A friction stir welding apparatus and method for high melting point materials

Abstract

The application provides a friction stir welding device and method for high melting point materials, wherein a support assembly is sleeved on a stirring needle of the friction stir welding device, a heating element is arranged on the support assembly, the support assembly can be laterally translated synchronously with the stirring needle but cannot rotate, and a space between a shaft shoulder and a top surface of the support assembly can just clamp a workpiece; the welding method comprises the following steps: adjusting the relative position of a friction stir welding machine and a plate to be welded, centering the plate to be welded on the stirring needle, and adjusting the space height between the shaft shoulder and the top surface of the support assembly again, so that the space height is smaller than the thickness of the plate to be welded by 0.1-0.2 mm; the shaft shoulder and the stirring needle are synchronously rotated at a rotating speed of 20-1000 rpm in the welding process, and the shaft shoulder and the stirring needle are translated at a speed of 20-100 mm / min. The application fundamentally avoids the problem of stirring needle fracture and prolongs the service life of the friction stir welding equipment.

Description

Technical Field

[0001] This invention belongs to the field of friction stir welding technology, specifically relating to a friction stir welding device and welding method for high melting point materials. Background Technology

[0002] Friction stir welding (FSW) involves a high-speed rotating stirring head interacting with the material, causing intense plastic deformation, thermoplastic flow, and recrystallization to form fine equiaxed crystals, thus joining the workpieces. FSW effectively avoids defects such as cracks, porosity, and inclusions associated with traditional fusion welding, and is commonly used for joining low-melting-point metals such as aluminum, magnesium, and their alloys.

[0003] For high-melting-point plates (melting point not lower than 1400℃, such as titanium alloys), especially medium-thick plates (thickness 6-12mm), due to their low thermal conductivity, welding defects often occur at the bottom of the weld due to insufficient heat input. When the length and pressure of the stirring pin are not matched with the thickness of the plate to be welded, incomplete penetration defects are prone to occur at the root of the joint. In addition, due to the high plasticizing temperature and large rheological stress of high-melting-point materials, low rotation speed and low welding speed process parameters are usually used in friction stir welding, which seriously affects welding efficiency. All these factors severely limit the development and application of friction stir welding technology for high-melting-point materials.

[0004] Although the use of biaxial shoulder friction stir welding can increase heat generation at the weld root and reduce the temperature gradient along the thickness direction of the material, when applied to high melting point materials, the stirring pin will be subjected to high process load (metal rheological stress) during the welding process, which can easily cause instability in the welding process and breakage of the stirring pin.

[0005] In the prior art, document CN108890118A discloses a back auxiliary heating device for friction stir welding of titanium and titanium alloys. The back plate for welding is provided with heating components distributed along its length. However, its heating temperature is not easy to adjust and it is prone to overheating, making it unsuitable for welding high melting point thin plates (thickness 3-5mm). Document CN104551379A discloses a method for friction stir welding assisted by heat sources such as electric arc and MIG. However, this method of adding auxiliary heat sources from the front of the weld cannot effectively improve the large temperature gradient field caused by the low thermal conductivity of the material or the increased thickness of the welded material. Instead, it will cause the temperature gradient to be even greater. Document CN 108907448A discloses a friction stir welding process method for moving heating the back of thick copper and aluminum dissimilar metals. This method heats the steel back plate by the alternating magnetic field of an induction cooker. However, its back support device is relatively complex and does not fundamentally solve the problem of incomplete penetration at the root of the weld.

[0006] More importantly, existing friction stir welding equipment has very high requirements for the fixing accuracy of the plates to be welded. If the flatness is not good, it is easy to cause defects in the weld. In particular, when welding high melting point thin plates with long welds (length not less than 500mm), multiple long strip welding defects will appear in the weld area. Summary of the Invention

[0007] At least in order to solve the technical problems mentioned in the background art, the present invention aims to provide a friction stir welding device and welding method for high melting point materials.

[0008] The present invention adopts the following technical solution.

