A dual-impeller friction stir welding apparatus and method

Abstract

This invention relates to the field of friction stir welding technology, and more particularly to a dual-head friction stir welding apparatus and method. The welding apparatus includes: a first stirring unit and a second stirring unit; the first stirring unit includes a first static pressure block and a first stirring head, the first static pressure block having a first through hole offset along a first direction, and the first stirring head disposed within the first through hole; the second stirring unit includes a second static pressure block and a second stirring head, the second static pressure block having a second through hole offset along the first direction, opposite to the offset direction of the first through hole, and the second stirring head disposed within the second through hole. This invention enables flexible application of the stirring unit to workpieces within a certain thickness range, eliminates welding defects such as incomplete penetration / incomplete welding / weak connections, and reduces the rotational torque and forward resistance of the stirring unit.

Description

Technical Field

[0001] This invention relates to the field of friction stir welding technology, and in particular to a dual-stirring-head friction stir welding apparatus and method. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Friction stir welding is a novel solid-state joining technology that overcomes the welding defects such as cracks and porosity that are easily generated by fusion welding. It enables high-quality welding of certain materials that were previously difficult to weld by fusion, and has become the preferred welding method for aluminum, magnesium and their alloys.

[0004] However, conventional friction stir welding has certain drawbacks. First, the dimensions of the stirring tool (commonly known as the stirring head, which consists of a shoulder and a stirring pin) must match the dimensions of the workpiece to be welded. Typically, the length of the stirring pin should be equal to or slightly less than the thickness of the workpiece. If the thickness of the workpiece changes, a new stirring head must be replaced. Second, during welding, the bottom of the workpiece is only affected by the heat from the tip of the stirring pin, resulting in poor material flow at the tip, which easily leads to defects such as incomplete penetration, incomplete fusion, or weak connections, severely reducing the joint strength. Furthermore, the stirring pin bears significant rotational torque and forward resistance, easily forming void-type or tunnel-type defects on the weld's advancing side. Therefore, the welding speed should not be too fast, the stirring head life is short, and the welding efficiency is low. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a dual-stirring-head friction stir welding device, which enables flexible application of the stirring unit to the workpieces within a certain thickness range, eliminates welding defects such as incomplete penetration / incomplete welding / weak connection, enhances the plastic flow of the workpiece material, reduces the rotational torque and forward resistance of the stirring unit, significantly reduces the tendency to form pores or tunnel-type defects, improves welding efficiency, and further improves the microstructure and properties of the welded joint.

[0006] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0007] A dual-head friction stir welding apparatus is disclosed for welding workpieces to be welded. The workpieces have a first direction along the weld seam and a second direction perpendicular to the first direction. The welding apparatus includes a first stirring unit and a second stirring unit. The first stirring unit includes a first static pressure block and a first stirring head. The first static pressure block is provided with a first through hole offset along the first direction, and the first stirring head is disposed within the first through hole. The second stirring unit includes a second static pressure block and a second stirring head. The second static pressure block is provided with a second through hole offset along the first direction, and the offset direction is opposite to that of the first through hole. The second stirring head is disposed within the second through hole. The first static pressure block and the second static pressure block are located on both sides of the workpiece to be welded and aligned along the second direction. The first stirring head and the second stirring head are arranged back and forth along the first direction.

[0008] Optionally, the first static pressure block and the second static pressure block have the same shape, both being cuboids. The inner end faces of the first static pressure block and the second static pressure block facing the workpiece to be welded are both planes. At least the inner end faces are provided with rounded corners along the front edge of the first direction. The first through hole and the second through hole are both round holes, and the axes of the first through hole and the second through hole are perpendicular to the inner end faces.

[0009] Optionally, the inner end face of the first static pressure block facing the workpiece and the inner end face of the second static pressure block facing the workpiece have the same contour.

