A friction stir spot welding method and tool

Abstract

This application relates to a friction stir spot welding method and welding fixture. The friction stir spot welding method includes: stacking a first part and a second part of the workpiece to be welded; preparing a clamping ring and a stirring head, pressing the clamping ring against the welding area of ​​the first part away from the second part; rotating the stirring head, with the shoulder sliding into the clamping ring, and the stirring needle inserting into the first part and partially into the thickness of the second part; the stirring head continuing to rotate, the frictional heat plasticizing the material of the first and second parts around the stirring needle, the plasticized material displacing around the stirring needle, and part of the plasticized material entering the area enclosed by the clamping ring, the shoulder, and the first part; the stirring head suddenly stopping, the stirring needle withdrawing from the second and first parts, the plasticized material cooling and solidifying to form a weld nugget, and the spot welding process is completed. This application can achieve the connection between the same or different materials without any added materials, the process is simple and low-cost, with good sealing performance and high structural strength.

Description

Technical Field

[0001] This application relates to the field of friction stir welding technology, and in particular to a friction stir spot welding method and welding tool. Background Technology

[0002] Friction stir spot welding (FSSW) is a solid-state welding technology developed on the basis of friction stir welding technology, suitable for joining lightweight alloys. This process can not only obtain excellent mechanical properties of the joint, but also save energy consumption and reduce the weight of the joint structure. It has significant advantages compared with traditional resistance spot welding and riveting connection technologies. There are two main types of FSSW welding methods: conventional FSSW and backfill FSSW.

[0003] The principle of conventional FSSW welding is as follows: the stirring head rotates at high speed and penetrates the lap area of ​​the workpiece at a certain rate. After reaching the predetermined depth, the rotation speed is maintained and the workpiece is held for a certain period of time. Under the friction and stirring action of the stirring head, the material heats up and softens and produces plastic flow, causing the lap surface to break and achieve metallurgical bonding. After that, the stirring head is withdrawn from the workpiece and the welding is completed. However, the weld structure formed by conventional FSSW welding is relatively thin, resulting in low strength. Summary of the Invention

[0004] In view of the problems existing in the background technology, this application provides a friction stir spot welding method and welding tool, which can achieve the connection of the same and different materials without any added materials. The process is simple, low cost, good sealing performance, and high structural strength.

[0005] According to one aspect of the present invention, a friction stir spot welding method is provided, comprising: stacking a first part and a second part of a workpiece to be welded; preparing a clamping ring and a stirring head, the stirring head including a stirring shaft, a shoulder, and a stirring pin; pressing the clamping ring against the welding area of ​​the first part away from the second part, bringing the first part and the second part closer together; the stirring head rotating, the shoulder sliding into the clamping ring, the stirring pin inserting into the first part and into a portion of the thickness of the second part; the stirring head continuing to rotate, frictional heat plasticizing the material of the first part and the second part around the stirring pin, the plasticized material displacing around the stirring pin, and part of the plasticized material entering the area enclosed by the clamping ring, the shoulder, and the first part, forming a prefabricated boss; the stirring head abruptly stopping, the stirring pin moving away from the second part until the stirring pin exits the second part and the first part, the plasticized material cooling and solidifying to form a weld nugget, and the spot welding process completed.

[0006] By using the friction stir spot welding method in this technical solution, after the stirring needle is inserted into the predetermined position of the first and second parts, the stirring head rotates at high speed while the clamping ring does not rotate. The frictional heat plasticizes the material of the first and second parts around the stirring needle. The plasticized material is displaced around the stirring needle, and part of the plasticized material enters the area enclosed by the clamping ring, the shoulder, and the first part. The stirring head stops rotating abruptly, resulting in less heat input during the abrupt stop, which helps to enhance the strength of the spot weld joint and improve efficiency. After the abrupt stop, the stirring head withdraws from the second and first parts, and the plasticized material cools and solidifies to form a weld nugget with a prefabricated boss structure, which connects the first and second parts. This achieves the connection of the same and different materials without any added material. The process is simple, low-cost, has good sealing performance, and high structural strength.

