CN117047257A - Multistage shaft shoulder composite friction stir welding tool and composite plate channel forming method - Google Patents

Abstract

The invention provides a multistage shaft shoulder composite friction stir welding tool and a composite plate channel forming method. The clamping part lower extreme is connected one-level shaft shoulder, and the stirring needle subassembly is connected to one-level shaft shoulder lower extreme, and stirring needle subassembly's middle protruding lower part surface is as second grade shaft shoulder, and middle bellying's outline is spherical structure, and middle bellying upper half section outer wall and last stirring needle outer wall all are provided with right-hand thread, and middle bellying lower half section outer wall is smooth wall structure. The forming method comprises the following steps: the multistage shaft shoulder composite friction stir welding tool is controlled to rotate and press downwards until the lower end of the lower stirring pin is pricked into the first plate to a specified depth, so that the center of the lower stirring pin is higher than the joint surface of the first plate and the second plate, the lower end of the lower stirring pin is lower than the joint surface of the first plate and the second plate, and the first-stage shaft shoulder is attached to the upper surface of the first plate. The invention can smoothly process the approximately circular channel on the composite plate, and can realize the forming and welding connection of the composite friction stir channels of plates with different thicknesses and channels with different positions.

Description

Multistage shaft shoulder composite friction stir welding tool and composite plate channel forming method

Technical Field

The invention belongs to the technical field of friction stir processing, and particularly relates to a multistage shaft shoulder composite friction stir welding tool and a composite plate channel forming method.

Background

Friction stir channel/tunnel Forming (FSC) is a technique for processing a continuous closed channel in a sheet material based on the development of Friction Stir Welding (FSW). In the friction stir channel/tunnel forming process, void defects are easily generated inside the sheet when the process parameters are not selected, and when the void defects are continuously distributed along the weld direction, the channel defects are formed inside the sheet. The technology has wide application prospect in aspects of weight reduction in the structure, rapid forming of internal wiring pore channels and internal liquid cooling flow channels and the like.

However, the current FSC is only suitable for processing channels in a single plate (such as an aluminum plate), and in practical application, the FSC is also required to be attached to the copper component to be cooled by coating the pure aluminum cooling plate with heat conduction silicone grease, fastening by threads, and the like, which increases the contact thermal resistance between the pure aluminum cooling plate and the copper component to be cooled, thereby being unfavorable for heat conduction. If the FSC processing is performed after the aluminum or copper alloy is welded, there are problems such as complicated process flow and high cost. Therefore, for complex water-cooled panels such as web structures composed of aluminum-copper dissimilar materials, which are multi-panel composite structures made of similar or different materials, conventional FSC techniques will no longer be applicable.

In the prior art, document CN 213646302U discloses a welding tool for simultaneously realizing lap joint and friction stir tunnel formation, which comprises a stirring pin, a static shaft shoulder, and direct threads and a discharge port, and drives material transfer through the cooperation of the threads. However, this solution has problems of weak material flow ability, irregular channel shape, and failure to achieve channel formation at the composite sheet material bonding interface. CN111230188A discloses a stirring head for friction stir manufacturing, the stirring head comprises an upper mounting body and a lower stirring body, the upper mounting body and the lower stirring body are of an integrated structure, the upper mounting body is a cylinder, a clamping mounting surface is arranged on a cylindrical surface, the lower stirring body comprises a shaft shoulder and a stirring pin, and the upper end face and the lower end face of the shaft shoulder are respectively connected with the lower end face of the upper mounting body and the upper end face of the stirring pin. However, the water cooling channel prepared by the scheme still has the problem of irregular shape.

More importantly, the existing friction stir welding tool and the existing friction stir welding method can only be used for machining rectangular or irregular flat hole channels on the plate, and the rectangular or irregular flat hole channels are not beneficial to medium circulation. Ideally, circular, oval or nearly circular channels should be machined into the sheet. However, there is no technology capable of forming circular, oval or nearly circular channels on a plate, and it is not possible to form channels/tunnels on a composite plate, which can enhance the heat exchange capability of the channels/tunnels and ensure smooth flow of fluid.

