Friction stir deposition repairing tool head and method for aluminum alloy surface defects

Abstract

The invention relates to the technical field of friction stir deposition repair, and discloses a friction stir deposition repair tool head and method for aluminum alloy surface defects, and the tool head comprises a push rod, a bar, a stirring head, a working end and a shaft shoulder; the stirring head is of a hollow structure, and a pushing rod capable of axially moving is fixed in a hollow cavity; the section size of the bar is consistent with that of the pushing rod, and the bar is plugged from the bottom of the stirring head during material adding and is tightly combined with the hollow inner cavity of the stirring head; the stirring head comprises a cylindrical structure and a conical structure, the working end is of a conical structure with a taper angle of 5-30 degrees, the total length of the stirring head is 80mm, the length of the working end is 12mm, and the diameter of the bottom is 10mm. According to the invention, the conical tool head is designed to realize geometric matching with defect depth change, and a variable-pitch thread structure is adopted to realize accurate regulation and control of axial-radial flow of a material; and meanwhile, process parameters are dynamically adjusted in combination with real-time detection data, and finally efficient and high-quality repairing of aluminum alloy surface defects is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of friction stir deposition additive repair, and specifically to a friction stir deposition repair tool head and a repair method for surface defects of aluminum alloy. Background Art

[0002] As a lightweight and high-performance material, aluminum alloy is widely used in the fields of aerospace, rail transit, etc. However, during long-term service, surface cracks, corrosion pits and other defects are likely to appear, seriously affecting the structural safety and service life. At present, the mainstream repair technologies such as traditional fusion welding, laser cladding, etc. all have obvious limitations:

[0003] Although the traditional fusion welding technology has a wide range of equipment and mature processes, its high heat input characteristics will cause deformation of the aluminum alloy matrix, grain coarsening, and a significant decline in the performance of the heat affected zone. Moreover, defects such as pores and lack of fusion are easily generated;

[0004] Although the laser cladding technology has controllable heat input, due to the high laser reflectivity of aluminum alloy, low energy absorption efficiency, and the easy formation of brittle intermetallic compounds between the cladding layer and the matrix, the interfacial bonding strength is reduced;

[0005] Although the cold spraying technology can avoid thermal damage, its mechanical bonding characteristics result in insufficient bonding strength and poor filling ability for complex geometric defects.

[0006] As a new solid-phase additive manufacturing method, the friction stir deposition additive (AFSD) technology realizes metal softening deposition through the frictional heat of a rotating tool head, and has the advantages of low-temperature processing, grain refinement, environmental protection, etc., providing a new idea for the surface repair of aluminum alloy. However, the existing AFSD technology still faces many challenges in the application of surface defect repair:

[0007] During the repair of surface defects, the lateral flow of materials by a conventional cylindrical stirring pin is insufficient, which is likely to cause incomplete filling;

[0008] The flat tool has poor plasticizing effect on the bottom of deep and narrow defects, resulting in low repair efficiency;

[0009] Most of the existing process parameters are designed for uniform additive manufacturing, lacking a dynamic adjustment method for different defect characteristics;

[0010] The problem of heat accumulation during continuous repair is likely to cause over-softening of materials, affecting the repair quality.

[0011] Current technologies, such as the flat stirring pin used in Patent No. CN 114535850A, are only suitable for large-area deposition and difficult to adapt to the repair of curved surface defects. Although Patent No. US11253990B2 proposes a multi-pass process to improve the interlayer bonding, it does not optimize the tool geometry. Although Patent No. JP 2020507468A designs a tool cooling structure, it fails to combine a tapered tip to improve the material flow efficiency. None of these existing technologies can effectively solve the key problems in the repair of aluminum alloy surface defects. Therefore, we propose a friction stir deposition repair tool head and repair method for aluminum alloy surface defects. Summary of the Invention

[0012] (1) Technical Problems to be Solved

[0013] In view of the deficiencies of the prior art, the present invention provides a friction stir deposition repair tool head and repair method for aluminum alloy surface defects, which solves the problems of many defects in traditional repair technologies, low repair efficiency and difficult control of existing AFSD for complex defects.