[0007] In some embodiments of the present invention, a first flow guiding structure for driving the flow of plasticizing material is formed on the outer surface of the stirring needle.

[0008] In some embodiments of the present invention, the first flow guiding structure includes a recessed portion formed on the circumferential surface of the stirring needle and arranged along the length direction of the stirring needle.

[0009] In some embodiments of the present invention, the cross-sectional shape of the stirring pin is at least one of a circle, a triangle, an ellipse, and a semicircle, and the irregularly shaped circumferentially asymmetrical stirring pin forms an asymmetrical spot weld nugget; when the cross-sectional shape of the stirring pin is circular, the recessed portion is the circular region; when the cross-sectional shape of the stirring pin is triangular, the recessed portion is the region between the circumcircle of the triangle and each side of the triangle; when the cross-sectional shape of the stirring pin is elliptical, the recessed portion is the region between the concentric circumcircle of the ellipse and the opposite sides of the ellipse; when the cross-sectional shape of the stirring pin is semicircular, the recessed portion is the region between the full circle of the semicircle and the straight edge of the semicircle.

[0010] In some embodiments of the present invention, the first flow guiding structure further includes threads formed on the outer surface of the stirring needle.

[0011] In some embodiments of the present invention, a second flow guiding structure is formed on the end face of the shoulder near the stirring needle.

[0012] In some embodiments of the present invention, the ratio of the length of the stirring needle to the thickness of the first part is 1.5-3:1; the thickness of the second part is greater than or equal to the thickness of the first part.

[0013] In some embodiments of the present invention, the pressure of the clamping ring on the first part is 0.1-3.0KN, the rotation speed of the stirring head is 200-3000rpm, the speed at which the stirring needle penetrates the first and second parts is 10-500mm / min, the time for the stirring needle to continue stirring the first and second parts after penetrating the second part to a set depth does not exceed 5s, and the speed at which the stirring needle withdraws from the second and first parts is 10-500mm / min.

[0014] According to another aspect of the present invention, a welding tool is provided for performing friction stir spot welding on stacked first and second parts in the above-described friction stir spot welding method, the welding tool comprising a clamping ring and a stirring head.

[0015] In some embodiments of the present invention, the stirring head includes a stirring shaft, a shoulder, and a stirring pin; the diameter of the shoulder is equal to the inner diameter of the clamping ring, so that the shoulder can slide within the clamping ring and rotate freely relative to the clamping ring; a first flow guiding structure for driving the flow of plasticizing material is formed on the outer surface of the stirring pin. Attached Figure Description

[0016] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0017] Figure 1 This is a schematic diagram illustrating the friction stir spot welding process in the embodiments of this application;

[0018] Figure 2 This is a schematic diagram illustrating the recesses formed by different cross-sections of the stirring needle;

[0019] Figure 3 This is a structural schematic diagram illustrating the shape of the weld nugget;

[0020] Figure 4 This is a diagram of the spot welding structure formed in Example 1.

[0021] The reference numerals in the attached diagram represent the following: 1. Pad; 2. First part; 3. Second part; 4. Clamping ring; 5. Stirring head; 501. Stirring shaft; 502. Shoulder; 503. Stirring needle; 5030. Recess; 6. Weld nugget; 601. First part; 602. Second part; 603. Third part; 7. Tail hole. Detailed Implementation

[0022] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0023] In the following description, when referring to the accompanying drawings, the same numbers in different drawings denote the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0024] In the description of this application, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances. Furthermore, in the description of this application, unless otherwise stated, "multiple" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship.

[0025] This application discloses a friction stir spot welding method. The friction stir spot welding method includes the following steps:

[0026] S1, Select the workpiece to be welded, such as Figure 1 As shown, the workpiece to be welded includes a first part 2 and a second part 3. The first part 2 and the second part 3 are stacked. The thickness of the second part 3 is greater than or equal to the thickness of the first part 2. Then, friction stir spot welding is performed on the side of the first part 2 away from the second part 3. To facilitate welding, the first part 2 and the second part 3 can be placed on a pad 1, so that the side of the second part 3 away from the first part 2 is supported on the pad 1.

