Friction Stir Welding Tool Structure and Friction Stir Welding Equipment

Abstract

The present invention discloses a friction stir welding tool structure and a friction stir welding device, belonging to the technical field of friction stir welding. Among them, the friction stir welding tool structure includes a shoulder and a stirring pin. The stirring pin is coaxially and detachably arranged in the shoulder. The tip of the stirring pin extends out of the shoulder end face of the shoulder, and the root of the tip is located at the shoulder end face. A weak position is provided near the root of the tip itself, so that when the tip breaks during work, the fracture position is located at the weak position, and the broken tip will not scratch the shoulder. The present invention has low manufacturing cost, and the shoulder end face will not be damaged after the stirring pin breaks during work, and the shoulder can be reused.

Description

Technical Field

[0001] The present invention relates to the technical field of friction stir welding, and in particular, to a friction stir welding tool structure and a friction stir welding device. Background Art

[0002] Friction stir welding is a solid-phase welding technology. In the friction stir welding process, a welding tool needs to plunge into the weld seam and rotate to stir, generating heat by friction, and then move upward along the weld seam direction to achieve solid-phase welding. The welding tool is the core of this process. The welding tool generally consists of two parts, namely, the tip of the stirring pin that fully plunges into the material and the shoulder that tightly presses against the surface of the plate weld seam. Since the tip of the stirring pin bears a greater load, and the tip only accounts for a very small part of the entire volume of the welding tool, for the structure of the stirring pin that requires high performance, better materials are often needed. However, better materials have a higher price. Therefore, a split design of the stirring pin and the shoulder is often adopted, with the shoulder made of conventional materials and the stirring pin made of better materials to reduce the manufacturing cost of the welding tool.

[0003] In a conventional welding tool with a split design of the shoulder and the stirring pin, when the tip of the stirring pin breaks, it often breaks at the root of the tip (see the position indicated by arrow N in Figure 12 ). After the breakage, the welding device will continue to move forward. Even for a welding device with a broken pin monitoring function, there will be a certain delay. As a result, after the actual breakage of the pin, there is still a welding feed of 1 - 2 mm. Since the root of the tip of the stirring pin is adjacent to the end face of the shoulder, when the stirring pin breaks and continues to move forward, the broken tip will seriously scratch the shoulder, resulting in the scrapping of the shoulder and the shoulder cannot be reused. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. For this purpose, an object of the first aspect of the present invention is to provide a friction stir welding tool structure with low manufacturing cost, and when the stirring pin breaks during operation, it will not damage the end face of the shoulder, and the shoulder can be reused.

[0005] According to an embodiment of the first aspect of the present invention, the friction stir welding tool structure includes:

[0006] A shoulder;

[0007] A stirring pin, the stirring pin is coaxially and detachably arranged in the shoulder, the tip of the stirring pin extends out of the end face of the shoulder of the shoulder, and the root of the tip is located at the end face of the shoulder. A weak position is provided near the root of the tip itself, so that when the tip breaks during operation, the breakage position is located at the weak position, and the broken tip will not scratch the shoulder.

[0008] According to the friction stir welding tool structure of the first aspect embodiment of the present invention, on the one hand, the shoulder and the stirring pin are of a split design. By setting the weak position on the tip of the stirring pin near the root of the tip, the fracture position of the tip during operation can be stably at the weak position, ensuring that the fracture position of the tip does not occur at the root of the tip but at a position below the root of the tip and the end face of the shoulder, at a certain distance from the end face of the shoulder. In this way, even if the friction stir welding tool does not immediately stop the welding feed, the fractured tip will not scratch the end face of the shoulder, ensuring the reusability of the shoulder. On the other hand, the shoulder and the stirring pin are of a split design. The shoulder can be made of a conventional material with a lower cost, and the stirring pin can be made of a material with better performance but higher cost, thus reducing the manufacturing cost.

[0009] In some embodiments, the weak position is 1 - 2 mm away from the root of the tip.

[0010] In some embodiments, the tip is conical and a first thread with equal pitch is provided on the outer periphery of the entire length of the tip. The bottom of the first thread groove of the first turn starting from the root of the tip is shallower than the bottom of the reference thread groove of the thread, and / or the bottom of the first thread groove of the second turn starting from the root of the tip is deeper than the bottom of the reference thread groove.

[0011] In some embodiments, the taper of the tip is between 5° and 25°.

