, it is usually difficult to further finely balance this difference. This is mainly reflected in: First, the design inertia of existing heating units. Conventional heating units are usually designed according to the overall temperature requirements, and the temperature difference on both sides of the weld has not been considered. This means that the influence of temperature differences is not fully considered in the configuration of the heating system, resulting in limitations in subsequent technical improvements. Secondly, the complexity of thermodynamic regulation. In stir friction welding, the existence of temperature differences makes the heat diffusion mode, heat input and its influence on the weld quality on the forward and backward sides asymmetric. Traditional methods mainly focus on overall heating balance, and fail to effectively deal with such local differences, resulting in the "roughness" of overall compensatory heating. Even if heating units are set up on both sides, it is still difficult to accurately control different welding areas. In addition, usually, technicians have ensured the uniformity of the bottom temperature through the heating unit during design, but have not fully realized the profound impact of the temperature difference between the forward and backward sides on the weld quality, so there is no detailed compensation design specifically for this difference.

[0117] This application proposes a method of "setting the temperature difference between the forward side and the backward side of the weld to the desired quality" by deeply analyzing the profound influence of the temperature difference between the forward side and the backward side of the weld on the welding quality during the friction stir welding process. As the core decision factor, the temperature of the forward side and the backward side is finely balanced by modifying the formula of the target temperature. The core of this technical solution is reflected in the following aspects: First, it is the clear identification and quantification of the temperature difference. The present invention first accurately identifies and quantifies the temperature difference between the forward side and the backward side of the weld. , this temperature difference is a key factor affecting welding quality. The prior art usually ignores this point, but the present invention integrates it into the control system as a core parameter, which significantly improves the accuracy of the heating strategy. Secondly, the target temperature of the forward side and the backward side is corrected. The present invention uses the temperature difference The target temperature correction formula (see step S500 above) is introduced to adjust the target temperatures of the first heating unit 30 and the second heating unit 50 differently. This technical solution allows the heating temperatures of the forward side and the backward side to flexibly adapt to the temperature difference, thereby ensuring that the temperatures on both sides of the weld tend to be balanced. In addition, the correction coefficient is further determined through precise measurement and experimental verification. , , which makes the adjustment of the temperature on the forward and backward sides more precise, avoids over- or under-correction of temperature, and ensures the reasonable distribution of heat input during welding.

[0118] In summary: The difficulty of the prior art is that the design of the heating unit is usually based on the assumption of uniform heating, while ignoring the temperature difference between the forward side and the backward side caused by the characteristics of stir friction welding. To further consider the influence of temperature difference within this design framework, it involves the complex interaction of heat input, heat diffusion and heat compensation, which has not been fully valued in conventional design. Moreover, in conventional technology, technicians habitually believe that temperature difference is a natural phenomenon in the welding process, which can be compensated by uniform heating, and lack systematic thinking on temperature difference correction. The present invention breaks through this cognitive limitation by taking temperature difference as a decision factor, and proposes a temperature compensation scheme with practical application value. It breaks through the mindset in traditional heating unit design, makes temperature control in the welding process more refined and accurate, and significantly improves the quality of the weld. This innovative idea and technical solution provides a new solution for further improving welding quality and has significant engineering application value.

[0119] The above contents described in this specification are merely examples of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, as long as they do not deviate from the contents of the present specification or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A friction stir welding device, characterized in that: include: The welding table comprises a material placement plane for placing the plate, wherein the material placement plane is provided with a first mounting groove; A clamping mechanism, arranged around the welding table, to fix the plate at the material placement plane during welding; A first heating unit is arranged in the first mounting groove, the first heating unit comprises a first heating surface, the first heating surface is controlled to rise and fall, and the first heating surface is configured to be in contact with a side of the plate facing the loading plane when the plate is placed on the loading plane; and a distance between an orthographic projection of a center of the first heating surface on the loading plane and an orthographic projection of a weld of the plate placed on the loading plane on the loading plane is defined as a first target distance; A controller connected to the first heating unit to control the temperature rise and fall of the first heating surface; When the friction stir welding device is in working state, the controller controls the working temperature of the first heating surface according to the target parameters of the plate, the first target distance and the welding temperature of the plate, and the working temperature of the first heating surface is defined as the first target temperature.

2. A friction stir welding device according to claim 1, characterized in that: The orthographic projection of the first heating unit on the material placement plane is located on one side of the orthographic projection of the weld of the plate placed on the material placement plane on the material placement plane; The friction stir welding device also includes: A second heating unit is connected to the welding table, the second heating unit moves in a controlled manner, the second heating unit includes a second heating surface, the temperature of the second heating surface rises and falls in a controlled manner, and the second heating surface is configured to fit with a side of the plate facing the loading plane when the plate is placed on the loading plane; and a distance between an orthographic projection of the center of the second heating surface on the loading plane and an orthographic projection of a weld of the plate placed on the loading plane on the loading plane is defined as a second target distance, and the orthographic projection of the second heating unit on the loading plane is located on the other side of the orthographic projection of the weld of the plate placed on the loading plane on the loading plane; When the friction stir welding device is in working state, the controller controls the working temperature of the second heating surface according to the target parameters of the plate, the second target distance, the welding temperature of the plate and the first target temperature, and the working temperature of the second heating surface is defined as the second target temperature.

