Fiber wire preparation method and equipment for stir friction welding and welding method

Abstract

The present invention discloses a method and equipment for preparing fiber filaments for stir friction welding, as well as a welding method. The preparation method comprises the following steps: S1, stretching a bundled fiber material and pre-impregnating it with a shaping glue to form a unidirectional thin-layer fiber tape, melting and plasticizing a thermoplastic polymer and coating the unidirectional thin-layer fiber tape to form a fiber-coated tape; S2, axially winding the fiber-coated tape to form a unidirectional multi-layer fiber / polymer prepreg wire material with a circular cross-section; S3, cutting the unidirectional multi-layer fiber / polymer prepreg wire material and maintaining it in a semi-connected state, then performing a heat-melting treatment and cooling to obtain a cut and then fused fiber filament material. The fiber filament material of the present invention can be evenly and comprehensively distributed in the welding position during welding, thereby significantly improving the strength of the weld. The cut fibers can be distributed 360 degrees in all directions under the drive of a high-speed rotating stirring head, and each angle of the weld can be reinforced with fibers, thereby avoiding the anisotropy of the mechanical properties of the weld due to fiber reinforcement.

Description

Technical Field

[0001] The present invention relates to the field of welding technology, in particular to a method and equipment for preparing fiber filaments used for friction stir welding, and a welding method. Background Art

[0002] Material welding can significantly improve the continuity of product production. For more complex metal products, a reasonable welding process can significantly shorten the manufacturing cycle, reduce the weight of the product, and improve the flexibility of the product's appearance and structural design. Therefore, welding has become an important process method for product forming and has attracted widespread attention and is widely used. Among them, friction stir welding (FSW), as a solid-state welding process, relies on the friction between the rotating tool and the workpiece material to generate heat, which in turn causes the area near the friction stir welding tool to soften, mix, and ultimately achieve the joining of the workpieces. The workpiece often has better mechanical properties after friction stir welding. At present, this process is mainly used for the connection of light alloys and low-carbon steel, and is also used to weld polymers to a small extent.

[0003] Compared with other welding methods, stir friction welding of polymers has the advantages of low temperature, severe plastic deformation and high joint quality, but it also has many limitations and shortcomings. For example, the welding quality is greatly affected by the process, so the welding process window is narrow, and the optimal welding process is not easy to stabilize in actual application. The substantial reason is that the strength of the weld is still far lower than that of the parent material, resulting in the failure of the weldment during application mainly occurring in the welding area. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method and equipment for preparing fiber filaments for friction stir welding and a welding method, which can significantly improve the mechanical properties of weldments.

[0005] Technical solution: In a first aspect, the present invention provides a method for preparing a fiber filament for friction stir welding, comprising the following steps:

[0006] Step S1: After the bundled fiber material is widened and pre-impregnated with a shaping glue to form a unidirectional thin fiber tape, a thermoplastic polymer is melted and plasticized and then coated on the unidirectional thin fiber tape to form a fiber-coated tape; Step S2: The fiber-coated tape is axially wound to form a unidirectional multi-layer fiber / polymer prepreg wire material with a circular cross-section; Step S3: The unidirectional multi-layer fiber / polymer prepreg wire material is cut and kept in a semi-connected state, and then heat-melted and cooled to obtain a cut and then fused fiber wire material.

[0007] Furthermore, in step S1, the thermoplastic polymer is made of the same material as the base material to be welded.

[0008] Furthermore, in step S1, the fiber content of the fiber coating tape is 40% to 60%.

[0009] Furthermore, in step S2, the cross-sectional layering lines of the unidirectional multi-layer fiber / polymer prepreg are Archimedean spirals.

[0010] Furthermore, in step S3, the cutting ratio accounts for 70-90% of the entire circular cross section, and the cutting length is 1.5-2.5 times the diameter of the friction stir welding head.

[0011] Furthermore, in step S3, the slit unidirectional multi-layer fiber / polymer prepreg wire material is subjected to axial force extrusion and remelting during the hot melt treatment.

[0012] On the other hand, the fiber filaments prepared by the above method are applied to a thermoplastic polymer friction stir welding process. Specifically, the welding method comprises the following steps:

[0013] Step 1: Repair and level the welded area of the parts to be connected and remove material from the middle of the welded area;

[0014] Step 2: embedding or melting the prepared fiber filament into the area to be welded where the material has been removed, and then flattening the area to be welded;

[0015] Step 3: After the two parts to be connected are butted together, a lateral force is applied and they are pressed and fixed. After the stirring head rotates at high speed, the two parts are connected.

