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

Abstract

The invention provides a multi-stage shoulder composite friction stir welding tool and a composite plate channel forming method. The lower end of the clamping part is connected to the primary shoulder, and the lower end of the primary shoulder is connected to the stirring needle assembly. The lower surface of the middle convex part of the mixing needle assembly serves as the secondary shoulder. The outer contour of the middle convex part has a spherical structure, and the middle convex The outer wall of the upper half of the upper part and the outer wall of the upper stirring needle are both provided with right-hand threads, and the outer wall of the lower half of the middle convex part has a smooth wall structure. The steps of the forming method include: controlling the rotation and pressing down of the multi-stage shoulder composite friction stir welding tool until the lower end of the lower stirring needle penetrates into the specified depth inside the plate 1, so that the center of the lower stirring needle is higher than the joint surface of the plate 1 and the plate 2 , the lower end of the lower stirring needle is lower than the joint surface of plate one and plate two, and the primary shoulder is close to the upper surface of plate one. The invention can smoothly process approximately circular channels on composite plates, and can realize the formation and welding connection of composite friction stir channels of plates with different thicknesses and channels at different positions.

Description

A multi-stage 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 specifically relates to a multi-stage shoulder composite friction stir welding tool and a composite plate channel forming method.

Background technique

Friction stir channel/hole forming technology (FSC for short) is a technology derived from the development of friction stir welding (FSW for short) for processing continuous closed channels inside the plate. During the friction stir channel/channel forming process, when the process parameters are improperly selected, it is easy to produce hole defects inside the plate. When the hole defects are continuously distributed along the direction of the weld, channel defects are formed inside the plate. This technology has broad application prospects in terms of internal weight reduction of structures, rapid prototyping of internal wiring channels and internal liquid cooling channels.

However, the current FSC is only suitable for processing channels in a single plate (such as aluminum plate). In actual application, it is necessary to apply thermal conductive silicone grease on the pure aluminum cooling plate and fasten it with threads to fit it with the copper component to be cooled. This will increase the contact thermal resistance between the pure aluminum water-cooling plate and the copper components to be cooled, which is not conducive to heat conduction. If aluminum and copper alloys are welded and then processed by FSC, there will be problems such as complicated process flow and high cost. Therefore, conventional FSC technology will no longer be applicable for complex water-cooled panels such as multi-plate composite structures made of similar or different materials, such as rib plate structures composed of aluminum and copper dissimilar materials.

In the prior art, document CN213646302 U discloses a welding tool that simultaneously realizes overlap and friction stir tunnel forming. The welding tool includes a stirring pin, a stationary shoulder, and other direct threads and a discharge port. The material is driven by the cooperation of the threads. transfer. However, this solution has the problems of weak material flow ability, irregular channel shape, and cannot achieve channel forming at the composite plate lamination interface. CN111230188A discloses a stirring head for friction stir manufacturing. The stirring head includes an upper mounting body and a lower stirring body. The upper mounting body and the lower stirring body are an integrally formed structure. The upper mounting body is a cylinder with a cylindrical surface. Clamping the mounting surface, the lower stirring body includes a shoulder and a stirring needle. The upper and lower end surfaces of the shoulder are respectively connected to the lower end surface of the upper mounting body and the upper end surface of the stirring needle. However, the water-cooling channel prepared by this method still has the problem of irregular shape.

More importantly, existing friction stir welding tools and processing methods can only process rectangular or irregular flat hole channels on the plate, and these rectangular or irregular flat hole channels are not conducive to medium circulation. Ideally, circular, oval or nearly circular channels should be machined into the plate. However, there is currently no technology that can process circular, elliptical or nearly circular channels on plates, let alone prepare channels/holes on composite plates that can both enhance the heat exchange capacity of the channels/channels and ensure smooth fluid flow. .

Contents of the invention

At least in order to solve the technical problems mentioned in the background art, the purpose of the present invention is to provide a multi-stage shoulder composite friction stir welding tool and a composite plate channel forming method.

The present invention adopts the following technical solutions.

A multi-stage shoulder composite friction stir welding tool, including a clamping part, the lower end of the clamping part is connected to a primary shoulder, the lower end of the primary shoulder is connected to a stirring needle assembly, the stirring needle assembly includes an integrally formed upper stirring needle, a middle The raised part and the lower stirring needle, the lower surface of the middle raised part serves as the secondary shoulder, the outer contour of the middle raised part has a spherical structure; the outer wall of the upper half of the middle raised part and the outer wall of the upper stirring needle are both provided with right-hand threads , the outer wall of the lower half of the middle bulge is a light wall structure.

