A machining method for an outer fairing of an aero-engine

Abstract

This invention discloses a processing method for an outer fairing of an aero-engine, comprising: S1, determining the annular blanking profile according to the shape of the outer fairing, cutting the sheet metal to obtain an annular blank with a central hole; S2, placing the blank on the blanking ring of a deep drawing die, the die descending to press the blank to form a blanking force, and the punch drawing the blank into the die in one deep drawing to form the outer fairing profile, without a second deep drawing or solution treatment; S3, machining circumferentially distributed holes on the workpiece and positioning it on a flanging die, the die descending to flanging each hole with the same flanging direction in one step; S4, cutting circumferentially distributed slots using the profile and the circumferentially distributed holes as reference lines. This invention enables bidirectional material flow, one-time deep drawing without secondary deep drawing and solution treatment, effectively preventing surface cracking and wrinkling, ensuring uniform thickness and smooth surface transition, and features short process, low cost, and stable quality.

Description

Technical Field

[0001] This invention relates to the field of aero-engine component technology, and in particular to a method for processing an outer fairing for an aero-engine. Background Technology

[0002] The outer fairing is a key aerodynamic component of an aero-engine. It is typically manufactured from high-temperature alloy sheet metal through plastic forming, and is an overall annular thin-walled structure with a central hole. It features mounting holes and slots distributed circumferentially, primarily responsible for airflow regulation, aerodynamic guidance, and component protection. These parts have continuous surface curvature and thin walls, placing stringent requirements on surface contour accuracy, hole position accuracy, and slot dimensional precision. Their machining quality directly impacts the aerodynamic efficiency and assembly reliability of the aero-engine, making them a typical example of highly challenging parts to machine in the field of high-temperature alloy sheet metal.

[0003] In actual production, the traditional processing technology for aero-engine outer fairings has significant shortcomings. Due to the high deformation resistance and significant work hardening effect of high-temperature alloy materials, existing processes generally employ multi-pass deep drawing. During deep drawing, defects such as wrinkling, uneven wall thickness, and excessive springback are prone to occur. To eliminate forming stress and correct the profile, multiple heat treatment and shaping processes are required, resulting in a lengthy, cumbersome, and costly overall process. Furthermore, each process, such as deep drawing, hole making, and grooving, uses independent positioning datums. Multiple clamping operations can easily lead to cumulative datum errors, making it difficult to consistently meet the accuracy of hole positions, groove positions, and profile contours, resulting in a low first-pass yield. The multi-process turnaround also lengthens the production cycle, making it difficult to meet the efficiency requirements of mass production.

[0004] To address the aforementioned issues, the industry has conducted numerous process optimization studies. Among them, the patent technology with publication number CN120619773A, entitled "A Processing Method for a Combustion Chamber Head Fairing," represents a relatively typical solution. This patent uses a circular annular blank, undergoes initial deep drawing, heat treatment, and secondary deep drawing to ensure the surface profile accuracy. Then, a composite die is used to complete the punching of all elliptical and circular holes in one go, simultaneously removing the inner and outer flange edges. Finally, the end face anti-crack groove is prepared by machining and laser cutting. Its core principle is to control the deformation amount by forming twice using the same set of deep drawing dies, thereby improving the consistency of hole processing through concentrated punching and improving the quality and efficiency of part processing to a certain extent. However, this solution still has limitations: First, it still relies on two deep-drawing processes, and the secondary shaping requires adjusting the die stroke using shims, resulting in high costs for die debugging and part clamping. Second, the hole machining involves direct punching of through holes, making it impossible to achieve edge flanging and forming, which is difficult to adapt to the external fairing structure with flanged mounting holes, thus limiting its applicability. Third, the grooving uses laser processing, which is prone to heat-affected zones and remelted layer defects, and the hole-making, turning, and grooving processes do not form a unified positioning benchmark, leaving room for improvement in shape and position accuracy. Most other similar processing technologies only optimize single processes, failing to achieve process simplification and benchmark unification at the overall process chain level, and thus cannot simultaneously ensure forming quality, machining accuracy, and production efficiency. Therefore, there is an urgent need to develop a processing method for aero-engine external fairings that features simplified processes, unified positioning benchmarks, and stable forming quality to solve the many problems existing in current technologies. Summary of the Invention

[0005] This invention provides a method for processing an outer fairing for an aero-engine, which solves the problems of cumbersome processing procedures, wrinkling defects caused by multiple deep drawing passes, and low part forming accuracy and processing efficiency due to inconsistent processing positioning references in traditional aero-engine outer fairing processing.