[0016] Furthermore, the material removed from the middle of the part to be welded in step 1 is consistent with the volume of the fiber wire to be embedded or melted in step 2. During the welding process in step 3, the downward pressure is controlled so that the end face of the stirring head shoulder exceeds the upper surface of the welding wire by 0.05 to 0.15 mm after the welding wire is pressed in, and the downward pressure is less than or equal to the difference between the thickness of the weldment and the length of the stirring needle.

[0017] In another aspect, the present invention provides a fiber filament preparation apparatus for friction stir welding, comprising:

[0018] The extruder is used to melt and plasticize the thermoplastic polymer and then extrude it; the yarn spreading roller is used to widen the bundled fiber material to form a unidirectional thin fiber dry tape; the fiber tape bonding roller is used to pre-impregnate the unidirectional thin fiber dry tape with a shaping glue to form a whole piece of unidirectional thin fiber tape; the impregnation head is used to coat the unidirectional thin fiber tape after the melted and plasticized thermoplastic polymer to form a fiber coated tape; the axial winder is used to axially wind the fiber coated tape to form a unidirectional multi-layer fiber / polymer prepreg wire material; the traction roller is used to pull the unidirectional multi-layer fiber / polymer prepreg wire material onto the crawler traction machine; the longitudinal cutter is used to longitudinally cut the unidirectional multi-layer fiber / polymer prepreg wire material; the hot melt oven is used to remelt the fracture of the unidirectional multi-layer fiber / polymer prepreg wire after longitudinal cutting, and cool it after remelting to obtain the fiber wire material.

[0019] Furthermore, it also includes a speed-regulating pair of rollers, the speed of which is the same as the speed of the traction pair of rollers and is less than the speed of the crawler traction machine.

[0020] Beneficial effects: The present invention can significantly improve the strength of the weld; the present invention avoids the anisotropy of the mechanical properties at the weld caused by fiber reinforcement; the present invention can effectively avoid the probability of weld pores or gaps that are easily generated by ordinary polymer stir friction welding; the present invention is easy to use, and the re-fusion of the wire after slitting can significantly improve the convenience of use, and welding is easy to implement; the wire preparation and welding processes are both green and pollution-free. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the structure of the fiber filament preparation equipment of the present invention;

[0022] Figure 2 This is a photo of the fiber filaments of the present invention being cut and then fused;

[0023] Figure 3 This is a welding diagram of the present invention;

[0024] Figure 4 This is an SEM characterization image of the fiber filament material at the weld of the workpiece according to Example 1 of the present invention;

[0025] Figure 5 This is a SEM characterization image of Example 2 of the present invention after welding of fiber-free materials made of polycarbonate as raw material;

[0026] Figure 6 Figures 1 and 2 are sample appearances of welding test pieces before and after testing in Example 1 and Example 2 of the present invention;

[0027] Figure 7 This is an SEM characterization image of the weld of the workpieces connected in Example 3 of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0029] like Figure 1 The device for preparing the fiber wire used for friction stir welding of the present invention is shown. Figure 1 The figure also shows the preparation process of the fiber filament. The equipment mainly includes an extruder 1, a yarn frame 2, a yarn spreading roller 4, a fiber tape bonding roller 5, an impregnation head 7, an axial winder 8, a traction roller pair 9, a crawler traction machine 10, a longitudinal cutter 11, a hot melt oven 12 and a speed-adjustable roller pair 13.

[0030] The extruder 1 is connected to the impregnation head 7. On one side of the extruder 1, a yarn frame 2, a yarn spreading roller 4, and a fiber tape bonding roller 5 are arranged in sequence. On the other side of the extruder 1, an axial winder 8, a traction roller pair 9, a hot melt oven 12 and a speed-regulating roller pair 13 are arranged in sequence. In addition, a crawler traction machine 10 and a longitudinal cutter 11 are arranged between the traction roller pair 9 and the hot melt oven 12. The longitudinal cutter 11 is arranged directly above the crawler traction machine 10.

