Friction stir welding method based on additive assistance and powder filling

Abstract

The invention provides a friction stir welding method based on additive assistance and powder filling, and relates to the technical field of welding, the friction stir welding method comprises the following steps: step 1, pre-forming a groove in a welding part of a carbon fiber plate; step 2, filling SiC powder into the groove of the carbon fiber plate; thirdly, the aluminum alloy plate is placed at the bottom, the carbon fiber plate added with powder covers the aluminum alloy plate, then the aluminum alloy plate continues to cover the aluminum alloy plate, meanwhile, the welded part is clamped through a clamp, three layers of welding materials which are attached together are formed, and first-time welding is started; fourthly, after first welding, the depth condition of weld nuggets is observed, and flash on the surface of a weld joint is cleaned; fifthly, the carbon fiber plate continues to be covered with a layer of carbon fiber plate and a layer of aluminum alloy plate, and after a welding seam in the last time is completely cooled, the to-be-welded part is added again through the clamp, and second-time welding is conducted; and 6, the steps are repeated till the needed height of the aluminum alloy plate is reached, and welding operation is completed.

Description

Technical Field

[0001] This invention relates to the field of welding technology. Background Technology

[0002] With the rapid development of my country's aviation industry, especially the establishment of the major project for domestically produced large aircraft, the application scope of carbon fiber composite materials will be further expanded. Due to limitations in mold size, processing equipment, and usage requirements, it is inevitable that carbon fiber composite materials need to be connected to aluminum alloys, the primary material for aviation, in structures. The traditional connection methods are mainly adhesive bonding and mechanical bonding. However, both methods have certain limitations. The strength of adhesive joints is easily affected by temperature and other environmental conditions. Mechanical bonding is highly sensitive to stress concentration. To address this, a friction stir additive manufacturing method is proposed. This is a newly developed additive manufacturing method based on friction stir welding. Friction stir welding uses the heat generated by the stirring friction between the stirring pin and the connecting parts to soften the materials at the joint, and then uses axial pressure to join the materials together. This welding does not involve the melting and solidification of metals, but only plasticization, softening, and axial compression, so the resulting joint material has certain advantages in performance. Friction stir additive manufacturing is based on the principle of friction stir welding, transforming the "connection" of separate parts into a longitudinal "stacking". This technology has high production efficiency and can effectively reduce material waste.

[0003] For joining aluminum alloys and carbon fiber composites, traditional friction stir welding suffers from insufficient joint strength. To address this challenge, engineers have researched and experimented with external heating assistance, stirring head shape, and welding environment. However, the surface finish after welding is poor, with defects such as tunnels, burrs, and poor adhesion frequently appearing on the weld surface. Friction stir additive manufacturing (FSM) utilizes a rotating, non-consumable tool to generate pressure and heat to join and create additional metal layers. The non-consumable rotating tool falls vertically into the overlapping plates and moves in a specified direction to obtain the desired joining area. Therefore, FSM combines the rapid development and ease of manufacturing of additive manufacturing with the grain refinement and strength enhancement capabilities of friction stir welding, providing an excellent option and flexibility for obtaining complex and robust components within a limited timeframe. However, most current FSM technologies are only designed for single metals, and the resulting overlapping metal layers often exhibit defects such as gaps and voids. Friction stir additive manufacturing technology for single metals belongs to homogeneous joining and pursues structural complexity. However, the friction stir additive manufacturing technology for dissimilar materials of this invention belongs to heterogeneous synthesis. More importantly, it realizes the integration of functions of dissimilar materials and puts forward higher requirements for the crystallization of the weld.

[0004] Therefore, the present invention provides a method to improve the welding quality of materials. Summary of the Invention

[0005] To overcome the problem of poor welding quality in existing welding methods, this invention provides a friction stir welding method based on additive manufacturing and powder filling.

[0006] The technical solution adopted by the present invention to achieve the above objectives is as follows: The friction stir welding method based on additive manufacturing and powder filling includes the following steps: Step 1: Pre-cut grooves in the welding area of ​​the carbon fiber plate; Step 2: Fill the grooves in the carbon fiber plate with SiC powder; Step 3: Place an aluminum alloy plate at the bottom, cover it with a carbon fiber plate containing SiC powder, and then cover it with another layer of aluminum alloy plate. Simultaneously, clamp the workpiece with a jig to form three layers of welding material bonded together. Begin the first welding using a stirring head; Step 4: After the first welding, check the changes in the weld nugget area and weld nugget depth, and clean the burrs on the weld surface; Step 5: Cover the carbon fiber plate with another layer of carbon fiber plate and another layer of aluminum alloy plate. After the weld has completely cooled, evenly sprinkle SiC powder into the grooves, then clamp the workpiece with a jig and perform the second welding using a stirring head; Step 6: Repeat this process until the desired height of the aluminum alloy plate is reached, completing the welding operation.