In the present invention, the lower half of the outer wall of the middle convex portion is used as the secondary shoulder. With such a structure, the inner wall of the channel can be shaped with the help of the lower half of the outer wall of the middle convex portion, and the friction stir weld structure can be fully squeezed to make it more dense.

In order to reduce the resistance experienced by the upper stirring needle during processing, the upper stirring needle has a cylindrical structure with three milled planes.

In order to facilitate the outward movement of materials in the area where the channel is located, the lower end surface of the primary shoulder has a concave structure with a concave angle of 5 to 15°. The lower end surface of the primary shoulder is equipped with a vortex groove with a groove depth of 0.1 to 0.5 mm, slot width 0.4~1.0mm.

The outer side wall of the lower stirring needle is provided with a spiral groove, and the bottom wall of the lower stirring needle is provided with a plurality of grooves radially. Adopting such a structure can, on the one hand, enhance the material mixing between the contact interfaces of the two plates, and on the other hand, break up and evenly distribute the oxide film on the surface of the plate to a greater extent (the oxide film of some materials cannot be polished completely. For example, magnesium alloy will immediately regenerate an oxide film in the air after polishing), which is helpful to enhance the bonding strength between the two plates.

In order to further make the processed channel more regular, the transition between the upper stirring needle and the middle convex part adopts an arc transition structure.

Further, an annular convex edge is provided at the boundary between the middle protrusion and the lower stirring needle. Adopting such a structure, combined with the right-hand thread on the upper half of the outer wall of the middle convex portion, can make the upper half of the processed inner wall of the channel form continuous and regularly arranged ribs, so that the channel has better heat exchange enhancement performance.

One of the composite plate channel forming methods using the aforementioned multi-stage shoulder composite friction stir welding tool, the steps include:

Step 1: Clean the surfaces of plate one and plate two. The upper surface of plate two is provided with strip grooves along the length of the channel;

Step 2: Place plate two on plate one and position the plate with the help of a clamp; assemble the multi-stage shoulder composite friction stir welding tool on the friction stir welding machine;

Step 3: Start the friction stir welding machine, control the multi-stage shoulder composite friction stir welding tool to rotate and press down until the lower end of the lower stirring needle penetrates into the specified depth inside the plate, so that the center of the lower stirring needle is higher than the center of the plate. On the joint surface of plate two, the lower end of the lower stirring needle is lower than the joint surface of plate one and plate two, and the primary shoulder is close to the upper surface of plate one;

Step 4: Control the multi-stage shoulder composite friction stir welding tool to move forward according to the set path and parameters. In this process, friction stir welding and channel forming are simultaneously realized;

Step 5: After the processing is completed, evacuate the multi-stage shoulder composite friction stir welding tool, then close the friction stir welding equipment, and place the processed composite plate in the air to cool to room temperature.

A second composite plate channel forming method using the aforementioned multi-stage shoulder composite friction stir welding tool, the steps include:

Step 11: Clean the surfaces of plate one, plate two and plate three. The upper surface of plate three is provided with strip grooves along the length of the channel;

Step 12: Place plate three on plate two, place plate two on plate one, and position the plate with the help of a clamp; assemble the multi-stage shoulder composite friction stir welding tool on the friction stir welding machine;

Step 13, start the friction stir welding machine, control the multi-stage shoulder composite friction stir welding tool to rotate and press down until the lower end of the lower stirring needle penetrates into the specified depth inside the plate, so that the center of the lower stirring needle is higher than the center of the plate and On the joining surface of plate two, the lower end of the lower stirring needle is lower than the joining surface of plate one and plate two. The middle convex part is located inside plate two. The lower end of the upper stirring needle is located inside plate two. The first-level shoulder is close to the upper surface of plate one. ;

Step 14, control the multi-stage shoulder composite friction stir welding tool to move forward according to the set path and parameters. In this process, friction stir welding and channel forming are simultaneously realized;

Step 15: After the processing is completed, evacuate the multi-stage shoulder composite friction stir welding tool, then close the friction stir welding equipment, and place the processed composite plate in the air to cool to room temperature.