Disclosure of Invention

The invention aims at providing a multistage shaft shoulder composite friction stir welding tool and a composite plate channel forming method at least for solving the technical problems in the background art.

The invention adopts the following technical scheme.

The multi-stage shaft shoulder composite friction stir welding tool comprises a clamping part, wherein the lower end of the clamping part is connected with a first-stage shaft shoulder, the lower end of the first-stage shaft shoulder is connected with a stirring pin assembly, the stirring pin assembly comprises an upper stirring pin, a middle protruding part and a lower stirring pin which are integrally formed, the lower surface of the middle protruding part is used as a second-stage shaft shoulder, and the outer contour of the middle protruding part is in a spherical structure; the outer wall of the upper half section of the middle protruding part and the outer wall of the upper stirring pin are both provided with right-handed threads, and the outer wall of the lower half section of the middle protruding part is of a smooth wall structure.

In the invention, the outer wall of the lower half section of the middle protruding part is used as a secondary shaft shoulder. By adopting the structure, the inner wall of the channel can be shaped by means of the outer wall of the lower half section of the middle protruding part, and the friction stir welding seam structure is fully extruded to be more compact.

In order to reduce the resistance of the upper stirring pin in the processing process, the upper stirring pin is of a cylindrical structure with three milling planes.

In order to facilitate outward movement of materials in the area where the channel is located, the lower end face of the primary shaft shoulder is of a concave structure, the concave angle of the concave structure is 5-15 degrees, the lower end face of the primary shaft shoulder is provided with a vortex-shaped groove, the groove depth is 0.1-0.5 mm, and the groove width is 0.4-1.0 mm.

The outer side wall of the lower stirring pin is provided with a spiral groove, and a plurality of grooves are radially arranged on the bottom wall of the lower stirring pin. By adopting the structure, on one hand, the material mixing between the contact interfaces of the two plates can be enhanced, and on the other hand, the oxide films on the surfaces of the plates can be broken and uniformly distributed to a greater extent (part of the oxide films of the materials are not polished, such as magnesium alloy, and the oxide films can be regenerated in the air immediately after polishing), thereby being beneficial to enhancing the bonding strength between the two plates

In order to further enable the processed channel to be more regular, the transition part between the upper stirring pin and the middle protruding part is in an arc transition structure.

Further, an annular convex edge is arranged at the boundary part of the middle convex part and the lower stirring pin. By adopting the structure, the right-handed threads of the outer wall of the upper half section of the middle protruding part are matched, so that the upper half part of the inner wall of the processed channel forms continuous and regularly arranged edges, and the channel has better heat exchange strengthening performance.

One of the composite plate channel forming methods adopting the multi-stage shaft shoulder composite friction stir welding tool comprises the following steps:

step 1, cleaning the surfaces of a first plate and a second plate, wherein the upper surface of the second plate is provided with a strip-shaped groove along the length direction of a channel;

step 2, placing a second plate on the first plate and positioning the first plate by means of a clamp; assembling the multi-stage shaft shoulder composite friction stir welding tool on a friction stir welding machine;

step 3, starting the friction stir welding machine, controlling the multi-stage shaft shoulder composite friction stir welding tool to rotate and press downwards until the lower end of the lower stirring pin is pricked into the first plate to a specified depth, so that the center of the lower stirring pin is higher than the joint surface of the first plate and the second plate, the lower end of the lower stirring pin is lower than the joint surface of the first plate and the second plate, and the first-stage shaft shoulder is attached to the upper surface of the first plate;

step 4, controlling the multistage shaft shoulder composite friction stir welding tool to move forward according to a set path and parameters, and synchronously realizing friction stir welding and channel forming in the process;

and 5, evacuating the multi-stage shaft shoulder composite friction stir welding tool after the processing is completed, closing the friction stir welding equipment, and placing the processed composite board in air to cool to room temperature.