[0031] The steps of preparing fiber filaments by the above-mentioned equipment are as follows:

[0032] Step (1), the thermoplastic polymer is melted and plasticized through the extruder 1 and then enters the impregnation head 7;

[0033] Step (2) placing a specific fiber material in a creel 2, where the fiber material is in a bundle shape, and the fiber bundle 3 is spread by a spreading roller 4 to form a unidirectional thin fiber dry tape; the number of creels 2 can be one or more, and the number of spreading rollers 4 should be consistent with that of creels 2;

[0034] In step (3), the flattened dry fiber tapes are pre-impregnated with a trace amount of setting glue when passing through the fiber tape bonding roller 5 to form a whole piece of unidirectional thin layer fiber tape 6. The fiber tape 6 also enters the impregnation head 7, and the fiber tape 6 is evenly coated with the high-temperature polymer melt to form a fiber coating tape. Controlling the coating amount of the fiber coating tape can control the fiber content and ensure uniform distribution of the fibers in the coating tape. In this embodiment, the fiber content is maintained between 40% and 60%.

[0035] Step (4), the fiber coating tape is subsequently wound axially by an axial winder 8 to form a unidirectional multi-layer fiber / polymer prepreg wire material with a circular cross section;

[0036] Step (5), the wire material enters the crawler traction machine 10 under the action of the traction roller 9, and is cut by the longitudinal cutter 11 and kept in a semi-connected state;

[0037] In step (6), when the semi-connected wire passes through the hot melt oven 12, a small amount of polymer at the fracture is melted. At the same time, it is slightly blocked by the speed-adjustable roller 13 at the back, so that the molten polymer is compressed and adheres to each other, thereby forming a fiber wire 14 that is cut and then fused. The wire is subsequently wound or coiled for standby use. The speed of the speed-adjustable roller 13 can be consistent with the speed of the traction roller 9, and their speeds are 2 to 5% lower than the speed of the crawler traction.

[0038] The fiber filaments prepared by the above method are applied to the welding process of thermoplastic polymer friction stir welding, which specifically includes the following steps:

[0039] 1) After repairing and leveling the part to be welded, remove an appropriate amount of material from the middle of the part to be welded;

[0040] 2) embedding or melting the prepared wire into the area to be welded and then flattening the area to be welded;

[0041] 3) After the two parts to be connected are butted together, an appropriate amount of lateral force is applied, and then they are pressed and fixed on the workbench. Under the determined welding process conditions, the two parts are connected after the high-speed rotation of the stirring head.

[0042] The volume of the material removed from the middle of each portion to be welded in step 1) is consistent with the volume of the wire to be embedded or melted in step 2).

[0043] The welding process conditions in step 3) mainly include the downward pressure and welding speed. Generally, the downward pressure is controlled so that the end face of the stirring head shoulder extends 0.05 to 0.15 mm beyond the upper surface of the welding wire after the welding wire is pressed in, and the downward pressure is less than or equal to the difference between the thickness of the weldment and the length of the stirring needle.

[0044] Example 1

[0045] In order to more easily demonstrate the implementation effect, this embodiment carries out stir friction welding on transparent polycarbonate weldments. The main raw materials used include polycarbonate (PC, with a melting volume rate of 24 cm 3 / 10min, (300℃ / 1.2kg)) and carbon fiber (12K, T700), all of which are commercially available.

[0046] The whole process mainly includes two steps: wire preparation and welding. The wire preparation process is as follows:

[0047] First, polycarbonate is melted and plasticized through an extruder 1 and then enters an impregnation head 7. At the same time, a bundle of carbon fibers is placed in a creel 2. After being spread by a yarn spreading roller 4, a thin unidirectional fiber dry tape is formed. Then, when passing through a fiber tape bonding roller 5, it is pre-impregnated with a trace amount of setting glue to form a whole piece of unidirectional thin fiber tape 6. The fiber content is maintained at 50%. This fiber tape 6 also enters the impregnation head 7 and is evenly coated with the high-temperature polycarbonate melt to form a fiber-coated tape.