[0012] In some embodiments, the depth dimension of the first thread groove is 0.7 - 0.8 times the depth dimension of the reference thread groove, and the depth dimension of the second thread groove is 1.2 - 1.3 times the depth dimension of the reference thread groove.

[0013] In some embodiments, the radius of the arc at the bottom of the first thread is greater than 0.25 mm.

[0014] In some embodiments, a circular groove for avoiding the root of the tip is provided at the connection between the end face of the shoulder and the inner peripheral wall of the shoulder.

[0015] In some embodiments, the axial depth of the circular groove changes from deep to shallow gradually from the inner end to the outer end along the radial direction.

[0016] In some embodiments, the inner diameter of the circular groove is smaller than the root diameter of the tip, and the outer diameter of the circular groove is larger than the root diameter of the tip.

[0017] In some embodiments, the outer diameter of the circular groove is at least 0.8 mm larger than the root diameter of the tip.

[0018] In some embodiments, the axial depth of the annular groove at its radially inner end ranges from 0.6 mm to 0.1D, where D is the inner diameter of the shaft shoulder.

[0019] In some embodiments, a plurality of milling planes are circumferentially spaced on the tip, and the taper angle of the milling plane is smaller than the taper of the tip.

[0020] In some embodiments, the taper angle of the milling plane is 0.65 to 0.85 times the taper of the tip.

[0021] In some embodiments, a second non-uniform pitch thread is provided on the outer periphery of the entire length of the tip. The second thread forms a weak position at a distance of 1 - 2 mm from the root of the tip by designing its own thread parameters; or, except for the range of 1 - 2 mm from its own root on the tip, a third uniform pitch thread is provided on the remaining part of the tip, and the bottom of the thread groove of the third thread is consistent; or, a strengthening coating is provided on the outer peripheral surface of the tip within the range of 1 - 2 mm from its own root; or, a notch is provided at a distance of 1 - 2 mm from the root of the tip.

[0022] The second aspect of the present invention proposes a friction stir welding device.

[0023] The friction stir welding device according to the embodiment of the second aspect of the present invention includes the friction stir welding head structure according to the embodiment of the first aspect of the present invention.

[0024] Since the friction stir welding device according to the embodiment of the second aspect of the present invention adopts the friction stir welding head structure according to the embodiment of the first aspect of the present invention, therefore, the friction stir welding device according to the embodiment of the second aspect of the present invention has substantially the same technical effects as the friction stir welding head structure according to the embodiment of the first aspect of the present invention, which will not be elaborated here.

[0025] The additional aspects and advantages of the present invention will be partly given in the following description, partly will become obvious from the following description, or will be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, where:

[0027] Figure 1 is a schematic diagram of the friction stir welding head structure of the present invention;

[0028] Figure 2 is a partially enlarged schematic diagram of the friction stir welding head structure of the present invention;

[0029] Figure 3It is the effect diagram of the friction stir welding tool structure of the present invention;

[0030] Figure 4 It is the partial enlarged effect diagram of the friction stir welding tool structure of the present invention;

[0031] Figure 5 It is another partial enlarged schematic diagram of the friction stir welding tool structure of the present invention;

[0032] Figure 6 It is the partial sectional schematic diagram of the friction stir welding tool structure of the present invention;

[0033] Figure 7 It is another partial enlarged effect diagram of the friction stir welding tool structure of the present invention;

[0034] Figure 8 It is the sectional effect diagram of the friction stir welding tool structure of the present invention;

[0035] Figure 9 It is still another partial enlarged schematic diagram of the friction stir welding tool structure of the present invention;

[0036] Figure 10 It is still another partial enlarged effect diagram of the friction stir welding tool structure of the present invention;

[0037] Figure 11 It is the schematic diagram of the fracture position of the stirring pin of the friction stir welding tool structure of the present invention;

[0038] Figure 12 It is the schematic diagram of the fracture position of the stirring pin of the existing friction stir welding tool structure.

[0039] Reference numerals:

[0040] Friction stir welding tool structure 1000; Stirring pin 1; Tip 101; Weak position 1011; First turn of thread groove 1012; Second turn of thread groove 1013; Reference thread groove 1014; Radius R of the bottom arc of the groove; Milled plane 1016; Taper θ; Taper angle ɑ; Shoulder 2; Shoulder end face 201; Ring groove 2011; Clamping handle 3. Detailed implementation manners

[0041] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0042] The following will be combined with Figures 1 to 11 Describe the friction stir welding tool structure 1000 of the embodiments of the present invention.