A second method for forming a composite plate channel by adopting the multi-stage shaft shoulder composite friction stir welding tool comprises the following steps:

step 11, cleaning the surfaces of the first plate, the second plate and the third plate, wherein the upper surface of the third plate is provided with a strip-shaped groove along the length direction of the channel;

step 12, placing a third plate on the second plate, placing the second plate on the first plate, and positioning the first plate by means of a clamp; assembling the multi-stage shaft shoulder composite friction stir welding tool on a friction stir welding machine;

step 13, starting a friction stir welding machine, controlling a multi-stage shaft shoulder composite friction stir welding tool to rotate and press downwards until the lower end of a lower stirring pin is pricked into a specified depth in the first plate, so that the center of the lower stirring pin is higher than the joint surface of the first plate and the second plate, the lower end of the lower stirring pin is lower than the joint surface of the first plate and the second plate, a middle bulge part is positioned in the second plate, the lower end of an upper stirring pin is positioned in the second plate, and the first-stage shaft shoulder is abutted against the upper surface of the first plate;

step 14, controlling the multistage shaft shoulder composite friction stir welding tool to move forward according to a set path and parameters, and synchronously realizing friction stir welding and channel forming in the process;

and 15, evacuating the multi-stage shaft shoulder composite friction stir welding tool after the processing is completed, closing the friction stir welding equipment, and placing the processed composite board in air to cool to room temperature.

By adopting the scheme of the invention, the approximately circular channel can be smoothly processed on the composite board, the upper half part of the inner wall of the prepared channel forms continuous and regularly arranged ribs, the lower half part of the inner wall of the channel is of a smooth wall structure, and the specific channel has more excellent heat exchange strengthening performance compared with the conventional rectangular channel.

The multistage shaft shoulder compound friction stir welding tool with the specific structure is beneficial to smooth flow of materials in the area where the middle protruding part is located, and can prevent the materials from accumulating on the side wall part of the channel.

The multistage shaft shoulder composite friction stir welding tool provided by the invention is mainly divided into two parts, and the processing process is as follows: the lower stirring is used for friction stir welding in the contact boundary area of a plurality of plates, so that good metallurgical bonding among the plates is realized, and a welding seam is formed; the upper stirring pin and the middle protruding part jointly realize the transfer of the inner material of the plate to the upper surface groove, so that a stable continuous channel is formed in the plate, and finally, the inner closed channel is synchronously generated in the welding process of the multi-metal plate;

according to the invention, the diameter of the secondary shaft shoulder is obviously larger than the outer diameter of the primary stirring pin above the secondary shaft shoulder, in the processing process, plasticizing materials in the horizontal direction of the secondary shaft shoulder can flow upwards under the extrusion action of the secondary shaft shoulder, right-handed threads on the side surfaces of the secondary shaft shoulder and the upper stirring pin can promote the upward flow of the materials, the materials can be transferred into grooves on the surface of a plate, the materials are formed on the surface of the plate under the upsetting action of the primary shaft shoulder, a cavity is formed at the position of the middle protruding part due to no material backfilling, a continuous closed channel is formed, and the formed channel presents a regular-shaped structure.

In the invention, the clamping part is made of low-cost H13 steel material, the stirring head is made of hard materials such as high-temperature alloy, tungsten-rhenium alloy and the like, meanwhile, the stirring head can be freely detached and replaced according to the thickness of the plate, the length of the upper stirring pin can be freely adjusted according to the forming position of the required channel, the forming of the composite stirring friction channel of the plate with different thickness and channels with different positions can be realized, the replacement of the welding tool is flexible, the self-adaption and the implementation are strong, the economy is strong, and the invention is suitable for large-scale industrial production.