[0048] Secondly, the fiber coating tape is axially wound by the subsequent axial winder 8, and the cross section gradually forms an Archimedean spiral, forming a unidirectional multi-layer fiber / polymer prepreg wire material with a circular cross section. The wire material enters the crawler traction machine 10 under the action of the traction roller 9, and is cut by the longitudinal cutter 11 and kept in a semi-connected state; the cutting ratio accounts for 80% of the entire circular fiber / polymer prepreg cross section, and the cutting length is 12mm (the stir friction welding head diameter is 6mm). When the semi-connected wire material passes through the hot melt oven 12, a small amount of polymer at the fracture is melted. At the same time, since the speed of the speed regulating roller 13 is consistent with the speed of the traction roller 9, their speeds are 3% lower than the speed of the crawler traction. Therefore, the semi-connected wire material will be slightly blocked by the subsequent speed regulating roller 13, and the molten polymers are compressed and bonded to each other, thereby forming a fiber wire material 14 that is cut and then fused. The fiber wire material that is cut and then fused is subsequently wound or coiled for standby use. The appearance of the fiber wire material that is cut and then fused is as follows: Figure 2 As shown in the figure, fusion refers to the melting of polymers in the fiber filaments at the fracture, the molten polymers being compressed and mutually bonded, and the polymers at the fracture being connected by bonding after cooling, wherein at the fracture, the fibers cut after bonding still remain cut.

[0049] The prepared wire is then used for friction stir welding, which mainly includes:

[0050] 1) Obtain a part to be connected made of polycarbonate by hot pressing or other processes, repair and smooth the part to be welded, and remove material equivalent to the cross-section of the wire in the middle of the part to be welded;

[0051] 2) inserting the prepared wire into the area to be welded and then flattening the area to be welded again;

[0052] 3) After the two parts to be connected are butt-jointed, an appropriate amount of lateral force is applied, and then they are pressed and fixed on the workbench. Under the determined welding process conditions, the two parts are connected into one after the high-speed rotation of the stirring head.

[0053] The above process and the shape of the welded product are as follows Figure 3 shown.

[0054] Among them, since the wire is 0.2mm away from the outer upper wall of the weldment after being embedded in the weldment, the downward pressure of the welding head is controlled to be 0.30mm, the thickness of the weldment is 2mm, and the selected stirring needle length is 1.5mm.

[0055] The welds of the connected workpieces were characterized by SEM, and the results are as follows Figure 4 As shown, in Figure 4As can be seen in the figure, fibers of nearly equal length are evenly distributed in an arc shape, and their structure foreseeable fiber reinforcement. The split fibers can be distributed 360 degrees under the high-speed rotation of the stir head. This allows fiber reinforcement at every angle of the weld, avoiding the anisotropy of mechanical properties that may be caused by fiber reinforcement. The use of wire also effectively avoids the possibility of weld porosity or gaps that are prone to occur in conventional polymer friction stir welding.

[0056] A rectangular test piece was cut out from the connected workpiece and subjected to tensile mechanical property test. The appearance results are as follows: Figure 6 As shown, Figure 6 6a and 6b show the appearance of the sample before and after the test, respectively. Figure 6 As can be seen from Figure 2, the tensile fracture did not occur at the weld, but in the affected area slightly closer to the weld. This indicates that the mechanical properties of the weld are better than those of the affected area of the parent material. The test results are listed in Table 1.

[0057] As can be seen from the results in Table 1, the tensile strength of the weld obtained in this embodiment is close to that of the base material. Therefore, the wire-reinforced weldment of the present invention has a specific fiber distribution structure, exhibits excellent mechanical properties, and has excellent application prospects.

[0058] Example 2

[0059] For comparison with Example 1, similar to Example 1, this comparative example also uses commercially available polycarbonate (melt volume rate of 24 cm 3 / 10min) as the parent material, except that no fiber filament is used in Example 2. The welding process is mainly as follows: the parts to be connected are obtained from polycarbonate by hot pressing or other processes, and then the parts to be connected are butted together and a proper amount of lateral force is applied, and then they are pressed and fixed on a workbench. Under the determined welding process conditions, the two parts are connected into one after the high-speed rotation of the stirring head.

[0060] The welds of the connected workpieces were characterized by SEM, and the results are as follows Figure 5 As shown, in Figure 5 It can be seen that there are many gaps and clearances at the joint of the weld, so the strength of the weld can be expected to be not very good.