[0014] (2) Technical Solutions

[0015] To achieve the above objectives, the present invention is realized through the following technical solutions: A friction stir deposition repair tool head for aluminum alloy surface defects includes a push rod, a rod material, a stirring head, a working end and a shoulder; the stirring head is a hollow structure, and a push rod that can move axially is fixed in the hollow cavity; the cross-sectional size of the rod material is the same as that of the push rod. During additive manufacturing, the rod material is inserted into the bottom of the stirring head and tightly combined with the hollow inner cavity of the stirring head; the stirring head includes a cylindrical and a conical structure, the working end is a conical structure with a cone angle of 5° - 30°, the total length of the stirring head is 80 mm, the length of the working end is 12 mm, the bottom diameter is 10 mm, and the top diameter is 15 mm.

[0016] Preferably, the hollow cavity of the stirring head is a cuboid with side lengths of 10 mm × 10 mm × 120 mm, the push rod is made of tool steel with dimensions of 10 mm × 10 mm × 100 mm.

[0017] Preferably, the stirring head body is made of high-performance tungsten rhenium alloy W-25Re material, vacuum quenched at 1250 °C and tempered at 600 °C, with a hardness of HRC62 and good fracture toughness.

[0018] Preferably, the cone angle of the working end is preferably 15°, and its inclined side promotes the uniform flow of plastic material to the deposition area.

[0019] Preferably, the surface of the stirring head is provided with a variable pitch thread structure, the upper thread pitch is 1.0 - 1.5 mm and extends to the midpoint of the generatrix of the working end, and the lower thread pitch is 0.5 - 1.0 mm to enhance the lateral flow of the material.

[0020] Preferably, the stirring head can be installed on a numerically controlled machine tool or a parallel robotic arm to achieve precise motion control.

[0021] Preferably, a repair method for a repair tool head of friction stir deposition for aluminum alloy surface defects includes the following steps:

[0022] Step 1: Fix a 7075 or 6061 aluminum alloy substrate with a thickness of 10 - 50 mm, load a bar into the stirring head and position it to the deposition area to be repaired;

[0023] Step 2: Rotate the stirring head at a speed of 400 - 2000 r / min, and feed at a speed of 0.1 - 2 mm / s simultaneously. After the bar reaches the end face of the shoulder, press it down to contact the substrate at a traveling speed of 20 - 300 mm / min, form a plastic deposition layer through frictional preheating and move to obtain an additive layer with a thickness of 0.1 - 2 mm;

[0024] Step 3: Horizontally move the stirring head parallelly, and repeat Step 2 to achieve multi-pass deposition, ensuring that the side edges of adjacent deposition layers are tightly combined.

[0025] Preferably, in Step 2, for shallow and wide defects with a depth < 3 mm and a width-depth ratio > 2, a spiral path motion is adopted; for deep and narrow defects with a depth ≥ 3 mm and a width-depth ratio ≤ 2, a reciprocating multi-pass path is adopted to compact layer by layer.

[0026] Preferably, during the frictional preheating process between the end face of the shoulder and the substrate, a progressive plasticization and filling of materials in the depth direction of the defect are achieved through the gradient pressure distribution of the conical working end.

[0027] Preferably, the variable pitch thread structure generates an axial shear force through a large pitch in the upper part to push the material downward, and a small pitch in the lower part enhances the lateral flow, realizing the directional flow of materials from top to bottom and dispersing the wear area.

[0028] In summary, the technical effects and advantages of the present invention are as follows:

[0029] 1. In the present invention, the current coaxial feeding type of bar is the most developed technical category in the AFSD technology, and the equipment has been put on the market. The present invention can achieve the friction stir deposition repair of aluminum alloy surface defects only by modifying the tool head in this equipment. The technical means is simple, easy to implement, safe and reliable.

[0030] 2. In the present invention, through the design of the conical tool head, the geometric matching with the change of defect depth is realized, the variable pitch thread structure is adopted to accurately control the axial-radial flow of materials, and at the same time, the process parameters are dynamically adjusted in combination with real-time detection data. Different repair paths and parameter combinations are adopted for defects with different depths and shapes, and finally, the efficient and high-quality repair of aluminum alloy surface defects is achieved.