[0010] Optionally, the first stirring head and the second stirring head have the same shape, including a stirring rod and a stirring needle. The stirring needle is located at the end of the stirring rod facing the workpiece to be welded. The stirring rod is cylindrical, and the stirring needle is cylindrical or conical. The diameter of the circle where the stirring needle and the stirring rod intersect is smaller than the diameter of the stirring rod.

[0011] Optionally, the end face of the stirring rod facing the workpiece to be welded is a flat surface or a concave-convex surface, and the circumferential surface of the stirring pin is a smooth surface or a rough surface, and the end face facing the workpiece to be welded is a flat surface or a concave-convex surface.

[0012] Optionally, the first stirring unit and the second stirring unit are perpendicular to the workpiece to be welded; or, the first stirring unit and the second stirring unit have a set angle with the workpiece to be welded.

[0013] This invention also provides a welding method using the dual-stirring head friction stir welding device described above, comprising:

[0014] The two stirring units are moved to both sides of the starting point of the weld on the workpiece and aligned.

[0015] The two stirring heads start to rotate and approach the workpiece at the same speed together with the two static pressure blocks. The stirring needles of the two stirring heads are inserted into the workpiece until the end faces of the two static pressure blocks contact the surface of the workpiece with a predetermined pressure, so that the thermal state of the workpiece reaches a quasi-steady state.

[0016] The two stirring units move along the first direction at the same speed, and the material to be welded is subjected to the thermal action of the first stirring head and the second stirring head in sequence.

[0017] Upon reaching the final welding point, the two stirring units detach from the workpiece and stop rotating, completing the welding process.

[0018] Optionally, before the two stirring units come into contact with the workpiece to be welded, the shoulders of the stirring heads of the two stirring units are flush with the inner end face of the static pressure block.

[0019] Optionally, the two stirring heads can rotate at the same or different speeds.

[0020] Optionally, the two static pressure blocks and the two stirring heads move at the same speed along the first direction during the welding stage.

[0021] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0022] 1. With the coordinated action of the two stirring heads, it has great flexibility in welding workpieces of different thicknesses. When the total thickness of the workpiece varies within a certain range, welding can be completed without replacing the stirring unit.

[0023] 2. The first and second static pressure blocks press and fix the workpiece to be welded from the top and bottom directions, respectively. The two sets of stirring units work together from the top and bottom surfaces of the workpiece to solve the welding defects such as incomplete penetration / incomplete welding / weak connection caused by insufficient heat input and insufficient material flow at the bottom of the workpiece in conventional processes, and greatly improve the weld strength.

[0024] 3. Under the thermal action of the two stirring heads, the material undergoes two high-temperature and high-strain thermal processes. The thermal action time is longer and the material flow range is larger, thus reducing the tendency of void and tunnel defects to form, reducing the rotational torque and forward resistance borne by the stirring head, improving the microstructure of the joint, and increasing the welding speed and welding efficiency.

[0025] 4. The upper and lower static pressure blocks are aligned and press the workpiece to be welded from both top and bottom directions respectively. Each static pressure block has offset through holes with opposite offset directions, creating solid parts with different offset directions. When the two offset stirring heads are inserted into the workpiece, each stirring head has a corresponding solid part opposite to it to counteract the vertical pressure from the stirring head on the workpiece. This avoids problems such as twisting deformation or material collapse of the workpiece due to misalignment of the stirring heads, ensuring smooth welding.

[0026] Advantages of additional aspects of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application 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 only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the dual-stirring-head friction stir welding device and the workpiece to be welded according to an embodiment of the present invention;

[0030] Figure 2 This is a top view of the dual-stirring-head friction stir welding device according to an embodiment of the present invention;

[0031] In the diagram: 1. First static pressure block; 2. First stirring head; 3. Second static pressure block; 4. Second stirring head; 5. Part to be welded;

[0032] The distances or dimensions between parts have been exaggerated to show their positions; the diagram is for illustrative purposes only. Detailed Implementation

[0033] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0034] 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, unless otherwise expressly indicated by the invention, the singular form is intended to include the plural form as well. 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.