[0061] A rectangular test piece was cut out from the connected workpiece and subjected to tensile mechanical property test. The appearance result was also as shown in the figure. Figure 6 As shown, Figure 6 c and 6d show the appearance of the sample before and after the test, respectively. Figure 6 As can be seen from d, the tensile fracture occurs at the weld without any suspense at this time, which is enough to show that the mechanical properties of the weld need to be improved.

[0062] The tensile mechanical properties test results are also listed in Table 1. All tensile fractures occurred at the weld seam, indicating that the mechanical properties at the weld seam are still relatively low. As can be seen from the results in Table 1, the tensile strength of the weld obtained in this comparative example is significantly lower than that of Example 1, indicating that the use of fiber material has a significant impact on weld quality.

[0063] Example 3

[0064] In order to compare with Example 1, this comparative example also conducts friction stir welding on transparent polycarbonate weldments, and the main raw materials used include polycarbonate (melting volume rate of 24cm 3 / 10min) and carbon fiber (12K, T700), both of which are commercially available.

[0065] The entire process mainly includes two steps: wire preparation and welding. The wire preparation process is similar to existing conventional long fiber reinforced polymer granular materials, except that no cutting is performed: the polycarbonate is melted and plasticized through an extruder and then enters the impregnation head. At the same time, the carbon fiber tow placed in the creel is also introduced into the impregnation head. The fiber is impregnated with the high-temperature melt of polycarbonate in the impregnation head to form a fiber / polymer prepreg wire with an irregular cross-section. The wire is subsequently pulled, wound or coiled for use to form a continuous wire.

[0066] The prepared wire is then used for friction stir welding as follows:

[0067] 1) Obtain a part to be connected made of polycarbonate by hot pressing or other processes, repair and smooth the part to be welded, and remove material equivalent to the cross-section of the wire in the middle of the part to be welded;

[0068] 2) After the prepared wire is embedded in the part to be welded, it is cut as needed and the part to be welded is flattened again;

[0069] 3) After the two parts to be connected are butt-jointed, an appropriate amount of lateral force is applied, and then they are pressed and fixed on the workbench. Under the determined welding process conditions, the two parts are connected into one after the high-speed rotation of the stirring head.

[0070] The welds of the connected workpieces were characterized by SEM, and the results are as follows Figure 7 As shown, in Figure 7 It can be seen from the figure that the fiber distribution at the weld is very chaotic, the fiber length difference is large, and the distribution of fibers in various directions is also relatively chaotic.

[0071] Rectangular test specimens were cut from the connected workpieces and subjected to tensile mechanical property testing. The results are also listed in Table 1. All tensile fractures occurred at the weld seam, indicating that the mechanical properties at this location are still relatively low. As can be seen from the results in Table 1, the tensile strength of the weld obtained in this comparative example differs significantly from that of the example, indicating that the fiber preparation method has a significant impact on weld quality.

[0072] Example 4

[0073] In this embodiment, friction stir welding is carried out on nylon weldments. The main raw materials used include nylon (PA66, with a melting volume rate of 23 cm 3 / 10min) and glass fiber (12K, T700), both of which are commercially available.

[0074] The whole process mainly includes two steps: wire preparation and welding. The wire preparation process is as follows:

[0075] First, PA66 is melted and plasticized through an extruder 1 and then enters an impregnation head 7. At the same time, two bundles of carbon fibers are placed in two creels 2 respectively. After being spread by two yarn-spreading rollers 4, they form unidirectional thin fiber dry tapes. The two unidirectional thin fiber dry tapes are then pre-impregnated with a trace amount of setting glue when passing through a fiber tape bonding roller 5 to form a whole piece of unidirectional thin fiber tape 6. The fiber content is maintained at 60%. The fiber tape 6 also enters the impregnation head 7 and is evenly coated with the PA66 high-temperature melt to form a fiber-coated tape.

[0076] Secondly, the fiber coating tape is axially wound by the subsequent axial winder 8, and the cross section gradually forms an Archimedean spiral, forming a unidirectional multi-layer fiber / polymer prepreg wire material with a circular cross section. The wire material enters the crawler traction machine 10 under the action of the traction roller 9, and is cut by the longitudinal cutter 11 and kept in a semi-connected state; the cutting ratio accounts for 90% of the entire circular fiber / polymer prepreg cross section, and the cutting length is 9cm (the stir friction welding head has a diameter of 6mm). When the semi-connected wire material passes through the hot melt oven 12, a small amount of polymer at the fracture is melted. At the same time, since the speed of the speed regulating roller 13 is consistent with the speed of the traction roller 9, their speeds are 5% lower than the speed of the crawler traction. Therefore, the semi-connected wire material will be slightly blocked by the subsequent speed regulating roller 13, and the molten polymers are compressed and bonded to each other, thereby forming a fiber wire material 14 that is cut and then fused. The wire material is subsequently wound or coiled for standby use. The appearance of the fiber wire material that is cut and then fused is also similar to the shape of the fiber wire material. Figure 2 similar.