[0007] The specific improvement involves machining a square groove on the surface of the carbon fiber sheet in step one. The groove is located at the overlap between the aluminum alloy sheet and the carbon fiber sheet. The height of the groove is less than the thickness of the carbon fiber sheet, the length of the groove is equal to the length of the carbon fiber sheet, and the width of the groove is less than the shoulder diameter of the stirring head.

[0008] The specific improvement involves filling the entire groove with SiC powder, with the filling thickness of the SiC powder equal to the groove depth.

[0009] Specifically, in step three, the grooves and welding interfaces of the plates to be welded are cleaned before welding to remove residual impurities and oxides from the surface; then, a needleless stirring head is used to seal the SiC powder in the groove, and then a needle-type stirring head is used for the first welding; the downward pressure of the needleless stirring head is in the range of 0.1mm-0.3mm.

[0010] Specifically, in step five, a needle-type stirring head is selected, made of H13 steel, with a shoulder diameter ranging from 15 to 30 mm; the stirring head rotation speed ranges from 900 to 1600 r / min, and the welding speed ranges from 10 to 150 mm / min; during welding, the stirring needle is inserted into the plate below.

[0011] The specific improvements include controlling the rotation speed of the stirring head at 1200 r / min, using a welding speed of 100 mm / min for the first weld, 80 mm / min for the second weld, and 60 mm / min for the third weld, with each weld speed reduced by 20 mm / min compared to the previous one.

[0012] The specific improvement involves controlling the welding speed at 50 mm / min. The first welding operation uses a low speed of 900 r / min, the second welding operation uses 1000 r / min, and the third welding operation uses 1100 r / min. The stirring head speed is increased by 100 r / min for each welding operation.

[0013] The specific improvement is that the pressure of the needleless stirring head in step three is controlled to be below 0.3mm.

[0014] In this invention, the bottom layer welding employs high welding speed or low rotation speed to rationally control heat input, while the top layer welding selects low welding speed or high rotation speed to increase heat input. This balances the heat input differences between layers, resulting in uniform grain size across all layers. Doping with SiC powder refines the grain structure of the weld, improving its toughness and plasticity. It also prevents the overflow of plastic material, further ensuring weld quality. Attached Figure Description

[0015] Figure 1 This is a top view of the carbon fiber plate and aluminum alloy plate of the present invention after being overlapped.

[0016] Figure 2 This is a side view of the carbon fiber plate and aluminum alloy plate after they are joined together according to the present invention.

[0017] Figure 3 This is a diagram showing the welding process of this invention.

[0018] Figure 4 This is a schematic diagram of the three-layer welding operation of the present invention.

[0019] Figure 5 This is a side view of the three-layer welded structure of the present invention.

[0020] Figure 6 This is a schematic diagram of the seven-layer welding operation of the present invention.

[0021] Figure 7 This is a side view of the seven-layer welded aluminum alloy plate of the present invention.

[0022] The markings in the diagram are: 1. Aluminum alloy plate, 2. Groove, 3. Stirring needle, 4. Shoulder, 5. Stirring head, 6. Weld nugget, 7. Carbon fiber plate, 1-1. First welding layer, 1-2. Second welding layer, 1-3. Third welding layer, 1-4. Fourth welding layer, 1-5. Fifth welding layer, 1-6. Sixth welding layer, 1-7. First welding layer, 6-1. Weld nugget one, 6-2. Weld nugget two, 6-3. Weld nugget three. Detailed Implementation

[0023] The present invention will be further explained and described below with reference to the accompanying drawings and embodiments.