[0009] A friction stir welding apparatus for high melting point materials includes a clamping part, an upper section of which is fixedly connected to the spindle of a friction stir welding machine, and a shoulder fixedly connected to the upper section of the clamping part. A stirring pin integrally formed with the shoulder is provided on the shoulder, and a support assembly is sleeved on the stirring pin. A heating element is provided on the support assembly. The support assembly can move laterally synchronously with the stirring pin but does not rotate. The space between the shoulder and the top surface of the support assembly is just enough to hold the workpiece. The top surface of the support assembly is a standard plane and is used to closely fit the workpiece. The stirring pin passes through the weld seam of the workpiece.

[0010] To further improve welding quality, the support assembly includes a cylindrical body with a flat top, a heating coil on the cylindrical body as the heating element, a circulating cooling channel on the cylindrical body, a bearing assembly in the inner cavity of the cylindrical body, the bearing assembly being sleeved on the stirring needle, and a bearing end cap fixed to the lower end of the cylindrical body below the bearing assembly.

[0011] Preferably, the bearing assembly includes an upper angular contact ball bearing and a lower angular contact ball bearing arranged coaxially, with a washer placed between the upper and lower angular contact ball bearings. This structure avoids generating additional axial forces, maintains stable movement, and improves the service life of the entire welding device.

[0012] To further improve the stability of the welding process, as one of the preferred solutions, a fixing ring is provided on the inner side of the bearing end cover. The fixing ring is sleeved and fixedly connected to the stirring needle. The lower end of the fixing ring is flush with the lower end of the bearing end cover, and the outer side wall of the fixing ring is against the inner side wall of the bearing end cover. The height of the space between the shoulder and the top surface of the support assembly is 0.1 to 0.2 mm less than the thickness of the workpiece.

[0013] A welding method using the aforementioned friction stir welding apparatus includes the following steps:

[0014] Step 1: First, wipe the surface of the plates to be welded with an organic solvent, then fix the plates to be welded on the workbench so that the plates are joined together and on the same horizontal plane.

[0015] Step 2: Adjust the height of the space between the shoulder and the top surface of the support assembly according to the thickness of the plate to be welded, so that the height of the space is greater than or equal to the thickness of the plate to be welded.

[0016] Step 3: Turn on the coolant supply system connected to the circulating cooling channel to allow the coolant to circulate.

[0017] Step 4: Set the induction heating power according to the melting point of the material to be welded, turn on the power of the heating element, and control the temperature of the material to be welded to be maintained between 400-1000℃ before welding.

[0018] Step 5: Adjust the relative position of the friction stir welding machine and the plate to be welded so that the butt joint area of ​​the plate to be welded is aligned with the stirring pin. Then, readjust the height of the space between the shoulder and the top surface of the support assembly so that the height of the space is 0.1 to 0.2 mm less than the thickness of the plate to be welded.

[0019] After adjusting the welding parameters, proceed with the welding process, ensuring that the shoulder and stirring pin rotate synchronously at a speed of 20-1000 rpm, and that the shoulder and stirring pin move horizontally at a speed of 20-100 mm / min until the entire welding process is completed.

[0020] To further improve the stability of the welding process, as a second preferred option, a fixing ring is provided on the inner side of the bearing end cover. The fixing ring is sleeved and movably sleeved on the stirring needle. The lower end of the fixing ring is flush with the lower end of the bearing end cover, and the outer wall of the fixing ring is against the inner wall of the bearing end cover. A flexible pressing mechanism is provided below the cylinder. The flexible pressing mechanism is used to support the cylinder, the bearing end cover, and the fixing ring, so that the height of the space between the shoulder and the top surface of the support assembly is 0.1 to 0.2 mm less than the thickness of the workpiece.

[0021] To prevent multiple elongated welding defects in long weld seams, the flexible pressing mechanism includes a linear slide rail parallel to the top surface of the support assembly. A movable seat is mounted on the linear slide rail, and a servo motor is mounted on the movable seat. The output end of the servo motor is connected to three vertically arranged and parallel ball screws via a gear transmission mechanism. Each of the three ball screws is fitted with a nut seat, which is fixedly connected to a support plate. The top surface of the support plate is flat and is used to support the cylinder, bearing end cap, and fixing ring. When the servo motor is running, it drives the three ball screws to rotate synchronously through the gear transmission mechanism, which in turn drives the nut seat and the support plate to move up and down synchronously, thereby driving the entire assembly consisting of the cylinder, bearing end cap, fixing ring, bearing assembly, and heating coil to move up and down.