[0031] 3. In the present invention, specifically aiming at the surface repair requirements of high-strength aluminum alloy components in fields such as aerospace, key technical problems such as incomplete material filling and unbonded edges during friction stir deposition repair, fluctuations in tissue properties caused by uneven thermal-mechanical distribution, low repair efficiency for deep and narrow defects, and large heat-affected zones are solved, providing an innovative solution for the life extension and performance restoration of aluminum alloy components. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 FIG. is a schematic diagram of the overall structure of a friction stir deposition repair tool head for aluminum alloy surface defects according to the present invention;

[0034] Figure 2 FIG. is a schematic diagram of the structure of a friction stir deposition repair tool head for aluminum alloy surface defects according to the present invention from another angle;

[0035] Figure 3 FIG. is a schematic diagram of the repair path planning of a friction stir deposition repair tool head for aluminum alloy surface defects according to the present invention;

[0036] Figure 4 FIG. is another set of schematic diagrams of the repair path planning of a friction stir deposition repair tool head for aluminum alloy surface defects according to the present invention.

[0037] In the figures: 1, push rod; 2, bar stock; 3, main shaft; 4, stirring head; 5, large pitch thread groove; 6, small pitch thread groove; 7, working end; 8, shoulder. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0039] Embodiment 1

[0040] Reference Figure 1 - Figure 2 , this embodiment provides a friction stir deposition repair tool head for aluminum alloy surface defects, including the following implementation contents:

[0041] The friction stir deposition repair tool head is composed of the following components:

[0042] Propulsion system: The propulsion rod 1 is a tool steel rod with dimensions of 10mm×10mm×100mm, which is in sliding fit with the hollow inner cavity (a 10mm×10mm×120mm cuboid) of the stirring head 4 and can be axially moved by a servo motor; The rod stock 2 is made of the same material as the substrate, aluminum alloy (such as 7075), with the same cross-sectional dimensions as the propulsion rod 1. After being loaded from the bottom of the stirring head 4, it fits tightly with the inner cavity.

[0043] Stirring head body: The total length of the stirring head 4 is 80mm, consisting of an upper cylindrical end (diameter 15mm, length 68mm) and a lower conical working end 7 (cone angle 15°, length 12mm, bottom diameter 10mm); The body material is W-25Re tungsten rhenium alloy, which is treated by vacuum quenching at 1250°C (holding for 2h) + tempering at 600°C (holding for 1.5h). The hardness test is HRC62, and the room temperature impact toughness is ≥25J / cm 2 。

[0044] Thread structure: The surface of the stirring head 4 is processed with variable pitch threads. The upper pitch Pu = 1.2mm (extending from the cylindrical end to the midpoint of the generatrix of the working end 7, that is, 6mm from the bottom), the lower pitch Pl = 0.8mm, the thread depth is 0.5mm for both, and the thread profile angle is 60°.

[0045] Example 2

[0046] Reference Figure 3 - Figure 4 , This example provides a repair method for the repair tool head of friction stir deposition for aluminum alloy surface defects, which is used for repairing typical shallow and wide defects (taking a 6061 aluminum alloy pit as an example), including the following implementation contents:

[0047] Substrate preparation:

[0048] Substrate material: 6061 aluminum alloy, with a thickness of 20mm, and a circular pit with a diameter of 8mm and a depth of 2mm is processed on the surface;

[0049] Fixing method: Fixed to the processing cylinder by a vacuum fixture, with a flatness error ≤0.05mm.

[0050] Tool head installation and parameter setting:

[0051] Installation equipment: Five-axis CNC machine tool (model Mazak INTEGREXi-200AM), with the spindle 3 speed control accuracy of ±5r / min;

[0052] Rod stock 2: 6061 aluminum alloy rod, with dimensions of 10mm×10mm×150mm;

[0053] Process parameters:

[0054] Stirring head speed: 1800r / min, feeding speed: 1.0mm / s (axial feed of the propulsion rod 1);

[0055] Travel speed: 150 mm / min, single deposition thickness: 0.6 mm;

[0056] Motion path: spiral path (pitch 4 mm), spirally expanding from the center of the pit to the edge.

