A remanufacturing repair method for hole damage in variable thickness steel tubular parts for helicopters.

Abstract

This invention discloses a method for repairing damaged holes in a variable-thickness steel tubular part for helicopters, belonging to the field of repair and remanufacturing technology. First, a hole-filling structure is prepared, comprising three parts: Part 1, Part 2, and Part 3. The hole-filling structure is made of the same or similar material as the helicopter tubular connector. Next, the small holes to be repaired on the connector are pre-treated, and X-ray inspection is used to confirm the absence of cracks around the holes. Based on this, this invention, by using a hole-filling structure of the same or similar material as the base material combined with electron beam welding, achieves hole damage repair without being limited by unilateral wear, avoids peeling, flaking, and cracking defects caused by excessive stress in the thick coating, and simultaneously solves the problems of uneven coating thickness and insufficient adhesion.

Description

Technical Field

[0001] This invention relates to the field of repair and remanufacturing technology, specifically to a remanufacturing repair method for damaged holes in variable thickness steel tubular parts for helicopters. Background Technology

[0002] Figure 3 The part shown is a connector for the horizontal tail of a certain type of helicopter. Wear on the locating pin holes on its mounting surfaces at both ends directly causes the part to fail to meet dimensional requirements, affecting the helicopter's flight performance. The main failure mode of this part is wear on the locating pin holes on the mounting surfaces at both ends. Figure 3 The presence of eight locating pin holes at both ends (as shown) results in out-of-tolerance hole diameters, leading to significant gaps after bolt assembly and failing to meet usage requirements. Replacement of the connectors is necessary to meet gap control requirements. Furthermore, wear on the connectors necessitates replacement and repair, increasing helicopter maintenance costs.

[0003] In the field of aircraft repair, the core of repairing worn apertures is to select a technical approach that prioritizes minimally invasive repair and load-bearing adaptation, based on the degree of wear, the material of the part, and the performance requirements of the aircraft. Currently, the three main methods for repairing apertures are as follows: (1) Electroplating repair: Suitable for minor wear with a single-sided wear of less than 0.15mm. The special graphite anode ensures uniform coating on the hole wall. After plating, low-temperature tempering eliminates internal stress, which can restore the dimensional accuracy and wear resistance of the hole. The coating thickness can be controlled between 0.005 and 0.2mm.

[0004] (2) Laser cladding repair: It is suitable for medium to heavy wear with unilateral wear between 0.1 and 0.5 mm. Fiber laser combined with coaxial powder feeding is used to form a metallurgical bonding cladding layer on the inner wall of the hole with a spiral scanning path. After cladding, the hole size is restored by precision reaming and honing.

[0005] (3) Thin-walled bushing repair: Suitable for severe wear with a single-sided wear greater than 0.5mm. Select a thin-walled bushing of the same material as the base, and insert it into the enlarged hole by liquid nitrogen cold fitting or high-temperature structural adhesive bonding, and machine it to the target size.

[0006] Based on the above, the objective disadvantages of the existing technology are as follows: 1. Electroplating is only suitable for minor damage with unilateral wear ≤0.15mm. When the plating thickness exceeds 0.2mm, the internal stress increases sharply, making it prone to defects such as peeling, flaking, and cracking, which cannot meet the repair needs of severely worn connectors. Furthermore, hole repair requires the fabrication of an anode tool matching the hole diameter to ensure a uniform gap between the anode and the hole wall. This uniformity is difficult to guarantee, easily leading to uneven plating thickness.

[0007] 2. Laser cladding is suitable for repairing moderate to severe hole wear. It requires a miniature coaxial powder feeding cladding head and a high-precision CNC motion platform. The equipment investment is large. Due to the limitation of the inner hole space, it is difficult to guarantee the coaxiality of the laser beam and the powder feeding tube. Defects such as sidewall powder adhesion, local incomplete fusion, and porosity are prone to occur. Currently, the smallest hole diameter that laser cladding can repair is 30mm. The positioning pin hole diameter of this connector is 8mm, so it cannot be repaired by laser cladding.