[0077] The prepared wire is then used for friction stir welding as follows:

[0078] 1) Obtain a part to be connected made of polycarbonate by hot pressing or other processes, repair and smooth the part to be welded, and remove material equivalent to the cross-section of the wire in the middle of the part to be welded;

[0079] 2) inserting the prepared wire into the area to be welded and then flattening the area to be welded again;

[0080] 3) After the two parts to be connected are butt-jointed, an appropriate amount of lateral force is applied, and then they are pressed and fixed on the workbench. Under the determined welding process conditions, the two parts are connected into one after the high-speed rotation of the stirring head.

[0081] Among them, since the wire is 0.2mm away from the outer upper wall of the weldment after being embedded in the weldment, the downward pressure of the welding head is controlled to be 0.35mm, the thickness of the weldment is 2mm, and the selected stirring needle length is 1.5mm.

[0082] Rectangular test specimens were cut from the connected workpieces and subjected to tensile mechanical property testing. The test results are listed in Table 1. As can be seen from the results in Table 1, the tensile strength of the weld obtained in this example is close to that of the parent material. Therefore, the wire-reinforced weldment of the present invention has a specific fiber distribution structure, exhibits excellent mechanical properties, and has excellent application prospects.

[0083] Example 5

[0084] In order to compare with Example 4, this comparative example also carries out friction stir welding of fiber wires without cutting treatment for nylon weldment, and the main raw materials used include nylon (melting volume rate of 23cm 3 / 10min) and carbon fiber (12K, T700), both of which are commercially available.

[0085] The entire process mainly includes two steps: wire preparation and welding. The wire preparation process is similar to existing conventional long fiber reinforced polymer granular materials, except that no cutting is performed: the nylon is melted and plasticized through an extruder and then enters the impregnation head. At the same time, the carbon fiber tow placed in the creel is also introduced into the impregnation head. The fiber is impregnated with high-temperature nylon melt in the impregnation head to form a fiber / polymer prepreg wire with an irregular cross-section. The wire is subsequently pulled, wound or coiled for use to form a continuous wire.

[0086] The prepared wire is then used for friction stir welding as follows:

[0087] 1) Obtain the parts to be connected using nylon as raw material through hot pressing or other processes, repair and smooth the parts to be welded, and remove the material equivalent to the cross-section of the wire in the middle of the parts to be welded;

[0088] 2) After the prepared wire is embedded in the part to be welded, it is cut as needed and the part to be welded is flattened again;

[0089] 3) After the two parts to be connected are butt-jointed, an appropriate amount of lateral force is applied, and then they are pressed and fixed on the workbench. Under the determined welding process conditions, the two parts are connected into one after the high-speed rotation of the stirring head.

[0090] The welds of the connected workpieces were characterized by SEM, and the results were similar to those in Example 3. The fiber distribution at the welds was very chaotic, the fiber lengths varied greatly, and the distribution of the fibers in all directions was also relatively chaotic.

[0091] Rectangular test specimens were cut from the connected workpieces and subjected to tensile mechanical property testing. The results are also listed in Table 1. All tensile fractures occurred at the weld seam, indicating that the mechanical properties at this location are still relatively low. As can be seen from the results in Table 1, the tensile strength of the weld obtained in this comparative example differs significantly from that of the example, indicating that the fiber preparation method has a significant impact on weld quality.

[0092] Example 6

[0093] Different from Example 1, in this embodiment, the fiber content of the fiber-coated tape is 40%; the cutting ratio accounts for 70% of the entire circular cross-section, the cutting length is 15 mm, and the downward pressure of the welding head is controlled to be 0.25 mm.

