Ultrasonic elliptical vibration friction stir welding device and method

Abstract

The invention provides an ultrasonic elliptical vibration friction stir welding device and method, and relates to the technical field of friction stir welding machining. The device comprises an ultrasonic elliptical vibration system, a clamping device and a stirring head, the ultrasonic elliptical vibration system comprises an ultrasonic generator, an electric energy transmission system, an ultrasonic transducer and an amplitude-change pole, the ultrasonic generator is connected with the electric energy transmission system, the electric energy transmission system is connected with the ultrasonic transducer, and the clamping device is connected with a machine tool spindle. The vibration node position of the amplitude-change pole is connected with the clamping device, the two sides of the amplitude-change pole are connected with the ultrasonic transducer and the stirring head, the stirring head conducts ultrasonic elliptical vibration, and ultrasonic elliptical vibration friction stir welding is conducted on a workpiece to be welded. A more complex periodic movement track is generated through ultrasonic elliptical vibration, the stirring capacity of the stirring head on materials is improved, the materials under the action of a stirring tool are promoted to be mixed more sufficiently, the material fluidity and the filling effect are improved, welding defects are reduced, and the welding quality is improved.

Description

Technical Field

[0001] This invention relates to the field of friction stir welding technology, and more particularly to an ultrasonic elliptical vibration friction stir welding apparatus and method. Background Technology

[0002] Friction stir welding (FSW) is a solid-state joining technology that uses a high-speed rotating stirring head inserted into the mating surfaces of the workpieces to achieve a connection through frictional heat and plastic deformation. It is widely used in aerospace, rail transportation, shipbuilding and other fields.

[0003] In recent years, its application scope has gradually expanded to the joining of high-melting-point, difficult-to-deform metals such as titanium alloys and stainless steel. However, the material properties of these metals lead to multiple technical challenges for the FSW process: First, the material maintains a high strength level during the welding thermal cycle, resulting in limited plastic deformation capacity, insufficient material flow, and thus inducing defects such as pores and grooves, forming local weak connection areas and a narrow process window; Second, the severe abrasive wear effect of hard phase particles on the stirring head, coupled with high upsetting force and welding advance resistance, poses a severe challenge to the performance of welding equipment and stirring head; Third, when welding dissimilar material systems (such as Al / Mg, Al / Fe, Al / Ti), thick intermetallic compounds (IMCs) are easily formed at the interface. Their hard and brittle characteristics cause cracks to preferentially initiate in the IMCs layer, severely degrading the mechanical properties of the joint.

[0004] To address the aforementioned issues, many scholars have explored various approaches, including applying ultrasonic vibrations along or perpendicular to the centerline of the stirring head, or directly applying ultrasonic vibrations to the workpiece to be welded. Patent publication CN112809219B discloses an ultrasonic friction stir welding composite system, connecting a high-power multi-vibrator ultrasonic vibration system along the centerline of the stirring head to assist in friction stir welding. Patent publication CN103894721A discloses a pre- and post-weld dual ultrasonic vibration-assisted friction stir welding method, placing an ultrasonic vibration system on each of the workpieces before and after the stirring head to assist in friction stir welding. Patent publication CN112935514B discloses an ultrasonic friction stir welding device and method, connecting an ultrasonic vibration system perpendicular to the centerline of the stirring head to assist in friction stir welding. All of these patents represent innovations in device design or vibration application direction, and their essence lies in one-dimensional reciprocating linear ultrasonic vibration. However, linear ultrasonic vibration has a single direction and its effectiveness is limited in the welding and processing of some high-melting-point and difficult-to-deform metal materials, especially in improving the material flow pattern. Summary of the Invention

[0005] To address the aforementioned technical problems, an ultrasonic elliptical vibration friction stir welding apparatus and method are provided. This invention primarily introduces high-frequency elliptical mechanical vibration into the friction stir welding process, driving a high-speed rotating stirring head to perform two-dimensional ultrasonic elliptical vibration. This reduces welding force, enhances the stirring head's ability to agitate materials, improves material flowability, promotes more thorough mixing of materials below the stirring tool, reduces welding defects, improves welding quality, and reduces wear on the stirring head.