[0043] As Figures 1 to 4 shown, the friction stir welding tool structure 1000 according to the first aspect embodiment of the present invention includes a shoulder 2 and a pin 1.

[0044] Among them, the shoulder 2 and the pin 1 are of a split design, and the shoulder 2 and the clamping shank 3 are of a split or integral design (see Figure 1 and Figure 3 ), so that the shoulder 2 and the clamping shank 3 can be made of conventional materials with lower costs, and the pin 1 can be made of materials with higher costs and better performance. Thus, the overall manufacturing cost of the friction stir welding tool structure 1000 can be reduced.

[0045] The pin 1 is axially detachably arranged in the shoulder 2. The shoulder 2 and the pin 1 are of a split design, and the pin 1 can be conveniently replaced. The tip 101 of the pin 1 extends out of the shoulder end face 201 of the shoulder 2 and the root of the tip 101 is located at the shoulder end face 201. In this way, it is beneficial for the tip 101 to fully penetrate into the plate and the shoulder end face 201 to tightly press the surface of the plate weld, meeting the requirements of the friction stir welding process. A weak position 1011 is provided near the root of the tip 101, so that when the tip 101 breaks during work, the fracture position is at the weak position 1011, and the broken tip 101 will not scratch the shoulder 2; since the weak position 1011 is provided near the root of the tip 101 itself, that is, the weak position 1011 is at a certain distance from the root of the tip 101 and the shoulder end face 201. When the tip 101 penetrates into the material for work, the load borne by the tip 101 is very large. When the tip 101 breaks, the fracture position is at the weak position 1011, which is at a certain distance from the root of the tip 101 and the shoulder end face 201. For example, in reference to Figure 11 , the three arrows M show that the fracture position of the tip 101 of the pin 1 in the actual experiment is at a certain distance from the shoulder end face 201, and the broken tip 101 will not scratch the shoulder end face 201, enabling the shoulder 2 to be reused.

[0046] According to the friction stir welding tool structure 1000 of the first aspect embodiment of the present invention, on the one hand, the shoulder 2 and the pin 1 are of a split design. By providing a weak position 1011 at the root of the tip 101 of the pin 1 near the tip 101, the fracture position of the tip 101 during operation can be stabilized at the weak position 1011, ensuring that the fracture position of the tip 101 does not occur at the root of the tip 101 but at a position below the root of the tip 101 and below the shoulder end face 201, at a certain distance from the shoulder end face 201. In this way, even if the friction stir welding tool structure 1000 does not immediately stop the welding feed, the fractured tip 101 will not scratch the shoulder end face 201, ensuring the reusability of the shoulder end face 201. On the other hand, the shoulder 2 and the pin 1 are of a split design. The shoulder 2 can be made of a conventional material with a lower cost, and the pin 1 can be made of a material with better performance and a higher cost, thus reducing the manufacturing cost.

[0047] In some embodiments, the weak position 1011 is 1-2 mm away from the root of the tip 101. In this way, the fracture position of the tip 101 does not occur at the root of the tip 101 but at the weak position 1011 which is 1-2 mm away from the root of the tip 101. The fractured tip 101 will not scratch the shoulder end face 201, enabling the shoulder 2 to be reused.

[0048] In some embodiments, as Figures 1 to 10 shown, the tip 101 is conical and has a first thread with an equal pitch on the outer periphery of the entire length of the tip 101, which can meet the process requirements of friction stir welding. The bottom of the first thread groove 1012 of the first turn of the first thread starting from the root of the tip 101 is shallower than the bottom of the reference thread groove 1014 of the thread, and the bottom of the second thread groove 1013 of the second turn of the first thread starting from the root of the tip 101 is deeper than the bottom of the reference thread groove 1014. Among them, the bottoms of the remaining thread grooves except for the bottom of the first thread groove 1012 and the bottom of the second thread groove 1013 are consistent and are all the bottom of the reference thread groove 1014. Thus, the bottom of the second thread groove 1013 is the weak position 1011 of the tip 101. When the tip 101 fractures during operation, the fracture position is stabilized at the second thread groove 1013. The fractured tip 101 will not scratch the shoulder end face 201, enabling the shoulder 2 to be reused. At the same time, the pin 1 can better meet the welding process requirements of friction stir welding.