[0027] In some embodiments of the present invention, the wall thickness of the first part 2 is 1mm-10mm, and the materials of the first part 2 and the second part 3 are independently one of light alloy metal materials such as aluminum alloy, magnesium alloy, and titanium alloy. That is, the materials of the first part 2 and the second part 3 can be the same or different.

[0028] S2, prepare to tighten ring 4, as follows Figure 1As shown, the clamping ring 4 is a circular tube structure with a certain length. Specifically, the appropriate length and inner diameter of the clamping ring 4 can be selected according to the overall thickness of the workpiece to be welded and the spot welding structure to be formed. Then, the clamping ring 4 is pressed on the welding area of ​​the first part 2 away from the second part 3, so that the first part 2 and the second part 3 are close together. The position where the first part 2 and the second part 3 are located inside the ring of the clamping ring 4 is the position used to form the spot welding structure.

[0029] It should be noted that the clamping ring 4 can be pressed against the first part 2 by applying a certain pressure through linear drive structures such as cylinders or electric push rods connected around it.

[0030] In some embodiments of the present invention, the pressure of the clamping ring 4 on the first part 2 is 0.1-3.0KN, which can be specifically set according to the overall thickness and metal strength of the first part 2 and the second part 3, so as to ensure the stability of subsequent welding operations and reduce the squeezing deformation of the first part 2 and the second part 3 before and during welding.

[0031] S3, prepare the stirring head 5, as follows Figure 1 As shown, the stirring head 5 includes a stirring shaft 501, a shoulder 502, and a stirring needle 503. The diameter of the shoulder 502 is not greater than the inner diameter of the clamping ring 4, so that the shoulder 502 can slide inside the clamping ring 4 and rotate freely relative to the clamping ring 4. Preferably, the diameter of the shoulder 502 is equal to the inner diameter of the clamping ring 4, which ensures that the shoulder 502 can slide inside the clamping ring 4 and rotate freely relative to the clamping ring 4, while reducing the gap between the shoulder 502 and the inner wall of the clamping ring 4.

[0032] The stirring head 5 is coaxially arranged with the clamping ring 4 and the stirring needle 503 is facing the first part 2. The stirring head 5 is rotated at high speed and moved toward the first part 2 at a certain speed by an external drive mechanism (not shown) until the shoulder 502 slides into the clamping ring 4 and the stirring needle 503 is inserted into the first part 2 and into part of the thickness of the second part 3. At this time, there is a certain gap between the shoulder 502 and the first part 2.

[0033] It should be noted that the external drive mechanism can adopt known technologies, which may include a rotary driver for driving the stirring head 5 to rotate at a certain speed and a linear driver for driving the stirring head 5 to reciprocate along the axis of the clamping ring 4. For example, the rotary driver may be a motor, and the linear driver may be a linear module. Specifically, the motor and the stirring head 5 can be coaxially connected and fixed together on the linear module. While the motor drives the stirring head 5 to rotate, the linear module can drive the stirring head 5 to reciprocate along the axis of the clamping ring 4.

[0034] In some embodiments of the present invention, the ratio of the length of the stirring needle 503 to the thickness of the first part 2 is 1.5-3:1. Specifically, it can be selected according to the thickness ratio of the first part 2 and the second part 3 to ensure that the stirring needle 503 is inserted into the first part 2 and into part of the thickness of the second part 3.

[0035] After the stirring needle 503 is inserted into the predetermined position of the first part 2 and the second part 3, the stirring head 5 continues to rotate at high speed, while the clamping ring 4 does not rotate. During this period, the frictional heat plasticizes the material of the first part 2 and the second part 3 around the stirring needle 503. The plasticized material is displaced around the stirring needle 503, and part of the plasticized material enters the area enclosed by the clamping ring 4, the shoulder 502, and the first part 2. Furthermore, when there is a small gap between the first part 2 and the second part 3 in the welding area, a small portion of the plasticized material can enter the small gap between the first part 2 and the second part 3 from around the stirring needle 503 and spread outward a certain distance.