[0006] To solve the above problems, the technical solution adopted by the invention is as follows: A method for manufacturing an outer fairing for an aircraft engine, characterized by comprising the following steps: S1. Blanking: Determine the circular blanking outline according to the shape of the outer fairing, and cut the sheet metal according to the blanking outline to obtain a circular blank with a central hole in the middle. One circular blank corresponds to one outer fairing. S2. One-time deep drawing: The annular blank is placed on the blank holder of the deep drawing die. The die of the deep drawing die moves downward and contacts the blank holder, and then continues to move downward to apply pressure, pressing the blank tightly against the surface of the blank holder to form a blank holder force to prevent wrinkling. The die continues to move downward, and the punch of the deep drawing die gradually pulls the blank into the die, causing the blank to undergo plastic deformation and conform to the surface of the punch and the die, thus forming the surface of the outer fairing in one deep drawing. S3, Flanging: Holes distributed in a circumferential direction are machined on the workpiece after one deep drawing process. The workpiece is positioned on the flanging die. The die of the flanging die moves down and flanging each hole on the outer fairing with the same flanging direction in one go. S4. Grooving: Using the outer fairing's profile and circumferentially distributed holes as positioning references, the outer fairing is grouted circumferentially with wire cutting.

[0007] The principle and advantages of this scheme are as follows: The core principle of this solution lies in constructing a streamlined and precision-controllable outer fairing processing system through process coordination of blank shape adaptation, single-pass forming control, synchronous flanging of unidirectional holes, and composite datum positioning. First, the annular blanking profile is determined based on the structural shape of the outer fairing. Annular blanks with a central hole are used, and each blank corresponds to a single finished product. This ensures that the material distribution of the blank matches the material flow pattern during deep drawing, reducing flow instability caused by excess material at the blank shape level and minimizing the causes of wrinkling during forming. Second, during deep drawing, the die descends and, in conjunction with the blank holder, applies a uniform blank holder force to the annular blank, constraining the radial flow of material in the flange area. Then, the punch gradually pulls the blank into the die cavity, allowing the sheet metal to undergo continuous plastic deformation within a single deep drawing stroke and completely conform to the surfaces of the punch and die. Under controllable deformation conditions... The outer fairing is formed in one step. Then, circumferentially distributed pre-made holes are machined on the workpiece after one deep drawing. After the workpiece is positioned on the flanging die, the downward movement of the die applies deformation force to all holes with the same flanging direction at the same time, causing the material at the edge of the hole to undergo tensile and enlargement deformation, and the flanging of all holes in the same direction is completed in one step. Finally, the formed surface and the circumferentially distributed holes are used as a composite positioning reference, while constraining the radial, circumferential and axial degrees of freedom of the part, ensuring the uniqueness and stability of the part position during wire EDM, so as to process circumferential slots with consistent positional accuracy, and realize the unified transfer of reference between the forming process and the subsequent machining process.

[0008] Compared to existing technologies, which require multiple deep drawing passes combined with intermediate heat treatment and shaping processes to form high-temperature alloy annular thin-walled fairings, the proposed solution utilizes a single deep drawing pass to form the part's profile. This eliminates the need for secondary deep drawing, intermediate heat treatment, and repeated shaping, significantly shortening the process flow, reducing mold investment and processing energy consumption, and avoiding the accumulation of work hardening and multiple clamping errors caused by multiple deformation passes. The resulting part also exhibits less springback and superior profile stability. Secondly, the single-pass flanging forming process for unidirectional holes, compared to the conventional approach that only processes through holes, directly yields a flanged hole structure without adding any additional steps. Under the premise of improving the structural strength and installation reliability of the holes, the synchronous forming method ensures the consistency of all flange heights and angles, eliminating the dimensional dispersion caused by hole-by-hole processing. Thirdly, a composite positioning datum of "profile + circumferentially distributed holes" is established for the grooving process, solving the problem of cumulative errors caused by independent positioning and inconsistent datums in the traditional process of deep drawing, hole making, and grooving. This significantly improves the positional accuracy of the slot opening relative to the part profile and mounting holes, effectively reducing the assembly deviation of the parts. Fourthly, the circumferential slot opening is processed by wire cutting. Compared with the laser cutting method commonly used in existing technologies, there is no remelting layer defect in the heat-affected zone, resulting in better surface quality of the cut and avoiding the adverse effects of hot working defects on the fatigue performance of the parts. Overall, this solution simplifies the process and improves processing efficiency while simultaneously achieving a dual improvement in forming quality and processing accuracy, effectively solving the core problems of cumbersome processes, numerous forming defects, and inconsistent positioning datums in the traditional process.