[0035] To address the problems mentioned in the background section, researchers have successively proposed improved friction stir welding methods such as static shoulder friction stir welding, double shoulder friction stir welding, hot / cold source assisted friction stir welding, and ultrasonic energy field assisted friction stir welding, which have achieved certain results. However, the above-mentioned improved processes all have their own limitations and have not completely solved all the problems existing in conventional methods. Based on this, the present invention proposes a novel dual-stirring head friction stir welding device, which can solve the above-mentioned problems existing in the existing process, realize the flexible application of the stirring unit to the workpiece within a certain thickness range, eliminate welding defects such as incomplete penetration / incomplete fusion / weak connection, enhance the plastic flow of the workpiece material, reduce the rotational torque and forward resistance of the stirring unit, significantly reduce the tendency of void or tunnel-type defects to form, improve welding efficiency, and further improve the microstructure and properties of the welded joint.

[0036] like Figure 1 As shown, one embodiment of the present invention provides a dual-stirring-head friction stir welding device for welding a workpiece 5. The workpiece 5 has a first direction along the weld seam and a second direction perpendicular to the first direction. The workpiece 5 can be butt-jointed, lap-jointed, or other possible joint forms. The first direction refers to... Figure 1 The horizontal direction, i.e., the direction of the arrow, is the second direction. Figure 1 The vertical direction in the text refers to the up-down direction.

[0037] The welding apparatus includes: a first stirring unit (i.e., an upper stirring unit) and a second stirring unit (i.e., a lower stirring unit); the first stirring unit includes a first static pressure block 1 and a first stirring head 2, the first static pressure block 1 being provided with a first through hole offset along a first direction, such as... Figure 2 As shown, the first stirring head 2 is disposed within the first through hole; the second stirring unit includes a second static pressure block 3 and a second stirring head 4. The second static pressure block 3 is provided with a second through hole offset along a first direction, and the offset direction is opposite to that of the first through hole, as shown below. Figure 1As shown, the first through hole is offset to the right, the second through hole is offset to the left, and the second stirring head 4 is disposed in the second through hole; the first static pressure block 1 and the second static pressure block 3 are respectively located on both sides of the workpiece 5 to be welded, and are aligned along the second direction; the first stirring head 2 and the second stirring head 4 are arranged front and back along the first direction. Here, "front and back" refers to the front and back along the first direction, i.e., the direction indicated by the arrow is the front, and the back side indicated by the arrow is the back.

[0038] The first stirring unit and the second stirring unit are respectively placed above and below the workpiece 5 to be welded, and are both driven by different servo motors to achieve rotation, upward movement, downward movement, translation and other actions to complete the welding.

[0039] During welding, the first static pressure block 1 and the second static pressure block 3 press and fix the workpiece 5 to be welded from the top and bottom directions, respectively. The upper and lower stirring units work together and move along a predetermined trajectory. The first stirring head 2 and the second stirring head 4 (with stirring needles) are inserted into the workpiece 5 to be welded and rotate at high speed. Under the action of frictional heat, the material of the workpiece 5 to be welded undergoes the thermal action caused by the two stirring units, and finally the welding is completed.

[0040] Both stirring units are designed separately and work together, providing great flexibility when welding workpieces 5 within a certain thickness range. The two stirring units act from the upper and lower surfaces of the workpieces 5 respectively, effectively avoiding welding defects such as incomplete penetration, incomplete fusion, and weak connection, and significantly improving the weld strength. The material undergoes two high-temperature and high-strain thermodynamic processes, resulting in a wider flow range, reducing the tendency for the formation of void and tunnel-type defects, improving the microstructure of the joint, and increasing welding speed and efficiency.