[0057] Repair process:

[0058] Step 1: The stirring head 4 descends to a position 5 mm from the surface of the substrate, starts to rotate and approaches the substrate at a speed of 0.5 mm / s.

[0059] Step 2: After the rod material 2 contacts the end face 8 of the shoulder, the tool head presses down to contact the substrate, and is friction preheated for 3 s (infrared temperature measurement shows that the temperature of the contact area reaches 350 °C) to form a plastic deposition layer.

[0060] Step 3: Move along the spiral path. After completing the first pass of deposition, translate 3 mm laterally (i.e., the pitch interval) for the second pass, and a total of 3 passes are deposited.

[0061] Repair effect:

[0062] The surface roughness Ra of the deposition layer = 1.2 μm, and the pit filling rate is 100%;

[0063] Microstructure observation: A dynamic recrystallization layer of 10 - 20 μm is formed at the interface, and there are no defects such as pores and cracks;

[0064] Mechanical properties: Tensile strength 275 MPa (base material 280 MPa), bonding strength ≥ 250 MPa.

[0065] Example 3

[0066] This example provides a repair method for the tool head of friction stir deposition for repairing surface defects of aluminum alloy, which is used for repairing deep and narrow cracks (taking the crack of 7075 aluminum alloy as an example), and includes the following implementation contents:

[0067] Substrate preparation:

[0068] Substrate material: 7075 - T6 aluminum alloy, thickness 30 mm, with a prefabricated straight crack on the surface with a depth of 5 mm and a width of 3 mm (width - depth ratio = 0.6);

[0069] Pretreatment: Grind the oxide layer on both sides of the crack, and the roughness Ra ≤ 3.2 μm.

[0070] Tool head and process parameters:

[0071] Tool head adjustment: The cone angle of the working end 7 is 10°, and the pitch of the lower thread 6 is 0.5 mm (to enhance lateral flow);

[0072] Process parameters:

[0073] Rotation speed: 1000 r / min, feeding speed: 0.5 mm / s, traveling speed: 60 mm / min;

[0074] Motion path: Reciprocating multi-pass path (the reciprocating direction is perpendicular to the crack length, with a spacing of 2 mm), single-pass deposition thickness 0.2 mm.

[0075] Repair process:

[0076] Perform the first-pass linear deposition along the crack direction. After reaching the end, return to the starting point, and shift laterally by 2 mm for the second pass. A total of 8 passes are deposited;

[0077] Cool for 5 s between each pass to avoid heat accumulation (monitor the temperature in the heat-affected zone with an infrared thermal imager ≤ 300 °C).

[0078] Repair effect:

[0079] The filling in the crack depth direction is uniform, and the density of the bottom material is 99.2%;

[0080] The width of the heat-affected zone is 1.0 mm, which is 50% less than that of traditional flat tools;

[0081] Fatigue test: Under a cyclic load of 200 MPa, the life of the repaired area reaches 5 × 10^6 times, equivalent to that of the base material.

[0082] Example 4

[0083] This example provides a repair method for a friction stir deposition repair tool head for aluminum alloy surface defects, which is used for automated repair of multiple defect types and includes the following implementation contents:

[0084] For a complex defect substrate with both shallow and wide pits (depth 1.5 mm, diameter 10 mm) and deep and narrow grooves (depth 4 mm, width 4 mm) existing simultaneously, the following scheme is adopted:

[0085] Defect identification and path planning:

[0086] Obtain the defect geometric data through a 3D vision scanner (accuracy ±0.02 mm), and import it into CAM software to generate a differentiated path:

[0087] Shallow and wide area: Spiral path (cone angle 20°, pitch 3 mm);

[0088] Deep and narrow area: Reciprocating multi-pass path (cone angle 15°, reciprocating interval 1.5 mm).

[0089] Dynamic parameter adjustment:

[0090] Shallow and wide area: Rotation speed 2000 r / min, traveling speed 200 mm / min, single pass thickness 0.8 mm (completed in 2 passes);

[0091] Deep and narrow area: Rotation speed 800 r / min, feeding speed 1.2 mm / s, traveling speed 50 mm / min, single pass thickness 0.3 mm (completed in 6 passes).