[0009] Further, in step S1, the sheet material is GH4648 high-temperature alloy sheet, and it is in a solution-treated and pickled state. The sheet is cut using laser cutting according to the specified blanking contour. After blanking, the cutting burrs and remelted layer are removed by grinding, and the sheet is cleaned. The solution-treated and pickled GH4648 high-temperature alloy sheet is selected as the raw material because this state of sheet material has a uniform internal structure, low internal stress, and excellent plastic forming performance, which can reduce the risk of cracking and springback during subsequent single deep drawing processes. Laser cutting is used to cut the sheet along a preset circular contour, resulting in high cutting precision and accurate matching of the inner and outer diameter dimensions of the annular blank required for the outer fairing. Each blank corresponds to a single piece. Finished products can reduce material waste; after laser cutting, grinding removes burrs and remelted layers from the cut and cleans the workpiece. This eliminates the potential for burrs and hard remelted layers to scratch the mold cavity and part surface during deep drawing, and also avoids uneven plasticity caused by excessive hardness of the remelted layer, which can lead to wrinkling and wall thickness difference defects. At the same time, cleaning removes surface dust, oil, and oxidation impurities, preventing impurities from embedding into the surface of the sheet during deep drawing and forming, thus ensuring the surface quality and forming adaptability of the raw material from the state of the raw material, the blanking method, and the post-processing process. This lays a stable blank foundation for subsequent deep drawing, hole turning, and grooving processes.

[0010] Further, after step S2, the drawn flange edges on both sides of the workpiece after one deep drawing are removed, while retaining the outer fairing profile. The workpiece is then placed flat in the vacuum annealing furnace without stacking for vacuum stress-relief annealing to remove the deep drawing stress. By first removing the excess drawn flange edges on both sides of the part after one deep drawing, and only retaining the effective fairing profile, the stress concentration area caused by the residual material on the flange edges can be eliminated, and the stress on the flange edges can be avoided from being transmitted to the effective profile during the annealing process, causing local deformation. The workpiece after removing the flange edges is placed flat in a single layer without stacking and sent into the vacuum annealing furnace for vacuum stress-relief annealing. On the one hand, the vacuum environment can isolate air and avoid... GH4648 high-temperature alloy does not oxidize or form an oxide scale on the surface during high-temperature heating. No additional grinding is required to remove the oxide layer. On the other hand, single-layer placement eliminates compression and superimposed stress. The surface can freely expand during annealing heating and cooling without extrusion deformation, bumps, or scratches. It can evenly release the residual stress of plastic deformation generated by the sheet metal during a single deep drawing process, significantly reducing the amount of springback deformation during subsequent flanging and wire EDM grooving, stabilizing the surface contour accuracy, and eliminating the superposition of processing stress caused by residual stress. This reduces processing defects such as flanging cracks and groove position misalignment, improving the dimensional stability of subsequent processes and the yield rate of finished parts.

[0011] Furthermore, the processing method does not perform a second deep drawing after the first deep drawing in step S2, and does not perform solution treatment on the workpiece. The second deep drawing process is omitted after the single deep drawing, and the solution treatment step is also eliminated. Firstly, this eliminates the need for mold adjustment, secondary clamping of parts, and hydraulic press equipment occupation required for the second deep drawing, significantly shortening the overall processing flow and reducing mold wear and equipment time costs. Secondly, it eliminates the need for high-temperature solution heat treatment, avoiding the risks of overall oxidation and high-temperature deformation of parts caused by high-temperature solution treatment. It also eliminates the need for subsequent pickling and oxide scale removal processes after solution treatment. The process can be shortened in one step; combined with pre-vacuum stress-relief annealing, the residual stress generated by a single deep drawing can be fully released. Relying on the excellent original plasticity of the solution-treated and acid-washed GH4648 sheet, the part's surface forming requirements can be met in a single deep drawing. This avoids the defects of increased work hardening, wrinkling and uneven wall thickness caused by repeated plastic deformation of multiple deep drawings, and eliminates the problems of coarse grains and large-scale springback of part dimensions caused by solution treatment. It also reduces the multiple clamping reference offsets caused by multiple cold and hot processing, stabilizes the surface accuracy of the part, and simultaneously achieves multiple advantages such as reduced production costs, improved processing efficiency and optimized forming quality.