[0049] Alternatively, the bottom of the first thread groove 1012 of the first thread starting from the root of the tip 101 is shallower than the bottom of the reference thread groove 1014 of the thread, wherein the bottoms of the remaining thread grooves except the bottom of the first thread groove 1012 are consistent and are all the bottom of the reference thread groove 1014; thus, the weak position 1011 of the tip 101 is at a certain distance from the root of the tip 101, and the fracture position when the tip 101 breaks during operation is at a certain distance from the root of the tip 101. The broken tip 101 will not scratch the shoulder end face 201, enabling the shoulder 2 to be reused; at the same time, the stirring needle 1 can better meet the welding process requirements of friction stir welding.

[0050] Alternatively, the bottom of the second thread groove 1013 of the first thread starting from the root of the tip 101 is deeper than the bottom of the reference thread groove 1014; wherein the bottoms of the remaining thread grooves except the bottom of the second thread groove 1013 are consistent and are all the bottom of the reference thread groove 1014; thus, the bottom of the second thread groove 1013 is the weak position 1011 of the tip 101, and the fracture position when the tip 101 breaks during operation is stable at the second thread groove 1013. The broken tip 101 will not scratch the shoulder end face 201, enabling the shoulder 2 to be reused; at the same time, the stirring needle 1 can better meet the welding process requirements of friction stir welding.

[0051] In some embodiments, the taper θ of the tip 101 is between 5° and 25°, whereby the stirring needle 1 can better meet the welding process requirements of friction stir welding.

[0052] In some embodiments, the depth dimension of the first thread groove 1012 is 0.7 to 0.8 times the depth dimension of the reference thread groove 1014, and the depth dimension of the second thread groove 1013 is 1.2 to 1.3 times the depth dimension of the reference thread groove 1014. Thus, the bottom of the second thread groove 1013 is the weak position 1011 of the tip 101, and the fracture position when the tip 101 breaks during operation is stable at the second thread groove 1013. The broken tip 101 will not scratch the shoulder end face 201, enabling the shoulder 2 to be reused; at the same time, the stirring needle 1 can better meet the welding process requirements of friction stir welding. Optionally, the depth dimension of the first thread groove 1012 is 0.7 times, 0.75 times or 0.8 times the depth dimension of the reference thread groove 1014; the depth dimension of the second thread groove 1013 is 1.2 times, 1.25 times or 1.3 times the depth dimension of the reference thread groove 1014.

[0053] In some embodiments, the radius R of the arc at the bottom of the first thread is greater than 0.25 mm. In this way, stress concentration at the bottom of the first thread groove can be avoided, which is beneficial for the fracture position of the tip 101 to be stable at the second thread groove 1013.

[0054] In some embodiments, as Figures 5 to 8 shown, a ring groove 2011 for avoiding the root of the needle tip 101 is provided at the connection between the end face 201 of the shoulder and the inner peripheral wall of the shoulder 2. Thus, on the one hand, even if the friction stir welding equipment has a broken needle monitoring function, since there is still a certain lag delay from when the broken needle monitoring function detects the breakage of the stirring needle to when the friction stir welding equipment stops working, during the welding feeding process of the friction stir welding head structure 1000 during the lag delay, the ring groove 2011 can avoid the broken stirring needle 1, further ensuring that the broken needle tip 101 will not scratch the end face 201 of the shoulder. On the other hand, the ring groove 2011 is conducive to gathering the material towards the center.

[0055] In some embodiments, the axial depth of the ring groove 2011 changes from deep to shallow gradually from the inner end to the outer end in the radial direction. For example, in the figure, a ring groove 2011 is schematically shown at the connection between the end face 201 of the shoulder and the inner peripheral wall of the shoulder 2, forming a notch with a cross-section similar to a sector. Among them, the axial depth at the inner end of the ring groove 2011 in the radial direction is the deepest, and the axial depth at the outer end of the ring groove 2011 in the radial direction is the shallowest. Thus, the ring groove 2011 is conducive to ensuring that the broken needle tip 101 will not scratch the end face 201 of the shoulder, and at the same time is also conducive to gathering the material towards the center.

[0056] In some embodiments, the inner diameter of the ring groove 2011 is smaller than the root diameter of the needle tip 101, and the outer diameter of the ring groove 2011 is larger than the root diameter of the needle tip 101. Thus, there is an interference fit between the stirring needle 1 and the shoulder 2. The ring groove 2011 is conducive to ensuring that the broken needle tip 101 will not scratch the end face 201 of the shoulder, and at the same time is also conducive to gathering the material towards the center.