[0094] Example 7

[0095] Different from Example 1, in this embodiment, the fiber content of the fiber-coated tape is 60%; the cutting ratio accounts for 90% of the entire circular cross-section, the cutting length is 15 mm, and the downward pressure of the welding head is controlled to be 0.32 mm.

[0096] Table 1 Comparison of tensile properties of several weldments

[0097]

Claims

1. A method for preparing fiber filaments for friction stir welding, characterized in that: The following steps are involved: Step S1: After the bundled fiber material is stretched and pre-impregnated with a shaping adhesive to form a unidirectional thin fiber tape, a thermoplastic polymer is melted and plasticized and then coated on the unidirectional thin fiber tape to form a fiber coating tape; Step S2, axially winding the fiber-coated tape to form a unidirectional multi-layer fiber / polymer prepreg with a circular cross-section; Step S3: cutting the unidirectional multi-layer fiber / polymer prepreg and maintaining it in a semi-connected state, then heat-melting and cooling it to obtain a cut and then fused fiber filament; wherein the cutting ratio accounts for 70-90% of the entire circular cross-section.

2. The method for preparing a fiber filament for friction stir welding according to claim 1, wherein: In the step S1, the thermoplastic polymer is made of the same material as the base material to be welded.

3. The method for preparing a fiber filament for friction stir welding according to claim 1, wherein: In step S1, the fiber content of the fiber coating tape is 40% to 60%.

4. The method for preparing a fiber filament for friction stir welding according to claim 1, wherein: In the step S2, the cross-sectional layering lines of the unidirectional multi-layer fiber / polymer prepreg are Archimedean spirals.

5. The method for preparing fiber filaments for friction stir welding according to claim 1, wherein: In step S3, the cutting length is 1.5 to 2.5 times the diameter of the friction stir welding head.

6. The method for preparing fiber filaments for friction stir welding according to claim 1, wherein: In step S3, the cut unidirectional multi-layer fiber / polymer prepreg is subjected to axial force extrusion and remelted during the hot melt treatment.

7. A method for welding fiber filaments prepared by the method for preparing fiber filaments for friction stir welding according to any one of claims 1 to 6, characterized in that: The steps include: Step 1: Repair and level the welded area of the parts to be connected and remove material from the middle of the welded area; Step 2: embedding or melting the prepared fiber filament into the area to be welded where the material has been removed, and then flattening the area to be welded; Step 3: After the two parts to be connected are butted together, a lateral force is applied and they are pressed and fixed. After the stirring head rotates at high speed, the two parts are connected.

8. The welding method according to claim 7, characterized in that: The material removed from the middle of the part to be welded in step 1 is consistent with the volume of the fiber wire to be embedded or melted in step 2. During the welding process in step 3, the downward pressure is controlled so that the end face of the stirring head shoulder protrudes from the upper surface of the welding wire by 0.05~0.15mm after the welding wire is pressed in, and the downward pressure is less than or equal to the difference between the thickness of the weldment and the length of the stirring needle.

9. The preparation equipment used in the method for preparing fiber filaments for friction stir welding according to claim 1, characterized in that: include: An extruder (1) is used for melting and plasticizing a thermoplastic polymer and then extruding it; A spreading roller (4) is used to spread the bundled fiber material to form a unidirectional thin fiber dry tape; A fiber tape bonding roller (5) is used to pre-impregnate the unidirectional thin-layer fiber dry tape with a shaping adhesive to form a whole piece of unidirectional thin-layer fiber tape (6); An impregnation head (7) is used for coating the unidirectional thin fiber tape (6) with the melted and plasticized thermoplastic polymer to form a fiber-coated tape; An axial winder (8) is used to axially wind the fiber coating tape to form a unidirectional multi-layer fiber / polymer prepreg; A pair of traction rollers (9) for pulling the unidirectional multi-layer fiber / polymer prepreg wire material onto a crawler traction machine (10); A longitudinal cutter (11) for longitudinally cutting the unidirectional multi-layer fiber / polymer prepreg; The hot melt oven (12) is used for remelting the fracture of the unidirectional multi-layer fiber / polymer prepreg after longitudinal cutting, and cooling after remelting to obtain the fiber filament material.

10. The preparation equipment according to claim 9, characterized in that: It also includes a speed-regulating roller pair (13), the speed of which is the same as the speed of the traction roller pair (9) and is less than the speed of the crawler traction machine (10).

Images