[0012] Furthermore, in step S3, the workpiece after one deep drawing is placed on a milling fixture, and the workpiece is adhered and fixed to the milling fixture with adhesive. Holes distributed circumferentially are machined using a three-axis milling method according to a digital model. The workpiece after one deep drawing is placed on the milling fixture and adhered and fixed with adhesive. This eliminates the need for process positioning holes on the thin-walled surface of the fairing and avoids the use of chucks for hard clamping, thus preventing localized dents and surface deformation of the thin-walled parts caused by the clamping force generated by hard clamping. Adhesive fixing can uniformly conform to the curved surface of the part to achieve flexible constraint across the entire surface, ensuring stable clamping. Without damaging the already formed precision surface; relying on the three-dimensional digital model of the part, the circumferentially distributed holes are machined by three-axis milling. The machining trajectory is directly driven by the digital model, and the hole position coordinates and hole diameter dimensions are controllable. It can accurately ensure the positional accuracy requirements of the uniform distribution of each hole in the circumference. Compared with punching pre-made holes, the milled hole wall is smooth without tearing or corner collapse defects, providing a high-quality pre-made hole base for subsequent hole turning and flanging. It effectively prevents stress concentration and cracking at the edge of the hole wall during the flanging process. At the same time, this clamping and machining method is simple to operate, and the single-piece clamping and alignment time is short, improving the processing efficiency of the hole making process and the forming quality of the pre-made holes.

[0013] Furthermore, in step S3, the workpiece with the pre-drilled holes is positioned using the first punch and stripper plate of the flanging die. The concave die of the flanging die moves downward, flipping up the edges of each hole to form a flanged edge. The first punch of the flanging die, in conjunction with the stripper plate, positions the workpiece with the pre-drilled holes. This simultaneously conforms to the inner and outer surfaces of the part, constraining radial and axial displacement, and precisely locking the coaxiality of all pre-drilled holes with the die punch. This prevents circumferential and radial offset of the part during the flanging process, avoiding uneven flanging height and angle. The overall flanging is achieved by the concave die simultaneously pressing the edges of each pre-drilled hole as it moves downward. Edge forming eliminates the need for processing each hole individually in multiple steps, significantly reducing the processing time for flanging. Under synchronous stress, the tensile deformation of each hole edge is uniform and consistent, preventing defects such as insufficient flanging or localized tearing in single holes. Relying on rigid mold forming to replace manual or single-point hydraulic flanging, the flanging radius and thickness are uniform and controllable. The perpendicularity of the formed flanging structure meets the standards, providing a high-precision and consistent circumferential positioning reference for subsequent grooving processes. At the same time, rigid mold forming effectively counteracts the springback characteristics of GH4648 high-temperature alloy, reducing the workload of dimensional correction after flanging, and balancing flanging forming accuracy with batch processing efficiency.

[0014] Further, after the flanging forming in step S3, a second punch is installed in the flanging mold, so that the edges of the second punch and the first punch are aligned without misalignment. The part is positioned and pressed with the stripper plate, and each small hole is flanged and formed into a convex shape using a punch. The flanging of the small holes is pressurized by a hydraulic forming machine with a forming pressure of 5~8MPa and a holding time of 5-8min. After the small holes are flanged, the height of the convex shape is ground to the design size.

[0015] Further, in step S4, the outer fairing is supported and fixed on the wire cutting fixture. The outer fairing is positioned using its profile and circumferentially distributed holes as positioning references. Eight slots are cut using wire cutting. After slotting, the outer fairing is deburred, and the profile is inspected using fluorescence. After the flanging is completed, a second punch aligned with the edge of the first punch is replaced within the same flanging mold. The original stripper plate is used to position and clamp the part, eliminating the need for disassembly and reassembly, thus avoiding reference offset and positioning time losses caused by secondary clamping. This ensures the coaxiality of the large hole flanging and the small hole protrusion forming. Small hole protrusions are processed one by one using a hydraulic forming method with a pressure of 5-8 MPa and a holding pressure of 5-8 minutes, with moderate forming pressure to avoid... The GH4648 high-temperature alloy small hole wall is torn under high pressure. Sufficient holding time can fully release the material deformation and springback, making the convex bulge wall thickness uniform and the forming full. It avoids the defects of springback collapse and inconsistent convex bulge height after the flanging of thin-walled small holes. After processing, the convex bulge height is uniformly ground to the design size, which can eliminate the small dimensional dispersion error caused by single hole forming. It makes all convex bulge dimensions uniform and regular, which not only meets the assembly structure requirements of the parts, but also forms a high-precision, multi-point circumferential positioning reference together with the previously flanged large hole. It provides a stable and reliable positioning reference for subsequent wire EDM grooving. The entire process relies on the same set of molds to complete the forming of different hole structures in stages, simplifying the number of tooling accessories and simultaneously improving the forming quality, dimensional consistency and overall processing efficiency of small hole convex bulges.