[0057] In some embodiments, the outer diameter of the ring groove 2011 is at least 0.8 mm larger than the root diameter of the needle tip 101. Thus, the ring groove 2011 is conducive to ensuring that the broken needle tip 101 will not scratch the end face 201 of the shoulder, and at the same time is also conducive to gathering the material downward and towards the center, with better effects.

[0058] In some embodiments, the axial depth range of the ring groove 2011 at the inner end in the radial direction is 0.6 mm to 0.1D, where D is the inner diameter of the shoulder 2. Thus, the ring groove 2011 is conducive to ensuring that the broken needle tip 101 will not scratch the end face 201 of the shoulder, and at the same time is also conducive to gathering the material downward and towards the center, with better effects.

[0059] In some embodiments, as Figures 5 to 10 shown, a plurality of milling planes 1016 are circumferentially spaced on the needle tip 101. The cone angle ɑ of the milling plane 1016 is smaller than the taper θ of the needle tip 101, that is, the material removal thickness of the milling plane 1016 changes from thick to thin gradually from the direction close to the root of the needle tip 101 to the end of the needle tip 101. For exampleFigure 9 and Figure 10 In Figure 10 , it is shown that the thickness of the removed material of the milling plane 1016 near the root of the tip 101 is greater than the thickness of the removed material of the milling plane 1016 near the end of the tip 101, that is, more material is removed near the root of the tip 101. For example, the thickness of the removed material is 1.05 mm, and less material is removed at the end section of the tip 101. For example, the thickness of the removed material is 0.88 mm. In this way, by setting the milling plane, the material fluidity is good, which can meet the requirements of the friction stir welding process. At the same time, it can also better ensure that the fracture occurs at the weak position 1011 near the root of the tip 101 by 1-2 mm, so that the fracture position of the tip 101 is stable at the root of the tip 101 by 1-2 mm.

[0060] In some embodiments, the taper angle ɑ of the milling plane 1016 is 0.65-0.85 times the taper θ of the tip 101. More material is removed from the root of the tip 101 and less material is removed from the end section of the tip 101. In this way, on the one hand, it can meet the requirements of the friction stir welding process. At the same time, it can also better ensure that the fracture occurs at the weak position 1011 near the root of the tip 101 by 1-2 mm, so that the fracture position of the tip 101 is stable at the root of the tip 101 by 1-2 mm.

[0061] In some embodiments, a second non-uniform pitch thread (not shown in the figure) is provided on the outer periphery of the entire length of the tip 101. The second thread forms a weak position 1011 on the tip 101 at a distance of 1-2 mm from the root of the tip 101 by designing its own thread parameters; or, except for the range of 1-2 mm from its own root on the tip 101, a third uniform pitch thread (not shown in the figure) is provided on the rest of the tip 101. The bottom of the thread groove of the third thread is consistent, so as to form a weak position 1011 on the tip 101 at a distance of 1-2 mm from its own root; or, a strengthening coating (not shown in the figure) is provided on the outer peripheral surface of the tip 101 within the range of 1-2 mm from its own root, so as to form a weak position 1011 on the tip 101 at a distance of 1-2 mm from its own root; or, a notch (not shown in the figure) is provided on the tip 101 at a distance of 1-2 mm from its own root, so as to form a weak position 1011 on the tip 101 at a distance of 1-2 mm from its own root. When the tip 101 penetrates into the material during work, the load borne by the tip 101 is very large. When the tip 101 breaks, the fracture position is at the weak position 1011, and there is a distance of 1-2 mm from the root of the tip 101 and the shoulder end face 201. The broken tip 101 will not scratch the shoulder end face 201, so that the shoulder 2 can be reused.

[0062] The second aspect of the present invention proposes a friction stir welding device.

[0063] The friction stir welding equipment according to the embodiment of the second aspect of the present invention includes the friction stir welding tool head structure 1000 of the embodiment of the first aspect of the present invention.

[0064] Since the friction stir welding equipment according to the embodiment of the second aspect of the present invention adopts the friction stir welding tool head structure 1000 of the embodiment of the first aspect of the present invention, therefore, the friction stir welding equipment according to the embodiment of the second aspect of the present invention has basically the same technical effects as the friction stir welding tool head structure 1000 of the embodiment of the first aspect of the present invention, which will not be elaborated herein.