[0008] 3. Insert repair is suitable for severely worn holes. Before repair, the worn hole needs to be enlarged to remove some of the base material. Enlarging the hole will reduce the load-bearing capacity and rigidity of the part. It is not suitable for repairing critical holes of thin-walled structural parts.

[0009] 4. This connector is made of ultra-high strength steel. Due to the material's thermal expansion and contraction properties, when using electron beam welding with a filler material during small hole repair, the high power required for electron beam welding (which requires full penetration) can cause the entire filler material to melt. After solidification, this can result in a depression below the substrate plane. For example... Figure 4 As shown. Summary of the Invention

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A remanufacturing repair method for damaged holes in a variable-thickness steel circular tube part for helicopters includes the following specific steps: S1, Prepare a hole-filling structure, the hole-filling structure includes part one, part two and part three, the hole-filling structure is made of the same or similar material as the helicopter cylindrical connector; S2, pre-treat the small holes on the connector that need to be repaired, and use X-ray to inspect the area around the small holes to confirm that there are no cracks or defects; S3, Preheating and stress release before welding: The area to be repaired and the hole filling structure of the connector are preheated as a whole. The preheating temperature is adapted to the material characteristics of the connector. After slowly heating to the preset temperature, the temperature is kept constant for a period of time. S4. Assemble the hole-filling structure and the small hole to be repaired in the connector. After assembly, use electron beam welding to weld around the assembly interface gap to form a metallurgical bond between the hole-filling structure and the connector, and control the depression generated during the welding process on part one. S5. After welding, the area to be repaired and the hole filling structure of the connector are kept warm and cooled slowly. The area to be welded is wrapped with insulation cotton, the cooling rate is controlled, and the area is cooled slowly to room temperature. S6, use machining to remove part one, part two and part three, and re-drill holes at the original hole positions of the connector; S7, Post-repair precision inspection and secondary stress relief: The repair hole after re-drilling is inspected for dimensional accuracy, roundness and surface roughness. The repair area that passes the inspection is subjected to low-temperature tempering treatment to eliminate residual stress in the second stage, thus completing the repair of small hole damage.

[0011] As a preferred embodiment of the remanufacturing repair method for hole damage in a variable thickness steel circular tube part of a helicopter according to the present invention, the material of the hole filling structure includes 30CrMnSiA, 35Cr2Ni4MoA, and 30CrMnSiNi2A.

[0012] As a preferred embodiment of the remanufacturing repair method for hole damage in a variable thickness steel cylindrical part for helicopters according to the present invention, the thicknesses of parts one, two, and three are adjusted according to the wall thickness of the connector; when the wall thickness of the connector is small, the thicknesses of parts one, two, and three are increased; when the wall thickness of the connector is large, the thicknesses of parts one, two, and three are decreased.

[0013] As a preferred embodiment of the remanufacturing and repair method for hole damage in a variable thickness steel cylindrical part for helicopters according to the present invention, the number of the three parts is determined according to the diameter of the cylindrical connector.

[0014] As a preferred embodiment of the remanufacturing repair method for hole damage in a variable thickness steel cylindrical part for helicopters according to the present invention, wherein: part one provides excess filler metal for surface shaping after electron beam welding, so that the depression formed after welding melting is only formed in part one, and the electron beam welding penetrates to the upper surface of part two.

[0015] As a preferred embodiment of the remanufacturing and repair method for hole damage in a variable thickness steel cylindrical part for helicopters according to the present invention, the pretreatment in S2 includes polishing the inner wall of the hole.

[0016] As a preferred embodiment of the remanufacturing repair method for hole damage in a variable thickness steel circular tube part of a helicopter according to the present invention, wherein: the preheating temperature in S3 is set to 150-250℃, the holding time is set to 10-20min, and the heating rate is set to ≤100℃ / h.