[0022] Furthermore, the servo motor, gear transmission mechanism, and ball screw segments are located inside the housing. Multiple through holes are provided on the support plate and the top of the housing for the ball screw and stirring needle to pass through. A force sensor is installed between the support plate and the cylinder.

[0023] A welding method using the aforementioned friction stir welding apparatus includes the following steps:

[0024] Step 1: First, wipe the surface of the plates to be welded with an organic solvent, then fix the plates to be welded on the workbench so that the plates are joined together and on the same horizontal plane.

[0025] Step 2: Adjust the height of the space between the shoulder and the top surface of the support assembly according to the thickness of the plate to be welded, so that the height of the space is greater than or equal to the thickness of the plate to be welded.

[0026] Step 3: Turn on the coolant supply system connected to the circulating cooling channel to allow the coolant to circulate.

[0027] Step 4: Set the induction heating power according to the melting point of the material to be welded, turn on the power of the heating element, and control the temperature of the material to be welded to be maintained between 400-1000℃ before welding.

[0028] Step 5: Adjust the relative position of the friction stir welding machine and the plate to be welded so that the butt joint area of ​​the plate to be welded is aligned with the stirring pin. Then, readjust the height of the space between the shoulder and the top surface of the support assembly so that the height of the space is 0.1 to 0.2 mm less than the thickness of the plate to be welded.

[0029] After adjusting the welding parameters, perform welding, so that the shoulder and the stirring pin rotate synchronously at a speed of 20-1000 rpm, and the shoulder and the stirring pin move horizontally at a speed of 20-100 mm / min until the entire welding process is completed.

[0030] During the welding process: whenever the pressure value fed back by the force sensor is less than the preset threshold, the servo motor is controlled to move upward, so that the nut seat moves upward until the feedback pressure value is 10-20KN; whenever the pressure value fed back by the force sensor is greater than the preset threshold, the servo motor is controlled to move downward, so that the feedback pressure value is 10-20KN.

[0031] As a preferred embodiment, at the beginning of the weld, the control shoulder and stirring pin are kept for 2-5 seconds; the high melting point material is a titanium alloy plate.

[0032] This invention can not only effectively reduce the plastic deformation resistance of high-melting-point materials, reduce the temperature gradient and microstructure inhomogeneity in the weld thickness direction, improve the plastic flow of materials at the weld root, and suppress joint tunnel defects, but also effectively avoid root incomplete penetration defects and obtain high-quality welded joints. This invention significantly reduces the load-bearing capacity of the stirring pin, improves welding efficiency, and broadens the process parameters of friction stir welding of high-melting-point materials. It also has advantages such as energy saving and environmental protection, simple structure, and convenient operation.

[0033] The specific structure in this invention can replace the rigid backing plate in the conventional friction stir welding process. The follow-up support component will not rotate during the welding process, which fundamentally avoids the problem of stirring pin breakage and extends the service life of the friction stir welding equipment.

[0034] This invention is not only applicable to welding medium-thick plates with high melting points, but also to welding thin-walled plates with high melting points smoothly. More importantly, it can adaptively adjust the welding accuracy deviation caused by the flexible bending of thin-walled plates, and can stably and smoothly weld high-melting-point thin plates with long welds (length not less than 500mm), avoiding the problem of multiple defects in thin-walled long strip welds. Attached Figure Description

[0035] Figure 1 This is a partial three-dimensional schematic diagram of the friction stir welding device in Example 1;

[0036] Figure 2 for Figure 1 A cross-sectional schematic diagram;

[0037] Figure 3 This is a partial three-dimensional schematic diagram of the friction stir welding device in Example 2;

[0038] Figure 4 for Figure 3 A cross-sectional schematic diagram. Detailed Implementation

[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] Combination Figure 1 and Figure 2 As shown, a friction stir welding device for high melting point materials includes a clamping part 1 (also referred to as a stirring pin 3 mounting part). The upper section of the clamping part 1 is fixedly connected to the spindle of the friction stir welding machine, and the upper section of the clamping part 1 is fixedly connected to a shoulder 2. A stirring pin 3 integrally formed with the shoulder 2 is provided on the shoulder 2. A support assembly is sleeved on the stirring pin 3. A heating element is provided on the support assembly. The two terminals of the heating element are respectively connected to an external heating power supply. The support assembly can move laterally synchronously with the stirring pin 3 but does not rotate. The space 12 between the shoulder 2 and the top surface of the support assembly is just enough to hold the workpiece. The top surface 13 of the support assembly is a standard plane and is used to closely fit the workpiece. The stirring pin 3 passes through the weld of the workpiece.