[0006] The technical means employed in this invention are as follows: An ultrasonic elliptical vibration friction stir welding device includes: an ultrasonic elliptical vibration system, a clamping device, and a stirring head. The ultrasonic elliptical vibration system includes an ultrasonic generator, a power transmission system, an ultrasonic transducer, and an amplitude transformer. The ultrasonic generator is electrically connected to the power transmission system, and the power transmission system is electrically connected to the ultrasonic transducer. The ultrasonic transducer is a longitudinal bending composite vibration transducer or a longitudinal vibration transducer combined with a vibration mode conversion structure. The power transmission system is installed on one side of the clamping device, and the ultrasonic transducer is placed inside one side of the clamping device. One end of the clamping device is used to connect to a machine tool spindle. One side of the amplitude transformer is inserted into the clamping device and fixedly connected to the ultrasonic transducer. The vibration node position of the amplitude transformer is fixedly connected to the other side of the clamping device. The other side of the amplitude transformer is located outside the clamping device and fixedly connected to the stirring head. The stirring head performs ultrasonic elliptical vibration to perform ultrasonic elliptical vibration friction stir welding on the workpiece to be welded.

[0007] Furthermore, the clamping device includes a cylindrical sleeve and a baffle. One end of the cylindrical sleeve is used to connect to the machine tool spindle. A flange is provided at the vibration node position of the amplitude transformer. The other end face of the cylindrical sleeve contacts one end face of the flange, and the other end face of the flange contacts one end face of the baffle. The flange, cylindrical sleeve, and baffle are threaded together by short screws.

[0008] Furthermore, the ultrasonic generator is a multiphase universal ultrasonic power supply.

[0009] Furthermore, the power transmission system is a rotary contactless transformer or a rotary contact transformer.

[0010] Furthermore, the rotary contactless transformer includes a primary winding and a secondary winding connected to each other. The secondary winding is fixedly connected to the cylindrical sleeve of the clamping device, and the primary winding is fixed to the machine tool spindle box and electrically connected to the ultrasonic generator.

[0011] Furthermore, the ultrasonic transducer includes a front cover plate, a bending vibration piezoelectric ceramic wafer, a longitudinal vibration piezoelectric ceramic wafer, and a rear cover plate connected in sequence by long screws. One side of the amplitude transformer is fixedly connected to the front cover plate, and the bending vibration piezoelectric ceramic wafer and the longitudinal vibration piezoelectric ceramic wafer are electrically connected to the secondary winding of the power transmission system.

[0012] Furthermore, the ultrasonic elliptical vibration direction is set to be parallel to, perpendicular to, or at a certain angle to the welding direction.

[0013] Furthermore, the workpieces to be welded are butted or overlapped.

[0014] The present invention also provides an ultrasonic elliptical vibration friction stir welding method, which uses the above-mentioned ultrasonic elliptical vibration friction stir welding device and includes the following steps: S1. Connect the ultrasonic elliptical vibration system, clamping device and stirring head in sequence; S2. Prepare the workpiece to be welded and fix it in place; S3. Determine and set the welding process parameters for ultrasonic elliptical vibration friction stir welding based on the geometric parameters, physical parameters, and joint type of the workpiece to be welded. S4. Start the ultrasonic generator; S5. Control the stirring head to rotate and press down to insert into the workpiece to be welded, and drive the stirring head to move along the welding position of the workpiece; S6. Stop moving, raise the stirring head, and turn off the ultrasonic generator; S7. Complete ultrasonic elliptical vibration friction stir welding and remove the workpiece.

[0015] Compared with the prior art, the present invention has the following advantages: The present invention provides an ultrasonic elliptical vibration friction stir welding device and method, which forms a composite energy field that combines high-frequency micro-forging and continuous multi-directional shearing by applying ultrasonic elliptical vibration to the stirring head, thereby realizing multi-dimensional control of the rheological behavior and thermodynamic cycle of the material in the plastic zone during the FSW process.