Drawings

FIG. 1 is a schematic perspective view of a multi-stage shoulder composite friction stir welding tool according to example 1;

FIG. 2 is a schematic perspective view of the stirring pin assembly of example 1;

FIG. 3 is a schematic view of the stirring pin assembly of example 1 in a forward direction;

FIG. 4 is a schematic view of the material flow field around the pin assembly in the use state of the welding tool in example 1;

FIGS. 5 and 6 are schematic views illustrating the application of the welding tool and the double-layer composite board according to the embodiment 1;

FIGS. 7 and 8 are schematic views showing the application of the bonding tool of the embodiment 1 and the three-layer composite board;

FIG. 9 is a schematic perspective view of the stirring pin assembly of example 2;

FIG. 10 is a schematic perspective view of the stirring pin assembly of example 3.

Detailed Description

The following description of the embodiments of the present invention will be made more apparent and fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

Example 1

Referring to fig. 1 to 3, a multi-stage shoulder composite friction stir welding tool includes a clamping portion 51 (H13 steel), a first-stage shoulder 52 is connected to the lower end of the clamping portion 51, and a stirring pin assembly (tungsten-rhenium alloy) is connected to the lower end of the first-stage shoulder 52. The stirring pin assembly comprises an upper stirring pin 55, a middle protruding part 58 and a lower stirring pin 56 which are integrally formed, wherein the surface of the lower part (lower half section) of the middle protruding part 58 is used as a secondary shaft shoulder, and the outer contour of the middle protruding part 58 is in a spherical structure; right-handed threads 59 are arranged on the outer wall of the upper half section of the middle protruding part 58 and the outer wall of the upper stirring pin 55, and the outer wall of the lower half section of the middle protruding part 58 is of a smooth wall structure. In the embodiment, the upper stirring pin 55 is in a cylindrical structure with a three-milling plane, the pitch of the upper stirring pin 55 is 0.8mm, and the diameter is 5mm; the pitch of the outer wall of the upper half section of the middle bulge 58 is 0.8mm; the top diameter of the lower pin 56 is 4mm smaller than the largest diameter of the middle boss 58; the lower end face of the primary shaft shoulder 52 is of a concave structure, the concave angle of the concave structure is 8 degrees, a vortex-shaped groove 53 is formed in the lower end face of the primary shaft shoulder 52, the groove depth is 0.4mm, and the groove width is 0.8mm; the transition part between the upper stirring pin 55 and the middle protruding part 58 is in an arc transition structure.

The method for forming the composite board channel by adopting the multi-stage shaft shoulder composite friction stir welding tool in the embodiment is used for processing the channel in the double-layer composite board, and is combined with the figures 5 to 6, and comprises the following steps:

step 1, cleaning the surfaces of a first plate 1 and a second plate 2, removing oxide films on the surfaces of the first plate 1 and the second plate 2 by mechanical polishing, wiping the surfaces of the first plate 1 and the second plate 2 by a chemical reagent (absolute ethyl alcohol or acetone solution) to remove oil stains on the surfaces, and the like, wherein a strip-shaped groove is formed in the upper surface of the second plate 2 along the length direction of a channel in advance, wherein the first plate 1 is an aluminum plate, and the second plate 2 is a copper plate;

step 2, placing a second plate 2 on the first plate 1 and positioning the first plate by means of a clamp; assembling the multi-stage shaft shoulder composite friction stir welding tool on a friction stir welding machine;

step 3, starting a friction stir welding machine, controlling a multi-stage shaft shoulder composite friction stir welding tool to rotate and press downwards until the lower end of a lower stirring pin 56 is pricked into a specified depth in a first plate 1, enabling the center of the lower stirring pin 56 to be higher than the joint surface of the first plate 1 and a second plate 2, enabling the lower end of the lower stirring pin 56 to be lower than the joint surface of the first plate 1 and the second plate 2, and enabling a first-stage shaft shoulder 52 to be abutted against the upper surface of the first plate 1, wherein the state is shown in fig. 5;