Using the solution of the present invention, an approximately circular channel can be smoothly processed on the composite plate. The upper half of the inner wall of the channel forms continuous and regularly arranged ribs, and the lower half of the inner wall of the channel has a smooth wall structure. This kind of Specific channels have better heat transfer enhancement performance than conventional rectangular channels.

The multi-stage shoulder composite friction stir welding tool with a specific structure of the present invention is conducive to the smooth flow of materials in the area where the middle convex portion is located, and can prevent material from accumulating on the side wall of the channel.

The multi-stage shoulder composite friction stir welding tool provided by the present invention is mainly divided into two parts. During the processing: the lower stirring needle performs friction stir welding on the contact area of multiple plates to achieve good metallurgical bonding between the multiple plates to form a weld. seam; the upper stirring needle and the middle convex part jointly realize the transfer of the internal material of the plate to the groove on the upper surface, forming a stable continuous channel inside the plate, and ultimately achieving the simultaneous generation of internal closed channels during the welding process of multi-metal plates, and the entire processing process The process is simple, high efficiency and short processing cycle;

In the present invention, the diameter of the secondary shoulder is significantly larger than the outer diameter of the primary stirring needle above it. During the processing, the plasticized material in the horizontal direction of the secondary shoulder will move upward under the extrusion of the secondary shoulder. Flow, the right-hand thread on the secondary shoulder and the side surface of the upper stirring needle can promote the upward flow of the material, which is conducive to the transfer of the material to the groove on the surface of the plate, and is formed on the surface of the plate under the upsetting action of the primary shoulder , the location of the middle convex portion creates a cavity due to lack of material backfill, forming a continuous closed channel, and the formed channel presents a regular-shaped structure.

In the present invention, the clamping part is made of low-cost H13 steel material, and the mixing head is made of hard materials such as high-temperature alloy, tungsten-rhenium alloy, etc. At the same time, the mixing head can be freely disassembled and replaced according to the thickness of the plate, and can be freely adjusted according to the required channel forming position. The length of the stirring needle can be used to form composite friction stir channels with different thickness plates and channels at different positions. The welding tool can be replaced flexibly, has strong adaptability, implementability, and economy, and is suitable for large-scale industrial production.

Description of the drawings

Figure 1 is a three-dimensional schematic diagram of the multi-stage shoulder composite friction stir welding tool in Embodiment 1;

Figure 2 is a three-dimensional schematic diagram of the stirring needle assembly in Embodiment 1;

Figure 3 is a schematic diagram of the main direction of the stirring needle assembly in Embodiment 1;

Figure 4 is a schematic diagram of the material flow field around the stirring needle assembly when the welding tool is in use in Example 1;

Figures 5 and 6 are schematic diagrams of the use state of the welding tool and the double-layer composite panel in Embodiment 1;

Figures 7 and 8 are schematic diagrams of the use state of the welding tool used with the three-layer composite board in Embodiment 1;

Figure 9 is a three-dimensional schematic view of the stirring needle assembly in Embodiment 2;

Figure 10 is a schematic three-dimensional view of the stirring needle assembly in Embodiment 3.

Detailed ways

The technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

Example 1

As shown in Figures 1 to 3, a multi-stage shoulder composite friction stir welding tool includes a clamping part 51 (H13 steel). The lower end of the clamping part 51 is connected to a primary shoulder 52, and the lower end of the primary shoulder 52 is connected. There is a stirring needle assembly (tungsten-rhenium alloy). The stirring needle assembly includes an integrally formed upper stirring needle 55, a middle convex portion 58 and a lower stirring needle 56. The lower (lower half) surface of the middle convex portion 58 serves as a secondary shoulder, and the outer contour of the middle convex portion 58 is Spherical structure; the outer wall of the upper half of the middle convex portion 58 and the outer wall of the upper stirring needle 55 are both provided with right-hand threads 59, and the outer wall of the lower half of the middle convex portion 58 has a smooth wall structure. In this embodiment, the upper stirring needle 55 has a cylindrical structure with three milled planes. The pitch of the upper stirring needle 55 is 0.8mm and the diameter is 5mm. The pitch of the outer wall of the upper half of the middle protrusion 58 is 0.8mm. The lower stirring needle The diameter of the top of 56 is 4 mm smaller than the maximum diameter of the middle protrusion 58; the lower end surface of the primary shoulder 52 is a concave structure, and the concave angle of the concave structure is 8°. The lower end surface of the primary shoulder 52 is provided with a vortex groove 53 , the groove depth is 0.4mm, the groove width is 0.8mm; the transition part between the upper stirring needle 55 and the middle convex part 58 is an arc transition structure.