[0041] Two static pressure blocks are aligned and press the workpiece 5 to be welded from both top and bottom directions. Each static pressure block has an offset through-hole with opposite offset directions, creating solid parts with different offset directions. When the two offset stirring heads are inserted into the workpiece 5, each stirring head has a corresponding solid part opposite to it to counteract the vertical pressure from the stirring head on the workpiece 5. This avoids problems such as twisting or deformation of the workpiece 5 or material collapse caused by misalignment of the stirring heads, ensuring smooth welding.

[0042] The first static pressure block 1 and the second static pressure block 3 have the same shape, both being cuboids. The inner end faces of both the first static pressure block 1 and the second static pressure block 3 facing the workpiece 5 are flat, and at least the inner end faces have rounded corners along their front edges in the first direction. The first through hole and the second through hole are both circular holes, and their axes are perpendicular to the inner end faces. The inner end faces of the first static pressure block 1 and the second static pressure block 3 facing the workpiece 5 have the same contour.

[0043] like Figure 1 , Figure 2 As shown, the first static pressure block 1 and the second static pressure block 3 are both cuboids with hollow cylinders. They may have rounded corners on the outside and flat ends. The dimensions of the first static pressure block 1 and the second static pressure block 3 (length 2mm to 1000mm, width 2mm to 1000mm) should be equal, and they should be kept aligned vertically during the welding process. They should press and fix the workpiece 5 to be welded from the top and bottom directions respectively to avoid adverse factors such as twisting and deformation or material collapse of the workpiece 5 due to the misalignment of the first stirring head 2 and the second stirring head 4.

[0044] The first stirring head 2 and the second stirring head 4 have the same shape, including a stirring rod and a stirring needle. The stirring needle is located at the end of the stirring rod facing the workpiece 5 to be welded. The stirring rod is cylindrical, and the stirring needle is cylindrical or conical. The diameter of the circle where the stirring needle and the stirring rod intersect is smaller than the diameter of the stirring rod. The end face of the stirring rod facing the workpiece 5 is a flat surface or a convex-concave surface, and the circumferential surface of the stirring needle is a smooth surface or a rough surface, and the end face facing the workpiece 5 is a flat surface or a convex-concave surface.

[0045] like Figure 1 As shown, both the first stirring head 2 and the second stirring head 4 comprise a stirring rod and a stirring needle. A shoulder is formed at the connection between the stirring rod and the stirring needle. The stirring rod is cylindrical with a flat / convex / concave end face and features such as grooves, involutes, and protrusions. The stirring needle is cylindrical / conical with features such as threads, flat surfaces, and grooves on its sides, and a flat or textured surface at its end. The dimensions of the first stirring head 2 and the second stirring head 4 (stirring rod diameter 1mm–500mm, stirring needle diameter 1mm–200mm, length less than the total thickness of the workpiece 5 to be welded) should be equal or slightly different, and they are arranged longitudinally in a front-to-back, top-to-bottom configuration during welding.

[0046] When the first stirring unit (first static pressure block 1 and first stirring head 2) and the second stirring unit (second static pressure block 3 and second stirring head 4) move along the welding direction, the angle of deviation from the vertical direction is 0° to 15°.

[0047] Based on the above-described apparatus, this embodiment also provides a dual-stirring-head friction stir welding method, specifically including the following steps:

[0048] Step 1: Fix the workpiece 5 to be welded with a specific clamp. Move the first stirring unit (first static pressure block 1 and first stirring head 2) and the second stirring unit (second static pressure block 3 and second stirring head 4) to the upper and lower sides of the starting point of the workpiece 5 and align them. The shoulder of the first stirring head 2 is flush with the end of the first static pressure block 1, and the shoulder of the second stirring head 4 is flush with the end of the second static pressure block 3.