3. A friction stir welding device according to claim 1, characterized in that: The number of the first installation grooves is several, and the first installation grooves are arranged along a first direction, and the first direction is parallel to the extension direction of the weld of the plate placed on the material placement plane; There are a plurality of first heating units, and each of the first heating units is installed in each of the first installation grooves in a one-to-one correspondence.

4. A friction stir welding device according to claim 2, characterized in that: The number of the first installation grooves is several, and the first installation grooves are arranged along a first direction, and the first direction is parallel to the extension direction of the weld of the plate placed on the material placement plane; There are a plurality of first heating units, and each of the first heating units is installed in each of the first installation grooves in a one-to-one correspondence; The number of the second heating units is multiple, and each of the second heating units is configured to be arranged along the first direction when the friction stir welding device is in a working state.

5. A friction stir welding device according to claim 4, characterized in that: The first heating unit further includes a first temperature sensor, the first temperature sensor is connected to the controller, and the first temperature sensor is configured such that when the plate is placed on the material placement plane, a temperature measuring portion of the first temperature sensor contacts a side of the plate facing the material placement plane; The second heating unit also includes a second temperature sensor connected to the controller. The second temperature sensor is configured so that when the plate is placed on the material placement plane, a temperature measuring portion of the second temperature sensor contacts a side of the plate facing the material placement plane.

6. A control method for a friction stir welding device according to claim 4 or 5, characterized in that: include: The welding temperature at the weld seam of the plate when the plate is in a welding state is obtained according to the target parameters of the plate to be welded; Determine, according to the welding temperature and the target parameter, the actual temperature of the weld facing the welding station when the plate is in a welding state; determining the first target temperature according to the actual temperature, the target parameter, and the first target distance, and determining the second target temperature according to the actual temperature, the target parameter, the first target temperature, and the second target distance; The first heating surface and the second heating surface are controlled to operate at the first target temperature and the second target temperature, respectively.

7. The control method of a friction stir welding device according to claim 6, characterized in that: The target parameters include the material of the plate and the thickness of the plate; The step of obtaining the welding temperature at the weld of the plate when the plate is in a welding state according to the target parameters of the plate to be welded comprises: Determine the optimal moving speed and rotating speed of the stirring member when the quality of the plate weld is in the optimal range according to the material and thickness of the plate; The welding temperature at the weld of the plate when the plate is in a welding state is obtained according to the material of the plate, the thickness of the plate, the optimal moving speed of the stirring piece and the optimal rotating speed of the stirring piece.

8. The control method of a friction stir welding device according to claim 7, characterized in that: The friction stir welding device also includes a thermometer to obtain the ambient temperature; The target parameters also include the thermal conductivity of the plate; The step of determining the actual temperature of the side of the weld facing the welding station when the plate is in a welding state according to the welding temperature and the target parameter comprises: Determine the conduction temperature of the weld toward the welding table when the plate is in a welding state according to the thickness of the plate, the thermal conductivity of the plate and the welding temperature; The actual temperature of the weld facing the welding station after heat dissipation correction is determined according to the ambient temperature and the conduction temperature.

9. The control method of a friction stir welding device according to claim 8, characterized in that: The target parameters of the plate also include the specific heat capacity of the plate and the plastic temperature range of the plate: The determining the first target temperature according to the actual temperature, the target parameter and the first target distance, and determining the second target temperature according to the actual temperature, the target parameter, the first target temperature and the second target distance, comprises: Determine the deformation sensitive parameter of the bottom of the plate according to the plastic temperature range of the plate, the thickness of the plate, the thermal conductivity of the plate and the specific heat capacity of the plate; Determine a first target temperature according to a deformation sensitive parameter of the bottom of the plate, the first target distance and the actual temperature; The second target temperature is determined according to the deformation sensitive parameter of the bottom of the plate, the second target distance and the actual temperature.

10. The control method of a friction stir welding device according to claim 9, characterized in that: The two sides of the plate weld are defined as the advancing side and the retreating side respectively according to the rotation direction of the stirring member of the friction stir welding device; The control method further comprises: Correcting the first target temperature and the second target temperature according to the temperature difference between the advancing side and the retreating side of the weld of the plate in the welding state to obtain a third target temperature and a fourth target temperature; The first heating surface and the second heating surface are controlled to operate at the third target temperature and the fourth target temperature, respectively.

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