[0092] Transition zone treatment:

[0093] In the junction area between the two types of defects, the feed rate is adjusted in real time through the main shaft 3 (accuracy ±0.01 mm), so that the thread action depth gradually changes from 0.8 mm to 0.3 mm, avoiding stress concentration;

[0094] Ultrasonic flaw detection is used to detect the transition zone, and no lack of fusion or interlayer defects are found.

[0095] The tool head adopts a hollow structure, with a built-in axially movable push rod (tool steel of 10 mm×10 mm×100 mm), which is adapted to the equal-section bar stock loaded from the bottom to ensure stable material transportation. The stirring head body is made of high-performance tungsten rhenium alloy (W-25Re), vacuum quenched at 1250 °C + tempered at 600 °C, with a hardness of HRC62, having both high-temperature stability and creep resistance. The working end is designed as a conical structure with a cone angle of 5° - 30° (preferably 15°), with a total length of 80 mm, a bottom diameter of 10 mm, and a top diameter of 15 mm, which can achieve progressive plasticization filling according to the defect depth; the variable pitch thread on the surface (upper part 1.0 - 1.5 mm, lower part 0.5 - 1.0 mm) controls the material flow through "upper pressing and lower spreading". The large pitch in the upper part enhances the axial shear force to push the material downward, and the small pitch in the lower part improves the lateral flow to fill the edge, extending the tool life by 48%.

[0096] Develop exclusive solutions for different defect types:

[0097] Shallow and wide defects (such as 6061 aluminum alloy pits, 2 mm deep): Adopt a spiral path (pitch 4 mm), deposit at a rotation speed of 1800 r / min and a traveling speed of 150 mm / min, and complete the filling in 3 passes. The surface roughness Ra = 1.2 μm, the filling rate is 100%, a dynamic recrystallization layer is formed at the interface, and the bonding strength ≥ 250 MPa.

[0098] Deep and narrow cracks (such as 7075 aluminum alloy cracks, 5 mm deep): Adopt a reciprocating multi-pass path (interval 2 mm), adjust the cone angle to 10°, and the lower pitch of 0.5 mm strengthens the lateral flow. Compact in 8 passes, the bottom density is 99.2%, the width of the heat affected zone is 1.0 mm (reduced by 50% compared with the traditional), and the fatigue life reaches 5×10 6 times, equivalent to the base material.

[0099] Multi-defect composite repair: The path is planned through 3D vision scanning. For the shallow and wide area, a spiral path (cone angle 20°) is used, and for the deep and narrow area, a reciprocating path (cone angle 15°) is used. The pitch ratio and deposition thickness are dynamically adjusted. In the transition area, the spindle feed rate is gradually changed to avoid stress concentration. There are no defects detected by ultrasonic flaw detection, and the repair efficiency is increased by 40%.

[0100] The comparative test shows that the variable pitch design increases the continuous working time of the tool from 3.5 hours to 5.2 hours, reduces the wear amount by 58%, and increases the repair qualification rate from 82% to 96%. The established pitch ratio - material flow model supports intelligent parameter matching, and automatically adjusts the process according to the width-depth ratio of the defect (for example, when the width-depth ratio > 2, a pitch ratio of 1.5 is recommended). This tool head can directly replace the traditional stirring head of the commercially available AFSD equipment, and is adapted to numerical control machine tools and robotic arms. It has been verified in the fields of aerospace (such as the skin repair of Boeing 787) and automotive wheels. The repair efficiency is increased by 3 times compared with traditional fusion welding, the cost is reduced by 40%, there is no thermal deformation, and the mechanical properties are close to those of the base material, providing an innovative solution for extending the service life of aluminum alloy components.

[0101] All the electrical components mentioned in this article are connected to the external main controller and 220V mains electricity, and the main controller can be a conventional known device such as a computer for control.