[0017] As a preferred embodiment of the remanufacturing and repair method for hole damage in a variable thickness steel circular tube part of a helicopter according to the present invention, wherein: the heat preservation temperature in S5 is set to 150-200℃, the heat preservation time is set to 15-30min, and the cooling rate is controlled to be ≤50℃ / h.

[0018] As a preferred embodiment of the remanufacturing repair method for hole damage in a variable thickness steel circular tube part of a helicopter according to the present invention, wherein: the tempering temperature in S7 is set to 180-220℃ and the holding time is set to 2-3h.

[0019] Compared with existing technologies: 1. By adopting a hole-filling structure that is the same as or similar to the base material and combining it with an electron beam welding metallurgical bonding process, it can achieve hole damage repair without being limited by the amount of wear on one side, avoid peeling, flaking and cracking defects caused by excessive stress in the thick coating, and solve the problems of uneven coating thickness and insufficient bonding force. 2. By using an external filling structure in conjunction with circumferential electron beam welding, it can repair damage to small-diameter positioning pin holes without the need for a dedicated micro cladding head and a high-precision motion platform, thus avoiding defects such as powder adhesion, incomplete fusion, and porosity caused by the limitation of inner hole space. 3. The process of re-drilling holes after assembling and welding the hole-filling structure with the original hole has the effect of eliminating the need for hole enlargement of worn holes in the base material, avoiding the decrease in load-bearing capacity and stiffness of parts caused by the removal of base material, and adapting to the critical hole repair needs of thin-walled structural parts. 4. By setting a machine-removable part on the outside of the hole to be repaired as a filling allowance receiving structure, the depression caused by welding melting can be completely controlled on the removable process auxiliary part, avoiding the weld seam from being lower than the base material plane after repair, and ensuring the forming quality of the part base surface. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the assembly of the combined components to be welded according to the present invention; Figure 2 This is a schematic diagram of the metallographic structure of the welded connection interface of the present invention; Figure 3 This is a schematic diagram of the connector for the horizontal tail of a certain type of helicopter. Figure 4 This image shows the indentation phenomenon that occurs during electron beam welding of small holes in steel parts. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0022] This invention provides a remanufacturing repair method for damaged holes in variable-thickness steel tubular parts used in helicopters. Please refer to [link to relevant documentation]. Figures 1-2This method addresses issues such as poor adhesion in electroplating repairs, limited coating thickness, large aperture limitations in laser cladding repairs, and weakened structural strength in insert repairs. It aims to achieve a method for repairing worn apertures on thin-walled or thicker circular tubes. The method involves creating "hole-filling" materials of varying thicknesses and introducing them into the aperture. Utilizing the high energy density and deep penetration of electron beam welding, a strong metallurgical bond is formed between the "hole-filling" material and the aperture in the substrate. Combined with other machining methods to restore the aperture size, this method achieves remanufacturing repair of worn inner walls of the aperture. The specific steps are as follows: S1, Prepare a hole-filling structure, which includes part one, part two, and part three. The hole-filling structure is made of the same or similar material as the helicopter cylindrical connector, such as 30CrMnSiA, 35Cr2Ni4MoA, 30CrMnSiNi2A, etc. The thickness of part one, part two, and part three is adjusted according to the wall thickness of the connector. When the wall thickness of the connector is small, the thickness of part one, part two, and part three is increased to provide rigid fixation and prevent welding deformation. When the wall thickness of the connector is large, the thickness of part one, part two, and part three is decreased to increase the penetration rate and reduce the cost. At the same time, the number of part three is determined according to the diameter of the cylindrical connector, and can be one or more, without affecting the width of part two to ensure the welding qualification rate. S2, pre-process the small holes on the connector that need to be repaired, including polishing the inner wall of the small hole to remove oil, oxide scale and impurities, and using X-ray to inspect the area around the small hole to confirm that there are no cracks or defects; S3, Preheating and Stress Release Before Welding: The entire area to be repaired and the hole-filling structure of the connector are preheated. The preheating temperature is adapted to the material characteristics of the connector. After slowly heating to the preset temperature, the temperature is held for a period of time to achieve uniform stress release in the area to be welded, avoid thermal stress cracks caused by excessive temperature difference during welding, and improve the metallurgical bonding stability between the hole-filling structure and the connector, laying the foundation for subsequent welding. The preheating temperature is set to 150-250℃, the holding time is set to 10-20min, and the heating rate is set to ≤100℃ / h. S4. Assemble the hole-filling structure and the small hole to be repaired in the connector. After assembly, use electron beam welding to weld around the seam of the assembly interface to ensure that a "ring" is formed at the joint on part one, so that the hole-filling structure and the connector form a metallurgical bond. At the same time, the depression formed by the melting of the center due to heat focus is controlled on part one. After subsequent machining removal, the depression will not form at the inner hole of the connector. Among them, part one provides excess filler metal for the surface shaping after electron beam welding, so that the depression formed after welding melting is only shaped in part one, avoiding the weld from being lower than the surface base material of the connector. Moreover, the electron beam welding penetrates to the upper surface of part two, ensuring that the upper and lower surfaces of the connector repair hole are shaped on both sides after welding, avoiding the generation of incomplete fusion defects. S5. After welding, the area to be repaired and the hole-filling structure of the connector are subjected to overall heat preservation and slow cooling. The area to be welded is wrapped with heat preservation cotton, and the cooling rate is controlled to slowly cool to room temperature. This avoids the formation of hardened structure and residual stress in the welded area due to rapid cooling, further optimizes the metallographic structure of the welded joint, improves the density of the welded bond, reduces welding defects, and lays a good foundation for subsequent machining. The heat preservation temperature is set at 150-200℃, the heat preservation time is set at 15-30min, and the cooling rate is controlled at ≤50℃ / h. S6. By removing parts one, two, and three using machining methods, and re-drilling holes at the original hole positions of the connector, the wear of the inner hole can be repaired and its performance restored. This method is not limited by the amount of wear of the inner hole, and the bonding strength after repair is much higher than that of the electroplated layer. S7, Post-repair precision inspection and secondary stress relief: The repair holes after re-drilling are inspected for dimensional accuracy, roundness and surface roughness. The repaired areas that pass the inspection are subjected to low-temperature tempering treatment to eliminate residual stress for the second time, complete the repair of small hole damage, further improve the structural stability and fatigue resistance of the repaired parts, and extend the service life of the parts; the tempering temperature is set to 180-220℃ and the holding time is set to 2-3h.