[0024] The present invention provides a friction stir welding method based on additive manufacturing and powder filling, comprising the following steps: Step 1: Pre-grooving the carbon fiber plate 7; Step 2: Fill the groove 2 of the carbon fiber plate 7 with SiC powder with a narrow distribution of D50=50nm. The SiC powder fills the entire groove 2, and the filling thickness of the SiC powder is the thickness of the groove 2. Step 3: Place the aluminum alloy plate at the bottom, cover it with the carbon fiber plate 7 with added powder, and then cover it with another layer of aluminum alloy plate 1. At the same time, use the clamp to clamp the workpiece and use the needleless stirring head to start the first welding along the center of the groove 2. Step 4: After the first welding, clean the burrs from the weld surface; Step 5: Then continue to cover with a layer of carbon fiber plate 7 and a layer of aluminum alloy plate 1. After the previous weld has cooled down, perform the second weld to avoid serious deformation of the plates due to the cumulative effect of heat input. Step 6: Repeat the above welding operation until the desired height of the aluminum alloy sheet is achieved.

[0025] like Figure 1 and Figure 2 As shown, in step one, a square groove 2 is machined on the surface of the carbon fiber plate 7. The groove 2 is located at the overlap between the aluminum alloy plate and the carbon fiber plate 7. The groove 2 mainly provides space for the addition of SiC powder and also promotes the flow of material after plasticization in the welding area. The groove 2 is rectangular in shape. The height H1 of the groove 2 is less than the thickness H of the carbon fiber plate 7, the length D1 of the groove 2 is equal to the length D of the carbon fiber plate, and the width of the groove 2 is less than the shoulder diameter of the needleless stirring head.

[0026] In step two, the groove 2 of the plate to be welded and the welding interface need to be cleaned to remove residual impurities and oxides from the surface.

[0027] The purpose of using a needle-free stirring head for welding is to seal the powder within groove 2, preventing spatter during welding. The downward pressure of the needle-free stirring head ranges from 0.1mm to 0.3mm, and the welding process is as follows: Figure 3 As shown.

[0028] In step three, before welding, the groove 2 of the substrate and the welding interface are cleaned to remove residual impurities and oxides. Then, a needleless stirring head is used to seal the SiC powder within the groove 2, followed by a needle-type stirring head for the first welding operation. The needle-type stirring head is made of H13 steel, with a shoulder diameter ranging from 15-30 mm. The rotation speed of the needle-type stirring head is 900-1600 r / min, and the needles of the stirring head need to penetrate the carbon fiber plate and aluminum alloy plate to reach the lower substrate. The welding speed range is 10-150 mm / min. A welding diagram is shown below. Figure 4 As shown.

[0029] In step four, the burrs from the previous weld must be removed before the next weld. To minimize burrs, the welding parameters are different for each weld. A diagram of the second weld is shown below. Figure 6 As shown.

[0030] Because the stacking of plates restricts heat dissipation from the lower layers, even though the weld from the previous weld needs to cool before each weld, residual heat remains inside the stacked structure. Therefore, during the bottom layer welding, a high welding speed or low rotation speed can be used to control heat input. During the top layer welding, a low welding speed or high rotation speed can be chosen to increase heat input, thereby balancing the heat input differences between layers and homogenizing the grain size. Since SiC has a high melting point, the addition of silicon carbide powder improves the thermal conductivity of the cleaned weld nugget, enhances the fluidity of the medium in the weld nugget area, making the weld nugget area more homogeneous, and effectively improving the toughness of the weld.

[0031] In this embodiment, the stirring head speed is controlled at 1200 r / min. Therefore, the welding speed for the first weld is a high welding speed of 100 mm / min, the second weld is at 80 mm / min, the third weld is at 60 mm / min, and so on. Conversely, if the welding speed is controlled at 50 mm / min, the speed for the first weld is 900 r / min, the second weld is at 1000 r / min, the third weld is at 1100 r / min, and so on.

[0032] Because the welding parameters change each time, the area of ​​the weld nugget also changes each time. For example... Figure 7 As shown, the area of ​​the weld nugget gradually increases from weld nugget 1 (6-1) to weld nugget 2 (6-2), and finally to weld nugget 3 (6-3). This pattern can be used to adjust the rotation speed of the stirring head and the welding speed. According to image segmentation methods, the increase in size is 5-15 mm each time. 2However, excessively high rotation speeds can lead to overly widened weld nugget areas, resulting in coarse grains and even defects. Therefore, the stirring head rotation speed needs to be controlled between 900-1600 r / min. As the welding speed decreases with each weld, the area of ​​the weld nugget area increases accordingly. Using image segmentation processing, the increase is estimated to be 8-15 mm per weld. 2 The welding speed should be between 10-150 mm / min. Too low a welding speed will lead to excessive heat accumulation, an excessively wide weld nugget, and microstructure.