[0036] In some embodiments of the present invention, the stirring head 5 is made of a red hard and high-temperature wear-resistant material. In order to improve the stirring performance of the stirring head 5 on the plasticized material, a first flow guiding structure for driving the plasticized material to flow is formed on the outer surface of the stirring needle 503, and a second flow guiding structure is formed on the end face of the shoulder 502 near the stirring needle 503. The first flow guiding structure includes a recess 5030 arranged along the length of the stirring needle 503 on the circumferential surface of the stirring needle 503 and a thread (not shown) on the outer surface of the stirring needle 503. The second flow guiding structure is a concentric ring or spiral groove structure (not shown) provided on the end face of the shoulder 502.

[0037] Specifically, such as Figure 2As shown, the stirring pin 503 can be an irregularly shaped, circumferentially asymmetrical stirring pin 503 with a cross-sectional shape such as circular (not shown), triangular, elliptical, semi-circular, or cross-shaped. The asymmetrical weld nugget formed by the irregularly shaped, circumferentially asymmetrical stirring pin is beneficial to improving the strength of the weld joint. When the cross-sectional shape of the stirring pin 503 is circular, the recessed part is a circular region. The longitudinal cross-sectional shape of this circular stirring pin is trapezoidal or rectangular, that is, a uniformly thick round rod or a frustum-shaped rod. The circular stirring pin and the shoulder are irregularly shaped and asymmetrically connected, that is, the circular stirring pin and the shoulder are not coaxially connected, thus forming an irregularly shaped, circumferentially asymmetrical stirring pin 503; when the stirring pin When the cross-sectional shape of the stirring needle 503 is triangular, the recessed portion 5030 is the area between the circumcircle of the triangle and each side of the triangle; when the cross-sectional shape of the stirring needle 503 is elliptical, the recessed portion 5030 is the area between the concentric circumcircle of the ellipse and the opposite sides of the ellipse; when the cross-sectional shape of the stirring needle 503 is semi-circular, the recessed portion 5030 is the area between the full circle of the semi-circle and the straight edge of the semi-circle; similarly, when the stirring needle 503 adopts a cross-shaped or other irregularly shaped circumferentially asymmetrical stirring needle 503, it can be understood that the recessed portion 5030 is formed by artificially creating a missing part around the conventional cylindrical stirring needle 503.

[0038] The stirring pin 503, in conjunction with the shoulder 502, plasticizes the materials of the first part 2 and the second part 3 around the stirring pin 503. The spatial defect formed by the recess 5030 agitates the plasticized material, driving the material to flow and mix evenly. Through the concentric ring or spiral groove structure, the plasticized material entering the area enclosed by the clamping ring 4, the shoulder 502, and the first part 2 is agitated, driving the material to flow and mix evenly. This can maximize the homogenization of the plasticized material of the first part 2 and the second part 3. This homogenization effect is more obvious when the materials of the first part 2 and the second part 3 are different. It can make the homogenized plasticized material more similar to the material properties of the first part 2 and the second part 3, improving the stability of the connection and the strength of the spot welded structure.

[0039] In some embodiments of the present invention, the stirring head 5 rotates at 200-3000 rpm, the stirring needle 503 penetrates the first part 2 and the second part 3 at a speed of 10-500 mm / min, the stirring needle 503 continues to stir the first part 2 and the second part 3 for no more than 5 seconds after penetrating the second part 3 to a set depth, and the stirring needle 503 withdraws from the second part 3 and the first part 2 at a speed of 10-500 mm / min. Specifically, this can be adjusted according to the thickness of the first part 2 and the second part 3 and the specifications of the spot welded structure.