[0065] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples", etc. means that the specific features, structures, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0066] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A friction stir welding stirring head structure, characterized in that: include: Shoulder; A stirring needle, wherein the stirring needle is coaxially detachably arranged in the shoulder, the tip of the stirring needle extends out of the shoulder end face of the shoulder and the root of the needle tip is located at the shoulder end face, a weak position is provided on the needle tip near its root, and the weak position is 1-2mm away from the root of the needle tip, so that when the needle tip breaks during operation, the breaking position is located at the weak position, and the broken needle tip will not scratch the shoulder; the needle tip is conical and the taper of the needle tip is between 5 and 25°; A first thread with equal pitch is arranged on the outer circumference of the full length section of the needle tip, the bottom of the first thread groove of the first thread from the root of the needle tip is shallower than the bottom of the reference thread groove of the thread, and / or the bottom of the second thread groove of the first thread from the root of the needle tip is deeper than the bottom of the reference thread groove; Alternatively, a second thread with non-equal pitch is provided on the outer circumference of the entire length of the needle tip, and the second thread forms a weak position on the needle tip at 1-2 mm from the root of the needle tip by designing its own thread parameters; alternatively, except for the range of 1-2 mm from the root of the needle tip, a third thread with equal pitch is provided on the rest of the needle tip, and the thread groove bottoms of the third thread are consistent; alternatively, a reinforcing coating is provided on the outer circumferential surface of the needle tip within a range of 1-2 mm from the root of the needle tip; alternatively, a notch is provided on the needle tip at 1-2 mm from the root of the needle tip.

2. The friction stir welding stirring head structure according to claim 1, characterized in that: When a first thread with equal pitch is provided on the outer circumference of the entire length section of the needle tip, the bottom of the first circle thread groove of the first thread starting from the root of the needle tip is shallower than the bottom of the reference thread groove of the thread, and / or the bottom of the second circle thread groove of the first thread starting from the root of the needle tip is deeper than the bottom of the reference thread groove, the depth dimension of the first circle thread groove is 0.7~0.8 times the depth dimension of the reference thread groove, and the depth dimension of the second circle thread groove is 1.2~1.3 times the depth dimension of the reference thread groove.

3. The friction stir welding stirring head structure according to claim 1, characterized in that: When a first thread with equal pitch is provided on the outer circumference of the entire length section of the needle tip, the bottom of the first circle thread groove of the first thread starting from the root of the needle tip is shallower than the bottom of the reference thread groove of the thread, and / or the bottom of the second circle thread groove of the first thread starting from the root of the needle tip is deeper than the bottom of the reference thread groove, the arc radius of the bottom of the first thread is greater than 0.25 mm.

4. The friction stir welding stirring head structure according to any one of claims 1 to 3, characterized in that: An annular groove for avoiding the root of the needle tip is provided on the connection between the end surface of the shaft shoulder and the inner peripheral wall of the shaft shoulder.

5. The friction stir welding stirring head structure according to claim 4, characterized in that: The axial depth of the annular groove changes from deep to shallow along the radial inner end toward the outer end.

6. The friction stir welding stirring head structure according to claim 5, characterized in that: The inner diameter of the annular groove is smaller than the root diameter of the needle tip, and the outer diameter of the annular groove is larger than the root diameter of the needle tip.

7. The friction stir welding stirring head structure according to claim 6, characterized in that: The outer diameter of the annular groove is at least 0.8 mm larger than the root diameter of the needle tip.

8. The friction stir welding stirring head structure according to claim 5, characterized in that: The axial depth of the annular groove at the radial inner end ranges from 0.6 mm to 0.1D, wherein D is the inner diameter of the shoulder.

9. The friction stir welding stirring head structure according to any one of claims 1 to 3, characterized in that: When a first thread with equal pitch is provided on the outer circumference of the entire length section of the needle tip, the bottom of the first circle thread groove of the first thread starting from the root of the needle tip is shallower than the bottom of the reference thread groove of the thread, and / or the bottom of the second circle thread groove of the first thread starting from the root of the needle tip is deeper than the bottom of the reference thread groove, the needle tip is provided with a plurality of milling planes at intervals along the circumferential direction, and the cone angle of the milling plane is smaller than the taper of the needle tip.

10. The friction stir welding stirring head structure according to claim 9, characterized in that: The taper angle of the milling plane is 0.65 to 0.85 times the taper of the needle tip.

11. A friction stir welding device, characterized in that: It comprises a friction stir welding stirring head structure as described in any one of claims 1-10.

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