[0033] The shape of the stirring needle in a needle-type stirring head can be cylindrical, conical, or threaded conical, and is not limited to any particular shape.

[0034] The shoulder 4 of the needle-type stirring head is a flat shoulder, which can avoid the generation of flash as the stirring head rotates and reduce the loss of welding material.

[0035] As an additive material, the addition of SiC powder can be uniformly distributed in the weld, thereby refining the grain structure of the weld and improving its toughness and plasticity. It can also prevent the overflow of plastic material, further ensuring weld quality.

[0036] The additive-assisted and powder-filled friction stir welding method of this invention can be used in industrial production of complex parts, such as a spacecraft support with a complex curved exterior, integrated internal cooling channels, and extremely high local rigidity. Traditional all-aluminum supports are too heavy, while all-carbon fiber supports have poor thermal conductivity and weldability. Therefore, friction stir additive manufacturing technology is used to embed carbon fiber composite materials as reinforcing ribs into the aluminum alloy body, achieving an optimal distribution of rigidity and weight.

[0037] This invention has been described through embodiments. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of this invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, this invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of this invention.

Claims

1. A friction stir welding method based on additive manufacturing and powder filler, comprising the following steps: Step 1: Pre-cut grooves (2) in the welding area of ​​the carbon fiber plate (7); Step 2: Fill the groove (2) of the carbon fiber plate (7) with SiC powder; Step 3: Place the aluminum alloy plate (1) at the bottom, cover it with the carbon fiber plate (7) with added SiC powder, and then cover it with another layer of aluminum alloy plate (1). At the same time, use the clamp to clamp the workpiece to form three layers of welding material that are bonded together. Use the stirring head (5) to start the first welding. Step 4: After the first welding, check the changes in the area of ​​the weld nugget and the depth of the weld nugget (6), and clean the burrs on the surface of the weld. Step 5: Cover the carbon fiber plate with another layer of carbon fiber plate (7) and another layer of aluminum alloy plate (1). After the weld has completely cooled, sprinkle SiC powder evenly into the groove, then clamp the workpiece to be welded with a clamp and use a stirring head (5) to perform the second welding. Step Six: Continue in this manner until the desired height of the aluminum alloy sheet is reached, at which point the welding operation is complete.

2. The friction stir welding method according to claim 1, characterized in that: In step one, a square groove (2) is machined on the surface of the carbon fiber plate (7). The groove (2) is located at the overlap of the aluminum alloy plate (1) and the carbon fiber plate (7). The height of the groove (2) is less than the thickness of the carbon fiber plate (7), the length of the groove (2) is equal to the length of the carbon fiber plate (7), and the width of the groove (2) is less than the diameter of the shoulder (4) of the stirring head (5).

3. The friction stir welding method according to claim 1, characterized in that: The SiC powder fills the entire groove (2), and the filling thickness of the SiC powder is equal to the groove depth.

4. The friction stir welding method according to claim 1, characterized in that: In step three, before welding, the groove (2) of the plate to be welded and the welding interface are cleaned to remove residual impurities and oxides on the surface; then, a needleless stirring head is used to seal the SiC powder in the groove (2), and then a needle stirring head is used for the first welding; the downward pressure of the needleless stirring head is in the range of 0.1mm-0.3mm.

5. The friction stir welding method according to claim 1, characterized in that: In step five, the stirring head (5) is a needle-type stirring head made of H13 steel, and the diameter of the shoulder (4) is 15-30mm. The rotation speed of the stirring head (5) is 900-1600r / min, and the welding speed is 10-150mm / min. During welding, the stirring needle (3) is inserted into the plate below.

6. The friction stir welding method according to claim 1, characterized in that: The rotation speed of the stirring head (5) is controlled at 1200 r / min. The welding speed for the first welding is 100 mm / min, the welding speed for the second welding is 80 mm / min, and the welding speed for the third welding is 60 mm / min. The welding speed is reduced by 20 mm / min each time.

7. The friction stir welding method according to claim 1, characterized in that: The welding speed was controlled at 50 mm / min. The first welding speed was 900 r / min, the second welding speed was 1000 r / min, and the third welding speed was 1100 r / min. The stirring head (5) speed was increased by 100 r / min each time compared to the previous welding.

8. The friction stir welding method according to claim 4, characterized in that: In step three, the downward pressure of the needleless stirring head should be controlled below 0.3 mm.

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