[0040] S4, as Figure 1 and Figure 3As shown, after the materials of the first part 2 and the second part 3 around the stirring needle 503 are plasticized and enter the predetermined position, the stirring head 5 stops rotating abruptly. The heat input of the stirring head 5 is small when it stops abruptly, which is beneficial to enhance the strength of the spot weld and improve efficiency. The stirring head 5 is moved away from the second part 3 at a certain speed by an external drive mechanism until the stirring needle 503 exits the second part 3 and the first part 2. The plasticized material cools and solidifies to form a weld nugget 6, and the spot welding process is completed. The weld nugget 6 is a boss structure, which can improve the strength of the spot weld. The first part 601 of the boss structure protrudes from the surface of the first part 2, and the second part 602 directly connects the first part 2 and the second part 3. In the case that there is a small gap between the first part 2 and the second part 3 in the welding area, the boss structure also has a third part 603 that is directly connected between the first part 2 and the second part 3 and surrounds the second part 602. The first part 601, the second part 602 and the third part 603 form a stable whole.

[0041] Moreover, such as Figure 3 As shown, when the stirring pin 503 adopts an irregularly shaped, circumferentially asymmetrical stirring pin with a cross-sectional shape such as triangle, ellipse, semicircle, or cross, after the stirring pin 503 exits the second part 3 and the first part 2, the tail hole 7 of the weld nugget 6 formed by the cooling and solidification of the plasticized material is approximately the corresponding shape of triangle, ellipse, semicircle, or cross, so that the first part 601 and the second part 602 of the weld nugget 6, especially the second part 602, form an alternating thin and thick structure, which further improves the strength of the spot welded structure.

[0042] Then, S2-S4 can be repeated to continue friction stir spot welding on other areas of the first part 2 and the second part 3.

[0043] To more clearly describe the technical solution of the present invention and demonstrate its technical effects, the technical solution of the present invention will be further explained and illustrated below with reference to specific embodiments.

[0044] Example 1:

[0045] Welding of 6061 aluminum alloy sheet

[0046] Two 2mm thick 6061 aluminum alloy plates are selected as the first part 2 and the second part 3, respectively. The two plates are stacked on the pad 1. The pressure of the clamping ring 4 on the two plates is 0.2KN. The stirring needle 503 is 3mm long with an elliptical cross-section and rotates at 1200rpm. Then, the stirring needle 503 is inserted into the two plates through the clamping ring 4 at a speed of 300mm / min, and the dwell time after insertion is 0.5s. Then, the stirring needle 503 is withdrawn from the two plates at a lifting speed of 300mm / min. The resulting spot welded joint is shown below. Figure 4 As shown.

[0047] Depend on Figure 4 The cross-sectional results of the spot welding structure show that by using the clamping ring 4 and stirring head 5 in this invention and optimizing the welding process parameters, two plates can be spot welded by friction stir without any added materials. This can achieve the connection of the same and different materials, with a simple process, low cost, good sealing performance, and high structural strength.

[0048] This application also proposes a welding tool corresponding to the above-described friction stir spot welding method embodiment, which is used for friction stir spot welding of stacked first part 2 and second part 3 in the above-described friction stir spot welding method, such as... Figure 1 As shown, the welding fixture includes a clamping ring 4 and a stirring head 5; the stirring head 5 includes a stirring shaft 501, a shoulder 502, and a stirring pin 503; the diameter of the shoulder 502 is equal to the inner diameter of the clamping ring 4, allowing the shoulder 502 to slide within the clamping ring 4 and rotate freely relative to the clamping ring 4; a first flow guiding structure for driving the flow of plasticized material is formed on the outer surface of the stirring pin 503, and a second flow guiding structure is formed on the end face of the shoulder 502 near the stirring pin 503. The first flow guiding structure includes a recess 5030 arranged along the length of the stirring pin 503 on the circumferential surface of the stirring pin 503 and a thread (not shown) on the outer surface of the stirring pin 503; the second flow guiding structure is a concentric ring or spiral groove structure (not shown) provided on the end face of the shoulder 502.