[0042] The support assembly includes a cylindrical body 5 with a flat top, a heating coil 4 set on the cylindrical body 5 as the heating element, a circulating cooling channel 6 set on the cylindrical body 5, a cooling liquid circulation supply system connected to the circulating cooling channel 6, a bearing assembly set in the inner cavity of the cylindrical body 5, the bearing assembly being sleeved on the stirring needle 3, and a bearing end cap 7 fixed to the lower end of the cylindrical body 5 below the bearing assembly.

[0043] The bearing assembly is fixedly connected to the stirring needle 3. The bearing assembly includes an upper angular contact ball bearing 8 and a lower angular contact ball bearing 10 arranged coaxially. A washer 9 is provided between the upper angular contact ball bearing 8 and the lower angular contact ball bearing 10 to separate the upper angular contact ball bearing 8 and the lower angular contact ball bearing 10.

[0044] In this embodiment, a fixing ring 11 is provided on the inner side of the bearing end cover 7. The fixing ring 11 is sleeved and fixedly connected to the stirring needle 3 by countersunk screws. The lower end of the fixing ring 11 is flush with the lower end of the bearing end cover 7, and the outer side wall of the fixing ring 11 is close to the inner side wall of the bearing end cover 7. The height of the space between the shoulder 2 and the top surface 13 of the support assembly is 0.15mm less than the thickness of the workpiece.

[0045] In this embodiment, the diameter of the shoulder 2 is 25mm, the diameter of the stirring needle 3 is 6mm, the outer diameter of the cylinder 5 is 25mm, the inner diameter of the fixing ring 11 is 8mm and the outer diameter is 12mm, the diameter of the circulating cooling channel 6 is 2mm, and the number of turns of the heating coil 4 is 1.

[0046] A welding method using the friction stir welding apparatus of this embodiment includes the following steps:

[0047] Step 1: First, wipe the surface of the plate to be welded (400mm long and 6mm thick titanium alloy plate) with an organic solvent (acetone). Then, fix the plate to be welded on the workbench so that the plates are joined together and on the same horizontal plane.

[0048] Step 2: Adjust the height of the space between the shoulder 2 and the top surface of the support component according to the thickness of the plate to be welded, so that the height of the space is greater than or equal to the thickness of the plate to be welded.

[0049] Step 3: Turn on the liquid supply system connected to the circulating cooling channel 6 to allow the coolant (using ethylene glycol coolant) to circulate.

[0050] Step 4: Set the induction heating power according to the melting point of the plate to be welded, turn on the power of the heating element, and control the temperature of the plate to be welded to be maintained at 800±5℃ before welding.

[0051] Step 5: Adjust the relative position of the friction stir welding machine and the plate to be welded so that the butt joint area of ​​the plate to be welded is aligned with the stirring pin 3, and readjust the height of the space between the shoulder 2 and the top surface of the support assembly so that the height of the space is 0.15mm less than the thickness of the plate to be welded.

[0052] After adjusting the welding parameters, welding is carried out, with the shoulder 2 and the stirring pin 3 rotating synchronously at 250 rpm, and the shoulder 2 and the stirring pin 3 moving horizontally at 50 mm / min until the entire welding process is completed. At the beginning of the weld, the shoulder 2 and the stirring pin 3 are controlled to stay for 3 seconds. After the dwell time, the stirring pin 3 is controlled to move along the butt joint area of ​​the plates to be welded.