[0102] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A friction stir deposition repair tool head for surface defects of aluminum alloy, comprising a main shaft (3), a large pitch thread groove (5) and a small pitch thread groove (6), characterized in that: It includes a push rod (1), a rod stock (2), a stirring head (4), a working end (7) and a shoulder (8); the stirring head (4) is of a hollow structure, and a push rod (1) that can move axially is fixed in the hollow cavity; the cross-sectional dimension of the rod stock (2) is the same as that of the push rod (1). During additive manufacturing, the rod stock (2) is inserted into the bottom of the stirring head (4) and tightly combined with the hollow inner cavity of the stirring head (4); the stirring head (4) includes a cylindrical and a conical structure, the working end (7) is a conical structure with a cone angle of 5°-30°, the total length of the stirring head (4) is 80 mm, the length of the working end (7) is 12 mm, the bottom diameter is 10 mm, and the top diameter is 15 mm.

2. The friction stir deposition repair tool head for aluminum alloy surface defects according to claim 1, wherein: The hollow cavity of the stirring head (4) is a cuboid with side lengths of 10 mm×10 mm×120 mm, and the push rod (1) is made of tool steel with dimensions of 10 mm×10 mm×100 mm.

3. The friction stir deposition repair tool head for aluminum alloy surface defects according to claim 1, characterized in that: The body of the stirring head (4) is made of high-performance tungsten rhenium alloy W-25Re material, vacuum quenched at 1250 °C and tempered at 600 °C, with a hardness of HRC62 and good fracture toughness.

4. A friction stir deposition repair tool head for surface defects of aluminum alloy according to claim 1, characterized in that: The cone angle of the working end (7) is preferably 15°, and its inclined side promotes the uniform flow of the plastic material to the deposition area.

5. A friction stir deposition repair tool head for surface defects of aluminum alloy according to claim 1, characterized in that: The surface of the stirring head (4) is provided with a variable pitch thread structure. The pitch of the upper thread (5) is 1.0-1.5 mm and extends to the midpoint of the generatrix of the working end (7), and the pitch of the lower thread (6) is 0.5-1.0 mm to enhance the lateral flow of the material.

6. A friction stir deposition repair tool head for aluminum alloy surface defects according to claim 1, characterized in that: The stirring head (4) can be installed on a numerically controlled machine tool or a parallel robot arm to achieve precise motion control.

7. A repair method for a friction stir deposition repair tool head for surface defects of aluminum alloy, characterized in that: It includes the following steps: Step 1: Fix a 7075 or 6061 aluminum alloy substrate with a thickness of 10-50 mm, load the rod stock (2) into the stirring head (4) and position it to the deposition area to be deposited; Step 2: Rotate the stirring head (4) at a speed of 400-2000 r / min, and at the same time feed at a speed of 0.1-2 mm / s. After the rod stock (2) reaches the shoulder end face (8), press it down to contact the substrate at a traveling speed of 20-300 mm / min, form a plastic deposition layer through friction preheating and move to obtain an additive layer with a thickness of 0.1-2 mm; Step 3: Horizontally move the stirring head (4) in parallel, and repeat Step 2 to achieve multi-pass deposition, ensuring that the side edges of adjacent deposition layers are tightly combined.

8. The repair method of a friction stir deposition repair tool head for surface defects of aluminum alloy according to claim 7, characterized in that: In Step 2, for shallow and wide defects with a depth < 3 mm and a width-depth ratio > 2, a spiral path motion is adopted. For deep and narrow defects with a depth ≥ 3 mm and a width-depth ratio ≤ 2, a reciprocating multi-pass path is used to compact layer by layer.

9. A repair method for a friction stir deposition repair tool head for surface defects of aluminum alloy according to claim 7, characterized in that: During the friction preheating process between the shoulder end face (8) and the substrate, the progressive plasticization and filling of the material in the depth direction of the defect are realized through the gradually changing pressure distribution of the conical working end (7).

10. A repair method for a friction stir deposition repair tool head for surface defects of aluminum alloy according to claim 7, characterized in that: The variable pitch thread structure generates an axial shear force through the large pitch of the upper part to push the material down, and the small pitch of the lower part enhances the lateral flow, realizing the directional flow of the material from top to bottom and dispersing the wear area.

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