[0016] Furthermore, the circumferentially distributed holes serving as positioning references are the holes obtained through flanging in step S3. The flanged holes obtained in step S3 are selected as the circumferential positioning references for the grooving process. The flanged structure forms a raised support surface. Compared to plain holes without flanging, the fixture positioning pins can simultaneously conform to the inner wall of the hole and the flanged end face, achieving dual circumferential and axial constraints. This results in a larger positioning contact area and stronger clamping stability, effectively suppressing slight movement and vibration during the wire cutting of the GH4648 thin-walled fairing. These flanged holes are integrally formed structures of the part body, integrated with the outer fairing profile. Since the holes are formed in the same process chain, there is no cumulative error in the position of the holes relative to the datum surface due to secondary clamping. The datum transfer is continuous and consistent, avoiding the datum offset caused by the use of auxiliary process holes in post-processing. At the same time, all the flanged holes are evenly distributed circumferentially, and multi-point synchronous positioning can evenly distribute the clamping stress, prevent local pressure deformation of thin-walled surfaces, ensure the positional accuracy of the slots and grooves in wire EDM relative to the part surface and mounting holes, reduce slot deviation and dimensional defects, eliminate the need for additional processing of special process datum holes, simplify the tooling structure, and simultaneously improve the grooving accuracy and process efficiency. Attached Figure Description

[0017] Figure 1 is a full sectional view of the drawing die of the present invention in the closed state; Figure 2 is a full sectional view of the closed state of the hole-flipping mold of the present invention; Figure 3 This is a schematic diagram of the punched small hole structure of the present invention; Figure 4 This is a schematic diagram of the product structure of the present invention; Figure 5 This is a schematic diagram of the product wire cutting fixture structure of the present invention.

[0018] Figure 6 This is a flowchart of the method of the present invention.

[0019] Figure reference numerals: 1. Drawing punch; 2. Drawing die; 3. Blank holder; 4. Annular positioning step; 5. First punch; 6. Flanging boss; 7. Second punch; 8. Stripper plate; 9. Flanging die; 10. Punch; 11. Wire cutting fixture; 12. Contouring support block; 13. Positioning pin; 14. Outer fairing; 15. Center hole; 16. Mounting hole; 17. Flanging; 18. Small hole protrusion; 19. Gap groove; 20. Profile. Detailed Implementation Example 1 like Figure 1-6 As shown, the outer fairing 14 for aero-engines processed in this embodiment is an annular thin-walled rotary structure with a central hole 15, made of GH4648 high-temperature alloy sheet, with a nominal wall thickness of 1.2mm. The outer fairing 14 has a maximum outer diameter of φ420mm, an inner diameter of φ180mm for the central through hole, and an axial drawing depth of 35mm for the profile 20. Twelve large mounting holes 16 with flanges 17 are evenly distributed around the circumference of the part, with a flange height of 3mm. At the same time, twelve small hole structures with small hole protrusions 18 are also evenly distributed around the circumference. Eight slots 19 are evenly opened around the outer edge of the part, with a slot width of 3mm and a slot length of 25mm.

[0020] The specific steps of the outer fairing processing method in this embodiment are as follows: S1, Material feeding GH4648 high-temperature alloy sheet in a solution-treated and acid-washed state was selected, with a sheet thickness of 1.2mm. The raw material grain size grade was not lower than level 4, and the surface was free of defects such as cracks, scratches, and oxide spots. Based on the finished dimensions and drawing deformation coefficient of the outer fairing 14, the circular blanking profile was calculated and determined: the outer diameter of the blank was φ480mm, the diameter of the pre-drilled hole in the center was φ160mm, and one circular blank corresponded to one finished outer fairing 14. A fiber laser cutting machine was used to cut along the preset blanking profile. The cutting process parameters were: laser power 1500W, cutting speed 1.2m / min, auxiliary gas 99.9% pure nitrogen, gas pressure 1.2MPa, ensuring a smooth cut without slag. After the material is cut, the cutting end face is first polished with an 80-grit alumina grinding wheel to remove macroscopic burrs. Then, the cut surface is finely polished with 240-grit silicon carbide sandpaper to completely remove the remelted layer produced by laser cutting. The depth of remelted layer removal is not less than 0.1mm. Subsequently, the material is placed in an alkaline cleaning solution for ultrasonic cleaning for 10 minutes at a cleaning temperature of 50℃. Then, it is rinsed twice with deionized water and dried with hot air to thoroughly remove surface oil, metal debris and polishing dust, resulting in a ring-shaped material with qualified surface quality.