[0053] Example 2

[0054] Combination Figure 3 and Figure 4 As shown, a friction stir welding device for high melting point materials includes a clamping part 1, the upper section of which is fixedly connected to the spindle of a friction stir welding machine, and a shoulder 2 fixedly connected to the upper section of the clamping part 1. A stirring pin 3 integrally formed with the shoulder 2 is provided on the shoulder 2. A support assembly is sleeved on the stirring pin 3. A heating element is provided on the support assembly. The two terminals of the heating element are respectively connected to an external heating power supply. The support assembly can move laterally synchronously with the stirring pin 3 but does not rotate. The space 12 between the shoulder 2 and the top surface of the support assembly is just enough to hold the workpiece. The top surface 13 of the support assembly is a standard plane and is used to closely fit the workpiece. The stirring pin 3 passes through the weld of the workpiece.

[0055] The support assembly includes a cylindrical body 5 with a flat top, a heating coil 4 set on the cylindrical body 5 as the heating element, a circulating cooling channel 6 set on the cylindrical body 5, a cooling liquid circulation supply system connected to the circulating cooling channel 6, a bearing assembly set in the inner cavity of the cylindrical body 5, the bearing assembly being sleeved on the stirring needle 3, and a bearing end cap 7 fixed to the lower end of the cylindrical body 5 below the bearing assembly.

[0056] The bearing assembly is fixedly connected to the stirring needle 3. The bearing assembly includes an upper angular contact ball bearing 8 and a lower angular contact ball bearing 10 arranged coaxially. A washer 9 is provided between the upper angular contact ball bearing 8 and the lower angular contact ball bearing 10 to separate the upper angular contact ball bearing 8 and the lower angular contact ball bearing 10.

[0057] In this embodiment, a fixing ring 11 is provided inside the bearing end cover 7. The fixing ring 11 is sleeved and movably sleeved on the stirring needle 3. The lower end of the fixing ring 11 is flush with the lower end of the bearing end cover 7, and the outer side wall of the fixing ring 11 is against the inner side wall of the bearing end cover 7. A flexible pressing mechanism is provided below the cylinder 5. The flexible pressing mechanism is used to support the cylinder 5, the bearing end cover 7 and the fixing ring 11, so that the height of the space between the shoulder 2 and the top surface 13 of the support assembly is 0.1 mm less than the thickness of the workpiece.

[0058] In this embodiment, the diameter of the shoulder 2 is 30mm, the diameter of the stirring needle 3 is 4mm, the outer diameter of the cylinder 5 is 28mm, the inner diameter of the fixing ring 11 is 10mm and the outer diameter is 12mm, the diameter of the circulating cooling channel 6 is 2.5mm, and the number of turns of the heating coil 4 is 1.

[0059] In this embodiment, the flexible pressing mechanism includes a linear slide rail 20, which is parallel to the top surface 13 of the support assembly. A movable seat 21 is provided on the linear slide rail 20, and a servo motor 22 is provided on the movable seat 21. The output end of the servo motor 22 is connected to three vertically arranged and parallel ball screws 23 through a gear transmission mechanism 26. The three ball screws 23 are located at the 0°, 120°, and 240° positions on the same circumference, and each of the three ball screws 23 is fitted with a nut seat 2. 4. The nut seat 24 is fixedly connected to the support plate 25. The top surface of the support plate 25 is flat and is used to support the cylinder 5, the bearing end cover 7, and the fixing ring 11. When the servo motor 22 is running, the servo motor 22 drives the gear transmission mechanism 26 to run. Through the gear transmission mechanism 26, the three ball screws 23 rotate synchronously, thereby driving the nut seat 24 and the support plate 25 to move up and down synchronously, and thus driving the whole assembly consisting of "cylinder 5, bearing end cover 7, fixing ring 11, bearing assembly, and heating coil 4" to move up and down. Among them, the servo motor 22, the gear transmission mechanism 26, and the ball screws 23 are partially located inside the housing 27. Multiple through holes are provided on the support plate 25 and the top of the housing 27 for the ball screws 23 and the stirring needle 3 to pass through. A force sensor 28 is set between the support plate 25 and the cylinder 5. As one of the key points of this embodiment, combined with Figure 4 As shown, the lower end of the stirring pin 3 is 5-10 mm lower than the lower end of the support plate 25, and the diameter of the stirring pin 3 is 0.5-1 mm smaller than the hole diameter in the middle of the support plate 25. This structure can not only improve the welding accuracy, but also keep the lateral movement deviation of the stirring pin 3 within a small range, and effectively prevent the stirring pin 3 from getting stuck.