A composite plate channel forming method using the multi-stage shoulder composite friction stir welding tool in this embodiment is used to process channels in double-layer composite plates. As shown in Figures 5 to 6, the steps include:

Step 1. Clean the surfaces of plates 1 and 2. Remove the oxide film on the surfaces of plates 1 and 2 through mechanical polishing. Use chemical reagents (absolute ethanol or acetone solution) to wipe the surfaces of plates 1 and 2 to remove surface oil stains, etc., in advance. The upper surface of plate two 2 is provided with a strip groove along the length direction of the channel, plate one 1 is an aluminum plate, and plate two 2 is a copper plate;

Step 2: Place plate 2 2 on plate 1 and position the plate with the help of a clamp; assemble the multi-stage shoulder composite friction stir welding tool on the friction stir welding machine;

Step 3, start the friction stir welding machine, control the multi-stage shoulder composite friction stir welding tool to rotate and press down until the lower end of the lower stirring needle 56 penetrates into the specified depth inside the plate 1, so that the center of the lower stirring needle 56 is higher than At the joint surface of plate one 1 and plate two 2, the lower end of the lower stirring needle 56 is lower than the joint surface of plate one 1 and plate two 2, and the primary shoulder 52 is close to the upper surface of plate one 1. The state at this time is shown in Figure 5 shown;

Step 4: Control the multi-stage shoulder composite friction stir welding tool to move forward according to the set path and parameters. During this process, friction stir welding and channel forming are simultaneously realized; during operation, the plasticized material flow field is shown in Figure 4 As shown in the figure, the material that is squeezed by the middle protrusion 58 and flows upward is transferred to the upper surface of the plate 2 with the drive of the thread on the surface of the stirring needle 55, and a channel 4 is formed inside the plate 1, as shown in Figure 6; at the same time, the The material driven by the rotation of the lower stirring pin 56 flows horizontally around its surface and is backfilled. The material away from the lower stirring pin 56 gradually flows upward and is backfilled to the lower stirring pin 56 under the upsetting and traction effects of the lower surface of the middle protrusion 58 . at the contact interface of plate one 1 and plate two 2, thus realizing the material mixing and metallurgical bonding at the contact interface of plate one 1 and plate two 2, forming the main weld area 5; and the material in the horizontal direction of the middle convex portion 58 is squeezed, and due to the middle convex portion 58 The larger shoulder on the upper part of 58 that has no direct contact exerts a downward forging force on the extruded material. Therefore, the material in this area is squeezed by the middle convex part 58 and flows upward. At the same time, the middle convex part 58 and the upper stirring needle 55 The thread structure on the surface will further promote the upward transfer of material, and eventually fill it into the grooves on the surface of plate 2, while the area where the middle protrusion 58 without material backfill will create a cavity, which will form a continuous seal as the welding tool moves. channel 4;

Step 5: After the processing is completed, evacuate the multi-stage shoulder composite friction stir welding tool, then close the friction stir welding equipment, and place the processed composite plate in the air to cool to room temperature.

A composite plate channel forming method using a multi-stage shoulder composite friction stir welding tool in this embodiment is used to process channels in a three-layer composite plate. As shown in Figures 7 to 8, the steps include:

Step 11: Clean the surfaces of plate one 1, plate two 2 and plate three 3. The upper surface of plate three 3 is provided with a strip groove along the length of the channel;

Step 12: Place plate three 3 on plate two 2, and plate two 2 on plate one 1, and position the plate with the help of a clamp; assemble the multi-stage shoulder composite friction stir welding tool on the friction stir welding machine ;

Step 13, start the friction stir welding machine, control the multi-stage shoulder composite friction stir welding tool to rotate and press down until the lower end of the lower stirring needle 56 penetrates into the specified depth inside the plate 1, so that the center of the lower stirring needle 56 is higher than At the joint surface of plate one 1 and plate two 2, the lower end of the lower stirring needle 56 is lower than the joint surface of plate one 1 and plate two 2, the middle protrusion 58 is located inside plate two 2, and the lower end of the upper stirring needle 55 is located inside plate two 2 , the primary shoulder 52 is close to the upper surface of plate 1, as shown in Figure 7;