[0016] Compared with traditional one-dimensional linear ultrasonic vibration-assisted welding (FSW), ultrasonic elliptical vibration-assisted FSW has the following significant advantages. First, it can generate continuous multi-directional shear forces, enhancing material mixing, improving mixing uniformity, material flowability, and weld filler quality, thereby effectively suppressing the formation of welding defects. Second, the high-frequency micro-forging effect can periodically compress the material in the plastic zone, promoting dynamic recrystallization, refining grains, and controlling the distribution behavior of precipitated phases. Third, the multi-directional characteristics of ultrasonic elliptical vibration more efficiently reduce the triaxial forces (including spindle torque, upsetting force, and forward resistance) during the welding process, reducing stirring head wear, extending tool life, and making the welding of high-melting-point, difficult-to-deform metals more feasible.

[0017] Based on the above reasons, this invention can be widely applied in fields such as welding processing. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the ultrasonic elliptical vibration stir friction welding device of the present invention.

[0020] Figure 2 This is a schematic diagram of the friction stir welding process in which the stirring head of the present invention performs ultrasonic elliptical vibration along the weld seam.

[0021] Figure 3 This is a schematic diagram of the ultrasonic elliptical vibration stirring friction lap welding of the stirring head along the weld seam according to the present invention.

[0022] Figure 4 This is a schematic diagram of ultrasonic elliptical vibration friction butt welding of the vertical weld seam of the stirring head of the present invention.

[0023] Figure 5 This is a schematic diagram of the ultrasonic elliptical vibration friction butt welding of the present invention, in which the stirring head and the weld are at a 15° angle.

[0024] In the diagram: 1. Workpiece a to be welded; 2. Stirring head; 3. Short screw; 4. Cylindrical sleeve; 5. Amplifier rod; 6. Front cover plate; 7. Secondary winding; 8. Primary winding; 9. Long screw; 10. Rear cover plate; 11. Longitudinal vibration piezoelectric ceramic wafer; 12. Bending vibration piezoelectric ceramic wafer; 13. Double-ended stud; 14. Baffle; 15. Workpiece b to be welded; 16. Multiphase universal ultrasonic power supply. Detailed Implementation

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments 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. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. 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.

[0027] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0028] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0029] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0030] For ease of description, spatial relative terms such as "above," "over," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation besides the orientation of the device as described in the figures. For example, if the device in the figures is inverted, a device described as "above" or "above" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0031] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0032] Example 1 Currently, the ultrasonic vibration design schemes for friction stir welding processes are all one-dimensional reciprocating linear ultrasonic vibrations. To solve this problem, such as... Figure 1 As shown, this invention provides an ultrasonic elliptical vibration friction stir welding device, including an ultrasonic elliptical vibration system, a clamping device, and a stirring head 2. The ultrasonic elliptical vibration system consists of an ultrasonic generator, a power transmission system, an ultrasonic transducer, and an amplitude transformer 5. The power transmission system is connected to the ultrasonic transducer, and the ultrasonic generator is connected to the power transmission system to supply power to the ultrasonic transducer. The clamping device consists of a cylindrical sleeve 4 and a baffle 14. The power transmission system is installed on one side of the cylindrical sleeve 4, the ultrasonic transducer is placed inside one side of the cylindrical sleeve 4, and one side of the amplitude transformer 5 is inserted into the sleeve. Inside the cylindrical sleeve 4, one end of the ultrasonic transducer is threadedly connected to one end of the amplitude transformer 5. The other end of the amplitude transformer 5 is located outside the cylindrical sleeve 4 and is threadedly connected to the stirring head 2. The amplitude transformer 5 has a flange at the vibration node position. One end face of the cylindrical sleeve 4 contacts one end face of the flange of the amplitude transformer 5, and the other end face of the flange of the amplitude transformer 5 contacts one end face of the baffle 14. The flange of the amplitude transformer 5 is threadedly connected to the cylindrical sleeve 4 and the baffle 14 by short screws 3. The cylindrical sleeve 4 is connected to the machine tool spindle, thereby realizing friction stir welding based on ultrasonic elliptical vibration.