[0060] A welding method using the friction stir welding apparatus of this embodiment includes the following steps:

[0061] Step 1: First, wipe the surface of the plate to be welded (a 600mm long and 4mm thick titanium alloy plate) with an organic solvent (acetone). Then, fix the plate to be welded on the workbench so that the plates are joined together and are basically on the same horizontal plane.

[0062] Step 2: Adjust the height of the space between the shoulder 2 and the top surface of the support component according to the thickness of the plate to be welded, so that the height of the space is greater than or equal to the thickness of the plate to be welded.

[0063] Step 3: Turn on the liquid supply system connected to the circulating cooling channel 6 to allow the coolant (using ethylene glycol coolant) to circulate.

[0064] Step 4: Set the induction heating power according to the melting point of the plate to be welded, turn on the power of the heating element, and control the temperature of the plate to be welded to be maintained at 800±5℃ before welding.

[0065] Step 5: Adjust the relative position of the friction stir welding machine and the plate to be welded so that the butt joint area of ​​the plate to be welded is aligned with the stirring pin 3, and readjust the height of the space between the shoulder 2 and the top surface of the support assembly so that the height of the space is 0.1mm less than the thickness of the plate to be welded.

[0066] After adjusting the welding parameters, welding is carried out, with the shoulder 2 and the stirring pin 3 rotating synchronously at 300 rpm, and the shoulder 2 and the stirring pin 3 moving horizontally at 70 mm / min until the entire welding process is completed. At the beginning of the weld, the shoulder 2 and the stirring pin 3 are controlled to pause for 2 seconds. After the pause time, the stirring pin 3 is controlled to move along the butt joint area of ​​the plates to be welded.

[0067] During the welding process: whenever the pressure value fed back by the force sensor 28 is less than the preset threshold (14.5KN), the servo motor 22 is controlled to run, causing the nut seat 24 to move upward until the feedback pressure value is 15±0.5KN; whenever the pressure value fed back by the force sensor 28 is greater than the preset threshold (15.5KN), the servo motor 22 is controlled to run, causing the nut seat 24 to move downward until the feedback pressure value is 15±0.5KN.

[0068] Example 3

[0069] In this embodiment, the friction stir welding device is the same as that in Embodiment 2. The main difference between the two embodiments is that the diameter of the shoulder 2 is 32mm, the diameter of the stirring needle 3 is 10mm, the outer diameter of the cylinder 5 is 32mm, the inner diameter of the fixing ring 11 is 11mm and the outer diameter is 8mm, the diameter of the circulating cooling channel 6 is 3.5mm, and the number of turns of the heating coil 4 is 3.

[0070] A welding method using the friction stir welding apparatus of this embodiment includes the following steps:

[0071] Step 1: First, wipe the surface of the plate to be welded (a titanium alloy plate 300mm long and 15mm thick) with an organic solvent (acetone). Then, fix the plate to be welded on the workbench so that the plates are joined together and on the same horizontal plane.

[0072] Step 2: Adjust the height of the space between the shoulder 2 and the top surface of the support component according to the thickness of the plate to be welded, so that the height of the space is greater than or equal to the thickness of the plate to be welded.

[0073] Step 3: Turn on the liquid supply system connected to the circulating cooling channel 6 to allow the coolant (using ethylene glycol coolant) to circulate.

[0074] Step 4: Set the induction heating power according to the melting point of the plate to be welded, turn on the power of the heating element, and control the temperature of the plate to be welded to be maintained at 800±5℃ before welding.

[0075] Step 5: Adjust the relative position of the friction stir welding machine and the plate to be welded so that the butt joint area of ​​the plate to be welded is aligned with the stirring pin 3, and readjust the height of the space between the shoulder 2 and the top surface of the support assembly so that the height of the space is 0.2mm less than the thickness of the plate to be welded.

[0076] After adjusting the welding parameters, welding is carried out, with the shoulder 2 and the stirring pin 3 rotating synchronously at 300 rpm, and the shoulder 2 and the stirring pin 3 moving horizontally at 30 mm / min until the entire welding process is completed. At the beginning of the weld, the shoulder 2 and the stirring pin 3 are controlled to remain stationary for 5 seconds. After the stationary period, the stirring pin 3 is controlled to move along the butt joint area of ​​the plates to be welded.