[0049] Step 2: The first stirring head 2 and the second stirring head 4 start to rotate, and together with the first static pressure block 1 and the second static pressure block 3, they move upward and downward at the same speed. In this way, the stirring needles of the first stirring head 2 and the second stirring head 4 are inserted into the workpiece 5 to be welded, until the end face of the first static pressure block 1 (the shoulder of the first stirring head 2) and the end face of the second static pressure block 3 (the shoulder of the second stirring head 4) respectively contact the upper and lower surfaces of the starting point of the weld on the workpiece 5 with a certain pressure, and stay there for a period of time, so that the material of the workpiece 5 around the two stirring units reaches the thermoplastic state, and the output torque of the two stirring heads is stable, that is, the thermal state on the workpiece 5 reaches the quasi-steady state.

[0050] Step 3: The first stirring unit (first static pressure block 1 and first stirring head 2) and the second stirring unit (second static pressure block 3 and second stirring head 4) move horizontally at the same speed to start welding. The material to be welded 5 in the forward direction of the stirring unit successively experiences the thermal action of the first stirring unit (first static pressure block 1 and first stirring head 2) and the second stirring unit (second static pressure block 3 and second stirring head 4).

[0051] Step 4: Upon reaching the final welding point, the first stirring unit (first static pressure block 1 and first stirring head 2) and the second stirring unit (second static pressure block 3 and second stirring head 4) move upward and downward respectively, moving away from the workpiece 5 to be welded. At the same time, the first stirring head 2 and the second stirring head 4 both stop rotating, completing the welding process.

[0052] The rotation speeds of the first stirring head 2 and the second stirring head 4 can be the same or different to adjust and optimize the heat generation and material flow in the welding process. The rotation speed can be 0 to 20,000 rpm.

[0053] The four tool components, namely the first static pressure block 1, the first stirring head 2, the second static pressure block 3, and the second stirring head 4, have the same translation speed during the welding stage, which is 0 to 10 m / min.

[0054] The distance between the first stirring head 2 and the second stirring head 4 should be related to the size of the stirring unit, the welding process parameters, the thermophysical parameters of the material to be welded 5, etc. It should be ensured that the thermoplastic area around the stirring unit overlaps to a certain extent, so that the material to be welded 5 undergoes sufficient thermo-mechanical coupling.

[0055] Therefore, the above steps are applicable for welding aluminum alloys, magnesium alloys, copper alloys, titanium alloys, high-entropy alloys, steel, and any two or more dissimilar metals, including butt welding, lap welding, and other possible joint types. This method offers significant improvements and advantages over conventional processes.

[0056] First, both the first and second stirring units are designed as separate units, which provides great flexibility for welding workpieces 5 of different thicknesses. The sum of the lengths of the upper and lower stirring pins only needs to be greater than the total thickness of the workpiece 5. Therefore, when the total thickness of the workpiece 5 varies within a certain range, welding can be completed without replacing the stirring unit.

[0057] Secondly, the two stirring units work together from the upper and lower surfaces of the workpiece 5 to solve the welding defects such as incomplete penetration / incomplete welding / weak connection caused by insufficient heat input and insufficient material flow at the bottom of the workpiece 5 in conventional processes, thus greatly improving the weld strength.

[0058] Finally, under the thermal action of the two stirring heads, the material undergoes two high-temperature and high-strain thermal processes. The thermal action lasts longer and the material flows over a wider range, thus reducing the tendency for void and tunnel defects to form, reducing the rotational torque and forward resistance borne by the stirring heads, improving the microstructure of the joint, and increasing the welding speed and welding efficiency.

[0059] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

[0060] Finally, it should be noted that, unless otherwise specified, the embodiments of the present invention and the various features thereof can be combined with each other, all of which are within the protection scope of the present invention. Furthermore, all or part of the steps in the above methods can be executed in a computer system such as a set of computer-executable instructions, and although the steps are listed in the order 1, 2, 3…, in some cases, the steps shown or described may be performed in a different order than that shown here.