[0033] Preferably, the ultrasonic generator is a multiphase universal ultrasonic power supply 16.

[0034] Preferably, the power transmission system is a rotary contactless transformer or a rotary contact transformer.

[0035] Preferably, the ultrasonic transducer is a longitudinal bending composite vibration transducer or a longitudinal vibration transducer used in conjunction with (or in combination with) a specially designed amplitude transformer 5 / vibration mode conversion structure.

[0036] The present invention also provides an ultrasonic elliptical vibration friction stir welding method, which uses the above-mentioned ultrasonic elliptical vibration friction stir welding device and includes the following steps: S1. Connect the ultrasonic elliptical vibration system, cylindrical sleeve 4, baffle 14 and stirring head 2 in sequence; S2. Prepare the workpiece to be welded and fix it in place; S3. Determine and set the welding process parameters for ultrasonic elliptical vibration friction stir welding based on the geometric parameters, physical parameters, and joint type of the workpiece to be welded. S4. Start the ultrasonic generator; S5. Control the stirring head 2 to rotate and press down to insert into the workpiece to be welded, and drive the stirring head 2 to move along the welding position of the workpiece to be welded; S6. Stop moving, raise stirring head 2, and turn off the ultrasonic generator; S7. Complete ultrasonic elliptical vibration friction stir welding and remove the workpiece.

[0037] Example 2 Combination Figure 1 and Figure 2 This embodiment describes an ultrasonic elliptical vibration stir friction welding device, comprising a cylindrical sleeve 4, a non-contact transformer, an ultrasonic transducer, an amplitude transformer 5, a baffle 14, a stirring head 2, and a multiphase universal ultrasonic generator 16. The non-contact transformer consists of a primary winding 8 and a secondary winding 7. The ultrasonic transducer is composed of a front cover plate 6, a bending vibration piezoelectric ceramic wafer 12, a longitudinal vibration piezoelectric ceramic wafer 11, and a rear cover plate 10 connected sequentially by long screws 9. The front cover plate 6 of the ultrasonic transducer is connected to one end of the amplitude transformer 5 via double-ended studs 13, and the other end of the amplitude transformer 5 is connected to the stirring head 2 via threads. The amplitude transformer 5 has a flange at the vibration node position. One end of the cylindrical sleeve 4 and the baffle 14 are threadedly connected to the flange of the amplitude transformer 5 via short screws 3, and the other end of the cylindrical sleeve 4 is connected to the machine tool spindle.

[0038] The primary winding 8 of the non-contact transformer is fixed to the machine tool spindle box. During operation, the primary winding 8 remains stationary. The multiphase universal ultrasonic power supply 16 is connected to the primary winding 8 of the non-contact transformer by wires, and a high-frequency alternating current is input. An induced electromotive force is generated in the secondary winding 7 of the non-contact transformer using an electromagnetic field as a medium. The secondary winding 7 is externally threaded to one end of the cylindrical sleeve 4. During operation, the secondary winding 7 rotates with the cylindrical sleeve 4. At the same time, the secondary winding 7 is connected to the bending vibration piezoelectric ceramic wafer 12 and the longitudinal vibration piezoelectric ceramic wafer 11 of the ultrasonic transducer by wires, respectively. The high-frequency alternating electrical signal is transmitted from the multiphase universal ultrasonic generator 16 to the longitudinal vibration piezoelectric ceramic wafer 11 and the bending vibration piezoelectric ceramic wafer 12, which excites the ultrasonic transducer to perform longitudinal and bending composite vibration. The vibration is transmitted to the stirring head 2 to synthesize ultrasonic elliptical vibration, thereby realizing stir friction welding based on ultrasonic elliptical vibration.