[0077] During the welding process: whenever the pressure value fed back by the force sensor 28 is less than the preset threshold (17.5KN), the servo motor 22 is controlled to run, causing the nut seat 24 to move upward until the feedback pressure value is 18±0.5KN; whenever the pressure value fed back by the force sensor 28 is greater than the preset threshold (18.5KN), the servo motor 22 is controlled to run, causing the nut seat 24 to move downward until the feedback pressure value is 18±0.5KN.

[0078] The solution in this embodiment can not only effectively reduce the plastic deformation resistance of high melting point materials, reduce the temperature gradient and microstructure inhomogeneity in the weld thickness direction, improve the plastic flow of materials at the weld root, and suppress joint tunnel defects, but also effectively avoid root incomplete penetration defects and obtain high-quality welded joints. This invention significantly reduces the load-bearing capacity of the stirring pin, improves welding efficiency, and broadens the process parameters of friction stir welding of high melting point materials. It also has advantages such as energy saving and environmental protection, simple structure, and convenient operation.

[0079] The specific structure in the embodiment can replace the rigid backing plate in the conventional friction stir welding process. The follow-up support component will not rotate during the welding process, which fundamentally avoids the problem of stirring pin breakage and extends the service life of the friction stir welding equipment.

[0080] Weld transmission electron microscopy (RT) was performed on the welds in Examples 1-3, and the results showed that all welds were qualified and the surface morphology of the welds was regular. This invention is not only applicable to welding medium-thick plates with high melting points, but also to welding thin-walled plates with high melting points smoothly. More importantly, it can adaptively adjust the welding accuracy deviation caused by the flexible bending of thin-walled plates, and can stably and smoothly weld high-melting-point thin plates with long welds (length not less than 500 mm), avoiding the problem of multiple defects in long thin-walled strip welds.

Claims

1. A friction stir welding apparatus for high melting point materials, comprising a clamping part (1), the upper section of which is fixedly connected to the spindle of a friction stir welding machine, and the upper section of which is fixedly connected to a shoulder (2), characterized in that: A stirring pin (3) integrally formed with the shoulder (2) is provided on the shoulder (2). A support assembly is sleeved on the stirring pin (3). A heating element is provided on the support assembly. The support assembly can move laterally synchronously with the stirring pin (3) but does not rotate. The space (12) between the shoulder (2) and the top surface of the support assembly is just enough to hold the workpiece. The top surface (13) of the support assembly is a standard plane and is used to closely fit the workpiece. The stirring pin (3) passes through the weld of the workpiece. The support assembly includes a cylindrical body (5) with a flat top, a heating coil (4) set on the cylindrical body (5) as the heating element, a circulating cooling channel (6) set on the cylindrical body (5), a bearing assembly set in the inner cavity of the cylindrical body (5), the bearing assembly being sleeved on the stirring needle (3), and a bearing end cap (7) fixed to the lower end of the cylindrical body (5) below the bearing assembly. A fixing ring (11) is provided inside the bearing end cover (7). The fixing ring (11) is sleeved and movably sleeved or sleeved and fixedly connected to the stirring needle (3). The lower end of the fixing ring (11) is flush with the lower end of the bearing end cover (7). The outer wall of the fixing ring (11) is close to the inner wall of the bearing end cover (7). A flexible pressing mechanism is provided below the cylinder (5). The flexible pressing mechanism is used to support the cylinder (5), the bearing end cover (7) and the fixing ring (11), so that the height of the space between the shoulder (2) and the top surface (13) of the support assembly is 0.1~0.2mm smaller than the thickness of the workpiece. The flexible pressing mechanism includes a linear slide rail (20), which is parallel to the top surface (13) of the support assembly. A movable seat (21) is provided on the linear slide rail (20), and a servo motor (22) is provided on the movable seat (21). The output end of the servo motor (22) is connected to three vertically arranged and parallel ball screws (23) through a gear transmission mechanism (26). Each of the three ball screws (23) is fitted with a nut seat (24), and the nut seat (24) is fixedly connected to the support plate (25). The support plate (25) is... The top surface is flat and is used to support the cylinder (5), bearing end cap (7) and fixing ring (11); when the servo motor (22) is running, it drives the three ball screws (23) to rotate synchronously through the gear transmission mechanism (26), thereby driving the nut seat (24) and support plate (25) to move up and down synchronously, thereby driving the whole consisting of "cylinder (5), bearing end cap (7), fixing ring (11), bearing assembly and heating coil (4)" to move up and down; a force sensor (28) is set between the support plate (25) and the cylinder (5).