[0021] S2, One-time deep drawing The deep drawing die structure used in this step is as follows: Figure 1 As shown, it mainly consists of three parts: a drawing punch 1, a drawing die 2, and a blank holder 3. The outer contour surface of the drawing punch 1 perfectly matches the inner surface of the outer fairing 14, and the inner cavity surface of the drawing die 2 perfectly matches the outer surface of the outer fairing 14. The single-sided forming gap between the drawing punch 1 and the drawing die 2 is set to 1.25 mm, slightly larger than the nominal thickness of the sheet metal, to compensate for the wall thickness change after plastic deformation. The upper surface of the blank holder 3 is provided with an annular positioning step 4, used to place the annular blank and achieve initial radial positioning.

[0022] Specific operation process of deep drawing: Apply high-temperature alloy special deep drawing grease evenly to the upper and lower surfaces of the annular blank to reduce frictional resistance during the forming process; Place the lubricated blank material flat on the annular positioning step 4 of the pressure ring 3, adjust the position of the blank material, and ensure that the coaxiality of the inner and outer circles of the blank material with the center of the mold is ≤0.2mm. Start the four-column hydraulic press and drive the drawing die 2 to descend at a speed of 5 mm / s. After the lower end face of the drawing die 2 contacts the blank holder 3, it continues to descend. Apply a constant blank holder force to the blank holder 3. The blank holder force is controlled at 120~150kN to tightly press the blank flange area onto the surface of the blank holder 3, constraining the radial flow of the material and preventing wrinkling defects during the forming process. The drawing die 2 continues to descend at a constant speed of 3 mm / s, while the drawing punch 1 moves upward relative to it, gradually drawing the blank into the cavity of the drawing die 2, causing continuous plastic deformation of the sheet metal. The blank holder force is kept stable throughout the process until the drawing punch 1 and the drawing die 2 are completely closed, and the blank is completely attached to the surfaces of the drawing punch 1 and the drawing die 2, completing the one-time drawing forming of the outer fairing 14 surface 20.

[0023] After this step is completed, no second deep drawing is performed, nor is the workpiece subjected to solution treatment; only a single deep drawing process is retained.

[0024] After deep drawing, the deep-drawn flange edges on both the inner and outer sides of the workpiece are first removed by CNC lathe turning. After turning, the effective profile 20 of the outer fairing 14 is retained, and the outer diameter is turned to φ422mm, leaving 0.2mm for subsequent finishing. The center hole 15 is turned to φ178mm, leaving 0.2mm allowance. Then, vacuum stress-relief annealing is performed: the workpiece with the turned flange edges is placed flat in a single layer on the ceramic rack of the vacuum annealing furnace, with no contact or stacking between the parts, ensuring that the profile 20 can stretch freely; after the furnace cavity is closed, a vacuum is drawn to the required level. The temperature is increased to 750℃ at a rate of 10℃ / min and held for 120min. After holding, the part is cooled to below 200℃ in the furnace and forced to cool with high-purity argon gas. The part is removed from the furnace when the temperature drops below 150℃. After this process, the residual stress removal rate of the deep-drawing part is ≥85%, the surface is free of oxidation and deformation, and the profile of the 20mm section is stable.

[0025] S3, Flanging Forming This process is divided into three stages: pre-drilled hole processing, simultaneous flanging of large holes, and convex forming of small holes. The flanging die structure used is as follows: Figure 2 , Figure 3 As shown, it includes an interchangeable first punch 5, a second punch 7, a stripper plate 8, and a flanging die 9. The upper surface of the first punch 5 is uniformly provided with flanging bosses 6 that correspond one-to-one with the mounting holes 16.