[0023] Specifically, this invention is also applicable to the repair of damaged threaded holes on steel round pipe parts of different thicknesses. In this case, the damaged threads need to be removed by machining. After the threads are removed, a corresponding part two is made according to the hole diameter. It is necessary to ensure that the outer diameter of the column matches the diameter of the hole after the threads are removed. After the electron beam welding repair hole is completed, the hole is re-drilled and tapped to restore the threads.

[0024] In summary, the present invention also includes, but is not limited to, the following embodiments: The connector has an outer diameter of 80mm and an inner diameter of 68mm at both ends, with a wall thickness of 6mm. Each end has four 6mm diameter locating pin holes, all of which are smooth holes. The inner wall of one of the worn holes was polished to remove oil, scale, and other impurities. X-ray inspection was used to check the area around the hole to confirm the absence of cracks.

[0025] Fabricate Part 1, Part 2, and Part 3. Part 1 has an outer diameter of 84mm, an inner diameter of 80mm, a wall thickness of 2mm, and a through hole diameter of 6mm. Part 2 has an outer diameter of 68mm, an inner diameter of 64mm, a wall thickness of 2mm, and a column diameter of 6mm. Fabricate one piece of Part 2 along a 90° circumference. Part 3 has an outer diameter of 68mm, an inner diameter of 64mm, and a wall thickness of 2mm. Fabricate three pieces of Part 3 along a 90° circumference.