step 4, controlling the multistage shaft shoulder composite friction stir welding tool to move forward according to a set path and parameters, and synchronously realizing friction stir welding and channel forming in the process; in the operation process, the plasticized material flow field is shown in fig. 4, the material which is extruded by the middle protruding part 58 and flows upwards is transferred to the upper surface of the plate 2 in cooperation with the driving of the surface screw thread of the upper stirring pin 55, and a channel 4 is formed in the plate 1, as shown in fig. 6; simultaneously, the material driven by the rotation of the lower stirring pin 56 flows horizontally around the surface of the material and is backfilled, the material far away from the lower stirring pin 56 flows upwards gradually, and the material is backfilled to the position of the lower stirring pin 56 under the upsetting and traction actions of the lower surface of the middle bulge part 58, so that the material mixing and metallurgical bonding at the contact interface of the first plate 1 and the second plate 2 are realized, and a main welding seam area 5 is formed; the material in the horizontal direction of the middle protruding part 58 is extruded, and because the upper part of the middle protruding part 58 is not provided with a larger shaft shoulder which is in direct contact with the extruded material, the material in the area is extruded by the middle protruding part 58 to flow upwards, meanwhile, the screw thread structures on the surfaces of the middle protruding part 58 and the upper stirring pin 55 further promote the upward transfer of the material, and finally the material is filled into the grooves on the surfaces of the two plates 2, and a cavity is formed in the area where the middle protruding part 58 without material backfilling is located, and a continuous closed channel 4 is formed along with the movement of a welding tool;

and 5, evacuating the multi-stage shaft shoulder composite friction stir welding tool after the processing is completed, closing the friction stir welding equipment, and placing the processed composite board in air to cool to room temperature.

The method for forming the composite board channel by adopting the multi-stage shaft shoulder composite friction stir welding tool in the embodiment is used for processing the channel in the three-layer composite board, and is combined with the steps shown in fig. 7 to 8, and comprises the following steps:

step 11, cleaning the surfaces of the first plate 1, the second plate 2 and the third plate 3, wherein the upper surface of the third plate 3 is provided with a strip-shaped groove along the length direction of the channel;

step 12, placing a third plate 3 on a second plate 2, placing the second plate 2 on the first plate 1, and positioning the plates by means of a clamp; assembling the multi-stage shaft shoulder composite friction stir welding tool on a friction stir welding machine;

step 13, starting a friction stir welding machine, controlling a multi-stage shaft shoulder compound friction stir welding tool to rotate and press downwards until the lower end of a lower stirring pin 56 is pricked into a specified depth in a first plate 1, enabling the center of the lower stirring pin 56 to be higher than the joint surface of the first plate 1 and a second plate 2, enabling the lower end of the lower stirring pin 56 to be lower than the joint surface of the first plate 1 and the second plate 2, enabling a middle protruding part 58 to be positioned in the second plate 2, enabling the lower end of an upper stirring pin 55 to be positioned in the second plate 2, and enabling a first shaft shoulder 52 to be attached to the upper surface of the first plate 1, as shown in fig. 7;

step 14, controlling the multistage shaft shoulder composite friction stir welding tool to move forward according to a set path and parameters, and synchronously realizing friction stir welding and channel forming in the process; in the operation process, the material which is extruded by the middle protruding part 58 and flows upwards is transferred to the upper surface of the plate 2 in cooperation with the driving of the surface screw thread of the upper stirring pin 55, a channel 4 is formed in the first plate 1, and a second welding seam area 6 is formed in the area where the upper stirring pin 55 passes through, as shown in fig. 8;

and 15, evacuating the multi-stage shaft shoulder composite friction stir welding tool after the processing is completed, closing the friction stir welding equipment, and placing the processed composite board in air to cool to room temperature.