[0026] (1) Prefabrication of circumferential holes The stress-relief annealed workpiece is placed on a contour milling fixture, with the fixture's support surface fully conforming to the inner surface of the outer fairing 14. Epoxy resin adhesive is evenly applied to the fixture's support surface, and the workpiece is pressed and bonded, then cured at room temperature for 4 hours to ensure a firm bond between the part and the fixture without relative displacement. A three-axis CNC milling machine is used, with a milling program developed based on the three-dimensional model of the outer fairing 14. A φ10mm carbide end mill is selected, with a spindle speed of 3000 r / min and a feed rate of 150 mm / min. Twelve pre-drilled through holes are evenly machined circumferentially on the workpiece, with a hole diameter of φ10mm and a positional tolerance of ≤0.15mm relative to the part's center. After machining, the fixture and workpiece are heated to 80℃ to soften the adhesive. The workpiece is then removed, and any remaining adhesive on the surface is wiped clean with alcohol.

[0027] (2) Large hole one-time flanging forming The pre-drilled parts are installed into the flanging mold. The outer surface of the first punch 5 and the stripper plate 8 are used for positioning. The stripper plate 8 presses against the part profile 20 to ensure that the coaxiality of each pre-drilled hole and the flanging boss 6 on the first punch 5 is ≤0.1mm. The hydraulic press is started to drive the flanging die 9 to descend at a uniform speed of 2mm / s, and the flanging deformation force is applied synchronously to the edge of all 12 pre-drilled holes, causing the edge material to be stretched and expanded along the side wall of the flanging boss 6 until the flanging die 9 descends to the set limit stroke, completing the flanging of all the large mounting holes 16 with the same flanging direction in one go. The finished hole diameter after flanging is φ12mm, the axial height of the flanging 17 is 3mm, the flatness of the end face of the flanging 17 is ≤0.08mm, the perpendicularity of the side wall of the flanging 17 is ≤0.1mm, and there are no cracks or wrinkles.

[0028] (3) Small hole convex hull forming After the large hole is flanged, keep the stripper plate 8 in a pressed state. Remove the first punch 5 from the flanging mold and replace it with the second punch 7. Adjust the position of the second punch 7 to align it with the parting edge of the original first punch 5, with a misalignment of ≤0.05mm, to ensure that the part positioning reference does not shift. Use a hydraulic forming machine with a single punch 10 to flanging and forming the circumferential small holes on the part one by one. The forming process parameters are: forming pressure 6MPa, holding time 6min. After each small hole is flanged, a small hole protrusion 18 structure with a height of 2mm is formed, and the root radius of the small hole protrusion 18 is R0.8mm. After all the small hole protrusions 18 are processed, install the part on a special grinding fixture. Using the profile 20 and the flanging 17 of the large hole 16 as the positioning reference, use a surface grinder to grind the top surface of all the small hole protrusions 18 to ensure that all protrusions have the same height, with the height tolerance controlled within ±0.05mm.

[0029] S4, wire EDM grooving This step uses a slow wire EDM machine to process the slot 19. The wire EDM fixture 11 adopts a composite positioning structure of contour support + hole positioning.

[0030] Specific operation: Place the outer fairing 14 with completed flanging on the contour support block 12 of the wire EDM fixture 11. The contour support block 12 fits the inner surface of the outer fairing 14, constraining the radial and axial degrees of freedom of the part. Select three circumferentially evenly distributed mounting holes 16 and flanges 17 as circumferential positioning references. Insert matching positioning pins 13. The positioning pins 13 simultaneously fit the inner wall of the hole and the end face of the flange 17 to achieve complete circumferential positioning. Finally, a composite positioning reference of "surface 20 + circumferentially evenly distributed holes" is formed. After positioning, the part has no movement gap, and the repeatability of positioning is ≤0.1mm. Compile a wire EDM machining program, using φ0.2mm molybdenum wire, setting the pulse width to 20μs, the pulse interval to 80μs, and the cutting speed to 80mm² / min. Cut eight circumferentially evenly distributed slots 19 along the preset trajectory in one go. The slots 19 are 3mm wide and 25mm long. The positional accuracy of the slots 19 relative to the mounting holes is ≤0.2mm. After the grooving is completed, the edges and end faces of the groove 19 are polished with 1000-grit metallographic sandpaper to remove all machining burrs. Then, the profile 20, hole edges and grooves of the entire outer fairing 14 are subjected to fluorescent penetrant testing. The testing is carried out in accordance with the HB / Z61 standard, and linear defects such as cracks and lack of fusion are not allowed. Finally, the finished outer fairing 14 is obtained.