[0049] Specifically, such as Figure 2As shown, the stirring pin 503 can be an irregularly shaped, circumferentially asymmetrical stirring pin 503 with a cross-sectional shape such as a circle (not shown), triangle, ellipse, semicircle, or cross. When the cross-sectional shape of the stirring pin 503 is circular, the recessed area is a circular region. When the cross-sectional shape of the stirring pin 503 is triangular, the recessed area 5030 is the region between the circumcircle of the triangle and each side of the triangle. When the cross-sectional shape of the stirring pin 503 is elliptical, the recessed area 5030 is the region between the concentric circumcircle of the ellipse and the opposite sides of the ellipse. When the cross-sectional shape of the stirring pin 503 is semicircular, the recessed area 5030 is the region between the full circle of the semicircle and the straight edge of the semicircle. Similarly, when the stirring pin 503 is an irregularly shaped, circumferentially asymmetrical stirring pin 503 with a cross-sectional shape such as a cross, it can be understood that the recessed area 5030 is formed by artificially creating a missing part around the conventional cylindrical stirring pin 503.

[0050] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for friction stir spot welding, characterized in that, include: Stack the first and second parts of the workpiece to be welded; Prepare a clamping ring and a stirring head, the stirring head including a stirring shaft, a shoulder and a stirring needle, press the clamping ring against the welding area of ​​the first part away from the second part, so that the first part and the second part are brought closer together; The stirring head rotates, the shoulder slides into the clamping ring, and the stirring needle is inserted into the first part and into part of the thickness of the second part; The stirring head continues to rotate, and the frictional heat plasticizes the material of the first and second parts around the stirring needle. The plasticized material is displaced around the stirring needle, and part of the plasticized material enters the area enclosed by the clamping ring, the shoulder, and the first part to form a prefabricated boss. The stirring head stops abruptly, and the stirring needle moves away from the second part until it exits both the second and first parts. The plasticized material cools and solidifies to form a weld nugget, and the spot welding process is completed.

2. The friction stir spot welding method according to claim 1, characterized in that, A first flow guiding structure for driving the flow of plasticizing material is formed on the outer surface of the stirring needle.

3. The friction stir spot welding method according to claim 2, characterized in that, The first flow guiding structure includes a recessed portion formed on the circumferential surface of the stirring needle and arranged along the length of the stirring needle.

4. The friction stir spot welding method according to claim 3, characterized in that, The cross-sectional shape of the stirring pin is one of triangle, ellipse, or semicircle, and the irregular circumferentially asymmetrical stirring pin forms an asymmetrical spot weld nugget. When the cross-sectional shape of the stirring needle is triangular, the recessed portion is the area between the circumcircle of the triangle and each side of the triangle; When the cross-sectional shape of the stirring needle is elliptical, the recessed part is the area between the concentric circumcircle of the ellipse and the opposite sides of the ellipse; When the cross-sectional shape of the stirring needle is semi-circular, the recessed portion is the area between the full circle of the semi-circle and the straight edge of the semi-circle.

5. The friction stir spot welding method according to claim 2, characterized in that, The first flow guiding structure also includes threads formed on the outer surface of the stirring needle.

6. The friction stir spot welding method according to claim 1, characterized in that, A second flow guiding structure is formed on the end face of the shoulder near the stirring needle.

7. The friction stir spot welding method according to claim 1, characterized in that, The ratio of the length of the stirring needle to the thickness of the first part is 1.5-3:1; the thickness of the second part is greater than or equal to the thickness of the first part.

8. The friction stir spot welding method according to any one of claims 1-7, characterized in that, The pressure of the clamping ring on the first part is 0.1-3.0KN, the rotation speed of the stirring head is 200-3000rpm, the speed at which the stirring needle penetrates the first and second parts is 10-500mm / min, the time for the stirring needle to continue stirring the first and second parts after penetrating the second part to a set depth does not exceed 5s, and the speed at which the stirring needle withdraws from the second and first parts is 10-500mm / min.

Images