Claims

1. A dual-head friction stir welding apparatus for welding workpieces, the workpieces having a first direction along the weld seam and a second direction perpendicular to the first direction, characterized in that... The welding apparatus includes: a first stirring unit and a second stirring unit; The first stirring unit includes a first static pressure block and a first stirring head. The first static pressure block is provided with a first through hole offset in a first direction, and the first stirring head is disposed in the first through hole. The second stirring unit includes a second static pressure block and a second stirring head. The second static pressure block is provided with a second through hole offset in a first direction and opposite to the offset direction of the first through hole, and the second stirring head is disposed in the second through hole. The first static pressure block and the second static pressure block are located on both sides of the workpiece to be welded and are aligned along the second direction. The first stirring head and the second stirring head are arranged back and forth along the first direction. Both static pressure blocks are provided with offset through holes, and the offset directions of the offset through holes are opposite, so that the two static pressure blocks form solid parts with different offset directions; when the two offset stirring heads are inserted into the workpiece to be welded, each stirring head has a corresponding solid part opposite to it to counteract the pressure of the stirring head on the workpiece to be welded in the vertical direction.

2. The dual-stirring-head friction stir welding device as described in claim 1, characterized in that, The first static pressure block and the second static pressure block have the same shape, both being cuboids. The inner end faces of the first static pressure block and the second static pressure block facing the workpiece to be welded are both planes. At least the inner end faces are provided with rounded corners along the front edge of the first direction. The first through hole and the second through hole are both round holes, and the axes of the first through hole and the second through hole are perpendicular to the inner end faces.

3. The dual-stirring-head friction stir welding device as described in claim 2, characterized in that, The inner end face of the first static pressure block facing the workpiece has the same contour as the inner end face of the second static pressure block facing the workpiece.

4. The dual-stirring-head friction stir welding device as described in claim 1, characterized in that, The first and second stirring heads have the same shape, including a stirring rod and a stirring needle. The stirring needle is located at the end of the stirring rod facing the workpiece to be welded. The stirring rod is cylindrical, and the stirring needle is cylindrical or conical. The diameter of the circle where the stirring needle and the stirring rod intersect is smaller than the diameter of the stirring rod.

5. The dual-stirring-head friction stir welding device as described in claim 4, characterized in that, The end face of the stirring rod facing the workpiece to be welded is a flat surface or a concave-convex surface, and the circumferential surface of the stirring pin is a smooth surface or a rough surface, and the end face of the stirring pin facing the workpiece to be welded is a flat surface or a concave-convex surface.

6. The dual-stirring-head friction stir welding device as described in claim 1, characterized in that, The first stirring unit and the second stirring unit are perpendicular to the workpiece to be welded; Alternatively, the first stirring unit and the second stirring unit have a set angle with the workpiece to be welded.

7. A welding method using the dual-stirring head friction stir welding apparatus as described in any one of claims 4-6, characterized in that, include: The two stirring units are moved to both sides of the starting point of the weld on the workpiece and aligned. The two stirring heads start to rotate and approach the workpiece at the same speed together with the two static pressure blocks. The stirring needles of the two stirring heads are inserted into the workpiece until the end faces of the two static pressure blocks contact the surface of the workpiece with a predetermined pressure, so that the thermal state of the workpiece reaches a quasi-steady state. The two stirring units move along the first direction at the same speed, and the material to be welded is subjected to the thermal action of the first stirring head and the second stirring head in sequence. Upon reaching the final welding point, the two stirring units detach from the workpiece and stop rotating, completing the welding process.

8. The welding method as described in claim 7, characterized in that, Before the two stirring units come into contact with the workpiece to be welded, the shoulders of the stirring heads of the two stirring units are flush with the inner end face of the static pressure block.

9. The welding method as described in claim 7, characterized in that, The two stirring heads may rotate at the same or different speeds.

10. The welding method as described in claim 7, characterized in that, The two static pressure blocks and the two stirring heads move at the same speed along the first direction during the welding stage.

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