[0031] The outer fairing 14 obtained in this embodiment, after three-coordinate measurement, has a profile 20 contour ≤ 0.3mm, a maximum wall thickness difference ≤ 0.15mm, and the hole position and slot position both meet the design requirements. The entire process involves only a single deep drawing pass, without the need for secondary deep drawing or intermediate solution treatment, simplifying the process. The first-pass yield of the parts is ≥ 95%, and the forming quality and processing accuracy are stable, making it suitable for mass production.

Claims

1. A method for manufacturing an outer fairing for an aircraft engine, characterized in that, Includes the following steps: S1. Blanking: Determine the circular blanking outline according to the shape of the outer fairing, and cut the sheet metal according to the blanking outline to obtain a circular blank with a central hole in the middle. One circular blank corresponds to one outer fairing. S2. One-time deep drawing: The annular blank is placed on the blank holder of the deep drawing die. The die of the deep drawing die moves downward and contacts the blank holder, and then continues to move downward to apply pressure, pressing the blank tightly against the surface of the blank holder to form a blank holder force to prevent wrinkling. The die continues to move downward, and the punch of the deep drawing die gradually pulls the blank into the die, causing the blank to undergo plastic deformation and conform to the surface of the punch and the die, thus forming the surface of the outer fairing in one deep drawing. S3, Flanging: Holes distributed in a circumferential direction are machined on the workpiece after one deep drawing process. The workpiece is positioned on the flanging die. The die of the flanging die moves down and flanging each hole on the outer fairing with the same flanging direction in one go. S4. Grooving: Using the outer fairing's profile and circumferentially distributed holes as positioning references, the outer fairing is grooved circumferentially distributed with wire cutting.

2. The method for processing an outer fairing for an aero-engine according to claim 1, characterized in that, In step S1, the sheet material is GH4648 high-temperature alloy sheet material, and it is in a solution-treated and pickled state; the sheet material is cut by laser cutting according to the cutting outline, and after cutting, the cutting burrs and remelted layer are removed by grinding and cleaning.

3. The method for processing an outer fairing for an aero-engine according to claim 1, characterized in that, After step S2, the deep-drawn flange edges on both sides of the workpiece after one deep drawing are removed, the outer fairing is retained, and the workpiece is then placed flat in the furnace cavity of the vacuum annealing furnace without stacking, and vacuum stress-relief annealing is performed to remove the deep drawing stress.

4. The method for processing an outer fairing for an aero-engine according to claim 3, characterized in that, The processing method does not perform a second deep drawing after the first deep drawing in step S2, and does not perform solution treatment on the workpiece.

5. The method for processing an outer fairing for an aero-engine according to claim 1, characterized in that, In step S3, the workpiece that has undergone one deep drawing is placed on a milling fixture, and the workpiece is adhered and fixed to the milling fixture with an adhesive. The holes distributed circumferentially are machined in a three-axis milling manner according to the digital model.

6. The method for processing an outer fairing for an aero-engine according to claim 1, characterized in that, In step S3, the workpiece with the holes machined is positioned and placed using the first punch and stripper plate of the hole-flipping mold. The concave die of the hole-flipping mold moves downward to flip up the edges of each hole to form a flange.

7. A method for processing an outer fairing for an aero-engine according to claim 6, characterized in that, After step S3, the second punch is inserted into the flanging mold, ensuring that the edges of the second punch and the first punch are aligned without misalignment. The part is positioned and pressed with the stripper plate. Each small hole is flanged and formed into a convex shape using a punch. The flanging of the small holes is performed using a hydraulic forming machine with a forming pressure of 5-8 MPa and a holding time of 5-8 minutes. After the small holes are flanged, the height of the convex shape is ground to the design size.

8. A method for processing an outer fairing for an aero-engine according to claim 1, characterized in that, In step S4, the outer fairing is supported and fixed on the wire cutting fixture. The outer fairing is positioned using the shape of the outer fairing and the circumferentially distributed holes as positioning references. Eight slots are cut out by wire cutting. After cutting the slots, the outer fairing is deburred and the shape is inspected by fluorescence.

9. A method for processing an outer fairing for an aero-engine according to claim 8, characterized in that, The circumferentially distributed holes that serve as positioning references are the holes obtained by flanging in step S3.

10. An outer fairing for an aircraft engine, characterized in that, The outer fairing is manufactured using the processing method described in any one of claims 1 to 9.

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