2. The friction stir welding apparatus according to claim 1, characterized in that: The bearing assembly includes an upper angular contact ball bearing (8) and a lower angular contact ball bearing (10) arranged coaxially, with a washer (9) provided between the upper angular contact ball bearing (8) and the lower angular contact ball bearing (10).

3. The friction stir welding apparatus according to claim 2, characterized in that: The servo motor (22), gear transmission mechanism (26) and ball screw (23) are located in the housing (27). Multiple through holes are provided on the support plate (25) and the top of the housing (27) for the ball screw (23) and stirring needle (3) to pass through.

4. A welding method using the friction stir welding apparatus according to any one of claims 1-3, characterized in that the steps include... include: Step 1: First, wipe the surface of the plates to be welded with an organic solvent, then fix the plates to be welded on the workbench so that the plates are joined together and on the same horizontal plane. Step 2: Adjust the height of the space between the shoulder (2) and the top surface of the support assembly according to the thickness of the plate to be welded, so that the height of the space is greater than or equal to the thickness of the plate to be welded; Step 3: Turn on the liquid supply system connected to the circulating cooling channel (6) to allow the coolant to circulate. Step 4: Set the induction heating power according to the melting point of the material to be welded, turn on the power of the heating element, and control the temperature of the material to be welded to be maintained between 400-1000℃ before welding. Step 5: Adjust the relative position of the friction stir welding machine and the plate to be welded so that the butt joint area of ​​the plate to be welded is aligned with the stirring needle (3), and readjust the height of the space between the shoulder (2) and the top surface of the support assembly so that the height of the space is 0.1~0.2mm less than the thickness of the plate to be welded; After adjusting the welding parameters, welding is carried out, so that the shoulder (2) and the stirring needle (3) rotate synchronously at a speed of 20-1000 rpm, and the shoulder (2) and the stirring needle (3) move horizontally at a speed of 20-100 mm / min until the entire welding process is completed.

5. A welding method using the friction stir welding apparatus of claim 4, characterized in that the steps include... include: Step 1: First, wipe the surface of the plates to be welded with an organic solvent, then fix the plates to be welded on the workbench so that the plates are joined together and on the same horizontal plane. Step 2: Adjust the height of the space between the shoulder (2) and the top surface of the support assembly according to the thickness of the plate to be welded, so that the height of the space is greater than or equal to the thickness of the plate to be welded; Step 3: Turn on the liquid supply system connected to the circulating cooling channel (6) to allow the coolant to circulate. Step 4: Set the induction heating power according to the melting point of the material to be welded, turn on the power of the heating element, and control the temperature of the material to be welded to be maintained between 400-1000℃ before welding. Step 5: Adjust the relative position of the friction stir welding machine and the plate to be welded so that the butt joint area of ​​the plate to be welded is aligned with the stirring needle (3), and readjust the height of the space between the shoulder (2) and the top surface of the support assembly so that the height of the space is 0.1~0.2mm less than the thickness of the plate to be welded; After adjusting the welding parameters, welding is carried out, so that the shoulder (2) and the stirring needle (3) rotate synchronously at a speed of 20-1000 rpm, and the shoulder (2) and the stirring needle (3) move horizontally at a speed of 20-100 mm / min until the entire welding process is completed. During the welding process: whenever the pressure value fed back by the force sensor (28) is less than the preset threshold, the servo motor (22) is controlled to run, so that the nut seat (24) moves up until the feedback pressure value is 10-20KN; whenever the pressure value fed back by the force sensor (28) is greater than the preset threshold, the servo motor (22) is controlled to run, so that the nut seat (24) moves down until the feedback pressure value is 10-20KN.

6. The welding method according to claim 4 or 5, characterized in that: At the start of the weld, the control shoulder (2) and stirring needle (3) are held for 2-5 seconds; the high melting point material is a titanium alloy plate.

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