Example 2

Referring to fig. 9, a multi-stage shaft shoulder composite friction stir welding tool comprises a clamping part 51, wherein a primary shaft shoulder 52 is connected to the lower end of the clamping part 51, and a stirring pin assembly is connected to the lower end of the primary shaft shoulder 52. The stirring pin assembly comprises an upper stirring pin 55, a middle protruding part 58 and a lower stirring pin 56 which are integrally formed, wherein the surface of the lower part (lower half section) of the middle protruding part 58 is used as a secondary shaft shoulder, and the outer contour of the middle protruding part 58 is in a spherical structure; right-handed threads 59 are arranged on the outer wall of the upper half section of the middle protruding part 58 and the outer wall of the upper stirring pin 55, and the outer wall of the lower half section of the middle protruding part 58 is of a smooth wall structure. In the embodiment, the upper stirring pin 55 is in a cylindrical structure with a three-milling plane, the pitch of the upper stirring pin 55 is 1mm, and the diameter of the upper stirring pin is 6mm; the pitch of the outer wall of the upper half section of the middle protruding part 58 is 1mm, and the top diameter of the lower stirring pin 56 is 3mm smaller than the maximum diameter of the middle protruding part 58; the lower end face of the primary shaft shoulder 52 is of a concave structure, the concave angle of the concave structure is 10 degrees, a vortex-shaped groove 53 is formed in the lower end face of the primary shaft shoulder 52, the groove depth is 0.3mm, and the groove width is 1mm; the transition part of the upper stirring pin 55 and the middle bulge part 58 is in an arc transition structure; the boundary between the middle bulge 58 and the lower stirring pin 56 is provided with an annular convex edge 54, the diameter of the annular convex edge 54 is 2mm larger than the maximum diameter of the middle bulge 58, and the thickness of the annular convex edge 54 is 2mm. In this scheme, the passageway lateral wall central part of processing out has annular groove, and this recess also can further strengthen passageway heat transfer performance, is favorable to main welding seam region 5 more compactly simultaneously.

Example 3

Referring to fig. 10, a multi-stage shoulder composite friction stir welding tool, referring to example 1, is different from example 1 in that: the outer side wall of the lower pin 56 is provided with a spiral groove, and the bottom wall of the lower pin 56 is radially provided with a plurality of grooves 50. In the scheme, on one hand, the mixing uniformity of materials between two plate contact interfaces can be enhanced, on the other hand, oxide films on the surfaces of the plates can be broken and uniformly distributed to a greater extent (partial oxide films of the materials are not polished, such as magnesium alloy, and the oxide films can be generated again immediately in the air after polishing), and the fluidity of the materials in the thickness direction of the plates can be optimized, so that the method is beneficial to driving more materials to flow mutually and be metallurgically combined.

In the present invention, the difference between the top diameter of the lower pin 56 and the maximum diameter of the intermediate boss 58 is also very critical, and the preferred range of the difference is 2.5-8 mm, and too large a difference easily results in an increase in the traveling resistance, and too small a difference easily results in an irregular cross section of the passage 4.

In the invention, as the middle protruding part 58 with threads on the upper half section and the smooth wall on the lower half section is matched with the stirring pin with the special structure, a part of plasticized material in the plate is smoothly transferred to the outside of the first plate 1 and forms a nearly circular regular channel 4 in the first plate 1, and the other part of plasticized material is remolded in the main welding seam area 5 to form a metallurgical bonding area, and meanwhile, the compactness of the metallurgical bonding area is ensured.

Claims (9)

1. The utility model provides a compound friction stir welding utensil of multistage shaft shoulder, includes clamping part (51), and clamping part (51) lower extreme is connected with one-level shaft shoulder (52), and one-level shaft shoulder (52) lower extreme is connected with stirring needle subassembly, its characterized in that: the stirring pin assembly comprises an upper stirring pin (55), a middle protruding part (58) and a lower stirring pin (56) which are integrally formed, wherein the lower surface of the middle protruding part (58) is used as a secondary shaft shoulder, and the outer contour of the middle protruding part (58) is in a spherical structure; the outer wall of the upper half section of the middle protruding part (58) and the outer wall of the upper stirring pin (55) are both provided with right-handed threads (59), and the outer wall of the lower half section of the middle protruding part (58) is of a smooth wall structure.

2. The multi-stage shoulder composite friction stir welding tool of claim 1, wherein: the outer wall of the lower half section of the middle protruding part (58) is used as a secondary shaft shoulder.

3. The multi-stage shoulder composite friction stir welding tool of claim 2, wherein: the upper stirring pin (55) is of a cylindrical structure with three milling planes.