[0039] This invention also provides a friction stir welding method based on ultrasonic elliptical vibration, comprising the following steps: S1. Connect the cylindrical sleeve 4, non-contact transformer, ultrasonic transducer, amplitude transformer 5, baffle 14, stirring head 2 and multiphase universal ultrasonic generator 16. S2. Prepare workpieces a1 and b15 to be welded, and fix workpieces a1 and b15 to be welded. Specifically, in one embodiment, the workpiece to be welded a1 is an aluminum alloy sheet, the workpiece to be welded b15 is a steel plate, and the workpiece to be welded a1 and the workpiece to be welded b15 are fixed by butt joint. S3. Based on the geometric parameters, physical parameters, and joint type of the workpieces a1 and b15 to be welded, determine and set the welding process parameters for ultrasonic elliptical vibration stir friction welding. Specifically, in one embodiment, the stirring head 2 rotates at a speed of 400 rpm to 1000 rpm, the welding speed is 50 mm / min to 200 mm / min, the distance between the shoulder of the stirring head 2 and the surfaces of the workpieces to be welded (a1 and b15) is 0 mm to 0.2 mm, the ultrasonic power is 100 W to 2000 W, the frequency is 15 kHz to 40 kHz, and the ultrasonic elliptical vibration direction is set to be parallel to the welding direction, which can promote longitudinal flow and effectively improve the migration of weld material. It is suitable for long straight welds with high requirements for longitudinal continuity of weld. S4. Start the multiphase universal ultrasonic generator 16; S5. Control the stirring head 2 to rotate and press down to insert into the workpieces a1 and b15 to be welded, and drive the stirring head 2 to move along the direction of workpiece welding. S6. Stop moving, raise stirring head 2, and turn off the ultrasonic generator; S7. Complete ultrasonic elliptical vibration friction stir welding and remove the workpiece.

[0040] Current technologies all employ one-dimensional reciprocating linear ultrasonic vibration, which has limited ability to control the material flow pattern in a single vibration direction, and thus has limited effect on improving material mixing uniformity and optimizing interfacial bonding.

[0041] The ultrasonic elliptical vibration of this invention generates a unique composite energy field (high-frequency micro-forging and continuous multi-directional shear). During the FSW process, this high-frequency micro-forging and continuous multi-directional shear coupling allows for multi-dimensional control of the transient rheological behavior and thermodynamic cycling process in the plastic zone. Specifically, unlike traditional one-dimensional linear ultrasonic vibration, ultrasonic elliptical vibration, through high-frequency composite vibration applied by the stirring head, generates continuous multi-directional shear force, significantly enhancing material stirring ability and mixing uniformity, improving flowability and filling effect. Simultaneously, its high-frequency micro-forging effect periodically compresses the material in the plastic zone, promoting dynamic recrystallization, refining grains, and controlling precipitated phase behavior. Furthermore, the multi-directional properties of ultrasonic elliptical vibration more effectively reduce the triaxial forces (spindle torque, upsetting force, and forward resistance) during the welding process, improving friction conditions and reducing stirring head wear. In other words, compared to one-dimensional reciprocating linear ultrasonic vibration, ultrasonic elliptical vibration offers greater advantages in overcoming the multiple technical challenges faced in the FSW process.

[0042] Example 3 Combination Figure 1 and Figure 3 In this embodiment, the workpieces a1 and b15 to be welded in step S2 are fixed by overlapping.

[0043] Example 4 Combination Figure 1 and Figure 4 This embodiment describes an ultrasonic elliptical vibration direction in step S3 that is set perpendicular to the welding direction. This enhances the mixing of materials on the advancing and retreating sides and eliminates the "flow barrier" between them. It is suitable for welding dissimilar materials or for applications requiring high uniformity of weld cross-section and shear resistance.