Step 14, control the multi-stage shoulder composite friction stir welding tool to move forward according to the set path and parameters. In this process, friction stir welding and channel forming are simultaneously realized; during operation, it is squeezed by the middle convex portion 58 and flows upward. The material cooperates with the driving of the surface thread of the upper stirring pin 55 and is transferred to the upper surface of the plate 2, and a channel 4 is formed inside the plate 1. The area passed by the upper stirring needle 55 forms the second weld zone 6, as shown in Figure 8;

Step 15: After the processing is completed, evacuate the multi-stage shoulder composite friction stir welding tool, then close the friction stir welding equipment, and place the processed composite plate in the air to cool to room temperature.

Example 2

As shown in Figure 9, a multi-stage shoulder composite friction stir welding tool includes a clamping part 51. The lower end of the clamping part 51 is connected to a primary shoulder 52, and the lower end of the primary shoulder 52 is connected to a stirring needle assembly. The stirring needle assembly includes an integrally formed upper stirring needle 55, a middle convex portion 58 and a lower stirring needle 56. The lower (lower half) surface of the middle convex portion 58 serves as a secondary shoulder, and the outer contour of the middle convex portion 58 is Spherical structure; the outer wall of the upper half of the middle convex portion 58 and the outer wall of the upper stirring needle 55 are both provided with right-hand threads 59, and the outer wall of the lower half of the middle convex portion 58 has a smooth wall structure. In this embodiment, the upper stirring needle 55 has a cylindrical structure with three milled planes. The pitch of the upper stirring needle 55 is 1 mm and the diameter is 6 mm. The pitch of the outer wall of the upper half of the middle protrusion 58 is 1 mm. The top of the lower stirring needle 56 The diameter is 3 mm smaller than the maximum diameter of the middle protrusion 58; the lower end surface of the primary shoulder 52 is a concave structure, and the concave angle of the concave structure is 10°. The lower end surface of the primary shoulder 52 is provided with a vortex groove 53. The depth is 0.3mm and the groove width is 1mm; the transition part between the upper stirring needle 55 and the middle convex part 58 is an arc transition structure; the boundary part between the middle convex part 58 and the lower stirring needle 56 is provided with an annular convex edge 54, and the annular convex edge The diameter of 54 is 2 mm larger than the maximum diameter of the middle protrusion 58, and the thickness of the annular protrusion 54 is 2 mm. In this solution, the center of the processed channel side wall has an annular groove, which can also further enhance the heat transfer performance of the channel and help the main weld area 5 become tighter.

Example 3

As shown in FIG. 10 , a multi-stage shoulder composite friction stir welding tool, referring to Embodiment 1, is different from Embodiment 1 in that: the outer side wall of the lower stirring needle 56 is provided with a spiral groove, and the bottom wall of the lower stirring needle 56 A plurality of grooves 50 are arranged radially. In this solution, on the one hand, the uniformity of material mixing between the contact interface of the two plates can be enhanced, and on the other hand, the oxide film on the surface of the plate can be broken up and evenly distributed to a greater extent (the oxide film of some materials cannot be polished completely) , such as magnesium alloy, because an oxide film will be formed immediately in the air after polishing), it can also optimize the fluidity of the material in the thickness direction of the plate, which is conducive to driving more materials to flow with each other and metallurgically bond.

In the present invention, the difference between the top diameter of the lower stirring needle 56 and the maximum diameter of the middle convex portion 58 is also very critical. The optimal range of this difference is 2.5-8mm. If the difference is too large, it will easily lead to an increase in travel resistance. If it is too small, It is easy to cause the cross section of channel 4 to be irregular.

In the present invention, since the middle protruding portion 58 with a thread in the upper half and a smooth wall in the lower half is used in conjunction with the stirring needle of a specific structure of the present invention, a part of the plasticized material in the plate is smoothly transferred to the outside of the plate and A nearly circular regular channel 4 is formed inside the plate 1, and the other part of the plasticized material is reshaped in the main weld area 5 to form a metallurgical bonding area while ensuring the tightness of the metallurgical bonding area.

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.