4. A multi-stage shoulder composite friction stir welding tool according to any of claims 1-3 wherein: primary shaft shoulder (52)

The lower end face is of a concave structure, the concave angle of the concave structure is 5-10 degrees, a vortex-shaped groove (53) is formed in the lower end face of the primary shaft shoulder (52), the groove depth is 0.1-0.5 mm, and the groove width is 0.4-1.0 mm.

5. The multi-stage shoulder composite friction stir welding tool of claim 4, wherein: the outer side wall of the lower stirring pin (56) is provided with a spiral groove, and a plurality of grooves (50) are radially arranged on the bottom wall of the lower stirring pin (56).

6. The multi-stage shoulder composite friction stir welding tool of claim 5, wherein: the transition part of the upper stirring pin (55) and the middle protruding part (58) is in an arc transition structure.

7. The multi-stage shoulder composite friction stir welding tool of claim 6, wherein: the boundary part between the middle bulge part (58) and the lower stirring pin (56) is provided with an annular convex edge.

8. A method of forming a composite sheet material channel using the multi-stage shoulder composite friction stir welding tool of any of claims 1-7, comprising the steps of:

step 1, cleaning the surfaces of a first plate (1) and a second plate (2), wherein a strip-shaped groove is formed in the upper surface of the second plate (2) along the length direction of a channel;

step 2, placing a second plate (2) on the first plate (1) and positioning the first plate by means of a clamp; assembling the multi-stage shaft shoulder composite friction stir welding tool on a friction stir welding machine;

step 3, starting a friction stir welding machine, controlling a multi-stage shaft shoulder compound friction stir welding tool to rotate and press downwards until the lower end of a lower stirring pin (56) is pricked into a specified depth in the first plate (1), enabling the center of the lower stirring pin (56) to be higher than the joint surface of the first plate (1) and the second plate (2), enabling the lower end of the lower stirring pin (56) to be lower than the joint surface of the first plate (1) and the second plate (2), and enabling a first-stage shaft shoulder (52) to be attached to the upper surface of the first plate (1);

step 4, controlling the multistage shaft shoulder composite friction stir welding tool to move forward according to a set path and parameters, and synchronously realizing friction stir welding and channel forming in the process;

and 5, evacuating the multi-stage shaft shoulder composite friction stir welding tool after the processing is completed, closing the friction stir welding equipment, and placing the processed composite board in air to cool to room temperature.

9. A method of forming a composite sheet material channel using the multi-stage shoulder composite friction stir welding tool of any of claims 1-8, comprising the steps of:

step 11, cleaning the surfaces of a first plate (1), a second plate (2) and a third plate (3), wherein a strip-shaped groove is formed in the upper surface of the third plate (3) along the length direction of the channel;

step 12, placing a third plate (3) on a second plate (2), placing the second plate (2) on the first plate (1), and positioning the plates by means of a clamp; assembling the multi-stage shaft shoulder composite friction stir welding tool on a friction stir welding machine;

step 13, starting a friction stir welding machine, controlling a multi-stage shaft shoulder composite friction stir welding tool to rotate and press downwards until the lower end of a lower stirring pin (56) is pricked into a specified depth in a first plate (1), enabling the center of the lower stirring pin (56) to be higher than the joint surface of the first plate (1) and a second plate (2), enabling the lower end of the lower stirring pin (56) to be lower than the joint surface of the first plate (1) and the second plate (2), enabling a middle protruding part (58) to be located in the second plate (2), enabling the lower end of an upper stirring pin (55) to be located in the second plate (2), and enabling a first-stage shaft shoulder (52) to be attached to the upper surface of the first plate (1);

step 14, controlling the multistage shaft shoulder composite friction stir welding tool to move forward according to a set path and parameters, and synchronously realizing friction stir welding and channel forming in the process;

and 15, evacuating the multi-stage shaft shoulder composite friction stir welding tool after the processing is completed, closing the friction stir welding equipment, and placing the processed composite board in air to cool to room temperature.