[0044] Example 5 Combination Figure 1 and Figure 5 In this embodiment, the ultrasonic elliptical vibration direction in step S3 is set to form a 15° angle with the welding direction, which can form a complex "spiral propulsion" flow. The tangential component of the vibration (along the weld direction) promotes longitudinal flow, and the normal component (perpendicular to the weld direction) promotes transverse mixing. It can efficiently transport and mix materials in both longitudinal and transverse directions at the same time, and is suitable for high-quality welding that requires comprehensive mechanical properties and uniformity of structure.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An ultrasonic elliptical vibration friction stir welding device, characterized in that, include: An ultrasonic elliptical vibration system, a clamping device, and a stirring head (2) are provided. The ultrasonic elliptical vibration system includes an ultrasonic generator, an electrical power transmission system, an ultrasonic transducer, and an amplitude transformer (5). The ultrasonic generator is electrically connected to the electrical power transmission system, and the electrical power transmission system is electrically connected to the ultrasonic transducer. The ultrasonic transducer is a longitudinal bending composite vibration transducer or a longitudinal vibration transducer combined with a vibration mode conversion structure. The electrical power transmission system is installed on one side of the clamping device. The ultrasonic transducer is placed inside one side of the clamping device. One end of the clamping device is used to connect to the machine tool spindle. One side of the amplitude transformer (5) is inserted into the clamping device and fixedly connected to the ultrasonic transducer. The vibration node position of the amplitude transformer (5) is fixedly connected to the other side of the clamping device. The other side of the amplitude transformer (5) is located outside the clamping device and fixedly connected to the stirring head (2). The stirring head (2) performs ultrasonic elliptical vibration to perform ultrasonic elliptical vibration stirring friction welding on the workpiece to be welded.

2. The ultrasonic elliptical vibration friction stir welding device according to claim 1, characterized in that, The clamping device includes a cylindrical sleeve (4) and a baffle (14). One end of the cylindrical sleeve (4) is used to connect with the machine tool spindle. A flange is provided at the vibration node position of the amplitude rod (5). The other end face of the cylindrical sleeve (4) is in contact with one end face of the flange. The other end face of the flange is in contact with one end face of the baffle (14). The flange is threadedly connected to the cylindrical sleeve (4) and the baffle (14) by short screws (3).

3. The ultrasonic elliptical vibration friction stir welding device according to claim 1, characterized in that, The ultrasonic generator is a multiphase universal ultrasonic power supply (16).

4. The ultrasonic elliptical vibration friction stir welding device according to claim 1, characterized in that, The power transmission system is a rotary contactless transformer or a rotary contact transformer.

5. The ultrasonic elliptical vibration friction stir welding device according to claim 4, characterized in that, The rotary contactless transformer includes a primary winding (8) and a secondary winding (7) connected to each other. The secondary winding (7) is fixedly connected to the cylindrical sleeve (4) of the clamping device, and the primary winding (8) is fixed to the machine tool spindle box and electrically connected to the ultrasonic generator.

6. The ultrasonic elliptical vibration friction stir welding apparatus according to claim 1, characterized in that, The ultrasonic transducer includes a front cover plate (6), a bending vibration piezoelectric ceramic wafer (12), a longitudinal vibration piezoelectric ceramic wafer (11), and a rear cover plate (10) connected in sequence by long screws (9). One side of the amplitude rod (5) is fixedly connected to the front cover plate (6). The bending vibration piezoelectric ceramic wafer (12) and the longitudinal vibration piezoelectric ceramic wafer (11) are electrically connected to the secondary winding (7) of the power transmission system.

7. The ultrasonic elliptical vibration friction stir welding device according to claim 1, characterized in that, The ultrasonic elliptical vibration direction is set to be parallel to, perpendicular to, or at a certain angle to the welding direction.

8. The ultrasonic elliptical vibration friction stir welding apparatus according to claim 1, characterized in that, The workpieces to be welded are butted or overlapped.

9. An ultrasonic elliptical vibration friction stir welding method, characterized in that, The ultrasonic elliptical vibration friction stir welding apparatus as described in any one of claims 1-8 comprises the following steps: S1. Connect the ultrasonic elliptical vibration system, clamping device and stirring head (2) in sequence; S2. Prepare the workpiece to be welded and fix it in place; S3. Determine and set the welding process parameters for ultrasonic elliptical vibration friction stir welding based on the geometric parameters, physical parameters, and joint type of the workpiece to be welded. S4. Start the ultrasonic generator; S5. Control the stirring head (2) to rotate and press down into the workpiece to be welded, and drive the stirring head (2) to move along the position to be welded of the workpiece; S6. Stop moving, raise the stirring head (2), and turn off the ultrasonic generator; S7. Complete ultrasonic elliptical vibration friction stir welding and remove the workpiece.

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