[0026] Assemble parts one, two, and three with the connecting parts. Figure 1The components are assembled as shown. Electron beam welding is used to scan and weld around the assembly boundary of the column, completing the welding of the assembled parts. After welding, parts one, two, and three are removed by machining, and the φ6mm locating pin holes of the connectors are remachined to repair the diameter of the worn holes. The metallographic structure of the cross-section of the repaired hole is as follows. Figure 2 As shown.

[0027] Although the present invention has been described above with reference to embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the invention. In particular, as long as there is no structural conflict, the features in the disclosed embodiments can be combined with each other in any manner. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for remanufacturing and repairing damaged holes in a variable-thickness steel circular tube part for helicopters, characterized in that, The specific steps are as follows: S1, Prepare a hole-filling structure, the hole-filling structure includes part one, part two and part three, the hole-filling structure is made of the same or similar material as the helicopter cylindrical connector; S2, pre-treat the small holes on the connector that need to be repaired, and use X-ray to inspect the area around the small holes to confirm that there are no cracks or defects; S3, Preheating and stress release before welding: The area to be repaired and the hole filling structure of the connector are preheated as a whole. The preheating temperature is adapted to the material characteristics of the connector. After slowly heating to the preset temperature, the temperature is kept constant for a period of time. S4. Assemble the hole-filling structure and the small hole to be repaired in the connector. After assembly, use electron beam welding to weld around the assembly interface gap to form a metallurgical bond between the hole-filling structure and the connector, and control the depression generated during the welding process on part one. S5. After welding, the area to be repaired and the hole filling structure of the connector are kept warm and cooled slowly. The area to be welded is wrapped with insulation cotton, the cooling rate is controlled, and the area is cooled slowly to room temperature. S6, use machining to remove part one, part two and part three, and re-drill holes at the original hole positions of the connector; S7, Post-repair precision inspection and secondary stress relief: The repair hole after re-drilling is inspected for dimensional accuracy, roundness and surface roughness. The repair area that passes the inspection is subjected to low-temperature tempering treatment to eliminate residual stress in the second stage, thus completing the repair of small hole damage.

2. The remanufacturing and repair method for hole damage in a variable thickness steel circular tube part for helicopters according to claim 1, characterized in that, The materials used for the pore-filling structure include 30CrMnSiA, 35Cr2Ni4MoA, and 30CrMnSiNi2A.

3. The remanufacturing and repair method for hole damage in a variable thickness steel circular tube part for helicopters according to claim 1, characterized in that, The thickness of parts one, two, and three is adjusted according to the wall thickness of the connector; when the wall thickness of the connector is small, the thickness of parts one, two, and three is increased; when the wall thickness of the connector is large, the thickness of parts one, two, and three is decreased.

4. The remanufacturing and repair method for hole damage in a variable thickness steel circular tube part for helicopters according to claim 1, characterized in that, The quantity of the third part is determined according to the diameter of the circular tube connector.

5. The remanufacturing and repair method for hole damage in a variable thickness steel circular tube part for helicopters according to claim 1, characterized in that, The first part provides excess filler metal for surface shaping after electron beam welding, so that the depression formed after welding melting is only formed in the first part, and the electron beam welding penetrates to the upper surface of the second part.

6. The remanufacturing and repair method for hole damage in a variable thickness steel circular tube part for helicopters according to claim 1, characterized in that, The pretreatment in S2 includes polishing the inner wall of the small hole.

7. The remanufacturing and repair method for hole damage in a variable thickness steel circular tube part for helicopters according to claim 1, characterized in that, The preheating temperature in S3 is set to 150-250℃, the holding time is set to 10-20min, and the heating rate is set to ≤100℃ / h.

8. The remanufacturing and repair method for hole damage in a variable thickness steel circular tube part for helicopters according to claim 1, characterized in that, The heat preservation temperature in S5 is set to 150-200℃, the heat preservation time is set to 15-30min, and the cooling rate is controlled to be ≤50℃ / h.

9. The remanufacturing and repair method for hole damage in a variable thickness steel circular tube part for helicopters according to claim 1, characterized in that, The tempering temperature in S7 is set to 180-220℃, and the holding time is set to 2-3h.

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